Technoeconomic assessment of hydrothermal liquefaction oil from lignin with catalytic upgrading for renewable fuel and chemical production

Lignin is a readily available by-product of the Kraft pulping process, and may be processed via hydrothermal liquefaction (HTL) to produce a bio-oil suitable for cofeeding into a petroleum refinery hydrotreatment unit. HTL of lignin is performed in near-critical water and, in addition to the bio-oil, produces an aqueous organic and solid char phase. The aqueous organics are primarily phenolics, which may be converted into valuable coproducts via liquid-liquid extraction and hydrotreatment to benzene, toluene, ethylbenzene, and xylenes (BTEX) compounds. Three technological scenarios were developed: a current technology case, a state-of-the-art research case, and an optimal case based on product targets provided by refiners. For a large Kraft pulp mill (400 metric tons/day of dry lignin), a renewable fuel production of 65-70 million L/year, with capital costs of $114-125 million and a final per liter cost of $0.41-0.44 were estimated. The BTEX coproduct yield ranged from 16.8-18.0 million L/year. An economic analysis of the process revealed that the hydrotreatment steps have the highest installed capital costs, while the liquid-liquid extraction process is the largest operating cost. Based on these results, the minimum selling price (MSP) of the biofuel is between $3.52 and $3.86/gallon, and the MSP of BTEX is between $1.65 and $2.00 per liter. With current technology, coproduction of BTEX does not offset the cost of biofuel production. Improved technology to further lower bio-oil oxygen content and decrease both capital and operating costs are needed to make HTL-based fuels competitive with fossil fuel-based options. This article is categorized under: Energy Research & Innovation > Science and Materials Bioenergy > Economics and Policy Bioenergy > Systems and Infrastructure