Sharif Digital Repository

A reduction in catalyst's activity with time-on-stream and the formation of side products are two of the problems associated with catalytic propane dehydrogenation (PDH). Previous studies have indicated that the presence of small amounts of oxygenated additives such as water can reduce coke formation and enhance catalyst activity. The aim of the present work was to develop an appropriate kinetic model for PDH over a commercial Pt-Sn/γ-Al 2O3 catalyst in the presence of small amounts of water. Experimental data were obtained from a previous study where catalytic PDH was carried out in a bench scale reactor system at atmospheric pressure in the temperature range of 575-620°C in the presence of... 

In this research, mathematical modelling of an anaerobic hybrid bioreactor for effluent treatment of a Poly-Ethylene Terephthalate (PET) unit in a petrochemical complex was performed. The developed model included a combination of a biofilm model for describing the substrate kinetics; a fluidized bed model for determination of species profiles along the reactor length and a bioreactor model for particle distribution inside the reactor. The reactions performed in the bioreactor included; i) the polymers hydrolysis; ii) fermentation of the resulting monomers; iii) the volatile fatty acids fermentation to Acetate and Hydrogen and iv) the Methane formation as the final product. The reactor was... 

The aim of this study was to develop an appropriate kinetic model for propane dehydrogenation (PDH) over an industrial Pt-Sn/γ-Al 2O 3 catalyst in the presence of small amounts of oxygenated compounds. Experimental data were obtained from a previous study where catalytic PDH was carried out in a laboratory scale reactor at atmospheric pressure in the temperature range of 575-620 °C in the presence of small amounts of water or methanol. The kinetics of the main dehydrogenation reaction was described and the effects of water and methanol on coke deposition and catalyst sintering were considered in a catalyst deactivation model to explain the observed optimum level in the amount of added... 

A reduction in catalyst activity with time-on-stream and formation of side products are the major problems associated with catalytic propane dehydrogenation. Coke formation on the catalyst surface is the most important cause for catalyst deactivation. Experiments have indicated that the presence of very small amounts of oxygenated additives such as water can reduce the amount of coke accumulated on the catalyst surface and enhance catalyst activity. Addition of water beyond an optimum level, however, would result in a loss of activity due to sintering of catalyst. Propane dehydrogenation over a Pt-Sn/γ-Al2O3 catalyst in the temperature range of 575 to 620 °C was investigated in the presence... 

In this study the kinetic modeling of visbreaking reactions for a number of vacuum residue feeds was investigated using available experimental data from the literature. A continuous lumping model was developed for kinetic analysis of visbreaking reactions. The normalized boiling point was used to describe each feed as a continuous mixture and the concentration distribution of the mixture would change under reaction conditions. A continuous model with five adjustable parameters was used to describe visbreaking reactions, and these parameters were optimized for each feed for reaction temperatures in the range of 400-430 C using available experimental data. The model was able to accurately... 

In this paper, the polymer chain of rotator (PCOR) equation of state (EOS) was used together with an EOS/GE mixing rule (MHV1) and the Wilson's equation as an excess-Gibbs-energy model in the proposed approach to extend the capability and improve the accuracy of the PCOR EOS for predicting the Henry's constant of solutions containing polymers. The results of the proposed method compared with two equation of state (van der Waals and GC-Flory) and three activity coefficient models (UNIFAC, UNIFAC-FV and Entropic-FV) indicated that the PCOR EOS/Wilson's equation provided more accurate results. The interaction parameters of Wilson's equation were fitted with Henry's constant experimental data... 

A new nonlinear optimization method for parameter estimation in Michaelis-Menten equation has been developed. This method is based on a special mathematical form of the Michaelis-Menten equation to finding the best fit of the linear plot of R versus S/(S + Km) where R, S, and Km are the reaction rate, concentration of substrate, and the Michaelis-Menten constant, respectively. By setting the intercept of this line to zero, the proper Km will be obtained and the slope would give the saturation rate, Vmax. As a result, a nonlinear, two-parameter optimization is simplified into finding the roots of a nonlinear equation. Generated data sets were used... 

Thermal cracking of a vacuum distillation residue of the Abadan refinery in Iran was performed under delayed coking conditions to investigate the effect of operating conditions on the yield and sulfur content of products. At reaction temperatures of 440-500 °C and pressures of 1, 3, and 5 bar, the products included gases, liquids, and coke. The yields of liquid products were higher at 1 bar compared to those for higher pressures. Increasing the reaction temperature at a given reaction pressure led to an increase in the yield of liquid products. Increasing the reaction pressure at a given reaction temperature led to higher yields of coke and gases as well as a decrease in the sulfur content... 

The deactivation of solid acid catalysts in liquid phase alkylation of isobutane with 2-butene was investigated. Since under liquid phase conditions the alkylation reaction is severely diffusion limited, effects of diffusion on the rate of reaction and deactivation pathways were considered. In the present work, an attempt has been made to implement more appropriate assumptions in order to properly model catalyst deactivation in a mixed reactor. Accordingly, spatial variation of diffusivity in the pores of the catalyst was considered as a function of time on stream. The effect of the pore mouth plugging was also investigated and it was found that this phenomenon had a pronounced effect on the... 

The disposal of used tires is a major environmental problem. With increasing interest on recovery of wastes, pyrolysis is considered as an alternative process for recovering some of the value in scrap tires. An accurate kinetic model is required to predict product yields during thermal or catalytic pyrolysis of scrap tires. Pyrolysis products contain a variety of hydrocarbons over a wide boiling range. A common approach for kinetic modeling of such complex systems is lumping where each lump is defined by a boiling point range. Available experimental data for thermal and catalytic pyrolysis of scrap tires from the literature were used to evaluate two types of lumping models; discrete and... 

Nickel nanoparticles supported on MgO-Al2O3 and Al2O3 were synthesized by an impregnation method using dinitrobisethylenediamine nickel and nickel nitrate hexahydrate as precursors and were used as catalysts for CO methanation. Different MgO contents (1.5-11.25 wt %) were employed for the preparation of supports, and NiO loadings were in the range of 10-40 wt %. The optimum catalyst prepared from proper amounts of MgO (∼2 wt %) and NiO loading (20 wt %) with [Ni(en)2(H2O)2](NO3)2 as precursor and a mesoporous support with a wide range of mesopores resulted in highly dispersed nickel nanoparticles that exhibited moderate metal-support interactions, lower acidic surface sites, and enhanced... 

In this paper, a comparative techno-economic evaluation of hydrogen production by glycerol reforming in aqueous and gaseous phases are presented. To accomplish the techno-economic evaluation, firstly the process modeling and design are presented. Based on the equipment purchased costs, with 80 kg/h hydrogen production, the total cost of hydrogen production is estimated 3.65 and 3.55 $/kgH2 for steam reforming and aqueous phase reforming plants, respectively. Regarding the installation factor in the equipment costs, the total cost of hydrogen production is estimated 7.49 and 7.45 $/kgH2 for steam reforming and aqueous phase reforming plants, respectively. To investigate the impact of... 

A simple optimization methodology is applied to estimate the intrinsic kinetic parameters for both reversible and irreversible unireactant immobilized enzyme systems that follow the Michaelis-Menten mechanism. The method utilizes a direct-search optimization algorithm along with the numerical solution of the governing differential equations. The usefulness and validity of the method is demonstrated by comparing the predicted values of the intrinsic kinetic constants using the proposed method with a series of experimental values reported in the literature for different immobilized enzyme systems with irreversible and reversible reactions