Optimal Synthesis of a High Purity Bioethanol Distillation Column Using Ionic Liquids

Abstract

In this work, we address the optimal economical synthesis of an extractive distillation column for bioethanol purification, using ionic liquids as a type of solvent that can be designed to feature sustainable characteristics, such as low toxicity and low volatility, among other desirable properties. For the optimal synthesis of the separation scheme, we propose a mixed-integer nonlinear programming (MINLP) formulation, merged with disjunctive programming tools, to take care of modeling logical decisions [Yeomans and Grossmann, Ind. Eng. Chem. Res. 2000, 39, 1637−1648]. In a previous work [Chavez-Islas et al., submitted to Ind. Eng. Chem. Res.], we have addressed the design of a novel ionic liquid to separate the ethanol/water azeotropic system, up to high purities. The MINLP synthesis of the distillation column considers the feed tray location, the number of trays, and the operating and design parameters as decision variables. Because the ionic liquid used in this work is a novel solvent, its physical and thermodynamic properties are yet not available. Therefore, the physical properties of the ionic liquid are estimated using group contribution methods. The MINLP formulation is based on the application of the MESH equations for conditional trays, to reduce the size of the nonlinear subproblems and increase the robustness of the optimization formulation. The MINLP problem was solved using the SBB solver embedded in GAMS. Using the proposed MINLP formulation, we attained ethanol purities as good as 99.9 mol %, and 90% of the ethanol presented in the feed stream was recovered.

Extractive distillation with ionic liquids: A review

“…For the single EDC, the simultaneous optimization of IL entrainers and the extractive distillation process has been addressed recently by some researchers. To this end, there are two optimization approaches: (1) the molecular structures of ILs were first designed by means of CAMD, and then, the separation scheme was optimized to determine the optimal design and operating variables using the multistage equilibrium model . (2) Both problems were solved in a simultaneous manner in which the MESH equations are incorporated into an MINLP formulation to simulate the EDC, as suggested by Valencia‐Marquez et al…”

Process synthesis for addressing the sustainable energy systems and environmental issues

“…Multiple desired and undesired side reactions in the biorenewable conversion process will lead to very complex and even azeotropic multicomponent mixtures, together with insolubility of biorenewables in conventional solvents require novel organic solvents for the pretreatment, molecular transformations and separation. As an example, ionic liquids are extensively used for biorenewable pretreatments65 and separation units 66, 67. As known, costs of separation units which are often energy extensive operations will be the dominating factor in the overall cost of a biorenewable conversion process.…”

Effect of ionic liquids as entrainers on the dynamic behavior of ethanol-water extractive columns

“…Several authors have reported that such solvents promote significant changes on the vapor-liquid equilibrium (VLE) properties of the ethanol-water system, improving the ethanol dehydration process with larger separation factors at low ethanol concentrations [11][12][13]. Some design methodologies have been suggested for extractive distillation columns for ethanol dehydration using ILs as entrainers, such as those proposed by Chavez-Islas et al [14], Roughton et al [15], Ramírez-Corona et al [16] and Zhu et al [17] Some experimental works have also evaluated the feasibility of using such solvents at a pilot plant scale that show promising perspectives for their application [18][19][20]. ILs have also been analyzed for the separation of other mixtures, such as methyl acetatemethanol [21] and those that need desulfurization tasks [22].…”