Production of limonene epoxides from tire pyrolysis oil by polyoxometalate immobilized on SBA-15

The goal of producing limonene epoxide and separating p-cymene from tire pyrolysis oil (TPO) could be achieved after epoxidation. However, the existing catalytic epoxidation process has the problem of cumbersome catalyst separation process, which is not conducive to industrial applications. In this work, the heterogeneous catalysts polyoxometalate-SBA-15 were prepared with the point of simplifying separation process. Heteropoly acid anions (phosphotungstic acid or peroxophosphotungstic acid) with catalytic active successfully enter the mesoporous pores of SBA-15, exhibiting high limonene conversion in the TPO system. The PW4 species produced by phosphotungstic acid after oxidation of H2O2 was favorable for improving the selectivity of epoxidation. The catalyst S-D-PW4 prepared showed high catalytic activity and epoxidation selectivity with the condition of H2O2 as an oxidant and free of solvent. Furthermore, A statistical experimental approach was used to comprehensively evaluate the reaction conditions. The conversion of limonene in TPO could reach 99.78%, and the yield of 1,2-limonene epoxide and diepoxide were 67.96% and 20.16%, respectively. A variety of characterization techniques such as 31P NMR, XPS, and ICP were employed to analyze the difference in catalyst before and after epoxidation. S-D-PW4 could be easily separated and the catalytic activity and epoxidation selectivity remained high after 5 cycles.