Silica concentration profile

A similar type of catalyst including a supported noble metal for regeneration was described extensively in a series of patents assigned to UOP (209-214). The catalysts were prepared by the sublimation of metal halides, especially aluminum chloride and boron trifluoride, onto an alumina carrier modified with alkali or rare earth-alkali metal ions. The noble metal was preferably deposited in an eggshell concentration profile. An earlier patent assigned to Texaco (215) describes the use of chlorinated alumina in the isobutane alkylation with higher alkenes, especially hexenes. TMPs were supposed to form via self-alkylation. Fluorinated alumina and silica samples were also tested in isobutane alkylation,... 

Most commonly observed pore-water concentration profiles, (a) A nonreactive substance, such as chloride (b) a chemical, such as O2, which undergoes removal in the surface sediment as a result of aerobic respiration (c) a chemical that is consumed by a reaction that occurs in a subsurface layer, such as Fe2+(aq) precipitating with S2-(aq) to form FeS2(s) (d) a chemical released in surface sediments, such as silica via dissolution of siliceous hard parts (e) a chemical released into pore waters from a subsurface layer, such as Mn +(aq) by the reduction of Mn02(s) and (f) a chemical released at one depth (reactive layer 1), such as Fe2+(aq) by reduction of FeOOFI(s), and removal at another depth (reactive layer 2), such as Fe +(aq) precipitating as FeS2(s). Source From Schulz,... 

Fio. 11. Concentration profiles as measured with the equipment depicted in Fig. 10 (open symbols) and by GC analysis (closed symbols) for an esterification reaction between octanol and hexanoic acid. Conditions 200 ml, of reactant, 0.4mol/L of octanol, 0.4mol/L of hexanoic acid, l.Og Nafion resin/ silica, 447 K. The profiles were constructed from signals at 1720 and 1745 cm , and the spectra were corrected for solvent, octanol, and catalyst (74). 

Figure 9. Compositional concentration profiles of a soda-lime-silica glass corroded for 30 min at 75°C in water. Obtained with SIMS. (Reproduced from Ref. 18. Copyright 1979, American Chemical Society.)...

Figure 2.9 shows part of the results Elperin et al. obtained for the axial relative concentrations profile of silica gel particles. The major feature of this distribution is that the concentration sharply increases towards the impingement plane and the value near the impingement plane can be as high as 20-28 times the concentration in the feeding stream. This is mainly accounted for by the penetration of particles to and fro... 

Figure 2.9 Axial-relative concentration profile of silica gel particles. clp = 1,23x 10 3 m p = 880 kgm-3...

It is interesting to note that the actual shape of the germanium concentration shows a maximum and a minimum, but this has not been fully investigated up to now. Of course, as for the profile of silica and germania alone, the concentration profile also depends on the experimental conditions. 

Temperature measurements (corrected for radiation) were made with silica-coated Pt-Pt/10% Rh thermocouples, about 4 mils in diameter. The temperature and species concentration profile as a function of distance through the flame provided the basic data for the kinetic analyses. 

In the design of upflow, three phase bubble column reactors, it is important that the catalyst remains well distributed throughout the bed, or reactor space time yields will suffer. The solid concentration profiles of 2.5, 50 and 100 ym silica and iron oxide particles in water and organic solutions were measured in a 12.7 cm ID bubble column to determine what conditions gave satisfactory solids suspension. These results were compared against the theoretical mean solid settling velocity and the sedimentation diffusion models. Discrepancies between the data and models are discussed. The implications for the design of the reactors for the slurry phase Fischer-Tropsch synthesis are reviewed. 

We consider a thin, horizontal, fused-silica plate of area. I and thickness H. Initially, both horizontal surfaces of the plate are in contact with air (Figure 2.3c). We assume that the air is completely soluble in silica. At time t 0. the air below the plate is replaced by pure helium, which is appreciably soluble in silica. The helium slowly penetrates into the plate by molecular motion, and eventually appears in the air above the plate. This molecular transport of one substance relative to another is known as diffusion. The air above the plate is removed rapidly, so that there is no measurable helium concentration there. In this system, the index / shows helium and j shows silica, and the concentrations are given by the mass fractions w, and i. respectively. Eventually, the concentration profile tends toward a straight line with increasing t, and we have w, = r(U at the bottom surface, and w, = 0 at the top surface of the plate. At steady-state diffusion, the molar flow vector that is the flow rate of helium per unit area j, is proportional to the concentration gradient in terms of the mass fraction V r,... 

Mariscal et al. [29] prepared a series of titania-silica honeycombs by impregnation and homogeneous deposition precipitation. Only small amounts of titania are deposited on the silica matrix by homogeneous deposition precipitation. It was shown that incipient wetness impregnation was the only method to control both the amount of deposited titania and the concentration profile across the wall of the honeycombs [29]. 

It is interesting to note the different concentration profiles exhibited by silica and aluminium, because these provide indirect evidence of the possible dissolution and/or precipitation rates of different aluminosilicate minerals in the reservoir when CO2 is added to the system. Silica exhibits the same... 

When the sample is the powder zeolite mixed with silica-alumina (60% weight of zeolite, length 25 mm), the benzene concentration profiles (Figure 5-a) present an adsorption fi ont which lasts more than 30 min. On one hand, the intercrystallite diffiision rate is decreased by the presence of the mesoporous silica-alumina, on the other hand benzene also adsorbs on the silica-alumina. In the case of a compressed mixed sample (length 12 mm) the profiles are rectangular as... 

Silica concentrations in pore waters particularly and also in other subsurface and surface waters were determined in dozens of samples as part of this study, using atomic absorption spectrophotometry as well as inductive coupled plasma. This was essential for silica budget estimations. Present-day and paleothermal profiles were obtained from measured temperatures in boreholes, vitrinite reflectance (Rq) in interlayered-with-sandstones shales and from basins thermal modeling. 

Bon and coworkers carried out a study on the fate of the nanoparticles throughout solids-stabilized emulsion polymerization [119], A quantitative method based on disk centrifugation was developed to monitor the amount of nanoparticles present in the water phase in solids-stabilized emulsion polymerizations of vinyl acetate, methyl methacrylate, and butyl acrylate. The concentration profile of nanoparticles in the water phase as a function of monomer conversion agreed with theoretical models developed for the packing densities in these systems [120]. Noteworthy was that in the case of silica-nanoparticle-stabilized emulsion polymerization of vinyl acetate, the event of late-stage limited coalescence, leading to small armored non-spherical clusters, could be predicted and explained on the basis of the concentration profiles and particle size measurements. Adjusting the amount of silica nanoparticles prevented this phenomenon. 

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