Elsevier

Fuel

Volume 111, September 2013, Pages 598-605
Fuel

Zr(O)Cl2 catalyst for selective conversion of biorenewable carbohydrates and biopolymers to biofuel precursor 5-hydroxymethylfurfural in aqueous medium

https://doi.org/10.1016/j.fuel.2013.03.031Get rights and content

Highlights

  • Investigated sustainable routes for HMF production in environmentally benign solvent.

  • Cheap, earth abundant and water tolerable ZrOCl2 catalyst achieved 84% HMF yield.

  • Potential of ZrOCl2 for HMF production has been compared with other metal chlorides.

  • Elucidated mechanism for glucose and sucrose dehydration by 1H NMR study.

Abstract

The catalytic activity of Lewis acidic metal chlorides were screened for the production of biofuel precursor platform chemical, 5-hydroxymethylfurfural (HMF), from carbohydrates and biopolymers in aqueous and biphasic solvents under microwave and conventional heating methods. The screening of metal chloride catalysts for dehydration of several carbohydrate substrates revealed that Zr(O)Cl2 catalyst is the most effective. Cheap and readily abundant Zr(O)Cl2 catalyst produced 63% and 42% HMF from fructose and glucose, respectively, in water using methylisobutylketone (MIBK) as the organic phase in biphasic solvent system. The yield of HMF increased to 84% and 66% when Zr(O)Cl2 catalyzed dehydration of fructose and glucose was carried out in [BMIM]Cl (1-butyl-3-methylimidazolium chloride)-MIBK biphasic solvent. 1H NMR studies revealed that the dehydration reactions progressed through the formation of fructofuranose as an intermediate. Accordingly, a mechanism for isomerization of glucopyranose to fructofuranose has been proposed. The catalyst was recycled for five catalytic cycles without a significant loss in its activity.

Introduction

Replacing fossil-based resources with renewable and sustainable alternative is the major objective [1], [2] of this generation due to the fact that consumption of carbon sources for energy and chemicals in irreversible manner would diminish fossil fuel reserves and increase the risk of global warming by CO2 emission [3], [4]. Furanics, such as 5-hydroxymethylfurfural (HMF) is a renewable platform chemical suitable for the production of a range of chemical intermediates [5], [6] and liquid transportation fuels [7], [8]. This necessitates the development of sustainable processes for the conversion of biomass and carbohydrates into HMF to bridge the growing gap between supply and demand of energy and chemicals [9], [10]. Besides effectiveness of the catalysts for high HMF production, solvents also play an important role to enhance HMF yields, its purity and easy separation to make the process economically viable. Apart from deriving HMF from carbohydrates with chromium halides catalysts in ionic liquids (ILs) [10], [11], several reaction media, including water [12], [13], [14], [15], [16], organic solvent [17], and biphasic water/organic solvents [18], have been utilized. Although excellent yield of HMF was reported in dimethylsulfoxide (DMSO) solvent, extraction of HMF, toxicity of DMSO, and possible formation of sulfurized products remain as significant drawbacks.

In recent years, HMF was derived from fructose, glucose and other carbohydrates by homogeneous Lewis acidic metal chloride catalysts such as Cr(II) or Cr(III) complexes of N-heterocyclic carbine (NHC) ligand [11], SnCl4 in 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]Cl [19], tungsten salts (WCl4, WCl6) in 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) [20], GeCl4 in [EMIM]Cl [21], boric acid (B(OH)3) [18] and AlCl3 [15], [22]. Besides carbohydrate substrates, Cr(II) and Cr(III) based catalysts were extensively used for the production of HMF from cellulose and untreated lignocellulosic biomass. Binder and Raines reported that CrCl2 catalyzed transformation of untreated biomass (corn stover) and purified cellulose can produce 48% and 54% HMF, respectively [9]. In the same year, Zhang et al. reported the formation of 58% HMF from cellulose using CrCl2/CuCl2 catalyst in ionic liquid [23]. Chromium based catalysts, such as CrCl2–NHC–carbene and CrCl2/RuCl3 have been recently utilized for the conversion of cellulose substrates, reporting 48% and 60% HMF yields, respectively, in ionic liquid [24], [25]. While chromium based homogeneous catalysts are reported to facilitate isomerization of glucopyranose to fructofuranose and hence produce moderate to high HMF, the effectiveness of the process was undermined by potential toxicity and environmental concerns of chromium metal for large commercial implementation. To overcome these challenges, several heterogeneous Lewis acidic mesoporous materials have been developed and tested as solid catalysts. These includes, anatase-TiO2 [14], self-assembled mesoporous TiO2 nanospheres prepared via templating pathways and hierarchically porous titanium phosphate (MTiP-1) having different Lewis acidity and surface area [16], [26], [27], [28]. Although, the Lewis acidic solid catalysts are promising in terms of recyclability and easy separation, these catalysts are also not promising due to poor yield of the desired HMF product particularly in aqueous medium.

As discussed above, several homogeneous metal chloride catalysts have been tested for the production of HMF, however, the application of zirconium-based Lewis acid catalyst, Zr(O)Cl2 (Scheme S1), for the dehydration of carbohydrates is rare even though the potential of Zr(O)Cl2 as a catalyst for other type of reactions are known for many years. It is only recently, a combined Zr(O)Cl2/CrCl3 catalytic system has been utilized for the production of HMF and 5-ethoxymethylfurfural (EMF) from cellulose and sugarcane bagasse [29]. Although this combined metal chloride catalyst produced maximum 57% and 42% HMF from cellulose fiber and sugarcane bagasse respectively, the use of toxic CrCl3 salt limits its potential industrial application.

While Zr(O)Cl2 is an attractive catalyst because of its abundance and cost-inexpensive nature, and hence can potentially address economic and environmental concerns for large scale HMF production technology, the catalytic effectiveness of Zr(O)Cl2 alone is not known for HMF production from carbohydrate substrates. Therefore, in the present report we investigate the potential of Zr(O)Cl2 catalyst for the transformation of biorenewable substrates, starch and carbohydrates (fructose, glucose and sucrose), to HMF in aqueous and biphasic media under mild reaction conditions (Scheme 1). The catalytic activities of RuCl3, CuCl2, FeCl3 and SnCl4 have also been tested and compared with the catalytic activity of Zr(O)Cl2.

Section snippets

Materials and experimental methods

All chemicals including fructose, glucose, sucrose, starch, [BMIM]Cl, HMF (for authentic reagent) were purchased from Sigma–Aldrich and were used without further purification. Unless otherwise stated, distilled water was used as aqueous phase for reactions in aqueous and aqueous-organic phase throughout the work. MIBK was purchased from Spectrochem, India. Metal salts, CrCl3·6H2O, FeCl3 (anhydrous), CuCl2·2H2O, Zr(O)Cl2·8H2O, and SnCl4·5H2O of ∼99% purity were purchased from Thomas Baker, India

Results and discussion

Several experiments were designed for screening the catalytic effectiveness of various metal chloride catalysts for HMF production from monosaccharides, disaccharides and starch under variable reaction conditions such as nature of solvents, catalysts, catalyst concentrations, nature of substrates, substrate concentrations, reaction time and temperature. The purpose for designing these experiments are: (i) identification of an effective catalyst combination and (ii) optimization of reaction

Conclusions

The catalytic effectiveness of cheap and readily abundant Zr(O)Cl2 catalyst was investigated for the production of HMF from carbohydrates and starch in water, water-MIBK and [BMIM]Cl-MIBK biphasic solvents under microwave and oil-bath heating conditions. The dehydration reaction of fructose, glucose, sucrose and starch with 10 mol% Zr(O)Cl2 catalyst produced 63, 42, 24 and 19 mol% HMF in water-MIBK solvent, respectively. A 20–29% improvement in HMF yield was recorded from all substrates when

Acknowledgement

BS gratefully acknowledge financial support by Council of Scientific and Industrial Research (CSIR), India and UGC, India. SD thanks UGC for a junior Research Fellowship.

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