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Consumption equilibrium studies

Much of the information on hydrate processes has come from macroscopic studies, that is, from the observation of gas consumption, pressure drop, particle size measurements, or crystal morphology observations. However clathrate hydrates in many ways are unique materials that make it imperative that studies on the molecular scale are also carried out. For instance, several structures of hydrate may coexist, and often this is not obvious from phase equilibrium studies ... [Pg.61]

When a biochemical half-reaction involves the production or consumption of hydrogen ions, the electrode potential depends on the pH. When reactants are weak acids or bases, the pH dependence may be complicated, but this dependence can be calculated if the pKs of both the oxidized and reduced reactants are known. Standard apparent reduction potentials E ° have been determined for a number of oxidation-reduction reactions of biochemical interest at various pH values, but the E ° values for many more biochemical reactions can be calculated from ArG ° values of reactants from the measured apparent equilibrium constants K. Some biochemical redox reactions can be studied potentiometrically, but often reversibility cannot be obtained. Therefore a great deal of the information on reduction potentials in this chapter has come from measurements of apparent equilibrium constants. [Pg.156]

The polymerization of trioxane in solution has been studied by Okamura (26) and his co-workers and by Kern and Jaacks (56, 58, 63). The initiators were borontrifluo-ride or its complexes and anhydrous perchloric acid. During the polymerization the eight-membered ring, tetroxane, is formed rapidly but this compound takes part in the polyoxymethylene formation. This results in an equilibrium concentration of tetroxane when the rate of formation becomes equal to the rate of consumption (27). Minor amounts of the ten-membered ring, pentoxane, are also formed (28). The authors conclude that tetroxane and pentoxane are formed by a back-biting mechanism. It is assumed that the active species in the reaction is a carbenium ion. Although this ion... [Pg.111]

Partitioning of volatile substances between the liquid and gas phases is mainly governed by aroma compound volatility and solubility. These physicochemical properties are expected to be influenced by wine constituents present in the medium, for instance polysaccharides, polyphenols, proteins among others. Consideration of the physicochemical interactions that occur between aroma compounds and wine constituents is necessary to understand the perception of wine aroma during consumption. The binding that occurs at a molecular level reflects changes at a macroscopic level of the thermodynamic equilibrium, such as volatility and solubility, or changes in kinetic phenomena. Thus, thermodynamic and dynamic approaches can be used to study the behaviour of aroma compounds in simple (model) or complex (foods) media. [Pg.418]

In terms of research in this area, historically much more work has focused on the studying flavour release under equilibrium conditions as opposed to dynamic conditions. In the future, research should focus to a greater extent on flavour release under dynamic conditions which better represents aroma release during wine consumption. [Pg.432]

A kinetic study of living radical polymerizations of acrylates initiated by the (tetramesitylporphyronato)-cobalt(III) organo complexes (TMP)Co—CH(CH3)C02-Me and (Br8TMP)Co—CH(CH3)C02Me has been reported by Wayland et al.122 They applied an initial excess of the free cobalt complex and obtained the equilibrium constant for the reversible dissociation of the complex—poly(methyl acrylate) bond as K = 4.2 x 10 10 M for (TMP)Co and K= 1.3 x 10 8 M for (BrgTMP)Co from the rate of monomer consumption at 50 °C. The temperature dependence led to a bond... [Pg.296]

Polymerizations are studied typically in time ranges between 100 s and 30 h, that is, in the equilibrium regime. Therefore, for polymerizing systems, one can use eq 20, insert it into the rate equation of the monomer consumption (21), integrate, and obtain eq 22. The further derivation of the control involves the calculation of the moments mk of the chain length distribution and of their time dependencies. [Pg.298]

Mainly PV aided conversions have been studied and more in particular esterifications, a typical example of an equilibrium limited reaction with industrial relevance and well-known reaction mechanisms. " This hybrid process has already made it to several industrial applications. The thermodynamic equilibrium in such a reaction can be easily shifted and obtained in a shorter reaction time by removing one of the products. Pervaporation is especially interesting because it is not limited by relative volatility or azeotropes and energy consumption is generally low, because only the fraction that permeates undergoes the liquid/vapor phase change. It can also be operated at lower temperatures, which can better match the optimal conditions for reaction. [Pg.1581]

The polymerization of 3,3-bis(chloromethyl)oxetane (BCMO) initiated with living polytetrahydrofuran (polyTHF) was studied by Saegusa 117). In this system, due to the high equilibrium concentration of THF, some monomer remains in equilibrium with the polymer after the first stage is completed (i.e. at the polyTHF THF equilibrium). After addition of the second monomer, the remaining THF may participate in copolymerization with added BCMO (cf. Sect. 15.2.2.1., copolymerization above T0), leading to random copolymer. Only after the complete consumption of THF the second monomer may form the required homoblock. Thus, the two homoblocks are separated by a third random BCMO/THF copolymer block ... [Pg.275]

Unaltered Pellets As an initial control experiment, the isomerization of xylose to xylulose was studied using Sweetzyme pellets, as received, before co-immobilization with urease. The time course of xylose consumption and xylulose formation was monitored for an initial xylose concentration of 60 g/1 with 0.13 g pellets at 34 °C. The isomerization mixture was buffered at pH 7.5, which is the optimal pH for XI activity. As seen in Fig. 2, curve A, the concentration of xylulose steadily increased and reached an equilibrium value of about 9 g/1, suggesting an equilibrium xylose/xylulose ratio of nearly 6 1 under these conditions. When the same experiment was repeated at a reduced pH of 4.5, no xylulose was detected in the reaction mixture, even after 40 h (data not shown). At a pH of 4.5, XI is 3 pH units below its optimum and displays essentially no activity. [Pg.232]


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See also in sourсe #XX -- [ Pg.231 ]




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