Hydrogen membrane reactor testing

The hydrogen membrane reactor was initially evaluated by measuring the performance of a pure palladium membrane. The permeability of pure palladium under various conditions has been well established and therefore can be used as a baseline test to verify if a new hydrogen membrane reactor is calibrated properly. At 440°C and under a simulated WGS feed stream, the pure palladium membrane exhibited a permeability of 2.0 x 10 mol m s Pa that is consistent with literature reports. 

Carbon molecular sieve membranes Resistant to contaminants Intermediate hydrogen flux and selectivity Intermediate hydrogen flux and selectivity High water permeability Pilot-scale testing in low temperature WGS membrane reactor application Need demonstration of long-term stability and durability in practical applications... 

Steam reformers equipped with the Pd membranes were developed and have been tested in Japan to produce pure hydrogen from city gas.3 Because of the working principle of the membrane reactor, the performance of this type of steam reformer directly depends on hydrogen permeability of the membranes. This has led us to develop membranes with higher hydrogen permeability. 

The unusual interaction of hydrogen with palladium-based membrane materials opens up the possibility of oxidative hydrogen pump for tritium recovery from breeder blankets. The feasibility for this potential commercial application hinges on the hot-fusion and cold-fusion technology under development [Saracco and Specchia, 1994]. At first, Yoshida et al. [1983] suggested membrane separation of this radioactive isotope of hydrogen followed by its oxidation to form water. Subsequently, Hsu and Bauxbaum [1986] and Drioli et al. [1990] successfully tested the concept of combining the separation and reaction steps into a membrane reactor operation. 

Fumeaux et al. [1987] used porous alumina membrane reactors to hydrogenate ethene to form ethane at 200X with Ft or Os as the catalyst impregnated in the alumina membranes. Conversion to ethane was detected but no data was provided. Suzuki [1987] tested porous stainless steel and nickel-aluminum alloys as membrane reactors for hydrogenation reactions. Hydrogenation of 2-butenc with stainless steel as the membrane... 

Test a bench-scale membrane reactor for carrying out shift conversion and hydrogen separation. 

A Phase II plan has been defined. The sequential reaetor proeess has been selected as a preferred proeess option. The first objective of Phase II is to develop a low-eost HTM (based on Pd alloy) with high hydrogen flux and tolerance for syngas components and thermal cycling. The next task will be to design and test a bench-scale membrane reactor... 

Tosti et al. tested Pd-Ag membrane reactor for 12 months for H2 permeation [14]. Excellent stability was observed for 12 months of operation. In fact, the complete hydrogen selectivity and none failure (formation of cracks, holes) were observed. They proposed that the reliability is a result of both the tube manufacturing procedure and the reactor design configuration (finger-like). Figure 6.11 shows the picture of membrane reactor before and after the 12 months of operation. 

Similar TS-1 films have been applied for phenol hydroxyl-ation reaction to dihydroxybenzenes (hydroquinone and catechol) [354] and catalytic oxidation of styrene to benzaldehyde and phenylacetaldehyde [355] with hydrogen peroxide as oxidant in batch-type membrane reactors. The dihydroxybenzenes and phenylacetaldehyde selectivity values increased with in-framework Ti content. In order to reduce the TS-1 membrane costs, Chen et al. [356] have successMly synthesized TS-1 on mullite tubes by replacing TPAOH with TPABr/EtjNH system (4% of the initial cost). The catalytic activity was tested in the probe reaction of isopropyl alcohol oxidation with hydrogen peroxide under pervaporation condition at 60°C. In general, future work on TS-1 film catalysts is required to improve mass transfer resistances and reaction conversion without compromising selectivity. 

For membrane reactors, many cmcial phenomena have to be included, as membrane permeability mechanism and hydrogen flux, reactions kinetics, heat and mass transport inside the reactor and from the external to the reactor. Therefore, a proper simulation certainly requires a deep study and a careful evaluation and definition of the system. The model developers have to work in a strict connection with test drivers, since reliable model parameters and coefficients definition is crucial designers can address reactors experimentation clarifying which information from test-benches are required. At the same time, a proper model development allows the number of experimental tests to be reduced drastically to those ones required for a complete reactor vahdation. 

A large number of hydrogenation and dehydrogenation reactions were tested in the early studies of dense-metal membrane reactors (see listing in Shu et al. [34], Hsieh [35], and Gryaznov and Orekhova [36]). Many works tested the dehydrogenation of cyclohexane to benzene as a model reaction since it can be carried out at low temperature with no side reactions and no deactivation a conversion of 99.5% was achieved with a palladium membrane, compared with 18.7% at equilibrium, at 200°C [31]. 

Recently, the first membrane reactor pilot plant has been realized. A staged membrane reactor for natural gas steam reforming, also called reformer and membrane modules (RMM) test plant, having the capacity of 20 Nm /h of hydrogen, has been designed and constructed to investigate at an industrial scale level the performance of such innovative architecture. 

Forced-flow polymeric membrane reactors have also been successfully tested for the oxidation of benzene to phenol by Molinari and co-workers. Mixed-matrix membranes consisting of CuO powder or CuO nanoparti-cles dispersed in PVDF were prepared by the inversion phase method, by using dimethylacetamide (DMAc), dimethylformamide (DMF) or N-methyl-2-pyrrolidone (NMP) as solvents and water as non-solvent. The membranes were assembled in a ultraliltration unit to which a solution of acetonitrile/benzene and hydrogen peroxide (HjOj) was fed. The best results were obtained with a PVDF membrane hlled with CuO nanoparticles, with a phenol yield of 2.3% at 35°C and a contact time of 19.4 s in a single pass, in the presence of ascorbic acid. 

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