Weight silica formers

The former represent the weight percent of carbon atoms on the adsorbent sample measured by elemental analysis. The bonding density of a given carbon load decreases with increasing surface area of the silica support porosity multiplies the available particle surface. The specific surface area (surface area in 1 g adsorbent) is said to be inversely proportional to pore diameter (at constant specific pore volume) and obviously increases with increasing specific pore volume. 

Other chromium catalysts for ethylene polymerization employ chromo-cene [246] and bis(triphenylsilyl) chromate [247] deposited on silica-alumina. The catalyst support is essential for high activity at moderate ethylene pressures (200—600 p.s.i.). The former catalyst is activated further by organo-aluminium compounds. Polymerization rates are proportional to ethylene pressure and molecular weight is lowered by raising the temperature or with hydrogen (0.1—0.5 mole fraction) in the monomer feed wide molecular weight distributions were observed. 

With two polymers of different chemical type, kinetic studies have shown that equilibrium adsorption and desorption are reached more rapidly than normally associated with polymer adsorption. Botham and Thies found that poly(vinyl acetate) (molecular weight 28000) could displace polystyrene (molecular weight 105 000) within one hour. This displacement study confirms the expected greater energy of the carbonyl group s interaction with silica compared with that of styrene. It is also demonstrated by the results of the competitive adsorption of polystyrene and poly(methyl methacrylate) on to silica. Here it was shown that the latter polymer was adsorbed in strong preference to the former indeed, no polystyrene was adsorbed until the poly(methyl methacrylate) had been completely removed from the solution. 

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