Communication Chemical Adsorption Strategy for DMC-MeOH Mixture Separation † Fucan Zhang 1,2, Ping Liu 1, Kan Zhang 1 and Qing-Wen Song 1,* molecules1 State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China; [email protected] (F.Z.); [email protected] (P.L.); [email protected] (K.Z.) 2 State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering and Environment, Communication Chinese China University of Petroleum, Beijing 102249, China * Correspondence: [email protected] Chemical Adsorption† Dedicated Strategy to the 100th anniversary for DMC-MeOH of Chemistry at Nankai MixtureUniversity. Separation † Abstract: The effective separation of dimethyl carbonate (DMC) from its methanol mixture through Fucan Zhang 1,2 , Ping Liu 1simple,, Kan Zhang inexpensive1 and Qing-Wen and low Song energy-input1,* method is a promising and challenging field in the process of organic synthesis. Herein, a reversible adsorption strategy through the assistance of 1superbaseState Key Laboratoryand CO2 of for Coal DMC/methanol Conversion, Institute separation of Coal Chemistry, at ambient Chinese Academy condition of Sciences, was described. The process Taiyuan 030001, China; [email protected] (F.Z.); [email protected] (P.L.); [email protected] (K.Z.) was demonstrated effectively via the excellent CO2 adsorption efficiency. Notably, the protocol was 2 State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering and Environment, alsoChinese suitable China to University other ofalcohol Petroleum, (i.e., Beijing monohydric 102249, China alcohol, dihydric alcohol, trihydric alcohol) mix- *tures.Correspondence: The study [email protected] provided guidance for potential separation of DMC/alcohol mixture in the † Dedicated to the 100th anniversary of Chemistry at Nankai University. scale-up production. Abstract: The effective separation of dimethyl carbonate (DMC) from its methanol mixture through simple,Keywords: inexpensive dimethyl and low carbonate; energy-input methodsuperbase; is a promising carbon and di challengingoxide; reversible field in the ad processsorption; separation ofmethod organic synthesis. Herein, a reversible adsorption strategy through the assistance of superbase Citation: Zhang, F.; Liu, P.; Zhang, and CO2 for DMC/methanol separation at ambient condition was described. The process was demonstrated effectively via the excellent CO adsorption efficiency. Notably, the protocol was also K.; Song, Q. Chemical Adsorption 2 suitable to other alcohol (i.e., monohydric alcohol, dihydric alcohol, trihydric alcohol) mixtures. The Strategy for DMC-MeOH Mixture study provided guidance for potential separation of DMC/alcohol mixture in the scale-up production. Separation. Molecules 2021, 26, x. 1. Introduction https://doi.org/10.3390/xxxxx Keywords: dimethyl carbonate; superbase; carbon dioxide; reversible adsorption; separation method Dimethyl carbonate (DMC), defined as a green chemical, has many applications in Academic Editor: Bhanu P.S. synthetic chemistry, and it is also used as a solvent, an additive in gasoline, a depurative, Chauhan Citation: Zhang, F.; Liu, P.; Zhang, and a surfactant [1–3]. During the past ten years, much attention has been paid to the 1. Introduction K.; Song, Q.-W. Chemical Adsorption carbon dioxide (CO2)-based synthetic routes to DMC, such as transesterification of cyclic Dimethyl carbonate (DMC), defined as a green chemical, has many applications in Received:Strategy 21 February for DMC-MeOH 2021 Mixture carbonate and methanol [4–7] and carbonylation of CO2 [8–12]/urea [13] with methanol synthetic chemistry, and it is also used as a solvent, an additive in gasoline, a depurative, Accepted:Separation 16 March . Molecules 2021 2021, 26, 1735. (Scheme 1). Notably, in these processes, because of the thermodynamic equilibrium and https://doi.org/10.3390/molecules and a surfactant [1–3]. During the past ten years, much attention has been paid to the Published: 17 March 2021 26061735 carbonlimited dioxide catalytic (CO2 )-basedability, synthetic excess methanol routes to DMC, was such generally as transesterification used for obtaining of cyclic the high effi- carbonateciency. Therefore, and methanol the [4 –target7] and carbonylationproduct was of COalways2 [8–12 mixed]/urea [with13] with methanol, methanol and the easily Publisher’sAcademic Note: Editor: MDPI Bhanu stays neu- (Schemeformed1 ) DMC/MeOH. Notably, in these binary processes, azeotrope because of(appr the thermodynamicoximate methanol/DMC equilibrium and composition of P.S. Chauhan tral with regard to jurisdictional limited70%:30%) catalytic increased ability, excess the methanolcomplexity was generallyof DMC used separation for obtaining [14–16]. the high Until efficiency. now, the available claims in published maps and insti- Therefore, the target product was always mixed with methanol, and the easily formed Received: 21 February 2021 separation methods have included extractive distillation, liquid–liquid extraction, selec- tutional affiliations. DMC/MeOH binary azeotrope (approximate methanol/DMC composition of 70%:30%) Accepted: 16 March 2021 increasedtive adsorption, the complexity lower of DMCtemperature separation crystalliz [14–16]. Untilation, now, and the availablethe membrane/distillation separation inte- Published: 19 March 2021 methodsgrated haveprocess, included etc. extractive Among distillation, them, pressure liquid–liquid distillation extraction, technique selective adsorption, is used in industrial lower temperature crystallization, and the membrane/distillation integrated process, etc. processes, and the energy input is very high. Therefore, improvement and innovation are Publisher’s Note: MDPI stays neutral Among them, pressure distillation technique is used in industrial processes, and the energy Copyright:with regard © 2021 to jurisdictionalby the authors. claims in inputurgently is very required high. Therefore, for the improvement enhancement and innovationof separation are urgently efficiency required and for the the decrease in en- Licenseepublished MDPI, maps Basel, and Switzerland. institutional affil- enhancementergy consumption. of separation efficiency and the decrease in energy consumption. iations. This article is an open access article O distributed under the terms and CO2 CO CH OH O O 2 OO 3 -H2O conditions of the Creative Commons CH3OH R O O Attribution (CC BY) license R Copyright: © 2021 by the authors. OH urea -NH (http://creativecommons.org/licensesLicensee MDPI, Basel, Switzerland. OH 3 R /by/4.0/).This article is an open access article Indirect route Direct route distributed under the terms and conditions of the Creative Commons Scheme 1. 1.CO CO2-sourced2-sourced routes routes to dimethyl to dime carbonatethyl carbonate (DMC). (DMC). Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ In 2005, Jessop et al. reported a reversible nonpolar-to-polar solvent [17]. In their 4.0/). work, a non-ionic liquid including an alcohol and an organic base was converted into Molecules 2021, 26, x. https://doi.org/10.3390/xxxxx www.mdpi.com/journal/molecules Molecules 2021, 26, 1735. https://doi.org/10.3390/molecules26061735 https://www.mdpi.com/journal/molecules Molecules 2021, 26, x 2 of 7 Molecules 2021, 26, 1735 2 of 7 In 2005, Jessop et al. reported a reversible nonpolar-to-polar solvent [17]. In their work, a non-ionic liquid including an alcohol and an organic base was converted into a salta salt in inliquid liquid form form upon upon exposure exposure to to a a CO CO2 2atmosphere,atmosphere, and and then then reverted reverted back back to its non-ionic form when exposed to nitrogen or argon gas. After this, the reversible process was employed as an effective strategy for CO 2 capturecapture [18–20]. [18–20]. Referring Referring to to these these studies, studies, we speculatedspeculated thatthat performing performing the the reversible reversible adsorption adsorption strategy strategy with with CO2 ,CO a suitable2, a suitable base baseand MeOHand MeOH could could also also be abe potential a potential candidate candidate for for the the separation separation of of the the MeOH/DMC MeOH/DMC mixture. AfterAfter thethe adsorption adsorption reaction, reaction, DMC DMC stays stays in the in liquidthe liquid phase phase and the and new the formed new formedsolid adduct solid precipitatesadduct precipitates (Scheme 2(Scheme). For the 2). mechanism, For the mechanism, methanol methanol is initially is activated initially activatedby 1,5-diazabicyclo(4.3.0)non-5-ene by 1,5-diazabicyclo(4.3.0)non-5-ene (DBN) and (DBN) subsequently and subsequently attacks on attacks the CO on2 molecule the CO2 moleculewith the generationwith the generation of ionic solid of ionic adduct solid which adduct precipitates which precipitates from the system.from the system. Scheme 2. ReversibleReversible CO CO22 adsorptionadsorption applied applied in in CH CH33OH/DMCOH/DMC separation. separation. Herein, a reversible adsorption strategy utilising superbase, CO , and methanol for Herein, a reversible adsorption strategy utilising superbase, CO2, and methanol for DMC separation from its methanol mixture at ambient condition was proposed, and the detailed parameters beingbeing relatedrelated to to the the adsorption adsorption efficiency efficiency such such as component,as component, solvent, sol- vent,temperature temperature and pressure and pressure were studied. were studied. The work The aims work to aims