Process for producing solid titanium trichloride

In a process for producing a fine solid titanium trichloride suitable for use as a catalyst for polymerization of an .alpha.-olefin which comprises:

• (a) forming a homogeneous solution or mixture comprising a liquid titanium trichloride complex by reducing titanium tetrachloride with an organoaluminum compound of the formula AlR.sub.n.sup.5 X.sub.3-n wherein R.sup.5 represents a C.sub.1 -C.sub.20 hydrocarbon moiety, n is a number of the value of 1 to 3 and X represents a halogen atom, in the presence of an ether of the formula R.sup.3 --O--R.sup.4 wherein R.sup.3 and R.sup.4 are the same or different and respectively represent an alkyl or alkenyl group at -30.degree. to 35.degree. C.;
• (b) heating the homogeneous solution or mixture in the presence of Lewis acid at a temperature between 40.degree. to 150.degree. C., to cause a precipitation of solid titanium trichloride;
• and
• (c) separating said precipitate, an improvement characterized in that the said precipitation is carried out in the presence of a monocarboxylic acid ester having the formula of ##STR4## wherein R.sup.1 and R.sup.2 respectively represent a hydrocarbon moiety and total carbon atoms of R.sup.1 and R.sup.2 are 12 or more wherein said ester is added before precipitating a substantial amount of the solid titanium trichloride from the homogeneous solution or mixture.