International Journal of Innovative Research in Engineering & Management (IJIREM) ISSN: 2350-0557, Volume-3, Issue-3, May-2016 Copyright © 2016. Innovative Research Publications. All Rights Reserved 200 Selectivity model of Fischer-Tropsch synthesis on the Cobalt-Based Catalyst Jaber Tayebi . Department of Chemical Engineering, Faculty of Engineering University of Sistan and Baluchestan, P.O.Box 98164-161, Zahedan, Iran Hossein Atashi . Department of Chemical Engineering, Faculty of Engineering University of Sistan and Baluchestan, P.O.Box 98164-161, Zahedan, Iran Corresponding author. Tel.: +98 9121193366. Neda Poudineh . Department of Chemical Engineering, Faculty of Engineering University of Sistan and Baluchestan, P.O.Box 98164-161, Zahedan, Iran mariam@usim.edu.my ABSTRACT CO conversion model and two models of selectivity of CH 4 and C 5 + productswere obtained for Fischer-Tropsch synthesis. The models were fitted to experimental data obtained by Co/SiO 2 catalystin isothermal packed-bed reactor. The operating conditions are as follows: temperature 473K, pressure 0.5 MPa, space velocity 0.08- 0.5 cm 3 / (g-s) and water partial pressure 0.01-0.26 MPa.The influence of operating parameters, interaction of them and the effect of water on the CO conversion and the selectivity of products were investigated. Results show that both of the two operating parameters, i.e., water partial pressureand space velocity are influenced.Also it has been shown that as water partial pressure increases, the C 5 + selectivity and the CO conversion are increased while the CH 4 selectivity is decreased. Keywords: CO conversion, Fischer-Tropsch synthesis, selectivity model, water effect 1. INTRODUCTION The Fischer-Tropsch synthesis (FTS) is a promising approach to efficientconversion of coal, natural gas and biomass into a mixture of alkenes, alkanes, alcohols and other oxygenates with a range of Carbon number [1-4].This process is very effective for the conversion of expressedcompounds intoenvironmental less damaging fuels and useful chemical with lower emissions of pollutants[5-8].Numerous studies investigated this process in different aspects [9-16].In thisprocess, ѴШgroup metals are used as catalyst [17].Among the metals of this group, Iron and Cobalt catalysts are the two mainlyused one. [18, 19].Of these two, the cobalt-based catalysts (Co/SiO2, Co/activated Carbon, etc) aremore interesting for production of hydrocarbons from synthesis gasbeacause of the cobalt’s intrinsic ability in hydrogenating dissociated carbon species, prompting chain growth and resistance to deactivation by carbonaceous deposits [17, 20]. Besides, other reasons of their widely usage in industrial process are: high selectivity and activity, low activity of water-gas shift reactionandtheir relatively low price. Also ithas been shown that cobalt-based catalysts are often suitablefor low temperatureFTS [21, 22].During the FT reaction,water isproduced in varyingquantities [23]. Whetherthis water isindigenous or added,it causesactivity increase [24, 25]and decrease on Co/SiO 2 catalysts[26].The deactivation process of this catalyst is increased in the high conversions and high partial pressure of water. In the low conversion when water is not added, the deactivation of catalyst is done much more slowly[25, 27].Decreasingthe deactivation of catalyst is irreversible in high waterpartial pressure [27]. Investigation of products selectivity in FT reaction is an important matter.To study the FTS products distribution, different wayshave been suggested in the literature which can be classified into two main categories: detailed Langmuir-Hinshelwood-Hougen- Watson (LHHW) kinetic models and hydrocarbon selectivity models [28].In achieving the optimum operating conditions for production, economical and temporal factors are of major significance.Hence, selectivitymodels can play an effective role in the designing ofFT process.In this study,appropriate modelswere obtainedfor products selectivity and CO conversion.Also the effects of operating parameters and their corresponding interactions on products selectivitywere studied by Analysis Of Variance (ANOVA) method. 2. EXPERIMENTAL Experimentaldata were obtained fromKrishnamoorthy et al. (2002) studythatinvestigatedthe effect of water on the rate and selectivity of Fischer-Tropsch on cobalt-based catalyst. This study is carried outinthe followingoperating conditions:different ranges of water partial pressure andspace velocity, temperature473 K,pressure 0.5 MPa and H 2 /CO=2 (Table 1). Co/SiO 2 (12.7 wt%, 1.75 g 100- to-180 µm particles) catalyst used, here, first, was diluted by the SiO 2 (2.8 g, 100-to 180-µm particles), then it was reduced by H 2 (12×10 3 Cm 3 /h. g-Cat) for 1 hour within reactor while being heated to 598 K at 0.17 K/S.The FTSrates and selectivity were measured by an isothermal reactor with plug-flow hydrodynamics. FT reactions were carried out at