超临界CO2萃取反应合成碳酸二甲酯

实验测定了不同条件下碳酸二甲酯(DMC)、甲醇、乙二醇(EG)、碳酸乙烯酯(EC)在超临界相和液相中的分配系数,计算了DMC相对于其他组分的分离因子. DMC相对于甲醇的分离因子随EC浓度的升高而降低,随DMC和EG含量增加而升高,随压力增加而增大,随温度升高而变小. 这种变化规律表明利用超临界萃取与反应耦合提高酯交换反应转化率的前提是：(1) 反应体系中DMC的浓度要高,即进料中环氧乙烷(EO)的浓度要高,且EC转化率要高;(2) 低的反应温度和高的反应压力. 在160℃和5~20 MPa下,以环氧乙烷、甲醇和CO2为原料,考察了超临界CO2萃取与反应相耦合提高酯交换反应转化率的可行性. 研究结果表明,DMC与甲醇间的分离因子是影响超临界萃取反应操作过程中DMC收率的关键因素. 采用耦合技术可以提高DMC的单级收率约4%以上.     

Techno-economic evaluation of the direct conversion of CO2 to dimethyl carbonate using catalytic membrane reactors

The production of dimethyl carbonate (DMC) caught more interest in the past decades due to its versatile use (e.g. as fuel additive), low toxicity and fast biodegradability. Different ‘green’ production routes are being developed to replace the conventional and rather toxic production of DMC via phosgene. The direct conversion of CO₂ and methanol toward DMC is an environmental and economically interesting production route for the chemical industry.This work describes the process design of the direct conversion of CO₂ to dimethyl carbonate, providing a valuable insight and a better understanding of the process limitations. In this design, membrane reactors are used for continuous removal of water by-product, in order to overcome the equilibrium limitations. The rigorous Aspen Plus simulations show that even when using an excess of methanol, the attainable conversion is low and the DMC concentration in the reactor effluent is less than 1.5 mol%. Purifying this diluted stream to the desired concentrations demands large size equipment and a substantial amount of energy (13.61 kWh/kg DMC) resulting in high investment and utility costs, thus making the process not profitable. The focus for new membrane reactors could be on the selective removal of DMC (instead of water) from the reaction area to allow for a more concentrated DMC stream.     

In situ FTIR study of the Cu electrode/ethylene carbonate + dimethyl carbonate solution interface

The interfacial phenomena between Cu electrode and solution of lithium perchlorate in ethylene carbonate (EC)-dimethyl carbonate (DMC) have been investigated using in situ reflection absorption Fourier transform infrared (FTIR) spectroscopy and single reflection ATR-FTIR spectroscopy. The ATR spectra confirmed the bands due to free EC and DMC and the molecules solvated to lithium ions in the solution. The bands due to the result of the interaction between ClO₄⁻ and DMC in the mixture solution also appeared in the ATR spectra. In the FTIR spectra, the potential dependence on the concentration of EC and DMC in the vicinity of the Cu electrode was observed. It was understood that the reversible changes in the concentration of free EC and DMC and solvated EC and DMC in the diffuse double layer take place with changing in potential. As the potential decreased, the free EC and DMC concentrations increased, while the concentration of the EC and DMC solvated to lithium ions decreased. Thus, it can be concluded that the equilibrium shifts from Li⁺(EC)₂(DMC)₂ to Li⁺(EC)₂(DMC) + DMC or Li⁺(EC)(DMC)₂ + EC as the potential decreases. The bands due to (CH₂OCO₂Li)₂ and CH₃OCO₂Li were observed for an irreversible reaction.     

Copolymerization of epoxides and carbon dioxide by using double metal cyanide complex (DMC) with high crystallinity

Zn₃ [Co(CN)₆]₂ based double metal cyanide complex(Co-Zn DMC) is synthesized and characterized by element analysis, FT-IR, TG-FTIR, XRD and TEM. The composition of Co-Zn DMC summarized by elemental analysis has been confirmed by TG-FTIR. The catalyst has high crystallinity according to strong crystalline peaks shown in XRD and diffraction spot observed by TEM. Copolymerization of epoxides and carbon dioxide are successfully catalyzed by Co-Zn DMC. The efficiency of catalysts is as high as 7488 g polymer/g catalyst for CO₂/propylene oxide (PO), 1100 g polymer/g catalyst for CO₂/ethylene oxide (EO), which are higher than that reported ever before. The effects of various reaction conditions such as amount of the catalyst, reaction time and temperature on the copolymerization are investigated. The results show that insertion of CO₂ into chains is significantly affected by the catalyst quantity and ambient temperature. The weight percentage of byproduct cyclic carbonate can be easily controlled to be less than 5% while the molar fraction of CO₂ in backbone (f_co2) is more than 30%.     

Novel amphiphilic polymer gel electrolytes based on (PEG‐b‐GMA)‐co‐MMA

Amphiphilic conetwork–structured copolymers containing different lengths of ethylene oxide (EO) chains as ionophilic units and methyl methacrylate (MMA) chains as ionophobic units were prepared by free radical copolymerization and characterized by FTIR and thermal analysis. Polymer gel electrolytes based on the copolymers complexed with liquid lithium electrolytes (dimethyl carbonate (DMC) : diethyl carbonate (DEC) : ethylene carbonate (EC) = 1 : 1 : 1 (W/W/W), LiPF₆ 1.0M) were characterized by differential scanning calorimetry and impedance spectroscopy. A maximum ion conductivity of 4.27 × 10^?4 S/cm at 25^oC was found for the polymer electrolyte based on (PEG2000‐b‐GMA)‐co‐MMA with long EO groups. Moreover, the effect of temperature on conductivity of the amphiphilic polymer electrolytes obeys the Arrhenius equation. The good room temperature conductivity of the polymer electrolytes is proposed to relate to the enhancement in the amorphous domain of the copolymers due to their amphiphilic conetwork structure. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Supported dicopper(II) complex catalyst Cu2(II)(μ-Br)2/SiO2: synthesis, characterization and catalytic properties for synthesis of ethylene carbonate

A μ-Br-bridged dicopper(II) complex, namely [Cu₂(μ-Br)₂·6H₂O](ClO₄)₂, has been prepared by metal ion grafting. A supported complex catalyst Cu₂(II)(μ-Br)₂/SiO₂was prepared by modifying the silica surface with NaOEt and anchoring the dicopper(II) complex precursor on the surface of the support. The structure of the complex catalyst has been characterized by elemental analysis, IR spectra and UV–VIS diffusion reflection spectra. Obtained data were compared with published data of the complex. TPD-MS and TPD-IR investigations indicated that CO₂ and ethylene oxide (EO) can be chemisorbed on the surface of the catalyst reversibly in a bridged state and can be desorbed from the surface at 105 and 115 K, respectively. In the high temperature range of 450–573 K, another reversible absorption state for CO₂ was also discovered. For EO, however, a decomposition absorption state was found which gave the dissociated species of CH₄ and CO. TPSR-MS experiments have shown that CO₂ and EO reacted on the surface effectively in the range of 343–413 K. An in situ IR method has been used to study the reactivity of the reactants on the surface of the catalyst, and the target product ethylene carbonate (EC) was detected in the range of 333–413 K. Catalytic experiments indicated that the one-way yield of EC is greater than 8.0% and that the selectivity of EC is greater than 82%. A synergic cyclization reaction pathway is proposed to account for the observed products.     

Surface film formation on a graphite negative electrode in lithium-ion batteries: AFM study on the effects of co-solvents in ethylene carbonate-based solutions

In situ AFM observation of the basal plane of highly oriented pyrolytic graphite (HOPG) was performed before and after cyclic voltammetry in 1 mol dm⁻³ LiClO₄ dissolved in ethylene carbonate (EC), EC+diethyl carbonate (DEC), and EC+dimethyl carbonate (DMC) to clarify the effects of co-solvents in EC-based solutions on surface film formation on graphite negative electrodes in lithium-ion cells. In each solution, surface film formation involved the following two different processes: (i) intercalation of solvated lithium ions and their decomposition beneath the surface; and (ii) direct decomposition of solvent molecules on the basal plane to form a precipitate layer. The most remarkable difference among these solvent systems was that solvent co-intercalation took place more extensively in EC+DEC than in EC+DMC or EC. Raman analysis of ion-solvent interactions revealed that a lithium ion is solvated by three EC molecules and one DEC molecule in EC+DEC, whereas it is solvated exclusively by EC in EC+DMC and in EC, which suggested that the presence of linear alkyl carbonates in the solvation shell of lithium ion enhance the degree of solvent co-intercalation that occurs in the initial stage of the surface film formation.     

氧化锌催化丁二酸二甲酯和碳酸乙烯酯的耦合反应

研究了ZnO催化碳酸乙烯酯和丁二酸二甲酯耦合反应合成聚丁二酸乙二醇酯预聚体和碳酸二甲酯的新工艺。考察了ZnO催化剂焙烧温度对耦合反应的催化活性,优化了反应条件。并对ZnO催化剂进行XRD、BET和NH₃-TPD表征。以FTIR和¹H NMR表征聚丁二酸乙二醇酯预聚体。结果表明,在225~235℃,EC/DMSu摩尔比为2,催化剂/(EC+DMSu)摩尔比为0.005,反应时间为3 h的反应条件下,碳酸二甲酯收率为59.7%,聚丁二酸乙二醇酯预聚物的特性黏度为0.3857 dl·g^-1。通过XRD和NH₃-TPD分析,推测ZnO表面的晶体缺陷和弱酸性是影响耦合反应催化活性的原因。     

Synthesis of organic carbonates from alcoholysis of urea: A review

Organic carbonates are green compounds with a wide range of applications. They are widely used for the synthesis of important industrial compounds including monomers, polymers, surfactants, plasticizers, and also used as fuel additives. They can be divided into two main classes: cyclic and linear carbonates. Dimethyl carbonate (DMC) and diethyl carbonate (DEC) are the important linear carbonates. Carbonyl and alkyl groups present in DMC and DEC make them reactive and versatile for synthesizing various other important compounds. Ethylene carbonate (EC), glycerol carbonate (GC) and propylene carbonate (PC) are well-known cyclic organic carbonates. Phosgenation of alcohols was widely used for synthesis of organic carbonates; however, toxicity of raw materials restricted use of phosgenation method. A number of new non-phosgene methods including alcoholysis of urea, carbonylation of alcohols using CO₂, oxy-carbonylation of alcohols, and trans-esterfication of alcohols and carbonates have been developed for synthesizing organic carbonates. Carbonylation of alcohols is preferred as it helps in utilization and sequestration of CO₂, however, poor thermodynamics due to high stability of CO₂ is the major obstacle in its large scale commercialization. Oxy-carbonylation of alcohols offers high selectivity but presence of oxygen poisons the catalyst. Recently, alcoholysis of urea has received more attention because of its inexpensive abundant raw materials, favorable thermodynamics, and no water-alcohol azeotrope formation. Also, ammonia evolved in this synthesis route can be recycled back to urea by reacting it with CO₂. In other words, this method is a step towards utilization of CO₂ as well. This article reviews synthesis of DMC, DEC, GC, PC, and EC from urea by critically examining various catalysts used and their performances. Mechanisms have been reviewed in order to give an insight of the synthesis routes. Research challenges along with future perspectives have also been discussed.     

Quaternary Ammonium Ionic Liquids as Bi-functional Catalysts for One-step Synthesis of Dimethyl Carbonate from Ethylene Oxide,Carbon Dioxide and Methanol

Abstract  

One kind of novel ionic liquids (ILs) with a tertiary amino moiety and a quaternary ammonium group were synthesized and identified by FT-IR, ¹H and ¹³C NMR. The elemental chemical state and basicity of ILs were determined by XPS and Hammett indicator method, respectively. Then the catalytic performance of these bi-functional catalysts was investigated in one-step synthesis of dimethyl carbonate (DMC) from ethylene oxide (EO), carbon dioxide and methanol. The best catalytic performance with 99% EO conversion and a maximum of 74% DMC selectivity was obtained using [N_111,6N11]I as catalyst under optimized reaction conditions. And the catalyst could be reused for several times. Normally, stronger basicity could be obtained by altering the anions with different nucleophilicity in ILs and a better catalytic activity could be achieved correspondingly. A mechanism that both the ring opening of epoxide through nucleophilic attacks and the transesterification play an important role in the reaction was proposed based on experimental results.     

CaO–ZrO2 Solid Solution: A Highly Stable Catalyst for the Synthesis of Dimethyl Carbonate from Propylene Carbonate and Methanol

CaO–ZrO₂ prepared by co-precipitation showed to be a well-performed catalyst for the transesterification of propylene carbonate (PC) and methanol. The characterization by X-ray powered diffraction (XRD) and Raman spectroscopy indicated that CaO was doped into the lattice of ZrO₂ to form CaO–ZrO₂ solid solution. Such a solid solution was a strong solid base, which was proved by CO₂ temperature program desorption (CO₂-TPD). As a result, the catalyst showed high stability towards the transesterification of propylene carbonate and methanol into dimethyl carbonate with high PC conversion, especially being subjected to the continuous production of dimethyl carbonate at reactive distillation reactor for 250 h without any obvious loss of activity at the PC conversion of 95%.     

Electrochemical characteristics of phase-separated polymer electrolyte based on poly(vinylidene fluoride-co-hexafluoropropane) and ethylene carbonate

A polymer electrolyte based on microporous poly(vinylidene fluoride-co-hexafluoropropane) (PVdF-HFP) film was studied for use in lithium ion batteries. The microporous PVdF-HFP (Kynar 2801) matrix was prepared from a cast of homogeneous mixture of PVdF-HFP and solvents such as ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). After evaporation of DMC and EMC, a sold film of the PVdF-HFP and the EC mixture was obtained. EC-rich phase started its formation in the PVdF-HFP/EC film at EC content of about 60 wt.% based on the total weight of PVdF-HFP and EC. The formation of the new phase resulted in the abrupt increase of the porosity of the PVdF-HFP matrix from 32 to 62%. The ionic conductivity of the film soaked in 1 M LiPF₆-EC/DMC=1/1 was significantly increased from order of 10⁻⁴ S/cm to order of 10⁻³ S/cm at the EC content of 60 wt.%. Thermal and spectroscopic investigations showed that most of the EC interact with PVdF-HFP with the EC content being below 60 wt.%. MCMB/polymer electrolyte/LiCoO₂ cells employing the microporous PVdF-HFP polymer film showed stable charging/discharging characteristics at 1C rate and good rate capability.     

Fluid phase equilibria of the reacting mixture in the dimethyl carbonate synthesis from supercritical CO2

In order to investigate the dimethyl carbonate synthesis from methanol and supercritical CO₂, the thermodynamic behaviour of the reacting mixture, i.e. the quaternary methanol–CO₂–DMC–water mixture, has to be known. The SRK equation of state with MHV2 mixing rules has been chosen to predict fluid phase equilibria in the reactor. The first part of this work is dedicated to the determination of binary interaction parameters, needed in the use of this model. These parameters are deduced from the fitting of experimental data concerning binary or ternary sub-systems existing in the quaternary mixture. Literature data was used for most of the binary sub-systems, but for the DMC–CO₂ and DMC–water mixtures, specific experiments were carried out. The agreement between experimental and predicted fluid phase equilibria was found to be satisfactory. With a view to studying of the operating conditions for the reaction, the thermodynamic model was used to predict fluid phase equilibria in the reactor, by considering several hypothetical feed ratios and conversions. This work shows that CO₂ has to be used in large excess in order to be sure of running the reaction in a homogeneous fluid medium.     

固载化离子液体催化环氧乙烷和二氧化碳合成碳酸乙烯酯

用溴化1-羟乙基-3-乙烯基咪唑、甲基丙烯酸钠、丙烯酸羟乙酯、苯乙烯4种单体共聚合成了高分子离子液体催化剂,表征了其结构. 将该催化剂固载到分子筛上制成固体颗粒催化剂,催化环氧乙烷(EO)与CO2合成碳酸乙烯酯(EC)的反应,考察了反应时间、温度、压力、催化剂用量对EO转化率及生成EC选择性的影响. 结果表明,在反应时间4 h、温度403.15 K、压力2.5 MPa、催化剂与环氧乙烷质量比9%的条件下,EO转化率为95%, EC选择性为98%,催化剂在循环使用10次后,EO转化率无明显下降,EC选择性接近100%. 该反应为一级反应,动力学方程为r=-dCEO/dt=9.872×104e-52.00/(RT)CEO.     

Effects of Catalyst Phase Structure on the Elementary Processes Involved in the Synthesis of Dimethyl Carbonate from Methanol and Carbon Dioxide over Zirconia

In situ infrared spectroscopy has been used to investigate the synthesis of dimethyl carbonate (DMC) from methanol and carbon dioxide over tetragonal (t-ZrO₂) and monoclinic zirconia (m-ZrO₂. While similar species were observed for both catalyst phases, the dynamics of the elementary processes were different. The dissociative adsorption of methanol to form methoxide species was approximately twice as fast on m-ZrO₂ as on t-ZrO₂. CO₂ insertion to form monomethyl carbonate, an intermediate in the synthesis of DMC, occurred more than order of magnitude more rapidly over m-ZrO. By contrast, the transfer of a methyl group from adsorbed methanol to monomethyl carbonate and the resulting formation of DMC proceeded roughly twice as fast over m-ZrO₂. The observed patterns are attributed to the higher Brønsted basicity of hydroxyl groups and cus-Zr⁴⁺O^2- Lewis acid/base pairs present on the surface of zirconia.     

Electrochemical synthesis of dimethyl carbonate from methanol,CO2 and propylene oxide in an ionic liquid

BACKGROUND: Dimethyl carbonate (DMC) can be used effectively as an environmentally benign substitute for highly toxic phosgene and dimethyl sulfate in carbonylation and methylation, as well as a promising octane booster owing to its high oxygen content. Two‐step transesterification from epoxide, methanol, and CO₂ is widely used in the bulk production of DMC. However, major disadvantages of this process are high energy consumption, and high investment and production costs. A one pot synthesis of DMC from carbon dioxide, methanol, and epoxide was, therefore, developed. But the yields of DMC are below 70% due to the thermodynamic limitation. RESULTS: Electrochemical synthesis of DMC was conducted with platinum electrodes from methanol, CO₂ and propylene oxide in an ionic liquid was conducted. The bmimBr (1‐butyl‐3‐methylimidazolium bromide)‐methanol‐propylene oxide system with CO₂ bubbling allows DMC to be effectively synthesized and a high yield (75.5%) was achieved. CONCLUSION: In this electrolysis, redox reactions of substrates, CO₂, methanol, and propylene oxide, on Pt electrodes were carried out, producing the activated particles, CH₃O^?, CH₃OH⁺, CO₂^? and PO^?, resulting in the effective synthesis of DMC with a 75.5% yield in an ionic liquid (bmimBr). Finally, a mechanism for this synthesis reaction was proposed, which is very different from those reported in the literature. Copyright © 2011 Society of Chemical Industry     

Effects of solvents and salts on the thermal stability of LiC6

Accelerating rate calorimetry (ARC) was used to study the thermal stability of Li_0.81C₆ in dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate (EC), and an EC/DEC mixture as well as in LiPF₆- and LiBOB-based electrolytes. ARC results show that linear carbonates like DMC or DEC react strongly with Li_0.81C₆ and that robust passivating layers do not form. By contrast, the cyclic carbonate, EC, creates a robust passivating film that limits the rate of reaction between Li_0.81C₆ and EC as the temperature increases. X-ray diffraction shows that the addition of LiPF₆ to EC/DEC changes the surface film that forms on Li_0.81C₆ at elevated temperature to one dominated by LiF instead of lithium-alkyl carbonate or lithium carbonate. This increases the thermal stability of Li_0.81C₆ in LiPF₆ electrolyte compared to pure EC/DEC solvent. By an apparently similar mechanism, the addition of only 0.2 M LiBOB to EC/DEC greatly improves the thermal stability of Li_0.81C₆. ARC results for Li_0.81C₆ in pure and mixed salt LiPF₆ and LiBOB EC/DEC electrolytes of various molarities shed light on the reasons for the beneficial effect of the salts.     

Synthesis and characterization of Ce–La oxides for the formation of dimethyl carbonate by transesterification of propylene carbonate

A series of cerium–lanthanum catalysts prepared using the co-precipitation method were investigated for transesterification of propylene carbonate (PC) with methanol to produce dimethyl carbonate (DMC). Synthesized catalysts were characterized by XRD, CO₂- and NH₃-TPD, N₂ adsorption/desorption and SEM–EDX techniques. Studies were carried out to study the effect of reaction conditions such as methanol/PC molar ratio (4–12), catalyst dose (2–10 wt.% of PC), reaction time (2–10 h) and temperature (140–180 °C) on the DMC yield. Highest PC conversion and DMC yield of 72% and 74%, respectively, were observed with catalysts having a 1:4 Ce/La molar ratio.     

Synthesis of Dimethyl Carbonate from Methyl Carbamate and Methanol Using a Fixed‐Bed Reactor

Several mixed oxide catalysts were prepared by coprecipitation for dimethyl carbonate (DMC) synthesis from methyl carbamate and methanol. During the batch process, the DMC yield was below 35 %. In order to minimize the unfavorable thermodynamic equilibrium and side reactions for the DMC synthesis, a fixed‐bed reactor was designed. A maximum DMC yield of ～ 73 % could be realized over a ZnO‐Al₂O₃ catalyst. The effects of reaction conditions for this type of reactor were investigated in detail.     

An in situ Raman study of dimethyl carbonate synthesis from carbon dioxide and methanol over zirconia

In situ Raman spectroscopy has been used to investigate the mechanism of dimethyl carbonate (DMC) synthesis via the reaction of methanol with carbon dioxide over zirconia. Methanol adsorption leads to the appearance of adsorbed methoxide groups, whereas CO₂ adsorption leads to the formation of carbonate species. Monomethyl carbonate species, (CH₃O)COO(Zr)₂, are formed by the reaction of methoxide and monodentate carbonate species and DMC is formed via the further reaction of monomethyl carbonate species with methanol. This sequence is supported by evidence that DMC decomposition on zirconia proceeds via the reverse of the proposed mechanism.