Comparing multistage liquid–liquid extraction with cold water precipitation for improvement of lignin recovery from deep eutectic solvents
Comparing multistage liquid–liquid extraction with cold water precipitation for improvement of lignin recovery from deep eutectic solvents
复制标题
DOI：
10.1016/j.seppur.2020.117395
复制
发表时间：
2020-12
影响因子：
8.6
通讯作者：
D. Smink;S. Kersten;B. Schuur
中科院分区：
文献类型：
--
作者：
D. Smink;S. Kersten;B. Schuur
在使用低共熔溶剂（DES）进行生物质分馏之后，溶剂回收是必不可少的步骤。与冷水沉淀相比，通过液-液萃取（LLX）从DES中回收木质素可以提供大量的能量节省。溶解在来自生物质分级分离的DES中的木质素是不均匀的，这意味着它具有不同摩尔重量的各种级分和官能团密度的可能变化。因此，比较LLX和冷水沉淀法各木质素级分的回收率是很重要的。在这项工作中，回收木质素从DES组成的30重量%氯化胆碱和70重量%的乳酸进行了研究。使用多达30重量%的氯化胆碱有利于限制乳酸的浸出。使用2-MTHF进行三次错流萃取。该方法回收了95%的约2000 g/mol的木质素级分和85%的约10，000 g/mol的木质素级分。通过杂原子单量子相干光谱（HSQC）在DES萃余液中剩余的木质素中没有发现芳族间醚键，表明DES中剩余的木质素具有高度缩合的性质。冷水沉淀可以使用3.5kg水/kg DES完全回收高于4000 g/mol的木质素级分。然而，仅回收了1000 g/mol的木质素级分的一半。简而言之，LLX更适合于回收低摩尔重量级分，而冷水沉淀更适合于重摩尔重量级分。对于工业应用，两种方法的组合对于完全回收木质素是必不可少的。
After biomass fractionation using deep eutectic solvents (DES), solvent recovery is an essential step. Recovery of lignin from DES by liquid–liquid extraction (LLX) may provide large energy savings compared to cold water precipitation. Lignin that is dissolved in DES from biomass fractionation is inhomogeneous, meaning it has various fractions with different molar weights and possibly variations in functional group densities. Therefore, it is important to compare recoverability of every lignin fraction by LLX with cold-water precipitation. In this work, the recovery of lignin from a DES comprised of 30 wt% choline chloride and 70 wt% lactic acid was studied. Using as much as 30 wt% choline chloride is beneficial to limit leaching of lactic acid. Three cross-current extractions were performed using 2-MTHF. This method recovered 95% of the lignin fractions around 2000 g/mol and 85% of the lignin fractions around 10,000 g/mol. No inter-aromatic ether bonds were found in the lignin remaining in the DES raffinate by heteronuclear single quantum coherence spectroscopy (HSQC), indicating the remaining lignin in the DES has a highly condensed nature. Cold water precipitation could fully recover the lignin fractions above 4000 g/mol using 3.5 kg water per kg DES. However, only half of the lignin fraction of 1000 g/mol was recovered. Briefly, LLX is more suitable for the recovery of low molar weight fractions, while cold water precipitation is more suitable for the heavy molar weight fractions. For industrial applications, a combination of both approaches is essential for full lignin recovery.