Liquid-Phase Hydrogenation of Maleic Acid Over Pd/Al2o3 Catalysts Prepared Via Deposition–Precipitation Method

energies Article Liquid-Phase Hydrogenation of Maleic Acid over Pd/Al2O3 Catalysts Prepared via Deposition–Precipitation Method Mi Yeon Byun 1,2 , Ji Sun Kim 3 , Jae Ho Baek 1, Dae-Won Park 2 and Man Sig Lee 1,* 1 Ulsan Regional Division, Korea Institute of Industrial Technology (KITECH), Ulsan 44413, Korea; [email protected] (M.Y.B.); [email protected] (J.H.B.) 2 Department of Polymer Science and Chemical Engineering, Pusan National University, Busan 46241, Korea; [email protected] 3 Department of Chemical & Biological Engineering, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada; [email protected] * Correspondence: [email protected]; Tel.: +82-52-980-6630; Fax: +82-52-980-6639 Received: 14 November 2018; Accepted: 16 January 2019; Published: 17 January 2019 Abstract: Succinic acid (SA) is a valuable raw material obtained by hydrogenation of maleic acid (MA). The product selectivity of this reaction is highly dependent on the reaction conditions. This study therefore investigated the effect of the reaction temperature, hydrogen pressure, and reaction time on the liquid-phase hydrogenation of MA by a Pd/Al2O3 catalyst. Complete conversion of MA and ◦ 100% selectivity for SA were achieved at a temperature of 90 C, H2 pressure of 5 bar, and reaction time of 90 min. Fumaric acid (FA) was formed as an intermediate material by hydrogenation of MA under nonoptimal conditions. The impact of the percentage of Pd dispersion and phase of the Al2O3 support (γ, θ + α, and α) was also examined. The Pd/Al2O3 catalyst with 29.8% dispersion of Pd and γ phase of Al2O3 exhibited the best catalytic performance. Thus, catalytic activity depends not only on the amount of Pd dispersion but also on the physicochemical properties of Al2O3. Keywords: hydrogenation; succinic acid; supported catalyst; Pd catalyst 1. Introduction The growth of the petrochemical industry has brought about environmental problems such as industrial waste, pollution, and global warming. Therefore, many researchers have been investigating sustainable and renewable resources. In this regard, succinic acid (SA) has attracted attention as an eco-friendly raw material for the production of biodegradable plastics and biosolvents. SA is widely used as an intermediate material in the production of high value products such as γ-butyrolactone, 1,4-butanediol, and tetrahydrofuran [1,2]. It is usually obtained by hydrogenation of maleic anhydride (MAN), although the product of this reaction varies depending on the reaction conditions. Several researches have investigated various catalysts for this reaction, such as Ru/C, Ni/HY–Al2O3, Pd/C, Pd/SiO2, Ni/TiO2 and Pd/Al2O3 [3–9]. The reaction pathways of hydrogenation of maleic acid (MA) are shown in Figure1. Kim et al. reported a yield of 99.97% SA using Pd/C as the catalyst and ◦ conducting the reaction under 1.0 MPa of H2 at 90 C for 150 min [3]. Torres et al. reported achieving 100% selectivity for succinic anhydride through the reaction catalyzed by a mesoporous Ni/TiO2 catalyst at low temperature [8]. Yuan et al. reported achieving MA conversion of 98% and succinic anhydride selectivity of 99% using Pd/Al2O3 catalyst under 1.0 MPa of H2 pressure and 1,4-dioxane as solvent [5]. Among the various catalysts, the Pd/Al2O3 catalyst has an advantage for the chemical industry due to the high thermal stability and high dispersion of Pd [10,11]. However, few studies have been performed on the optimization of reaction conditions for the hydrogenation of maleic acid (MA) Energies 2019, 12, 284; doi:10.3390/en12020284 www.mdpi.com/journal/energies Energies 2018, 11, x FOR PEER REVIEW 2 of 8 Energies 2019, 12, 284 2 of 8 on the optimization of reaction conditions for the hydrogenation of maleic acid (MA) to SA over a to SA over a Pd/Al2O3 catalyst. In our previous study, we reported that the particle size distribution Pd/Al2O3 catalyst. In our previous study, we reported that the particle size distribution of Pd is of Pd is influenced by the physicochemical properties of Al O (specific surface area and surface influenced by the physicochemical properties of Al2O3 (specific 2surface3 area and surface functional groups)functional and groups)catalyst preparation and catalyst conditions preparation (pH, conditions solution temperature, (pH, solution and temperature, reduction agent) and [12,13]. reduction Herein,agent) we [12 ,investigated13]. Herein, the we effect investigated of reaction the temperature effect of reaction (T), H2 pressure temperature (PH2), and (T), reaction H2 pressure time ( tP) H2), onand the reaction liquid-phase time ( thydrogenation) on the liquid-phase of MA over hydrogenation a Pd/Al2O3 ofcatalyst. MA over The a catalytic Pd/Al2O activities3 catalyst. of ThePd/Al catalytic2O3 withactivities varying of percentage Pd/Al2O3 ofwith Pd dispersion varying percentage and Al2O3 phase of Pd ( dispersionγ, θ + α, and and α) were Al2O also3 phase compared. (γ, θ +Finally,α, and α) thewere reusability also compared. of the Pd/Al Finally,2O3 catalyst the reusability was assessed. of the Pd/Al2O3 catalyst was assessed. Figure 1. Reaction pathways in hydrogenation of maleic acid in water. Figure 1. Reaction pathways in hydrogenation of maleic acid in water. 2. Experiment 2. Experiment 2.1. Catalyst Preparation 2.1. Catalyst Preparation The catalyst support, Al2O3 (≥99%, Alfa Aesar, γ phase, average particle size: 20 nm), was dried ◦ ◦ at 105TheC catalyst for 4 h support, and calcined Al2O3 at(≥99%, various Alfa temperatures Aesar, γ phase, (900, average 1100, andparticle 1150 size:C) 20 for nm), 4 h. was The dried Pd/Al at2 O3 105catalysts, °C for containing4 h and calcined 5 wt % at Pd, various were preparedtemperatures by the(900, deposition–precipitation 1100, and 1150 °C) for method.4 h. The ThePd/Al detailed2O3 catalysts,procedure containing has been 5described wt% Pd, were in our prepared previous by research the deposition–precipitation [12]. Briefly, Al2O3 wasmethod. dispersed The detailed in the Pd ◦ procedureprecursor has solution been atdescribed 60 C, and in our the pHprevious was adjustedresearch using[12]. Briefly, 0.25 M Al NaOH2O3 was solution. dispersed Reduction in the Pd of the precursorcatalyst was solution carried at out60 °C, in theand liquid the pH phase was usingadjusted formalin using solution0.25M NaOH (10 wt solution. %, Sigma Reduction Aldrich, of St. the Louis, catalystMO, USA). was Thecarried prepared out in Pd/Althe liquid2O3 catalystsphase using are denotedformalin assolution Pd/Al 2(10O3 wt%,(X)_pH SigmaY, where Aldrich).X is theThe heat preparedtreatment Pd/Al temperature2O3 catalysts of the are Al 2denotedO3 support, as Pd/Al and Y2Ois3 the(X)_pH pH.Y The, where physicochemical X is the heat properties treatment of the temperaturecatalysts are of summarized the Al2O3 support, in Table and1. Y is the pH. The physicochemical properties of the catalysts are summarized in Table 1. Table 1. Summary of physicochemical properties of Pd/Al2O3 catalysts [12,13]. Energies 2019, 12, 284 3 of 8 Table 1. Summary of physicochemical properties of Pd/Al2O3 catalysts [12,13]. Pd/Al O Pd/Al O Pd/Al O Pd/Al O Pd/Al O Catalysts 2 3 2 3 2 3 2 3 2 3 (105)_pH 7.5 (900)_pH 7.5 (900)_pH 11.5 (1100)_pH 7.5 (1150)_pH 7.5 1 Al2O3 phase γ γ γ θ + α α 2 Al2O3 surface area 195 146 146 54 6 2 Al2O3 Pore volume 0.82 0.62 0.62 0.28 0.007 3 Al2O3 Acidity (mmol/g) 0.47 0.37 0.37 0.22 0.07 Pd dispersion (%) 4 20.6 29.8 13.1 11.0 2.9 1 2 3 X-ray diffraction, Brunauer–Emmett–Teller analysis of N2 adsorption–desorption, NH3 temperature programmed desorption, 4 CO chemisorption. 2.2. Hydrogenation of Maleic Acid Liquid-phase hydrogenation of maleic acid was conducted in a 100 mL stainless steel autoclave. MA (0.29 mol), 46 g distilled water, and 0.1 g Pd/Al2O3 were placed in the autoclave. The reactor was purged with nitrogen three times to remove air, and hydrogen was then used to purge out nitrogen. The sealed autoclave was pressurized to the desired pressure and heated to the desired temperature, and the reaction mixture was stirred at 700 rpm. The catalytic reaction was carried out for 15–90 min. The reaction products were analyzed by high-performance liquid chromatography (HPLC, Shimadzu Co. Model Prominence) equipped with a refractive index detector and Agilent Hi-Plex −1 H(7.7 mm × 300 mm × 8 µm). The mobile phase was 5 mM H2SO4 with a flow rate of 6 mL min . The MA, SA, fumaric acid (FA), and malic acid (MLA) standards (Sigma Aldrich) were analytical grade and used without purification. The reaction was conducted at varying temperature, hydrogen pressure, and reaction time. Conversion and selectivity were calculated as follows: Initial mole of MA − final moleof MA Conversion (%) = × 100 (1) Initial mole of MA mole of desired product Selectivity (%) = × 100 (2) Initial mole of MA − final moleof MA 3. Results and Discussion 3.1. Effect of Reaction Temperature The effect of reaction temperature on MA hydrogenation over the Pd/Al2O3 (900)_pH7.5 catalyst was investigated within the range of 30–110 ◦C (Figure2). As the reaction temperature increased, the conversion of MA increased, while the selectivity for SA decreased from 100% to 85%. At temperatures above 90 ◦C, the selectivity for FA and MLA slightly increased. It has been reported that, at high temperature, MA is unstable and can isomerize to the more stable FA [14]. On the other hand, the isomer FA undergoes hydration to form MLA at high temperature. Thus, 90 ◦C is the optimal temperature for high conversion of MA and selectivity for SA.

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