Surface acid group distributions

Experimental. Characterizations of a heterogeneous surface by means of surface group titration utilizing visible and ultraviolet chemical indicators to define the titration end point have frequently been employed with white solid catalysts(7-12), (17-20). Aspects of the surface acid group distribution have often correlated with the catalytic activity of the solid(2-9), (21-25). An adaptation of the technique appears to be suitable for studying the interactions between the surface acid groups in mixtures of carbon black and white reference solids. 

Advantages and disadvantages of the titration technique are discussed in detail elsewhere(26) It suffices here to state that the surface acid group distributions on the white reference solids are sufficiently well defined by the experiment to provide a gauge by which to measure the interaction of carbon black with the white solids in binary mixtures. 

Figure I. Smoothed intrinsic acid group distribution normalized to total sample mass and total B.E.T. sample surface area for a alumina (a), and 86/13 silica-alumina (b). Monolayer coverage is defined as one (arbitrary) acid group per 20A2 of sample surface area.

The polymerisation of styrene and acrylic acid by seeded batch emulsion polymerisation was investigated. The effects of acrylic acid content and pH on the polymerisation rate and the amount of carboxyhc acid groups in the final latex product was studied. Aqueous conductometric titration and nonaqueous potentiometric titration were used to determine the distribution of the functional groups over the aqueous phase, the latex particle surface and the interior of the latex particle. The carboxylic acid group distribution along with kinetic results provided information about the process of incorporation of acrylic acid into the latex product. In order to increase the surface incorporation efficiency a two-step process in which a shot of acrylic acid was performed in the last stage of the reaction of investigated. 23 refs. 

Light olefins especially ethylene ( 2 ) and propylene ( 3 ) can be formed from methanol in the MTO process (Chang et al., 1979) using catalyst SAPO-34. Several other catalysts like ZSM-5 (Marchi and Froment, 1991), and Chabazite (Liu et al.. 1984) have been tested. Physical and chemical properties of the catalyst influence its selectivity to hydrocarbons. The physical factors that affect the selectivity of the catalyst are temperature, pressure of the fixed bed reactor, and space velocity of the feed. Other physical characteristics that influence selectivity are crystal size, crystal size distribution, pore size and pore size arrangement. The chemical characteristics that influence the selectivity are acid site density, strength of acid sites, and type of surface acid groups. 

Thus these characterization results not only give the distribution of the acrylic acid between the aqueous serum, particle surface, and particle interior, but also account satisfactorily for the total number of strong-acid groups arising from the anionic emulsifier and initiator. In addition, both the sodium lauryl ether sulfate and the nonylphenol polyoxyethylene adduct used in the polymerization were recovered from the fractions obtained by serum replacement. 

The nanotubes were first oxidized in nitric acid before dispersion as the acidic groups on the sidewalls of the nanotubes can interact with the carbonate groups in the polycarbonate chains. To achieve nanocomposites, the oxidized nanotubes were dispersed in THF and were added to a separate solution of polycarbonate in THF. The suspension was then precipitated in methanol and the precipitated nanocomposite material was recovered by filtration. From the scanning electron microscopy investigation of the fracture surface of nanotubes, the authors observed a uniform distribution of the nanotubes in the polycarbonate matrix as shown in Figure 2.3 (19). 

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