CO₂-to-Carbonates via Reaction–Separation Coupling: Pilot Performance of Continuous DMC/DPC

CO₂-to-Carbonates via Reaction–Separation Coupling: Pilot Performance of Continuous DMC/DPC | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article CO₂-to-Carbonates via Reaction–Separation Coupling: Pilot Performance of Continuous DMC/DPC Namgyu Son, Sukyong Jung, Joonwoo Kim, Jong Cheol Yun, Sang Ho Lee This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8011647/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 8 You are reading this latest preprint version Abstract This study develops and demonstrates integrated pilot plants for the continuous production of dimethyl carbonate (DMC) and diphenyl carbonate (DPC) as part of a carbon capture and utilization (CCU) strategy. DMC was synthesized from urea (derived from CO₂ + NH₃) and methanol over a zirconium-based catalyst. Across three campaigns totaling 211 h, the unit produced 570.5 kg of DMC, corresponding to an overall yield of 85.9% relative to the 663.9 kg theoretical maximum from 442.3 kg of urea. The product reached 99.93% purity, and electrolyte testing showed no statistically significant differences versus commercial battery-grade DMC. DPC was obtained via transesterification of phenol with DMC using a reactor–distillation configuration that enables in-situ removal of methanol. Over ~ 200 h of continuous operation, phenol conversion was ~ 100% and 65.8 kg of DPC were collected, equal to an overall yield of 32.1% versus the 204.98 kg theoretical limit. Yield shortfalls were attributed to hold-up of intermediates (e.g., phenyl methyl carbonate) and high-boiling residues within equipment. Both trains exhibited stable operability without catalyst bed plugging, and product specifications were consistently met. These results validate the technical feasibility of CCU-based carbonate ester production and identify clear levers—enhanced methanol removal, additional reaction stages, and tighter reaction–separation coupling—for yield intensification and scale-up. carbon capture and utilization dimethyl carbonate diphenyl carbonate transesterification continuous processing pilot demonstration Figures Figure 1 Figure 2 Figure 3 Figure 4 1. Introduction Mitigating CO₂ emissions from energy and hard-to-abate industrial sectors has intensified interest in carbon capture and utilization (CCU), which upgrades captured CO₂ into value-added chemicals [1–3]. For cement, steel, and petrochemicals—where process emissions are largely unavoidable—CCU remains one of the few scalable pathways for deep reduction [4–10]. Within this context, establishing robust routes that convert CO₂ into high-value molecules is central to carbon neutrality and greener process design. We focus on two strategic carbonate esters, dimethyl carbonate (DMC) and diphenyl carbonate (DPC). DMC (C₃H₆O₃) combines low toxicity and biodegradability with excellent solvency, making it a versatile platform used in lithium-ion battery electrolytes, coatings, pharmaceuticals/agrochemicals, and fuel additives [10–16]; demand for battery-grade DMC is rising in step with electrification trends [17]. DMC is also a key intermediate in non-phosgene polycarbonate (PC) synthesis [18]. Industrial DMC routes—direct CO₂–MeOH with dehydrants, cyclic-carbonate intermediates, and urea–MeOH methanolysis—share a common requirement: effective removal of by-products (H₂O, NH₃) to overcome equilibrium constraints and achieve industrial practicality [19–22]. DPC, the canonical carbonate donor for BPA-based PC, underpins non-phosgene PC manufacture that avoids phosgene toxicity and chlorinated wastes [23–25]. In the prevalent DMC–phenol transesterification route, however, methanol formation imposes a strong thermodynamic limitation on conversion and selectivity; hence multi-stage reaction/separation, in-situ MeOH removal, and catalysts with durable activity/selectivity/stability remain essential [26–27]. Despite decades of work on homogeneous and heterogeneous catalysts, challenges persist—low equilibrium conversions, catalyst deactivation, and retention of intermediates/high-boiling fractions—which motivate process intensification, including reactive distillation and membrane-based or gas-phase MeOH removal [28–30]. Much of the literature centers on lab- or bench-scale batch tests or single-unit optimization; by contrast, there are comparatively few pilot-scale continuous demonstrations reporting long-run operation (> 100–200 h) with closed material balances and spec-compliant product qualities (battery-grade or polymer-grade) [31–33]. For DMC, evidence indicates that specific hydrated zirconyl nitrate–hydroxide phases govern activity, yet systematic links between precursor phase (supplier/lot), drying history, and performance remain under-reported. For DPC, the roles of MeOH removal intensity, suppression of phenyl methyl carbonate (PMC) accumulation, and management of high-boiling hold-ups are recognized, but the quantitative effects of coupled reactor–distillation design and operating strategy (reflux, top/bottom temperatures, pressure step-downs) over extended continuous runs require more field-scale data [34]. Against this backdrop, the present work develops and operates integrated pilot plants for continuous DMC and DPC production, seeking to (i) elucidate the Zr-precursor phase–drying–performance relationship and demonstrate sustained throughput, yield, quality (water/purity), and stability for > 200 h in a urea–MeOH DMC train, and (ii) verify that reactor–distillation coupling with in-situ MeOH removal can relax equilibrium limits in the DMC–phenol route to DPC and deliver reproducible conversion, yield, and product quality over ~ 200 h of continuous operation [35]. We further diagnose overall yield losses mechanistically, attributing them to PMC/high-boiler hold-ups [36], and from these analyses derive actionable yield levers—enhanced MeOH removal, additional reaction stages targeting PMC → DPC conversion, tighter reaction–separation integration, and reduced catalyst toxicity for long-run operability [37, 38]. By providing pilot-scale, long-duration evidence for an integrated CO₂ → DMC → DPC platform—together with stable T/P profiles, controlled reflux and column ΔP, and material-balance closure within ± 5%—this study supplies the practical data needed to guide scale-up toward a fully non-phosgene carbonate chain and sets the stage for NH₃ valorization. 2. Materials and Methods 2.1 Materials and catalyst preparation Urea (≥ 99 wt%, industrial grade, SAMCHUN, Korea) and anhydrous methanol (≥ 99.9 wt%, SAMCHUN, Korea) were used as received, with methanol further polished to H₂O ≤ 50 ppm (Karl Fischer coulometry) prior to use. Zirconium precursor and additives. Zirconyl nitrate hydrates, ZrO(NO₃)₂·xH₂O, were procured from Thermo Fisher, STREM, and Alfa Aesar (lot information to be recorded in the SI). Choline chloride (≥ 99%, SAMCHUN, Korea) was employed as the ionic-liquid medium. Synthesis of the Zr-based catalyst precursor. Following a literature-adapted protocol [39, 40], 5.0 L of choline chloride was charged to a jacketed glass reactor and heated with stirring. ZrO(NO₃)₂·xH₂O (1.00 kg) was introduced portionwise, after which methanol (3.0 L) was added and the mixture was stirred until homogeneous. The slurry was held at 120°C for 1 h to partially remove solvent, then ramped to 180°C and maintained for 36 h. Under these conditions, the zirconium precursor undergoes hydrolysis–condensation, yielding an active catalyst precursor gel. The gel was filtered, thoroughly washed with methanol to remove soluble by-products, and oven-dried at 105°C to constant mass. The dried precursor was stored as a free-flowing powder in sealed containers under dry nitrogen until use. 2.2 Pilot plant and operating conditions — DMC The DMC continuous-production pilot was sized for a design throughput of ~ 5 kg DMC·day⁻¹. The reaction section comprised two jacketed, corrosion-resistant stirred packed reactors in series. Stage-1 effected urea methanolysis to methyl carbamate (MC), and Stage-2 completed MC decomposition/transesterification to DMC + NH₃. Catalyst charge and internals. Each reactor was loaded with 200 g of the dried Zr-based catalyst precursor (powder form) contained within a perforated hold-down assembly to prevent carryover. Gas disengagement space and a top off-gas outlet were provided to vent NH₃ continuously while minimizing liquid entrainment. Operating window and control. Reactors were maintained at 180–190°C with cascade temperature control. To suppress methanol vaporization and stabilize liquid-phase kinetics, the system operated under 3–5 bar total pressure using a back-pressure regulator. Feed urea (melt, ~ 133°C) and polished methanol (H₂O ≤ 50 ppm) were metered independently to set the target residence time/WHSV (values summarized in Table 1). Agitation was adjusted to avoid channeling while limiting shear of the packed catalyst layer. Effluent handling and purification. The combined reactor effluent consisted of NH₃-rich off-gas and a liquid phase containing DMC, MeOH, and minor by-products. Off-gas was routed to a scrubbed vent. The liquid stream was directed to a multi-stage distillation for separation and polishing: the first column removed light ends (NH₃/MeOH-rich overhead) with DMC recovery, the second column split DMC from high-boiling residues, and the final column produced spec-grade DMC (target purity ≥ 99.9%, water ≤ 10 ppm). Column operating set-points (top/bottom temperatures, reflux ratios, ΔP) are listed in Table 1; overhead condensers were used on each column to minimize DMC loss[41]. Monitoring and data logging. Reactor T/P, feed rates, column top/bottom temperatures, reflux ratios, and pressure drops were trended at 1-min intervals. Routine material-balance closure within ± 5% was maintained over steady operation. Safety interlocks covered over-pressure, heater runaway, and off-gas line blockage[42]. 2.3 Pilot plant and operating conditions — DPC Scale and process concept. The continuous DPC pilot was designed for a nominal throughput of ~ 10 kg DPC·day⁻¹. Because the DMC–phenol transesterification is strongly limited by the concentration of the by-product methanol (MeOH), the unit employed a coupled reactor–distillation flowsheet to remove MeOH in situ and shift the equilibrium. Feed and reactor operation. A liquid blend of DMC:phenol ≈ 1:1.2 (mol) was continuously metered to a pressure-rated stirred reactor packed with a fixed bed of PbO solid catalyst retained by an internal screen to prevent carryover. The reactor was maintained at 195–200°C and ~ 4 bar. Under these conditions, MeOH generated in the first transesterification step preferentially partitioned to the gas phase and was disengaged via the top off-gas line, while the reaction mixture flowed to the downstream separation[43]. Reactive separation and recycle. The reactor effluent entered a pressure step-down to about 1 bar and was fed to the distillation column operated at ~ 140°C (top) and ~ 218°C (bottom). Overheads removed MeOH together with a small fraction of phenol; MeOH was condensed and purged, whereas recovered phenol was returned to the reactor feed (liquid recycle). The bottoms comprised DPC-rich liquid with minor high-boiling residues; this stream was cooled and passed through a guard filter before product collection. Catalyst containment and integrity. The PbO bed was immobilized within a perforated hold-down assembly and protected by internal filtration screens to avoid fines entrainment. No bed plugging was observed during steady operation[44]. Control, monitoring, and analytics. Reactor temperature/pressure, column top/bottom temperatures, reflux ratio, and column ΔP were monitored continuously and trended at 1-min intervals. Periodic grab samples from the reactor outlet bottoms were analyzed by GC to quantify DPC content and residual phenol; overheads were checked for MeOH and phenol slip. Operating targets were chosen to maintain a high conversion in the first step (phenol + DMC → PMC + MeOH) and to promote the second step (PMC + phenol → DPC + MeOH) via continual MeOH removal, thereby increasing overall DPC yied[45]. 2.4 Product analysis Product analyses were performed by gas chromatography using an Agilent GC-8790A equipped with thermal conductivity (TCD) and flame ionization (FID) detectors; Carboxen® 1000 and Molsieve 5A columns were employed to confirm the presence of DMC, DPC, and other impurities. Catalyst characterization was conducted by X-ray diffraction on a Rigaku SmartLab SE using Cu Kα radiation (9 kW, 45 kV, 200 mA). 2.5 Battery evaluation of DMC To benchmark the pilot-produced DMC against a commercial product, R2032 coin cells were assembled with NCM811 cathodes and graphite anodes (mixture of artificial and natural graphite). The electrolyte formulation was 1.2 M LiPF₆ in EC/EMC/DMC (20/40/40, vol/vol/vol) with 1.5% vinylene carbonate (VC) and 1.0% lithium difluorophosphate (LDFP). Charge–discharge cycling was performed between 2.5–4.2 V at a 1C rate for 400 cycles. All tests were conducted in a sealed isothermal chamber at 45°C. 3. Result & Discussion 3.1 Zr-Based Catalysts for Urea–Methanol DMC Synthesis X-ray diffraction (XRD) patterns of the zirconium nitrate–based precursors from three suppliers (Strem, Alfa Aesar, Thermo Scientific) after identical drying show supplier-dependent phase evolution (Fig. 1 ). Upon ≥ 2 h drying, both the Strem and Alfa Aesar precursors converged to similar diffraction profiles dominated by a broad amorphous halo assignable to poorly crystalline Zr(OH)₂(NO₃)₂·1.3H₂O, with only weak residual features. By contrast, the Thermo Scientific precursor exhibited, already at the early drying stage, distinct reflections attributable to a more highly hydrated phase (e.g., Zr(OH)₂(NO₃)₂·4.7H₂O), and traces of this hydrate persisted after 2 h drying, indicating incomplete de-hydration/rearrangement relative to the other two materials. These structural differences translated directly to catalytic performance in batch DMC synthesis under identical conditions. The 2 h-dried Thermo catalyst delivered a DMC conversion/yield of ~ 52%, whereas the 2 h-dried Alfa Aesar catalyst achieved ~ 85% conversion, closely matching the commercial Strem benchmark (87.8%). The higher activity of Strem and Alfa Aesar correlates with the amorphous, poorly crystalline Zr–OH/NO₃ network formed after drying, which is expected to provide a higher density of accessible Lewis/weak Brønsted sites. In contrast, the persistence of a highly hydrated nitrate–hydroxide phase in the Thermo precursor is consistent with a lower fraction of catalytically competent sites after the same drying period, together with a greater propensity to introduce residual water into the reaction environment—both factors detracting from DMC formation(Fig. 2 ). Overall, the data establish a clear structure–performance relationship: precursors that evolve to an amorphous Zr(OH)₂(NO₃)₂·1.3H₂O–like state under the specified drying protocol yield superior DMC conversion, while retention of a more highly hydrated crystalline hydrate is associated with depressed activity. These results underscore the sensitivity of DMC synthesis to the hydration state and short-range order of zirconium nitrate precursors and justify controlling precursor drying to reproducibly access the high-activity amorphous phase. 3.2 Process Stability and Product Quality in Continuous DMC Operation The continuous-production pilot was validated over three campaigns. Campaign-1 (42 h) and Campaign-2 (18 h) focused on start-up stabilization and operating-window optimization, while Campaign-3 implemented an extended 150 h continuous run. The DMC quantities produced in each campaign were 113.1 kg, 51.5 kg, and 405.9 kg, respectively, for a total of 570.5 kg over 211 h (average productivity 2.70 kg·h⁻¹; 2.69, 2.86, and 2.71 kg·h⁻¹ for Campaigns 1–3). Based on 442.3 kg of urea feed corresponding to a theoretical maximum of 663.9 kg DMC at 100% conversion, the overall yield of the continuous process was 85.9%. Throughout continuous operation, reaction and separation conditions remained essentially constant. The reactor temperature was stably maintained at ≈ 190°C (189–191°C), and the system pressure within 3–5 bar. As summarized in Table 1, column top temperatures were controlled in the 60–140°C range to efficiently remove methanol (MeOH), dissolved ammonia (NH₃), and light ends, while bottom temperatures of 180–220°C consistently effected the split between the DMC-rich fraction and high-boiling residues (polymeric species, etc.). Reflux ratios and column pressure drops (ΔP) stayed within target bounds, and the material balance closure was maintained within ± 5%. These indicators collectively demonstrate that the Zr-based catalyst sustained stable activity without measurable physical loss or deactivation over the entire campaign set, and that the integrated reaction–separation stage achieved long-term operability with consistent product quality. 3.3 Physicochemical Purity and Cell Performance of Pilot DMC in Comparison with Commercial Grade Gas-chromatographic analysis of the pilot-produced DMC confirmed 99.93% purity, indicating a high-purity product. Minor impurities consisted of trace methanol and trace high-boiling residues (e.g., polymeric/heavy ends). The water content was 30–50 ppm, close to the battery-electrolyte solvent specification (< 20 ppm); this residual moisture can be readily reduced below specification by routine post-treatment drying during storage/polishing. Color (APHA/Pt–Co) was 1.0 for the pilot DMC versus 1.8 for the commercial comparator, indicating equivalent or better optical quality for the pilot product. Electrochemical benchmarking showed no statistically significant differences versus commercial battery-grade DMC: charge–discharge cycling behavior, internal resistance/impedance, and initial Coulombic efficiency were all comparable. After long-term cycling, capacity retention was 85.1% for the pilot DMC and 84.9% for the commercial DMC (1C, 2.5–4.2 V, 45°C, 400 cycles)(Fig. 3 .), confirming no meaningful performance gap. Collectively, these results verify that the DMC produced by the present process is suitable for use as an electrolyte solvent in lithium-ion batteries. 3.4 Batch pre-evaluation prior to the DPC pilot Prior to the DPC pilot run, we conducted lab-scale batch experiments to assess the reaction mechanism and catalyst performance. A 1:1 molar mixture of phenol and DMC was reacted at 200°C for 24 h in the presence of PbO. The phenol conversion reached ~ 45%, but phenyl methyl carbonate (PMC) remained as a major product alongside DPC, resulting in a DPC selectivity below 50%. This outcome reflects an equilibrium limitation: the reaction proceeds readily through the first transesterification step (phenol + DMC → PMC + MeOH), whereas the second step (PMC + phenol → DPC + MeOH) remains reversible and less favorable under these conditions. Guided by this, we introduced timely removal of methanol to drive the equilibrium forward. Using a reflux configuration with continuous MeOH removal, a single-batch test achieved phenol conversion of 86% and DPC yield of ~ 85%. Based on comparative screening of several transition-metal oxides and organometallic candidates, PbO exhibited relatively high DPC selectivity and good catalyst longevity, and was therefore adopted for the pilot. 3.5 DPC pilot continuous operation The DPC continuous-production pilot was operated for ~ 180 h to verify performance. During this period, 180.2 kg of phenol and [DMC feed: to be inserted] kg were charged. The first ~ 20 h were devoted to process stabilization, after which ~ 180 h of steady continuous production ensued. Periodic sampling from the reactor outlet and the distillation bottoms showed that phenol conversion was nearly quantitative (~ 100%) from the onset of steady operation through shutdown, consistent with feeding phenol as the limiting reactant and real-time removal of MeOH shifting the equilibrium toward DPC formation. The final DPC yield was 32.1%, i.e., roughly one third of the theoretical 204.98 kg obtainable if all 180.2 kg of phenol were converted to DPC. Given that phenol conversion was ~ 100%, the remaining two thirds of carbon necessarily resided in intermediates (notably phenyl methyl carbonate, PMC) and by-products rather than in DPC. Post-run inspection confirmed residual PMC and solid high-boiling deposits in the reactor and lines. Recovering these hold-ups for further conversion to DPC or dissolution/rework should raise the overall yield. The collected DPC during operation was 55.3 kg; adding an estimated 10.5 kg of in-equipment DPC hold-up gives a total of 65.8 kg. Throughout continuous operation, process conditions and performance were stable. The reactor temperature held at 195–198°C, and the reactor pressure, initially 7–8 bar, declined toward ~ 4 bar as methanol stripping became more effective—consistent with reduced MeOH accumulation and a more favorable equilibrium. The distillation column maintained ~ 140°C at the top and ~ 218°C at the bottom, ensuring steady removal of MeOH and partial phenol with recycle. No significant changes in the physical state of the catalyst were observed, and no bed plugging or abnormal pressure drop occurred. However, a thin film of polymeric, high-boiling residue was found on catalyst surfaces after shutdown, likely arising from side-reaction polymerization of phenol/intermediates. This suggests that periodic washing/regeneration or catalyst replacement cycles may be required for extended commercial operation; accordingly, scheduled maintenance should be planned for long campaigns. 3.6 DPC Product analysis and properties Gas-chromatographic analysis of the pilot-produced DPC showed DPC as the dominant component, with no residual DMC detected. This indicates that the distillation stage removed DMC essentially completely and, together with the near-quantitative phenol conversion, that the reaction proceeded efficiently. Aside from peaks attributable to the extraction solvent (e.g., THF), no distinct impurity peaks were observed, confirming the high quality of the DPC product. Note that intermediate PMC and poly-phenolic high-boiling species were found as solid residues adhering to catalyst surfaces rather than in the product; while they do not contaminate the product, they can contribute to catalyst poisoning and shortened lifetime. For commercialization, mitigation strategies to reduce catalyst deactivation—such as surface coatings or appropriate additives—are recommended. The DPC produced here meets polymer-grade requirements. Trial polymerization with bisphenol-A (BPA) yielded polycarbonate with a relative viscosity ≥ 0.5, comparable to materials derived from commercial (phosgene-route) DPC, thereby demonstrating the practical suitability of the present DPC for polycarbonate synthesis. 4. Conclusions This study designed, constructed, and long-run tested an integrated continuous DMC–DPC pilot as a CCU pathway converting CO₂ into value-added carbonate esters. In the DMC train, urea (CO₂-derived) and methanol were reacted over a Zr-based catalyst to produce 570.5 kg over 211 h, achieving an overall yield of 85.9% relative to the 663.9 kg theoretical maximum from 442.3 kg urea. The product met the target purity (~ 99.9%) and delivered electrolyte performance on par with commercial battery-grade DMC. In the DPC train, phenol–DMC transesterification was implemented as a reactor–distillation sequence enabling in-situ methanol removal; over ~ 200 h of continuous operation, ~ 100% phenol conversion was maintained and 65.8 kg of DPC were collected (32.1% of the 204.98 kg theoretical). Across both trains, process conditions were stable, separations reproducible, and material balances well controlled, yielding spec-compliant products (battery-grade DMC, polymer-grade DPC). Future work will prioritize DPC yield intensification, focusing on stronger MeOH-removal driving forces, additional reaction stages (notably PMC → DPC conversion), and tighter reaction–separation integration. On the catalyst side, migration toward non-toxic metal or solid-acid systems and mitigation of deactivation are key. For the DMC train, NH₃ by-gas handling/valorization and catalyst life extension are identified as important tasks. In the medium term, integrating the present trains with polycarbonate production to realize a fully non-phosgene CO₂ → DMC → DPC → PC chain is expected to advance practical CO₂ valorization in sustainable chemical manufacturing. Declarations Author Contribution Writing – original draft: N. SonInvestigation: S. Jung; (Battery investigation: J. C. Yun, S. H. Lee)Writing – review & editing: N.Son, J. Kim (with input from J. C. Yun, S. H. 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Marković J.P., Milonjić S.K.: Synthesis of zirconia colloidal dispersions by forced hydrolysis, J. Serb. Chem. Soc., 71(6), 613–619 (2006). Wang D., Zhang X., Gao Y., Xiao F., Wei W., Sun Y.: Synthesis of dimethyl carbonate from methyl carbamate and methanol over lanthanum compounds, Fuel Process. Technol., 91(9), 1081–1086 (2010). Fitriyano G., Sari F.: Mini review: Study of the synthesis of dimethyl carbonate and methyl carbamate through urea methanolysis route, AIP Conf. Proc., 2702, 070009 (2023). Contreras-Zarazúa G., Vázquez-Castillo J.A., Ramírez-Márquez C., Pontis G.A., Segovia-Hernández J.G., Alcántara-Ávila J.R.: Comparison of intensified reactive distillation configurations for the synthesis of diphenyl carbonate, Energy, 135, 637–649 (2017). Cao M., Meng Y., Lu Y.: Synthesis of diphenyl carbonate from dimethyl carbonate and phenol using O₂-promoted PbO/MgO catalysts, Catal. Commun., 6(12), 802–807 (2005). Yin X., Zeng Y., Yao J., Du Z., Zhang Hua, Sun T., Wang G.: Intrinsic reaction kinetics and mechanism for the reverse disproportionation reaction to methyl phenyl carbonate, Chem. Eng. Sci., 199, 478–485 (2019). Scheme 1 Scheme 1 is available in the Supplementary Files section. Table 1 Table 1 is not available with this version. Additional Declarations No competing interests reported. Supplementary Files sc1.png Scheme 1. Schematic of the continuous DMC reactor Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 17 Nov, 2025 Reviewers agreed at journal 11 Nov, 2025 Reviews received at journal 10 Nov, 2025 Reviewers agreed at journal 10 Nov, 2025 Reviewers invited by journal 10 Nov, 2025 Editor assigned by journal 05 Nov, 2025 Submission checks completed at journal 05 Nov, 2025 First submitted to journal 02 Nov, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8011647","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":546583886,"identity":"334ded96-efa6-484a-832e-ef3b7dafd1cf","order_by":0,"name":"Namgyu 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1","display":"","copyAsset":false,"role":"figure","size":166788,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of hydrated zirconyl nitrate precursors as a function of pre-treatment (drying) time: (a) Strem Co. ZrO(NO₃)₂·xH₂O, (b) Thermo Fisher ZrO(NO₃)₂·xH₂O, (c) Alfa Aesar ZrO(NO₃)₂·xH₂O.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8011647/v1/fff0bed1094026ab136714d6.png"},{"id":96426123,"identity":"81f12a80-bd56-4f42-9b65-5435f67759b9","added_by":"auto","created_at":"2025-11-21 02:28:44","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":127948,"visible":true,"origin":"","legend":"\u003cp\u003eDMC conversion yield as a function of pre-treatment (drying) time and catalyst source.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8011647/v1/8dadc2dc62de854159d70705.png"},{"id":96426121,"identity":"f362ca33-7192-415b-a09f-d36593a33006","added_by":"auto","created_at":"2025-11-21 02:28:44","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":52132,"visible":true,"origin":"","legend":"\u003cp\u003eCoulombic efficiency vs. cycle number for coin cells using commercial DMC (Reference) and pilot-produced DMC (This work).\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8011647/v1/2b544071f17bd8a52eaf7911.png"},{"id":96426125,"identity":"3fcd4511-95a8-4466-9a4d-08c444c6aef2","added_by":"auto","created_at":"2025-11-21 02:28:44","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":13397,"visible":true,"origin":"","legend":"\u003cp\u003eContinuous DMC operation—production rate (left, kg) and feed flow (right, L·h⁻¹).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8011647/v1/d9b49f04ab8e74215a165ba7.png"},{"id":96457001,"identity":"c4a68a6c-75d6-49f7-bae4-a516c96b77d0","added_by":"auto","created_at":"2025-11-21 10:09:01","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":936942,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8011647/v1/30cd05f5-ee37-4d87-ab8a-5898093757b8.pdf"},{"id":96426122,"identity":"4a67adc9-b380-44c5-b34b-7645f81e6bb6","added_by":"auto","created_at":"2025-11-21 02:28:44","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":237299,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 1\u003c/strong\u003e. Schematic of the continuous DMC reactor\u003c/p\u003e","description":"","filename":"sc1.png","url":"https://assets-eu.researchsquare.com/files/rs-8011647/v1/334a617516f570791f6ba90a.png"}],"financialInterests":"No competing interests reported.","formattedTitle":"CO₂-to-Carbonates via Reaction–Separation Coupling: Pilot Performance of Continuous DMC/DPC","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eMitigating CO₂ emissions from energy and hard-to-abate industrial sectors has intensified interest in carbon capture and utilization (CCU), which upgrades captured CO₂ into value-added chemicals [1\u0026ndash;3]. For cement, steel, and petrochemicals\u0026mdash;where process emissions are largely unavoidable\u0026mdash;CCU remains one of the few scalable pathways for deep reduction [4\u0026ndash;10]. Within this context, establishing robust routes that convert CO₂ into high-value molecules is central to carbon neutrality and greener process design. We focus on two strategic carbonate esters, dimethyl carbonate (DMC) and diphenyl carbonate (DPC). DMC (C₃H₆O₃) combines low toxicity and biodegradability with excellent solvency, making it a versatile platform used in lithium-ion battery electrolytes, coatings, pharmaceuticals/agrochemicals, and fuel additives [10\u0026ndash;16]; demand for battery-grade DMC is rising in step with electrification trends [17]. DMC is also a key intermediate in non-phosgene polycarbonate (PC) synthesis [18]. Industrial DMC routes\u0026mdash;direct CO₂\u0026ndash;MeOH with dehydrants, cyclic-carbonate intermediates, and urea\u0026ndash;MeOH methanolysis\u0026mdash;share a common requirement: effective removal of by-products (H₂O, NH₃) to overcome equilibrium constraints and achieve industrial practicality [19\u0026ndash;22].\u003c/p\u003e\u003cp\u003eDPC, the canonical carbonate donor for BPA-based PC, underpins non-phosgene PC manufacture that avoids phosgene toxicity and chlorinated wastes [23\u0026ndash;25]. In the prevalent DMC\u0026ndash;phenol transesterification route, however, methanol formation imposes a strong thermodynamic limitation on conversion and selectivity; hence multi-stage reaction/separation, in-situ MeOH removal, and catalysts with durable activity/selectivity/stability remain essential [26\u0026ndash;27]. Despite decades of work on homogeneous and heterogeneous catalysts, challenges persist\u0026mdash;low equilibrium conversions, catalyst deactivation, and retention of intermediates/high-boiling fractions\u0026mdash;which motivate process intensification, including reactive distillation and membrane-based or gas-phase MeOH removal [28\u0026ndash;30]. Much of the literature centers on lab- or bench-scale batch tests or single-unit optimization; by contrast, there are comparatively few pilot-scale continuous demonstrations reporting long-run operation (\u0026gt;\u0026thinsp;100\u0026ndash;200 h) with closed material balances and spec-compliant product qualities (battery-grade or polymer-grade) [31\u0026ndash;33]. For DMC, evidence indicates that specific hydrated zirconyl nitrate\u0026ndash;hydroxide phases govern activity, yet systematic links between precursor phase (supplier/lot), drying history, and performance remain under-reported. For DPC, the roles of MeOH removal intensity, suppression of phenyl methyl carbonate (PMC) accumulation, and management of high-boiling hold-ups are recognized, but the quantitative effects of coupled reactor\u0026ndash;distillation design and operating strategy (reflux, top/bottom temperatures, pressure step-downs) over extended continuous runs require more field-scale data [34]. Against this backdrop, the present work develops and operates integrated pilot plants for continuous DMC and DPC production, seeking to (i) elucidate the Zr-precursor phase\u0026ndash;drying\u0026ndash;performance relationship and demonstrate sustained throughput, yield, quality (water/purity), and stability for \u0026gt;\u0026thinsp;200 h in a urea\u0026ndash;MeOH DMC train, and (ii) verify that reactor\u0026ndash;distillation coupling with in-situ MeOH removal can relax equilibrium limits in the DMC\u0026ndash;phenol route to DPC and deliver reproducible conversion, yield, and product quality over ~\u0026thinsp;200 h of continuous operation [35]. We further diagnose overall yield losses mechanistically, attributing them to PMC/high-boiler hold-ups [36], and from these analyses derive actionable yield levers\u0026mdash;enhanced MeOH removal, additional reaction stages targeting PMC \u0026rarr; DPC conversion, tighter reaction\u0026ndash;separation integration, and reduced catalyst toxicity for long-run operability [37, 38]. By providing pilot-scale, long-duration evidence for an integrated CO₂ \u0026rarr; DMC \u0026rarr; DPC platform\u0026mdash;together with stable T/P profiles, controlled reflux and column ΔP, and material-balance closure within \u0026plusmn;\u0026thinsp;5%\u0026mdash;this study supplies the practical data needed to guide scale-up toward a fully non-phosgene carbonate chain and sets the stage for NH₃ valorization.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Materials and catalyst preparation\u003c/h2\u003e\u003cp\u003eUrea (\u0026ge;\u0026thinsp;99 wt%, industrial grade, SAMCHUN, Korea) and anhydrous methanol (\u0026ge;\u0026thinsp;99.9 wt%, SAMCHUN, Korea) were used as received, with methanol further polished to H₂O\u0026thinsp;\u0026le;\u0026thinsp;50 ppm (Karl Fischer coulometry) prior to use. Zirconium precursor and additives. Zirconyl nitrate hydrates, ZrO(NO₃)₂\u0026middot;xH₂O, were procured from Thermo Fisher, STREM, and Alfa Aesar (lot information to be recorded in the SI). Choline chloride (\u0026ge;\u0026thinsp;99%, SAMCHUN, Korea) was employed as the ionic-liquid medium. Synthesis of the Zr-based catalyst precursor. Following a literature-adapted protocol [39, 40], 5.0 L of choline chloride was charged to a jacketed glass reactor and heated with stirring. ZrO(NO₃)₂\u0026middot;xH₂O (1.00 kg) was introduced portionwise, after which methanol (3.0 L) was added and the mixture was stirred until homogeneous. The slurry was held at 120\u0026deg;C for 1 h to partially remove solvent, then ramped to 180\u0026deg;C and maintained for 36 h. Under these conditions, the zirconium precursor undergoes hydrolysis\u0026ndash;condensation, yielding an active catalyst precursor gel. The gel was filtered, thoroughly washed with methanol to remove soluble by-products, and oven-dried at 105\u0026deg;C to constant mass. The dried precursor was stored as a free-flowing powder in sealed containers under dry nitrogen until use.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Pilot plant and operating conditions \u0026mdash; DMC\u003c/h2\u003e\u003cp\u003eThe DMC continuous-production pilot was sized for a design throughput of ~\u0026thinsp;5 kg DMC\u0026middot;day⁻\u0026sup1;. The reaction section comprised two jacketed, corrosion-resistant stirred packed reactors in series. Stage-1 effected urea methanolysis to methyl carbamate (MC), and Stage-2 completed MC decomposition/transesterification to DMC\u0026thinsp;+\u0026thinsp;NH₃. Catalyst charge and internals. Each reactor was loaded with 200 g of the dried Zr-based catalyst precursor (powder form) contained within a perforated hold-down assembly to prevent carryover. Gas disengagement space and a top off-gas outlet were provided to vent NH₃ continuously while minimizing liquid entrainment. Operating window and control. Reactors were maintained at 180\u0026ndash;190\u0026deg;C with cascade temperature control. To suppress methanol vaporization and stabilize liquid-phase kinetics, the system operated under 3\u0026ndash;5 bar total pressure using a back-pressure regulator. Feed urea (melt, ~\u0026thinsp;133\u0026deg;C) and polished methanol (H₂O\u0026thinsp;\u0026le;\u0026thinsp;50 ppm) were metered independently to set the target residence time/WHSV (values summarized in Table\u0026nbsp;1). Agitation was adjusted to avoid channeling while limiting shear of the packed catalyst layer.\u003c/p\u003e\u003cp\u003eEffluent handling and purification. The combined reactor effluent consisted of NH₃-rich off-gas and a liquid phase containing DMC, MeOH, and minor by-products. Off-gas was routed to a scrubbed vent. The liquid stream was directed to a multi-stage distillation for separation and polishing: the first column removed light ends (NH₃/MeOH-rich overhead) with DMC recovery, the second column split DMC from high-boiling residues, and the final column produced spec-grade DMC (target purity\u0026thinsp;\u0026ge;\u0026thinsp;99.9%, water\u0026thinsp;\u0026le;\u0026thinsp;10 ppm). Column operating set-points (top/bottom temperatures, reflux ratios, ΔP) are listed in Table\u0026nbsp;1; overhead condensers were used on each column to minimize DMC loss[41].\u003c/p\u003e\u003cp\u003eMonitoring and data logging. Reactor T/P, feed rates, column top/bottom temperatures, reflux ratios, and pressure drops were trended at 1-min intervals. Routine material-balance closure within \u0026plusmn;\u0026thinsp;5% was maintained over steady operation. Safety interlocks covered over-pressure, heater runaway, and off-gas line blockage[42].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Pilot plant and operating conditions \u0026mdash; DPC\u003c/h2\u003e\u003cp\u003eScale and process concept. The continuous DPC pilot was designed for a nominal throughput of ~\u0026thinsp;10 kg DPC\u0026middot;day⁻\u0026sup1;. Because the DMC\u0026ndash;phenol transesterification is strongly limited by the concentration of the by-product methanol (MeOH), the unit employed a coupled reactor\u0026ndash;distillation flowsheet to remove MeOH in situ and shift the equilibrium. Feed and reactor operation. A liquid blend of DMC:phenol\u0026thinsp;\u0026asymp;\u0026thinsp;1:1.2 (mol) was continuously metered to a pressure-rated stirred reactor packed with a fixed bed of PbO solid catalyst retained by an internal screen to prevent carryover. The reactor was maintained at 195\u0026ndash;200\u0026deg;C and ~\u0026thinsp;4 bar. Under these conditions, MeOH generated in the first transesterification step preferentially partitioned to the gas phase and was disengaged via the top off-gas line, while the reaction mixture flowed to the downstream separation[43].\u003c/p\u003e\u003cp\u003eReactive separation and recycle. The reactor effluent entered a pressure step-down to about 1 bar and was fed to the distillation column operated at ~\u0026thinsp;140\u0026deg;C (top) and ~\u0026thinsp;218\u0026deg;C (bottom). Overheads removed MeOH together with a small fraction of phenol; MeOH was condensed and purged, whereas recovered phenol was returned to the reactor feed (liquid recycle). The bottoms comprised DPC-rich liquid with minor high-boiling residues; this stream was cooled and passed through a guard filter before product collection. Catalyst containment and integrity. The PbO bed was immobilized within a perforated hold-down assembly and protected by internal filtration screens to avoid fines entrainment. No bed plugging was observed during steady operation[44].\u003c/p\u003e\u003cp\u003eControl, monitoring, and analytics. Reactor temperature/pressure, column top/bottom temperatures, reflux ratio, and column ΔP were monitored continuously and trended at 1-min intervals. Periodic grab samples from the reactor outlet bottoms were analyzed by GC to quantify DPC content and residual phenol; overheads were checked for MeOH and phenol slip. Operating targets were chosen to maintain a high conversion in the first step (phenol\u0026thinsp;+\u0026thinsp;DMC \u0026rarr; PMC\u0026thinsp;+\u0026thinsp;MeOH) and to promote the second step (PMC\u0026thinsp;+\u0026thinsp;phenol \u0026rarr; DPC\u0026thinsp;+\u0026thinsp;MeOH) via continual MeOH removal, thereby increasing overall DPC yied[45].\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Product analysis\u003c/h2\u003e\u003cp\u003eProduct analyses were performed by gas chromatography using an Agilent GC-8790A equipped with thermal conductivity (TCD) and flame ionization (FID) detectors; Carboxen\u0026reg; 1000 and Molsieve 5A columns were employed to confirm the presence of DMC, DPC, and other impurities. Catalyst characterization was conducted by X-ray diffraction on a Rigaku SmartLab SE using Cu Kα radiation (9 kW, 45 kV, 200 mA).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5 Battery evaluation of DMC\u003c/h2\u003e\u003cp\u003eTo benchmark the pilot-produced DMC against a commercial product, R2032 coin cells were assembled with NCM811 cathodes and graphite anodes (mixture of artificial and natural graphite). The electrolyte formulation was 1.2 M LiPF₆ in EC/EMC/DMC (20/40/40, vol/vol/vol) with 1.5% vinylene carbonate (VC) and 1.0% lithium difluorophosphate (LDFP). Charge\u0026ndash;discharge cycling was performed between 2.5\u0026ndash;4.2 V at a 1C rate for 400 cycles. All tests were conducted in a sealed isothermal chamber at 45\u0026deg;C.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Result \u0026 Discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Zr-Based Catalysts for Urea\u0026ndash;Methanol DMC Synthesis\u003c/h2\u003e\u003cp\u003eX-ray diffraction (XRD) patterns of the zirconium nitrate\u0026ndash;based precursors from three suppliers (Strem, Alfa Aesar, Thermo Scientific) after identical drying show supplier-dependent phase evolution (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Upon \u0026ge;\u0026thinsp;2 h drying, both the Strem and Alfa Aesar precursors converged to similar diffraction profiles dominated by a broad amorphous halo assignable to poorly crystalline Zr(OH)₂(NO₃)₂\u0026middot;1.3H₂O, with only weak residual features. By contrast, the Thermo Scientific precursor exhibited, already at the early drying stage, distinct reflections attributable to a more highly hydrated phase (e.g., Zr(OH)₂(NO₃)₂\u0026middot;4.7H₂O), and traces of this hydrate persisted after 2 h drying, indicating incomplete de-hydration/rearrangement relative to the other two materials.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThese structural differences translated directly to catalytic performance in batch DMC synthesis under identical conditions. The 2 h-dried Thermo catalyst delivered a DMC conversion/yield of ~\u0026thinsp;52%, whereas the 2 h-dried Alfa Aesar catalyst achieved\u0026thinsp;~\u0026thinsp;85% conversion, closely matching the commercial Strem benchmark (87.8%). The higher activity of Strem and Alfa Aesar correlates with the amorphous, poorly crystalline Zr\u0026ndash;OH/NO₃ network formed after drying, which is expected to provide a higher density of accessible Lewis/weak Br\u0026oslash;nsted sites. In contrast, the persistence of a highly hydrated nitrate\u0026ndash;hydroxide phase in the Thermo precursor is consistent with a lower fraction of catalytically competent sites after the same drying period, together with a greater propensity to introduce residual water into the reaction environment\u0026mdash;both factors detracting from DMC formation(Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eOverall, the data establish a clear structure\u0026ndash;performance relationship: precursors that evolve to an amorphous Zr(OH)₂(NO₃)₂\u0026middot;1.3H₂O\u0026ndash;like state under the specified drying protocol yield superior DMC conversion, while retention of a more highly hydrated crystalline hydrate is associated with depressed activity. These results underscore the sensitivity of DMC synthesis to the hydration state and short-range order of zirconium nitrate precursors and justify controlling precursor drying to reproducibly access the high-activity amorphous phase.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Process Stability and Product Quality in Continuous DMC Operation\u003c/h2\u003e\u003cp\u003eThe continuous-production pilot was validated over three campaigns. Campaign-1 (42 h) and Campaign-2 (18 h) focused on start-up stabilization and operating-window optimization, while Campaign-3 implemented an extended 150 h continuous run. The DMC quantities produced in each campaign were 113.1 kg, 51.5 kg, and 405.9 kg, respectively, for a total of 570.5 kg over 211 h (average productivity 2.70 kg\u0026middot;h⁻\u0026sup1;; 2.69, 2.86, and 2.71 kg\u0026middot;h⁻\u0026sup1; for Campaigns 1\u0026ndash;3). Based on 442.3 kg of urea feed corresponding to a theoretical maximum of 663.9 kg DMC at 100% conversion, the overall yield of the continuous process was 85.9%. Throughout continuous operation, reaction and separation conditions remained essentially constant. The reactor temperature was stably maintained at \u0026asymp;\u0026thinsp;190\u0026deg;C (189\u0026ndash;191\u0026deg;C), and the system pressure within 3\u0026ndash;5 bar. As summarized in Table\u0026nbsp;1, column top temperatures were controlled in the 60\u0026ndash;140\u0026deg;C range to efficiently remove methanol (MeOH), dissolved ammonia (NH₃), and light ends, while bottom temperatures of 180\u0026ndash;220\u0026deg;C consistently effected the split between the DMC-rich fraction and high-boiling residues (polymeric species, etc.). Reflux ratios and column pressure drops (ΔP) stayed within target bounds, and the material balance closure was maintained within \u0026plusmn;\u0026thinsp;5%. These indicators collectively demonstrate that the Zr-based catalyst sustained stable activity without measurable physical loss or deactivation over the entire campaign set, and that the integrated reaction\u0026ndash;separation stage achieved long-term operability with consistent product quality.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Physicochemical Purity and Cell Performance of Pilot DMC in Comparison with Commercial Grade\u003c/h2\u003e\u003cp\u003eGas-chromatographic analysis of the pilot-produced DMC confirmed 99.93% purity, indicating a high-purity product. Minor impurities consisted of trace methanol and trace high-boiling residues (e.g., polymeric/heavy ends). The water content was 30\u0026ndash;50 ppm, close to the battery-electrolyte solvent specification (\u0026lt;\u0026thinsp;20 ppm); this residual moisture can be readily reduced below specification by routine post-treatment drying during storage/polishing. Color (APHA/Pt\u0026ndash;Co) was 1.0 for the pilot DMC versus 1.8 for the commercial comparator, indicating equivalent or better optical quality for the pilot product. Electrochemical benchmarking showed no statistically significant differences versus commercial battery-grade DMC: charge\u0026ndash;discharge cycling behavior, internal resistance/impedance, and initial Coulombic efficiency were all comparable. After long-term cycling, capacity retention was 85.1% for the pilot DMC and 84.9% for the commercial DMC (1C, 2.5\u0026ndash;4.2 V, 45\u0026deg;C, 400 cycles)(Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.), confirming no meaningful performance gap. Collectively, these results verify that the DMC produced by the present process is suitable for use as an electrolyte solvent in lithium-ion batteries.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.4 Batch pre-evaluation prior to the DPC pilot\u003c/h2\u003e\u003cp\u003ePrior to the DPC pilot run, we conducted lab-scale batch experiments to assess the reaction mechanism and catalyst performance. A 1:1 molar mixture of phenol and DMC was reacted at 200\u0026deg;C for 24 h in the presence of PbO. The phenol conversion reached\u0026thinsp;~\u0026thinsp;45%, but phenyl methyl carbonate (PMC) remained as a major product alongside DPC, resulting in a DPC selectivity below 50%. This outcome reflects an equilibrium limitation: the reaction proceeds readily through the first transesterification step (phenol\u0026thinsp;+\u0026thinsp;DMC \u0026rarr; PMC\u0026thinsp;+\u0026thinsp;MeOH), whereas the second step (PMC\u0026thinsp;+\u0026thinsp;phenol \u0026rarr; DPC\u0026thinsp;+\u0026thinsp;MeOH) remains reversible and less favorable under these conditions. Guided by this, we introduced timely removal of methanol to drive the equilibrium forward. Using a reflux configuration with continuous MeOH removal, a single-batch test achieved phenol conversion of 86% and DPC yield of ~\u0026thinsp;85%. Based on comparative screening of several transition-metal oxides and organometallic candidates, PbO exhibited relatively high DPC selectivity and good catalyst longevity, and was therefore adopted for the pilot.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e3.5 DPC pilot continuous operation\u003c/h2\u003e\u003cp\u003eThe DPC continuous-production pilot was operated for ~\u0026thinsp;180 h to verify performance. During this period, 180.2 kg of phenol and [DMC feed: to be inserted] kg were charged. The first\u0026thinsp;~\u0026thinsp;20 h were devoted to process stabilization, after which\u0026thinsp;~\u0026thinsp;180 h of steady continuous production ensued. Periodic sampling from the reactor outlet and the distillation bottoms showed that phenol conversion was nearly quantitative (~\u0026thinsp;100%) from the onset of steady operation through shutdown, consistent with feeding phenol as the limiting reactant and real-time removal of MeOH shifting the equilibrium toward DPC formation. The final DPC yield was 32.1%, i.e., roughly one third of the theoretical 204.98 kg obtainable if all 180.2 kg of phenol were converted to DPC. Given that phenol conversion was ~\u0026thinsp;100%, the remaining two thirds of carbon necessarily resided in intermediates (notably phenyl methyl carbonate, PMC) and by-products rather than in DPC. Post-run inspection confirmed residual PMC and solid high-boiling deposits in the reactor and lines. Recovering these hold-ups for further conversion to DPC or dissolution/rework should raise the overall yield. The collected DPC during operation was 55.3 kg; adding an estimated 10.5 kg of in-equipment DPC hold-up gives a total of 65.8 kg.\u003c/p\u003e\u003cp\u003eThroughout continuous operation, process conditions and performance were stable. The reactor temperature held at 195\u0026ndash;198\u0026deg;C, and the reactor pressure, initially 7\u0026ndash;8 bar, declined toward ~\u0026thinsp;4 bar as methanol stripping became more effective\u0026mdash;consistent with reduced MeOH accumulation and a more favorable equilibrium. The distillation column maintained\u0026thinsp;~\u0026thinsp;140\u0026deg;C at the top and ~\u0026thinsp;218\u0026deg;C at the bottom, ensuring steady removal of MeOH and partial phenol with recycle. No significant changes in the physical state of the catalyst were observed, and no bed plugging or abnormal pressure drop occurred. However, a thin film of polymeric, high-boiling residue was found on catalyst surfaces after shutdown, likely arising from side-reaction polymerization of phenol/intermediates. This suggests that periodic washing/regeneration or catalyst replacement cycles may be required for extended commercial operation; accordingly, scheduled maintenance should be planned for long campaigns.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003e3.6 DPC Product analysis and properties\u003c/h2\u003e\u003cp\u003eGas-chromatographic analysis of the pilot-produced DPC showed DPC as the dominant component, with no residual DMC detected. This indicates that the distillation stage removed DMC essentially completely and, together with the near-quantitative phenol conversion, that the reaction proceeded efficiently. Aside from peaks attributable to the extraction solvent (e.g., THF), no distinct impurity peaks were observed, confirming the high quality of the DPC product.\u003c/p\u003e\u003cp\u003eNote that intermediate PMC and poly-phenolic high-boiling species were found as solid residues adhering to catalyst surfaces rather than in the product; while they do not contaminate the product, they can contribute to catalyst poisoning and shortened lifetime. For commercialization, mitigation strategies to reduce catalyst deactivation\u0026mdash;such as surface coatings or appropriate additives\u0026mdash;are recommended.\u003c/p\u003e\u003cp\u003eThe DPC produced here meets polymer-grade requirements. Trial polymerization with bisphenol-A (BPA) yielded polycarbonate with a relative viscosity\u0026thinsp;\u0026ge;\u0026thinsp;0.5, comparable to materials derived from commercial (phosgene-route) DPC, thereby demonstrating the practical suitability of the present DPC for polycarbonate synthesis.\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThis study designed, constructed, and long-run tested an integrated continuous DMC\u0026ndash;DPC pilot as a CCU pathway converting CO₂ into value-added carbonate esters. In the DMC train, urea (CO₂-derived) and methanol were reacted over a Zr-based catalyst to produce 570.5 kg over 211 h, achieving an overall yield of 85.9% relative to the 663.9 kg theoretical maximum from 442.3 kg urea. The product met the target purity (~\u0026thinsp;99.9%) and delivered electrolyte performance on par with commercial battery-grade DMC. In the DPC train, phenol\u0026ndash;DMC transesterification was implemented as a reactor\u0026ndash;distillation sequence enabling in-situ methanol removal; over ~\u0026thinsp;200 h of continuous operation, ~\u0026thinsp;100% phenol conversion was maintained and 65.8 kg of DPC were collected (32.1% of the 204.98 kg theoretical). Across both trains, process conditions were stable, separations reproducible, and material balances well controlled, yielding spec-compliant products (battery-grade DMC, polymer-grade DPC). Future work will prioritize DPC yield intensification, focusing on stronger MeOH-removal driving forces, additional reaction stages (notably PMC \u0026rarr; DPC conversion), and tighter reaction\u0026ndash;separation integration. On the catalyst side, migration toward non-toxic metal or solid-acid systems and mitigation of deactivation are key. For the DMC train, NH₃ by-gas handling/valorization and catalyst life extension are identified as important tasks. In the medium term, integrating the present trains with polycarbonate production to realize a fully non-phosgene CO₂ \u0026rarr; DMC \u0026rarr; DPC \u0026rarr; PC chain is expected to advance practical CO₂ valorization in sustainable chemical manufacturing.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eWriting \u0026ndash; original draft: N. SonInvestigation: S. Jung; (Battery investigation: J. C. Yun, S. H. Lee)Writing \u0026ndash; review \u0026amp; editing: N.Son, J. Kim (with input from J. C. Yun, S. H. Lee)All authors: Final approval of the version to be published\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e\u003cp\u003eThis work was financially supported by the CCU Technology Development Program (20225A10100080) of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) funded by the Ministry of Trade, Industry and Energy, Republic of Korea.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003e McLaughlin H., Littlefield A.A., Menefee M., Kinzer A., Hull T., Sovacool B.K., Bazilian M.D., Kim J., Griffiths S.: Carbon capture utilization and storage in review: Sociotechnical implications for a carbon-reliant world, Renew. Sustain. Energy Rev., 177, 113215 (2023).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003e Nagireddi S., Agarwal J. R., Vedapuri D.: Carbon dioxide capture, utilization, and sequestration: Current status, challenges, and future prospects for global decarbonization, ACS Eng. 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Sci., 199, 478\u0026ndash;485 (2019).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Scheme 1","content":"\u003cp\u003eScheme 1 is available in the Supplementary Files section.\u003c/p\u003e"},{"header":"Table 1","content":"\u003cP\u003eTable 1 is not available with this version.\u003c/p\u003e\n"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"advances-in-industrial-and-engineering-chemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Advances in Industrial and Engineering Chemistry](https://link.springer.com/journal/44405)","snPcode":"44405","submissionUrl":"https://submission.springernature.com/new-submission/44405/3","title":"Advances in Industrial and Engineering Chemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Open","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"carbon capture and utilization, dimethyl carbonate, diphenyl carbonate, transesterification, continuous processing, pilot demonstration","lastPublishedDoi":"10.21203/rs.3.rs-8011647/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8011647/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study develops and demonstrates integrated pilot plants for the continuous production of dimethyl carbonate (DMC) and diphenyl carbonate (DPC) as part of a carbon capture and utilization (CCU) strategy. DMC was synthesized from urea (derived from CO₂ + NH₃) and methanol over a zirconium-based catalyst. Across three campaigns totaling 211 h, the unit produced 570.5 kg of DMC, corresponding to an overall yield of 85.9% relative to the 663.9 kg theoretical maximum from 442.3 kg of urea. The product reached 99.93% purity, and electrolyte testing showed no statistically significant differences versus commercial battery-grade DMC. DPC was obtained via transesterification of phenol with DMC using a reactor\u0026ndash;distillation configuration that enables in-situ removal of methanol. Over ~\u0026thinsp;200 h of continuous operation, phenol conversion was ~\u0026thinsp;100% and 65.8 kg of DPC were collected, equal to an overall yield of 32.1% versus the 204.98 kg theoretical limit. Yield shortfalls were attributed to hold-up of intermediates (e.g., phenyl methyl carbonate) and high-boiling residues within equipment. Both trains exhibited stable operability without catalyst bed plugging, and product specifications were consistently met. These results validate the technical feasibility of CCU-based carbonate ester production and identify clear levers\u0026mdash;enhanced methanol removal, additional reaction stages, and tighter reaction\u0026ndash;separation coupling\u0026mdash;for yield intensification and scale-up.\u003c/p\u003e","manuscriptTitle":"CO₂-to-Carbonates via Reaction–Separation Coupling: Pilot Performance of Continuous DMC/DPC","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-21 02:28:39","doi":"10.21203/rs.3.rs-8011647/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-11-18T00:13:15+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"166415423220306609913641877087152901927","date":"2025-11-11T14:07:04+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-11T03:16:56+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"93570230835210850244858045468519890657","date":"2025-11-11T03:14:57+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-11-11T01:03:42+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-11-05T07:52:19+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-11-05T07:51:53+00:00","index":"","fulltext":""},{"type":"submitted","content":"Advances in Industrial and Engineering Chemistry","date":"2025-11-02T14:34:27+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"advances-in-industrial-and-engineering-chemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Advances in Industrial and Engineering Chemistry](https://link.springer.com/journal/44405)","snPcode":"44405","submissionUrl":"https://submission.springernature.com/new-submission/44405/3","title":"Advances in Industrial and Engineering Chemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Open","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"9f0b37af-a927-46e9-9b55-2e610791d926","owner":[],"postedDate":"November 21st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-11-27T06:23:13+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-21 02:28:39","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8011647","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8011647","identity":"rs-8011647","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}