US3487012A - Processes for the improvement of initial color and long-term color stability of aromatic concentrates - Google Patents

Description

United States Patent O 3,487,012 PROCESSES FOR THE IMPROVEMENT OF INITIAL COLOR AND LONG-TERM COLOR STABILITY OF AROMATIC CON CENTRATES Mark A. Plnmmer and Alan H. Peterson, Littleton, Colo., assignors to Marathon Oil Company, Findlay, Ohio, a corporation of Ohio No Drawing. Filed Feb. 23, 1968, Ser. No. 707,445 Int. Cl. C10g 31/14, 23/00, 17/06 U.S. Cl. 208-264 5 Claims ABSTRACT OF THE DISCLOSURE The invention comprises processes for the improvement of both initial color and long-term color stability of aromatic concentrates boiling within the range of 400 to 750 F. without substantially reducing the aromaticity thereof, said processes comprising in combination the steps of: hydrotreating, acid treating followed by caustic washing, and vacuum distilling said aromatic concentrates at 5 to 250 millimeters of mercury absolute pressure with corresponding temperatures in the range of from 150 to about 650 F.

CROSS REFERENCES TO RELATED APPLICATIONS U.S. Patents 2,973,317; 3,069,351; 3,052,742; 2,921,- 896; and 2,734,019 all relate to the general field of the present invention inasmuch as they teach various methods of hydrocarbon purification. To the applicants knowledge, there are no patents which teach the invention described herein.

BACKGROUND OF THE INVENTION Field of the invention Art which bears upon this invention is found in the following U.S. patent classifications: 208-264; 208-89; 260-674; 208-212; and 196-24. Classification 208 contains patents directed to processes and products of mineral oils.

Description of the prior art U.S. Patent 3,069,351 to Davis discloses the hydrogenation of petroleum fractions in contact with a hydrodesulfurization catalyst as an effective means for producing a stable fuel oil with respect to color after storage.

U.S. Patent 2,921,896 to Jezel teaches the removal of non-hydrocarbon constituents from petroleum by hydrogenating the petroleum charge; and, treating the charge with an acid; in the presence of an alkanol or ketone. Jezel believed his invention improved the color and oxidation stability of the petroleum charge material treated due to the reaction of the acid-treating agent with nonhydrocarbons (which are basic in the reaction,) and the extraction of the reaction products by the alkanol or ketone. (Column 1, lines 64-71.)

U.S. Patent 2,734,019 to Miller discloses a method for producing low, cold-test lubricating oils by contacting the petroleum fraction with hydrogen, and a cobalt molybdate on silica-free alumina catalyst. Miller mentions that a Tag-Robinson color as low as 7 is considered quite desirable, and that a finished lubricating oil fraction having such a color might be produced in accordance with his invention. (Column 4, lines 33-44.)

U.S. Patent 2,973,317 to Watson teaches the efficacy of hydrogenating petroleum oils prior to an acid treatment which produces less overall costs than the sulfuric acid-treating refinery methods known to the art.

U.S. Patent 3,052,742 to Mills also teaches the eifectiveness of hydrogenating petroleum oils prior to an acid treatment. In the case of Mills, these refinery techniques Patented Dec. 30, 1969 "ice 7 SUMMARY Statement of the invention The present invention teaches for the first time the critical procedures and operating conditions which, in combination, improve both the initial color and the long-term color stability of aromatic concentrates.

Acid-treating has long been useful as a process for refining petroleum oils. U.S. Patent 3,052,742 to Mills and U.S. Patent 2,973,317 to Watson show the improvement in refining techniques obtained when the raw feedstock is first hydrogenated, and then acid-treated. The present invention demonstrates that the improvement of initial color, and long-term color stability of aromatics does not depend upon hydrogenating hydrocarbon fractions and then acid-treating them, as the art teaches. Rather, these commercially valuable improvements derive from the felicitous combination of processes summarized below.

According to the invention, aromatic concentrates boiling within the range of 400 to 750 F. are: (a) hydrotreated at conditions described herein such that the aromaticity of the product is not substantially reduced below that of the feed to the hydro-treating step; (b) acid-treated with sulfuric acid at specified conditions; (0) caustic washed following the acid-treatment; and, (d) vacuumdistilled within the critical parameters given.

The criticality of the vacuum-distillation process for purposes of this invention is not taught in the patent literature. Furthermore, the processes which the invention comprises need not be utilized in any particular sequence, with one exception: the caustic washing step must directly follow the acid treatment. But, the acid-treating and caustic washing processes may precede the hydrotreating process followed then by vacuum-distillation. See Example VIII. Or, the aromatic feed material may be hydrotreated, then vacuum-distilled, then acid treated and caustic washed. See Example VI.

Utility of the invention A preferred color and an inoffensive odor are among the important standards which aromatic products must meet in order to sell at satisfactory prices. This invention provides good improvement in color and odor at low cost. The value of the invention in terms of product improvement and commercial benefits deriving therefrom will be obvious to those skilled in the art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Starting materials The aromatic concentrates to be used in the invention boil in the range of about 400 to about 750 F. Aromatic products derived from the extraction of catalytic cycle oils such as are described in U.S. Patent 3,317,422 to Benham are suitable starting materials for the invention.

Processes (a) Hydr0treating.-The original aromatic concentrates are hydrotreated preferably at 250 to 1500 p.s.i.g., a hydrotreating temperature of 550 to 800 F., a liquid hourly space velocity of 0.5 to 10 hours and with hydrogen in an amount of from 500 to 2500 standard cubic feet per barrel of feed to the hydrotreating process. The entrained gases produced by the process are thereafter moved. Although the optimum conditions of the hydrotreatment will vary with the boiling range of the material to be hydrotreated and the particular catalyst 1 Liquid hourly space velocity is defined as the volumetric flow rate of the feed divided by the volume of catalyst.

used, it is important that these conditions be adjusted within the parameters set forth above so as not to substantially reduce the aromaticity of the hydrotreated product below that of the feed to the hydrotreating process.

The hydrotreatment will reduce the concentration of olefins, sulfur, and nitrogen, in the feedstock, but it should not result in excessive hydrogenation of more than 5% of the aromatics therein.

Preferably, the hydrotreatment is conducted at 350-650 p.s.i.g., at a temperature of 600 to 750 F., and at a liquid hourly space velocity of 1 to 5 hrsi A variety of catalysts are useful in the hydrotreatment. Metals of Groups VIB and VIII of the Periodic Table may be used either singly or in combination. Generally, however, catalysts containing cobalt, molybdenum, nickel or tungsten used singly or in combination will be preferred. These metals may be present as the sulfide and will be supported on a porous refractory oxide support such as aluminum or silica-alumina.

(b) Acid treatment.The aromatic material from step (a) is acid-treated with sulfuric acid containing at least about 85% by weight H 80 at a temperature of from 40 to 120 F., wherein the sulfuric acid is present in a quantity of from 5 to 40 pounds per barrel of the aromatic feed to the acid-treatment process. The acid is brought into contact with the aromatic feed for a time ranging from 5 seconds to 5 minutes. Contact times for this process are not narrowly critical to the invention. Following the process, the sulfuric acid is substantially removed from the feed material.

(c) Caustic wash.The aromatic material is then Washed with an aqeous caustic solution having a density greater than said aromatics for a time and in an amount suflicient to neutralize the acid values remaining therein. Complete removal of the caustic from the aromatic concentrate results in improved odor characteristics for the aromatics. Any suitable process for the removal of entrained caustics may be utilized.

((1) Vacuum distillatin.The aromatic concentrates from (b) are vacuum distilled at to 250 millimeters of mercury absolute pressure with corresponding temperatures in the range of from 150 to about 650 P. so that substantially all the feed material boiling higher than the boiling range of the original aromatic concentrate remains as bottoms from the vacuum-distillation process. Preferably, the process is carried out at 50 to 250 millimeters of mercury absolute pressure with corrresponding temperatures in the range of from 175 to 650 F.

EXAMPLES The following examples illustrate the practice of the invention.

The phrase initial color is used herein to denote the color of the freshly prepared product.

The phrase long-term color stability refers to the ability of the product to resist darkening during storage or use; or the ability of the product to resist darkening during an accelerated test which predicts darkening during storage or use.

Example I An aromatic concentrate obtained by solvent extraction of a light catalytic cycle oil by the procedure of U.S. Patent 3,317,422 and having a boiling range of approximately 400 to 700 F. is first hydrotreated at 665 F., 425 p.s.i.g. at a liquid hourly space velocity of 2.0 hrscand a hydrogen to oil ratio of 800 s.c.f./bbl. using a commercial cobalt-molybdenum hydrotreating catalyst. The hydrotreated product is then intimately contacted with lbs/bbl. of 97% sulfuric acid in a stirred contactor at about 75 F. The hydrocarbon layer is separated from the acid sludge and is similarly contacted with 20% of its volume with an aqueous sodium hydroxide solution containing about 10 wt. percent of sodium hydroxide. After separation, the hydrocarbon layer is then dehydrated and distilled into three product distillation ranges (400 to 500 F., 500 to 600 F. and 600 to 700 F.) using three continuous distillation columns. All columns are operated at about 250 mm. Hg. The product cuts are all lighter than an ASTM color of 2.0. Exposure to a 150 watt flood lamp and air at 140 F. causes a color degradation of less than 2.0 ASTM units in 5 days.

Example II The procedure of Example I is repeated except that the hydrotreating step is omitted. The initial color of the distillation cuts is similar to that of Example I but the color deteriorates rapidly on aging in the presence of light.

Example III The procedure of Example I is repeated except that the acid treating step is omitted. The initial color of the product cuts is inferior to Example I, particularly for the heavier outs, and the color stability is also inferior.

Example IV Elimination of the caustic treating step in Example I results in products which are extremely unstable to color change on aging.

Example V The procedure of Example I is repeated except that the entire distillation is carried out at an absolute pressure of 400 mm. of Hg. The 600 to 700 F. cut is markedly less color stable than that of Example I.

Example VI The feedstock of Example I is hydrotreated and is then distilled into the desired boiling ranges, 400 to 500 F., 500 to 600 F. and 600 to 700 F. as in Example I. These distillation cuts are then acid treated and caustic treated. The products are essentially equal in quality to those prepared in the first example.

Example VII A 550 to 650 F. bottoms cut from a 400 to 650 F. aromatic concentrate prepared by the method of US. Patent 3,317,422 having an ASTM color of 7.0 is treated in the following sequence. First, hydrotreated using a commercial cobalt molybdenum hydrotreating catalyst, American Cyanamide Co. HDS2A, at 665 F., 425 p.s.i.g., liquid hourly space velocity of 2.0 hrs? and hydrogen to oil ratio of 800 s.c.f./ per bbl. Residual hydrogen sulfide is removed by steam stripping or nitrogen purging. Secondly, the hydrotreated material is acid treated with to 98 wt. percent sulfuric acid with vigorous agitation for 2 minutes using 10 lbs. of acid per bbl. of oil. Essentially all of the acid sludge is removed and the acid treated oil is neutralized by mixing with 20% by volume of 10 wt. percent sodium hydroxide solution. The oil is separated from the caustic solution and dried using a suitable dehydrating agent such as anhydrous magnesium sulfate. Finally, the product is vacuum distilled at 10 mm. Hg to collect 95 volume percent of the charge as an overhead cut boiling within the approximate range of 302 to 365 F. at 10 mm. Hg. This product has an initial ASTM color of less than 0.5 and darkens to less than 2.0 in an accelerated aging test in which the material is exposed to a 150 watt spot light at a distance of 12 inches and a temperature of F. for 5 days in the presence of air and of iron. Under these conditions the 550 to 650 F. feedstock which has merely been vacuum distilled or hydrotreated and vacuum distilled darkens to an ASTM color of 4.0 to 4.5.

Example VIII The procedure of Example VII is followed except that the order of the hydrotreatment step is changed. First, the 550 to 650 F. charge stock is acid treated and caustic washed, under the conditions of Example VII. Then this material is. hydrotreated and vacuum distilled also MODIFICATIONS OF THE INVENTION 5 It should be understood that the invention is capable of a variety of modifications and variations which will be made apparent to those skilled in the art by a reading of the specification and which are to be included within the spirit of the claims appended hereto.

What is claimed is: 1. Processes for the improvement of both initial color (a) catalytically hydrotreating at 250 to 1500 p.s.i.g.

and at 500 to 800 F., at liquid hourly space velocities between 0.5 to 10 hrswith hydrogen in an amount of from 500 to 2500 standard cubic feet per barrel of feed to said hydrotreating process, and thereafter removing the entrained gases produced, said conditions being adjusted within the above ranges so as not to substantially reduce the aromaticity of the product below that of the feed to said hydrotreating step;

(b) acid treating with sulfuric acid containing at least about 85% by Weight H 80 by intimately mixing said sulfuric acid with said feed material and thereafter removing substantially all of said sulfuric acid, wherein said acid is contacted with said feed at a temperature of between to F., and wherein said acid is present in a quantity of from 5 to 40 lbs. per barrel of feed to the acid treating step;

(c) caustic washing after said acid treating step by intimately contacting the feed material with an aqueous caustic solution having a density greater than said feed material for a time and in an amount sufiicient to neutralize acid values remaining in said feed;

(d) vacuum distilling at 5 to 250 millimeters of mercury absolute pressure with corresponding temperatures in the range of from to about 650 F., so that substantially all material boiling higher than the boiling range of said original aromatic concentrate remains as bottoms from said vacuum distillation step.

2. The processes of claim 1 wherein the hydrotreatment is carried out at 350 to 650 p.s.i.g. and at 600 to 750 F., at liquid hourly space velocities between 1 and 5 hrs- 3. The processes of claim 1 wherein the vacuum distillation is carried out at 50 to 250 millimeters of mercury absolute pressure with corresponding temperatures in the range of to 650 F.

4. The processes of claim 1, utilized in the following sequence: (a) Hydrotreat; (b) vacuum distill; (0) acid treat; and (d) caustic wash.

5. The processes of claim 1, utilized in the following sequence: (a) Acid treat; (b) caustic wash; (0) hydrotreat; and (d) vacuum distill.

References Cited UNITED STATES PATENTS 2,973,317 2/1961 Watson 208264 3,052,742 9/1962 Mills 208-264 3,093,576 6/ 1963 Campbell 208273 3,370,001 2/ 1968 King 208-464 HERBERT LEVINE, Primary Examiner Us. 01. X.R. I f 208271, 272, 273, 286