科研之友
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摘要
Vapor-liquid-liquid equilibrium (VLLE) during product recovery and separation after Fischer-Tropsch synthesis affects the efficiency of downstream processing. Proper prediction of the VLLE is necessary to improve this processing step in the Fischer-Tropsch process; however, there is little guidance on what thermodynamic models to use. A similar problem presents itself in processes related to biomass conversion. The selection of an appropriate thermodynamic model to describe the nonideal VLLE of water-oxygenate-hydrocarbon mixtures was investigated. Cubic equations of state, virial equations of state, activity coefficient models, and equations of state with advanced mixing rules were considered. The evaluation was conducted using both default and optimized parameters. Predictive performance was improved when binary interaction parameters were optimized using experimental data, but parameter optimization is onerous and it is not always practical. It was found that cubic equations of state should not be used for nonideal systems, and even when combined with advanced mixing rules, there is a risk of poor predictive performance. Although the nonrandom two-liquid (NRTL) activity coefficient model is often considered for polar compounds, this investigation found that the predictive performance of NRTL degraded as the nonideality of the system increased. The universal quasi-chemical (UNIQUAC) activity coefficient model was the best all-around model for predicting the phase behavior of water-oxygenate-hydrocarbon systems. The Hayden-O'Connell virial equation of state predicted the vapor-liquid phase equilibrium of hydrogen bonding materials well. UNIQUAC in tandem with the Hayden-O'Connell equation of state is recommended for the modeling of Fischer-Tropsch syncrude VLLE when the partitioning of oxygenates between phases is important.
- 出版日期2015-10-14
