US3053751A - Fractionation of bituminous substances - Google Patents

Description

United States Patent Ofifice Patented Sept. 11, 1962 3,053,751 FRACTIONATION F BITUMINQUS SUBSTANCES Leo Garwin, Oklahoma City, Okla, assignor to Kerr- McGee Oil industries, line, a corporation of Delaware Filed May 14, 1958. Ser. No. 795,882 13 Claims. (Cl. 208- 45) This invention relates to the fractionation of bituminous substances with normally gaseous hydrocarbons to obtain at least a heavy fraction and a light fraction, and more particularly to an improved process for separating and recovering a heavy bituminous fraction having a lower oil content and/ or higher softening point than may be obtained in conventional fractionation operations.

This application is a continuation-in-part of my copending application Serial No. 683,866 filed September 13, 1957, now abandoned for Fractionation of Bituminous Substances.

The separation of low softening point, high oil content asphaltic materials from bituminous materials such as reduced crudes by means of a single-stage extraction with a normally gaseous hydrocarbon is old in the art. Such fractionating operations are usually carried out at moderate temperatures, e.g., within a temperature range of 70160 F. when treating Mid-Continent reduced crude with propane to yield a heavy phase asphaltic fraction in varying yields, the yield depending upon the asphaltene content, temperature, and propane to oil ratio employed. In addition to this conventional propane fractionating operation, it is known that enhanced fractionation may be obtained through the use of reflux and several stages, at temperatures from about 140 F. up to about the critical temperature of propane. The pressures employed in the foregoing fractionation operations are substantially the equilibrium pressure of the solvent at the temperature of operation, or only slightly in excess thereof.

In conventional propane fractionation of certain reduced crudes, particularly reduced crudes commonly referred to as low asphalt crudes, plugging of the fractionating tower may occur. For example, in the fractionation of certain Mid-Continent reduced crudes with propane in a conventional co-untercurrent contacting tower and at a propane to reduced crude ratio of about 7: 1, with temperatures ranging from about 195 F. at the top of the tower to about 175 F. at the bottom of the tower, an S.A.E. 4050 oil is continuously separated overhead as the lighter phase and a soft asphalt is continuously separated as the heavier phase without operating difficulties. When another apparently similar Mid-Continent reduced crude is charged to the process under the identical operating conditions described above, a similar fraction of lubricating oil may be obtained initially, but the fractionating tower rapidly plugs with hard asphaltic material in the stripping section, i.e., the section between the point of feed of reduced crude and the point of feed of propane, thereby making continuous operation of the fractionating tower impossible. This phenomenon is commonly termed tower plugging and is almost always encountered when fractionating residues from certain low asphalt crudes. However, tower plugging may occur even when operating with non-plugging reduced crudes Where an attempt is made to separate a heavy phase asphaltic fraction having a softening point in excess of about 180 F. It has been ecognized that the tendency toward tower plugging increases with an increase in concentration of asphaltenes and a decrease in oil content of the separated asphaltic product. In general, it is considered that when about 50-80% asphaltenes are present in the separated heavy phase asphaltic product, such a composition of the separated asphaltic product is sufficient to give rise to tower plugging difficulties when butane is the solvent. Also, the art has taught heretofore that variations in temperature at essentially equilibrium pressures are ineffective in eliminating tower plugging problems while at the same time maintaining the softening point of the heavy separated phase, and that a change in the pressure to values substantially above the equilibrium pressure of the solvent at the operating temperature is likewise ineffective in achieving this objective. Thus, the common belief has developed that tower plugging caused by precipitation of the heavy phase within the fractionating apparatus as a semi-solid to solid material which plugs the fractionating apparatus is not a function of these factors, i.e., temperature and pressure, and that variations thereof would not solve the tower plugging problem Without at the same time incurring the penalties of an increase in the yield of the heavy separated phase or fraction and a corresponding lowering of the softening point of the separated heavy phase, and loss of valuable oils.

A number of processes have been proposed for solving the tower plugging problem in instances where normally gaseous hydrocarbon solvents such as ethane, propane, butane, and isobutane are used as the fractionating solvent, but each proposed process has inherent shortcomings such as leaving a relatively large amount of high value oil in the low value separated asphaltic product, or requiring additional processing of the separated asphaltic product to remove additional oil and provide a higher softening point asphaltic product. Also, the prior art processes required much complicated and eXpensive processing equipment and the heat requirements for producing a given quantity of product were extremely high. As a result, the art has long sought a simple, efiicient process which will produce a separated heavy phase asphaltic product having a low oil content, high softening point and low penetration in a single stage process. Such a process would eliminate the need for multiple extraction or other additional processing of the separated asphaltic product, allow the high value oil and solvent to be recovered directly, greatly reduce the requirements for expensive processing apparatus, and have many other economic advantages.

By the term low-asphalt crude oil as used herein is intended a crude oil having a maximum asphalt content of about 5% by weight. Such low asphalt containing crudes may be distinguished from conventional asphaltic crude oils such as California crudes which contain about 12-65% asphalt by weight, or from Wyoming and Arkansas crudes which contain about 30% asphalt by weight. The asphalt content of the crude oil may be conveniently expressed as the percent of residue (e.g., from vacuum distillation of the crude oil) having a maximum penetration (ASTM 13243-36) of at 77 F. With reference to Oklahoma City crudes, the asphaltic residue so defined constitutes about 2% by weight of the crude oil.

It is an object of the present invention to provide a novel method of operating fractionating apparatus whereby tower plugging difficulties may be avoided.

It is a further object of the present invention to provide a novel method of operating fractionating apparatus to prevent tower plugging when fractionating a residue derived from low asphalt crude oil.

It is still a further object of the present invention to provide a novel method of operating fractionating apparatus to prevent tower plugging when fractionating a reduced crude of the non-plugging type into a heavy phase asphaltic fraction having a lower oil content, higher softening point, and lower penetration than may be obtained by conventional methods of operation.

It is still a further object of the present invention to provide an improved method of obtaining a more complete recovery of oils contained in a bituminous material.

It is still a further object of the present invention to provide an improved method of obtaining a heavy fraction having high softening point and low peneration properties from a bituminous material.

It is still a further object of the present invention to provide improved, simplified apparatus for fractionating bituminous material and a novel highly efiicient method of operating the same without tower plugging difficulties to produce a heavy fraction and a solvent solution of a lighter fraction wherein complicated processing equipment may be eliminated and the heat requirement for producing a given quantity of product is greatly reduced.

Still other objects of the present invention and the advantages thereof will be apparent to those skilled in the art by reference to the following detailed description and the drawing which diagrammatically illustrates a suitable arrangement of apparatus for practicing the invention.

It has been discovered that the problems associated with tower plugging of a fractionating system may be avoided by operation at elevated temperatures and pressures; provided, the temperature and pressure are so adjusted as to obtain a density of the solvent which is substantially the same or higher than the solvent density at which plugging of the fractionating system occurs, with the temperature within the fractionating system being raised to a value sufliciently high under the increased pressure conditions to render the precipitated heavy asphaltic fraction, containing asphaltic material and small amounts of solvent, fluid and readily flowable from the fractionating system.

The apparatus may comprise a more or less conventional arrangement for propane fractionation of a bituminous material to yield a lighter fraction overhead and a heavier fraction as bottoms and may include a fractionating tower such as is disclosed in the drawing of United States Patent No. 2,664,384 to Benedict. The fractionating tower may be provided with a plurality of inlet and outlet connections, and may also be provided with suitable contacting apparatus therein in the form of baffies, plates, and the like. A bituminous material feed line may be provided at about mid-point of the tower for introduction of the bituminous material feedstock, while a solvent feed line may be provided for introduction of liquefied normally gaseous hydrocarbon solvent into the bottom portion of the fractionating tower. Bottoms material comprising the precipitated heavier fraction of the bituminous material, together with small amounts of solvent, may be removed via a conduit leading from the bottom of the fractionating tower as a liquid phase, while overhead material comprising a solvent solution of the lighter separated fraction of the bituminous material may be removed via a conduit leading from the top of the fractionating tower. A heating coil having an inlet end and an outlet end may be provided in the upper portion of the fractionating tower for heating the contents in the top of the fractionating tower to a desired temperature. The inlet end 28 may serve to conduct a heating fluid such as, for example, steam from a source not shown to the heating coil, while the outlet end may serve to conduct the spent heating fluid from the heating coil.

When operating according to conventional practice, liquid phase conditions are normally maintained throughout the fractionating tower with the interface between the upper solvent-oil phase and the lower precipitated heavier phase being below the point of feed. The bituminous material feed line is generally placed at least as high as the intermediate portion of the fractionating tower in order to allow the precipitated heavy fraction sufiicient contact with the solvent before reaching the lower portion of the fractionating tower. The volume ratio of solvent to bituminous material, the bituminous material and solvent being continuously fed to the fractionating tower, is at least 2:1, and preferably at least 4:1. In general, satisfactory volume ratios of solvent to bituminous material may vary from 2:1 to 20:1, or higher, if desired, but the preferred volume ratio of 4 solvent to bituminous material is generally around 4:1 to 10:1.

When following conventional practice, with propane as the solvent and reduced crude as the bitumen-containing feed material, the fractionating tower is maintained under a pressure which is substantially the equilibrium pressure for propane at the temperature of operation. The temperature of the reduced crude feed to the fractionating tower is generally about 175-190 F., with the intermediate portion of the fractionating tower in the vicinity of the feed point being approximately at this temperature. The temperature in the lower section of the fractionating tower is generally about -170 F. and may be controlled by the temperature of the propane feed and/or the ratio thereof to the reduced crude feed. The temperature in the upper section of the tower is regulated by means of the heating coil and is such as to maintain a temperature of about 180195 F. in the lighter overhead fraction, i.e., the oil-propane solution with drawn from the top of the fractionating tower. When operating under such conditions, the volume ratio of propane to reduced crude is generally above 2:1, about 8:1 normally being preferred in most instances. Under such temperature and pressure conditions, the propane density varies from about 0.35 g./cc. in the upper portiOn of the tower, to about 0.45 g./cc. in the bottom portion of the tower.

Since propane and reduced crude are continuously fed to the fractionating tower with liquid phase conditions normally being maintained throughout the fractionating tower and the interface between the precipitated heavy phase and the separated lighter phase being substantially below the point of feed, it will be apparent that the propane is continuously rising as a discontinuous phase through the precipitated heavier phase in the lower portion of the fractionating tower until it reaches the interface, and then passes upward through the fractionating tower as a continuous propane-rich phase. The propane intimately contacts the incoming reduced crude and dissolves the soluble lighter fraction or oil content, while causing the heavier insoluble or asphaltic content to precipitate and fall downwardly in the fractionating tower and it is subsequently withdrawn, together wtih relatively small amounts of propane contained therein. The soluble lighter fraction of the reduced crude which is dissolved in the propane passes upwardly and is ultimately withdrawn from the top of fractionating tower. The propane content of the lighter fraction is subsequently flashed off to yield the separated lighter fraction. Likewise, the small amount of propane contained in the heavier separated fraction is flashed off to yield the heavier phase.

The above described conditions of operation of the fractionating tower may be successfully used to fractionate a reduced crude which is not derived from a low asphalt type crude oil, or to separate from a non-plugging crude a heavier phase which has a softening point less than about F., i.e., a low softening point, high penetration asphaltic material which contains considerable amounts of high priced oils. However, when these conditions of operation are used in attempting to fractionate a reduced crude derived from low asphalt crude oil or to separate from reduced crudes derived from nonplugging crudes an asphaltic material having a softening point in excess of about F., i.e., a heavier phase having a relatively low oil content, high softening point and low penetration, the separated asphaltic material deposits within the fractionating tower as a semi-solid to solid which plugs the fractionating tower and prevents continuous operation. Since the fractionating tower normally contains apparatus such as baffles, plates, and the like adapted to promote contact between the propane and the reduced crude feed being treated, it is obvious that such equipment presents even a greater surface area for precipitation of the asphaltic material and this further aggravates the tower plugging problem. The fractionating tower then must be taken otfstream and the precipitated semi-solid to solid asphaltic material removed at frequent intervals, thereby rendering the process uneconomic.

In accordance with the present invention, the above described tower plugging ditficulties are avoided by operation at elevated temperature and pressure provided certain critical conditions are met. In operating the fractionating tower in accordance with the present invention, when there is a tendency toward tower plugging or when plugging is present, the temperature and pressure are so adjusted as to obtain a solvent density substantially the same, or higher, than the solvent density at which plugging of the fractionating tower occurs, with the temperature within the fractionating tower being raised to a value sufficiently elevated to render the heavy separated phase readily flowable. The temperature of the precipitated heavy fraction within the fractionating tower may frequently be substantially below its softening point when operating under such conditions. Not only is the temperature within the fractionating tower elevated to a value sufiicient to render the precipitated heavy fraction readily flowable, but the pressure must be increased correspondingly to obtain a solvent density substantially the same or higher than that at which the plugging occurs or the resulting heavy fraction will have a lower softening point than the fraction which plugged the tower. In general, the minimum temperature of separation in the tower must be not less than about 165 F., with a higher minimum temperature such as 175 F. being preferred in most instances. Best results are often obtained when operating the tower at a minimum temperature of separation of about 190210 F.

For example, in the described operating conditions with propane as the solvent, the propane density varied from 0.35 g./cc. in the upper portion of the tower to about 0.45 g./cc. in the lower portion of the tower and the temperature within the tower was so regulated as to be about 140-170 F. in the lower portion of the tower, 175190 F. in the intermediate portion of the tower, and 180-195 F. in the upper portion of the tower, with the pressure being substantially the equilibrium pressure for propane at the maximum operating temperature within the tower. When operating under such conditions and should tower plugging difficulties be present, the propane density is maintained at about 0.35 g./cc. in the upper portion of the tower and about 0.45 g./cc. in the lower portion of the tower, but the temperature is raised, with a simultaneous increase in pressure to give approximately the previously existing propane density, until the precipitated heavy fraction is rendered readily flowable. The precipitated heavy fraction of substantially the same softening point or higher then may be removed via line 27 in a fluid condition and without any tendency toward tower plugging.

The liquefied normally gaseous hydrocarbons used in practicing the present invention may contain from 2 to 3 carbon atoms, inclusive and saturated hydrocarbon having 4 carbon atoms. Examples of such solvents are ethane, propane, n-butane, isobutane and propylene. It is understood that the use of such solvents in the fractionating tower for the purpose of separating a bituminous material into a lighter fraction and a heavier fraction, in general, is similar in all respects to conventional fractionation processes when fractionating a non-plugging reduced crude and when separating a heavier phase having a softening point less than about 150 F. In other words, the fractionating tower may be operated with the foregoing solvents following conventional practice up to the point where tower plugging difliculties are exhibited and then the operating conditions are modified in accordance with the teachings herein to thereby eliminate tower plugging.

The physical properties of the separated heavier fraction will vary depending upon the operating conditions, or more accurately stated, upon the density of the solvent under the operating conditions. For example, when butane is the solvent and the temperature and pressure conditions maintained within the fractionating tower are such as to provide a solvent density within the range of 0.55- 0.60 g./cc., the separated heavier phase will consist essentially of asphaltenes having a softening point above 300 F. and will be present in the tower as a fluid phase. Thus, the present invention contemplates the separation in a single extraction step of a heavy fraction or fractions from bituminous material, depending upon the solvent density, which may comprise essentially asphaltenes having a softening point above 300 F., or a fraction comprising essentially asphaltenes and resins, or a high softening point, low oil contact asphalt containing asphaltenes, resins and oils. It also will be apparent to those skilled in the art that by adjusting the temperature and pressure conditions within the fractionating tower to provide a solvent density which will selectively precipitate a heavy fraction comprising essentially asphaltenes, the light frac tion removed overhead will contain substantially the entire resin and oil content of the bituminous material. The light fraction thus obtained may be subsequently fractionated at a lower solvent density, e.g., a solvent density of less than 0.55 g./cc. and greater than 0.30 g./cc. when butane is the solvent, to thereby provide a second heavy fraction comprising essentially resins and a second lighter fraction comprising essentially oils. The resin fraction generally has a softening point of about 120160 F., but in some cases up to 200 F. or somewhat higher, while the oil fraction may have a furol viscosity at 210 F. of 10 seconds. The preferred method of removing the solvent from the fraction separated in accordance with the invention comprises increasing the temperature and maintaining the pressure on the separated fraction at such a pressure as to obtain a solvent density of 0.23 g./cc. or less. Then the solvent and separated fraction will demix with the solvent going overhead from the demixer and the separated fraction being withdrawn from the bottom thereof. Hence, the recovered solvent may be recycled, after heat exchange, to the tower without incurring costs for recompression of the solvent, loss of heat, etc., normally associated with reclaiming the solvent by flashing off or by distillation.

The drawing diagrammatically illustrates a presently preferred arrangement of apparatus for use in practicing the present invention wherein solvent may be recovered from the separated solvent solution of lighter fraction by demixing to thereby obtain the advantages mentioned above, as well as many additional advantages which will be apparent to those skilled in the art. Referring now to the drawing, make-up solvent is withdrawn from solvent storage (not shown) via conduit 40 and pumped at a controlled rate by means of pump 41 into a conventional solvent mixing device 42. Simultaneously, recovered solvent from. the system to be described hereinafter having an elevated temperature is fed into mixing device 42 via conduit 43 where it may be mixed with the make-up solvent to provide solvent feed for the system at substantially the desired operating temperature. The resulting mixture of make-up solvent and recovered solvent is withdrawn from mixing device 42 and passed to solvent feed tank 44 via conduit 45 where it may be temporarily stored awaiting use at substantially the operating temperature of the separation vessel. Solvent is Withdrawn from solvent feed tank 44 via conduit 46 and pumped via conduit 47 at a controlled rate by means of pump 48 into a conventional solvent-bituminous material mixing device 49. Simultaneously, bituminous material feed preferably preheated to substantially the operating temperature of the separation vessel is withdrawn from storage (not shown) and pumped at a controlled rate by means of pump 50 via conduit 51 into mixing device 49.

The volume ratio of make-up solvent to recovered solvent fed to mixing device 42 may vary over wide limits but, preferably, the volume ratio and initial temperature of the make-up and recovered solvents are such so as to provide a solvent feed for the process upon mixing the two which has a temperature substantially that of the desired operating temperature. The volume ratio of solvent to bituminous material fed to mixing device 49 must be at least about 2:1 and, preferably, at least about 4:1, with a range of about 4:1 to :1 usually giving excellent results. However, a range of about 2:1 to :1 may be used in most instances. The pump 48 provides the desired operating pressure for the system to be described hereinafter and also provides for circulation of fluids within the entire system. Usually, the pressure drop within the system is not more than about 100 p.s.i. and additional pumps are not necessary.

The mixture of solvent and bituminous material is withdrawn from mixing device 49 via conduit 60 and fed to an intermediate portion of separation vessel 61. The vessel 61 may be a fractionating tower such as described above and it may be operated in the manner previously described. Since the feed mixture preferably is preheated to the operating temperature, heating means within vessel 61 is not necessary and the temperature is substantially the same throughout vessel 61. The minimum temperature of operation of vessel 61 is about 165 F., but a higher minimum temperature such as 175 F. or higher is usually preferred. However, the temperature and pressure conditions for the operation of vessel 61 may be generally as set forth above for the operation of the previously described fractionating tower. Under such temperature and pressure conditions, a fluid heavy fraction separates Within vessel 61 which may be easily removed together with relatively small amounts of solvent via conduit 62 including throttle valve 63, while the solvent solution of the lighter fraction which separates is removed via conduit 64.

The solvent solution of the lighter fraction, which may contain oils alone or a resin-oil mixture depending upon the conditions of operation within vessel 61, is passed to heat exchanger 66 via conduit 64 where it passes in heat exchange effecting relation with recovered solvent. The solvent solution of lighter fraction is withdrawn from heat exchanger 66 via conduit 67 at a higher temperature and passed to heater 68 where it is heated to a still higher temperature by means of a fluid heating medium supplied thereto at a controlled rate via conduit 69 including open valve 70 and withdrawn therefrom via conduit 71. The heated solvent solution of lighter fraction is withdrawn from heater 68 via conduit 75 and passed to an intermediate portion of demixer 76. The temperature and pressure conditions maintained within demixer 76 are such so as to cause the solvent and lighter fraction to demix, i.e., the lighter fraction is precipitated from the solution to form a fluid layer of lighter fraction which settles to the bottom of demixer 76 and is withdrawn therefrom together with relatively small amounts of solvent via conduit 77 including throttle valve 73, and a fluid layer of solvent which rises in demixer 76 and is withdrawn therefrom via conduit 79. The temperature and pressure conditions within demixer 76 are such so as to provide a solvent density less than about 0.23 g./cc. and, preferably, such as to provide a solvent density of about 0.10 0.20 g./cc.

Preferably, recovery of solvent and oils or a resin-oil mixture from the solvent solution of the lighter fraction withdrawn from vessel 61 via conduit 64 is eifected by maintaining substantially the same pressure as used in vessel 61 and merely increasing the temperature of the solvent solution of lighter fraction until the solution demixes," i.e., rorms a fluid upper layer of solvent and a fluid lower layer of oils or a resin-oil mixture. The two layers then may be readily separated. However, both the temperature and the pressure may be adjusted to provide the necessary solvent density to effect separation When this is desirable.

The relatively hot solvent Withdrawn via conduit 79 is passed through heat exchanger 66 in heat exchange effecting relation with the relatively cold solvent solution of lighter fraction in conduit 64,. The solvent then may be passed to cooler via conduit 36. While within cooler 85, the solvent is cooled by means of a fluid cooling medium such as air, the quantity of which provides for control of the temperature of the solvent withdrawn by conduit 43 from cooler 85. The cooling medium is supplied to cooler 85 via conduit 91 including throttle valve 92 and withdrawn therefrom via conduit 93. The relatively cool solvent withdrawn via conduit 43 and passed to mixer 42 may be at a higher temperature than the desired temperature of operation of vessel 61 and, preferably, it is at a sufliciently elevated temperature to provide a solvent feed for the process having a temperature which is substantially the desired temperature of operation upon mixing with the proper amount of make-up solvent. Normally, the heat exchanger 66 is constructed so as to recover substantially all of the excess heat in the solvent and the cooler 85 is not used extensively, if at all, during operation of the system and it is used merely during startup operations or to effect small temperature changes in the solvent within conduit 43.

The system illustrated in the drawing and described above has many desirable features and advantages which are not present in a conventional system where the solvent is recovered by flashing. For example, much less apparatus is required than in a system recovering solvent by flashing and the apparatus which is required may be of a very simple, low cost construction and yet result in a highly efiicient system. It may be noted that design of the system is such that only one pump is necessary to achieve the necessary operating pressure and effect circulation of the fluids throughout the system, while conventional systems require several pumps. Even more important, a much smaller heat exchanger, cooler, and heater are required with the attendant savings in construction, maintenance and operating costs of these pieces of equipment. In addition, large quantities of cooling water often difiicult to obtain in hot, arid areas are not necessary for the eflicient operation of the system, since the one small cooler required may be readily air cooled.

Although the process of this invention has been disclosed and illustrated in connection with a bituminous material such as reduced crude or asphalt, it is also applicable to certain crudes having an API gravity at 60 F. of about 10 or less such as a Mississippi asphaltic crude. Thus, the term bituminous material is also intended to include the low gravity crudes.

The foregoing detailed description of the present invention and the following examples are for purposes of illustration only and are not intended as being limiting to the spirit or scope of the appended claims.

Example I A reduced crude of the Oklahoma type known to give tower plugging difficulties is subjected to vacuum distillation to remove substantially all of the S.A.E. 10 and 20 grades of lubricating oil. This reduced crude containing S.A.E. 30 and higher viscosity grades of lubricating oil and asphalt is fed to a fractionating tower. The incoming reduced crude feed has a temperature of 175190 F., and the temperature within the fractionating tower in the vicinity of the feed point is approximately this temperature. Liquefied propane is pumped into the bottom portion of the fractionating tower through a feed line at such a rate that the volume ratio of liquefied propane to reduced crude feed is maintained at about 8:1. The temperature in the lower section of the fractionating tower is maintained at about -165 F. by controlling the temperature of the entering liquefied propane, and/or by varying the volume ratio of propane to reduced crude. The temperature Within the upper portion of the fractionating tower is regulated by means of a heating coil to maintain a temperature of ISO-195 F. in the solution of oil and propane passing from the top of the fractioning tower. Thus, the fractionating tower is so regulated as to provide a temperature of 140165 F. in the lower portion of the fractionating tower, a temperature of about 180- 195 F. in the upper portion of the fractionating tower, and a temperature in the intermediate portion of the fractionating tower in the vicinity of the point of feed of about 175190 F. The fractionating tower is maintained under a pressure of 6 50 p.s.i.g., i.e., substantially the equilibrium pressure of propane at the maximum operating temperature. When the temperatures of the various portions of the fractionating tower are so regulated, and when the pressure is about 650 lbs. p.s.i.g., then the propane density varies from about 0.35 g./ cc. to about 0.45 g./ cc. between the upper and lower portions of the fractionating tower, respectively.

When the fractionating tower is operated under the above described conditions and on the particular Oklahoma reduced crude described above, the fractionating tower rapidly plugs with semi-solid to solid asphalt in the general area between the point of feed and the point of introduction of liquefied propane. After the expiration of a very short period of time, the fractionating tower is plugged to such an extent that further operation is impossible and it is necessary to suspend operations in order to remove the semi-solid to solid deposits of asphalt. Thus, it is impossible to continuously operate the fractionating tower under the operating conditions described in this example.

Example II The fractionating apparatus and Oklahoma reduced crude feed used in this example were identical with that of Example I, only the operating conditions being changed.

Under the operating conditions of this example, reduced crude feed at a temperature of about 195 F. was pumped through a feed line into the fractionating tower. The temperature in the vicinity of the point of feed was also about 195 F. The liquefied propane entering the fractionating tower via the propane feed line was maintained at a temperature suflicient to give a temperature within the lower section of the fractionating tower of abou r175 F. The volume ratio of propane to reduced crude was the same as in Exampde I. The solution of oil and propane leaving the top of the fractionating tower was maintained at a temperature of about 220 F. by means of a heating coil. The pressure within the fractionating tower was maintained at 1000 p.s.i.g., and under such temperature and pressure conditions the propane density in the upper and lower portions of the fractionating tower was about 0.36 and 0.43 g./cc., respectively. The fractionating tower was operated continuously over extended periods of time under the above operating conditions without any indication of tower plugging. Thus, it is apparent that tower plugging difficulties may be avoided by operating the fractionating tower in such a manner as to maintain a relationship between the temperature and pressure such as necessary to obtain a solvent density substantially the same or higher than the solvent density at which plugging of the fractionating tower occurs, and with the temperature being so regulated as to render the heavy phase fraction removed from the fractionating tower in an easily fiowable condition under the operating conditions. During this period of continuous operation of the fractionating tower, the oil-propane solution after the removal of the propane solvent produced S.A.E. 4050 viscosity grade oil, and the heavy phase fraction removed from the fractionating tower after the removal of small amounts of propane contained therein produced asphalt of 80-120 penetration at 77 F. in yields comparable to those obtained in Example I or slightly smaller.

When the fractionating tower was operated under the identical conditions described above with the exception of regulating the temperature within the lower portion so as to provide a temperature of 190 F., and raising the pressure to 3000 p.s.i.g. to give a solvent density of about 0.51 g./cc., the oil fraction was heavier than S.A.E. 50 grade oil and the heavy asphaltic fraction was found to have a softening point of 223 F. There was no indication of tower plugging. Thus, in accordance with the present invention, it is possible to separate from bituminous material an asphaltic fraction having a softening point substantially in excess of the temperature of separation.

When the fractionating tower is operated under the conditions described in the paragraph immediately above, with the exception of substituting liquefied butane for the liquefied propane and maintaining a pressure of 2000 p.s.i.g. to give a solvent density of about 0.55 g./cc., heavy asphaltic fractions are obtainable having softening points in excess of 200 F. without experiencing tower plugging difficulties. Also, it should be noted that when operating at the aforesaid temperature and pressures with both propane and butane to separate a 200 F. plus softening point heavy fraction, the separation was occurring at a temperature below the softening point of the heavy fraction.

Example III This example illustrates the separation of a heavy, high softening point asphaltic fraction consisting essentially of asphaltenes from vacuum reduced asphalt (117 F. softening point; 87 penetration at 77 F.) using liquefied commercial butane as the solvent. A sample of the particular commercial butane used indicated the following mol percent composition: 71.84% n-butane, 22.78% isobutane, 5.26% propane, and 0.12% isopentane.

The operating conditions for the fractionating tower in this example were essentially as described for propane in the first portion of Example II, with the exception of substituting a 10:1 volume ratio of the above described commercial butane solvent to asphalt, increasing the heavy fraction separation temperature in the lower portion of the fractionating tower from F. to 187 F., and increasing the pressure on the system from 1000 p.s.i.g. to 2950 p.s.i.g. to give a solvent density of about 0.57 g./cc.

The fractionating system was continuously operated under the above conditions for an extended period of time without any evidence of tower plugging. During this period of continuous operation, the precipitated heavy phase which was separated had a softening point of 310 F. (after removal of small amounts of solvent) and was obtained in 20% yield, based upon the weight of asphalt charged to the fractionating system. Again, it is demonstrated that it is possible to operate a butane deasphalting tower in accordance with the invention to separate a heavy phase or fraction having a softening point substantially above the operating temperature without the occurrence of the tower plugging problem. The light fraction separated overhead comprised essentially the entire resin and oil content of the asphalt charge and was used in the following example.

Example IV The butane solution of light overhead fraction separated in Example III and comprising esesntially the entire resin and oil content of the asphalt of Example 111 was fed to a fractionating tower identical with that of Example III.

The fractionating tower was operated continuously without any evidence of tower plugging over an extended period of time at a heavy fraction separation temperature of 280 F. and under a pressure of 545 p.s.i.g. Under such temperature and pressure conditions, the solvent density in the lower portion of the fractionating tower was 0.40 g./cc. Slightly higher temperatures than 280 F. were used in the intermediate and upper portions of the tower with correspondingly lower solvent densities.

The separated heavy fraction comprised essentially resins (after removal of small amounts of solvent), while 11 the light fraction separated overhead comprised essentially a solvent solution of oils.

Example V This example illustrates operation of the system disclosed in the drawing in accordance with the invention. The reduced crude feed used in this example was identical with that of Example I and the solvent was propane.

The feed mixture to separation vessel 61 comprised volumes of propane for each volume of reduced crude and the mixture was preheated to a temperature of 200 F. The temperature within vessel 61 was substantially 200 F. throughout the vessel and the pressure was maintained at 1000 p.s.i.g. Under these temperature and pressure conditions, the solvent density was substantially 0.39 g./cc. throughout the vessel 61 and a fluid phase heavy fraction readily separated from the solvent solution of lighter fraction.

The fluid phase heavy fraction thus separated had a temperature of substantially 200 F. and was easily withdrawn from vessel 61 via conduit 62. The heavy fraction contained about one volume of solvent per volume of heavy fraction and, after flashing off the solvent, the heavy fraction had a softening point substantially above 200 F. The solvent solution of the lighter fraction withdrawn via conduit 64 was heated to a temperature of 350 F. in heat exchanger 66 and heater 68 and then fed to demixer 76. The temperature within demixer 76 was substantially 350 F. throughout the demixer and the pressure was about 950 p.s.i.g. Under these temperature and pressure conditions, the solvent density was 0.12 g./cc. and the solvent solution of the lighter fraction readily demixed to form an upper layer of solvent and a fluid phase lower layer of the lighter fraction. The lower layer of lighter fraction was withdrawn at a temperature of about 350 F. via conduit 77 along with about one volume of solvent per volume of lighter fraction. The solvent was flashed off. The lighter phase was a mixture of soft resins and oils.

The solvent was withdrawn from demixer 76 via conduit 79 at a temperature of about 350 F. and passed through heat exchanger 66 in heat exchange effecting relation with the solvent solution in conduit 64, then through cooler 85 with no cooling medium being required in cooler 85 in this case. About 8 volumes of the recovered solvent and 2 volumes of make-up solvent were fed to mixer 42 via conduits 43 and 40, respectively, to thereby provide 10 volumes of solvent for feed to the system. The mixture of recovered and make-up solvent was at a temperature of about 200 F. and the pressure within solvent feed tank was about 900 p.s.i.g. About 10 volumes of the solvent were then withdrawn from feed tank 44 and pumped to mixing device 49 where the solvent Was mixed with about one volume of preheated reduced crude. The resulting feed mixture had a temperature of 200 F. and a pressure of about 1000 p.s.i.g., and was used as feed mixture to the system.

What is claimed is:

1. In a process for fractionating a bituminous material derived from petroleum and containing asphaltenes into at least a heavy fraction and a light fraction under elevated temperature and pressure conditions wherein each volume of the bituminous material is treated in a fractionating zone with at least two volumes of a solvent consisting essentially of at least one liquefied normally gaseous hydrocarbon selected from the group consisting of hydrocarbons containing 2 through 3 carbon atoms inclusive and parafiin hydrocarbons containing 4 carbon atoms under temperature and pressure conditions providing a solvent density whereby the heavy fraction is precipitated as a solid to semi-solid which plugs at least a portion of the fractionating zone thereby preventing continuous operation, the improvement which comprises increasing the temperature and pressure within the fractionating zone while maintaining a relationship between the temperature and pressure such that the solvent density within the fractionating Zone is at least about as great as the solvent density at which plugging of the fractionating zone occurs, the temperature being raised to at least F. and sufliciently high under the increased pressure conditions to render the precipitated heavy fraction liquid Within the fractionating zone and readily flowable therefrom, and the pressure being at least sufiicient to maintain liquid phase conditions in the fractionating zone.

2. The process of claim 1 wherein the solvent consists essentially of propane.

3. The process of claim 2 wherein the solvent density is not less than about 0.43 g./cc. in at least that section of the fractionating apparatus where plugging tends to occur.

4. In a process for fractionating a bituminous material derived from petroleum and containing asphaltenes into at least a heavy fraction and a light fraction under elevated temperature and pressure conditions wherein each volume of the bituminous material is treated in a fractionating zone with at least four volumes of a solvent consisting essentially of at least one liquefied normally gaseous hydrocarbon selected from the group consisting of hydrocarbons containing 2 through 3 carbon atoms inclusive and paraffin hydrocarbons containing 4 carbon atoms under temperature and pressure conditions providing a solvent density whereby the heavy fraction is precipitated as a solid to semi-solid which plugs at least a portion of the fractionating zone thereby preventing continuous operation, the improvement which comprises increasing the temperature and pressure within the fractionating zone while maintaining a relationship between the temperature and pressure such that the solvent density within the fractionating zone is at least about as great as the solvent density at which plugging of the fractionating zone occurs, the temperature being raised to at least 165 F. and sufiiciently high under the increased pressure conditions to render the precipitated heavy fraction liquid while within the fractionating zone and readily flowable therefrom, the pressure being at least suflicient to maintain liquid phase conditions in the fractionating zone, and separating a heavy fraction from the fractionating zone having a softening point higher than the temperature of separation.

5. The process of claim 4 wherein the solvent consists essentially of paratfin hydrocarbons containing 4 carbon atoms.

6. The process of claim 5 wherein the solvent density is not less than 0.43 g./cc. at least within that section of the fractionation apparatus where plugging tends to occur.

7. A process for continuously fi-actionating an asphaltic bituminous material derived from petroleum and containing asphaltenes into at least a light fraction and a heavy fraction wherein the heavy fraction has a softening point at least within the fractionating zone plugging range comprising treating in a fractionating zone each volume of bituminous material with at least 2 volumes of a solvent consisting essentially of liquefied paraflin hydrocarbons containing 4 carbon atoms at elevated temperature and pressure, said temperature being at least F., maintaining a relationship between the temperature and pressure such as to obtain a solvent density of about 0.55- 0.60 g./cc. to thereby separate a heavy fraction having a softening point of at least 300 F. as a fluid phase, the pressure being at least sutficient to maintain liquid phase conditions in the fractionating zone and withdrawing the heavy fraction from the fractionating zone.

8. In a process for fractionating a bituminous material derived from petroleum and containing asphaltenes into at least a heavy fraction and a light fraction under elevated temperature and pressure conditions wherein each volume of the bituminous material is treated in a fractionating zone with at least two volumes of a solvent consisting essentially of at least one liquefied normally gaseous hydrocarbon selected from the group consisting of hydrocarbons containing 2 through 3 carbon atoms inclusive and paraffin hydrocarbons containing 4 carbon atoms under temperature and pressure conditions providing a solvent density whereby the heavy fraction is precipitated from the hydrocarbon solution of the lighter fraction as a solid to semi-solid which plugs at least a portion of the fraetionating zone thereby preventing continuous operation, the improvement which comprises increasing the temperature and pressure within the fractionating zone while maintaining a relationship between the temperature and pressure such that the solvent density within the fractionating zone is at least about as great as the solvent density at which plugging of the fractionating zone occurs, the temperature being raised to at least 165 F. and sufiiciently high under the increased pressure conditions to render the precipitated heavy fraction liquid within the fractionating zone and readily flowable therefrom, the pressure being at least sufiicient to maintain liquid phase conditions in the fractionating zone, separating the hydrocarbon solution of the lighter fraction from the heavy fraction, precipitating the lighter fraction from hydrocarbon solvent by increasing the temperature of the hydrocarbon solution of lighter fraction, the temperature at a given pressure being adjusted so as to provide a solvent density of less than about 0.23 g./cc., and separating hydrocarbon solvent from the lighter fraction.

9. The process of claim 8 wherein the solvent consists essentially of paraffin hydrocarbons containing 4 carbon atoms.

10. The process of claim 8 wherein the solvent density is not less than about 0.43 g./ cc. in at least that section of the fractionating apparatus where plugging tends to occur.

11. In a process for fractionating a bituminous material derived from petroleum and containing asphaltenes into at least a heavy fraction and a light fraction under elevated temperature and pressure conditions wherein each volume of the bituminous material is treated in a fractionating zone with at least four volumes of a solvent consisting essentially of at least one liquefied normally gaseous hydrocarbon selected from the group consisting of hydrocarbons containing 2 through 3 carbon atoms inclusive and parafiin hydrocarbons containing 4 carbon atoms under temperature and pressure conditions providing a solvent density whereby the heavy fraction is precipitated from the hydrocarbon solution of the lighter fraction as a solid to semi-solid which plugs at least a portion of the fractionating zone thereby preventing continuous operation, the improvement which comprises increasing the temperature and pressure within the fractionating zone while maintaining a relationship between the temperature and pressure such that the solvent density Within the fractionating zone is at least about as great as the solvent density at which plugging of the fractionating zone occurs, the temperature being raised to at least F. and sufficiently high under the increased pressure conditions to render the precipitated heavy fraction liquid within the fractionating zone and readily fiowable therefrom, the pressure being at least sufficient to maintain liquid phase conditions in the fractionating zone, separating the hydrocarbon solution of the lighter fraction from the heavy fraction, precipitating the lighter fraction from hydrocarbon solvent by increasing the temperature of the hydrocarbon solution of lighter fraction, the temperature at a given pressure being adjusted so as to provide a solvent density of less than about 0.23 g./cc., and separating hydrocarbon solvent from the lighter fraction.

12. The process of claim 11 wherein the solvent consists essentially of propane.

13. The process of claim 11 wherein the solvent density is not less than about 0.43 g./ cc. in at least that section of the fractionating apparatus where plugging tends to occur.

References Cited in the file of this patent UNITED STATES PATENTS 2,116,188 Churchill May 3, 1938 2,148,716 Whiteley et a1. Feb. 28, 1939 2,188,012 Pilat et al Jan. 23, 1940 2,202,389 Lewis et al. May 28, 1940 2,252,864 Schaafsm-a Aug. 19, 1941 2,383,535 Dickinson et al. Aug. 28, 1945 2,527,404 De Vault Oct. 24, 1950 2,538,220 Willauer I an. 16, 1951 2,558,809 Benedict July 3, 1951 2,570,044 Benedict Oct. 2, 1951 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,053,751 I i September 11, 1962 Leo Garwin It is hereby certified that error appears in the above numbered pat ent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 56, strike out "28"; column 6, line 16. for "contact" read content column 10, line 8, .after 'Tfrom" insert a Signed and sealed this 19th day of February 1963.

(SEAL) Attest:

ESTON G. JOHNSON DAVID L. LADD Attesting Officer Commissioner of Patents

Claims (1)

1. IN A PROCESS FOR FRACTIONING A BITUMINOUS MATERIAL DERIVED FROM PETROLEUM AND CONTAIN ING ASPHALTENES INTO AT LEAST A HEAVY FRACTION AND A LIGHT FRACTION UNDER ELEVATED TEMPERATURE AND PRESSURE CONDITIONS WHEREIN EACH VOLUME OF THE BITUMINOUS MATERIAL IS TREATED IN A FRACTIONATING ZONE WITH AT LEAST TWO VOLUMES OF A SOLVENT CONSISTING ESSENTIALLY OF AT LEAST VOLUMES OF A SOLVENT GASEOUS HYDROCARBON SELECTED FROM THE GROUP CONSISTING OF HYDROCARBONS CONTAINING 2 THROUGH 3 CARBON ATOMS INCLUSIVE AND PARAFFIN HYDROCARBONS CONTAINING 4 CARBON ATOMS UNDER TEMPERATURE AND PRESSURE CONDITIONS PROVIDING A SOLVENT DENSITY WHEREBY THE HEAVY FRACTION IS PRECIPITATED AS A SOLID OF SEMI-SOLID WHICH PLUGS AT LEAST A PORTION OF THE FRACTIONING ZONE THEREBY PREVENTING CONTINUOUS OPERATION, THE IMPROVEMENT WHICH COMPRISES INCREASING THE TEMPERATURE AND PRESSURE WITHIN THE FRACTIONING ZONE WHILE MAINTAINING A RELATIONSHIP BETWEEN THE TEMPERATURE AND PRESSURE SUCH THAT THE SOLVENT DENSITY WITHIN THE FRACTIONATING ZONE IS AT LEAST ABOUT AS GREAT AS THE SOLVENT DENSITY AT WHICH PLUGGING OF THE FRACTIONATING ZONE OCCURS, THE TEMPERATURE BEING RAISED TO AT LEAST 165*F. AND SUFFICIENTLY HIGH UNDER THE INCREASED PRESSURE CONDITIONS TO RENDER THE PRECIPITATED HEAVY FRACTION LIQUID WITHIN THE FRACTIONING ZONE AND READILY FLOWABLE THEREFROM, AND THE PRESSURE BEING AT LEAST SUFFICIENT TO MAINTAIN LIQUID PHASE CONDITIONS IN THE FRACTIONATING ZONE.

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