Abstract
Effective conversion of molasses into 5-(hydroxymethyl)furfural (HMF) to develop it as an additive in diesel was performed using an amberlyst-15-supported Cr3+ catalyst (CrAm15) in a reduced pressure vessel at 115 °C for 30 min, receiving a yield of 43.37%. The as-prepared CrAm15 catalyst was characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS), showing a Cr content of 6.64 wt % on the surface of amberlyst-15. For further investigation, the 5-(hydroxymethyl)furfural derivative, HMF-Palmitic-OCH3 (3), was synthesized by a three-step sequential esterification of HMF and fatty acid, reduction of aldehyde to alcohol, and methylation of the hydroxyl group to the ether form. The structure was confirmed by spectroscopic techniques (NMR, mass, and FT-IR). The clear solution of additive 3 in diesel at 1% w/v improved the cetane number to 55, which is higher than that of commercial diesel.
1. Introduction
Air and environmental pollution problems affect the world, including Thailand, whether it is in the life of humans, animals, or other living things. The use of fuel in transportation creates various gases such as carbon dioxide (CO2), carbon monoxide (CO), and nitrogen oxide (NO x ). There is also dust (suspended particulate matter, SPM) floating in the air, which is polluting the respiratory system. Nevertheless, the use of petroleum fuel is still a top necessity because it is convenient and does not take long to refuel each time. Nowadays, fuel is being improved continuously to increase the efficiency of engine combustion and reduce the release of pollutants. − The next most important issue is reducing costs in both production and importing fuel with higher prices, which induce a chance for researchers to search. 5-(Hydroxymethyl)furfural (HMF) is an organic compound that has both groups, alcohol (−OH) and aldehyde (−CHO), functioning as components. It is a product of the dehydration of monosaccharide (glucose and fructose) that uses an acid-catalyzed reaction. HMF can be used to produce biofuels, polymers, and various chemical precursors used in industry. − There is continuous research on the synthesis of additives by increasing the cetane value of fuels, including organic acid glycol nitrate or nitro derivatives of long-chain fatty acids, ,,, cyclic peroxides, etc. However, improving the quality of fuel to achieve a higher cetane number by modifying the structure including HMF is still limited.
In Thailand, molasses are considered an agricultural waste containing sucrose as the main component. Sucrose can be transformed through dehydration into fructose for use as a starting material to synthesize HMF. A previous publication has shown the transformation of molasses into valuable substances such as levulinic acid and HMF. Herein, this research aims to precede molasses into HMF to combine with fatty acids via esterification, reduction, and methylation, respectively, for use as an additive in diesel. As-synthesized (hydroxymethyl)furfural derivatives have been further investigated for solubility in a ratio of diesel and alcohol, followed by the determination of various properties such as viscosity, density, heat value, and cetane number to be useful in the future.
2. Experimental Apparatus and Methodologies
2.1. General
Molasses were bought from a supermarket. Diesel used in this experiment was obtained from PTT Global Chemical Public Co., Ltd., Bangkok, Thailand. All chemicals were purchased from standard chemical companies without purification and used as received; the chemicals are as listed: chromium trichloride hexahydrate (CrCl3·6H2O, 97%, LOBA Chemie), amberlyst-15 (Fluka), concentrated hydrochloric acid (37% w/w HCl, Supelco, Inc.), sodium sulfate anhydrous (anh.Na2SO4, 99%, QRëC), palmitic acid (C16H32O2, >97%, Tokyo Chemical Industry Co., Ltd.), triethylamine (>99%, Tokyo Chemical Industry Co., Ltd.), cyanuric chloride (C3Cl3N3, >98%, Tokyo Chemical Industry Co., Ltd.), sodium borohydride (NaBH4, >95%, Tokyo Chemical Industry Co., Ltd.), sodium hydride (NaH, 60% dispersion in paraffin liquid, Tokyo Chemical Industry Co., Ltd.), and dimethyl sulfate (C2H6O4S, Fluka). The solvents for extraction and chromatography are as listed: dichloromethane (CH2Cl2), ethyl acetate (EtOAc), and hexane (C6H14), which were of commercial grade from LSP Chemical (Thailand) Co., Ltd. and distilled at their boiling point ranges prior to use. Toluene (C7H8) was obtained without purification from LSP Chemical (Thailand) Co., Ltd. Methanol and tetrahydrofuran were of analytical grade (RCI Labscan) and ACS reagents for HPLC were obtained from Honeywell. Deionized (DI) water was obtained from Nanopure Analytical Deionization Water with an electrical resistance of ≥18.2 MΩ/cm. The stationary phase used for column chromatography is silica gel 60 #7734 CAS Number 112926–00–8 (25 kg) and silica gel 60 PF254 CAS Number 7631–86–9 (2.5 kg) from Merck KGaA. An Environmental Express HotBlock digestion system (54-well) was used specifically to digest fructose into 5-(hydroxymethyl)furfural (HMF). The specific signal of synthesized structures was recorded by using nuclear magnetic resonance (NMR) spectroscopy (Bruker AVANCE 400 (400 MHz) spectrometer (Bruker, Massachusetts)) with tetramethylsilane (TMS) and chloroform-d as the internal standard and dissolved solvent, respectively. For the product, the yield was calculated from the peak of the selected area analyzed by using quantitative nuclear magnetic resonance spectroscopy (80 MHz) in water suppression mode (Bruker/F80) with sodium acetate as an internal standard. The functional groups were characterized by using Fourier transform infrared spectroscopy (Bruker Invenio-S FT-IR spectrometer), and the molecular weight was acquired by using gas chromatography–mass spectrometry (GC–MS/MS TQ model 8890GC/7000DGC/MS triple Quad). The catalyst appearance was characterized by scanning electron microscopy (SEM, HITACHI/FlexSEM1000 II). High-performance liquid chromatography (HPLC, Agilent/1260 Infinity II) was used to analyze the amounts of starting sugar types in molasses.
2.2. Catalyst Preparation
The Cr3+ support on the amberlyst-15 catalyst was prepared by the modifying the preparation method mentioned in a previous publication. To 3 g of amberlyst-15 in a reduced pressure glass tube, a solution (1 g of CrCl3·6H2O in 10 cm3 of methanol) was added. The mixture was then heated at 80 °C in a silicone oil bath for 12 h, followed by filtration under vacuum, and washed subsequently with 100 cm3 of deionized (DI) water and 100 cm3 of methanol and kept under an atmosphere for 12 h.
2.3. Dehydration of Molasses to HMF
The experimental procedure was modified under quantitative adjustments by a previously published work, and molasses were used instead of fructose. To a solution of molasses (1.1 g) in 25 cm3 of deionized (DI) water in a 50 cm3 digest tube, the catalyst by a percentage (50, 100, 150, 200% w/w) of molasses was added. Next, the solution was digested into a digest block (Environmental Express HotBlock digestion system, 54-well) at 115 °C for 30 min and cooled down to room temperature. The mixture was extracted with CH2Cl2 (30 cm3 × 2), dried over anh.Na2SO4, separated out, and evaporated in vacuo, sequentially. A brown liquid was obtained with a yield of 43.37% measured by quantitative nuclear magnetic resonance spectroscopy, which was calculated based on the amount of fructose in molasses.
2.4. Synthesis of HMF-Palmitic-OCH3 (3)
The starting compound HMF-Palmitic (1) was synthesized by modifying conditions as per the literature. Five g of as-synthesized HMF from molasses and palmitic acid (10.25 g, 40 mmol) were mixed in a 500 am3 round-bottom flask using toluene (300 cm3) as a solvent, triethylamine (4.35 g, 43 mmol) as a base, and cyanuric chloride (7.37 g, 40 mmol) as a catalyst. Then, the mixture was refluxed at 100 °C. After 16 h of reaction, it was cooled down to room temperature and filtered in vacuo by washing with EtOAc (150 cm3). The filtrate was then evaporated to extract the crude product and finalized to yield the product by column chromatography (silica gel 60 #7734) using the gradient system (0–50% EtOAc/Hexane). A yellow solid (7.29 g) was obtained.
To a solution of HMF-Palmitic (1) (7.29 g) in THF 50 cm3 in 250 cm3 Erlenmeyer flask, freshed and cooled solution of NaBH4 (1.14 g, 30 mmol) 5 cm3 was added dropwise and continue to stir for 2 h. Added 50 cm3 of deionized (DI) water was added to work up the reaction. The mixture was extracted by EtOAc (50 cm3 × 2), dried over anh.Na2SO4, separated out and evaporated under vacuo, sequentially. The desired product, HMF-Palmitic–OH (2) is used in the next step without purification. White solid, (6.23 g).
To a solution of HMF-Palmitic–OH (2) (1.83 g) in 50 cm3 of THF in a 250 cm3 Erlenmeyer flask, NaH (0.36 g, 15 mmol) and dimethyl sulfate (0.63 g, 10 mmol) were added sequentially. The mixture was then refluxed at 60–65 °C for 12 h. After the reaction was completed, it was cooled down to ambient temperature; 50 cm3 of deionized (DI) water was added, and the mixture was continuously stirred to work up the reaction. The mixture was extracted by CH2Cl2 (50 cm3 × 4) followed by deionized (DI) water (50 cm3 × 4). The organic layer was dried over anh.Na2SO4, separated out, and evaporated in vacuo, sequentially. The crude product was purified by preparative chromatography (silica gel 60 #7747) using an isocratic system as 10% EtOAc/Hexane. Preferred HMF-Palmitic-OCH3 (3) is a yellowish white solid (0.67 g). M w: 380.56 g/mol; mp: 39.83 °C; chemical formula: C23H40O4. FT-IR: ν, (cm–1) 2914.79–2847.93 (−CH2, −CH3), 1733.79 (CO), 1471.51–1386.65 (CC), 1157.15 (C–O in O–CO), 1097.36 (C–O in O–CH3). 1H NMR (400 MHz, CDCl3): δ (ppm) 6.262 (d, J = 3.2 Hz, 1H), 6.200 (d, J = 3.2 Hz, 1H), 4.949 (s, 2H), 4.291 (s, 2H), 3.286 (s, 3H), 2.232 (t, J = 7.2 Hz, 2H), 1.565–1.513 (m, 2H), 1.268–1.174 (m, 24H), 0.858–0.812 (m, 3H). 13C NMR (100 MHz, CDCl3): δ (ppm) 173.38, 152.34, 149.91, 111.15, 111.14, 68.09, 57.95, 57.93, 31.92, 30.36, 29.69, 29.67, 29.65, 29.59, 29.44, 29.36, 29.26, 29.24, 29.16, 29.08, 28.92, 26.14, 14.15. ESI-MS (m/z): calcd exact mass 403.2824 (found: 403.2824 [M+Na+]).
2.5. Solubility Testing
The soluble ability of additives in diesel was tested by dissolving additives (1, 3, 5% w/v) in 2 cm3 of diesel. The mixture was stirred for 2 h and left overnight to observe the homogeneity of the mixture.
2.6. Fuel Analysis
The sample for testing of fuel properties was prepared by the same method as that of solubility testing with a ratio of 1% w/v by adjusting the volume of diesel to 100 cm3. The values for fuel analysis were chosen by the standard method as ASTM D976 (cetane index), ASTM D445 (viscosity at 40 °C), ASTM D4052 (specific gravity at 15 °C), and ASTM D240 (heat of combustion).
3. Results and Discussion
3.1. Morphology of the Catalyst
The CrAm15 catalyst revealed a spherical shape and a pale green color of Cr3+ coated on amberlyst-15. Scanning electron microscopy (SEM) was used for surface characterization of amberlyst-15 and CrAm15 catalysts. The surface of amberlyst-15 is smooth, while the CrAm15 catalyst has cracks and gaps which have similar characteristics to a previous research as compared in Figure . The EDS mapping image (Figure ) showed the appearance of Cr coated on the CrAm15 catalyst, which was calculated as 6.64 wt %.
1.
SEM images of (a) amberlyst-15 and (b) CrAm15 catalysts.
2.
EDS mapping image of the CrAm15 catalyst.
3.2. Determination of HMF
Molasses received from the supermarket (Mitr Phol Brand, Thailand) contain fructose (3.40 ± 0.09% w/w), glucose (3.96 ± 0.08% w/w), and sucrose (39.77 ± 0.27% w/w), measured by using HPLC analysis from Science Innovation Facility (SIF), Faculty of Science, Burapha University, Thailand. In theory, fructose can be dehydrated directly to HMF because it has a 5-membered ring structure similar to HMF, while glucose has a 6-membered ring structure and needs to be isomerized to fructose first and then dehydrated to HMF. In the case of sucrose, the reaction is even more difficult because sucrose is a disaccharide (glucose and fructose) that must first be broken down into a monosaccharide. Therefore, the order of reactivity of the reactants in molasses can be ranked as fructose > glucose > sucrose. It can be confirmed that only entries 7 and 8 can produce products (Table ). The % yield was calculated from Q-NMR based on the number of protons of the standard. To understand the calculated percentage of HMF, see the Supporting Information (SI). The feasibility study of using molasses as a starting material in the synthesis of HMF via a dehydration reaction was conducted by varying the amounts of the CrAm15 catalyst as shown in Table . As a starting amount of the CrAm15 catalyst (50 wt %, 3.4%Cr), the production showed a low yield (8.43%, entry 4), whereas 100 wt %, 6.6%Cr produced HMF in the highest yield of 43.37% (entry 5). After that, the percentage would gradually decrease (entries 6 and 7) as the amount of the CrAm15 catalyst was increased (≥10.0%Cr). It is predicted that HMF may undergo ring-opening to levulinic acid due to the acidic conditions caused by the increased catalyst amount.
1. Percentage of HMF Production Catalyzed by CrAm15 and Analyzed by Q-NMR.
| entry | feedstock | catalyst | Cr (wt %) | % yield |
|---|---|---|---|---|
| 1 | glucose | No | ||
| 2 | Cr3+ | |||
| 3 | amberlyst-15 | |||
| 4 | 50 wt % CrAm15 | 3.4 | ||
| 5 | fructose | No | ||
| 6 | Cr3+ | |||
| 7 | amberlyst-15 | 2.27 | ||
| 8 | 50 wt % CrAm15 | 3.4 | 1.69 | |
| 9 | sucrose | No | ||
| 10 | Cr3+ | |||
| 11 | amberlyst-15 | |||
| 12 | 50 wt % CrAm15 | 3.4 |
2. Various CrAm15 Catalysts Convert Molasses into HMF Analyzed by Q-NMR .
| entry | catalyst | Cr (wt %) | % yield |
|---|---|---|---|
| 1 | No | ||
| 2 | Cr3+ | ||
| 3 | amberlyst-15 | ||
| 4 | 50 wt % CrAm15 | 3.4 | 8.43 |
| 5 | 100 wt % CrAm15 | 6.6 | 43.37 |
| 6 | 150 wt % CrAm15 | 10.0 | 39.76 |
| 7 | 200 wt % CrAm15 | 13.3 | 32.53 |
% Yield was calculated corresponding to % fructose in molasses (3.40 ± 0.09% w/w) in 25 cm3 of the reaction volume.
3.3. Characterization of HMF-Palmitic-OCH3 (3)
To continue the synthesis of additive materials in diesel, HMF-Palmitic-OCH3 was designed via the esterification of HMF and palmitic acid, reduction of aldehyde to alcohol, and methylation of the hydroxyl group to the ether form. It is desirable that the desired product can be synthesized with moderate to high purity even from a mixture (Figure ). The characteristic proton signal at approximately δ 3.286 ppm (s, 3H) represents the methoxy proton (−OCH3) in the structure.
3.
1H NMR (400 MHz) spectrum of HMF-Palmitic-OCH3 (3) in CDCl3.
The result elucidated by using the FT-IR technique confirmed that HMF-Palmitic-OCH3 can actually be synthesized. Figure exhibits that the vibrational bands still appear as the main residue of the C–H bond (2914.09–2848.52 cm–1) in the long-chain alkyl group and the separated band of CC (1471.51–1386.65 cm–1) in the furan ring. The formation of an ester group from HMF and palmitic acid could be confirmed by the vibrational band of the C–O bond at a wavenumber range of 1159.05–1157.15 cm–1 including the disappearance of the vibrational band in the O–H bond of HMF at a wavenumber of 3400.01 cm–1. Moreover, the wavenumber of the CO bond (1733.79 cm–1) is slightly increased due to more vibration caused than that of the carboxylic group in palmitic acid (1697.11 cm–1). There is also a wavenumber of vibration in the C–O bond at 1097.36 cm–1 caused by methylation.
4.
FT-IR spectra of HMF-Palmitic-OCH3 (3) compared to substrates.
3.4. Homogeneity of Diesel Mixing Additives
The amount of additives mixed into diesel affects the solubility and compatibility of the mixture. By adjusting the amount of additives (1, 3, and 5% w/v) compared to diesel, it was found that 1% w/v exhibited good compatibility and appeared as a clear solution (Figure ).
5.
Appearance at various amounts of additives in diesel.
3.5. Fuel Properties
The results indicated that diesel-mixed HMF-Palmitic-OCH3 (D99) complies with standard requirements for diesel. In order to explain the standard values by comparing D99 to diesel (D100) and others, it can be compared individually, as illustrated in Table .
3. Fuel Properties of Diesel-Mixed HMF-Palmitic-OCH3 (D99).
| sample | cetane index | viscosity at 40 °C (cSt) | specific gravity at 15 °C (60 °F) | heat of combustion (MJ/kg) |
|---|---|---|---|---|
| standard method | ASTM D976 | ASTM D445 | ASTM D4052 | ASTM D240 |
| standard value | ≥50 | 1.8–4.1 | 0.81–0.87 | |
| diesel (D100) | 53.5 | 2.681 | 0.8260 | 46.5 |
| B-15 (used frying oil) | 48 | 4.35 | 0.845 | N/A |
| B-15 (frying oil) | 50 | 4.65 | 0.854 | N/A |
| D99 | 55 | 3.6527 | 0.8268 | 45.2405 |
Cetane index: Diesel with a higher cetane index helps to ignite better and makes combustion more complete, resulting in a marked improvement in engine power. In addition, the engine will run smoother, including the release of smoke, and waste will be less. The measured cetane index of D99 is higher than the standard value and is also higher than that of diesel.
Viscosity at 40 °C: Viscosity using the measurement method at a standard temperature (40 °C) is a value that indicates the flow resistance properties of a fuel. A higher value means the fuel is very thick or viscous. A lower value means less viscosity. The standard value for the viscosity of fuel is in the range of 1.8–4.1 cSt. In the case of D99, it is 3.6527 cSt, which is within the specified standard range. D99 has a higher viscosity than diesel. This helps protect the engine from wear and tear and reduce the rate of consumption of fuel that is depleted from evaporation.
Specific gravity, 15 °C: Specific gravity (relative density) measures the density of a substance compared to the density of water. In this work, the specific gravity at 15 °C was found to be 0.8268, falling within the standard range of 0.81–0.87.
Heat of combustion: The heating value of a substance is the amount of heat released during combustion to change into mechanical energy for driving. However, D99 has slightly less heat release after combustion than diesel.
4. Conclusions
Utilization of molasses can be achieved by using a catalytic dehydration reaction under acidic conditions (CrAm15), producing 5-(hydroxymethyl)furfural (HMF) with a moderate yield. HMF can be further developed to synthesize additives in diesel via a series of esterification, reduction, and methylation reactions. The HMF-Palmitic-OCH3 additive showed promising results in enhancing the cetane number of diesel, indicating its potential to improve fuel quality and combustion efficiency. This study has the potential to convert agricultural waste products into valuable fuel additives, thus promoting the development of more sustainable transport fuels in the future.
Supplementary Material
Acknowledgments
This research was also supported by the Faculty of Science at Sriracha, Kasetsart University (Code No.: Sci-Src-RA02/2567) and Kasetsart University, Sriracha Campus. Their financial assistance has been instrumental in carrying out the research and achieving the presented results. Furthermore, we would also like to express our gratitude to Chemistry and Applied Chemistry, Faculty of Science and Technology, Suratthani Rajabhat University; the Department of Physical Science, Faculty of Science and Digital Innovation, Thaksin University; the Center of Excellence for Agricultural Innovation and Bioproducts, Thaksin University; and the Nuclear Technology Research and Development Center, Thailand Institute of Nuclear Technology for their valuable contributions and assistance throughout the project. Their expertise, guidance, and collaboration have greatly enriched the quality of this work.
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.5c13585.
ESI-MS spectrum (Figure S1) and DEPT-135 NMR (100 MHz) spectrum (Figure S2) of the pure additive HMF-Palmitic-OCH3 (3), Q-NMR analysis of the yield in reaction mixtures (Figure S3), and yield calculation of the product and %Cr in the catalyst (PDF)
L.C.C.: Conceptualization, idea creation, hypothesis, methodology, validation, data analysis, data curation, formal analysis, visualization, discussion, conclusion, writingoriginal draft, reviewing & editing, and supervision. N.P.: Conceptualization, idea creation, hypothesis, methodology, validation, data analysis, data curation, recommendation, and discussion. P.K.: Methodology, validation, data analysis, data curation, recommendation, and discussion. R.C.: Investigation. P.T.: Investigation. N.C.: Investigation. J.R.: Investigation. P.S.: Investigation. S.K.: Conceptualization, idea creation, hypothesis, methodology, validation, data analysis, data curation, formal analysis, visualization, discussion, conclusion, writingoriginal draft, reviewing & editing, supervision, project administration, and funding acquisition.
The authors declare no competing financial interest.
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