Synthesis Of Diethyl Carbonate Research Articles

Effects of support composition and pretreatment on the activity and selectivity of carbon-supported PdCu nCl x catalysts for the synthesis of diethyl carbonate

The oxidative carbonylation of ethanol to diethyl carbonate (DEC) has been investigated on catalysts prepared by dispersing CuCl 2 and PdCl 2 on activated carbon and carbon nanofibers. The objectives of this work were to establish the effects of support structure and pretreatment on the dispersion of the catalytically active components and, in turn, on the activity and selectivity of the catalyst for DEC synthesis. At the same surface loading of CuCl 2 and PdCl 2, partially oxidized carbon nanofibers resulted in a higher dispersion of the active components and a higher DEC activity than could be achieved on activated carbon. Catalyst characterization revealed that nearly atomic dispersion of CuCl 2 and PdCl 2 could be achieved on the edges of the graphene sheets comprising the carbon nanofibers. Over oxidation of the edges or their removal by heat treatment of the nanofibers resulted in a loss of catalyst activity. The loss of catalyst activity with time on stream could be overcome by the addition of ppm levels of CCl 4 to the feed. While catalysts prepared with CuCl 2 alone were active, a fivefold increase in activity was realized by using a PdCl 2/CuCl 2 ratio of 1/20. It is proposed that the Pd 2+ cations interact with [CuCl 2] − anions to form Pd[CuCl 2] 2 complexes that are stabilized through dative bonds formed with oxygen groups present at the edges of the graphene sheets of the support. A mechanism for DEC synthesis is discussed, and a role for the Pd 2+ cations as part of this mechanism is proposed.

Synthesis of diethyl carbonate from dimethyl carbonate and ethanol using KF/Al 2O 3 as an efficient solid base catalyst

Diethyl carbonate, an efficient oxygen-containing fuel additive was synthesized from dimethyl carbonate and ethanol using KF/Al 2O 3. The catalysts prepared with different KF loading were characterized using X-ray diffraction, BET surface area and basicity measurement analyses. The effects of different reaction parameters such as temperature, reactant ratio and amount of catalyst were optimized. Among the different alkali halides, 20 wt.% KF supported on alumina exhibited 61.6% diethyl carbonate selectivity with 96% dimethyl carbonate conversion under optimum reaction conditions. The plausible reaction mechanism is proposed based on the results obtained. The possibility of recycling the catalyst was ensured without appreciable loss in activity for four cycles.

Catalytic synthesis of diethyl carbonate by oxidative carbonylation of ethanol over PdCl 2/Cu-HMS catalyst

Direct synthesis of diethyl carbonate (DEC) by oxidative carbonylation of ethanol offers a prospective “green chemistry” strategy to eliminate the phosgene used in the traditional preparation processes. PdCl 2/Cu-HMS catalyst has been investigated, which demonstrated excellent selectivity to DEC by oxidative carbonylation of ethanol in the gas-phase reaction. The Si/Cu molar ratio of mesoporous Cu-HMS supports showed a remarkable effect on catalytic activities. An optimized Si/Cu molar ratio existed for catalytic performance, which was about 50/1. From XPS, ICP, XRD, nitrogen physisorption and IR characterization and analysis, it could be concluded that copper species incorporated into HMS frame and was highly dispersed in the frame of silica. The catalytic performances of PdCl 2/Cu-HMS were related with both Cu content in the Cu-HMS and the order degree of mesoporous structure for Cu-HMS.

Catalytic synthesis of dialkyl carbonate from low pressure CO 2 and alcohols combined with acetonitrile hydration catalyzed by CeO 2

Dialkyl carbonates have attracted much attention from the viewpoint of sustainable chemistry because they are useful intermediates and solvents and can be synthesized from renewable resources. One promising synthesis method of the dialkyl carbonates is the reaction of CO 2 with the corresponding alcohols. Direct synthesis of diethyl carbonate and dipropyl carbonate from ethanol + CO 2 and 1-propanol + CO 2 was promoted remarkably by the combination of acetonitrile hydration. The yield based on CO 2 reached 42 and 33% for diethyl carbonate and dipropyl carbonate, respectively. All the reactions were catalyzed by CeO 2 as a heterogeneous catalyst. It is characteristic that the combination with in situ dehydration enabled the conversion of low pressure CO 2 to dialkyl carbonate.

Characterization of KF/γ-Al2O3 Catalyst for the Synthesis of Diethyl Carbonate by Transesterification of Ethylene Carbonate

KF/γ-Al2O3 catalysts were prepared by impregnation method and investigated for the transesterification of ethylene carbonate (EC) with ethanol to synthesize diethyl carbonate (DEC). The KF/γ-Al2O3 catalysts were characterized by nitrogen physisorption, XRD and FT-IR techniques, and three new species: K3AlF6, KOH and K2CO3 were found on the catalysts. Experimental results indicate that KOH and K2CO3 are the major active species and K3AlF6 is inactive for DEC synthesis. Increasing the KF loading favors the formation of K2CO3 and consequently enhances the activity of the KF/γ-Al2O3 catalysts. However, when KF loading exceeded 50 mmol/g, the activity of the KF/γ-Al2O3 catalysts decreased. This may be due to the presence of intact KF on the catalyst, which may dilute the content of active species in the catalyst and cover the active species. The KF/γ-Al2O3 (50 mmol/g) catalyst exhibits the best catalytic performance. With this catalyst, a 72 mol% yield of DEC (based on EC) was obtained at 298 K. KF/γ-Al2O3 catalyst was prepared and employed for diethyl carbonate (DEC) synthesis. Three new species: K3AlF6, KOH and K2CO3 were formed on the KF/γ-Al2O3 catalysts. Among of them, KOH and K2CO3 are the major active species and K3AlF6 is inactive for DEC synthesis.

CuCl/phen/NMI in Homogeneous Carbonylation for Synthesis of Diethyl Carbonate: Highly Active Catalyst and Corrosion Inhibitor

The effects of N-donor ligands on CuCl-catalyzed oxidative carbonylation of ethanol were investigated. It was found that 1,10-phenanthroline (phen) and N-methyl imidazole (NMI) exhibited a synergic effect on the catalytic activity. Catalytic efficiency of the CuCl system was enhanced dramatically, and corrosion of the reaction system was effectively inhibited when phen and NMI were simultaneously used as the ligands. Under the reaction conditions of cCuCl = 0.2 mol/L, nCu:nphen:nNMI = 2:1:1, T = 393 K, P = 2.4 MPa with PCO/PO2 = 2:1, and time = 3 h, conversion of ethanol and selectivity to diethyl carbonate (DEC) were 15.2% and 99.0%, respectively. As compared to pure CuCl, the catalytic activity of CuCl/phen/NMI is much higher (3.6-fold). Furthermore, the high catalytic activity could be kept for a long time of service during the reaction. Corrosion of CuCl was also inhibited by using phen and NMI as ligands. For example, the inhibition efficiencies of CuCl/phen/NMI catalyst system on stainless steel 304...

Crystal structures, acid–base properties, and reactivities of Ce xZr 1− xO 2 catalysts

Direct synthesis of diethyl carbonate from ethanol and CO 2 is attractive since starting materials are cheap and easily obtainable, and the initial operational procedures are quite simple. We present results showing that Ce x Zr 1− x O 2 solid solution catalysts are effective and selective for producing diethyl carbonate and could be recyclable without loss of any activity. High calcination temperature is favorable based on results of catalytic test. X-ray diffraction and temperature-programmed desorption of NH 3 and CO 2 provide evidence indicating that catalytic properties of Ce x Zr 1− x O 2 are closely dependent on the crystal structures and the acid–base sites on the surface with varied Ce/Zr ratios. Strong acid–base sites on the surfaces of catalysts are unfavorable for diethyl carbonate formation.

Effect of SSIE structure of Cu-exchanged β and Y on the selectivity for synthesis of diethyl carbonate by oxidative carbonylation of ethanol: A comparative investigation

Cu-exchanged β and Y catalysts were investigated by oxidative carbonylation of ethanol in the gas-phase reaction. Cuβ catalyst has shown better catalytic selectivity for oxidative carbonylation of ethanol to diethyl carbonate (DEC), without the principal by-product 1,1-diethoxyethane (DEE) for CuY catalysts. In order to investigate the effect of zeolite structure on the selectivity for products, computational analysis of molecular dimensions and diffusion parameters of DEC and DEE within Cuβ and CuY catalysts zeolite framework has been performed using molecular mechanics and quantum mechanics methods. The computational analysis results are in good agreement with the experimental results to some extent. DEC having a kinetic diameter of 3.663 Å and the lowest energy barrier was formed preferentially over both zeolites. However, the DEE molecule was not detected among the products over Cuβ because of its greater kinetic diameter 6.059 Å and higher energy barrier. The special architecture of β zeolite did not allow the diffusion of DEE molecules through its pores. The formation of the higher sterically hindered DEE over CuY catalyst could be explained by involvement of the outer surface.

An investigation of carbon-supported CuCl 2/PdCl 2 catalysts for diethyl carbonate synthesis

The synthesis of diethyl carbonate (DEC) by the oxidative carbonylation of ethanol was investigated using catalysts prepared by the dispersion of CuCl 2 and PdCl 2 on amorphous carbon promoted with KCl and NaOH. Catalysts were characterized extensively by XRD, XAFS, SEM and TEM with the aim of establishing their composition and structure after preparation, pretreatment, and use. It was observed that after preparation and pretreatment in He at 423 K copper is present almost exclusively as Cu(I), most likely in the form of [CuCl 2] − anions, whereas palladium is present as large PdCl 2 particles. Catalysts prepared exclusively with copper or palladium chloride are inactive for DEC synthesis, indicating that both components must be present together. Evidence from XANES and EXAFS suggests that the DEC synthesis may occur on [PdCl 2− x ][CuCl 2] x species deposited on the surface of the PdCl 2 particles. As-prepared catalysts exhibit an increase in DEC synthesis activity and selectivity with time on stream, but then reach a maximum activity and selectivity, followed by a slow decrease in DEC activity. The loss of DEC activity is accompanied by a loss in Cl from the catalyst and the appearance of paratacamite.

Methods for synthesizing diethyl carbonate from ethanol and supercritical carbon dioxide by one-pot or two-step reactions in the presence of potassium carbonate

Carbon dioxide sequestration was studied by synthesizing diethyl carbonate (DEC) from ethanol and CO 2 under supercritical conditions in the presence of potassium carbonate as a base. The co-reagent was ethyl iodide or a concentrated strong acid. This sequestration reaction occurs in two steps, which were studied separately and in a one-pot reaction. An organic–inorganic carbonate hybrid, potassium ethyl carbonate (PEC) is generated at the end of the first step. This intermediate was characterized and was found to be a target molecule for CO 2 capture. Different co-reactants, such as ethyl iodide and concentrated strong Brönsted acid, were compared in the second step and used to investigate the reactivity of the hybrid. With ethyl iodide as the co-reactant, one-pot DEC synthesis gave higher yields (46%) than two-step production. The supercritical CO 2 acts as a swelling solvent and compatibilizing agent in the reaction medium, favoring interactions between ethanol and CO 2 and between PEC and ethyl iodide. The use of a phase transfer catalyst (PTC) increased DEC production (yield 51%) without increasing the amount of diethyl ether (DEE) produced as a by-product (yield 2%).

The effects of promoters over PdCl2-CuCl2/HMS catalysts for the synthesis of diethyl carbonate by oxidative carbonylation of ethanol

Diethyl carbonate (DEC) has been produced by the oxidative carbonylation of ethanol in the gas phase over a heterogeneous PdCl2-CuCl2 catalyst supported on hexagonal mesoporous silica (HMS). The various quaternary ammonium salt (QAS) promoters have a great effect on the performance of the catalyst, which was due to the high dispersal of the active species on the film composed of nonpolar groups. The catalytic performance of the PdCl2-CuCl2/HMS catalyst was greatly improved by the addition of promoter tetraethyl ammonium bromide (TEAB). Under the PdCl2-CuCl2-TEAB/HMS catalyst system, space time yield (STY) of DEC was 210.9 g DEC/(L-cat h), and conversion of EtOH was 13.6%. An optimized TEAB/Pd mole ratio existed for catalytic activity, which was about 12/1. From X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), low-temperature electron spin resonance (ESR) spectroscopy, and infrared resonance (IR) spectroscopy, it could be concluded that the essential role of TEAB not only promoted the formation of surface-stabilized copper species but also improved a high dispersal of the active species, which enhanced catalytic performance in the gas phase DEC synthesis.

Synthesis of diethyl carbonate by catalytic alcoholysis of urea

The production of diethyl carbonate (DEC) from urea and ethanol was investigated in a batch process. The catalytic activities of many metal oxides were evaluated, the influences of various operation conditions on the DEC yield were explored, and the catalytic mechanism was also analyzed. Among the tested catalysts, ZnO showed the best catalytic activity toward DEC synthesis. The optimum reaction conditions were as follows: ethanol/urea molar ratio of 10, catalyst concentration of 6%, reaction temperature of 463 K, reaction time of 5 h and the reaction pressure of 2.5 MPa, respectively. The highest DEC yield was 14.2%. The reaction of producing N-ethyl ethyl carbamate (N-EEC) was the main side reaction in this process, which consumed both ethyl carbamate and DEC. It is necessary to remove DEC from the reactor as quickly as possible.

Effect of treatment temperature on the crystal structure of activated carbon supported CuCl2–PdCl2 catalysts in the oxidative carbonylation of ethanol to diethyl carbonate

Diethyl carbonate (DEC) was prepared via oxidative carbonylation of ethanol over a heterogeneous Wacker-type catalyst supported by activated carbon (AC). The active species of copper chloride hydroxide crystals has a great effect on the catalytic performance and chemical adsorption capacities. Cu(OH)Cl crystal is the most active catalyst for the diethyl carbonate synthesis. In situ XRD technique was used to analyze the effect of treatment temperature on the crystal structures of catalyst in the oxidative carbonylation of ethanol to diethyl carbonate. Cu(OH)Cl was easily formed at 523K, which showed the best catalytic activities. γ-Cu2(OH)3Cl was formed at 573K, which showed lower catalytic activities in the synthesis of DEC. CuO was formed at the treatment temperature of 673K, which increased the yield of by-products—acetaldehyde and ethyl acetate. The catalytic performance of three catalysts of CuCl2–PdCl2–KCl–NaOH/AC prepared at the different treatment temperatures above indicated the same trend which could be ascribed to the in situ effects on the catalysts under the reaction conditions.

Study on Wacker-type catalysts for catalytic synthesis of diethyl carbonate from ethyl nitrite route

CO catalytic synthesis of diethyl carbonate in vapor phase had been studied in a continuous flow system and a fixed-bed reactor at atmospheric pressure. PdCl 2–CuCl 2/AC (activated carbon) catalyst exhibited better catalytic activity compared with other Wacker-type catalyst systems using SiO 2, α-Al 2O 3 and hexagonal mesoporous silica (HMS) as the carriers. The catalytic activity of the catalyst could be effectively improved by chemical pretreatment with H 2. The suitable Pd content was 2.0 wt.% considering both factors of DEC production and DEC selectivity, and an optimum Pd/Cu mole ratio existed for catalytic activity, which was 1/2. The study also revealed that CH 3OH was an excellent solvent for PdCl 2–CuCl 2/AC catalyst preparation.

A new type of catalyst PdCl 2/Cu-HMS for synthesis of diethyl carbonate by oxidative carbonylation of ethanol

A new type of catalyst, PdCl 2/Cu-HMS, for diethyl carbonate (DEC) synthesis by oxidative carbonylation of ethanol in the gas-phase reaction was investigated. The modified support Cu-HMS which was synthesized using the neutral templating pathway at the room temperature kept its mesoporous structure even after it was calcined repeatedly at 550 °C for 3 h to remove the template. From XRD, XPS and ICP analysis, it can be concluded that copper incorporated into HMS frame and was highly dispersed in the frame of silica. Notably, the degree of order of mesoporous molecular sieves was improved in a certain extent after PdCl 2 was loaded on Cu-HMS samples. The PdCl 2/Cu-HMS catalyst exhibited excellent selectivity for DEC. The catalytic reaction mechanism was illuminated by the interaction between Pd 2+ loaded on the surface and Cu 2+ in Cu-HMS frame.

Vapor-phase oxidative carbonylation of ethanol over CuCl–PdCl 2/C catalyst

CuCl–PdCl 2/C catalysts were prepared, characterized, and used for the synthesis of diethyl carbonate. Conventional impregnation was adopted for the preparation of the catalyst. Water-insoluble cuprous chloride, CuCl, was dissolved in hydrochloric acid. Catalytic properties were characterized by XRD, XPS and TPD. The activities of the catalysts in the oxidative carbonylation of ethanol were measured using a continuous flow micro-reactor. The results revealed that CuCl–PdCl 2/C catalyst was not only active but also very selective for the production of diethyl carbonate. The selectivity was 100% at a reaction temperature below 120 °C. However, despite all its merits, the catalyst was easily deactivated in the reaction. The main causes of the deactivation were the sintering of the cuprous chloride and the decomposition of the palladium chloride.

Effect of crystal structure of copper species on the rate and selectivity in oxidative carbonylation of ethanol for diethyl carbonate synthesis

The oxidative carbonylation of ethanol for diethyl carbonate synthesis offers prospects for a “green chemistry” replacement of phosgene used for polymer production and other processes. Effects of a potassium promoter on the CuCl 2–PdCl 2–NaOH/AC catalyst for diethyl carbonate synthesis were evaluated. The catalytic activity was improved significantly when KCl was added to the catalyst while other promoters only had little influence on the catalytic performance. Further investigations on the KCl promoter indicated that the conversion of ethanol reaches over 30% while the selectivity is around 95%. The optimal molar ratio of the reactant (CO:O 2:C 2H 5OH) is around 10:1:4. Analysis by X-ray diffraction and XPS showed that copper chloride hydroxides (Cu(OH)Cl) is formed when KCl is added to the catalyst and is beneficial for the catalytic activity for the oxidative carbonylation of ethanol. The great improvement on the catalytic performance of the catalyst CuCl 2–PdCl 2–KCl–NaOH/AC is attributed to the efficient electronic transfer between PdCl 2 and Cu(OH)Cl.

Study on the catalytic synthesis of diethyl carbonate from CO and ethyl nitrite over supported Pd catalysts

A vapor phase synthesis of diethyl carbonate (DEC) from carbon monoxide and ethyl nitrite (EN) was studied in a continuous flow micro fixed-bed reactor at atmospheric pressure. PdCl 2–CuCl 2/AC (activated carbon) catalyst exhibited better catalytic activity compared with other binary catalyst systems. The suitable Pd-loading is about 2.0 wt%, and some additives (LaCl 3, CeCl 3, PrCl 3) are benefit for the DEC yield and selectivity. Influences of various reaction parameters on the DEC yield and selectivity were tested. The optimum reaction temperature lies in 378–388 K and the suitable gas hourly space velocity (GHSV) range is 2500–3000 h −1 considering both factors of DEC production and CO conversion. An optimum CO/C 2H 5ONO mole ratio exists for catalytic activity, which is about 1/1. The stability of PdCl 2–CuCl 2/AC catalyst and PdCl 2–CuCl 2–CeCl 3/AC catalyst was also investigated. The possible reason of the deactivation behavior of catalysts was discussed with the help of XRD.

Production of diethyl carbonate from ethanol and carbon monoxide over a heterogeneous catalytic flow reactor

Diethyl carbonate (DEC) is a candidate for use as an oxygen-containing additive in gasoline and diesel fuel to diminish pollutant emissions. The synthesis of DEC by the oxidative carbonylation of ethanol in the gas phase over heterogeneous CuCl 2/PdCl 2 catalysts supported on activated carbon (AC) has been investigated using a laboratory-scale continuous flow reactor with online GC/MS. Influences of various reaction conditions and catalyst pretreatment on the DEC yield and selectivity have been tested. Yield of DEC at 150 °C reached a maximum of 12.5 wt.% and was found to increase with an increase of residence time, reaction temperature, and reaction pressure as expected. The relationship between CO flow rate and production of DEC showed three distinct regions of DEC production. A by-product, diethoxymethane (DEM), was formed when ethanol was introduced in stoichiometric excess. Catalyst pretreated with KOH presented the best catalytic performance, and all metal hydroxides tested enhanced the yield of and selectivity for DEC simultaneously. However, the CuCl 2/PdCl 2/AC–KOH catalyst with a higher OH/Cu mole ratio than 2.0 showed an even lower DEC yield than that found using a CuCl 2/PdCl 2/AC catalyst without KOH.

Characterization of CuCl2/PdCl2/Activated Carbon Catalysts for the Synthesis of Diethyl Carbonate

X-ray diffraction (XRD), low-temperature electron spin resonance (ESR) spectroscopy, and magnetometry are employed to determine the electronic and structural properties of over a dozen samples of fresh and KOH-treated CuCl2/PdCl2/activated carbon (AC) catalysts used in the synthesis of diethyl carbonate (DEC) from ethanol and CO. The percentage yields of DEC from the preceding paper by Dunn et al. are compared with the results from XRD and ESR to determine the nature of the active species. Temperature variation (4 to 300 K) of the ESR spectra of CuCl2/AC for different loadings of Cu reveals two Cu2+ species: Cu2+−carbon and nanoclusters of CuCl2 precipitated during impregnation. An excellent correlation is observed between the ESR intensity of Cu2+−carbon species and weight percent of DEC produced, although the maximum yield for CuCl2/AC is only about 4% for Cu loading of 9% (wt). For the CuCl2/PdCl2/AC catalysts, the yield increases to 10%, signifying the important role of Pd2+. For the CuCl2/PdCl2/AC catalysts treated with KOH for different ratios of OH/Cu = x between 0 and 5, wt % of DEC produced increases to 18% for x = 1, but drops to negligible amounts for x = 3 and 5. In XRD studies, the intensity of the paratacamite peaks correlates well with the % yield of DEC for all values of x, showing paratacamite as the active species in the KOH-treated catalysts. For x = 3 and 5, paratacamite converts to calumetite, corresponding to the drastic drop in the yield for DEC conversion.