Organic compounds -- part of the class 532-570 series – Organic compounds – Unsubstituted hydrocarbyl chain between the ring and the -c-...
Reexamination Certificate
2001-03-01
2002-09-17
Kifle, Bruck (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Unsubstituted hydrocarbyl chain between the ring and the -c-...
Reexamination Certificate
active
06452002
ABSTRACT:
The invention relates to a process for preparing an aqueous mixture of &egr;-caprolactam and 6-aminocaproic acid and/or 6-aminocaproamide by reductively aminating 5-formylvaleric acid and/or an alkyl 5-formylvalerate in water with hydrogen and an excess of ammonia in the presence of a ruthenium on carrier catalyst.
A process for preparing &egr;-caprolactam is described in U.S. Pat. No. 4,730,040. In this process, methyl 5-formylvalerate is first hydrolyzed (step a) in the presence of water and an acidic agent to yield 5-formylvaleric acid. In this process, the 5-formylvaleric acid is reductively aminated in water through contact with ammonia and hydrogen using a ruthenium/zirconium on alumina catalyst, a Raney Nickel catalyst or a Raney Cobalt catalyst to obtain a 6-aminocaproic acid containing reaction mixture. After separation of ammonia, the reaction mixture obtained from the reductive amination is heated to 300° C. to form &egr;-caprolactam by cyclization of the 6-aminocaproic acid.
A disadvantage of the process according to U.S. Pat. No. 4,730,040 is the poor yields obtained from the reductive amination which prevent it from being a commercially attractive process. According to the experimental results, the best yield of the hydrolysis step is only about 78%, the best yield of the reductive amination step is only about 77% and the best yield of the final step is only about 95%. Hence, the overall yield is at most 57%.
Another disadvantage is that when the reductive amination is performed for a prolonged period of time, a decrease in particle size of the Raney Nickel and alumina catalyst particles has been found to occur. This is not desired because these small particles may disturb any filtration operation or lead to catalyst losses due to entrainment of the catalyst in the product stream.
A further disadvantage of this process is that the initial activity of the catalyst system is relatively small.
A still further disadvantage is that after some hours of continuous operation the activity of the catalyst can decrease.
An object of the present invention is to reproducibly obtain a higher yield to &egr;-caprolactam and &egr;-caprolactam precursors (6-aminocaproic acid and 6-aminocaproamide) in the reductive amination with an improved initial catalyst activity without suffering the above described problems, including the decrease of the catalyst particle size or loss of catalyst activity.
This object is achieved in that the carrier is titanium oxide, zirconium oxide, graphite or carbon and the catalyst also contains at least one of the metals of group 8-11, or a compound of these metals.
It has been found that when the process according to the invention is performed a high yield to &egr;-caprolactam and &egr;-caprolactam precursors can be achieved in the reductive amination, and the catalyst retains its particle size and activity over a prolonged period of time. Another advantage is that the initial activity of the catalyst system is improved. Another advantage is that the selectivity of &egr;-caprolactam precursors is also improved. Another advantage is that when starting from an alkyl 5-formylvalerate a separate hydrolysis step in order to prepare 5-formylvaleric acid, such as described in U.S. Pat. No. 4,730,040, is not needed. This is very advantageous because the separate hydrolysis of the alkyl 5-formylvalerate as described in U.S. Pat. No. 4,730,040 showed a low yield (78%) to 5-formylvaleric acid. It has been found that the alkyl 5-formylvalerate can be directly used in the present process, resulting in a high yield to &egr;-caprolactam while avoiding the low-yield-hydrolysis step described in U.S. Pat. No. 4,730,040.
According to EP-A-729943 and EP-A-729944 &egr;-caprolactam can be prepared by first contacting methyl 5-formylvalerate with ammonia and subsequently reacting the intermediate compounds thus formed, probably imine-caproic acid derivatives, with hydrogen in the presence of ammonia and, for example, a ruthenium on alumina catalyst or Raney Nickel. These patent applications mention copper, iron and/or chrome as possible additional metal in addition to nickel, cobalt or ruthenium on alumina, silica, titanium oxide, magnesium oxide, zirconium oxide or carbon as possible carrier material. However, only ruthenium on alumina carriers containing no substantial amount of a further metal are used in the examples of EP-A-729943 and EP-A-729944. However when using the exemplified ruthenium on alumina catalyst the earlier mentioned problem of particle size reduction also takes place. It was therefore not expected that by using a ruthenium and at least one further group 8-11 metal on zirconium oxide, titanium oxide, graphite or carbon carrier in a one-step reductive amination that a high yield to &egr;-caprolactam precursors and a high initial catalytic acitiviy could be achieved while at the same time avoiding loss of catalyst activity and reduction of catalyst particle size.
According to the publication WO-A-9835938 &egr;-caprolactam and &egr;-caprolactam precursors are prepared in water starting from methyl 5-formylvalerate in the presence of ruthenium on titanium oxide or zirconium oxide as catalyst. The use of a group 8-11 metal as further catalyst component is not disclosed or suggested.
The catalysts used in the process of the present invention are combinations of ruthenium and at least one further group 8-11 metal or compounds thereof, on a carrier selected from titanium oxide, zirconium oxide, graphite or carbon. Of the further group 8-11 metal Co, Rh, Ir, Ni, Pd, Pt and Cu are preferred. The most preferred further group 8-11 metal is Rh and Ni.
The carrier is titanium oxide, zirconium oxide, graphite or carbon. Titanium oxide and zirconium oxide are preferably used as the carrier because of its high chemical and mechanical stability and because the selectivity to the preferred (intermediate) compounds is found to be relatively high when these supports are used.
A relatively small but catalytically effective amount of the catalyst is used in the present process. The amount of ruthenium (as metal) in the catalyst (metal plus carrier) is generally between 0.1 and 10 wt %. The amount of the group 8-11 metal (as metal) in the catalyst (metals plus carrier) is generally between 0.05 and 30 wt. %, preferably between 0.1 and 10 wt. % and more preferably between 0.1 and 5 wt. %. The molar ratio of ruthenium to the other metal is generally within the range from 100:1 to 1:10, preferably from 20:1 to 1:1. The mean particle size (d
50
) of the catalyst is preferably between 10 and 100 &mgr;m, when the catalyst is present as a slurry in the reaction mixture or between 0.001 and 0.05 m, when the catalyst is present in a fixed bed. The BET surface area can be between 1 and 100 m
2
/g. The BET surface area is preferably between 30 and 100 m
2
/g. Preferably anatase is used as carrier to reach such a high BET surface area of titanium oxide. The high BET surface area is advantageous because higher catalyst activity can be obtained.
The catalyst can be prepared by any of the processes known for a man skilled in the art. The supported catalyst is suitably prepared by adding at least one group 8-11 metal salt to a ruthenium on carrier and subsequently precipitation of the group 8-11 metal salt by means of evaporation the solvent, so called impregnation or by means of reduction of the catalyst. Another suitable method for preparing the catalyst is adding a group 8-11 metal salt to a ruthenium on carrier and subsequently precipitation of the group 8-11 metal salt by means of adjustment of the pH of the solution.
The alkyl 5-formylvalerate compound is preferably a C
1
-C
6
alkyl 5-formylvalerate compound. Examples of suitable alkyl groups are methyl, ethyl, propyl, iso-propyl, tert-butyl, n-butyl, iso-butyl, cyclohexyl. More preferably methyl and ethyl groups are used because methyl- and ethyl-5-formylvalerate are readily obtainable such as, for example, by the processes described in U.S. Pat. No. 5,527,950, WO-A-9404482 and WO-A-9506025. A method for preparing 5-formylvaleric aci
Pestman Robert
Van Lieshout Lambertus H. W. M.
DSM N.V.
Kifle Bruck
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