This invention pertains to a process for decolorizing organic carbonates, particularly, cyclic alkylene carbonates. In another aspect, this invention pertains to a decolorized organic carbonate composition.
As used hereinafter, the term "organic carbonate" includes cyclic alkylene carbonates and di(hydrocarbyl) carbonates, such as dialkyl carbonates, diaryl carbonates, and alkyl aryl carbonates.
Cyclic alkylene carbonates, such as propylene carbonate and butylene carbonate, have numerous uses including use in paint remover compositions and as developers and stripping solvents for photoresist materials. Dialkyl carbonates, such as dimethylcarbonate, are useful as solvents for cellulose derivatives and as starting materials for the preparation of diaryl carbonates, aliphatic and aromatic polycarbonates, pharmaceuticals, and plant protection agents. Diaryl carbonates, such as diphenyl carbonate, find utility in the preparation of thermoplastic polycarbonates.
Organic carbonates may exhibit a discoloration which may range from a light yellowish tinge to a rather intense yellow. Discoloration may arise from the formation of colored impurities or by-products during synthesis of the organic carbonate. The presence or absence of color in organic carbonates may also reflect the degree of refinement or purification to which the carbonate has been subjected. Alternatively, discoloration may arise from contaminants acquired during storage or handling of the carbonate. Discoloration in organic carbonates disadvantageously lowers product value. Reduction of the color may be desirable for esthetic reasons or for other reasons, such as when a high purity product is required for a given end use. High color in the carbonate can interfere with its use in coating applications, urethanes and epoxies where clear or light colors are required.
Distillation methods are known for removing impurities from organic carbonates. These methods are expensive and can only be used with carbonates which are capable of being distilled. Other purification methods, such as recrystallization and adsorption over a solid adsorbent, may be employed to remove color, but these methods are also expensive. In fact with carbonates, the color often cannot be removed by single distillation unless a very deep distillation cut is taken and the light material (10-40%) is discarded. This is very costly and wastefull. Further, it is often observed that early distillation cuts, though at first appearing clear in color, will turn yellow upon aging. In view of the above, it would be desirable to find a method for decolorizing organic carbonates which is inexpensive, easy to implement, and adaptable to a wide variety of organic carbonate products.