Analytical Sciences

Determination of Titanium and Vanadium in Ziegler-Natta Catalysts by Inductively Coupled Plasma Atomic Emission Spectrometry

Cristiane F. PETRY, Larissa B. CAPELETTI, Fernanda C. STEDILE, João H. Z. dos SANTOS, and Dirce POZEBON

Instituto de Química, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves, 9500, 91500-790, Porto Alegre, RS, Brazil

A method for the determination of Ti and V using inductively coupled plasma atomic emission spectrometry (ICP OES) in Ziegler-Natta polymerization catalysts is proposed. The concentrations of both Ti and V are efficiently determined after catalyst acid digestion with a mixture of HNO₃ + HCl + HF and heating (160°C for 6 h) or with 10% (v/v) H₂SO₄ and heating (160°C for 6 h) or with 10% (v/v) H₂SO₄ and sonication (during 2 min). The V and Ti detection limits are 0.002% and 0.08%, respectively, using 0.20 g of catalyst sample in 50 ml. The method is validated by a comparison with the Rutherford backscattering spectrometry (RBS) technique. In this case, catalyst samples are only pressed as pellets before analyte determination. Despite the fact that both the V and Ti concentrations cannot be determined individually by means of RBS, because the atomic numbers of Ti and V are very close, the sum of the V and Ti contents is in accordance with that attained by means of ICP OES. According to scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX) it is observed that the Ti distribution on the catalyst grain is not homogenous.

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