Clay dehydrations

Interpretation of the mechanisms of the hydrocarbon desorption reactions mentioned above was considered (31,291) with due regard for the possible role of clay dehydration. While this water evolution process is not regarded as a heterogeneous catalytic reaction, it is at least possible that water loss occurs at an interface (293) so that estimations of preexponential factors per unit area can be made. On this assumption, Arrhenius parameters (in the units used throughout the present review) were calculated from the available observations in the literature and it was found (Fig. 9, Table V, S) that compensation trends were present in the kinetic data for the dehydration reactions of illite (+) (294), kaolinite ( ) (293,295 298), montmorillonite (x) (294) and muscovite (O) (299). If these surface reactions are at least partially reversible,... 

From the discussion presented in the previous paragraphs, we identify the kinetic characteristics of the hydrocarbon evolution reactions (31,291,292) and the clay dehydration processes with the common mechanistic features reversibility and similar characteristic temperatures of onset of the water evolution step. The compensation effects observed for the two groups of related reactions (Table V, R and S) were not identical, however, since the species participating in the equilibria on the surfaces (believed to be represented by the kinetic characteristics described in Appendix I) are different. Undoubtedly, the interaction of hydroxyl groups to yield water was common to both types of reaction (surface desorption and lattice dehydration) and the properties and reactivities of these species probably determine the temperature at which significant surface activity and product evolution becomes apparent. This surface reaction is... 

In order to further validate our in-situ approach, we have realised a dehydration/re-hydration cycle for Ca-Montmorillonite in the same conditions as for Tobermorite. As presented in Figure 6 , the clay dehydration occurs at constant atmospheric pressure with increasing temperature the interlayer distance shifts from 16 A to 11 A. The inverse process, rehydration, is easily obtained at 300 K by increasing the water vapour pressure the interlamellar distance first shifts from 11.5 A to 14 A for P/Po<0.2 at larger pressure the swelling is more progressive and easily detected as shown in Figure 6 . 

In summary, the new technique developed at BP uses a proprietary transformation that relates velocity directly to effective stress, temperature and gross lithology, takes account of the major causes of overpressure in clastic basins (namely, undercompaction, clay dehydration and diagenesis, buoyancy and charging of fluids in dipping, permeable beds), and predicts effective stress directly, which is the most fundamental quantity for pressure prediction. 

The mechanism of dehydration of layer silicates [51] is believed to differ from the mechanism of dehydration of crystalline hydrates and this has been used to explain the observed differences in parameters E (in vacuum) and in decomposition temperatures. This view is reflected, in particular, in the fact that the special term dehydroxylation is used in the literature to describe clay dehydration. However, this belief is not justified. As can be... 

Description Water-washed china clay dehydrated to produce a very white extender, with high opacity ... 

Hydrating bentonite in fresh water before adding it to the mud greatly increases its efficiency when the makeup water is contaminated with salt and/or hardness. Prehydrated bentonite can be protected from dehydration by flgnosulfonate (70) or sulfomethylated tannin when used in saturated salt water. Salt water clays, such as sepioflte and attapulgite, provide no filtration control and are normally used with suitable filtration control agents. 

Dehydration of 1-pentanol or 2-pentanol to the corresponding olefins has been accompHshed, in high purity and yields, by vapor-phase heterogeneous catalyzed processes using a variety of catalysts including neutral gamma —Al Og catalyst doped with an alkah metal (23), zinc aluminate (24,25), hthiated clays (26), Ca2(P0 2 montmorillonite clays (28). Dehydration of 2-methyl-1-butanol occurs over zinc aluminate catalyst at... 

Hydration and Dehydration. Succinic anhydride reacts slowly with cold water and rapidly with hot water to give the acid. For this reason it must be carefully stored in anhydrous conditions. Succinic acid can be dehydrated to the anhydride by heating at 200°C, optionally in the presence of a solvent (31). Dehydration can also be performed with clay catalysis in the presence of isopropenyl acetate under microwave irradiation (32) or with his (trichi oromethyl) carbonate at room temperature (33). 

Succinic anhydride can be prepared from succinic acid by dehydration it operates in high boiling solvent (31), in the presence of clays as a catalyst (32), or at room temperature with triphosgene (33). 

In foundry practice the same sand is used repeatedly. Because the high temperature of the metal dehydrates and vitrifies some of the clay, fresh clay must be added contiauously as the sand is used. The only completely adequate test for the satisfactory use of a clay ia bonding mol ding sands is the result obtained by actual use ia foundry practice. 

J. w. Geus, The interlayer collapse during dehydration of synthetic Na -beidellite a %a solid -state magic-angle spinning NMR study. Clays Clay Minerals. 25 457 (1992). 

Total Salinity. The salinity control of oil-base mud is very important for stabilizing water-sensitive shales and clays. Depending upon the ionic concentration of the shale waters and of the mud water phase, an osmotic flow of pure water from the weaker salt concentration (in shale) to the stronger salt concentration (in mud) will occur. This may cause a dehydration of the shale and, consequently, affect its stabilization. 

Dehydration loss of chemically combined water and modification of clay structure... 

During the dehydration stage (between 450°C and 600°C), hydroxyl (OH ) ions in the clay are dislodged from their molecules, combine with each other to form water vapor, and are thus removed from the clay structure and released into the atmosphere. It is during this stage, as a consequence of the displacement of the hydroxyl ions, that the chemical composition and the structure of the clay are irreversibly altered and converted to fired clay. 

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