Supercritical water gasification of microalgal biomass for hydrogen production-A review

Due to their potential for a high growth rate microalgae are seen as promising feedstocks for hydrogen production, but their high-water content makes them unsuitable for traditional gasification. An alternative method, such as supercritical water gasification, is required to maximise this potential. This review assesses the literature involving the supercritical water gasification of microalgae and other relevant feedstocks. The impact on hydrogen yield, of biomass composition, catalysts, operating conditions, and the integration of the reactor into larger systems are considered. A high carbohydrate and low protein feed is usually preferable for maximum hydrogen yield. Homogeneous alkali metal salts and heterogeneous transition metals are desirable as catalysts. Issues such as recyclability, deactivation, and poor selectivity towards hydrogen production of these catalysts remain problematic. High temperatures and low biomass concentrations are suitable for high yields but require high energy inputs, so may not be advantageous when considering a whole system energy balance.