IL22877A - Catalyst regeneration - Google Patents

Description

CATALYST HB&BRERATIOH THIS INVENTION relates to the regeneration of palladium catalysts.

Catalytic hydrogenations , especially of organic nitro compounds, often involve the use of noble metal catalysts, such as palladium. Such catalysts are relatively expensive and their efficient recovery and re-use, particularly the regeneration of catalysts which have lost their catalytic activity, are therefore important economic factors in the success of such processes.

The batchwise reduction of organic nitro compounds to the corresponding amines by catalytic hydrogenation in the presence of palladium catalysts supported on inert carriers such as charcoal, barium sulphate and the like, is well known. Such reductions are efficient and catalysts which have lost their catalytic activity can readily be regenerated by washing with a dilute aqueous solution of a volatile organic acid, e.g. a 2% aqueous solution of oxalic acid.

However, this method of regenerating spent palladium catalysts, although effective, involves the loss of valuable palladium metal, probably as a result of removal of part of the palladium from the carrier. Such a lose in a process operated on a very large scale is too costly to be practical. Attempts to regenerate the spent palladium catalysts obtained in such batch procedures by steaming, ignition, and other methods conventional in the catalyst regeneration art, have been either inefficient or impractical or both.

In the hydrogenation of organic nitro compounds to the corresponding amines, in many instances, the conversion of batch processes to continuous operation has involved little or no change in the chemical steps involved, the difficulties, if any, in converting a chemical procedure from batch to continuous operation, being associated primarily with the engineering problems. How ver, we have made the reduction of organic nitro compounds to the corresponding amines can be efficiently and economically regenerated hy washing them with hot water. The activity of the catalyst thus regenerated can be substantially that of fresh catalyst, Moreover, there is substantially no loss of palladium values, other than that due to mechanical handling. The surprising nature of the invention resides in the fact that in batch processes for converting organic nitro compounds to the corresponding amines, it is necessary to regenerate the catalyst by washing with an organic acid, the process of the present invention being unsuitable for regenerating the catalyst of the batch type process. Generally a chemist skilled in catalytic processes would not even consider the use of plain hot water for the regeneration of catalysts, since, as indicated, usual practice involves the use of considerably more radical treatment .

The palladium catalyst referred to in this description is generally in particulate form, such as pellets, granules or the like, and supported on a carrier such as carbon, alumina, silica gel, kiesel-guhr, barium sulphate, zirconium oxide, etc. A particularly effective, and hence preferred, palladium catalyst is that which is commercially available as palladium on a charcoal support, and contains o palladium, probably in the form of the oxide or a mixture of the metal and the oxide .

The exact mechanism by which the palladium loses its catalytic activity in reducing organic nitro compounds, is not known, but it is assumed to be one or more of the known mechanisms, such as poisoning, deposition of carbonaceous material on the surface of the catalyst, etc. It is unlikely that the loss of catalytic activity arises from impurities in the nitro compounds for our experience has indicated that even analytically pure nitro compounds on reduction give rise to spent catalysts almost as rapidly as relatively crude nitro compounds. corresponding amines in the presence of catalysts regenerated in accordance with the present invention include, for example, nitrobenzene, dinitrotoluene, m-nitrotoluene, m-dinitrobenzene , p_~dinitrobenzene, m-chloronitrobenzene and oc-nitronaphthalene . Mixtures of nitro compounds, such as the approximately 80$ 2,^- and 20$> 2,6-dinitrotoluene obtained on dinitration of toluene, are also suitable.

The temperature of the water used to wash the spent catalyst can be varied over a broad range. The catalyst poisons produced in the continuous process are evidently soluble in warm water and water of at least about 60°C. should preferably be used. Preferably the water is at a temperature from 80° to 100°C. Obviously, the hotter the water the faster the removal of the contaminants will be and hence the time required will vary inversely as the temperature of the water. In general, at least one hour of washing will be required, but this parameter too can vary not only with the temperature and amount of the water but also with the degree of contamination of the catalyst, that is the greater the poisoning of the catalyst, the more time is required to regenerate the catalyst. In a preferred procedure the washing comprises two stages in each of which 1 part by weight of catalyst is agitated with at least 8 parts by weight of hot water.

In order to avoid the possibility of contamination of the catalysts by metal salts or other impurities which may be present in the wash water, deionized, distilled or other substantially pure water is preferably used.

The catalyst ig preferably washed by slurrying it with the hot water. However, it can also be washed on the filter, though this generally takes longer and channeling may occur.

The following Example illustrates the invention. Parts and percentages are by weight and temperatures are in degrees centigrade.

EXAMPLE A feed stream of mixed dinitrotoluenes comprising about 80?e 2 ,4- and about 20?£ 2 ,6-dinitrotoluenes at the rate of 785Ο parts per hour is mixed continuously with 7· 8 parts per hour of a commercial % palladium on charcoal catalyst, at the feed stream rate of 785Ο parts per hour. The mixture is fed into a hydrogenator with 2500 parts per hour of recycled gas containing 168Ο parts per hour hydrogen, 266 parts per hour water and parts per hour inert gases. The mass is maintained at 125° and 2.1 kg./cm^. Effluent gas from the hydrogenator is separated, partially condensed and recycled.

The effluent product stream is charged to a second stage hydrogenator maintained at 125° and 1 .75 kg/crn^ and reacted with 429 parts per hour fresh hydrogen containing 359 parts/hr hydrogen, 57 parts/hr water and 12.7 parts/hr inert gases. The effluent gas stream is then separated, partially condensed and recycled.

The effluent product stream is -charged to a third stage hydrogenator operated at 125° and 1 ,4 kg./cm^ .and reacted with an ascending' countercurrent stream of hydrogen containing 188 parts per hour of hydrogen and 6.7 parts per hour of inerts. The reaction mass emanating from the bottom of the third stage is run into a scrubbing column operated at 125° and 2.1 kg./cm^ and reacted with an ascending stream of gas containing 17 parts per hour hydrogen and 0,6 parts per hour inert gases.

The reaction mixture leaving the bottom of the scrubbing column is passed through a filter to remove spent catalyst from the tolylene diamine mixture.

For regeneration, the filter cake of spent catalyst is slurried in hot ( 80° to 85°) deionised water having a specific conductance of less than 10 mmhos/ml. About 10 parts of water per part of catalyst is used, and thereafter the slurry is heated to and agitated at 90° to 95° for one hour. The hot slurry is filtered and sucked "dry". The filter cake is reslurried in about 10 parts of the deionized water (at 80-85°), the slurry is heated to and agitated at 90° to 95° for one hour, and filtered. The filter cake is washed with sufficient deionized water to cover the cake and then sucked ''dry".

The resultant regenerated catalyst can be recycled to the hydrogenation process with) loss in efficiency. The recovery is substantially quantitative.

Claims (2)

1. ft V HAVUNG NOW PARTICULARLY DESCRIBED AND ASCERTAINED THE ATURE OF OUR SAID INVENTION ANO IN WHAT MANNER THE SAME IS TO BO PERFORMED, we DECLARE, THAT WHAT WE CLAIM IS:- 1. A method of regenerating a palladium-containing catalyst which has been used in the continuous hydrogenation of an organic nitro compound to the corresponding amine, which comprises washing the used catalyst with hot water.

2. A method according to Claim 1 wherein the used catalyst is washed with water at a temperature of at least 60°C. 3>. A method according to Claim 2 wherein the used catalyst is washed with water at a temperature of 80° to 100°C. *. , A method according to any one the preceding claims wherein the washing comprises two stages in each of which 1 part by weight of catalyst is agitated with at least 8 parts by weight of hot water. 5. A method according to any one of the preceding claims wherein the total washing time is at least 1 hour. 6. A method according to any one of the preceding claims wherein deionized or distilled water is used. 7. A method according to Claim 1 substantially as described in the foregoing Example. 8. A regenerated palladium-containing catalyst obtained by a method as claimed in any one of the preceding claims. DATED THIS 29 H DAY OF JANUARY ,1965 FOR THE APPLICANTS, DR. RE I jHOLOy C OHN & CO.