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

Abstract: 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.