US2768127A - Improved residual oil conversion process for the production of chemicals - Google Patents

Description

IMPROVED RESIDUAL OIL CONVER SION PROCES Oct. 23, 1956 c. N. KIMBERLIN, JR ET AL 5 2,768,127

FOR THE PRODUCTION OF CHEMICALS Filed May 17, 1951 2 Sheets-SheetZ J f T 0 m m T J L9 2 Q) L9 L10 8 T +5 2: W I

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- CELczrlL EL. dclanzs 45g NW (lbborrzeg U itr d es Paten IMPROVED RESIDUAL on. CONVERSION" PROC- ESS FOR THE PRODUCTION OF CHEMICALS Charles N. Kimberlin, Jr., and Clark E. Adams, Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Application May 17, 1951, Serial No. 226,892

1 Claim; (Cl. 196-55) The present invention relates to the production of valuable chemical materials from hydrocarbonaceous mate- More particularly, the invention pertains to the aromatc and unsaturated compounds which are useful as chemicals or starting materials therefor. In brief compass, the invention provides for contacting heavy residues of the type specified with subdivided solids at conditions conducive to the formation of lower boiling highly aromatic or unsaturated hydrocarbons and coke, in the absence of added steam.

In conventional petroleum refining the crude oil is first distilled to produce various distillate fractions and a residue boiling above about 700 F. or, with the more modern vacuum distillation equipment, the residue may boil above about 1050 F. Motor fuels being the most valuable product of commercial refining, the value of the various fractions of the crude distillation is determined chiefly by their utility for the production of high quality motor fuels. Aside from virgin naphthas, the gas oil fractions are the most valuable from this point of view, because they may be readily converted by thermal or catalytic cracking into high quality gasoline. The distillation residue is the least valuable petroleum product since it yields excessive amounts of coke and only relatively small proportions of volatile products useful for the production of motor fuels.

It has been found that distillate oils such ,as naphthas and gas oils are converted into more aromatic and unsaturated products useful for chemicals production when these oils are subjected to thermal cracking in fired coils at high temperatures of about 1000-1400 F., particularly in the presence of steam. However, as pointed out above, the value of these oils as starting materials for motor fuels is normally too high to make their utilization for the production of chemicals desirable under normal circumstances. The situation with respect to distillation residues is reversed. They are plentiful and inexpensive enough to serve as starting materials for chemicals on a theoretically economical basis. However, experiments have shown that high temperature thermal steam cracking in a manner similar to that used for the aromatization of distillate oils is inoperative on the basis of residual oils as the feed stock. Excessive coke formation and deposition in the cracking coils leading to overheating and equipment plugging preclude operation on a commercial scale. In addition, it has been found that the steam reacts with the coke at the prevailing high temperatures to form substantial amounts of CO which dilutes the product vapors and seriously complicates product recovery. When the steam supply is reduced or omitted coke formation is further increased to become entirely prohibitive even from the point of view of product distribution. The present invention overcomes these difficulties.

It is, therefore, the principal object of the present invention to provide an improved process of producing highly aromatic and unsaturated volatile materials by cracking heavy hydrocarbonaceous residues. Other and more specific objects and advantages will appear from the following description of the invention wherein reference will be made to the accompanying drawing in which Figure l is a semi diagrammatical illustration of a system suitable to carry out the process of the invention; and

Figure 2 is a similar illustration of a preferred application of the process illustrated by Figure 1.

It has now been found that heavy residues of the type specified may be converted into lower boiling products rich in unsaturated and aromatic compounds in commercially feasible operation by contacting the feed with subdivided solids at coking conditions comprising high temperatures in the range of about 12001400 F., preferably in excess of about 1250 F., in the absence of added steam. The contacting of the oil with the solids is accomplished by use of a transfer line reactor and/or a fluid bed reactor, the latter being the preferred embodiment of this invention.

In carrying out this preferred embodiment, the liquid or partially vaporized reduced crude or similar heavy residue is injected into a relatively dense turbulent bed of subdivided contact solids having a particle size of about 30-400 mesh, fluidized by a gaseous medium flowing upwardly through the bed at a linear superficial velocity of about 0.3-5 ft. per second to give the bed the appearance of a boiling liquid separated by a definite interface from an upper dilute suspension of solids in gasiform products. Hydrocarbon gases, such as propane or other light hydrocarbons such as butanes, ethane or mixtures thereof are used in place of steam as the auxiliary fluidizing medium required to maintain the solids bed in the fluidized state. The amount of these hydrocarbon gases used as auxiliary fluidizing agents will ordinarily be in the range of 1-10 wt. percent of the residuum feed. However, these gases themselves are converted into valuable chemicals and under some circumstances it may be economically attractive to use much higher proportions of these gases; in such cases the amount of light hydrocarbon gases fed may be 23 times the amount of the residuum feed.

The temperature of the fluidized bed is maintained at about l2501400 F. conducive to the deposition of coke on the fluidized solids and to the formation of highly aromatic and olefinic volatile products which are withdrawn overhead to be worked up into chemicals by fractional distillation, solvent extraction, selective adsorption, azeotropic and extractive distillation, and other methods.

The heat required to maintain the fluidized bed at the desired temperature may be supplied by indirect heating. However, in accordance with the preferred method of heat supply coke-carrying solids are continuously passed from the coking zone to a combustion zone wherein coke is burnt oif to heat the solids to a temperature higher than coking temperature. Hot solids are continuously recirculated to the coking zone in amounts suflicient to supply the required heat therein. The carrier solids may be either inert or catalytically active, such as coke, sand, silica gel, various natural or activated clays, used cracking catalysts, etc. However, coke produced in the coking stage is the preferred carrier solid in normal operation.

When operating in the manner described, coke deposition on the reactor walls is prevented by the scouring effect of the highly turbulent solids and by the fact that coke is preferentially deposited on the finely divided solids which have a large surface area. In addition, the exposure of the feed to this large surface area increases overall conversion and the yield of valuable volatile products. The high temperatures employed are conducive to the formation of aromatics and olefins in large proport atenred oer-.23, s

ored at the coking and product recovery conditions of the process.

Having set forth its objects and general nature, the in vention .will be best understood from the following more detailed description I of the system illustrated by the drawing.

Referring now to Figure 1 of the drawing, a heavy residual oil such as vacuum still bottoms from the distillation of a South Louisiana crude, said bottoms having anAPI gravity of about 12- and a Conradson carbon content of about 17% which may be, preheated to about 500-700 F.- is supplied through: line-1 to a lower portion of coker 3. Line 1 may discharge, into reactor 3 at apoint above a suitable gas distributing means, such as a perforated plate or grid 5, through a spray nozzle 7 of conventional design adapted to eject the predominantly liquid feed in the form of a fine mist or spray. Coker 3 contains a mass M3 of subdivided solids, preferably coke, having an average particle size of about 50200 mesh. Mass Ma is maintained in reactor 3 at about atmospheric or any desired higher pressure in the form of a dense highly turbulent fluidized solids bed having an upper interface L3, with the aid of hydrocarbon gases, preferably rich in propane, introduced through line 9 and grid in amounts sufiicient to establish a linear superficial gas velocity within mass Ma of about 0.3-1.5 ft. per second. Mass N13 is maintained at a temperature of about 12501400 F., preferably above 1300 F., conducive to coking and the formation of highly aromatic and olefinic volatile coking products as will appear hereinafter.

The vaporous coking products are carried by the fluidizing gas overhead from level L3 and may be withdrawn from coker 3 via suitable gas solids separation means, such as cyclone separator 13 provided with solids return pipe 15. Product vapors now substantially free of entrained solids are passed via line 17 to product separation and recovery equipment schematically indicated at 18 to be worked up therein as hereinafter described. The hot products leaving reactor 3 by line 17 preferably have theirtemperature reduced to the range of 850-1100 F. by means of a quench fluid introduced from line 19 into line 17. This quench oil may be water but is preferably a recycle fraction of intermediate boiling range of about 400700 F.

Returning now to mass M3, coke-carrying solids are withdrawn downwardly through a conventional standpipe 21 aerated and/ or stripped by one or more taps t. Product coke amounting to about -22% of the residuum when feeding the South Louisiana residuum specified may be recovered through branch standpipe 23. The remaining solids are supplied to line 25 wherein they are picked up by air and carried in suspension to a bottom portion of burner 27 preferably through a suitable distributing device, such as grid 29. Flow conditions are so controlled that a dense, turbulent, fluidized mass M27 is formed above grid 29, similar to mass Ma. Combustion takes place in mass M27 as a result of which the solids are heated to about 1300-l600 F., preferably about 50200 F. higher than the temperature of mass M3. Flue gases are withdrawn overhead via line 31 preferably after. fines separation and return by cyclone 33 and dippipe 35. Reheated solids are withdrawn downwardly from mass M27 through standpipe 37 aerated and/or stripped through taps t. The hot solids may discharge from standpipe 37 directly into mass M3 at a rate sutficient to supply as sensible heat of solids the heat required in, coker 3. It maybe desirable to re-adjust the particle size of the circulating solids continuously orat intervals to prevent accumulation of particles of excessive size.

This may be accomplished by subjecting the solids withdrawn through. standpipeZl to grinding in. any. suitable...

conventional manner. A supersonic attriter may be arranged in any portion of the solids circulation system in a manner known per se in the art of catalytic cracking.

The system illustrated in Figure 1 permits of various modifications. For example, the feed may be supplied together. with. the fluidizing gas throughgrid 7 without.

the use of a spray nozzle. In thiscase, it may be desirable to feed the reheated solids'from line 37 into the residuum feed line further to preheat, and vaporize the.

feed. In another. modification, the reheated solids may be mixed with theresiduum feed via lines 38 and 40 and passed into a cyclone 42 whence. cracked vapors discharge into line 17' and solids containing unvaporized feed discharge into mass. Ma This modification allows for a very short contact time for the bulk of the feed with the hot solids and thus favors liquid yield over gaseous yield. Other modifications will appear to those skilled in the art without deviating from the spirit of the invention;

When operating in the manner described above, the.

products recovered throughline 17 may amount to about wt. percent of the light hydrocarbon gases fed plus about 75-82 wt. percent of the residuum fed. The products from the-light hydrocarbons comprise hydrogen and methane and olefinic and diolefinic gases in the range of C2. to C4. The products obtained from the residuum feed (South Louisiana residuum, for example) are as,

follows:

(1). 30to 50 wt. percent .(based on residuum feed) of hydrogen and C1 to C3 hydrocarbons. The C2 hydrocarbons comprise 65-80% ethylene and 2035% ethane.

The Ca hydrocarbons comprise 80-95% propylene and.

5,20% ethane.

(2) 5 to .15 vol. percent C4 hydrocarbons comprising. about 15' to 30% butadiene, l to 5% butanes, and the.

remainder butenes.

(3) 2 m6 vol. percent Cs hydrocarbons comprising 30-50% diolefins (isoprene, piperylene, and cyclopentadiene) and the remainder pentenes.

(4) 8 to 20 vol. percent gasoline range hydrocarbons boiling about -400" F. and comprising about 50 80% aromatics; these aromatics are about fl benzene, toluene, and the remainder xylenes and C9 to C11 aromatics.

(5) 2 to 10-volume percent of intermediate fractionboiling at about 400700 F. having an- API gravity of about 4l2.

(6) 2 to 10 vol. percent of tar boiling above 700 F. and having an API gravity of about 20 -5.

One of the standard procedures used for upgrading crude residua in commercial refining practice is a thermal viscosity breaking or visbreaking operation involving:

fuel oil, which is highly undesirable for economical reasons, since the tar amounts even in operations of highest cracking severity to at least 50 wt. percent on feed. There is practically no outlet for the tar except as a residual fuel which is a low value product; furthermore in order for the tar to be suitable even as a residual fuel it is necessary to blend with it a part of the gas oil product in order to reduce the viscosity of the tar. Thus there are 3 highly desirable improvements of this process, viz., (l) to increase visbreaking severity in order to increase the yield of naphtha and particularly of gas oil (which may beultimately converted into high quality gasoline by catalytic cracking) and to decrease the yield of tar, (2) to avoid the blending of the gas oil fractions in the tar for use as residual fuel, and (3) to convert the tar itself into products more valuable than residual fuel. The present invention may be combined with conventional high severity visbreaking to provide a process so improved. A combination process of this type is schematically illustrated in Figure 2.

Referring now to Figure 2, the system shown therein comprises a conventional visbreaking stage 52, a visbreaker product fractionator 58, and a coker 3 of the type of coker 3 of Figure 1. The functions and cooperation of these elements will now be described using the conversion of crude still bottoms as an example. Other feeds may be treated in a substantially analogous manner.

In operation, a crude still residuum such as an atmospheric or vacuum distillation residue boiling above about 800 F., preferably above 1050 F., may be supplied from line 50 to visbreaking stage 52 at a preheating temperature of about 500750 F. and at a pressure of about 100-1500 p. s. i. g. suitable for high severity visbreaking. visbreaking stage 52 may comprise one or more conventional furnace coils operated in parallel and discharging into a soaking drum. The oil feed is cracked in the coils and soaking drum at an elevated pressure preferably not lower than about 500 p. s. i. g., a temperature of about 8501000 F. and a residence time at visbreaking temperatures of about 1-30 minutes, corresponding to an oil throughput of about 75-2 volumes of liquid oil per volume of visbreaker space per hour (v./v./hr.). Up to this point the operation is conventional but preferably carried out at very high severity limited by the operability, i. e. coking, of the equipment.

7 Now, rather than separating the visbroken eflluent into total liquids and total vapors under pressure as it is common practice, the efiluent is directly flashed through line 54 provided with pressure release valve 56 into a fractionator 58 which is preferably operated at atmospheric pressure. Slightly elevated pressures of, say, up to about 100 p. s. i. g. may be used. Stripping steam is admitted through line 60 to the bottom of fractionator 58. Distillation in fractionator 58 is so conducted that an overhead fraction of gas and naphtha boiling up to about 350-400 F. is removed through line 62, gas oil is recovered through line 64 and heavy bottoms boiling above about 800 F. are withdrawn through line 66. This bottom fraction serves as feed to a coking system of the type illustrated in Figure 1 and shown in Figure 2 at 3 in a simplified manner using like reference characters to identify like system elements.

A portion of the overhead fraction leaving fractionator 58 through line 62 is branched off through line 68 and supplied to line 9 to serve as the auxiliary fluidizing medium for mass M3 substantially as described with reference to Figure 1. The fractionator bottoms in line 66, representing the oil feed to coker 3 are fed together with the fluidizing medium via line 9 and grid 5. Solids circulation and heat supply take place through standpipes 21 and 37 as described with reference to Figure 1. Volatile products withdrawal and recovery are likewise substantially identical with those described above. The gas oil fraction Withdrawn by line 64 may be used for any desired purpose, but is preferably converted into high quality motor fuels by catalytic cracking.

Regarding product distribution, the products from the visbreaker tar are essentially the same as those from the virgin residuum feeds described with reference to Figure 1 except that the yield of coke is higher and the yields of gaseous and liquid products are proportionally less. The yield of coke from the visbreaker tar will depend upon the severity of the visbreaking operation and may vary from 20% higher to 100% higher than the coke yield from the virgin residuum from which the tar was derived.

In general, the products will vary with the relative proportions of residuum or tar and lighter hydrocarbons feed to the coker. The residual feed tends to give more bydrogen-deficient products, i. e., higher concentrations of aromatics and somewhat higher concentrations of olefins and diolefins in the non-aromatic products.

The system of Figure 2 may be modified in several respects. For example, if desired the entire overhead fraction, gas and naphtha leaving fractionator 58 by line 62 may be diverted by line 68 into line 69, since the naphtha from the visbreaking operation is of relatively low octane number and ordinarily requires further processing, such as reforming, before use as a motor fuel. When so diverted the naphtha fraction is converted into (1) about 3555 wt. percent of gases comprising hydrogen plus C1 to C3 hydrocarbons, the C and C3 being highly olefinic, (2) 5-l5 vol. percent C4 and C5 comprising olefins and diolefins, (3) 2045 vol. percent gasoline range hydrocarbons boiling in the range of about 400 F. and comprising 30-55% of aromatics, and (4) about 5-10 vol. percent of heavier product boiling above about 400 F. 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 embodiments of the invention but are not intended to be limiting in scope.

What is claimed is:

A fluidized solids coking process of producing volatile products rich in aromatic and olefinic constituents from heavy hydrocarbonaceous residues, which comprises passing said residues in contact with a substantial mass of substantially non-catalytic subdivided solids heated to a temperature of about 13001600 F. and a normally gasiform hydrocarbon conveying gas through a narrowly confined extended path at a conversion temperature of about 1250-1400 F. in the absence of steam and for a relatively short time adapted to convert a portion of said residues into said volatile products while leaving another portion of said residues substantially unconverted, said unconverted portion being deposited on said solids, separating said solids from the volatile products formed, passing said separated solids carrying said deposited portion substantially at said conversion temperature to a coking zone, maintaining said solids in said coking zone in the form of a dense, turbulent, fluidized mass for a relatively long time sufficient to complete conversion of said deposited portion into coke and volatile products, introducing normally gasiform hydrocarbons into said coking zone to promote fluidization and to convert at least a portion of said gasiform hydrocarbons, withdrawing volatile coking products overhead from said coking zone, separately withdrawing coked solids from said coking zone, reheating said withdrawn solids to said first-named temperature and supplying solids so reheated to said path.

References Cited in the file of this patent UNITED STATES PATENTS 1,419,123 Rittman June 6, 1922 2,114,416 Donnelly Apr. 19, 1938 2,133,344 Cooke Oct. 18, 1938 2,326,186 Watson Aug. 10, 1943 2,340,974 Myers Feb. 8, 1944 2,445,328 Keith July 20, 1948 2,527,575 Roetheli Oct. 31, 1950 2,543,884 Weikart Mar. 6, 1951 2,636,844 Kimberlin, Jr. et a1 Apr. 28, 1953 2,661,324 Letter Dec. 1, 1953 OTHER REFERENCES Sachanen; Conversion of Petroleum, 2d edition 1948 pp. 252-254.

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