常压下玉米秸秆多元醇液化的研究及其产物分析

利用合适的溶剂液化生物质不仅可以把木质纤维资源转化成液体燃料，还可以将得到的低分子降解产物制备成所需的化学品和化工原料。选用价格低廉的多羟基醇类液化剂进行液化，研究了二甘醇(diethylene glycol, DEG)混合1,2-丙二醇(1,2-propanediol, PG)、传统的乙二醇(ethylene glycol, EG)混合PG (均6∶1 ω/ω)分别作为液化剂对玉米秸杆液化得率和所得生物油产品性能的影响。并采用气质联用技术（GC-MS）、傅里叶红外光谱技术（FTIR）、热裂解气相色谱-质谱联用技术（Py-GC/MS）和X-射线衍射技术（XRD）对玉米秸秆、生物油及液化残渣的纤维特性进行了分析。结果表明，当DEG与PG混合液化时，玉米秸秆生物油的得率为98.57%；而EG混合PG时的液化得率为96.08%。GC-MS分析表明，玉米秸秆生物油的主要组成成分为醇类和有机酸类，总含量高达97%以上，而EG混合PG液化所得的生物油中含有有机酸将近60%，这是造成生物油具有酸性和腐蚀性的主要原因，不利于液化反应的进行；利用FTIR检测生物油中一些分子量较大的低聚物的相应官能团，以弥补GC-MS检测的局限性，结果表明了液化体系中生成了很多活泼化学键，提高了反应体系的活性，并且生物油中包含了大量的C-O和C=O官能团，有力地佐证了GC-MS的检测分析结果。对两种液化残渣进行表征，Py-GC/MS结果表明，液化残渣的成分比较复杂，含有一定量非常难降解的大分子物质。这些物质可能是反应后期裂解的小分子重新聚合生成的大分子物质；可能是玉米秸秆本身存在一些不能被液化降解的成分；还有可能是降解的小分子物质与液化剂之间相互反应生成的新的高分子化合物。通过FTIR表明，在液化过程中，液化残渣中纤维素、半纤维素和木质素的特征吸收峰都消失了，表明三大组分的基本结构单元都被破坏，三大组分都发生了液化，并且木质素降解程度最大。利用XRD对液化残渣进行表征，液化破坏了碳水化合物所构成的聚合物晶体结构，导致纤维素大分子被裂解，表明纤维素在液化作用下遭到降解，液化程度高。最终，该实验选取液化效果较好的DEG复配PG作为玉米秸秆液化时的溶剂，这也为玉米秸秆液化生产低成本、高品质的生物油提供了一种高效、环保的工艺流程。

Study on the Polyhydric Alcohol Liquefaction of Corn Stalk under Atmospheric Pressure and Analysis of Liquefied Products

It is a significant technique for choosing proper solvents during liquefaction of biomass process to produce fuel additives and valuable chemicals. In this study, the mixtures of new low-cost diethylene glycol (DEG) with 1,2-Propanediol (PG) and the traditional ethylene glycol (EG) with PG (6∶1 ω/ω) were adopted as liquefying agents. And analyses were conducted to throw light on the effects of these two different liquefying agents on the liquefaction yield and the properties of the biomass liquefaction oil products. The properties of the corn stalk, bio-oil and residue were studied with gas chromatography and mass spectrometry (GC-MS), Fourier transform infrared spectroscopy (FTIR), pyrolysis-gas chromatrography/mass spectrometry (Py-GC/MS) and X-rays diffraction (XRD). The results indicated that when the DEG and PG were cooperatively used as liquefying agent, the liquefaction yield was 98.57%. And there was a liquefaction yield of 96.08%, with the mixture of EG and PG as liquefying agent. GC-MS analysis results showed that the main components of bio oils were alcohols and organic acids, with a total content of more than 97%. However, the bio oil obtained by EG mixed PG liquefaction contained nearly 60% of organic acids, which was the main cause of the acidity and corrosiveness of the bio oil, and was not conducive to the liquefaction. The characteristic absorption peaks of the corresponding functional groups of some oligomers in the bio oil were detected by FTIR to compensate for the limitation of the GC-MS characterization. It turned out that many active chemical bonds were generated in the liquefaction system, leading to improving the activity of the reaction system, and the bio oil contained a large number of C-O and C=O functional groups, which strongly supported the results of the conclusions of GC-MS. Furthermore, Py-GC/MS, FTIR and XRD were applied for the characterization of the liquefaction residues. Py-GC/MS explained that the liquefaction residue composition produced in this way was complicated and contained a certain amount of large molecular substances which were very difficult to degrade. The liquefaction residues were mainly originated from the polycondensates or derivatives of interactions between small molecules of lignin or hemicellulose degradation or unreacted cellulose, and the macromolecular substances generated by the reaction of the degradation products of three components and liquefying agents. The signals of FTIR reported that the functional groups of cellulose, hemicellulose and lignin were disappeared and the liquefaction degree of lignin was the largest. Results from XRD presented that because of the destruction of crystalline structure of carbohydrates, the cellulose molecules was cracked, indicating that the cellulose was degraded and the degree of liquefaction was high. Consequently, all the results successfully confirmed that the liquefaction effect of DEG mixed PG was better than the mixture of EG and PG. Even it provided an efficient and environmental process for generating bio-oil from lignocellulosic mass at a low cost in liquefaction of corn stalk.