Process for preparation of overbased petroleum oxidates, the obtained overbased petroleum oxidates and their use

Abstract: A method is disclosed for preparing overbased petro­ leum oxidates which comprises carbonating a petroleum oxi­ date in the presence of a base selected from the group consisting of alkali metal compounds and alkaline earth metal compounds. The petroleum oxidate is made by oxidiz­ ing petroleum oil in the presence of a base. The over­ based petroleum oxidates are useful as rust inhibitors, dispersants, detergents, friction modifiers and as a sub­ strate for overbased sulfonates, phenates, and salicy­ lates. The overbased sulfonates, phenates and salicylates are easily overbased and have improved storage stability and improved rust inhibition.

Description: Field of the Invention This invention relates to a method of preparing overbased petroleum oxidates. More particularly, it relates to a process for preparing an alkali or alkaline earth metal overbased petroleum oxidate by carbonating the petroleum oxidate in the presence of a solubilized alkali or alkaline earth metal compound and to the overbased petroleum oxidate prepared thereby. The overbased alkali metal or alkaline earth metal petroleum oxidate can be an overbased calcium petroleum oxidate, an overbased magnesium petroleum oxidate, or an overbased sodium petroleum oxidate, as well as other overbased petroleum oxidates. The operation of diesel and spark ignition internal combustion engines is typically accompanied by the formation of sludge, lacquer and resinous deposits which adhere to the moving engine parts and thereby reduce engine efficiency. In order to prevent or reduce the formation of these deposits, a wide variety of chemical additives has been developed for incorporation into lubricating oils. These additives, which are commonly referred to as detergents or dispersants, have the ability to keep deposit-forming materials suspended in the oil so that the engine remains in a clean and efficient operating condition for extended periods of time. Among the many additives which have been developed for this purpose, certain alkaline earth metal salts have been found to be highly effective detergents for lubricating oils. In addition to serving as highly efficient detergents additives for lubricating oils, alkaline earth metal salts are also excellent oxidation and corrosion inhibitors. Further, these salts have the ability to neutralize acidic combustion products which are formed during engine operation. The formation of these acidic products is a particular problem during engine operation with high sulfur fuels. These acids appear to cause degradation of the lubricating oil and are corrosive to metal engine components such as bearings. If uncontrolled, the corrosion induced by acidic combustion products can cause rapid engine wear and a resulting early engine breakdown. To further improve the ability of alkaline earth metal salt additives to neutralize acidic combustion products, these additives are commonly overbased. Although overbased calcium and barium phenates and sulfonates, among other salts, have been widely known and used as detergents and sulfonates, overbased petroleum oxidates and the easy ability to make and use highly overbased petroleum oxidates have not been previously known. The present invention is predicated on the discovery that petroleum oils, oxidized in the presence of an amount of a basic metal salt, such as metal hydroxides or, preferably, an amount of an overbased petroleum oxidate of the same composition as the overbased petroleum oxidate product, can be overbased by carbonation in the presence of an inorganic base. The carbonated overbased product of the petroleum oxidate can be used directly in a lubricant formulation as a rust inhibitor or as a lubricating oil detergent. Description of the prior art The preparation of oxidized petroleum oils and their use as detergents in lubricating oils is known in the art. U.S. Patent No. 3,083,161 and U.S. Patent No. 3,055,828 describe the oxidation of oil in the presence of am alkali metal or alkaline earth metal compound at either one or two temperatures with a dispersant present. All of the metal is added in the beginning of the process. U.S. Patent No. 2,779,737 to Koft discloses the preparation of calcium salts of oxidized petroleum oils by a process which comprises the steps of oxidizing a petroleum oil in the presence of calcium hydroxide and reacting the product thus obtained with a calcium salt selected from the group consisting of calcium chloride, calcium hypochlorite and a mixture of calcium chloride and calcium hydroxide in the presence of water. The oxidation step is carried out at a temperature within the range of from about 121° C (250°F) to about 316° C (600°F) while passing air or oxygen through the reaction mixture. By reacting the oxidation product with a calcium salt, calcium content of the oxidized oil product is increased from about 3 equivalents of calcium in the oxidized product to about 3.35 to about 3.65 equivalents of calcium in the reacted product. U.S. Patent No. 2,864,846 to Gragson discloses the preparation of alkaline earth salts of oxidized petroleum oils by a process which comprises the steps of oxidizing petroleum oil with air in the presence of an oxidation catalyst, preferably a P₂S₅-terpene reaction product, and neutralizing the treated oil with an alkaline earth hydroxide or oxide. U.S. Patent No. 2,895,978 to Brooks discloses a process for oxidation of petroleum oils in the presence of excess amounts of a metal hydroxide over and above that which is eventually taken up by the oil during the oxidation. The metal salts produced contain about 2 equivalents of metal per equivalent of acid-hydrogen formed during the oxidation. U.S. Patent No. 2,975,205 to Lucki discloses a process for preparation of metal salts of oxidized petroleum oils which comprises oxidizing petroleum oil in the presence of a metal hydroxide to incorporate the metal hydroxide into the oil and then reacting the product obtained with more metal hydroxide in the presence of water to incorporate an additional amount of metal hydroxide into the product. U.S. Patent No. 2,978,470 to Christensen discloses a process for air oxidation of petroleum oils in the presence of a catalyst such as potassium permanganate or potassium stearate. The oxidation is carried out until the change has a saponification number of about 100 to 150. Accordingly, although the oxidation of petroleum oils to prepare a petroleum oxidate has been known, the prior art neither teaches nor suggests the invented process comprising carbonation of a petroleum oxidate in the presence of an inorganic base to produce a highly overbased petroleum oxidate, which is useful as a detergent, dispersant and rust inhibitor. Also, the prior art neither teaches nor suggests that petroleum oxidate as a process modifier improves overbasing processes for preparing overbased sulfonates, phenates and salicylates useful as lubricating oil detergents and dispersants. Summary of the Invention A process is disclosed for preparation of novel lubricant additives useful in lubricating oils and greases comprising overbased alkali metal and alkaline earth metal petroleum oxidates. Detailed Description of the Invention The invention comprises the method of overbasing an oxidized petroleum oil to produce an overbased petroleum oxidate and the products resulting from the overbasing process. The term "overbased" is applied to designate the presence of basic metal salts wherein the metal is present in stoichiometrically larger amounts than the organic acid radical. The petroleum oil is oxidized by an oxygen-containing gas or compound in the presence of a base. The presence of a base is an essential element of the oxidation process. The base can be insoluble, such as sodium hydroxide, but a soluble base such as an overbased sulfonate is preferred. Air oxidation in the presence of an overbased petroleum oxidate of calcium, magnesium or sodium as catalyst is more preferred. Other overbased petroleum oxidates of barium, potassium and strontium can also be used. The resulting petroleum oxidate has a TBN of about 1-10. The petroleum oxidate can be treated with inorganic base and carbonated to yield a clear, overbased oxidate of high TBN. A satisfactory feedstock for the invented process is that prepared from topped crude oils obtained from any source, for example, Pennsylvania, Mid-Continent, California, East Texas, Gulf Coast, Venezuela, Borneo and Arabian crude oils. In this method, a crude oil is topped, i.e., distilled to remove therefrom more volatile and light gas oil, and then vacuum-reduced to remove heavy gas oil and light lubricating oil of the SAE-10 and 20 viscosity grade. The vacuum-reduced crude is them propane fractioned to remove additional heavier fractions of lubricating quality hydrocarbons. Following the propane fractionation step, the overhead oil fraction is solvent-extracted with a selective solvent which will separate the paraffinic hydrocarbons from the more aromatic type hydrocarbons. This solvent extraction step for the removal of the more highly aromatic compounds can be carried out in accordance with the well-known concurrent or countercurrent solvent extraction techniques which are well known in the art. The resulting solvent-extracted material, before or after the removal of the more aromatic hydrocarbons, is preferably dewaxed. The dewaxing can be carried out by any conventional method, e.g., by solvent dewaxing using propane or other known solvents and solvent mixtures such as methylethylketone or methylisobutylketone with benzene at a suitable temperature. A preferred feed material for the oxidation reaction is a substantially saturated hydrocarbon fraction having at least 40 carbon atoms per molecule, preferably between 40 and 80 carbon atoms per molecule, a refractive index n D ²⁰ of between 1.440 and 1.520, an average molecular weight between 550 and 1300, a viscosity of between 50 and 1400 SUS at 99°C (210°F), and a viscosity index, when determinable, of between 50 and 125. The oxidizing reaction of the petroleum feed material is accomplished in the presence of a basic catalyst by contacting the selected hydrocarbon fraction, as hereinbefore described, under suitable conditions of temperature and pressure with an oxidizing agent such as free oxygen, sulfur trioxide, nitrogen dioxide, nitrogen trioxide, nitrogen pentoxide, acidified chromium oxide and chromates, permanganates, peroxides, such as hydrogen peroxide, and sodium peroxide, nitric acid and ozone. Any oxygen-containing material capable of releasing molecular oxygen under the condition can be used. Air is a preferred oxidizing agent from the standpoint of economy. Generally, the oxidation reaction is carried out at a temperature in the range of from -40° C (-40° F) to 427° C (800° F). When air is used as the oxidizing agent, temperatures in the range of 37,8° C (100° F) to 427° C (800° F), preferably 199° C (390° F) to 302° C (575° F), are generally used. When nitric acid is used as the oxidation agent, temperatures ranging from room temperature up to 93,3° C (200° F), preferably 60°C (140° F) to 76,7° C (170° F), are ordinarily used. The oxidation reaction can be carried out at sub-atmospheric, atmospheric or super-atmospheric pressure. The reaction is preferably carried out at a pressure of between about 0,689 bar to 6,89 bar (about 10 to 100 pounds per square inch) absolute depending upon the composition of the oxidizing gas. A basic catalyst must be present during the oxidation of the petroleum feed stock. An oxidation catalyst also can be present to promote the oxidation reaction. The oxidation catalyst can be selected from the group of well-known oxidation catalysts such as oil-soluble salts and compounds containing such metals as copper, iron, cobalt, lead, zinc, cadmium, silver, manganese, chromium and vanadium. Any base may be used as the basic catalyst. It can be soluble or insoluble. Typical basic catalysts include calcium hydroxide, sodium hydroxide, overbased sodium, calcium or magnesium sulfonate, or an overbased oxidate of high TBN (one of the products of this invention process). Powdered, insoluble catalysts such as calcium hydroxide are inexpensive, but the oxidate must then be filtered to remove inreacted base. In order to eliminate the need for this filtering step, it is preferred to use a homogeneous base, for example, a high-base calcium sulfonate. Enough base must be used so that the total mass of oil and base has a TBN of at least 2 before oxidation. There is no upper limit to the amount of homogeneous base which can be used, but economically it is undesirable to use more than 3% of this component. For example, if the basic catalyst is sodium hydroxide, calcium hydroxide, 300 TBN calcium sulfonate, 400 TBN magnesium sulfonate, or 400 TBN sodium oxidate, the minimum base levels necessary to yield a highly overbasable oxidate would be 0.14%, 0.13%, 0.67%, 0.5%, or 0.5%, respectively. Chemically, there is no upper limit for these bases, but there are practical upper limits. For the inexpensive insoluble bases such as sodium or calcium hydroxide, unreacted base must be filtered, and it is convenient to limit the level of base to about 2-3%. For the more expensive soluble bases such as overbased sulfonates, 2-3% is always adequate and can be described as the upper practical limit. The use of very high levels of overbased sulfonate as catalyst would thwart the very usefulness of this invention, namely, a less expensive overbasing substrate (soap) than sulfonate. Since the product, high-base petroleum oxidate, of the invented process is less expensive than high-base sulfonate, it is less costly to use the high base petroleum oxidate as catalyst instead of high-base sulfonate. Homogeneous catalysts, such as high base calcium sulfonate, have been used at levels of 1% to 3% in the base oil. The resulting petroleum oxidate has a TBN of at least 2. Although the oxidate can have a high TBN, the upper limit should be about 12 TBN for economic reasons. Typical petroleum oxidates will have TBNs of about 5-8. Unexpectedly, it has been found that highly overbased products (100 TBN and higher) can be made using these oxidates as an inexpensive substrate instead of the usual phenate, sulfonate, or salicylate. The oxidates prepared as described above can be overbased by carbonating to clear, highly alkaline products. The exact reason as to why clear, highly alkaline products result from using petroleum oxidate as the substrate is not known, but it is believed that the alkaline salts of Group I and Group II metals are finely dispersed by the oxidate. The products have TBNs much higher than previously achieved, as taught in the prior art. The commonly employed methods for preparing the basic salts involves heating a mineral oil solution of an acid with a stoichiometric excess of a metal neutralizing agent such as the metal oxide, hydroxide, carbonate, bicarbonate or sulfide at a temperature about 50°C and filtering the resulting mass. The use of a "promoter" in the neutralization step and the incorporation of a large excess of metal likewise is known. Examples of compounds useful as the promoter include phenolic substances such as phenol, naphthol, alkylphenol, thiophenol, sulfurized alkylphenol, and condensation products of formaldehyde with a phenolic substance; alcohols such as methanol, 2-propanol, octyl alcohol, Cellosolve, Carbitol, ethylene glycol, stearyl alcohol, and cyclohexyl alcohol, amines such as aniline, phenylenediamine, phenothamine, phenyl beta-naphthylamine, and dodecylamine. A particularly effective method for preparing the basic salts comprises mixing an acid with an excess of a basic alkaline earth metal neutralizing agent, a phenolic promoter compound, and a small amount of water and carbonating the mixture at an elevated temperature such as 60°-200°C. The overbasing process is carried out in the presence of an organic solvent if more fluidity is desired. Such solvents can be benzene, toluene, xylene or rafinate, among others. The invented process for preparation of an overbased alkali metal or alkaline earth metal petroleum oxidate additive for lubricants with detergent, dispersant, anti-rust and friction modifying properties accordingly comprises: (a) introducing into a reaction zone a petroleum oil, (b) a base selected from the group consisting of an alkali metal compound or an alkaline earth metal compound to form a mixture, (c) contacting said mixture with an oxidizing gas or compound at a temperature from about -40° C (-40°F) to about 427°C (800° F) to effect oxidation of said petroleum oil and reaction of said base with the oxidized oil, (d) optionally, filtering said mixture to separate the base-reacted oxidized oil, (e) carbonating said base-reacted oxidized oil in the presence of a base selected from the group consisting of an alkali metal compound and an alkaline earth metal compound to form a mixture comprising water and an overbased alkali metal or alkaline earth metal petroleum oxidate, (f) optionally filtering said mixture to remove unreacted alkali metal compound or alkaline earth metal compound, and (g) stripping said overbased alkali metal or alkaline earth metal oxidate additive to remove water. The alkali metal compound or alkaline earth metal compound for step (b) is selected from the group consisting of the oxides, hdyroxides and carbonates of sodium, potassium, calcium, magnesium, barium and strontium. The alkali metal compound or said alkaline earth metal compound for steps (b) and (e) also can be selected from the group consisting of oxides, hydroxides, carbonates, sulfonates, phenates, salicylates and an overbased petroleum oxidate. The alkali metal compound or alkaline earth metal compound of step (b) also can be selected from the group consisting of oxides, hydroxides and carbonates of sodium, potassium, calcium, magnesium, barium and strontium, and said alkali metal or alkaline earth metal compound of step (e) can be selected from the group consisting of sulfonates, phenates, salicylates, and an overbased petroleum oxidate. The following examples are illustrative of typical embodiments of this invention and should not be considered as limiting the scope of the invented process and compositions. Example I The following example illustrates the preparation of an oxidized calcium mineral oil which can be overbased to yield oil-miscible alkaline agents. A suitable vessel was charged with: 679 g Amoco Oil HX-40 21 g high-base calcium sulfonate (300 TBN) 0.283 m³/hr (10 ft. ³/hr.) air The mixture was heated to a temperature of 204° C (400° F) 4 hours. The product exhibited an activity of 68 % on silica gel with hexane as eluent in an elution column. It needed no filtering because the basic catalyst was soluble. It had a TBN of 7. Example II In the procedure of Example I, a sodium oxidate was prepared. A suitable vessel was charged with: 980 g Amoco Oil HX-40 20 g 400 TBN Sodium-Overbased Oxidate (as prepared in Example V) 0.283 m³/hr (10 ft. ³/hr) air The mixture was heated to a temperature of 204° C (400° F) for 7.5 hours. Water collected overhead was 14 g. Light oil collected in a dry ice condenser was 9 g. The product was 50% active on silica gel in an elution column using hexane as the eluent. The product needed no filtering, and it had a TBN of 6. The product could also be made using NaOH as the basic catalyst, but then it would have to be filtered to remove unreacted base. Example III In the procedure of Example I, a magnesium oxidate was prepared. A suitable vessel was charged with: 2,910 g Amoco Oil HX-40 90 g high-base magnesium sulfonate (400 TBN) 0.283 m³/hr (10 ft.³ air/hr) The mixture was heated at 202° C (395° F) for 4 hours. The product was 39% active on silica gel in an elution column, using hexane as the eluent. The product was clear without filtration and had a TBN of 9. Example IV The product from Example I was overbased with calcium as follows: To a 2-liter, 3-neck round bottom flask fitted with a heating mantle, reflux condenser, stirrer and dropping funnel there was added 100 ml calcium oxidate from Example I, 300 ml xylene, and 10 grams calcium oxide. The mixture was then heated, and 5.5 grams of methanol were added when its temperature reached 38°C, and 0.9 grams of water were added when its temperature reached 60°C. Heating was continued and the resulting mixture heated at reflux (about 81°C.) for 10 hours. A Dean Stark water trap was placed between the reaction flask and the reflux condenser. After cooling to 38°C, the mixture was treated with gaseous carbon dioxide which was introduced below the surface of the reaction mixture at a rate of .41 liter/minute over a period of 8 minutes while the reaction mixture was maintained at a temperature of 38°-46°C. A total of 3.3 liters of carbon dioxide were absorbed by the reaction mixture. The mixture was then heated to 121°C to remove water by way of a Dean Stark water trap. Next, 10 grams calcium oxide, 0.9 grams water and 5.5 ml methanol were added and the resulting mixture carbonated with carbon dioxide for 9 minutes. An additional 2.0 liters of carbon dioxide were absorbed. Finally, the mixture was cooled to 37,8° C (100° F) and filtered The filtrate was nitrogen-stripped at a temperature of about 182° C (360° F) to remove water and methanol. The overbased calcium oxidate had a TBN of 120, a level of calcium oxidate overbasing not previously known in the prior art. To my knowledge, use of petroleum oxidate as the substrate for overbasing to such a high TBN was not taught or suggested in the prior art. Although acidic substrates such as sulfonic acids, phenols, carboxylates and other acidic compounds are widely used to make overbased products and, although it has long been known that mineral oils oxidize in the presence of air at high temperatures, it has not been previously known that mineral oil can be oxidized to make clear substrates which can be overbased to make highly (e.g., TBNs 100-500) alkaline agents suitable as rust inhibitors or detergents. Example V The petroleum oxidate from Example II was overbased with sodium as follows: To a 2-liter, 3-neck round bottom flask fitted with a heating mantle, reflux condenser, stirrer and dropping funnel there was added 100 grams petroleum oxidate from Example II, 200 ml xylene and 370 grams of 20% NaOH in methanol. The mixture was stirred and heated to about 107° C (225° F), removing and condensing the volatiles coming off as overhead. Then 16.8 liters of carbon dioxide were introduced into the mixture at a rate of 0.6 l/minute at a temperature of 107° C (225° F). Carbonation was then stopped, and the mixture was cooled to 37,8° C (100° F) and filtered. The filtrate was then heated to about 182° C (360° F) and nitrogen-stripped for a period of about 1 hour to remove water and xylene. The resulting product was a clear, amber viscous fluid and had a TBN of 413. To my knowledge, an overbased sodium oxidate with a high TBN has not been previously known, and the prior art does not suggest the possibility. Example VI Petroleum oxidate from Example III was overbased with magnesium as follows: To a 2-liter, 3-neck round bottom flash fitted with a heating mantle, reflux condenser, stirrer and dropping funnel, there was added 65 grams of magnesium petroleum oxidate from Example III, 100 grams xylene, 20 grams magnesium oxide and 25 ml methanol. The mixture was refluxed at a temperature of about 82,2° C (180° F) for a period of about one minute. Water, 40 ml, was added and the mixture was again refluxed at a temperature of about 104,4° C (220°F) for about one hour. The mixture was then nitrogen-stripped at a temperature of about 138° C (280° F) for a period of about 20 minutes ro remove methanol which also removed some water. The mixture was cooled to about 48,8° C (120° F) and 17 ml water was added. Carbon dioxide was introduced into the mixture at a rate of 0.6 l/min. for a period of about 30 minutes. Approximately 5 liters of carbon dioxide were absorbed. The mixture was cooled and filtered. The filtrate was nitrogen-stripped at 182° C (360° F) to remove water, xylene and remaining methanol. The product, an overbased magnesium oxidate, was a clear amber liquid with a TBN of 147. To my knowledge, overbased magnesium oxidates of such high TBN have not been reported in the prior art.

Claims: A process for the preparation of an overbased alkali metal or alkaline earth metal petroleum oxidate additive for lubricants useful as a detergent, dispersant, and antirust friction modifier, said additive having a TBN of 100 to 500, said process comprising: (a) introducing into a reaction zone a petroleum oil and a base selected from the group consisting of an alkali metal compound or an alkaline earth metal compound in relative proportions to form a mixture having a TBN of at least 2; (b) contacting said mixture with an oxidizing gas or compound at a temperature from -40° C (-40° F) to 427° C (800° F) to effect oxidation of said petroleum oil and reaction of said base with the oxidized oil, to thereby form a basic petroleum oxidate; (c) optionally filtering said basic petroleum oxidate to separate solids therefrom, the basic petroleum oxidate resulting from (b), or (c) if used, having a TBN in the range of 2 to 12; (d) introducing into the basic petroleum oxidate resulting from (b), or (c) if used, an alkali or alkaline earth metal base, a promoter and carbon dioxide gas and maintaining the reaction mixture under conditions causing carbonation and overbasing to occur and thereby form a reaction mixture comprising an overbased alkali metal or alkaline earth metal petroleum oxidate; (e) optionally filtering the reaction product mixture to remove unreacted alkali or alkaline earth metal base; and (f) stripping the reaction product mixture to remove water therefrom; the basic petroleum oxidate, alkali or alkaline earth metal base, promoter and carbon dioxide gas used in (d) being proportioned such that the stripped reaction product resulting from (f) has a TBN in the range of 100 to 500. The process of Claim 1 wherein the metal of the bases for steps (a) and (d) is selected from the group consisting of sodium, potassium, calcium, magnesium, barium or strontium. The process of Claim 1 or 2 wherein said alkali metal compound or alkaline earth metal compound for step (a) and said alkali or alkaline earth metal base for step (d) is selected from the group consisting of oxides, hydroxides and carbonates. The process of any of Claims 1 to 3 wherein the promoter is an alcohol, a phenol or an amine. The process of any of Claims 1 to 3 wherein the promoter is methanol and wherein the promoter is used in the presence of a small amount of water. The process of any of Claims 1 to 5 wherein said petroleum oil is a substantially saturated hydrocarbon fraction having at least 40 carbon atoms per molecule, a refractive index n 20 / D of between 1.440 and 1.520, an average molecular weight between 550 and 1300, a viscosity of between 50 and 1400 SUS at 99° C (210° F), and a viscosity index, when determinable, of between 50 and 125. The overbased alkali metal petroleum oxidate additive or overbased alkaline earth meal petroleum oxidate additive prepared by the process of any of Claims 1 to 6. The overbased petroleum oxidate of Claim 7 wherein said overbased petroleum oxidate is an overbased calcium petroleum oxidate. The overbased petroleum oxidate of Claim 7 wherein said overbased petroleum oxidate is an overbased magnesium petroleum oxidate. The overbased petroleum oxidate of Claim 7 wherein said overbased petroleum oxidate is an overbased sodium petroleum oxidate. A lubricating composition comprising a lubricating oil or grease and an overbased alkali metal petroleum oxidate or an overbased alkaline earth metal petroleum oxidate of any of Claims 7 to 10. The use of the overbased alkali metal or alkaline earth metal petroleum oxidates obtained by the process of any of Claims 1 to 6 as additives for lubricants. The use of the overbased alkali metal or alkaline earth metal petroleum oxidates obtained by the process of any of Claims 1 to 6 as a detergent, dispersant and/or antirust friction modifier for lubricants.

Inventors: SLAMA FRANCIS JOHN, SLAMA, FRANCIS JOHN
Applicants: ETHYL CORP, ETHYL CORPORATION
Application year: 1987
Main classification: C10M159
IPC codes: C10N50, C10N40, C10M159, C10N30, C10N10