Green hydrogen production from biomass – A thermodynamic assessment of the potential of conventional and advanced bio-oil steam reforming processes

Abstract

Steam reforming of bio-oil derived from biomass pyrolysis is one of the most promising methods for the production of green hydrogen with minimal carbon footprint. In this context, this work investigates the thermodynamic potential of hydrogen production from bio-oil steam reforming. Four routes – conventional steam reforming (CSR) and three advanced reforming processes – sorption-enhanced steam reforming (SESR), chemical looping steam reforming (CLSR) and sorption-enhanced chemical looping steam reforming (SE-CLSR) - were modeled for this purpose. Bio-oil was modeled as a complex mixture of model compounds belonging to all major oxygenate families in order to have a closer resemblance with raw bio-oil. CaO was selected as the sorbent, while NiO was selected as oxygen carrier. Furthermore, the effect of process parameters such as steam to carbon, sorbent to carbon, oxygen carrier to carbon ratios, and reforming temperature was explored. H2 purity and yield along with energy demand, served as the parameters for comparing the performance of the four processes. SESR provided the highest H2 yield (0.216 kgH2 kgBio-oil−1) among all the processes under optimum conditions along with a purity greater than 99 %. CLSR, meanwhile, had the lowest H2 yield and purity (0.178 kgH2 kgBio-oil−1 and 64.6 %, respectively). The combined SE-CLSR process had H2 yield greater than both CSR and CLSR (0.197 kgH2 kgBio-oil−1) and a H2 purity greater than 99 %. High in-situ heat generation was noted in the reforming reactor for both SESR and SE-CLSR, pointing towards a good potential for auto-thermal operation. Overall, SE-CLSR process is a highly intensified process with substantially lower energy requirements than all the other processes. The results highlight that by combining CO2-sorption and chemical looping with traditional reforming, H2 can be obtained in higher yields and purity and lower energy consumption.