不同Si/Al的氢型分子筛催化热解对生物油特性的影响

为考察对于氢型分子筛(HZSM-5)的Si/Al变化和添加量对生物质热解液化的影响,该文通过离子交换法制备HZSM-5催化剂,采用激光粒度分析仪、比表面积及孔径分析仪和X射线衍射仪对催化剂的粒度、孔隙及晶体结构等性质进行表征,并在最佳油产率温度下进行木屑的催化热解。对无催化剂和不同催化条件下得到的生物油进行气相色谱质谱联用分析,结果表明,分子筛作用下,生物油产率明显降低(最大降幅8%),含水率增加。同时,液体产物中醛类、酯类、酮类、呋喃等含氧化合物及酸含量均有所降低,提高了烃类和酚类的含量,峰面积百分比最高达到12.57%和39.36%,对催化剂催化调控改善生物油品质提供了一定的科学依据。

Effect of HZSM-5 catalyst with different Si/Al ratios on characterization of pyrolysis bio-oil

Abstract: In order to investigate effects of HZSM-5 zeolite under different silica to alumina ratios and addition amounts on biomass pyrolysis bio-oil, the HZSM-5 (hydrogen zeolite) catalysts obtained by ion-exchange method were characterized using laser particle size analyzer, specific surface area and pore size analyzer with Brunauer-Emmett-Teller (BET) method and X-ray diffraction (XRD), and applied for the catalytic pyrolysis of wood at the optimum temperature of best oil yield. The bio-oils obtained from direct liquefaction with and without catalysts were characterized by GC-MS (Gas Chromatograph-Mass Spectrometer) analyses. The results indicated that: Compared with ZSM-5 zeolite, the crystal grain size of HZSM-5 zeolite was increased, and the particle size distribution was more concentrated, meanwhile, the catalyst had a preferable crystalline tacticity and a increased crystallinity, in addition, the surface area and the pore volume of HZSM-5 catalyst decreased, while pore size did not change significantly. When the HZSM-5 zeolite with different silica to alumina ratios were applied to pyrolysis, the yield of bio-oil decreased significantly (the maximum was up to 8%), and the moisture content of the bio-oil increased. However, the composition of bio-oil and the relative content of the product changed a lot, it indicated that there was obvious catalytic effects during direct liquefaction of biomass under HZSM-5 zeolite. Compared with non-catalyst pyrolysis, the contents of aldehydes, esters, ketones, furans and acid (oxygenated compounds) were reduced. It showed that HZSM-5 zeolite promoted a series of decarboxylation, decarbonylation reactions during the pyrolysis process, resulted to the reduction of the oxygen content in bio-oil, therefore, the stability of bio-oil was improved. With increasing the silica to alumina ratios, the catalytic activity weakened a little. When the addition amounts of HZSM-5 zeolite were increased, a small variation of the yield of bio-oil occurred, the moisture content of the bio-oil continued to go up, while the content of oxygen-containing compounds and acid aldehydes, esters, ketones, furans further reduced, promoting the formation of hydrocarbons, phenols, alcohols. The maximum percentage of the peak area of hydrocarbons and phenols could be up to 12.57% and 39.36%. Because HZSM-5 zeolite help to provide rich aperture on the surface, which was conducive to the formation of positive carbon ions, then the products of first thermal decomposition carried on isomerization, cracking formation to convert as small molecules alkanes and alkenes, after that, they go through polymerization reaction, cyclization reaction and a series of reactions to generate aromatic substances and so on. Owing to the above reaction procedure, there was a greater overall increasing in hydrocarbon substances. After the addition ratio was greater than 10%, the changing rate of various components decreased. Comprehensive analysis results of the type and amount of added catalyst showed HZSM-5 (25) zeolite with the addition amount of 10% played a more significant role on the catalytic liquefaction control of wood dust.