Aminosilane-Grafted SiO2-ZrO2 Polymer Hollow Fibers as Bifunctional Microfluidic Reactor for Tandem Reaction of Glucose and Fructose to 5-Hydroxymethylfurfural

Significance 

Various building blocks like liquid biofuels and polymers can be converted into a wide variety of useful chemicals. This requires the use of biobased precursor molecules such as 5-Hydroxymethylfurfural (HMF). Despite its versatility and multifunctionality nature, industrial-scale production of this biochemical has remained a challenge. This has led to the investigation of the possibility of producing HMF from sugar molecules such as fructose and glucose. This was particularly intensified by the discovery of bifunctional catalysts that uses two different active species to catalyze reaction steps at a higher reaction rate. Consequently, the tandem reaction of glucose to HMF has been widely researched, including immobilization and anchoring of homogenous catalysts on solid surfaces like microstructured reactors.

Dr. Yingxin He, Abdo-alslam Alwakwak (PhD candidate), Dr. Ming Huang and Dr. Fatene Rezaei from Missouri University of Science and Technology together with Dr. Arun K. Itta from the Georgia Institute of Technology presented a new method for direct conversion of fructose and glucose to HMF in a continuous flow manner without separating the intermediates and catalysts. The tandem reaction concept was demonstrated in an aminosilane-grafted SiO2-ZrO2 polyamide-imide hollow fiber representing a bifunctional heterogeneous catalyst and microfluidic reactor. The work is currently published in the journal, ACS Sustainable Chemistry & Engineering.

In brief, the research team started by forming the bifunctional heterogeneous catalysts. This was achieved by embedding the SiO2 and ZrO2 nanoparticles into a polyamide-imide polymer that underwent a phase variation process followed by post grafting with aminosilane. Furthermore, the first step of glucose isomerization was integrated with the subsequent step of dehydrating the fructose to HMF over the bifunctional Bronsted and Lewis sites of the hollow microfluidic reactors at varying temperatures and reaction times. Eventually, they evaluated the factors affecting catalytic activities as well as the HMF selectivity by optimizing the Lewis and Bronsted acid sites ratio in the hollow fiber catalysts.

By using fructose and glucose as feedstock respectively, the HMF selectivity was enhanced from 21% to 34% and 21% to 82% respectively. The key factors affecting the catalytic activity were observed to be aminosilane grafting and the cooperation of Lewis and Bronsted acids. Also, waster exhibited reliable effects on the glucose isomerization and fructose dehydration to HMF. With remarkably good catalytic efficiency and stability at different reaction temperatures, the bifunctional catalysts proved to be a promising microfluidic system for the tandem conversion of carbohydrates by controlling the reaction temperatures and contact time.

As proof of the concept, hollow fiber catalysts were recycled three times producing over 50% HMF yield. The tandem reaction based on the bifunctional SiO2-ZrO2 exhibited a 100% glucose conversion with an HMF selectivity of up to 34%. Besides, the tandem microfluidic system enabled precise control of the reaction parameters: temperature, flow rate and time. As such, the need for additional catalyst separation steps was eliminated. Based on the results, Dr. He the first author in a statement to Advances in Engineering highlighted the significance of the study and its role in advancing large-scale conversion of fructose into HMF for industrial use.

Reference

He, Y., Itta, A., Alwakwak, A., Huang, M., Rezaei, F., & Rownaghi, A. (2018). Aminosilane-Grafted SiO2–ZrO2 Polymer Hollow Fibers as Bifunctional Microfluidic Reactor for Tandem Reaction of Glucose and Fructose to 5-HydroxymethylfurfuralACS Sustainable Chemistry & Engineering, 6(12), 17211-17219.

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