RU2150452C1 - 1,1-difluoroethane production process - Google Patents

Abstract

FIELD: industrial organic synthesis. SUBSTANCE: vinyl chloride is fluorinated with hydrogen fluoride in presence of tin tetrachloride. Fluorination products are separated from major part of vinyl chloride, distilled in presence of anhydrous hydrogen fluoride, and freed from hydrogen chloride via rectification under pressure 6 to 16 atm, in the course of which hydrogen chloride in the form of fraction with boiling range from -12 to -40 C is distilled off. Residual vinyl chloride is removed from products when in contact with tin tetrachloride at 30-75 C and pressure up to 15 atm. Final rectification gives desired product and hydrogen fluoride fraction to be recycled into fluorination stage. Level of vinyl chloride in product is below 0.0002%. EFFECT: increased purity of product and improved environmental condition because of more complete utilization of raw material. 6 tbl, 4 ex

Description

 The invention relates to chemical technology, and in particular to methods for producing 1,1-difluoroethane (chladone 152a), an ozone-safe fluorocarbon used as a component of refrigerants, propellant in aerosol containers, blowing agent and as a raw material for the production of fluorine-containing monomers and chladones.

 A known method for producing 1,1-difluoroethane by fluorination of vinyl chloride with hydrogen fluoride in the presence of tin tetrachloride as a catalyst, comprising the purification of 1,1-difluoroethane from vinyl chloride, forming an azeotropic mixture with 1,1-difluoroethane, by distillation in the presence of anhydrous hydrogen fluoride (ed. St. USSR N 341788, class С 07 С 19/08, 1972).

 The known method for producing 1,1-difluoroethane allows to obtain a product with a vinyl chloride content of an average of 0.2%. Vinyl chloride has a carcinogenic effect, so the indicated concentration of vinyl chloride is undesirable, especially when using 1,1-difluoroethane as a propellant in aerosol containers.

 The technical task of the present invention is to obtain 1,1-difluoroethane with a reduced content of vinyl chloride, as well as improving the environmental parameters of the process and increasing the efficiency of production due to a more complete use of raw materials.

The problem is solved in that in the method for producing 1,1-difluoroethane, including fluorination of vinyl chloride with hydrogen fluoride in the presence of tin tetrachloride and the release of fluorination products from vinyl chloride using distillation in the presence of anhydrous hydrogen fluoride, the fluorination products after distillation are freed from hydrogen chloride and It was further purified by vinyl chloride by contacting with tin tetrachloride at a temperature of 30-75 ^o C and a pressure up to 15 atm after uyuschim separating 1,1-difluoroethane from the hydrogen fluoride by distillation.

The liberation of fluorination products from hydrogen chloride is preferably carried out by distillation under a pressure of 6-16 atm with the selection of hydrogen chloride in the form of a light fraction with a temperature in the range from -12 to -40 ^o C.

 The hydrogen fluoride fraction after separation from 1,1-difluoroethane can be returned to the vinyl chloride fluorination step.

 The method was tested in laboratory conditions.

 Example 1. In experiments on the production of 1,1-difluoroethane, vinyl chloride is used according to TU 6-01-14-90, anhydrous hydrogen fluoride according to GOST 14022-88 grade A and tin tetrachloride according to TU 6-09-3182-87. The experiments are carried out in a continuous laboratory apparatus made of nickel-chromium steel. The installation consists of a unit for the synthesis of 1,1-difluoroethane combined with the main stage of purification of fluorination products from vinyl chloride, a unit for the separation of hydrogen chloride by distillation, a unit for an additional purification stage, and a unit for isolating the target product.

 The synthesis unit and the main purification stage contain a 1-liter reactor equipped with a thermometer, a siphon for feeding vinyl chloride, reagent dispensers, a distillation column with an efficiency of about 8 tons, installed directly above the reactor, a refrigerator, at the outlet of which there is a thermometer, pressure gauge, valve for the selection of gaseous products and a protective membrane. The synthesis unit is designed for 20 ati. The reactor is installed in a glycerin bath.

 A predetermined amount of catalyst, tin tetrachloride, is poured into the reactor. The reactor is sealed, heated to a predetermined temperature, the refrigerator is cooled. Then, the supply of reagents in liquid form begins continuously at a constant speed from the dispensers by extrusion with nitrogen. Vinyl chloride is fed via a siphon to the liquid phase of the reactor, and hydrogen fluoride is fed to the middle of the distillation column, from where it flows by gravity into the reactor. Gaseous reaction products enter the distillation column for distillation in the presence of hydrogen fluoride, then to the refrigerator. Condensable products flow through a distillation column into a reactor. Upon reaching the set pressure in the installation, a continuous selection of gaseous reaction products begins, which at the first stage is condensed and collected in a two-liter cylinder made of chromium-nickel steel cooled with liquid nitrogen, and in subsequent experiments they are directed to the separation of hydrogen chloride by distillation. The reaction products are weighed and analyzed for the content of hydrogen chloride, hydrogen fluoride and organic substances by gas chromatographic method.

 At this stage, simultaneously with the synthesis of the product, the resulting 1,1-difluoroethane is purified from the main amount of vinyl chloride impurity due to the reaction of the latter with hydrogen fluoride in the presence of the resulting hydrogen chloride.

 Specific conditions and test results are shown in table 1.

 From the table. 1 shows that the organic product contains up to 0.2% vinyl chloride. Before further purification from vinyl chloride, the products obtained at this stage are freed from hydrogen chloride at the next unit of the laboratory setup. This node is also designed for 20 ati. It is a distillation column with an efficiency of 30 tons, a height of 1.2 m and an inner diameter of 18 mm, with a head and a cube. Column nozzle - nichrome spirals. The head is equipped with a refrigerator, a manometer, a thermometer for measuring the reflux temperature and viewing windows for measuring the amount of reflux, a valve for selecting a light fraction at the outlet of the refrigerator. The cube is equipped with a heater, a valve for power supply and a thermometer. The rectification mode is semi-continuous: with continuous power supply and selection of a light fraction (hydrogen chloride) and the accumulation of organic products and hydrogen fluoride in the cube. There is a light fraction processing system.

 The product from the previous step is loaded from the weighed balloon into the cube of the prepared column. The column is introduced into the work by creating the necessary temperature in the cube and, accordingly, reflux at a given pressure. After working "for yourself" for 1.5-2 hours, the selection of the light fraction begins, which is sent to washing the hydrogen chloride to obtain hydrochloric acid, then to drying with calcium chloride and to condensate the remaining product.

 The specific conditions at this stage and the results of the experiments are presented in table 2. From table. 2 shows that the bottom fraction obtained at this stage consists mainly of organic products. It is sent for additional purification from vinyl chloride.

 The additional purification unit is a 0.5 liter reactor equipped with a reflux condenser. The refrigerator is cooled with brine or water. The reactor is equipped with a thermometer, and a manovacuum meter and a needle valve for sampling products are installed at the outlet of the refrigerator.

 Tin tetrachloride is charged into the reactor, the reactor is sealed, frozen, vacuumized. Through the valve, the analyzed bottoms fraction from the previous step is loaded by weight. Refrigerant is served in the refrigerator. The reactor is placed in a thermostatic bath with a given temperature. Upon reaching a predetermined pressure, a continuous selection of products through a flushing tank with water is started using a valve to absorb hydrogen chloride and hydrogen fluoride. Then the product is dried with calcium chloride and condensed in a cylinder cooled by liquid nitrogen. At the end of the wash water analysis experiment, the mass of hydrogen chloride and unreacted hydrogen fluoride formed is determined. By weighing and subsequent chromatographic analysis, the mass and composition of the condensed organic product are determined. The conversion of hydrogen fluoride is calculated as the fraction of the reacted hydrogen fluoride from the charged with bottoms fraction. The degree of purification of the organic product from vinyl chloride is calculated as the fraction of the reacted vinyl chloride from the original. Specific conditions and experimental results are shown in table 3.

From the table. 3 shows that the organic product is sufficiently deeply purified from vinyl chloride in the proposed conditions. In this case, the purification process is accompanied by an increase in the yield of the target product due to the reaction with hydrogen fluoride not only vinyl chloride, but also a non-fluorinated product - 1,1-fluorochloroethane (CH ₃ CHClF).

 From the organic products obtained at this stage by distillation, the target product is isolated. This operation is described below (see example 4).

 Example 2. The synthesis products of 1,1-difluoroethane were obtained and freed from hydrogen chloride, as described in example 1. The stage of additional purification of the organic product from vinyl chloride is carried out with more intensive mass transfer due to stirring due to reflux circulation.

 The experiments were carried out in a 0.32 liter reactor made of chromium-nickel steel, designed for a pressure of 20 ati, equipped with a heating jacket, a thermometer, a sight glass in the middle part to observe the mixing of the reaction mixture, pipes for loading reagents and condensate return and a reflux condenser. At the entrance to the refrigerator there is a viewing window, and at the exit there is a manovacuum meter and a valve to remove air and select reaction products from the gas phase. To supply condensate from the refrigerator to the lower part of the reactor, a siphon with a removable fluoroplastic bubbler is installed in the latter.

The reactor and the refrigerator are prepared for the experiment, tin tetrachloride and bottoms are charged from the previous stage, as described in Example 1. Next, the coolant is fed into the reactor jacket. The contents of the reactor for 2-5 minutes are heated to a predetermined temperature, which is maintained during the experiment. In this case, the reaction mass boils, which is observed through the viewing window of the reactor, and abundant reflux forms (it is noticed through the viewing window at the inlet to the refrigerator), which is fed via a siphon to the lower part of the reactor. Due to this, intensive mixing takes place in the reactor. Upon reaching the set pressure, non-condensable products in the refrigerator are taken through a valve, washed with water from hydrogen chloride and fluoride, and collected either in a gas meter or after drying with calcium chloride, they are condensed in a cylinder cooled with liquid nitrogen. At the end of the experiment, the reactor is quickly cooled to -10 ^o C, and its contents are subjected to chemical analysis for the content of hydrogen chloride and fluoride and chromatographic analysis for the composition of the organic product. By analyzing all the products in each experiment, balance is struck. Specific conditions and experimental results are presented in table 4.

 From the table. Figure 4 shows that in all experiments, a high degree of purification of the organic product from vinyl chloride is observed - to a content of not higher than 0.0002 mol. % The cleaning process is accompanied by the additional formation of the target product.

 Example 3. The synthesis products of 1,1-difluoroethane were obtained and freed from hydrogen chloride, as described in example 1. The stage of additional purification of the organic product from vinyl chloride is carried out in a reactor with circulation of heavy products.

 The laboratory setup includes a reactor with a capacity of 0.33 l of chromium-nickel steel, designed for 20 ati. The reactor is equipped as in example 2 and is additionally equipped with an external heat exchanger - a boiler. The latter is connected by regrind in the upper and lower parts, respectively, with the upper and lower parts of the reactor vessel, equipped with a jacket for the coolant and a thermometer. In contrast to the reactor, in example 2, the sight glass is installed in the upper part of the reactor, opposite the entry point of the upper regrind from the boiler. In addition, the reactor does not have a siphon: condensate return from the refrigerator to the reactor is organized on the surface of the reaction mass.

 The experiments begin, as described in example 2 until the moment of heating. Heating is carried out by supplying a coolant to the boiler jacket. After 1-3 minutes, the set temperature is established in the reactor, which is maintained during the experiment by regulating the heating of the boiler. Intensive mixing of the reaction mass occurs due to the circulation of heavy components (hydrogen fluoride and catalyst) through the reaction mass. The circulation is carried out by heating in the boiler part of the reaction mass, selected by regrinding from the bottom of the reactor and consisting mainly of hydrogen fluoride and tin tetrachloride. The heated vapor-liquid mixture from the boiler through the upper regrind enters the reactor, and the liquid part goes directly to the surface of the reaction mass, and the vaporous part goes to the refrigerator, from where products also enter the surface of the reaction mass in the form of condensate. Heavy products descend, causing intense mixing of the reaction mass.

 The reaction products are collected and analyzed as in example 2. The specific conditions and results of the experiments are shown in table 5. Experiment 3 is a control, carried out in the absence of a catalyst and proves the need for the latter at this stage of the process.

 Examples 1-3 prove the effectiveness of additional purification of the reaction products under the proposed conditions, while the process of obtaining 1,1-difluoroethane is accompanied by a slight increase in the yield of the target product due to the involvement of non-fluorinated impurities in the process and more complete use of hydrogen fluoride. In this case, secondary contamination of the target product does not occur, since all the resulting impurities are due to the composition of the raw materials and occur in the known method. So, 1,1,1-difluorochloroethane and 1,1,1-trifluoroethane are formed from an impurity - vinylidene chloride, which is present in organic raw materials. Methyl chloride is formed from methanol, which is present in the feed as a stabilizer. All of these by-products are easily separated by distillation in the next stage of the process (see example 4).

 Example 4. The combined organic product obtained in examples 1-3, containing 1,1-difluoroethane, hydrogen chloride and fluoride and organic impurities, is subjected to periodic rectification on a column of chromium-nickel steel with an efficiency of 20 tons, calculated on the pressure of 20 MPa. In this case, the target fraction is obtained, intermediate and still. The fraction of fractions from the load and the composition of the fractions, as well as the conditions of rectification during the selection of fractions are presented in table 6.

In experiment 1, 1.35 mol of hydrogen fluoride, 0.09 mol of hydrogen chloride and 8.87 mol of an organic product of the composition, mol.%, Were fed for rectification with the initial product.
1,1-Difluoroethane (CH ₃ CHF ₂ ) - 99.81
Methyl Chloride (CH ₃ Cl) - 0.07
1,1-Fluorochloroethane (CH ₃ CHClF) - 0.11
1,1-Dichloroethane (CH ₃ CHCl ₂ ) - 0.01
Vinyl Chloride (C ₂ H ₃ Cl) - Less than 0,0002
The target fraction was washed with water and dried with calcium chloride. When this is obtained the target product composition, mol.%:
1,1-Difluoroethane - 99.92
Methyl Chloride - 0.08
Vinyl Chloride - Less than 0.0002
In experiment 2 receive two fractions: target and still.

 The distillation residue from the rectification (i.e., the bottoms fraction), containing mainly hydrogen fluoride with a small amount of 1,1-difluoroethane and impurities of underfluorinated products (see Table 6), is to be returned to the beginning of the process, to the stage of fluorination of vinyl chloride. This will not worsen the process at this stage, since the bottom residue is practically free of hydrogen chloride and other undesirable impurities.

Thus, the proposed method in comparison with the prototype has several advantages, because it provides:
- greater purity of the target product, mainly in relation to vinyl chloride;
- a higher degree of reaction of vinyl chloride;
- higher yield of the target product;
- almost full use of hydrogen fluoride;
- lack of substandard products.

 The experiments confirm the efficiency, effectiveness and feasibility of industrial use of the proposed method. The necessary equipment is standard and not difficult to manufacture.

Claims (3)

1. The method of producing 1,1-difluoroethane, comprising the fluorination of vinyl chloride with hydrogen fluoride in the presence of tin tetrachloride and the release of fluorination products from vinyl chloride using distillation in the presence of anhydrous hydrogen fluoride, characterized in that the fluorination products after distillation are freed from hydrogen chloride and subjected further purification of vinyl chloride by contacting with tin tetrachloride at a temperature of 30 - 75 ^o C and a pressure of 15 atm, followed by separation m 1,1-difluoroethane from the hydrogen fluoride by distillation. 2. The method according to claim 1, characterized in that the liberation of fluorination products from hydrogen chloride is carried out by distillation under a pressure of 6 to 16 atm with the selection of hydrogen chloride in the form of a light fraction with a temperature in the range from -12 to -40 ^o C.  3. The method according to claim 1, characterized in that the fraction of hydrogen fluoride after separation from 1,1-difluoroethane is returned to the stage of fluorination of vinyl chloride.

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