Luca Paturzo

The partial oxidation of methane to syngas in a palladium membrane reactor : simulation and experimental studies

Abstract Among numerous potential applications of inorganic membrane reactors, the partial oxidation of methane (POM) may offer an alternative route, with respect to steam reforming of methane, for producing synthesis gas. Inorganic membrane reactors are considered to be multifunctional reactors because they are able to combine catalytic reactions with membrane separation properties. In particular, dense palladium membranes are characterised by the fact that: (1) only hydrogen might permeate through them; (2) both Arrhenius and Sievert laws are followed. In this investigation, a dense palladium membrane reactor (PMR) concept is analysed referring both to experimental data and to simulation study. The partial oxidation of methane (POM) reaction to produce synthesis gas was chosen as a model reaction to be investigated. A membrane reactor model that includes the membrane, the gas phase and the catalyst activity is proposed. The experimental results in terms of methane conversion obtained by using a pin-hole free palladium membrane permeable to hydrogen only were compared with model predictions. The effect of reaction temperature on methane conversion at different time factors and sweep gas flow rates was considered. In particular, the effects of temperature profiles on the methane conversion are taken into account in the kinetic model.

An Ru-based catalytic membrane reactor for dry reforming of methane : its catalytic performance compared with tubular packed bed reactors

The methane reforming with CO2 seems to be a promising reaction system useful to reduce the greenhouse contribution of both gases into the atmosphere. On this basis, and considering the potentiality of this reaction system, the dry reforming reaction has been carried out in an Ru-based ceramic tubular membrane reactor, in which two Ru depositions have been performed using the co-condensation technique. Experimental results in terms of CH4 and CO2 conversion versus temperature during time are presented, as well as product selectivity and carbon deposition. These experiments have also been carried out using a traditional reactor. A comparison with literature data regarding dry reforming reaction is also provided. Experimental evidence points out a good catalyst activity for the methane dry reforming reaction, confirming the potentiality of a catalytic membrane applied to the reaction system.

HIGH TEMPERATURE MEMBRANE REACTORS AND INTEGRATED MEMBRANE OPERATIONS

Membrane reactors have attracted considerable attention in recent years, due also to the recent extensive investigations into microporous ceramic membranes, since in such systems reaction and separation are performed simultaneously. Moreover, conversions greater than traditional equilibrium may be obtained, while in a conventional plug-flow reactor conversions are limited by thermodynamic constrains. When the membrane integrated in this new kind of reaction system is highly selective for the product of interest, its recovery directly during the reaction is possible, avoiding or reducing the separation units downstream the reactor. It is also possible to perform two or more reactions in the same device: the membrane could be selectively permeated by a product of the first reaction, and then this product becomes the reactant of the second reaction. In this paper, recent applications of these systems are presented and discussed.

Co-current and counter-current modes for water gas shift membrane reactor

In this study the performances of a membrane reactor (MR) are estimated when both shell side stream (sweep gas) and lumen side stream are continuously either in parallel flow configuration (co-current mode) or in counter-flow configuration (counter-current mode). Two mathematical models have been formulated and steady-state mass-balance gave two-dimensional differential equations, which were solved by using the orthogonal collocation technique. Simulation results for both co-current mode and counter-current mode have been compared in terms of hydrogen molar fraction (in the shell side) vs. axial co-ordinate at different hydrogen permeances, temperatures, and lumen pressures. At the operative conditions considered, a very similar CO conversion value has been obtained for both modes.

An experimental study of multilayered composite palladium membrane reactors for partial oxidation of methane to syngas

Abstract Today only a small percentage of methane is used as a chemical feedstock to produce syngas that is a valuable feedstock for the production of higher hydrocarbons or methanol. Currently, the process extensively used in industry for the production of syngas is the steam reforming of methane in large furnaces. The reaction is industrially operated under strong conditions resulting in several undesirable consequences: sintering of the catalyst, danger of explosion, very high carbon deposition and the use of high-temperature resisting materials. A potential alternative technique to steam reforming processes for producing syngas is the partial oxidation of methane with oxygen, having over steam reforming the disadvantage that pure oxygen is required. Utilisation of air instead of pure oxygen is beneficial only if it can be performed by using a membrane reactor in which the membrane is permselective to oxygen. Another route to produce syngas using the partial oxidation of methane is offered by membrane reactors, i.e. engineering systems that combine the separation properties of membrane with the typical characteristics of catalytic reactions. It is well known that the use of dense palladium as membrane enables hydrogen product to permeate out through the membrane, shifting thereby conversions towards the values higher than thermodynamic equilibrium ones and providing pure hydrogen product. In fact, only hydrogen is allowed to permeate through dense palladium membranes. In this work five reactors are investigated with respect to the partial oxidation of methane. In particular, the performance of a traditional reactor (TR), three composite ceramic palladium membrane reactors (MRa, MRb and MRc), and a dense palladium membrane Reactor (PMR), all having the same geometrical dimensions and using the same Ni-based catalyst, are evaluated in terms of experimental results of methane conversion to syngas and in terms of hydrogen selectivity. A comparison between methane conversion at various temperatures and data in literature is also presented.

Membrane reactor for the production of hydrogen and higher hydrocarbons from methane over Ru/Al2O3 catalyst

It is known that higher alkanes can be produced from methane over Ru, Pt or Co supported on silica by using a two-step reaction sequence. In this investigation, a dense Pd/Ag flat membrane reactor (FMR) and a traditional reactor (TR) are analysed referring to experimental data. The two-step reaction over Ru-based catalyst was chosen as a model reaction to be investigated. The experiments carried out in this study confirm that, using a membrane reactor, it is possible to obtain consumed methane values greater than the ones obtained in a TR for the first step operating at the same experimental conditions. A direct consequence should be an increase of the yield in higher hydrocarbons. In addition, this work shows that the membrane reactor performances can be improved by properly tuning the operating conditions. Experimental results of this work are compared with both experimental data obtained in a previous work using a dense Pd/Ag tubular membrane reactor (TMR) and experimental data reported in the literature.