Wide-pore silica

Narrow pore silica Wide pore silica (e.g., TLC silica) Alumina Florisil Magnesia- ... 

Imprinted Polymer Layers on Silica. Wide pore silicas (mean pore diameter 500 and 1000 k) were surface-modified by 3-(trimethoxysilyl)propyl methacrylate by formation of siloxane bon s. To such a silica, layers of approximately 50 - 100 A thickness of the usual monomeric mixture containing 1 were applied (56,57). The monomeric mixture was radically polymerized giving silicas with pores coated... 

Fig. 5.7 Adsorption isotherms of n-p>entane vapour on A), quartz and pyrex glass and (B), wide-pored silica gel. O,, quartz pyrex glass A, A wide-pored silica gel. Solid symbols denote desorption. (Courtesy...

Thus, in this case the simple form of equation (34) is quite adequate. Alternatively, employing a wide pore silica base in LC for separating small molecular weight... 

The Phillips Cr/silica catalyst is prepared by impregnating a chromium compound (commonly chromic acid) onto a support material, most commonly a wide-pore silica, and then calcining in oxygen at 923 K. In the industrial process, the formation of the propagation centers takes place by reductive interaction of Cr(VI) with the monomer (ethylene) at about 423 K [4]. This feature makes the Phillips catalyst unique among all the olefin polymerization catalysts, but also the most controversial one [17]. 

Fig. 3.23 shows pore volume distributions of some commercially important porous materials. Note that zeolites and activated carbon consist predominantly of micropores, whereas alumina and silica have pores mainly in the me.sopore range. Zeolites and active carbons have a sharp peak in pore size distribution, but in the case of the activated carbon also larger pores are present. The wide-pore silica is prepared specially to facilitate internal mass-transfer. 

Figure 3.23. Pore volume distributions (Nt physi.sorption) of a. wide-pore silica, b. y-alumina, c. a-alumina, d. activated carbon, e. Raney Nickel and f. ZSM-5.

Tanaka, N., Kimata, K., Mikawa, Y., Hosoya, K., Araki, T., Ohtsu, Y., Shiojima, Y., Tsuboi, R., Tsuchiya, H. (1990). Performance of wide-pore silica- and polymer-based packing materials in polypeptide separation the effect of pore size and alkyl chain length. J. Chromatogr. 535, 13-31. 

Dalai, A.K., Das, T.K., Chaudhari, K.V., Jacobs, G., and Davis, B. H. 2005. Fischer-Tropsch synthesis Water effects on Co supported on narrow and wide-pore silica. Appl. Catal. 289 135-42. 

Co/Si02 (PQ2133) CSTR Positive Wide pore silica Catalyst , S BET = 226 m2/g, pore volume 0.77 cm3/g, aver, pore diam. 13.6 nm, DCo = 7.3%... 

Dalai et al.31 investigated the effect of water on the performance of narrow and wide-pore silica-supported cobalt catalysts for Fischer-Tropsch synthesis. Three catalysts were studied 12.4 wt% Co on a wide-pore silica, 20 wt% Co on a... 

The separation of basic and metal-sensitive compounds is difficult on silica-based stationary phase materials, but these separations can be performed on vinyl alcohol copolymer gels. Examples are the separation of methallothionein from dolphin kidney, a-, j8-, and y-endorphin, and nucleotide and nucleoside mixtures.8 However, an analytical-scale separation may also be performed on surface-modified wide-pore silica gels (pore size 300 A or more), using columns which showed a negative response in the heavy metal test described above. 

Sander et al. [63] investigated the effect of microparticulate silica pore size on the properties of solution-polymerized Cig stationary phases and observed both an increase in bonding density and shape recognition for wider pore (>120 A) silica. A size-exclusion mechanism was proposed, in which the reaction of the silane polymer on the surface is enhanced for wide pores and reduced for narrow pores. Polymeric Ci8 phases prepared on substrates with narrow pores exhibited monomeric-like chromatographic properties. This effect may be the result of an increase in competitive surface linkage with the less sterically hindered monomers that coexist with the bulkier oligomers that have polymerized in the reaction solution (Figure 5.13). 

Structure EANPS = electrostatic agglomerated nonporous substrate, EAWPS = electrostatic agglomerated wide-pore substrate, PGPS = polymer grafted porous substrate, SMPSS = silane modified porous silica substrate, CMS = chemically modified substrate, APCS = adsorbed polymer coated substrate. 

Mercury poroslmetry data of these packings are given In Table IV. It Is of Interest to note that the pore-size distribution of CPG Is significantly more narrow than that of Syn-Chropak, a surface-modified porous silica (LlChrospher). These different physical characteristics may help to explain the existence of micropores In SynChropak. Because of the wide pore-size distribution of this packing. It seems reasonable that this material also contains a population of micropores which are only accessible to D2O. In mercury poroslmetry measurements, the lower pore size limit Is about 30A. 

From these studies with SynChropak SEC packings and controlled porosity glass, it is concluded that the silica packing contains a population of micropores which are differentially accessible to low molecular weight probes of total permeation volume. It is not known, however, if the microporosity in the 100 and 300A SynChropak SEC packings is the result of the rather wide pore-size distribution and whether all silicas contain micropores. 

FIGURE 2.8 Hydrophobic retention and selectivity with RP columns. The stationary phases are ordered according to the increasing retention of toluene in methanol-water 50-50 v-v. Dashed line Stationary phases with a silica pore diameter below lOnm. Solid line Stationary phases with a silica pore diameter >12nm. ( ) Stationary phases with polar-embedded functional groups. (( ) Stationary phase based on a wide pore silica (30 nm)). 

The most useful CSPs for the resolution of many varied, structurally different racemates are the following the peracetates, benzoates (and derivatives) and carbamates (and derivatives) of cellulose and amylose coated on wide pore silica gel. Some of these polymer derivatives are also potentially useful as pure polymeric bead material, but mainly for preparative purposes. 

Figure 2 shows the cumulative pore volume vs. pore radius for AC-ref SC-100 and SC-155 obtained by mercury intrusion technique. The curve corresponding to AC-ref shows a wide pore radius distribution instead, the curves assigned to SC-100 and SC-155 showed sharpened zones with maximum slope in 459A and 524A respectively, denoting a small increase of these values with the increase of the synthesis temperature. This phenomenon is probably produced by the growing of the big pores of the silica network at the expense of the... 

The Phillips Cr/silica polymerization catalyst is prepared by impregnating a chromium compound onto a wide pore silica and then calcining in oxygen to activate the catalyst. This leaves the chromium in the hexavalent state, monodispersed on the silica surface. Chromium trioxide (Cr03) has been impregnated mast commonly, but even a trivalent chromium salt can be used since oxidation to Cr(VI) occurs during calcining. 

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