Propane Dehydrogenation over a Commercial Pt-Sn/Al2O3 Catalyst for Isobutane Dehydrogenation： Optimization of Reaction Conditions

The applicability of a commercial Pt-Sn/Al2O3 isobutane dehydrogenation catalyst in dehydrogenation of propane was studied. Catalyst performance tests were carded out in a fixed-bed quartz reactor under different operating conditions. Generally, as the factors improving propane conversion decrease the propylene selectivity, the optimal operating condition to maximize propylene yield is expected. The optimal condition was obtamed by the experimental design method. The investigated parameters were temperature, hydrogen/hydrocarbon （HE/HC） ratio and space velocity, being changed in three levels. Constrains such as the susceptibility of the catalyst components to sintering or phase transformation were also taken into account. Activity, selectivity and stability of the catalyst were considered as the measured response factors, while the space-time-yield （STY） was considered as the variable to be optimized due to its commercial interest. A STY of 16 mol.kg^-1.h^-1 was achieved under the optimal conditions of T= 620 ℃, H2/HC = 0.6 and, weight hourly space velocity （WHSV） = 2.2 h^-1. Single carbon-carbon bond rupture was found to be the main route for the formation of lower hydrocarbon byproducts.

Preparation of nanocrystalline γ-Al_2O_3 catalyst using different procedures for methanol dehydration to dimethyl ether

A series of nanocrystalline γ-alumina are synthesized by different procedures, namely, thermal decomposition method （sample A）, precipita-tion method （sample B） and sol-gel method using sucrose and hexadecyltrimethyl ammonium bromide （CTAB） as templates （samples C and D, respectively）. Textural and acidic properties of γ-alumina samples are characterized by XRD, N2 adsorption-desorption and NH3-TPD techniques. Vapor-phase dehydration of methanol into dimethyl ether is carried out over these samples. Among them, sample C shows the highest catalytic activity. NH3-TPD analysis reveals that the sample with smaller crystallite size possesses higher concentration of medium acidic sites and consequently higher catalytic activity. Thermal decomposition method leads to decrease in both surface area and moderate acidity, therefore it is the cause of lower catalytic activity.

Kinetic study of propane dehydrogenation and catalyst deactivation over Pt-Sn/Al_2O_3catalyst

The kinetics of propane dehydrogenation and catalyst deactivation over Pt-Sn/Al2O3 catalyst were studied.Performance test runs were carried out in a fixed-bed integral reactor.Using a power-law rate expression for the surface reaction kinetics and independent law for deactivation kinetics,the experimental data were analyzed both by integral and a novel differential method of analysis and the results were compared.To avoid fluctuation of time-derivatives of conversion required for differential analysis,the conversion-time data were first fitted with appropriate functions.While the time-zero and rate constant of reaction were largely insensitive to the function employed,the rate constant of deactivation was much more sensitive to the function form.The advantage of the proposed differential method,however,is that the integration of the rate expression is not necessary which otherwise could be complicated or impossible.It was also found that the reaction is not limited by external and internal mass transfer limitations,implying that the employed kinetics could be considered as intrinsic ones.

Conversion of carbon dioxide to valuable petrochemicals:An approach to clean development mechanism

The increase of atmospheric carbon dioxide and the global warming due to its greenhouse effect resulted in worldwide concerns. On the other hand, carbon dioxide might be considered as a valuable and renewable carbon source. One approach to reduce carbon dioxide emissions could be its capture and recycle via transformation into chemicals using the technologies in C1 chemistry. Despite its great interest, there are difficulties in CO2 separation on the one hand, and thermodynamic stability of carbon dioxide molecule rendering its chemical activity low on the other hand. Carbon dioxide has been already used in petrochemical industries for production of limited chemicals such as urea. The utilization of carbon dioxide does not necessarily involve development of new processes, and in certain processes such as methanol synthesis and methane steam reforming, addition of CO2 into the feed results in its utilization and increases carbon efficiency. In other cases, modifications in catalyst and/or processes, or even new catalysts and processes, are necessary. In either case, catalysis plays a crucial role in carbon dioxide conversion and effective catalysts are required for commercial realization of the related processes. Technologies for CO2 utilization are emerging after many years of research and development efforts.

Synthesis of nanocrystalline γ-Al_2O_3 by sol-gel and precipitation methods for methanol dehydration to dimethyl ether

The capability of sol-gel and conventional precipitation techniques for the synthesis of nanocrystalline γ-alumina was investigated. These catalysts were used for vapor-phase dehydration of methanol to dimethyl ether in a fixed-bed reactor under the same operating conditions （T = 300 ？C, P = 1 bar, LHSV = 2.8, 11.7, 26.1 h？1） and characterized by means of N2 adsorption-desorption, NH3-TPD, XRD, TGA and SEM techniques. According to the experimental results, the catalysts prepared using sol-gel method in non-aqueous medium showed better performance compared with those prepared by other methods.

Experimental Study and Modeling of an Adiabatic Fixed-bed Reactor for Methanol Dehydration to Dimethyl Ether

One-dimensional heterogeneous plug flow model was employed to model an adiabatic fixed-bed reactor for the catalytic dehydration of methanol to dimethyl ether.Longitudinal temperature and conversion profiles predicted by this model were compared to those experimentally measured in a bench scale reactor.The reactor was packed with 1.5mm γ-Al2O3 pellets as dehydration catalyst and operated in a temperature range of 543-603K at an atmospheric pressure.Also,the effects of weight hourly space velocity(WHSV)and temperature on methanol conversion were investigated.According to the results,the maximum conversion is obtained at 603.15K with WHSV of 72.87h-1.

Rule of 100:An inherent limitation or performance measure in oxidative coupling of methane?

The oxidative coupling of methane over La203/CaO type-catalyst in a fixed-bed reactor is studied under a wide range of operating conditions （973〈T〈 1103 K, 55〈 Ptotal 〈220 kPa, and 3.7〈 mcat/VTp 〈50 kg.s/m^3）. A ten-step kinetic model incorporating all main products was used to predict the behavior of the system. Methane conversions and C2 selectivities were calculated by varying methane to oxygen ratios in the feed under different operating conditions which were also compared with the rule of 100. The results show that deviation from this rule depends on the operating conditions. Within the range studied, an increase in pressure, temperature and contact time results in smaller deviation from the rule. This rule is best approximated when the catalyst operates near its optimal performance. For negative deviations, common to the most catalysts, it is found that the optimal performance should occur at methane conversion levels lower than 50%. A plot of selectivity versus conversion for high-yield reported performance data of a large variety of catalysts shows that data points concentrated roughly in 20%-50% methane conversion region, confirming the generality and prediction of modeling.

Carbon dioxide sequestration in petrochemical industries with the aim of reduction in greenhouse gas emissions

The mitigation of greenhouse gas emissions to acceptable levels is arguably the greatest environmental challenge these days.Vast utilization of fossil fuels and forest destruction are main causes of CO_(2) increase in the atmosphere.Carbon dioxide sequestration that consists of separation,transportation and utilization or storage of CO_(2),is one way for reduction of its emission,in which the most costly section is separation.Different methods can be used for carbon dioxide separation such as absorption,mem-brane separation,adsorption and cryogenic distillation.Economic,technical and environmental issues should be considered in selection of the technology for particular application.Carbon dioxide concentration,temperature,pressure andflow rate are influential operating parameters in the selection of the appropriate separation method.Nowadays,absorption is the worldwide industrial separa-tion method.New researches are focused on developing new stable solvents and efficient column configuration with suitable internals to minimize pressure drop.Membrane separation and adsorption(PSA type)are other long-term alternatives that can increase separation efficiency and decrease separation cost.The level of energy consumption in various separation methods are in the order:chemical absorption>physical absorption>membrane separation.Because of high investment costs,current separation technologies are suitable for large concentrated sources.In the present paper,different processes for carbon dioxide separation are investigated and compared.Available technologies and commercial plants for CO_(2) sequestration are provided.