Greenwood Ava A, Farrell Troy W, Zhang Zhanying, O'Hara Ian M
Mathematical Sciences, Queensland University of Technology, 2 George Street, Brisbane, 4001 QLD Australia.
Centre for Tropical Crops and Biocommodities, Queensland University of Technology, 2 George Street, Brisbane, 4001 QLD Australia.
Biotechnol Biofuels. 2015 Feb 19;8:26. doi: 10.1186/s13068-015-0211-5. eCollection 2015.
Acid hydrolysis is a popular pretreatment for removing hemicellulose from lignocelluloses in order to produce a digestible substrate for enzymatic saccharification. In this work, a novel model for the dilute acid hydrolysis of hemicellulose within sugarcane bagasse is presented and calibrated against experimental oligomer profiles. The efficacy of mathematical models as hydrolysis yield predictors and as vehicles for investigating the mechanisms of acid hydrolysis is also examined.
Experimental xylose, oligomer (degree of polymerisation 2 to 6) and furfural yield profiles were obtained for bagasse under dilute acid hydrolysis conditions at temperatures ranging from 110°C to 170°C. Population balance kinetics, diffusion and porosity evolution were incorporated into a mathematical model of the acid hydrolysis of sugarcane bagasse. This model was able to produce a good fit to experimental xylose yield data with only three unknown kinetic parameters k a ,k b and k d . However, fitting this same model to an expanded data set of oligomeric and furfural yield profiles did not successfully reproduce the experimental results. It was found that a "hard-to-hydrolyse" parameter, α, was required in the model to ensure reproducibility of the experimental oligomer profiles at 110°C, 125°C and 140°C. The parameters obtained through the fitting exercises at lower temperatures were able to be used to predict the oligomer profiles at 155°C and 170°C with promising results.
The interpretation of kinetic parameters obtained by fitting a model to only a single set of data may be ambiguous. Although these parameters may correctly reproduce the data, they may not be indicative of the actual rate parameters, unless some care has been taken to ensure that the model describes the true mechanisms of acid hydrolysis. It is possible to challenge the robustness of the model by expanding the experimental data set and hence limiting the parameter space for the fitting parameters. The novel combination of "hard-to-hydrolyse" and population balance dynamics in the model presented here appears to stand up to such rigorous fitting constraints.
酸水解是一种常用的预处理方法，用于从木质纤维素中去除半纤维素，以生产可用于酶促糖化的可消化底物。在本研究中，提出了一种用于甘蔗渣中半纤维素稀酸水解的新模型，并根据实验得到的低聚物分布进行了校准。还研究了数学模型作为水解产率预测器以及作为研究酸水解机理工具的有效性。
在110°C至170°C的温度范围内，获得了甘蔗渣在稀酸水解条件下的实验木糖、低聚物（聚合度为2至6）和糠醛产率分布。将群体平衡动力学、扩散和孔隙率演变纳入甘蔗渣酸水解的数学模型。该模型仅用三个未知动力学参数ka、kb和kd就能很好地拟合实验木糖产率数据。然而，将同一模型应用于扩展的低聚物和糠醛产率分布数据集时，未能成功再现实验结果。结果发现，模型中需要一个 “难水解” 参数α，以确保在110°C、125°C和140°C下实验低聚物分布的可重复性。通过在较低温度下拟合得到的参数能够用于预测155°C和170°C下的低聚物分布，结果令人满意。
仅根据一组数据拟合模型得到的动力学参数的解释可能不明确。虽然这些参数可能正确地再现了数据，但它们可能并不代表实际的速率参数，除非已谨慎确保模型描述了酸水解的真实机理。通过扩展实验数据集从而限制拟合参数的参数空间，可以检验模型的稳健性。本文提出的模型中 “难水解” 和群体平衡动力学的新颖组合似乎能够经受住这种严格的拟合约束。
