DRY REFORMING OF PROPANE- THERMODYNAMIC AND MODELING STUDY

Abstract

Among others, the light hydrocarbon (Cl-C4 alkanes) dry reforming process has attracted considerable attention with increasing global oil price, for developing sustainable environmentally-compatible synthesis gas (H2/CO mixtures) production and utilization technologies. However, the foremost advantage of immediate suitability for gas-to-liquids (GTL) fuels' conversion has been prevented by severe carbon deposition, the main challenge that rapidly deactivates the catalyst and the attendant economic implications. As a result, the principal goal of this study was to improve the dry reforming process through two main strategies, namely: carbon-resilient catalyst design, and reactor operation. The dry reforming of propane is a reversible endothermic process and is therefore limited by the thermodynamic equilibrium. According to thermodynamics, if a reaction proceeds with an increase in total no of moles, the inert material dilution in feed will increase the equilibrium yield. Propane dry reforming system comprises with increase in total no of moles. 1-lence, the addition of inert gas, shifts the equilibrium in favor of syngas production and suppress the formation of the undesired products (methane and carbon). The thermodynamic analysis of any process provides the equilibrium compositions of all products which may be desirable or undesirable, at given operating conditions. It also ensures whether or not an experimental investigation would be worthwhile. Before running a process, it is always beneficial to get optimized operating conditions enhancing the formation of desired product and suppressing the formation of undesired product. Theoretical conversion is the maximum value one can achieve under the given conditions; practically one can reach the conversion value equal to or less than the theoretical value not more than that. Knowing the optimum conditions, there is an idea to make suitable catalyst for the process or to modify the catalyst conditions i.e. stability, selectivity or activity of catalyst with respect to the desired process. Therefore, from the operational point of view, it is desired to access the operating conditions under which high quality syngas production with low concentrations of undesired products Cl-I4 and carbon are thermodynamically favoured. In the present work, thermodynamic analysis of propane dry reforming with and without inert gas dilution in feed, has been presented to evaluate the effect of temperature, pressure, CO2 to propane feed ratio, N2 to propane feed ratio, yields of 1-12, CO. Cl-I4 and carbon, propane and CO2 conversion. Optimized operating conditions found suitable for complete conversion of propane and producing high quality syngas are J'value of 3-4, atmospheric pressure and temperature of 923-1023K. 1-ugh temperature, low pressure, low CO2 to propane feed ratio and high inert gas dilution favor the high syngas production in propane dry reforming with relatively low content of undesired products. The consumption of thermal energy is the key issue in the analysis of fuel reforming system. Therefore, the actual performance of any fuel reforming system is quantified also by the thermal efficiency of the reacting system along with fuel conversion, yields and selectivity of the products. Thermal efficiency of all there reforming process namely: dry reforming, steam reforming and steam and oxidative reforming, have been computed and compared. The maximum thermal efficiency observed in dry reforming system is 90.6 % or less than 90.6 % at all operating conditions. The optimal thermal efficiency is achieved with temperature 1000K and CO2 to propane feed ratio (/) 6 in dry reforming system. in oxidative steam reforming, the thermal efficiency has been found minimum among the all reforming system. The maximum thermal efficiency reported in oxidative steam reforming is only 69.3%. In steam reforming process, the highest thermal efficiency has been reported when 1-12 or CO2 are removed simultaneously from the product stream. Among the various reforming systems, dry reforming and steam reforming with H2 or CO2 removal are found most efficient for syngas production in terms of thermal efficiency. Experimental studies on various catalysts in the literature, for dry reforming of propane, are important to verify the results. Thus, it is suggested that suitable catalyst should be chosen for high quality syngas production with low concentrations of undesired products CH4 and carbon. In the modeling work, one dimensional, steady state isothermal model fixed bed reactor has been developed for propane dry reforming system. CPR=3-4, high temperature and low pressure at temperature equal to or greater than 923 K are the optimized condition for complete propane conversion and production of high quality syngas.