Yingkou Hengyang New Energy Chemical Co., Ltd.
Address: Xianren Island Energy and Chemical Zone, Yingkou City, Liaoning Province, via the west side of the Fourth Road
Analysis of diethyl carbonate shows that diethyl carbonate can make the dyeing evenly divided and improve the fading property in the sun in textile printing and dyeing. Solvents used as plasticizers or solvents used directly as plasticizers or as plasticizers in the processing of plasticizers have broad market prospects. Chapter II Development Trends of Technology
Diethyl Carbonate (DEC) is an important material in carbonate and has a wide range of applications. Its molecular formula is C5H10O3 and its structural formula is (C2H50)2.
C 0, molecular weight 118.13, colorless liquid with special aroma at room temperature, melting point - 43 C, boiling point 126.8 C, density 0.98g/cm 3 (40 C), flash point 31 C, spontaneous combustion temperature 445 C. When DEC is discharged into the environment, it can be slowly hydrolyzed into two harmless products, carbon dioxide and ethanol. Environmental Protection Agency's Chemicals Reference points out that diethyl carbonate (CAS-58-8) has not found environmental problems in existing intelligence resources. DEC contains ethyl, ethoxy, carbonyl and carbonyl ethoxy groups in its molecular structure, so its chemical properties are very active. It can react with alcohols, phenols, amines, esters and other compounds. It is an important intermediate in organic synthesis and has high industrial application value. DEC can be used as solvent, cathode fixing paint for vacuum tube, surfactant and additive for lithium battery liquid, etc. Electronic grade pure DEC can be used as a detergent for color TV picture tubes. Diethyl carbonate with 40.6% oxygen content is much higher than methyl tert-butyl ether (MTBE) (18.2%). Diethyl carbonate can be used as an oxygen-containing additive for gasoline and diesel fuel to improve the combustion performance of gasoline and reduce emissions of pollutants. In the United States and Western Europe, the use of MTBE has been gradually restricted. Among possible alternatives, DEC has better oil/water partition coefficient and volatility resistance than dimethyl carbonate and ethanol. Therefore, DEC will have more competitive advantages than dimethyl carbonate and ethanol as one of the alternatives to MTBE and will be the most potential use. In this paper, the progress of synthesis methods of DEC at home and abroad in recent years is reviewed, and the active synthesis methods of oxidative carbonyl of ethanol are emphatically introduced. 1. Diethyl carbonate is prepared by phosgene and absolute ethanol. The reaction equation is as follows: HCl reacts with phosgene in anhydrous ethanol, the molar ratio of phosgene to ethanol is 1.05-1.10, and the reaction temperature is 70-90 C. The phosgene was heated and refluxed for 2 hours. Hydrogen chloride gas is released from the reaction and by-product hydrochloric acid can be obtained by cooling. The product was distilled at 125 - 128 (?) C to collect the reaction product, and the industrial product with the content of Diethyl Carbonate over 99% was obtained. The phosgene process uses highly toxic phosgene as raw material, which seriously pollutes the environment. At the same time, by-product hydrogen chloride can corrode pipeline equipment. Although many improvements have been made in the process, its development has been limited because of its shortcomings which are difficult to overcome. 2. Transesterification is a commonly used method in organic synthesis. It is difficult to synthesize esters from a readily available ester. According to the different raw materials used in transesterification process, the main production processes are transesterification of diethyl sulfate and carbonate, and transesterification of carbonate and ethanol. 2.1 Diethyl sulfate and diethyl carbonate sulfate can be transesterified with carbonate to form diethyl carbonate and sulfate, which can be carried out directly without catalyst. However, the reactant uses highly toxic diethyl sulfate and by-product sulfate, which can easily lead to scale formation in the reactor. This method is no longer used at present. 2.2 Carbonate in transesterification of dimethyl carbonate with ethanol carbonate and ethanol can be propylene carbonate, vinyl carbonate, dimethyl carbonate, etc. The synthesis of diethyl carbonate by transesterification of dimethyl carbonate with ethanol is as follows:
The reaction is a parallel series reaction. The complex of alkali metal carbonate and polyethylene glycol (PEG) is used as catalyst. At the same time, polyethylene glycol can form homogeneous complex with alkali metal carbonate to avoid reacting with a large number of existing carbonates causing catalyst deactivation and blockage of pipelines. The reaction temperature is generally 25 - 130 C and the reaction time is 10 - 120 min. The reaction is carried out under normal pressure. Among them, the molar ratio of alkali metal carbonate to polyethylene glycol is 0.5-3, the conversion of dimethyl carbonate is about 90%, and the selectivity of diethyl carbonate is about 50%. This method uses the green chemical dimethyl carbonate as raw material, the reaction conditions are mild, the requirements for equipment are not high, and it is easy to realize in industry. However, because of the parallel series reaction, reactive distillation is needed to improve the yield of the reaction. 2.3 The mechanism of transesterification of propylene carbonate (Ethylene) with propylene carbonate (PC) or vinyl carbonate (EC) with ethanol is that ethanol acts as a nucleophilic agent to attack carbon on the carbonyl group of PC (or EC) to produce DEC and propylene glycol (or ethylene glycol). Frevel et al. took the lead in 1972 in the synthesis of dialkyl carbonate by transesterification. The catalytic system of this reaction can be divided into homogeneous catalysis and heterogeneous catalysis. The commonly used homogeneous catalysts are alkali metal or alkali metal derivatives, aliphatic triamines, alkyl salts, alkyl salts of zinc (aluminium or titanium), thallium compounds, 1ewis acid compounds and organic bases containing nitrogen, etc. Commonly used heterogeneous catalysts are cationic exchange resin, titanium-silica solid acid, alkali or alkaline earth metal silicate impregnated on silica or ammonium crosslinked molecular sieve, zirconium (titanium or tin) oxide, Mg0+Al203, etc. The specific examples are shown in Table 1.
If PC is used as raw material, the reaction is as follows:
PC (or EC) in the reactants can be formed by the reaction of propylene oxide (or ethylene oxide) with carbon dioxide, or by the catalysis of zinc oxide with ethylene glycol and urea. The transesterification synthesis of diethyl carbonate homologue dimethyl carbonate using PC or FC as raw materials has been deeply studied and industrialized. However, the direct application of transesterification synthesis to diethyl carbonate has not been reported. The transesterification reaction is also a reversible reaction, and the chemical equilibrium constant of the reaction is small. When the product is separated, the reverse reaction speed will be accelerated due to the decrease of ethanol concentration, thus the product yield will be reduced. Reactive distillation and other means should be used to improve the reaction yield.