Installation for purification by distillation of organochlorine products and methods for purification by distillation of carbon tetrachloride, chloroform, trichlorethylene, methylene chloride and perchlorethylene. Carbon tetrachloride poisoning Toxic concentrations, in
UNION OF SOVIETSHIRISHI EDRESPUBLIK 07 S 07 S 19/06 RETENI RUSSKY ICHAIYU UPRO- ESKIY ushchnichennshitkob xo zoldnazole, ORS 12 general to ots-Khkhloushkinn and peSTATE CONITET OF THE USSR MADE OF INVENTIONS AND ABOUT 3 NRT Yu DESCRIPTION I(71) Institute of Inorganic Chemistry.. , and electrochemistry of the Academy of Sciences of the Georgian SSR "Foreign literature", 1958, p. 393-396.2. Workshop on organic chemistry I., "Iir", 1979, p. 376 (prototype) , FOUR CARBON by drying with a desiccant and distillation, due to the fact that, for the purpose of process technology and degree of drying, a mixture of the formula CoK C 1 + Soy where 11- benz, 1,3- is used. tnadi1 - benz, 1,3-selenium at a mass ratio: Co K C 1 (25-30): in the presence of a mixture of 2.0-3.0 to the original fourth carbon, and the stages of oregon are combined in time. 117295 The 2nd includes the boiling stage solvent at reflux for 18 hours using R O as a drying agent and subsequent 5th distillation on a column. The consumption of P05 per 1 liter of solvent is 25-30 g, and the water content in the target product is not lower than 0.00523.0 The disadvantages of the known method are complexity 1, the presence of two stages - drying and distillation and the duration of the process, which significantly complicates its technology, and also15 high water content in the target product. The purpose of the invention is to simplify the technology of the process and increase the degree of drying. - 20 This goal is achieved by the fact that according to the method of purifying carbon tetrachloride by drying over a drying agent and distillation, a mixture of cobalt complexes of the formula is used as a drying agent. method for purifying carbon tetrachloride. Water is the main undesirable impurity of CC and therefore all purification methods, as a rule, include the stage of drying and distillation of the solvent. Drying and distillation are the final stages of the purification process of CC 1 and therefore removing water from CC 1 is an important task, CC 1 does not mix well with water. (0.08%) and in many cases, distillation is sufficient for purification. Water is removed in the form of a azeotropic mixture, which boils at bb C and contains 95.9 solvents. A ternary azeotropic mixture of water (4.3%) and ethanol (9.7) boils at 61.8 C. When higher requirements are imposed on the purification of CC 1, distillation without first drying the solvent is unsuitable. There is a known method for purifying carbon tetrachloride, according to which CC 1 is pre-dried and then distilled on a column. Drying is carried out over CaC 1, followed by distillation and P 05 CC 1, dried over calcined CaC 1 and distilled from a flask with an effective reflux condenser in a water bath, and in some cases - from a quartz flask with a reflux condenser. When using SS 14, for thermochemical measurements, the solvent is subjected to fractional distillation twice on a column with a vacuum jacket, each dispersing the first and last portions with a volume of a quarter of the total amount of distillate G 1. However, simple distillation of the solvent without the use of drying agents does not allow obtaining a solvent with a low water content. In methods based on the use of desiccants and subsequent distillation, preliminary long-term contact of the solvent with the desiccant is required, the choice of which for CC 1 is limited. Among desiccants, calcined CaC 1 is the most acceptable. It has been shown that 50CC 1 cannot be dried over sodium, since under these conditions an explosive mixture is formed. This cleaning method is time-consuming, has many steps and is ineffective. 55 The closest to the invention is the method of purifying CC 1, which is CoC C 1, + CoC C 1where d" benz, 1,3-thiadiaeol; k - benz, 1,3-selendiazole; with a mass ratio of Co KS 1Co K., C 1 25"30:1 and the total amount of the mixture is 2.0-3.0 wt. .L in relation to the original carbon tetrachloride, and the stages of drying and distillation are combined in time and space. The Co K C 1 and Co C C 1 complexes are prepared according to the well-known method 3.1. The essence of the proposed method is that cobalt complexes the indicated Pu K ligands disintegrate quantitatively in the presence of traces of water. These complexes are insoluble in all common solvents. In solvents with impurities of water, instead of the usual dissolution, the destruction of the complex takes place with the formation of a free ligand and hydrated cobalt ion. In solvents containing In the molecule there is a trivalent nitrogen atom, and a reaction of replacement of ligand molecules with solvent molecules occurs. Such solvents include amines, amides, itriles, as well as some heterocycles.g1117295 10 In solvents that do not contain a trivapentine nitrogen atom in the molecule, but contain impurities of water, in particular in CC 1, as a result of the reaction in the solution, decomposition products of the cobalt complex with sulfur- or selenium-containing diazoles. Using polarography, as well as UV and visible spectra of the resulting solutions, it was shown that there is no interaction between the ligand and the complexing agent in nitrogen-containing media or in media containing traces of water. Complexes of cobalt with aromatic diazoles can only be obtained in absolutely anhydrous media that do not contain a nitrogen atom. In all cases, when these complexes are introduced into solvents containing moisture impurities, the sum of the spectra of the ligand and the cobalt ion corresponds to the resulting spectrum, and the waves of the ligand and the cobalt ion are clearly recorded on the polarograms. 25 The decomposition reaction of cobalt complexes with the indicated diazoles under the influence of water molecules proceeds very quickly and the solvent takes on the color of the hydrated cobalt ion. Instant binding of traces of water by the desiccant (cobalt complexes occurs through the mechanism of hydrate formation (translation of the coordinated cobalt atom in the complex into a hydrated non-dissolved solution; therefore, coloring of the solvent in the color of hydrated cobalt ions can serve as a characteristic sign of the removal of water impurities from the solvent. It is known that the anhydrous solid has a pale blue color; di-, -tri-, tetra- and hexahydrates are violet, purple, red and red-brown, respectively.: The cobalt complex with diazoles is olive-colored plates, which, when added to CC 14, depending on the amount of water in it, the solvent is colored in one of the indicated colors of hydrated Co. The ability of cobaptate complexes with benzo, 1,3-thia- and selendiazoles to be destroyed in the presence of traces of water depends on the nature of the ligand, more precisely. on the nature of the key heteroatom in the ligand molecule. 4 Consequently, the effectiveness of this complex as a drying agent also depends on the nature of the heteroatom (R, Re) in the ligand and increases significantly when the sulfur atom is replaced by a selenium atom in the diazole heteroring. When the water content in CC 1 is very low, the most effective desiccant is a complex of cobalt with benz, 1,3-selenium piaol. When the water content in the solvent does not exceed 0.013, a cobalt complex with benzo,1,3-tidiaol can also serve as a drying agent. Consequently, a mixture of these complexes can serve as a drying agent in a wide range of water content in the solvent. For deep drying CC 14 the cobalt complex with benzo,1,3-selendiaeol can be mixed as an admixture to the cobalt complex with benzo,1,3-thiadiazole, which will bind the main amount of water in the solvent. The required degree of purification of CC 1 in each specific case can be achieved by varying the proportion of the components of the mixture. However, in order for the composition to have maximum efficiency as a drying agent, it is necessary to use a minimum weight fraction of the cobalt complex with benzo,1,3-selendiaeol in the mixture. Thus, simultaneously with the effect of hydrate formation from an anhydrous cobalt complex, which is easily the basis of the proposed method, the composition of the drying mixture of cobalt complexes with aromatic diazoles is a characteristic feature of this method of purification of CC 14. The instant binding of traces of water by cobalt complexes based on the indicated diaeols when introduced into CC 14 eliminates the need for preliminary 18-hour refluxing of the solvent over RO. Therefore, the mixture of complexes can be introduced into the solvent directly at the distillation stage, thereby combining the drying and drying stages distillationThe products of the decomposition of complexes - the ligand aromatic diaeol and the hydrated cobalt ion have a much higher boiling point than CC, therefore, during distillation they cannot pass into the distillate. The latter is collected in a receiver with a 7295 ratio of cobalt complexes cbene, 1,3- thiadiaeol and bene,1,3-selendiaeol. The results are shown in the table, designed to prevent contact of the distillate with air. The excess mixture of cobalt complexes with diaeols, when introduced into CC 1, settles at the bottom of the flask of the distillation apparatus, in which the solvent being purified retains the color of the hydrated cobalt ion until the end of the process. Water content in the distillate is determined by standard titration according to Fleur. Example 1. 300 ppm CC+ is added to the flask of a distillation apparatus, a mixture consisting of 10 g of cobolt complex with beneo,1,3-thiadiazole and O, 4 g is added cobalt complex with benzoate 2,1,3-selendiazole ( total quantity mixtures of cobalt 23 complexes and distilled. A fraction with a boiling point of 76.5-77.0 C (" 200 ppm) is selected. The first fraction with a boiling point of up to 76.5 C 2 is discarded (30 ppm). The water content in the distillate is 0.00073, the transfer speed p 5 mp/min. Duration t- O 3 0750 10: 15: 1.0007 25 30 0.0005 0 Distillation process Thus, the invention simplifies the process technology by eliminating the stage of preliminary contact of the solvent30 with the drying agent of the drying and distillation stage. combined in time and space, reducing the time required for cleaning CC 1 due to the rapid binding of traces of water in the solvent with a mixture of cobalt complexes with aromatic dia, aeols, and achieving the drying depth of CC 1, up to 0.00053 residual water, which increases the degree of drying is about the same, Sevnoarat, from 14 g of 2 1,3-ticobalone (generally added to the mixture is a complex of adiazolota with ben, the amount of frak "200 mp) e 0.0005 F Prodol Xt is obtained at a fast rate Compiled by A. Arteedaktor N. Dzhugan Techred I. Astvlosh Correction V, Vutyaga Circulation 409 of the Dietary Committee of Acquisitions and Discovery, Zh, Raushskaya nsnoye d. 4/5 al PPP "Patent", g.uzh st. Proektnaya, 4 P P P, Patent Zak. 4 measures 2, 300 mp bu distillation a mixture consisting of cobalt with beneo and 0.4 g o,1,3-selendiae complex; the complex mixture is distilled, Select ip. up to 76.5-77 OS e water in distillation distillation 5 ppm process. measures 3-8. Process for example 2 with different degrees Order 7145/16 VNIIIII State Affairs Committee 113035, Ios
Bid
3521715, 16.12.1982
INSTITUTE OF INORGANIC CHEMISTRY AND ELECTROCHEMISTRY AS GSSR
TSVENIASHVILI VLADIMIR SHALVOVICH, GAPRINDASHVILI VAKHTANG NIKOLAEVICH, MALASHKHIYA MARINA VALENTINOVNA, KHAVTASI NANULI SAMSONOVNA, BELENKAYA INGA ARSENEVNA
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Carbon tetrachloride purification method
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Since carbon tetrachloride (CTC) is a prohibited ozone depleting substance under the Montreal Protocol, but is inevitably formed as a by-product in the production of chloromethanes, choosing the most effective method for processing CTC is an urgent task.
Various transformations of CCA have been especially intensively studied recently; there is a large amount of experimental data. Below we will evaluate various options for converting CCC based on our own research and data from other authors.
The works examine the problem of processing CCM into environmentally friendly products, but they do not fully cover possible processing options, and also, in our opinion, the advantages and disadvantages of individual methods of recycling CCM are not sufficiently objectively reflected.
It is possible to note some contradictions in the articles .
Thus, the topic of the articles is the processing of CHCs into environmentally friendly products; in the text and conclusions, the conversion of CCCs into chloromethane is recommended as promising methods, and in the introduction, chloromethanes are called the main chemical pollutants of the environment. In fact, chloromethanes are not included in the Stockholm Convention on Persistent Organic Pollutants, and in terms of toxicity and release volume, chloromethanes are not the main pollutants even among other organochlorine compounds.
The articles talk about the high persistence of chloromethanes. At the same time, it is known that all chloromethanes, except methyl chloride, are unstable products and require stabilization to maintain their properties. The decomposition of chloromethanes occurs in the boilers of rectification columns, in the evaporator for supplying chemical chemicals to the reactor. According to the encyclopedia, chloroform without a stabilizer is unlikely to last without changing its properties for 24 hours if it is in contact with the atmosphere.
CHC processing processes can be classified according to the degree of usefulness of the resulting processed products. This does not mean that the usefulness of the recycling processes themselves will be in the same sequence, since much will depend on the cost of processing and subsequent separation of the resulting products.
The choice of method is also influenced by the presence of a large number of other products in the processed waste in addition to ChC (for example, in distillation stills for the production of chloromethane), when the separation of ChC from this waste can require significant costs. The same situation arises when neutralizing chemical chemicals contained in small quantities in gas emissions. In this case, non-selective complete combustion to produce CO2 and HCl with practically zero utility due to the low profitability of their extraction may be the most acceptable solution. Therefore, in each specific case, the choice can be made only after a technical and economic comparison.
CHC combustion
When burning CHC using air as an oxidizer, a simultaneous supply of hydrocarbon fuel is required to supply heat and bind chlorine into hydrogen chloride. Alternatively, if there is a small amount of hydrogen chloride, it can be converted to sodium chloride by injecting a sodium hydroxide solution into the combustion gases. Otherwise, hydrogen chloride is separated from combustion gases in the form of hydrochloric acid.
Disposal of hydrochloric acid itself can be a problem due to supply exceeding demand. The separation of hydrogen chloride from hydrochloric acid by stripping makes it more expensive than chlorine. In addition, hydrogen chloride has limited use in oxychlorination and hydrochlorination processes. The conversion of hydrogen chloride to chlorine using hydrochloric acid electrolysis or oxygen oxidation (Deacon process) is a rather expensive and technologically complex operation.
The authors of the works give preference to catalytic oxidation as a method of complete oxidation of CCC compared to conventional thermal combustion. According to comparison with combustion, catalytic oxidation processes are characterized by a greater depth of destruction of organochlorine waste and are not accompanied by the formation of dioxins.
These statements are not true and may lead to misconceptions about the effectiveness of the methods being compared. The article does not provide any data to support higher conversion rates in catalytic oxidation. In the references cited in support of this statement, for example, the degree of conversion is indeed high 98-99%, but this is not the level that is achieved during thermal combustion. Even if the conversion rate is stated as 100% or 100.0%, this only means that the accuracy of this data is 0.1%.
The US Resource Conservation and Recovery Act requires destructive removal efficiency of at least 99.9999% for major organic hazardous contaminants. In Europe, it is also recommended to adhere to this minimum value for the degree of decomposition of unusable pesticides and polychlorinated biphenyls in combustion plants.
A set of requirements for the combustion process has been developed, called BAT - Best Available Technique (best acceptable method). One of the requirements, along with a temperature of 1200°C and a residence time of 2 s, is the turbulence of the reaction flow, which allows, basically, to eliminate the problem of breakthrough of the burnt substance in the near-wall layer and ensure ideal displacement mode. Apparently, in a tubular reactor filled with a catalyst, it is more difficult to eliminate the leakage of the burned substance in the near-wall layer. In addition, there are difficulties in uniformly distributing the reaction flow throughout the tubes. At the same time, further progress in eliminating the “near-wall effect” made it possible to achieve a conversion degree of 99.999999% during combustion in a liquid rocket engine.
Another controversial statement by the authors is the absence of PCDD and PCDF in the catalytic oxidation products. No numbers are provided to support this. The work provides only two references confirming the absence of dioxins during catalytic oxidation. However, one of the references, apparently due to some error, has nothing to do with catalytic oxidation, since it is devoted to the biotransformation of organic acids. Another paper discusses catalytic oxidation, but does not report any evidence that it does not involve dioxins. On the contrary, data are provided on the formation of another persistent organic pollutant - polychlorinated biphenyl during the catalytic oxidation of dichlorobenzene, which may indirectly indicate the possibility of the formation of dioxins.
The work rightly notes that the temperature range of catalytic processes of oxidation of organochlorine wastes is favorable for the formation of PCDD and PCDF, however, the absence of PCDD and PCDF may be due to the catalytic destruction of the sources of their formation. At the same time, it is known that processes for the synthesis of high-molecular compounds even from C1 compounds are successfully carried out using catalysts.
European countries have environmental requirements for waste incineration, according to which limit value emissions into the atmosphere for dioxins is 0.1 ng TEQ/nm3.
The above environmental indicators of the process of thermo-oxidative (fire) neutralization of liquid organochlorine waste are available in. Finally, it should be noted that in the Inventory of Existing PCB Destruction Facilities, the most widely used and proven method for PCB destruction is high-temperature incineration. Catalytic oxidation is not used for this purpose.
In our opinion, catalytic oxidation, despite the use of precious metals on a carrier as a catalyst, has an advantage in destroying residual quantities toxic substances in gas emissions, since due to the low temperature of the process, significantly less fuel consumption is required to heat the reaction gas than during thermal combustion. The same situation arises when optimal combustion conditions are difficult to create, for example, in catalytic afterburners in automobile engines. In addition, the catalytic oxidation of organochlorine waste under pressure (the "catoxide process") has been used by Goodrich to directly feed combustion gases containing hydrogen chloride into an ethylene oxidative chlorination reactor to produce dichloroethane.
The combination of thermal and catalytic oxidation of waste gases has been reported to achieve higher efficiencies than pure catalytic oxidation. Qualified processing of organochlorine waste is also discussed in. In our opinion, it is more expedient to use conventional thermal combustion to burn CHC in the form of a concentrated product.
To conclude this section, it is advisable to consider one more aspect of the oxidation of CCA. According to CHC, it is a non-flammable substance, so its combustion can only be carried out in the presence of additional fuel. This is true when using air as an oxidizing agent. In oxygen, CHC is capable of burning with an insignificant thermal effect, the calorific value is 242 kcal/kg. According to another reference book, the heat of combustion of liquid is 156.2 kJ/mol (37.3 kcal/mol), and the heat of combustion of steam is 365.5 kJ/mol (87.3 kcal/mol).
Oxidation with oxygen can be one of the methods for processing CCC, in which the carbon component is lost, but the chlorine spent on producing CCC is regenerated. This process has an advantage over conventional combustion due to the production of concentrated products.
CCl4 + O2 → CO2 + 2Cl2
The process of oxidative dechlorination of CHC also makes it possible to obtain carbon dioxide and, if necessary, phosgene.
2CCl4 + O2 → 2COCl2 + 2Cl2
Hydrolysis of CHC
Another interesting, in our opinion, process of processing CHC into carbon dioxide and hydrogen chloride is hydrolysis.
CCl4 + 2H2O → CO2 + 4HCl
There are few publications in this area. The interaction of OH-groups with chloromethanes in the gas phase is discussed in the article. The catalytic hydrolysis of ChCA to HCl and CO2 on magnesium oxide at temperatures above 400°C was studied in. The rate constants for homogeneous hydrolysis of CHC in the liquid phase were obtained in the work.
The process works well, according to our data, at relatively low temperatures of 150-200°C, uses the most accessible reagent and should not be accompanied by the formation of dioxins and furans. All you need is a reactor that is resistant to hydrochloric acid, for example, coated inside with fluoroplastic. Perhaps such a cheap and environmentally friendly recycling method can be used to destroy other waste.
Interaction of CCA with methanol
Close to hydrolysis and actually proceeding through this stage is the process of vapor-phase interaction of ChCU with methanol to produce methyl chloride in the presence of a catalyst - zinc chloride on activated carbon. Relatively recently, this process was first patented by Shin-Etsu Chemical (Japan). The process proceeds with high conversions of CHC and methanol close to 100%.
CCl4 + 4CH3OH → 4CH3Cl + CO2 + 2H2O
The authors believe that the interaction of ChC with methanol occurs in 2 stages: first, the hydrolysis of ChC occurs to carbon dioxide and hydrogen chloride (see above), and then the hydrogen chloride reacts with methanol to form methyl chloride and water.
CH3OH + HCl → CH3Cl + H2O
In this case, to initiate the reaction, a small amount of water present in the atmosphere is sufficient. It is believed that the first stage limits the speed of the overall process.
With a close to stoichiometric ratio of CTC to methanol (1:3.64), the reaction proceeded stably during the experiment, which lasted 100 hours, with a conversion of CTC of 97.0% and methanol of 99.2%. The selectivity for the formation of methyl chloride was close to 100%, since only traces of dimethyl ether were detected. The temperature in the catalyst layer was 200 o C.
Then it was proposed to divide the process into two reaction zones: in the first, the hydrolysis of CCA occurs, and in the second, the interaction of hydrogen chloride with methanol introduced into this zone occurs. Finally, the same company patented a method for producing chloromethanes without the formation of ChC, which includes the following stages:
. production of chloromethanes by chlorination of methane;
. interaction of hydrogen chloride released in the first stage with methanol to form methyl chloride and dilute hydrochloric acid;
. hydrolysis of diluted CCA hydrochloric acid in the presence of a catalyst - metal chlorides or oxides on a carrier.
The disadvantage of the heterogeneous catalytic process of interaction of CCC with methanol is the relatively short service life of the catalyst due to its carbonization. At the same time, high-temperature regeneration to burn out carbon deposits is undesirable due to the volatilization of zinc chloride, and when using activated carbon as a carrier, it is generally impossible.
In conclusion of this section, it can be mentioned that we have made attempts to move away from solid catalysts in the process of processing CCC with methanol. In the absence of a catalyst at a molar ratio of methanol:BCC = 4:1 and with an increase in temperature from 130 to 190°C, the conversion of PCQ increased from 15 to 65%. The manufacture of the reactor requires materials that are stable under these conditions.
Carrying out a catalytic liquid-phase process at relatively low temperatures of 100-130°C and a molar ratio of methanol: ChC = 4:1 without pressure made it possible to achieve a conversion of ChC of only 8%, while it is possible to obtain almost 100% conversion of methanol and 100% selectivity for methyl chloride. To increase the conversion of CCA, an increase in temperature and pressure is required, which could not be achieved in laboratory conditions.
A method of alcoholysis of ChCU has been patented, including the simultaneous supply of ChCC and ³
1 alcohol ROH (R = alkyl C 1 - C 10) into the catalytic system, which is an aqueous solution of metal halides, especially chlorides I B, I I B, V I B and V I I I groups . During the liquid-phase interaction of methanol and ChC (in a ratio of 4:1) in a laboratory reactor with a magnetic stirrer in the presence of a catalytic solution of zinc chloride at a temperature of 180°C and a pressure of 3.8 bar, the conversion of ChC and methanol was 77%.
Chlorination using ChC
CCA is a safe chlorinating agent, for example, in the preparation of metal chlorides from their oxides. During this reaction, CHC is converted into carbon dioxide.
2Ме2О3 + 3CCl4 → 4МеCl3 + 3СО2
Work was carried out on the production of iron chlorides using ChCA as a chlorinating agent; the process takes place at a temperature of about 700°C. By chlorination using ChC in industry they are obtained from oxides of elements of groups 3-5 Periodic table their chlorides.
Interaction of CHC with methane
The simplest solution to the problem of processing ChCC would be the interaction of ChCC with methane in a methane chlorination reactor to produce less chlorinated chloromethanes, since in this case it would practically only require the organization of recycling of unreacted ChCC, and the subsequent isolation and separation of reaction products can be carried out on the main system production.
Previously, when studying the process of oxidative chlorination of methane, both in the laboratory and in a pilot plant, it was noticed that when the reaction gas from the process of direct chlorination of methane containing all chloromethanes, including ChC, is fed into the reactor, the amount of the latter after the oxychlorination reactor decreases, although it should was with increasing amounts of all other chloromethanes to increase.
In this regard, it was of particular interest to conduct a thermodynamic analysis of the reactions of methane with ChC and other chloromethanes. It turned out that the most thermodynamically probable is the interaction of CHC with methane. At the same time, the equilibrium degree of conversion of CHC under conditions of excess methane, which is realized in an industrial chlorinator, is close to 100% even at the highest temperature (the lowest equilibrium constant).
However, the actual occurrence of a thermodynamically probable process depends on kinetic factors. In addition, other reactions can occur in the CCA system with methane: for example, pyrolysis of CCA to hexachloroethane and perchlorethylene, the formation of other C2 chlorine derivatives due to the recombination of radicals.
An experimental study of the interaction reaction between CCA and methane was carried out in a flow reactor at temperatures of 450-525 ° C and atmospheric pressure, with an interaction time of 4.9 s. Processing of experimental data gave the following equation for the rate of exchange reaction of methane with CHC:
r = 1014.94 exp(-49150/RT).[СCl 4 ]0.5.[CH 4 ], mol/cm 3 .s.
The data obtained made it possible to evaluate the contribution of the exchange interaction of CCC with methane in the process of methane chlorination and to calculate the necessary recycle of CCC for its complete conversion. Table 1 shows the conversion of ChC depending on the reaction temperature and concentration of ChC at approximately the same concentration of methane, which is realized in an industrial chlorinator.
The conversion of CCC naturally decreases with decreasing process temperature. Acceptable CHC conversion is observed only at temperatures of 500-525 o C, which is close to the temperature of bulk methane chlorination at existing chloromethane production facilities of 480-520 o C.
The total conversions of CHC and methane can be characterized by the following summary equation and material balance:
CCl 4 + CH 4 → CH 3 Cl + CH 2 Cl 2 + CHCl 3 + 1,1-C 2 H 2 Cl 2 + C2Cl 4 + HCl
100.0 95.6 78.3 14.9 15.2 7.7 35.9 87.2 mol
The second line gives the amounts of reacted methane and the resulting products in moles per 100 moles of reacted CCA. The selectivity of the conversion of CHC into chloromethanes is 71.3%.
Since the separation of commercial CCS from distillation stills of chloromethane production was a certain problem, and difficulties periodically arose with the sale of distillation stills, the processing of CCS in a methane chlorination reactor aroused interest even before the ban on the production of CCS due to its ozone-depleting ability.
Pilot tests of CHC processing in a methane chlorination reactor were carried out at the Cheboksary settlement. "Khimprom". The results obtained basically confirmed the laboratory data. The selectivity of the conversion of CCA to chloromethanes was higher than under laboratory conditions.
The fact that the selectivity of the reaction process of CCA in an industrial reactor turned out to be higher than in a laboratory reactor can be explained by the fact that when methane is chlorinated in a laboratory reactor, the outer walls, heated by a casing with an electric coil, overheat. Thus, at a temperature in the reaction zone of 500°C, the temperature of the walls of the laboratory chlorinator was 550°C.
In an industrial reactor, heat is accumulated by the central brick column and lining, and the outer walls of the chlorinator, on the contrary, are cooled.
Pilot tests of the return of chemical chemicals to the methane chlorination reactor were previously carried out at the Volgograd settlement. "Khimprom". ChC was fed into an industrial chlorinator without separation as part of the distillation still, along with all the impurities of C2 chlorinated hydrocarbons. As a result, about 100 m3 of distillation stills were processed within a month. However, processing the data obtained caused difficulties due to the large number of components in low concentrations and the insufficient accuracy of the analyzes.
To suppress the formation of by-product chlorohydrocarbons of the ethylene series during the interaction of ChC with methane, it is proposed to introduce chlorine into the reaction mixture at a ratio of chlorine to ChC 0.5.
The production of chloromethanes and other products by the interaction of CCA with methane at temperatures of 400-650 o C in a hollow reactor is described in the patent. An example is given where the conversion of CCA was in mol %: to chloroform - 10.75, methylene chloride - 2.04, methyl chloride - 9.25, vinylidene chloride - 8.3 and trichlorethylene - 1.28.
Then the same company "Stauffer" patented a method for producing chloroform by reacting ChC with C2-C3 hydrocarbons and C1-C3 chlorohydrocarbons. According to the examples given, only chloroform is obtained from CCA and methylene chloride at a temperature of 450°C in a hollow reactor, and at a temperature of 580°C - chloroform and perchlorethylene. From CCA and methyl chloride at a temperature of 490°C, only methylene chloride and chloroform were formed in equal quantities, and at a temperature of 575°C, trichlorethylene also appeared.
A process was also proposed for the production of methyl chloride and methylene chloride by the interaction of methane with chlorine and ChC in a fluidized contact bed at a temperature of 350-450 o C. The process of chlorination of methane to chloroform in a fluidized contact bed with the introduction of CCA into the reaction zone to ensure heat removal is described. In this case, the reaction of CHC with methane occurs simultaneously.
The exchange reaction between CCA and paraffin leads to the formation of chloroform and chlorinated paraffin.
When developing the process of oxidative chlorination of methane, it was found that the oxidative dechlorination of ChC in the presence of methane is more efficient than the interaction of methane and ChC in the absence of oxygen and a catalyst.
The data obtained indicate that the process of oxidative dechlorination of ChCC in the presence of methane and a catalyst based on copper chlorides occurs at a lower temperature than the interaction of ChCC with methane in the absence of oxygen, producing only chloromethanes without the formation of by-product chlorinated hydrocarbons. Thus, the conversion of CCC at temperatures of 400, 425 and 450°C averaged 25, 34 and 51%, respectively.
An additional advantage of oxidative processing of CCC is the absence of carbonization of the catalyst. However, the need for a catalyst and oxygen reduces the advantages of this method.
A method for producing chloromethanes by oxidative chlorination of methane without obtaining chemical chemicals in the final products due to its complete recycling into the reaction zone has been patented. One of the claims of this application states that it is possible to obtain chloroform alone as the final product by returning methane and all chloromethanes except chloroform to the reaction zone.
Processing of chemical chemicals with hydrogen
Hydrodechlorination of ChCC with hydrogen (as well as methane), in contrast to oxidative transformations with oxygen, allows for the beneficial use of the carbon component of ChCC. Catalysts, kinetics, mechanism and other aspects of hydrodechlorination reactions are discussed in reviews.
One of the main problems of the CCA hydrodechlorination process is selectivity; often the reaction proceeds before the formation of methane, and the yield of chloroform, as the most desirable product, is not high enough. Another problem is the fairly rapid deactivation of the catalyst, mainly due to carbonization during the decomposition of CCS and reaction products. At the same time, selective production of chloroform can be achieved more easily than catalyst stability. Recently, quite a lot of works have appeared where high selectivity for chloroform is achieved; there is much less data on the stability of the catalyst.
In the patent, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag or Au are proposed as catalysts for the hydrogenolysis of PCI and chloroform. On a catalyst containing 0.5% platinum on alumina, at temperatures of 70-180 o C, 97.7-84.8% chloroform and 2.3-15.2% methane were obtained from ChC; with more high temperatures Methylene chloride is also formed.
In the works, the hydrodechlorination of CCA was carried out on platinum catalysts. The choice of MgO as a support was made on the basis of higher selectivity for chloroform and duration of catalyst operation compared to other supports: Al2O3, TiO2, ZrO2, SiO2, aluminosilicate and NaY zeolite. It has been shown that for stable operation of the Pt/MgO catalyst with a PTC conversion of more than 90%, it is necessary to maintain a reaction temperature of 140°C, an H2/PCC ratio of more than 9, and a space velocity of 9000 l/kg.h. Influence of nature discovered starting compounds platinum on the activity of the resulting catalyst - 1% Pt/Al2O3. On catalysts prepared from Pt(NH 3) 4 Cl 2, Pt(NH3)2(NO3)2 and Pt(NH3)4(NO3)2, the CCA conversion is close to 100%, and the selectivity to chloroform is 80%.
Modification of the catalyst - 0.25% Pt/Al2O3 with lanthanum oxide made it possible to obtain a chloroform yield of 88% with a selectivity of 92% at 120°C, a space velocity of 3000 h-1 and a molar ratio of H2:CCl4 = 10.
According to the data, calcination of the support - aluminum oxide at temperatures of 800 - 900 ° C reduces Lewis acidity, thereby increasing the stability and selectivity of the catalyst. On aluminum oxide with a specific surface area of 80 m2/g, containing 0.5% Pt, the conversion of PTC is 92.7% with a selectivity for chloroform of 83% and is retained for 118 hours.
In contrast to the data in the patent, when producing methylene chloride and chloroform by hydrodechlorination, ChCU recommends treating the carrier with hydrochloric acid or hydrochloric acid and chlorine, and promoting platinum with small amounts of metals, for example, tin. This reduces the formation of by-products and increases the stability of the catalyst.
When hydrodechlorination of ChCC on catalysts containing 0.5-5% Pd on sibunit (coal) or TiO2 at a temperature of 150-200°C, the conversion of ChCC was 100%. Non-chlorinated C2-C5 hydrocarbons were formed as by-products. The catalysts worked stably for more than 4 hours, after which regeneration was carried out by blowing with argon while heating.
It is reported that when using a bimetallic composition of platinum and iridium promoted with small amounts of third metals, such as tin, titanium, germanium, rhenium, etc., the formation of by-products is reduced and the duration of the catalyst is increased.
When studying the non-catalytic interaction of CCA with hydrogen using the pulse compression method in a free-piston installation at a characteristic process time of 10-3 s, two areas of the reaction were found. At a temperature of 1150K (degree of conversion up to 20%), the process proceeds relatively slowly. By adjusting the composition of the initial mixture and the process temperature, it is possible to obtain a 16% yield of chloroform with a selectivity close to 100%. In a certain temperature range, under conditions of self-ignition of the mixture, the reaction can be directed to the predominant formation of perchlorethylene.
Great advances in the development of an active, stable and selective catalyst for the gas-phase hydrodechlorination of CCC with hydrogen were achieved by Sud Chemie MT. The catalyst is precious metals V groups deposited on microspherical aluminum oxide (the composition of the catalyst is not disclosed by the company). The process is carried out in a fluidized bed of catalyst at temperatures of 100-150°C, pressure of 2-4 ata, contact time of 0.5-2 seconds and a hydrogen:BC ratio in the reaction zone of 6-8:1 (mol.).
The conversion of CCA under these conditions reaches 90%, selectivity for chloroform is 80-85%. The main by-product is methane, with methyl chloride and methylene chloride formed in minor quantities.
The works investigated the hydrodechlorination of CCC on palladium catalysts in the liquid phase. At temperatures of 20-80°C on palladium acetate with the addition of acetic acid and when using C7-C12 paraffins, methyl ethyl ketone, dimethylformamide, dioxane and benzyl alcohol as solvents, the only reaction product was methane. Carrying out the reaction in isopropyl and tert-butyl alcohols as solvents made it possible to obtain chloroform and methyl chloride as the main products; methane formation ranged from trace amounts to 5%.
It is noted that the side reaction of hydrochlorination of alcohols used as solvents occurs with a conversion of 7-12% of the supplied amount and the formation of isomers of chlorine derivatives, which creates a problem of their disposal and complicates the isolation of marketable products. Therefore, there are no plans to implement this method yet.
Apparently, to exclude by-products, the patent proposes to carry out the reaction of hydrodechlorination of CCA to chloroform in a halogenated aliphatic solvent, in particular in chloroform. The catalyst is a suspension of platinum on a carrier. The conversion of ChC is 98.1% with a selectivity of chloroform formation of 99.3%.
The same process for producing chloroform in the presence of Pt and Pd catalysts on a carrier using 1 solvent (pentane, hexane, heptane, benzene, etc.) is described in the patent. The process is said to be carried out continuously or batchwise on an industrial scale.
The most commonly used catalysts for the hydrodechlorination of CCA to chloroform and other chloromethanes are supported palladium, platinum, rhodium and ruthenium. Such a catalyst is sprayed and suspended in liquid ChCU and treated with hydrogen at a pressure of 8000 kPa and a temperature below 250°C. The method is reported to be suitable for producing chloroform on an industrial scale.
When studying the hydrochlorination of CCA in a liquid-phase bubbling reactor, it was shown that the most active and selective catalyst is palladium supported on activated carbon. The advantage of activated carbon as a carrier is due to a more uniform distribution of the metal on its surface compared to such inorganic carriers as aluminum oxide and silica gel. According to the activity of metals, catalysts can be arranged in the series Pd/C Pt/C Rh/C Ru/C Ni/C. The main by-product is hexachloroethane.
Later it was discovered that the speed of the process is limited chemical reaction on the surface.
Transformation of CHC into PCE
In tough temperature conditions perchlorethylene is formed from CHC. The process of producing perchlorethylene from CCS involves the absorption of heat and the release of chlorine, which is fundamentally different from the production of perchlorocarbons (perchlorethylene and CCS) from methane or waste from the production of epichlorohydrin, where the processes occur with the supply of chlorine and the release of heat.
At 600°C H = 45.2 kcal/mol, and the equilibrium degree of conversion at atmospheric pressure is 11.7% 5. It should be noted that the data of various authors on the magnitude of the thermal effect of the reaction differ significantly, which raised doubts about the possibility of complete processing of CCC into perchlorethylene in the production of perchlorocarbons due to the lack of heat for this reaction. However, complete recycling of CHC has currently been carried out in the production of perchlorocarbons at the Sterlitamak JSC "Kaustik".
The thermal transformation of CHC increases significantly in the presence of chlorine acceptors. It is obvious that the acceptor, by binding chlorine, shifts the equilibrium of the reaction:
2CCl 4 → C 2 Cl 4 + 2Cl 2
towards the formation of perchlorethylene.
The transformation of CCA into perchlorethylene in the presence of a chlorine acceptor performs another very important function - it turns an endothermic process into an exothermic one and eliminates the almost impossible supply of heat through the wall at such temperatures in the presence of chlorine.
The introduction of organic chlorine acceptors (methane, ethylene, 1,2-dichloroethane) during the thermal dechlorination of CCA made it possible to increase the yield of PCE to 50 wt%. , however, at the same time, the amount of by-products (hexachloroethane, hexachlorobutadiene, resins) also increased simultaneously. Therefore, in work 53, to implement the process in industry, it is recommended to add an acceptor (methane or ethylene) in an amount of 0.3 of the stoichiometry.
Patent 54 proposes to carry out the process of non-catalytic thermal transformation of CHC into perchlorethylene at a temperature of 500-700 o C using hydrogen chlorine as an acceptor, due to which few by-product chlorohydrocarbons are formed.
The conversion of CCS into PCE, if there is a sale of the latter, has very important advantages over other methods of processing CCS from the production of chloromethanes:
. for processing, it is not necessary to separate CCS from distillation stills;
. C2 chlorohydrocarbons contained in stills are also converted into PCE.
The process of converting CCA into perchlorethylene in the presence of CH4 is accompanied by the formation of a large number of by-products, some of which (hexachloroethane, hexachlorobutadiene) are processed during the process, others (hexachlorobenzene) are sent for disposal. At the same time, methane, by binding chlorine, turns into ChC, which also needs to be processed, i.e. CHC processing capacity is increasing.
When hydrogen is used as a chlorine acceptor, the amount of by-products decreases, only the yield of hydrogen chloride increases. The process is carried out in a fluidized bed of silica gel. Process temperature 550-600 o C, ratio ChC:H2 = 1:0.8-1.3 (mol.), contact time 10-20 s. CHC conversion reaches 50% 55. The disadvantage of this process is the need to create a separate large technological scheme, as well as the presence of difficult-to-dispose waste - hexachlorobenzene.
The formation of heavy by-products can also be minimized when producing perchlorethylene by chlorinating hydrocarbons and their chlorine derivatives in the presence of ChC and hydrogen.
Other methods for processing CCC
Some methods for restoring CCS are proposed in. For example, chloroform can be obtained by slow reduction of CCl4 with iron with hydrochloric acid, zinc dust with a 50% NH4Cl solution at 50-60 o C, ethanol at 200 o C.
The electrochemical reduction of CCA produces mainly chloroform and methylene chloride. In the presence of aluminum chloride, CCA alkylates aromatic compounds. In free radical reactions and telomerization reactions, CCA serves as a halogen carrier.
Conclusions
1. Since CHC is inevitably formed during the chlorination of methane and chloromethanes, the development of methods for its effective processing is an urgent task.
2. When destroying chemical chemicals by high-temperature combustion, existing environmental requirements for a destructive removal efficiency of 99.9999% and a dioxin content in emissions of no more than 0.1 ng TEQ/nm3 are achieved. Similar indicators were not revealed during the catalytic oxidation of ChC.
During the catalytic oxidation of CCA with oxygen, it is possible to obtain chlorine and/or phosgene.
3. Interesting method Processing of CHC from the point of view of a cheap reagent and low temperature of the process is hydrolysis to carbon dioxide and hydrogen chloride.
4. The combination of hydrolysis of ChC and the interaction of the resulting HCl with methanol also gives a rather interesting process of processing ChC with methanol to produce methyl chloride and CO 2.
5. Hydrodechlorination with hydrogen makes it possible to utilize CCA to obtain the desired less chlorinated chloromethanes. The main disadvantage of this process, as well as the interaction with methanol, is the gradual decrease in catalyst activity due to carbonization.
6. The simplest solution to the problem of processing CCS is the interaction of CCS with methane when it is returned to the methane chlorination reactor. However, in addition to chloromethanes, impurities of C2 chlorohydrocarbons are formed. The formation of impurities can be avoided by reacting CCA with methane in the presence of a catalyst and oxygen at a lower temperature, but this will require the creation of a separate stage and the presence of oxygen.
7. Pyrolysis of CHC in the presence of methane, hydrogen or other chlorine acceptors allows one to obtain perchlorethylene. The process is complicated by the formation of high-molecular-weight by-products.
8. CCA is a safe chlorinating agent, for example, when producing metal chlorides from their oxides.
9. There are a number of other methods for processing CCC, for example, electrochemical reduction or using reducing reagents. CCA can also be used as an alkylating agent.
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Table 1. Interaction of CHC with methane
| T-ra, | Concentrations, % mol. | CHC conversion, % | |||
| p/p | o C | SS l 4 | CH 4 | for chlorine | by carbon |
| 1 | 525 | 22,5 | 53,4 | 27,4 | 25,4 |
| 2 | 525 | 9,7 | 53,0 | 29,4 | 31,9 |
| 3 | 500 | 24,9 | 48,8 | 12,0 | 11,9 |
| 4 | 475 | 23,4 | 47,8 | 6,4 | 5,7 |
| 5 | 450 | 29,5 | 51,1 | 2,9 | 1,9 |
Physical and chemical properties:
Carbon tetrachloride (methane tetrachloride, CHCl 4) is a colorless liquid. Sol. water in CCl 4 is about 1% (24°). Does not ignite. On contact with flame or heated objects, it decomposes to form phosgene. May contain CS 2, HCl, H 2 S, and organic sulfides as impurities.
Scope of application:
Used as a solvent; for extraction of fats and alkaloids; in the production of freons; in fire extinguishers; for cleaning and degreasing clothes in everyday life and in industrial conditions.
Receipt:
It is obtained by chlorination of CS 2 in the presence of catalysts; catalytic chlorination of CH 4 (together with CH 2 C1 2 and CHCl 3); by heating a mixture of coal and CaCl 2 at the temperature of a voltaic arc.
General nature of the toxic effect:
A drug with less vapor potency than chloroform. Regardless of route of entry, it causes severe liver damage: centrilobular necrosis and fatty degeneration. At the same time, it affects other organs: the kidneys (proximal renal tubules), alveolar membranes and pulmonary vessels. Lesions in the kidneys and lungs are less significant, developing, as a rule, after liver damage and as a result of a violation of general metabolism, but in some cases they play a significant role in the picture and outcome of poisoning. The earliest sign of toxicity is considered to be a change in the level of a number of blood enzymes. A greater ability of the liver to regenerate after poisoning was revealed. Drinking alcohol while inhaling C.U. vapors, cooling, and increased oxygen content in the air increase the toxic effect. When extinguishing a flame with fire extinguishers and in general during strong heating, poisoning can occur from inhalation of thermal decomposition products of Ch.U.
According to existing views on the pathogenesis of the toxic effect of Ch.U., it is associated with free radical metabolites (type CC13) formed as a result of the hemolytic rupture of CCl 4 molecules. As a result of increased peroxidation of lipid complexes of intracellular membranes, the activity of enzymes and a number of cell functions (protein synthesis, ß-lipoprotein metabolism, drug metabolism) are disrupted, destruction of nucleotides occurs, etc. It is assumed that the main place of formation of free radical metabolites is the endoplasmic reticulum and microsomes cells.
Poisoning picture:
If very high concentrations are inhaled (by carelessly entering tanks and reservoirs, when extinguishing fires with fire extinguishers with C.U. in small enclosed spaces, etc.), either sudden death, or loss of consciousness or anesthesia are possible. With milder poisoning and a predominant effect on nervous system characterized by headache, dizziness, nausea, vomiting, confusion or loss of consciousness. Recovery occurs relatively quickly. Excitement sometimes has the character of strong attacks of a violent state. Poisoning in the form of encephalomyelitis, cerebellar degeneration, peripheral neuritis, optic neuritis, hemorrhage and fat embolism of the brain has been described. There is a known case of epileptiform convulsions and loss of consciousness on the 4th day after poisoning without significant damage to the liver and kidneys. At autopsy (in case of quick death) there are only hemorrhages and cerebral edema, pulmonary emphysema.
If poisoning develops slowly, symptoms of damage to the central nervous system within 12-36 hours are accompanied by severe hiccups, vomiting, often prolonged, diarrhea, sometimes intestinal bleeding, jaundice, and multiple hemorrhages. Later - enlargement and tenderness of the liver, severe jaundice. Even later, symptoms of severe kidney damage appear. In other cases, symptoms of kidney damage precede signs of liver disease. Observations have shown that liver damage is pronounced in the first period and the stronger the faster death occurs; with later death, regenerative processes already exist in the liver tissue. Changes in the kidneys with early death are insignificant. If the kidneys are damaged, the amount of urine decreases; in the urine - protein, blood, cylinders. The content of non-protein nitrogen in the blood is increased, but the content of chlorides, calcium, and proteins is decreased. In severe cases, oliguria or complete anuria occurs (both the filtration and secretory functions of the kidneys are impaired). High blood pressure, edema, seizures, uremia - Pulmonary edema may develop and is often the immediate cause of death (edema is sometimes attributed to the administration of excess fluid during treatment). In more favorable cases after anuria - abundant diuresis, gradual disappearance of pathological elements in the urine, complete restoration of kidney function. Sometimes, apparently at not very high concentrations of Ch.U., the only sign poisoning may result in a decrease or cessation of urine output.
The consequence of acute poisoning with C.U. vapors can be duodenal ulcer, pancreatic necrosis, anemia, leukocytosis, lymphopenia, changes in the myocardium, acute psychosis (Vasilieva). The outcome of poisoning can be yellow atrophy of the liver, as well as cirrhosis.
When taking C.U. orally, the picture of poisoning is the same as when inhaling vapors, although there are indications that the liver is predominantly affected in these cases.
The most characteristic pathological changes: parenchymal and fatty degeneration of the liver, as well as numerous necrosis in it; acute toxic nephrosis; nephrosonephritis (kidney tubules are affected along their entire length); cerebral edema; inflammation and edema of the lungs; myocarditis.
Toxic concentrations causing acute poisoning.
For humans, the threshold for odor perception is 0.0115 mg/l, and the concentration affecting the light sensitivity of the eye is 0.008 mg/l (Belkov). At 15 mg/l after 10 minutes headache, nausea, vomiting, increased heart rate; at 8 mg/l the same after 15 minutes, and at 2 mg/l - after 30 minutes. Workers with 8-hour exposure to a concentration of 1.2 mg/l experienced fatigue and drowsiness. When cleaning the floor Ch.U. (concentration in the air 1.6 mg/l), the worker felt a headache, dizziness after 15 minutes and was forced to leave work. The poisoning turned out to be fatal (the victim was an alcoholic). Mass poisoning has been reported during cleaning of evaporator coils on a ship (air concentration 190 mg/l). The victims, with the exception of one, survived. Exposure to a concentration of 50 mg/l can be fatal if inhaled for 1 hour. Severe poisoning with damage to the liver, kidneys and intestinal bleeding is known when working 2 shifts in a row under normal conditions of washing equipment.
When ingesting 2-3 ml of Ch.U., poisoning may already occur; 30-50 ml lead to severe and fatal intoxication. Cases of mass poisoning with 20 deaths have been described from ingestion of a hair wash containing 1.4% Ch.U. (the rest is alcohol). Victims have bronchitis, pneumonia, bloody vomiting, diarrhea, liver and kidney damage. However, there is a known case of recovery after taking 220 ml of Ch. U. with developed anesthesia and severe kidney failure. Paraffin (vaseline) oil was used for gastric lavage.
In chronic poisoning, in relatively mild cases, the following is observed: fatigue, dizziness, headache, pain in different parts of the body, muscle tremors, memory loss, inertia, weight loss, heart disorders, irritation of the mucous membranes of the nose and throat, dysuric disorders. The most common complaints are abdominal pain, lack of appetite, and nausea. Enlargement and tenderness of the liver are detected; changes in motility, spasms of different parts of the intestine, bilirubinemia, etc.
On the skin, carbon tetrachloride can cause dermatitis, sometimes eczema, and urticaria. Irritates skin more than gasoline. When the thumb is immersed in Ch, U, for 30 minutes, after 7-10 minutes a feeling of cold and burning appears. After ersepoaicia there is erythema, which goes away after 1-2 hours. A case of polyneuritis as a result of constant contact of the C.U. with the skin during work is described. Penetrates in large quantities through burned skin; Poisoning is probably possible when extinguishing clothes that are burning on people using Ch.U.
Urgent Care.
In case of acute inhalation poisoning - fresh air, rest. Long-term inhalation of humidified oxygen using nasal catheters (continuous for the first 2-4 hours; subsequently, 30-40 ppm with breaks of 10-15 minutes). Heart remedies: camphor (20%), caffeine (10%). cordiamine (25%) 1-2 ml subcutaneously; sedatives, strong sweet tea. Inject intravenously 20-30 ml of 40% glucose solution with 5 ml of 5% ascorbic acid, 10 ml of 10% calcium chloride solution. For hiccups and vomiting - intramuscularly 1-2 ml of a 2.5% solution of aminazine with 2 ml of a 1% solution of novocaine. In case of respiratory depression, inhale carbogen repeatedly for 5-10 minutes, intravenously 10-20 ml of a 0.5% solution of bemegride, subcutaneously 1 ml of a 10% solution of corazol. In the event of a sharp weakening (stopping) of breathing, artificial respiration using the “mouth to mouth” method with a transition to controlled respiration. In severe cases, immediate hospitalization in a resuscitation center.
When taking poison orally, thoroughly lavage the stomach through a tube, a universal antidote (TUM), 100-200 ml of petroleum jelly, followed by the administration of a saline laxative; cleansing the intestines to clean wash water (siphon enema); Bleeding (150-300 ml) followed by partial blood replacement. To enhance diuresis, inject into a vein 50-100 ml of 30% urea in a 10% glucose solution or 40 mg of Lasix. With the development of a collaptoid state, intravenously 0.5 ml of a 0.05% solution of strophanthin in 10-20 ml of a 20% glucose solution, or korglykon (0.5-1 ml of a 0.06% solution in 20 ml of a 40% glucose solution); according to indications - mezaton. In the future, to restore acid-base balance, intravenous drip administration of 300-500 ml of 4% sodium bicarbonate solution is performed. Vitamins B6 and C, lipoic acid, unithiol are recommended (5% solution intramuscularly, 5 ml 3-4 times a day on the first day, 2-3 times a day on the second and third days).
Contraindicated: sulfa drugs, adrenaline and chlorine-containing sleeping pills (chloral hydrate, etc.). Alcohol and fat consumption is not allowed!
Based on materials from the book: Harmful substances in industry. Handbook for chemists, engineers and doctors. Ed. 7th, lane and additional In three volumes. Volume I. Organic substances. Ed. honorable activities science prof. N.V. Lazareva and Dr. honey. Sciences E. N. Levina. L., "Chemistry", 1976.
Methods for purifying organic solvents depend on the nature and purpose of the solvent. In most cases, organic solvents are individual compounds and can be characterized by their physicochemical properties. The most basic solvent purification operation is simple or fractional distillation. However, distillation often fails to get rid of a number of impurities, including small amounts of water.
Traditional purification methods can produce a solvent that is approximately 100% pure. With the help of adsorbents, in particular molecular sieves (zeolites), this problem is solved more efficiently and with less time. In laboratory conditions, ion exchangers are most often used for this purpose - zeolites of the NaA or KA brands.
When preparing pure anhydrous solvents, precautions should be taken especially strictly, since most organic solvents are flammable substances, the vapors of which form explosive mixtures with air, and in some of them (ethers) explosive peroxide compounds are formed during long-term storage. Many organic solvents are highly toxic, both when their vapors are inhaled and when they come into contact with the skin.
All operations with flammable and combustible organic solvents must be carried out in a fume hood with ventilation running, gas burners and electric heating devices turned off. Liquids should be heated and distilled in a fume hood in preheated baths filled with an appropriate coolant. When distilling organic liquids, it is necessary to constantly monitor the operation of the refrigerator.
If flammable solvents (gasoline, diethyl ether, carbon disulfide, etc.) are accidentally spilled, it is necessary to immediately extinguish all sources of open fire and turn off electric heating devices (de-energize the work area during the day). The area where the liquid has been spilled should be filled with sand, the contaminated sand should be collected with a wooden scoop and poured into a garbage container placed outdoors.
When drying solvents, active drying agents should not be used until preliminary rough drying has been carried out using conventional drying agents. Thus, it is forbidden to dry crude diethyl ether with sodium metal without first drying it with calcined CaCl2.
When working with ethers and other substances (diethyl ether, dioxane, tetrahydrofuran), during storage of which peroxide compounds can form, peroxides are first removed from them, and then distilled and dried. Anhydrous organic solvents must be distilled carefully. All elements of the distillation installation (distillation flask, reflux condenser, refrigerator, still, distillate receiver) are pre-dried in an oven. The distillation is carried out without access to air, and the distillation is provided with a calcium chloride tube filled with ascarite and fused CaCl2 to absorb CO2 and H2O. It is advisable to discard the first portion of distillate, which serves to wash all equipment.
Methods for purification and dehydration of the most commonly used solvents are discussed below.
Acetone
Acetone CH3COCH3 is a colorless liquid; d25-4 = 0.7899; tboil = 56.24 °C; n20-D = 1.3591. Highly flammable. Vapors form explosive mixtures with air. Technical acetone usually contains water, with which it is mixed in any proportion. Sometimes acetone is contaminated with methyl alcohol, acetic acid and reducing agents.
A test for the presence of reducing substances in acetone is carried out as follows. To 10 ml of acetone add 1 drop of 0.1% aqueous solution of KMnO4; after 15 minutes at room temperature the solution should not become discolored.
To purify, acetone is heated for several hours with anhydrous K2CO3 (5% (wt.)) in a flask with a reflux condenser, then the liquid is poured into another flask with a reflux condenser 25-30 cm high and distilled over anhydrous K2CO3 (about 2% (wt.)) ) and crystalline KMnO4, which is added to acetone until a stable purple color appears in a water bath. The resulting acetone no longer contains methyl alcohol, but contains a small amount of water.
For complete removal water, acetone is re-distilled over anhydrous CaCl2. To do this, pour 1 liter of acetone into a 2-liter round-bottomed flask equipped with an effective reflux condenser closed with a calcium chloride tube containing CaCl2, add 120 g of CaCl2 and boil in a water bath with closed electric heating for 5-6 hours. Then the reaction flask is cooled and acetone is poured in into another similar flask with a fresh portion of CaCl2 and boil again for 5-6 hours. After this, the reflux condenser is replaced with a downward condenser, to which, using a longge connected to a calcium chloride tube filled with CaCl2, a receiver bottle cooled with ice is attached, and acetone is distilled over CaCl2.
Instead of such a lengthy and labor-intensive operation, which often leads to condensation of acetone, it is better to use NaA zeolite. By keeping acetone over this zeolite for a long time (5% (mass)), acetone is absolutized.
In small quantities, very pure acetone can be obtained from the adduct (addition product) of acetone and NaI, which decomposes even with low heating, releasing acetone. To do this, when heating in a water bath, dissolve 100 g of NaI in 440 ml of dry, freshly distilled acetone. The resulting solution is quickly cooled to -3°C by immersing the vessel in a mixture of ice and NaCl. The separated solid NaI-C3H6O adduct is separated on a Buchner funnel, transferred to a distillation flask and heated in a water bath. When slightly heated, the adduct decomposes, and the released acetone is distilled off. The distillate is dried with anhydrous CaCl2 and re-distilled with a reflux condenser over CaCl2. The regenerated NaI can be reused for the same reaction.
An express method for purifying acetone from methyl alcohol and reducing substances is as follows: add a solution of 3 g of AgNO3 to 700 ml of acetone in a 1-liter flask. in 20 ml of distilled water and 20 ml of 1 N. NaOH solution. The mixture is shaken for 10 minutes, after which the precipitate is filtered off on a funnel with a glass filter, and the filtrate is dried with CaSO4 and distilled with a reflux condenser over CaCl2.
Acetonitrile
Acetonitrile CH3CN is a colorless liquid with a characteristic ethereal odor; d20-4 = 0.7828; tboil = 81.6°C; n20-D = 1.3442. It is miscible with water in all respects and forms an azeotropic mixture (16% (wt.) H2O) with boiling point = 76°C. Good solvent for row organic matter, in particular amine hydrochlorides. It is also used as a medium for carrying out certain reactions, which it accelerates catalytically.
Acetonitrile is a strong inhalation poison and can be absorbed through the skin.
For absolutization, acetonitrile is distilled twice over P4O10, followed by distillation over anhydrous K2CO3 to remove traces of P4O10.
You can pre-dry acetonitrile over Na2SO4 or MgSO4, then mix it with CaH2 until the evolution of gas (hydrogen) stops and distill it over P4O10 (4-5 g/l). The distillate is refluxed over CaH2 (5 g/l) for at least 1 hour, then slowly distilled, discarding the first 5 and last 10% of the distillate.
Benzene
Benzene C6H6 is a colorless liquid; d20-4 = 0.8790; tmelt = 5.54 °C; tboil = 80 10°C; n20-D = 1.5011. Benzene and its homologues - toluene and xylenes - are widely used as solvents and media for azeotropic drying. Benzene should be handled with caution due to its flammability and toxicity, as well as the formation of explosive mixtures with air.
Benzene vapors with repeated exposure disrupt normal function hematopoietic organs; in its liquid state, benzene is strongly absorbed through the skin and irritates it.
Technical benzene contains up to 0.02% (wt.) water, a little thiophene and some other impurities.
Benzene forms an azeotropic mixture with water (8.83% (mass) H2O) with boiling point = 69.25°C. Therefore, when distilling wet benzene, the water is almost completely distilled off with the first portions of the distillate (turbid liquid), which are discarded. As soon as the clear distillate begins to distill, the drying process can be considered complete. Additional drying of distilled benzene is usually carried out with calcined CaCl2 (for 2-3 days) and sodium wire.
In the cold season, care must be taken to ensure that the distilled benzene does not crystallize in the refrigerator tube, washed with cold water (4-5°C).
Benzene and other hydrocarbons dried with sodium metal are hygroscopic, meaning they can absorb moisture.
Commercial technical benzene contains up to 0.05% (wt.) of thiophene C4H4S (tbp = 84.12°C; tm = 38.3°C), which cannot be separated from benzene either by fractional distillation or crystallization (freezing). Thiophene in benzene is detected as follows: a solution of 10 mg of isatin in 10 ml of conc. H2SO4 is shaken with 3 ml of benzene. In the presence of thiophene, the sulfuric acid layer turns blue-green.
Benzene is purified from thiophene by repeated shaking with conc. H2SO4 at room temperature. Under these conditions, thiophene is preferentially sulfonated rather than benzene. For 1 liter of benzene take 80 ml of acid. The first portion of H2SO4 turns blue-green. The bottom layer is separated, and benzene is shaken with a new portion of acid. Purification is carried out until a faint yellow color of the acid is achieved. After separating the acid layer, the benzene is washed with water, then with a 10% Na2CO3 solution and again with water, after which the benzene is distilled.
A more effective and simpler method for purifying benzene from thiophene is to boil 1 liter of benzene with 100 g of Raney nickel in a flask under reflux for 15-30 minutes.
Another way to purify benzene from thiophene is to fractionally crystallize it from ethyl alcohol. A saturated solution of benzene in alcohol is cooled to approximately -15°C, solid benzene is quickly filtered off and distilled.
Dimethyl sulfoxide
Dimethyl sulfoxide (CH3)2SO is a colorless, syrupy liquid without a distinct odor; d25-4 = 1.1014; tboil = 189°С (with decomposition); tmelt = 18.45 °C; n25-D = 1.4770. Miscible with water, alcohols, acetone, ethyl acetone, dioxane, pyridine and aromatic hydrocarbons, but immiscible with aliphatic hydrocarbons. A universal solvent for organic compounds: ethylene oxide, heterocyclic compounds, camphor, resins, sugars, fats, etc. It also dissolves many inorganic compounds, for example, at 60°C it dissolves 10.6% (wt.) KNO3 and 21.8% CaCl2. Dimethyl sulfoxide is practically non-toxic.
To purify, dimethyl sulfoxide is kept for 24 hours over active Al2O3, after which it is distilled twice at a pressure of 267-400 Pa (2-3 mmHg) over fused KOH (or BaO) and stored over NaA zeolite.
Under the influence of reducing agents, dimethyl sulfoxide is converted into (CH3)2S sulfide, and under the influence of oxidizing agents - into (CH3)2SO2 sulfone, and is incompatible with acid chlorides of inorganic and organic acids.
N,N-Dimethylformamide
N,N-Dimethylformamide HCON(CH3)2 is a colorless, highly mobile liquid with a weak specific odor; d25-4 = 0.9445; tboil = 153°C; n24-D = 1.4269. Miscible in any ratio with water, alcohol, acetone, ether, chloroform, carbon disulfide, halogen-containing and aromatic compounds; dissolves aliphatic hydrocarbons only when heated.
Dimethylformamide is distilled at atmospheric pressure without decomposition; decomposes when exposed to ultraviolet rays with the formation of dimethylamine and formaldehyde. The dimethylformamide reagent, in addition to methylamine and formaldehyde, may contain methylformamide, ammonia and water as impurities.
Dimethylformamide is purified as follows: 10 g of benzene and 4 ml of water are added to 85 g of dimethylformamide and the mixture is distilled. First, benzene is distilled off with water and other impurities, and then the pure product.
Diethyl ether
Diethyl ether (C2H5)2O is a colorless, highly mobile, volatile liquid with a peculiar odor; d20-4 = 0.7135; tboil = 35.6°C; n20-D = 1.3526. Extremely flammable; vapors form explosive mixtures with air. Vapors are approximately 2.6 times heavier than air and can spread across the surface of the desktop. Therefore, it is necessary to ensure that all gas burners nearby (up to 2-3 m) from the place of work with ether are extinguished, and electric stoves with an open spiral are disconnected from the network.
When diethyl ether is stored under the influence of light and atmospheric oxygen, explosive peroxide compounds and acetaldehyde are formed in it. Peroxide compounds cause extremely violent explosions, especially when trying to distill ether to dryness. Therefore, when determining the boiling point and non-volatile residue, the ether should first be checked for the content of peroxides. In the presence of peroxides, these determinations cannot be made.
Many reactions have been proposed for the detection of peroxide in diethyl ether.
1. Reaction with potassium iodide KI. A few milliliters of ether are shaken with an equal volume of a 2% aqueous solution of KI, acidified with 1-2 drops of HCl. The appearance of a brown color indicates the presence of peroxides.
2. Reaction with titanyl sulfate TiOSO4. The reagent is prepared by dissolving 0.05 g of TiOSO4 in 100 ml of water, acidified with 5 ml of diluted H2SO4 (1:5). When shaking 2-3 ml of this reagent with 5 ml of the test ether containing peroxide compounds, a yellow color appears.
3. Reaction with sodium bichromate Na2Cr2O7. To 3 ml of ether add 2-3 ml of a 0.01% aqueous solution of Na2Cr2O7 and one drop of diluted H2SO4 (1:5). The mixture is shaken vigorously. The blue color of the ether layer indicates the presence of peroxides.
4. Reaction with ferrothiocyanate Fe(SCN)2. A colorless solution of Fe(SCN)2, when exposed to a drop of liquid containing peroxide, turns red due to the formation of ferrithiocyanate (Fe2+ > Fe3+). This reaction allows the detection of peroxides at concentrations up to 0.001% (wt). The reagent is prepared as follows: 9 g of FeSO4-7H2O is dissolved in 50 ml of 18% HCl. Add granulated zinc and 5 g of sodium thiocyanate NaSCN to the solution in an open vessel; after the red color disappears, add another 12 g of NaSCN, shake gently and the solution is separated by decantation.
To remove peroxides, iron (II) sulfate is used. When shaking 1 liter of ether, usually take 20 ml of a solution prepared from 30 g of FeSO4-7H2O, 55 ml of H2O and 2 ml of conc. H2SO4. After washing, the ether is shaken with a 0.5% KMnO4 solution to oxidize acetaldehyde into acetic acid. Then the ether is washed with a 5% NaOH solution and water, dried for 24 hours over CaCl2 (150-200 g CaCl2 per 1 liter of ether). After this, CaCl2 is filtered on a large folded paper filter and the ether is collected in a dark glass bottle. The bottle is tightly closed with a cork stopper with a curved bottom inserted into it. acute angle calcium chloride tube filled with CaCl2 and glass wool swabs. Then, opening the bottle, quickly add sodium wire into the ether at the rate of 5 g per 1 liter of ether.
After 24 hours, when hydrogen bubbles stop evolving, add another 3 g of sodium wire per 1 liter of ether and after 12 hours the ether is poured into a distillation flask and distilled over the sodium wire. The receiver must be protected by a calcium chloride tube containing CaCl2. The distillate is collected in a dark glass flask, which, after adding 1 g of sodium wire per 1 liter of ether, is closed with a cork stopper with a calcium chloride tube and stored in a cool and dark place.
If the surface of the wire has changed significantly and when adding wire, hydrogen bubbles are released again, then the ether should be filtered into another bottle and another portion of sodium wire should be added.
Convenient and very effective way purification of diethyl ether from peroxides and at the same time from moisture - passing the ether through a column with active Al2O3. A column 60-80 cm high and 2-4 cm in diameter, filled with 82 g of Al2O3, is sufficient to purify 700 ml of ether containing a significant amount of peroxide compounds. Spent Al2O3 can be easily regenerated if a 50% acidified aqueous solution of FeSO4-7H2O is passed through a column, washed with water, dried and thermally activated at 400-450 °C.
Absolute ether is a very hygroscopic liquid. The degree of moisture absorption by ether during its storage can be judged by the blueness of the anhydrous white powder CuSO4 when added to ether (a colored hydrate CuSO4-5H2O is formed).
Dioxane
Dioxane (CH2)4O is a colorless flammable liquid with a slight odor; d20-4 = 1.03375; tboil = 101.32 °C; tmelt = 11.80° C; n20-D = 1.4224. Miscible with water, alcohol and ether in any ratio. Forms azeotropic mixtures with water and alcohol.
Technical dioxane contains ethylene glycol acetal, water, acetaldehyde and peroxides as impurities. The method for purifying dioxane should be chosen depending on the degree of its contamination, which is determined by adding sodium metal to the dioxane. If a brown precipitate is formed, then the dioxane is highly contaminated; if the surface of the sodium changes slightly, then dioxane contains few impurities and is purified by distilling over a sodium wire.
Heavily contaminated dioxane is purified as follows: 0.5 l dioxane, 6 ml conc. HCl and 50 ml of H2O are heated in a silicone (oil) bath in a stream of nitrogen in a flask with reflux at 115-120 °C for 12 hours.
Once cooled, the liquid is shaken with small portions of fused KOH to remove water and acid. Dioxane forms the top layer, it is separated and dried with a fresh portion of KOH. The dioxane is then transferred to a clean distillation flask and refluxed over 3-4 g of sodium wire for 12 hours. The purification is considered complete if the surface of the sodium remains unchanged. If all the sodium has reacted, then you need to add a fresh portion and continue drying. Dioxane, which does not contain peroxide compounds, is distilled on a column or with an effective reflux condenser at normal pressure. The purification of dioxane from peroxides is carried out in the same way as the purification of diethyl ether.
Methyl alcohol (methanol)
Methyl alcohol (methanol) CH3OH is a colorless, highly mobile flammable liquid with an odor similar to that of ethyl alcohol; d20-4 = 0.7928; tboil = 64.51 °C; n20-D = 1.3288. Miscible in all respects with water, alcohols, acetone and other organic solvents; does not mix with aliphatic hydrocarbons. Forms azeotropic mixtures with acetone (tbp = 55.7 °C), benzene (tbp = 57.5 °C), carbon disulfide (tbp = 37.65 °C), as well as with many other compounds. Methyl alcohol does not form azeotropic mixtures with water, so most of the water can be removed by distilling the alcohol.
Methyl alcohol is a strong poison that primarily affects the nervous system and blood vessels. It can enter the human body through the respiratory tract and skin. Particularly dangerous when taken orally. The use of methyl alcohol in laboratory practice is allowed only in cases where it cannot be replaced by other, less toxic substances.
Synthetic absolute methyl alcohol, produced by industry, contains only traces of acetone and up to 0.1% (wt.) water. In laboratory conditions, it can be prepared from technical CH3OH, in which the content of these impurities can reach 0.6 and even 1.0%. In a 1.5 liter flask with a reflux condenser protected by a calcium chloride tube with CaCl2, place 5 g of magnesium shavings, fill them with 60-70 ml of methyl alcohol containing no more than 1% water, add an initiator - 0.5 g of iodine (or the corresponding amount of methyl iodide, ethyl bromide) and heat until the latter dissolves. When all the magnesium has converted to methylate (a white precipitate forms at the bottom of the flask), add 800-900 ml of technical CH3OH to the resulting solution, boil in a flask with reflux for 30 minutes, after which the alcohol is distilled off from the flask with a reflux condenser 50 cm high, collecting fraction with a boiling point of 64.5-64.7 ° C (at normal pressure). The receiver is equipped with a calcium chloride tube containing CaCl2. The water content in the alcohol obtained in this way does not exceed 0.05% (mass.). Absolute methyl alcohol is stored in a vessel protected from air moisture.
Additional drying of methyl alcohol containing 0.5-1% water can be accomplished with magnesium metal without initiating the reaction. To do this, add 10 g of magnesium shavings to 1 liter of CH3OH and the mixture is left in a flask with a reflux condenser, protected by a calcium chloride tube with CaCl2. The reaction begins spontaneously, and soon the alcohol boils. When all the magnesium has dissolved, the boil is maintained by heating in a water bath for some more time, after which the alcohol is distilled, discarding the first portion of the distillate.
Anhydrous methyl alcohol is also obtained by keeping it over NaA or CA zeolite or passing it through a column filled with these molecular sieves. To do this, you can use a laboratory-type column.
The presence of acetone in methyl alcohol establish a test with sodium nitroprusside. The alcohol is diluted with water, made alkaline and a few drops of a freshly prepared saturated aqueous solution of sodium nitroprusside are added. In the presence of acetone, a red color appears, which intensifies upon acidification with acetic acid.
To remove acetone, the following method has been proposed: 500 ml of CH3OH is boiled for several hours with 25 ml of furfural and 60 ml of 10% NaOH solution in a flask with reflux, and then the alcohol is distilled off on an efficient column. A resin remains in the flask - a product of the interaction of furfural with acetone.
Petroleum ether, gasoline and naphtha
When distilling light gasoline, a number of low-boiling hydrocarbon fractions are obtained, which are used as solvents. The vapors of these hydrocarbons have a narcotic effect.
The industry produces the following reagents:
The high volatility of petroleum ether, gasoline and naphtha, their easy flammability and the formation of explosive mixtures with air require special care when working with them.
Petroleum ether, gasoline and naphtha should not contain impurities of unsaturated and aromatic hydrocarbons.
The presence of unsaturated hydrocarbons is usually determined using two reagents: a 2% solution of Br2 in CCl4 and a 2% aqueous solution of KMnO4 in acetone. To do this, add a reagent solution drop by drop to 0.2 ml of hydrocarbon in 2 ml of CCl4 and observe the color change. The test is considered negative if no more than 2-3 drops of bromine solution or KMnO4 solution are discolored.
Unsaturated hydrocarbons can be removed by repeatedly shaking a portion of hydrocarbons with 10% (vol.) conc. on a mechanical shaker for 30 minutes. H2SO4. After shaking with each portion of acid, the mixture is allowed to settle, then the bottom layer is separated. When the acid layer is no longer colored, the hydrocarbon layer is shaken vigorously with several portions of a 2% KMnO4 solution in a 10% H2SO4 solution until the color of the KMnO4 solution ceases to change. In this case, unsaturated hydrocarbons are almost completely removed and aromatic ones are partially removed. To completely remove aromatic hydrocarbons, you need to shake hydrocarbons (petroleum ether, etc.) with oleum containing 8-10% (wt.) SO3. A bottle with a ground-in stopper, in which shaking is done, is wrapped in a towel. After separating the acid layer, the hydrocarbon fraction is washed with water, a 10% Na2CO3 solution, again with water, dried over anhydrous CaCl2 and distilled over a sodium wire. It is recommended to store petroleum ether over CaSO4 and distill it before use.
The traditional chemical method of purifying saturated hydrocarbons from unsaturated ones is very labor-intensive and can be replaced by adsorption. Impurities of many unsaturated compounds are removed by passing the solvent through a glass column with active Al2O3 and especially on zeolites, such as NaA.
Tetrahydrofuran
Tetrahydrofuran (CH2)4O is a colorless mobile liquid with an ethereal odor; d20-4 = 0.8892; tboil = 66°C; n20-D = 1.4050. Soluble in water and most organic solvents. Forms an azeotropic mixture with water (6% (wt.) H2O), boiling point = 64°C. Tetrahydrofuran is prone to the formation of peroxide compounds, so you must check for the presence of peroxides in it (see Diethyl ether). Peroxides can be removed by boiling with a 0.5% Cu2Cl2 suspension for 30 minutes, after which the solvent is distilled and shaken with fused KOH. The upper layer of tetrahydrofuran is separated, 16% (mass) KOH is added again and the mixture is boiled for 1 hour in a flask under reflux. Then tetrahydrofuran is distilled over CaH2 or LiAlH4, 10-15% of the head fraction is discarded and about 10% of the residue is left in the cube. The head fraction and bottoms are added to the technical products intended for purification, and the collected middle fraction is dried over a sodium wire. The purified product is stored without access to air and moisture.
Chloroform
Chloroform CHCl3 is a colorless mobile liquid with a characteristic sweetish odor; d20-4 = 1.4880; tboil = 61.15°C; n20-D = 1.4455. Soluble in most organic solvents; practically insoluble in water. Forms an azeotropic mixture with water (2.2% (wt.) H2O), boiling point = 56.1 °C. It is non-flammable and does not form explosive mixtures with air, but is toxic - it affects internal organs, especially the liver.
Chloroform almost always contains up to 1% (wt.) ethyl alcohol, which is added to it as a stabilizer. Another impurity of chloroform may be phosgene, which is formed during the oxidation of chloroform in light.
The test for the presence of phosgene is performed as follows: 1 ml of a 1% solution of n-dimethylaminobenzaldehyde and diphenylamine in acetone is shaken with chloroform. In the presence of phosgene (up to 0.005%), an intense yellow color appears after 15 minutes. Chloroform is purified by shaking three times with separate portions of conc. H2SO4. For 100 ml of chloroform, take 5 ml of acid each time. Chloroform is separated, washed 3-4 times with water, dried on CaCl2 and distilled.
Purification of chloroform is also achieved by slowly passing the drug through a column filled with active Al2O3 in an amount of 50 g per 1 liter of chloroform.
Chloroform should be stored in dark glass bottles.
Carbon tetrachloride
Carbon tetrachloride CCl4 is a colorless, non-flammable liquid with a sweetish odor; d20-4 = 1.5950; tboil = 76.7°C; n25-D = 1.4631. Practically insoluble in water. With water it forms an azeotropic mixture (4.1% (wt.) H2O), boiling point = 66°C. Dissolves a variety of organic compounds. It has a less narcotic effect than chloroform, but is superior in toxicity, causing severe liver damage.
Carbon tetrachloride is sometimes contaminated with carbon disulfide, which is removed by stirring CCl4 at 60°C in a reflux flask with a 10% (v/v) concentrated alcohol solution of KOH. This procedure is repeated 2-3 times, after which the solvent is washed with water, stirred at room temperature with small portions of conc. H2SO4 until it stops coloring. Then the solvent is washed again with water, dried over CaCl2 and distilled over P4O10.
Drying of CCl4 is achieved by azeotropic distillation. Water is removed with the first cloudy portions of the distillate. As soon as the clear liquid begins to distill, it can be considered anhydrous.
Ethyl acetate
Ethyl acetate CH3COOC2H5 is a colorless liquid with a pleasant fruity odor; d20-4 = 0.901; tboil = 77.15°C; n20-D = 1.3728. Forms an azeotropic mixture with water (8.2% (wt.) H2O), boiling point = 70.4 °C.
Technical ethyl acetate contains water, acetic acid and ethyl alcohol. Many methods have been proposed for purifying ethyl acetate. In one of them, ethyl acetate is shaken with an equal volume of a 5% NaHCO3 solution and then with a saturated CaCl2 solution. After this, ethyl acetate is dried with K2CO3 and distilled in a water bath. For final drying, 5% P4O10 is added to the distillate and shaken vigorously, then filtered and distilled over a sodium wire.
Ethanol
Ethyl alcohol C2H5OH is a colorless liquid with a characteristic odor; d20-4 = 0.7893; tboil = 78.39 °C; n20-D = 1.3611. Forms an azeotropic mixture with water (4.4% (wt.) H2O). It has a high dissolving ability for a wide variety of compounds and is indefinitely miscible with water and all common organic solvents. Industrial alcohol contains impurities, the qualitative and quantitative composition of which depends on the conditions of its production.
The produced absolute alcohol, which is obtained by azeotropic distillation of 95% technical alcohol with benzene, may contain small amounts of water and benzene (up to 0.5% (wt.)).
Dehydration of 95% alcohol can be done by prolonged boiling with calcined CaO. For 1 liter of alcohol take 250 g of CaO. The mixture is boiled in a 2-liter flask with a reflux condenser, closed with a tube containing CaO, for 6-10 hours. After cooling, the flask is connected to a distillation unit at atmospheric pressure and the alcohol is distilled off. Yield 99-99.5% alcohol 65-70%.
Barium oxide BaO has higher dehydrating properties. In addition, BaO is able to dissolve somewhat in almost absolute alcohol, turning it yellow. This sign is used to determine when the process of absolutization is completed.
Further dehydration of 99-99.5% alcohol can be carried out using several methods: using magnesium (ethyl alcohol with a water content of no more than 0.05%), sodium and diethyl oxalic acid.
Pour 1 liter into a 1.5 liter round-bottomed flask with a reflux condenser and a calcium chloride tube containing CaCl2. 99% ethyl alcohol, after which 7 g of sodium wire is added in small portions. After the sodium has dissolved, 25 g of oxalic acid diethyl ether is added to the mixture, boiled for 2 hours and the alcohol is distilled off.
Absolute alcohol is prepared in the same way using orthophthalic acid diethyl ester. In a flask equipped with a reflux condenser and a calcium chloride tube with CaCl2, place 1 liter of 95% alcohol and dissolve 7 g of sodium wire in it, then add 27.5 g of phthalic acid diethyl ether, boil the mixture for about 1 hour and distill off the alcohol. If a small amount of sediment forms in the flask, this proves that the original alcohol was sufficiently good quality. Conversely, if a large amount of sediment falls out and boiling is accompanied by shocks, then the original alcohol was not dried enough.
Drying of ethyl alcohol is currently carried out in column-type devices with NaA zeolite as a packing. Ethyl alcohol containing 4.43% water is fed for drying into a column with a diameter of 18 mm with a packing layer height of 650 mm at a speed of 175 ml/h. Under these conditions, in one cycle it is possible to obtain 300 ml of alcohol with a water content of no more than 0.1-0.12%. Zeolite is regenerated in a column in a nitrogen stream at 320 °C for 2 hours. When distilling ethyl alcohol, it is recommended to use thin-section devices; In this case, the polished sections are thoroughly cleaned and not lubricated. It is advisable to discard the first part of the distillate and complete the distillation when a little alcohol remains in the distillation flask.
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