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Vapour phase hydrogenolysis of glycerol to 1,2-propanediol over Cu/Al2O3 catalyst at ambient hydrogen pressure. María Laura Dieuzeide, Matias Jobbagy, and Norma Amadeo Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b03004 • Publication Date (Web): 11 Feb 2016 Downloaded from http://pubs.acs.org on February 19, 2016
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VAPOUR PHASE HYDROGENOLYSIS OF GLYCEROL TO 1,2-PROPANEDIOL OVER Cu/Al2O3 CATALYST AT AMBIENT HYDROGEN PRESSURE M.L. Dieuzeide1, M. Jobbagy2, N. Amadeo.1 1
ITHES (UBA-CONICET). Laboratorio de Procesos Catalíticos. Departamento de Ing. Química. Facultad de Ingeniería. Universidad de Buenos Aires. Pabellón de Industrias. Ciudad Universitaria. 1428 C.A.B.A. Argentina.
[email protected] 2 INQUIMAE. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Pabellón II. Ciudad Universitaria. 1428 C.A.B.A. Argentina.
Abstract In this paper we report that the hydrogenolysis of glycerol can be carried out at atmospheric pressure and low temperature with high selectivity to 1-2 PDO, over reduced copper catalyst. The vapour phase reaction was performed over the copper based catalysts supported on alumina at ambient pressure and the effects of temperature, space time and H2 molar fraction in the feed were analysed. The textural and structural characteristics of the catalysts with increasing copper loading were determined by N2 sorptometry (BET), inductively coupled plasma-atomic spectroscopy (ICP-AES), powder X-ray diffraction (PXRD), temperature programmed reduction (TPR), N2O chemisorption (metallic area). Based both on characterization and activity results, it was possible to conclude that the hydrogenolysis of glycerol to 1,2-propanediol in vapour phase at atmospheric pressure over copper based catalysts, is a structure sensitive reaction. Activity results suggests that the most probable pathway for the glycerol conversion into 1,2 propanediol under the employed conditions is: glycerol is dehydration to hydroxyacetone (acetol), followed by its hydrogenation into 1,2 propanediol.
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Complete glycerol conversion and a selectivity of 60% to 1,2- propanediol was achieved, using CuO(15)Al2O3 catalyst at 200ºC, H2 molar fraction of 61% and atmospheric pressure.
1. Introduction In the last years, biodiesel has gained attention as an attractive biofuel, especially because it can replace significant fractions of petroleum-derived fuels. This green vector is mainly produced by the transesterification of vegetable oils and fats, being glycerol the major by product (10wt% of production). The growth in biodiesel production has caused an overproduction of glycerol. Consequently, glycerol became a low cost building block with high potential, which could be employed to produce other chemicals with high added value [1]. Among the different alternatives to add value to glycerol, the catalytic production of 1,2 propanediol (1,2-PDO) by hydrogenolysis of bio-glycerol is of great interest due to the renewable character of this route. Traditionally, 1,2-PDO is produced by the hydration of propylene oxide or ethylene oxide derived from propylene or ethylene [2]. One of the applications of 1,2-PDO is as functional fluids, such as antifreeze, de-icing and heat transfer [3]. The market of anti-freezing and de-icing products derived from 1,2-PDO is growing, as a consequence of the concern over the toxicity of ethylene glycol [3]. In the presence of a metallic catalyst and hydrogen, depending mainly on reaction conditions and catalyst characteristics, glycerol can be converted to 1,2-PDO, 1,3-PDO and ethylene glycol [4, 5].
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The catalysts employed for hydrogenolysis of glycerol to 1,2–PDO are based on metals such as Ru, Pd, Rh and Cu [2. 3, 6-11]. In contrast to noble metal catalysts which present low selectivity to 1,2-PDO due to the cleavage of C-C bond, copper based catalysts combine high glycerol conversion with high selectivity to 1,2-PDO [2, 13]. Copper is well known for its low ability to break the C-C bonds of the glycerol molecule, resulting in minor formation of undesired products and major efficiency for C-O hydrodehydrogenation reactions [13, 14]. Various supports including Cr2O3 [15], ZnO [16, 17], SiO2 [17] and Al2O3 [19] have been explored. Xiao et al [15] have found that glycerol hydrogenolysis occurs via a two site mechanism over Cu-Cr catalyst in liquid phase. Previous reports [16, 17] showed that hydrogenolysis to 1,2-PDO, on Cu/ZnO supported catalysts, proceeds via dehydration of glycerol to acetol on the acid sites of the support. Recently Vasiliadou et al [18] have demonstrated in their studies in liquid phase at high pressure over Cu/SiO2 catalysts, that SiO2 does not exhibit catalytic activity in the glycerol hydrogenolysis. Vila et al [19] have found that Al2O3 support is not involved in glycerol activation and that copper species are responsible for converting selectively the glycerol. The main concern reported in literature with the reaction in liquid phase is the high pressure employed in order to increase hydrogen solubility to obtain higher selectivity to 1,2-PDO [3]. In the liquid phase hydrogenolysis of glycerol, high reaction pressure is the common drawback. Then gas phase hydrogenolysis has been studied recently [10, 10, 20, 21] as the natural alternative scenario. Akiyama et al [10, 11] have reported that 1,2-PDO can be formed from glycerol with high selectivity over supported Cu/Al2O3 catalyst at ambient pressure, by the application of a temperature gradient over the catalytic bed, since the 3 ACS Paragon Plus Environment
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hydrogenation of acetol to 1,2-PDO is thermodynamically favoured at lower temperatures. Feng et al. [21] have found that Cu/ZnO/Al2O3 and Cu/ZnO/ZrO2 exhibit good glycerol conversion but low selectivity towards 1-2PDO in the gas phase hydrogenolysis of glycerol under 0,1 MPa of H2 . Considering that gas phase hydrogenolysis of glycerol is a potential alternative to liquid phase from the viewpoint of the process cost; in this paper we reported that 1,2 PDO can be produced at atmospheric pressure and low temperature with high selectivity from glycerol dehydrogenation. To achieve this goal, the loading of copper supported on alumina was varied between 3 wt.% and 20 wt.%.CuO; and the effects of temperature, space time and H2 molar fraction in the feed were analysed. 2. Experimental 2.1 Catalysis Preparation Catalysts with different CuO contents supported over γ-Al2O3, were prepared by incipient wetness impregnation method with aqueous solutions of Cu(NO3)2.3H2O (99.5% Merck), 1.5M and 10.1M. The employed catalyst support was γ-Al2O3 (Alumina Harshaw Chemical Co. AL-0104 T 1/8"), being previously crushed and sieved in order to obtain particles with diameters between 44 µm
