US2687986A - Hydrocarbon conversion - Google Patents

Description

Patentecl Aug. 31, 1954 TATS OFFlCE HYDROCARBON CONVERSION of Delaware Application May 1, 1951, Serial No. 223,938

Claims.

The present invention relates to a process for the thermal conversion of hydrocarbonaceous materials. More particularly the invention pertains to an improved method of reducing the viscosity of heavy hydrocarbonaceous residues of the type of topped or reduced crude or similar materials by a thermal treatment suitable toy produce fuel oils of improved quality, gas oils and increased proportions of motor fuel range hydrocarbons. Broadly, the invention provides for subjecting heavy residues of the type specified to a viscosity-reducing or visbreaking treatment at severe conditions suitable for the production of higher yields of gasoline and revisbreaking the high-severity visbreaker tar in a second visbreaking stage at relatively mild conditions conducive to the production of high quality fuel Oil.

In refining crude oil the first step is normally a simple distillation or topping to produce distillate fractions and a heavy residue. In order to obtain maximum yields of high quality motor fuels, all fractions boiling above the gasoline range and particularly those boiling above the heating oil range must be subjected to catalytic cracking. However, the heavy residum of conventional crude distillation boiling above about 800 F. does not, as such represent a feed stock suitable for catalytic cracking. Among the methods developed to produce satisfactory catalytic cracking feed stocks from these residues, viscosity reduction or visbreaking is one of the most widely used.

Visbreaking involves a treatment of reduced crude or the like at temperatures of about 780- 950 F. and pressures of about 10G-1500 p. s. i. g. at feed rates of 1-'75 volumes per hour of oil at 60 F. per cracking volume above '750 F. to produce by a mild type of thermal cracking about 5-15 vol. per cent of gas oil, about 515 vol. per cent of gasoline and about 90-'70 Vol. per cent of heavy fuel oil. Speciiic conditions within the ranges specified depend on the type of the visbreaker feed. The gas oil so formed represents a feed stock suitable for the production of additional amounts of high quality gasoline by catalytic cracking or,l after suitable finishing, an acceptable distillate fuel. Of the products formed in visbreaking, the gasoline has the highest and the fuel oil the lowest value. In order to obtain the greatest product realization it is highly desirable, therefore, to reduce the fuel oil yields to a minimum while simultaneously increasing the gasoline and gas oil yields to a maximum. This may be accomplished by increasing the severity of the thermal cracking treatment, that is, by raising the temperature and/or extending the cracking time. However, when so operating the quality of the product fuel cil, particularly its sedimentation characteristics are impaired to an extent which makes the fuel oil unacceptable for most purposes. Therefore, a visbreaking operation permitting the production of increased yields of gasoline and gas oil and simultaneously of fuel oil in` smaller amounts but of satisfactory sediment characteristics, has become a need strongly felt in the art of petroleumrening. The present invention provides an operation of this type.

It is, therefore, the principal object of this invention to provide improved means for visbreaking heavy petroleum residues of the type specified, permitting the production of maximum yields of motor and distillate fuels and relatively small yields of a high quality heavy fuel oil. Other objects and advantages will appear from the subsequent description of the invention wherein reference will be made to the accompanying drawing, the single ligure of which is a schematical flow diagram of a system suitable to carry out an embodiment of the invention.

It has now been found that the yields of low boiling distillates such as gas oils and gasoline may be substantially increased over conventional visbreak-ing at relatively mild conditions,

without detrimentally affecting the quality of the fuel oil product, by subjecting the heavy visbreaking feed stock first to a visbreaking treatment carried out at severe conditions conducive to the formation of increased proportions of lower boiling distillate oils and thereafter revisbreaking the visbreaker tar from the severe visbreaking treatment in a second visbreaking stage at conventional conditions, which are comparatively mild. The pitch feed to the second visbreaking stage is preferably asphaltic or virgin asphalt is preferably added to this pitch inamounts of 242%, in order further to improve the quality of the fuel oil produced.

First stage severe visbreaking conditions include temperatures of about 35o-975 F., preferably about 920-960 F., pressures of about 200- 1100 p. s. i. g., preferably about 3004000 p. s. i. g. and oil residence times at visbreaking conditions, corresponding to about 'l5 to 50 volumes per hour of oil at F. per first stage visbreaker volume above 750 F. 'Specific conditions vary with the type of visbreaker feed. However, the conditions to be applied in this stage should be more severe, Within the ranges specified, thanthe more conventional conditions employed in the second stage. Particularly, the temperature should be about 50-100 F. higher than the conventional temperatures of the second stage. Similar results may be accomplished by increasing residence time, by, say, about 50-200%. By way of example, conventional visbreaking conditions to be maintained in the second stage may include temperatures of about 'TO0-900 F., preferably about r{8O-900" F., pressures of about 20G-1000 p. s. i. g., preferably about 500 to 1000 p. s. i. g., and residence times when using coil and upflow or downflow soakers corresponding to about 2.5 to 30 volumes per hour of oil at 60 F. per second stage visbreaker volume above '750 F. (v./v./hr.) or 10-30 v./v./hr. when using only a visbreaker coil.

All types of conventional visbreaking systems such as coil only, tube-and-tank type arrangements, suspensoid, fluid or moving bed type of operations may be readily adapted to the present invention. In accordance with a preferred ernbodiment of the invention, a tar-containing portion or all of the liquid product from the severe visbreaking stage is retreated in a visbreaking zone wherein fresh visbreaker feed is simultaneously visbroken at conventional mild conditions.

The beneficial effects of the process of the invention are demonstrated by the data reported below which were obtained in commercial visbreaking operations. Two visbreaking units A and B were operated in parallel. Unit A was a conventional tube-and-tank type system in which a 13-15 API mixture of vacuum reduced asphaltic and parainic reduced crude, gas-oilfluxed asphalt from a propane deasphalting operation and bottoms from a slop rerunning operation was heated in furnace coils to about 840 to 850 F., at a feed rate of about 16,000 bbl/day and at a pressure of about 300 to 1,000 p. s. i. g. at about 15 v./v./hr. above '750 F. The feed so heated was discharged into a downow soaking drum maintaining no appreciable liquid level, or an incremental residence time therein, substantially at the conditions of the visbreaker coil. The visbroken product was passed from the soaking drum to a separator maintained at about '720 to 760 F. and about 25 to- 35 p. s. i. g. pressure. Separator overhead was fractionated in a product fractionator While separator bottoms were flashed into a ilash drum to atmospheric pressure and at temperatures of about 500 to 600 F. The flash drum overhead was recovered tgether with the separator overhead While the flash drum bottoms were recovered as fuel oil stock, all in a substantially conventional manner.

Unit B was a coil only system in which the feed consisting of -12" API mixture of vacuum reduced South Louisiana and Louisiana-Mississippi crudes was heated in a furnace coil of semicommercial scale to about 940 to 955 F. at a pressure of 700 to '750 p. s. i. g. and a throughput of about 24-29 v./v./hr. to obtain high severity visbreaking. The visbroken product was directly passed to a separator maintained at about 350 to 450 F. and about 100 to 125 p. s. i. g. pressure. The liquid product from the separator was iluXed with 30% light catalytic gas oil and flashed in the flash drum of unit A, so that the fuel oil stock recovered from this joint flash drum represented a mixture of tars produced at conventional mild and high severity conditions. This stock was blended with light catalytic gas oil and tested for its sediment characteristics by a standard filtration procedure in which sediment Table I Run No I II III Tar Production Rate, 13, OOO-14, 000 13, 000-14, O00 13, OOO-14, 000

Unit A, Bbl/day.

TarProduction Rate, 100+ 50 Unit B, BbL/day.

Sediment of Com- Too High Too High. 0. 13

bined Tars, Wt. Percent.

The data of Table I show that even blends containing as little as 100 bbl. of high severity tar per 13,000-l4,000 bbl. of satisfactory tar, i. e., less than 1%, exceed permissible sediment limits.

Following the operation reported above the liquid product from the separator of high severity unit B was fed t0 the furnace coil of unit A together with the regular feed of unit A. Summarized results of this operation are given in Table II below:

Table II Run No I II Conditions-Feed Rates to Unit:

Regular Feed, BbL/day 13,000 13,000. Liquid Product from Unit B, 1, 500 2,500.

Bbl/day. Total Feed Rate, Bbl./day 14, 500 15,500. Coil Outlet Temperature, F 820-850 820-850. Pressure, p. s. i. g 400 400. Flash Drum Tar, Bbl/day (Es- 13,000-14,000 13,000-14,000.

timat Flash Drum Tar Inspection: 0.11 Met Specifica Sediment, Wt. Percent. tion.

The data of Table II demonstrate that when operating in accordance with the present invention a visbreaker tar having satisfactory sedimentation characteristics may be produced from a feed about 15-25% of which is visbroken at high severity conditions conducive to increased yields of lower boiling distillates. Comparison of these results with those reported in Table I proves the significant advantages of the process of the invention with respect to the sediment characteristics of the fuel oil which may be produced in high severity visbreaking operations. The considerable increase in the severity tolerance of the visbreaking process thus aiforded also permits a corresponding increase in total visbreaker conversion and distillate yields without detriment with respect to fuel oil quality. While the coil outlet temperature in the second stage of runs I and II was at times lower that that specined above for conventional operation, subsequent operations indicate that no such temperature reduction is required in the second stage.

Having set forth its objects and general nature, the invention will be further explained by the following description of the system shown in the drawing which illustrates a preferred mode of practicing the invention.

Referring now in detail to the drawing, the

system illustrated therein essentially comprises a conventional type low-severity visbreaking unit A and a high-severity type visbreaking unit B the functions and cooperation of which will be forthwith explained.

In operation, a virgin crude distillation residuum such as a vacuum distillation residue boiling above about 800 F. may be supplied from line i by feed pump via line 5 to visbreaking coil '1. This feed stock is preferably an asphaltic pitch or contains virgin asphalt. The oil supplied from line i may have the temperature at which it is recovered from the crude still, say, about 50o-750 F. In line 5, the virgin oil feed is mixed with about 15 to 20% of liquid high-severity visbreaker product obtained as` will appear hereinafter and supplied from line 9 at a temperature f about 300 to 400 F. The mixed feed enters low severity visbreaking coil 'l at a pressure of about '700 to 750 p. s. i. g. and is heated therein to about 820 to 860 F. within a residence time of about 2 to 5 minutes. The eiuent from coil l is passed through line il to downflow or upflow soaker i3 wherein it may be maintained substantially at the temperature and pressure of coil 'i for an additional say 1-15 minutes depending on the soaker type, to complete the visbreaking reaction. The visbroken product is withdrawn from soaker i3 through line i5 provided with pressure release valve Il and passed to a vapordiduid separator I9 maintained at a pressure of about 30 to 35 p. s. i. g. and a temperature of about 720 to '760 F. Vapors separated in separator l0 leaving via line 2l, are fed to a conventional product fractionator 25. Distillate fractions may be recovered from fractionator 25 in any desired manner as exemplified by lines 2i, 2Q and 3l. Bottoms are withdrawn Via line 33 and and can be recovered wholly or in part through line 35 for reprocessing in other operations or may be returned to low severity coil 'l via line 35 with the fresh feed.

Returning now to separator I9, the separated liquid product is withdrawn through line 31 provided with pressure release valve 39 and ashed at atmospheric pressure into flash drum 4|. Flash drum Si may be maintained at a temperature of about 500 to 600 F. Stripping steam may be injected through lines 42. A distillate vapor fraction boiling below about 800 to 850 F. may be removed via line dit to be further treated in any conventional manner. The bottoms of flash drum li are recovered through line 45 as product tar complying with fuel oil specifications.

A second residual feed stock which may be the same as, or different from, that supplied via line l is fed from line 41, preferably at its production temperature, by feed pump 49 to high severity visbreaking coil 5l which it may enter at a pressure of about "700 to 800 p. s. i. g. Coil 5i may be maintained at an outlet temperature of about 900 to 975 F. and provide for an oil residence time of about 1 to 4 minutes to complete the visbreaking reaction. The visbroken product is withdrawn via line 53 and may be passed through lines 55 and 5i provided with pressure release valve 59 to vapor-liquid separator 8l which may be maintained at a pressure of about 0 to 150 p. s. i. g. and a temperature of about 350 to 450 Overhead vapors from separator El are withdrawn through line 53 provided with release valve 65 and may be passed to product fractionator 25 to ce treated therein together with the overhead from separator i9 as described above. The liquid products separated in separator 6I are withdrawn through line 61 and supplied by pump 6,9 to .line 9 to be combined in line 5 with the virgin feed to coil 'l as described above.

When operating substantially as described above, the gasoline and gas oil yields obtained from the total oil feed to Sections A and B are substantially higher than those obtained by processing of the same amount of feed in a system of the type of section A alone. The increase in gasoline yield amounts to about 20 to ri0% and the increase in gas oil yield to about 10 to 60% based on conventional yields. The amount of fuel oil produced in the case of two stage processing is about 3 to 8% less on the same basis than that obtainable in single stage processing in section A; however, fuel oil quality is equally satisfactory in both cases. When the total feed of sections A and B is processed in a system of the type of section B alone, the amounts of gasoline and gas oil produced are higher, and the amount of fuel oil produced lower than in the case of processing as described with reference to the drawing. However, the fuel oil produced by all-high-severity processing is not a saleable product.

The operation described with reference to the drawing permits of various modifications without a significant change in the contemplated results. For example, soaker li may be used in high sever` ity cracking section B providing for a larger oil residence time substantially at the temperature and pressure of coil 5i. In this case, the residence time in coil 5i may be substantially reduced and its eiuent passed through line 55 to soaker l l. The soaked product is withdrawn through line 'i3 and may be passed directly to line 9 and from there 'to line 5 and coil 7. All or any desired por-,- tion of the effluent of soaker 7l may be passed via line 'i5 provided with release valve il to separator 5i and treated therein substantially as de scribed above with reference to separator 9|. Rather than passing the total effluent of coil 5 i to soaker il it may be fed from line 53 via line i9 to lines 9 and 5 and coil l. If desired, soaker i3 of section A may be by-passed by the effluent of coil 'l via line 8l, in which case the residence time in coil 'l will be correspondingly increased to make up for the residence time of the by-passed soaker. In all modications, except in the case in which soaker i3 is by-passed by line 8i, the high-severity visbreaker product owing through line 9 may be added via lines 83 and Il directly to soaker i3 to be subjected therein to the mild conditions of visbreaking section A. In place of, or in addition to, the virgin oil feed supplied through line I, an asphalt material such as asphalt-containing pitch or extraneous virgin asphalt in proportions of about 2 to 12 wt. percent based on the material in line 9, may be supplied through line to be mixed with high severity visbreaker product in line 9. The addition of such materials through line 85 is particularly desirable in cases in which a feed stock of relatively low asphalt content is supplied via line l. Either one or both of the visbreaker coils 7 and 5I may have the form of double coils operated in parallel, in a manner known as such. Other modifications within the spirit of the invention may appear to those skilled in the art.

The above description and exemplary operations have served to illustrate specific embodiand high quality residual fuel oils of low-sediment content by visbreaking heavy virgin crude distillation residues, the improvement which comprises passing a feed stream consisting essentially of a virgin distillation residue boiling essentially above 800 F. through a visbreaking zone under relatively severe conditions including a reaction temperature of 850 to 975 F., separating the resulting hydrocarbon product into a vapor fraction and a first-stage residual tar fraction, mixing at least a portion of the separated tar fraction with another feed stream of a distillation residue of an asphalt-containing virgin crude stock boiling essentially above 800 F. to give a mixture containing about 15 to 20 parts of the tar fraction per 100 parts of the virgin stock, passing the mixture through a second visbreaking zone under relatively mild conditions including a reaction temperature of about 750 to 900 F. and a residence time corresponding to about 2.5 to 30 v./v./hr. above 750 F., the reaction temperature in said second visbreaking Zone being about 50 to 100 F. lower than the temperature in said rst visbreakng zone, separating the resulting hydrocarbon mixture into a vapor fraction and a low-sediment residual tar fraction, and recovering the low-sediment tar.

2. A process according to claim 1 wherein the mixture fed to the mild second visbreaking zone contains about 2 to 12% of virgin asphalt based on the tar fraction present in the mixture.

3. A process according to claim 1 wherein the residence time in the severe first visbreaking zone is 50 to 200% longer than the residence time in the mild second visbreaking zone.

4. A process according to claim 1 wherein the virgin residue fed to both visbreaking zones is a vacuum reduced crude, about 15 to 25% of this reduced crude being introduced directly to the severe first visbreaking zone While the balance of the reduced crude is introduced directly to the mild second visbreaking zone.

5. In the process of producing distillate oils and high quality residual fuel oil by visbreaking crude distillation residues, the improvement which comprises passing a feed stream consisting essentially of a virgin crude distillation residue boiling essentially above 800 F. through a visbreaking zone under relatively severe conditions including a reaction temperature of 920 to 960 F., a pressure of about 700 to 800 p. s. i. g. and an oil residence time of about 1 to 4 minutes, separating the resulting hydrocarbon product into a vapor fraction and a rst-stage residual tar fraction, mixing the separated tar fraction with another feed stream of a distillation residue of an asphaltic virgin crude boiling essentially above 800 F. to give a mixture containing about 15 to 20 parts of the tar fraction per 100 parts of the virgin stock, passing the mixture through a Second visbreaking zone under relatively mild conditions including a reaction temperature of about 820 to 900 F., a pressure of about 300 to 1000 p. s. i. g. and an oil residence time corresponding to about 2.5 to 30 v./v./hr. above 750 F., the reaction temperature in said second visbreaking zone being about to 100 F. lower than the temperature in said rst visbreaking Zone, separating the resulting hydrocarbon mixture into a vapor fraction and a second-stage residual tar fraction, and recovering the said second-stage tar.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,981,842 Keith, Jr. Nov. 20, 1934 2,132,137 Watson Oct, 4, 1938 2,161,676 Houdry June 6, 1939 2,166,177 Peterkin July 18, 1939 2,244,632 Phinney June 3, 1941 2,366,218 Ruthruff Jan. 2, 1945 2,388,055 Hemminger Oct. 30, 1945 2,507,523 Houdry May 16, 1950

Claims (1)

1. IN THE PROCESS OF PRODUCING DISTILLATE OILS AND HIGH QUALITY RESIDUAL FUEL OILS OF LOW-SEDIMENT CONTENT BY VISBREAKING HEAVY VIRGIN CRUDE DISTILLATION RESIDUES, THE IMPROVEMENT WHICH COMPRISES PASSING A FEED STREAM CONSISTING ESSENTIALLY OF A VIRGIN DISTILLATION RESIDUE BOILING ESSENTIALLY ABOVE 800* F. THROUGH A VISBREAKING ZONE UNDER RELATIVELY SEVERE CONDITIONS INCLUDING A REACTION TEMPERATURE OF 850 TO 975* F., SEPARATING THE RESULTING HYDROCARBON PRODUCT INTO A VAPOR FRACTION AND A FIRST-STAGE RESIDUAL TAR FRACTION, MIXING AT LEAST A PORTION OF THE SEPARATED TAR FRACTION WITH ANOTHER FEED STREAM OF A DISTILLATION RESIDUE OF AN ASPHALT-CONTAINING VIRGIN CRUDE STOCK BOILING ESSENTIALLY ABOVE 800* F. TO GIVE A MIXTURE CONTAINING ABOUT 15 TO 20 PARTS OF THE TAR FRACTION PER 100 PARTS OF THE VIRGIN STOCK, PASSING THE MIXTURE THROUGH A SECOND VISBREAKING ZONE UNDER RELATIVELY MILD CONDITIONS INCLUDING A REACTION TEMPERATURE OF ABOUT 750 TO 900* F. AND A RESIDENCE TIME CORRESPONDING TO ABOUT 2.5 TO 30 V./V./HR. ABOVE 750* F., THE REACTION TEMPERATURE IN SAID SECOND VISBREAKING ZONE BEING ABOUT 50 TO 100* F. LOWER THAN THE TEMPERATURE IN SAID FIRST VISBREAKING ZONE, SEPARATING THE RESULTING HYDROCARBON MIXTURE INTO A VAPOR FRACTION AND A LOW-SEDIMENT RESIDUAL TAR FRACTION, AND RECOVERING THE LOW-SEDIMENT TAR.

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