Bio-lubricant production from black liquor as a sustainable biorefinery strategy

Abstract

The paper and pulp industry annually generates approximately 170 million tons of black liquor, yet research directly target- ing its utilization remains scarce. Addressing this gap, our study tackles the challenge of revalorizing black liquor through innovative techniques. Concurrently, the lubricant industry’s pursuit of eco-friendly alternatives necessitates effective thick- eners for semi-solid lubricant formulations derived from vegetable oils. Our research focuses on revalorizing weak black liquor via supercritical water hydrolysis, presenting a novel avenue for semi-solid bio-lubricant production. We obtained and treated four lignin waste fractions, including original black liquor and depolymerized variants through supercritical water hydrolysis, followed by additional processes such as spray-drying, oven-drying, and ethyl acetate extraction. These lignin fractions were then incorporated into epoxy-modified vegetable oils to formulate sustainable lubricants. Evaluation of these formulations revealed promising rheological and tribological properties. The resulting castor oil-based bio-lubricants not only exhibited excellent stability and appearance but also demonstrated notable performance improvements in rheological and tribological tests, noticing a maximum wear scar size reduction of around 50%, while maintaining friction factor values. Our findings highlight the potential of depolymerization hydrolysis in enhancing the lubricating properties of castor oil-based formulations, thus advancing the revalorization of weak black liquor.