Carbon dioxide hydration and

The carbonato complexes of lanthanides and actinides are of importance with regard to the metal ion speciation in the environment. These are, however, not linked with the enzyme models for carbon dioxide hydration and hence are not dealt with in further detail. 

Johnson, K. S. (1982) Carbon dioxide hydration and dehydration kinetics in seawater. Limnol. Oceanogr. 27, 849-55. 

Reactions in a single phase are said to be homogeneous. Examples of experimentally observed homogeneous reaction rates in aqueous solution for carbon dioxide hydration, and ferrous iron oxidation in water are presented in Tables 9.2 and 9.3, respectively. The overall reaction is presented first, followed by the reaction rate equation and then some suggestions for a reaction mechanism that shows the connection between these two. The reaction mechanism is sometimes a h5T)othesis if it is not based on experimental evidence. 

Pocket, Y. and D. W. Bjorkquist (1977) Stopped-flow studies of carbon dioxide hydration and bicarbonate dehydration in H2O and D2O. Acid-base and metal ion catalysis./. Am. Chem. Soc. 99, 6537-43. 

Carbon dioxide hydration and HCO dehydration are often coupled to rapid processes, particularly transport processes. Thus, almost all organisms contain enzymes, referred to as carbonic anhydrases, that increase the rate of reaction beyond the already reasonable spontaneous... 

Carbon-dioxide hydration and its mechanism in living systems are of fundamental importance for bioinorganic chemistry. In 1932 the existence of an enzyme catalyzing CO2 hydration in red blood cells was established. The enzyme was named carbonic anhydrase (abbreviated CA). In 1939 the enzyme was recognized to contain zinc. Because CO2 is either the starting point for photosynthesis or the endpoint of substrate oxidation, carbonic anhydrases are now known to be ubiquitous, occurring in animals, plants, and several bacteria. Different... 

To prepare gas for evacuation it is necessary to separate the gas and liquid phases and extract or inhibit any components in the gas which are likely to cause pipeline corrosion or blockage. Components which can cause difficulties are water vapour (corrosion, hydrates), heavy hydrocarbons (2-phase flow or wax deposition in pipelines), and contaminants such as carbon dioxide (corrosion) and hydrogen sulphide (corrosion, toxicity). In the case of associated gas, if there is no gas market, gas may have to be flared or re-injected. If significant volumes of associated gas are available it may be worthwhile to extract natural gas liquids (NGLs) before flaring or reinjection. Gas may also have to be treated for gas lifting or for use as a fuel. 

Englezos, P. and S. Hull, Phase Equilibrium Data on Carbon Dioxide Hydrate in the Presence of Electrolytes, Water Soluble Polymers and Montmorillonite , CanJ. Chem. Eng, 72, 887-893 (1994). 

M S. Zhurko, F.V. (2006a). Formation and decomposition of ethane, propane, and carbon dioxide hydrates in silica gel mesopores under high pressure. J. Phys. Chem. B, 110 (39), 19717-19725. 

Kang, S.-P. Lee, H. (2001). Enthalpies of dissociation of clathrate hydrates of carbon dioxide, nitrogen, (carbon dioxide + nitrogen), and (carbon dioxide + nitrogen + tetrahydrofuran). J. Chem. Thermodynamics, 33 (5), 513-521. 

Moudrakovski, I.L. McLaurin, G.E. Ratcliffe, C.I. Ripmeester, J.A. (2004). Methane and Carbon Dioxide Hydrate Formation in Water Droplets Spatially Resolved Measurements from Magnetic Resonance Microimaging. J. Phys. Chem. B, 108, 17591-17595. 

Servio, P. Englezos, P. (2003a). Morphology of methane and carbon dioxide hydrates formed from water droplets. AlChEJ., 49 (1), 269-276. 

Vlahakis, J.G., Chen, H.-S., Suwandi, M.S., Barduhn, A.J., The growth rate of ice crystals properties of carbon dioxide hydrate, a review properties of 51 gas hydrates, Syracuse U. Research and Development report 830, prepared for U S. Department of the Interior, November (1972). 

To illustrate this a model transesterification reaction catalyzed by subtilisin Carls-berg suspended in carbon dioxide, propane, and mixtures of these solvents under pressure has been studied (Decarvalho et al., 1996). To account for solvent effects due to differences in water partitioning between the enzyme and the bulk solvents. Water sorption isotherms were measured for the enzyme in each solvent. Catalytic activity as a function of enzyme hydration was measured, and bell-shaped curves with maxima at the same enzyme hydration (12%) in all the solvents were obtained. The activity maxima were different in all media, being much higher in propane than in either CO2 or the mixtures with 50 and 10% CO2. Considerations based on the solvation ability of the solvents did not offer an explanation for the differences in catalytic activity observed. The results suggest that CO2 has a direct adverse effect on the catalytic activity of subtilisin. 

The best-known gas hydrates are those of ethane, ethylene, propane, and isobulaue. Others include methane and I butene, most of the fluorocarbon refrigerant gases, nitrous oxide, acetylene, vinyl chloride, carbon dioxide, methyl and ethyl chloride, methyl and ethyl bromide, cyclopropane, hydrogen sulfide, methyl mercaptan, and sulfur dioxide. 

Hara et al., 2005). THP, cyclobutanone, and cyclohexane also showed pressure reductions for carbon dioxide hydrate formation (Mooijer-van den Heuvel et al., 2001). THP, cyclobutanone, cyclohexane, and methylcyclohexane all reduced not only the pressure for propane hydrate formation, but also shifted the H-Lw-Lc3H8 line to lower temperature (Mooijer-van den Heuvel et al., 2002). 

Long and Sloan (1996) performed a series of measurements to investigate the site of nucleation for natural gas and carbon dioxide hydrate initiation in a sapphire tube. 

A number of other researchers have also confirmed that nucleation and subsequent growth typically occurs at the water-hydrocarbon interface for methane hydrate (Huo et al., 2001 0stergaard et al., 2001 Taylor, 2006) and carbon dioxide hydrate (Kimuro et al., 1993 Fujioka et al., 1994 Hirai et al., 1995 Mori, 1998). 

Servio and Englezos (2003a) examined the effect of pressure driving force on the morphology of methane and carbon dioxide hydrates grown from water droplets... 

In situ neutron diffraction studies have provided insight into the mechanism of surface conversion of ice particles to carbon dioxide hydrate particles (Henning et al., 2000). The experiments were performed at 230-276 K and around 6.2 MPa. It was proposed from these measurements that after the initial period of fast... 

Coexistence of si and sll carbon dioxide hydrate has been detected from x-ray diffraction measurements during hydrate growth (Staykova and Kuhs, 2003). Similarly, metastable sll hydrate phases were detected using NMR spectroscopy during si xenon hydrate formation (Moudrakovski et al., 2001a) and during si methane/ethane hydrate formation (Bowler et al., 2005 Takeya et al., 2003). 

Rehder et al. (2004) measured the dissociation rates of methane and carbon dioxide hydrates in seawater during a seafloor experiment. The seafloor conditions provided constant temperature and pressure conditions, and enabled heat transfer limitations to be largely eliminated. Hydrate dissociation was caused by differences in concentration of the guest molecule in the hydrate surface and in the bulk solution. In this case, a solubility-controlled boundary layer model (mass transfer limited) was able to predict the dissociation data. The results showed that carbon dioxide hydrate dissociated much more rapidly than methane hydrate due to the higher solubility in water of carbon dioxide compared to methane. 

Anomalous self-preservation stabilizes methane hydrate and carbon dioxide hydrate particles at atmospheric pressure at 242-271 K for up to 2-3 weeks. This phenomenon can have implications for natural gas storage. 

The distribution coefficient method, often called the A -value method, was conceived by Wilcox et al. (1941) and finalized by Carson and Katz (1942). The best methane, ethane, and propane charts are from the latter reference. Updated charts are presented for carbon dioxide (Unruh and Katz, 1949), hydrogen sulfide (Noaker and Katz, 1954), nitrogen (Jhaveri and Robinson, 1965), isobutane (Wu et al., 1976), and n-butane (Poettmann, 1984), as well as for a method that is a function of hydrate structure (Mann et al., 1989). 

Structure identification, quantifying relative cage occupancies. 1II NMR has been used for ethane, propane, and isobutane hydrates (Davidson et al., 1977 Garg et al., 1977), while 2H, 19F, 31P, and 77 Se NMR have been used for several si guests (Collins et al., 1990). 13C cross-polarization and magic angle spinning (MAS) NMR techniques have been applied to study hydrates of carbon dioxide, methane, and propane (Ripmeester and Ratcliffe, 1988, 1999 Wilson et al., 2002 Kini et al., 2004). 

Figure 6.49 Acid, base, and salt inhibition of simple carbon dioxide hydrates.

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