Research On Arenes Production From Biomass Fast Catalytic Pyrolysis

Biomass is acknowledged as an abundant source of renewable energy and has the potential for replacing fossil fuels in the future. The fast pyrolysis process of producing pyrolysis-oil has short cycle, low cost and high efficiency. And thus, pyrolysis-oil has obvious advantages such as low cost and wide material sources. However, due to its high oxygen content, pyrolysis-oil has characteristics of high acidity, high viscosity and low energy density. Therefore, it is chemically unstable and not suitable to be used in combustion engines. In order to compatible with fuel infrastructure, pyrolysis-oil needs catalytic upgrading to remove oxygen functional groups. Besides, catalytic fast pyrolysis is another method to improve the quality of pyrolysis-oil. It is an in situ catalytic cracking process of pyrolysis vapors from biomass fast pyrolysis and favorable to produce hydrocarbon fuels. Based on this background, this work concerned in this thesis can be divided into four parts.1. Preliminary study of regulative mechanism of biomass fast pyrolysis technology.Fast pyrolysis of biomass is one of the most promising technologies to utilize lingocellulosic biomass and a highly complex process which is influenced by many factors, such as the properties of raw materials and the operating conditions. In the pyrolysis process, biomass is usually heated to moderate temperatures (400-600℃) in the absence of oxygen to produce liquid, solid and gaseous products. The walnut is one kind of dried fruits, and mainly produced in Asia, Europe and North America. The presence of extensive cross-linking polymeric structures in these species makes structural elucidation of the components of the walnut shell difficult. In this study, the walnut shell was taken from Ningguo which located in the south of Anhui Province. Anhui is a big agricultural province with annual production of3000tons.The pyrolysis experiments were performed in a helium atmosphere in a pyrolyser (CDS5250, CDS company). The objectives of this study are:(1) determine the effect of pyrolysis temperature and reaction time on pyrolytic products,(2) characterize liquid product obtained under optimum pyrolysis conditions to detect if it can be used for chemical feedstocks. With the increasing of temperature, the peak areas of typical compounds showed rises first and falls later, which reaches a peak at600℃. The experimental conditions is600℃and20s. the main products of walnut shells fast pyrolysis are composed largely of phenolic compounds and a trace of alcohols, aldehydes and hydrocarbons.2. Preparation and characterization of new catalyst W2C/MCM-41W2C/MCM-41catalysts were synthesized by temperature programmed reduction (TPR) method and incipient wetness method, which can produce W2C/MCM-41catalysts with different Si/W molar ratio by aqueous solution of Ammonium tungstate at required concentration. It can be found that the catalyst has a high surface area (880cm2/g) and a uniform pore size distribution (3mm). The porous structure of the samples was analyzed by an automatic surface area and pore analyzer. TEM and SEM analysis were used for measurement of mental particle size in the surface of the support. The surface area, pore size and pore volume of MCM-41decrease slightly after the loading of tungsten trioxide and tungsten carbide to MCM-41.,and most of the tungsten are present as small particles and are evenly dispersed on the surface of support.3. Preliminary research on catalytic effect of lignin fast catalytic pyrolysis with W2C/MCM-41catalystsThe catalyst W2C/MCM-41was tested to obtain arene-rich fuels. Catalytic fast pyrolysis of lignin with W2C/MCM-41was investigated using a micro pyrolyzer-gas chromatography-mass spectrometry system. This paper carried out a series of studies on the effects of silica-to-tungsten molar ratio (Si/W), pyrolysis temperature and catalyst-to-lignin mass ratio (C/L) on the aromatic generation and the stability of W2C/MCM-41. MCM-41catalysts have the excellent activity to catalyze the formation of monocyclic arenes from pyrolysis vapors. It also features a good stability in the lignin catalytic fast pyrolysis process. In the presence of W2C/MCM-41(Si/W50), the arenes yield is about20%of volatile product and the selectivity for monocyclic arenes is over85%at750℃. The yield of arenes increases significantly with the increase of catalyst-to-lignin mass ratio (C/L).4. Research on the proposed reaction pathway and mechanism for catalytic fast pyrolysis of lignin with W2C/MCM-41catalystsThe proposed reaction pathway for catalytic fast pyrolysis of lignin can be summarized in four steps. In the first step, lignin decomposes into char, intermediates, and some small molecules (mainly COx, SOx, and H2O). Those intermediates composed of phenol, cresol, and guaiacol syringol, can diffuse into the catalyst pores. In the next step, the-OH on aromatic ring is removed by dehydration and then phenols are converted into arenes. In the meantime, part of intermediates can be converted into polycyclic arenes by dehydration and decarboxylation at high temperature. And then, coke is formed from those polycyclic molecules. In addition, the water gas shift reaction exists in the process reactions which supplies hydrogen for hydrogenation reaction. In the third step, the PhO-CH3bond is broken while the methyl group turns into methane or transfers to aromatic ring with synergistic effect. In the final step, the phenols further cracked into aromatics by the cleavage of-OH, to form benzene, toluene, xylene, and trimethylbenzene.