RU2066307C1 - Method of 1,1,1-difluorochloroethane synthesis - Google Patents

Abstract

FIELD: chemical technology. SUBSTANCE: reagent 1: 1,1-difluoroethane. Reagent 2: chlorine. Synthesis conditions: in medium of diluent - perhalogenated carbon and initiating agent - fluorine which is contacted preliminary with liquid diluent. Process is carried out at temperature not above diluent boiling point followed by diluent condensation, its separation from reaction gases and recovery to the process head. Synthesized 1,1,1-difluorochloroethane shows low toxicity and activity with respect to ozone layer. EFFECT: improved method of synthesis. 4 cl

Description

 The invention relates to chemical technology, and in particular to methods for producing 1,1,1-difluorochloroethane (freon-142), which is low-toxic and inactive to the ozone layer, the freon used as a refrigerant and as a raw material for the production of 1,1-difluoroethylene (monomer 2) .

 Known methods for producing 1,1,1-difluorochloroethane by chlorination of 1,1-difluoroethane with initiation of the process by active light. So, according to British patent N 785209 (class C 2 C, prior. 1955), the process is carried out in carbon tetrachloride; according to USSR author's certificate N 1083541 with priority from 08/31/81 photochlorination of 1,1-difluoroethane in the presence of water. The main disadvantage of these methods is the complexity of the industrial design of the chlorination process, due to the lack of domestic industrial photochemical reactors and washing active light sources necessary for industrial production.

Known methods for producing 1,1,1-difluorochloroethane from 1,1-difluoroethane by thermal chlorination in the presence of a nitric oxide initiator [US Pat. Belgium N 760506, class С07с, declared 12/18/70, publ. 03.03.76] or fluorine [a. from. USSR N 400565, class С07с 19/08, declared 09/19/69, publ. 10/01/73] These methods are carried out in the gas phase. The first of them is carried out at high temperature (295-304 ^o C). It has a low selectivity (maximum yield of the target product 86.4%) and a low degree of conversion of difluoroethane (not more than 35%).

The closest of those mentioned in technical essence and effectiveness is the method described in a. from. USSR 400565, in which 1,1,1-difluorochloroethane is obtained by gas-phase chlorination of 1,1-difluoroethane at elevated temperature (100-200 ^° C) in the presence of a diluent (argon and carbon tetrachloride) and an elementary fluorine initiator in an amount of 0.05- 1% by weight, counting on 1,1-difluoroethane, followed by isolation of the target product from the reaction gases. The method is quite selective. The yield of the target product is 92.5-96% with the conversion of 1,1-difluoroethane 57-65%. However, it should be noted that the mixture of 1,1-difluoroethane with chlorine is explosive, and in a fairly wide range: from 13.1 ± 0 , 5 to 30.0 ± 0.2% vol. difluoroethane at atmospheric pressure, room temperature, in the absence of actinic light ["Puncture of experiments to determine the concentrated ignition limits of 1,1-difluoroethane in a mixture with chlorine" dated 05.19.88. Obninsk, branch of NIPHI im. L. Ya. Karpova] under UV irradiation, the ignition limits of this mixture are wider: from 13.4 ± 0.3 to 34.0 ± 0.4% vol. ["Protocol of experiments on determining the concentration limits of ignition of 11,1-difluoroethane (152A freon) in chlorine when a mixture is ignited with UV light" from 01.30.90, M, Higher Fire Engineering School of the USSR Ministry of Internal Affairs, n / a. N 7 / 32-63 from 02/07/90]
Thus, the disadvantage of the latter method, as well as other previous gas-phase methods, is the danger during the chlorination process in the gas phase, when an explosive concentration of difluoroethane in a mixture with chlorine can be created when the supply of diluent is reduced or the supply of reagents decreases. This disadvantage excludes the possibility of industrial use of the known method.

 The purpose of the present invention is to increase the safety and stability over time of the chlorination process.

 The goal is achieved in that in the known method for producing 1,1,1-difluorochloroethane by chlorination of 1,1-difluoroethane with chlorine in the presence of a perhalogenated carbon diluent and an elementary fluorine initiator, followed by isolation of the target product, a fluorine-containing perhalogenated carbon selected from the group is used as a diluent including 1,1,2-trifluorotrichloroethane (HFC 113), 1,2-difluorotetrachloroethane (HFC 112), performylcyclohexane (HFC 350), performethylcyclohexane (HFC 400), the starting reagents and the initiator re-contact with the liquid diluent, and the process is conducted at a temperature not exceeding the boiling point of the diluent, followed by condensation of the diluent, separating it from the reaction gases and returning to the beginning of the process.

 Another difference is that 1,1,2-trifluorotrichloroethane is taken as the perhalogenated carbon of the diluent.

 In addition, the process is conducted in a reactor with an inner surface of a metal selected from the group comprising nickel, nichrome, fluoroplastic.

 The use of these diluents is due to their indifference to chlorine, fluorine, hydrogen fluoride and reaction products, good solubility of raw materials in them, their high ability to remove heat of the chlorination reaction, low boiling point, and their availability. Materials for the reaction equipment are selected experimentally.

 The method is given in laboratory conditions. The invention is illustrated by the following examples.

 PRI me R 1.

In the experiments used:
1,1-difluoroethane obtained by hydrofluorination of vinyl chloride according to a. from. 341788, С 07 С 19/08 and purified from impurities (the content of organic impurities in it is indicated in specific examples) with an oxygen content of not more than 0.002% vol.

 liquefied chlorine according to GOST 6718-86, i.e., not containing oxygen.

 To initiate the chlorination process in the experiments of all examples, fluorine was used, obtained by electrolysis of potassium trifluoride and without additional purification from impurities of hydrogen fluoride, with a content of 10-25% mol. hydrogen fluoride.

 Helium according to TU 51-940-80 is used for dilution of fluorine.

 The oxygen content in diluted fluorine was monitored.

 For each experiment, we used one of the column type reactors equipped with a level gauge made of transparent fluoroplast-4MB, a thermostatic jacket and a reflux condenser cooled by any water, or a cold brine. Nickel reactor dimensions: inner diameter 37 mm, height 600 mm; nichrome 54 and 240 mm, respectively, fluoroplastic (from fluoroplast-4) and 700 mm.

 A reflux condenser, supply lines for raw materials and thermowells for thermocouples for metal reactors are made of nickel, for fluoroplastic of fluoroplast-4D. The fluoroplastic made supply communications and bubblers for fluorine.

 The supply of chlorine and 1,1-difluoroethane is provided for in the lower liquid layer in the reactor through tubular distributors with perforations with a diameter of about 1 mm, the fluorine supply is also in the lower part of the reactor, but in the lower liquid layer (30-80 mm lower than the feed ) through a bubbler with holes with a diameter of about 0.2 mm.

 A predetermined volume of liquid diluent was poured into the reactor, the reactor was thermostated, and the supply of the starting gaseous reagents from the cylinders was started at a constant speed, supported by rheometers. At the same time, fluorine was diluted with helium to a 1-2% concentration, also at a constant speed, which was established using a calibrated washer and a needle valve and controlled by pressure loss in a cylinder with a previously analyzed mixture of fluorine with helium.

 The reaction gases in the reflux condenser were freed from the main part of the evaporated diluent (the resulting phlegm drained into the reactor) and sent for washing first with water from hydrogen chloride, then with a 4% solution of sodium hydroxide from chlorine. Wash solutions were analyzed at the end of each experiment, determining the content of the formed hydrogen chloride and unreacted chlorine. According to the results of water analysis, the consumption of chlorine was calculated for each experiment and the degree of its conversion.

 The washed gaseous products were dried with calcium chloride, their volume was accurately measured by a pelvic counter and analyzed chromatographically, taking into account both the helium content and entrained vapor of the diluent. The helium consumption and the initial fluorine content in it determined the exact fluorine consumption. The amount of the obtained target product was determined by the volume of gases and their composition.

 The exact consumption of 1,1-difluoroethane was determined by the weight loss in the supply cylinder.

 Some experiments were carried out with an additional supply of liquid diluent to the reactor to compensate for its entrainment with the reaction products and to maintain a constant level in the reactor.

The specific conditions and results of the experiments are presented in table 1. The composition of the products obtained in these experiments and selected after the processed refrigerator, as well as the composition of the starting organic raw materials are presented in table 2 (the numbering of the experiments in tables 1 and 2 is the same). The composition of the products obtained depends on the temperature in the reflux condenser, which is cooled either with tap water (op. 4-8, 11), or thermostatically controlled water (op. 12, 13, 18), or with a brine minus 40 ^o C (other experiments). As a diluent in the experiments used:
1,1,2-trifluorotrichloroethane (freon 113) according to GOST 23844-79;
1,1, -Difluorotetrachloroethane (Freon 112) 99.9% with a moisture content of less than 0.002% wt.

perfluoromethylcyclohexane (freon 350) according to TU 044-10-84;
perfluorodimethylcyclohexane (freon 400) according to TU 95-1693-88.

 From tables 1 and 2 it is clearly seen that under the described conditions, 1,1,1-difluorochloroethane is formed in high yield and at high conversion of the feedstock. Moreover, the chlorination process proceeds calmly and without popping, without sharp fluctuations in temperature and fluid emissions. By carrying out the reaction in solution, a reliable and constant heat removal of the reaction is ensured. The result of the reaction in the diluent medium is the saturation of the starting materials and reaction products with chladones 113, 112, 350 and 400. At the same time, the concentrations of difluoroethane and chlorine in the reaction mixture are reduced due to the diluent, so that the ignition concentrations of 1,1-difluoroethane in chlorine are not reached , which increases the safety of the chlorination process.

 The following examples are given to substantiate the significance of the distinguishing features of the proposed method.

 PRI me R 2.

The experiment was carried out as described in example 1, but using carbon tetrachloride as a diluent. Specific experimental conditions: nichrome reactor, 400 ml diluent, reactor temperature 22 ^o C, reflux 5 ^o C, feed rate of 1,1-difluoroethane 10.8 l / h, chlorine 10.2 l / h, helium 6 , 1 l / h, fluorine 0.56 l / h (2.2% by weight of difluoroethane). The duration of the experiment is 3 hours.

 After the experiment, the diluent was analyzed: it contained 2.31% mole. fluorotrichloromethane (freon 11).

 Experience proves the unsuitability of carbon tetrachloride as a diluent, since it is fluorinated under the conditions of the experiment to HFC 11.

 PRI me R 3.

The trial was performed as described in Example 1, a nichrome reactor, but the reactor pre-placed stainless steel foil with a surface mark 12X18H10T 326 cm ² and a known mass. Specific conditions of the experiment: diluent Freon 113, temperature in the reactor 14 ^o C, in the reflux condenser minus 15 ^o C, feed rate of 1,1-difluoroethane, chlorine and fluorine 15; 12 and 0.11-0.13 l / h, respectively. The duration of the experiment is 8 hours.

At the end of the experiment, the foil was removed from the reactor and weighed; the corrosion rate was determined by mass loss: 0.32 g / m ² • h.

The diluent in the reactor was replaced with a new portion of HFC 113 (500 ml) without washing the reactor, and another experiment was carried out under the same conditions, but at a temperature in the reactor of 22 ^o C, in a reflux condenser of 5 ^o C and with an additional supply of HFC 113 to maintain a constant level in the reactor, with sampling for analysis every 0.5 hours and an increased supply of fluorine by the end of the experiment. Specific conditions and results of the experiment are presented in table 3.

 The table shows that at the beginning of the experiment, the degree of conversion of the reagents is lower than in a similar experiment, but in the absence of foil (see option 11 of Example 1), and after 3.5 hours from the beginning of the experiment, the degree of conversion of the reagents decreased by half, despite increased feed initiator.

 Upon visual inspection of the reactor after liberation from the liquid, a yellow precipitate was found on its inner walls, which, according to elemental analysis, contained 4.6% iron.

 Experience dismantles the inapplicability of steels (including steel 12X18H10T) as the material of the working surface of the reactor.

 PRI me R 4.

The experiment was carried out, as described in example 1, in a nickel reactor using undehydrated freon 113. Test conditions: temperature in the reactor 11-13 ^o C, in a reflux condenser minus 13 ^o C. Other conditions and results of the experiment are shown in table 4.

 From table 4 shows a low conversion of reagents. The reason for this was revealed at the end of the experiment: green drops of moisture with dissolved nickel salts of the corrosion products of the reactor under the action of the formed acids were found in the diluent extracted from the reactor.

 Experience dismantles the necessity of using dry reagents and diluent in the proposed method.

 PRI me R 5.

The experiment was carried out as described in example 1. Experimental conditions: nickel reactor, HFC-113 diluent, its amount was 500 ml, the temperature in the reactor was 14-15 ^o C, in a reflux condenser 5 ^o C. A constant level of diluent (500 ml) was maintained by additional filing it during the experiment.

 The diluent used met the technical requirements of GOST 24844-79 amended. 1.2, a moisture content of less than 0.003% wt. Chlorine and 1,1-difluoroethane were dried by phosphor spotting before being fed to the reactor.

 The duration of the experiment is 8 hours. Periodically (after 0.5 h), organic products were taken for analysis and the feed rate of the reagents was measured. The results in table 5.

 From table 5 it is seen that the process of formation of 1,1,1-difluorochloroethane was quite stable over time, fluctuations in the degree of conversion of the reactants are negligible.

 Thus, examples 4 and 5 dismantle the need to use in the proposed method, reagents and diluent that do not contain moisture.

 PRI me R 6.

2 experiments were carried out, as described in example 1. In the first experiment, the fluoroplastic reactor described in example 1 was used, with slight differences: in the upper part the reactor was equipped with an expander with two reflux coolers from fluoroplast-4. In the lower part, 115 mm from the bottom, the reactor had a fluoroplastic-4 distribution grid with 230 openings with a diameter of 0.5 mm and a free section of 45 mm ² . Chlorine, 1,1-difluoroethane and fluorine were introduced into the diluent HFC 113 under the grid: 1,1-difluoroethane and the uppermost part of the sublattice, chlorine 50 ml lower and fluorine 50 mm lower. The course of the chlorination process was monitored by the composition of the products and by the temperature of the diluent in the reactor (thermocouple in the middle of the reactor) and in the sublattice. As a diluent, Freon 113 was used in accordance with GOST 23844-79 amended. 1,2. Reagents were dried by spotting phosphorus before use.

 Experiment 2 was carried out with the only difference, the fluoroplastic lattice was removed, and the reagents were fed as in example 1.

 The starting organic product contained 99.85% mole. 1,1-difluoroethane and 0.15% mol. vinyl chloride.

 More specifically, the conditions and results of these experiments are shown in tables 6, 7. The numbers of the experiments of these tables are the same.

 The experiments began with the fact that Freon 113 was poured into the reactor at room temperature. Then fluorine and reagents are fed at certain rates.

The chlorination process of 1,1-difluoroethane is accompanied by heating of the HFC 113. In experiment 1, the HFC temperature became 34 ^° C after 0.5 hours. Then the HFC temperature dropped sharply, and the outer surface of the lower part of the reactor (near the grate) became hot to the touch (temperature the outer wall is above 60 ^o C. In the future, the temperature of the diluent was slowly applied (see column 9 of Table 6), and the lower part of the reactor was heated.

 From the readings of the thermocouple in the reactor it follows that the reaction was completely completed in the sublattice space of the reactor. The temperature drop in the reactor is due to the cooling of the diluent with reflux from the reflux condenser.

 As can be seen from table 6, this process was accompanied by a sharp drop in the degree of conversion of reagents from 75-80% at the beginning of the experiment to 22-29% after 3 hours of operation, as well as a drop in the yield of the target product. The described is a consequence of the chlorination of 1,1-difluoroethane in the sublattice region of the reactor, from which freon 113 was displaced by the reagents into the reactor above the lattice. The reaction began to proceed in the gas phase and in the absence of contact of the reactants with the diluent, moreover, with a low conversion of the reactants and a low yield of the target product. 3 boiling unknown impurities appeared in the organic product and the content of HFC 143 increased (see Table 7). Due to the unproductive expenditure of fluorine on the formation of freon 143, the chain reaction of chlorination was terminated, resulting in a low degree of conversion of the reactants, as well as a sharp decrease in the yield of the target product due to the formation of by-products.

Under industrial conditions, the process of chlorination in the gas phase and without heat removal is extremely described, because due to the heat of chlorination of 1,1-difluoroethane (about 25 kcal / mol), the products can be heated from 1000 ^o C and their volume can increase dramatically (by 4 -5 times).

Experiment 2 (see Tables 6 and 7) was carried out in the liquid phase in Freon 113 medium. Moreover, during the experiment, the temperature in the reactor (30-31 ^o C), the conversion of the reactants and the yield of the target product are subject to slight fluctuations. The process is without clapping, without sudden fluctuations in temperature or liquid spills. Moreover, throughout the experiment, a high conversion of reagents with a high yield of the target product is maintained. In this experiment, fluorine is not spent on the formation of a by-product of HFC 143, but on the initiation of a chlorination process, the proof of which is the low concentration of this compound in the reaction products, the high conversion of the feed and the high yield of the target product.

 It follows from Example 6 that a liquid diluent functions as a medium in which, under mild conditions, a solution of chlorination of 1,1-difluoroethane and, which is also important, a medium that dissipates the reaction heat well due to the high heat of evaporation (for freon 113, the heat of vaporization is 6.57 kcal / mol).

 The results of experiments 1 and 2 of example 6 confirm that the goal is achieved when carrying out the chlorination process of 1,1-difluoroethane only in a diluent medium and under the proposed conditions.

As can be seen from the above examples, the proposed method allows to stably obtain the target product with high yield at a high degree of conversion of the reagents. The explosiveness of the process is ensured by saturation of the starting reagents with pairs of an inert heat-intensive diluent before contact, the reaction in the diluent medium and the possibility of the reaction in the gas phase in the absence of diluent, which is guaranteed by the presence of reflux of the diluent, all this prevents the formation of explosive concentrations even if the coordination in supply of reagents. The process is simple to implement, since the main apparatus is a volume reactor, which can be made of available materials. The method requires a uniform distribution of gas in the liquid, in this domestic industry has the necessary means. The process is carried out at a relatively low temperature (not higher than the maximum temperature of 102 ^o C in HFC 400 and preferably not higher than 47.6 ^o C in HFC 113), which is also an advantage of the method. But the most important advantage of the proposed method compared to the prototype is the higher domestic reliable safety and process stability over time.

 The expected economic effect of the use of the invention is 366.8 rubles. calculated per ton of the target product is 1,1,1-difluorochloroethane. TTT8

Claims (3)

 1. The method of producing 1,1,1-difluorochloroethane by chlorination of 1,1-difluoroethane with chlorine in the presence of a perhalogenated carbon diluent and an elementary fluorine initiator, followed by isolation of the target product, characterized in that, in order to increase process safety and stability, as a diluent, a fluorine-containing perhalogenated carbon selected from the group consisting of 1,1,2-trifluorotrichloroethane, 1,2-difluorotetrachloroethane, perfluoromethylcyclohexane, perfluorodimethylcyclohexane is used, with the starting reagent and the initiator pre-contact with a liquid diluent and the process is conducted at a temperature not exceeding the boiling point of the diluent, followed by condensation of the diluent, separating it from the reaction gases and returning to the beginning of the process.  2. The method according to claim 1, characterized in that 1,1,2-trifluorotrichloroethane is taken as the perhalogenated carbon of the diluent.  3. The method according to p. 1, characterized in that the process is conducted in a reactor with an inner surface of a material selected from the group comprising nickel, nichrome, fluoroplastic.

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