ScCO2/Green Solvents: Biphasic Promising Systems for Cleaner Chemicals Manufacturing

Abstract : Solvents play a key role in the chemical industry; novel classes ofsolvents such as gas expanded liquids and switchable solvents have attracted greatinterest in recent years as their emergence and utilization in chemical processeshold many promises to develop benign environmental technologies. Thisperspective paper aims at reflecting on the state of the art concerning biphasicscCO2/green solvent systems. Rather than discussing the reactions that have beenperformed in each major type of scCO2/green solvent biphasic system, this paper isstructured instead in terms of the problems or difficulties that these innovativesystems help to solve in processes engineering by taking advantage of the uniqueadvantages of these systems such as greenness, solubility enhancement, andpressure-tunable properties, allowing for overcoming issues concerning mono-phasic systems that the chemical engineer is confronted with when scCO2or agreen solvent are used separately and that have limited their utilization at industrialscales. Among such issues, one can cite (1) difficulties in the solubilization of these compounds, (2) difficult separation ofreactants, products, and catalysts, and (3) loss of the catalyst. These problems arise on one hand from the poor solvent power ofscCO2when used in homogeneous phase and on another hand from the need for a decrease in the usage of distillation as aseparation technique. However, their association in biphasic systems allows for overcoming these problems and provides uniqueopportunities and perspectives to develop future versatile,flexible, and atom economical chemical processes in full accordancewith the principles of green sustainable engineering. The green solvents considered in this perspective paper are water, ionicliquids, biobased ionic liquids, and other green solvents such as glycerol and liquid polymers. Ionic liquids have been consideredin this paper as they have been claimed as“green”because they allow the prevention of volatile emissions; however, some ofthem present toxic issues together with a high environmental impact because of their nonbiodegradability and highmanufacturing costs.1We have then tried to attract special attention to biosourced ionic liquids that may have better toxicologicaland environmental properties and that may hold promise for their future use in chemical processes. This paper presents also thestudies concerning phase equilibrium between scCO2and green solvents where biphasic systems can be obtained, as phasebehavior control is an interesting tool for designing effective catalytic reactions and catalyst-product separation processes. Theunique properties of green solvents that have been proposed as a homogeneous phase in previous studies have prompted us toinclude them in this perspective paper with the aim of interesting the scientific community in testing them in biphasic systemsincluding scCO2. Finally, some reflections about the next steps toward greener processes using scCO2/green solvent biphasicsystems are presented and concern technical and scientific requirements to take full advantage of the capabilities of thesesystems.This perspective paper does not intend to be comprehensive but instead tries to attract attention on recent usages ofthese systems in order to stimulate future advances in the study and development of such systems.
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Yaocihuatl Medina-Gonzalez, Séverine Camy, Jean-Stéphane Condoret. ScCO2/Green Solvents: Biphasic Promising Systems for Cleaner Chemicals Manufacturing. ACS Sustainable Chemistry & Engineering, American Chemical Society, 2014, 2 (12), pp.2623-2636. ⟨10.1021/sc5004314⟩. ⟨hal-02099765⟩

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