Process for Preparing Overbased Calcium Sulfonates

This invention is an improved process for preparing overbased calcium sulfonates which are used as detergent and reserve alkalinity lubricating oil additives.

In the course of operation, internal combustion engines convert lubricating oil to acidic degradation products. Those acidic degradation products attack and corrode engine parts and catalyze the formation of sludge, thereby reducing lubricity and accelerating wear of moving parts in contact with the lubricating oil.

It is desirable to add basic substances to the lubricating oil which neutralize acids as they are formed in the engine before they reach concentrations sufficient to cause corrosion or to catalyze the sludge reaction. Adding an alkalinity agent to the detergent in motor oil is known as overbasing. Colloidal carbonates of the alkaline earth metals have been found to be well suited for this purpose. These carbonate dispersions are stabilized by oil soluble surface active agents with the sulfonates of the alkaline earth metals in which the sulfonic acid portion of the molecule has a molecular weight of preferably 450 to 600. The sulfonates are made by sulfonation of lubricating oil fractions from petroleum and by sulfonation of alkyl benzenes having the desired molecular weight for this purpose. Benzene alkylates with straight chain alkyl groups are especially desirable.

In general the process of preparing oils which contain overbased calcium sulfonates comprises reacting a solution of alkylbenzene sulfonic acids having a molecular weight greater than 400, in oil with calcium oxide or hydroxide and bubbling carbon dioxide through the reaction mixture; thereby incorporating an excess of calcium carbonate into the calcium sulfonate which confers reserve alkalinity to the product.

U.S. Pat. No. 4,427,559 to J. R. Whittle teaches that a mixture of calcium oxide and calcium hydroxide can be used in the overbasing reaction to provide reserve alkalinity to neutral calcium sulfonates. It is reported that when mixtures containing up to 30% CaO are used, satisfactory products were obtained. When mixtures of 30 to 50% CaO were used, a gelatinous material which plugged the filter were obtained. Concentrations of CaO above 70% produced a fluid product containing finely divided particles which could not be filtered and were reflective of light. In this regard the patent teaches the criticality of the ratio of the calcium oxide to calcium hydroxide in the absence of a promoter in producing acceptable products.

U.S. Pat. No. 4,604,219 to J. R. Whittle teaches that calcium oxide may be used as the sole reserve alkalinity source in overbasing calcium sulfonates. This patent teaches in the absence of a promoter, that water addition rate and amount are critical in producing a low solids content, filterable product.

U.S. Pat. No. 4,086,170 to De Clippeleir et al. teaches overbased calcium sulfonates are prepared by reacting a solution of alkylbenzene sulfonic acids with an excess of a calcium oxide having a medium or low activity toward water and with carbon dioxide. Improved overbasing and filterability of the overbased sulfonate solution were obtained by the use of a promoter for the conversion of the calcium oxide to calcium hydroxide. Recommended promoters include ammonia or organic bases such as monoamines or diamines, e.g. ethylene diamine.

The invention is an improved process for preparing an overbased calcium sulfonate. Calcium sulfonates are overbased by diluting a neutral calcium sulfonate with a light hydrocarbon solvent and a lower alkanol. Next, calcium oxide and the total charge of water is added in an amount of 15 to 30 mole %, preferably 20 to 25 mole % of the calcium oxide to be added. The calcium oxide is added as a mixture with calcium hydroxide wherein the calcium oxide is 80 mole % to 40 mole %, preferably 65 mole % to 55 mole %. Calcium hydroxide is fully hydrated and is not accounted for in the addition of water. The admixture is then heated to about 100.degree. F. to 170.degree. F. at 0 to 50 psig and carbonated for 1 to 4 hours. A diluent oil is then added and the admixture filtered to remove solids. The liquid is stripped of solvent and the resulting liquid product recovered.

The invention is an improvement in U.S. patent. application Ser. No. 07/129,618 filed Dec. 12, 1987 for a Method of Preparing Overbased Calcium Sulfonates to Tze-chi Jao.

A process for overbasing calcium sulfonates has been discovered based on the use of a mixture of calcium oxide and calcium hydroxide in specified proportion as the source of inorganic calcium. The entire charge of water is added before the carbonation in an amount of 15 to 30 mole % of the calcium oxide. A clear product with a low solid waste is produced.

It is known to produce overbased sulfonates by means of calcium oxide alone or a mixture of calcium oxide and calcium hydroxide. Overbased sulfonates produced from calcium oxide-calcium hydroxide mixtures are noted for a hazy product with a relatively low level of overbasing. The instant invention is distinguished in the recognition that calcium oxide:calcium hydroxide ratio is essential to produce a clear, low solids content mixture for filtering.

The use of calcium hydroxide alone is undesirable because it typically produces a high solids content product and demonstrates low sulfonate utilization. Applicant's Ser. No. 07/129,618 filed Dec. 7, 1987 achieved an improvement in using calcium oxide alone. This process produced a clear product containing only amorphous calcium carbonate and a higher sulfonate utilization. The instant process is distinguished from Ser. No. 07/129,618 by a simplified process scheme while demonstrating equivalent sulfonate utilization and low solids content.

The operating parameters of the present process are tabulated in Table I.

Examples of useful and preferred reactants which may be employed in the practice of the invention are listed in Table II.

This invention is better shown by way of example.

A blend containing 32 parts by weight of a neutral calcium sulfonate, 91 parts heptane, 8 parts methanol, 10.6 parts calcium oxide and 9.3 parts calcium hydroxide was brought to reflux at 60.degree. C. in a 500 ml reaction flask. The resultant mixture was refluxed for 10 minutes. Water, 0.7 parts was added immediately before CO.sub.2 charge. CO.sub.2 was then introduced into the reaction mixture at a rate of 40 ml/min. The CO.sub.2 treatment was stopped after 135 minutes. Then 10 parts of pale oil was added and stirred for 10 minutes.

The filtered and solvent-stripped final product had a TBN value of about 400. Its IR spectrum showed a symmetric band at a frequency of 865 cm(-1), indicating amorphous calcium carbonate. The volume of solid waste in the crude product was about 11% to 15%.

The procedure of Example I was repeated. The following results were recorded:

A blend containing 11.8 parts by weight neutral calcium sulfonate, 32 parts crude heptane, 2.83 parts methanol, 3.8 parts calcium oxide and 3.3 parts calcium hydroxide was heated to 40.degree. C. in a 10-gallon reactor. Water, 0.24 part, was added. The reaction mixture was then brought to reflux at 60.degree. C. CO.sub.2 was introduced into the reaction mixture at a rate of 5.33 liter/min as soon as the reaction mixture reached the reflux temperature. The CO.sub.2 treatment was stopped after 165 minutes. Then 5.6 parts pale oil was added and stirred for an additional 10 minutes.

The filtered and solvent stripped final product had a TBN value of 398. Its IR spectrum showed a symmetric band with a frequency of 865 cm(-1) indicating amorphous calcium carbonate. The lime utilization was 86% and sulfonate utilization was 100%, while the solid volume in the crude product was about 13%. In a comparable commercial calcium hydroxide process under the same conditions, lime utilization was 60% and sulfonate utilization was 84%, while the solid volume in the crude product was about 40 to 50%.

TBN; ranging from 0 to 400, is the measure of the overbasing of 10 to 40 wt % calcium sulfonate with 0 to 50 wt % CaO, Ca(OH).sub.2, CaCO.sub.3 or mixture thereof.

While particular embodiments of the invention have been described, it will be understood, of course, that the invention is not limited thereto since many modifications may be made, and it is, therefore, contemplated to cover by the appended claims any such modifications as fall within the true spirit and scope of the invention.