Biomass & Bioenergy, Vol.126, 130-141, 2019
Hydrothermal gasification of sucrose
The earlier proposed two-step process, consisting of hydrogenation followed by hydrothermal gasification, for the conversion of carbohydrates is further developed by increasing its productivity, through the use of Pt and Ru catalysts in series. Aqueous sucrose is used as a model system to represent carbohydrate-rich waste water streams. In the first step, stabilisation, sucrose in a mass fraction of 10% in water is treated in a 45 cm(3) batch autoclave reactor with H-2 and is fully converted to sorbitol and mannitol at 413 K using a Ru catalyst with a 5% metal loading on a carbon support. A pseudo-first order kinetic model is developed and parameterised to support process development. In the second step, the stabilised mixture is gasified at 573 K using Pt and Ru catalysts with mass fractions of 5% on gamma-Al2O3 and carbon supports respectively. The novel sequential combination of these two catalysts for gasification provides high H-2 yields as well as high carbon to gas conversion (X-CG). The carbon based weight hour space velocity (WHSVc) is increased from ca. 0.04 h(-1) in previous work to 1 h(-1) in this work. An energy balance shows that the ratio of the useable energy to the energy import, also termed 'Energy Return On Energy Investment' (EROEI) is ca. 5. This process provides an opportunity to simultaneously obtain clean water (TOC similar to 4.7 gm(-3)) and produce valuable fuels (H-2 and CH4) from carbohydrate-rich waste streams such as wastewaters from potato processing, fruit and vegetable processing industries.