Production of Terephthalic Acid from Lignin-Based Phenolic Acids by

Letter pubs.acs.org/acscatalysis

Production of Terephthalic Acid from Lignin-Based Phenolic Acids by a Cascade Fixed-Bed Process Zhiyu Bai,†,‡ Wen Chuen Phuan,†,‡ Jun Ding,‡ Teck Huat Heng,† Jizhong Luo,† and Yinghuai Zhu*,† †

Institute of Chemical and Engineering Sciences, 1 Pesek Road, Jurong Island, Singapore 627833 Department of Materials Sciences & Engineering, National University of Singapore, Engineering Drive 1, Singapore 117575

‡

S Supporting Information *

ABSTRACT: Vanillic acid and syringic acid were converted to terephthalic acid via a two-step process using a fixed-bed reactor. The cascade route includes hydrogenation demethoxylation and carboxylation reactions. Activated carbon (AC)supported MoWBOx and PdNiOx were determined to be suitable catalyst precursors for the process. An intermediate of p-hydroxybenzoic acid (HBA) was produced from the demethoxylation in 71.6% selectivity, and the terephthalic acid was obtained in 58.7% yield with 66.4% HBA conversion.

KEYWORDS: biomass conversion, terephthalic acid, hetegeneous catalysis, hydrogenation demethoxylation, carboxylation reaction

T

Scheme 1. Synthesis of TA from Lignin through Phenols

erephthalic acid (TA) has wide applications in daily life, such as utilization in the production of commonly used polyethylene terephthalate.1 In the existing arts, TA is mainly produced via the oxidation of fossil feedstocks such as paraxylene.2 Producing TA from a renewable material has been attracting much research effort in the past decades. However, the biggest remaining challenge is due to the complex biomass streams. A couple of routes have been explored to convert biomass to TA.3−10 p-Xylene is the targeted intermediate in most reported procedures. Conversion of biomass to p-xylene could be achieved by different methods such as fermentation,3 multistep chemical method,4 and [4 + 2] reactions.5−8 Recently, diethyl terephthalate was prepared by an in situ [4 + 2] reaction between ethanol and muconic acid in a overall yield of 80.6%.8 However, preparations of the substrates from biomass are multiple-step processes. Furthermore, both yield and selectivity must be significantly improved to produce biobased muconic acid and highly pure ethanol. Lignin is a suitable renewable resource to produce aromatic chemicals in nature, because of its unique chemical structure. A yield of 33.24% of phenolics comprising mainly vanillin, vanillic acid, syringic acid, and syringaldehyde has been reached from organosolv beech wood lignin.11,12 In addition, separation and purification processes of the lignophenol derivatives have been developed, and 99% of the phenolics can be recovered.11−15 We believe that the conversion of lignin to TA is a relatively straightforward method and thus attracts much more interest and effort. As outlined in Scheme 1, the reduction or oxidation depolymerization of lignin leads to the formation of aromatics, and the major products are methoxyl-group-functionalized phenols.16 In path A, after hydrogenation demethoxylation © XXXX American Chemical Society

reactions, the resulting phenols can be converted to phydroxybenzoic acid (HBA) by existing arts.16−18 HBA is a suitable substrate to prepare TA via a bioprocess.19 In this work, methoxyl-group-functionalized phenolic acids such as vanillic acid (VA) and syringic acid (SA), which can be produced from a deep oxidation depolymerization of lignin or related intermediates such as vanillin,11,20 were used as model compounds to demonstrate the concept as shown in path B in Scheme 1. In this path, HBA intermediate was produced for the first time via the demethoxylation of the functional phenolic acids, and further converted to TA by a PdNiOx/AC-catalyzed carboxylation process. Herein, we reported our preliminary Received: July 21, 2016 Revised: August 10, 2016

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different morphologies, because of the different support material of AC and zeolite. In the 5-nm-scaled TEM images (see Figures 1c and 1f), crystalline lattices were detected and thus could further confirm the successful loading of the metal species on the surface of the support, although they were not observed in the XRD spectra. The particle size of the supported metal species is ∼5 nm. The background image of the amorphous AC support did not show a crystalline structure. However, the XRD spectra showed typical absorptions for carboxylation catalysts, as presented in Figure 2a. Catalyst Pd/

results regarding the catalytic demethoxylation of VA and SA, as well as carboxylation of HBA. To date, the demethoxylation of guaiacol and other ligninderived phenols to produce corresponding arenes have been explored.21−27 However, to our knowledge, demethoxylation of the methoxyl-functionalized phenolic acids has not been reported yet. In our work, VA and SA were used as model compounds to examine the designed catalysts. It was reported that group 6 transition-metal-based heterogeneous catalysts showed good activities in the demethoxylation reaction of guaiacol.21−27 In addition, it was reported that the incorporation of boron additives could reduce/minimize the coke formation during the reaction process;28 therefore, borondoped group 6 metal oxides were prepared. In the work, supported metal oxides of MoOx/AC (where AC denotes activated carbon), WOx/AC, CoOx/AC, RuOx/AC, PdRhOx/ AC, MoBOx/AC, MoWBOx/AC, MoWBOx/zeolite, MoCoBOx/AC, MoCoBOx/zeolite and MnOx/zeolite (zeolite refers to β-zeolite) were prepared via a wet method with a metal loading amount of 5.0 wt % for all catalysts and calcination in N2 (see the Supporting Information for details) and examined in the demethoxylation reactions of the model compounds. The catalysts that showed good activities were characterized by Xray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer−Emmett−Teller (BET) surface area analysis, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Catalysts MoWBOx/AC and MoWBOx/zeolite, together with their supports, were analyzed using XRD (Figure S1 in the Supporting Information). The pristine zeolite and catalyst MoWBOx/zeolite showed well-defined similar narrow peaks, suggesting the presence of a periodic array of atoms and, thus, a crystalline structure. Whereas for an AC support and catalyst MoWBOx/AC, only large bumps were found, distributed over a wide 2θ range. This could be contributed from the amorphous AC. In addition, no absorptions were observed for the metal species in the XRD spectra, because of their very limited loading amounts or small crystallite size (i.e., nanocrystalline), which might cause the peak broadening. Figure 1 demonstrates the SEM and TEM images of the catalysts MoWBOx/AC and MoWBOx/zeolite, respectively. They showed significantly

Figure 2. (a) XRD spectra, (b) SEM photomicrograph, and (c, d) TEM photomicrographs of catalyst PdNiOx/AC.

AC exhibited sharp diffraction peaks at 40.2° (111), 48.3° (200), and 68.2° (220) in 2θ, which is consistent with fcc palladium (JCPDS File Card No. 03-065-2867). Catalyst NiOx/ AC showed strong and broad absorptions at 2θ values of 44.5° (111), 52.0° (200), and 78.2° (220), respectively. It could be assigned to the diffraction plane (111) of the fcc structure of nickel, according to JCPDS card No. 03-065-2865. For catalyst PdNiOx/AC, well-defined diffraction peaks both for metallic Pd and Ni were detected, and that observation confirmed successful loading. The lower intensities of metallic Ni peaks occurring on the XRD pattern were probably due to (1) lower loading amount; (2) partial conversion to NiO species during the preparation for XRD measurement, since exposure of the sample to air could lead to the oxidation of Ni to NiO; and (3) the ultrasmall and highly dispersed Ni particles. AC-supported catalysts, such as MoWBOx/AC (568.08 m2/ g), generally showed larger surface areas than zeolite-supported ones, e.g., MoWBOx/zeolite (427.41 m2/g), based on BET analysis (see Table S1 in the Supporting Information). It was also observed that, for all of the catalysts, the BET surface areas reduced slightly after hydrogen reduction (see Table S1). The catalysts were also characterized by XPS to identify the oxidation states of the supporting metal species. The catalyst samples were stored in a glovebox after preparation. When preparing and transferring for XPS analysis, the samples were permitted to interact briefly with air. As shown in Figure 3, the catalyst MoWBOx/AC exhibited carbide peaks at 228.6 and 231.6 eV for Mo2C and 31.3, 33.4 eV for W2C, respectively. The results are in good agreement with the binding energy of molybdenum and tungsten carbide species reported elsewhere.29−31 The absorptions at 235.6 and 232.2 eV (Figure 3a) are assigned to MoOx (2 < x < 3) with a Mo6+ dominant

Figure 1. (a, d) SEM and (b, c, e, f) TEM images of catalysts MoWBOx/AC (panels (a)−(c)) and MoWBOx/zeolite (panels (d)− (f)). 6142

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For catalyst PdNiOx, the Pd 3d and Ni 2p core level regions are shown in Figures 3c and 3d. In Figure 3c, the Pd 3d spectra exhibit two peaks at 335.4 and 341.0 eV for Pd 3d3/2 and Pd 3d5/2, respectively. The observation suggests the existence of metallic state Pd.32 The Ni 2p spectra (Figure 3d) show complex peaks due to its multielectron excitation.33 Taking into account the satellite absorptions, two main peaks can be deconvoluted from the Ni 2p3/2 regional spectra, located at 852.8 and 853.6 eV, which are assigned to metallic Ni and NiO, respectively.34 The atomic percentage of NiO and Ni0 are 61.0% and 39.0%, respectively. Similar to formations of the MoOx and WOx, the NiO is most likely produced from partial oxidation of the metallic Ni by air in the course of sample preparation and transformation to the XPS equipment. However, no typical absorptions were observed for NiO species in the corresponding XRD spectrum. The results suggest that the NiO particles are ultrasmall and highly dispersed. These results suggest that metallic Pd and Ni are active phases for the carboxylation reaction of HBA. During the course of hydrogenation demethoxylation reactions of the model compounds VA and SA, the literature conditions were adopted initially.22 Catalyst precursors were pretreated under flowing H2 gas at 700 °C for 2 h. Reactions were conducted in a micro fixed-bed reactor at a temperature of 400 °C and a total pressure of 40 bar. Substrates VA and SA were either dissolved in anhydrous MeOH or KOH aqueous solution (pH 13), respectively. Product samples were collected, pretreated, and subjected to analysis by either gas chromatography (GC), high-performance liquid chromatography (HPLC), 1H NMR spectroscopy, or 13C NMR spectroscopy (see details in the Supporting Information). Initially, demethoxylation reactions were conducted in pure H2 gas, and in the presence of catalyst MOx/AC for 2 h and 12 h, the product of HBA was not detectable via gas

Figure 3. XPS spectra of the catalysts: (a, b) MoWBOx/AC and (c, d) PdNiOx/AC. Dashed lines represent oxide peaks, and round dots represent the carbide and metallic state peaks.

species in MoOx, according to the literature.29−31 The corresponding atomic percentages of MoOx and Mo2C are 67.0% and 33.0%, respectively. The peaks at 37.2 and 35.2 eV (Figure 3b) are contributed from WOx (2 < x < 3), and the W6+ species are the main component.29−31 The atomic percentage of WO x and W 2 C are 63.2% and 36.8%, respectively. The presence of these oxidation states can be explained by partial oxidation of the carbide due to exposure to air during the course of sample preparation and transformation to the XPS equipment. Therefore, the active sites are Mo2C and W2C, which is consistent with the literature.29−31 In addition, there are no obvious boron absorptions due to low loading amounts.

Table 1. High-Performance Liquid Chromatography (HPLC) Results for Demethoxylation Reactions of Vanillic Acid and Syringic Acida Product Class Selectivity (%) No.

catalyst

substrate conversion (%)

mass balance (%)

HBA

GA

AS

SG

VT

1 2 3c 4 5 6 7 8 9 10 11 12 13d 14 15e 16e

blank MoBOx/AC MoBOx/AC MoWBOx/AC MoWBOx/Z MoCoBOx/AC MoCoBOx/Z MoWBOx/AC (CO2/H2 = 1/5) MoWBOx/AC (CO2/H2 = 2/1) MoWBOx/AC (CO2/H2 = 3/1) MoCoBOx/AC (CO2/H2 = 2/1) MoWBOx/Z (CO2/H2 = 2/1) MoWBOx/AC PdRhOx/AC blank MoOx/AC

40.9 93.1 98.5 100.0 78.5 96.1 78.5 99.2 100.0 100.0 100.0 100.0 91.6 99.3 44.5 53.8

91.5 92.6 90.4 91.1 90.2 91.3 90.6 93.7 92.5 90.7 89.4 92.9 86.1 88.4 92.6 89.5

NDb 2.7 1.2 12.0 13.1 7.8 4.8 0.6 71.6 51.4 11.9 45.7 1.2 1.2 NDb 0.4

29.8 29.4 26.0 44.7 3.8 15.4 12.2 28.9 5.7 16.8 20.6 8.7 21.3 19.7 47.4 39.7

4.6 14.8 16.7 15.0 37.2 15.8 33.1 18.4 4.0 9.3 9.4 17.6 13.5 16.5 NDb 4.1

56.6 36.0 33.4 17.3 12.9 39.0 16.9 35.6 8.1 14.9 47.6 7.4 47.0 42.5 50.0 50.6

4.9 13.6 17.9 7.9 27.4 18.6 24.5 11.6 4.9 3.1 5.3 14.3 11.1 11.8 NDb NDb

a

VA = vanillic acid, SA = syringic acid, HBA = p-hydroxybenxoic acid, GA = guaiacol, AS = anisole, SG = syringol, VT = veratrole, AC = activated carbon, Z = zeolite beta (SiO2/Al2O3 molar ratio = 300). Substrates (VA+SA) were dissolved in anhydrous MeOH in 7.8 mg/mL, respectively. Reactions conditions: CO2/H2 = 1/1, P(CO2+H2) = 40 bar, T = 400 °C, gas flow rate = 100 mL/min, liquid flow rate = 1.0 mL/min; samples were collected at 30 min, and selectivity was obtained from HPLC analysis. Mass balance was calculated based on the amount of added substrates. bND = not detected. cReaction temperature = 500 °C. dReaction temperature = 300 °C. eSubstrates (VA + SA) were dissolved in aqueous KOH (pH 13.0) in 7.8 mg/mL, respectively. 6143

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based on adding substrates of VA and SA. The remainder could be heavy products that could not be identified by GC and HPLC methods.35 No significant change in weight was observed for the catalyst samples after reaction. It indicated that the coke formation could be excluded.37 Although the real mechanism is unclear, the formation of several different products suggests that hydrogenation demethoxylation and decarboxylation pathway occurred simultaneously.11−15,28,29,35 The conversion of HBA to TA was realized via a biological process.19 Nevertheless, the yield was too low to meet the largescale requirements in industry. On the other hand, both Pdand Ni-based catalysts were reported to be highly active in a carboxylation reaction with CO2.38,39 This work demonstrated the potential of the AC-supported Pd- and Ni-based catalysts for catalyzing the carboxylation reaction of HBA to form TA. The reaction was conducted in the same micro fixed-bed reactor as described above, at a temperature of 400 °C and a total pressure of CO2/N2 (v/v = 1/1) of 40 bar. Catalyst precursors were pretreated under flowing H2 gas at 400 °C for 2 h before reaction. Substrate HBA was dissolved in KOH aqueous solution (pH 13). Product samples were collected at 30 min in a substrate flow rate of 1 mL/min and a gas flow of 100 mL/min. The samples were subjected to analysis by 1H and 13C NMR spectroscopy in DMSO-d6 in the presence of an internal standard of nitromethane (see the Supporting Information for procedure details). The results are presented in Table 2. It was found that catalyst Pd/AC showed medium activity in the reaction and

chromatography−flame ionization detection (GC-FID) analysis at temperatures of 300, 360, and 400 °C, respectively. The results were not consistent with the literature.22 It could be due to decarboxylation where the CO2H group was removed to produce CO2 gas. Therefore, CO2 gas was later introduced to the hydrogen to maintain the CO2H functional group, which would increase the yield of HBA.35 Single-metal-based catalysts, such as MOx/AC (where M = Mo, MoB, W, Co, and Ru), which exhibited good activity in the hydrogenation demethoxylation of guaiacol methoxybenzenes,36,37 showed low HBA selectivity ( Pd/AC > NiOx/AC under the same conditions. The results suggest that the presence of Ni species could be crucial to significantly enhance the activity of the Pd-based catalyst, although the actual mechanism is still unclear. In addition, the formation of heavy products indicated that two reaction pathsnamely, carboxylation and polymerizationoccurred simultaneously in the reaction course. 6144

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(14) Mota, M. I. F.; Rodrigues Pinto, P. C.; Loureiro, J. M.; Rodrigues, A. E. Sep. Purif. Rev. 2016, 45, 227−259. (15) Roberts, V. M.; Stein, V.; Reiner, T.; Lemonidou, A.; Li, X.; Lercher, J. A. Chem.Eur. J. 2011, 17, 5939−5948. (16) Zakzeski, J.; Bruijnincx, P. C.; Jongerius, A. L.; Weckhuysen, B. M. Chem. Rev. 2010, 110, 3552−3599. (17) Komiyama, M.; Sugigura, I.; Hirai, H. J. Mol. Catal. 1986, 36, 271−282. (18) Suerbaev, K. A.; Aldabergenov, M. K.; Kudaibergenov, N. Zh. Green Process. Synth. 2015, 4, 91−96. (19) Choi, W. J.; Ahn, J. H.; Byun, J. W.; Ha, Y. W. U.S. Patent Application No. 20140155570A1, 2014. (20) Upton, B. M.; Kasko, A. M. Chem. Rev. 2016, 116, 2275−2306. (21) Jongerius, A. L.; Gosselink, R. W.; Dijkstra, J.; Bitter, J. H.; Bruijnincx, P. C. A.; Weckhuysen, B. M. ChemCatChem 2013, 5, 2964−2972. (22) Chang, J.; Danuthai, T.; Dewiyanti, S.; Wang, C.; Borgna, A. ChemCatChem 2013, 5, 3041−3049. (23) Wang, X.; Rinaldi, R. Angew. Chem., Int. Ed. 2013, 52, 11499− 11503. (24) Zakzeski, J.; Bruijnincx, P. C. A.; Jongerius, A. L.; Weckhuysen, B. M. Chem. Rev. 2010, 110, 3552−3599 and references therein.. (25) Bu, Q.; Lei, H.; Zacher, A. H.; Wang, L.; Ren, S.; Liang, J.; Wei, Y.; Liu, Y.; Tang, J.; Zhang, Q.; Ruan, R. Bioresour. Technol. 2012, 124, 470−477 and references therein.. (26) Güvenatam, B.; Kursun, O.; Heeres, E. H. J.; Pidko, E. A.; Hensen, E. J. M. Catal. Today 2014, 233, 83−91. (27) Rogers, K. A.; Zheng, Y. ChemSusChem 2016, 9, 1750−1772. (28) Jo, H. K. U.S. Patent 5,567,305 A1, 1996. (29) Wagner, C. D., Muilenberg, G. E. Handbook of X-ray Photoelectron Spectroscopy; Perkin-Elmer Corp.: Eden Prairie, MN, USA, 1979; pp 112−172. (30) Leclercq, L.; Provost, M.; Pastor, H.; Grimblot, J.; Hardy, A.; Gengembre, L.; Leclercq, G. J. Catal. 1989, 117, 371−383. (31) Hollak, S. A. W.; Gosselink, R. W.; van Es, D. S.; Bitter, J. H. ACS Catal. 2013, 3, 2837−2844. (32) Moulder, J. F., Stickle, W. F., Sobol, P. E., Bomben, K. D. Handbook of X-ray Photoelectron Spectroscopy; Physical Electronics, Inc.: Eden Prairie, MN, USA, 1995; pp 142−143. (33) Park, K.-W.; Choi, J.-H.; Kwon, B.-K.; Lee, S.-A.; Sung, Y.-E.; Ha, H.-Y.; Hong, S.-A.; Kim, H. H.; Wieckowski, A. J. Phys. Chem. B 2002, 106, 1869−1877. (34) http://xpssimplified.com/elements/nickel.php. (35) Kluger, R. Acc. Chem. Res. 2015, 48, 2843−2849. (36) Ishikawa, M.; Tamura, M.; Nakagawa, Y.; Tomishige, K. Appl. Catal., B 2016, 182, 193−203. (37) Jongerius, A. L.; Jastrzebski, R.; Bruijnincx, P. C. A.; Weckhuysen, B. M. J. Catal. 2012, 285, 315−323. (38) Correa, A.; Martin, R. J. Am. Chem. Soc. 2009, 131, 15974− 15975. (39) Correa, A.; León, T.; Martin, R. J. Am. Chem. Soc. 2014, 136, 1062−1069.

Nonetheless, the study of the mechanism is currently underway in our laboratories. In summary, this work demonstrates a potential route to produce terephthalic acid from lignin-based sustainable resources. The vanillic acid and syringic acid were converted to terephthalic acid in two steps. The selectivity of 71.6% of phydroxybenzoic acid was achieved by using catalyst precursor MoWBOx/AC. Furthermore, the high yield of 58.7% of terephthalic acid with 88.4% selectivity was achieved by using catalyst precursor of PdNiOx/AC. Considering its broader applications in material industry, such as production of biobased polyethylene terephthalate, this technology show promising potential in biomass conversion. It is highly expected that the prototype technology will find a broad range of applications in both academia and the materials industry.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acscatal.6b02052. Experimental operation and characterization details (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Funding

We thank Singapore-MIT Alliance for Research and Technology (SMART) and Institute of Chemical and Engineering Sciences (ICES A*STAR) for their financial support. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The timely help of Mr. Zhao Wenguang, in analyzing SEM, is hereby gratefully acknowledged. REFERENCES

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