Research On The Process Of Nitrocyclohexane Hydrogenation Under Dimethyl Sulfoxide Solvent System

Cyclohexanone oxime is an important chemical intermediate, mainly used for preparing caprolactam by Beckmann rearrangement.As a basic chemical material,caprolactam can produce a wealth of daily necessities of raw materials by the polymerization process and further processing,such as plastics, paints, medical supplies, leather and so on.Currently the craft of caprolactam is quite mature, but there are still many problems such as low utilization of atomic、serious environmental pollution、equipment corrosion and other issues. Now nitrocyclohexane route is favored by many researchers as its mild reaction conditions without ammonium sulfate.The hydrogenation process of nitrocyclohexane to cyclohexanone oxime and the rearrangement process of cyclohexanone oxime to caprolactam are mature, but the one step hydrogenation process of nitrocyclohexane to caprolactam still has much room for improvement,Wherein the solvent effects the the results of hydrogenation and rearrangement most,alkaline reaction condition beneficial to hydrogenation to cyclohexanone oxime while neutral and acidic reaction condition beneficial to rearrangement.This article taking palladium as the active metal of the supported catalyst, so we researched the process not only suitable for hydrogenation to cyclohexanone oxime but also suitable for nitrocyclohexane hydrogenation under rearrangement solvent,to lay the foundation of one step hydrogenation of nitrocyclohexane to caprolactam.The reaction raw material nitrocyclohexane is produced by a simple device.The purity of nitrocyclohexane can reach more than 93%.We conform that the products of hydrogenation are cyclohexanone oxime、cyclohexane、cyclohexanone and cyclohexyl hydroxylamine by GC-MS.We establish the best analysis conditions by using the dimethyl phthalate as the internal standard.This paper examines the impact of rearrangement solvent to hydrogenate nitrocyclohexane such as benzonitrile、acetonitrile、DMF, DMSO and chlorobenzene, we found that DMSO shows better hydrogenation properties. We inspected the effects of carbon material and molecular sieve as the carrier material and Palladium as the active component in hydrogenation,wherein the carbon nanotubes have good hydrogenation performance. We deal the with steam treatment、 alkali treatment and nitric acid treatment, the results shows that nitric acid treatment of carbon nanotubes has better catalytic activity. In this article,we use DMSO as the solvent and 5%Pd/CNT as the catalyst for the catalytic hydrogenation of nitrocyclohexane, we optimal the conditions and find that when the reaction is under the condition of 130 ℃ and 0.9MPa for 6 hours, the conversion of nitrocyclohexane is 98.76%, the yield of cyclohexanone oxime was 35.07%.In order to improve the selectivity of cyclohexanone oxime, this article introduce alkali metals into the 5%Pd/CNT, the results shows that sodium can inhibit excessive hydrogenation of nitrocyclohexane.By changing the content of sodium and optimization of reaction conditions,we found that when the reaction is under the condition of 130℃, 0.5MPa for 6 hours, adding sodium can improve the yield of cyclohexanone oxime from 35.07% to 62.30%. In this article, we characterized the catalyst with BET, XRD, TEM etc., and found that the adding of sodium make the catalyst with better dispersion,the nitrocyclohexane can be hydrogenated more easily; BET results displays that by adding sodium make the catalyst with smaller surface area 、smaller capacity and bigger pore size, so we guess that by adding sodium can inhibit excessive hydrogenation of nitrocyclohexane.In addition, this article verified the variation of cyclohexylhydroxylamine which is the intermediates of nitrocyclohexane hydrogenation process by a series of experiments, suggesting a reaction mechanism of nitrocyclohexane and more in-depth study of it.