Why must titanium tetrachloride be more than 99.9 percent pure for titanium metal production?

Titanium tetrachloride ($TiC{l}_4$) must be purified to a level exceeding 99.9 percent because any contaminants present in the compound will be reduced alongside the titanium metal during the production process.1

To achieve this high level of purity, raw $TiC{l}_4$ undergoes a rigorous cleaning process. This includes removing fine particles of entrained coke and ore, followed by distillation to eliminate volatile impurities with high and low boiling points. Additionally, specific impurities like vanadium oxychloride are removed through chemical reaction with mineral oil, and the product is redistilled in a reflux distillation column. Maintaining this high standard of quality is essential to ensure the production of high-quality titanium metal.1