Hydrogen recovery performance

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]. 

The system design must address the performance target to be readied (such as a particular conversion value or hydrogen recovery, etc.). For example, if both conversion and separation must be the highest possible, then a large membrane area is needed. On the contrary, if lower yields are acceptable, lower membrane areas are required, but the retentate stream needs to be further treated. A comparison between the costs assodated with the two cases leads, usually, to the final design. 

The hydrogen produced at the reaction device exit is recovered in a separation unit downstream (Fig. 9.15). In the study performed, the two reactors plus the separator were compared in terms of capital and operating costs, with a Pd-based membrane reactor in which the pure hydrogen is recovered at the permeate side (Fig. 9.16). Table 9.8 shows the main operating conditions of the industrial plant considered. The membrane reactor unit was designed in order to operate with industrial quantities and to achieve the same industrial hydrogen recovery. An integrated membrane system in which the feed stream is first fed to a Pd-based... 

Using the membrane performance listed in Table 7.2, the required membrane surface areas for the two modules have been calculated for the OA scheme, adopting a Hydrogen Recovery Factor (HRF) of 70%. The effect of inlet pressure and H2 permeance on the membrane smface area is reported in Fig. 7.6 for the first and second modules. The membrane surface area required to achieve the fixed HRF under the conditions dictated by the heat and material balance was calculated using a one-dimensional, steady-state model assuming a steam sweeping ratio of 50%. 

Commercial membranes for CO2 removal are polymer based, and the materials of choice are cellulose acetate, polyimides, polyamides, polysulfone, polycarbonates, and polyeth-erimide [12]. The most tested and used material is cellulose acetate, although polyimide has also some potential in certain CO2 removal applications. The properties of polyimides and other polymers can be modified to enhance the performance of the membrane. For instance, polyimide membranes were initially used for hydrogen recovery, but they were then modified for CO2 removal [13]. Cellulose acetate membranes were initially developed for reverse osmosis [14], and now they are the most popular CO2 removal membrane. To overcome state-of-the-art membranes for CO2 separation, new polymers, copolymers, block copolymers, blends and nanocomposites (mixed matrix membranes) have been developed [15-22]. However, many of them have failed during application because of different reasons (expensive materials, weak mechanical and chemical stability, etc.). 

The reforming performance is plotted in terms of the product hydrogen flux, the hydrogen recovery and the conversion. The conversion is much... 

To evaluate RMM performance regarding methane conversion and hydrogen recovery, it is necessary to measure the content of the output stream from the reformer and membrane modules. The composition of the reformed gas and retentate streams was detected by an ABB analyzer. CHi, CO and CO2 concentrations were measured by the online non-dispersive infrared (NDIR) multiple analyzer, ABB URAS14. H2 was analyzed using the thermal conductivity detector ABB Caldos 17. A Perkin Ehner Gas Chromatographer unit (CLARUS 500) was used to analyze the composition of the permeate streams. 

The long Ufetime of a Pd composite membrane was also studied by Dittmar et al. (2013) at different temperature, showing that the membrane performance was stable at 923 K for a long time. During this period, the MSR reaction was performed and 60% methane conversion and 70% hydrogen recovery were attained. 

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