US2272285A - Conversion of hydrocarbon oils - Google Patents

Description

Feb. 10, 1942. c. H. ANGELL 2,272,235

CONVERSION OF HYDROCARBON OILS I Filed Feb. 25, 1938 w 67 ms FRACTIONATOR e5 CONDEN SER 69 VAPORIZING AND SEPARATING CHAMBER REFORMIN@\ (COIL FURNACE 60,

DISTILLING AND 42 43 FRACTIONATING 8 COLUMN a: 6 7 FRACTIONATOR VAPORIZINC AND CONDEN SER a, SEPARATING CONDEN SER 44 4 1;; 1 CHAMBER so so 9 25 f/ as as 34 20A? T 7 lgaz as y 38 L 4 INVENTOR HEAVY OIL CRACKING COIL CHARLES H. ANGELL ATTORNEY Patented Feb. 10, 1942 CONVERSION or HYDROCARBON OILS Charles H. Angell, Chicago, Ill., assignor to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware Application February 25, 1938, Serial No. 192,520

3 Claims. (01. 196-49) This invention relates to an improved process whereby major yields both straight-run and cracked Diesel fuels of good quality and good antiknock gasoline may be produced from paraffinic or mixed-base crude, with minor yields of heavy liquid residue and normally gaseous products.

It is well known that the gasoline contained in asphaltic-base crudes is almost invariably of better antiknock value than that contained in paraflinic crudes since the compounds which dominate in paraffinic crudes are of poor antiknock value, while the gasoline fractions of the asphaltic crudes normally contain substantial quantities of naphthenes which are of good antiknock value. For the same reason, the materials of Diesel fuel boiling range contained in paraf finic crudes are superior in quality to those present in the asphaltic crudes, since knocking tendencies are desirable in Diesel fuel.

Certain'mixed-base crudes may contain gasoline or gasoline" fractions of satisfactory anti knock value While other mixed-base crudes may contain good Diesel fuel, but the same crude will seldom contain light naphthenic fractions (with in the boiling range of gasoline) and heavier parafiinic fractions (Within the boiling range of Diesel fuel) in the proper proportions to yield both good antiknock gasoline and good quality Diesel'fuel'.

The pyrolytic conversion of hydrocarbon oils; in a conventional manner, normally produces high yields ofol'efinic and'aromatic compounds. The presence ofsubstantial quantities of such materials imparts a good antiknock value to most gasolines resultingfrom cracking. How ever, the presence of olefinic and aromatic compounds in cracked products boiling within the range of Diesel fuel impairs the quality of the latter on account of their non-de'tonating tend encies.

It will be apparent from the above that a process which will produce substantial yields of both straight-run and cracked Diesel fuels of good qualtity with the simultaneous production of substantial yields of good antiknock gasoline, all from the same crude charging stock and selected intermediate products of the process, is both novel and highly advantageous. This is the object of the present invention and is accomplished by a cooperative and an interdependent combination of steps which comprise fractional distillation of the crude to separate therefrom low-boiling fractions (consisting of mate rials boiling below the range of the desired straight-run Diesel fuel and including any gasoline components of the crude) intermediate fractions (which consist of the desired straight-run Diesel fuel and are recovered from the fractional distilling step) and high-boiling fractions (comprising materials boiling above the range of the desired Diesel fuel), cracking said low boiling fractions under conditions of elevated temperature, substantial superatmospheric pressure and prolonged cracking time to produce therefrom high yields of good antiknock gasoline, separately cracking said high-boiling fractions under conversion conditions of elevated temperature, relatively low superatmospheric pressure and relatively short conversion time regulated to produce high yields of good quality Diesel fuel therefrom, recovering the latterseparate from the lower boiling and higher boiling liquid products of the last mentioned cracking operation and returning said lower boiling liquid products (including gasoline produced in the last mentioned cracking operation) to the first mentioned cracking step for further treatment therein to produce additional quantities of good antiknock gasoline, which is recovered together with a good antiknock gasoline produced from said low-boiling fractions of the crude. v

' A process, of which the present applicant is a joint inventor, for producing good quality Diesel fuel, comprising distillate fractions boiling within the approximate range of 450 to 750 F., by the cracking of residual oils under carefully regulated conditions of high temperature, relatively low superatmospheric pressure and short conversion time, is disclosed in co-pending application Serial Number 151,135 filed June 30, 1937. This type of cracking operation is employed as one of the steps in the present process. While good Diesel fuel may be produced in this manner, this type of cracking operation also produces appreciable quantities of lower boiling fractions including gasoline. The gasoline thus produced does not contain the substantial quantities of olefinic and/or aromatic compounds characteristic of other types of cracking operations and is therefore of inferior antiknock value. In the present process the special type of cracking operation, above mentioned, for the production of Diesel fuel, is advantageously combined with fractional distillation of the crude charging stock and cracking of the low-boiling fractions of the crude to produce high yields of good antiknock gasoline, and, as a special feature from the heavy fractions of the crude are returned to the light oil cracking operation and therein converted, together with the light fractions of the crude, into substantial yields of good antiknock gasoline.

The accompanying diagrammatic drawing illustrates one specific form of apparatus in which the process of the invention may be conducted.

Referring to the drawing, the crude charging stock which has been previously heated to distillation temperature by any well known means, not illustrated, is supplied through line I and valve 2 to distilling and fractionating column 3 wherein its fractiona1 distillation is accomplished without appreciable cracking. The desired straight-run Diesel fuel, which comprises intermediate fractions of the crude, is removed as condensate from one or a plurality of suitable intermediate points in column 3, provision being made, in the case here illustrated, for withdrawing the same through line 4 and valve 5 wherefrom it passes to cooling and storage or elsewhere, as desired. Fractions of the crude charging stock which boil at a lower temperature than the desired Diesel fuel fractions are removed in vaporous state from the upper portion of column 3 and directed through line 6 and valve I to cooling and condensation in condenser 8. The resulting distillate passes, together with any normally gaseous fractions of the crude, through line 9 and valve I I) to collection and separation in receiver II. Uncondensed gases may be released from the receiver through line I2 and valve I3. The distillate collected in receiver II includes any fractions of the crude boiling within the range of gasoline and may also include somewhat higher boiling fractions, such as naphtha, kerosene, kerosene distillate and the like, the end-boiling point of the distillate being dependent upon the desired initial boiling point of the Diesel fuel recovered from column 3. This distillate is directed, all or in part, from receiver 'II through line I4 and valve I5 to pump I6, by means of which it is fed through line I! and valve I8 to light oil cracking coil I9, the function of which will be later explained.

Fractions of the crude charging stock boiling above the range of the desired straight-run'Diesel fuel product are directed from the lower portion of column 3 through line 20 and valve 2I to pump 22 by means of which they are fedthrough line 23 and valve 24 to heavy oil cracking coil 25.

Coil 25 is supplied with heat from furnace 26 wherein it is disposed and, although illustrated in a conventional manner in the drawing, this heater is preferably one of the well known forms whereby heat is imparted at a high rate to the oil passing through coil 25 and the oil thereby quickly heated to a high cracking temperature without allowing it to remain at an active cracking temperature in the heating coil for a sufficient length of time to permit secondary cracking reactions which result in the formation of olefins and other products detrimental to Diesel fuel.

In order to definitely control and minimize the time during which the heavy oil supplied to coil 25 is subjected to active cracking, the heated products discharged from heating coil 25 are cooled sufliciently to retard or arrest cracking upon their discharge from the heating coil, wherefrom they pass through line 21 and valve 28 to vaporizing and separating chamber 29. In the particular case here illustrated, provision is made for introducing suitable cooling oil into line 2! on either or both sides of valve 28 through lines 30 and valves 3 I. Any other suitable means of cooling the heated products discharged from coil 25 may be employed within the scope of the invention, either alone or in conjunction with the use of cooling oil in the manner mentioned, and preferably cooling is assisted by substantially reducing the pressure imposed upon the stream of conversion products passing through valve 28.

vaporization is assisted in chamber 29 by employing a reduced pressure in this zone relative to that employed at the outlet of heating coil 26 and the resultant vaporous and residual liquid products are separated in this zone. The residual liquid may be removed from the lower portion of chamber 29 and directed through line 32 and valve 33 to cooling and storage or to any desired further treatment and, when desired, regulated quantities of this material may be supplied through line 34 and valve 35 to pump 36 by means of which they are returned through line 31 and valve 38 to further treatment in heating coil 25. This recycling of the heavy residual oil to heating coil 25 serves to decrease the rate of cracking required in this zone to produce the desired products as compared with an operation in which the oil is passed only once through the cracking coil. The ratio of recycled oil to virgin oil supplied to heating coil 25 may be regulated to suit requirements and produce a minimum of heavy residual liquid as a final product of this stage of the process. A greater quantity of oil passing through coil 25, as a result of recycling residual liquid thereto from chamber 29, will decrease the time factor in heating coil 25 and assist in preventing deleterious secondary reactions in this zone.

The vaporous conversion products separated from the liquid residue in chamber 29 pass from the upper portion of this zone to fractionation in fractionator 39 and, preferably, suitable fractionating means or the like, not illustrated, are provided in the upper portion of chamber 29 to assist in separating from the vapors in this zone substantially all of their components which boil above the range of the desired Diesel fuel.

The high-boiling components of the vapors supplied to fractionator 39, comprising the components of these vapors which boil within the range of the desired Diesel fuel product, are condensed therein as reflux condensate and this material is withdrawn as the cracked Diesel fuel product of the process from the lower portion of fractionator 39 and directed through line 40 and valve 4| to cooling and storage or elsewhere, as desired.

Fractionated vapors of the desired end-boiling point and normally gaseous conversion products, including the gasoline produced by the cracking operation in coil 25 and, preferably, also including the other components of the vapors supplied to the fractionator which boil below the range of the desired Diesel fuel, are directed from the upper portion of this zone through line 42 and valve 43 to cooling and condensation in condenser The resulting distillate and uncondensed gases pass through line 45 and valve 46 to collection and separation in receiver 41. Uncondensed normally gaseous products may be released from the receiver through line 48 and valve 49. Distillate may be withdrawn from this zone through line 50 and valve 5| to storage or to any desired further treatment. Preferably, however, all or at least a portion of the distillate collected .in receiver 41' is directed therefrom through line 52 and valve 53 to pump 54 by means of which it is supplied through line"55, valve 56 and line H to further treatment in light oil cracking coil I9.

Coil I9 is disposed Within furnace 60 which supplies the required heat to the relatively light oils passing through this coil to effect the desired cracking thereof. Coil l9 and furnace 66, although shown diagrammatically in the drawing, are preferably of the type, now well known in the art, in which the oil is heated to a high cracking temperature and then maintained for a predetermined time at a substantially constant temperature relatively close to the maximum previously attained. This prolonged cracking or soaking favors the formation of antiknock compounds, such as olefins and aromatics and when carefully regulated insures the production of high antiknock gasoline. A substantial superatmospheric pressure is preferably maintained throughout coil l9 and the highly heated products discharged therefrom through line 6| are cooled sufiiciently to prevent any excessive continued cracking thereof and. thence discharged into vaporizing and separating chamber 63, the latter zone preferably being maintained at a substantially reduced pressure relative to that employed at the outlet of the heating coil by reducing the pressure imposed upon the stream of conversion products as they pass through valve 62 in line 6!. Cooling of the hot conversion products and vaporization in chamber 63 is assisted by the reduced pressure employed in this zone but ordinarily additional cooling of the hot conversion products is required and other methods of accomplishing this, one of which will be later described, are preferably untilized in conjunction with the reduction of pressure.

Separation of vaporous and residual liquid conversion products is accomplished in. chamber 63 and the latter are removed from the lower portion of the chamber through line 64 and valve 65 to cooling and storage or to any desired further treatment. The residual liquid removed from chamber 63 may, when desired, be reduced to substantially dry coke in any suitable type of auxiliary coking equipment, not illustrated in the drawing.

Relatively clean vaporous products pass from the upper portion of chamber 63 into fractionator 66 wherein their components which boil above the range of the desired light distillate products of this stage of the system are condensed as reflux condensate.

The fractionated vapors, which comprise good antiknock gasoline of the desired end-boiling point and normally gaseous conversion products, are directed from the upper portion of v fractionator 66 through line 61 and Valve 68 to cooling and condensation in condenser 69. The resulting distillate and uncondensed gases pass through line H! and valve H to collection and separation in receiver 12. The uncondensed normally gaseous products may be released from receiver 12 through line 13 and valve 14 to storage or elsewhere, as desired. Distillate collected in receiver 12 is removed therefrom through line and valve 16 to storage or to any desired fur- X ther treatment.

When desired, regulated quantities of the distillate collected in receiver I2 may be recirculated by well known means, not illustrated in the drawing, to the upper portion of fractionator 66 to serve as a cooling and refluxing medium in this zone. The invention also contemplates returning regulated quantities of the distillate from receiver II to the upper portion of column 3 and regulated quantities of the distillate from receiver 41 to the upper portion of fractionator 39, although the well known means whereby this may be accomplished are not shown in the drawmg.

Reflux condensate resulting from fractionation of the vapors in fractionator 66 is directed from the lower portion of thiszone through line H and valve 18 to pump 19 wherefrom this material is fed through line and may be directed, all or in part, when desired, through valve 8| in this line and through line H to coil [9 for further cracking treatment in this zone. Preferably, however, regulated quantities of this material are utilized as a cooling medium for maintaining the desired temperatures at various points in the light oil cracking stage of the system. To accomplish this, regulated quantities of the reflux condensate are diverted from line 36 through line 62 and valve 83 to cooler 86 wherein the reflux condensate is cooled to the desired temperature and Wherefrom it is thence directed through line 85 and valve 86 into line 81. The cooled reflux condensate may be directed in regulated quantities from line 8'! into' line 6! to directly commingle therein with the relatively hot conversion products discharged from coil 19 and cool the same to the desired temperature prior to their introduction into chamber 63. The cooling oil may be injected into line 6| from either or both sides of pressure reducing valve 62 by means of lines 88 controlled by valves 89. The invention also contemplates the return of regulated quantities of the reflux condensate formed in fractionator 66 to the upper portion of chamber 63 Wherein it is directly contacted with the vaporous products in this zone and serves to partially c001 and assist the removal therefrom of undesired high boiling components such as entrained heavy liquid particles and the like, prior to the introduction of these vapors in fractionator 66. This is accomplished, in the case here illustrated, by means of line 81 and valve 96. 1

When desired, regulated quantities of the reflux condensate formed in fractionator 66 may be removed from the system to storage or elsewhere through line 9| and valve 92 and, when desired, regulated quantities of this material may be blended with the residual liquid recovered fromchamber 63 to reduce the viscosity of the latter.

When the distillates supplied to light oil cracking coil 19 consist essentially of gasoline or gasoline fractions, a very high proportion of these materials (up to 90%, or more) may be converted into good antiknock gasoline in a single pass through the heating coil and the quantity of reflux condensate formed in fractionator 66 will, therefore, be relatively small. In such cases this material is preferably not returned to heating coil 59 for further cracking but may be either removed from the system through line El and valve 92 or utilized as a cooling medium in line 6| and/or chamber 63. When utilized as a cooling medium, in the manner described, a cycle of this material will be built up within the system and by repeatedly recirculating the same to line 6|, the mild cracking to which it is subjected by being repeatedly commingled with the hot conversion products from coil It? may eventually result in the substantially complete conversion of this material into lighter and heavier fractions,

the resulting products being recovered as components of the residual liquid removed from chamber 63 and components of the distillate recovered in receiver 12.

When the distillate supplied to light oil cracking coil I 9from the heavy oil cracking step and/or the fractional distilling step of the process contains substantial quantities of materials boiling above the range of gasoline, the extent of its conversion into good antiknock gasoline in a single pass through the light oil cracking coil will be less than when only gasoline or gasoline fractions are supplied to this zone. In such cases the quantity of reflux condensate formed in fractionator 66 will be correspondingly greater and in most instances this material may be advantageously returned, as previously described, to coil IQ for further conversion into additional yields of good antiknock gasoline.

It will, of course, be understood that the invention is not limited to the use of the specific form of apparatus illustrated in the accompanying drawing. The use of any well known means for reboiling the Diesel fuel recovered from column 3 and fractionator 39, to substantially free the same of undesired light fractions, is specifically contemplated, although their illustration is omitted for the sake of simplicity. The invention also specifically contemplates the transfer of excess heat in various relatively hot intermediate and/or final products of the process, to the charging stock and/or other intermediate products which require heating, this being accomplished by the use of well known means such as heat exchangers, reboilers, preheaters and the like for transferring heat from one or more fluids to another or others. As an example, the crude charging stock may be supplied with a portion or all of the heat required for its fractional distillation by passing the same in indirect heat exchange relatively with hot conversion products discharged from coil l9 and/or coil 25 and/or by indirect heat exchange with the Dieselfuel fractions removed from column 3 or fractionator 39 or with reflux condensate from fractionator 66 or residual liquid from chamber 63 or chamber 29.

The preferred range of operating conditions which may be employed to accomplish the desired results, in an apparatus, such as illustrated and above described, may be approximately as follows: Fractional distillation of the crude charging stock may be accomplished at any desired pressure which may range from sub-atmospheric to several hundred pounds superatmospheric pressure. The temperature employed in the fractional distilling step will depend upon the boiling range characteristics of the charging stock and, more particularly, upon the boiling range of its good Diesel fuel fractions, as well as upon the pressure employed in this stage of the system. In any case, the conditions under which the crude charging stock is distilled are regulated to preclude any substantial cracking of its Diesel fuel fractions and, when necessary, subatmospheric pressure or steam or both may be employed in the fractional distilling step to insure the desired distillation of the charging stock without appreciable cracking.

The temperature maintained at the outlet of the heavy oil cracking coil may range, for example, from 900 to 1050 F., preferably with a superatmospheric pressure at this point in the system of from 75 to 300 pounds per square inch. The time during which the heavy oil passing through coil 25 is maintained at a temperature above 750 F. is preferably of the order of 1 to 10 seconds calculated on the basis of the relatively cold oil entering the coil without allowing for expansion due to heating. The heated products discharged from coil 25 are preferably cooled prior to their introduction into chamber 29 to a temperature of the order of 600 to 750 F. and preferably the pressure maintained in the latter zone is substantially lower than that employed at the outlet of heating coil 25, the reduced pressure ranging, for example from substantially atmospheric to pound gauge. Substantially the same or somewhat lower pressures may be employed in the fractionating, condensing and collecting equipment succeeding chamber 29.

The temperature employed at the outlet of the light oil cracking or reforming coil I9 is preferably of the order of 950 to 1050 F. or more and preferably a superatmospheric pressure of the order of 200 to 1000 pounds, or thereabouts, per square inch is employed at this point in the system. The conversion products discharged from coil l9 are preferably cooled to a temperature of the order of 650 to 780 F., or thereabouts, prior to their introduction into chamber 63 and the latter zone is preferably operated at a substantially reduced pressure relative to that employed at the outlet of heating coil IS, the reduced pressure ranging, for example, from substantially atmospheric to 150 pounds, or thereabouts, per square inch, superatmospheric pressure. The succeeding fractionating, condensing and collecting equipment may employ pressures substantially the same or somewhat lower than that utilized in chamber 63.

As a specific example of the operation of the process provided by the invention, as conducted in an apparatus of the character illustrated and above described: The charging stock is a California crude of approximately 35 A. P. I. gravity having an initial boiling point of about F. and containing approximately 40% of material boiling up to 410 F. and which is of poor antiknock value. The crude is heated to a temperature of approximately 680 F. and distilled at substantially atmospheric pressure. Overhead distillate amounting to approximately 50% by volume of the crude and containing substantially all of its gasoline and light kerosene fractions is removed from the fractional distilling step and supplied to the light oil cracking coil of the system. Approximately 20% by volume of the crude, comprising its intermediate fractions, is recovered as good quality Diesel fuel from the fractional distilling step and the heavier fractions of the crude are supplied to the heavy oil cracking coil of the system. The latter employs an outlet conversion temperature of approximately 980 F. with a superatmospheric pressure at this point in the system of approximately pounds per square inch. The resulting heated products are quickly cooled to a temperature of approximately 630 F. and discharged into vaporizing and separating cham ber 29 at a superatmospheric pressure of about 30 pounds per square inch. Residual liquid from chamber 29 is, in part, removed from the sys tem and, in part, returned to heating coil 25 for further cracking. Reflux condensate formed in fractionator 39 is removed from the system as good quality, light, cracked Diesel fuel and the lighter cracked products are recovered in receiver 4'1. Regulated quantities of the distillate recovered from receiver 27 are returned,

in part, to line 21 as a cooling medium and, in part, to the upper portion of fractionator 39. The remainder of this distillate is supplied to the light oil cracking coil of the system. The conversion temperature employed at the outlet of the light oil cracking coil is approximately 1000 F. and a superatmospheric pressure of about 600 pounds per square inch is employed at this point in the system. The resulting highly heated products are cooled to a temperature of approximately 680 F. and introduced into vaporizing and separating chamber 63 at a superatmospheric pressure of about 80 pounds per square inch. Reflux condensate formed in fractionator 66 is cooled and utilized in regulated quantities as a cooling medium in line El and in the upper portion of chamber 63 and fractionator 66, the remainder being blended with the residual liquid removed from chamber 63. End-point gasoline is recovered in receiver 12 as the overhead distillate product from fractionator 66.

The above described operation will yield per barrel of charging stock approximately 40% of 400 F. end-point gasoline having an octane number of approximately '70 by the motor method and approximately 33% of straight-run and cracked Diesel fuel of good quality. The residual liquid products amount to approximately by volume, of the charging stock and the remainder is chargeable principally to normally gaseous products and loss.

I claim as my invention:

1. A process for producing high yields of good quality Diesel fuel and good antiknock gasoline from hydrocarbon oil of relatively wide boiling range, which oil comprises low-boiling fractions including gasoline of poor antiknock value, intermediate fractions boiling within the range of the desired Diesel fuel and higher boiling fractions, said process comprising the concomitant steps of separating such an oil by fractional distillation without appreciable cracking into the aforementioned components, recovering said Diesel fuel fractions of the desired characteristics from the fractional distilling step, supplying said low-boiling fractions to a heating coil and therein heating and maintaining the same at a high cracking temperature and at substantial superatmospheric pressure for a time regulated to produce therefrom high yields of good antiknock gasoline, quickly cooling the resulting stream of highly heated products discharged from said heating coil, materially reducing the superatmospheric pressure imposed thereon and introducing said stream into a vaporizing and separating chamber, whereby to prevent excessive continued conversion of said products and cracking step.

separate the same into vaporous and residual liquid components, removing the latter from said vaporizing and separating chamber, fractionating said vaporous components to condense and separate therefrom their components boiling above the range of good antiknock gasoline, condensing the resulting fractionated vapors, recovering the resulting distillate as said good antiknock gasoline, supplying said higher boiling fractions from the fractional distilling step to a separate heating coil, therein quickly heating the same to a cracking temperature of the order of 900 to 1050 F. at superatmospheric pressure, limiting the time during which the oil is maintained at an active cracking temperature in the last mentioned heating coil to preclude any substantial formation of good antiknock compounds and quickly cooling the stream of highly heated products discharged therefrom sumciently to prevent undesirable secondary cracking reactions, thence discharging said stream into another vaporizing and separating chamber wherein the vaporous components of said products, including materials boiling within the range of the desired Diesel fuel, are separated from their higher boiling non-vaporous components, removing the latter from the last mentioned vaporizing and separating chamber, fractionating the last named vapors out of contact with the vaporous products of the first mentioned cracking operation to condense and separate therefrom their components boiling within the range of said desired Diesel fuel, recovering the latter and returning lower boiling components of the last named vapors, comprising gasoline of poor antiknock value, to the first mentioned cracking step for further treatment therein in commingled state with and under the same conditions to which said low-boiling fractions are subjected, whereby to produce additional yields of good antiknock gasoline.

2. A process such as defined in claim 1 wherein condensate formed in the fractionating step of the first described cracking system is, in part, cooled and thence directly commingled with the heated products discharged from the first mentioned heating coil as a cooling medium therefor, while another regulated portion of said condensate is returned to and subjected to further cracking in the first mentioned heating coil,

3. A process such as defined in claim 1 wherein regulated quantities of said higher boiling non-vaporous components removed from the last mentioned vaporizing and separating chamber are returned to and subjected to further cracking in the heating coil of the last described CHARLES H. ANGEIL.

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