Experiment And Characteristics Study On Pyrolysis Of Bamboo-Based Biomass Assisted By Microwave Heating

Biomass, as the most abundant renewable resources, is considered as one of the most important alternatives to fossil fuels. China has the richest bamboo resource all over the world. The amount of moso bamboo which can be felled accounts for 1/5 of that of the wood annual cut in China. However, the utilization of bamboo resources in China is still at a low level since most of the bamboo resources were used for the raw material primary processing. Applying the advanced pyrolysis technology to the deep processing of bamboo resources can realize the efficient utilization of bamboo resources in China. However, most studies were focused mainly on the study on conventional pyrolysis. Compared to conventional pyrolysis, microwave pyrolysis can achieve a relatively high heating rate, uniformity of temperature distribution and high economical efficiency. Currently, the reports on the influence of metal ions on microwave pyrolysis of biomass have not yet been found and the mechanism of microwave-induced pyrolysis of biomass has not been well understood. In this dissertation, the studies on the kinetics of moso bamboo pyrolysis, influences of metal ions and catalysts on bamboo pyrolysis under microwave condition were conducted via several advanced analyzer, including gas chromatography (GC), gas chromatography-mass spectrometer (GC/MS), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS)inductively coupled plasma optical emission spectrometer (ICP-OES), and so on. This study would be helpful for the comprehensive and efficient utilization of bamboo resources in China.A comparative study on the pyrolysis kinetics of moso bamboo was conducted in a conventional thermogravimetric analyzer and a microwave thermogravimetric analyzer respectively. Compared to conventional pyrolysis, no obvious glass transition stage was found and the pyrolysis started at a lower temperature. The values of both activation energy and frequency factor were decreased under microwave. However, the effect of the decrease in activation energy was the dominant factor on the reaction rate of biomass pyrolysis compared to the decrease in frequency factor. A comparative study on bamboo pyrolysis was also carried out between microwave and conventional conditions by analyzing the product distribution and the properties of pyrolysis products. The results showed that microwave heating was more effective on the pyrolysis of bamboo than electric heating. The yields of gaseous products obtained from microwave heating were always higher than those from electric heating. Meanwhile, microwave heating could favor the reaction between carbon and CO2.In this study, a microwave reactor was developed for the direct conversion of biomass into various products. The effects of several reaction conditions (including microwave power, moisture content and particle size) on the pyrolysis characteristics of moso bamboo under microwave were investigated in terms of the characteristics of temperature rise, product distribution and properties of the obtained products. Both the heating rate and the highest temperature increased with the increase in microwave power. Higher power could lead to a higher extent of bamboo pyrolysis. The yields of obtained gases were all higher than those of liquid products. The heating rate, the highest temperature of bamboo and the yield of gases could all be enhanced by decreasing the particle size. The yields of the solid products decreased with the moisture content increasing. Moisture content had a remarkable influence on microwave pyrolysis of bamboo at high powers since the extent of the involvement of mositure in the pyrolysis process could be increased.In consideration of the effects of metal ions on biomass pyrolysis and the special behaviors under microwave condition, the influences of several different types of dilute acid washing on mineral contents, chemical structure and bamboo pyrolysis were firstly studied. On the basis of obtained results, HF pretreatment was selected as the pilot process to investigate the effects of Mg2+、K+、Ca2+ and Fe3+ on the characteristics of microwave pyrolysis bamboo. The results indicated that HF washing could effectively remove a large portion of inorganics and at the same time had the smallest disruption effect on the chemical structure. The presence of Mg2+、K+ and Ca2 +inhibited the temperature rise of bamboo since the addition of those would enhanced the thermal resistance between particles. The yields of gaseous products could increase at the expense of liquid products after adding K+ and Ca2+ both of which could promote the production of CO2 and H2. A promotion effect on the temperature rise of bamboo was discovered because of the formation of Fe2O3 which could absorb microwave energy well. Among all the metal ions, the promotion effect of Fe3+ on the gaseous production was the most significant. Meanwhile, the presence of Fe3+ was favorable to the formation of CO and H2.On the basis of the above obtained results and the characteristics of the interaction of carbon materials with microwave, the effects of residual char, activated carbon and graphite on bamboo pyrolysis under condition were investigated. And activated carbon supported Fe3+ catalyst was prepared and its effect on microwave pyrolysis was studied. Although activated carbon had the weakest promotion effect on the temperature rise, the yields of gaseous products were the highest among the three carbon materials. The yields of gaseous products could reach up to the range of 59～68 wt.%. Activated carbon supported Fe3+ catalyst had a significant promotion effect on the production of syngas (H2+CO). The gaseous product with a syngas content of 78.14 vol.%was produced by using adding 20 wt.%(based on the bamboo) of the catalyst with a FeCl3 concentration of 5%. The value of H2/CO increased with the concentration of Fe3+, indicating that the promotion effect of Fe3+ on the formation of H2 was more significant than that on the formation of CO.