DOI: 10.3303/CET2292058 Paper Received: 24 January 2022; Revised: 28 March 2022; Accepted: 25 April 2022 Please cite this article as: Ramos V.H.S., Miranda N.T., Lunelli B.H., Fregolente L.V., Maciel Filho R., Wolf Maciel M.R., 2022, Diethyl Carbonate Production from CO2 and Ethanol in an Isothermal Pfr via Aspen Plus Simulation, Chemical Engineering Transactions, 92, 343-348 DOI:10.3303/CET2292058 CHEMICAL ENGINEERING TRANSACTIONS VOL. 92, 2022 A publication of The Italian Association of Chemical Engineering Online at www.cetjournal.it Guest Editors: Rubens Maciel Filho, Eliseo Ranzi, Leonardo Tognotti Copyright © 2022, AIDIC Servizi S.r.l. ISBN 978-88-95608-90-7; ISSN 2283-9216 Diethyl Carbonate Production from CO2 and Ethanol in an Isothermal PFR via Aspen Plus Simulation Victor Hugo S. Ramosa,*, Nahieh T. Mirandaa, Betânia H. Lunellib, Leonardo V. Fregolentea, Rubens Maciel Filhoa, Maria Regina W. Maciela aLaboratory of Optimization, Design, and Advanced Control, School of Chemical Engineering, University of Campinas, Av. Albert Einstein 500, Campinas, 13083-852, Brazil bSchool of Chemical, Pontifical Catholic University of Campinas, Professor Dr. Euryclides de Jesus Zerbini 1516, Campinas, 13087-571, Brazil v264227@dac.unicamp.br In this work, diethyl carbonate (DEC) production from CO2 and ethanol, coming from the bioethanol plant, is studied using 2-cyanopyridine (2-CP) as a dehydrating agent and CeO2 as a catalyst. Aiming to integrate existing plants and applying the concept of circular economy, this work has the appeal of not emitting carbon dioxide and valuing renewable carbon in the production of diethyl carbonate, a compound with high added value that can be applied as lithium battery electrolyte and as an intermediate in obtaining ketones, tertiary alcohols, and heterocyclic components. The DEC production proposed in this work was simulated via Aspen Plus V10 software. The reaction system is composed of the following reagents: carbon dioxide (CO2), ethanol (EtOH), diethyl carbonate (DEC), water (H2O), 2-cyanopyridine (2-CP), picolinamide (2-PA), ethyl picolinimidate (EPI), ethyl picolinate (EP), ammonia (NH3), and ethyl carbamate (EC). The mixture properties were calculated using the Non-Random-Two-Liquid (NRTL) method. The reaction mixture composition used was 10 kmol/h of ethanol, 15 kmol/h of CO2, and 5 kmol/h of 2-CP. The reactor was simulated as a multi-tubular isothermal plug flow reactor (PFR). The kinetic reactions were modeled using power law equations. The effect of reactor operating temperature (range 130–150 °C) and reactor dimensions on ethanol conversion was studied. At 50 atm and 130 °C, 4.01 kmol/h of DEC was obtained at the output stream of the reactor, corresponding to 11.37 t/day with an ethanol conversion of 82.85 %. From the open literature, this is the first work that the DEC production from ethanol and CO2 is simulated in a multi-tubular reactor. 1. Introduction Diethyl carbonate (DEC) is a biodegradable colourless liquid with moderate toxicity and low bioaccumulation (Shukla and Srivastava, 2016; PubChem, 2022). Due to its high oxygen content (40.6 %), it can act as a fuel additive replacing methyl tert-butyl ether (MTBE) containing 18.2 % oxygen content, to improve gasoline octane number while requiring less additive to achieve the same effect (Wang et al., 2007; Shukla and Srivastava, 2018; De Groot et al., 2014). Among other organic carbonates, DEC has also been studied as an electrolytic solvent for lithium batteries (Zhang et al., 2020; Jote et al., 2020). Alternative routes such as urea alcoholysis (Wang et al., 2007), transesterification of ethanol with ethylene carbonate (Iida et al., 2018), decarboxylation of diethyl oxalate (Hao et al., 2009), direct synthesis by carbonylation of ethanol using CO2 (Giram et al., 2018) and supercritical CO2 (Gasc et al., 2009) have been studied to obtain DEC. Applying the concept of Circular Economy, obtaining DEC from ethanol and CO2 from the sugarcane bioethanol plant appears as an ecologically friendly alternative to the conventional process that uses the toxic compound phosgene (Denardin and Valença, 2020; Arbeláez et al., 2020). This route’s appeal is the use of renewable carbon and the reduction of CO2 emissions applied to the integration of existing industrial plants. 343 This work addresses the reactional step of obtaining DEC via Aspen Plus simulation in order to support future experimental activities and process design. An in-depth discussion of the parameters involving the reactor in simulating the production of DEC from ethanol and CO2 is presented. 2. Materials and Methods In this work, the reaction step of a DEC plant aiming at the production of 10 t/day (3.53 kmol/h) is presented. The simulation was performed using Aspen Plus V10 software. The reaction system is composed of the following components: carbon dioxide (CO2), ethanol (EtOH), diethyl carbonate (DEC), water (H2O), 2-cyanopyridine (2- CP), picolinamide (2-PA), ethyl picolinimidate (EPI), ethyl picolinate (EP), ammonia (NH3), and ethyl carbamate (EC). The properties of the mixture were calculated using the Non-Random Two Liquid Activity Coefficient (NRTL) model and the missing data extracted from the database presented by Yu et al. (2020). Table 1 shows the reaction system and the kinetics of DEC production from ethanol and CO2 as contributions from the studies by Yu et al. (2020) and Giram et al. (2018). In this work, the reactor was simulated as an isothermal multi-tubular Plug Flow Reactor (PFR) considering the vapor-liquid equilibrium and the Power Law kinetic equations. The reactor bed was simulated assuming a CeO2 catalyst density of 7,130 kg/m3 (Sigma Aldrich, 2021) and 0.4 voidage. The reactor feed flowrate was set at 10 kmol/h of ethanol, 15 kmol/h of CO2, and 5 kmol/h of 2-CP. The effect of reactor operating temperature (range 130–150 °C) on ethanol conversion was studied, as well as the influence of the length and number of tubes on the PFR. Table 1: Reaction system and kinetic parameters of DEC production (Yu et al., 2020; Giram et al., 2018) Reaction Equation Ea (kJ/kmol) k0 (kmol/kgcat.s) CO2 + 2(EtOH) r1 → DEC + H2O 𝑟1 = 𝑘1exp⁡(− 𝐸𝑎1 𝑅𝑇 ⁄ ) 150,163 4.608 × 1014 DEC + H2O r2 →CO2 + 2(EtOH) 𝑟2 = 𝑘2exp⁡(− 𝐸𝑎2 𝑅𝑇 ⁄ ) 𝑋𝐷𝐸𝐶𝑋𝐻2𝑂 𝑋𝐶𝑂2𝑋𝐸𝑡𝑂𝐻 2⁄ 125,359 5.550 × 1017 2CP + H2O r3 →2PA 𝑟3 = 𝑘3⁡T⁡exp⁡(− 𝐸𝑎3 𝑅𝑇 ⁄ )𝑋2−𝐶𝑃𝑋𝐻2𝑂 258 7.048 2CP + EtOH r4 →EPI 𝑟4 = 𝑘4exp⁡(− 𝐸𝑎4 𝑅𝑇 ⁄ )𝑋2−𝐶𝑃𝑋𝐸𝑡𝑂𝐻 15,259 3.851 × 10-5 2PA + EtOH r5 →EP + NH3 𝑟5 = 𝑘5exp⁡(− 𝐸𝑎5 𝑅𝑇 ⁄ )𝑋2−𝑃𝐴𝑋𝐸𝑡𝑂𝐻 6,919 2.151 × 10-2 EP + NH3 r6 →2PA + EtOH 𝑟6 = 𝑘6exp⁡(− 𝐸𝑎6 𝑅𝑇 ⁄ )𝑋𝐸𝑃𝑋𝑁𝐻3 1,937 8.726 DEC + 2PA r7 →EC + EP 𝑟7 = 𝑘7exp⁡(− 𝐸𝑎7 𝑅𝑇 ⁄ )𝑋𝐷𝐸𝐶𝑋2−𝐶𝑃 69,837 7.133 × 105 EC + EP r8 →DEC + 2PA 𝑟8 = 𝑘8exp⁡(− 𝐸𝑎8 𝑅𝑇 ⁄ )𝑋𝐸𝐶𝑋𝐸𝑃 12,915 3.133 × 10 EPI + H2O r9 →EP + NH3 𝑟9 = 𝑘9⁡T⁡exp⁡(− 𝐸𝑎9 𝑅𝑇 ⁄ )𝑋𝐸𝑃𝐼𝑋𝐻2𝑂 14,952 1.114 × 102 3. Results and Discussion The biggest challenge in using CO2 to produce chemical compounds is the thermodynamic limitation due to the high stability of CO2, a topic that has been widely discussed previously in the literature (Denardin and Valença, 2020; Tomishige et al., 2020; Wang et al., 2017). Among the technological advances in the route to obtain organic carbonates from CO2, the use of catalysts based on CeO2 and 2-cyanopyridine as a dehydrating agent has been consolidated as a promising route although there is still room to increase the yield and selectivity of the carbonate production (Tomishige et al., 2020; Honda et al., 2014; Pawar et al., 2020; Daniel et al., 2021; Zhang et al., 2021). The presence of the dehydrating agent promotes a shift in the chemical balance, leads to greater formation of diethyl carbonate (DEC) and the formation of undesirable products by parallel reactions (Table 1). For the simulation via Aspen Plus, the experimental conditions presented by Giram et al. (2018) and the kinetic study presented by Yu et al. (2020) were considered. From the open literature, this is the first work that simulated the DEC production from ethanol and CO2 in a multi-tubular reactor. The simulation presented in this work corresponds to the DEC production stage, focusing on the variables of the reaction system and the reactor design. Thus, it is important to emphasize that the complete DEC plant also includes the steps of separation and purification of the products. Figure 1 shows the flowsheet designed to simulate the reaction system. The liquid streams of ethanol (ETOH- F) and 2-CP-F are initially mixed in the mixer (MIX-LIQ) and then pumped up to 50 atm. The CO2-F stream is compressed up to 50 atm and sent to the MIX-F feed mixer. The FEED stream is sent to a heater to adjust the reaction temperature (range 130–150 °C) and then sent to the isothermal PFR (RPLUG). 344 Figure 1: Flowsheet of the reactional step of DEC production – MIX-LIQ = liquid mixer; COMPRESS = compressor; PUMP = pump; MIX-F = feed mixer; HEATER1 = heater; RPLUG = plug flow reactor Initially, the PFR was simulated in a single tube (results presented in Figure 2) to analyze the behavior of ethanol conversion and DEC production as the reactor length varies, keeping the diameter at 2.54 cm (1 in). It was observed that, in a small reactor length, the effect of temperature is relevant, favoring the conversion of EtOH as the temperature increases (Giram et al., 2018). However, as the reactor length increases from 0.5 m to 200 m, this influence decreases leading to similar levels of ethanol conversion around 90%. The use of a 200 m reactor in this plant is impractical due to the large occupied space, production and maintenance costs. Because of these impeditive values, it was proposed to use multi-tubular PFR. Figure 2: Influence of reactor length on ethanol conversion – Simulation conditions: 50 bar, 10 kmol/h of ethanol, 15 kmol/h of CO2, and 5 kmol/h of 2-CP, catalyst density of 7,130 kg/m3, and 0.4 of bed voidage and diameter of the reactor of 2.54 cm After this preliminary study, the reactor was then simulated as a multi-tubular PFR with a tube diameter of 2.54 cm and reactor length of 5 m. Figure 3 shows the influence of the number of tubes on ethanol conversion and DEC production. Similar to the behavior observed in Figure 2, it can be seen that from 20 tubes onwards, the influence of temperature on the ethanol conversion is practically negligible. In addition to increasing ethanol conversion, increasing the number of tubes increases the reactor thermal stability since the reaction system is exothermic, favoring the cooling and control of axial and radial temperature profile of the reactant fluid (Overtoom et al., 2009). 345 Figure 3: Influence of number of tubes on ethanol conversion – Simulation conditions: 50 bar, 10 kmol/h of ethanol, 15 kmol/h of CO2, and 5 kmol/h of 2-CP, catalyst density of 7,130 kg/m3, and 0.4 of bed voidage, reactor diameter of 2.54 cm, and reactor length of 5 m In addition to the conversion of ethanol, the formation of side products throughout the reactor at different temperatures was also analyzed. Despite the complexity of the reaction system (Table 1), Figure 4 shows that the excess of the dehydrating agent 2-CP ensures the capture of water. It leads to the formation of the hydrated form 2-PA in the same proportion as the formation of DEC. The increase in temperature and number of reactor tubes showed little influence on the formation of parallel products EP, NH3, EC, and EPI. Figure 4 – Influence of product formation with the variation in the number of reactor tubes: (a) 130 °C, (b) 140 °C, and (c) 150 °C – Simulation conditions: 50 bar, 10 kmol/h of ethanol, 15 kmol/h of CO2, and 5 kmol/h of 2- CP, catalyst density of 7,130 kg/m3, and 0.4 of bed voidage. Reactor diameter of 2.54 cm and reactor length of 5 m 346 Table 2 shows the flowrate of the components in the reactor outlet stream at different temperatures. Under the simulated conditions, it was observed that the increase in temperature favors the conversion of EtOH to form DEC. However, the percentage difference of DEC flow at the reactor output at 130 °C and 150 °C was 3.07 %. Thus, it justifies the use of a lower temperature, reducing the amount of heat required. The production of 4.01 kmol/h of DEC corresponds to 474.02 kg/h of DEC or 11.37 t/day reaching the target set in the project. Table 2: Composition of the outlet stream of the multi-tubular isothermal PFR Components (kmol/h) Temperature (°C) 130 135 140 145 150 CO2 10.8832 10.7910 10.7412 10.7084 10.6854 EtOH 1.7153 1.5378 1.4424 1.3799 1.3360 DEC 4.0126 4.0870 4.1197 4.1349 4.1397 H2O 0.0000 0.0000 0.0000 0.0000 0.0000 2-CP 0.8728 0.7827 0.7341 0.7020 0.6793 2-PA 3.9720 4.0511 4.0868 4.1043 4.1111 EP 0.1448 0.1579 0.1720 0.1872 0.2035 NH3 0.0406 0.0359 0.0328 0.0305 0.0287 EC 0.1042 0.1220 0.1391 0.1567 0.1749 EPI 0.0104 0.0083 0.0071 0.0064 0.0061 Heat Duty (kW) -117.2365 -122.2291 -126.2047 -129.9003 -133.5410 EtOH conv. (%) 82.85 84.62 85.57 86.20 86.64 Simulation conditions: 50 bar, 10 kmol/h of ethanol, 15 kmol/h of CO2, and 5 kmol/h of 2-CP, catalyst density of 7,130 kg/m3, and 0.4 of bed voidage. Reactor diameter of 2.54 cm, reactor length of 5 meters, number of tubes equal to 20 This study allowed to evaluate the influence of temperature on the production of DEC when simulated in a multi- tubular reactor. In addition to dimensioning the reactor to increase the production of DEC, it was also observed that the temperature has less influence in a multi-tubular reactor than when simulated in a single tube reactor, justifying the use of a lower temperature. Thus, it allows the reduction of the energy expenditure. Quantifying energy expenditure in the energy supply to heat the reagents in comparison to the DEC production is suggested as future work. 4. Conclusions In this work, the production of DEC from ethanol and CO2 with dehydrating agent 2-cyanopyridine on CeO2 catalyst was simulated for the first time in a multi-tubular reactor using Aspen Plus commercial software. The simulation was carried out in a multi-tubular isothermal PFR, obtaining a production of 11.37 t/day of DEC in the reactor outlet. The importance of the simulation stage in the development and advancement of process technologies was evidenced in favouring the DEC production when using a multi-tubular reactor. Nomenclature conv. – conversion, % Ea – activation energy, kJ/kmol k0 – velocity constant, kmol/kgcat.s r0 – reaction number X – mole fraction of component R – universal gas constant, kJ/kmol.K T – reaction temperature, °C Acknowledgments The authors thank CAPES (grant 8887.495488/2020-00), São Paulo Research Foundation (FAPESP) (grant #2015/20630-4), The National Council for Scientific and Technological Development (CNPq) (grant 313952/2020-5), and University of Campinas (UNICAMP). 347 References Arbeláez O., Santis A., Villegas A., Villa A., Ivanova S., Centeno M., 2020. 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