US3159563A - Wax-oil separation process - Google Patents

Description

Dec, 1, 1964 v. ANAs'rAsol-F IETAI.4 3,159,563

WAX-OIL SEPARATION PROCESS Filed July 25. 1960 2 Sheets-Sheet 1 31A f|c.1 I

INVENTORS:

VLADIMIR ANASTASOFF LOUIS J. LANDRY VICTOR E. Mc DANIEL THEIR AGENT Dec. 1, 1964 V. ANASTASOFF ETAL WAX-OIL SEPARATION PROCESS 2 Sheets-Sheei'I 2 Filed July 25. 1960 W 1 Y .l. m R ANH w w HNH .O m A TTM. .M m R J. E 22:: 5....... .2.5: ...i m M s w D l T w m. w m w l V L V B f..

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United States Patent O 3,159,563 WAX-GEL SEPARATIN PROCESS Vladimir Anastasot and Louis l. Landry, Houston, and Victor E. McDaniel, Pasadena, Tex., assgnors to Shell @il Company, New York, NX., a corporation of Delaware Filed July 25, 196), Ser. No. 45,677 2 Claims. (Cl. 208-30) The present invention -relates to the separation of oil and wax from their mixtures including both the fractionation of waxy oils and of oily waxes.

In one conventional process for separating wax from oil, the wax-oil mixture is chilled to a temperature sufiiciently low to crystallize the wax contained in the oil. The precipitated wax is then separated from the oil by high pressure liltration. This type of loperation is limited to oils of relatively low viscosity since more viscous oils cannot be ltered successfully in this manner at the temperatures necessary to employ in order to obtain the desired degree of wax removal. This results in only partial dewaxing of lubricating oils.

When waxy oils of higher viscosity areto be dewaxed,

this is normally effected by dissolving the waxy oil in a solubility for oil over wax at the dewaxing temperature such as various mixtures of benzene and acetone, benzene and methyl ethyl ketone, propane, etc. These solvents are very lluid at low temperatures and reduce the Viscosity of the oil to such an extent that very low temperatures may be employed, so that oil which is dewaxed by this type of operation may have pour points lower than F.

However, the matrix assumed by the wax when precipitated from the solvents adapted for use in such a process results in a wax cake which is very voluminous and porous. This leads to rapid iiltrationgbut the wax retains a large amount of solvent and dissolved oil and its porosity causes it to wash poorly. Such wax cakes may contain as much as 60 percent or more of oil. This type of operation gives a soft wax cake which cracks badly and such cracking leads to very poor washing.y

In normal solvent ldeoiling or dewaxing procedures it is usually necessary to employ relatively largevolumes of diluents if desirable viscosities of the mixture are .to be Such a requirement, of course, reduces the eiiiciency of the wax separation process since itk requires handling unduly large volumes of materials and necessitates the use `of excessive refrigeration in order to cool the diluents to the required low temperatures. While this is decreased to a certain extent by incremental dilution of the waxy oil mixture with diluent, it nonetheless results in the use of large volumes of diluent (solvent).

It has been the goal of workers in the eld of dewaxing to design a process whereby in one or two operations a wax-oil mixture might be completelyA separated into Waxfree oil and oil-free wax. The meager success attending ing temperatures (ltration temperatures) without having the wax set up to a matrix which is essentiallyimmobile or grease-like. n

The so-called delayed injection process wherein initial A limited amount of success has been at-V 3,159,563 Patented Dec. l, 1964 ice injection of solvent is delayed to a point below the crystallization temperature of a majority of the wax, is achieved according to the literature only by the use of slow cooling and of slow `stirring during the cooling period. By slow cooling is meant a process in which the rate of cooling is no greater than about 7 F. per hour. It will be immediately apparent to experts in the art of processing waxes that while a desirable end is achieved in the avoidance of a wax matrix, the process is obviously inetiicient in requiring the use of slow chilling and slow agitation. Y

' An improvement in the process for the separation of waxes from oils has been found 'in which the wax-oil mixture is warmed to form a homogeneous phase and then subjected to rapid chilling while being sheared at a high rate of speed in an enclosed heat transfer unit. The use of this particular chilling device enables the so-called delayed injection of oil solvent (diluent) which has benelicial eiects outlined brieily hereinbefore. With many wax-oil mixtures this process can be used without difliculty and with advantage since it enables the rapid chilling and hence high throughput combined with delayed solvent injection not heretofore found to be possible or practical. y

j However, as wax is crystallized from an oil, particularly in this period, it is necessary in many cases toincrease theV power'input to the rotating blades of the heat transfer unit in order to provide the desired high speed of rotation and at the same time overcome the high viscosity of the oilwax mixture. This high power input may result in an undesirable degree of heating of the mixture thus reducing the ultimate elliciency of the heat transfer unit whose chief objective is rapid chilling. Consequently, with many oil-wax mixtures, the eciency of the unit is substantially reduced and optimum performance is'v not achieved.

It is an object of the present invention to provide an improved process for the separation of waxes from oil. It is a Vspecial object of the invention to provide a process for the improved separation of wax from oil which isV for the rapid separation `of wax from oil wherein initial injection of oil solvent is delayed without previously experienced penalties. Other objects will become apparent during the following detailed description of theinvention.

ln describing the invention, reference willbe made to FIGURE I, showing the type of apparatus required for successful operation of the invention, the FIGURE II, which isa cross-sectional view of the preferred apparatus and to FIGURE III, which is a diagram of a suitable process of steps of this invention. v

Now, in accordance with this invention, an improved process of wax separation'from oil is eectedby rapid chilling of a homogeneous wax-oil solution (mixture) in an enclosed heat transfer unit wherein a 'film of oil and wax between 1A; and l inch thick is pumped through the unit while the film is being agitated by rotating scraper blades which are rotating at a speed of about 20G-800 rpm. and wherein the power input requirement is materially reduced and the degree of cooling in the unit is substantially improved by the presence of 0.05-05 volume y of water per volume of the oil-Wax mixture'. The cooling in this unit, aided by the presence of water,v is suflicient to crystallize at least a major` proportion of the wax pres` tion is separated from the crystallized wax. In its preferred version, the essential steps of the wax separation process is carried out to such an extent that the temperature of the wax-oil mixture at the exit of the high shear enclosed heat transfer unit is at least 25 F. below the average melting point of the wax being crystallized. This optimum type of operation is greatly aided by the presence of a minor amount of water recited above.

The presence of the water appears to function in several aspects. First, the viscosity of the oil-wax mixture is drastically reduced by its presence, thus decreasing the power input requirement to attain and maintain a desired speed of rotation of the scraper blades. This is particularly true when the waxy oils or oily waxes are relatively high viscosity mixtures such as residual stocks and low oil content crude waxes. Secondly, because of the reduction in power requirements caused by the presence of water, the heat generated by the power may be reduced to a remarkable extent so that the ultimate cooling of the oil-wax mixture passing through the unit is far greater than if water is omitted. The presence of water has another function later in the process wherein the wax tends at times to stick to metallic surfaces of the apparatus employed. It has been found that water appears to preferentially wet such surfaces and that the sticking of wax thereto is reduced.

The requirement for use of high shear rapid heat transfer in delayed diluent injection wax separation is based upon the wax matrix which results if a wax-oil mixture is rapidly cooled in the presence of substantial proportions of a diluent or solvent. This results in a waxy structure which forms a bulky filter cake. It has been discovered that the advantages of efiicient dewaxing processes are made practical by the use of the above-described high shear rapid chilling method, since by this means the objectionable characteristics of the wax-oil solvent matrix are circumventcd and solvent injections may be delayed as long as desired.

The desired operation of chilling under a high rate of shear to a point at least about 20 F. below the average melting point of the wax present also overcomes difficulties encountered in this temperature range. It has been observed that the'wax passes through an extremely sticky (soft) crystalline phase at temperatures between about the average melting point of the wax and about 20 F. below. At approximately this lower limit, the wax crystal form apparently changes and provides a more or less fluid slurry which is amenable to being pumped and readily transported.

A suitable cooling unit is shown in some detail in FIG- URES I and II. This cooling unit includes a chamber 26 formed as a thin annular confined space between the peripheral wall 27 of a cylindrical vessel and a comparatively large core of shaft 28 mounted therein. The core is provided with Scrapers 29 which engage the wall 27 and is preferably operated at relatively high speed in a suitable manner as for instance, by an electric motor driven on a shaft extension 30. The speed or rotation of these blades in commercial operation should vary from about 200 to about 800 r.p.m. depending upon the waxoil mixture being treated and the size of the heat transfer unit. Surrounding and spaced from the wal127 is a jacket 31 providing an annular space for cooling fluid which may be delivered through a valve controlled inlet 32 at one end and discharged through an outlet 33 at the other end. A pump delivers waxy oilv to an inlet 34 at one end of the cooling unit and the cooled and highly sheared mixture is discharged through an outlet 35 at the opposite end. The jacket for the cooling medium is preferably encircled by a layer of insulation 36. The waxy oil mixture, preferably initially in a uni-phase (homogeneous) state, is forced continuously through the unit by the action of a pump and is cooled. It may be required to crystallize a major proportion of the wax present in the mixture and most preferably to a point at least about 20 F.

' below the average melting point of the wax.

The injection of water into the oil-wax mixture may be made prior to or during treatment of the mixture in the rapid heat transfer unit. This may be by means of a line or lines from a source not shown in FIGURES I and II. The water may be injected in one step or incrementally. One of the surprising features is the drastic reduction in viscosity which occurs, apparently only under the high shear treatment being effected upon the oil-wax mixture. For example, the addition of 0.1 volume of water per volume of mixture results in as much as about 8 fold reduction in viscosity of the mixture. Consequently, it has been found that power requirements for rotation of the scraper blades can be drastically reduced under such circumstances.

In the cooling unit the temperature of the waxy oil mixture is reduced to a point which is substantially below that at which the wax is soluble in the oil. The extremely rapid rate of cooling obtained in the cooler of FIG- URES I and II is brought about by reason of the fact that the originally warm wax-oil mixture is passed through the cooler in a thin confined layer. Thus, only a relatively small quantity of material is in residence therein at any time. The films on the heat transfer wall are continuously removed and rapidly removed from the wall and mixed with the remainder of the mixture in the cooler. This is effected by the rapidly rotating Scrapers which rotate at a speed of from about to 800 r.p.m., dependent upon the particular oil-wax mixture being treated. Thus, fresh material, as it were, is continuously being brought into contact with the heat transfer wall and the temperature of the mass within the cooler is rapidly and substantially uniformly lowered to the desired temperature with no substantial portion of the mass being cooled slowly on the one hand, or on the other hand below the temperature ultimately achieved by the mass as a whole.

Various other cooling units may be employed providing they have a rate of heat transfer and a shearing device at least substantially equivalent to that obtained in the cooling unit described and shown in FIGURES I and II. lu other words, what is required of the cooling unit is that it shall have a rate of cooling sufiiciently rapid to enable one to take advantage of the delayed injection process (involving the initial pressure of no more than a minor proportion of diluent) while at the same time the disadvantage of slow cooling with slow agitation is avoided.

In the foregoing, reference has been made to a thin confined layer. The word thin is to be interpreted as relative to the diameter of the chamber of the heat transfer surface. Ordinarily the thickness of the layer to be agitated should not be over about l5 percent of the diameter of the heat transfer wall. For instance, a 10-inch diameter chamber might have an 81/2-inch shaft or core, leaving an annular space for a 2i-inch thick layer. Thus there is provided `a large surfaoe-to-volume ratio. This space may vary from about ls-inch to about 3 inches in thickness consistent with these observations.

In addition to scraper blades as shown in FIGURES I and II, the apparatus may contain, if desired, a nonscraping bl-ade provided with a small clearance GAM-1%: inch) to cause a breaking down of any gel structure which tends to form between the oil and wax. This results in a more fluid mixture.

It will be understood that the layer of oil-wax mixture referred to here also includes the minor amounts of water added as described hereinbefore.

In carrying out the process of the invention an essentially single phase, homogeneous mixture (solution) of the wax and oil is first formed. The requirements for this will depend at least in part on the proportions of the wax and oil components. Where the wax is at relatively low concentration, the mixture may already be in homogeneous form, that is, the wax is in solution in the oil. If, however, the wax is present in amounts over approximately 20 percent by weight of the mixture it may be Warming of the mixture to create a homogeneous wax-oil phase.

The success of delayed solventinjection depends upon the cooling of this homogeneous wax-oil mixture to such a point and under such conditions that a major proportion of the wax is crystallized in a separate phase before suiicient diluent is injected into the mixture to provide it with a relatively fluid (non-plastic) body. Thus, while.

it is preferred that this initial agitated rapid cooling be double pipe Chillers.

conducted in the absence of any diluent, it is also possible with some stocks which may require it to conduct the rapid agitated cooling in the presence of a limited amount of diluent sufficient to reduce the viscosity of the wax-oil mixture but insufficient in yamount to maintain the waxyoil iuid at the dewaxing temperature in the absence of rapid agitation. The precise amount which will meet this limitation will vary, of course, from one wax-oil mixture to another.

The rate at which the wax-oil mixture is cooled is far greater than that previously. employed in delayed diluent injection processes. Normally this cooling will be in the order of from about l to about 40 F. per minute, preferably 3-20? F. per minute. l

Following rapid high shear cooling of the wax-oil mixture to such a point that at least a major proportion of the wax present is in crystalline form, the initial injection of diluent is made (unless a limited amount of diluent as referred to hereinbefore was added prior to or during high shear chilling). The diluent may be chosen from any one of a number of diluents (solvents) known inthe art of wax-oil separation. They may be single diluents s uch as aliphatic ketones (methyl ethyl ketone, methyl isobutyl ketone, methyl isopropyl ketone, etc.) or mixtures thereof with aromatic hydrocarbons (benzene, toluene, Xylenes, etc.) of liquefied normally gaseous hydrocarbons such asA propane or other combinations of these or other well-known dewaxing diluents. The addition of fractional amounts of the dewaxing (deoiling) diluent Vto the mixture emerging from the high 4shear chiller results in a sharp drop in viscosity, thus enabling ready transportation of the mixture through further chilling devices and transportation to filters or centrifuges thereafter.

In its preferred form, the diluent is added in a series of stages yas the temperature is further decreased rather than adding the diluentall .in one stage. This is to be referred to yas incremental dilution as opposed to singlestage ldilution such as is used in many prior art processes.

The use of incremental dilution has a two-fold advantage f in that there is a smaller totaldiluent requirement vas compared with single-stage dilution. At the same time,

the load on the apparatus in vvolumes of materialbeing 5 followed byl reduced diluent requirement when employed in the incremental dilution technique.

The mixture proceeds from the high shear Chiller through one or more additional high shear chillers orl through a series of other Chillers normally referred-to as double pipe Chillers. A double pipe chiller involves a pair of pipes one inside of another and scraper blades or their near equivalents are or may be present. The essential difference between this type of chiller and the high shear type previously described lies in the lack of high speed of rotation of the rotating blades within the The blades are present in the latter primarily to advance the flow of the material therethrough and not for providing any appreciable or effective means of shear upon the contents being so treated. Solvent injection may be effected before, during or after passage of the oil-wax mixturel through the double pipe chiller.

The mixture is finally cooled to a filtration temperature which is chosen as being optimum for the particular mixture of wax and oil being treated and is then passed to a suitable separation means which may be conveniently a filter or a centrifuge.

In the operation of the high shear rapid heat transfer unit, the rate of heat transfer varies sharply with speed of rotation of the Scrapers at relatively low speeds. Thus, between 100 and about 200 r.p.m., the rate of heat transfer approximately doubles at the higher rate. However, between about 200 r.p.m. and up to practical speeds in the order of 800 rpm. the rate of heat transfer does not appear to be affected to any appreciable degree by the speed of rotation as long as the wax-oil slurry is reasonably duid. lf, however, the wax-oil slurry is of a relatively viscous character (such as at high wax contents) then the speed of rotation becomes a major factor in determining the change in temperature which may be effected by this apparatus without resorting to modifying means for reducing this factor.

lt has been found that if the oil content is below about 15 percent, the speed of rotation becomes an important contributing factor as far as heat input to the highly viscous mixture is concerned. This effect is especially apparent at relatively slow speeds in the order of 100 rpm. lf the oil content, however, is increased toabove l5 percent and preferably 15-25 percent by weight based on theoil-Wax mixture, the speed of rotation vdoes not become a major concern since at reasonable speeds the degree of cooling is approximately the same for any rate of rotation.

per volume of wax-oil mixture) itiis preferred and more v efficient to utililze two or more stages of incremental dilution of the oil-wax mixture.

Preferably, theinitial dilution (pn'or to or subsequent to passagetlirough the high shear chiller) is inthe order of 0.3-0.75 volume ofV diluent per volume of wax-oil mixture. Thereafter two or more increments of diluent may Theaddition of water .within the recited ranges enables the use of much higher speeds of rotation of the scraper blades without encountering the penalty of heat build-up because of power input forrotation of rthese blades.

The overall heat transfer coefficient of this type of rapid high shear chiller is in the order of 10U-500 B.t.u./ hr. x ft2 x F. As compared with this, the double pipe Chillers have an overall heat transfer coefficient of about 40 B.t.u./hr. x ftx F. Use of the rapid chilling high shear coolers results in a savings in solvent requirement `in the order of 50 percent over ordinary deoiling procedures where solvent is present at all times.

In carrying out a pilot plant scale example of the present process, a crude distillate paraiiin wax containing 8 percent oil, obtained in dewaxingV a medium viscosity lubricating oil, was utilized. The high shear chilling unit, known commercially as a Votator, was operated with the blades being rotated at 200 rpm., the inlet temperature being V10-155 F. and the outlet temperature being about 10S-104 F. In order to maintain a feed throughput rate of lb./hour, a power input of 10.0 amperes was required. However, dilution of the crude wax with 0.1 volume of water reduced the power requirement to 7.5 amperes, a 25 percent reduction.

- "Utilizing the lrapid Chillerl high shear unit a study made of the effect of initial solvent injection showed that as the temperature of initial injection is lowered solvent retention and pore volume of the wax filter cake is decreased. The extent of diluent to oil-wax mixture ratio has a powerful effect upon primary filtration rates. At relatively high ratios in the order of or more the rate is relatively unaffected by the temperature of initial injection. However, at the desirably lower ratios of diluent to oil-wax the temperature of initial injection is a sensitive governor upon filtration rates. Desirable rates are obtained by the use of initial injection temperatures in the order of 90-115" F.

After the wax is deposited on a filter surface it is a desirable step to wash the wax cake to displace any adherent oil film. The time required for displacement decreases as the pore volume of the cake decreases until the wax particles are so close together that the resistance to fiow offsets the lower solvent retention and an increase in wash time requirements occurs. Hence, it is evident that too low a temperature of initial solvent injection can be harmful in this respect. Consequently, optimum temperatures of solvent injection for waxes from intermediate range lube oil cuts appear to lie in the range of 90-l15 F. This temperature also results in a less viscous slurry after addition of solvent than those obtained under other circumstances. This becomes an irnportant factor in that the less viscous slurries lead to reduced pressure drops in subsequent double pipe scraped exchangers even when reduced solvent ratios are employed. Surprisingly enough, increasing the temperature of initial injection above about 115 F. results in a more viscous slurry and under those conditions more diluent may be required.

High shear chillers (one commercially available form of which has the tradename Votator) may be used in more elaborate processes, two or more chillers following in subsequent steps for the most rapid heat exchange under favorable conditions promoting the use of reduced amounts of dilution to obtain a filterable product.

A suitable process involving the steps of the present invention is illustrated in FIGURE III. A crude wax melting over the general range of 130-137 F. and having an oil content of 8-23 percent is heated in an area 1 to a homogeneous state at about 140 F. Water from a source 1B is injected into the melted mass by means of line 1A just before reaching the rapid chiller 2. This is then conducted to the high shear rapid chiller 2 wherein it is cooled at a high rate of shear (200-800 rpm.) to a temperature of 110 F. It is passed through a series of double pipe exchangers or chillers 3 and 4, being reduced therein to a filtration temperature and then sent to the primary filter 5. Fresh solvent is added to the wax cake for the purpose, first, of washing it and then of repulping it for later filtration on secondary filter 6. The repulp filtrate, which comprises fresh solvent only slightly contaminated with oil or soft wax fractions, is recycled and utilized as the diluent throughout the process. According to FIGURE III, it will be seen that this repulp filtrate from a central source 7 is conveyed by means of line 8 and injected incrementally at indicated points along the lines starting with the exit line from the rapid Chiller and proceeding through the double pipe chillers or exchangers. A portion of this repulp filtrate is then utilized for washing the filter cake on primary filter 5. The filtrate from this primary filter is referred to as a soft wax filtrate since it contains low melting point waxes and oils. Since this has been reduced to a low filtration temperature, it is efficient to utilize it in a recycle operation as the cooling medium in one or more of the heat exchangers. Hence, the soft wax filtrate may be sent from primary filter 5 to a central collection point 9 and then recycled through one or more of the exchangers or chillers.

The wax-oil mixtures which may be treated according to the process of this invention include both distillate paraffin waxes and residual microcrystalline waxes. The process contemplates both a dewaxing operation, i.e., separation of a minor amount of wax from a major amount of oil as well as deoiling wherein a major amount of wax is separated from a minor amount of oil contamination. Distillate waxes include not only the normal paraffin waxes but also isoparaflins and naphthenic waxes, associated with the normal parafiins. Microcrystalline waxes are often associated with high melting point normal paraffin waxes and may be fractionated in the process of this invention. In a case where waxes of different solubility characteristics are being fractionated in the process of this invention, it will be understood that the wax which is maintained in a fluid or solution state is regarded as the oil component of the wax mixture.

We claim as our invention:

1. A process for the deoiling of a crude petroleum wax containing 7.5-30 percent by weight of oil which comprises warming the mixture to form a homogeneous phase of wax with the oil, adding thereto 0.05-0.25 volume of water per volume of mixture, rapidly chilling the watercontaining mixture at a rate in excess of 1 F. per minute in the substantial absence of an oil solvent to a temperature at least about 30 F. below the average melting point of the wax, said cooling being carried out in an enclosed heat exchange unit wherein the water-containing mixture is pumped through the unit in a film it-341 inch thick, the film being agitated by scraper blades rotating at 300- 600 r.p.m., the cooling being sufficient to crystallize a major portion of the wax, and thereafter injecting incremental amounts of a cooled oil solvent while the watercontaining mixture is being cooled to a filtration temperature and filtering the crystallized wax from the oil solution.

2. A process according to claim 1 wherein the oil solvent is added in 3-6 increments.

References Cited in the file of this patent UNITED STATES PATENTS 2,260,994 Knowles oct. 2s, 1941 2,274,223 Tuttle Feb. 24, 1942 2,349,039 Goodson et al May 16, 1944 2,397,868 Jenkins Apr. 2, 1946 2,463,845 Backlund et al. Mar. 8, 1949 2,484,728 Pattillo Oct. 1l, 1949 2,567,646 Little sept. 11, 1951 2,743,213 Backlund Apr. 24, 1956 2,903,411 Shuman Sept. 8, 1959 FOREIGN PATENTS 455,667 Great Britain Oct. 26, 1936 OTHER REFERENCES Petroleum Processing, Hengstebeck, McGraw-Hill, New York, 1959, page 254.

Claims (1)

1. A PROCESS FOR THE DEOILING OF A CRUDE PETROLEUM WAX CONTAINING 7.5-30 PERCENT BY WEIGHT OF OIL WHICH COMPRISES WARMING THE MIXTURE TO FORM A HOMOGENEOUS PHASE OF WAX SITH THE OIL, ADDING THERETO 0.05-0.25 VOLUME OF WATER PER VOLUME MIXTURE, RAPIDLY CHILLING THE WATERCONTAINING MIXTURE AT A RATE IN EXCESS OF 1*F. PER MINUTE IN THE SUBSTANTIAL ABSENCE OF AN OIL SOLVENT TO A TEMPERATURE AT LEAST ABOUT 30*F. BELOW THE AVERAGE MELTING POINT OF THE WAX, SAID COOLING BEING CARRIED OUT IN AN ENCLOSED HEAT EXCHANGE UNIT WHEREIN THE WATER-CONTAINING MIXTURE IS PUMPED THROUGH THE UNIT IN A FILM 1/4-3/4 INCH THICK, THE FILM BEING AGITATED BY SCRAPER BLADES ROTATING AT 300600 R.P.M., THE COOLING BEING SUFFICIENT TO CRYSTALLIZE A

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