Solvent-free Aerobic Baeyer-villiger Oxidation To ε-caprolactone Catalyzed By Carbon Nanotubes

ε-caprolactone(ε-CL)is an important chemical intermediate,and its derivative polycaprolactone has been widely used in medicine,packaging,coatings and other fields because of its good biocompatibility and degradability.The current ε-CL production process uses peroxic acid as the main oxidant,which limits the release of ε-CL production capacity due to its strong corrosiveness and instability.In this study,and the ε-CL was prepared from cyclohexanone and co-oxidant without solvent using nitrogen-doped carbon nanotubes(NCNTs)as the catalyst and oxygen as the oxidant.The main contents of the paper are as follows:(1)Aerobic Baeyer-Villiger oxidation with solvent-free based on the cyclohexanoneacrolein system to achieve high yield of ε-CL catalyzed by NCNTs was performed.The optimized conditions are: mole ratio of ketone/aldehyde is 1,40 °C,1.5 MPa,1000 rpm,5 mg NCNTs,4 hours.Under this condition,the conversion rates of cyclohexanone and acrolein were12.7%,and 40.1%,respectively.The conressponding selectivities of ε-CL and acrylic acid were93.7% and 65.4%,while the aldehyde efficiency was only 0.29.After analyzing the influence of nitrogen content and oxygen content on the catalytic performance,the volcanic-curve relationship between the catalytic activity and nitrogen content was obtained,indicating that nitrogen content is significance for this reaction;at the same time,oxygen-containing functional groups displayed a negative influence on the catalytic efficiency.This study provides a new solvent-free process for the large-scale preparation of ε-CL.(2)To further improve the aldehyde efficiency,benzaldehyde was selected to replace acrolein in the aerobic Baeyer-Villiger oxidation.The optimized process conditions are: 35 °C,ketone/aldehyde ratio 4,1500 rpm,1 MPa,5 mg NCNTs,1 hour.Under this condition,the conversion rate of cyclohexanone was 11.19%,and the selectivity of ε-CL was 90%.At the same time,the aldehyde efficiency was 0.7.After studying the structure-activity relationship,the volcanic-curve relationship between the catalytic activity and nitrogen content was obtained,and the existence of oxygen-containing functional groups showed a negative effect on the catalytic performance as well.Based on the above results,the large scale(kilogram-level)experiment under the optimal condition was conducted,showing a feasibility of this strategy for the production of ε-CL.Meanwhile,the cost calculation was carried out based on the experimental results,in which 8,000 yuan RMB/t could be obtained for this process.This study provides basic reference data and cost feasibility instructions for large-scale preparation of ε-CL.