IE912056A1 - Process for the production of 1,1,1,2-tetrafluoroethane - Google Patents

Abstract

Process for the preparation of 1,1,1,2-tetrafluoroethane by reaction of hydrogen fluoride with 1,1,2-trifluorethylene in the gas phase in the presence of a catalyst consisting of at least one aluminium compound.

Description

The invention relates to a process for the production of 1,1,1,2-tetrafluoroethane (HFA-134a) by reaction of hydrogen fluoride with 1,1,2-trifluoroethylene in the gaseous phase in the presence of a catalyst formed of an aluminium compound.

Belgian Patent No. 870,530 discloses a process for the production of 1,1,1,2-tetrafluoroethane by reaction of hydrogen fluoride with 1,1,2-trifluoroethylene in the gaseous phase in the presence of a hydrofluorination catalyst formed of chromium oxide which is optionally deposited on a support.

However, the preparation of the known catalysts in this field is often long, tedious and difficult to realise industrially. Moreover, these catalysts generally Ϊ5 lose a part of their activity in the course of time, and the rate of conversion decreases with the reaction time.

The invention relates to a process using a catalyst which no longer presents these disadvantages and which leads to an excellent selectivity and an increased rate of conversion. In fact, a process has been found which has a good efficiency. In the process according to the invention, few by-products are formed and the selectivity for 1,1,1,2-tetrafluoroethane is increased.

The activity of the catalysts according to the invention is increased and remains stable with time. The catalysts according to the invention are simply prepared, are non-toxic and cost very little. Their regeneration is therefore not necessary, nor is any support necessary for the catalysts according to the invention since they equally play the role of support as well as being the active catalysts. In addition, they do not contain transition metals, which avoids the problems of disposal of heavy metals. Moreover, the catalysts are particularly stable with time. - 2 The invention relates in this respect to a process for the production of 1,1,1,2-tetrafluoroethane by reaction of hydrogen fluoride with 1,1,2-trifluoroethylene in the gaseous phase in the presence of a cata5 lyst formed of at least one aluminium compound.

In the process for the production of 1,1,1,2tetrafluoroethane according to the invention, the residence time of the reagents, that is to say of hydrogen fluoride and of 1,1,2-trifluoroethylene, in the reactor is generally at least 2 seconds. Most often, this residence time is at least 5 seconds. Good results are obtained with the residence time not exceeding 50 seconds. Excellent results are obtained with the residerice time not exceeding 25 seconds.

The quantity of hydrogen fluoride used in the process is generally between 0.5 and 4 mol per mole of 1,1,2-trifluoroethylene used and preferably between 0.8 and 2.5 mol per mole of 1,1,1-trifluoroethylene used.

The temperature at which the reaction is carried out is above 150°C. Most often, this temperature does not exceed 250°C. Preferably, it is at least 200°C.

The pressure at which the reaction is carried out is selected in such a way as to maintain the reaction medium in the vapour state. It is most frequently near to atmospheric pressure.

The process of the invention can be carried out in any reactor or apparatus which allows the conditions described above to be combined. The process can be carried out batchwise or continuously.

The catalyst used in the process according to the invention is formed of at least one aluminium compound. Generally, it is formed of at least 97% of one or more aluminium compounds, usually of at least 98% and preferably of at least 98.5% of one or more aluminium compounds. Good results have been obtained when the catalyst is formed exclusively of one or more aluminium compounds, that is to say that no transition metal is added and that the customary impurities contained in the aluminium compounds do not interfere with the action of the catalyst. - 3 Generally, the catalyst according to the invention is formed of one or more salts or oxides of aluminium. Customarily it is formed of an alumina and/or an aluminium halide. Preferably, the catalyst is formed of the compound or compounds resulting from contacting alumina and hydrogen fluoride. Good results have been obtained when, after contacting alumina and hydrogen fluoride, the catalyst is formed of approximately 30 to 95% by weight of aluminium fluoride, preferably approxi10 mately 55 to 75%.

The invention also relates to a preparation process for the catalyst. Customarily one alumina alone is used but all types of alumina are suitable. Preferably, an alumina is used of specific surface area between 5 and 500 m2/g and of pore volume between 0.05 and 0.8 cm3/g. Good results have been obtained when alumina is contacted with hydrogen fluoride until there was no further absorption of fluoride.

The 1,1,1,2-tetrafluoroethane obtained according to the invention can be used in all the applications known for this product, such as, for example, as a refrigerant or aerosol propellant.

The examples which follow illustrate the invention.

Example 1: a) Preparation of the catalyst Alumina having the following characteristics: Harshaw alumina (Engelhard) 0104 T 1/8 : - specific surface area 100 m2/g - pore volume 0.39 cm3/g, is dried overnight at 150°C under reduced pressure (vacuum oven : 5 mm Hg) 245 g of this dried alumina are introduced into a reactor formed by an Inconel tube of capacity 250 cm3, heated by means of 6 electrical resistances, provided with an axial sheath equipped with 12 thermocouples in order to regulate and to control the temperature along the length of the reactor.

The reactor is then heated to 325°C and, at a rate of 0.8 mol per hour, hydrogen fluoride diluted in - 4 nitrogen (2.5 1 of N/h) is supplied at 325°C at atmospheric pressure.

The supply of hydrogen fluoride is terminated when there is no longer any absorption of fluoride, that is to say when the flow of hydrogen fluoride leaving the reactor is equal to the flow entering.

The catalyst thus obtained has a specific surface area of less than 10 m2/g, a pore volume of 0.05 cm3/g and a fluorine content of approximately 425 g/kg which cor10 responds to a degree of fluorination of approximately 50, molar % Al (which is equivalent to 62% of A1F3 by weight) . b) Hydrofluorination of 1,1,2-trifluoroethylene The reactor containing the catalyst prepared above is supplied with 1,1,2-trifluoroethylene at a rate of 270 mmol per hour and with hydrogen fluoride at 520 mmol per hour at 332°C under atmospheric pressure. The residence time is estimated at 23 seconds.

After operation for 2 hours, the rate of conversion of 1,1,2-trifluoroethylene is 96.4% and the selectivity is 99.9% for 1,1,1,2-tetrafluoroethane (results established on the basis of analysis by gas phase chromotography in the gas effluent line leaving the reactor).

After operation for 35 hours, this rate of con25 version and this selectivity are unchanged.

Examples 2,3 and 4 a) Preparation of the catalyst The catalyst is prepared following the procedure described in Example la.

The catalyst is formed of alumina such as that described in Example 1.

The reactor used is identical to that of Example 1. b) Hydrofluorination of 1,1,2-trifluoroethylene The hydrofluorination conditions and the results are collated in Table 1. - 5 TABLE 1 Example 2 3 4 Temperature °C 346 347 350 Residence time seconds 27 20 32 Results after operation for 2 hours Rate of conversion in % of 1,1,2-trifluoroethylene 92.5 89.1 93.7 Selectivity in % for 1,1,1,2-tetrafluoroethane 99.95 99.9 99.95 After operation for 35 hours, this rate of conversion and this selectivity remain unchanged.

Example 5: a) Preparation of the catalyst 252 g of Harshaw alumina (Engelhard) 3983 T 1/8 previously dried for 24 h at 150eC at reduced pressure (vacuum oven : 5 mm Hg) are introduced into a 300 cm3 Inconel reactor, sited vertically.

This alumina has the following characteristics: - specific surface area 133 m2/g; - pore volume 0.39 cm3/g.

The reactor, supplied with nitrogen (5 1 of N/h), is progressively heated to 200°C, at atmospheric pressure.

A current of hydrogen fluoride and nitrogen, at rates of respectively 17.5 and 25 N/h (ratio 0.7:1) is then introduced at the top of the reactor. The fluorination is continued in this manner for 5 hours, then the flow of nitrogen is progressively decreased to 5 1 of N/h and the temperature is raised to 350°C. - 6 After a total time of 12 hours, the direction of passage of hydrogen fluoride is reversed (introduction at the bottom of the reactor) so as to standardise the rate of fluorination. The current of nitrogen is stopped and the flow of hydrogen fluoride is raised to 25 1 of N/h; the treatment is continued under these conditions for 11 hours.

At this time, there is no longer any absorption of hydrogen fluoride, that is to say the flow of hydrogen fluoride leaving the reactor is equal to the flow entering.

At the end of the treatment, the introduction of hydrogen fluoride is stopped and the reactor is cooled with nitrogen flushing (5 1 of N/h). The catalyst thus obtained has a specific surface area of 15 m2/g, a pore volume of 0.09 cm3/g and a fluorine content of 551 g/kg, which corresponds to a degree of fluorination of approximately 72 molar % relative to the aluminium (which is equivalent to 81% of A1F3 by weight) . b) Hydrofluorination of trifluoroethvlene The reactor filled with catalyst prepared above is supplied with trifluoroethylene at a rate of 235 mmol/h and with hydrogen fluoride at a rate of 470 mmol/h, at 300 °C and at atmospheric pressure. The residence time is estimated at 10 seconds.

After operation for 2 hours, as seen from the gas phase chromatography analysis in the effluent line leaving the reactor, the rate of conversion of 1,1,2trifluoroethylene is above 99.5% and 1,1,1,2-tetrafluoro30 ethane is the only product detected (selectivity > 99.9%).

Examples 6 to 11 a) Preparation of the catalyst The catalyst is prepared following the procedure described in Example 5a.

The catalyst is formed of alumina such as that described in Example 5a.

The reactor used is identical to that of Example . - Ί b) Hydrofluorination of trifluoroethvlene The conditions of hydrofluorination and the results are collated in Table 2.

TABLE 2 Example 6 7 8 9 Temperature °C 250 200 250 250 Residence time seconds 12.5 12.7 6.3 6.0 HF:TFE ratio, mol/mol 1.8 1.8 2.0 05 Results after 2 hours of operation Rate of conversion in % of 1,1,2-trifluoroethylene 99 73 91 50 (*) Selectivity in % for 1,1,1,2-tetrafluoroethane > 99.9 > 99.9 > 99.9 > 99.9 (*) Corresponding to the complete transformation of HF used.

Examples 10R and HR (reference) a) Preparation of the catalyst The catalyst is prepared following the procedure described in Example 5a.

The catalyst is formed of alumina such as that described in Example 5a.

The reactor used is identical to that of Example . b) Hydrofluorination of trifluoroethvlene The hydrofluorination conditions and the results are collated in Table 3.

It ΪΠ2056 - 8 TABLE 3 Example 10R HR Temperature °C 120 120 Residence time seconds 16.6 38.8 HF:TFE ratio, mol/mol 2.1 2.5 Results after 2 hours of operation Rate of conversion in % of 1,1,2-trifluoroethylene > 1 > 2 Selectivity in % for 1,1,1,2-tetrafluoroethane (*) (*) (*) : as in the examples above according to the invention, 1,1,1,2-tetrafluoroethane is the only product detected; however, with such a low conversion, the content of 1,1,1,2-tetrafluoroethane is so low that it is advisable not to estimate the selectivity.

Claims (8)

1. - Process for the production of 1,1,1,2-tetrafluoroethane by reaction of hydrogen fluoride with 1,1,2trifluoroethylene in the gaseous phase in the presence of 5 a catalyst, characterised in that the catalyst is formed of at least one aluminium compound and in that the reaction temperature is above 150’C.

2. - Process according to Claim 1, characterised in that the catalyst is formed of at least 97% of one or 10 more aluminium compounds.

3. - Process according to Claim 1 or 2, characterised in that the catalyst is formed of the compound or compounds resulting from contacting of alumina and hydrogen fluoride. 15

4. - Process according to Claim 1, 2 or 3, characterised in that the catalyst is formed of approximately 30 to 95% by weight of aluminium fluoride.

5. - Process according to any one of the preceding claims, characterised in that the residence time of the 20 reagents in the reactor is at least 2 seconds, without exceeding 50 seconds.

6. - Process according to any one of the preceding claims, characterised in that the quantity of hydrogen fluoride used is between 0.5 and 4 mol per mole of 1,1,225 trifluoroethylene.

7. - A process for the production of 1,1,1,2-tetrafluoroethane substantially as hereinbefore described by way of Example.

8. - 1,1,1,2-tetrafluoroethane whenever prepared by a process as claimed in any one of the preceding claims.