Abstract
Fischer-Tropsch Synthesis (FTS) is a process which converts synthesized gas (a mixture of H2 and CO) to synthetic liquid fuels and valuable chemicals with the existence of metal catalysts and suitable operational conditions. Less costly and plentiful biomass from agricultural waste can be converted into synthesized gas by thermal gasification. FTS derived Biofuel is a high quality, clean fuel and have a very low sulfur content in comparison to conventional fuel. In this study, FTS reaction was investigated in a tubular fixed bed reactor on prepared Co-Ni bimetallic catalysts supported by walnut shells derived activated carbon (AC) to study the synergistic effect of the active metals on the catalyst’s physical properties as well as hydrocarbon liquid product distribution. Employed catalysts were synthesized by wet impregnation method and were characterized afterwards by XRD, TPR-H2, BET surface area and FESEM-EDX techniques to identify the morphology and physical properties of the catalysts. Maximum gasoline selectivity of 69% was achieved on the 7Co7Ni/AC bimetallic catalyst, which was considered as the best bimetallic catalyst among others. Temperature increase from 220°C to 300°C enhanced gasoline selectivity from 69% to 92%. In addition, carbon monoxide (CO) conversion increased as well from 43% to 65% on the 7Co7Ni/AC bimetallic catalyst. On the contrary, increased reaction pressure from 1 bar to 9 bar decreased gasoline selectivity from 92% to 36% but increased CO conversion is from 65% to 84% on the 7Co7Ni/AC bimetallic catalyst. The optimum reaction conditions were considered based on the maximum selectivity of gasoline which was 300°C reaction temperature and 1 bar reaction pressure. In conclusion, the employing of bimetallic Co-Ni catalysts supported by AC in Fischer-Tropsch reaction has significantly enhanced the catalytic activity and improved gasoline selectivity due to the achieved high metal dispersion, better reduction degree and large surface area. Higher reaction temperatures increased gasoline selectivity whereas, higher reaction pressures decreased gasoline selectivity.
Highlights
Hydrogenation of the carbon monoxide takes place through a highly exothermic, heterogeneous catalysed polymerisation reaction that converts syngas into a wide range of organic products
cobalt supported on silica fibre (Co/SF) catalysts prepared by strong electrostatic adsorption (SEA), DPNH and DPNa had the largest Co3O4 particle size of 9, 12 and 14 nm respectively and were more selective for higher molecular weight hydrocarbons fraction (C12+) with values of 22%, 24% and 25% respectively; due to the dissociative adsorption of carbon monoxide (CO), which leads to the formation of the −CH2− fragments that required for chain growth
The amorphous structure of carbonized walnut shells was drastically increased after acid refluxed and thermal activation treatment, which proves the great effect that has been given on the structure of the carbon after those two steps
Summary
Hydrogenation of the carbon monoxide takes place through a highly exothermic, heterogeneous catalysed polymerisation reaction that converts syngas into a wide range of organic products (hydrocarbons, oxygenates and some functional groups). Bechara and colleagues have mentioned that their catalyst 15Co/Al2O3 which was tested in a fixed bed reactor, achieved selectivity of 37% towards light liquid hydrocarbons (gasoline fraction) at a reaction conditions of 180°C temperature, 1 bar pressure, H2/CO = 2 and 500°C reduction temperature. Reaction was carried out by a fixed bed reactor under reaction conditions of 240°C, 10 bar and 400°C They found that the activity and selectivity of the catalysts were strongly affected by the catalyst preparation method. The present work was conducted to study the performance of prepared mono and bimetallic catalyst of Co and Ni active metals supported by activated carbon on the Fischer-Tropsch reaction, and to investigate the influence of the corresponding metal loading ratios and operating conditions on the gasoline selectivity and carbon monoxide conversion
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