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GEA MDI Splitting Process

Methylene diphenyl diisocyanate (MDI) is an organic chemical which is one of the main components for the production of polyurethanes. Crude MDI is still only commercially produced via the phosgene route and contains three diisocyanate isomers, oligomeric polyisocyanates (tri,tetra,penta ,etc isocyanates), byproducts and impurities. The present market requires separate products or blends thereof to make polyurethanes with a wide range of properties. The MDI splitting plant is responsible for producing the commercially viable fractions from this crude feed. The typical MDI fractions of commercial importance can be generally classified as:
(a) Polymeric MDI (mixtures of oligomeric and 2,4 / 2,2 & 4,4 MDI),
(b) Pure MDI (mostly 4,4 with some 2,4 MDI) and
(c) Mixed MDI Isomers (a range of 2,4 / 2,2 & 4,4 MDI excluding oligomeric)

This novel hybrid configuration provides significant advantages over the conventional process; more than 50% energy reduction can be realized through the combination of optimized distillation with an efficient crystallization system and reduced vacuum load The product quality is improved by reducing temperature related product degradation, less generation of toxic light impurities and reduced dimer formation. Fewer and smaller components provide for reduced CAPEX.

Flexible operation is key to the design; higher 2,4 MDI compositions can be realized depending on the crude feed composition. The crystallization capacity is based on a pure 4,4 MDI output and increased 2,4 MDI can easily be handled on the same equipment (filtrate flow is not limiting). The ratio of 2,4 MDI in the feed to 2,4 MDI in the Pure 4,4 MDI product is thus maximized resulting in a high overall rejection in the Pure 4,4’ MDI fraction of the close boilers that are not removed in the distillation process.

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GEA Wiegand

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