3. Literature Survey

3. Literature Survey

Many processes are available for the manufacture of ethylene carbonate. They are described below.

3.1 Conventional Process

Ethylene carbonate can be commercially produced by the reaction of ethylene glycol with phosgene. However all the plants based on this process were phased out due to serious handling and corrosion problems in using phosgene.

3.2 Oxidation of 1,3 dioxolane

Ethylene carbonate can be prepared by the oxidation of 1,3 dioxolane with ozone in a solution of tertiary butanol. Ethylene carbonate of 20% yield is obtained.

3.3 Chlorohydrin Route (Steimmig and Wittwer 1933)

The reaction of ethylene chlorohydrin with alkali metal carbonate/bicarbonate gives ethylene carbonate at a temperature of 60 ^o C. Water is formed as byproduct. Water has to be continuously removed during the reaction by adding to reaction mixture, a low boiling solvent such as benzene or ethylene chloride. The probability of ethylene glycol formation is going to be higher due to presence of water. Hence, purity of ethylene carbonate obtained is not high.

3.4 Transesterfication (Grey 1992)

Potassium carbonate catalyses the reaction between ethylene glycol and diethyl carbonate to give ethylene carbonate. Metallic sodium, transition metal compounds catalyse the above reaction. But usage of these catalysts often results in product mixture that contains unwanted polycarbonates. Hence purity of the compound is low. This problem can be partially overcome by using catalyst such as alkyl ammonium salts, tertiary amines and ion exchange resins. Ethylene carbonate with 64% yield is obtained.  But still considerable amount of polycarbonate is formed.

3.5 Olefin Halohydrin Route (Wu 1975)

Ethylene is reacted with oxygen in the presence of an iron halide to produce ethylene halohydrin. This product is treated with carbon dioxide at a temperature of 100^o C in presence of an amine catalyst to give ethylene carbonate and amine hydrochloride salt. The reaction is carried out at 40 atm pressures. Methanol or acetone can be used as a solvent. 90% selectivity with respect to ethylene carbonate is possible.

3.6 Oxidation of Olefin (Verdol et.al. 1962)

Liquid phase oxidation of ethylene with gaseous mixtures of CO₂ and O₂ gives ethylene carbonate. Cobalt naphthenate is used as a catalyst. Benzene is used a solvent.  A temperature of 150^o C and a pressure of 300 atm are maintained. Ethylene carbonate of 30% yield is obtained.

3.7 Commercial Process (Wagner et.al 1994)

Most industrial processes for the manufacture of ethylene carbonate are based on this route. Ethylene oxide reacts with carbon dioxide at a temperature of 150^o C and at a pressure of 15 bar in the presence of tetra ethyl ammonium bromide as a catalyst to give ethylene carbonate. Ethylene carbonate is used as solvent for this process. Ethylene carbonate with 90% yield is obtained.