Continuous hydrodeoxygenation of lignin derived phenolics to cycloalkanes

Lignin, a major constituent of lignocellulosic biomass, holds significant potential as a renewable feedstock for advanced biofuel production. However, the bio-oil derived from lignin often suffers from poor thermal stability, limiting its direct application as a fuel. Hydrodeoxygenation (HDO) is an essential upgrading process that selectively removes oxygen from lignin-derived bio-oil, converting it into high-quality hydrocarbon fuels. This study investigates the continuous HDO of representative phenolic compounds (phenol and 4-ethylphenol) using a Ni/h-BN catalyst for cycloalkane production in a fixed-bed reactor. The effects of various operational parameters on product distribution and catalyst stability were systematically evaluated. Under optimized conditions, a phenol conversion of 87.6% with 86.6% selectivity to cyclohexane was achieved. Similarly, 4-ethylphenol exhibited a conversion of 78% and 75.2% selectivity to ethylcyclohexane. In a co-feeding experiment, the conversion of phenol and 4-ethylphenol reached 78.1% and 76.2%, with cyclohexane and ethylcyclohexane selectivities of 84% and 81%, respectively. Notably, the catalyst demonstrated stable performance over 8 h of continuous operation, maintaining conversions above 75% and cycloalkane selectivities exceeding 81%. The product distribution containing both aromatic hydrocarbons and cycloalkanes, indicates that the direct deoxygenation pathway predominated under the evaluated conditions.