Effect of co-liquefaction of lignin and laminaria saccharina on optimization of bio-oil yield

Abstract

• Co-liquefaction of Laminaria saccharina with lignin is studied. • The synergistic effect is negative in most mild and lignin-rich conditions. • The synergistic effect is positive in severe and lignin-poor conditions. • Residence time showed an impact on bio-oil quality. • Co-liquefaction synergistically enhanced the bio-oil quality at specific conditions. Hydrothermal liquefaction (HTL) is a valuable technology to convert and use wet biomass feedstocks. Lignin, waste from the paper industry and the main component of lignocellulosic biomass, is co-liquefied with laminaria saccharina, a commonly available seaweed in Norway. The aim is to conduct statistical analysis and investigate the possibility of increasing bio-oil yield while lowering the char yield through a synergistic effect. The bio-oil and char yields are measured with different operating temperatures, residence times, and blending ratios (mass ratio of laminaria saccharina to the total mass) to find out the optimized process conditions for better outputs statistically. Response surface methodology (RSM) with a Box Behnken design methodology is used to optimize the liquefaction yields of laminaria saccharina, lignin, and the different blends of the two biomasses. The results explicitly revealed that the biomass blend's optimal bio-oil and char yields are 0.2513 (w/w 0 ) and 0.1791 (w/w 0 ) respectively at 573 K, 20 min with the blending mass ratio of 0.2. The synergistic effects on the bio-oil yield are detected at comparatively severe reaction conditions. According to the RSM, residence time does not affect bio-oil and char yields as much as the operating temperature and the blending ratio. Nevertheless, temperature, residence time, and blending ratio have different impacts on the functional groups. The temperature increase has helped increase the alcohol and phenolic compounds production while the residence time consumes the C-O bonds. The increase of laminaria saccharina mass ratio in the feedstock has improved the phenolic compounds, long-chain aliphatic hydrocarbons, carboxylic acids, ketones, aldehydes, and esters in the bio-oils. Co-liqueafctio has produced bio-oil with significantly lower N content than from bio-oil produced from laminaria saccharina liquefaction.