Thin Film- and Short Path Evaporation Systems for the Distillation of Isocyanates

Isocyanates are basic components for the production of polyurethanes. Basic materials for the prepolymer are multifunctional isocyanates, like TDI (Toluene diisocyanate), MDI (Methyldiphenyldiisocyanate) or HDI (Hexamethylendiisocyanate) and various polyols. Unconverted isocyanates are toxic and must be eliminated from the pre-polymer as completely as possible. Safety regulations constantly demand lower residual contents, which can no longer be reached with conventional technologies. Depending on the original concentration of isocyanates, lower residual levels can be achieved in a single- or two-stage evaporation process.

The first stage distillates the major part of the isocyanates. The second stage reduces the isocyanates content to the permitted residual contents. The reactivity of the pre-polymer requires the separation of the isocyanates under high vacuum at specific temperatures.
Our horizontal thin film evaporator type SAKO KH meets the challenges in the first evaporation stage. Depending on the specific requirements, we either use a vertical thin film evaporator or a short path evaporator in the second stage. In pilot trials, we optimise the evaporator configuration for the specific isocyanates-polyol composition.

SMS delivers key equipment and engineering as well as complete systems for this demanding application.