Oxidation of Hydrocarbon Waxes in the Presence of Sulfobetaines

This invention relates to the oxidation of hydrocarbon waxes. More particularly, it is concerned with a process for oxidizing hydrocarbon waxes to produce useful oxygenated products.

Oxidized petroleum fractions including waxes and petrolatums have, in the past, been employed as the source of saponifiable material in the production of lubricating greases and in the formulation of protective coatings. The oxidates employed for these purposes have been obtained by oxidizing selected petroleum fractions under controlled conditions such that the oxidation proceeds only to a limited extent.

Oxidation of petroleum fractions by the above described method had, associated with it, certain difficulties. Some petroleum fractions are not easily oxidized by the prior art processes and even though oxidizable, in some instances, require a preliminary induction period before the rate of oxidation becomes appreciable. Another problem associated with oxidizing petrolatums is the discoloration of the final wax product rendering it aesthetically unattractive for use in some formulations.

One object of this invention is to provide an improved process for the oxidation of petrolatums. Another object of the invention is to provide a process for oxidizing petrolatums more easily than has heretofore been possible.

Briefly stated, this invention comprises a process for oxidizing hydrocarbons comprising blowing through a molten mixture of hydrocarbon wax an oxidizing gas in the presence of a minor amount of a sulfobetaine or mixture thereof.

The oxidation is conducted under suitable conditions of gas flow, pressure and temperature to oxidize the hydrocarbon wax to a predetermined acid number.

The sulfobetaines used in the process of this invention may be represented by the structural formula: ##STR1## wherein R.sub.1 is a high molecular alkyl radical having from 10 to 18 carbon atoms or the amido radical RCONH(CH.sub.2).sub.3 wherein R is a higher alkyl radical of 10 to 18 carbon atoms. R.sub.2 and R.sub.3 are each alkyl radicals having from about 1 to 3 carbon atoms. R.sub.4 is an alkylene or hydroxyalkylene radical having from 1 to 4 carbon atoms, and X is an SO.sub.3 radical. R.sub.1 and R may be a mixture of a high molecular weight alkyl radical and may contain one or more intermediate linkages such as ether or polyether linkages or non-functional substituents such as hydroxyl or halogen radicals. Examples of sulfobetaines useful herein include coco dimethyl sulfopropyl betaine, stearyl dimethyl sulfopropyl betaine, lauryl bis-(2 hydroxypropyl) sulfopropyl betaine and the like, amido betaines and amidosulfobetaines, wherein the RCONH(CH.sub.2).sub.3 radical is attached to the nitrogen atom of the betaine.

A preferred sulfobetaine is coco dimethylsulfopropyl betaine. Ordinarily, the sulfobetaine is added in a concentration of between 0.2 and 2 parts by weight per 100 parts of hydrocarbon wax. Generally, the sulfobetaine will be in the form of an aqueous solution.

The hydrocarbons useful in this process are the conventional feedstocks previously used as oxidizer feedstock. Ordinarily, said feedstock comprises a mixture of saturated hydrocarbons having an average number of carbon atoms per molecule of 20 to 100. A particular characteristic of some feedstocks is the high concentration of nitrogen present in the molecular structure of some of the hydrocarbons making up the feedstock. The presence of nitrogen appears to inhibit the initiation of the oxidation of the hydrocarbons to their corresponding acids when blown with air.

Accordingly it may be desirable to add a promoting agent to overcome this initial inhibition of oxidation and to initiate the oxidation process.

I prefer to add as an oxidation promoter a quaternary ammonium compound having the formula: ##STR2## where R.sub.1 is an aliphatic hydrocarbon radical of 10 or more carbon atoms, R.sub.2 is an aliphatic hydrocarbon radical of 1 to 12 carbon atoms, and X.sup..crclbar. is chloride, bromide, iodide, sulfate, or bisulfate.

Although a number of quaternary compounds are deemed suitable for the promoter catalyst in the process of this invention, preferred promoters are dodecyltrimethylammonium chloride or a mixture of quaternary compounds having the formula: ##STR3## wherein R collectively represents the alkyl residue of a primary alcohol mixture composed of 30-70 wt. percent of (a) straight-chain C.sub.16 -C.sub.22 alcohols and correspondingly from 70-30 wt. percent fo (b) C.sub.8 -C.sub.15 Oxo alcohols consisting essentially of a mixture of straight-chain and single methyl branched isomers, said (a) and (b) being in relative proportions so that from about 95-80 wt. percent of said R.sub.1 groups are straight-chain alkyl and correspondingly from 5-20 percent are said branched alkyl, R is a C.sub.1 -C.sub.3 alkyl group, X represents a chloride, bromide or iodide anion, and wherein said mixture of quaternaries is essentially composed of 0-10 wt. percent of compounds of Formula I, 60-85 wt. percent of compounds of Formula II, and 5-25 wt. percent of compounds of Formula III, said mixture being prepared by ammonolysis of a mixture of the corresponding R.sub.1 OH alcohols and subsequent quaternization of the ammonolysis product.

The preparation and composition of these quaternary compounds is disclosed in U.S. Pat. No. 3,803,137 which is hereby incorporated by reference. The quaternary compound is added to the hydrocarbon fraction in a minor amount, preferably in a concentration of between 0.5 and 2 parts by weight per 100 parts of hydrocarbon.

Ordinarily, the process will be carried out as a batch process. Air or another oxidizing gas is forced through the reaction mixture of hydrocarbon, sulfobetaine and quaternary compound, if the latter is used, at a rate of between 0.5 and 10 liters (measured at 760 mm of mercury and 25.degree. C.) per liter of hydrocarbon per minute at a temperature of between 150.degree. and 180.degree. C. Ordinarily, the temperature will rise as the oxidation proceeds so that only minimal heat may be required for the oxidation. The oxidation process is conducted at a pressure of between 50 and 400 psig (4.4-28.2 atmospheres). The process is discontinued when a desired acid number is reached. The term "acid number" is defined to mean the number of milligrams of potassium hydroxide required to neutralize 1 gram of sample.

The following example represents the best mode of conducting the process of this invention known to applicant at the date of filing this application.

A number of air oxidations were conducted in laboratory tests using a 1 liter Parr bomb. In each test, the reactor charge amounted to approximately 500 cc of hydrocarbon. To the hydrocarbon material was added the weights of sulfobetaine, (in a 28-30% solution in water) shown in the accompanying table. For comparison purposes runs were also made in which no sulfobetaine was added. The feedstocks studied included both slack waxes and petrolatum samples. The reaction conditions were approximately three hours for each reaction at a temperature of approximately 320.degree. F. (160.degree. C.), a pressure of 200 psig (14.6 atmosphere), and an air input rate of 3.8 liters of air (measured at 25.degree. C. and 1 atmosphere) per liter of reactor charge per minute. Acid number determinations were made at the end of each three-hour run. The results are shown in Table I. Table I also shows the acid numbers obtained when the same hydrocarbon materials were oxidized under the same conditions in the absence of sulfobetaine.

From a comparison of Runs 1-A, 2-A and 3-A in which the sulfobetaine was added with Runs 1-B, 2-B and 3-B in which sulfobetaine was absent indicates that without the addition of the sulfobetaine no oxidation of the hydrocarbons would have resulted.