Partial oxidation using membrane reactors

BERNSTEIN ET AL. Partial Oxidation Using Membrane Reactors... 

Caro, J., Caspary, K., Hamel, C., etal. (2007). Catalytic Membrane Reactors for Partial Oxidation Using Perovskite Hollow Fiber Membranes and for Partial Hydrogenation Using a Catalytic Membrane Contactor, Ind. Eng. Chem. Res., 46, pp. 2286-2294. 

In addition to using membrane reactors to remove a reaction product in order to shift the equilibrium toward completion, we can use membrane reaettn-s to increase. selectivity in multiple reactions. This increa.se can be achieved by injecting one of the reactants along the length of the reactor. It is particularly effective in partial oxidation of hydrocarbons, as well as chlorination, ethoxy-lation, hydrogenation, nitration, and sulfunation reactions, to name a few. ... 

A packed-bed nonpermselective membrane reactor (PBNMR) is presented by Diakov et al. [31], who increased the operational stability in the partial oxidation of methanol by feeding oxygen directly and methanol through a macroporous stainless steel membrane to the PB. Al-Juaied et al. [32] used an inert membrane to distribute either oxygen or ethylene in the selective ethylene oxidation. By accounting for the proper kinetics of the reaction, the selectivity and yield of ethylene oxide could be enhanced over the fixed-bed reactor operation. 

One example of membrane reactors is oxidation, in which oxygen from one phase diffuses from one side of an oxygen-permeable membrane to react with a fuel on the other side of the membrane. This avoids a high concentration of O2 on the fuel side, which would be flammable. A catalyst on the fuel side of the membrane oxidizes the fuel to partial oxidation products. One important process using a membrane reactor is the reaction to oxidize methane to form syngas,... 

The viability of one particular use of a membrane reactor for partial oxidation reactions has been studied through mathematical modeling. The partial oxidation of methane has been used as a model selective oxidation reaction, where the intermediate product is much more reactive than the reactant. Kinetic data for V205/Si02 catalysts for methane partial oxidation are available in the literature and have been used in the modeling. Values have been selected for the other key parameters which appear in the dimensionless form of the reactor design equations based upon the physical properties of commercially available membrane materials. This parametric study has identified which parameters are most important, and what the values of these parameters must be to realize a performance enhancement over a plug-flow reactor. 

The present study investigates a different approach. The membrane is used to allow the desired intermediate product to escape from the reaction zone before it is consumed by further reaction. This use of a membrane reactor was first suggested by Michaels [15]. The partial oxidation of methane, which is a challenging reaction of the type propos for this application of membrane reactors, has been analyzed herein. There is no thermodynamic limitation for the production of carbon dioxide and water, actually these products are favored. It is desired to remove any partial oxidation product, for example formaldehyde, before it has a chance to be further oxidized. 

In this section some experimental results obtained in our laboratories on PM Rs are reported. In particular two different photocatalytic membrane reactors, used in total and partial photocatalytic oxidations are described. 

Several profound theoretical and experimental studies performed on the laboratory scale have been reported which focus on the use of various configurations of membrane reactors as a reactant distributor in order to improve selectivity-conversion performances. In particular, several industrially relevant partial oxidations have been investigated, including the oxidative coupling of methane [56], the oxidative dehydrogenations of propane [57], butane [58], methanol [59, 60], the epoxidation of ethylene [61], and the oxidation of butane to maleic anhydride [62]. 

Experiments were conducted at the University of Magdeburg to examine the partial oxidation of ethane to ethylene by dosing oxygen into the fluidized bed of porous catalysts using immersed sintered metal and ceramic membranes. These studies were related to a DFG (German Research Association) research group (DFG-Nr. FOR 447/1-1) Membrane supported reaction engineering in the subproject Fluidized-bed membrane reactor . 

In addition to a proper membrane, CMRs also need a good catalyst. Due to the specific conditions under which catalysts are placed in CMRs, conventional active phases could behave differently from when under classical conditions. For example, in dehydrogenation reactions, due to the removal of H2, the hydrogen hydrocarbon ratio is smaller in CMRs when compared to other reactors, which will probably affect the stability of the catalyst. The low oxygen partial pressure used in CMRs for selective oxidation (Section A9.3.3.2) could also lead to some changes in catalyst behavior. These aspects could necessitate the specific design of catalysts for CMRs. 

The use of Pd-based membrane reactors can increase the hydrogenation rates of several olefins by more than 10 times higher than those in conventional premixed fixed>bed reactors. Furthermore, it has been pointed out that the type and state of the oxygen used to carry out partial oxidation of methane can significantly affect the conversion and selectivity of the reaction. The use of a solid oxide membrane (e.g., a yttria-stabilized zirconia membrane) not only can achieve an industrially acceptable C2 hydrocarbon yield but also may eliminate undesirable gas-phase reactions of oxygen with methane or its intermediates because oxygen first reaches the catalyst through the solid oxide wall [Eng and Stoukides, 1991]. 

The process of catalytic partial oxidation of methanol with air in a fuel-rich mixture has been commercialized to produce formaldehyde since about 1890. Various catalysts have been used but silver catalyst is by far most widely used. Song and Hwang [1991] used a packed-bed porous membrane tubular reactor wi the catalyst packed on the shell side. They used a model consmicted essentially from Equations (10-36) and (10-44) with the permeation terms replaced by some terms similar to Equation (10-56) and k- =0. The partial oxidation of methanol can be conveniently described by... 

Gasoline and other higher hydrocarbons may be converted to hydrogen on board cars by the autothermal processes, using suitable catalysts (Ghen-ciu, 2002 Ayabe et ah, 2003 Semelsberger et ah, 2004). Partial oxidation may also be combined with the palladium-catalyst membrane reactors mentioned in section 2.1.1 (Basile et ah, 2001). 

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