Method for making overbased PVC stabilizer

Claim 1

A process for producing an overbased mixture of carboxylate salts of one or more aromatic acids selected from the group consisting of benzoic acid and benzoic acid substituted with one, two or three alkyl groups each of which contain from 1 to 6 carbon atoms, and one or more aliphatic fatty acids containing about 12 to 30 carbon atoms with zinc and of magnesium, comprising: (a) dissolving zinc oxide in a molten acid precursor composed of at least a stoichiometrically equivalent quantity of said one or more aliphatic fatty acids wherein up to about 10 mole percent of the amount of said one or more aliphatic fatty acids present is replaced by one or more of said aromatic acids, in the presence of water in an amount up to about 10 wt %, said amount of water being effective to increase the rate of reaction of said zinc oxide with said one or more aliphatic fatty acids, under conditions effective to achieve complete reaction between said zinc oxide and said acid precursor to maximize formation of the corresponding zinc carboxylate while minimizing formation of other reaction products and to provide thereby a liquid reaction product; (b) adding said one or more aromatic acids to said liquid reaction product under conditions effective to maintain it in the liquid state while minimizing side reactions between said zinc carboxylate and said aromatic acids, wherein the mole ratio of said one or more aromatic acids to aliphatic carboxylates is 0.5:1 to 2:1; (c) adding magnesium oxide, either magnesium hydroxide, or mixtures thereof to the product of step (b), in an amount effective to provide a stoichiometric excess thereof up to about 5 wt. % based on the carboxylate, under conditions effective to achieve complete reaction of said one or more aromatic acids with said added compound or compounds to form said mixture of carboxylate salts while minimizing formation of side reaction products; and (d) conditioning the product of step (c) under conditions effective to volatilize and remove therefrom unreacted products and side reaction products.