Toward Sustainable and Cost‐Effective CO₂ Conversion Processes to Propylene Carbonate Based on Ionic Liquids

Abstract

in ammonia production. Then, CO 2 can be used directly in a variety of applications, as a solvent, [3] refrigerant, [4] or carbonating agent in the beverage industry as well as as a raw material for the synthesis of other products. There are different types of CO 2 conversion to other products, which can be divided into reactions that incorporate the complete CO 2 molecule (carboxylation) or merely a part of the mole cule (reduction); [1a] presenting the former reactions much lower energy demand than the latter, which increases the interest in carboxylation reactions. Some products that can be obtained by carboxylation are ureas, [5] lactones, [1a] carboxylic acids, [1a] carbonates, [6] polycarbonates, [7] or polyurethanes. [8] To produce cyclic carbonates which find applications in common separations in the chemical industry [9] as well as being electrolytes for batteries [10] as final use, or are well-known monomers in the polymer industry [7,10] finding applications even in the biomedical field, [11] the use of ionic liquids (ILs) as catalysts in both homogeneous and heterogeneous phases has been suggested. [12] Figure 1 shows the reaction scheme to produce propylene carbonate from propylene oxide using ILs with the corresponding pressure and temperature conditions considered in this work. Given their high CO 2 solubility, ILs are very competitive absorbents compared to amines [13] plus they can also be used as catalysts, [14] allowing for the integration of CO 2 capture and conversion. [15] However, carbonate and IL separation by distillation has been revealed to be high energy-consuming. [15a,16] Therefore, it was recently proposed to carry out this separation by liquid-liquid extraction, which reduces energy consumption. [16,17] Depending on whether the IL is hydrophilic or hydrophobic, either water or a long-chain alcohol would be the preferred extracting solvent, respectively. [18] To advance in the development of more effective and sustainable IL-based CCU processes, techno-economic assessment and environmental impact evaluations need to be addressed comprehensively. It is necessary to analyze these systems globally, including the synthesis of the necessary compounds as well as the implications of their energy consumption and energy sources. [19] In this line, several studies have already been conducted on the environmental sustainability of CO 2 capture and storage processes, [20] including those based on ILs. [21] However, in the case of carbon utilization processes, due to the variety of The use of ionic liquids (ILs) for CO 2 capture and utilization into a valuable product is attracting interest even though literature evaluating their sustainability is scarce. A liquid-liquid extraction (LLE)-based separation is recently proposed as an alternative to the high energy-consuming distillation-based reference approach to produce propylene carbonate (PC). In this work, the environmental impacts associated to the distillation-based reference and two proposed LLE-based approaches to produce PC are eval...

Process Simulation and Optimization on Ionic Liquids

“…However, in addition to the software (SimaPro, GaBi, openLCA, etc. ), the database that is applied for the LCA inventory (Ecoinvent is the most used database ,, ) and the impact calculation method are important. With respect to the latter, methods, such as ReCiPe , or CML, have been used to calculate several impact categories, such as the human toxicity, water ecotoxicity, terrestrial acidification, and CO 2 -equivalent emissions that lead to global warming; on the contrary, the IPCC impact assessment only computes the global warming potential.…”

“…Regarding the cost calculation, only four studies calculated the utility costs (for producing propylene and diethyl carbonates), ,,, and only two examples of detailed capital costs (for producing PC) were available in the literature. , For the utility costs calculated for producing PC, the values obtained in these studies were consistent and in the same range (0.4–9.3 $/t product ). ,, The utility costs for producing diethyl carbonate, on the other hand, were considerably higher. When ILs were used, the utility costs amounted to 303 $/t product , which was similar to that of other technologies that do not involve IL (e.g., the utility cost for producing dimethyl carbonate with catalytic membrane reactors was 209 $/t product ) .…”

“…The literature on these products is diverse in terms of the studied variables and number of available studies, as listed in Table . Cyclic carbonates can be synthesized from epoxides and CO 2 using an IL catalyst, , as shown in Figure A. In addition, other value-added products can be generated utilizing these CO 2 -derived cyclic carbonates as reactants.…”

“…Studies on the influence of the reactor temperature on the process, on the other hand, are scarce. Hernández et al recently conducted a sustainability study and concluded that for the same conversion between 40 and 120 °C, a lowertemperature was not always beneficial for the energy demands and sustainability, as shown in Figure A, which contradicted the conventional criteria for designing catalysts to operate at mild temperatures. However, a previous study has shown that higher temperatures (120 °C versus 80 °C) could be balanced by increasing the IL load in the reactor to ensure the same conversion without altering the energy consumption, as shown in Figure B.…”

“…The limitations of the regeneration of a mixture of ILs and some solutes could only be evaluated based on the required vacuum, energy consumption, and/or operating costs, for which process simulation required mass and energy balances through the use of simple industrial (flash distillation units) or complex (distillation or stripping columns) devices . Therefore, process simulation has enabled the conformity of multifactorial and consistent sets of criteria (thermodynamic, kinetic, technical, energetic, environmental, and economic) for selecting ILs with optimized properties for improving the process performance of specific industrial applications. − ,− …”