Overbased metal carboxylate precursor and process for making

The invention relates to a shelf stable, flowable liquid of an alkaline earth metal salt of a fatty acid and a process for preparing the liquid. More particularly, the invention relates to a shelf stable, flowable precursor of an overbased alkaline earth metal carboxylate and a process for preparing the precursor. Even more particularly, the invention relates to a shelf stable, flowable precursor of an overbased calcium carboxylate and a process for preparing the precursor.

The preparation of overbased calcium or barium salts of carboxylic acids, alkyl phenols, and sulfonic acids are disclosed in the following U.S. Pat. Nos. 2,616,904; 2,760,970; 2,767,164; 2,798,852; 2,802,816; 3,027,325; 3,031,284; 3,342,733; 3,533,975; 3,773,664; and 3,779,922. The use of these overbased metal salts in the halogen-containing organic polymer is described in the following U.S. Pat. Nos. 4,159,973; 4,252,698; and 3,194,823. The use of overbased barium salt in stabilizer formulations has increased during recent years. This is due, in the main, to the fact that overbased barium salts possess performance advantages over the neutral barium salts. The performance advantages associated with overbased barium salts are low plate-out, excellent color hold, good long-term heat stability performance, good compatibility with the stabilizer components, etc. Unfortunately, most of the overbased barium salts are dark in color and, while these dark colored overbased barium salts are effective stabilizers for halogen-containing organic polymer, their dark color results in the discoloration of the end product. This feature essentially prohibits the use of dark colored overbased barium salts in applications where a light colored polymer product is desired.

According to the teachings of U.S. Pat. No. 4,665,117, light colored alkali or alkaline earth metal salts are prepared where alkyl phenol is used as a promoter. However, alkyl phenol is also a major cause for the development of color in the final product. This problem is overcome by the use of propylene oxide which displaces the hydrogen of the phenolic hydroxyl group and thereby restricts the formation of colored species. However, there are disadvantages associated with this approach, principally due to the toxic nature of propylene oxide. Propylene oxide is classified as a possible carcinogen and laboratory animal inhalation studies have shown evidence of a link to cancer. Propylene oxide is also listed as a severe eye irritant, and prolonged exposure to propylene oxide vapors may result in permanent damage to the eye. Furthermore, propylene oxide is extremely flammable and explosive in nature under certain conditions. Propylene oxide boils at 94° F. and flashes at −20° F. As a result, extreme precautions are required to handle propylene oxide at the plant site. Special storage equipment is required for propylene oxide and other safety features are necessary. U.S. Pat. No. 4,665,117 describes the use of propylene oxide at 150° C. At this temperature, propylene oxide will be in the gaseous phase. Under these operating conditions, more than stoichiometric amounts of propylene oxide are required to carry the reaction to completion because propylene oxide will escape from the reaction mixture and this requires additional handling of the excess propylene oxide.

Liquids of overbased metal carboxylate salts are also used in the preparation of greases. In particular, grease manufacturing includes a multi-step process and numerous additives to provide property enhancements which present an increasing challenge to the specialty, food-grade and bio-based grease formulators. The resulting grease performance is also strongly dependent upon the processing conditions such as temperature, pressure, residence times and saponification stoichiometry.

Thixotropic greases or grease-like overbased metal carboxylate or other overbased metal-containing compositions having corrosion-inhibiting properties, and having utility for a variety of uses such as, for instance, in automobile and truck body undercoatings, and for various other purposes, are known to the art. Such greases or grease-like compositions have gone into quite widespread use either as such, or admixed with other ingredients to produce compositions for use in a variety of environments, and, generally speaking, they are characterized by reasonably good extreme pressure and antiwear properties, high dropping points, reasonably good resistance to mechanical breakdown, salt spray and water-corrosion resistance, thermal stability at high temperatures, and other desirable properties.

Whether the liquid of an overbased metal carboxylate salt is utilized in halogen-containing organic polymers or in the preparation of greases, volatile components, including volatile organic compounds (VOCs), of the overbased metal carboxylate should be minimized for health, safety and environmental reasons.

Notwithstanding the state of the art as described herein, there is a need for further improvements in preparing overbased alkaline earth metal salts of fatty acids for use in halogen-containing organic polymers and in the preparation of greases, wherein the overbased alkaline earth metal salts have substantially reduced levels of volatile components within the final product.

In general, one aspect of the invention is to provide a shelf stable liquid of an overbased alkaline earth metal salt of a fatty acid, wherein the alkaline earth metal content is at least about 14.5% and the non-volatile matter content is at least about 95%.

In yet another aspect of the invention, a shelf stable, flowable liquid of an overbased alkaline earth metal salt of a fatty acid is provided. The liquid includes at least one hydrocarbon liquid, a polyol, an alcohol, wherein the alcohol has at least 8 carbon atoms, and an overbased alkaline earth metal salt of a fatty acid, wherein the alkaline earth metal salt has an alkaline earth metal content of at least about 14.5% and a non-volatile matter content of at least about 95%.

In another aspect of the invention, a method for preparing a shelf stable, flowable liquid of an overbased alkaline earth metal salt of a fatty acid is provided, the method includes the steps of:

(a) preparing a precursor mixture comprising a carboxylic acid, wherein the carboxylic acid is a fatty acid; at least one hydrocarbon liquid; a polyol; and an alcohol, wherein the alcohol has at least 8 carbon atoms;

(b) neutralizing the carboxylic acid with an initial amount of alkaline earth metal base to form an alkaline earth metal carboxylate precursor mixture;

(c) heating the alkaline earth metal carboxylate precursor mixture;

(d) adding an additional amount of an alkaline earth metal base to the alkaline earth metal carboxylate precursor mixture;

(e) carbonating the precursor mixture to neutrality;

(f) filtering the precursor mixture; and

(g) distilling the precursor mixture until an alkaline earth metal content of at least about 14.5% and a non-volatile matter content of at least about 95% is achieved.

These and other advantages and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description.

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