Abstract
The use of polyurethanes and, therefore, the quantity of its scrap are increasing. Considering the thermoset characteristic of most polyurethanes, the most circular recycling method is by means of chemical depolymerization, for which glycolysis is finding its way into the industry. The main goal of polyurethane glycolysis is to recover the polyols used, but only limited attempts were made toward recovering the aromatic dicarbamate residues and derivates from the used isocyanates. By the split-phase glycolysis method, the recovered polyols form a top-layer phase and the bottom layer contain transreacted carbamates, excess glycol, amines, urea, and other side products. The hydrolysis of carbamates results in amines and CO2 as the main products. Consequently, the carbamates in the bottom layer of polyurethane split-phase glycolysis can also be hydrolyzed in a separate process, generating amines, which can serve as feedstock for isocyanate production to complete the polyurethane material cycle. In this paper, the full recycling of polyurethanes is reviewed and experimentally studied. As a matter of demonstration, combined glycolysis and hydrolysis led to an amine production yield of about 30% for model systems. With this result, we show the high potential for further research by future optimization of reaction conditions and catalysis.
Highlights
DicarbamateHexane-1,6-diyl bis(phenylcarbamate) (1) (reaction (a) on Scheme 3) was synthesized. 3) was as follows:
After the synthesis of dicarbamates (1 and 2) and polyurethane (3), they were used for multistage recycling
The synthesized polyurethane as well as both dicarbamates were characterized via Fourier-transform infrared spectroscopy (FT-IR) in order to investigate the urethane bond formation and the possibility of remaining isocyanates in the products
Summary
Hexane-1,6-diyl bis(phenylcarbamate) (1) (reaction (a) on Scheme 3) was synthesized. 3) was as follows:. Hexane-1,6-diyl bis(phenylcarbamate) (1) (reaction (a) on Scheme 3) was synthesized. 1,4atmosphere, and the mixture was(b) heated to 1003) °C for two hours. (reaction on Scheme was synthesized under the same (0.001 eq.) of tin 2-ethylhexanoate as catalyst were added to a three-neck flask under phenylenedicarbamate 2mixture mL for of was water was added neutralize the catalyst and non-reacted isocyanate. Of water was added to neutralize the catalyst and isocyanate. The mixture was transferred toon a the separation funnel and extracted three4,times withand. MgSO filtered, the(3 solvent was removed separation funnel and extracted three times with The organic fractions were combined, dried over MgSO4, filtered, and the solvent was removed on the rotavapor. Were combined, dried over MgSO4 , filtered, and the solvent was removed on the rotavapor.
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