US2150119A - Cracking asphaltic oil - Google Patents

Description

March 7, 1939'.

11 c; hisnsncs CRACKING ASPHALTIC oIL` Filed oct. 10, 195e BY IM ATTORNEY Patented Mar. 7, 1939 UNITED STATES CRACKING ASPHALTIC OIL Theodore Charles Heisig, Beacon, N. Y., asslgnor to The Texas Company, New York, N. Y., a corporation-of Delaware Application October 10,

4 Claims.

This invention Arelatesto the manufacture of motor fuel from cracking stocks containing asphalt. More particularly, the invention has to do with the separation of asphalt from cracking 5 stocks by the use of a normally gaseous hydrocarbon solvent and the cracking of the deasphalted oil in the presence of the solvent.

In the cracking of oils containing asphalt, considerable diiiiculty is often encountered by the lo formation of coke. It has been found that a cracking stock from which the asphalt has been separated may be cracked at much higher crack per pass and at considerably higher temperatures than the same stock before the removal of the 1.', asphalt. As a consequence, the yield and quality of the gasoline may be improved, a longer cycle of operation obtained without shut-down due to coke formation, and a valuable asphaltic product obtained from the process.

The high temperatures obtainable in the cracking of a deasphalted charging stock makes possible the use of conversion conditions which are favorable for the formation of normally liquid products from gases during the cracking of oils ,5 containing appreciable amounts of gaseous hydrocarbons. It has been found, therefore, that an advantageous method of operation when cracking stock which has been deasphalted by precipitation with gaseous hydrocarbon solvents n is to leave a portion or all of the solvent in the deasphalted oil charged to the cracking operation. In this way,` it is unnecessary to remove all the solvent from the cracking stock and, in fact, its presence becomes advantageous in that increased quantities of low boiling hydrocarbons are formed, dueto a reaction with the oil undergoing cracking and polymerization to liquids of the gaseous hydrocarbons of the solvent.

A cracking stock suitable for use according to the invention may be any higher boiling oil containing asphalt, such as reduced crude, or gas oil. Although the invention is particularly suitable for treatment of heavy oils or residuums containing substantial amounts of asphaltic ma- 5 terials, the invention is useful for the treating of lighter materials of the character of gas oil which may contain resinous materials which tend to form coke when subjected to-cracking conditions.

The oil to be treated may contain both hard and soft asphalt or resins in which case it may be desirable to conduct the deasphalting operation in two or more stages in which the hard asphalt may be removed in one stage and the soft asphalt or resins in subsequent stages. The amount of materials of asphalticior resinous character which 1936, serial No. 104,928

(C1. 19e-5o) is necessary to be removed to clean the cracking stock and the degree of such cleaning will be de termined by the type of cracking to be carried out, particularly with respect to the temperature and pressure conditions. In case it is intended to operate at a relatively high temperature and obtain a maximum amount of gas reversion or gas polymerization, it is advantageous to utilize a comparatively clean charging stock in order to avoid coke formation and attain adequate reaction time.

The deasphalting solvent is preferably a fraction of casnghead gasoline consisting mainly of a mixture of ethane, propane, butane and iso; butane. An overhead fraction from the stabilization of casinghead gasoline consisting of about 5% ethane, 73% propane, 20% isobutane and 2% normal butane is satisfactory. Such a fraction is liquidat ordinary temperatures under pressures .of around 125 pounds and is commonly referred to as propane which is the predominating constituent and may in some cases be substantially the only ingredient. Other light hydrocarbons from liquefaction of refinery gases of about the same number of carbon atoms as those mentioned above and containing considerable amounts of defina-particularly propylenes and butenes,` may7 also be used. The latter materials may show some advantage when subjected to the subsequent conversion operation in the presence of the deasphalted oil.

The deasphaning'step is carried out by mixing the liquefied hydrocarbon solvent with the oil I and adjusting the temperatures suitable for the precipitation of the asphalt. Ordinarily, proportions of solvent and oil are in the'ratio of about 4 parts by volume of solvent to one of the oil to be deasphalted. The temperature may vary between about F. and 180 F., the higher tem- 1 peratures usually being used to precipitate the resins. In the deasphalting of heavy reduced crude, using 400% propane, a temperature of about F. has been found to be satisfactory.

The entire mixture of oil and solvent may be charged to the cracking unit but I prefer to distill off a portion of the solvent from the deasphalted oil and recirculate the distilled solvent in the system. The amount. of solvent left in the oil charged to the cracking unit may vary Within considerable limits and will depend to a certain extent on'the volatility of the deasphalted oil and the temperatures used in the cracking operation. Y

When operating at a high temperature and with a relatively light crackingstbck, a large proportion of the solvent may be employed with satisheavy charging stock and below the maximum temperature obtainable, a relatively large proportion of the solvent may also be employed. It is intended that the conditions be maintained such thatv the solvent does not vaporize too readily from the oil thereby providing an opportunity for the heavy oil to cook down and go vto coke. It is advantageous that the maximum amount of volatilization of the cracking stock be obtained and one skilled in the art will be able to regulate the proportion of :solvent in cracking stock to obtain optimum results. For an ordinary reduced crude of around to 40 gravity, at least and often 10D-150% or more or solvent may advantageously be used.

The cracking operation may be carried out in any preferred or well known type of cracking unit.

It has been found advantageous to operate with a heating and soaking section which may consist of coils or a coil and drum. A coil and drum operation has been found to be particularly suitable and it is preferable that-.the operation bez-carried out so that the products to travel downward through the reaction drum. When using a hydrocarbon solvent in combination with the cracking stock, the degree of vaporization of the cracking stock is increased whereby the cracking taking place in the reaction is largely in the vapor phase and less tendency for the less volatile constituents to drop through the drum and form a pool of liquid in the bottom of the drum and increase the tendency to form coke. While Ino theory of reaction is adhered to, nevertheless it is believed that in addition to increased vaporization due to the partial vapor pressure of the solvent, considerable gas reversion takes place whereby the normally gaseous hydrocarbons react with heavier constituents with the oil 4undergoing cracking to form intermediate boiling point, liquid products.- It is also believed that polymerization of the gaseous hydrocarbon solvent takes place to alarge extent.

'Ihe temperature and pressure conditions maintained in the cracking operation may vary within suitable limits and in general it may be stated that temperatures-sbetween.. Boo-12m F. `,anni pressures of about 300-600 pounds, or higher,

may be used. It has been found. by using a de-v BSDhalted charging stock and a considerable proportion of hydrocarbon solvent in admixture therewith, that much higher temperaturesmay be maintained than ordinarily would be possible with the undeasphalted stock. Residuums which may be cracked only with dii'ilculty under a maximum temperature of S50-900 F. have been cracked satisfactorily after deasphalting and in the presence of the solvent at increased temperatures of 50100 F., or more, and at the same time obtain an increased crack per pass and higher yield.

For example, in the cracking of a reduced asphaltic crude of about 18 gravity, a cracking tern`- perature of about 850 F. and a crack per pass of about 14% was the maximum without excessive coke formation. The same crude was deasphalted with 400% propane at a temperature of about F. and about 75% of a clean infraction was obtained, which could be crackedat temperatures4 of around 900 F. and a crack per pass of around 32%. Byleaving about 50% ofthe propane in the clean stock, the temperature and crack per pass may be further increased whereby there is obtained a 5-10% increase in crack per pass of the asphalted oil, a crack per passy of around 15-20% on the propane component and an infactory result. Likewise, when operating with a crease in the octane number of about 5-15 points.

lhe separated asphalt ,of the cracked distillate may be cracked separately and the resultant cracked. distillate advantageously combined with the cracked distillate from the conversion of a mixture of deasphalted oil and propane to further increase the yield and the quality of the product. By carrying out the cracking in the form of recycling operations, the ultimate yields of gasoline are greatly increased by operating according to the invention, and will be determined by the amount of the propane left in the clean charging stock and whether the asphalt fraction is cracked or used otherwise.

For a further description of the lnvention,ref erence will now be made to the accompanying drawing which shows s, schematic arrangement ,of the apparatus for carrying out the process of the invention.

Referring to the drawing, the ,charging stock is introduced into the system through the line I,

and charged by the pump 2 to a heater I wherein the oilis raisedto a temperature-suitable fordeasphalting by means of heating fluid such as steam or by heat exchange with another oil in the system. Propane is drawn from a suitable source of supply, not shown, by the pump I through the line 6 and introduced into the charging oil through the line 1. The mixture of propane and oil is discharged from the heater through the line 8 into the asphalt separator III. The asphalt is precipitated from the propane and settles'out of the bottom of the separator Il where it may be drawn oi! by the valved control line Il. Although it is not shown, it is intended that this asphalt may be given a washing treatment with a further quantity of propane, preferably at a slightly higher temperature than that maintained in the asphalt separator Il, toremove from lthe asphalt a further quantity of oil which may be returned to the fractionator I2.-

'I'he separated asphalt may be further treated for the manufacture of a, merchantable asphalt or used as a cracking stock as desired. 3

The solution of clean'oil and propanel is removed from the top of separator Il and con- -ducted through the,.llne Iltc fractinnator i2,

referred to heretofore. 'I'he fractionator I2, as well as the asphalt separator III are maintained under. superatmospheric pressure and in case it is desired to vaporize a portion of the propane the pressure may be lowered in the fractionator I2 by reducing the pressure by means of valve Il in the line I 5. Also vaporization of the propane may be increased by the addition of heat by means of the heating coil 20 in the lower portion of the fractionator. The propane distilled in fractionator I2 is conducted through line 2| to condenser 22 and then through the valved run down line 23 toa tank 25. The propane may be withdrawn from the tank 25 by means of pump 26 through the line 21 and charged through lines 2l and 'I to the charge line I to be mixed with raw charging stock. A

'I'he deasphalted oil containing a portion or all of the propane is withdrawn from the bottom oi' the fractionator I2 through the line 30 and charged by means of pump 3| to the heating coil 32 of a cracking furnace. heated to a high temperature which may be to the point of incipient cracking so that very little conversionoccurs, or heated so as to attain a cracking temperature midway the coil whereby considerable conversion takes place in the coll. I'he products of the cracking temperature are 'I'he cool mixture is 'l0y farsene conducted through thev transferiline 33 to the upper portion of the reaction chamber 35, and

discharged downwardly therethrough. This reaction chamber is of such size as to provide sumcient reaction time to effect the desired conversion, which may be in the nature of cracking oil of the reaction chamber through the valve line 36. In case coke formation takes place in the reaction chamber, the line II may be replaced by a removable head. In case tar is drawn oi! from4| the bottom of the reaction chamber 35,' this tar may be further processed, as desired. It is contemplated thatv this tar may be deasphalted and used as a cracking stock, according tothe teachings'of the present invention. For example, the tar may be reprooessedin the system by recirculating it to the deasphalting step to be treated in conjunction withwthe fresh charge.

The cracked products are transferred from the reaction chamber to the fractionator 4l through the line 31, vthe fractionator maintained under such conditions of temperature and pressure that substantially all the constituents heavier than a gasoline are condensed and collect in the lower portion of the condenser as a reflux condensate. 'Ihis reiiux condensate or recycle stock lis withdrawn from the bottomof the fractionator and ordinarily returned to the line 4I and charged by the pump 3i to the cracking coil 32. If the recycle stock withdrawn from. the bottom of the fractionator contains objectionable amounts of asphaltic materials, tars or resins, this recycle stock may be deasphalted prior to further cracking. Such deasphalting may be conducted as a separate step or preferably mixed with a fresh feed charged-through the line I and the mixture deasphalted substantially as described heretofore.

'Ihe gasoline vapors pass from the top of the fractionator through line 42 to condenser and the condensate ,and uncondensed gases are then conducted through the run down line I4 to stabilizer l5. The stabilized gasoline is withdrawn from the bottom of the' stabilizer through the line 4t. Uncondensable gases which are not suitable for use in deasphalting are released from Y the top of the stabilizer through the pipe l. The

condensate lighter than gasoline and suitable for recycling and further use in the deasphalting operation is withdrawn from the stabilizer through the line Il by means of the pump Il and forced through the line l2 to the propane tank 25. In case itis undesirable to use a lighter fraction for k deasphalting it may be recycled to the conversion operation by means of the line It and returned to the cracking coil by means o'f the branch line 51 together with the clean' oil and propane, or

introduced into transfer line 33 between the cracking. coil and the'reaction chamber by means -of the branch line Il.- The light condensable fraction removed from the stabilizer l5 through the line 5l will contain considerable amount of which are suitable for mail D01?- merization. Itis contemplated, as an alternative, that this material may be withdrawn from the system through the line l! and charged to a catalytic polymerization unit. Y

Obviously many modifications and variations of the invention, as hereinbeiore set forth, may

be made without departing from the spirit and scope` thereof, and therefore only such limitations should be imposed as are indicated in the appended claims. l

I claim:

1. A process for the conversion ofheavy hydro carbon oils containing asphalt and normally tending to form coke when heated to conversion temperatures. which comprises' separating asphaltic bodies from the oil by precipitation with a normally gaseoushydrocarbonsolvent. then subjecting the mixture of deasphalted oil. in thel presence of said solvent to conversion. substantially in the vapor phase at temperatures sufiiciently high to eifect substantial vconversion of the oil and normally gaseous hydrocarbons into products within the gasoline boiling range, whereby said tendency to coke formation is substantially less than without said deasphalting treatins.

2. A process for the treatment of hydrocarbon oils which comprises *.gnixing an oil containing asphalt with a liquefied normally gaseous hydrocarbon solvent thereby precipitating asphalt and forming a deasphalted mixture having less tendency to coke on cracking, subjecting the solution of oil and solvent toa conversion operation sub- Y stantially in the vapor phase under temperatures suihciently high to crack the oil and convert a substantial amount of the gaseous hydrocarbons into liquid hydrocarbons and separating from the conversion products a fraction suitable for motor fuel manufacture.

3. A process for the manufacture of motor fuel which comprises treating a cracking stock containing asphalt with a` liquefied normally gaseousv hydrocarbon 'consisting mainly of propane and butane to precipitate the asphalt to reduce the tendency of the oil to coke on cracking, separating a mixture of deasphalted oil andsolvent, and

subjecting the oil containing at leastl a portion of the solvent to cracking temperatures substantialiyin the vapor the oil is cracked in the presence of the normally hydrocarbons to lower boiling products and recovering motor fuel from the cracked products.

' 4. A process 'for the treatment of hydrocarbon oils which comprises mixing a propane solvent with a heavy cracking stock to precipitate asphalt, separating the asphalt from the mixture of oil and solvent, partially removing the solvent and meeting the reminder of` the solvent and oil minture substantiallyinzthe vapor-phase tol' conversion conditions of temperature and pressure in a conversion zone including a heating coil whereby the oil is cracked to lower boiling products anda substantial amount of said solvent is formation in said '.I'HEODORE `CHARLES HEISIG.

- converted into liquids without -substantial coke

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