Bioethanol catalytic pre-reforming for renewable hydrogen production

Abstract

The bioethanol catalytic steam pre-reforming stage in a steam reforming process is a sustainable and interesting method that breaks down alcohol molecules into simpler gas products which are later transformed into H2. Técnicas Reunidas S.A. (TR) is a Spanish company that is currently working on validating commercial catalysts for multifuel pre-reformers as part of their ongoing low-carbon hydrogen production projects. This master’s thesis assesses the technical feasibility of using bioethanol in the catalytic pre-reforming stage, employing a double-bed packed reactor under process conditions pre-defined by TR. A deep understanding of the performance of the pre-reformer was done with a DOE to determine the influence of the Gas Hourly Space Velocity (GHSV) in the range of (2500 to 4200) h−1 and Steam to Carbon ratio (S/C) between 2 and 3.5, followed by long-run stability tests and an exploratory reaction mechanistic study; the experimental work finished by validating the use of bioethanol at the selected best operating conditions. The results showed that GHSV and S/C had an effect on the H2, CH4 yield and their distribution in the overall composition profile; in contrast, these variables had no effect on the distribution of CO and CO2. An interaction effect of both independent variables was statistically significant on the ethanol conversion, but showed no practical significance considering that all results were over 95%. The long-run test proved a stable performance in which 4200 h−1 and S/C 2 were selected as the best operating conditions. A reaction mechanism network was prosed to explain the composition evolution along the reactor bedding and the T profile. Finally, it was validated that bioethanol could be used in the catalytic pre-reforming stage at the best operating conditions by comparing the performance of the reactor to its performance while working with synthetic ethanol. The results of this work provided a detailed insight about the steady-state performance of the pre-reformer operating with synthetic ethanol and real 2nd generation bioethanol that will be used by TR for the future pilot-scale testing, scale up, and industrial commercialization of this technology.