Burdeniuc, J.; (EVONIK DEGUSSA) US Patent 10,472,459, 12-Nov-2019
Polyurethanes are formed by reacting isocyanates with polyols in the presence of catalysts and other additives (e.g., blowing agent for polyurethane foam). Amine catalysts are effective but they have the disadvantage of odor and emissions. Other catalysts include transition metals that can be expensive and toxic. The amine and transition metal catalysts can be replaced by an inexpensive alkali metal sulfite (produced by passing sulfur dioxide through an alkaline solution) that is not volatile. The challenge of bringing the inorganic sulfite anion into contact with the organic isocyanates and polyols is solved by using a quaternary ammonium phase-transfer catalyst.
The use of tetrabutylammonium chloride (TBAC) with potassium sulfite could be used to totally replace amine catalyst and transition metal catalyst. Under the same conditions cetyl trimethyl ammonium chloride did not work. Neither did the surfactant sodium dodecylbenzenesulfonate. This suggests that a true phase-transfer mechanism for the sulfite is at work, not just reducing interfacial tension to promote reaction at an interface.
Also tested was the use of a mixture of amine catalysts (including DABCO) typically used to produce polyurethane foam. The amount of amine catalyst could be reduced by 75% by using potassium sulfite with TBAC or the very inexpensive benzyl trimethyl ammonium chloride.
We speculate (without data; not mentioned in the patent) that the inventors used expensive TBAC rather than the much less expensive than TBAB due to the potential suppression of sulfite extraction by the bromide. Chloride typically enables 10 times more extraction of hydrophilic anions (such as sulfite) relative to bromide.
In 1989, I briefly served as a manager of isocyanate process research group at a major polyurethane company. One of the quality control methods used for making polyurethane foam was a “top of cup” rise test. The picture shows a typical test for rise of foam in a cup.
If your company wants to improve process performance for a reaction of any anion that is or may be reacted with an organic substrate, now contact Marc Halpern of PTC Organics to integrate highly specialized expertise in industrial phase-transfer catalysis with your commercial goals to achieve low-cost high-performance green chemistry.
