Suckling Ian D, Jack Michael W, Lloyd John A, Murton Karl D, Newman Roger H, Stuthridge Trevor R, Torr Kirk M, Vaidya Alankar A
Scion, 49 Sala St, Rotorua, 3046 New Zealand.
Department of Physics, University of Otago, PO Box 56, Dunedin, 9054 New Zealand.
Biotechnol Biofuels. 2017 Mar 9;10:61. doi: 10.1186/s13068-017-0748-6. eCollection 2017.
Conversion of softwoods into sustainable fuels and chemicals is important for parts of the world where softwoods are the dominant forest species. While they have high theoretical sugar yields, softwoods are amongst the most recalcitrant feedstocks for enzymatic processes, typically requiring both more severe pretreatment conditions and higher enzyme doses than needed for other lignocellulosic feedstocks. Although a number of processes have been proposed for converting softwoods into sugars suitable for fuel and chemical production, there is still a need for a high-yielding, industrially scalable and cost-effective conversion route.
We summarise work leading to the development of an efficient process for the enzymatic conversion of radiata pine () into wood sugars. The process involves initial pressurised steaming of wood chips under relatively mild conditions (173 °C for 3-72 min) without added acid catalyst. The steamed chips then pass through a compression screw to squeeze out a pressate rich in solubilised hemicelluloses. The pressed chips are disc-refined and wet ball-milled to produce a substrate which is rapidly saccharified using commercially available enzyme cocktails. Adding 0.1% polyethylene glycol during saccharification was found to be particularly effective with these substrates, reducing enzyme usage to acceptable levels, e.g. 5 FPU/g OD substrate. The pressate is separately hydrolysed using acid, providing additional hemicellulose-derived sugars, for an overall sugar yield of 535 kg/ODT chips (76% of theoretical). The total pretreatment energy input is comparable to other processes, with the additional energy for attrition being balanced by a lower thermal energy requirement. This pretreatment strategy produces substrates with low levels of fermentation inhibitors, so the glucose-rich mainline and pressate syrups can be fermented to ethanol without detoxification. The lignin from the process remains comparatively unmodified, as evident from the level of retained β-ether interunit linkages, providing an opportunity for conversion into saleable co-products.
This process is an efficient route for the enzymatic conversion of radiata pine, and potentially other softwoods, into a sugar syrup suitable for conversion into fuels and chemicals. Furthermore, the process uses standard equipment that is largely proven at commercial scale, de-risking process scale-up.
对于软木是主要森林树种的地区而言，将软木转化为可持续燃料和化学品至关重要。虽然软木有较高的理论糖产量，但却是酶促过程中最难处理的原料之一，通常比其他木质纤维素原料需要更苛刻的预处理条件和更高的酶用量。尽管已经提出了许多将软木转化为适合燃料和化学品生产的糖的工艺，但仍需要一种高产、工业可扩展且具有成本效益的转化路线。
我们总结了一系列工作，这些工作促成了一种将辐射松高效酶促转化为木糖的工艺的开发。该工艺包括在相对温和的条件下（173℃，3 - 72分钟）对木片进行初始加压蒸煮，不添加酸催化剂。蒸煮后的木片然后通过压缩螺杆挤出富含溶解半纤维素的压榨液。压榨后的木片进行盘磨和湿球磨以生产一种底物，该底物使用市售酶混合物可快速糖化。发现在糖化过程中添加0.1%的聚乙二醇对这些底物特别有效，可将酶用量降低到可接受水平，例如5 FPU/g OD底物。压榨液单独用酸水解，提供额外的半纤维素衍生糖，总糖产量为535 kg/ODT木片（理论值的76%）。总的预处理能量输入与其他工艺相当，磨耗所需的额外能量被较低的热能需求所平衡。这种预处理策略产生的底物发酵抑制剂含量低，因此富含葡萄糖的主线糖浆和压榨液糖浆无需解毒即可发酵成乙醇。该工艺中的木质素相对未被改性，从保留的β - 醚单元间键的水平可以明显看出，这为转化为可销售的副产品提供了机会。
该工艺是将辐射松以及潜在的其他软木酶促转化为适合转化为燃料和化学品的糖浆的有效途径。此外，该工艺使用的是在很大程度上已在商业规模得到验证的标准设备，降低了工艺放大的风险。
