(575g) A New Approach to Study Selected Aspects of Biomass Oxidation in Supercritical Water

A variety of reactor systems are used in supercritical water oxidation (SCWO) including stirred reactors, transpiring wall reactors, flow through reactors and centrifugal reactors. Chemical reactions using SCWO technology take place in the thermodynamically favorable supercritical regime where high conversion rates and are not noticeably limited by heat transfer and mass transfer rates.

 One of the advantages of using SCWO for biomass conversion is that supercritical water acts as an environmentally green solvent. Because biomass has an initial water content of 10-25 wt.%, SCWO technology is advantageous because the supercritical water serves as a solvent to breakdown the organic material prior to oxidation without the need for a drying step. However, conventional thermo-chemical techniques, such as pyrolysis and gasification utilized for the production of green fuels and chemicals, require the biomass to at least be partially dried.

 During this study a portable SCWO reactor system, the SCWO Test Facility developed by NASA, has been utilized to study the conversion of beetle-infested wood into valuable fuels and chemicals. The SCWO Test Facility is originally designed for studying the use of SCWO for processing waste streams comprising plastics, papers and bio-wastes that would be generated during extended space missions. However, this unique system can also be used for processing aqueous waste streams containing small organic molecules such as methanol and acetic acid that would otherwise be difficult to be removed by conventional methods. A detailed study involving both biomass model compounds and the raw biomass has been undertaken to evaluate the system’s overall conversion efficiency.

 One of the salient features of the NASA SCWO Test Facility is that it can be operated as a constant volume batch reactor or a constant pressure continuous reactor. A piston accumulator is installed downstream to regulate the reactor gas pressure. Real-time in-situ measurements of the reactant and product concentrations are performed using the high temperature optical fiber and laser-assisted probe connected to a Raman spectrometer.

 During this study the SCWO reactor temperatures and pressures have been varied in the range of 400-500 ⁰C and 3400-4400 psi by maintaining a constant feed/water ratio. The primary objective of this green technology is to recover synthetic gas (H₂–CO) as a gaseous fuel while maximizing the production of value-added chemicals such as levoglucosan, furfural, hydroxyacetaldehyde, acetic acid, and methanol. Both gas and liquid product yields are investigated, analyzed (GC-MS, NMR and FTIR) and presented.