不同醇类对磷钨酸催化超临界醇解液化木屑的影响

Effect of solvent on the solvolysis liquefaction of sawdust with phosphotungstic acid under supercritical condition

以可溶解于醇类的磷钨酸为催化剂,在超临界醇体系下液化木屑,探讨甲醇、乙醇、正丙醇、异丙醇等不同醇类溶剂对木屑醇解液化的影响,同时采用FT-IR和GC-MS等对液化产物进行了表征分析。结果表明,反应压力和溶剂的极性大小对木屑的液化效率以及液化产物影响显著。甲醇、乙醇、正丙醇、异丙醇反应体系的液化率和主要液化产物酯类化合物的含量比率,分别为54.75%和43.759%、90.29%和23.531%、85.90%和41.761%、89.15%和28.619%,特别在甲醇体系中,乙酰丙酸甲酯的含量高达33.374%;在异丙醇体系中酚类化合物可达到24.342%;醛类化合物只出现在甲醇体系中。在正丙醇体系中没有酚类产物,表明极性最小的正丙醇,提供很少的H*,更不容易将木质素降解。

Phosphotungstic acid is an efficient,green and highly acidic heterogeneous catalyst. Different from other solid heteropholy acids,phosphotungstic acid is dissoluble in alcohols. This research makes the best use of the physicochemical properties of phosphotungstic acid combining with high solubility of supercritical alcohols.Sawdust was liquefied in the supercritical solvent using phosphotungstic acid as catalyst. The effects of different solvents on the solvolysis liquefaction and the compositions of bio-oil were investigated. Each solvolysis experiment was conducted at 260 ℃ for 30 min in a stainless-steel autoclave,in which 1 g of fir sawdust,0.5 g of phosphotungsic acid,150 g of alcohol（ such as methanol,ethanol,n-propanol or iso-propanol） were added.The liquefaction products were separated by filtration after quenching the reaction. Then, the filtrate was extracted with n-hexane and separated into light bio-oil and heavy bio-oil after removing the solvent.Simultaneously,the residue,heavy bio-oil and light bio-oil were characterized by Fourier transform infrared（ FT-IR） and Agilent 7890 A /5975 C gas chromatography-mass spectrometry（ GC-MS）. The results showthat the reaction pressure and polarity of alcoholic solvents significantly impact the liquefaction efficiency and liquefaction products. The liquefaction yield using methanol,ethanol,n-propanol and iso-propanol is 54.75%,90.29%,85.90% and 89.15%,respectively,while the relative content of main compound esters in liquefaction products is 43.759%,23.531%,41.761% and 28.619%,respectively. Especially,the relative content of methyl levulinate in methanol system is 33. 374%. The main compounds in liquefaction products using methanol,ethanol,iso-propanol as solvent are esters and phenols,while n-propanol system are esters,ketones and alcohols. Meanwhile,levulinate erster,which is produced through the reaction of cellulose / hemicellulose and alcohols,is detected in the liquefaction products of all four solvents. Phenols is determined in the liquefaction products in iso-propanol system with relative content of 24.342%. The aldehyde compounds only exist in methanol system. The absence of phenols in n-propanol system indicates that its weakest polarity provides less hydrogen radical and may lead to difficult degradation of lignin.