Thermodynamic Equilibrium Analysis of Propane Dehydrogenation with Carbon Dioxide and Side Reactions

Abstract

A thermodynamic analysis of propane dehydrogenation with carbon dioxide was performed using constrained Gibbs free energy minimization method. Different reaction networks corresponding to different catalytic systems, including non-redox and redox oxide catalysts, were simulated. The influences of CO 2 /C 3 H 8 molar ratio (1-10), temperature (700-1000 K) and pressure (0.5-5 bar) on equilibrium conversion and product composition were studied. In the presence of CO 2 with a molar ratio of CO 2 /C 3 H 8 =1, the temperature of dehydrogenation can be 30 K lower than that of dehydrogenation in the presence of steam (H 2 O/C 3 H 8 =1) and about 50 K lower than that of simple dehydrogenation without dilution to achieve 60% propane conversion. It was found that the occurrence of dry reforming of propane and coke forming side reactions could strongly impact the equilibrium product composition of the multi-reaction system and, therefore, these reactions should be kinetically controlled. Comparison of the simulated reactant conversions with those reported in the literatures revealed that the experimental conversion levels of propane are far below the corresponding equilibrium values due to rapid catalyst deactivation by coke implying that research efforts should be directed towards formulation of more active and selective catalysts. Downloaded by [University of Otago] at 21:19 12 July 2015 2

Oxidative Dehydrogenation of Propane to Propylene with Soft Oxidants via Heterogeneous Catalysis

“…32,33 Coke formation (eq 2-10) is one of the major causes of deactivation of the catalysts for CO 2 −ODHP. 34 This reaction is endothermic and not a spontaneous reaction at room temperature because of its highly positive Gibbs free energy. However, it becomes spontaneous starting from ∼400 °C (i.e., ΔG 400°C = −6.5 kJ mol −1 ), resulting in catalyst deactivation in turn.…”

“…In addition, the decomposition reactions are one of the major causes of severe catalyst deactivation through coking, with the extent varying depending on the catalysts used. For example, the decomposition reaction (eq ) dominates and causes severe deactivation in the case of Fe–Ce solid solution catalysts, while the cracking reaction (eq ) may occur on precious Pt catalysts. , Coke formation (eq ) is one of the major causes of deactivation of the catalysts for CO 2 –ODHP . This reaction is endothermic and not a spontaneous reaction at room temperature because of its highly positive Gibbs free energy.…”

Elucidating the Role of CO2 in the Soft Oxidative Dehydrogenation of Propane over Ceria-Based Catalysts

“…Therefore, reducible metal oxides capable of activating CO 2 at lower temperatures could be potential candidates for this reaction. 18 Cerium(IV) oxide (ceria) is widely used in catalysis, primarily as a component of support materials for metal nanoparticles. However, it has been reported that ceria can be an effective catalyst in its own right for the oxidative dehydrogenation of ethylbenzene to styrene in the presence of CO 2.…”

“…There is, however, a tradeoff to operation of the reaction at higher temperatures (>550 °C), which favor combustion of both the reactants and products. Therefore, reducible metal oxides capable of activating CO 2 at lower temperatures could be potential candidates for this reaction …”

Catalytic performance of gallium oxide based-catalysts for the propane dehydrogenation reaction: effects of support and loading amount

“…Nevertheless, under such high temperatures, the undesirable side reactions such as hydrogenolysis, cracking and coke deposition are inevitable. 4,5 Currently, many studies are devoted to developing novel and potential catalysts in propane dehydrogenation (PDH), such as ceria-based catalysts, 6 calcined hydrotalcite-supported platinum catalysts, 7 Sn/SiO 2 catalysts, 8 Pd-based catalysts, 9 mesoporous carbons, gallium oxide-based catalysts 10,11 and so on. Among these, gallium oxide-based catalysts have been recognized as new promising alkane dehydrogenation materials due to their unique capability to activate hydrocarbon species and excellent catalytic efficiency as compared to conventional Cr 2 O 3and V 2 O 5 -based catalysts.…”