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Hydrothermal Gasification of Low Grade Biomass at Supercritical Condition

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Title: Hydrothermal Gasification of Low Grade Biomass at Supercritical Condition
Author: Tushar, Mohammad Shahed Hasan Khan
Department: School of Engineering
Program: Engineering
Advisor: Dutta, AnimeshXu, Chunbao (Charles)
Abstract: Hydrogen is considered the cleanest fuel as it does not create any pollution during combustion. However, hydrogen is not readily available in nature as a primary energy source, but a secondary energy generated from the primary energy sources via various conversion processes. Supercritical water gasification (SCWG) process in contrast to the conventional gasification process does not require biomass drying, and rather it uses the moisture and external water in the reaction. In this study an effort was made to introduce a novel dual-metal dual-support catalyst for the first time for supercritical water gasification (SCWG) of biomass. Besides, in this study, kinetic study of the process described through mechanistic models using elementary steps is proposed to determine the rate determining step (RDS). Simulation of the SCWG of model biomass (glucose and mixture of phenol and furfural) was performed using AspenPlus® in order to justify the experimental scheme. Ten catalysts were prepared and tested using 5wt% glucose to screen the best catalyst in terms of hydrogen yield. Pressure was kept constant 25 MPa since, according to the literature and the simulation study performed in this study, pressure does not have any significant effect on product yield. It was found that novel 10%Ni-0.08%Ru/Al2O3-ZrO2 catalyst showed highest hydrogen yield and carbon gasification efficiency for not only model biomass but also for real biomass biocrudes. Stability test also suggests that this novel catalyst can run for a longer period of time without any loss in performance in terms of hydrogen yield. However, the SEM-EDX and TGA study showed evidence of the formation of char on the spent catalyst. Two different approaches were used to liquefy raw biomass. It was also observed that biocrude preparation method also affects the product yield and performance of the catalyst. This study also used mechanistic models with elementary steps to describe the kinetics of the SCWG of biomass for the first time. It was observed that an Eley-Rideal based adsorbed carbohydrate dissociation that required two active sites of a catalyst was the slowest step and thusly termed as the rate determining step. It was also found that comparing the carbon gasification efficiency, the supercritical water gasification process reaches equilibrium even at a lower temperature and at a higher feed concentration in the presence of catalyst while the real biomass biocrudes were used.
Date: 2016-02

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