Hedzer J. van der Kooi

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.

Positioning heat exchangers in binary tray distillation using isoforce operation

The best way of adding two interstage heat exchangers to a binary distillation column is studied using irreversible thermodynamics. A distillation column is simulated with a computer program using the tray-to-tray calculation method. The purpose of the analysis is to find the locations of the two interstage heat exchangers which give the minimum entropy production rate in the column. According to the isoforce principle, minimum entropy production rate is obtained in distillation when the driving forces are uniformly distributed over the trays. This implies that the entropy production rate, in the optimum case, varies according to the value of the phenomenological coefficient. Therefore, locations with the largest deviations from this behavior are good locations for additional heat exchangers. A column separating n-pentane and n-heptane is used to demonstrate how the optimum variation in the coefficient may be used in practice.

Exergy and sustainability

A thorough qualitative investigation of the relation between exergy losses and the environmental aspect of sustainability has been conducted. It is concluded that almost all environmental effects can be taken into account by studying the waste of feedstocks and energy, and the emission and dispersion of pollutants. On the basis of the results of two case studies, i.e., the production of aluminium and polystyrene, it can be made plausible that exergy losses and environmental impact are related. It is concluded that exergy loss is at least a qualitative measure that can be used in environmental policy making regarding technological processes.