Silica drying

Coal, bituminous, mined, sized 50 D26PT Sand, silica, dry 90-100 B18... 

Applications Identification of polymer additives by TLC-IR is labour intensive and comprises extraction, concentration of extracts, component separation by TLC on silica, drying, removal of spots, preparation of KBr pellets and IR analysis. The method was illustrated with natural rubber formulations, where N-cyclohexyl-2-benzothiazyl sulfenamide, IPPD and 6PPD antioxidants, and a naphthenic plasticiser were readily quantified [765]. An overview of polymer/additive type compounds analysed by transfer TLC-FTIR is given in Table 7.80. 

Fig. 8. Infrared spectrum of silica measured at room temperature (a) undried silica (b) silica dried at 200°C for 3 hr (16).

Transition metal alkyl compounds react with the -OH groups on the surface of silica in a manner similar to that described for the silanol [reaction (13)] and as with the latter more than one type of bonding is possible. Silica dried at 200°C reacts with Zr(allyl)4 to give two molecules of propene per metal atom and utilizing in the course of this process two -OH groups per metal atom. The chemistry of the process is accurately described by the equation... 

In addition to the simple chemical methods for following these processes, infrared spectroscopy may also be used. In Fig. 9 is shown the spectrum of silica dried at 200°C before and after reaction with Zr(allyl)4- The characteristic absorption bands of the transition metal-allyl group are clearly displayed, also a significant reduction in the number of hydroxyl groups (3740 cm-1) is also clearly evident. 

Fig. 9. Reaction of silica dried at 200°C with Zrfallylh. Infrared spectrum measured at room temperature,---SiCb,----Si02/Zr(allyl)i (16).

The pyrogenic flame hydrolyzed silica Aerosil 200, a commercial product from Degussa, was used as a dispersion in doubly distilled water (1). The precipitated silica was prepared by hydrolysis of orthosilicic acid tetraethylester in ammoniacal solution according to the method of Stober, Fink and Bohn (11). The prepared suspension was purified by repeated centrifugation, separation from solvent and redispersion of the sediment in fresh water. Finally, the water was evaporated and the wet silica dried at 150°C for about half an hour. 

A sample of silica, dried at 150°, representing about 10 m /gm, is added to 25 ml of a methyl red solution in benzene containing 0.6-0.7 gm of the azo compound per liter. After agitating for about 2 hours at room temperature, the concentrations of equilibrium solution and original solution are compared by spectrophotometry at 4750 A. The specific hydroxylated surface area in m /gm is calculated from the formula ... 

ESR Studies. The isotropic ESR spectra of a solution of Nb (7r-allyl) 4 in THF and the frozen solution are shown in Figure 10. The spectra at —180 °C and room temperature of Nb(7r-allyl)4 after reaction with silica (Manosil VN3) dried at 650°C are shown in Figure 11 the corresponding spectra for silica dried at 250°C are in Figure 12. 

Figure 11. ESR spectra of Nb(7r-allyl)/t after reaction with silica dried at 650°C (a) at —180°C, (b) at room temperature...

Experiments to determine the mode of bonding of the metal hydrocarbyl with silica dried above 200 °C were not attempted because of Reaction 4. Strained siloxane bridges are not present on silicas dried below 200°C (63). 

After washing the resin with DMA and MeOH, it was dried in vacuo to yield 640 mg peptide-resin. A part (350 mg) of the resin sample was treated with 95% TFA (5mL) for 90 min to deprotect the Glu(OtBu) and remove the peptide from its resin support. The suspension was filtered, the resin washed with TFA (15mL), and the combined filtrates were triturated with Et20 (3x20mL) and dried in vacuo over silica drying gel. The S-acetyl di-K2K core 37 was used without further purification. 

Figure 5. Spectrum of silica dried at 450°C (A) diethylamine adsorbed on (B) the cross-hatched areas are attributable to diethylamine (11).

All silicas dried from water at less than 150°C have a fully hydroxylated surface in which the surface structure terminates in silanol groups. This is readily wettable by water and water-soluble organic molecules. 

Sequentially add solvent fractions to the funnel according to the quantities indicated in Table 11.1, sucking the silica dry in between each fraction, and keeping fractions separate. For each successive fraction increase the solvent polarity by increasing the proportion of the more polar solvent by about 5-10% (e.g. from 50% EtOAc/50% petrol to 55% EtOAc, for a 10% increase). Analyse the fractions by tic to determine the locations of the components of interest, but as a rough guide, the solvent mixture which would give the compound a tic Rf value of about 0.5 will probably elute it. 

Silicon, as silicate, has a large biochemistry in the plant kingdom, which is only beginning to be explored. Silicate appears to be transferred as the ester of a serine OH in the active site of a silicatein, an enzyme with sequence homology to cysteine proteinases, but with the crucial cysteine replaced by serine. "" Plant cell walls contain considerable amounts of silica - dry rice straw can contain 8wt% silica. Although deposition of silica in diatoms is mediated in the first instance by cationic proteins, a secondary role for a (1 ->3)-linked mannan has been suggested Figure 6.25. " ... 

Figure 12. Isoelectric points of DS-coated titanias O, titania dispersed in aqueous silica , dried, coated titania powders. The hose titania was 20 m2/g.

At Al/Zr = 200, a variety of metallocene—MAO catalysts were supported on silicas dried at various temperatures (Table 2). Supports dried at lower temperatures afforded catalysts of higher activities pretreating the support with AlMes also diminished activity. Analysis of the distribution of aluminum and silicon indicates a very even distribution of cocatalyst on the support, with no more catalyst on the outer surface than within the pores. ... 

Many determinations of the numbers of Silanol groups have been done in the past and have generally determined that there are about 4-5 silanol groups per square nanometer. L.T. Zhuravlev [3] has summarized much of this work. From this work the most likely value is 4.6 silanol units per nm was determined. However, all of this work was done on silica dried at temperatures above 100°C. Most of the work was done on samples dried above... 

Synthesis of modified silica 61 Different types of silica dried at 200 °C under vacuum were placed in a 250-mL flask with 150 mL dried m-xylene. 2 g (10 mmol) 3-chloropropyltrimethoxysilane and 1.4 g (20 mmol) imidazole were added, and the mixture was refluxed for 8 h. An excess of imidazole was used to bind the hydrochloric acid formed. The filtered product was washed with 0.01 M NaOH to remove hydrochloric acid and unbonded imidazol. Afterwards the solids were washed thoroughly with water and acetone. The solids were dried under vacuum at 80 °C. 

A more practical precipitated silica of lower surface area that can be dried from water, yet retains an open structure with easy dispersibility, is described in detail in another patent to Alexander et al. (271). The main difference from the above is that the initial sol was made in a more concentrated solution 123 part of sodium silicate solution containing 3.71 grams SiOj per 100 cm was heated to 90 C, and 10.1 parts 13% H2SO4 solution was added in 30 min. Then added simultaneously over a 2 hr period were 119 parts of sodium silicate solution containing 8 grams SiOj per 100 cm and 111 parts 3.11% H3SO4 solution. At the end of the reaction more acid was added to reduce the pH to 7. To the product slurry, 3 parts of 1% cetyltrimethylammonium bromide solution was added to aid filtration. The recovered wet silica was washed to remove salt, the pH adjusted to 8, and the silica dried at 110 C. This... 

We have tried to estimate critical pressure needed to explode a catalyst particle. We believe the main critical pressure range is within the region 2-20 bar. This estimate is based on the pure silica rupture strength of about 500 bar and a typical porosity of 80%, as well as on the implosive force of liquid water in the pores during the silica drying operation. 

Polymerization experiments were carried out to determine the effect of the following factors on the catalytic activities silica drying temperature, presence of Mg, pore volume and surface area of the silica, and monomer pressure. 

The effect of drying temperature and pressure of Mg on the catalytic activity can be seen clearly by looking at Fig. 3 for polymerization runs at 5 atm. monomer pressure. As published before (22), silica dried at 600"C and having Isolated hydroxyl groups produce catalysts with higher activities, compared with those prepared on silica dried at 150 C. In both cases, acceleration-type kinetic curves were obtained with maximum activities (A ) of 2000 and 200 gPE x gTi x h x atm." respectively. 

Histograms of acoustic activity in gels made from fumed silica, dried at relative humidities of 36Vo (a) and 70% (b), and with surfactant added to solution (c). Shrinkage stopped at point indicated by arrow and letter S. From Simpkins el al. [IS]. 

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