Jakob de Swaan Arons

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 CO2 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 CO2. 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.

Thermodynamics of phase separation in aqueous solutions of polymers

Abstract A thermodynamic theory for small-molecule systems, developed in our previous work (Yu et al., 1992), is extended to describe the phase separation of aqueous polymer solutions by modifying the combinatorial term to correct the overly large combinatorial contribution. Our model is based on the physical picture of Hirchfelder (1937). The hydrogen bonds between unlike components are dealt with using a cross association model, the excess entropy introduced by mixing molecular species with Flory-Huggins theory and the intermolecular interaction with NRTL model. Although polymers are commonly mixtures with a molecular weight distribution of finite width, we treat them as single components. Theoretical predictions of phase equilibria from this model are in good agreement with experimental findings for the systems of PEG-water and PPG-water.

DENBIGH REVISITED: REDUCING LOST WORK IN CHEMICAL PROCESSES

A new way of calculating lost work in a reacting, diffusing mixture is presented. We show that a fast chemical reaction can be treated within the framework of coupled transport equations for heat and mass, after elimination of dependent components. Two approaches to reduction of lost work follow from the equations: reduction of driving forces and utilization of coupling. When Ficks and Fouriers laws apply, losses can be minimized, but not avoided, by reduction of driving forces. When transport processes are coupled, as expressed by the theory of irreversible thermodynamics, loss reductions can be obtained also through the coupling coefficients. Maximum reduction is obtained for strict coupling, i.e. unique flux relationships. Coupling implies physical interaction and is discussed for isothermal and non-isothermal systems. The relation between irreversible thermodynamics and exergy analysis is also discussed.

Enzymatic Reaction in Organic Solvents and Supercritical Gases

The enzymatic esterification of glycidol and butyric acid, catalysed by porcine pancreatic lipase (ppl), has been performed in different organic solvents and compared with equilibrium conversions estimated from theory. Preliminary results show that the predicted equilibrium conversions were in good agreement with experiments for most of the organic solvents tested. In different organic solvents the enzyme exhibited enantioselectivity. It appears that the more polar the organic solvent, the higher was the selectivity towards the R-isomer. Conversions were also predicted for supercritical solvents. The conversion in supercritical carbon dioxide was predicted to be greater than that in the organic solvents. Moreover, the conversion in carbon dioxide was predicted to be greater than that in supercritical ethane. In the phase behavior of the glycidol and carbon dioxide binary two liquid phase coexisted near the critical point of pure carbon dioxide. Taking into account the three phase (liquid-liquid-vapor) lines of glycidol-carbon dioxide, the gas phase reaction conditions should be selected at temperatures above 310 K and pressures above 80 bar.

Phase behaviour of hydrocarbon-water systems from a simple lattice-fluid equation of state

Abstract Yu M., de Swaan Arons J., 1991. Phase behaviour of hydrocarbon-water systems from a simple lattice-fluid equation of state. Fluid Phase Equilibria, 67: 1-14. The lattice-fluid equation of state (EOS) of Panayiotou and Vera is modified by assuming that the non-random distribution of molecules is independent of the density of the system. By introducing a term representing the well-studied hydrophobic effect into this EOS, the liquid-liquid and vapour-liquid equilibria of some binary mixtures containing hydrocarbon and water were calculated. Good results have been obtained for temperatures of 0-200°C with three parameters.