Catalytic influence of alkali and alkali earth metals in black liquor on the gasification process: a review

During the pulping process, either alkali or alkali earth metals are added in a cooking solution to turn wood chips into pulp, and these alkali and alkali earth metals (AAEMs) end up in the black liquor. These AAEMs are known to catalyze the gasification process, by lowering the reaction temperature and degrading tar in the syngas. Of the various black liquor valorization methods, gasification is a promising process that can be integrated into existing pulping processes to recover the process energy via syngas utilization. It is, therefore, important to firmly understand how AAEMs in black liquor catalyze the gasification process. This review paper also discusses how black liquor is generated from both the Kraft pulping and the sulfite pulping process. The paper also examines advances that have been made in terms of an integrated gasification process into the existing pulping process. The paper explores the supercritical water gasification of back liquor and syngas as fuel in the pulp and paper industry. A discussion of the co-gasification of black liquor with either fossil fuels or biomass, focusing on the catalytic effect of AAEMs in the co-gasification process as well as the synergistic effects of fossil fuels and biomass is presented.