On the feasibility of producing hydrogen with net carbon fixation by the decomposition of vegetable and microalgal oils

Abstract

The decomposition of vegetable and microalgal oils was herein analysed as a process of high interest for the production of both hydrogen and carbon, which potentially entails the advantage of attaining a negative CO₂ balance through carbon fixation. The feasibility of a series of oil decarbonization systems was evaluated by means of energy and CO₂ balances, which comprised not only the direct decarbonization process itself but also the cultivation and oil extraction stages. Three potential scenarios were assessed, embracing different options to meet the energy requirements of the systems. For each scenario, a wide range of case studies were evaluated, involving the use of rapeseed, sunflower, soybean, jatropha, Botryococcus braunii and Chlorella vulgaris oils as raw materials. Favourable energy and CO₂ balances were found for a variety of crops in different scenarios. In particular, jatropha oil from high seed yield crops and rapeseed oil from high seed yield and high oil content crops were identified as the most promising biomass feedstocks for oil decarbonization since they led to net hydrogen production as well as to negative balances of CO₂ emissions, therefore showing a carbon fixation effect. When compared to vegetable/microalgal oil transesterification to produce biodiesel, oil decomposition proved to be a more suitable alternative from a combined energy and environmental approach.