(627f) Catalytic and Non-Catalytic Gasification of Cysteine in Supercritical Water for Hydrogen Production

The catalytic supercritical water gasification process principle is to utilize the drastic changes of the physical and chemical properties of water above its critical conditions. These properties allow for a nearly complete conversion of wastebiomass such as sludges into energy-rich fuel gases such as hydrogen. Hydrogen production from sewage sludge may be a solution for cleaner fuel as well as the sewage sludge disposal problem. Cysteine; is an amino acid with the chemical formula HO2CCH(NH2)CH2SH and is classified as a hydrophobic amino acid. Because of the high reactivity of this thiol, cysteine is also an important structural and functional component of many proteins. As cysteine contains the sulfide group in its structural formula, it makes it well suitable model compound that represents sewage sludge proteins. In this study, the catalytic and non-catalytic supercritical water gasification (CSCWG) of cysteine for hydrogen production in the presence of two ruthenium catalysts, namely., Ru/Al2O3, Ru/AC has been investigated in a heated batch reactor. To avoid the reactions in subcritical conditions, de-ionized water and the catalyst were first heated and pressurized to desired temperature. The reactants were then injected into the reactor against it pressure at the reaction supercritical conditions by employing syringe pump. The effect of using CaO as a CO2 sorbent on hydrogen production was also investigated solely and in combination with the metallic catalysts. This paper presents the experimental results obtained at reaction conditions of 400-500°C, 28 MPa, and 30 minute reaction time. The product distribution and corresponding reaction pathways were the main focus of this study. The behaviour of the volatile fatty acids (VFA's), ethanol, methanol, ammonia, H2S, sulfide and Sulfate was investigated experimentally and discussed. The composition of residual liquid products was also studied, characterized using gas chromatography/mass spectrometry (GC-MS), and a generalized reaction pathway of cysteine decomposition in SCW was reported.