Circular polymers

Polyurethanes are ubiquitous. For the past 90 years, these all-rounders of the plastics world have been bringing comfort, stability and weather-proofness to our lives. As liquid coatings, they impart hard-wearing surface finishes to cars and floors. In the form of adhesives, they hold shoes and books together. The synthetic polymers are also essential to the furniture industry, in the form of flexible foams used for upholstery and mattresses. They are in rigid foams too, the kind that thermally insulate refrigerators and millions of buildings, thus boosting energy efficiency and making a significant contribution to climate protection.

IN THE MIDST OF CHANGE

Yet polyurethanes have some catching up to do in terms of their own sustainability. Like almost all of the world’s 414-million-tonne annual plastics output, they are generally made from petroleum products – a pathway that generates CO₂ emissions and drives climate change. And, at end of life, they wind up in landfills or incinerators. According to the OECD, only nine percent of the world’s plastic waste is recycled. But things are changing. “More and more chemicals companies are starting to rethink polymers. The industry is in the midst of a fundamental transformation process,” says Thomas Pellender, technical sales manager for the chemical industry at Endress+Hauser Germany. The pioneers here include Covestro, one of the world’s leading manufacturers of high-quality plastics and plastics intermediates. “The circular economy has been a guiding principle for us since 2019, and we are fully committed to it. We can’t achieve climate neutrality without circularity,” explains Dr Thorsten Dreier, chief technology officer at Covestro.

Covestro’s aim with its strategic program is to transition the production of plastics and their chemical constituents to environmentally friendly and climate-neutral alternatives wherever possible. Hence, the company makes increasing use of bio-based raw materials and renewable energy in its production processes. Alongside this, it is developing innovative, energy-efficient technologies to optimize the mechanical and chemical recycling of end-of-life products and unavoidable waste. The idea is that products and processes should be circular by design. Thorsten Dreier: “In all areas, we are cooperating with actors from across the value chain and the science community and forging new partnerships to find solutions that are best for the circular economy.”

The fruits of these efforts can be seen at Covestro headquarters in Leverkusen, Germany. On the factory campus there is a pilot facility with a vast array of reactors, columns, vessels and heat exchangers that occupies no fewer than four levels of an expansive laboratory and testing center. The facility, a world first, also has 600 meters of pipework as well as over 150 measuring points and sensors – many of them made by Endress+Hauser. The colorless liquid produced by this facility may in future be instrumental in expediting the transition to circularity – for the chemicals and plastics industry generally, and for Covestro in particular. “We have pioneered a process for producing aniline, one of our most important precursors, that uses plant biomass instead of petroleum-derived benzene,” explains project lead Thomas Vössing.

Covestro produces about a million tonnes of this organic compound annually, or about one sixth of worldwide output. “We use the aniline to produce MDI,” Thomas Vössing explains. MDI stands for methylene diphenyl diisocyanate – one of the main chemical building blocks used in the manufacture of rigid polyurethane foam. Covestro’s investment in the pilot plant runs into the single-digit millions of euros. The plant is the culmination of eight years of research conducted in partnership with RWTH Aachen and the universities of Düsseldorf and Stuttgart, also supported by government funding. “Commissioning the pilot plant was a major milestone,” Vössing says. “The biggest challenge with this project was to develop a holistic process concept from scratch and then translate it to a technical scale. That involved designing items of equipment that had never been built before.”

Bio-based aniline is produced in a series of steps. To begin with, a customized bacterium is used to ferment plant-based industrial sugar into an intermediate product that is isolated and then, in a following step, catalytically converted to aniline. “Once purified through distillation, this product can be used as a bio-based ‘drop-in’ alternative to petro-based aniline – the two are chemically identical,” explains Thomas Vössing.

Production of the basic chemical aniline is now possible without the use of crude oil or other fossil raw materials – thanks to a research breakthrough by Covestro.