Research Article pubs.acs.org/journal/ascecg
Strategic Designing on Selection of Solvent Systems for Conversion of Biomass Sugars to Furan Derivatives and Their Separation Sampath Gajula,†,‡ Kanagaraj Inthumathi,† Sowthri R. Arumugam,† and Kannan Srinivasan*,†,‡ †
Inorganic Materials and Catalysis Division, CSIR-Central Salt and Marine Chemicals Research Institute, Council of Scientific and Industrial Research (CSIR), GB Marg, Bhavnagar-364 002, India ‡ Academy of Scientific and Innovative Research, CSIR-Central Salt and Marine Chemicals Research Institute, GB Marg, Bhavnagar-364 002, India
ABSTRACT: Production of furan compounds from biomass sugars has become an important field of research. However, designing suitable protocols for their production and separation is still a challenge in real practice. With an endeavor to realize this, different solvents have been screened by studying their mixtures through physicochemical properties such as solubility, stability, phase separation, phase extraction, and saturation and precipitation points. Using DMSO as a model solvent, 2,5furandicarboxylic acid, 2,5-diformylfuran, and sugar were successfully separated by a precipitation method with the addition of water or organic solvent. 5-Hydroxymethylfurfural was extracted using organic solvents through a phase extraction method with either addition of glucose or water for phase separation, and the reasons for high extraction efficiency of the MIBK solvent are discussed. Finally, integration of these individual steps is invoked to design efficient solvent systems for the production and separation of furan derivatives. By using these data sets, efficient solvent systems can be designed based on the requirements. KEYWORDS: Phase extraction, Biomass, 5-Hydroxymethylfurfural, Furandicarboxylic acid, Diformylfuran, Dimethyl sulfoxide
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INTRODUCTION In the modern world, multidisciplinary approaches became necessary to understand systems and solve problems.1 In chemical sciences, removing the barriers between chemistry and chemical engineering is a key step in developing this type of science.2 Part of this is the study of solvent roles in chemical systems to design or develop more efficient reactions and separation processes.3 In the research field of biomass conversion to chemicals, solvents play crucial roles, and finding suitable solvents is one of the major challenges.4 To reduce the concerns of CO2 emissions, biomass is progressively being explored as an alternative source for production of chemicals and materials.5 In this field, production of 5-hydroxymethylfurfural (HMF) from biomass sugars and its further conversion to commercially useful chemicals like 2,5furandicarboxylic acid (FDCA) and 2,5-diformylfuran (DFF) (Scheme 1) has become a hot topic.6 However, no efficient methods are available for commercial production of these furan compounds due to some limitations. In some cases, the solubility problems limit the use of high concentration substrates. In other cases, isolation of the product is difficult, © 2017 American Chemical Society
and yet in other cases, products or intermediates deposit or polymerize causing catalyst deactivation. Recently, some reviews have reported on the efficiency of solvent systems pertaining to HMF production.4−6 Despite water being a green solvent, the concentration of substrates used and the selectivity of HMF are very low. This is mainly due to the formation of levulinic acid and humin polymers. The formation of levulinic acid is more prevalent in water, which acts as both reagent and as catalyst. Few of them used biphasic solvent mixtures to improve the HMF yield by continuous extraction from the aqueous reaction phase into the organic extraction phase. However, it requires a relatively larger amount of organic phase for better selectivity.6 Recently, the efficiency of solvents for the extraction of HMF from an aqueous medium and the effect of sugars and salts on extraction coefficient were studied.7,8 However, the production and separation of other products like DFF, FDCA, and unreacted sugars were not Received: March 4, 2017 Revised: April 19, 2017 Published: May 15, 2017 5373
DOI: 10.1021/acssuschemeng.7b00681 ACS Sustainable Chem. Eng. 2017, 5, 5373−5381
Research Article
ACS Sustainable Chemistry & Engineering Scheme 1. Conversion of Biomass Sugars to Furan Compounds
Table 1. Details and Properties of Chemicals Useda compound
abbreviation
MW
density (g/mL)
bp (°C)
5-hydroxymethylfurfural 2,5-furandicarboxylic acid 2,5-diformylfuran fructose glucose water dimethyl sulfoxide N,N-dimethylformamide γ-valerolactone tetrahydrofuran 1-butyl,3-methyl imidazolium chloride acetone acetonitrile dichloromethane 1,2-dichloroethane diethyl ether 2-propanol ethyl acetate acetic acid toluene cyclohexane benzene carbontetrachloride methylisobutylketone ethylene glycol
HMF FDCA DFF − − − DMSO DMF GVL THF BMImCl − ACN DCM DCE DEE − EA − − − − CCl4 MIBK EG
126.1 156.0 124.0 180.1 180.1 18.0 78.1 73.0 100.1 72.1 174.6 58.0 41.0 84.9 98.9 74.1 88.1 88.1 60.0 92.1 84.1 78.11 153.8 100.1 62.0
1.29 1.60
>200 >200 >200 >200 >200 100 189 155 207 66 >200 56 82 40 84 35 82 77 118
1.69 1.54 1 1.09 0.94 1.04 0.88 1.08 0.78 0.78 1.32 1.25 0.71 0.78 0.89 1.04 0.86 0.78 0.88 1.59 0.80 1.11
81 80 77 117 197
DE
78.5 46.7 36.7 36.4 7.6 conductor 20.7 37.5 9.1 10.4 4.3 18.3 6.0 6.1 2.4 2.0 2.3 2.2 13.1 37.7
DM
8.6 1.8 3.96 3.86 1.63 ions 2.91 3.44 1.6 1.8 1.1 1.66 1.78 1.74 0.36 0 0 0 2.8 2.36
polarity
9.0 7.2 6.4 4.0 5.1 5.8 3.1 3.5 2.8 3.9 4.4 6.2 2.4 0.2 2.7 1.6 2.7
source
purity min. (%)
Sig Sig Sig Sd Sd − Sd Sd Alf Sp Sig Sd Sd Sp Si Sd Sd Fi Sd Lo Sd Sd Sd Sd Ra
99.0H 97.0 97.0H 99.8A 99.7A − 99.5 99.5 98 99.9G 98H 99G 99.5G 99G 99G 99G 99G 99G 99.8 99.5G 99G 99G 99G 99G 99
a
MW: molecular weight, DE: dielectric constant, DM: dipole moment in D units, bp: boiling point, Sig: Sigma-Aldrich (Germany), Sd: Sd-fine (India), Alf: Alfa-Aeser (USA), Fi: Fisher-Scientific (USA), Lo: Loba (India), Ra: Ranbaxy (India), Sp: Spectrochem (India), Si: Sisco (India), H: HPLC grade purity, A: ACS grade purity, G: GC purity.
FDCA and also for direct conversion of sugars to DFF.14 The major drawback of this solvent, however, is the separation of products from it. In addition to the above majorly explored solvents, some other solvents were also reported like DMF, DMA, acetonitrile, supercritical CO2, γ-valerolactone, THF, etc. with each having some drawbacks. Although many solvents were found as suitable for HMF production, many of them are not suitable for further processing of HMF like oxidation, reduction, polymerization, etc.15 From the literature, it can be concluded that the individual steps like the conversion of sugars to HMF and conversion of HMF to other furan derivatives are easy when conducted separately by using separate solvent systems, while the systems that can work for both steps and with easy separation are lacking. In a green and economical perspective, it may be necessary to study the possibility for further conversion of HMF to useful derivatives/products like DFF and FDCA from sugars directly that would avoid additional processes such as separation. The main challenges in this field for commercial implementation are the use of high substrate concentration,
reported by these systems. In a report, the solubility of FDCA and DFF was studied in both water and an acetic acid medium which showed very less solubility (around 0.1 wt %),9 creating doubt on the efficiency of these systems. Although selectivity of FDCA from HMF can be improved with a base as an additive in water, the produced FDCA gets converted into its salt form which requires an additional step to recover.10 Few classes of ionic liquids (ILs) like alkyl imidazolium salts were found suitable for the efficient conversion of sugars to HMF. Currently, they have some limitations such as high cost, moisture sensitivity, and low stability, and further conversion of HMF to other products is doubtful. Dimethyl sulfoxide (DMSO) is a polar aprotic solvent known as a reaction medium for a wide variety of reactions and also is involved as a ligand in transition metal-catalyzed reactions.11 It can act as a promoter or catalyst in the conversion of sugars.12 Further, it improves the stability of HMF by interacting strongly with it through solvation and restricts the contact of HMF with intermediates, thereby preventing undesired side reactions.13 It was also reported as a solvent for HMF oxidation to DFF or 5374
DOI: 10.1021/acssuschemeng.7b00681 ACS Sustainable Chem. Eng. 2017, 5, 5373−5381
Research Article
ACS Sustainable Chemistry & Engineering
percentage (wt %) with respect to the solvent, the mole ratio of solute to solvent, and molality of solution. Stability of HMF. Stability of HMF in presence or absence of water at different temperatures (80, 100, and 120 °C) was checked by taking HMF and water in 1 g of solvent and stirring at 500 rpm for 15 h using a Mettler-Toledo’s Easymax automated synthesis system (Easymax 102). The quantification of solute and solvent was analyzed by gas chromatography (GC) with biphenyl as the internal standard using a ZB-5 ms column (30 m) and flame ionization detector (FID) in the Varian-450 gas chromatograph. The sample was diluted in methanol at a 1:10 ratio before the analysis. Solubility and Precipitation Studies of FDCA and DFF. Saturation and precipitation points were checked for both DFF and FDCA in DMSO in the presence of water. Here, saturation point indicates the solubility of the compound in DMSO in the presence of a given amount of water. Precipitation point indicates the required amount of water needed to precipitate out the dissolved compound at a given concentration in DMSO. Saturation and precipitation points in solvent mixtures were checked by first taking 100 mg of DMSO to which FDCA or DFF was first added until the maximum solubility. Then, water was added in aliquots of 20 mg until this dissolved compound precipitates out as solid, and this point/state was considered as a precipitation point. Following which, DMSO was added again in aliquots of 20 mg to this mixture for redissolution. The point at which the compound dissolved again completely was considered as the saturation point. This process was continued with water and DMSO sequentially until very diluted. The values of concentration of both compound and water in DMSO were calculated at different dilutions with water and DMSO using the following equations:
improving the selectivity, use of multifunctional systems, isolation of product, and reuse of the system.15 Hence, the major studies needed in this field are to critically assess the physical properties of systems and chemical engineering. It is necessary to study thoroughly on solvent roles in all the steps of reactions and separations to develop more efficiently integrated systems. Data on the solubility of reactants and products in solvents is useful in predicting the possibility of reaction progress and in designing the suitable medium. As HMF is less stable at higher temperatures, it is recommended for storage temperature below 4 °C. Hence, it is necessary to check the stability of this compound at reaction conditions. There is no efficient method available on separation of FDCA and DFF from the reaction medium; hence, it is necessary to solve this problem that would help in commercial implementation. As the complete conversion of the substrate may not be possible in some cases, methods are necessary for the separation of the unreacted substrate from the medium. Likewise, both in the production and conversion of HMF, separation of HMF from the reaction medium is also an important step. Among the many methods reported, phase extraction was found to be more amenable. Although this method is widely reported for extraction from water and ionic liquids, less is studied for DMSO probably due to its high miscibility with many organic solvents. Furthermore, the reason that MIBK is an efficient solvent for HMF extraction is not clearly known. Finally, a critical comprehensive look into the results of various steps will be useful that might avoid the use of excess elements such as solvents, processing steps, and energy by integrating them into simple and combined systems. In this work, these issues are addressed to make protocols for the design of systems for reaction and separation by studying some basic properties of mixtures of solvents with sugars, HMF, DFF, and FDCA. The solubility of reactants and products in solvents, stability of HMF in reaction solvents, separation of products (DFF and FDCA) from the reaction medium, removal of unreacted sugars from the reaction medium, and extraction of HMF from reaction medium are studied. Further, selection of suitable solvents and conditions for effective production and separation of HMF and its derived products such as FDCA and DFF is addressed, and at the end, the design of solvent systems by integrating the individual steps are discussed. These methods of studies can help in the selection of suitable solvents for the reaction, separation, and storage of compounds. The integration of the individual steps will help in developing an efficient process for reaction and separation by reducing the number of solvents, their amounts, and the process steps which are addressed in this study.
Conc. of compound in DMSO (wt%) =
Conc. of water in DMSO (wt%) =
Wcompound WDMSO
× 100
Wwater × 100 WDMSO
(1)
(2)
A graph was plotted between the concentration of the compound in DMSO against the concentration of water in DMSO. From this data, the saturation point was derived from the wt % of the compound in DMSO, and the precipitation point was derived from the wt % of water in DMSO. Separation of Sugars from Solvent. For the selection of suitable precipitants, first, the solubility of glucose was checked in different organic solvents by adding glucose in little amounts to 1 g of the solvent under stirring. The solubility of glucose in DMSO in the presence of organic solvent was checked by taking the mixtures of DMSO and organic solvent with their amounts in 1 g + 2 g and 2 g + 1 g to which glucose was added with stirring until the saturation level. The data of saturation and precipitation points for glucose in the DMSO + solvent mixture was collected by first dissolving 0.44 g of glucose in 1 g of DMSO and then adding precipitant to it in aliquots (with stirring for 10 min at intervals) until the glucose is precipitated. The data of saturation points was collected by adding DMSO to this precipitated mixture until the glucose redissolves again. This process was continued until a very low concentration, where the glucose stops precipitating. The values of concentration of both glucose and precipitate in DMSO were calculated at different dilutions with precipitant and DMSO using the following equations:
2. EXPERIMENTAL SECTION Materials and Their Data. The chemicals listed in Table 1 were used as received without any treatment. Except for stability studies, all other experiments were conducted at ambient temperature (26 ± 3 °C). The experiments were done twice, and it was found that the results are reproducible with negligible variation (±2%). Solubility of Substrates and Products. For solubility studies, solute was added in little amounts into the solvent taken in a 10 mL glass reactor tube followed by magnetic stirring at 500 rpm until the final amount added remains insoluble, and finally, the mixture was stirred for 1 h for the confirmation of complete saturation. For the saturated samples, the values of mass and molecular weight were used for calculating the physical properties like solubility in weight
Conc. of compound in DMSO (wt%) =
Conc. of precipitant in DMSO (wt%) =
Wglucose WDMSO
× 100
Wprecipitant WDMSO
× 100
(3)
(4)
A graph was plotted between the concentrations of sugar in DMSO against the concentration of precipitant in DMSO. From the precipitation points, we can deduce the amount of precipitant required to precipitate out the glucose dissolved in a certain concentration in 5375
DOI: 10.1021/acssuschemeng.7b00681 ACS Sustainable Chem. Eng. 2017, 5, 5373−5381
Research Article
ACS Sustainable Chemistry & Engineering Table 2. Solubility of Compounds in Solvents at 25 °Ca glucose
fructose
DFF
FDCA
solventb
wt %
M
n/n
wt %
M
n/n
wt %
M
n/n
wt %
M
n/n
water DMSO DMF BMImCl GVL THF
90 44 6 35
