RU2005539C1 - Process for manufacturing catalyst for vapor pase fluorination of halogenohydrocarbons - Google Patents

Abstract

FIELD: manufacture of catalytic materials. SUBSTANCE: magnesium compound is treated with fluoric acid at 20-80 C to obtain suspension with final pH value of 3-6. The precipitated magnesium fluoride with particulate size of 10-250 microns is dried at 300-550 C and mixed with solution of chromic chloride having density 1.35-1.38 g/cm³. The resulting mixture is pelletized, and the pellets are treated thermally at 50-200 C and activated with hydrogen fluoride-containing gas at 100-450 C. The resulting catalyst includes 10-15 % by weight of chromic fluoride and 85-90 % by weight of magnesium fluoride, and has specific particle surface 50-100 m²/g, polydispersion porous structure and acts more 1000 hrs. EFFECT: increased durability.

Description

 The invention relates to catalytic chemistry, in particular to methods for producing chromium magnesium fluoride catalyst for gas-phase fluorination of halogenated hydrocarbons, including for the synthesis of chladones.

 It is known that gas-phase fluorination of organic compounds is catalyzed by fluorides of various metals.

 In the synthesis of chladones by gaseous fluorination of the corresponding halogenated hydrocarbons, mainly chromium compounds in the form of fluorides or oxyfluorides are used as a catalyst.

 A method of producing catalyzers based on chromium (III) compounds is reduced to precipitation of chromium (III) hydroxide, followed by treatment of the precipitate with water vapor, air and hydrogen fluoride. The catalyst obtained by this technology was used to synthesize HFC 134a. However, the yield of the target product did not exceed 18.2%.

 It is known to use two-component catalysts in the synthesis of chladones obtained by impregnating supports (alumina, aluminum fluoride, activated carbon) with solutions of chromium (III) salts, followed by heat treatment and activation with hydrogen fluoride. On a catalyst prepared by impregnating aluminum fluoride with a solution of chromium chloride, the yield of HFC 134a was 17.1%.

Hrommagnievye catalysts for the synthesis of Freon gas phase fluorination of the corresponding halocarbon prepared according to the patent (prototype) precipitation of chromium hydroxide (III) and magnesium from solutions of their salts (sulfates, nitrates, chlorides), followed by washing with ammonia precipitation, drying them at 120-140 ^C. calcination at 350-500 ^о С, by mixing the formed chromium and magnesium oxides, molding by extrusion and heat treatment of granules. The composition of the catalyst is 2-30% magnesium oxide and 98-70% chromium oxide. The specific surface area of the catalyst, depending on the content of chromium oxide 100-158 m ² / g

The catalyst was activated prior to use hydrogen fluoride and tested in gas phase fluorination of HFC 113 (R-113) at 300-400 ^{° C} and a molar ratio HF: R-113 - 1.5: 1. Under these conditions the conversion of HFC 113 99.1 -99.5% yield of HFC 115 was 46-50% for 40 hours of synthesis.

The specified method for producing chromium magnesium catalyst has a number of significant disadvantages:
metal hydroxides, in particular Cr (OH) ₃ and Mg (OH) ₂ , are fine precipitates that require thorough washing from anions (SO ₄ ^2- , NO ₃ ^- , Cl ^- ), additional filtration, drying, grinding and sieving, which leads to a significant complication of the technology for the preparation of the catalyst, the presence of a large amount of wastewater contaminated, in particular, highly toxic chromium compounds;
the catalyst contains 70-98% chromium oxide, which is a more expensive and scarce component compared to magnesium oxide;
based on the specific surface area of 100-158 m ² / g, it can be assumed that the catalyst has a finely porous structure, which leads to a decrease in the degree of utilization of the inner surface of the granules;
when activated with hydrogen fluoride due to fluorination of chromium and magnesium oxides, a significant amount of heat is generated, which makes it difficult to maintain the required temperature in the catalyst bed, and therefore does not guarantee uniformity of the chemical composition and reproducibility of the physicochemical and strength characteristics of the catalyst;
the catalyst has a short service life of 40 hours in the synthesis of freon 115.

 The essence of the claimed invention is as follows.

Chromium fluoride catalyst for gas-phase fluorination of halocarbons is obtained by mixing precipitated and dried magnesium fluoride fractions of 10-250 microns with a solution of chromium chloride with a density of 1.35-1.38 g / cm ³ .

 Obtaining a catalyst is as follows.

Precipitate magnesium fluoride by reacting hydrofluoric acid with a magnesium compound (oxide, hydroxide, carbonate, basic carbonate) at a temperature of 20-80 ^{° C} to a final slurry pH 3-6. In this case, a well-precipitated precipitate of magnesium fluoride is formed with a particle size of 10-250 microns, not contaminated with extraneous anions and therefore does not require washing. Magnesium fluoride is dried at 300-550 ^about C and mixed with a solution of chromium chloride with a density of 1.35-1.38 g / cm ³ .

 The use of a solution of chromium chloride allows, firstly, to uniformly apply the active component to the surface of magnesium fluoride and, secondly, due to the high acidity of the solution plasticize the crystalline powder of magnesium fluoride.

The resulting plastic mass is formed into pellets, which are subjected to heat treatment at 50-200 ^C. The catalyst was activated prior to use gas containing a hydrogen fluoride at 100-450 ° ^C.

 Since only chromium chloride is subjected to fluorination, the content of which in the catalyst does not exceed 15 wt. % exothermic heating of the catalyst layer during the activation process is negligible, which allows maintaining the temperature regime of fluorination within specified limits.

0,25-0,50 см³/г.The finished catalyst contains 10-15 wt. % chromium fluoride and 90-85% magnesium fluoride, has a specific surface area of 50-100 m ² / g and a polydisperse porous structure with a pore volume of a radius of 30-10000

0.25-0.50 cm ³ / g.

 The presence of a significant amount of macro- and mesopores in the catalyst makes it possible to eliminate intra-diffusion inhibitions and to efficiently use the inner surface of the catalyst during its operation.

 Thus, the combination of these features in the present method allows to obtain a low-waste technology catalyst with an optimal porous structure and uniform distribution of the active component chromium fluoride by volume of magnesium fluoride. Due to this, a high catalyst activity is achieved in the gas-phase fluorination of halogenated hydrocarbons, despite the low content of the active component, chromium fluoride, which is the most scarce and expensive compound in comparison with magnesium fluoride, which is confirmed by the following examples.

PRI me R 1. In a reactor made of corrosion-resistant metal, equipped with a jacket and a stirrer, loaded 13.5 kg of basic magnesium carbonate, poured 39.3 l of distilled water. The suspension was stirred at 30-40 ^° C then poured 14.2 kg of 40% hydrofluoric acid, the medium was adjusted to pH 3-4. The suspension of precipitated magnesium fluoride was maintained for 1 hour and then dried at 300-500 ^° C Ready magnesium fluoride had a fraction of 10-250 um.

A solution of chromium chloride was prepared in a reactor with a stirrer and a jacket. 24.4 L of distilled water and 40 kg of chromium hexahydrate were charged into the reactor. Within 1 h, the chromium salt dissolution at 60-70 ^C. The resulting solution had a density of 1.375 g / cm ^3.

The mixing of magnesium fluoride with a solution of chromium chloride was carried out in portions in a mechanical mixer. 13 kg of magnesium fluoride powder of a fraction of 10-250 μm were loaded into the mixer and a solution of chromium chloride with a density of 1.375 g / cm ³ in an amount of 5.6 l was poured with stirring. The components were mixed until a homogeneous plastic mass was formed.

The catalyst was molded by extrusion. The obtained granules were dried and calcined for 24 hours at 50-200 ^about C.

The catalyst was activated with hydrogen fluoride in the synthesis reactor chladones at 200-400 ° ^C.

0,39 см³/г. Величина удельной поверхности катализатора 74 м²/г.The finished catalyst contained 12.3% chromium fluoride and 87.7% magnesium fluoride. Had a pore volume of radius 30-8600

0.39 cm ³ / g The specific surface area of the catalyst is 74 m ² / g.

The catalyst was tested in a pilot plant gas phase during the fluorination of freon 113. The reactor was charged 60 kg of catalyst, the temperature in the catalyst bed was raised to 480 ^{° C} and was fed a mixture of freon 113 and hydrogen fluoride at a molar ratio of 1: (2-2.5). Under these conditions, the conversion of HFC 113 was 100-97%, the yield of HFC 115 was 50-55%. The service life of the catalyst is more than 3000 hours

PRI me R 2. The catalyst obtained in example 1 was tested in a pilot plant during the gas-phase fluorination of trichlorethylene. The reactor was charged 20 kg of catalyst, the catalyst bed temperature was raised to 300 ^{° C} and was fed a mixture of trichlorethylene and hydrogen fluoride at a molar ratio of 1: (2-3.5). Under these conditions, the conversion of trichlorethylene was 100-99.7%, the yield of freon 133a was 93-95%, the yield of freon 134a was 7-5%. The service life of the catalyst is more than 1000 hours

PRI me R 3. The catalyst obtained in example 1 was tested in a pilot plant during gas-phase fluorination of freon 133a. The reactor was charged 20 kg of catalyst, the temperature in the catalyst bed was raised to 350 ^{° C} and the mixture was fed Freon 133a and hydrogen fluoride at a molar ratio of 1: (10-12). Under these conditions, during the conversion of HFC 133a 40-50%, the yield of HFC 134a 35-47% was achieved. The service life of the catalyst is more than 1000 hours

 As can be seen from examples of specific performance, the chromium magnesium fluoride catalyst obtained by the present method is superior in activity and service life in the synthesis of freon 115 chromium magnesium catalyst obtained by the prototype.

 The technology for producing chromium magnesium fluoride catalyst was tested in a pilot plant. The good reproducibility of the physicochemical properties of the experimental batches of the catalyst and their activity in experimental plants in a number of gas-phase fluorination of halogenated hydrocarbons is shown. The use of this catalyst in the pilot production of freon 134a is intended. Freon 134a is an ozone-safe freon - an alternative replacement for ozone-hazardous freons 11,12 used as refrigerants for domestic and industrial refrigerators. (56) Simons J. Fluorine and its compounds. M.: Foreign Literature, 1953.

 UK patent N 1091103, CL B 1 E, published. 1965.

 U.S. Patent No. 3,235,612, cl. 570-169, published. 1962.

 Patent EP N 408005, cl. C 07 C 19/08, published. 1991.

 Japan patent N 43922 - cl. 2 (2-68) 190, published. 1974.

Claims (1)

METHOD FOR PREPARING THE CATALYST FOR GAS-PHASE FLORIATION OF HALOGEN-HYDROCARBONS, including the mixing of magnesium and chromium (III) compounds, molding, heat treatment and activation with gaseous hydrogen fluoride, characterized in that magnesium fluoride obtained by treatment with 10–250 μm magnesium is used as a magnesium compound and dried, a chromium chloride solution with a density of 1.35 - 1.38 g / cm ^{3 is} used as a chromium (III) compound.