Modeling Vapor–Liquid–Liquid Phase Equilibria in Fischer–Tropsch Syncrude

Abstract

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.

A Comparative Study of the Perturbed-Chain Statistical Associating Fluid Theory Equation of State and Activity Coefficient Models in Phase Equilibria Calculations for Mixtures Containing Associating and Polar Components

“…For instance, none of thermodynamic models available in commercial software was found to be sufficiently accurate for applications in the Fischer−Tropsch synthesis. 75 The advent of PC-SAFT EOS potentially eliminates the need for a large variety of thermodynamic models. As a result, it is possible to develop a process simulator or thermodynamic package with PC-SAFT as the only underlying model.…”

Power-to-fuel conversion based on reverse water-gas-shift, Fischer-Tropsch Synthesis and Hydrocracking: Mathematical modeling and simulation in Matlab/Simulink

“…They are present in the vapor and the liquid phase. Ideal behavior for both phases is assumed, as elsewhere in literature [56]. Hence, only a vapor-liquid equilibrium instead of a vapor-liquid-liquid equilibrium can be considered.…”

“…Hence, only a vapor-liquid equilibrium instead of a vapor-liquid-liquid equilibrium can be considered. Under low-temperature FT conditions with an operating pressure below 30 bar, water is in the vapor phase anyway [56].…”

Supporting plots and tables on vapour–liquid equilibrium prediction for synthesis gas conversion using artificial neural networks

“…The experimental VLE data used in this study was obtained from Breman et al [2] . Phase equilibrium modeling is a crucial element in describing the behavior of the Fischer–Tropsch (FT) reaction [3] , [4] , [5] , [6] , [7] , [8] , [9] , [10] , [11] , [12] . The FT reaction produces a range of hydrocarbons from light olefins and paraffins to heavy wax.…”