Study and design of a Polyurethane foam recycling plant

Abstract

As a result of scientific progress, different polymers with very different properties and uses have been developed. The use of these materials is very common, therefore, an unsustainable amount of waste is generated. One of these polymers is polyurethane (PU). The most common type of PU manufactured and the one that generates the most waste are foams, both rigid and flexible. In Spain, there is no defined route for this polymer, causing most of them to end up in landfills. Currently, we are avoiding storing them indefinitely in a landfill, trying to revalue them by reusing or recycling them, and if this is not possible, trying to convert them into energy and heat. Among all recycling methods, the most promising is chemical recycling through glycolysis, which is based on the depolymerization of PU to split it into its monomers using low molecular weight glycols. The industrial development of glycolysis in the split phase is limited by the fact that an excess of glycolysis agent is needed in order to obtain a recycled polyol with better properties that can be used to synthesize new PU foams. This excess of agent makes the process not economically viable. For this reason, an agent has been sought to provide a polyol with good properties from a cheaper agent than diethylene glycol (DEG). Crude glycerol, which is a by-product of biodiesel production, has been considered as an agent capable of depolymerizing PU and at a lower price than DEG. In order to treat a part of the polyurethane flexible (PUF) foam waste generated in Catalonia, a preliminary design of a glycolysis recycling plant has been carried out in the starting phase, to treat 440 t/year of PUF foam waste from mattresses using crude glycerol, as glycolysis agent, and stannous octoate as catalyst