Interface water-carbon dioxide

The yeast cell wall confers certain important properties from the point of view of brewing. Thus, some brewing yeasts rise to the surface of the fermenting wort towards the end of fermentation (top yeasts) while others sediment (bottom yeasts). This distinction is a reflection of differences in composition of the yeast cell wall, although the chemical nature of these differences is not known. The ability of top yeasts to accumulate at the liquid-air interface can be demonstrated in water [51]. Shaken in a very clean tube, the yeast persists so well at the interface that what appears to be a type of skin is visible at the meniscus. Bottom yeasts fail to form such a skin and this simple test is therefore valuable in practice for distinguishing between top and bottom yeasts. Other factors are undoubtedly involved in head-formation such as the transport of yeast clusters to the surface on the interfaces of carbon dioxide bubbles. Chains of cells or loosely-packed floes are particularly favoured by such flotation. 

Foam formation in a boiler is primarily a surface active phenomena, whereby a discontinuous gaseous phase of steam, carbon dioxide, and other gas bubbles is dispersed in a continuous liquid phase of BW. Because the largest component of the foam is usually gas, the bubbles generally are separated only by a thin, liquid film composed of several layers of molecules that can slide over each other to provide considerable elasticity. Foaming occurs when these bubbles arrive at a steam-water interface at a rate faster than that at which they can collapse or decay into steam vapor. 

Carbon dioxide is absorbed in water from a 25 per cent mixture in nitrogen. How will its absorption rate compare with that from a mixture containing 35 per cent carbon dioxide, 40 per cent hydrogen and 25 per cent nitrogen It may be assumed that the gas-film resistance is controlling, that the partial pressure of carbon dioxide, at the gas-liquid interface is negligible and that the two-lilm theory is applicable, with the gan film thickness the same in the two cases. 

Yoon el al. [112] reported an all-solid-state sensor for blood analysis. The sensor consists of a set of ion-selective membranes for the measurement of H+, K+, Na+, Ca2+, and Cl. The metal electrodes were patterned on a ceramic substrate and covered with a layer of solvent-processible polyurethane (PU) membrane. However, the pH measurement was reported to suffer severe unstable drift due to the permeation of water vapor and carbon dioxide through the membrane to the membrane-electrode interface. For conducting polymer-modified electrodes, the adhesion of conducting polymer to the membrane has been improved by introducing an adhesion layer. For example, polypyrrole (PPy) to membrane adhesion is improved by using an adhesion layer, such as Nafion [60] or a composite of PPy and Nafion [117],... 

The possible existence of an interface resistance in mass transfer has been examined by Raimondi and Toor(12) who absorbed carbon dioxide into a laminar jet of water with a flat velocity profile, using contact times down to 1 ms. They found that the rate of absorption was not more than 4 per cent less than that predicted on the assumption of instantaneous saturation of the surface layers of liquid. Thus, the effects of interfacial resistance could not have been significant. When the jet was formed at the outlet of a long capillary tube so that a parabolic velocity profile was established, absorption rates were lower than predicted because of the reduced surface velocity. The presence of surface-active agents appeared to cause an interfacial resistance, although this effect is probably attributable to a modification of the hydrodynamic pattern. 

Uchida, T. Ebinuma, T. Kawabata, J. Narita, H. (1999b). Microscopic observations of formation processes of clathrate-hydrate films at an interface between water and carbon dioxide. J. Crystal Growth, 204 (3), 348-356. 

Carbon dioxide has a source/sink rate of - A C, where C is the water concentration of carbon dioxide. The concentration profile in the concentration boundary layer would be steeper near the interface, as illustrated in Figure E8.7.1. 

Carbon dioxide mainly exits the oceans at the interface with the atmosphere. Warm surface waters easily release carbon dioxide into the atmosphere. When warm waters rise to the surface, mainly near the equator, carbon dioxide is transferred from the water to the air. Because of this, the sea is a source of carbon for the carbon cycle as well as a carbon sink. 

Thus, when deahng with gas transfer in aerobic fermentors, it is important to consider only the resistance at the gas-liquid interface, usually at the surface of gas bubbles. As the solubihty of oxygen in water is relatively low (cf. Section 6.2 and Table 6.1), we can neglect the gas-phase resistance when dealing with oxygen absorption into the aqueous media, and consider only the liquid film mass transfer coefficient Aj and the volumetric coefficient k a, which are practically equal to and K a, respectively. Although carbon dioxide is considerably more soluble in water than oxygen, we can also consider that the liquid film resistance will control the rate of carbon dioxide desorption from the aqueous media. 

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). 

House W.A., Howard J.R. and Skirrow G. (1984) Kinetics of carbon dioxide transfer across the air/water interface. Faraday Discuss. Chem. Soc. 77, 33-46. 

Lipases are the most common enzymes used in non conventional media like organic solvents and supercritical carbon dioxide. Lipases usually hydrolyse fats into fatty acids and glycerol. The special property of lipases is their ability to act at the interface between water and oil. In these experiments lipase (EC 3.1.1.34) from Rhizopus arrhizus (Boehringer Mannheim) was used to investigate the effects of lipase under hydrostatic pressure. The analysed reaction was the hydrolysis of p-Nitrophenyllaureate at different concentrations at 35 °C. The dependance of the kinetic constants between 1 bar and 3000 bar is presented in table 2. Like the thermophilic GDH at 1000 bar lipase is activated under pressure as well. The initial reaction rate increases by a factor of 1.5 at 1000 bar compared to the initial reaction rate at ambient... 

Supercritical fluids are unique solvents and reaction media due to liquid like density and gas like viscosity. Diffusion is not limited by any interface. Under ambient conditions hydrocarbons and water are nearly unmiscible. Phase equilibrium changes significantly in the supercritical region of water (Tc = 647 K, pc = 22.1 MPa). Hydrocarbons and supercritical water become miscible at any ratio, whereas supercritical carbon dioxide and hydrocarbons still have a broad miscibility gap [4],... 

The balance between calcium carbonate production and dissolution is the major pH buffering mechanism of seawater over periods of time at least on the order of thousands of years ( ). The atmospheric carbon dioxide reservoir is less than 2 percent the size of the seawater reservoir ( ) and there is active exchange between these two reservoirs across the air-water interface. Consequently, the carbon dioxide content of the atmosphere and accumulation of calcium carbonate in the deep oceans are closely coupled. 

---