Hydration rate

Catacarb process An extraction process used to remove carbon dioxide from process gases by scrubbing the hot gases with potassium carbonate solution containing additives which increase the hydration rate of the gas in the solution. The Vetrocoke process is similar. See Benfield process. 

The stmctures of STP-I and -II differ primarily in the ionic coordination of cations. In STP-II all sodium ions are octahedraHy coordinated by oxygen, whereas in STP-I some sodium ions are surrounded by only four oxygen atoms. In STP-II a distinct sheet-like arrangement occurs. The faster hydration rates are attributed to these properties. 

The hydration rate of sodium tripolyphosphate to its stable hexahydrate, Na P O Q 6H20, directly affects detergent processing and product properties. The proportion of STP-I (fast-hydrating form) and STP-II (slow-hydrating form) in commercial sodium tripolyphosphate is controUed by the time—temperature profile during calcination. In most processes, a final product temperature of near 450°C results in a product containing about 30%... 

According to this mechanism, the reaction rate is proportional to the concentration of hydronium ion and is independent of the associated anion, ie, rate = / [CH3Hg][H3 0 ]. However, the acid anion may play a marked role in hydration rate, eg, phosphomolybdate and phosphotungstate anions exhibit hydration rates two or three times that of sulfate or phosphate (78). Association of the polyacid anion with the propyl carbonium ion is suggested. Protonation of propylene occurs more readily than that of ethylene as a result of the formation of a more stable secondary carbonium ion. Thus higher conversions are achieved in propylene hydration. 

There was studied dependence of sorption rate values of microamounts high listed elements from time of their contact with sorbents, pH media and means of equilibrium concentration. It is shown that owing to exchange of sorbents surface characteristics, its hydrating rate value and heterogeneity of sorbate and hydrolyzed forms of metals investigated interaction with surface can simultaneously proceed on several mechanisms. The contributions of various factors into adsorption of elements-analogues are depended from sorption conditions and nature of sorbent surface. 

Hydration of compounds 2, 3, 4, 5 was found to be first order both in substrate and in hydronium ion (4-10). Furthermore, a careful kinetic study of compounds 2c-g and the sulfur analog 4 revealed that the hydration rate at constant ionic strength was dependent on the buffer concentration and hence was general acid catalyzed. 

Stevenson, C. M., J. J. Mazer, and B. E. Scheetz (1992), Laboratory obsidian hydration rates Theory, method, and application, in Shackley, S. (ed.), Method and Theory in Archaeological Volcanic Glass Studies, Plenum, New York, pp. 181-204. 

Plan mol enzyme/L => (1) molecules enzyme/L => (2) hydration rate (molecules C02/L-s)... 

The rate of hydration of obsidian, which is diffusion limited, forms the basis for Obsidian Hydration Dating [f]. A date refers to "the time a fresh surface of obsidian was created, either naturally or by man.. ..Laboratory and field studies have confirmed that the time indicated by a hydrated layer is proportional to the thickness squared of the layer. The hydration rate is independent of the relative humidity of the environment, but the chemical composition of the obsidians affect the rate by orders of magnitude. Si02 increases the rate, whereas CaO, MgO, and H20 decrease it. A 6 - 8 °C temperature increase causes doubling of the rate." The method is quite inexpensive, and it is applicable to ages between a few hundred and several million years. 

The initial hydration rate v and the equilibrium hydration amount were obtained as parameters reflecting the hydration behavior of LB films (see Figure 8). Temperature dependencies of the hydration behavior (v0and W ) of 10 layers of DMPE (Tc = 49 °C) LB films are shown in Figure 9. Large W and v0 values were observed only around the phase transition temperature (7C) of DMPE membranes. Thus, DMPE LB films were hydrated only near the Tc, but not in the solid state below the Tc and in the fluid state above the Tc. This indicates that the... 

Figure 9 Effect of temperatures on the hydration amount (O) and the initial hydration rate v0 (Z of 10 layers of DMPE LB films...

Figure 10 shows effects of the membrane thickness of DMPE LB films on the hydration behavior at three different temperatures. The hydration amount (W ) increased linearly with increasing the number of layers of LB films only around Tc, but not temperatures below and above Tc. This indicates that water molecules deeply penetrate into LB layers around Tc. The hydration rate (v<,) was very large and hardly depended on the membrane thickness around Tc. This means that water can penetrate from the top surface of the membrane, but not from the side part of LB films. 

Elizalde, B. E., Pilosof, A. M. R., and Bartholomai, G. B. (1996). Empirical model for water uptake and hydration rate of food powders by sorption and Baumann methods. /. Food Sci. 61, 407-409. 

Acrolein (CHj=CHCHO, also known as 2-propenal) is a a,P-unsaturated aldehyde that can be transformed reducfively to saturated or unsaturated alcohols by reduction of the C = 0 or C = C double bonds (Claus 1998). In addition, a,P-unsaturated aldehydes may undergo hydration reactions in aqueous solutions. It was observed that, under acidic (pH12) conditions, acrolein is hydrated to 3-hydroxypropanal (Jensen and Hashtroudi 1976). In a natural subsurface environment, where pH may range from 6.5 to 8.5, the hydration rate of acrolein increases with the pH and its half-life decreases. Based on an experiment to analyze effects of iron on acrolein transformation, Oh et al. (2006) note that, under acidic conditions (e.g., pH = 4.4), acrolein disappears rapidly from solution in the presence of elemental iron (Fig. 16.1). Moreover, the formation of... 

For oxide CMP, the purpose of the solution is two fold. First, water weakens the Si—O bond in a silicon dioxide film and softens the surface as it becomes hydrated with Si—OH bonds [6,7]. Figure 10 shows the reaction mechanism. Second, the solution is to provide a basic environment (pH > 10), which accelerates the hydration rate. An environment with high pH values will allow the polishing-induced reaction to be further accelerated because the surface Si(OH) species will be partially dissolved into water. In the meantime, the zeta potential of silica increases with increasing pH values. At high zeta potentials silica particles will repel each other, whereby a better-suspended slurry is formed. 

High temperatures during hot-weather concreting result in an increase of the amount of mixing water required to produce a given slump [91, 94]. This effect of temperature is attributable to its accelerating effect on the hydration rate of the cement. At temperatures in excess of 25 °C, the mix... 

Different grades of Methocel and Metolose are supplied, with nominal viscosities of 4000 mPa s (measured with a Brookfield viscometer on a 2% w/v solution). Methocel 4M types E and are different in their hydration rates, type being the quickest. Metoloses SH4000 differ in their gel temperature. Grades 60 and 90 were used. Another polymer of 4000 mPa s viscosity was used hydroxyethylcellulose, in order to observe effects on the dissolution rate. 

On the other hand, the deposition process is also important to prepare blend samples. A mixture of homopolypeptide solutions in which they take a random coiled structure are added into a poor solvent. For polypeptides, water is a poor solvent in general. If the hydration rate is different for each polypeptides, they form their preferred secondary structures by themselves and then do not blend with each other. On the basis of this assumption, in order to make the hydration at the same time, the solution is added to alkaline water. In this review, two kinds of quieting solvents such as water and alkaline water have been used. (Methods 1-4 and Method 5). Method 1 Helical polypeptide and (3-sheet polypeptide are dissolved in DCA and agitated... 

The hydration rate constant of C02, the dehydration rate constant of carbonic acid (H2C03), and p pK2 values (pTf, =6.03, pTf2 = 9.8 at 25 °C, 7=0.5 M) (63) are such that nearly 99% of dissolved carbon dioxide in water at pH < 4 exists as C02. However, these four different species may be considered as the reactive species under different pH conditions which can react with aqua metal ions or their hydroxide analogues to generate the metal carbonato complexes. The metal bound aqua ligand is a substantially stronger acid than bulk H20 ( )K= 15.7). Typical value of the p of H20 bound to a metal ion may be taken to be 7. Hence the substantial fraction of such an aqua metal ion will exist as M-OH(aq)(ra 1) + species at nearly neutral pH in aqueous medium. A major reaction for the formation of carbonato complex, therefore, will involve pH controlled C02 uptake by the M-OH(" 1)+ as given in Eq. (17). 

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