Simple and Efficient Furfural Production from Xylose in Media

Research Note pubs.acs.org/IECR

Simple and Efficient Furfural Production from Xylose in Media Containing 1‑Butyl-3-Methylimidazolium Hydrogen Sulfate Susana Peleteiro,† Andre M. da Costa Lopes,‡,§ Gil Garrote,† Juan Carlos Parajó,† and Rafał Bogel-Łukasik*,‡ †

Downloaded by KAROLINSKA INST on September 13, 2015 | http://pubs.acs.org Publication Date (Web): August 14, 2015 | doi: 10.1021/acs.iecr.5b01771

Chemical Engineering Department, Faculty of Science, University of Vigo (Campus Ourense), Polytechnical Building, As Lagoas, 32004 Ourense, Spain ‡ Unidade de Bioenergia, Laboratório Nacional de Energia e Geologia, 1649-038 Lisbon, Portugal § LAQV/REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal ABSTRACT: The acidic 1-butyl-3-methylimidazolium hydrogen sulfate ([bmim][HSO4]) ionic liquid was explored as both a reaction medium and a catalyst in the furfural production from xylose. Preliminary experiments were carried out at 100−140 °C for 15−480 min in systems containing just xylose dissolved in [bmim][HSO4] in the absence of externally added catalysts. More than 95% xylose conversion was achieved when operating at 120 or 140 °C for 300 and 90 min, respectively; but just 36.7% of the initial xylose was converted to furfural. Operation in biphasic reaction systems (in the presence of toluene, methyl-isobutyl ketone or dioxane as extraction solvents) at 140 °C under selected conditions resulted in improved furfural production (73.8%, 80.3%, and 82.2% xylose conversion to furfural for the cited extraction solvents, respectively).

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INTRODUCTION The fast exhaustion of fossil resources and the need of safe supply of raw materials are major challenges to be addressed in the very near future. In this context, the development of environmentally and economically viable processes for manufacturing chemicals, fuels, and materials from widespread, renewable resources (among which lignocellulose plays a key role) is mandatory. The biorefinery concept enables an efficient utilization of lignocellulosic materials via the fractionation of their polymeric components (cellulose, hemicellulose, and lignin), which are separated (intact or as derived products) to take advantage of the different chemical and physical properties of the resulting fractions. Hemicellulosic polymers are composed of many sugar structural units. Among them, the most abundant is xylan, which is composed of (1−4)-linked β-D-xylopyranosyl residues. Typical lignocellulosic materials containing xylan are corncobs, hulls, straws, grasses, hardwoods, or some industrial byproducts (for example, bagasse or brewery spent grains). The acidic processing of xylan-containing substrates under mild conditions leads to a solid (mainly composed of cellulose and lignin) suitable for further processing, and to a liquid phase containing xylose.1 Dehydration of xylose leads to the formation of furfural (OC4H3CHO), which is a heterocyclic aldehyde that has been identified as a possible target product for biorefineries.2,3 Furfural is used for multiple purposes (for example, as a selective extraction agent, a solvent, an agrochemical, a flavoring agent, an intermediate in the manufacture of resins, and as the starting compound for the production of a broad range of chemicals). The manufacture of furfuryl alcohol accounts for most of the furfural demand, whereas other alcohols and furan derivatives are also commercialized. Furfural, which can also be © 2015 American Chemical Society

converted to green fuels and coupling products, was selected as one of the value-added chemicals from biomass.4,5 The generation of furfural from xylose goes through a complex mechanism (Figure 1). In aqueous media, xylose can either undergo retroaldol fragmentation into acids, aldehydes, and ketones, or converted to intermediates whose chemical nature is controversial.6−8 In further reactions, furfural is first produced and then consumed9 by direct decomposition and/or by secondary reactions with itself, with xylose10 or with intermediates, leading to the formation of humins.11,12 The furfural yield is also decreased by increased xylose concentrations, because of the enhanced rate of side reactions. Currently, the commercial production of furfural (performed in acidic, aqueous media) suffers from low yields and technological challenges related to corrosion, neutralization, and disposal of sludges.14 Several alternatives have been proposed to improve the production of furfural in aqueous media. In order to limit furfural decomposition, it can be removed from the reaction medium during the reaction, for example, by extraction. Ionic liquids (ILs) are considered as an example of moresustainable solvents, which contribute to a greener processing of biomass,15−24 and are suitable for furfural production. Most studies performed on furan production from carbohydrates (including monosaccharides, oligosaccharides, or polysaccharides) in ILs (frequently, imidazolium salts) have been performed in the presence of catalysts such as Lewis acids, Brönsted acids, and solid acids.16,25 Generally, either taskspecific ILs with metals incorporated in the IL structure or Received: Revised: Accepted: Published: 8368

May 13, 2015 August 10, 2015 August 12, 2015 August 12, 2015 DOI: 10.1021/acs.iecr.5b01771 Ind. Eng. Chem. Res. 2015, 54, 8368−8373

Research Note


Industrial & Engineering Chemistry Research

Figure 1. Possible reaction pathways for the dehydration of xylose to furfural: (a) initiated by the dehydration of xylose at position 2 and (b) via an acyclic pathway that features xylulose as a reactive intermediate. Reproduced with permission from ref 13. Copyright 2012, The Royal Society of Chemistry, London.

only in the presence of [emim][HSO4] and organic solvents with required high xylose concentration (100 g/L), is the furfural yield obtained after at least 6 h as high as that reported in this work.31 The reduction of initial xylose concentration decreases the yield of furfural, demonstrating that the results obtained in this work are superior to those presented by Valente and co-workers.31 Other authors presented the use of task-specific ionic liquid (1-(4-sulfonic acid)-butyl-3-methylimidazolium hydrogen sulfate); however, contrary to expectations, the presence of one extra SO3H group in the IL cation provides only an insignificant increase of the furfural yield (91.45%) under the application of very favorable conditions for furfural production, such as high xylose concentration, high temperature (150 °C), and a significantly excessive amount of organic extraction solvent (close to 4 times greater than the volume of the reaction mixture).36 Serrano-Ruiz et al.30 also examined the conversion of xylose to furfural using microwave heating. Although the reaction time was much shorter (within a matter of hours), the temperatures were higher (150 or even 180 °C) than that reported in this work and the xylose conversion to furfural was lower or, in the best-case scenario, at a level similar to that presented in this work. Based on the above ideas, this work delivers an experimental evaluation of the production of furfural from xylose in [bmim][HSO4], including monophasic and biphasic systems, in the absence of externally added catalysts. Preliminary experiments were performed to examine the influence of selected operational conditions (temperature and reaction time) on the furfural production to identify the operational conditions leading to an optimal production of the target product. In further experiments, xylose dehydration was carried out in biphasic media, containing [bmim][HSO4] and an

nonacidic ionic liquids were used and even in the presence of external catalysts, the formation of furfural or 5-HMF was moderate.15,24 Thus, these methods present a need of moreexpensive task-specific IL synthesis and/or additional problem of catalyst extraction after the reaction end. In particular, chromium halide catalysts enabled the furfural synthesis from xylose under mild conditions in ILs, through the isomerization of xylose into xylulose, and the further dehydration of the latter to furfural.26 In the reaction media, furfural consumption takes place, leading to the formation of solid humins.11,12 Lately, acidic ionic liquids (AILs) have found successful application in many organic transformations,16,27 because of their ability to perform as reaction media and catalysts simultaneously. Because of their catalytic activity, AILs offer the advantage of avoiding the problems of the catalyzed systems related to pollution, separation, and recycling28,29 and, as such, can be used to produce furans from sugars in the presence of water, and optionally, of an organic extraction solvent.30−32 For example, the conversion of D-glucose into HMF in AILs was achieved at 15.7% yield in DMSO catalyzed with 1-(1propylsulfonic)-3-methylimidazolium chloride,29 whereas four AILs have been employed to cause the hydrolysis of xylan into xylose.33 Another example of AILs is 1-butyl-3-methylimidazolium hydrogen sulfate ([bmim][HSO4]), which contains hydrogen sulfate as the anion, making the pretreatment with this IL more similar to acid hydrolysis without the disadvantages that are typical for this type of pretreatment, such as corrosion and other problems. Recently, this IL was employed to perform the fractionation of different types of biomass,34,35 and the hydrolysis−dehydration of polysaccharides to furans (including furfural and HMF) was noticed. Lima et al. examined series of temperatures and ILs and found that 8369

DOI: 10.1021/acs.iecr.5b01771 Ind. Eng. Chem. Res. 2015, 54, 8368−8373

Research Note

Industrial & Engineering Chemistry Research

in the literature.26,37−41 In this work, in order to assess the dual behavior of [bmim][HSO4] as both a reaction medium and a catalyst, xylose was directly mixed with the IL and heated at 100−140 °C for the desired reaction time. The experimental results are depicted in Figure 2.

organic extraction solvent (toluene, methyl isobutyl ketone (MIBK), or 1,4-dioxane), in order to improve the furfural yields by limiting the participation of the furfural-consuming reactions taking place in the IL phase.


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MATERIALS AND METHODS Materials. The materials employed and their suppliers were as follows: [bmim][HSO4] (≥94.5% purity), xylose (≥99.0% purity), acetic acid (≥99.7% purity), formic acid (≥95.0% purity), levulinic acid (≥97.0% purity), and furfural (99.0% purity), from Sigma−Aldrich; toluene (99.0% purity), from Riedel-de Haën; 1,4-dioxane (>99.0% purity) and sulfuric acid (95−98% purity), from Fisher Scientific; and methyl-iso-butyl ketone (MIBK) (99.0% purity), from Merck. All starting materials were used as received. Reaction in Homogeneous Media. [bmim][HSO4] was used after vacuum drying at 0.1 Pa and room temperature for 24 h. In single-phase experiments, xylose and [bmim][HSO4] were mixed at a mass ratio of 1:10 under stirring, and heated up in an oil bath to the desired temperature. Zero time corresponded to the complete dissolution of mixture determined visually with the naked eye. After the required reaction times, the reaction was cooled in an ice bath to quench the process. Samples from the reaction media were taken, diluted immediately with distilled water, homogenized and assayed for composition. All samples were filtered through a 0.45 μm nylon membrane prior to analysis. Reaction in Biphasic Media. [bmim][HSO4 ] was prepared analogously to the reaction in homogeneous media. The reaction media were prepared by adding xylose and the selected typical organic extraction solvent (toluene, dioxane, or MIBK) to AIL. The xylose:[bmim][HSO4] mass ratio was kept as noted above, and the extraction solvent was added at the desired proportion. At the end of experiments, samples from the AIL and extraction solvent phases were taken (just after cooling and phase separation), and subjected immediately to dilution with distilled water and analyzed to determine the composition. Analytical Methods. Samples were assayed by HPLC for furfural, xylose, and organic acids (formic, acetic, and levulinic acids) using an Agilent 1100 equipped with refractive index (RI) and diode array (DA) detectors. All compounds were analyzed from the signal of the RI detector, whereas organic acids and furfural were also quantified using the signal from the DA detector (wavelengths: λ = 210 nm for organic acids and λ = 280 nm for furans). Separation was performed in an Aminex HPX-87H column (BioRad, Life Science Group, Hercules, CA) employing the conditions: mobile phase, 5 mM H2SO4; flow, 0.6 mL/min; temperature, 50 °C. Error Analysis. The standard uncertainty (u) was determined for all of the obtained results. Each weighing was made considering an uncertainty of u(m) = 0.1 mg. The reactions in monophasic and biphasic systems were performed with a temperature uncertainty of u(T) = 1 °C. Each sample was subjected to HPLC analysis (ran twice), and the average values are presented in this work. The differences between them were 80% of the stoichiometric value.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +351210924600, ext. 4224. Fax: +351217163636. Email: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful to the Spanish “Ministry of Science and Innovation” for supporting this study, in the framework of the research Project “Advanced Processing Technologies for Biorefineries” (Reference No. CTQ2014-53461-R), partially funded by the FEDER program of the European Union. Ms. Susana Peleteiro thanks the Ministry for her predoctoral grant. This work was also supported by the Fundaçaõ para a Ciência e a Tecnologia (FCT, Portugal) through Bilateral Cooperation project FCT/CAPES 2014/2015 (No. FCT/1909/27/2/2014/ S) and Grant Nos. SFRH/BD/90282/2012 (AMdCL), IF/ 00424/2013 (RBL), and the authors acknowledge CAPES (Brazil) for supporting the project Pesquisador Visitante Especial 155/2012. Authors also wish to thank Mrs. Maria do Céu Penedo for help in the execution of the HPLC analysis.

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REFERENCES

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Simple and Efficient Furfural Production from Xylose in Media

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