Renewable plastic precursor from biomass

ENGINEERS at the University of Wisconsin–Madison, US, have developed a way to make 1,5-pentanediol, a commodity chemical used in plastic manufacture, from biomass.

The team, led by George Huber, professor of chemical and biological engineering, are working to develop bio-derived commodity chemicals to replace their petroleum-derived counterparts. These chemicals would be produced as co-products in a cellulosic biorefinery, improving the economics of bio-derived fuels and chemicals. Currently, cellulosic biofuels are more expensive than first-generation biofuels made from sugar or starch fermentation.

Biomass contains up to 40% oxygen by weight, while petroleum contains just 0.1%, making chemical production a challenge. However, the UW-Madison team’s method uses the oxygen within the biomass to make the oxygenated chemical 1,5-pentanediol. They have so far tested the process on corn stover, white birch and switch grass feedstocks.

Huber explains that the process begins with hemicellulose, the five-carbon fraction of lignocellulosic biomass. This undergoes hydrolysis to form xylose, then dehydrogenation to form furfural. The furfural is then hydrogenated to make tetrahydrofurfuryl alcohol (THFA). Huber says that there are already commercial processes available to make furfural from biomass and to turn it into THFA.

THFA is the starting point for the team’s new process. The first stage uses a solid acid catalyst, γ-Al₂O₃ to turn THFA into dihydropyran (DHP), at a temperature of 648 K at 1 atm. DHP is converted into hydroxytetrahydropyran (2-HY-THP) and its ring-opened tautomer, 5-hydroxyvaleraldehyde (5-HY-Val), at 373 K in water. This equilibrium mixture is then hydrogenated with a ruthenium catalyst at 383-393 K with hydrogen at a pressure of 45 bar, making the 1,5-pentanediol.

Huber and the team say that their process to make 1,5-pentanediol is the first economically viable way to make the chemical from biomass, being six times cheaper than a previously-reported method, which although having one step rather than several, uses expensive noble metal catalysts with low specific activity.

“This breakthrough shows how biomass-derived commodity chemicals can economically be used to replace petroleum-derived products,” said Huber. “It also shows how we might improve the rural economies in which biomass grows.”

1,5 pentanediol is, as yet, not widely used, but Huber tells The Chemical Engineer that this is largely due to a lack of C5 feedstocks. However, the chemical could replace two more common plastic precursors, 1,4 butanediol and 1,6-hexanediol. These cost US$1,600–2,800/t and US$2,500–4,500/t respectively, and together, the chemicals have an annual market of more than US$6m. Huber says that their method can produce 1,5 pentanediol for below US$2,488/t. The researchers believe that the technique could eventually be used to make 1,4 butanediol and 1,6-hexanediol.

Leigh Cagan, chief technology commercialisation officer for Wisconsin Alumni Research Foundation (WARF), says that there has already been commercial interest in the process. The team will now work to refine and scale up the work.

ChemSusChem doi.org/f9thdj