US2796388A - Preparation of petroleum pitch - Google Patents

Description

' to degrade any cutter oil to fuel oil.

United PREPARATION F PETROLEUM BITCH Harold'euther, Penn Township, Allegheny County, and

Applicationnluly 2, 1953, Serial No. 365,582

. 2 IClaims. (Cl.196-76) This invention relates to a petroleum pitch, and more `particularly to asolidl -petroleum pitch Iand a process for lits preparation from asphaltic or naphthenic'cr'udes.

l In a conventional'process for the reiiningof petroleum crudes,?ftherude is fractionatedinan atmospheric dis- -tillation-tower to separate -thedistillates from the heavy ynonevolatile residue. 1 a'visbreaking operation in which itis'thermally cracked at rnildcracking conditions -toy reduce its viscosity.' Ga-s l.oil or other distillates produced inthe visbreakingop- `-eration arethen ordinarily recycled through othercrackingvoperations at increased` severity toproduce gasoline having improved anti-knock and other-characteristics L l:The visbroken bottomsV are blended with a-relatively light oil, for example a-virgin distillate or a cycle stock from azcrackingprocess, designated as acutter oil, to yield I a. fuel oil,-ordinarily. identified as No. 6 fuel oil, having van :acceptable-viscosity. Since insutlicient light oil'to blend 'withf the bottoms and cut their viscosity to the Theresidue is then 'passed through desired range is produced in the refining of certain heavy crudes, it is sometimes necessary to obtain cutter oil from an outside source. The price of No. 6 `fuel oil i-s frequently lowerithan the price ofthe crude, and isconsiderably lower lthan the price of distillate: productssuch as domesticheating oils, -in which the light oils used as cutter oils ordinarily .are employed. For this reason, a process for refining petroleum crudes which. will result in a minimum degradation of cutter oils to No. 6 vfuel oil` is desirable.

YThe processes for the catalytic. crackingrof vgas oils havefrequently caused refiners rto alter .their refining processes bythe substitution of vacuum distillation for .thermal cracking or other treatment of the bottoms from Ithe atmospheric distillation. ylnthis manner, the amounts of virgin stock for charging to catalytic cracking operations is increased. However, the bottoms from the .vacuum reduction-are highly viscous andmust'be blended with a cutter oi-l to produce a fuel oil havinganacceptkable viscosity. The vacuum reduction, therefore, in-

creases .the amount of virgin catalytic cracking charge stock obtained from the crude, but still has the disadvantage of requiring blending of cycle stock withbottoms I. to form No.y 6 fuel oil.

One process that is used to reduce the amount of No. 6 fuel oil produced from a crude is the coking operation.

In that process, the bottoms from adistillationI tower or from other cracking processes are discharged from a cracking furnace into a coking drum in which `they Vare held for a suiiicientperiod of time to convert the heavy material to coke. Ordinarily, no No. 6 tuel oil is produced in a coking operation; hence, it is not necessary However, the coking operation is expensive ,because of high labor and utility costs resulting from the diiiiculty in removing coke from the coking drum.

According to this invention, certain heavy asphaltic for naphthenic crudes of low hydrogen to carbon ratio -are extremely deeply reduced in a continuous vacuum rates Patent1 2,796,388" Patented June 18, 1957 flash-distillation. Theiresiduefrom the 'vacuum reduc- `tion is a'solid petroleum'pitch having a very high softenvingpointmaking it suitable for useas a solid fuel, or, l-in-some instances, as 'abinden By the vproductionof *the solid petroleum pitch in thismanner, the hydrogen to-carb'on'ratio Aof'thedistillates isincreased by removal of a high proportion of the'carbon of the lcrude'oil in thepitch. In'addition', ans increased 'amount of virgin -idistillate ysuitablev'as a charge s-tock for catalytic cracking petroleum pitches fof' 'this' invention.

I lReferring to the'ldrawings; the heavy crude feed passes through Lline'lOto aA pre-heater l2 in which it is heated 20` p. s..i.-vgauge.l In'zthe usual operation, a gasoline v to a temperature sullicient to volatilize a portion 'of the zdistillable fractions of the crude.

Pre-heater l2= may -be of anyi suitable typek such .as a heat exchanger or a tired heater. The heated crude is discharged from thepre- .fh-eater flZvinto. an 'atmospheric distillation tower l14 in which :gases :and1:lowboiling fractions ofv thel crude are vaporized 'and'di-soharged -overhead through a line I16.. Typical ,conditions at .the inlet to the tower are atem- ;perature of-..iapproximately 700 F.v and `a pressure of fraction will bewwlthdrawn through aside drawoff 18 and a-gas=oilthrough the side-drawoff 20. Atmospheric distillation tower 14 may be-of any conventional design and thedistillate Aproducts Withdrawnfrom the tower will dependuprimarilyz'upon the design of'ithe tower; the -requirements-of the particular refinery, and :the vcharac- .terist-ics -of the feedstock.

The bottoms from atmospheric distillation tower 14 are withdrawn -through a-line 22 and passed through a heater 24 in which they are heated to a temperature suiciently-high to\permit an extremely deep vacuum ,reduction of the bottoms. .high-softening point petroleum pitches of this invention,

In the preparation 0f vthe the formation of-coke should be avoided; hence,v the maximum temperature in heater 24 will be limited by the cracking of the bottoms to form coke and will be dependent upon'the'characteristics of -the bottoms and the .heatingcurve of the furnace 24. Ordinarily, the temperature-inheater 24 will range from approximately 650 F. to a maximum of approximately 850 F. The temperature actuallyl employed will be governed, in part, upon the rate at which the bottoms are passed through `the furnace, the pressure employed in the vacuum distillation, and the lamount of steam addedto the bottoms ,to aid in thev distillation.

The hot bottoms from heater 24 are passed through 1ine726into a lcontinuous ilash vacuum distillation tower 28. Steam is preferably added to the bottoms, as through line 27, to reduce the vacuum required for the distillation. The/temperature and pressure in tower 28 imust'be such as to cause avery deep reduction rof the crudes to form the petroleum pitch of this Ainvention as la residue. The minimum distillation temperature that may be employed in tower 2S will depend in part upon the particular crude being treated, and in general the heavier andmore naphthenic the crude, the lower the distillation temperature required. yIn general, the distillation temperature in tower range 28, corrected to 760 millimeters of mercury will range from a minimum of 1050 F. for very heavy crudes such as Baxterville crudes 4to a maximum in the range `of approximately 1200 F. Distillation temperatures higher than 1200" F. might be employed if the heatingrcharacteristics of the heater 24, and other conditions, permitted heating to higher temperatures without -excessive coking.

The distillationtemperature in tower'28 is directly de- Y tower, a pitch having a softening point, determined by ASTM D36-26 ring and ball test, of 360 F. may be obtained by vacuum distillation in tower 28 at a flash temperature of approximately 1070 F. (corrected to 760 millimeters of mercury). On the other hand, if a pitch having a softening point of 472 F. is desired, a temperature lof `approximately 1200 ^F. (corrected to 760 millimeters of mercury) in the vacuum distillation tower is required.

It is necessary in the preparation of petroleum pitches to make an extremely deep cut into the heavy asphaltic crudes without substantial formation 'of coke. Continuous ash vaporization at high vacuum is particularly suitable. Volatile components remaining in the reduced crude, together with steam which is generally added, aid in the vaporization of extremely heavy oils in a continuous ash vacuum distillation tower to facilitate their removal from the pitch Without employing excessively high temperatures. Batch distillation processes are not satisfactory because of the very high temperatures required to distill the heavy oils, and the long periods at which the residue is at a high temperature.

A gas oil is withdrawn overhead from Vacuum distillation tower 28 through line 30 and passed to a condenser 32. Non-condensable gas is Withdrawn from the system by a steam ejector or other vacuum pump 34 to maintain a vacuum on the tower 28. The gas oil condensed in condenser 32 is suitable for use as a furnace oil or catalytic cracking charge stock, `and is delivered from the system by a pump 36. The residue from the bottom of vacuum distillation tower 28 constitutes the novel petroleum pitch of this invention, and is withdrawn Ias a liquid through line 38 by means of a pump 40 and delivered to any suitable cooling and solidiiication equipment.

The petroleum pitches of this invention are characterized by a high but finite softening point above 350 as determined by the ring and ball ASTM test D36-26. The specific gravity of the pitch is in the range of 1.050 to approximately 1.20 and in most instances in the range of 1.10 to 1.20.

The petroleum pitches are brittle, dark and resemble gilsonite rather than petroleum coke in their characteristics. In addition to having a nite softening point, the petroleum pitches are substantially completely soluble in carbon disulfide, benzene, and trichloroethylene. The petroleum pitches contain less than 0.4% material insoluble in refined creosote solvents (Kolineum). 'The acetone insoluble materials in the pitches will range from approximately 80 to 95%, 4and the Conradson car-bon residue (ASTM test D189*46) is above about 40%. The petroleum pitches `of this invention have a low penetration ofthe order of about to 5 at 210 F./ 100 grams/5 seconds as determined in accordance with ASTM test D5-49, and `are characterized by a susceptibility factor yof about 15 to 25. The susceptibility factor may be calculated from the following formula:

Penetration (a) 150/100 g./5 sec. L 114/200 g./5 sec. V

Penetration 185/ 50 g./5 sec.

@ 150/100 g./5 sec.)

Eastern Venezuela, Coastal, and California crude oils are also suitable for the preparation of petroleum pitches by the method herein described.

Whether or not a crude oil is a satisfactory charge stock from which high softening point pitches may be prepared according to this invention may be determined by the following test procedure. Furnace oil is distilled from the crude oil Iand the bottoms from that distillation are cut at a 1030 F. flash temperature, corrected to 760 millimeters of mercury absolute pressure, `and the asphaltene `content of the resulting Abottoms determined in accordance with the pentane precipitation technique of ASTM test D893-50T. The asphaltene content of the bottoms form a 1030 F. flash temperature of furnace loil-free crude oils suitable for the preparation of pitches according to this invention is above :about 30%.

Example 1 A Baxterville, Mississippi, crude having a gravity of approximately 15.3 API was reduced to 95.2% bottoms in an atmospheric distillation. The bottoms were then vacuum reduced in a continuous flash distillation at a flash temperature of approximately 700 and an absolute pressure of 41/2 millimeters of mercury. Steam was added to the reduced crude at the rate of 26.1 pounds per barrel of charge. The flash temperature, corrected to 760 millimeters of mercury, was l068 F. The distillate taken overhead from the vacuum distillation constituted approximately 69.4% of the crude by Volume and had a gravity of 22.4 API. The petroleum pitch from the vacuum distillation upon solidification had a specific gravity of 1.099 and a softening point, by the ring and ba'l'l test, ASTM D36-26, of 360 F. The penetration of the pitch at 210 F./ 100 grams/5 seconds was 4. The Conradson carbon residue of the pitch was 431/2% and the percent of the pitch insoluble in trichloroethylene was 0.08.

Example 2 The reduced crude from the atmospheric distillation described in Example l was vacuum distilled at a flash temperature of 775 F., a ash pressure of 5.9 millimeters of mercury, and a steam addition rate of 28.1 pounds per barrel of charge. The flash temperature, corrected to 760 millimeters of mercury, was l160 F. The pitch recovered as bottoms from the vacuum distillation constituted 20.8% of the crude by volume and had a softening point by the ring and barl'l test method of 390 F. The Conradson carbon residue of the pitch was 481/2 percent and the percent of the pitch insoluble in trichloroethylene was 0.11. The penetration of the pitch at 210 F./ grams/5 seconds by ASTM test D5-49 was 0.

Example 3 The reduced crude from the atmospheric distillation described in Example l was ashed at a temperature of 799 F., a pressure of 7.4 millimeters of mercury, and a steam addition rate of 31.8 pounds per barrel of charge. The ash temperature, corrected to 760 millimeters of mercury, was 1201 F. The pitch recovered as bottoms from the vacuum distillation constituted 1.7.9 percent of the crude and had a softening point of 441 F. as determined by the ring and ball test method. The penetration of the pitch as determined by ASTM test D5-49 at 210 F./ 100 grams/ 5 seconds was 2. The pitch contained 0.11 percent material insolubles in trichloroethylene and had a Conradson carbon residue of 55.2%.

Example 4 An Eastern Venezuela crude oil having a gravity of 33.2 API was distilled in an atmospheric distillation tower to yield 46.8 percent bottoms. The bottoms were then vacuum distilled at a flash temperature of 788 F., an absolute pressure of 8.6 mm. of mercury and a steam addition rate of 22.3 pounds per barrel of charge. The flash temperature, corrected to 760 mm. of mercury, was

5 1138 F. The pitch recovered as bottoms from the vacuum distillation had a specific gravity, in the solid state, of 1.124, a ring and ball softening point of 426 F., a Conradson carbon residue of 53.7 percent and contained 0.13 percent material insoluble in trichloroethylene.

Example 5 An Eastern Venezuela tar oil having a gravity of 14.8 API was distilled in an atmospheric distillation tower to yield 98.0 percent bottoms. The bottoms were then flashed in a vacuum distillation tower at a ash temperature of 761 F., absolute pressure of 6.6 mm. of mercury and a steam addition rate of 36.8 pounds per barrel of charge. The flash temperature corrected to 760 mm. of mercury was 1170. The pitch recovered as bottoms from the vacuum distillation had a specific gravity of 1.123, a ring and ball softening point of 369 F., a penetration at 77 F., 100 grams, in 5 seconds of 1. The Conradson carbon residue was 46.4 percent and the pitch contained 0.25 percent material insoluble in triclrloroethylene.

Example 6 A mixture of Western Venezuela crudes having a gravity of 12.5 API was distilled in an atmospheric distillation tower to yield 96 percent bottoms. The bottoms were then vacuum distilled at a ash temperature of 785 F., a pressure of 8.7 mm. of mercury absolute and steam added at the rate of 31.7 pounds per barrel of charge. The ash temperature of the vacuum distillation corrected to 760 mm. of mercury was 1180 F. The petroleum pitch recovered as bottoms had a specific gravity of 1.118, a lsoftening point of 356 F. and a penetration of at 77 F., 100 grams and 5 seconds. The Conradson carbon residue was 46.7 percent and the pitch contained 0.24 percent material insoluble in trichloroethylene.

Example 7 A Mara tar oil having a gravity of 15.0 API was distilled in an atmospheric distillation tower to yield 81.8 percent bottoms. The bottoms were vacuum distilled at a ash temperature of 776 F., a pressure of 9.6 mm. of mercury absolute and a steam addition rate of 33.0 pounds per barrel of charge. The flash temperature corrected to 760 mm. of mercury was 1170. The petroleum pitch recovered as bottoms from the vacuum distillation had a ring and ball softening poiht od 388 and a specilc gravity of 1.139. The penetration of the pitch at 77 F., 100 grams and seconds was 1. The Conradson carbon residue of the pitch was 43.7 percent and the pitch contained 0.51 percent material insoluble in trichloroethylene.

We claim:

1. A process for the preparation of a petroleum pitch having a softening point above about 350 F. and substantially complete solubility in benzene consisting essentially of distilling in an atmospheric distillation a petroleum crude oil selected from the group consisting of naphthenic base crude oils, asphaltic base crude oils and mixtures thereof, said petroleum crude oils having at least 30 percent asphaltenes in the residue from a ilash distillation at a temperature of 1030 F., corrected to 760 millimeters of mercury absolute pressure,fof the furnace oilfree bottoms of the crude oil, heating the bottoms from the atmospheric distillation under conditions of temperature and residence time substantially to avoid cracking of the bottoms, adding steam to the heated bottoms, and vacuum distilling the mixture of bottoms and steam at an actual temperature in the range of 700 to 800 F., the actual temperature and the amount of steam and the absolute pressure in the vacuum distillation being correlated to provide a flash temperature of 1050 F. to about 1200 F., corrected to 760 millimeters of mercury absolute pressure, to form the pitch as a residual product of the vacuum distillation.

2. A process for the preparation of a solid petroleum pitch having a ring and ball softening point above about 350 F. and characterized by substantially complete solubility in benzene consisting essentially of continuously vacuum distilling virgin bottoms of a crude oil having at least 30% asphaltenes in the residue from a flash distillation at a temperature of 1030" F., corrected to 760 mm. of mercury absolute pressure, of the furnace oil-free bottoms of the crude oil, injecting steam into the vacuum distillation, the actual ash temperature being in the range of about 700 to 800 F. and correlated with the absolute pressure and the rate of steam addition to provide a distillation temperature, corrected to 760 mm. of mercury absolute pressure, in the range of 1050 F. to about 1200 F., the rate of heating to the ash temperature being such as substantially to avoid cracking of the virgin bottoms, and cooling the residual product from the vacuum distillationv to produce a solid pitch.

References Cited in the tile of this patent UNITED STATES PATENTS 1,615,407 Rogers et al Ian. 25, 1927 2,175,817 Slawson Oct. 10, 1939 2,305,440 Noel Dec. 15, 1942 2,366,657 Sorem Jan. 2, 1945 2,651,601 Taff et al. Sept. 8, 1953 2,662,051 Pelzer Dec. 8, 1953 2,717,866 Doering et al Sept. 13, 1955

Claims (1)

1. A PROCESS FOR THE PREPARATION OF A PETROLEUM PITCH HAVING A SOFTENING POINT ABOVE 350*F. AND SUB STANTIALLY COMPLETE SOLUBILITY IN BENZENE CONSISTING ESSENTIALLY OF DISTILLING IN AN ATMOSPHERIC DISTILLATION A PETROLEUM CRUDE OIL SELECTED FROM THE GROUP CONSISTING OF NAPHTHENIC BASE CRUDE OILS ASPHALTIC BASE CRUDE OILS AND MIXTUTES THEREOF, SAID PETOLUM CRUDE OILS HAVING AT LEAST 30 PERCENT ASPHALTENESS IN THE RESIDUE FROM FLASH DISTILLATION AT A TEMPERATURE OF 1030*F., CORRESTED TO 760 MILLIMETERS OF MERCURY ABSOLUTE PRESSURE, OF THE FURNACE OILFREE BOTTOMS OF THE CRUDE OIL, HEATING THE BOTTOMS FROM THE ATMOSPHERIC DISTILLATION UNDER CONDITIONS OF TEMPERATURE AND RESIDENCE TIME SUBSTANTIALLY TO AVOID CRACKING OF THE BOTTOMS, ADDING STEAM TO THE HEATED BOTTOMS, AND VACUUM DISTILLING THE MIXTURE OF THE BOTTOMS AND STEAM AT AN ACTUAL TEMPERATURE IN THE RANGE OF 700* TO 800*F., THE ACTUAL TEMPERATURE AND THE AMOUNT OF STEAM AND THE ANSOLUTE PRESSURE IN THE VACUUM DISTILLATION BEING CORRELATED TO PROVIDE A FLASH TEMPERATURE OF 1050*F. TO ABOUT 1200*F., CORRECTED TO 760 MILLIMETERS OF MERCURY ABSOLUTE PRESSURE, TO FORM THE PITCH AS A RESIDUAL PRODUCT OF THE VACUUM DISTILLATION.

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