You might not recognize the words acetone and isopropanol (IPA), but the chances are that you use them. While these chemicals are beneficial — serving as the building blocks for thousands of products, including fuels, materials, acrylic glass, fabrics, and even cosmetics — they are generated from fossil inputs, leading to emissions of climate-warming carbon dioxide into the air.
Researchers led by LanzaTech, Northwestern University, and Oak Ridge National Lab have developed an efficient new process to convert waste gases, such as emissions from heavy industry or syngas generated from any biomass source, into either acetone or IPA. The secret to the new platform is Clostridium autoethanogenum, or C. auto, a bacterium engineered at LanzaTech that can convert waste carbon selectively into either ethanol, acetone, or IPA.
Their methods, including a pilot-scale demonstration and life cycle analysis (LCA) showing the economic viability, are published in the journal Nature Biotechnology. The new technology actually uses greenhouse gas (GHG) emissions destined for the atmosphere, avoids burning fossil fuels and removes carbon dioxide from the air. According to LCA, this carbon-negative platform could reduce GHG by over 160%, playing a critical role in helping the U.S. reach a net-zero emissions economy.
"This discovery is a major step forward in avoiding a climate catastrophe," said Jennifer Holmgren, LanzaTech CEO. "Today, most of our commodity chemicals are derived exclusively from new fossil resources such as oil, natural gas, or coal. Acetone and IPA are two examples with a combined global market of $10 billion. The acetone and IPA pathways and tools developed will accelerate the development of other new products by closing the carbon cycle for their use in multiple industries."
Acetone and IPA are necessary industrial bulk and platform chemicals. For example, acetone is used as a solvent for many plastics and synthetic fibers, thinning polyester resin, cleaning tools, and nail polish remover. IPA is a chemical used in antiseptics, disinfectants, and detergents and can be a pathway to commercial plastics such as polypropylene, used in both the medical and automotive sectors. Both are used in acrylic glass. IPA also is a widely used disinfectant, serving as the basis for one of the two World Health Organization (WHO) -recommended sanitizer formulations, which are highly effective against SARS-CoV-2.
The collaborators developed a gas fermentation process for carbon-negative production of either acetone or IPA by reprogramming LanzaTech's commercial ethanol-producing bacterial strain through cutting-edge synthetic biology tools, including combinatorial DNA libraries and cell-free prototyping advanced modeling, and omics. The scientists relied on a three-pronged approach that comprised innovations in pathway refactoring, strain optimization, and process development to achieve the observed level of performance. "These innovations, led by cell-free strategies that guided both strain engineering and optimization of pathway enzymes, accelerated time to production by more than a year," said Michael Jewett, the Walter. P Murphy Professor in Chemical and Biological Engineering in Northwestern's McCormick School of Engineering and director of the Center of Synthetic Biology.
The optimized process was scaled up to the pilot plant, and LCA showed significant GHG savings. "Conversion pathways for the production of any biofuel or bioproduct, including acetone and IPA, inevitably involve chemical byproducts that can cause or be the result of major bottlenecks," said ORNL's Tim Tschaplinski. "We used advanced proteomics and metabolomics to identify and overcome these bottlenecks for a highly efficient pathway. This approach can be applied to create streamlined processes for other chemicals of interest."
By proving scalable and economically viable bulk chemical production, the researchers have set the stage for implementation of a circular economic model in which the carbon from agriculture, industrial and societal waste streams can be recycled into a chemical synthesis value chain to perpetually displace ever-increasing volumes of products made from virgin fossil resources. Thereby, chemical synthesis would become a path to capturing, recycling and utilizing waste carbon resources.
The acetone strain and process development, genome-scale modeling, life cycle analysis, and initial pilot runs were supported by the Bioenergy Technologies Office in DOE's Office of Energy Efficiency and Renewable Energy. The cell-free prototyping and omics analyses were funded by the Biological and Environmental Research program in DOE's Office of Science. DNA sequencing and synthesis was supported by the Joint Genome Institute, a DOE Office of Science User Facility.
The journal article can be found at https://www.nature.com/articles/s41587-021-01195-w.
