Chemical Recovery of Flexible PU Foam Wastes by Hydrolysis

5 Chemical Recovery of Flexible PU Foam Wastes by Hydrolysis [12-24, 27] 

The idealised reaction for the hydrolysis of the crosslinked structure of flexible PU foams is shown in reaction 20.16. - - -x 

By the hydrolysis of a flexible foam based on toluene diisocyanate (TDI) one obtains toluene diamine (2,4 and 2,6 isomers), the polyether triol and, of course, carbon dioxide. The difficulty of the process is the separation of the amine. The amine may be used for TDI synthesis (after a previous purification), or be transformed into a valuable rigid polyol (aminic polyol) by alkoxylation with PO and EO. 

The industrial process uses high pressure steam at 230-315 °C, which hydrolyses the flexible foam rapidly. The resulting diamines can be distilled and extracted from the steam stream. The polyols can be recovered from the residue and reused together with virgin polyol to make new flexible PU foams. 

A variation of steam technology is a hydrolysis-glycolysis process at 190-200 °C. LiOH proved to be an excellent catalyst of these reactions and the degradation process is accelerated markedly to just a few minutes while the temperature may be decreased at 170-190 °C [12,34]. 

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