The Effect Of Catalytic Pyrolysis Of Corn Stalks Using Modified HZSM-5

Agriculture and forest waste can be converted to bio-oil by fast pyrolysis technology, which is very important for environment and alleviating energy crisis since high value added products can be generated through this process. However, bio-oil obtained from traditional pyrolysis process has some shortcomings, for instance, high oxygen content, low calorific value, high viscosity, high acidity and low storage stability, etc. The quality of bio-oil may be enhanced if appropriate catalysts were used(such as HZSM-5) during the process of fast pyrolysis. Though catalysts of HZSM-5 can improve producing bio-oil, they have some big trouble(like deactivation since coking, etc.) due to their small aperture.In this study, HZSM-5 zeolite was modified by Ni and/or Mo using impregnation methods. To study the performance of the modified HZSM-5, they were characterized with electron scanning electron microscope(SEM), energy dispersive spectrometer(EDS), BET surface area detector, X-ray Diffraction(XRD), inductively coupled plasma-atomic emission spectrometer(ICP-AES) and pyridine adsorption fourier-transform infrared(Py-IR). Then, the experimental studies of catalytic pyrolysis of corn stalks were carried out in a Self-developed pyrolysis platform. The effect of catalytic pyrolysis was studied via analysis of pyrolysis products like bio-oil etc.In general, the results of characterization shown that loading Ni and/or Mo could not only maintain the crystal structure stability of the original HZSM-5, but also make the pore structure and acidity distribution improved. Specifically speaking, loading Ni and/or Mo could make: 1) the surface loads be uniformly distributed in the molecular sieve and existed highly dispersed; 2) the specific surface area, pore volume and average pore size of zeolite catalysts were decreased with the increase of Ni and Mo loads; and 3) total acidity, the B acid sites decreased and L acid sites increased of modified HZSM-5, indicating that modified catalyst has higher catalytic activity for the oxidation potential. In addition, thermogravimetric analysis of modified HZSM-5 showed that its anti-coking performance significantly enhanced under the same treating time of modified process. Furthermore, in terms to separately modified using Ni and Mo, the best anti-coking performance was achieved when the load capacity is 10%; in terms to synergistic modified using Ni and Mo, the best anti-coking performance was achieved under Ni7Mo3/HZSM-5.The other important studies were catalytic pyrolysis of corn stalks. The results showed that:Firstly, compared with the group of non-catalytic fast pyrolysis, using HZSM-5 could make: 1) the liquid yield decreased slightly from 34.05% to 33.49%, gas slightly increased and solids hardly unchanged; 2) The ratio of the heavy components to the light components in bio-oil decreased significantly from 2.16 to 2.50, while the heating value of light components was increased from 17.80 MJ/kg to 19.47 MJ/kg, and the p H value was increased from 3.67 to 3.92; and 3) the relative contents of acids, aldehydes and furans(oxygenated organic compounds) in bio-oil decreased, while the relative contents of alcohols and phenols in bio-oil increased significantly.Secondly, compared with the group of original HZSM-5, the modified HZSM-5 could make: 1) decreased the bio-oil yield and increased gas production; 2) the heating value of light components in bio-oil was increased and the p H value was increased; and 3) the relative contents of ketones and acids(oxygenated organic compounds) in bio-oil decreased, while the relative contents of phenols in bio-oil increased significantly. At the same time, the different catalysts also showed different characteristics: 1) Ni modified HZSM-5 decreased water content of bio-oil significantly; 2) After Mo modification, the ratio of the heavy components to the light components in bio-oil decreased significantly from 2.50 to 3.50, especially for ketones and phenol content; and 3) After synergistic modification using Ni and Mo, aldehydes and nitrogenous compounds decreased significantly.