La/P/Ni改性分子筛催化裂解生物油模型化合物

为研究不同分子筛催化剂对生物油催化裂解特性的影响,该文采用稀土元素La、非金属元素P以及活泼金属元素Ni对ZSM-5分子筛催化剂进行改性,在连续式固定床反应器中对乙酸乙酯、二丙酮醇、糠醛和愈创木酚等生物油模型化合物进行催化裂解试验,进而对比HY、HZSM-5、ZSM-5催化剂以及改性后ZSM-5催化剂对模型化合物的催化裂解反应特性以及脱氧效果。试验结果表明:在反应温度为400℃、反应质量空速为4/h条件下,经La/P/Ni改性ZSM-5分子筛催化剂,模型化合物有机相收率提高,结焦率下降;HY分子筛所得有机相收率最低,结焦率最高。模型化合物各组分裂解难易程度由易到难为二丙酮醇乙酸乙酯糠醛愈创木酚;改性后ZSM-5分子筛使组分单一转化率和总转化率均出现下降;HZSM-5分子筛作用下,反应转化率达到最高。模型化合物催化裂解脱氧产物以芳香烃为主,经La改性ZSM-5分子筛作用后,其芳香烃选择性较ZSM-5略微上升;P和Ni改性后,芳烃选择性下降;HZSM-5对于芳香烃选择性最高,达7.36%;HY对于芳香烃选择性最低,仅为3.15%。通过液体产物组分分析进一步探讨模型化合物反应路径,从而为生物油的催化裂解提供一定的理论基础和科学依据。

Catalytic pyrolysis of bio-oil model compounds over La/P/Ni modified ZSM-5

In recent years, the rapidly growing consumption of fossil fuels negatively affects the environment and public health has attracted much attention. Much effort has been made to find a clean and renewable alternative energy. Bio-oil, produced by flash pyrolysis, is one of the more encouraging products for valorisation of biomass. It has been identified as a promising alternative energy source for fossil fuel owing to its outstanding characteristics such as higher energy density, more suitable for storage and transportation, less capital investment than any other products of biomass. However, the nature of bio-oil contains high acidity, strong corrosiveness, low heating value, thermal instability and chemical complexity, which severely restrict its wide range of applications as a high quality energy. Therefore, it is necessary to upgrade bio-oil. The upgrading techniques include steam reforming, esterification, emulsification, hydrodeoxygenation, catalytic pyrolysis etc. In this paper, catalytic pyrolysis experiments were performed in a fixed bed with inner diameter of 16mm and height of 380mm for bio-oil model compounds (diacetone alcohol, furfural, ethyl acetate and guaiacol) over different characteristics zeolites (HY, HZSM-5, ZSM-5, P/ZSM-5, La/ZSM-5, Ni/ZSM-5) at the condition of T=400℃, WHSV=4 h-1. The catalysts physical properties were investigated by BET (Brunauer-Emmett-Teller surface area) analyse. Water content was detected by using the method of Karl Fischer (870 KF Titrino). The GC-MS was used to analyze the major constituents of the pyrolytic products qualitatively and quantitatively. After the addition of La, the pore size increased from 0.61 nm (ZSM-5) to 0.89 nm (La-ZSM-5). On the contrary, the pore size of P modified ZSM-5 is 0.49 nm which is smaller than that of ZSM-5. The pyrolytic products of the model compounds included organic fraction, water, coke and gas. Compared with ZSM-5,the coke deposition over the La modified ZSM-5 decreased from 2.61% to 1.99% and the organic fraction increased dramatically from 46.10% to 61.51%, which showed the best performance in terms of products distribution among all modified catalyst. The conversions of overall model components and single model component were calculated respectively. The difficulty of the model components pyrolysis is guaiacol>furfural>ethyl acetate>diacetone alcohol. By adding catalysts, the conversion of totally compounds were increased in different degrees, which meaned zeolite promoted the degree of catalytic pyrolysis. HZSM-5 had a best catalytic pyrolysis activity with the highest totally compounds conversion rate of 65.98%. There was a slight decline in the conversion of model compounds contrasted ZSM-5 with La/P/Ni modified ZSM-5. The major components of catalytic pyrolysis were aromatic hydrocarbons, ketones, phenols and so on. It means that a series of decarboxylation and decarbonylation reactions were taken place during the pyrolysis process. On the one hand, the reduction of the oxygen content of bio-oil help to improve its stability, on the other hand it will enhance its heating value. The optimal selectivity of aromatic reached 7.36% over HZSM-5. The La modified ZSM-5 improved the selectivity of aromatic from 6.72%to 7.28%. The highest yield of saturated alcohol was 7.1%over ZSM-5 and decreased using modified ZSM-5. According to the catalytic pyrolysis products distribution, the different reaction pathways for model compounds were discussed, which provided a theoretical basis for experimental study of upgrading bio-oil.