Chemistry of hydrocarbon compounds – Adding hydrogen to unsaturated bond of hydrocarbon – i.e.,... – Hydrocarbon is aromatic
Patent
1997-06-19
1999-01-05
Yildirim, Bekir L.
Chemistry of hydrocarbon compounds
Adding hydrogen to unsaturated bond of hydrocarbon, i.e.,...
Hydrocarbon is aromatic
585274, 585276, C07C 510
Patent
active
058566031
DESCRIPTION:
BRIEF SUMMARY
The invention is directed to a process for the production of cyclohexane by catalytic hydrogenation of benzene in the presence of a supported nickel catalyst.
Cyclohexane is an important chemical, especially as intermediate for the production of caprolactam, a monomer for the production of nylon-6. Cyclohexane is produced in huge quantities, mainly by hydrogenation of benzene in the presence of hydrogen, for example in a fixed bed of a (supported) nickel catalyst, or in the presence of a noble metal catalyst. A review of the production of cyclohexane by hydrogenation of benzene has been given in Uhlmanns' Enzyklopadie der technischen Chemie, 4th. ed, Band 9, page 680 ff.
Although the hydrogenation reaction proceeds with good activity and relatively high selectivity (over 99.95% at optimal reaction conditions), there is an increasing interest in reducing the amount of byproducts to a level below the presently obtained level of about 200 ppm. Conventionally the hydrogenation of benzene leads to the production of n-hexane, methyl-cyclopentane, methylpentane, n-pentane and methane as predominant byproducts.
This interest in reducing the amounts of byproducts comes especially from the end users of the nylon-6, who require very low levels of byproducts in the nylon-6 in order to improve the properties of the nylon. One of the methods of decreasing the amount of byproducts in caprolactam and subsequently in the endproduct is the reduction of the amount of byproducts in the cyclohexane.
Reduction of the production of byproducts can usually be obtained by a reduction of the activity, for example by lowering the reaction temperature. However, this leads to an increase in production costs, due to the necessity of larger equipment for the production and/or larger recycle of unconverted benzene. This is accordingly not a preferred option for reduction of the amount of byproducts.
It is an object of the present invention to provide an improved process for the production of cyclohexane by catalytic hydrogenation of benzene in the presence of a supported nickel catalyst.
The invention is based on the surprising feature that promoting the nickel catalyst with sulfur results in an increase of selectivity that is much larger than would be expected on the basis of the decrease of activity. Restoring the activity to the original level, for example by the use of a different method of producing the catalyst, or the use of more nickel, results in a catalyst that still has a higher selectivity than the original unpromoted catalyst of the same activity. Accordingly the use of sulfur as promoting agent for the catalyst improves the ratio of selectivity to activity.
Additionally it has been noted that surprisingly the life time of the catalyst is increased. The life time of a catalyst is also a function of activity. At the same activity the catalyst life time is generally increased.
Accordingly the invention concerns a process for the production of cyclohexane by catalytic hydrogenation of benzene using hydrogen, said process comprising the hydrogenation of benzene in the presence of a supported nickel catalyst having a nickel content of at least 10 wt. %, calculated as nickel, said catalyst containing sulfur, or compounds thereof as promotor.
The amount of the promotor can be selected within wide ranges. The lower limit of the amount is determined by the minimal amount required to give a reasonable improvement, which improvement is especially influenced by the atomic promotor to nickel ratio. This means that at higher nickel amounts the amount of promoter will usually be higher. The suitable catalysts are usually promoted with sulfur in an atomic sulfur
ickel ratio of between 0.01 and 1, preferably between 0.02 and 0.5. The level of sulfur in the catalyst can be used to tune the activity to the required value. As each type of benzene hydrogenation process requires different activity, for example due to different reactor geometry and heat exchange capacity, the promotor amount may be varied to meet the requirements of the actual pro
REFERENCES:
patent: 2744052 (1956-05-01), Nozaki
patent: 3859370 (1975-01-01), Carter et al.
Borninkhof Frederik
Reesink Bernard Hendrik
Rekker Tjalling
Engelhard Corporation
Yildirim Bekir L.
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