Sorption-enhanced membranes

Below, we first briefly describe conventional hydrogen production. Then the combination of hydrogen production and CCS is described. Finally, we elaborate on two of the technologies for more efficient hydrogen production with C02 capture that are currently in the R D phase hydrogen membrane reactors and C02 sorption enhanced reactors. 

For combined hydrogen production and C02 capture several novel technologies are in development, most of them for the application in a pre-combustion C02 capture combined cycle. The main focus is to reduce the efficiency penalties and other associated costs of CO2 capture. The most important technologies in the R D phase, membrane reactors and sorption-enhanced reactors, are described below, with special attention paid to the catalytic aspects. 

The following catalytic and material challenges can be extracted from an overview of the literature on membrane and sorption-enhanced reforming ... 

There is a need for low-cost methane steam reforming catalysts that are active at low temperature and resistant to coke formation under membrane reactor conditions. Low-cost (Ni-based) catalysts are also needed that can withstand regeneration conditions in a sorption-enhanced reformer. 

In this section the methods developed in the previous section will be applied to analyze the dynamic behavior of integrated reaction separation processes. Emphasis is placed on reactive distillation and reactive chromatography. Finally, possible applications to other integrated reaction separation processes including membrane reactors and sorption-enhanced reaction processes will be briefly discussed. More details about reactive distillation processes were provided in Ref. [39]. For chromatographic reactors the reader should refer to Chapter 6 of this book, for sorption-enhanced reaction processes to Chapter 7, and for membrane reactors to Chapter 12. 

The theory presented above also applies to other integrated reaction separation processes which fall into the class of systems illustrated in Fig. 5.1. Typical examples are sorption-enhanced gas phase reactions (as described in Chapter 7) or membrane reactors (as described in Chapter 12). 

As in reactive distillation and reactive chromatography, many sorption-enhanced reaction processes are controlled by phase equilibrium in addition to reaction equilibrium. The situation is different for membrane reactors, where phase equilibrium between the phases adjacent to the membrane is often trivial and the process is... 

Steam reforming of methane Natural gas + Water Heat (Medium temp.) [Membrane or sorption enhanced reaction]] SFR, SCWR MHI-ARTEC-TGC-NSA Tokyo Tech... 

In recent years, new concepts to produce hydrogen by methane SR have been proposed to improve the performance in terms of capital costs reducing with respect to the conventional process. In particular, different forms of in situ hydrogen separation, coupled to reaction system, have been studied to improve reactant conversion and/or product selectivity by shifting of thermodynamic positions of reversible reactions towards a more favourable equilibrium of the overall reaction under conventional conditions, even at lower temperatures. Several membrane reactors have been investigated for methane SR in particular based on thin palladium membranes [14]. More recently, the sorption-enhanced steam methane reforming (Se-SMR) has been proposed as innovative method able to separate CO2 in situ by addition of selective sorbents and simultaneously enhance the reforming reaction [15]. 

Barelli, L., G. Bidini, R Gallorini, and S. Servili. 2008. Hydrogen production through sorption-enhanced steam methane reforming and membrane technology A review. Energy 33 554 70. 

An increased electrolyte concentration within the membrane may enhance accessibility and improve rates of proton sorption and permeation though the membrane. Maintenance of constant electrolyte concentration may be desirable for obtaining stable proton conductivity, and replenishment of vaporized or leached electrolyte may be continuously performed during operation. On a morphological level, dynamic fluctuations between electrolyte domains may provide conductive pathways through the polymeric continuous phase. Thus, the ability of the polymeric phase to mechanically comply with the anodic proton flux may enable proton percolation though the membrane and enhance conductivity. 

Sorption-enhanced polymer membranes are beneficial to obtain superior permeability as well as advanced selectivity especially for carbon dioxide, hydrocarbons and VOCs because condensable gas molecules are easier to be adsorbed on the polymer surface." Recent research has focused on incorporating ethylene oxide into a polymer backbone, which has unique interaction with quadruple momentum of carbon dioxide poly(ethylene oxide) (PEO), cross-linked PEO, PEO-based block copolymers such as poly(ethylene oxide-Z)-amide) (Pebax), poly(ethylene oxide- -butylene terephthalate) (PEO-6-PBT)." ... 

It may also be economical to remove the inhibitory product directly from the ongoing fermentation by extraction, membranes, or sorption. The use of sorption with simultaneous fermentation and separation for succinic acid has not been investigated. Separation has been used to enhance other organic acid fermentations through in situ separation or separation from a recycled side stream. Solid sorbents have been added directly to batch fermentations (18,19). Seevarantnam et al. (20) tested a sorbent in the solvent phase to enhance recovery of lactic acid from free cell batch culture. A sorption column was also used to remove lactate from a recycled side stream in a free-cell continuously stirred tank reactor (21). Continuous sorption for in situ separation in a biparticle fermentor was successful in enhancing the production of lactic acid (16,22). Recovery in this system was tested with hot water (16). 

Transcellular transport Sorption promoters can be used to enhance the transcellular transport in the intestine, including bile salts and fatty acid esters. They tend to fluidize the lipid bilayer and enhance drug permeation across the membrane. 

The implication of the theoretical considerations given above is that the permeation can be increased in cases of low adsorption amd sticking coefficients by application of a mesoporous top layer with better sorption properties on top of the microporons membranes. Selective sorption should then also lead to an enhanced separation factor (see Eq. (9.71)). Indications for this effect are reported for dense membranes by Deng et al. [106] and for microporous silica membranes by Nair [107]. 

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