US2900327A - Visbreaking of reduced crude in the presence of light catalytic cycle stock - Google Patents

Description

Aug- 18, 1959 H. BEUTHER E E -vIsBREAKING oF REDUCED CRUDE 1N THE PRESENCE OF' LIGHT CATALYTIC CYCLE STOCK Filed March 9, 1955 2,900,327 .Patented Aug. 1s, 1959 ice VPaul Siecke, and Harold Beuther, filed December 20, 1951. 2 900 327 This invention provides a process in which' a better dis- 'VISEREAIQNG yon REDUCED CRUDE 1N THE PRESENCE or Lrorrr CATALYTIC CYCLE sToCK assigner to Gulf Research & Development Company,

Pittsburgh, Pa., a corporation of Delaware H l, Y tions comparable to those used for vis-breaking-'the'v'ery Application March 9, 1953,' Serial N0# 341,126 deeply reduced residues from vacuum stills mentionedE V5 Clainm (ci. 208 106) above. The yield of gasoline from the heating and crack'- Y ing'of the mixtureis'markedly increased over that ob` l "tained when, for example, the catalytic cycle voil and the'` 'ThS iHVeIltOn relates '0.21l thermal Conversion PrOCeSS v15' residue are separatelycracked under comparablecondiforthethermal conversion of 'petroleurnfractiona and xjmore particularly to a process in which catalytic cycle i stocks and very heavy Vpetroleum residues are converted" @to more volatile and valuable productsY by rthermal conjversion4V` I p, YInthe processing Iof petroleum crude oils, the crude 1s tribution of the products obtained from petroleum crudes is obtained andparticularly one 'in which the yield of gasoline is increased. According to this invention, alight catalytic cycle oil is mixed with avery heavy residue'from crude petroleum whichv has been deeply reduced by vacuum distillation, and the"` mixture is"A heated and thermally cracked in furnace coi-lsA at severe cracking conditions. "Moreover, the 'mixture may be cracked -at even more severe conditions than the very heavy residue alone withoutY excessive coke formation.

The single gure of the drawings isa diagrammatic representation of a ow sheet of the process of this invention. Valves, meters, pumps, condensers, reux lines and j -r tutordinarily first passed nthrough a distillationc'olumn at" {tisubstantially atmospheric pressure in Iwhich gas and i other control 'equipment have been omitted from the drawing for Simplification.

1 gasoline are removedas overhead products, naphtha and Referring to the drawings, the feed stock, Vwhich .ordi- Y perhapsfahlight gasoil are taken off as side streams, and' Y Y i the heavierfractions are discharged as bottornsfrom the u 1` tower. lfhebottoms from the atmospheric tower are then j passed through avacuuin distillation tower in which a Ypheavy, gas -oil is taken overhead and a heavy residual frac- 10 into an atmospheric distillation tower 12 from which gas is taken off Voverheadthrough line 14, and side. streams of gasoline, naphtha and light gas oil may be withdrawn Q -zgtion isnobtained from the bottom of' the vacuum tower.

l tdesirable crudes, hasforced renners to make deeper and i, I -having a relativ ely high content lofaromatics isproducedA' i through' side tower outlets 16, 18 and 20, respectively. The bottoms from the atmospheric tower `12 are with- ""dra`wn through line 22 and passed into a vacuum distil- 'lation' tower 24 in which a Very deep cut is made to produce an exceptionally heavy petroleumtresidue as bot- 35 toms. A heavy gas oil is withdrawn at the top of the tower 24 through line 26 and passed to'apparatus, not shown, for further processing, such as vbycatalytic cracking. A very heavy residual fraction is withdrawn from the bottom of tower 24 through line 28. It will be appreciated that the atmospheric tower 12 and vacuum tower i 24 are provided with the usual reflux equipment and other apparatus necessary for control of the operation of the towers'.V If necessary, 'a heater (not shown) may be used between theatmospheric and vacuum tower to supply the heat necessary for the deep vacuum reduction of the The large and *steadily increasing demands for the more 1 volatile petroleum products, notably gasoline and distillslate fuel oils, and-the necessity of processing heavier, less p deeper cuts into the crpde. g p p M Y Y, Gas oils obtained as :distillates from the atmospheric v and vacuum distillation towers are generally cracked by either thermalv or catalytic processes to for'rrrgasoline.4 I T *In catalytic cracking processes, a very refractory cycle oil aloggwith the gasoline. nAttempts to crack the cycle oils further, either catalytically or thermally, 'have generally i been unsatisfactory. In catalytic processes, large amounts "j f (ofk carbon are deposited onY the catalyst lowconverv .sions -zto gasoline are obtained. In thermal processes,""

wery vsevere cracking conditions, together with very h igh recycle ratios, Vvare `requiredto Vobtain a' satisfactory `cenversion to gasoline. yOften recycle ratios as highas4 parts of recycle'to L1 .part of fresh feed are employed, rwith a consequent serious reduction in the capacity of the ther'` mal cracking unit. Because of the difficulty in cracking vthe catalytic cycle oil further, that stock is largely used to Vcutpthe viscosity of heavy .fuel oils to meet specifications Y andjblendedlwith:virginfuels toformY furnace oil. Both of `these uses ofthe catalytic cycle oil,` and particularly p its usetocut the viscosity-Mofheavy fuel, oils, seriously l Ydecrease the'preturn troni the catalytic Vcycle'oil 'as com--V`-` bottoms from the atmospheric tower 12.

The extent ofthe reduction of the crude required to produce a charge stock suitable for use in the process of this invention will depend in part 4upon the nature of the crude. In some instances, 4for example, where the crude is of a paraiiin base, the residue withdrawn through line 28 may be only approximately 5% of the crude.

` With other crudes, such as a West Texas crude, the

pared with what might be obtained if the catalytic cycle oil could satisfactorily be convrtedto gasoline.

Residual stocks `from atmospheric distillation towers y l have customarily been subjected to a vis-breaking thermal "residue withdrawn from the bottom of the distillation tower 24 may constitute approximately 10% of the crude. In general the heavier the crude, the larger the percent of the total crude'that may be treated satiscracking operation which is essentially a mild cracking operationat temperatures usually in the range of 825 F.' to 900 F. More' severecracking conditions are not i Y possibleA because of excessive coke formation.` Recently,

it has been found that, contrary to expectations, residual `stocks much heavier than these from atmospheric distilla tion, towers, may be vis-broken under vmore severe condi- 950,:o F., without excessive coke formation.y That discov- A vtions, such astemperatures ofapproximately 900 F. to

`factorily accordingrv to this invention. Residues .from certain heavy crudes such as those from Kuwait and "Mississippi may constitute as muchas 20% and 30% 'of the crude, respectively.

It has been found that the residual fractions which may be successfully cracked according to this invention are those having a carbon ery-is the subject matter of Application Serial'No; 262,566 70' IlOW US. Patent N0. 2,762,754 Of William C. Olltt,

residue number of at least 18, a gravity in A.P.I. below 10 and an SUS viscosity at 210 F. of at least 6,000. The initial boiling point of the residual fractions will generally be from 900 to 950 F., lbut will depend in part on the fractionating eiciency of the vacuum tower 24.

According to this invention, thel residue 'from the bottom of tower 24 is mixed with a light catalytic cycle oil introduced into line 28 through a line 30. The light catalytic cycle oil may be obtained from any of the wellknown catalytic cracking processes such as the Houdry fixed bed process, moving bed processes, or iiuid catalytic cracking processes. The boiling range of the light catalytic cycle stock will ordinarily be within the range of 400 F. to 650 F., and preferably within the range of 400 to 600 F. It will be appreciated that any suitable method of mixing the two fractions may be employed, and that a mixture of the residue with the light catalytic cycle oil may be stored in suitable tanks and charged directly to the furnace, rather than mixing the two fractions in the line Z8. The ratio of catalytic cycle oil to the residue may range from approximately 2 to 1, to 1 to 6.

Preferably, in the operation of the process of this invention, it will be desirable to recycle fractions of the cracked product boiling above the gasoline range, as illustrated in the drawings. The recycle oil is introduced into line 28 from line 32 for admixture with the light catalytic cycle oil and the residue prior to heating in the furnace 34.

The mixing of the light catalytic cycle oil with the residue from the vacuum tower 24 permits the use of more severe cracking conditions in the furnace 34 than is possible in the usual visbreaking operation without the formation of the excessive coke which limits the cracking conditions in conventional visbreaking processes. For example, the short time conversion process of this invention will ordinarily be accomplished with a furnace outlet temperature in the range of about 900 F. to 1000 F., and preferably from approximately 950 F. to 1000 F. The upper temperature limit will be determined in part by the heating curve of the furnace. If extremely high heating rates are possible, temperatures above 1000 F. may be used, in some instances, Without excessive coke formation. The pressure `is not as important as the temperature in controlling the reaction rate and severity of cracking. A pressure in the range of 50 to volume above 750 F. will be from about 0.020 to 0.035 cubic lfeet per barrel per day. ln the preferred form of the invention illustrated in the flow sheet, the mixture of the light catalytic cycle oil, recycle oil, and the residue is quenched immediately after its discharge from the furnace outlet 'by means of a stream of quenching oil introduced through line 36.

The cracked products from the furnace 32 are discharged through line 38 into a separator 40 from which heavy fuel oil is withdrawn as a bottoms product through a line 42 and the more volatile products are withdrawn overhead through a line 44. The conditions in the separator are controlled to regulate the initial point of the fuel oil. In this manner, the end point of the recycle oil is also regulated, ordinarily to form a recycle oil having a boiling range of approximately 400 to 600 F.

The overhead product from the separator 40 is delivered through a line 44 into a fractionating tower 46 which separates the more volatile compounds from the y 400 to 600 recycle oil withdrawn from tower 46 through line 32 for recycling through the furnace 34. The overhead products from tower 46 are delivered through a line 48 into a stabilizer 50 from which gases are withdrawn as an overhead product through line 52. Gasoline is taken from stabilizer S as a side product through line S4, and 400 F. end point naphtha is withdrawn as bottoms through rline 56. The lfractionator and stabilizer illustrated are conventional and shown only to complete the disclosure. Clearly, other fractionating and stabilization apparatus and procedures may be employed without departing from this invention.

It has been found that the process of this invention gives an improved yield of gasoline particularly as compared with processes in which the light catalytic cycle oil and heavy reduced crude are separately cracked. In addition,`there is apparently less condensation to form in the tubes of the furnace and, as a result, increases the 1000 p.s.i. gauge will ordinarily be used. The coil velocity in the tubes to sweep any coke whichrmay be formed from the coils.

The following examples illustrate theimproved opera` tions made possible by this invention:

EXAMPLE 1 A West Texas crude oil was reduced in an atmospheric and vacuum distillation process of the type described to form a residual product constituting 9.9% of the crude. A light catalytic cycle stock boiling in the range of approximately 436 F. to 616 F. was added to the residue, in such proportions that the reduced crude constiuted 72% of the mixture and the catalytic cycle stock the remainder, to form a total charge. The charge Was cracked in a coil at a maximum temperature of 950 F. and a pressure of 400 p.s.i.g. in a short period cracking operation. The cracked products were fractionated to produce a 10 lb. Reid vapor pressure, 400 F. end point gasoline and a specification fuel oil. 'Ihe fraction boiling between the end point of the gasoline and the initial boiling point of the specification fuel oil was recycled to extinction. The recycle oil amounted to 112% of the total charge.

EXAMPLE 2 The residue constituting 9.9% of a West Texas crude employed in Example 1 was cracked in a single pass conversion without the addition of catalytic cycle stock. The single pass conversion lwas conducted in a coil at a maximum temperature of 950 F., and pressure of 200 p.s.i.g., and the cracked products were fractionated to produce a 10 1b. Reid vapor pressure, 400 F. end point, gasoline, and a specication fuel oil, as in Example 1.

EXAMPLE 3 A residue from vacuum distillation constituting 17.7% of Kuwait crude was mixed with a light catalytic cycle stock similar to that employed in Example l in proportions of 68% reduced crude and 32% catalytic cycle stock to form a total charge. The charge was cracked at a maximum temperature of 950 F. and a coil outlet pressure of 400 p.s.i. gauge. The cracked products were separated into 10 1b. Reid vapor pressure, 400 F. end point, gasoline, and specification fuel oil. The fraction boiling between the end point of the 400 F. gasoline and the initial boiling point of the specication fuel oil was recycled to extinction. The recycle oil amounted to 111% of the total charge.

EXAMPLE 4 A residue constituting 17.7% of a Kuwait crude was cracked in a single pass operation without the addition of catalytic cycle stock. The maximum temperature of the cracking operation was 955 F., and a pressure of 200 p.s.i.g. was employed.

In each of Examples 1 through 4, the time of cracking was substantially the same, as indicated by the coil volunie above .750 F. of approximately 0.02 cubic feet per barrel of throughput per day. 'I'he results of the operations in Examples l through 4 are illustrated in the following Table I:

Table I i Exain- Exam- Exam- Example 1 ple 2 ple 3 ple 4 Yallld of 10 RVP 400 F. E.P. gasoe: Percent by vol. of total charge... 27.8 12. 4 32.5 18. 4 Yields: Percent by vol. of crudey 10 RVP 400 F. El". gasoline.-- 3.8 1.2 8. 4 3. 3 Fuel oil 10.8 11.5 18. 7 20. 2 Catalytic cycle stock requirement 4. 7 2. 7 l). 8 5. 4 Charge 3.8 0.0 8. 0.0 Cutting 011 o. 9l 2. 7 1. 3 5. 4

If the light catalytic cycle stock added to the residue in Examples 1 `and 3 is cracked separately to extinction in a recycle operation at conditions corresponding to the severity of Examples 1 and 3, and the resultant products combined with the products from Examples 2 and 4, the yields of gasoline and fuel oil obtained by cracking the fractions separately are obtained. A comparison of the yields of gasoline and fuel oil obtained by processing of the combined heavy residues and light catalytic cycle stock according to this invention with yields obtained by processing of the stock separately is set lforth in Table II.

p The separate cracking of `cycle stock and the residue of Example 2 is reported as Example 5 and of cycle stock and the residue of Example 4, as Example 6.

Table II Exam- Exam- Exam- Example 1 ple 5 ple 3 ple 6 Yields: Percent by Vol. of Total Charge- 10 RVPAOOD F. E.P. Gasoline--- 27.8 20.4 32. 5 25.3 Fuel Oil 78. 3 8l. 2 71.4 72. 9

EXAMPLE 5 A West Texas crude was reduced by successive atmospheric and vacuum `distillation steps to form a residue constituting 9.9% of the original crude. A total charge was prepared by blending the residue with a light catalytic cycle stock having a boiling range of approximately 400 F. to 600 F. in proportions of 3 parts by volume of residue to 1 part by volume of cycle stock. The total charge was mixed with recycle oil and cracked in a furnace coil at a maximum temperature of 965 F. and a pressure of 400 p.s.i.g. The recycle oil consisted of the fraction of cracked products boiling between the end point of the gasoline (400 F.) and the initial boiling point of the specification fuel oil. The recycle oil amounted to approximately 128% of the volume of the total charge. The results of the conversion are illustrated in Table III:

Furnace pressure 400 p.s.i.g.

Furnace coil volume above 750?. 0.02 cu. -ft/bisl. f

1. A process for the thermal conversion of petroleum hydrocarbons comprising vacuum distilling a petroleum oil to form a Iheavy residue as a bottoms product having a gravity in API of less than 10, Conradson carbon residue number of at least 18, and an SUS viscosity at 210 F. of at least 6000, mixing the residue with a light catalytic cycle oil having a boiling range of approximately 400650 F. to form a mixture having a ratio of residue to light catalytic cycle oil ranging from 1:2 to 6:1, heating the mixture to .a temperature of 900 to 1000 F. in a short period to crack residue and light catalytic cycle oil in the mixture, separating the cracked products into fuel oil and a vapor phase, fractionating the vapor phase to produce gasoline and a recycle oil having a higher boiling range than gasoline as separate fractions, and returning recycle oil to the mixture for heating to cracking temperatures.

2. A process for the thermal conversion of a heavy residue from the vacuum distillation of a petroleum oil, said residue having `a gravity in API of less than 10, a Conradson carbon residue number of at least 18 and an SUS viscosity at 210 F. of at least 6,000, comprising mixing the residue with a light catalytic cycle oil boiling in the range of approximately 400-650 F. to` form a -mixture having a ratio of residue to light catalytic cycle oil ranging from 1:2 to 6:1, rapidly heating the mixture to a temperature of 950-1000 F. in a coil having a volume above 750 F. less than about 0.035 cubic feet per barrel of throughput per day to crack the mixture, the time at the high temperature causing cracking of hydrocarbons of both the residue and light catalytic cycle oil, separating the cracked products into a liquid phase and a vapor phase, fractionating the vapor phase to produce gasoline and a recycle oil having a higher boiling range than gasoline as separate fractions, `and returning recycle oil to the mixture for heating to cracking temperatures.

3. A process for the thermal conversion of a heavy residue from the vacuum distillation of a petroleum oil, said residue having a `graviting in API of less than 10, a Conradson carbon residue number of. at least 18, and an SUS viscosity `at 210 F. of at least 6,000, comprising mixing the residue with a light catalytic cycle oil having a boiling range of approximately 400-650 F., in a ratio of residue to light catalytic cycle oil range from 1:2 to 6:1, rapidly heating the resulting mixture to a temperature of 950-1000 F. in a coil having a volume above 750 F. not exceeding 0.035 cubic feet per barrel of throughput per 'day to crack residue and light catalytic cycle oil in the mixture, quenching the heated mixture, separating the cracked products into a fuel oil and a vapor phase, and -fractionating the vapor phase to separate a gasoline fraction.

4. A process for the thermal conversion of petroleum hydrocarbons comprising vacuum distilling a crude oil to form a heavy residue as a ibottoms product having a gravity in API less than 10, a Conradson carbon residue number of at least 18, and a SUS viscosity at 210 F. of at `least 6,000, mixing the residue with a light catalytic cycle oil boiling in the range of approximately 40G-650 F. to for-m a mixture having a ratio of residue to light catalytic cycle oil .ranging from about 1:2 to 6:1, heating the mixture to 'a' temperature of 900l000 F; to crack residue `and light catalyticV cycle 'oil in the mixture, and separating the cracked products into a cracked residual oil and cracked distillate fractions.

5. A process for the thermal conversion of petroleum hydrocarbons comprising vacuum distilling a petroleum oil to form a heavy residue having a gravity of degrees API less than l0, a Conradson carbon residue number of at least 18, and a SUS viscosity at 210 F. of atY least 6,000, mixing the residue with a light catalytic cycle oil boiling in the range of approximately 400 to 650 F. to form a mixture having a ratio of residue to light catalytic cracked distillate fractions.

References Cited in the le of this patent UNITED STATES PATENTS v2,197,460 Adams Apr; 16, 1940 FOREIGN PATENTS 463,042 canada Feb. 7, 1950 OTHER REFERENCES Sachanen: Chemical Constituents of Petroleum, page 404, Reinhold Publishing Corporation, (1945).

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No.. 2,900,327 August 18, 1959 Harold Beuther It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should readas corrected below.

Column 6, line 58, for "gravitng" read gravity column '7, linel2, for "gravity of" read mgravity in m- Signed and sealed this lst day of March 1960 (SEAL) Attest:

KARL H0 XLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents

Claims (1)

1. A PROCESS FOR THE THERMAL CONVERSION OF PETROLEUM HYDROCARBONS COMPRISING VACUUM DISTILLING A PETROLEUM OIL TO FORM A HEAVY RESIDUE AS A BOTTOMS PRODUCT HAVING A GRAVITY IN *API OF LESS THAN 10, CONRADSON CARBON RESIDUE NUMBER OF AT LEAST 18, AND AN SUS VISCOSITY AT 210*F. OF AT LEAST 6000, MIXING THE RESIDUE WITH A LIGHT CATALYTIC CYCLE OIL HAVING A BOILING RANGE OF APPROXIMATELY 400-650*F. TO FORM A MIXTURE HAVING A RATIO OF RESIDUE TO LIGHT CATALYTIC CYCLE OIL RANGING FROM 1:2 TO 6:1, HEATING THE MIXTURE TO A TEMPERATURE OF 900 TO 1000*F. IN A SHORT PERIOD TO CARACK RESIDUE AND LIGHT CATALYTIC CYCLE OIL IN THE MIXTURE, SEPARATING THE CARACKED PRODUCTS INTO FUEL OIL AND VAPOR PHASE, FRACTIONATING THE VAPOR PHASE TO PRODUCE GASOLINE AND A RECYCLE OIL HAVING A HIGHER BOILING RANGE THAN GASOLINE S SEPARATE FRACTIONS, AND RETURNING RECYCLE OIL TO THE MIXTURE FOR HEATING TO CARACKING TEMPERATURES.

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