Kaolinite Catalyst for the Production of a Biodiesel-Based Compound

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Cite This: ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX

Kaolinite Catalyst for the Production of a Biodiesel-Based Compound from Biomass-Derived Furfuryl Alcohol Taufik Abdillah Natsir,†,‡ Takayoshi Hara,† Nobuyuki Ichikuni,† and Shogo Shimazu*,† †

Graduate School of Engineering, Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522, Japan Department of Chemistry, Universitas Gadjah Mada, Sekip Utara Bulaksumur, Yogyakarta 55281, Indonesia

‡

S Supporting Information *

ABSTRACT: We report herein that pristine kaolinite was used to produce furanic ethers from furfuryl alcohol (FFA) with high catalytic performance (95% conversion and 96% selectivity). Kaolinite, supplied commercially and prepared without any treatment, was characterized by XRD, NH3-TPD, surface area analysis, and FT-IR spectroscopies. The result showed that the Lewis and Brønsted acid sites played a crucial role in the formation of furanic ether. The reusability tests showed that kaolinite was stable until the fifth consecutive run.

KEYWORDS: kaolinite, furfuryl alcohol, furfuryl ether, etherification, biodiesel

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Kaolinite (Al2Si2O5(OH)4) is a dioctahedral 1:1 clay mineral of the kaolin group that contains octahedral gibbsite Al(OH)3 and tetrahedral SiO4 sheets.14 Kaolinite has the same chemical composition as halloysite; however, the structure of kaolinite is different from halloysite. Kaolinite has a multilayer plate structure, while halloysite has a multilayer tubular structure.15 Kaolinite is known as an acidic catalyst.16 So far, the use of kaolinite for etherification of furanic ethers from furanic alcohols has not been reported. Therefore, the present work presents the use of kaolinite as an acidic catalyst for furanic ethers from furfuryl alcohol (FFA) with high catalytic performance. We also investigated the active sites of kaolinite for this reaction (Scheme 1). The detailed instrumentation and catalyst methods, and products analysis and quantification procedures, are described in the Supporting Information. In this experiment, kaolinite was supplied from Sigma-Aldrich and used without any further treatment (denoted as kal-raw). The etherification of FFA was conducted under a N2 pressure (0.8 MPa) and a reaction temperature of 453 K, and 2-propanol was utilized as a solvent and a reactant (3 mL). The Fourier transform infrared (FT-IR) spectrum of kal-raw showed the characteristic bands of O−H stretching of the inner-surface, the out-of-plane stretching vibration, and the inner hydroxyl group of kaolinite at 3695, 3653, and 3619 cm−1, respectively (Figure S1 and Table S1).17 The FT-IR spectra did

n recent decades, the demand for biomass-derived compounds in the chemical industry and for the production of alternative energy resources has been gaining interest, particularly due to the increasing concern over greenhouse gas emission, the worldwide shortage of fossil resources, and a willingness to move to more renewable resources.1 One of the most important uses of fossil-derived compounds is for jet and diesel fuels for transportation. Researchers have attempted to produce biodiesel from renewable resources such as biomass-derived compounds, e.g., furan compounds. One strategy to produce biodiesel fuels from furan compounds is by increasing the carbon number, such as through an etherification reaction.2 Biomass-derived furanyl ethers are suitable for diesel range molecules due to a high cetane number and high energy density, and these ethers can be used as an additive for petroleum-derived diesel fuels.3 Such ethers can be synthesized from furanyl alcohol. The etherification reaction of furanyl alcohol needs an acidic catalyst to proceed.4 Several acidic catalysts have been used to produce furanic ethers, such as modified zeolites,4−7 metal chlorides,3 metal oxides,8−10 modified montmorillonites,11 and resins.12,13 The most widely used catalysts for the etherification of furanyl alcohol are zeolite-based. There are two active sites in the etherification of furanic alcohol to furanic ethers, as shown in Scheme 1. The Vlachos group reported that the active sites of metal chlorides (CrCl3) were Brønsted acidic because the CrCl3 and alcohol produced induced HCl.3 Meanwhile, another study reported that a Lewis acid was the active site for the etherification of furanic alcohol.7,10 © XXXX American Chemical Society

Received: April 30, 2018 Accepted: May 30, 2018 Published: May 30, 2018 A

DOI: 10.1021/acsaem.8b00694 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX

Letter

ACS Applied Energy Materials

desorbed product on the catalyst. Therefore, the catalytic activity dropped. The time-dependent experiment showed that the conversion of FFA entirely produced isopropoxy furfuryl ether with a low reaction time (less than 60 min), as shown in Figure 1. It is

Scheme 1. Etherification of Furanyl Alcohol

Figure 1. Time profiles of FFA conversion using kal-raw. Reaction conditions: kal-raw = 0.05 g, furfuryl alcohol = 1.1 mmol, 2-PrOH = 3 mL, decaline = 0.07 g, reaction temperature = 453 K, and N2 pressure = 0.8 MPa.

clear that the etherification of FFA is the first reaction to proceed via the acidic sites of kal-raw. Byproducts appeared after the reaction proceeded more than 60 min, and the concentration gradually increased with increasing reaction time. The hydrogenation of CC in the furan ring to produce isopropoxy methyl tetrahydrofuran seemingly occurred. We speculate that the hydrogenation of the furan ring proceeded due to hydrogen transfer from 2-propanol or by using hydrogen produced from the dehydrogenation of 2-propanol.7 Meanwhile, methyl furan was produced from the hydrogenolysis of an hydroxyl group at high temperature using hydrogen produced from the dehydrogenation of 2-propanol.7 Additionally, isopropyl levulinate was produced through two routes, alcoholysis of FFA or through 4,5,5-tri-isopropoxy-pentan-2one (TIPP).3 However, we did not detect the presence of TIPP. When we changed 2-propanol with ethanol, the intermediate 4,5,5-triethoxy-pentan-2-one (TEPP) was detected. This result indicated that TIPP may not be stable in 2-propanol.3 To investigate the active sites of kal-raw, we used NaOH and pyridine as probe molecules (Figure S5). The addition of NaOH into the solution up to 0.03 and 1.25 μM decreased the catalytic activity of kal-raw below 43% and 0%, respectively. We speculate that the presence of NaOH in solution deprotonated the kaolinite surface because kaolinite has the lowest pKa value of AlOH compared with those of FFA and 2-propanol (pKa2 AlOH = 5.28−9.84, pKa FFA = 9.55, and pKa 2-propanol = 17.1).19−21 Furthermore, we also studied the effect of water in solution because the added NaOH was an aqueous solution. The result showed that, in a comparison with NaOH, the presence of water in solution slightly influenced the catalytic activity of the catalyst (Figure S6). Therefore, we assume that the addition of NaOH into the solution caused FFA and 2propanol to be hindered from approaching the surface of the

not reveal the presence of silanol groups on kal-raw. XRD spectra showed that kaolinite was the dominant phase with a basal spacing d001 of 7.15 Å, as shown in Figure S2. However, small phases of impurities, such as quartz, illite, montmorillonite, and albite appeared.18 The adsorbed pyridine on kalraw revealed that the Lewis and Brønsted acid sites were present on the surface of the catalyst (Figure S3). The numbers of Lewis and Brønsted acid sites were 1.41 and 2.90 × 10−2 mmol g−1, respectively. The catalytic performance of kal-raw showed that the etherification of FFA to isopropoxy furfuryl ether resulted in high catalytic performance; i.e., the conversion and selectivity were 95% and 96%, respectively, after the reaction proceeded at 2 h, as shown in Table S2. Isopropoxy methyl tetrahydrofuran was produced as the dominant byproduct. Other byproducts included methyl furan and isopropyl levulinate. The byproducts of the etherification process were confirmed using GC, GC− MS, and NMR. The effect of reaction conditions, such as N2 pressure and the reaction temperature, was studied, as shown in Table S3. An increase in the reaction temperature from 413 to 453 K promoted FFA conversion from 14% to 95% with a selectivity of isopropoxy furfuryl ether of more than 96%, as shown in Table S3 (entries 1−3). This result indicates that the etherification of FFA was sensitive to temperature. The effect of N2 pressure was studied in the range between 0.4 and 1.0 MPa. Increasing the N2 pressure accelerated FFA conversion, and the optimum conversion was achieved at 0.8 MPa. At a N2 pressure above 0.8 MPa, the conversion of FFA to isopropoxy furfuryl ether seemed to be suppressed. We assume that the use of a high N2 pressure increased the interaction between the substrate and the catalyst surface. The use of a high pressure that is greater than the optimum condition lowered the B

DOI: 10.1021/acsaem.8b00694 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX

Letter

ACS Applied Energy Materials

can adjust the addition of C atom number of the biomassderived FFA through the etherification process. The reusability of the kaolinite catalyst was conducted to determine the economic advantages of this catalyst to the etherification reaction. The spent catalyst was recovered after each reaction, washed with hexane, and dried at a temperature of 378 K. The catalyst was successfully recovered even after 5 runs without any loss in activity as shown in Figure 3. The

catalyst due to the deprotonation process on the catalyst surface, as shown in Scheme S1a. The presence of pyridine in solution (0.1 M) decreased the catalytic activity of the catalyst below 9%. We assume that pyridine adsorbed on the acidic sites prevented FFA from reacting on the surface of kaolinite, as shown in Scheme S1b. On the basis of FT-IR spectra of the aforementioned adsorbed pyridine on the kaolinite surface, pyridine was adsorbed on both the Lewis and Brønsted acid sites (Figure S3). To investigate the role of the Brønsted and Lewis acid sites, we treated kaolinite at different temperatures (Figure S7). The pretreated catalyst heated until 673 K showed a slight decrease in the selectivity of isopropoxy furfuryl ether, although the conversion of FFA increased up to 91%. We assume that the pretreated kaolinite at high temperatures increases the number of Lewis acid sites to enhance the catalytic activity. On the contrary, the pretreated catalyst under the same conditions decreases the number of Brønsted acid sites to reduce the selectivity of furanic ethers. In addition, the existence of small amount of water in the solution (up to 2.1 M) maintained the selectivity of isopropoxy furfuryl ether, as shown in Figure S5. Therefore, we assume that Brønsted acid sites played a crucial role in the selectivity of the product. Thus, we speculate that the active sites of kaolinite for this reaction are the Lewis and Brønsted acid sites. The effect of alcohol on the etherification of FFA was studied using various alcohols, such as primary alcohols (ethanol, 1propanol, and 1-butanol) and secondary alcohols (2-propanol and 2-butanol) as shown in Figure 2. The increase in C atom

Figure 3. Recyclable catalytic activity of kaolinite for the etherification reaction. Reaction conditions: kal-raw = 0.05 g, FFA = 1.1 mmol, 2PrOH = 3 mL, decaline = 0.07 g, reaction temperature = 453 K, reaction time = 2 h, and N2 pressure = 0.8 MPa.

catalyst showed high stability performance indicated by the high catalytic performance even after the fifth run. The comparison of kaolinite with the other catalysts showed that the etherification of furanyl alcohol has a comparable result with Amberlyst 15, as shown in Table S4. In conclusion, we have demonstrated the unique utility of pristine kaolinite for the production of biodiesel-based compounds from biomass-derived FFA through the etherification reaction with high catalytic performance and reusability. The reason behind the uniqueness of kaolinite is the acidic properties of this clay. The high number of Lewis acid sites and the low number of Brønsted acid sites influenced the catalytic performance of the kaolinite. The catalyst was easily used without any pretreatment and was successfully recycled. Therefore, kaolinite offers significant environmental advantages in the green chemistry processing of biodiesel-based compounds.

Figure 2. Effect of alcohol in the etherification of furanyl alcohol. Reaction conditions: kal-raw = 0.05 g, FFA = 1.1 mmol, alcohol solvent = 3 mL, decaline = 0.07 g, reaction temperature = 453 K, reaction time = 2 h, and N2 pressure = 0.8 MPa.

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ASSOCIATED CONTENT

S Supporting Information *

number of the alcohols remarkably raised the selectivity of the furanic ethers. We speculate that the polarity of alcohols may influence the selectivity of products as shown in Figure S8. The ether selectivity increased inversely with the dielectric constant of primary alcohol such as ethanol, 1-propanol, and 1-butanol. When the secondary alcohol was utilized, the ether selectivity was around 96% regardless of C number. The lower polar alcohols can easily enter into the two basal planes of kaolinite since the silica face of kaolinite is more hydrophobic than the alumina face.22 The effect of various alcohols suggests that we

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsaem.8b00694. Experimental details, IR spectra and data, TPD data, and catalysis results (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. C

DOI: 10.1021/acsaem.8b00694 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX

Letter

ACS Applied Energy Materials ORCID

(18) Altomare, A.; Corriero, N.; Cuocci, C.; Falcicchio, A.; Moliterni, A.; Rizzi, R. QUALX2.0: A Qualitative Phase Analysis Software Using the Freely Available Database POW_COD. J. Appl. Crystallogr. 2015, 48, 598−603. (19) Frini-Srasra, N.; Srasra, E. Determination of Acid-Base Properties of Hcl Acid Activated Palygorskite by Potentiometric Titration. Surf. Eng. Appl. Electrochem. 2008, 44 (5), 401−409. (20) Martin, T. J.; Vakhshori, V. G.; Tran, Y. S.; Kwon, O. Phosphine-Catalyzed B′-Umpolung Addition of Nucleophiles to Activated α-Alkyl Allenes. Org. Lett. 2011, 13, 2586−2589. (21) Serjeant, E. P.; Dempsey, B. Ionisation Constants of Organic Acids in Aqueous Solution. International Union of Pure and Applied Chemistry (IUPAC); IUPAC Chemical Data Series No. 23; 1979. (22) Yin, X.; Gupta, V.; Du, H.; Wang, X.; Miller, J. D. Surface Charge and Wetting Characteristics of Layered Silicate Minerals. Adv. Colloid Interface Sci. 2012, 179−182, 43−50.

Taufik Abdillah Natsir: 0000-0002-9915-7600 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported in part by JSPS KAKENHI Grant 15K06565 and JSPS Bilateral Joint Research Projects (2014−2017).

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REFERENCES

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DOI: 10.1021/acsaem.8b00694 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX