Unraveling the Effect of Solvent in Biomass Processing by ...

Unraveling the Effect of Solvent in BiomassProcessing by Means of Infrared Spectroscopy

Rebecca Della Croce Andrew [email protected] [email protected]

Miyu Ono Aditya [email protected] [email protected]

Matthew [email protected]

New Jersey Governor’s School of Engineering and Technology 2016

Abstract

5-hydroxymethylfurfural (HMF) and 2,5-furandicarboxylic acid (FDCA) are biomassderivatives that can provide environmentallysustainable fuel and industrial products. Thispaper investigates the interactions of HMF andFDCA with dimethyl sulfoxide (DMSO), a po-lar aprotic solvent that has been reported to havea significant effect on HMF yield. Intermolec-ular and intramolecular interactions of HMFand FDCA in DMSO and water were exam-ined at varying concentrations of DMSO solventby analyzing the spectra obtained from infraredspectroscopy. The results suggest that DMSOpromotes formation of the trans-HMF isomer.Moreover, it was inferred that DMSO might in-teract with FDCA by forming a solvation shell,although DMSO does not interact with FDCAvery strongly. The solubility limit of FDCAwas also tested. FDCA was determined to behighly soluble even in solutions of low DMSOconcentration, following a linear trend of in-creased solubility with increasing DMSO con-centration. These findings assist in scaling upHMF/FDCA production to an industrial level,

and in laying the groundwork for future stud-ies on HMF/FDCA interactions in DMSO/watermixtures.

1 IntroductionAlthough fossil fuels have consistently pro-

vided society with energy for more than a cen-tury, the long-term unsustainability and envi-ronmental hazards of petroleum-based fuels areinstigating a search for more efficient alterna-tives. Supplies of fossil fuels are limited dueto their slow rates of replenishment. Addition-ally, the burning of fossil fuels aggravates cli-mate change issues. Commonly used plasticsalso threaten the environment because they arenot biodegradable and cause litter and pollution.These issues have motivated a search for morereliable and environmentally friendly sources ofenergy and platform chemicals.

Biomass-derived energy sources provide re-liable energy while remaining environmentallyadvantageous. 5-hydroxymethylfurfural (HMF)has attracted attention in particular due to its ver-satility. HMF is in an intermediate essential tothe production of biofuels, plastics, and otherhigh-demand products. Specifically, fructose-

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Figure 1: Production of HMF from cellulose is a multistep process with potential for undesirablebyproducts [1], [5].

derived HMF has proven to be a critical contri-bution to biomass energy [1]. Products of HMF,such as 2,5-furandicarboxylic acid (FDCA),are extremely important in the production ofbiodegradable plastics and other important com-pounds. FDCA has the potential to replaceterephthalic acid in plastics [1], [2].Terephthalicacid is often used in polyethylene terephthalate(PET) plastics (referred to as PEF when FDCAis used). Z. Zhang and K. Deng have foundPEF to be superior to PET—for example, PEFhas superior barrier and thermal properties [2].

Unfortunately, the production of HMF is of-ten inefficient. In water, HMF is unstable andsusceptible to degradation. Research from Y.Román-Leshkov et al. has found dimethyl sul-foxide (DMSO) to improve the efficiency of thesugar dehydration process [3]. However, DMSOand HMF have very similar boiling points, mak-ing the extraction of HMF both energy-intensiveand costly. This research seeks to provide in-formation regarding the intermolecular interac-

tions between HMF and DMSO and betweenFDCA and DMSO. With this knowledge, it ispossible to select an optimal solvent that enablesthe generation of clean, sustainable energy frombiomass derivatives.

2 Background2.1 Process2.1.1 HMF Conversion Reaction

HMF is a biomass derivative formed fromsugars through a dehydration reaction that canbe used for energy and plastic production (forother production methods, see Section 2.1.2).Cellulose-derived fructose can undergo dehy-dration with an acid catalyst, such as hydrochlo-ric acid, to produce furan derivatives [1] (Figure1). While it is possible to produce HMF fromglucose, the stable ring structure of glucose pre-vents the formation of open sugar chains andinhibits enolization, the rate-determining stepof the HMF production process [4]. Conse-

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quently, the production of glucose-derived HMFis less selective than that of fructose-derivedHMF. Therefore, after obtaining glucose fromthe hydrolysis of cellulose, it is isomerized tofructose to begin HMF production. This prod-uct can then be converted to other biofuels andbiochemicals such as FDCA, 2,5-dimethylfuran(DMF), and gamma-valerolactone (GVL) [4].

2.1.2 Current Research and Problems

Although various methods of biomass pro-cessing have been attempted, none have madecompletely effective use of valuable organicmatter. Thermal conversion methods use heatto convert biomass to energy, often reaching ex-treme temperatures in the range of 500-800◦C(Figure 2). Maintaining these temperatures istedious and costly for industry. Biological con-version methods use enzymes from bacteria andother microorganisms to process biomass. Al-though less energetically costly, biological con-version transpires too slowly for mass produc-tion. Chemical conversion methods provide abalance between economic sustainability andexpediency. Since the reaction is performed insolution, HMF conversion occurs with vastly in-creased selectivity. Consequently, there is highdemand for an effective solvent.

Figure 2: Other methods are used for biomassconversion but many are either slow or requiretoo much energy [6].

Unfortunately, undesirable side reactions maydecrease HMF yields during production. Theseside reactions are affected by factors such astemperature, acidity, and the presence of H2O

[4]. Research from Y. Román-Leshkov and J.A. Dumesic has revealed that the optimal tem-perature for HMF production balances the highactivation energy of the reaction with the lowtemperature of degradation [1].

HMF degrades quickly during current pro-duction methods by means of fragmentation,condensation, rehydration, and additional de-hydration reactions. Reactive acidic catalystscontribute to these side reactions due to theirhighly functionalized nature. These processesresult in the formation of undesirable prod-ucts such as levulinic acid, formic acid, andhumins, which are furan-rich polymer networkswith functional oxygen groups [4] (Figure 1).Humins, while not fully understood, decreaseHMF yield. Therefore, new systems shouldwork to decrease these side products and reac-tions.

Current methods of HMF production in-clude utilization of high-boiling point polaraprotic solvents and biphasic systems (Figure3). Since polar aprotic solvents have strongdipole moments and do not dissociate in solu-tion, they can help to stabilize compounds suchas HMF. While high-boiling point solvents suchas DMSO can increase HMF yields, the sub-sequent separation of HMF is energy-intensive.Such aqueous reaction systems typically havemaximum HMF yields of 50-60 mole percent[5]. Because of these relatively low productyield rates, biphasic systems utilize both anaqueous phase and a water-immiscible organicphase to permit the in situ extraction of HMF.Once in the organic phase, the HMF is protectedfrom degradation reactions [3]. This system re-sults in a high HMF selectivity of 80-90 percent.In spite of this success, problems (further dis-cussed in Section 2.2) with the use of aqueous-phase solvents persist, limiting the efficacy ofsuch solutions.

FDCA production faces similar challenges.The process involves the selective oxidation ofHMF. While this is possible in water and or-ganic solvents, a high pH environment is neces-

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sary [7]. Currently, conversion to FDCA takesplace after the production of HMF in a differ-ent system. However, the integration of thesetwo systems would eliminate the need to extractthe HMF first, and increase overall energy effi-ciency.

Several reaction mechanisms have been pro-posed for the production of HMF, includingacyclic and cyclic intermediates [5]. While de-hydration kinetics have shown that DMSO actsas both a catalyst and a solvent, further knowl-edge of the intermolecular interactions betweenHMF/FDCA and DMSO is necessary to com-pletely understand the process and to optimizethe use of DMSO as a solvent.

Figure 3: Biphasic systems include an aqueousphase in which the reaction occurs and an or-ganic phase where the product can remain with-out degradation [3].

2.2 SolventsThe selection of a solvent that can properly

stabilize HMF may hold the key to increasingHMF yield and selectivity [3]. An ideal solventshould minimize side reactions with reactants,intermediates, and products. Typical solventsused in HMF stabilization include water, or-ganic solvents such as DMSO, various alcohols(2-butanol, pentanol, hexanol, et cetera), andmethyl isobutyl ketone (MIBK) [3]. However,

polar aprotic solvents such as DMSO, whichprovide high sugar solubility, are preferable inindustry because they allow large amounts ofsugar to undergo the dehydration process forconversion into HMF. Using DMSO decreasesside reactions and condensation, suppresses by-product formation, and inhibits acyclic reac-tions. On the other hand, using water causeslow selectivity due to rehydration and degrada-tion in solution. However, it is beneficial toexperiment with mixtures of DMSO and waterdue to the inevitable production of water in fruc-tose dehydration, and economic considerations.The interactions of HMF with mixtures of dif-fering DMSO and water concentrations need tobe investigated in order to understand the bio-chemical degradation and solvation of HMF inDMSO.

The disadvantages of using DMSO mustalso be taken into consideration. Since HMFand DMSO are separated primarily through dis-tillation, the high boiling point of DMSO causesthe product isolation process to be energeticallyand financially expensive. Furthermore, its us-age prompts environmental concerns that mustbe addressed by future work. DMSO itself isalso expensive in comparison to other HMF-stabilizing organic solvents, including the pre-viously mentioned alcohols and MIBK.

Currently, the precise mechanism by whichDMSO interacts with HMF and FDCA is notwell understood. Therefore, it is necessary tocharacterize the intermolecular and intramolec-ular interactions that DMSO exhibits in the pres-ence of HMF and FDCA.

2.3 ExtractionThe method used to extract HMF is a ma-

jor factor in selecting the optimal solvent. Insingle-phase aqueous systems, HMF is isolatedthrough the filtration of solids, neutralization,solvent extraction, and HMF purification [8].DMSO is a promising organic solvent in theaqueous phase, as predicted by high theoreti-cal yields after such isolation procedures [9].

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Distillation is a common method for extractionbut can lead to undesirable carbonization of theproduct [8]. Extraction processes such as low-temperature separation and vacuum distillationhave also been suggested [3], [8]. It has beenreported that aqueous biphasic systems, con-sisting of both an aqueous and organic phase,greatly facilitate and improve the efficiency ofHMF extraction. The addition of salts, includingNaCl and KCl, or alcohols, such as 2-butanol, asphase modifiers has been found to assist in ex-tracting HMF to the organic phase [1]. From theorganic phase, HMF can be easily removed.

Although it is known that FDCA is solublein DMSO and insoluble in water, its solubilityin a mixture of DMSO and water must also beexplored [10]. If FDCA is found to be solu-ble in DMSO/H2O solvent mixtures, the FDCAextraction process would be simpler and morecost-effective. For example, the possibility ofsingle-system production of FDCA from fruc-tose has been proposed as a more economicallysustainable method, but implementation neces-sitates a more precise understanding of the inter-actions between DMSO and FDCA [9]. There-fore, the goal of this study is to understand theintramolecular and intermolecular interactionsof HMF and FDCA in DMSO/H2O mixtures toprovide grounds for research regarding the pos-sibility of single-system FDCA production.

3 Experimental3.1 Apparatus

The primary apparatus of experimentationwas a Fourier transform infrared (FTIR) spec-trometer. The FTIR spectrometer emits infraredlight and measures the absorbance of the ana-lyzed liquid or solid at various wavenumbers.

Infrared spectroscopy reveals informationabout the vibrations of bonds in a sample. Anal-ysis of the resulting data can reveal the inter-molecular and intramolecular interactions of themolecules. This analysis focuses strictly on or-ganic compounds, which are particularly sen-

sitive to infrared light. Furthermore, other vi-brational spectroscopy methods, such as Ramanspectroscopy, are not as rapid and employ high-intensity monochromatic laser lights which canpotentially degrade HMF and FDCA and there-fore were not used [11].

3.2 Methods

3.2.1 DMSO/H2O Mixtures

Five mixtures of DMSO and water weremade with varying mole fraction ratios ofDMSO:H2O, respectively: 0:100, 25:75, 50:50,75:25, and 100:0. Two samples of each mixturewere transferred to 1 mL volumetric vials. Suf-ficient HMF was added to one sample of eachmolar concentration, creating 0.1 M HMF solu-tions. Then, sufficient FDCA was added to thefive remaining samples, with varying mole frac-tions of DMSO and H2O, creating 0.1 M FDCAsolutions.

All ten solutions, the solvent mixtures ofDMSO and H2O, and the samples of pure HMFand FDCA were analyzed using FTIR spec-troscopy. The data was normalized and analyzedusing Origin, a scientific graphing and data anal-ysis software. In order to ensure that accuratedata was collected, the refractive indices of eachsolution were taken into account. The spectraof the ten mixtures were superimposed on thespectra of their respective solvent mixtures with-out solute. The graphs were normalized withrespect to one another and the spectra of thesolvent mixtures were subtracted from the spec-tra of the DMSO/H2O mixtures with HMF orFDCA. The resulting graphs as well as the un-modified graphs were analyzed. The analysis fo-cused on the peaks of the spectra, which corre-spond to vibrating functional groups within themolecules.

3.2.2 Solubility Limit of FDCA

The solubility limit of FDCA in DMSO/H2Omixtures was also analyzed. Three of the sol-vent mixtures mentioned above (75:25, 50:50,

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25:75) were prepared again. For each solventmixture, a vial was filled with one milliliter ofthe mixture. FDCA was then added continu-ously in small amounts and the vial was vor-texed until the mixture became cloudy and un-solubilized FDCA was observed. The mass ofFDCA added was recorded for each solution.Thus, it was possible to calculate the maximumamount of FDCA soluble in differing concentra-tions of DMSO in water.

4 Results and Discussion4.1 Methodology of Analysis

The spectra obtained display the correspon-dence between wavenumber and absorbance.Peaks in the spectra indicate vibrations of thebonds within certain functional groups in themolecules of the analyzed sample. Peaks in aspecific range of wavenumbers correspond tovibrations in the bonds of certain functionalgroups. When different chemicals and solventsare added, the spectra may change in wavenum-ber or absorbance intensity. Thus, analysis ofthese shifts offers insight into the structures ofthe molecules and intermolecular interactionswithin the sample.

An observed decrease in the intensity of apeak of the solute with the change of solventmixture can be associated with a reduction inthe concentration of a specific functional groupor the formation of a solute-solvent complex[13]. Additionally, peaks can shift to loweror higher wavenumbers as a result of interac-tions; when molecules interact with each otherthe bonds of the functional groups at whichthey interact may elongate. Such elongationweakens the intramolecular bonds, thus decreas-ing the wavenumber range of the correspondingpeak. Conversely, an increase in wavenumbersindicates decreased intermolecular attractions,shortened functional group bond lengths, andstrengthened bonds. By observing these shifts inpeaks, the intermolecular interactions of a sam-ple can be revealed.

4.2 Analysis of Spectra

4.2.1 DMSO/H2O Mixture Spectra

a

b

Figure 4: IR spectra of four solvent mixtureswith DMSO at (a) 700 cm−1 and (b) 850-1100cm−1 shows shifts toward lower wavenumberwith the addition of water.

Because the wavenumber of the peaks islower when water is present, the water is break-ing the intermolecular attractions of DMSO withitself and is weakening the bonds within thefunctional groups of DMSO. This effect can be

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seen in the peaks around 700 cm−1, the symmet-rical C-S stretch in Figure 4a.

The sulfoxide peak (1060-1030 cm−1) alsoshifts to a lower wavenumber with increasingwater mole fraction in the solvent mixture (Fig-ure 4b). This likely occurs because the partiallypositive hydrogen atoms in H2O hydrogen-bondto the partially negative oxygen atom of thesulfoxide group. This interaction stretches thedouble bond between sulfur and oxygen. Thiscauses the vibration of the bond to decrease infrequency and thus shift to a lower wavenumberin the spectra.

However, many of these shifts are minor andDMSO still maintains the same peaks at simi-lar wavenumbers. Thus, the functional groupsin DMSO maintain their bonds, even in the pres-ence of water, allowing DMSO to be an effectivesolvent.

4.2.2 FDCA in Solvent Analysis

The spectra obtained from the FTIR analysisof the mixtures with solutes were superimposedon the spectra of their respective solvents (seeSection 8). It can be seen in Figure 5 that asthe mole fraction of DMSO increases, the sul-foxide bond strengthens, indicated by the shiftsto higher wavenumbers (Table 1). This observa-tion shows that when H2O is present, it is inter-acting with DMSO. Thus, it might interact withDMSO rather than FDCA or HMF, which couldhelp to prevent their degradation. However, thepossibility of self-association of DMSO dimerscannot be excluded due to the significantly in-creased concentration of DMSO (Figure 6).

Name Mixture1F FDCA in 100% H2O2F FDCA in 25% DMSO3F FDCA in 50% DMSO4F FDCA in 75% DMSO5F FDCA in 100% DMSO

Table 1: The table identifies the terms used forall of the FDCA mixtures in the spectra.

Figure 5: 1060-1030 cm−1: The S=O stretchin sulfoxides strengthens with the addition ofDMSO.

Figure 6: The diagram shows the potentialDMSO interaction that would create a dimer insolution.

Figure 7: The graph shows the C=O stretch ofa dimer in carboxylic acids (1710-1680 cm−1)and CH3 antisym. deformation in methyl groups(1470-1440 cm−1).

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The peak at 1470-1440 cm−1 in Figure 7corresponds to the CH3 antisymmetric deforma-tion in methyl groups. The addition of FDCAweakens the methyl groups of DMSO, indicat-ing that DMSO might also interact with FDCAmolecules via C-H...O bonds, as proposed byFigure 8a.

The peak in the wavenumber range of 1710-1680 cm−1, which corresponds to the C=Ostretch of a dimer in carboxylic acids, is shownto shift slightly to higher wavenumbers (Figure7). This suggests that in solutions with a highermole fraction of DMSO, the dimers of FDCA(Figure 9) are likely present in the form of free(non-hydrogen-bonded) FDCA molecules. Thismay be connected to the aforementioned obser-vation of the dimerization of DMSO itself.

Despite the slight shift in the C=O peak, theoverall consistency of the peak in the wavenum-ber range of 1710-1680 cm−1, which corre-sponds to the C=O stretch of a dimer in car-boxylic acids, signals that DMSO strongly in-teracts with the O-H groups of each solute prob-ably via O-H...O=S bonds. FDCA is highly sol-uble in DMSO and forms strong intermolecularinteractions. Thus, the low level of wavenumbershifts in this peak indicates that the intermolec-ular interactions must be occurring elsewherebesides the aldehyde group. The extended hy-droxyl group of the FDCA molecule, which canform hydrogen bonds with the oxygen of the sul-foxide group of DMSO, is the logical alterna-tive. However, even though the hydroxyl func-tional group bond is elongated by this interac-tion, the FDCA molecule remains stable, hint-ing that the degradation reaction is focused onanother functional group.

The relative consistency of the C=O bond in-dicates that there is little interaction with DMSOor H2O molecules at this functional group. Thismay be due to a shielding effect from DMSO.S. H. Mushrif et al. have suggested thatDMSO molecules surround and protect fructosemolecules from side reactions that would lead tocondensation or reversion products [13]. Like-

wise, DMSO may also create a solvation shellaround FDCA, which does not allow water to in-teract with the O-H groups of FDCA.The solva-tion shell mechanism is consistent not only withthe proposed ability of DMSO to self-associate,but also with the relatively small observed peakshifts in all functional group peak shifts. Pos-sible mechanisms for this are shown below inFigure 8.

a

b

Figure 8: The visualization of proposed interac-tions between DMSO and FDCA show how themolecules behave in solution. (a) Interaction ofH bonded O-H stretch in carboxylic acids (b) In-teraction of O-H and S=O interactions.

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Figure 9: FDCA may potentially form dimers insolution.

It was found that a 25 mol H2O:75 molDMSO solvent mixture interacted with waterin a way similar to the interaction of a 0 molH2O:100 mol DMSO mixture. This suggeststhere is a point at which the increased concentra-tion of DMSO does not further affect the inter-molecular interactions between the other speciesin solution. This observation underlines the ef-fectiveness of this solvent to retain its structureeven in the presence of DMSO/H2O/FDCA mix-tures. These diminishing returns of peak shiftsin increasing DMSO concentrations also sup-port the intermolecular interaction mechanismof a solvation shell, since the solvating DMSOmolecules "crowd out" other DMSO moleculesin solution.

4.2.3 HMF in Solvent Analysis

As the molar fraction of H2O in the solventmixture increases, there is a shift in the peaksof the C=O bond to lower wavenumbers on thespectra. The C=O bond is elongated and weak-ened as there is less DMSO in the mixture (Fig-ure 10). This suggests that the O-H groups inwater may form hydrogen bonds with the car-bonyl group of HMF (Figure 11), possibly offer-ing insight into the instability of HMF in water.As found earlier, DMSO interacts and elongatesthe hydroxyl group in FDCA, however does notdegrade it. Thus, this weakening of the car-bonyl group seen with a higher H2O concentra-tion may be an explanation for the degradationof HMF in water.

The spectra reveal a shift towards higherwavenumbers in the symmetric stretching of thedouble bonds in the furan ring. Moreover, weobserve that as the molar fraction of water in

the mixture is increased, the C=C bonds becomestronger (Figure 10).

Figure 10: The IR spectra of HMF in solventmixtures of DMSO and of H2O ·

Figure 11: The hydrogen in H2O might be at-tracted to the oxygen in the carbonyl group ofHMF.

Figure 12: The trans-HMF (left) isomer may bepreferable to the cis-HMF isomer (right).

The cis and trans conformers of HMF have dif-fering interactions with DMSO, as indicated bythe spectra. The structures of these moleculescan be seen in Figure 12. According the researchof S. H. Mushrif et al., spectra of trans-HMFshould have a prominent peak at 1567 cm−1 forthe asymmetric stretching of the C=C bonds inthe furan ring, while cis-HMF presents lower in-tensity [13]. Our findings show that as the mo-lar fraction of DMSO in mixture increases, theheight of this peak indicating trans-HMF also

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increases (Figure 13). These findings suggestthat DMSO shifts the conformational equilib-rium of HMF, increasing the ratio of trans-HMFto cis-HMF and thus may be promoting the for-mation of the stable isomer of HMF.

Figure 13: The increasing intensity of the peakaround 1575 cm−1 indicate that the amount oftrans-HMF in solution increases with at DMSOconcentrations.

Comparison of the absorbance of the C=Cbond to the absorbance of the C=O bond withrespect to the mole fraction of HMF revealsthat DMSO affects the absorbance more thanthe D2O (Figure 14). While the increase ofHMF in the solution only moderately affectsthe slope of the graph of the HMF/D2O mix-ture in Figure 14, a significant change can beseen in the graph of the HMF/DMSO/D2O mix-ture. Additionally, it can be seen that this curvefollows that of HMF/DMSO more closely thanHMF/D2O. This also indicates that the func-tional group with C=O was more strongly inter-

acted with than the C=C of the furan ring withinthe HMF.

Figure 14: The absorbance intensity of threeHMF solutions with varying mole fractionsof HMF shows that the intensity trend ofHMF/DMSO/D2O is very similar to the ofHMF/DMSO.

4.2.4 Comparison of HMF Mixture Spectrato FDCA Mixture Spectra

In general, the FDCA spectra reveal moredistinct peaks and reach higher absorbance in-tensities than did the HMF spectra, particularlyin the 1500-500 cm−1 wavenumber range. Onepossible explanation is that the carboxyl groupsof FDCA allow the methyl groups of DMSO andthe oxygen of the aldehyde group of DMSO toalign with the two ends of the carboxyl groupof FDCA to form hydrogen bonds. In contrast,HMF only has a single end on its aldehyde andalcohol functional groups, limiting the strengthof intermolecular interactions with DMSO. Inaddition, it was found that H2O hydrogen-bondsto the carbonyl group of HMF but hydrogen-bonds to the hydroxyl group of FDCA. This po-tentially indicates that DMSO forms stronger in-termolecular interactions with FDCA than withHMF, making DMSO optimal for use in appli-cations of FDCA production.

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4.3 FDCA SolubilityXDMSO Solubility of FDCA (g/mL)

0.25 0.02930.50 0.18620.75 0.4262

Table 2: This table shows the solubility of theexperimental solubility limits of FDCA (g/mL)at differing molar fractions of DMSO

It has been observed that FDCA is not solublein water but is highly soluble in DMSO [10].However, there is a possibility for FDCA tobe soluble in a DMSO/H2O mixture, as DMSOis a polar aprotic solvent and FDCA has po-lar functional groups. The solubility of FDCAwas found in varying concentrations of DMSOin water (Table 2). The trend seems to be alinear correlation between the molar fraction ofDMSO in the solvent and the amount of FDCAable to be dissolved (Figure 15).

This information invites the possibility ofthe production of FDCA from fructose in a sin-gle system. It would be much more energeticallyefficient to have the reaction of fructose to HMFand the reaction of HMF to FDCA occur in thesame system. This would allow for effective useof the solvents and a more expedient productionof FDCA. These findings prove that this reac-tion would not have to occur in pure DMSO, aspreviously assumed, making it a more feasibleoption.

It was also observed that the solution con-tained many small bubbles after vortexing, in-dicating an increase in viscosity. This vis-cosity likely emerges from the intermolecularforces between DMSO molecules and FDCAmolecules. With increasing viscosity, it be-comes more difficult to agitate the mixture,which is necessary during reactions. For large-scale production in a reactor, failure to thor-oughly agitate the mixture would lead to theemergence of a concentration gradient.The gra-dient would cause the conversion of the reactant

to differ throughout the reactor, as it would behigh near the center and decrease as it movedtoward the walls of the container. The systemwould need to be closely monitored and poten-tially adjusted to account for the complicationsthat result from the viscosity.

These findings prove that, because FDCAis fairly soluble in high water concentrations, itcould be produced in DMSO in large quantities.As a result, FDCA can be produced in bulk with-out requiring large amounts of costly DMSO.

Figure 15: There is a nearly linear relationshipbetween the solubility of FDCA and the concen-tration of DMSO.

5 ConclusionsSpectral analysis revealed the interactions of

FDCA and HMF in DMSO/H2O systems, aswell as the possibility for scaling up to indus-trial applications. It is inferred that the shiftsof FDCA peaks with increasing molar fractionsof DMSO indicate that a DMSO solvation shellmight form around FDCA. Furthermore, H2Oprefers to solvate the O-H of the carboxylicgroup as opposed to the sulfate group of DMSO.It was also revealed that the trans-conformerof HMF is more stable than its cis counter-part. Moreover, the solubility limit of FDCA inDMSO/H2O mixtures was found to follow a lin-ear trend with increasing DMSO concentration.

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The molecular interactions uncovered in thisstudy are critical to working towards the selec-tion of an optimal solvent and gaining a morethorough understanding of what is happeningat the molecular level in biomass processing.An ideal solvent would allow for the large-scaleproduction of HMF and its derivatives for theproduction of energy and chemical intermedi-ates. Furthermore, it could lead to the singlesystem production of FDCA. Due to time lim-itations, not all interactions and conformationscould be explored. Sources of error may includethe lack of replicated trials, due to these timeconstraints. Further studies would benefit fromthe use of nuclear magnetic resonance (NMR)spectroscopy to explore the orientations of themolecules in question. Additionally, experimen-tation with DMSO/H2O mixtures at closer inter-vals would provide a more accurate picture ofspectra trends in peak shifts and molecular in-teractions.

AcknowledgmentsThis research project could not have been

completed without the help of many, so the re-searchers would like to extend their gratitude tothose that made it possible. The authors wouldlike to thank Dr. Georgios Tsilomelekis for hisguidance and support throughout this project.They would also like to recognize graduate stu-dents Hualin Qiao and Yusheng Guo for theirassistance. The authors are grateful to SandraPelka, the Residential Teaching Assistant whooversaw the project. They would like to thankResidential Teaching Assistant Alex Hobbs forhis assistance in the research process and in re-viewing this paper as well as the other Residen-tial Teaching Assistants for their hard work anddedication. In addition, they wish to expresstheir appreciation toward the New Jersey Gov-ernor’s School of Engineering and Technology,the Director, Dr. Ilene Rosen, and the AssociateDirector, Dean Jean-Patrick Antoine, for pro-viding the opportunity to conduct this research.

Finally, the authors would like to acknowledgetheir sponsors: Rutgers, the State University ofNew Jersey, Rutgers School of Engineering, thestate of New Jersey, Lockheed Martin, SouthJersey Industries, and printrbot.

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[13] S. H. Mushrif et al., "Understanding Sol-vent Effects in the Selective Conversion ofFructose to 5-Hydroxymethylfurfural: AMolecular Dynamics Investigation," Phys.Chem. Chem. Phys., vol. 14, no. 9, pp.2637-2644. Feb 2012.

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Appendix

A

Figure A.1: Spectra analysis of FDCA in 100%H2O

Figure A.2: Spectra analysis of FDCA in 25%DMSO




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B

Name Mixture1H HMF in 100% H2O2H HMF in 25% DMSO3H HMF in 50% DMSO4H HMF in 75% DMSO5H HMF in 100% DMSO

Table 3: The table identifies the terms used forall of the HMF mixtures in the spectra.

Figure B.1: Spectra analysis of HMF in 100%H2O

Figure B.2: Spectra analysis of HMF in 25%DMSO




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