US2216968A - Method for refining lubricating oil distillates - Google Patents

Description

' crease the volume somewhat into the 100 to 500% The amount of the treating agent should Patented Oct. 8, 1940 UNITED METHOD FOR REFINING LUBRIOATING 01L DISTILLATES I Hans G. Vesterdal, Elizabeth, N. J., assignor to Standard Oil Development Company, a corporation of Delaware No Drawing. Application May 28, 1938,- Serial No. 210,749

6 Claims.

The present invention relates to an improved method for refining heavy hydrocarbon oils, especially' of the type obtained from naphthenic crudes,which are susceptible to loss of color on standing or which contain impurities such as soaps having high ash contents, The invention will be fully understood from the following description.

Lubricating oil distillates are frequently susceptible to loss in color on standing. This appears to be a marked characteristic of the products derived from naphthenic base crudes such as are obtained from Colombia and the Coastal regions of the United States. These oils are largely used for making low cold test lubricants for industrial purposes. The cause of the loss of color is not fully understood, but it is believed to be due to the presence of small amounts of naphthenic acids and frequently to the presence of complex phenolic materials. It is now customary to refine these oils by treatment with acid but in order to obtain color stable oils according to this method, large amounts of sulfuric acid are required in the treatment and the treating loss is quite large. Residual oil containing soaps and having high ash content are also troublesome to handle by present methods, which give satisfactory products only at the cost of a considerable loss of oil. It has been found that oils of these types can be readily refined Without any acid treatment whatever and they are satisfactory for most of the purposes to which they are now put. If better oils are required, a limited acid treatment or solvent extraction treatment or other refining method may be used such as limited oxidation which are followed, if desired, with either acid or solvent refining. These various refining methods are used prior to the present finishing process but'for most purposes this is not required. In the present process, the oil, whether a crude or a distillate or residue obtained by pipe still distillation or residue obtained in distillation over caustic soda, is treated under high temperature with say 10 to 500% of its volume of a dilute aqueous caustic alkali, preferably sodium hydroxide.

The concentration of the alkali may be from .25 to 5% depending to some extent on the character of the oil to be refined, its viscosity, and the amount of impurity to be removed. It is preferred to use solutions in the more dilute portion of the range specified hereinabove, and the volume used is preferably 10 to 100% of the oil to be treated, but when the amount of the extractable materials is high, it is preferable to inrange. be such as to form a dilute solution of the extractables for example less than 10% soap so as to avoid loss of oil inthe treating solution. The

extractable materials are more soluble in and therefore more readily removable by dilute rather than more concentrated soda solutions. The treatment is accomplished at temperatures above about 350 and preferably below about 500 F. 1

so as to avoid thermal decomposition. The more viscous the oil the higher the treating temperature will be to get a clear separation. Pressure is sufficiently high to prevent evaporation of the water from the treating solution. Residues which are solid at room temperatures may be successfully treated to remove salt, soaps, and the like.

The temperature should be kept well up within the range specified and if allowed to fall below about 350 F., there is found to be troublesome emulsification which prevents a clean separation of the aqueous from the oily layers. A small amount of oil will usually be included with the aqueous layer, which is removed while hot, but great care should be exercised to remove as completely as possible all traces of the aqueous from the oily layer. If this is carefully carried out under the conditions set forth above, no further purification of the oil is required. Water washing or cooling before separation of the water and oil layers should be avoided since this causes hydrolysis of the soda compounds of the extractable materials and causes the finished oil to have high neutralization value.

If the oil distillate is freshly obtained from crude stills while it still has a good color and is immediately subjected to the treatment with the dilute caustic alkali, no further treatment is required, but it is found that the distillate goes off color rapidly on standing and to obtain a finished oil'of good color, it is often necessary to redistill the oil after the caustic treatment. The distillation is preferably carried out under vacuum in order to avoid decomposition. When treatingiuel oils color and color hold are unimportant but the treatment is very effective in reducing ash content which is of great importance.

Frequently when such residues are obtained by distillation over caustic soda there is enough soda present so that Water may be used as the treating agent and the caustic solution is formed in situ.

The caustic treatment is capable of removing materials which cause the oil to go off in color on standing, but once these materials have developed color, the treatment is not effective in restoring color and distillation must be resorted to. The treatment may be in batch or continuous,- using counterfiow or parallel flow.

' The caustic soda may be recovered mainly by cooling to room temperature whereupon the extracted material or a large part thereof settles out apd the causticmay be reused many times,

only a small amount of make up being required before it must be replaced.

As examples of the operation of the present process, the following -may be considered:

EXAMPLE 1 A light Colombian lubricating oil distillate was heated in a closed pressure vessel with 25% of its volume of 2% aqueous caustic soda to a temperature of 400 F. A pressure of 250 pounds per square inch was maintained in the vessel so as to prevent evaporation of the causticsolution and the mixture was agitated until'tho'rough contact was assured. The mixture was then allowed to stratify, which it did cleanly, and the aqueous liquor was drawn 011 while hot. The oil was redistilled under Vacuum without any further treatment, giving 5.5% of light ends and 9 1% of a refined lubricating oil distillate.

The inspection of the original oil and the extracted and r'edistilled products is as follows:

The average lubricating oil standard is a measure of the color stability of an average lube oil, as determined on hundreds of samples of commercial lube oils. Thus an average lube oil having an initial color of 4% Robinson would have a color of 2 Robinson on heating in presence of air at 250 F. for 16 hrs., and one of 8 color would drop to 4R+ in the same test. The caustic treated oils are thus considerably better than the average oils.

Washed Washed bWith150% bwith150% Orig- Redisg; Y a o aq. of 3% aq. mal on tluvd caustic at caustic at 400 F. and 400 F. and

redistilled redistilled Percent cut 100 0-98 0-94 0-97 1S./100 F 274 Color, Robinson Dark 6 9% 8% Color after 16 hrs. at

250 F i 1 7% 4% Average lubricating oil standard 3+ 5% 4% 2. 15 2. 15 0. 08 0. 09 2. 30 2. 30 0. 14 0. 28

By the usual acid treating method used,'the yield of color stable refined oil from this stock is only about but the yield obtained by the'present method averages about 10% higher for similar or better quality.

EXAMPLE 3 A total Colombian lube cut was extracted countercurrently in a tower with 78% of its volume of 0.45% aqueous caustic solution at an average tower temperature of 385 F., keeping sufficient nitrogen pressure on the system to prevent boiling of the water and in another experiment the total Colombian lube out was extracted with 88% of its volume of 3.84% aqueous caustic solution 30 at an average tower temperature of 385 F. Good separations of caustic extract and oil were obtained. The oils were fractionated under vacuum and separated into several cuts. of the cuts and of the untreated oil is as follows:

' Color Average Percent Color Neut.

V1s./100 hold 16 hrs. lube oil cut Robmson at 250 F. standard Original oil 100 342 Black 2. 23 0-30 86 16% 16% 11+ 0. 05 Extracted once with 78% of 0.45% caustic at 30-50 239 10% 9% 9+ 0.08 385 F., and rerun 50-70 576 8% 8% 4% 0.09 70-90 1200 8 3% 4 0. 09 0-30 84 17 13% 11% 0. 01 Extracted once with 88% of 3.84% caustic at 30-50 243 10% 9% 8% 0.04 385 F., and rerun N 50-70 585 9% 6% 5% 0. 09 70-90 1235 8% 2% 4 0. 11

EXAMPLE 2 EXAMPLE 4 A medium Colombian distillate having a Viscosity of 274 seconds Saybolt at 100 F., was extracted with 50% or its volume of dilute caustic solution at 400 F., in the same man'nerdescribed in Example 1, using a 2% caustic solution in one case and a 3% caustic solution in another case. In both cases the oil separated readily from the caustic solutions on settling at 400 F., for 5 to 10 minutes. The oils were redistilled under vacuum A wide cut Sugarland lube distillate having a The inspection viscosity at 100 F., of 196 seconds Saybolt was 3 extracted twice in a countercurrent tower at an average tower temperature of 385 F., using 80% of its volume of 2% aqueous caustic solution in each treat. The original oil, and the caustic treated oil, were fractionated under vacuum and 55 separated into 10% cuts.

Inspections of these cuts were as follows:

Color after Average Percent Color Neut.

V1s./100 16 hrs. at lube 011 cut Robinson Standard No. 0

Original oil -4 100 39- 2 1 3 0.92 0-10 39. 2 21% 19 0. 28 10-20 53. 9 18% 17% 13% 0. 52 20-30 77 17 11% 11% O. 80 30-40 118 16% 10% 11 0. 6 5 Vacuum fractionated 40-50 196 13% 9 10 0.98 v I 1 50-60 338 8% 9; 0.95 60-70 617 10% 5 8 0. 92 70-80 1120 9 4% 4% 0. 88 80-90 1088 8% 3 4+ 0. 86 0-10 39. 8 21% 18% 0. 03 10-20 55. 0 18% 17% 12%+ 0. 03 20-30 78. 4 17 14% 11% 0. 05 70 Sample vacuum fractionated after 2 x 80% 30-40 25 6% 12 05 countercurrent treats with 2% caustic at 40-50 210 14% 10 10% 0.06 385 F 50-60 340 12% 9% 9% 0. 06 60-70 600 10% 9 9+ 0.08 70-80 1080 9% 6 5% 0. 11 89-90 1627 8% 4% 4+ 0. 14

In this case even'the cutsfroin' the untreated oil were fairly color stable especially the-light viscosity ones, but caustic treating improved-the color stability considerably. The treatment was particularly effective with the 1000 to 1600 viscosity cuts (70-80% and 89-90%) which were color stable while the untreated ones were not.

EXAMPLE 5 A light Colombian lube distillate was treated with 15 pounds of 91% sulfuric acid at about F. On settling, the sludge was drawn ofi and the oil was neutralized with caustic. The neutral oil so obtained which contained about 0.02% excooling the caustic extracts to room temperature or lower, practically all the extracted material separates out of solution, leaving a recovered caustic which may be used over again. In

order to prove that the recovered caustic is' just Oil treated with recovered caustic and redistilled I Oil treated with fresh caustic O11650Z 2011 Two counter current treats tercurrent rea a One 38% countercurrent Y treat at 3804300 F at 380390 F. (38+25% to 390 F.

treats) CutNo 1 2 3 4 1 2 3 4 1 2 a. 4

ViS./ 75.7 213 545 1301 79.1 221 555 1318 77 220 531 61298 Color, Robinson 11 9 7 16% 10% 9 7% 16% 11% ,9; 7% Color after 16 hrs. at 250 9% 4% 2% 1214 9 5% 254 163 9% 5 1% Average lube oil standard. 9% 434+ 3%,, 11+ 9 454+ 3%+ 11% 934+ 4B4. 3% Neut.No .05 .06 .09 .12 .03 03 v.05 .08 .05 .05 .08 .11

cess caustic was distilled under vacuum in a re- EXAMPLE 7 finery pipe still, and another sample of the same oil Was washed twice in a bomb with 25% of its volume of 2% caustic each time, at 400 F., and still another sample was washed twice with 50. of its volume of water each time at 460 F. Both the samples of washed oils were vacuum distilled in a laboratory still. Ash contents of the oils before distillation were as follows:

Per cent ash Acid treated and neutralized oil 0.65

Acid treated and neutralized oil washed with caustic at 400 F 0.008

Acid treated and neutralized oil washed with water at 460 F 0.04

Inspection of the distillates obtained from these oils was as follows:

Acid treated and neutralized A sample of pipe still bottoms obtained on stripping 01f the lubricating oil distillates from an acid treated and neutralized Colombian distillate in a refinery pipe still was washed with dilute caustic at 470 F. Analysis of the original pipe still bottoms showed that it had approximately the following composition:

Per cent Heavy oil 50 Inorganic salts 6 Soaps (by diiference) 44 and the ash content was 12.89%

On washing these bottoms with 300% of its volume of 0.5% caustic at 470 F. by mixing thoroughly in a closed bomb under equilibrium pressure for 30 minutes, followed by settling for 5 minutes, a clear separation of oil and extract was obtained. 42 volumes of oil were recovered from light Colombian distillate Washed with 2% caustic at Washed with water at 460 Fractlonatedlnre- 400 F. (2x25% treats) F. (2x50% treats and finery pipe still and iractlonated in the fractionated in the labolaboratory ratory Vis./l00 72.3 240 908 71.2 211 344 903 76.5 236 514 997 Color, Robinson 173 2 11% 8% 17% 14% 11% 8% 17 12% 9% 6V golor afterblfi hiiistat (215031 1%? gyi 2% 103% 32% y? 16% 1034 8% 2 4 verage u e0 s an ar z 4 2 9 4 11 .9 5 3 Nent. No 0. 04 0.05 0 0s 0. 04 0.04 0.07 0.0% 0. a? 1.1 6

It will be noted that on washing with water at 460 F., the neutralization values of the distillates were very high, showing that the soaps had been hydrolized to a large extent, whereas the very low ash content (0.008%) of the caustic washed oil and the low neutralization values of the distillates show that the soap was washed out thoroughly with 2% caustic solution at 400 F.

EXAMPLE 6 When using large volumes of caustic solution for extractions of acids and unstable compounds from petroleum oils, it is necessary to recover the excess caustic. This is easily done, since on each 100 volumes of bottoms charged to the bomb, indicating that 84% of the oil was recovered. This oil had a gravity (A. P. I.) of 17.0 and a viscosity at 210 F., of 263 seconds Saybolt-and is suitable as such for lubrication of heavy machinery or for grease manufacture or the like; if desired the oil may be redistilled for production of heavy cylinder oil. The extract from the soap bottoms was acidified with sulfuric acid, and the organic acids so liberated were washed with water at 200 F. On vacuum distillation of these acids, 60% of them distilled over at bottoms temperatures ranging from 400 F. to 600 F., under 5 mm. Hg pressure. The distillate teristic odor of crude naphthenic acids. Inspection of this distillate was as follows:

Color 8R Neut. No 123.5 Sap. No 123.5

.These acids may be further purified in various ways, but substantially oilfree acids may be ob.- tained by the method described above by increasing the amount of dilute caustic used for the extraction of the soaps from the pipe still bottoms, since the oil is relatively much less soluble in dilute soap solutions than in concentrated ones.

The present invention is not to be limited to any theory of the chemical reactions involved in the treatment nor to any particular alkali.

I claim:

1. An improved method for refining heavy hydrocarbon oils by extraction comprising treating the oil with dilute aqueous caustic soda of up to 5% concentration under pressure high enough to maintain the hydrocarbon oil and caustic solution liquid at the operating temperature, which is above 300 F., and below the decompos ing temperature of the hydrocarbon oil, and removing the dilute caustic soda solution and exhad a color of 8 Robinson and had the charac-- tracted material from the oil while hot by decantation.

2. An improved process according to claim 1 in which the treating solution is an aqueous solution containing .25 and 5% of caustic soda.

3. Process according to claim 1 in which the dilute caustic soda is recovered for reuse by cooling and separating the extracted material.

4. An improved process for refining lubricating oil from naphthenic crudes which are susceptible to serious loss of color on standing, consisting of the steps of bringing the oil into contact with an aqueous caustic soda solution of from .25 to about 5% while at a temperature between 350 and 500 F., under pressure sufficient to maintain the oil and caustic solution in liquid phase and separating the treating agent from the refined oil While hot by decantation.

5. An improved process according to claim 4 in which the treatment is efiected continuously by treating a flowing stream of the oil with caustic soda solution.

6. Process according to claim 4 in which the treatment is effected by treating a flowing stream of oil countercurrently with a stream of the caustic solution.

HANS G. VESTERDAL.