4. Process Selection

A systematic approach for the selection of the process involves two parameters.

They are as follows:

4.1 Viability parameters

•  This parameter considers the following factors:
•   Availability of raw materials
•  Availability of utilities
•   Safety Health and Environmental aspects of the process
•   Simplicity of the process
•   Proven track of process licensor
•   Valuable intermediates and coproducts
•   Scope for backward integration

4.2 Profitability parameters

They include:

•   Gross cost of production
•   Project cost

Since the study is done in the pre feasibility level, the process selection exercise is carried out entirely on the basis of viability parameters.

4.3 Process Selection Exercise

In the conventional process for the manufacture of ethylene carbonate, phosgene is used. Phosgene is a highly toxic and corrosive gas. Moreover, there are lot of problems in handling it. So considering Safety- Health –Environmental (SHE) aspects, this process can be neglected. Manufacture of ethylene carbonate by oxidation of 1,3 dioxolane is not economically viable, due to low yield of the product. In chlorohydrin route, along with ethylene carbonate, large quantities of water are generated. Hence probability of ethylene glycol formation is higher. Ethylene carbonate-ethylene glycol separation is going to cost. So it is economically unviable. In transesterification process, undesirable byproducts are formed. So there is an additional burden on project cost to separate this byproduct, which is anyway worthless. Olefin halohydrin route seems to be attractive with reasonable selectivity for ethylene carbonate. But this process has not been commercially tested. Oxidation of olefin under CO₂ atmosphere gives low yield of ethylene carbonate.

4.4 Conclusion

The industrial process of manufacturing ethylene carbonate from ethylene oxide and carbon dioxide can be selected because of

• High yield of ethylene carbonate
• Simplicity of the process

4.5 Catalyst Selection

The first catalyst used for the conversion of ethylene oxide and carbon dioxide was NaOH on activated carbon. This catalyst was short lived because of poor yields of ethylene carbonate. Also serious explosions may result if ethylene oxide and NaOH are inadvertently combined in the absence of CO₂. Halogenides from univalent and multivalent metals are also effective as catalyst. Primary and secondary amines are effective catalysts for this reaction. They are less suitable because they can react with oxirane to yield alkanol amine thereby leading to lower efficiency and larger catalyst requirements (Dunn et.al.1956). Ion exchange resins containing quaternary ammonium groups such as the resins Amberlite IRA-400 and Amberlite IRA-410 can be used as catalysts (McClellan 1959). In technical processes in which conversion and yield are to be as high as possible in a short residence time, practically tetra ethyl ammonium bromide is used. This compound has the property of being able to dissolve homogeneously in the initial epoxide and in the reaction product whereas a few mentioned catalysts do not fulfil this requirement. So it is selected as a catalyst.

4.6 Solvent Selection

Solvents are primarily used as diluents in this reaction. These solvents assist in temperature control and permit the handling of reactants at lower pressure than that are otherwise possible. Dioxane, benzene, water and ethylene carbonate can be used as a solvent. Usage of dioxane, benzene and water as solvents is not attractive due to additional burden on separating them from product. So choosing ethylene carbonate itself as a solvent can save this downstream separation cost.