Estimation of the components in titanation mixture used in the synthesis of polyolefin catalysts

摘要

Traditional Ziegler Natta catalysts used for making polyethylene and polypropylene involve titanation of Mg based supports like magnesium ethoxide using a mixture of TiCl4 and chlorobenzene. Chloroalkoxy titanium species like TiCl3(OEt) are generated in the process which gets mixed with the titanation mixture. This necessitates the need for a quick, reliable and easy method of analysis for arriving at the correct composition of the residual titanation mixture so that the same can be reused after adjusting the TiCl4 and chlorobenzene contents. Estimation of TiCl3(OEt) and TiCl4 separately and also in synthetic mixtures of both has been carried out through a simple acid-base titration. The method is based on the concept that TiCl3(OEt) and TiCl4 liberate stoichiometric amounts of HC1 on aqueous or alkaline hydrolysis which can be estimated by an acid-base titration. The analysis has been carried out using different synthetic mixtures of TiCl3(OEt) and TiCl4 in chlorobenzene. TiCl3(OEt) and TiCl4 were subsequently estimated by a combination of acid-base titration/UV-vis spectroscopy and gas chromatography (GC). By accounting for the titanium content due to TiCl3(OEt) and subtracting the same from the overall titanium content, the titanium content from TiCl4 was worked out. The concept and the method developed have been validated through a parity plot. A complementary method for estimating the ethoxy content in TiCl3(OEt) was also used wherein the ethoxy group was quantitatively converted into ethylbenzoate (EB) through esterification employing benzoyl chloride. The TiCl4.ethyl benzoate adduct was further hydrolysed to liberate an equivalent amount of ethylbenzoate which was estimated by quantitative GC.