Turning plastic waste into detergent - Qingdao Paint Chemical Group Co.,Ltd

Plastic waste can be used as a raw material for detergents, thanks to a catalytic method by researchers at the University of California, Santa Barbara.

In a paper published in the journal Chem, the researchers have improved a process that can turn polyolefins, the most common type of polymer in single-use packaging, into alkylaromatics — molecules that underlie surfactants, the active components of detergents and other chemicals.

Chemical Engineer Professor Susannah Scott said the process could reduce the need for fossil fuels to make surfactants while giving single-use plastics one more shot at usefulness.

The researchers built on previous work in which they used a catalytic method to break the carbon-carbon bonds that make plastic difficult to degrade, then rearrange the molecular chains into alkylaromatic rings.

Scott said that while effective, the original process, based on a platinum-on-alumina catalyst, was slow, and its yield of alkylaromatic molecules was low.

“What we’ve done in this paper is show how to do it much better,” she said.

Key to their method is increasing the acidity of the original alumina catalyst, with the addition of chlorine or fluorine. With the added acid sites, the team was able to boost the speed and selectivity of their process.

Scott said they focused on finding the optimal ratio of acid sites to metal sites in their catalyst.

“It turns out they work together. They have different roles, but you need both of them to be there and in the right ratio, so the catalytic cycle doesn’t get stuck.”

In addition, their one-pot process operates at moderate temperatures, requiring a low energy input. While the method originally took 24 hours to turn plastic into alkylaromatic molecules, the improved process can complete the task within a couple of hours, increasing the amount of plastic that can be converted in a reasonably-sized reactor.

With further improvements, this method could be on its way to becoming a viable commercial process, according to Scott.

The goal is to bring it into wide use, which would enable and incentivise the recovery of single-use plastics.

Scott said using waste plastics as an abundant raw material, chemical companies could take the alkylaromatic molecules resulting from this process and transform them into the surfactants that are formulated into soaps, washing liquids, cleansers and other detergents.

“Ideally you want to reuse waste plastic for a purpose with a large enough production volume, for which there is significant demand, in order to make a dent in the plastic problem,” Scott said.

To determine if this method is truly sustainable, she added, it would have to undergo a lifecycle assessment, in which the energy spent and greenhouse gasses emitted are calculated at each step.

Using waste material ensures that no additional greenhouse gas emissions are produced to create the feedstock, but the energy required to run the catalytic process and separate the desired molecules would have to be factored in before scaling up, Scott said.

If it passes muster, the method could displace the more fossil fuel-intensive processes that go into creating surfactants from scratch.

“We will need multiple targets to deal with the waste plastic problem, but this is a fairly big one,” Scott said. “This is worth doing.”

Research on this study was also conducted by Jiakai Sun, Yu-Hsuan Lee and Mahdi M. Abu-Omar at UCSB; Ryan D. Yappert and Baron Peters at University of Illinois, Urbana-Champaign; and Anne M. LaPointe and Geoffrey W. Coates at Cornell University.

For more information, visit: www.news.uscs.edu