Design of efficient catalysts for gasification of biomass-derived waste streams in hot compressed water

Abstract

The energy required for the globalized living standards of our society depends currently on fossil fuels. The availability and use of fossil fuels were taken for granted during the last century, but depletion of cheap oil and the environmental concerns related to combustion of fossil fuels force us to shift to alternative energy sources. Biomass is believed to be a promising renewable energy source for the future. Conversion of biomass waste to liquid fuels or hydrogen is projected to provide, partly, the required energy demand. The anticipated intensification of biomass conversion processes will result in an increase in biomass derived aqueous waste streams (i.e. the aqueous phase of flash pyrolysis oil). Gasification of these wastes to produce high energy value gases (e.g. hydrogen) is an interesting way of diminishing waste by making valuable products. Conventional steam reforming of these biomass derived streams is economically unattractive because of their high water contents (>80 wt%) and the energy required to carry out the reactions in gas phase. Aqueous phase reforming (APR) is a recently developed process and shows promising results for gasification of biomass derived aqueous feeds in liquid phase. During APR, water is kept in the liquid phase by applying elevated pressures. The exact reaction conditions of APR have a huge influence on the properties of water, which in turn affect the catalytic reforming reaction. Earlier work in this field shows the need for stable and active reforming catalysts to make APR of bio/organic aqueous waste streams a commercially feasible process. The study described in this thesis focuses on the development of such a catalyst. The main achievements of the work described in this thesis, involved the development of a stable catalyst support for APR in sub- and supercritical water, which formed the basis for the design of an efficient APR catalyst for reforming of challenging model compounds. The developed Ru/CNT catalyst not only showed remarkable stability for supercritical water APR of acetic acid but also showed commercially relevant reforming rates.