US3324029A - Process for manufacture of heavy aromatic solvent - Google Patents

Description

United States Patent O 3,324,029 PROCESS FOR MANUFACTURE OF HEAVY AROMATIC SOLVENT Laurence F. King, Mooretown, Ontario, and Clellie T.

Steele, Sarnia, Ontario, Canada, assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Sept. 23, 1963, Ser. No. 310,894 8 Claims. (Cl. 208-97) This invention relates to the production of improved heavy aromatic solvents. More particularly, it relates to the production of a heavy aromatic solvent which is superior to other oils in respect to vital properties such as odor.

Aromatic hydrocarbon fractions of 350-550 F. boiling range find wide use as solvents for insecticides such as DDT, aldrin and dieldrin.

Gas oil fractions recovered from steam cracked products are potentially useful as heavy aromatic solvents. However, for many agricultural uses, the color, sulfur content and odor of steam cracked gas oils leave much to be desired. Hyd-rofining and rerunning give improvement in color and sulfur but odor is deficient, probably because of heavy feed olefins which are very difiicult to hydrogenate with cobalt molybdate catalyst.

According to this invention a process is disclosed for treating overhead material from the flashing of aromatic t-ar after the tar has been heat soaked or destructively distilled. During this process, most of the olefins and other contaminants are thermally cracked and removed in the front ends, resulting in considerable color and odor improvement. A 350-550 F. boiling point heart out of the overhead from a heat treated tar is hydrofined and the hydrofined distillate is rerun to produce an improved heavy aromatic solvent. In some cases the hydrofined distillate does not require 'rerunning. However, for best color and backend fractionation, it is preferred to distill or rerun it in vacuo to about 90% overhead whereby most of the color bodies remain in the bottoms.

The aomatic tar feed needed to produce the solvent is obtained from steam cracking a gas oil or a mixed gas oil-naphtha. Traditionally, this tar was looked upon as a waste product and was only utilized as a low grade dark resin, or, more commonly, as bunker fuel. The steam cracking process is well known and involves cracking a 'gas oil having an initial boiling point between about 400 and 525 F. and a final boiling point between about 750 and 825 F. in the presence of about 60-85 mol. percent of steam; at a coil outlet temperature between about 1200 and 1450 F. and immediately quenching with an oil having a boiling range between about 500 and 675 F. to a temperature of about 540-560 F. The gas oil feed has an API gravity of about 20 to 25, mo-l. weight of about 210 to 270, weight percent aromatic rings of about 10 to 15 and weight percent naphthenic rings of about 30 to 40.

The gaseous steam cracked products containing hydrogen, saturated hydrocarbons, olefins, diolefins, etc., are taken overhead and the liquid hydrocarbons are fractionated to separate an aromatic gasoline boiling between about 100 and 460 F., and a higher boiling aromatic fraction boiling between about 370 and 570 F. which may be in part recycled to the quench zone of the steam cracking unit. The amount of residual aromatic tar obtained is about vol. percent to 25 vol. percent of the feed and has an initial boiling point above about 500- 600 F., and a 50% boiling point between about 700 and 800 F.

The aromatic tar thus obtained is then subjected to heat soaking. Temperatures which will be satisfactory fo-r heat soaking are between 700 and 1000 F. and preferred 3,324,029 Patented June 6, 1967 temperatures should be between 800 and 900 F. Pressure may vary between 150 and 300 p.s.i.-g. with about 200 p.s.i.g'. being preferred. Space velocities will vary with the unit. For a 700 cc. capacity continuous pilot plant space velocities between 0.5 and 8.9 v./v./hr. volume of liquid oil per volume of reactor space per hour are satisfactory. Periods of time for the heat soaking may range from a fe-w minutes to 5 hours depending on the temperature with about 2 hours being preferred for the range of 800-900 F.

Following the heat soaking, the tar is flashed. The flashing procedure may be either vacuum or atmospheric. If atmospheric flashing is utilized, the tar is at a temperature of about 700-900 F., preferably at 850-860 F. maximum or final temperature. Flashing pressure is generally atmospheric but may be between 15 and 30 p.s.i.g. if desired and in this manner an overhead hydrocarbon stream and -400 F. softening point pitch as bottoms is obtained. Flashed vapors are condensed and a 350- 550 F. boiling point fraction is recovered. The flashed distillate is passed to a hydrofiner.

An alternative route to flashing for obtaining this 350- 550 F. fraction is by destructive distillation of the aromatic tar obtained from steam cracking. The destructive distillation is carried on in the absence of air and with pot temperatures varying from ambient to about 900 F. as the distillation proceeds, with about 850-875 F. final pot temperature being preferred for atmosphere pressure operation. Atmospheric flashing, or destructive distillation, may be practiced in lieu of heat soaking rather than as a second step.

In either case, the 350-550 F. fraction is then passed to a hydrofiner. Temperatures within the hydrofiner may be in the range of 500-800 F., preferably a temperature of about 625 F. is utilized. Pressures of 100-3000 p.s.i.g. may be utilized; a preferred pressure would be in the range of 200-1000 p.s.i.g. Feed rate may vary between l-3 v./hr./v. (liquid) volume of liquid oil per hour per volume of catalyst, depending upon operating conditions. Hydrogen is used at a rate of 500-1000 s.c.f./b. of feed.

The hydrofining catalyst consists chemically of cobalt oxide and molybdenum oxide possibly combined as cobalt molybdate on a solid adsorbent carrier and can be purchased commerically. The carrier may be selected from many materials such as adsorptive alumina, bauxite, silica gel, clay, hydrogen fluoride promoted alumina and the like, which are usually employed for thi general purpose. A material which is particularly preferred as a carrier, however, is alumina. It is preferred that this catalyst contain about 2-5 wt. percent cobalt oxide and 8-15 wt. percent molybdenum oxide. About 3.6 wt. percent cobalt oxide and 12.5 wt. percent molybdenum oxide have been found to be especially effective.

The catalyst, as it is employed in the present invention, may be in the form of a fixed bed, a fluidized bed or a moving bed.

Example 1 In a specific embodiment of this invention a hydrofined distillate from heat soaked aromatic tar was produced. The tar was obtained as bottoms from cracked products obtained by steam cracking a 60-40 gas oil-naphtha at a temperature as set forth hereinafter and at 40-43% conversion to C and lighter.

Characteristics of the tar were as follows:

Inspections of tar:

Gravity, API 4.0 Flash pt., F. 320 V./210 SSU 213 Carbon, percent by wt 90.4

Residence time seconds about 3 Pressure, inlet p.s.i.g 80 Product yield, wt. percent:

Ethylene 25-27 Propylene 2021 Butylene Butadiene c -200 F. 13 200400 F. l3 Tar, vol. percent 7-11 The tar was then heat soaked at a temperature of 850 F. and at a feed rate of 1.0 v./v./hr. (cold liquid feed). Pressure was maintained at about 200 p.s.i.g. The heat soaked product was then flashed at 100 mm. to give a 430540 FVT distillate. The resulting distillate was hydrofined over a cobalt molybdate catalyst.

Hydrofining was conducted at a temperature of 625 F. and at a pressure of 250 p.s.i.g. The feed rate was 0.5 v./v./hr. and hydrogen used was 500 s.c.f. H /bbl. of feed. The hydrofined distillate was rerun or distilled to recover a distillate (up to 90 vol. percent) having a boiling range of 420552 F. The distillate obtained was lye washed with 15 volume percent of Baum caustic to remove traces of hydrogen sulfide remaining from the hydrofining step, and finally water Washed with about 3 volumes of water per volume of distillate.

The final distillate comprises the improved heavy aromatic solvent of the present invention and has the characteristics given in Table I. The improved heavy aromatic solvent is compared with a commercial product designated as such in Table I.

TABLE I.INSPECTIONS OF IIEA\Y AROMATIC SOLVENT Mixed Aniline Pt. F 76 67 Pour Pt. F 80 -55 ASTM Distillation:

IBP, 370 460 420 5% 400 478 430 10%... 415 .83 440 50% 450 505 488 90% 500 535 520 95% 525 454 539 F.B.P 550 560 552 Additionally, in an odor test by a 20-member panel, the distillate or solvent from the heat soaked tar was rated at +0.40 and the commercial solvent at -0.29. The needed difference for significance at the 95% confidence level is .25. Consequently, the distillate from the heat soaked tar scored significantly higher on the odor test. The distillate from the heat soaked tar also had a somewhat higher pour point, i.e. 25 F. higher but both were so low that the difference is immaterial.

Thus, as illustrated by Table I, without the benefit of rerunning during hydrofining, the tar showed improveent, the benefits would be increased by rerunning.

In solvency, the distillate or improved solvent of the present invention is significantly better than the more expensive commercial aromatic solvent. This is shown in Table I by the lower mixed aniline point (67 vs. 76 F.). The improved solvent also has a higher solvency for DDT at 74 F. (40 vs. 35 grams/ grams solution dissolved at the saturation point) as compared to the commercial solvent. This is the most important criterion of all from the viewpoint of insecticide manufacturers. The higher solvency is due to formation of condensed aromatic ring structures which have high solvency for insecticides.

What is claimed is:

1. A process for producing a heavy aromatic solvent having improved odor and superior solvency character istics which comprises steam cracking a gas oil whereby an aromatic tar is produced, said tar having a boiling point above about 500 F., heat soaking the said aromatic tar, flashing the heat soaked tar, recovering a 350 t 550 F. boiling point fraction and catalytically hydrotreating said 350 through 550 F. fraction whereby an improved solvent is produced.

2. The process of claim 1 wherein the said heat soaking takes place at a temperature between about 700 and 1000 F.

3. The process of claim 1 wherein said hydrofining takes place over a cobalt molybdate catalyst.

4. The process of claim 1 wherein said heavy aromatic tar has a boiling point above about 600 F.

5. A process for producing a heavy aromatic solvent with improved odor characteristics as well as improved solvency which comprises steam cracking a gas oil having an initial boiling point between 400 and 525 F. and a final boiling point between 750 and 825 F. whereby an overhead fraction and a residual aromatic tar are obtained, heat soaking said aromatic tar at a temperature between 700 and 1000 F., recovering a 350 to 550 F. fraction from said heat soaked tar and catalytically hydrotreating said 350 to 550 F. fraction in order to produce an improved heavy aromatic solvent.

6. The process of claim 5 wherein said heat soaked tar is flashed in order to recover said 350 to 550 P. fraction.

7. The process of claim 5 wherein said heat soaked tar is subjected to destructive distillation in order to recover said 350 to 550 F. fraction.

8. The process of claim 5 wherein said hydrofining takes place over a cobalt molybdate catalyst.

References Cited UNITED STATES PATENTS 2,608,522 8/1952 Niehaus et al. 208-203 2,752,290 6/1956 Beattie 20440l 3,108,935 10/1963 Penning et al. 208-97 3,140,248 7/1964 Bell et al. 20840 FOREIGN PATENTS 627,307 9/1961 Canada. 783,567 9/1957 Great Britain.

OTHER REFERENCES The Chemical Technology of Petroleum, W. A. Gruse and D. R. Stevens, Second edition (1942), pages 405-406, McGraw-Hill Book Co., New York.

DANIEL E. WYMAN, Primary Examiner.

P. E. KONOPKA, Assistant Examiner.