GB2073181A - Preparation of 1,1,1,3,3,3- hexafluoropropane-2-ol by Vapor Phase Hydrogenation of Hexafluoroacetone with Nickel Catalyst - Google Patents

Abstract

A process of preparing 1,1,1,3,3,3-hexafluoropropane-2-ol by vapor phase catalytic hydrogenation of hexafluoroacetone with hydrogen gas, characterized by the employment of a catalyst containing metallic nickel as its essential component. Because of high effectiveness of this catalyst the hydrogenation reaction can proceed even at relatively low temperature, so that the reaction temperature is maintained within the range from 30 DEG C to 140 DEG C to avoid formation of acidic compounds by side reactions. In this process nearly theoretical conversion of hexafluoroacetone can be achieved with 100% selectivity for 1,1,1,3,3,3-hexafluoropropane-2-ol.

Description

SPECIFICATION Preparation of 1,1,1 ,3,3,3-Hexafluoropropane- 2-ol by Vapor Phase Hydrogenation of Hexafluoroacetone with Nickel Catalyst This invention relates to a process of preparing 1,1,1 ,3,3,3-hexafluoropropane-2-ol by vapor phase catalytic hydrogenation of hexafl uoroacetone.

It has been reported that 1,1,1,3,3,3hexafluoropropane-2-ol is a compound useful as either a surface active agent or an emulsifying agent (according to Belgian Patent No. 634,368), as a solvent for some polymers such as vinyl polymers of carboxylic acids (according to U.S.

Patent No. 3,153,004) and as an intermediate of some anesthetic compounds (according to U.S.

Patent No. 3,346,448).

Usually 1,1,1 ,3,3,3-hexafluoropropane-2-ol is prepared from hexafluoroacetone, and various kinds of reduction or hydrogenation methods for this purpose have heretofore been proposed.

Typical examples of such proposals are: liquid phase reduction by using sodium boron hydride (U.S.S.R. Patent No. 138,604) or lithium aluminum hydride (U.S. Patent No. 3,227,674); liquid phase hydrogenation by using platinum oxide catalyst (U.S. Patent No. 3,607,952) or metallic palladium catalyst together with an inorganic basic salt of an alkali metal effective as a promoter (German Patent No.2,113,551); and vapor phase hydrogenation by using metallic copper-chromium oxide catalyst (Belgian Patent No. 634,368), platinum oxide catalyst without carrier (J. Am. Chem. Soc., Vol. 86(1964), 494852), palladium catalyst carried by aluminium oxide pellets (Dutch Patent Application No.

6610936) or palladium catalyst carried by carbon (German Patent No. 1,956,629).

among these methods, the liquid phase hydrogenation method and the vapor phase hydrogenation method are considered to be more suitable to industrial practice than the initially mentioned liquid phase reduction method.

However, the liquid phase hydrogenation method is rather disadvantageous in the necessity of using an expensive noble-metal catalyst and also in the need of performing the hydrogenation at a considerably high pressure.

The vapor phase catalytic hydrogenation method is advantageous in the possibility of accomplishing continuous hydrogenation of hexafluoroacetone at atmospheric pressures.

However, in the case of using a relatively economical catalyst such as a metallic copperchromium oxide catalyst in this method, the conversion of hexafluoroacetone to 1,1,1,3,3,3hexafluoropropane-2-ol remains at an unsatisfactory low level even when the reaction temperature is raised considerably and the contact time is prolonged. To raise the conversion factor to an industrially satisfactory level, it becomes necessary to employ a noble-metai catalyst though it is undesirable from the economical viewpoint. Moreover, the catalytic hydrogenation reaction must be performed at a temperature above 1 5000 to realize a satisfactorily high conversion factor.However, the employment of such a high reaction temperature often results in formation of acidic compounds such as hydrofluoric acid and/or some organic acids as by-products of the intended hydrogenation reaction, and in that case the acidic compounds tend to deactiveate the catalyst. Therefore, it becomes a requisite to employ an acid-resistant material for the carrier of the catalyst.

It is an object of the present invention to provide an improved process of preparing 1,1,1 ,3,3,3-hexafluoropropane-2-ol by vapor phase catalytic hydrogenation of hexafluoroacetone, which process can be performed under mild reaction conditions by using an economical catalyst but nevertheless can realize a very high rate conversion of hexafluoroacetone with an extremely high selectivity factor for 1,1,1,3,3,3- hexafluoropropane-2-ol, without forming any acidic by-products detrimental to the activity of the catalyst.

According to the present invention, vapor phase catalytic hydrogenation of hexafluoroacetone with hydrogen to form 1,1,1 ,3,3,3-hexafluoropropane-2-ol is performed by the employment of a catalyst which comprises metallic nickel as an essential component thereof, and the hydrogenation reaction temperature is maintained within the range from 300C to 1400C.

The process according to the invention can be performed at atmospheric pressures, and a relatively short contact time suffices to complete the hydrogenation reaction.

The catalyst is not required to be nickel alone and can be prepared in various forms and compositions as will later be described.

By this process it is easy to achieve nearly complete conversion of hexafluoroacetone introduced into the reaction apparatus, and the selectivity factor for 1,1 ,1 ,3,3,3- hexafloropropane-2-ol becomes 100%. Since no acidic compounds are formed as byproducts, the nickel catalyst in the reaction apparatus has a very long service life with only very small loss in its activity.

A catalyst used in the present invention comprises metallic nickel, which is preferably a reduced nickel obtained, for example, by reduction of a suitable nickel compound such as nickel oxide, nickel carbonate or nickel hydroxide in a hydrogen gas atmosphere or by thermal decomposition reduction of a nickel salt of an organic acid such as nickel formate, oxalate or acetate in the absence of oxygen. Of course it is possible to employ a catalyst substantially wholly consisting of metallic nickel, but it is also possible to use a catalyst in which metallic nickel is carried by a conventional carrier the material of which is exemplified by activated carbon or charcoal, activated alumina and zinc oxide.Furthermore, metallic nickel may be mixed with at least one kind of catalytic metal oxide such as cupric oxide and/or chromic oxide, and/or promoter(s) such as manganese dioxide and/or zirconium dioxide, and a resultant mixture may be shaped into granules or pellets by using a familiar support material such as diatomite (kieselguhr) or terra alba.

Usually it suffices to use 0.1 to 5 parts by weight of nickel for 100 parts by weight of hexafluoroacetone to be hydrogenated.

By using such a nickel catalyst it becomes possible to realize the intended hydrogenation reaction at a relatively low temperature which is required by the present invention to be within the range from 300C to 1 400C. If the reaction temperature is made to be lower than 300C, the product of the hydrogenation reaction tends to condense within the reaction tube. If the reaction temperature is raised beyond 1 400C, there arises the possibility of side reactions that will form acidic compounds as undesirable by-products of the process, with natural decrease in the yield of the intended compound.

Insofar as a nickel cayalyst is used and the reaction temperature is maintained within the specified range, theprocess according to the invention can be performed similarly to a known vapor phase catalytic hydrogenation of hexafluoroacetone by using a known apparatus.

As to the quantity of hydrogen gas used in the process of the invention, the minimum requirement is the mole equivalent to hexafluoroacetone to be hydrogenated. However, there arises no problem by using excess quantity of hydrogen gas to serve the function of carrier gas for hexafluoroacetone.

Usually the contact time in the hydrogenation reaction according to the invention is made shorter than about 30 seconds and can be made shorter as the reaction temperature is made higher. In most cases a relatively short contact time such as 5-10 seconds is sufficient to achieve nearly theoretical conversion of hexafluoroacetone to 1,1,1,3,3,3hexafluoropropane-2-ol.

The invention will be illustrated by the following non-limitative examples. Some references are also presented for the sake of comparison.

Example 1 Use was made of a reduced nickel catalyst which was in the form of pellets 5 mm in diameter and contained 45 47% of Ni, 27- 29% of diatomite, 2-3% of Cr, 2-3% of Cu and 4-5% of graphite by weight. 4 g of this catalyst was packed in a Pyrex tube having an inner diameter of 13 mm and preliminarily activated by heating at 185do in a hydrogen gas stream passed through the tube and then cooled to about 600C.

Thereafter a mixed gas of hexafluoroacetone (10 g/hr) and hydrogen (4800 ml/hr) was continuously passed through the tube packed with the activated catalyst to cause hydrogenation of hexafluoroacetone by vapor phase catalytic reaction. The hydrogenation reaction proceeded so rapidly that the reaction temperature in the tube soon rose to 800C, and thereafter the reaction temperature was maintained constantly at 8O0C. The length of the catalyst column in the tube and the flow rate of the mixed gas were such that the contact time in this hydrogenation reaction was 4 seconds.

At an initial stage soon after the rise of the reaction temperature to 800C, the conversion of the supplied hexafluoroacetone was 99.2%, and the selectivity factor for 1 , 1 .1,3,3,3- hexafluoropropane-2-ol was 100%. After continuation of the reaction for 20 hours, the conversion of hexafluoroacetone was 99.0%, and the selectivity factor for 1 ,1 ,1 ,3,3,3- hexafluoropropane-2-ol was 100%, meaning that the catalyst in the reaction tube exhibited no loss in its activity during the time period of 20 hours.

Reference 1 The materials, catalyst and apparatus of Example 1 were employed with no alteration. In this case, however, the reaction temperature in the vapor phase hydrogenation of hexafluoroacetone was raised up to and maintained at 1 500C, and the contact time was extended to 8 seconds.

The product of this hydrogenation process contained considerable amounts of water and acids as by-products. The conversion of hexafluoroacetone was 99.2%, but the selectivity factor for 1,1,1 ,3,3,3hexafluoropropane-2-ol was only 78.1%.

Example 2 Using the same catalyst and apparatus as in Example 1, hexafluoroacetone and hydrogen in the proportion of 1:3 by mole were passed through the reaction tube to undergo vapor phase contact reaction. In this example the reaction temperature was maintained at a relatively low level of 700C, but the contact time was 4 seconds similarly to the process of Example 1.

The conversion of hexafluoroacetone in this example was 97.5%, and the selectivity factor for 1,1,1,3,3,3-hexafluoropropane-2-ol was 100%.

Example 3 A mixture of 40 g of the reduced nickel catalyst used in Example 1 and 70 g of activated charcoal was packed in a Pyrex tube having an inner diameter of 25 mm. Hexafluoroacetone (40 g/hr) and hydrogen (three times the mole equivalent to the hexafluoroacetone were continuously passed through the thus prepared reaction tube to undergo vapor phase hydrogenation reaction with control of the reaction temperature to a very low level of 40dC and the contact time to 7 seconds.

In this case the conversion of hexafluoroacetone was 99.870, and the selectivity factor for 1,1,1 ,3,3,3-hexafluoropropane-2-ol was 100%. It was confirmed that no acidic compounds were formed as by-products of this reaction.

Reference 2 Use was made of a copper-chromium oxide catalyst containing 4446% of CuO, 43-44% of Cr2O3 and 45% of MnO2 by weight. 20 g of this catalyst was packed in a Pyrex tube having an inner diameter of 1 3 mm, and hexafluoroacetone (10 g/hr) and hydrogen (three times the mole equivalent to the hexafluoroacetone) were continuously passed through the tube. The reaction temperature was maintained at 800C, and the contact time was made to be 10 seconds.

In this experiment, however, hexafluoroacetone scarcely underwent hydrogenation: numerically, the conversion of hexafluoroacetone was only 0.5%.

Reference 3 The catalyst in Reference 2 was replaced by 10 g of a catalyst containing 0.5% of palladium supported on carbon, using the same Pyrex tube as in Reference 2. Hexafluoroacetone and hydrogen were passed through the tube at the same flow rates and molar ratio as in Reference 2.

In this case the reaction temperature was maintained at 2000 C, and the contact time was made to be 7 seconds.

As the result the conversion of hexafluoroacetone reached 96.5%, but the selectivity factor for 1,1,1,3,3,3hexafluoropropane-2-ol was as low as 70.4% since large amounts of acidic compounds were formed as by-products.

Claims (11)

Claims

1. A process of preparing 1,1,1,3,3,3hexafluoropropane-2-ol by vapor phase rection of hexafluoroacetone with hydrogen in the presence of a hydrogenation catalyst, characterized in that said catalyst comprises metallic nickel as an essential component thereof and that the reaction temperature is maintained within the range from 30into 14O0C.

2. A process according to Claim 1, wherein said metallic nickel is a reduced nickel.

3. A process according to Claim 1, wherein the catalytic component of said catalyst is entirely metallic nickel.

4. A process according to Claim 1, wherein said catalyst further comprises a metal oxide having a catalytic activity on vapor phase hydrogenation of hexafluoroacetone.

5. A process according to Claim 3 or 4, wherein said catalyst further comprises a carrier.

6. A process according to Claim 5, wherein the material of said carrier is selected from the group consisting of carbon, alumina and zinc oxide

7. A process according to Claim 3 or 4, wherein said catalyst further comprises a metal oxide effective as a catalytic activity promoter.

8. A.process according to Claim 7, wherein said catalyst further comprises a support material selected from the group consisting of diatomite and terra alba and takes the form of pellets.

9. A process according to Claim 1, wherein said catalyst further comprises a support material selected from the group consisting of diatomite and terra alba, at least a portion of said catalyst taking the form of pellets each of which contains said metallic nickel and said support material.

1 0. A process according to Claim 1 , wherein said vapor phase reaction is caused by continuouslypassing hexafluoroacetone and hydrogen through a reaction chamber in which is disposed said catalyst.

11. A process according to Claim 10, wherein hexafluoroacetone, hydrogen and said catalyst are allowed to contact with each other for a time period not longer than 30 seconds.

1 2. A process according to Claim 11, wherein said time period is in the range from 5 to 10 seconds.

1 3. A process of preparing 1,1,1,3,3,3hexafluoropropane-2-ol as claimed in Claim 1, substantially as herein described in any one of Example 1 to 3.