Phase equilibria for biomass conversion processes in subcritical and supercritical water

Abstract

The description of phase equilibria for two biomass conversion processes, the hydrothermal upgrading (HTU) process and supercritical water gasification (SCWG) process, has been carried out. The HTU process is a liquefaction process under subcritical water conditions, the product contains biocrude, organic compounds, gases, and water. In the SCWG process, the product is fuel gas containing more than 50% hydrogen on a mole basis. Biocrude is the target product in HTU, and hydrogen in SCWG. The description of phase equilibria indicates the possible routes and operating conditions for separating the target product from the product mixture. For the HTU process, the task has been accomplished by properly characterizing biocrude and the application of the Statistical Associating Fluid Theory (SAFT) equation of state. The calculated result for biocrude separation is in good agreement with the experimental data. In the SCWG process, for the removal of CO 2 from gas product to produce higher purity hydrogen, four equations of state of PSRK, PR, SRK, and SAFT have been applied to calculate the phase equilibria. Water and 1-hexanol are the solvents for dissolving CO 2. The amounts of solvent required have been indicated for achieving certain hydrogen purity in the vapor phase. The predicted comparison results show that 1-hexanol is a better solvent than water. Using the weight amount of one-tenth of water, 1-hexanol can make higher or comparable hydrogen purity in the vapor phase and less hydrogen dissolved in the liquid phase.