Center for Sustainable Environmental Technologies, 1140E Biorenewable Research Laboratory Building, Iowa State University, Ames, IA 50011, USA.
ChemSusChem. 2012 Nov;5(11):2228-36. doi: 10.1002/cssc.201200341. Epub 2012 Sep 13.
Depolymerization of cellulose offers the prospect of inexpensive sugars from biomass. Breaking the glycosidic bonds of cellulose to liberate glucose has usually been pursued by acid or enzymatic hydrolysis although a purely thermal depolymerization route to sugars is also possible. Fast pyrolysis of pure cellulose yields primarily the anhydrosugar levoglucosan (LG) whereas the presence of naturally occurring alkali and alkaline earth metals (AAEMs) in biomass strongly catalyzes ring-breaking reactions that favor formation of light oxygenates. Here, we show a method of significantly increasing the yield of sugars from biomass by purely thermal means through infusion of certain mineral acids (phosphoric and sulfuric acid) into the biomass to convert the AAEMs into thermally stable salts (particularly potassium sulfates and phosphates). These salts not only passivate AAEMs that normally catalyze fragmentation of pyranose rings, but also buffer the system at pH levels that favor glycosidic bond breakage. It appears that AAEM passivation contributes to 80 % of the enhancement in LG yield while the buffering effect of the acid salts contributes to the balance of the enhancement.
纤维素的解聚为从生物质中获得廉价糖提供了可能。尽管从理论上讲，也可以通过纯热解聚途径来获得糖，但通常通过酸或酶水解来打破纤维素的糖苷键以释放葡萄糖。纯纤维素的快速热解主要产生无水糖左旋葡聚糖（LG），而生物质中天然存在的碱金属和碱土金属（AAEM）强烈催化断环反应，有利于轻含氧化合物的形成。在这里，我们展示了一种通过纯粹的热方法从生物质中显著提高糖产量的方法，方法是将某些矿物酸（磷酸和硫酸）注入生物质中，将 AAEM 转化为热稳定的盐（特别是硫酸钾和磷酸钾）。这些盐不仅使通常催化吡喃糖环断裂的 AAEM 失活，而且还将系统缓冲到有利于糖苷键断裂的 pH 值。似乎 AAEM 的失活对 LG 产率提高的 80%有贡献，而酸式盐的缓冲作用对提高的平衡有贡献。
