Sugar-Based Biopolymers Beckon

Jan. 4, 2019

Researchers have overcome a major hurdle to production of commodity chemicals from sugar-based biomaterials.

Researchers have overcome a major hurdle to production of commodity chemicals from sugar-based biomaterials. In a study carried out jointly with Mitsubishi Chemical, Tokyo, scientists at the Institute of Catalysis at Hokkaido University, Hokkaido, Japan, and Eindhoven University of Technology, Eindhoven, The Netherlands, have found a way to oxidize 5-(hydroxymethyl) furfural (HMF), a compound formed by the dehydration of certain sugars, into a monomer suitable for biopolymer production.

HMF now most commonly is used as a food additive and flavoring agent. However, it has attracted the attention of researchers for its potential as a carbon-neutral feedstock for polymers, chemicals and fuels. This requires its oxidization to furan-2,5-dicarboxylic acid (FDCA), which, in turn, could enable replacing petroleum-derived terephthalic acid with biomaterials in plastic bottle applications.

Up until now, though, yield of FDCA hasn’t been anywhere near adequate for industrial application.

A high yield of FDCA does occur when HMF is oxidized in a diluted solution (under 2 wt.%) with various supported metal catalysts. However, industrial use would require a concentrated solution (10–20 wt.%), which gives an FDCA yield of only around 30%. Another drawback is the large amount of solid byproducts known as humins generated as a result of the complex side reactions that take place with the HMF molecules. Such humins have frustrated the development of either batch or continuous reactions.

Led by associate professor Kiyotaka Nakajima at Hokkaido University and professor Emiel J.M. Hensen at Eindhoven, the joint research team has succeeded in suppressing the side reactions that form humins while producing FDCA in high yields from 10–20 wt.% solutions of HMF.

Reaction Pathways

Figure 1. New route acetalizes HMF to suppress the formation of unwanted humins. Source: Hokkaido University/Eindhoven University of Technology.

To achieve this, the team first acetalizes HMF with 1,3-propanediol (1,3-PD) to block byproduct-inducing formyl groups (Figure 1). This HMF-acetal derivative exhibits excellent thermal stability and its oxidation with a CeO₂‐supported Au catalyst and Na₂CO₃ in water gives a 90–95% yield of FDCA, the researchers report.

About 80% of the 1,3-DP employed to protect the formyl groups can be reused for subsequent reactions.

“It’s significant that our method can reduce the total energy consumption required for complex work-up processes to isolate the reaction product,” notes Nakajima.

“Our next interest is to scale-up the lab experiment and to improve both catalyst efficiency and the 1,3-PD recovery process to further reduce its degradation. However, we do not expect to extend this lab-scale experiment to large-scale production,” he adds.