US2161581A - Dewaxing of mineral oils - Google Patents

Description

Patented June 6, 1939 PATENT OFFICE DEWAXING OF MINERAL OILS Edwin C. Knowles, Beacon,

The Texas Company, poration of Delaware N. Y., assignor to New York, N. Y., a cor- No Drawing. Application January 27, 1938, Serial No. 187,161

4 Claims.

This invention relates to the dewaxing. of hydrocarbon oil, and particularly to the separation of wax from a mineral lubricating oil.

The invention contemplates the separation-of wax from ployment of a wax crystal modifying material to facilitate dewaxing by filtration, centrifuging or cold settling. The use of various crystal modifiers in dewaxing processes employing a diluting or dewaxing solvent has heretofore been suggested. These suggested modifiers include metal soaps, such as aluminum stearate, and various esters, such as glycerol and glycol stearates. Certain monosaccharose and disaccharose derivatives of aliphatic acids have also been suggested as pour depressants for mineral oil; and by analogy from the wax crystal modifying effect of pour depressants, the use of these materialsas dewaxing aids might be reasoned.

In commercial dewaxing plants employing dewaxing solvents, it is found difficult if not economically impossible to maintain the solvent of the system in an anhydrous condition, the solvent frequently containing as much as /2% or more of water. -It is found that the majority of dewaxing aids, such as those mentioned above, lose at least a substantial part of their, effectiveness in the presence of wet solvent. Moreover, due to hydrolysis in the presence of the wet solvent, suchaids result in obj ectionably raising the saponification number and the neutralization number of the dewaxed oil. Other dewaxing aids of the character of asphaltenes, petroleum residuums, coil tar fractions and the like cause an objection-discoloration of a pale oil being dewaxed.

In accordance with the present invention, there is used as a wax crystal modifying material in the dewaxing of mineral oil a higher fatty acid ester of a polysaccharide of the general formula (Cal-11105011., where n is a large number. Polysaccharides contemplated herein in.- clude cellulose and starch. The fatty acid radical or radicals are preferably stearates, palmi- 45 tates, oleates, and other higher fatty acids or mixtures thereof. These esters of the polysaccharides are found to possess unusual effectiveness as dewaxing aids and overcome objections of the esters and related compounds speci- 50 fled above which have heretofore been suggested for this purpose.

The esters of the polysaccharides may be employed alone as dewaxing aids, but they are preferably used in conjunction with montan wax or 55 a material analogous in its properties to montan such a wax bearing oil by the emwax. Where the expression montan wax is employed herein, it is to be understood that this refers to the crude montan wax or to the active ingredients which may be extracted or otherwise separated from crude montan wax. The acid treated or bleached. .and refined montan wax is comparatively ineffective for this purpose. The dewaxing aid is preferably employed in a proportion of less than 1% by weight on the weight of the wax bearing oil charge. Where the polysaccharide. ester is used alone, satisfactory results may be secured with a proportion of about 0.150.50%, with a proportion of around 0.25% being preferred. Where the polysaccharide e..- ter is used in conjunction with montan wax, a proportion of 01-05% of theester together with about 0.02-0.20% of montan wax gives satisfactory results, with a proportion of about 0.2% of the ester and. about 0.1% or less of the montan wax being preferred.

In accordance with the present invention, the wax crystal modifying material is added to a wax bearing oil, and the oil then chilled with resultant precipitation of wax in a form which is found to facilitate separation by centrifuging or cold settling, and is also found to materially increase filtration rates and give other advantageous results where the wax is separated by filtration. Thus the use of the dewaxing aid gives an improved yield of dewaxed oil, a denser or more compact wax cake, a higher percentage of paraffin in the slack wax, and a slack wax of higher melting point.

The dewaxing aid is preferably employed in conjunction with a dewaxing solvent or solvent mixture. Various solvents can be used for this purpose, including the well known and conventional dewaxing solvents and solvent mixtures. Very satisfactory results are secured by the use of a mixture of a. wax anti-solvent and an oil solvent, such as a. mixture of acetone and benzol, methyl ethyl ketone and benzol, methyl ethyl ketone and isopropyl ether, acetone with benzol and toluol, and the like. In the case of methyl ethyl ketone-benzol or methyl ethyl ketone-isopropyl ether, generally a proportion of about 40-60% methyl ethyl ketone to 60-40% benzol or isopropyl ether is satisfactory.

The oil to be dewaxed is diluted with the dewaxing solvent or solvent mixture generally in the dilution ratio of about two parts of solvent to one of oil up to about four or five parts of solvent to one of oil, although a smaller dilution ratio may be employed in certain instances. The polysaccharide ester, or the ester with montan stripping ofi the solvent.

wax, is preferably dissolved in a small proportion of the lubricating oil at elevated temperatures up to about 300 F. to form a concentrate thereof. This concentrate is then added to the diluted wax bearing oil charge which may be at a lower temperature, say of the order of 120 F. In order to assure proper solution of the dewaxing aid so that it gives maximum effined Mid-Continent distillate oil of about S. A. E.

rating having a Saybolt viscosity of 67.3 at

210 F. A run was also made on the blank oil without dewaxing aid for comparative purposes. The solvent employed was with a mixture of methyl ethyl ketone and 50% isopropyl ether, or 40% methyl ethyl ketone with benzol, as indicated in the following table:

fectiveness, the diluted wax bearing oil containing the dewaxing aid may be heated to a supersolution temperature, or to a temperature substantially above the temperature of complete solution of oil in solvent, the latter being gen. erally about -140 F. Thus, the mix may be heated to a temperature of about -190 F. or to a temperature of approximately 20-? F. above the temperature of complete solution of oil in solvent. This is found to uniformly give im-. proved filtration rates and yields of dewaxed oil. The mix is then chilled to a dewaxing temperature of the order of .10 to 15 F. and the precipitated wax separated from the oil. This is preferably accomplished by filtration, such as on continuous rotary filters, although intermittent pressure filters may be used with advantageous results. The dewaxed oil is then stripped to remove the solvent and the recovered solvent is recycled for the dewaxing of additional oil. The bulk of the dewaxing aid precipitating along with the wax and remaining in the slack wax may be recovered therefrom for reuse in the process.

By way of example, a cellulose stearate was prepared in accordance with the method of Von G. Kita et al. as described in Kunststoffe, March 1926. In this process, cotton paper or fibre was refluxed with stearyl chloride in a pyridine and benzene solution for a substsantial period of time, and the solvents then distilled off. The residue was extracted with benzene to dissolve the cellulose stearate, and this recovered by This cellulose stearate was used alone and also in conjunction with montan wax in the dewaxing of a furfural re-L From the above table, it is noted that the polysaccharide ester, either alone or in conjunction with montan wax, gave markedly improved results with respect to filter rate, yield of Wax-v free oil and percent. of paraifin in the slack wax, produced a slack wax of higher melting point, and gave a wax cake of greater reduced weight indicating a more compact cake which is substantially reduced in occluded oil content. The dewaxing aid of this invention is also advantageous in that it does not discolor a pale oil.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made with-out departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. In the dewaxing of mineral oil, the method which comprises adding to the oil to be dewaxed a small proportion of montan wax and a higher fatty acid ester of cellulose, chilling the oil to precipitate wax, and separating the precipitated Wax from the oil.

2. The method of claim 1, in which the said ester is selected from the group consisting of stearates, palmitates and oleates.

3. The method of claim 1, in which the said ester is cellulose stearate.

4. In the dewaxing which comprises adding to the oil to be dewaxed about 0.1-0.5% of cellulose stearate and about 0.02-0.20% of montan wax, chilling the oil to precipitate wax, and separating the precipitated wax from the oil.

'EDWIN C. KNOWLES.

of mineral oil, the method