Conversion of Carbohydrates into Platform Chemicals Catalyzed by Alkaline Ionic Liquids

Xiaojia Du,Yuehai Wang,Jie Zhang,Yongshui Qu

doi:10.3390/catal7090245

Xiaojia Du, Yuehai Wang + Show 2 more

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https://doi.org/10.3390/catal7090245

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Abstract

A series of alkaline ionic liquids (ILs) including 1-butyl-3-methylimidazolium benzoate ([BMIM]PHCOO), 1-butyl-3-methylimidazolium carbonate ([BMIM]2CO3), 1-butyl-3-methylimidazolium acetate ([BMIM]OAc), 1-butyl-3-methylimidazolium hydroxide ([BMIM]OH), ethanolamine tetrafluoroborate ([MEA]BF4), and 1,1,3,3-tetramethylguanidine (TMG)-based ILs, etc., were synthesized and utilized as catalysts for the conversion of carbohydrates into 5-HMF. 1,1,3,3-tetramethylguanidine tetrafluoroborate ([TMG]BF4) was confirmed to exhibit excellent catalytic activity, and was much cheaper than other ILs such as 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) for use as a solvent in the conversion of C6 carbohydrates into 5-HMF. The 5-HMF yields from fructose, glucose, cellobiose, and microcrystalline cellulose (MCC) were 74.19%, 27.33%, 20.20%, and 17.73%, respectively. In addition, the possible pathway of carbohydrates (MCC, cellobiose, glucose, etc.) conversion into 5-HMF with [TMG]BF4 as a catalyst was speculated, and the conversion of glucose into 5-HMF was determined to likely be the committed step in the transformation of MCC catalyzed by [TMG]BF4.

Highlights

The continuous depletion of conventional fossil fuel resources and the risk of global climate change have forced researchers to search for alternative sustainable energy resources [1,2,3]
The mixture was filtered through a 0.45-μm pore size membrane and decanted into a volumetric flask using water as a diluent. 5-HMF and furfural were analyzed by HPLC
With [BMIM]BF4 as a catalyst, the conversion and yield were 5.15% and 3.44%, respectively. These results demonstrate that with the same anion BF4 −, [TMG]+ ion results in better catalytic activity compared to [BMIM]+

Summary

Introduction

The continuous depletion of conventional fossil fuel resources and the risk of global climate change have forced researchers to search for alternative sustainable energy resources [1,2,3]. Several researchers have investigated the efficient conversion of carbohydrates into high value-added chemicals, such as 5-hydroxymethylfurfural (5-HMF), levulinic acid (LA), formic acid (FA), acetic acid, furfural, etc. The US Department of Energy has already declared it to be among the “top 10 bio-based chemicals” [7] This chemical is highly reactive and can be used as a starting material for a number of products. Fructose is an expensive starting material for 5-HMF production compared to glucose. The use of glucose and cellulose (the most widespread natural polymer materials) cannot only significantly reduce the production cost of 5-HMF, but will improve the utilization efficiency of biomass. Zhang et al [17] first observed that ILs resulted in nearly 70% yield of 5-HMF from

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