Synthesizing Methanol from Biomass Derived Syngas

This dissertation, "Synthesizing Methanol From Biomass Derived Syngas" by Xiuli, Yin, 陰秀麗, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled Synthesizing Methanol from Biomass-Derived Syngas Submitted by Yin Xiuli for the degree of Doctor of Philosophy at The University of Hong Kong in November 2004 The production of methanol from biomass has attracted considerable interest globally because of its potential in alleviating environmental pollution, slowing global warming, and reducing our dependence on limited and dwindling petroleum resources. This study focused on the direct use of cheap biomass-derived syngases for methanol synthesis rather than the H -rich syngas used in traditional processes. Its aim was to investigate experimentally the characteristics of methanol synthesis from biomass-derived syngas. Biomass gasification experiments (air-steam gasification, catalytic gasification, and oxygen-rich gasification) were conducted to produce raw feed gases, which were then configured as model syngases for subsequent methanol synthesis study. Air-steam gasification was studied using an atmospheric and indirectly heated fluidized bed gasifier. Results indicated that a syngas with H /CO, H /(CO+CO ) and CO /CO ratios of 1.18, 0.75 and 0.58 respectively could be 2 2 2 produced at a temperature T = 900C, equivalence ratio ER = 0.22, and steam to biomass ratio S/B = 2.7. The H /CO ratio was found to be more sensitive to i temperature and S/B ratio, but less sensitive to ER and particle size. Catalytic gasification was performed with the direct use of calcined dolomite in the gasifier and a fixed bed of nickel-based catalysts installed downstream. It was found that the gas yield was increased greatly and more H was produced through the use of catalysts. The gas ratios H /CO, H /(CO+CO ) and CO /CO, lied between 2.58 and 2 2 2 2 3.54, 1.08 and 1.19, and 1.23 and 2.08 respectively. Oxygen-rich gasification was studied using a pilot-scale circulating fluidized bed gasifier. Results suggested that the optimal O concentration in gasifying media was around 90%. At this value, N 2 2 content in the product gas was about 7%, while initial capital and operating costs of the oxygen-producing device were 60% and 50% respectively of those of pure oxygen-producing device. Methanol synthesis experiments using the model syngases were performed in a high-pressure micro-reactor under varying operating parameters, i.e. pressure, temperature and space velocity, and with two commercial catalysts and three prepared catalysts. The yield and selectivity of methanol was found to depend on the operating parameters, the composition of the syngas and catalyst used. The yield of methanol was sensitive to the H /(CO+CO ) ratio, the H concentration, and the 2 2 2 activity of the catalyst. The selectivity of methanol was more sensitive to the CO /CO ratio, and decreased sharply when this ratio exceeded 1. The optimum selectivity of methanol for the syngas derived from air-steam gasification was 98%, which is higher than that from catalytic gasification. While the yield of methanol from the former syngas would be lower than the latter. With partial removal of CO, both the yield and selectivity could be improved. All the three prepared catalysts showed higher catalytic activity than commercial catalysts. ii A technical route of methanol production combined with power generation from biomass gasification which is feasible technically and economically