CO2 selectivity

We have been studying the novel process for CO2 separation named membrane/absorption hybrid method. The advantages of this process are that high gas permeance and selectivity were obtained. The concept of this process is shown in Fig. 1. Both feed gas and absorbent solution are supplied to the inside of hollow fibers. While Ae liquid flows upward inside the hollow fibers, absorbent solution absorbs CO2 selectively and it becomes a rich solution. Most of rich solution permeates the membrane to the permeate side maintained at reduced pressure, where it liberated CO2 to become a lean solution. Compared to a conventional gas absorption... 

CO2, selected Ci -C2 compounds Acetate fermentation CH3COOH CH4 + CO2 CO2 reduction C02 + 4H2 CH4 + 2H20... 

The major difference between copper and other transition metals is the CO2 selectivity. Several investigations [120, 123, 124] showed that CO concentrations up to 25% could be achieved during CSRM, a result comparable to the decomposition route. The influence of the support was demonstrated to be significant. The high CO concentrations obtained for these transition metals make them highly unsuitable for fuel cell applications. 

Reaction temperature also strongly influences the activity and selectivity of the CPOM. It has been often observed that the conversion of methanol increases with temperature, whereas the CO2 selectivity decreases. 

CO2 Selective Ceramic Membrane for Water-Cas-Shift Reaction with Simultaneous Recovery of CO2. This project aims to develop a high temperature C02-selective membrane to enhance... 

We report here on the structure and gas transport properties of asymmetric membranes produced by the LB deposition of a polymeric lipid on porous supports. The effects of temperature on the structure and gas transport is described. The selectivity of CO2 over N2 permeation through the LB polymer films is determined. The polymerized lipid used in this study contains tertiary amines which may influence the CO2 selectivity over N2. The long term objective of our work is to understand how structure and chemistry of ultrathin films influence the gas permeation. 

The very high H2/CO2 permselectivity for the 825°C fired standard silica membrane is remarkable. It is even more remarkable that the H2/CH4 selectivity is lower, which is contrary to the common observation that the H2/CO2 selectivity is lower than the H2/CH4 selectivity. 

The role of gold in the Pd/Au/K acetate catalysts is to stabilize the size of Pd crystallites and avoid sintering. The role of potassium acetate is to maintain the catalyst activity and decrease CO2 selectivity. Potassium acetate favours a strong adsorption of acetic acid on palladium, lowering the barrier to vinyl acetate formation. Gold by itself is inactive in the catalysis of vinyl acetate. Pd only catalysts produce vinyl acetate at much lower rates than the Pd/Au/K catalyst system and their activity decays rapidly. 

On iron, CO2 is an important secondary product (45,46) as was shown by the results of a classical experiment. The CO2 selectivity on a potassium-promoted iron catalyst was found to approach zero at infinitesimally short contact times (low inverse space velocities), a pattern that is characteristic of a secondary product (Figure 1). In the absence of potassium, a fraction of the CO2 may be a primary product. 

The metal ions (e.g., radioactive wastes) are com-plexed by negatively-charged ligands and rendered neutral. Then, supercritical CO2 selectively dissolves them it has a critical temperature of 31.1 °C and a critical pressure of 73.8 bar. Nonetheless, many extractions can be performed well below this pressure. 

The lower CO2 selectivity observed on small pellets (Table V) apparently reflects the transport-limited removal of water, a product of the FT synthesis. CO2 selectivity also increases with increasing site density, CO conversion, and water concentration in the catalyst bed this suggests that CO2 forms in secondary water-gas shift reactions that become significant as intrapellet water fugacities rise because of transport restrictions. Transport rates of CO and H2O in hydrocarbon liquids are qualitatively similar and the reaction stoichiometry requires that one water molecule must be removed... 

Due to the environmental focus on CO2 emissions around the world, there are numerous CO2 selective materials under development—several hundred polymers are reported (articles and patents). The main challenge for bringing these membranes into commercialization is to document durability over time (maintaining separation properties) during real operating conditions. 

Catalysts Conv. of CO2 (% ) Selectivity (Vo) Distribution of hvdrocarbonst% ) Ratio of olefins ( % Yield of 1 i-Ca... 

It has been shovm that membranes can enhance the conversion of a water-gas shift membrane reactor and concurrently separate hydrogen from carbon dioxide. The efficiency of CO2 control using the membrane reactor with a H2/CO2 selectivity of 15 is significantly higher compared to a conventioncd technique (i.e. wet washing with a sorbent). It is not necessary to exceed a selectivity of approximately 40 for H2/CO2 for the process under consideration, because further increase in reactor performance seems marginal. Enlargement of the permeation is an important aspect on the other hand, so that the total surface area necessary for the full-scale application can be reduced. 

For the Au/Ce02 catalysts, the CO2 selectivity increased substantially with increasing reaction temperature, whereas the ethylene oxide selectivity decreased (see Table 9.2). The Au on Ce02 prepared by the sol-gel/impregnation method was found to favor the total oxidation reaction over the epoxidation reaction as compared to that prepared by the single-step sol-gel method. This is because the impregnation method provides more active Au reaction sites than single-step... 

Fuel ceUs membrane systems are present not only as proton-exchange membrane (PEM), which aUows protons to pass from the anode to the cathode, to combine with oxygen and electrons producing water, but also for the production and purification of the H2 (see Fig. 9.4). This system provides a CO2-selective membrane process for the purification and water-gas shift reaction of a reformed gas, generated from on-board reforming of a fuel, for example, hydrocarbon, gasoline, diesel, methanol, or natural gas, to hydrogen for fuel ceU vehicles [74]. 

Ho WSW, CO2 selective membrane process and system for reforming a fuel to hydrogen for a fuel cell, USP No 6,579,331. BI. 

Holzinger, M., Maier, J. and Sitte, W. (1996) Fast CO2-selective potentiometric sensor with open reference electrode. Solid State Ionics, 86-88, 1055-62. 

Figure 3. Methanol and Oj conversions (a) and Hj and CO2 selectivities (b) over a Cu/ZnO catalyst at 495 K.

The formation of nonselective oxidation products seems to be favoured at lower contact times and higher temperature and higher ethanol concentration (since these conditions showed higher CO2 selectivity). 

T.M. Nenoflf F. Bonhomme "Zeolite Membranes with High CO2 Selectivity". US Patent submitted to Sandia National Laboratories, August 2002. 

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. 

Figure 1. Schematic of a Countercurrent CO2 Selective Membrane Reactor Containing Catalyst Particles...

Table 2. Average ethylene conversion CO2, selectivity and fluorocarbons distribution over 5 pulses.

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