Investigating the Phase Equilibria of Branched Alcohol/Water/Salt Mixtures

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Branched alcohols are more suitable to produce fuel additives and biofuels than methanol and ethanol because their properties are similar to those of gasoline. However, their production at large scale in biorefineries is currently not economically viable because of the higher cost of purification through distillation. The addition of some salts to the fermentation broth reduces the affinity of the alcohol with the broth, facilitating the purification. Therefore, the phase behaviour of these electrolyte systems is required for designing cost-efficient purification operations. The proposed research has the following objectives, which aim to address critical gaps in the fundamental understanding of the thermodynamics of branched alcohols/water/salt mixtures to advance in the development of modelling tools for the design and simulation of purification operations in biorefineries. Objective 1-Develop a Data-Validated Activity Coefficient Model Using Data Collected from Liquid- Liquid Equilibrium (LLE) Studies: The addition of some salts to an alcohol/water mixture forces the alcohol to separate off the mixture. However, the LLE data required to shed light on the thermodynamics of the mixture are scarce and available models are correlative rather than predictive. It is proposed to collect LLE data for branched alcohol/water/salt mixtures over a range of temperatures and pressures to investigate its thermodynamics, and to incorporate it into an activity coefficient-based model. Objective 2- Develop a Data-Validated Hybrid Model Using Data Collected from Vapor-Liquid Equilibrium (VLE) Studies: The addition of some salts to an alcohol/water mixture increases the relative volatility of the alcohol facilitating its separation from the mixture by distillation. However, VLE data for branched alcohol/water/salt mixture are scarce. It is proposed to investigate the effect of the salt on the VLE of these mixtures and to develop a Cubic Equation-of-State/Activity Coefficient hybrid model. Objective 3- Propose an Equation-of-State-Based Modelling Methodology: The electrolyte version of the Cubic Plus Association (e-CPA) equation of state (EoS) has the potential to be applied to model the phase behaviour of branched alcohol/water/salt mixtures across the phase diagram. However, this EoS does not produce accurate phase compositions for LLE and has not been tested on data at high pressure. It is proposed to develop a suitable e-CPA based methodology suitable for biorefinery applications. The results from this research will allow biorefinery operators to design cost-effective purification operations to produce fuel-grade branched alcohols. Canada will benefit from more competitive and greener biorefineries. In addition, two M.Sc. and one Ph.D. students will receive background and training suitable for careers in the industry and academia.