Chen Xue, Zhang Kaili, Xiao Ling-Ping, Sun Run-Cang, Song Guoyong
1Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing, 100083 China.
2Center for Lignocellulose Science and Engineering, Liaoning Key Laboratory of Pulp and Paper Engineering, School of Light Industry and Chemical Engineering, Dalian Polytechnic University, Dalian, 116034 China.
Biotechnol Biofuels. 2020 Jan 6;13:2. doi: 10.1186/s13068-019-1644-z. eCollection 2020.
Lignocellulosic biomass, which is composed of cellulose, hemicellulose and lignin, represents the most abundant renewable carbon source with significant potential for the production of sustainable chemicals and fuels. Current biorefineries focus on cellulose and hemicellulose valorization, whereas lignin is treated as a waste product and is burned to supply energy to the biorefineries. The depolymerization of lignin into well-defined mono-aromatic chemicals suitable for downstream processing is recognized increasingly as an important starting point for lignin valorization. In this study, conversion of all three components of into the corresponding monomeric chemicals was investigated using solid and acidic catalyst in sequence.
Lignin was depolymerized into well-defined monomeric phenols in the first step using a Pd/C catalyst. The maximum phenolic monomers yield of 49.8 wt% was achieved at 240 °C for 4 h under 30 atm H. In the monomers, 4-propanol guaiacol (12.9 wt%) and 4-propanol syringol (31.9 wt%) were identified as the two major phenolic products with 90% selectivity. High retention of cellulose and hemicellulose pulp was also obtained, which was treated with FeCl catalyst to attain 5-hydroxymethylfurfural, levulinic acid and furfural simultaneously. The optimal reaction condition for the co-conversion of hemicellulose and cellulose was established as 190 °C and 100 min, from which furfural and levulinic acid were obtained in 55.9% and 73.6% yields, respectively. Ultimately, 54% of sawdust can be converted into well-defined chemicals under such an integrated biorefinery method.
A two-step process (reductive catalytic fractionation followed by FeCl catalysis) allows the fractionation of all the three biopolymers (cellulose, hemicellulose, and lignin) in biomass, which provides a promising strategy to make high-value chemicals from sustainable biomass.
木质纤维素生物质由纤维素、半纤维素和木质素组成，是最丰富的可再生碳源，在生产可持续化学品和燃料方面具有巨大潜力。当前的生物精炼厂主要关注纤维素和半纤维素的价值利用，而木质素则被当作废品处理并燃烧以为生物精炼厂提供能源。将木质素解聚为适合下游加工的特定单芳族化学品日益被视为木质素价值利用的重要起点。在本研究中，依次使用固体催化剂和酸性催化剂研究了将木质纤维素生物质的所有三种成分转化为相应单体化学品的过程。
第一步使用钯碳催化剂将木质素解聚为特定的单体酚类。在240℃、30个大气压氢气条件下反应4小时，酚类单体的最大产率达到49.8重量%。在这些单体中，4-丙醇愈创木酚（12.9重量%）和4-丙醇丁香酚（31.9重量%）被确定为两种主要酚类产物，选择性达90%。同时还获得了纤维素和半纤维素纸浆的高保留率，然后用氯化铁催化剂处理以同时获得5-羟甲基糠醛、乙酰丙酸和糠醛。半纤维素和纤维素共转化的最佳反应条件确定为190℃和100分钟，在此条件下糠醛和乙酰丙酸的产率分别为55.9%和73.6%。最终，在这种集成生物精炼方法下，54%的锯末可转化为特定化学品。
两步法（还原催化分馏后接氯化铁催化）能够将木质纤维素生物质中的所有三种生物聚合物（纤维素、半纤维素和木质素）进行分馏，这为从可持续生物质中制备高价值化学品提供了一种有前景的策略。
