A method for the extraction of the titanium and aluminium from Ziegler -Natta catalyst systems into aqueous sulphuric acid followed by EDTA titration of each metal without prior separation is described. The sum of the two metals is determined in one aliquot by addition of excess of EDTA and isopropyl alcohol and back-titration with zinc to the dithizone end-point a t pH 4.5. The titanium in a second aliquot is back-titrated a t pH 1.2 in the presence of hydrogen peroxide with bismuth to the xylenol orange end-point. The aluminium concentration is obtained by difference.ZIEGLER -NATTA catalyst systems consist of a halide compound of group IV to VIII transition elements, such as TiCl,, and an alkyl metal, such as A1(C2H5),.1 In a polyolefin process study involving a titaniumaluminium catalyst system, it became necessary to develop a chemical method for determining titanium and aluminium in solid catalyst and in hydrocarbon slurries and solutions. The method had to be rapid and cover a weight ratio of titanium to aluminium varying from 6 : 1 to 1 : 6. Recognised procedures for extracting the titanium and aluminium into aqueous sulphuric acid were available and, consequently, a method for determining the metal ions in the presence of each other was required. An initial evaluation of selective precipitation methods involving 8-hydroxyquinoline led to the almost immediate conclusion that the simplest and most rapid procedure would involve a chelometric titration with EDTA.Piibil has critically reviewed complexometric titration methods for quadrivalent and tervalent metal ions2 and has reported a procedure applicable to the determination of the two metals when present in nearly equal ~oncentrations.3~~ At higher concentrations of aluminium, however, it was necessary first to separate the titanium by precipitation with sodium hydroxide in the presence of triethanolamine. In the method reported here titanium is determined in the presence of much higher concentrations of aluminium at low pH, and the sum of titanium and aluminium is determined at a higher pH with a second aliquot of the same solution. The aluminium concentration is obtained by difference. EXPERIMENTAL REAGENTS-Bufer solution-Add 273g of sodium acetate to 1 litre of distilled water and adjust the pH to 4.5 with acetic acid.Indicators-Xylenol orange, 0.2 per cent. aqueous solution. Dithizone, 0.0125 g in 50 ml of acetone. Prepare fresh dithizone solution weekly.Zinc solution, 0.05 M-Prepare by dissolving analytical-reagent grade zinc metal in hydrochloric acid (1 + 3).EDTA solution, 0.05 M-Standardise by placing 40-00 ml of this solution in a 250-ml beaker. Add 10 ml of buffer solution, 75 ml of isopropyl alcohol, 1 ml of dithizone indicator solution and 25 ml of distilled water. Titrate with the standard zinc solution to a red colour. Calculate the exact molarity.Bismuth solutim, 0-025 M-Dissolve 12.1 g of analytical-reagent grade bismuth nitrate, Bi(N0,),.5H20, in 50 ml of nitric acid (1 + 1). Dilute with distilled water to 1 litre. The bismuth nitrate solu...
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