Titel
"Thermodynamic Modelling of Gas Solubility in Water, Ethanol and Acetic using (gamma-phi) UNIQUAC"
Abstract:
Syngas fermentation it is one of several emerging technologies for the production of biofuels from renewable sources biomass is gasified to syngas (CO and H2), which is then fermented by acetogenic bacteria to produce ethanol, acetic acid or other chemical commodities.
The rate-limiting step of this process is generally gas-toliquid mass transfer. One way to improve the mass transfer is achieved by increasing the driving force by raising the partial pressure of the syngas. To estimate the equilibrium condition at high solute concentration the liquid phase non-ideality need to be taken in to account, especially above 5-10 bar and a mole fraction larger than 0.03.
The focus of this work is a thermodynamic model which can be of relevance to process simulation studies regarding syngas fermentation at higher pressure and concentration in relation to synthesis of new solvents, chemicals and production of biofuel.
A thermodynamic model is presented which describes the solubility of CO, H2, CO2, CH4 and N2, i.e. the main component of biomass derived syngas, in combination with the three polar hydrogen bonding solvents: water, ethanol and acetic acid.
The gas solubility equilibria investigated in this study are of also for many others industrial applications such as ethanol and acetic acid fermentation, carbonation of alcoholic beverages and soft drinks, gas absorption, stripping columns, waste-water treatment, etc.
The selected method is a approach: UNIQUAC-Peng-Robinson (PR) for system containing water and ethanol, and the UNIQUAC-Hayden-O'Connell Virial EoS for the system containing acetic acid. Both the symmetric activity coefficient at infinite dilution, and Henry’s law constant, depend on the nature of the solute-solvent interaction. Their ratio is a property of the gaseous component alone and it must be identical in any solvent or solvent mixture.
This prosperity, the hypothetical liquid fugacity for supercritical components, is discussed in relation to a new expression for obtaining the Henry’s law constant in mixed solvents. The relation between symmetric activity coefficient at infinite dilution and Henry’s law constant is further exploited to reduce the uncertainty during parametrization of the UNIQUAC model. The method provides a more accurate prediction of symmetric activity coefficients at infinite dilution; in particular for those systems where the supercritical component show a very low solubilities.