Carbon dioxide selectivity

The methane and the carbon dioxide selectivities as well as the selectivities concerning the product fractions C2 to C3 and C4+ with the respective conversion degrees and a-values at 513 K are shown in Table 2.5. 

In addition to the microchannel technology, Battelle has developed a stable, nonpyrophoric, carbon dioxide selective, methanol reforming catalyst. - The catalyst has been demonstrated to be stable in... 

Under stationary conditions, at reaction temperatures between 250 and 260 °C, > 95% conversion and a carbon dioxide selectivity of > 95% were achieved [119],... 

Ammonium carbamates are readily and reversibly produced on reaction of secondary amines with carbon dioxide. In the presence of a ruthenium catalyst precursors such as Ru3(CO)12 [3], (arene)RuCl2(PR3) [4] or Ru(methallyl)2(dppe) [5] (dppe=bis(diphenylphosphino)ethane) complexes, the three-component combination of a secondary amine, a terminal alkyne, and carbon dioxide selectively provides vinylcarbamates resulting from addition of carbamate to the terminal carbon of the triple bond (Scheme 2). 

Using platinum electrodes (167, 238) requires +0.6 V versus SCE to oxidize H2O2. However, this potential precludes selective measurements of uric acid because it is also oxidized at the electrode surface (167). Thus, to improve the selectivity, bienzyme amperometric devices using a redox mediator (hexa-cyanoferrate) have been constructed (239). The enzymes uricase and peroxid ise are immobilized together and the hexacyanoferrate(III) is measured at 0.0 V versus Ag/AgCl. Alternatively, a carbon dioxide selective electrode is used for the detection of the enzymatically liberated CO2 (240, 241). 

Fonong and Rechnitz (1984a) entrapped the enzyme physically with a dialysis membrane at the sensing tip of a carbon dioxide selective electrode. The sensor was suitable for salicylate concentrations in the range 0.04-2.2 mmol/l. 

A combination of sc carbon dioxide and light has been used in flow reactors to make some metal complexes not possible by other methods, for example, cyclopentadi-enylMn(CO)2(H2) and Cr(CO)s(ethylene).179 A man ganese hydride has been added to olefins in carbon dioxide.180 A zeolite in sc carbon dioxide selectively adsorbs 2,7-dimethylnaphthalene so that it can be separated from the desired 2,6-dimethylnaphthalene.181 The latter is oxidized to the dicarboxylic acid for conversion to a highermelting analogue of poly(ethylene terephthalate). A pillared clay made in supercritical carbon dioxide had a higher... 

Methane reduces carbon dioxide selectively to carbon monoxide under hght irradiation in the presence of zirconium oxide [57],... 

The CO gas conversions versus time-on-stream for the SBCR and CSTR systems are displayed in Figure 2. The CO conversion for the enhanced SBCR with level control reached a maximum of 78% after 72 hours time-on-stream (TOS). After this catalyst initiation period, the gas conversion started to steadily decline to about 72% after 192 hours TOS. Carbon dioxide selectivity stabilized to 45% while the methane selectivity averaged 4%. 

Selectivity The mole % carbon dioxide selectivity was found to be very low and was reported to vary only slightly with increasing molar % added H2O in increments 0.27, 0.21, and 0.34. Data were not reported for CO2 at the 50 molar % H2O addition level. The mole %, methane selectivity was reported to decrease significantly in increments of 10.5, 7.1, 5.8, and 4.0, suggesting a favorable shift in the product distribution toward heavier products. 

Selectivity Carbon dioxide selectivity was not reported. In mole %, methane selectivity was reported to decrease favorably from 9.7% without added H2O to 6.7% after H2O addition, while concurrently, the C5+ selectivity was reported to increase from 80.2% to 83.0%. In separate data, the I-olefin to paraffin ratio for C3 was reported to increase with increasing H2O addition (Conditions No H2O at 44.8% conversion, 20% H2O at 34.5% conversion, and 33%H20 at 25.8% conversion) in increments of 2.3,2.3, and 3.8, respectively. 

In mole %, carbon dioxide selectivity was very low and was found to increase only slightly with increasing molar % added H2O from < 0.01 with no added H2O to approximately 0.23 with 25 molar % H2O addition (Table 6). In mole %, methane selectivity decreased in small increments from about 5.6% without H2O addition to approximately 3.8% with 25 molar % H2O addition. Finally, C5+ product selectivity was found to increase slightly after 5 molar % H2O Edition from 89.1% without H2O to 90%. At 8 molar % H2O addition, the C5+ selectivity further increased to about 91.6%, and leveled off at close to 92% above that condition. A detectable increase in the 1-olefin to paraffin ratios in C3 and C4 products was also observed. For C3, the 0/P ratio increased from 0.70 without added water to about 0.76 at 25 molar % H2O addition. For C4, the change observed was from 0.61 to about 0.69. Although there is a slight increase in CO2 selectivity with a decrease in CH4 selectivity, if one considers their sum, it appears to be that there may not be a direct tradeoff between the two products. 

Pt-15%Co/AUOy. In mole %, carbon dioxide selectivity was found to increase with addition of H2O to the feed (Table 8). The effect was more pronounced after reaching the point of catastrophic deactivation, at 28 molar % H2O addition. For example, with no H2O addition, the CO2 selectivity was approximately 0.26%, increasing to 3.8% with 25 molar % H2O addition. By contrast, after co-feeding 28 molar % H2O, the CO2 selectivity jinnped to 11.5%. 

Co/Al203. Carbon dioxide selectivity was also found to increase for the more heavily loaded C0/AI2O3 catalyst, increasing from 0.49% to 1.4% (and increasing to 2.64% with time on stream after that) after addition of 25 molar % H2O. The CO2 selectivity decreased to its previous levels after H2O was switched off. The methane selectivity was found to reversibly decrease somewhat with H2O addition from 7.43% without added H2O to approximately 5.4% with externally added H2O. Methane increased again after H2O was switched off to about 7.1%, while CO2 selectivity receded to previous low levels (-0.41%). Interestingly, before and after H2O addition the sum of the CO2 and CH4 selectivities is very close. It is not clear whether or not there is a direct inverse relationship between the two products in this case. 

Baneijee, R. et al.. Control of pore size and functionality in isoreticular zeolitic im-idazolate frameworks and their carbon dioxide selective capture properties. J. Am. Chem. Soc. 2009,131(11), 3875-3877. 

Promoters also have an important influence on activity. Alkali metal oxides and copper are common promoters, but the formulation depends on the primary metal, iron versus cobalt (Spath and Dayton, 2003). Alkali oxides on cobalt catalysts generally cause activity to drop severely even with very low alkali loadings. C5+ and carbon dioxide selectivity increase while methane and C2-C4 selectivity decrease. In addition, the olefin to paraffin ratio increases. 

Bai H, Ho WSW (2009) New carbon dioxide-selective membranes based on sulfonated polybenzimidazole (SPBI) copolymer matrix for fuel cell applications. Ind Eng Chem Res 48(5) 2344-2354... 

Figure 10,5 Carbon dioxide selectivity of [hmim]ITf2N] on cross-linked nylon - without CO 5% CO O Wppm CO O WOppm CO A...

Figure 10,9 Carbon dioxide selectivity of [H2NC3HemimHTf2N] on cross-linked nylon —> without contaminants 5% CO A 0.9 %...

Figure 10.11 Carbon dioxide selectivity of [hmim][Tf2N] etnd [H2NC3Hemim][Tf2NI on cross-linked nylon with simulated fuel gas...

D. Shekhawat, D. R. Luebke, H. W. Pennline, A review of carbon dioxide selective membranes, A Topical Report, DOE/NETL-2003/1200 December 1, 2003. 

Reuse et al. [16] combined endothermic methanol steam reforming with exothermic methanol combustion in a plate heat exchanger reactor, which was composed of a stack of 40 foils (Figure 24.5). Each foil carried 34 S-shaped channels. Cu/ZnO catalyst from Siid-Chemie (G-66MR) was coated into the channel system for the steam reforming reaction. Cobalt oxide catalyst served for the combustion reaction. The reactor was operated in co-current mode. The steam reformer was operated at a S/C ratio of 1.2. At reaction temperatures between 250 and 260 °C, more than 95% conversion and more than 95% carbon dioxide selectivity were achieved. 

Bravo et al. [14] coated commercial CuO/ZnO/Al203 catalyst into capillaries and achieved 97% conversion at 97% carbon dioxide selectivity at a volume hourly space velocity (VHSV) of 3.91 (h which is a typical value and is comparable... 

Tsue and co-workers have discovered that (NH) -azacalix[n]arenes (n = 5—7) are solid materials able to absorb carbon dioxide selectively [25, 27, 78, 79]. The desolvated polycrystalline powder of azacalix[6]arene, which is obtained after... 

Rao et al. studied ethanol oxidation reaction in a real fuel cell using 40% Pt/C as cathode and Pt/C (20% and 40%), PtRu/C, and PtaSn/C as anodes [51]. Their DBMS sensor consisted on a cylindrical detection volume through which anode outlet flow passes. This volume was separated from the vacuum system of the mass spectrometer by a microporous Teflon membrane (pore size 0.02 (im and thickness of 110 (im) supported by a Teflon disk. For Pt/C and 0.1 M ethanol the carbon dioxide selectivity increased with the reaction temperature. The selectivity was highest at 0.5-0.6V and doubled from 60°C (40%) to 90°C (ca. 85%). At higher potentials the CO2 selectivity decreased and increased the acetaldehyde production. CH3CHO formation also increased at lower temperatures (at 90 °C and low, ethanol concentration was almost absent). At high ethanol concentrations the selectivity to carbon dioxide decreased but this effect was less significant than temperature effect at least for ethanol concentrations lower than 1M. 

Li T, Pan Y, Peinemann K-V, Lai Z. Carbon dioxide selective mixed matrix composite membrane containing ZIF-7 nanofiller. J Membr Sci 2013 425 235-12. 

Carbon-dioxide-selective separation is becoming an important issue in areas such as petrochemical engineering (e.g., CO2 removal from natural gas), environment (e.g., CO2 removal from flue gas), agriculmre (e.g., control of CO2 concentration), and other related industries. Membranes can selectively separate CO2 from industrial processes. 

This chapter reviews the recent developments of two types of facilitated transport membranes (1) supported liquid membranes (SLMs) with strip dispersion and (2) carbon-dioxide-selective polymeric membranes, for environmental, energy, and biochemical applications. 

This chapter reviews and discusses recent advances in carbon-dioxide-selective polymer membranes for hydrogen purification and carbon dioxide removal. 

---