WGS membrane reactor

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... 

By using palladium or other inorganic H2-selective WGS membrane reactors, many researchers have achieved high CO conversion values beyond the equilibrium ones or close to 100%.35-40 However, the difficulty to prepare thin, flawless, and durable membranes is still the remaining challenge for the commercial application of this type of membrane reactor.41... 

In the present study, a new solid facilitated transport membrane has been prepared by incorporating both fixed and mobile carriers in cross-linked PVA. Based on the membrane transport properties, we have also developed a mathematical model to study the performance of the C02-selective WGS membrane reactor. 

As one of the two common types of membrane modules, the hollow-fiber membrane module has shown excellent mass transfer performance due to its large surface area per unit volume (about 1000-3000ft2/ft3 for gas separation). In the modeling work, the WGS membrane reactor was configured to be a hollow-fiber membrane module with catalyst particles packed inside the fibers. 

Gas permeation results presented in this work, especially above 150 °C, showed that the polymeric membranes that we prepared were capable of applications at high temperatures, such as WGS membrane reactors. The membrane reactor incorporates both C02 removal and WGS reaction to produce high-purity H2.6... 

A reference case for the C02-selective WGS membrane reactor was chosen with the C02/H2 selectivity of 40, the C02 permeability of 4000 Barrer, the inlet sweep-to-feed molar flow rate ratio of 1, the membrane thickness of 5jum, 52,500 hollow libers (a length of 61 cm, an inner diameter of 0.1 cm, and a porous support with a porosity of 50% and a thickness of 30jLon), both inlet feed and sweep temperatures of 140 °C, and the feed and sweep pressures of 3 and latm, respectively. With respect to this case, the effects of C02/H2 selectivity, C02 permeability, sweep-to-feed ratio, inlet feed temperature, inlet sweep temperature, and catalyst activity on the reactor behavior were then investigated. 

Figure 9.22. Schematic diagram of rectangular flat-sheet WGS membrane reactor.

Figure 9.23. The results of CO in the H2 product for the inlet 1% CO feed gas at various flow rates from the rectangular WGS membrane reactor.

The potential of the WGS membrane reactor in CO2 control in IGCC installations has been studied in greater detail [57]. The possibilities of the reactor and demands set for the membranes have been determined by carefully assessing the process integration options, by experimental membrane characterisation and by using a membrane reactor model. 

Fig. 14.12. Layout of an IGCC with CO2 control using a WGS membrane reactor.

Microporous carbon membranes have been developed [59] but their possibilities in high temperature hydrogen separation are still unclear, although it is believed that there are opportunities. Scaling-up of these membranes seems possible from a technical point of view. All these membrane types are potentially suitable for application in the WGS membrane reactor concept, provided their endurance is sufficient. 

Through membrane reactor model calculations it has been shown that membranes can enhance the conversion of a WGS membrane reactor and concurrently separate hydrogen from carbon dioxide. This system can be used to control the release of CO2 to the atmosphere from a IGCC power plant. Through process... 

NETL has been actively investigating through both experimental and computational studies the potential of Pd-Cu alloys because of their potential applicability for gasifier and post-gasifier water-gas shift (WGS) membrane reactors and similar harsh environment hydrogen separation applications. Recent computational studies by Sholl and Alfonso have focused on the prediction of alloy membrane permeability values and the interaction of S with potential membrane materials . Our experimental studies on the permeability of a series Pd-Cu alloys in pure hydrogen and in the presence of H2S have also been recently reported . 

Develop a mathematical model for the novel water-gas-shift (WGS) membrane reactor with a carbon dioxide (C02)-selective membrane to elucidate the effects of system parameters on the reactor and to show the feasibility of achieving hydrogen (H2) enhancement via CO2 removal and carbon monoxide (CO) reduction to 10 parts per million (ppm) or lower from the modeling study. 

Develop a non-isothermal model for the novel WGS membrane reactor by taking material and energy balances and reaction into account. 

We have developed a mathematical model for the countercurrent WGS membrane reactor with a CO2-selective membrane in the hollow-fiber configuration using air as the sweep gas. With this model, we have elucidated the effects of system parameters on the novel WGS membrane reactor for synthesis gases from steam reforming and autothermal reforming. The modeling results show that H2 enhancement via CO2 removal and CO reduction to 10 ppm or lower are achievable. For comparison and the completeness of the modeling work, we have also developed a similar model for the cocurrent WGS membrane reactor. 

We have developed a one-dimensional non-isothermal model for the countercurrent WGS membrane reactor with a C02-selective membrane in the hollow-fiber configuration using air as the sweep gas. Figure 1 shows the schematic of each hollow-fiber membrane with catalyst particles in the reactor. The modeling study of the membrane reactor is based on (1) the CO2 / H2 selectivity and CO2 permeance reported by Ho [1, 2] and (2) low-temperature WGS reaction kinetics for the commercial catalyst copper oxide, zinc oxide, aluminum oxide (CuO/ZnO/ AI2O3) reported by Moe [3] and others [4]. In this modeling study, the model that we have developed has taken into account critical system parameters including temperature, pressure, feed gas flow rate, sweep gas (air) flow rate, CO2 permeance, CO2 /H2 selectivity, CO concentration, CO conversion, H2 purity, H2 recovery, CO2 concentration, membrane area, water (H20)/C0 ratio, and reaction equilibrium. 

A. Khan, P. Chen, P. Boolchand, P. Smimiotis, Modified nano-crystalline ferrites for high-temperature WGS membrane reactor applications, J. Catal. 253 (2008) 91-104. 

Based on the membrane properties, water-gas shift (WGS) membrane reactors are classified into two categories, namely, CO2 selective membrane reactors and H2 selective membrane reactors. In the CO2 selective membrane reactors, CO2 was removed from the catalytic membrane reactor and the reaction mixture becomes H2-rich steam. This may cause over reduction of Fe- or Cu-based catalysts. However, in the H2-selective membrane, CO2 will be present at a higher concentration in the reaction medium, affecting the reaction rate. 

J. Huang, W. S. W. Ho, Effects of system parameters on the performance of C02-selective WGS membrane reactor for fuel cells, J. Chin. Inst. Chem. Eng. 39 (2008) 129-136. 

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