US2266553A - Process of dewaxing hydrocarbon oils - Google Patents

Description

Filed Dec. 2, 1938 Dec. 16, 1941.

Patented 'Dec.'16 1941 UNITED 'STATE S PATIENT OFFICE PROCESS F DEWIG HYDEOCABBO Leo D. Jones. Philadelphia. Pa., asslgnor to The Sharples Corporation, Philadelphia, Pa., a corporation of Delaware Application December z, 193s.' serial N5. 243,559

(ci. isc- 19) 3Claims.

' centric layers and discharging the materials of these layers separately from the influence of centrifugal force. It is concerned primarily with a process of effecting such separation and separate discharge, but includes as an additional feature a machine having particular utility for performing the steps constituting the process of the invention. While both the process and machine of the invention will probably be found useful in the solution of various separation problems, the invention was conceived as a solution of problems arising incident to the separation of wax from petroleum stock, and has been found to be particularly useful in connection with these particularproblems. In the followingv description, the invention will therefore be discussed in its relationship to separation of wax from oil, it being understood that this method of description is adopted merely for the purposes of convenience of illustration, and not with any intent to limit its scope to this single use.

The invention may be considered as an improvement over the process of dewaxing petroleum stocks described in the patent to P. T. Sharples No. 1,351,265 of August 3l, 1920. That process has gone into extensive commercial use in the United States and foreign countries. In

i the practice of the process of that patent, the

stock to be dewaxed is first diluted with a sufficient amount of relatively low-boiling hydrocarbon solvent to render the oil phase, upon subsequent chilling to precipitate wax, distinctly lighter than the precipitated wax. The diluted stock, containing both oil and wax, is thereafter chilled to a temperature below 0 F. in order to precipitate the wax from solution in the diluent. The oil solution containing the precipitated wax is thereafter centrifuged to eect stratification of the wax and separate discharge of the wax and diluted oil phases from the centrifugal rotor.

In the practice of a process of this charactern attempts have heretofore been made to employ centrifugal rotors of the familiar type having a so-called disc-block; i. e., a series of nested, closely spaced frusto-conical discs affording a plurality of superimposed stratifying chambers from which the wax passes outwardly beyond the outer circumference of the disc-block and the'oil passes inwardly beyond the inner circumference, the wax and oil being discharged over' separate weirs or ring-dams which control the desired balance of the material discharged from Y the wax outlet against the constituents in the main body of the centrifugal rotor. In the separation of substances from each other in separators of this type, the mixture which is subjected to centrifugation is commonly fed to an intermediate zone of the rotor between the outer and inner circumferences of the discs and is passed longitudinally of the rotor through openings in the discs at that zone to points between the discs within which stratification occurs. In attempted separation of wax from diluted petroleum stock by such a process, difficulty is frequently encountered because of the fact that the wax clogs the spaces between successive stratifying discs and thus renders continuous centrifugation over a substantial period of time difficult or impossible. An object of the present invention has been to solve this problem.

In the process described in the patent to P, T. Sharples No. 1,351,265, a carrier liquid which is immiscible with the oil and wax is employed to facilitate flow of the wax phase through the centrifugal rotor and discharge of wax from the rotor. This carrier liquid fulfills the important functions of preventing stickage of Wax to parts of the rotor. It also facilitates ow of the wax circumferentially of the rotor to the points from which it is discharged from the rotor. An improvement invented by the present applicant was later used in the practice of the process of Patent No. 1,351,265, and this improvement is described and claimed in the patent to Jones No. 1,649,117. It consists in the feed of the carrier liquid to the centrifugal rotor adjacent the point of discharge of wax therefrom. An important advantage of this improvement consists in the fact that it enables the operator to employ carrier liquid in a heated condition, thereby melting the wax and preventing stickage thereof in the apparatus into which it is discharged from the rotor. If an attempt were made to feed hot carrier liquid together with the oil into the centrifugal rotor, this carrier liquid would remelt much of the wax precipitated by the preceding chilling loperation and thereby cause resolution of this wax in the oil phase, resulting in discharge of this dissolved wax with the `oil and consequent inadequate dewaxing. By feedingthe carrier liquid at the point of wax discharge, it is possible to employ hot carrier liquid. since the hot carrier liquid does not in this case come into contact with the wax until the wax has been separated from the oil layer by stratiiication.

Wax discharged from the centrifugal separator in any centrifugal dewaxing operation contains a substantial quantity of entrained oil, the oil content of the wax varying between and 50%. It is, of course, desirable to reclaim this entrained oil in case this can be done economically. A particular object of the present invention has beento aord a process whereby the oil entrained in the wax can be economically recovered. f

When a hot carrier liquid is fed to the wax discharge point of a centrifugal rotor provided with a disc-bloc, diiiiculty is encountered by reason of the fact that the hot carrier liquid transmits heat through the thin dividing wall between the wax discharge outlet and the main body of the rotor. This transmission of heat results in re-meltng of wax which is between the individual discs nearest to the point of wax discharge with the consequence that this wax is re-dissolved in the oil and discharged with the oil. Another feature of the invention consists in the development of a machine and process for avoiding this defect.

A still further object of the invention consists in the development of a process in which the wax stratified from the oil in the main body of the rotor is supported on an auxiliary spacing liquid which lies adjacent to the inner circumference of the rotor wall and prevents adhesion of wax to that wall, but in which that spacing liquid is not discharged with the wax and does not therefore contaminate the discharged wax.

In cases in which hot carrier liquid is discharged with the wax, the carrier liquid must be separated from the wax by somewhat elaborate procedure before an attempt is made to treat the wax to separate further oil therefrom. This procedure involves separating the bulk of the carrier liquid by gravity settling and partial distillation to evaporate the last traces of carrier liquid. In case a procedure of this type is adopted, the wax must also be diluted and re-chilled to reprecipitate the wax prior to the second step of centrifugation. A particular feature of the present invention consists in the performance of the dewaxing operation in such a way as to avoid pollution of the separated wax with carrier liquid, and to discharge the wax in dilution in a liquid which can be advantageously used in the second step of centrifugation employed to remove entrained oil from the wax. A further feature of the invention consists in the discharge of wax in such dilution in a chilled state, thereby avoiding expensive additional chilling to re-precipitate the wax prior to the second centrifuging step.

Further objects and advantages of the invention will be evident from a reading of the following specification in the light of the attached drawing, in which the single figure is a crosssectional view of a centrifugal separator embodying the mechanical features of the invention and in which the process features of the invention may be practiced.

Referring to the drawing by reference characters, the rotor I8 of the centrifugal separator is driven by suitable. means such as the shaft 28 illustrated in the drawing. 'I'hs rotor comprises a main body portion Il and-a top portion I2 secured to the main body portion in conventional manner by a clamping ring I3. A disc-bloc I4, consisting of a plurality of nested frusto-conical stratifying discs, is secured in position within the rotor between the top portion I2 and the main body portion II. The construction of these discs constitutes an important feature of the invention,

` as will be discussed hereinafter. A tube I5 may be secured to the interior of the rotor and receives from the feed conduit I 6 the material to be treated. The tube I5 communicates with the main body of the rotor through a plurality of openings 29 adjacent the base of the rotor, these openings directing the mixture under treatment into the space 26 surrounding the outer circumference 25 of the disc-bloc. The rotor is provided with a plurality of discharge outlets I1 communicating with the 'outer portion of the separating space 26 and adapted to receive the heavy eiiiuent from the rotor after that effluent has passed around the outer circumference of the frusto-conical disc I8 which constitutes the dividing wall for separating and separately discharging the light and heavy eiliuents respectively. Material passing upwardly through outlet I1 passes around ring-dam I9 into a cover 20 of conventional design. The light eiiiuent from the rotor passes inwardly between the respective discs of the disc-bloc I4 and is discharged through space 2I communicating with the inner circumference of the disc-bloc, into the light eiiiuent receiving cover 22.

A conduit 23 is provided between the covers 28 and 22 and conveys liquid to a nozzle 24 similar to that described in the patent to Jones No. 1,649,117, and this liquid is thereafter directed into the centrifugal rotor adjacent the point of discharge of light eiliuent'from the rotor over ring-dam I8, just as in the case of applicants prior Patent 1,649,117.

The bottom of the upper cover 22 is separated from the top of the lower cover 28 by an insulating air space, thereby preventing undesired chilling of wax discharged into cover 20 by oil discharged into cover 22. Y

A feature of the invention consists in the provision of a dividing Wall I8, which is in laminated form and provided with insulation 21 between its upper and lower surfaces.

The advantages of the above described centrifugal separator and the nature of the process of the present invention will be obvious from the following description of that process in the illustrative embodiments discussed hereinafter.

In the practice of the process of the invention using the machine described above, a mixture containing oil diluted with naphtha, hexane, or other diluent of sufficiently low specific gravity and in sufficient quantity to render the oil phase substantially lighter than the precipitated wax phase, and containing precipitated wax, is fed through conduit I6 into the feed tube I5 of the rotor. This mixture passes outwardly through openings 28 into the stratifying space 26. In accordance with the invention, this space 25 is relatively large, thediscs of disc-bloc I4 being relatively small in diameter, and terminating a considerable distance radially within the zone occupied by the plastic wax layer which separates from the oil solution. It will thus be seen that the principal stratifying action of the rotor occurs in the space 26, which lies entirely outwardly of the disc-bloc. Oil passing inwardly into the disc-bloc has therefore been deprived of the major part of its wax, and the wax content of such oil consists entirely of small quantities of finely divided wax which have not been removed incident to the stratifying action which takes place in the outer circumferential zone 26. By reason of this fact, the cloggage of discs by wax,

assauts such as heretofore occurred inthe attempted use of a disc-bloc in centrifugal dewaxing is avoided. The disc-bloc is used only to separate the last traces of wax from oil and deliver into the space 2l and cover 22 a thoroughly dewaxed oil. Since only small quantities of wax pass outwardly from the disc-bloc into the space 26, cloggage is avoided.

The wax which separates as an outer stratum in the outer part of the space 28 passes upwardly around the outer edge of the dividing wall I8 and is discharged through passages I1 and around ring-dam I9 into the cover 20, this wax being balanced against the concentric strata of wax and oil in the main body of the rotor.

A carrier liquid, such as hot water or brine, may be introduced through the conduit 23 and nozzle 24 into the upper part of the passages I1 adjacent the ring-dam I9. In case such carrier liquid is used, a part of this carrier liquid will pass downwardly through the passages I1 into the main body of the rotor. If a hot carrier liquid were used in this manner in a machine of conventional design employing a disc-bloc, the hot carrier liquid would transmit heat through the dividing Wall and cause melting of Wax within the upper section of the disc-bloc. This would result in re-solution of that wax in the oil and discharge thereof with the oil, thereby impairing the efliciency of the centrifugal dewaxing operation. In accordance with the present invention, this undesired re-melting of wax is avoided by providing an insulating strip 2l, which eii'ectively prevents the undesired conduction of heat to the mixture of oil and wax adjacent the dividing wall I Q8.

In the preferred embodiment of the invention, no carrier liquid is used, since it is desirable that wax be free of contamination with carrier liquid in order that it may be promptly subjected to further processing in a chilled condition to remove residual oil and thus reclaim that oil. This result is accomplished by feeding through the conduit 23 and nozzle 24 a diluent for the wax which is miscible with the oil and of lower specific gravity than the wax itself. This diluent may be a light hydrocarbon such as hexane or naphtha, or it may be any liquid capable of softening the wax and preventing adhesion thereof to the parts of the cover 2U. By adding this diluent in a sufiicient proportion to effect the desired softening and avoid stickage at these points, it has been found possible to'perform the dewaxing operation without the use of an aqueous carrier liquid and consequent discharge of the carrier liquid with the wax.

A further feature of the invention consists in the provision of an auxiliary spacing liquid which prevents adhesion of wax to the inner circumferential wall of the rotor and facilitates flow of wax circumferentially around the rotor to the discharge points, but is not discharged with the wax. Thus, a liquid such as water or brine may be introduced into the centrifugal rotor in sufficient quantity to form a thin spacing layer of liquid within the wall of the centrifugal rotor. This layer prevents adhesion of wax to the rotor wall, but it is suiciently thin so that it does not extend inwardly as far as the outer circumference of the dividing wall IB, and does not therefore prevent continuous discharge of wax from the rotor. This feature -of the use of a layer of spacing liquid may be advantageously used in conjunction with the feed of a non-aqueous softening liquid to the upper end of the rotor to assist in discharge of wax over the ring-dam I9.

The injection of a hydrocarbon diluent adjacent the zone of discharge of wax over ringdam Il has an additional advantage in connec-J tion .with further processing of the wax by centrifugation or otherwise to remove entrained oil. In prior art practice in which a hot carrier liquid was employed, the use of such liquid introduced two factors of expense into any processv designed to recover entrained oil from the wax. In the first place, the carrier liquid. being hot, heated the wax, and the wax therefore required further chilling to precipitate it before being re-centrifuged. In the second place, the carrier liquid had to be removed before such re-chilling and re-running, thereby causing expense incident to this removal step.v

When a softening liquid such asnaphtha or hexane, which is miscible with the oil entrained in the wax, is introduced through the nozzle 24, all of these items of expense are avoided. In the first place, the hydrocarbon or other liquid added through the nozzle 24 may be at approximately the same temperature as the wax, and it does not therefore melt the wax. In the second place, this liquid acts as a very desirable diluent in the performance of the ensuing operation of centrifugation to remove further oil and diluent from the wax. The addition of a diluent prior to the recentrifuging of the wax is desirable in any case. and the amount of diluent which is added through the nozzle 24 is usually considerably less than the amount of such diluent actually required in order to re-centrifuge the mixture of oil and wax discharging over the ring-dam I9. In view of the fact that the mixture discharged from the cover 20 is already at approximately the same temperature as that of the mixture introduced into the feed tube i5, the wax is in a precipitated condition in the hydrocarbon diluent-oil solution discharged from cover 20, and this mixture therefore requires no further chilling, or at least only slight further chilling 'prior to the second step of centrifugation by which further oil is recovered from the wax.

In a typical example of the practice of the present invention, a hydrocarbon stock containing wax was mixed with three times its volume of naphtha,. The solution so produced Was chilled tated wax was then fed to the centrifugal separator of the invention at a rate of ten gallons per minute, and a spacing layer of brine was fed to the centrifugal rotor before this feed of petroleum stock thereto was commenced, this brine occupying a thin annular space about the inner circumference of the rotor section I i, but not extending inwardly as far as the outer circumference of the dividing wall i8. The mixture of oii and wax was passed into the separating space 2@ of the rotor and the wax was stratified from the oil, forming a plastic wax layer occupying a zone extending inwardly from the inner circumference of the layer of spacing liquid to a point about midway radially between the outer circumference of the dividing wall I8 and the outer circumference of the disc-bloc Irl. The oil passing inwardly into the disc-bloc I4 contained only residual traces of wax. Such wax was removed from the oil centrifugally in the disc-bloc and impelled outwardly under the iniluence of centrifugal force into the Wax stratum occupying the outer portion of the stratifying space 26. A thoroughly dewaxed oil was discharged inwardly through the space 2l into cover 22. Wax from the plastic wax layer was discharged continuously around the outer circumference of the dividing wall I8 and through the passages Il over ring-dam I9. Naphtha was fed through nozzle 24 to this plastic wax eiiiuent at a point just Within the rotor adjacent ring-dam I9. The rate of discharge from the plastic wax stratum aroundv ring-dam i9 was 1.5 gallons per minute. The rate of feed of naphtha from nozzle 24 was 1.2 gallons per minute. The wax diluted with naphtha from nozzle 24 was discharged from the cover 20 and was thereafter mixed with an equal volume of naphtha, which had been previously chilledl to the dewaxing temperature. The mixture so produced was thereafter passed to a secondcentrifugal separator to eilect further removal of oil solution from the wax.

Modifications will be obvious to those skilled in the art, and I do not therefore wish to be limited except by the scope of the sub-joined claims.

I claim:

1. Method of centrifugally classifying components of a mixture consisting of a solid having a higher specific gravity characteristic than a liquid admixed therewith that comprises introducing the mixture initially into an external substantially unobstructed annular rst zone of a centrifugal rotor having a volume at least sumcient to accommodate the entire separated heavier components; stratifying the mixture while in said rst zone; passing the lighter components to an internal second zone immediately contiguous said first zone wherein stratification discs assist further separation of the components; withdrawing the separated lighter components from a locality near the center of the second zone; withdrawing the separated heavier components from near the outerperiphery of the rst zone in the presence of a hot carrier liquid, immiscible with said heavier components, and having a higher specific gravity than the heavier components, introduced into said heavier components near the place of discharge thereof.

2.. The process of separating into its constituents a mixture of liquid and solids of higher specic gravity than said liquid, which comprises passing said mixture directly to a zone of a centrifugal rotor free of stratifying discs, centrifugally stratifying solids from liquid in said zone of said rotor free of stratifying discs to form a stratum of solids lying entirely-within said unobstructed zone, passing the liquid from which solids have been removed by said rst-mentioned stratifying action inwardly to a disc-bloc zone of said rotor occupied by nested stratifying discs, subjecting said liquid to further centrifugation within said disc-bloc zone to remove residual solids therefrom, separately discharging liquid, and solids from said stratum of solids, under liquid balance from said centrifugal rotor, passing a hot carrier liquid which is immiscible with the solids and is of higher specic gravity than said solids to the centrifugal rotor and into said solids stratum adjacent the zone of discharge of 'solids from the centrifugal rotor and insulating the disc-bloc zone of said rotor from the zone of said rotor at' which the carrier liquid enters the rotor.

3. The process of dewaxing a mixture which consists o! precipitated wax in an oil solution consisting of oil and solvent of such character, and present in such amount, as to make said oil solution of lower specific gravity than said wax, which comprises passing said solution directly to a zone of a centrifugal rotor free of stratifying discs, centrifugally stratifying Wax from said oil solution in said zone of said rotor free of stratitying discs to form a plastic wax stratum lying entirely within said unobstructed zone, passing the oil solution from which wax has been removed by said first-mentioned stratifying action inwardly to a disc-bloc zone of said rotor, subjecting said oil solution to further centrifugation within said disc-bloc zone to remove residual wax therefrom, separately discharging oil solution, and wax from said plastic wax stratum, under liquid balance from said centrifugal rotor, passing a hot carrier liquid which is immiscible with the wax and is of higher specic gravity than said plastic wax stratum' to the centrifugal rotor and into said wax stratum adjacent the zone of discharge of wax from the centrifugal rotor and insulating the disc-bloc zone of said rotor from the zone of said rotor at which the carrier liquid enters the rotor.

LEO D. JONES.

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