Three-stage pyrolysis-reformer-shift system for hydrogen production from waste biomass

One of the most feasible way of recycling waste materials in a sustainable way is thermal processing. There has been a few studies that investigated the steam reforming process for syngas and hydrogen production from biomass, there has also been a few studies that Investigated water gas shift reactions from biomass, but due to the limited research related to both catalytic steam reforming and water gas shift steam reforming in one process using a three stage reactor, this became the focus of this research This research has used pyrolysis ofpelletisedwood, followed by steam reforming reactions of the pyrolysis products to produce syngas, which is a mixture of hydrogen and carbonmonoxide. This was followed by water gas shift steam reforming reactions to convert more carbon monoxide to hydrogen and, reduce the amount of carbon dioxide being produced in the experiments. A preliminary analysis was conducted in order to have a general understanding of the effects each components of biomass has on the pyrolysis gases.A two-stage pyrolysis catalytic steam reforming reactor was used to investigate various process conditions and types of catalyst to maximize syngas and hydrogen production. A consistent average char yield of 22% was obtained and the GC/MS analysis of the product gases indicated that gas components were chiefly; CO, CO2, H2and CH4. One key finding from this two-stage fixed bed reaction systems was that H2increased in the N2atmosphere. Nickel based catalysts with different metal supports (Alumina, Zeolite, Silica, Dolomite and MCM41) were selected for the investigation of pyrolysis steam reforming of waste biomass. Based on the review of literature, it was concluded that wet impregnation is the most efficient technique for synthesizing catalysts for thermochemical reactions. Among the catalysts tested, the 20wt% Nickel dolomite catalysts presented the highest catalyticactivity resulting in a syngas production of 43mmolsyngas with no detectable carbon formation on the catalysts surface. In contrast to nickel dolomite catalyst, increased in nickel loading from 10wt% to 20wt% resulted in a steep decrease in hydrogen yield.A three-stage pyrolysis-catalytic steam reforming water gas shift reactor was used to investigate various process conditions and types of catalyst to maximize hydrogen production. Various process parameters such as metal supports, steam to carbon ratio, reforming temperature, steam federate and catalystto biomass ratio were tested. It was evident that third stage water gas shift reactor deficit of a catalyst was ineffective in optimizing total gas and H2yield. Another finding was that the use of iron and alkali earth oxide bimetallic catalysts, the optimal content of Fe andCaOinFeCaO-alumina catalysts for enhancing CO2absorption was found to be 10 wt. %Fe and 20 wt. % CaO. This catalyst produced the lowest CO2and the second highest H2, yields representing 9.14 mmol and 45.59 mmol per gram ofbiomass respectively. This was also supported by the Temperature-Programmed Oxidation (TPO)results since it has the lowest weight. It was also found out that steam injection into the water gas shift reactor led to an increase in the hydrogen yield in the presence of reduced CaO-alumina catalyst, in contrast reduction in hydrogen yield was obtained in the presence of unreduced CaO-alumina catalyst.An optimal condition of 10 wt. % CaO-alumina catalysts was the best suitable for maximizing hydrogen production because it produced the highest hydrogen yield of 51.58 mmolg-1biomass. It was also found that the addition of Fe to FeCaO-alumina inhibited CO2absorption by the CaO but at the same time. Water gas shift reaction was promoted. The XRD result confirmed that spent CaO-alumina catalysts have good catalytic performance at high temperatures due to the presence of fewer oxidized species. The commercial scale practice utilized in the deconstruction of biomass to char, syngas, and hydrogen gas were not compared with the laboratory scale results obtained in this research, and this was primarily owing to the current limitations in the large-scale technologies.Overall, this research work showed that there is a promising opportunity in hydrogen production from biomass through a three-stage thermochemical process