Hydrodeoxygenation of guaiacol to bio-hydrocarbons over Ni catalyst supported on activated coconut carbon in alkaline condition

Abstract

Pulping black liquor is a serious source of water pollution worldwide, which is very difficult to subsequently treat. Lignin is the main component of the black liquor and is the only natural aromatic recyclable resource, which is burnt as waste in the Kraft pulping industry. Designing an efficient lignin conversion catalyst that suitable for the strong alkaline environment of black liquor harbors tremendous carbon-neutral potential but still remains a scientific and technological challenge. In this work, the strong alkaline environment of black liquor was simulated, and low-cost pretreated Ni/AC catalysts were adopted to the hydrodeoxygenation (HDO) of a lignin model (guaiacol), and a breakthrough was achieved in the efficient transformation of lignin compound into hydrocarbons. By multitechniques, (e.g., FT-IR, XPS, Boehm titration, HRTEM), the relevance between introducing functional acid groups and the surface properties of catalysts was revealed. It is found that the increased acidic groups are responsible for the enhanced C(sp2)-O cleavage reactions, while improving the dispersion of Ni NPs and thus enhance the HDO efficiency. It is worth noting that better selectivity of benzene and lower hydrogen consumption are achieved on Ni/NOAC during the HDO process. Furthermore, the reaction routes of guaiacol on catalysts with different functional acid groups were proposed. This work provides guidance for efficient utilization of lignin in waste black liquor, and is of great significance to the development of sustainable carbon-neutral biorefinery and environmental protection.