Conversion of Lignin to Cyclohexanol via Mild Catalytic Depolymerization Coupled with Hydrogenation
Xiaoting Xing, Wenlong Cao, Jinliang Yan, Yuchun Zhang, Payam Ghorbannezhad, Zhiyu Li, Peng Fu
Abstract
Cyclohexanol is a crucial intermediate in the synthesis of nylon and other chemical industry materials. However, directly hydrogenating phenol to cyclohexanol presents challenges, including harsh reaction conditions and low selectivity for the desired product. To address these issues, a two-step method was proposed, involving the mild catalytic decoupling and hydrogenation of lignin, which enables the efficient production of cyclohexanol. Lignin was initially depolymerized into 18.08 % phenol and 60.63 % guaiacol in a dilute alkaline aqueous solution at 200°C under atmospheric nitrogen. Subsequently, the effects of catalytic hydrogenation of phenol in different solvents were examined. When water was used as the solvent, phenol conversion reached 100 % within 2 hours at 30°C, with a selectivity of 94.69 % to cyclohexanol. The hydrogenation process, catalyzed by 5 wt% Pd/AC, was studied under these conditions. It was found that phenol was first partially hydrogenated to cyclohexenol, which quickly isomerized to cyclohexanone and was further hydrogenated to cyclohexanol. The two steps create a low-temperature and low-pressure pathway for efficiently converting lignin to cyclohexanol, thereby enhancing lignin's potential value.