氧化钙-二氧化碳处理杨木预水解液的物理化学变化及其对膜过滤性能的强化

Physical and Chemical Changes of the Calcium Oxide-Carbon Dioxide in the Treatment of Poplar Prehydrolysate and the Enhancement of the Membrane Filtration Performance

预水解是生物质精炼过程中重要的一部分,大量的半纤维素在预水解过程中通过自水解转化为可溶性的低聚糖和单糖。通过对预水解液中木素等非糖类物质的选择性去除,回收高附加值的半纤维素糖类物质,符合生物质精炼的理念。探讨了利用氧化钙-二氧化碳处理预水解液,研究结果表明:加入氧化钙使得pH为11.6时,碱性条件使得木素酚羟基离子化,从而结合钙离子而使胶体木素沉淀,木素去除率48.1%。但是过高的pH将导致糖类物质的碱性降解,因此通过通入二氧化碳来降低水解液的pH,从而降低糖类的碱性降解;另外,纳米级碳酸钙在碳酸化处理过程中形成,并通过表面吸附作用将木素去除率提升至56.9%;氧化钙-二氧化碳处理能够显著强化预水解液的过滤性能,表现为过滤速度衰减的弱化和浓缩倍数的提高。截留分子量为1000Da的超滤结果表明,在相同的超滤时间内浓缩倍数提高2.5倍。鉴于氧化钙、二氧化碳是纸浆厂碱回收工艺的过程产物,此文所述的氧化钙-二氧化碳工艺,具有很强的应用价值。

The prehydrolysis of wood is being deemed as a significant step for the biorefinery of forest biomass because a great amount of soluble oligosaccharides（OS） and monosaccharides are generated owing to the autohydrolysis ofhemicelluloses. Specific elimination of non-saccharide compounds（NSCs） for hemicellulose-derived saccharides（HDSs） separation from wood hydrolysate is coincident with concept of biorefinery. In this paper,prehydrolysis liquor（PHL） was treated by calcium oxide and carbon dioxide. The results showed that addition of Ca O to pH11 resulted in 48. 1% removal of lignin-derived NSCs because of the association of calcium ions to phenolic hydroxyl groups and the subsequent destabilization of lignin-derived NSCs. Further addition of Ca O led to significant alkaline degradation of HDSs. To avoid alkaline degradation of saccharides,carbon dioxide was fed into PHL to consume the excess calcium hydroxide and keep a mild alkaline condition. In addition,nano-calcium carbonate was formed in the process of carbonation,resulting NCSs removal up to 56. 9% because of surface adsorption on nano-particles. The treatment of calcium oxide and carbon dioxide can significantly enhance the filtration performance of the prehydrolysate,presented as the improvement of the filtration rate and the increase of concentration times. The results of ultrafiltration using membrane with molecular weight cutoff 1k Da showed that the concentration times increased 2. 5 times at the same filtration time. The combined process of calcium oxide and carbon dioxide has great applicable value since calcium oxide and carbon dioxide are byproducts of alkali recovery process in pulp mills.