Korean J. Chem. Eng., 36(7), 1051-1056 (2019) pISSN: 0256-1115 DOI: 10.1007/s11814-019-0294-y eISSN: 1975-7220 INVITED REVIEW PAPER INVITED REVIEW PAPER Selective synthesis of acetonitrile by reaction of ethanol with ammonia over Ni/Al2O3 catalyst Ye-Seul Jeong, Sang Hee An, and Chae-Ho Shin† Department of Chemical Engineering, Chungbuk National University, Cheongju, Chungbuk 28644, Korea (Received 28 March 2019 • accepted 7 May 2019) AbstractA highly selective synthesis of acetonitrile was carried out by the reaction of ethanol with ammonia on a 10 wt% Ni/Al2O3 catalyst. The conversion of ethanol and selectivity to acetonitrile, ethylene, and monoethylamine were examined by varying experimental parameters such as ammonia partial pressure, reaction temperature, and space time. The increase in the ammonia partial pressure led to a considerable decrease in the conversion and small increase in the acetonitrile selectivity up to a molar ratio of NH3/ethanol of 3, followed by almost constant values. The partial reaction order of ethanol obtained by controlling the space time was one, while that of ammonia was negative, 0.4. The deacti- vation behavior of the catalyst after 100 h on stream reaction at 230 oC was analyzed by X-ray photoelectron spectros- copy and temperature programmed oxidation of the catalyst used. The catalyst deactivation was attributed to the gradual formation of nickel carbonitride on the catalyst surface. Keywords: Acetonitrile, Nickel Catalyst, Ethanol, Carbonitride, Deactivation INTRODUCTION face in a metallic state, so that a gradual deactivation is observed. The development of a highly selective acetonitrile synthesis catalyst Acetonitrile is used mainly as a solvent of extractive distillation, by controlling these simple experimental parameters is important isolation of butadiene from C4 hydrocarbons, in battery applica- to guide the development of novel catalysts in the future. tions owing to its relatively high dielectric constant and ability to In this study, the reaction of ethanol with ammonia for the highly dissolve electrolytes. In addition, it can be used as a solvent for syn- selective acetonitrile synthesis on a Ni/Al2O3 catalyst was investi- theses of various pharmaceutical intermediates and pesticides. It gated by changing the reaction temperature, ammonia partial pres- can be used as a raw material for synthesis of acrylonitrile by reac- sure, and weight hourly space velocity (WHSV). The temperature tion of acetonitrile and methanol and as a raw material for aceto- programmed technique was used to observe the desorption behav- nitrile hydrogenation for synthesis of ethylamine [1-3]. Acetonitrile ior of ethanol and ammonia on the catalyst surface. The causes of is a byproduct of the manufacture of acrylonitrile by ammoxida- deactivation affecting the catalyst stability are discussed. tion of propylene and can also be produced by many other meth- ods, including dehydration of acetamide and hydrogenation of mix- EXPERIMENTAL tures of carbon monoxide and ammonia [4-7]. Various catalysts and reactants have been reported for the syn- 1. Catalyst Preparation thesis of acetonitrile [8-15]. Reductive amination of ethanol over The Ni-loaded (10 wt%) Al2O3 catalyst was prepared by the im- Cu/-Al2O3, direct synthesis of acetonitrile by reaction of ethanol pregnation method using Ni(NO3)2∙6H2O (>98%, Samchun) and with ammonia over Ni-doped Co/-Al2O3 [9], bimetallic Ni-Co/- -Al2O3 (Procatalyse). Nickel nitrate was dissolved in distilled water Al2O3 [10,11], ammoxidation of ethanol, acetaldehyde, or acetic and -Al2O3 was dispersed into the aqueous solution under vigor- acid over Sb-V-P-O/Al2O3 catalyst [12], ammoxidation of ethanol ous stirring for 1h. The solution was then evaporated to dryness over molecular sieves such as silicoaluminophosphate (SAPO), V- at 80 oC using a rotary evaporator. The obtained powder was dried SAPO, NaY, and V-NaY [13], ammoxidation of ethane over nio- at 100 oC for 12 h and calcined at 500 oC for 2 h under air flow. bia-supported bulk-NiO catalysts [14], and aerobic dehydrogena- 2. Characterization tion of ethylamine over supported ruthenium catalysts [15] have X-ray diffraction (XRD) patterns of the prepared 10 wt% Ni/ been used for the synthesis of acetonitrile. Al2O3 catalyst after the calcination and H2 reduction treatment and In the reaction of ethanol and ammonia on a metal catalyst, the H2 temperature programmed reduction (H2-TPR) profile are shown main product in the presence of hydrogen are ethylamines, while in Figs. S1 and S2, respectively. The Brunauer-Emmett-Teller (BET) 2 1 that in the absence of hydrogen is acetonitrile [16]. However, in the surface area of the support -Al2O3 was 194 m g , while that of the 2 1 absence of hydrogen, it is challenging to maintain the catalyst sur- calcined 10 wt% Ni/Al2O3 catalyst was 157 m g . Table S1 shows the results of H2 chemisorption, reduction degree obtained from † To whom correspondence should be addressed. an O2 titration method, and TPR behavior [16]. E-mail: [email protected] A temperature programmed desorption of ethanol (EtOH-TPD) Copyright by The Korean Institute of Chemical Engineers. was carried out to confirm the desorption behaviors of ethanol as 1051 1052 Y.-S. Jeong et al. a reactant using a quadruple mass spectrometer (QMS, Balzers QMS 200). Prior to the experiment, the sample (0.2 g) was reduced o 3 1 at 600 C for 3 h under H2 flow (50 cm min ). After cooling to room temperature, the reduced sample was exposed to ethanol vapor (3 kPa) with an Ar gas stream for 2 h and purged in the Ar stream to remove the physisorbed ethanol at the same tempera- ture. The sample was heated at a rate of 10 oC min1 from room tem- perature to 700 oC. The effluent gases were detected using a QMS. QMS fragments with m/z=44, 31, 29, 28, 27, 18, 15, and 2 were set for CO2, C2H5OH, CH3CHO, CO, C2H4, H2O, CH4, and H2, respectively. A temperature programmed surface reaction (TPSR) experi- ment of pre-adsorbed ethanol with NH3 was carried out over the o Ni/Al2O3 catalyst. After the H2-treated catalyst at 600 C was cooled to room temperature, it was exposed to ethanol (3 kPa) with Ar gas (30 cm3 min1) for 0.5 h. The reactor was then purged with Ar Fig. 1. EtOH-TPD profiles of 10 wt% Ni/Al2O3 catalyst reduced at gas for 0.5 h. Subsequently, the sample was heated from 50 to o 3 1 o 3 1 600 C for 3h under the flow of H2 (50 cm min ). Ethanol 700 C under a flow of 9 vol% NH3/Ar (30 cm min ). The effluent was pre-adsorbed at room temperature. gases were analyzed continuously using the QMS instrument. The mass signals of m/z=29 (·CHO) from CH3CHO, 31 (·CH2OH) from C2H5OH, 41 (·CH3CN) from CH3CN, and 30 (·CH2NH2) (C2H4, monoethylamine, and acetonitrile), respectively. MWEtOH is from CH3CH2NH2 were detected using a QMS detector. the molecular weight of ethanol, and Ci is the carbon number of i To investigate the catalytic deactivation behavior, X-ray photo- component. electron spectroscopy (XPS) and temperature programmed oxida- tion (TPO) were performed. The XPS was carried out with a PHI RESULTS AND DISCUSSION Quantera-II instrument using an Al K X-ray source. In the TPO experiment, the used catalyst was exposed to a 5% O2/Ar mixed 1. EtOH-TPD and TPSR 3 1 o o 1 gas (30 cm min ) and heated to 600 C at a rate of 10 C min . EtOH-TPD profiles of the Ni/Al2O3 catalyst are shown in Fig. 1. The effluent gases were analyzed continuously with the QMS. The The desorption of ethanol as a reactant exhibits two main peaks, mass signals of m/z=46, 44, 32, and 14 were referenced to NO2, corresponding to the physisorption of ethanol at a lower tempera- o o CO2, O2, and N, respectively. ture (130 C) and chemisorption of ethanol at approximately 200 C. 3. Catalytic Activity Test With the increase in the desorption temperature, various fragments The selective synthesis of acetonitrile was performed in a fixed- formed by the interaction between the catalyst surface and adsorbed bed reactor at atmospheric pressure. Prior to the reaction, 0.2 g of ethanol are observed. Fragments including CH3CHO, H2O, CO, o 3 1 o catalyst was reduced at 600 C for 3 h under H2 flow (50 cm min ). C2H4, CH4, and H2 are detected at approximately 130 and 226 C, The reaction parameters such as the partial pressure of ammonia obtained by [17]: (1.5-21 kPa), reaction temperature (180-240 oC), and WHSV (0.55- C H OHCH CHO+H H +CO+CH Dehydrogenation and cracking 1.64 h1) controlled by variations in total flow rate (25-100 cm3 min1) 2 5 3 2 2 4 C H OHC H +H O Dehydration and catalyst quantity (0.1 and 0.2 g) were varied. The partial pres- 2 5 2 4 2 sure of ethanol was fixed at 3 kPa. The products were analyzed using The desorption peak of CO2 is generated by oxidizing the ad- a gas chromatograph (CP9001) equipped with a CP-Volamine cap- sorbed CO on the surface with lattice oxygen of the catalyst. The o illary column (60m×0.32mm) and a flame ionization detector. The peaks of CH3CHO and C2H4 at 226 C are attributed to the dehy- conversion of ethanol, selectivity, WHSV, and deactivation rate were drogenation and dehydration of ethanol. Moreover, C2H4 generated defined as: in the dehydration of EtOH was easily desorbed, while the strongly adsorbed H2O was desorbed at a higher temperature than that for FEtOH reacted o Conversion % ------------------------------- 100% C2H4. At a high temperature of approximately 300 C, the peaks of FEtOH fed CO2 and H2 increased, while the CO and H2O peaks decreased.