Hydrogen recovery with membranes

Comagliaa et al. [15] reported Pd-Ag membranes using Pt/La-Si catalyst. They conducted WGS reaction for 100 h. The WGS selectivity remained constant at almost 100%. They did simulation studies using 1 D model and concluded that 100% CO conversion and complete hydrogen recovery with the membrane can be achieved. 

Liguori et al. [29] evaluated porous stainless steel supported Pd tubular membranes for more than 4000 h. They investigated H2 permeation measurements for 1200 h. The H2 permeance decreased about 8%. They also observed that H2 permeance decreases in the presence of steam and CO. In the presence of syngas MR was able to achieve up to 76% of CO conversion and 75% of hydrogen recovery with a H2 permeate purity exceeding 97%. 

Schell, W. J., and Houston. C. D., 1985, Refinery Hydrogen Recovery with SEPAREX Membrane Systems, Presented at the National Petroleum Refiners Association Annual Meeting. San Antonio. TX, March 24-26. 

It may be necessary to improve membrane selectivities, so that further purification of the produced hydrogen before re-use in the desulphurisation units can be limited as far as possible. Moreover the membrane reactor can be optimised for various variables, such as H2S conversion, hydrogen recovery, membrane area and temperature. In a techno-economic evaluation combined with advanced process design the impact of different operating parameters on the investment and operating costs should be studied. 

When pure hydrogen is to be used as fuel, the gas must first be recovered from the process stream where it is produced. Membranes may be used for this purpose, and several of the new materials under development may be suitable depending on gas volume to be handled and process conditions like temperature and pressure. Along with the introduction of fuel cells, development of small-scale gas-processing units will follow. Several small, integrated production units with direct conversion of fuel to hydrogen gas combined with a membrane unit for hydrogen recovery are patented [125,126]. 

Hydrogen from the membrane reactor is converted in a gas turbine with a high efficiency. The process efficiency will increase when the hydrogen production (CO conversion) and recovery (on the permeate side) from the membrane reactor is raised. CO2 abatement increases with increasing recovery of carbon components on the retentate side of the membrane. The performance of the reactor can be measured in terms of these three parameters. The boundary conditions for the membrane reactor in the total system depends upon final... 

Gas separation membrane technologies are extensively used in industry. Typical applications include carbon dioxide separation from various gas streams, production of oxygen enriched air, hydrogen recovery from a variety of refinery and petrochemical streams, olefin separation such as ethylene-ethane or propylene-propane mixtures. However, membrane separation methods often do not allow reaching needed levels of performance and selectivity. Polymeric membrane materials with relatively high selectivities used so far show generally low permeabilities, which is referred to as trade-off or upper bound relationship for specific gas pairs [1]. 

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