Biomass gasification in supercritical water

The gasification of cellulose and lignin and model compounds (guaiacol and phenol) in supercritical water at 400-700°C was studied. The reactions were conducted in quartz tubes, at times with Ni added wires. Homogeneous supercritical water gasification (SCWG) of cellulose (no catalyst or metal present) produced CO₂ as the major compound, except at the lowest cellulose loadings where CH₄ became the major product. Results from SCWG of cellulose in quartz reactors differed from those obtained from nominally "uncatalyzed" SCWG in stainless steel reactors. In quartz, the total gas yields were lower and the H₂ mole fraction in the gas was also lower. These comparisons indicated that the reaction surface influenced both the rate of gas formation and the composition of the gas. Guaiacol was mainly gasified into H₂, CO₂, CO, and CH₄. Nickel significantly changed the gas product compositions. Phenol was mainly gasified into H₂, CO₂, and CH₄. The gas compositions measured experimentally were consistent with those anticipated at chemical equilibrium. Thus, homogeneous gasification in supercritical water was slow, but rates were greatly increased by added nickel. The pseudo-first order rate constant at 600°C for homogeneous gasification of phenol was 3 × 10^-4/sec, and the rate constant for Ni-catalyzed gasification was 2.7 × 10^-4 cm/sec. This is an abstract of a paper presented at the 2007 AIChE Annual Meeting (Salt Lake City, UT 11/4-9/2007).