Study On The Catalytic Pyrolysis Of Pubescens Over Zeolite

Pubescens is a kind of bamboo, which is distributed widely in the world and grows very fast. The catalytic pyrolysis of pubescens to energy carrier and chemicals was studied in the present work. The effects of the operating conditions on the liquid products were discussed and the reaction parameters were optimized. The structural variation of the zeolite NaY catalyst was also studied. Furthermore, the catalytic pyrolysises of pubescens were carried out in N₂ flow and H₂ flow respectively using zeolite or modified zaolite catalysts.The effects of zeolite NaY dosage, initial moisture content, reaction temperature, reaction time, and the deactivation of NaY on the pyrolysis of pubescens were investigated in a fixed bed reactor. Under the optimized conditions investigated, a 97.3 wt. % conversion of pubescens and a 74.5 wt. % yield of liquid products were obtained respectively. When the NaY/P ratio increased over 1:1, certain intermediate species, which lead to gaseous products by thermal decomposition, was converted catalytically into liquid compounds. The yield of liquid products increased to the maximum as the NaY/P ratio increased to 3:1 within the experimental range. Acetic acid was found to be the main component and it accounted for 56.7-92.9 wt. % of liquid products in the presence of NaY. And other different monomers such as phenol and 2/3/4-methyl-phenol can be obtained by controlling the reaction parameters. The water contained in the Fresh NaY would facilitate the conversion of pubescens and the formation of 2/3/4-methyl phenol in the pyrolysis. The thermal pretreatment of NaY would change its sueface, pore and crystal stucture significantly while slight changes were observed when used in the pyrolysis at the same temperature. The interaction between NaY and the intermediates product from the pyrolysis of pubescens could stabilize the structure of the NaY catalyst. NaY would deactivate after four repeated runs(40h), and the deactivation could be attributed to the destruction of the crystalline structure and the deposition of coke. X-ray Diffraction(XRD) and Scanning Electron Microscope(SEM) results showed that the fine structure of zeolite NaY would in situ reconstruct after used in the pyrolysis.Under N₂ flow, the catalytic pyrolysis of pubescens at different temperatures were tested using HY,HZSM-5,1%Pt-HZSM-5(NR),1%Pt-HZSM-5(R),1%Pt-HY(NR),1%Pt-HY(R),1%Co-HZSM-5(NR) and 1%Co-HZSM-5(R) as catalyst respectively. And the influence of different catalysts on the liquid components distribution and the gas products formation were studied. The results showed that the presence of HY-or HZSM-5-supported Pt and Co catalysts increased the yield of the pyrolytic oil, although the distribution of the liquid products was still decentralized. It was found that under the catalysis of molecular sieves and the metal-loaded zeolite catalysts, the formation of the main carboxylic acid compounds, such as acetic acid, was inhibited. The presence of the catalysts HY, HZSM-5 or Pt-HY could improve the content of polyhydroxyphenol, but suppress the formation of monohydroxyphenol. On the contrary, after Pt or Co being supported on HZSM-5, the content of monohydroxyphenol, 2-furanmethanol and cyclopentenone increased. In general, using molecular sieves and molecular sieves supported Pt and Co catalysts could raise the output of H₂, but had little effect on the amounts of CO,CH₄ during the pyrolysis.Under H₂ flow, the catalytic pyrolysis pubescens at different temperatures were tested using NaY,HY,HZSM-5,1%Pt-HY,1%Pt-HZSM-5,2%Co-HZSM-5,γ-Al₂O₃,5%NiO-Al₂O₃ as catalyst respectively. And the influence of different catalysts on the liquid components distribution and the gas products formation were studied comparestively with that obtained under N₂ flow. It was found that in the absence of catalyst, the pyrolysis of pubescens under H₂ flow was in favor of the formation of liquid product compared to under N₂ flow. In the pyrolysis under H₂ flow, the higher pyrolysis temperature used, the higher conversion of biomass obtained, and the highest yield of liquid product, 48.30%, was obtained at 1073 K. Acetic acid was the major component in the liquid product and methanol ranked the second. The effect of pyrolysis temperature on the distribution of liquid products under H₂ flow was not as obvious as that under N₂ flow. Under H₂ flow, methanol, cyclopropyl carbinol and so on were obtained with high contents, while they were not detected under N₂ flow. The content of methanol reached 10.5% at 673 K while cyclopropyl carbinol reached 5% at 973 K.When pubescens was pyrolyzed under N₂ flow, H₂ was one gas product, however, under H₂ flow, H₂ was observed to be consumed. It was found that with the catalysis of molecular sieves and the metal-loaded zeolite catalysts, the yield of liquid and gas products were different. The highest yield of liquid product(54.18%) and the lowest amount of residue(14.39%) was obtained over HY. The use of ZSM-5 as the catalyst also increased the liquid product and decreased the amount of residue. The presence ofγ-Al₂O₃ would restrain the conversion of biomass to liquid and residue, but promote the formation of gas product. The use of NaY,HY and HZSM-5 would go against the formation of CH₄ and CO₂, and the restrained C atom may enter the liquid product or the residue, and then giving out more liquid product.