DMC Synthesis Research Articles

Experimental Verification of Low-Pressure Kinetics Model for Direct Synthesis of Dimethyl Carbonate Over CeO2 Catalyst

AbstractDimethyl carbonate (DMC) has emerged as a promising candidate for sustainable chemical processes due to its remarkable versatility and low toxicity. From a green chemistry perspective, the direct synthesis of DMC has been considered the most promising route, as water is the only byproduct generated in the reaction between CO2 and methanol. However, this synthetic route has faced significant thermodynamic limitations, even at elevated pressure conditions. Therefore, a two-part study explored low-pressure synthesis of DMC via the direct route, and a low-pressure kinetic model for the CeO2 catalyst was developed based on the results. Proposed Langmuir–Hinshelwood mechanisms were verified using experimental data generated in our labs. The investigation suggests that DMC formation in the direct synthetic route is a surface reaction of CO2 and methanol on the catalyst. The kinetic model predictions closely aligned with experimental data, demonstrating a 17% mean absolute percentage error and indicating a high level of predictability. Additionally, a rigorous assessment was conducted on CO2 fixations in DMC synthesis, quantifying CO2 capture and its conversion into stable or high-value products, formally designated as CO2 Fixation (CO2Fix). The CO2Fix analysis revealed that, at a conversion rate of 27%, the process can achieve a "net zero" state when operated at an approximate pressure of 30 bar, thereby supporting the viability of low-pressure synthesis. Increasing the conversion rate to levels exceeding 95% significantly enhances the CO2Fix metric, potentially surpassing 3.5 or higher.

Diversification of product-derived ionic liquids and application in DMC synthesis without introducing any impurities

Various strongly basic ionic liquids with distinctive structures, including single and double ended quaternary ammonium and phosphorus salts, were first synthesized based on hydroxyethoxy anion (HOCH2CH2O–) from the product ethylene glycol. Nature was characterized by NMR, FTIR, TG and acid-base titration. Its alkali strength was equivalent to that of sodium methoxide, demonstrating superior alkalinity. Influences of cation structures and C1-C4 alcohols structures on transesterification efficiency were investigated. Under mild conditions (68 °C for 5 min), DMC yield was 42.8% with a TOF value of 2853.6 h−1 when [TBAB]OCH2CH2OH as catalyst with only 0.18% EC molar content, indicating good catalytic performance. Comparison was made for reaction results between the synthesized catalysts and reported catalysts in literatures. The reaction mechanism was further deduced. Activation energies of positive and reverse reactions were determined as Ea+=32.0 kJ·mol−1 and Ea-=15.3 kJ·mol−1 through kinetics calculation. Relying on its decomposability and recyclability of decomposition products, a new catalyst circulation process without introducing any impurities was proposed and verified.

Green Synthesis of Dimethyl Carbonate from CO2 and Methanol: New Strategies and Industrial Perspective

AbstractDimethyl carbonate (DMC) is a commonly used and environmentally sustainable chemical compound and intermediate in a variety of industrial applications. To date, several large‐scale industrial DMC synthesis routes have been developed, including methanol phosgenation, transesterification, and oxidative carbonylation of methanol. However, these manufacturing routes have several disadvantages, such as the use of hypertoxic phosgene as raw material, costly processing, and explosion risks. The most encouraging and ecofriendly path is the green production of DMC from CO2 and methanol. Various catalytic materials have been examined concerning their suitability for DMC synthesis. The issues of low yield and difficulty in tests have not been resolved fundamentally, which is caused by the inherent problems of the synthetic pathway and limitations imposed by thermodynamics. The search for more efficient production routes has driven the activation of CO2 via electro‐assisted synthesis as well as membrane reactors, which can isolate products in real‐time to maximize DMC yield. The green synthesis of dimethyl carbonate catalyzed by different catalysts including Zr/Ce/Cu‐based nanocomposites, organometallic compounds, heteropoly acid, ionic liquid, metal‐organic frameworks, etc, is discussed in detail. Further, the structure–activity relationships and insights into molecular activation and catalytic mechanisms, as well as the identification of active sites on catalysts are addressed.

The confinement effects of ordered mesoporous carbon on copper nanoparticles for methanol oxidative carbonylation

The confinement of Cu nanoparticles in narrow mesopores strengthens the Cu–carbon interactions. This can promote the auto-reduction of CuO to form active Cu2O species, resulting in high activity and stability during DMC synthesis.

CoZn-ZIF-derived carbon-supported Cu catalyst for methanol oxidative carbonylation to dimethyl carbonate

Carbon materials derived from CoZn-ZIFs were used to load Cu catalysts and were applied for DMC synthesis, and the effects of the graphitization degree and the (N1 + N3)/N2 ratio were studied.

La2O3 nanorods - reduced graphene oxide composite as a novel catalyst for dimethyl carbonate production via transesterification route

A highly efficient G/La heterogeneous catalyst comprising of reduced graphene oxide (rGO) and lanthanum oxide (La2O3) was developed using the in-situ hydrothermal technique. Four different catalyst samples with graphene content of 0.2, 0.5, 1.0, and 2.0 were prepared and tested against dimethyl carbonate synthesis (DMC) synthesis using the transesterification method. Structural analysis by scanning electron microscopy revealed that La2O3 displayed nanorod morphology. DMC synthesis results showed that G/La-3 composite with 1% graphene content outperformed others and showed the highest DMC yield of ~84% at 180 ºC. The excellent performance of G/La-3 was attributed to the synergistic effect of 2-D rGO and 1-D La2O3 nanorods, which showed the highest surface area of 76.54 m2/g. Moreover, the existence of acidic and basic active sites as identified by the temperature-programmed desorption (TPD) technique facilitates DMC production over the surface of G/La-3 catalyst. Recyclability and reusability experiments showed a gradual decrease in DMC yield owing to catalyst deactivation. It is expected that the present work provides valuable visions of the applicability of graphene/rare earth metal oxide heterogeneous catalysts in the given or similar chemical transformation processes.

Dimethyl carbonate production via transesterification reaction using nitrogen functionalized graphene oxide nanosheets

Nitrogen-functionalized graphene oxide (GO) nanocatalysts were prepared using ammonia, methylamine, ethylamine, and hydrazine hydrate as a nitrogen source. Nanocatalysts samples were thoroughly characterized using XRD, Raman, FTIR, XPS, FESEM, TEM, and TGA techniques. Quantitative and qualitative analyses of surface acidic and basic sites were done by NH3- and CO2-TPD techniques. Nanocatalysts were further examined for DMC production via transesterification reaction of propylene carbonate (PC) with CH3OH. Quantitative analysis of nitrogen-containing functional groups in the prepared sample with respect to other functional moieties was performed. Among various nanocatalysts, ammonia functionalized GO (AGO) was found to be the best for DMC production. At optimized reaction conditions of temperature (180 °C), time (6 h), and catalyst dose (1 wt% with respect PC), the highest DMC yield of ∼50% was observed. Reusability studies using AGO nanocatalyst were conducted up to four consecutive test cycles to evaluate catalysts' potentiality towards DMC synthesis. Thus, N-functionalized GO is a useful metal-free nanocatalyst that could also be explored for other chemical processes.

Optimization of Catalytic Distillation for the Synthesis of Dimethyl Carbonate by Response Surface Methodology

AbstractDimethyl carbonate (DMC) was synthesized from methanol and ethylene carbonate (EC) in a reactive distillation column by transesterification using different composite oxide catalysts. The catalysts were characterized by XRD, N2 adsorption‐ desorption, CO2‐TPD, and NH3‐TPD. The results show that the Zr−Al catalyst has the most strong base sites and weak acid sites compared with other catalysts. The synergistic effect of acid‐base sites makes it show excellent catalytic performance for DMC synthesis. The operation parameters including reflux ratio, feed molar ratio, liquid hourly space velocity (LHSV) and catalyst dosage were optimized by factorial design based on response surface methodology (RSM). The best optimization conditions was: reflux ratio=5.23 : 1, feed molar ratio=6.05 : 1, LHSV=0.48 h−1, catalyst dosage=119.04 ml, the relative error between measured value and predicted value is small, which indicated that the reliability of the optimized process is high.

Role of metal co‐cations in improving CuY zeolite performance for DMC synthesis: A theoretical study

First principle calculations based on density functional theory are conducted to investigate the influence of metal cations including Mg2+, Ca2+, Sr2+, Ba2+, La (OH)2+ and Ce (OH)2+ in the small cage of zeolite on the electronic environment of adjacent active center, Cu+ in CuY zeolite as well as the process of CO insertion into CH3O to form CH3OCO for oxidative carbonylation of methanol. The study explains the theoretical reasons for the effects of metal cations on the catalytic activity of zeolites. It was found that, the presence of co‐cations in the small cage can affect the electronic properties and also the catalytic activity in two ways. Firstly, the presence of co‐cations, viz., Ca2+, Sr2+, Mg2+, Ba2+ and La species in small cage hinders the migration of active Cu+ cations from the super cage to small cage. Secondly, the co‐cations greatly affect the charge transfer from zeolite framework to Cu+ present in the adjacent super cage, leading to the increase of the net charge and binding energy of Cu+. The findings can improve the CO adsorption and insertion efficiencies, and the stability of transition states, which results in the enhanced catalytic activity of corresponding zeolites.

Review on the synthesis of dimethyl carbonate

Dimethyl carbonate (DMC, (CH3O)2CO), as an important and environmentally friendly chemical intermediate, has been widely used in industrial fields. Several large-scale industrial routes of DMC production, e.g., phosgene route, transesterification route, and the liquid-phase oxidative carbonylation of methanol, have been developed to date. Nevertheless, these industrial routes suffer from different drawbacks, such as the use of hypertoxic phosgene as raw material, high production cost, and explosion risk. Currently, vapor-phase methyl nitrite (MN) carbonylation to DMC, a route developed by the UBE Company, can be the most promising new-generation industrial route. This route exhibits many advantages, including environmental friendliness, low cost, and high efficiency. The key to industrialization is the development of an efficient and stable catalyst. Heterogeneous supported Pd-based catalysts have been widely investigated in this system. In this review, we provide detailed introduction regarding the existing DMC synthesis methods and the vapor-phase MN carbonylation to DMC route with related catalyst research progress. Opportunities and challenges for synthesizing DMC are also presented.

MgFeCe Ternary Layered Double Hydroxide as Highly Efficient and Recyclable Heterogeneous Base Catalyst for Synthesis of Dimethyl Carbonate by Transesterification

A series of Mg3:Fex + Ce1−x LDHs (3:1) were synthesized by co-precipitation method by varying molar ratio of Fe:Ce between 1:0 to 0:1 (LDH-1 to LDH-6). All synthesized LDHs were characterized by XRD, FT-IR, TEM, N2 sorption, benzoic acid titration and XPS in detail and evaluated for selective synthesis of dimethyl carbonate by transesterification of ethylene carbonate with methanol. It was demonstrated that the structural and basic properties of synthesized LDHs were strongly dependent on the Fe:Ce molar ratio (Ce concentration). The correlation between their physicochemical properties and catalytic performance was studied in detail. Among all synthesized LDHs the best result was obtained with LDH-3 (Fe:Ce = 0.85:0.15) where LDH structure remained intact, and showed high number of strong basic sites on LDH surface. LDH-3 was recycled 7 times while maintaining high catalyst activity and selectivity towards DMC. The obtained results elucidate the important role of Ce in modifying the basic properties of LDH in enhancing the catalytic activity for DMC synthesis.

Direct and generalized synthesis of carbon-based yolk–shell nanocomposites from metal-oleate precursor

This contribution describes the facile preparation of functional yolk–shell nanoparticles (YSNs) made up of different compositions confined within a hollow porous carbon shell (M@Carbon, M=multiple Cu, NiO nanoparticles or ZnO nanowires). These new yolk–shell hybrid materials have been successfully synthesized using metal-oleate complex and phenolic resin monomers as raw materials through a one-step co-pyrolysis method. A relevant characteristic of these yolk–shell composites is the excellent thermal stability. The Cu@Carbon nanospheres with diameters ranging from 330 to 390nm and cavity size ranging from 190 to 220nm can be controlled by varying synthetic parameters. Comprehensive characterizations reveal that Cu-oleate complex, benefiting from the oleate bilayer, serves as an organometallic precursor while simultaneously acting as a soft template for the formation process. The resultant Cu@Carbon nanocomposite exhibits a promising catalytic properties toward DMC synthesis via oxidative carbonylation of methanol. Taking such complex as precursor, a single-step synthetic fashion is expected to simplify the preparation of yolk–carbon shell nanostructure.

The effect of Si/Al ratios on the catalytic activity of CuY zeolites for DMC synthesis by oxidative carbonylation of methanol: a theoretical study

Cu-exchanged Y zeolites with different Si/Al ratios have been investigated using a density functional theory method in order to determine the effect of Si/Al ratios on the catalytic activity for producing DMC by the oxidative carbonylation of methanol. The stable structures and catalytic activity of the CuY zeolites with different Si/Al ratios are identified. In addition, CO adsorption and the effect of CH3O on CO adsorption, including the changes in the adsorption energy and stretching vibrational frequency for the adsorbed CO, are obtained. Our results indicate that the CuY zeolite with a Si/Al ratio = 6.5 has the highest catalytic activity for producing DMC by oxidative carbonylation of methanol among all the Si/Al ratios considered in this work, which is supported by the experimental facts. Finally, our results suggest that theoretical calculations can be used as a useful tool and provide good theoretical guidance for the experimental design of CuY zeolites.

Porous Diatomite‐Immobilized Cu–Ni Bimetallic Nanocatalysts for Direct Synthesis of Dimethyl Carbonate

A series of diatomite‐immobilized Cu–Ni bimetallic nanocatalysts was prepared under ultrasonication and evaluated for the direct synthesis of dimethyl carbonate under various conditions. Upon being fully characterized by TPR, TPD, BET, SEM, XRD, and XPS methodologies, it is found that the bimetallic composite is effectively alloyed and well immobilized inside or outside the pore of diatomite. Under the optimal conditions of 1.2 MPa and 120∘C, the prepared catalyst with loading of 15% exhibited the highest methanol conversion of 6.50% with DMC selectivity of 91.2% as well as more than 10‐hour lifetime. The possible reaction mechanism was proposed and discussed in detail. To our knowledge, this is the first report to use diatomite as a catalyst support for direct DMC synthesis from methanol and CO2.

Adsorption and dissociation of O 2 on CuCl(1 1 1) surface: A density functional theory study

The adsorption and dissociation of O 2 on CuCl(1 1 1) surface have been systematically studied by the density functional theory (DFT) slab calculations. Different kinds of possible modes of atomic O and molecular O 2 adsorbed on CuCl(1 1 1) surface and possible dissociation pathways are identified, and the optimized geometry, adsorption energy, vibrational frequency and Mulliken charge are obtained. The calculated results show that the favorable adsorption occurs at hollow site for O atom, and molecular O 2 lying flatly on the surface with one O atom binding with top Cu atom is the most stable adsorption configuration. The O–O stretching vibrational frequencies are significantly red-shifted, and the charges transferred from CuCl to oxygen. Upon O 2 adsorption, the oxygen species adsorbed on CuCl(1 1 1) surface mainly shows the characteristic of the superoxo (O 2 −), which primarily contributes to improving the catalytic activity of CuCl, meanwhile, a small quantity of O 2 dissociation into atomic O also occur, which need to overcome very large activation barrier. Our results can provide some microscopic information for the catalytic mechanism of DMC synthesis over CuCl catalyst from oxidative carbonylation of methanol.

Direct Synthesis of DMC from CO<sub>2</sub> and CH<sub>3</sub>OH over Ce<sub>x</sub>Zr <sub>1-x-0.1</sub>Y <sub>0.1</sub> O<sub>2</sub> Catalysts

The solid solution series CexZr(1-x-0.1)Y0.1O2 with various x values was prepared by the citric acid sol-gel method, using cerium and zirconium nitrides as precursors, respectively.The characterization results of the XRD, N2 sorption measurements indicated that the physical properties of the solid solutions were significantly affected by the x values in CexZr(1-x-0.1)Y0.1O2 and the calcination temperatures. These solid solutions can be used as catalyst for the direct synthesis of dimethyl carbonate from CH3OH and CO2. Results indicated that the catalytic activity for DMC synthesis was influenced by the structure of the solid solutions and the x values in CexZr(1-x-0.1)Y0.1O2. The optimized Ce0.5Zr0.4Y0.1O2 with bimodal pore structure exhibited higher catalytic performance to DMC synthesis.

Plant-wide design and control of DMC synthesis process via reactive distillation and thermally coupled extractive distillation

In the study, reactive distillation is designed to produce dimethyl carbonate and ethylene glycol by the transesterification of ethylene carbonate and methanol. The products of the reactive distillation column include ethylene glycol and a dimethyl carbonate/methanol mixture, close to azeotropic composition. The azeotrope is separated in the study by pressure-swing distillation and extractive distillation using phenol as an extractive agent. The extractive distillation is found to be much more economical than the pressure-swing distillation. Thermal coupling technology is also implemented between the two columns of the extractive distillation. Thermally coupled extractive distillation provides the best energy efficiency. Proper selection and pairing of controlled and manipulated variables are determined by using steady-state analysis. A simple temperature control scheme is sufficient to maintain stoichiometric balance between the reactant feeds and product purities at or around their designed values for the plant-wide process of reactive distillation + thermally coupled extractive distillation.

Modeling of the Catalytic Distillation Process for the Synthesis of Dimethyl Carbonate by Urea Methanolysis Method

A nonequilibrium model of the catalytic distillation was developed for the process of DMC synthesis by a urea methanolysis method over a solid base catalyst at the bench scale, and the Wilson model was used to account for the nonideality of the liquid phase. The superiority of the catalytic distillation on the removal of the products to restrain the reverse reaction was illustrated in the present work. Furthermore, the influence of total pressure and the reaction temperature on DMC yield and the sensitivity analysis to the reaction kinetics were discussed in detail. The results revealed that the catalytic distillation was appropriate for the process of DMC synthesis.

Synthesis of dimethyl carbonate and dimethoxy methane over Cu-ZSM-5

An investigation was carried out of the oxidative carbonylation of methanol to dimethyl carbonate over Cu-ZSM-5. The catalyst was prepared by solid-state ion exchange of H-ZSM-5 with CuCl and then characterized by X-ray absorption spectra (XAS). The XANES portion of the XAS data showed that all of the copper is present as Cu + cations, and analysis of the EXAFS portion of the data shows the Cu + cations have a Cu-O coordination number of ∼2.7, suggesting that the cations are doubly and triply coordinated. Under DMC synthesis conditions, cuprous cations can be identified by two sorts of sites, one site covered by methanol only and a second on which CO and methanol co-absorb. In the absence of CO, DMM is the primary product formed, but when CO is present DMC becomes the primary products. DMM and MF are presumed to form via the coupling of formaldehyde and formic acid, respectively, with methanol. Consistent with this reasoning, the rates of DMM and MF formation increase with oxygen partial pressure. DMC is formed by carbonylation of methanol, and the rate of its formation increases with CO partial pressure. Increasing methanol partial pressure has an equivalent effect on the rates of DMM and DMC formation, suggesting that both products are formed from a common precursor derived from methanol, for example a methoxide group.

Isobaric Vapor−Liquid Equilibria of Binary Mixtures Containing the Carbonate Group −OCOO−

Isobaric vapor−liquid equilibria (VLE) data for the four systems of dimethyl carbonate + ethylene carbonate, methanol + ethylene carbonate, dimethyl carbonate + ethylene glycol, and ethylene glycol + ethylene carbonate containing the carbonate group −OCOO−, which exist in the process of synthesizing DMC by transesterification of ethylene carbonate with methanol, have been measured at atmospheric pressure or under vacuum in an Ellis equilibrium still. The experimental VLE data are thermodynamically consistent, and the activity coefficients have been evaluated with the Wilson and NRTL equations, showing that the systems of dimethyl carbonate + ethylene glycol and ethylene glycol + ethylene carbonate have stronger nonideality. The results of this work are useful to the research on DMC synthesis by transesterification.