Researchers from the University of Minnesota, with colleagues at the University of Massachusetts Amherst, have developed a new high-yield process—a hybrid of fermentation followed by thermochemical catalysis—to produce renewable isoprene from biomass.
In the process, fermentation of sugars produces itaconic acid, which undergoes catalytic hydrogenation to produce 3-methyltetrahydrofuran (MTHF). The MTHF then undergoes catalytic dehydra-decyclization to isoprene. This catalytic process dehydrates MTHF to isoprene via several combinations of temperatures, pressures, and space velocities (reactant volumetric flow rate per volume of catalyst) and achieves selectivity of MTHF to isoprene.
The University of Minnesota, through its Office for Technology Commercialization, has applied for a patent on the renewable rubber technology and plans to license the technology to companies interested in commercializing the technology. A paper on the basis of the process was published earlier this year in ACS Catalysis.
The search for a commercially viable process for renewable isoprene is not new. In 2010, for example, Dr. Joseph McAuliffe from Genencor noted that:
An intensive search has been underway for years for alternative sources of isoprene, in particular those from renewable resources such as biomass. One technical challenge has been the development of an efficient process for converting sugars into isoprene.—Dr. Joseph McAuliffe (earlier post)
Although processes exist for the production of isoprene from biomass, these processes suffer from low overall yields or low conversion rates, preventing them from being economically feasible. With a less expensive precursor and a high yield,; the Minnesota method is not only economically viable, but economically competitive with current petroleum processes, the University claims.
Natural rubber is the precipitated polymer chain product (~106 Da) obtained from the latex of rubber trees (Hevea brasiliensis) as an important material for automobile tires. The dominant form of natural rubber consists of isoprene units (2-methyl-1,3-butadiene) polymerized to form poly(cis-1,4- isoprene), a natural polymer from southeast Asia. Isoprene is also currently manufactured as a byproduct of naphtha and gas oil cracking, serving as one of the major monomers for rubber and elastomers. The majority of fossil-derived isoprene is used to produce poly(cis-1,4-isoprene) as a synthetic ‘natural’ rubber, providing a non-renewable source of rubbery material at the scale of one million tons per year.
Renewable synthetic ‘natural’ rubber (RSNR) or ‘biobased poly-isoprene’ requires isoprene from alternative renewable feedstocks such as glucose. Genencor and Goodyear have pursued microbial fermentation to BioIsoprene via engineered bacteria, with competitive synthetic biology routes to renewable isoprene pursued by Amyris and Michelin. Five existing thermochemical pathways to isoprene also include: (i) acetone addition to acetylene followed by partial hydrogenation and dehydration, (ii) propylene dimerization, (iii) isoamylene dehydrogenation, (iv) isopentane dehydrogenation, and (v) the Prins condensation of isobutene and formaldehyde. Any of these five processes can be renewable provided the feedstocks are sourced from biomass; for example, dehydration of glucose-derived isobutanol produces isobutene.—Abdelrahman
The first step of the new process is microbial fermentation of sugars, such as glucose, derived from biomass to the intermediate itaconic acid. In the second step, itaconic acid is reacted with hydrogen to MTHF. This step was optimized when the research team identified a unique metal-metal combination that served as a highly efficient catalyst.
The process technology breakthrough came in the third step to dehydrate methyl-THF to isoprene. Using a catalyst recently discovered at the University of Minnesota called P-SPP (Phosphorus Self-Pillared Pentasil), the team was able to demonstrate a catalytic efficiency as high as 90% with most of the catalytic product being isoprene. By combining all three steps into a process, isoprene can be renewably sourced from biomass.
The performance of the new P-containing zeolite catalysts such as S-PPP was surprising. This new class of solid acid catalysts exhibits dramatically improved catalytic efficiency and is the reason renewable isoprene is possible.—Paul Dauenhauer, a University of Minnesota associate professor of chemical engineering and materials science and lead researcher
The invention of renewable tire technology is part of a larger mission of the Center for Sustainable Polymers, an NSF-funded Center for Chemical Innovation led by the University of Minnesota. Initiated in 2009, the CSP has focused on transforming how plastics are made and unmade through innovative research. Researchers aim to design, prepare and implement polymers derived from renewable resources for a wide range of advanced applications.
Omar A. Abdelrahman, Dae Sung Park, Katherine P. Vinter, Charles S. Spanjers, Limin Ren, Hong Je Cho, Kechun Zhang, Wei Fan, Michael Tsapatsis, and Paul J. Dauenhauer (2017) “Renewable Isoprene by Sequential Hydrogenation of Itaconic Acid and Dehydra-Decyclization of 3-Methyl-Tetrahydrofuran” ACS Catalysis 7 (2), 1428-1431 doi: 10.1021/acscatal.6b03335 DOI: