Optimization Experimental Studies On Two-Step Catalytic Pyrolysis Of Agricultural And Forestry Waste

Two-step catalytic pyrolysis process including catalytic pyrolysis and catalytic reforming was adopted to obtain high quality bio-oil. In view of serious carbon deposition on catalyst and low quality of bio-oil during the traditional catalytic fast pyrolysis (CFP) of biomass, experimental studies concentrated on two aspects of catalyst and raw materials:1. EDTA chemical modification methods, Py-GC/MS and tube furnace experiment devices were used to find suitable modification time, and the obtained catalyst with the unchanged catalytic effects and best coke reduction; 2. Co-catalytic pyrolysis of biomass and high efficient hydrogen carbon ratio material was used to explore the effects of mass ratio and processes on pyrolysis product distribution and carbon deposition on catalyst.X-ray diffraction (XRD), nitrogen-adsorption and ammonia temperature programmed desorption (NH3-TPD) techniques were used to investigate and compare the porosity and acidity characteristics of original and modified catalysts by EDTA chemical modification method. Results showed that EDTA treatment did not damage the crystal structure of HZSM-5 zeolites, but gave rise to a slight increase of pore volume and pore size. Meanwhile, the elimination of the strong acid peak indicated the dealumination of outer surface of HZSM-5 zeolites. The catalyst of treatment time of 2h (labeled EDTA-2H) has the closest physical parameters to HZSM-5. One-step and two-step Py-GC/MS confirmed the positive role of dolomite and the modification effects of EDTA-2H. Compared with the effects of HZSM-5, EDTA-2H achieved a higher positive composition content of 81.91% and a less amount of carbon yield of 1.98%.Tube furnace devices were used to enlarge experiment researches. Acids were the main product of two-step catalytic pyrolysis, followed by alcohols, saccharides, forans, ketones, etc. The positive composition content was increased from 31.86% by direct pyrolysis to 52%～53%. There was no clear difference on the pyrolysis product distribution and positive compound content of HZSM-5 and EDTA-2H, but the coke yield of EDTA-2H was less and only 2.85%. Experiments of catalyst for continuous use and regeneration for many times were made and results showed that the activity of catalyst was not weakened after the first use. EDTA modification methods could extend the deactivation time and increase regeneration times. The anti-coking ability of EDTA-2H was stronger than that of HZSM-5. Therefore, positive effects of EDTA-2H were further confirmed by tube furnace experiments.One-step co-catalytic pyrolysis of com stalks and polypropylene (PP) overcame the shortcomings of poor oil quality and serious carbon deposition during corn stalks catalytic fast pyrolysis. There existed coupling effects in the process of co-catalytic pyrolysis. The mass ratio of 1:1 got the best result with the hydrocarbon yield 71.7%,6.49% of negative composition content in the oxygenated compounds and 1.92% of coke yield. For two-step co-catalytic pyrolysis, the ratio dolomite to raw material 1:2 had the highest oil yield (25.5%), 86.03% of hydrocarbon yield and 2.55% of coke yield, which was slightly increased compared with one-step co-catalytic pyrolysis. However, either one-step or two-step co-catalytic pyrolysis could enhance the oil quality and reduce the coke yield.The curves of thermogravimetry (TG) and derivative thermogravimetry (DTG) showed that there were two typical weightless stage:room temperature to 200℃ and 300℃ to 650℃, corresponding to the weight loss of water and carbon, respectively, and the weight loss of water toke up 70% to 85% of the total. Coats-Redfern method and Distributed Activation Energy Model (DAEM) model were used to calculate the activation energy during the stage of coke weight loss. During the fitting process of Coats-Redfern method, the fitting curve of the reaction order of 0.5 did not conform to the actual situation. As for 1,1.44 and 2, the degree of fitting and activation energy increased as the growth of reaction order. The calculation results of DAEM model were in good agreement with the actual value, which were different to the result of the same reaction order but close to 1.44 through Coats-Redfern method.