BBSRC Sustainable Bioenergy Research Centre, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, UK.
Biotechnol Biofuels. 2014 Mar 29;7(1):45. doi: 10.1186/1754-6834-7-45.
The use of a microwave synthesis reactor has allowed kinetic data for the hydrothermal reactions of straw biomass to be established from short times, avoiding corrections required for slow heating in conventional reactors, or two-step heating. Access to realistic kinetic data is important for predictions of optimal reaction conditions for the pretreatment of biomass for bioethanol processes, which is required to minimise production of inhibitory compounds and to maximise sugar and ethanol yields.
The gravimetric loss through solubilisation of straw provided a global measure of the extent of hydrothermal deconstruction. The kinetic profiles of furan and lignin-derived inhibitors were determined in the hydrothermal hydrolysates by UV analysis, with concentrations of formic and acetic acid determined by HPLC. Kinetic analyses were either carried out by direct fitting to simple first order equations or by numerical integration of sequential reactions.
A classical Arrhenius activation energy of 148 kJmol-1 has been determined for primary solubilisation, which is higher than the activation energy associated with historical measures of reaction severity. The gravimetric loss is primarily due to depolymerisation of the hemicellulose component of straw, but a minor proportion of lignin is solubilised at the same rate and hence may be associated with the more hydrophilic lignin-hemicellulose interface. Acetic acid is liberated primarily from hydrolysis of pendant acetate groups on hemicellulose, although this occurs at a rate that is too slow to provide catalytic enhancement to the primary solubilisation reactions. However, the increase in protons may enhance secondary reactions leading to the production of furans and formic acid. The work has suggested that formic acid may be formed under these hydrothermal conditions via direct reaction of sugar end groups rather than furan breakdown. However, furan degradation is found to be significant, which may limit ultimate quantities generated in hydrolysate liquors.
微波合成反应器的使用使得可以从短时间内建立秸秆生物质水热反应的动力学数据，从而避免了传统反应器中缓慢加热或两步加热所需的校正。获得实际的动力学数据对于预测生物乙醇过程中生物质预处理的最佳反应条件很重要，这是为了最小化抑制性化合物的产生并最大化糖和乙醇的产率。
秸秆的溶解导致的重量损失提供了水热解构程度的整体衡量标准。糠醛和木质素衍生抑制剂的动力学谱通过 UV 分析在水热水解物中确定，通过 HPLC 确定甲酸和乙酸的浓度。动力学分析要么通过直接拟合简单的一级方程进行，要么通过顺序反应的数值积分进行。
已经确定了 148kJmol-1 的经典 Arrhenius 活化能，用于初步溶解，这高于与历史反应严重程度测量相关的活化能。重量损失主要是由于秸秆半纤维素成分的解聚，但一小部分木质素以相同的速率溶解，因此可能与更亲水的木质素-半纤维素界面有关。乙酸主要是通过对半纤维素上支链乙酸酯基团的水解释放出来的，尽管这种水解速度太慢，无法为初步溶解反应提供催化增强。然而，质子的增加可能会增强导致呋喃和甲酸生成的次级反应。这项工作表明，在这些水热条件下，甲酸可能通过糖端基的直接反应而不是呋喃的分解形成。然而，发现呋喃的降解非常显著，这可能会限制水解液中生成的最终量。
