CA1113960A - Catalyst for hydration of nitriles - Google Patents

Abstract

IMPROVED CATALYST FOR HYDRATION OF NITRILES
ABSTRACT OF THE DISCLOSURE

In the use of reduced copper chromium oxide as catalyst for the hydration of nitriles, the tendency towards formation of by-products during an initial period of use of the catalyst, is reduced by pretreating the reduced catalyst with dilute mineral acid solution before the catalytic use.

Description

The invention relates to improvements in the catalytic hydration of acrylonitrile to produce acrylamide using solid heterogeneous catalysts that contain elemental copper.
One preferred catalyst for the hydration of acrylo-nitrile to produce acrylamide is reduced copper chromium oxide which is conveniently prepared by the reduction of a copper chromium oxide catalyst such as Adkins cata]yst in a stream of hydrogen diluted with nitrogen. The preparations of several reduced catalysts for this use were described in United States Patent No. 3,631,104, patented December 28, 1971. It is found in practice using such catalysts for the hydration of acry-lonitrile in a continuous catalytic process, tha-t the feed solution of water and nitrile reactan-ts percolating through the catalyst bed will leach hydroxide from the catalyst during the first several hours of use. This causes an increase of the pH
of the reaction feed mixture which in turn causes increased by-product formation, particularly the production of beta-hydroxypropionitrile. Since acrylamide can usually be produced by this process with no more than tolerable, very small formation of by-product except during the ini-tial period of leaching as described, it is desirable to eliminate or at least reduce the exceptional by-product formation that occurs only during the initial period.
The present invention provides an improved process. In the catalytic hydration of acrylonitrile with water in presence of reduced copper chromium oxide catalyst, the present invention relates to the improvement where~n the reduced catalyst is treated, after reduction of the copper catalyst and before the catalytic use, with a dilute aqueous solution of 0~1 Normal to 0.01 Normal mineral acid to neutralize hydroxicles in the catalyst.

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According to the inyention a reduced copper chromium oxide catalyst prepared for use as a catalyst in the hydration of acrylonitrile with water to produce acrylamide, is treated with a dilute aqueous solution of mineral aeid preferably sulfuric aeid, and then is washed with pure water to remove said residue, all before the feed solution of nitrile and water is introduced to the catalyst. It is found that such treatment will substantially reduee the produetion of hydroxypropionitrile during the hydration reaction when using a fresh new catalyst.

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. The invention i~ de~cribed in more detail by ref-erence to specific examples set out below, Harshaw copper-chromium oxide catalyst No. 0203T
i~ reduced in hydrogen diluted with nitrogen at L75C. re-ducing temperature by Imown procedure until the reduction Or copp~r compounds ;n the catalyst to elemental copper is com plete. The reduced catalyst is divîded into aliquot portions ~or pretreatment as rollows One portion i9 not treated, to be u~sed as a control, One portion is wa~hed with water alone, a3 a con-trol.
One portion is wa~hed in an aqueous 0.1 Normal HN03 solution for one-hal~ hour, another for two hours One portion is washed in aqueou~ 0 OlN~HN03 solution for one-half hour, another for two hour3.
Similarly, other portions are washed in ~olutions - of O.lN and O.OlN.H2S04 ~olution, one in e~ch ~or one-halr hour and one in each for two hours.
After such waghes each portion is thoroughly wa~hed with pure water before the catalytic use. At all times the reduced cat-alyst i9 protected rrom contact with air and all ~olutions are deaerated before contact with the catalyst to avoid de-activation b~ oxidation o~ reduced copper in the cataly~t A one-gram catalyst sample i9 taken rrom each o~ the portion~
treated as described and each sample i~ used as catalyst in a ~tandard test in which 0.3 gram~ acrylonitrile, 5 grams water and 1 gram catalyst are mixed and agitated at 57C. ror one hour, At the end Or the hour each test portion i3 ana~
lyzed to determine the percent conversion Or acrylonitrile (AN~ to acrylamide (AMD~ and the amount Or ~-hydroxypropio-- nitrile (HPN) produced, expre3sed a~ a porcentage b~ weight of the acrylamide. The result~ ~re tabulated in Table I.
TABLE I

Treatment Batch Test Results_ Concen- Conver-tration Time ~ion to HPN as Acid ~ Hours AMD Or AMD
None --- --- 37.4 107 None, 2 37.3 1,2 water only HN03 0.01 1/2 45.4 0,61

2 43.5 0.75 HN03 0.10 1/2 36,3 o,87 2 35.9 0.95 H2S04 ' O r 01 1/2 32.6 0.29 2 40.3 o,o65 H2S04 0.10 1/2 3~,8 0.037 2 38.3 0.069 As shown in Table I, the two control sample3 produced about equal conversion &nd respectively produced 1.7 percent and 1.2 percent ~-hydroxypropionitrile while the ~amples that had been treated before use with mineral acids produced conver-sions to acrylamide from slightly le~ to more than the con-trols and con~iderably reduced the by-product HPN. Samples wa3hed with sulfuric acid produced the ]east amounts o~ HPN, - For continuous processing~ the catalyst is prepared and used in a fixed bed. ~he catalyst is fir~t reduced b~
circulation of heated reducing gas through the bed until the copper has been completely reduced, Then the cataly~t bed i~
- washed with a selected mineral acid solution for time su~
cient to neutralize the catalyst, and then ls washed with water until the catalyst is rinsed clear o~ the acid. The bed is then ready ror introduction of the continuous ~eed of acrylonitrile and water feed mixture to start the hydration reaction.
In continuous bed reactions uaing freshly reduced

- 3 -, catalyst that ha~ not been treated by the process of the in-vention it is found that ~-hydroxypropionitrile i9 produced for about the first 20-30 hours of production after which thi~ by-product gradually decline~ as a percentage o~ the product. By pre-washing the catalyst with mineral acid as de~cribed, the initial relatively high production of h~droxy-propionitrile is substantially reduced.
For the mineral acid wash we may use any of the mineral acids such a~ nitric, sul~uric, phosphoric, hydro-10. chloric, and the like. Some are better than others, ~ul-~uric acid being the be~t, We prefer to u~e a dilute aqueous 901ution of the 3elected strong acid, for example rrom about 0.1 to about 0 01 Normal solution o~ the acid, for this treat-ment.

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Claims (3)

WE CLAIM:

1. In the catalytic hydration of acrylonitrile with water in presence of reduced copper chromium oxide catalyst, the improvement wherein the reduced catalyst is treated, after reduction of the copper catalyst and before the catalytic use, with a dilute aqueous solution of 0.1 Normal to 0.01 Normal mineral acid to neutralize hydroxides in the catalyst.

2. An improved process defined by Claim 1 wherein the defined mineral acid is sulfuric acid.

3. An improved process defined by Claim 1 wherein the defined mineral acid is nitric acid.