Sustainable chemical engineering: Brian Pfleger’s experiments toward a “paradigm shift” for chemical feedstocks

This article, by William Beimers, is part of a series highlighting members of the Office of Sustainability’s Experts Database. In a collaboration with instructor Madeline Fisher’s course, LSC 561: Writing Science for the Public, students interviewed campus sustainability experts and produced short feature stories. 

Brian Pfleger headshotWhen you hear the words “chemical engineering,” living things probably aren’t the first to come to mind. UW–Madison professor Brian Pfleger is trying to change that. 

Pfleger’s research lab is leading a paradigm shift in chemical engineering, which is moving from traditional carbon sources like oil and gas toward a circular chemical economy. Pfleger’s concentrates on biomanufacturing, or using microorganisms to produce the same industrial products in a more sustainable way. Although this shift isn’t new, it’s accelerating now as the climate crisis worsens.

“As we turned the century when I graduated college, the sustainability focus was growing,” Pfleger said. “This is something we have to do as a planet.” 

Pfleger’s graduate work focused on metabolic engineering of bacteria to produce useful chemicals. Normally chemicals are produced from starting materials sourced from the oil and gas industry, but bacteria can produce them with less waste and pollution. Now the Karen and William Monfre Professor of Chemical and Biological Engineering, Pflegeer has expanded to harnessing many types of microbes for sustainable chemical production.

According to Pfleger, chemical engineering and biological engineering of organisms have long been intertwined.

“We’ve used biotechnology or organisms to do synthesis of chemicals for many millennia, ethanol fermentation has been around for a long time, and it wasn’t necessarily a chemical engineer doing it,” he said. 

However, the full connection between engineering and biology wasn’t realized until the mid-twentieth century, when the mass production of antibiotics began to require huge amounts of microorganisms. It wasn’t just a question of understanding the biology of the organisms, but also of how to keep sterility, design more efficient industrial fermenters, and regulate heat generation, all problems related to engineering.

But what really accelerated the field in the late twentieth century was new ways of improving the cellular producers themselves with genetic engineering. In the 1970s scientists learned how to directly change genes through recombinant DNA technology, inserting new pieces of genetic material into yeast and bacteria. As this technology improved and became more widespread, microorganisms became the main industrial producers of many proteins, chemicals, and drugs.

As you might expect, modifying organisms for industrial production can be both highly rewarding and highly challenging. There are almost endless possibilities, so how does Pfleger choose a focus? He uses the concept of a “grand challenge,” a global problem facing humanity that we absolutely must solve. 

“Sustainability is one of the grand challenges, but there are many others,” he said. “Nutrition is another, and one of the other big ones is going to be antibiotic resistance.” 

Pfleger’s sustainability “grand challenge” focuses on using microorganisms to produce industrial chemicals, moving away from oil and gas as sources. To displace non-renewable resources, biomanufacturing processes must feed microbes, and sugars remain the preferred food. Pfleger is taking this production scheme a step further by removing sugars from the equation and engineering organisms to start making chemical feedstocks from just carbon dioxide and sunlight using photosynthesis. 

“The paradigm for sustainable chemical production has been and is still dominated by sugars, but there are ways that we can get from photosynthesis and carbon dioxide to some other chemical intermediate,” he said. Photosynthesis is a carbon-neutral or even carbon-capturing process, whereas sugars still need to be harvested and processed and transported, generating emissions.

Partnering with LanzaTech, Pfleger hopes to use the Chicago company’s expertise in gas fermentation to create a paradigm shift. The idea is to couple two bioreactors, one where a chemical intermediate can be created simply from carbon dioxide and renewably generated hydrogen. The intermediate is fed to another reactor that can produce a downstream product like plastics or fuels.

Pfleger is hopeful his research can help overcome the limitations of using sugars as feedstocks for bioproduction. The two-step bioreactor process would allow for more combinations and reactions to occur that a single bioreactor fed with sugars doesn’t allow. 

“This is an exciting project, there’s lots of technical challenges to this, but a wide list of things we can start to look at, like other types of microorganisms,” he said. “I think we’re going to see a paradigm shift away from ‘what we can make from sugar’ to thinking a little bit more like a chemist and saying what is the best feedstock to make this product.”