Effect of La2O3 addition on Ni/Al2O3 catalysts to produce H2 from glycerol
N.D. Charisiou1, G. Siakavelas1, K.N. Papageridis1,2, M.A. Goula1,2
1
Department of Environmental and Pollution Control Engineering, Technological Educational Institute of Western Macedonia (TEIWM), GR – 50100, Koila, Kozani, Greece 2
Catalysis and Environmental Protection MSc, School of Science and Technology, Hellenic Open University, Parodos Aristotelous 18, GR - 26335, Patras, Greece Keywords: hydrogen, glycerol, steam reforming, nickel supported catalysts Presenting author e-mail:
[email protected] ABSTRACT
Glycerol is one of the most versatile and valuable chemicals, with more than 1500 known end-uses, as an ingredient or processing aid in cosmetics, toiletries, personal care products, pharmaceutical formulations and foodstuffs. The surplus of glycerol associated with biodiesel production can generate a plethora of opportunities in transformations or other processes, in which the glycerol has been displaced by other raw materials. Arguably, the development of new processes to obtain products that until now were not derived from glycerol (due to its high cost as raw material) needs to be explored. The generation of useful products with added value and thus, the elevated volume of consumption taking advantage of the excess glycerol, will favor its global net economic balance and improve the sustainability of the biodiesel production plants. This global increase in the production of biodiesel has led to a simultaneous co-production of glycerol. ‘Crude glycerol’ is the principal by-product of biodiesel production. It accounts for up approximately 10% of the transesterification product output, i.e. about 99.8 g of glycerol is obtained per liter of biodiesel produced. In other words, for every 9 kg of biodiesel produced, 1 kg of crude glycerol is obtained [Dasari et al., 2005]. Finding alternative feasible uses for crude glycerol has become imperative as such processes would not only solve the environmental problems associated with its disposal, but also, the discovery of new and innovative uses for pure glycerol would greatly increase its market demand. Thus, the development of new uses for glycerol is the subject of heightened research interest. The chemical and biochemical conversion of glycerol to other useful products such as, hydrogen, 1,3-propanediol, 1,2-propanediol, succinic acid, dihydroxyacetone, polyglycerols and polyesters has been reported [Pachauri et al., 2006]. Steam reforming is a highly energy efficient technology and can be carried out at atmospheric pressure. The steam reforming of glycerol has similarities to the reforming of light alcohols, as methanol and ethanol [Goula et al., 2004], that has intensively been investigated experimentally with various catalysts (e.g. with unpromoted and Ce–Zn-promoted Cu, Ni, Rh, Pd, Co, Ir, Ni on carriers, such as CeO2, CeO2/ZrO2 or alumina). Nickel is the most investigated active metal in the glycerol reforming, due to its well known property to promote the necessary C–C rupture [Douette et al. 2007; Zhang et al., 2007]. Nickel catalysts were shown to be active and selective with a strong dependence on the reaction temperature with glycerol conversion to gaseous products [Buffoni et al., 2009]. In this contribution a comparative study of catalytic performance for nickel (Ni) supported on un-promoted and promoted with La2O3 alumina catalysts is reported. Catalysts were synthesized applying the wet impregnation method at a constant metal loading (8wt%). The synthesized samples, at their calcined or/and reduced form, were characterized by X-Ray Diffraction (XRD) and N 2 adsorptiondesorption technique (BET). The chemical composition of the catalysts was determined by inductively coupled plasma (ICP), while the deposited carbon on the catalytic surface was measured by a CHN analyzer. The catalytic performance of the catalysts concerning the glycerol steam reforming reaction, was studied in order to investigate the effect of the reaction temperature on (i) glycerol conversion, (ii) hydrogen selectivity, (iii) H2/CO molar ratio, (iv) gaseous and liquid products’ concentration of the mixtures at the outlet of the reactor.
100
50 CO2
H2
CH4
CO
8Ni/Al2O3 8Ni/LaAl
40
Concentration (% v/v)
Conversion (%)
80
60
40
XC3H8O2
20
SH2
30
20
10
8Ni/Al2O3 8Ni/LaAl
0 350
400
450
500
550
600
650
700
750
800
o
T( C)
Fig. 1 Glycerol conversion, H2 selectivity
0 350
400
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500
550
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o
T( C)
Fig.2 Gaseous products’ concentration
In Figures 1&2 the glycerol conversion and the hydrogen (H2) selectivity with varying the reaction temperature is presented. From Fig.1 it is depicted that the glycerol’s conversion values are very high (80-100%) for both catalysts and for the whole temperature range. On the other hand, hydrogen (H2) selectivity value increase with increasing temperature reaching almost 90% at temperature value equals to 600 oC and 700 oC for the catalysts Ni/La2O3-Al2O3 and Ni/Al2O3, respectively. From Fig.2 it is depicted that the H2 and CO2 concentration values at the gaseous products mixture are higher for the Ni/La2O3-Al2O3 compared with the ones for the Ni/Al2O3 and for the whole temperature range. The opposite trend concerning the un-promoted and promoted with La2O3 catalysts is observed for the CO concentration, even if these take their maximum values at T=550 oC for both catalysts. It is also observed that methane (CH4) production is very low for both catalysts and for the whole temperature range. Liquid phase’s composition determined by GC-MS analysis, revealed chemical substances as acetaldehyde, acetone, allyl alcohol, acetic acid, acetol, phenol, acrolein, propylene glycol for the lower reaction temperatures (below 600 oC). It can be concluded that the Ni/La2O3-Al2O3 catalyst exhibits improved gaseous products’ concentration, concerning hydrogen (H2) and carbon dioxide (CO2), due to the fact that lanthanum oxide favours the coke gasification and water gas shift reaction, and it improves the redox reversibility of metallic phase.
References [1] Buffoni I.N., Pompeo F., Santori G.F. and Nichio N.N. (2009) Catal. Commun., 10, 1656–1660. [2] Dasari M.A., Kiatsimkul P.P. and Sutterlin W.R. (2005) Appl. Catal. A: Gen, 281, 225–231. [3] Douette A.M.D., Turn S.Q., Wang W. and Keffer W.I. (2007) Energy Fuels, 21, 3499–3504. [4] Goula M.A., Kontou S.K. and Tsiakaras P.E. (2004) Applied Catalysis B: Environ., 49(2), 135-144. [5] Pachauri N. and He B. (2006) ASABE meeting presentation, Portland, Oregon, USA, p. 16. [6] Zhang B., Tang X., Li Y., Xu Y. and Shen W. (2007) Int. J. Hydrogen Energy, 32, 2367–2373. Acknowledgements Financial support by the program THALIS implemented within the framework of Education and Lifelong Learning Operational Programme, co-financed by the Hellenic Ministry of Education, Lifelong Learning and Religious Affairs and the European Social Fund, Project Title: ‘Production of Energy Carriers from Biomass by Products. Glycerol Reforming for the Production of Hydrogen, Hydrocarbons and Superior Alcohols’ is gratefully acknowledged.
