Orthophthalic Unsaturated Polyester Production

The process under analysis comprises three major sections: (1) Esterification; (2) Cross-linking; and (3) Glycols Recover.

Esterification. This first step involves the polycondensation between a combination of phthalic anhydride and maleic anhydride, and a combination of glycols. Initially, the glycols (propylene glycol, MEG and DEG) are charged to the reactor. Subsequently, maleic anhydride and phthalic anhydride are added to the mixture. The esterification reactor is equipped with stirrers and heating. It is fed with nitrogen to generate an inert blanket. The high temperatures in the reactor cause the evaporation of the glycols and the water generated in the reaction.

Cross-linking. The cross-linking is carried out in a different vessel, where the polycondensation product is dissolved in styrene and the reaction takes place. In this reaction, the vinyl radical in styrene monomer reacts with the unsaturation in the polyester chains, thus linking different chains. Also during this step, promoters are added to initiate the copolymerization and inhibitors are added to moderate the reaction and keep temperature within required limits to avoid product degradation. At last, the final product is charged into drums and stored in a warehouse.

Glycols Recover. A water separation column receives the overhead vaporous glycol-water mixture from the reactor. The column top temperature is kept at 100 - 105 °C in such a way that the column overhead product contains only water, which is further routed to a condenser and discarded. The glycol-rich bottom product is recycled to the reactor.