Water-Reduced Cases

Another method of combating hydrate formation is to remove the water from the stream. No water, no hydrate - it is that simple. 

The mixture requires a certain water content in order to fall on the curves shown in figures 5.1 and 5.2. If the water content is reduced below this level, then the hydrate temperature, at a given pressure, is reduced. Reducing the water content is a common method for combating hydrate formation in acid gas injection systems. 

If the stream has a sufficient amount of water (greater than about 500 ppm), then at 3447 kPa a hydrate will form at about 8°C (see figure 5.1). However, if the water content is reduced to 250 ppm (190 mg/Sm3), the hydrate does not form until about 2.5°C if the fluid is a gas and about -19°C if the fluid is a liquid. 

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A water-reducible coating or resin is one that is diluted with water before use. Water-reducible alkyds give comparable drying performance to solvent-bome alkyds. However, they are not widely used because film properties tend to be poorer than those of solvent-bome alkyds, especially in air-dry systems (26). This is pardy because of alcoholysis of the alkyd by primary alcohols such as 1-butanol [71-36-3] C H qO, a common solvent in water-reducible alkyds (27,28) secondary alcohols such as 2-butanol [78-92-2] C qH O, minimize this problem (27). In any case, the slow loss of amine or ammonia leads to short-term high sensitivity to water. Even in the fully dry films, the presence of unreacted carboxyHc acid groups leads to films having comparatively poor water resistance limiting their usehilness. 

However, an evaluation of the observed (overall) rate constants as a function of the water concentration (5 to 25 % in acetonitrile) does not yield constant values for ki and k2/k i. This result can be tentatively explained as due to changes in the water structure. Arnett et al. (1977) have found that bulk water has an H-bond acceptor capacity towards pyridinium ions about twice that of monomeric water and twice as strong an H-bond donor property towards pyridines. In the present case this should lead to an increase in the N — H stretching frequency in the o-complex (H-acceptor effect) and possibly to increased stabilization of the incipient triazene compound (H-donor effect). Water reduces the ion pairing of the diazonium salt and therefore increases its reactivity (Penton and Zollinger, 1971 Hashida et al., 1974 Juri and Bartsch, 1980), resulting in an increase in the rate of formation of the o-complex (ik ). 

The accelerating water-reducing admixtures are simple blends of either calcium chloride, nitrate, thiocyanate or formate with a lignosulfonate or a hydroxycarboxylic acid salt. In some cases it may not possible to obtain a completely sediment-free solution and agitation of store tanks may be necessary. Typically, a mixture of approximately 33% calcium chloride and 4% calcium lignosulfonate by weight in water would be used. 

Air-entraining water-reducing admixtures containing lignosulfonates can be based on impure lignosulfonate raw materials, as stated earlier, where only 2-3% additional air is required. However, this air may not be of the amount, type, and stability required, therefore additions of surfactants are made. Several different types can be used but in the majority of cases they are based on alkyl-aryl sulfonates (e. g. sodium dodecyl benzene sulfonate) or fatty-acid soaps (e.g. the sodium salt of tail-oil fatty acids). Additions of these types will allow incorporation of sufficient stable air of the correct bubble size to meet durability requirements under freeze-thaw conditions. 

When a normal, accelerating, or retarding water-reducing admixture is utilized to increase the workability of a concrete mix by direct addition, it would be reasonable to assume that the extent of the effect would be markedly affected by changes in mix design parameters such as cement content, aggregate size, shape and grading, and the water-cement ratio. A study of many hundreds of results, however, indicates that this is not the case and Fig. 

In the case of lignosulfonate water-reducing agents, the effectiveness in reducing the water-cement ratio diminishes with an increase in either the the C3A or alkali content. In a comparative experiment with three... 

Dampproofing admixtures are formulated to affect the properties of the hardened concrete, and not those of concrete in its plastic state. In the case of materials based solely on calcium and aluminum stearates, stearic acid in solid or emulsion form, bitumens and hydrocarbon resins, there will be no effect on the properties of the plastic concrete with regard to air content, workability, mix design parameters, etc. When water-reducing admixtures or accelerators are included in the formulation, the effect on the concrete will be a function of the particular type of material used (see relevant section). The wax emulsions do appear to have an effect on the properties of the plastic concrete because of the lubrication effect of the very small... 

Passage of 1.0 mol of electrons (one faraday, 96,485 A s) will produce 1.0 mol of oxidation or reduction—in this case, 1.0 mol of Cl- converted to 0.5 mol of Cl2, and 1.0 mol of water reduced to 1.0 mol of OH- plus 0.5 mol of H2. Thermodynamically, the electrical potential required to do this is given by the difference in standard electrode potentials (Chapter 15 and Appendix D) for the anode and cathode processes, but there is also an additional voltage or overpotential that originates in kinetic barriers within these multistep gas-evolving electrode processes. The overpotential can be minimized by catalyzing the electrode reactions in the case of chlorine evolution, this can be done by coating the anode with ruthenium dioxide. 

Grant and Higuchi (1990) commented on the solution behavior of solvates in their book on the solubility of organic compounds. The hydrated form will be more stable (less soluble) than the anhydrate in the general case. When the solvate is formed from a nonaqueous solvent that is miscibli in water, the free energy of solution of the solvent into the water reduces the activity of water and increases the apparent solubility of the solvate. An example is cited in which caffeine hydrate is less soluble in water than the anhydrate, but the solubility order reverses in ethanol. 

The fact that the water-reducing effects of superplasticizers are similar to those of conventional water reducers used in similar concentrations suggests that the modes of action are similar, and that the essential difference is that the properties that limit the concentrations in which conventional water reducers can be used are weaker or absent in superplastizers. These properties comprise retardation, air entrainment and in some cases flash setting. 

Graneli, E., and Graneli, W. (1999). Reducing nitrogen transport to Swedish coastal waters—A case study. In Marine Research and Policy Interface. Links, Interdisciplinary Co-operation, Availability of Results, Case Studies (Cornaert, M., and Lipiatou, E., eds.). Third European Marine Science and Technology Conference, Luxembourg, pp. 21—34. 

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