Synthesis of bio-based caprolactam through dehydration and cyclization of 6-hydroxycaproamide

The preparation of caprolactam (CPL) from biomass as raw material is a very hot topic of current concern. In this paper, a new way to synthesize CPL from 5-hydroxymethylfurfural (HMF) was proposed, and the catalytic reaction of cyclization of the intermediate 6-hydroxycaproamide (6-HCM) was studied to provide a basis for the synthesis of bio-based CPL. A bimetallic catalyst, Ru–Co/TiO₂, was prepared using the impregnation method and characterized using XRD, XPS, H₂-TPR, and TEM. The investigation delves into the impact of various parameters, including metal loading, choice of solvent, solvent ratio, catalyst dosage, and reaction time, on the yield of the final product. The findings demonstrate a significant synergistic effect between Ru and Co in the bimetallic Ru₅Co₆/TiO₂ catalyst, leading to improved catalytic performance. Under the optimized reaction conditions (250 °C, 1 MPa N₂, 1,4-dioxane: NH₃·H₂O = 2:1 as the solvent ratio), the conversion rate of 6-HCM reaches 99.0%, with CPL yield of 62.2%.