Патент USA US2134331код для вставки
Oct. 25, 19358.> y 2,134,331 W. P.- GEE SEPARATION OF WAI` FROM MINERAL OIL BY FILTRATION 4 ‘Sheds-Sheet 1 l ì Filed March 31, 1934 rm DN ms mëwQEM,» s QS Wk@NRik |I1.» l| m,., QMRSQ , " INvENToR ATTORNEY Oct. 25, 1938. W. PA GEE ' 2,134,331 n SEPARATION OF WAX FROMl MINERAL OIL BY FILTRATION Filed March 31, , 1954 -4 Sheets-Sheet, 2 . ' Oct. 25, 1938. w;l P. GEF.> l2,134,331 SEPARATION OF WAX FROM MINERAL OIL BY FILTRATION Filed March 31, 1934 4 sheets-snaai 5 y m9 Klv@ INVENTOR _ BYvfwWAM, ATTORNEY Oct. 25, -1938. y2,134,331 W. P. GEE SEPARATION OF WAX FROM MINERAL Filed March 3l , BY FILTRATION 1934 4 sheets-sheet '4 @wee/7 Fkk-up of' ?ÍÍÍe/'Í/y ifea /7/y /76 INVENTOR W/Y//à/r/f/.gâee BY/z/s A TORNEY 2,134,331 Patented Oct. 25, 1938 f -UNITED STAT kSEPARATION » ' `2,134,331> 0FA WAX FROM'. MINERAL> _, , BY FILTRATION " william P. Gee, Plainfield, N. 1.-,'assimor :one _ - Texas Company, New York, N. Y., a corpora- ' tion of Delaware Application March 31, >193:4, Serial No. .718,347 «4 Claims. ` y (cl. 19o-1s) ' ' , l Í _` » ` ` VThis invention relates to an improved process j tempting to .meer preeipltated wax freinr cold of dewaxing mineral oil by filtration, and to an wax-bearing oil, or mixturesfof such oil and sol improved process of continuous filtration ap vent, with a continuous or intermittent typeof , plicable thereto: and the presentapplication is t filter where changev of >temperature is involved, 5 a continuation-in-part of my application Serial the initial filtering rate may be fairly high >but ` it almost immediately decreases and. drops of!" No. 607,270, filed April 25, 1'932. exceedingly rapidly.. This is due torplugging up 'I'he invention contemplates a process of filter ing solid hydrocarbons or paramn wax vfrom liquid . of the pores'or interstices ofthe filter fabric >with hydrocarbons comprising consecutively submerg waxy »material which has- vbecome liquid and penetrated the. fabric'duringthe time- the cake.vk 10 ing a hollow filtering surface within a cold mix and -filter surface is exposed- -in the relatively* warmer zone above the> cold- ñltering. mixture.> .During ,this time the filter cake _and the fi1ter_ surface to form a ñlter cake while the liquid Y ñows through the surface into its’interior, then ` cloth or fabric become substantially'wa'r'mer due 15 moving the surface out ` of the mixture to‘ contact .t with the vvsurrounding atmosphere, ' ture of solid and liquid hydrocarbons during which solid hydrocarbons are deposited on the particularly duringthe cake drying, operation where air or gasis drawn throughthe cake vand through a zone of cake washing, dryingl and discharge while maintaining the filter cake and filtering surface at a temperature below that "at ' the cloth from‘the relatively warmer »surround which the solid hydrocarbons tend to soften or v ings. t Contact with the .warmer gas and'exposure liquefy. During passage of the ñlter surface to the warm surrounding'sf causes. the- wax ~toV through this zone, chilled gas is forced through soften and redissolve inthe oil vadhering toor the> cake and the ñlter surface to maintain the absorbed in the cake, or in the wash liquid, and this solution penetrates the fabric or filtering cake and surface in a cold condition thus pre venting vsoftening or re-solution- of the wax in medium along with thek gas or air which isbeing drawn therethrough».l Upon submergenceof the 25 the liquid contained in. thevcake, or applied 25 thereto as a wash, `with consequentpenetration >'fabric in the cold. niixturein >the bowl of thè . and plugging of the filter 4fabric by the dissolved ' `ñlter, lsolidiilcation of this wax occurs within waxy material. the interstices of .the fabric and >also within the . fibres of the ,fabric itself. Consequently, 'the nl My invention may be employedfin connection 30 with either continuous or intermittent filters. ¿ tering surface soon becomes substantially kcom-_ _`30 One form- of ñlter may, for example, comprise a pletely plugged and iìltration is rendered prac hollow rotating cylinder or hollow rotating leaves tically impossible. with means for creating vacuum within the in- _. I have. found that by completely enclosing and surrounding the exposed illteringrsurface, and terior of the ñlter element or for exerting posi 35 tive pressure upon the exterior thereof. In operation, the rotating cylinder is kept ., l ' circulating -chilled gas throughthe surface dur ing the time it is out of contact with the cold partially submerged in ~the Afiltering mixture. ' filteringmixture so as yto maintain the tem Solids are deposited on the submerged portion #perature of the cake as well as that ofthe fabric of the surface to form a cake while liquid ñows . at -substantially `that of the- coldmixture, >or nearly so, I am able to prevent the aforemen >40 through the surface into the interior of the cyl ~ _ inder from which it is withdrawn asfñltrate. tioned plugging effect. By this means, I am As the. cylinder rotates the cake is exposed able .to maintain a continual high economic rate whereupon it may be dried and washed byap of plying `solvent liquid to the surface ofthe cake, 45 the liquid being drawn through thecake into the interior ofthe cylinder for removal. The'cake filtration. v g , Y l. 50 pressure to the interior of the filtering element . - , Fig. l is a diagrammatic `view of apparatus for carryingv out the method of the present- in vention; _ . _ t . causing distention of the fabric and consequent - Flg.».2 is a diagrammatic viewof a modified loosening of the cake, complete removal of which arrangement, .illustrating t, the `invention as lap plied to a ñlter aid dewaxing process with'VA re is facilitated by suitable means located adjacent ‘ to the exterior surface of the filter fabric. , f 55 . ing drawings which >>disclosepreferred embodi-VY may bey subjected to further drying to remove ’l ments of the invention, and in which ~ remaining wash liquid following which the cake is removed, usually by applying a slight reverse .~ In orderto better understand the invention, reference will now be made to the accompany Experiments have indicated that when at covery` of illter aid; - ' _ „ . Fig. 3-is a diagrammatic view of still another amasar modified form of apparatus for carrying out the ing liquid, such as naphtha,_for example, from method of the present invention in a plant in which filter aid is not employed; Fig. 4 is a diagrammatic view illustrating the filtering cycle and the method of supplying wash f ing solvent to the filter cake; Fig. 5 is an elevational view of a continuous* filter suitable for carrying out thepresent inven tion, certain> parts being broken away and in 10 section in order to illustrate the construction a tank I3 is applied to the surface of the nlter cake through a pipe I4 and a nozzle I5 positioned within the hood G adjacent to the filter cake. 'I'his spray liquid is drawn through the cake into the interior of the drum and is separately with drawn therefrom through the'hollow shaft l, filter valve l and pipe IO into the storage tank Il. The vacuum pump I I also communicates with the tank Il by means of a pipe I1 for the 10 purpose of creating a vacuum in the tank and Fig. 6 is a perspective’view of a portion yof'- also within the interior of the filter drum. This the filtering surface; vacuum is continued «after the filter cake has ad Fig. 7 is a partial sectional view taken on the _vanced beyond the nozzle I5 to permit drying the 15 plane of the line 1-1 of Fig. 6; and cake and maintaining it in a cold condition by Fig. 8 is a partial sectional view taken on the drawing cold gas therethrough as will now be 15 plane of the line 3_8 of Fig. 6. . explained in more detail. »Referring to Fig. 1, the wax-bearing mineral While the vacuum pump II is shown as taking oil, such as cylinder stock, is advantageously direct suction on the tanks `III and I3, it may be 20 mixed with a solvent liquid or wax-fprecipitating _ _advantageous to interpose a foam' trap between medium. This solvent liquid may comprise a these tanks and the vacuum pump to remove thereof; . light petroleum fraction, such as naphtha or vari "entrainedmatter from the gas. _Such a trap is preferably mounted about 35 or'40 feet above the ous otherV organic solvent liquids or mixtures thereof, including alcohols, ketones, aldehydes, tank and ' provided with a water' leg through cyclic hydrocarbona‘benzolor its homologues, or which liquid matter removed in the trap may be derivatives of these various‘materials. ‘ drawn The mixture of oil and solvent liquid is deliv ofi'. y ' ` o ` The exhaust gases from- the vacuum pump II ered from a source not shown in the diagram and ' arel advantageouslyk conducted, directly to _ a gas conducted through a chilling coil I wherein it may be cooled to a temperature of around 0° F. or below. The chilled mixture is then introduced to a mixer 2 wherein itis admixed if desired, with a comminuted solid filter aid material introduced to the mixer from a hopper 3. The mixer is pref erably provided with a jacket into which a refrig erant may be introduced. or through which it may be circulated in order to maintain the mixture in a chilled condition. Y cooler I9. If desired, a fan or blower I8 may be used to reduce the back lpressure on the vacuum The cooler I! comprises a column packed with Raschig rings or other'sultable packing means. Cooling liquid, preferably the solvent being used such as cold naphtha, at a temperature, for ex-` ample, of about >--40° F., is sprayed overlthe packing by which means it is brought into inti mate contact with the gas passing upwards there o _’ This chilled mixture of oil, precipitated wax 40 and filter aid material is then conducted to the bowlzfâ' of a filter 4. through. The naphtha collecting in the bottom of the column, and at a temperature of about- This filter is advantageously ' +40° F., is withdrawn by a pump 20 and passed of the continuous rotating drum type, somewhat through a >chiller 2| wherein it is again chilled by similar -" in general principles to that ' employed interchanging heat with a refrigerant. Liquid heretofore in industrial .iiltrationg The exterior ammonia may be expanded into the shell of the vchiller to effect the necessary refrigeration. The temperature to which the naphtha is 45 of the filter shell is'covered` with heat-insulating’ materialto facilitate maintaining the interior in >a cool condition. y ‘ ' ' chilled depends on the extent to which it is de During rotation of the hollow drum 5, the cy sired to cool the gas, -and this in turn depends lindrical surface thereof, comprisingv a filtering ~ upon the character of th'e solid material being Y50 surface or medium formed from cloth or metal fabric or any porous' filtering material, passes’ through the body of filtering mixture maintained in the bowl 3' of the filter, and then .emerges therefrom during passage through the upiîe?’and Filtered. 'Usually it is desirable to keep the cake at’ substantially the same temperature as the rntering mixture. ‘By maintaining the ybottom of the column at a temperature above +32° F. any water removed from the gas may be withdrawn ' ` from the bottom of the column. It is desirable 55 55 hooded portion 6 of the filter. The precipitated wax and admixedá‘ïfllter aid ~ to keep the circulatinggas free from water which material is deposited upon thelexterior and sub: merged portion of thesurface to' form î‘a filter might penetrate the cake and the fabric'and deter filtration. ._ ~ ' _ > - cake, while the solvent'ari‘d dissolved oil are forced Y ` The chilled gas at a temperature, for example, 60 through the filter surface into the interior of the of about _30° F., is then conducted through a 60 drum. The liquid~ within-the interior of the drun-l pipe 22 to the hood 6 of the filter wherein it _sur is withdrawn therefrom through the hollow ro- ~ rounds the filtering surface during its emergence tating shaft ‘L_„the filter valve 8, the pipe 9 in com from the filtering solution. This chilled' gas is munication therewith, and into a. filtrate'storage forced through the filter fabric prior tovandy sub sequent tothe removal of the filter cake there tank _HIJ -'The tank Ik is maintained under a re duced _ pressuregfby. ‘means of vacuum exerted from.4 In this way, the cake and- the filter sur through a vacuum‘punip o II communicating with face are continually maintained at a temperature the top of the _tank through a pipe I2.'v When that portion o_f filter surface over'which 70 ñlter cake is deposited emerges from the _cold filtering, mixture into the hooded portion, of the filter, the application of vacuum upon thein terior -of that portion of the surface .is continued substantially nearly the same as that of the cold mixture undergoing filtration; for' example, in this case at a temperature of from about 0° F. to _10° F. ‘ ' ' 70 ' ‘ To take care of gas losses, fresh gas may be drawn from the storage tank or gasometer 23 by the fan I8. Q The gas referred to herein may in 75 tained in the cake. Upon further rotation, wash-_ ' clude air, flue gas, hydrocarbon vapor, fixed gases 75 _ ~for the purposeyof removing mother' liquor con I have found it of advantage to use -ñue gas which~ is relatively ~ auch as `nitrogen and so forth. inexpensive. - '. ` ' ' - The cake is discharged from the ñlter'surface lafter washing and drying by introducing, for a short period of time, a positive gas pressure to the interior of the particular segment of the'filter drum in> question, causing the- filter fabric to bulge and loosen the cake which is then removed 10’ therefrom by scrapersv24. This reverse gas pres sure may be effected by introducing chilled gas through the filterv valve >8 from a line 25 leading Y from a suitable Vsource of supply, aszfor example, the cooler y15 I9. . . » , covery. The wash- nltrate ~-discharge may' be` in common with'the oil filtrate discharge, as shown, where' the wash filtrate is passedV froxn'ta‘nk 50 » by pump t4 through lines 65 -a'nd 62 to discharge 63~for solvent recovery. Lines 4| andïf5|ï~are - 'provided with valves 4|" and 5|’ respectively.-> so f that the vacuum 'producedby-pump ` 46 inthe " tanks`40 and 58 may be independently controlled.y -’ Inl-some gases, fit 'is found «desirable to‘maintain 10 La higher vacuum or pressure’l differential’on they ` `filtering surfaceduring the _washingstage than during the- pick-up' or cake forming'stag'e. vFor i examplepimproved results have been> secured by » The dislodged cake removed'from the filter sur face falls through thev chutes 26 into a closed storage tank 21 from which it may be withdrawn lfor further treatment including the removal therefrom of retained Aoil and solvent as well as 1 for the Aseparation and recovery of the filter aid .materiaL point of `storage for `distillation forflolvent re-l ' While a vacuum type of continuous ñlter has maintaining a vacuum'v or pressure differential of 15 about vl5 inches of -mercury on the filtering sur- , , face during the time that the -filtering’ sur'iîface'ïis'` immersed in the chilled wax-bearing mixture and when the cake is being built up on the filtering surface, and` a vacuum orY pressuredifferential 20 l `of about 25> inches of mercury onthefiltering surface throughout the washing and drying vpor been described, it is contemplated that the in tion of the. cycle.v> This‘ is conveniently effected vention is equally well adapted `to pressure filtra by adjustment of the valves~ 4|* and 5|’j`which tion wherein superatmospheric pressures may be «controlthe‘ application of suction to the men- " as maintained on the exterior .of the filtering sur tioned stages' of the filtering cycle ,through the face. lines`39 and 49 respectively. ’ ' Referring to Fig. 2,v there is disclosed a plant for filter` aid dewaxing by continuous filtration with continuous recovery'of filter aid, in which a foam trap is mounted between the filtrate and the wash solvent tanks and the vacuum pumpin the manner described above.Y Wax-bearing oil is supplied from line 30 by pump 3| through heat exchanger 32’~ and chilling coils 33 to a mixing tank 34, where it is mixed‘with recovered filter aid supplied through chute 35. 'I'he mixture then passes by line 36 to an enclosed rotary vac uum `filter 31 `of the type described above, and which operates with a. continuous filtering cycle \- The mixed wax and filter aid continuously re- ' moved by blow-back 58, assisted if desired bya ` suitable- scraper of defiector blade, falls vinto a-` so discharge trough 18 containing 'a scroll 1 I, which ' »feeds the material to a discharge 12 terminating in' 'a -hopper -13, `which in'turn feeds through chute- `14into~a hot mix tank 15. A solvent, such as vnaphtha, is» supplied tothe >'tank by linej_16. l35 The tank-is equipped vwith a suitable agitator and a steam ~ coilV or .ietÀ (not shown)`, whereby the contents are mixed and heated to dissolve >the waxin the’sol'vent andv to form a pumpable' >slurry of‘the’filter aid suspendedin the 'wax including pick-up or cake forming, washing, dry ` solution; The slurry iswithdrawn through line ing -and cake discharge. In the cake forming 11 by pump 18 and passed by lln'e`_19\to a‘conf `stage, filtered oil is discharged from thefvalve 38 tinuousenclosed filter 88, which may be of simi of the `filter through line 39 to tank 49. >Thelat A.lar constructionv to the ñlter 31, operatingjwith 45 ter is connected by line 4| to a common suction stages of pick-up, washing, Adrying and Acake >dis 45 line 42 leading to a` foam trap 43‘having a gravity charge. _In rthe pick-upv or" cake.P forming stage leg 44 through which any trapped or entrained ofthe'cycle, the; filtrate of wax >solution is'dis' liquidi» is discharged into a barometric’seal or chargedfthrough the line 82 into tank 83, from ' drum, the separated gas passing by line 45` to the which the wax solution maybe withdrawn by suction side of vacuum pump 46. Chilled wash solvent, supplied by pump 41 through chiller`4'l' and line 48 to the distributing means of the filter 31 at the washing stage of the filtering cycle, passes through the filter cake; and the mixed 55 Wash solvent and extracted oil discharges through line 49 to solvent storage tank 58. The latter is connected by pipe 5| to the common suc tion line 42 leading to the foam trap 43 and, thence to suction pump 46 as described above. The separated gas'is suppliediby pump 46 under pump 84 andy passed through line 85 for‘recovery 50 of thev solvent from the contained.. wax.v The upper portion of -tank 83 communicates by lines 86 and`81 with a foam trap 88 having .agravity4 discharge leg 89 for any enti'alned liquid, and >a gas discharge‘90 communicating with thesuction 55 side ofavacuumjpump 9|` which dischargesv into an equalizlng tank`92. Gas from tank 92 passes through lines 93 and 94, the latter- containing pressure reducing valve 95, tothe interior of the casing ofthe filter'88, to completethe‘g'as cycle 60 pressure through a preliminary cooling tank 53 which minimizes solvent loss.- During thewash and- a chiller 54 to`line 55, and then’through ing stage on filter 80'„`heated wash lsolvent,'such ' pressure- reducing valve 56 to the interior of asnaphtha, supplied from line l96 by pump „91 the filter casing, to continuously maintain the through heater 98 -and line 99, is' directed Lonto chilled gaseous atmosphere surrounding the fil the formed~filtercake lto remove contained'wax es tering surface. Chilled gas at a suitablev presi solutionl therefrom. -The vresulting “solution is sure, such as about 2 to 5 pounds gauge, may Withdrawn iìhrougii‘llrie- |00 tó Solution tank Inl, be passed through branch >58 to the proper pas the' vapor spacev'of which’j is connected by line sage .in the valve 38 Voi’ the filter, to assistV in ` |02 with the common 'suctioniine a1 leading to" 70 the discharge of the cake in the blow-back por-- foam trap 88 and vacuum pump 9|.' The 'resulte 70' tion of the cycle. Dewaxed oil is withdrawn from ing solution is_ withdrawn from tank |8| byv pump tank 40 by pump 60 and supplied through lines 6| and 62 to the heat exchanger 32, where it serves to partially cool the incoming oil »to be 75 dewaxed; and then passes by line 63 toa suitable |03 andï‘returnedby line 16 tovserve,asfsolventl liquid in the hotrmlx tank 15. "Pressure'gas from line 93 is >supplied by'branchy line '|05 as bloW-. back tov remove the washedand drled‘ cake of , . 4 arena: nlter aid material from nlte'r l0. VThis cake is «ma m. ma thence by une m controlled by discharged into chute Il, which returns the filter valve |24- to »continuous enclosed filter indi aidto mixer“ for reuse in the process. ' cated generally at |24. A drain line |25 con , VA- pump |05 withdraws flue gas from a genera trolled by valve |25 is provided for draining the tor -|01 through a scrubber and dehydrator |00, filter tank.;Í . i . and forces the gas under a controlled pressure 'I'he continuous filter may be of the type pre intoa gasometer |08, which maintains a bal viously described, operating with stages of pick _anced pressure on the system. vFlue. gas is sup up, washing, drying and cake discharge. In p1ied¿from_the gasometer |09 throughv line ~||0 the pick-up or cake forming stage of the cycle, to the interior ofthe filter casing 51 by means filtrate is discharged from the usual control4T of line |I|, and t9 the interior of> filter 00 by valve> |20 throughl line |29 to tank |30. Wash 10 ymeans `of line H2.. Thevgasorneter thus fioatszon 2filtrate is discharged through line |32 to tank the system, supplying a small amount of make |33. 'I'he upper portions cftanlrsv |30 and |35 up gasas required-to maintain the desired-quan communicate through lines |35 and |31, respec 15 tity andpressure of gas within the system. The tively provided withvalves |35and |39, with a pressure within the gasometer |09 isV controlled 4to the desired pressure which is to bemaintained withinv the filter casings by suitable regulation of pump |05. . _» common suction line |40 leading to a foam trap |4| having a gravity discharge leg |42. >Gas is withdrawn from 'foam trap> |4| through line |43 l by vacuum pump |44, and supplied under‘low pressure to preliminary cooler |45 and thence 20 ploy filter aid kin connection with the dewaxing through chiller |45 and line | 41 containing pres of certain distillateand residual oils by filtra vsure reducing valve |48 to the interior of the tion. It has now been found that the use of filter closed filter casing to maintain the-chilled gas It was formerly considered essential to em aid can be dispensed v with in certain dewaxing -processes employing filtration. »This is advan tageously accomplished-by the >employment of certain selective solvents . or solvent mixtures. which at lowered temperatures aresolvents for the oil, but in which the precipitated wax is sub stantially completely insoluble; or by the use of solvents'of low viscosity which give a crystalline wax on chilling. Examples of such selective sol vents include a ’mixture of acetone and benzol, and a mixture of acetone, benzol and toluol; and propane is an example of thelatter. typeof; sol vent >of low'viscosity.` Very satisfactory results have been secured where a `solvent consisting of substantially 35% by volume of acetone and 65% by volume of benzol is employed in the ratio >of from two to four parts of solvent mixture to one part of wax-bearing oil. ~'In the case .of residual oils, a very satisfactory solvent mixture consists of about 28-35% acetone, ifi-57% ben-_ zol and 15-l8% >toluol in substantially the same proportions of solvent mixture to oil'. In „such case, it is also found highly desirable to wash with the same selective solvent mixture. By the use of a solventmixtureV of this character, the wax is precipitated in a formwhich admits of satisfactory filtration at commercial rates. By the Ause of such a selective solvent mixture for washingv the formedA wax filter cake, re-solu tion of some of the wax is avoided, and conse quentlythe oil removed in the wash stage has substantially the same pour test as the filtrate, whereby the two `may be mixed to give an in creased dewaxed oil yield of the desired low pour test. l When this is coupled with a gas recircu lation system of the character disclosed herein, which maintains the filtering surface >at all times at substantially the -temperature of the wax . bearing mixture being filtered,- successfuliopera tion of the fllter'over substantial periodsof time is assured. Thus, by the cooperation of the several features,- including the precipitation of the wax in a Vmore suitable form for filtration, the maintenance of the filtering surface vin a . condition of high effectiveness, and the avoid ance of re-solution Vof the wax cake, separation 70 of wax by continuous filtration may be accom plished without the use of filter` aid. _ . Referring to Fig. 3, there is shown a simpli fied plant for continuous filtration, in vwhich filter aid is not employed. The chilled wax bearing oil is supplied through line |20 to feed - eous atmosphere therein. _ . - » Where a solvent.l mixture of the character offv acetone-benzol'is employed for dewaxing, it is found desirable to u_se an indirect chiller'. |45, rather tharï>4 the direct chiller shown vin Fig'. l. For’example,- the chiller maybeof suitable heat exchanger construction, having a bank of tubes through which the> gas passesin indirect'heat exchanger relationship with a refrigerant,l such for example y.as chilled brine,- ammonia, SO2 or other suitable- refrigerant. A branch line |49 leads from chiller |45 to an auxiliary pump |50, » which serves to force chilled gas at a regulated positive pressure, which is independent of fluc tuations of pressure in the main circulation sys tem, through the blow-back line | 5| for discharge of the cake.y _ . . A liquid dischargepump |53 servesto dis charge the oil filtrate and the wash filtrate through lines |54 and |55, respectively controlled by valves `|55 and |51, to a'discharge line |55 leading `to solvent` recovery. Pump |52 draws flue gas from .generator |53 through scrubber and dehydrator |54, andY discharges the gas into .gasometer |55. From the latter, gas is supplied through line |55 to line |41 beyond valve |40, ` and ythus to the interior of the filter casing, to make up for any gas loss and to maintain the quantity and pressure of gas within the circu lating system. Inasmuch as the gas loss is very small, the quantity of gas passing from the gasometer to the, filter casing is insufficient to materially affect the temperature ofV the gaseous atmosphere therein. ~ _ » Fig. 4 shows diagrammatically and in outline 'a rotary vacuum continuousÍ filterof the type used in Fig. .1 to 3 for wax filtration, with the fll teringy cycle indicated thereon. rThe filtering sur face is shown at |1||,A and is divided by division strips | 1| into a plurality- of longitudinal seg mentafindicated as 2,4 in vnumber about the pe riph’ery of the filter, although of course' the number >may bevaried. The customary filter valve which controls the application of suction and the'` supply of pressure blow-back gas to the interior of the filtering segments at various stages in the cycle of rotation of the filter, is indicated Aat |12. The liquid level of the chilled wax-bearing mixture within the vat or casing of the filter is shown at |13. The filter rotates in the >direction of the arrow |14, and cake formation starts at |15. Atrthis'point. the filter u 5 2,184,831 valve opens to communicate suction to the ñlter-V the terminationv of the vacuum andthe initia ing surface, which suction continues throughout , tion of _blowfback at„|9i.` At this point, chilled gas~ under pressureisdischarged throughr the n the extent of the _immersed portionof` the filter, ‘ rpassage in the valve to'theuinteriorsof the seg to provide the pick-up'or cake forming'uare‘a y|16. ments of the filter, _#causing distention v‘of the vassisted through the> filtratezline as previously, described. ’ filter cloth asindicated »at |82.` Á As the ñltering’segments consecutively -emerge by’thejscraper|93,"serves to` remove the formed from the "chilled mixture, their communication and dried filtercake. ‘The reverse'ìflow of chilled with the filtrate outlet is cut ,oi‘fa’t'` |18;‘and gas or blow-backterminates jat |84, and a; full .'I'hefiltered oil fromv this section is discharged 10 afterashort rotation, _communication with Vthe ' block indicated‘at |95vseparates'thetermination 10 washing'and drying discharge po'rt of the valve is initiated at |18. Theaction of the vacuum then creates .a pressure differential on` the filter , ing surface, which causes the chilled gaseous at of 'the'cake discharge` zone from> _the beginning of the rcake forming,v zone at l'lñçfwhereupon the cycle is repeated. ' "_" '_ y . n c In fdewaxingI ,byy pressure filtration, it `has ¿been surrounding the -filter to act upon'fthe customary ~to employ pressures, ‘of from about 15 mosphere cake. during the drying stage |80, to Adrain or ' >>‘foto oofpoundsper squareA inch or. higher. Í In ' _strip retained oil from the cake. The washing applying‘the principles of pressure',` `filtration tor .of the drained cake then commences, asjindi-A , an ‘enclosed vacuum filter, the, obvious thing cated at I8I. y So far as I am aware„all prior suggestions for washing a wax _cake on a filter have beento l is to use a gas pressure’within the’ filter casing ofv substantially thisA amount, Mini.’ order n to` in crease v_the pressure` differential" acting onjthe apply sprays of washing solvent thereto. I have filteringv surface, with‘a view to increasing fil-v` discovered that superior resultsl are obtained by ltering'rates and capacity. ¿I have found, how supplying the washingy solvent- to the cake in -ever, that instead of being'beneiicial, such in theform of a continuous- liquid film 'which iiows creased pressures may beyaçtually harmful, `due 25 ._ continuously onto the cake. This is accomplished Y to the reduction in filterirígffrates. This' is'> ap by the weir feed, comprising the trough |82 parently vdue -tothe fact Y, that' the wax‘cake,l which is mounted yto extend- longitudinally ` tends to compact under >the increased pressure, "throughout the length ofthe ñlter, ’beingsup thereby` losing its pervióus'__fo_rm of interwoven _ walls. ‘Washing solvent is continuously sup " imperviousi‘mass." -In accordance with the "pres ported in any >suitable manner from the casing ' crystals, and becoming more'or lessl of va slimy plied to the trough by"supply pipe |83 so as to ' ent invention, the 'u chilled 'gaseousatmosphere!` e maintain a continuous overñow‘at ,the Weir |80. within :the viilter’casing' vis purposely maintained tion opposite to the direction of rotation of the ed. This'is preferably 'accomplished by' main- . 'I'his forms a sheet or vfilm of liquid throughout >at'such a pressure that a pressure‘differential on the length of` the filter, which flows down an "thejfiltering surface equivalent to notA more than 35 about 15 to 20 poundsper square inchjisaffo'rd inclined guide |85 onto the filter cake in a direc filter. Sufiicient washing liquid is supplied so a taining the gaseousv atmosphere within theiilter casing- at substamtiallyï'atmospheric- pressure, `or‘ as to maintain’a thin liquid film over the ex posed portion of the filtering surface substantial- ’ at, onlya few pounds above atmospheric'l pressure, 40 ly throughout the extent of the washing zone the pressure diiîerentialfbeing then secured'byv indicated at |86, the film being of course thick- ' means of vacuumappliedbyi‘thevacuum pump.: er at the upper portion adjacent the weir feed. The outer portion of the film flows downwardly over the filter cake countercurrent to the direc tion of the rotation of the filter, _while the in yThis is-` efiectedin Figs. Zand 3 by staging down the pressure‘of the gas being vreturned -tothe filter casing, as bythe pressure_.reducin'g,valves 56_and |48 respectively. This' has' the further ner portionof the >film adjacent thecake as- ` advantage of" minimizingfgas leakage, thereby . sumes movement along with the filter cake. The c avoiding loss of associated solvent vapor. pressure >differential existing upon opposite sides of the cake land liquid `film, tends to force the -wash liquid down into the cake to'displace re `Previous practice in connection with enclosed vacuum filters employing a pressure gas atmosf 50 phere therein, has been to either enclose the entire filter in alarga casing Vforrningin effect y of wash liquid supplied, and the extent of the` Va filtering room,vor'tofattempt to secure the washing zone, is controlled to afford substantially 'cover of the filter casing to the vatY creasing maining oil therefrom. Preferably, the quantity complete displacement of retained oil _from the proper is gas tight relationship byy bolting' with 55 the aid of sealing gaskets.` The former'pr'actice solvent which would needlessly drain` through the cake after oil has been expelled. This dis the objection that frequent removal of the cover, 55 cake, while avoiding the use of an excess of is highly expensive; andthe latter practice has , which is `necessary for adjustment, repairor re use of wash solvent, obtains an increased yield placement of parts, renders it diiliculttol main 60 of dewaxed oil, and avoids solvent loss which I ' tain the proper- sealing »relationship when> the ' have found toi'be inherent in the use of sprays, cover is replaced. The presentinvention overcomes these objec when volatile solvents are employed. placement weìr wash affords ìeconomy lin-the Following the washing zone, the cake is then subjected tofurther pressure differential during the drying stage |88, at which time cold gas from tions in the manner ‘shown inA Fig. l15,'in'which a commercial formfofuenclos‘ed vacuum @filter is shown inl end elevation. The_iilter casing 200 the atmosphere surrounding the filter is drawn lisxformed. ,at its upper endwlth an 'outwardly through the ñltering surface to displace 'wash extending flange 20|." Entirelyv about the'inner _solvent as well as to maintain the filtering sur- j 1periphery of the‘upper portion‘of casing Y200 is ' a narrow trough 2702, 'to which is suppliedy a `suit 70 face chilled to a low temperature. The liquids able sealing liquid 203. The removable cover 204 and gases drawn through the filter during the zone from |19 to |88, at which latter point the yis formed with a surrounding reinforcing bar discharge passage is closedby the valve, are 202iV carryingan outwardly extending flange A206 discharged through» the _wash solvent line as adapted to seat upon the` flange 20| to support the cover. The latter carries-a'ldownward‘ly ex 75 previously described. A full block |90 separates ` 65 70. . 8,184,881 tending flange 2li about lits periphery, which features of -the present invention were incor depends nearly- to theV bottom of the troughV 202, porated. The advantages of this method of con and thus provides a liquid seal. Due tothe fact . tinuous filtration over the heretofore used inter that only- a.. comparatively small gas pressure is " mittent pressure filtration include such consider ` maintained'within the filter casing, a >compara ations as greatly increasedplant capacityl for a tively shallow trough .202 suflices to maintain 'given - amountfof ,fllten area, simplified _plant , the liquid seal. V_The cover is equipped with longi ' operation;y simplified means of applying a `dis-v `>t'udinally extending handles 208'at opposite sides placement wash tothe filter _cake so' ‘as to obtain thereof, by which the cover may be attached to highen yields, Y and lconsiderable reduction.` in 1 suitable chains or hooks of a conventional lift installation costs, l* ing mechanism or hoist, so that the >cover may . -beeasily and instantly removed andreplaced. ll has been to fasten‘the filtering cloth- over the filter .by `means of an exteriorwire wrapping, _’ generally in >the fermer a splrauy wound wire. 1 factory` discharge of >awax cake. The scraper , . s tinuous filtration 'for' yvax separation has >here tofore proved impractical in the industry, two fPrior practice ingthe' -construction of rotary drum ñlters of the lcharacter disclosed herein, ~ have found that this `may interfere with the satis _ " While thereare a'nuìnber of reasonswhy con of thev outstanding reasons are no doubt First: _ The inability to maintain `the filtering surfacev in highly effective filtering condition throughout a long period of continuous'operation, . and , , ‘y i Second:;The inability to `continuously form a filter cake at commercially 'practical rates which or deiiector, which assists in removal. of ythe , cake, generallybears against or near this outer s could be satisfactorily removed from lthe con wire wrapping.l Consequently. there ,is a sub tinuously rotatinglfilter. ‘.` ' ' ' lstantialsgap between the scraper and thefilter The first_reason for failure asl notedabove, ing’surface depending on the size of the wire has been overcome by aV combination of features used; Due to the peculiar natureof the „wax of the present invention, including the chilled _, cake, a portion fof the wax tends to be ,retained about the wires on either sidey thereof, which ` eventuallymay slime or plug the filtering sur faceto a certain~ extent, reducingfiltering rates. gas recirculation/system which maintains the fil tering surfaceat all times at a temperature ap proximating that’of the chilledVwax-bearing mix ture being'filtered," such as to prevent re-solutlon of the wax'with plugging ofthe Afilter cloth; the This is overcome in >accordance with the present invention by the construction shown in Figs. 6 use of wax-bearing mixtures resulting _from sol- ‘ to 8 inclusive. Two ofthe longitudinal segments yent dew’axin'g of suchv character that the lpre y ' ' ofva sealing V.conventional blocks'for the, filter ends areofshown, the filter thechambers >annular as ofthe segments being indicatedat 2li. and the division between >two segments at 2li. Indi vidual filterV clothsA 2l2 are provided> foreach segment. Along’ the end surfaces of each seg ment. as indicated at 12H; the filter cloth is 4o caulked in place within a. mortise and tenori type of >groove >2M (Fig, 7) >extending about the pe' riphery of the blocks 2|0.` The filter cloth >is laid over the grooves, with a substantial extent overlapping the blocks 2N;V and then a cotton 45 rope or other suitable cord is pounded into the groove as shown at- 2lb, thereby forcing the filter cipitated wax is in a better: form for filtration; `the employmentl for washing >of the cake of a selective solvent 'mixture'of such character that the wax is substantially completely insoluble >therein- at the temperature of treatment; and the use offiltration pressures or pressure differentials, together with a reduced filtering timeper cycle” i to which'jtheöwax cake is subjected to such 40 pressure differential, such that compactlng of the *_ cake down 'into the pores of the ~filter-cloth is avoidedT y Y Y l r , .In explanation of thes'econ'd reason for failure noted above', comparison is4 herein: made with the customary practice of dewaxing on intermittent cloth securely into the groove and lockingit in pressure filters. A typicalfilteringz cycle vonrthel place therein. 'I‘he construction is such that vthe _latter is the following: „ adjacent portions yof the cloth at the upper end The period~ of filtration, in `which the filter of the groove, indicatedy at 2IS, are substantially . press -or pressure filter is filled with the chilled 50 in contact witheach Aother.Y Fig. 8 shows the. wax-bearing mixture under pressure, and the oil vmanner in which the side _edges ofthe individual forced through the filter cloths while the wax filter cloths are fastened in place. 2|! is’a ,builds upin a cake on the exterior thereof, gen-4 division strip which extends longitudinally of erallyl consuming .about 20~ to 30 minutes; the period of >blow-back, in which the wax-bearing 2i9. yOverlapping portionssoftwo adjacent cloths mixture remaining in the filter at the termina 2|2 are secured within the groove by a longi -tion of the filtering operation is blown back to _Ítudinally extending caulking rope 220. kThe 55 the filter,land is provided with a slmilargroqve >outer surfaces of the cloths »arethus free and fully exposed, giving full filtering area, and en abling the cloths to be more euectively distended by the blow-back gas, to thereby secure an efii 'i cient discharge ofthe calce.` Í-v _ The advantages'of continuous filtration on ro 65 tary vacuum filters> orv analogous ~continuous filters as opposed to intermittent'V filtration on pressure filters orfilter presses, has long been recognized in the filtration art generally. 'I'here ¿. have been lscattered proposals to employ con- ‘ 70 tinuous rotaryfilters for dewaxing. The fact Are mains, however, that priorvto the invention dis closed herein, `the dewaxing art continued to em _ ploy the old intermittent pressure filters or filter presses. Successful dewaxing on continuous fil 75 ters on a commercial scale was not achieved until the supply tanks,- generally consuming about 3 to 5‘minutes; the period of washing, in-,which the filteris filled with wash solventV under «pres sure to wash- retained-oil out of the cake,_gen- erally consuminguabout 15 to 20 minutes; ythe period of drying, in which gas pressure .is ap V.plied to the filter cake >to remove retained solvent', ` generally consuming about 10 minutes; andthe~ period, of removing the wax >cake from the filter, generally >consuming about 10 minutes. It is thus apparentvthat the overall filtering cycle consumes approximately 5‘0 >to' 65 minutes, in Y which less than 50% of that time is‘employed in 70 actual wax filtration; A Applying the above periods of time to a con tinuous filtration cycle necessitates that the filter»A rotate at an extremely low rate of speed, given difficulties in the drive and reduction gearing 75 2,134,331» 7 . therefor. In attempting to speedup the. con nitrati@ rates' during continuous nltr'anoh. „In tinuous 4filter by reducing the time for-,the ~`vari explanation, it is pointed .outA that Vthe actual ous operations vcarried out in theY cycle, difficulty rate of ñow of a ñltrate for agivenrlengthof was experienced in the building up of a cake .of filtering time -at' a constant effective pressure _ dif- l sufficient thickness to enable satisfactory con ferentlal is about the same for both a pressure tinuous removal. In general, it may be stated that-a cakeV of not substantially lessthan 1/4". in flow» is ¿ at lthe „ beginningî~ ofv the filtering`> period, y filter and a vacuum filter. `The highestrateof and this rapidlydecreases as `’the thickne’ssof rthe deposit of solids increasesbeyond a certain value. In an intermittent pressurey filter, for example, 10 thickness should be formed for satisfactory „re moval. However, where the cake is compacted during the cycle, a still thicker cake appears nec essary for securing -satisfactory removal. r`The use of filter aid'has assisted in- this problem. substantially _70% to 80% of _the/filtrate may , pass >through the filter in thefirst>2 to 4 minutes of the filtering time. Continuedßpplication of In accordance with the present invention, this the .pressure ,upon the cake _thus builtl upcom pacts this cake, so that the filtering rate then 15 drops off rapidly. However, due to the length of' objection has been satisfactorily overcome, and a _ cake forming time of ‘as short as from .about -1 to 4 minutes or even less has been made prac ticable. This is accomplished by the use of a wax time consumed in the 'other treatments. ofy wash-V ' crystal 4modifying material of suchy .character ing, drying, dumping of _the cake'. etc.„inf,the that crystal formation .is modified upon- chilling ’intermittent filtration cycle, it ismcommercially the wax-bearing oil in thc presence of such ma .impractical to terminate ythe filtrationfperiód> ferial, coupled with'other> features of the 'present invention including the comparatively low pres sure differential which' avoids compacting of- the cake. By the use -of waxcrystal modifying ma ' terials of this character, filtration -rates of the oil may be increased as much as 100% or more. `'I'his is of peculiarcooperation with continuous filtration, because‘it enables a cake of -satisfac tory thickness to be built up while employing a 30 commercially practicalv rate of rotation: of ¿the filter, such as to give a cake. forming time of not . more than 4 minutes per cycle. In addition, -it is pointed out that a 100% increase’in filtration rate on a continuous filter results in' a `100% in crease-in capacity‘of the plant; whereas, a sim-k 1 until a cake approaching about 1". >in thickness L'nas-been built up, which as set forth above'nor' mally requires-‘fromabout 20 to 30minutes. vOn -the other hand, the cakev forming'timel ofthe.y present method of -continuous filtration is limited 25 to onlythat initial part of the filtration> period of the intermittent filter, in which substantially the highest filtering rates occur.: This further .improvesfthe overall efiiciencyof vthe continuous filtration, giving a materially increased-'plant capacity. For example, the cake forming-time isY coordinated `with the filtration rate so that only the ,highflltration »rates normally obtained with an >uncompactedcakejof a thickness less thanv 1/2" are utilized, such a` cake forming time being y ilar increase in filtration rate in an intermittent ' generally not more ‘than 4 minutes in extent, and filtration process gives only a fraction of such `often as little as 1 minuteI or'less. Nevertheless, increase in plant capacity, due to the ‘fact that with such a short period ofcake formation, the the actual filtering time is only -a fraction of the high filtration rates .enable arwaxfcake of a. [thickness in excessof 1/4" to be formed; and 40 I Various wax crystal modifying materials vmay » often a Vcake of about %" to 1/2'1 or ,more in ’ be employed for this purpose, such’for example, thickness results. This is readily? removed in continuous operation.` ' ' ‘as a cracked pitchy residue resulting from the re The successive steps of> thev filtering cycle ’arel craoking of a cracked'cycle fuel, as' set forthin 40 complete operating time in the cycle. co-pending application Serial No. 686,244, filed also performed in proportionatelyshort intervals August 22, 1933; the high vacuum distillation of time.` In connection with the washing time, residue of a condensation product of naphthalene it is vfound :that the,v yields j of- dewaxed oil in- , in the presence of valuminum chloride,ïas de» . crease with an increase in ratio of washing time scribed in co-pending ,application Serial No. _. to pick-up time.l 'Ordinarily, fa .washingl time 710,564, filed March 21,- 1934. Also', other types , which is not less than one-third _the pick-up time of wax crystal modifying »'materials, such as a is employed,.which means that the peripheral ex- _ condensation product of a chlorinated‘wax with tent of the washin'gzone'isat least one-third the“ peripheral extent of the> pick-up or "cake forming an aromatic hydrocarbon in the presence of Aalu minum chloride,` certain mineral oil distillation ' zone; `andthe highestylelds appear to '_'be >ob-> . residues, coal tar residues, etc., may be‘used for _tained when the washingtimeis increased so as this purpose. As the methods of» forming such materials and of using themas wax crystal mod ifying materials generally, form no Hpart' of the present invention, apart from their particular 60 adaptation to continuous filtration, no further description thereof‘is thought needed. However, it may be stated that such materials are gener ally added in a proportion of from about 0.3% to 6% by weight on the weight of the wax-bear ing oil and are dissolved in the oil; the oil is then chilled in the presence of the materials, and wax is precipitated in a resulting form which to` be substantially _equal _to [the pick-up time. However, ,the Iactual differences in yields. ’of de waxed o_ilfor variation in >the' washing time from one-third the pick-uptime to a Atime [equal to the pick-up time,- are comparatively small, so that operations Within this range are. satisfac tory.,_ The resulting -'average orcyc’le _rate _of fflow of the continuousfllteroperating inaccord ance withthe present .invention is thus much higher than that commonly obtained on _anin-.l termittent filter. By way of example, _a filtration rate of about 0.4 to 0.6 gallons of Vwax-,free oil yper hour >per square footof filtering surface is increases filtration rates. » . ` In accordance with the present invention, there considered a very-satisfactory rate for an inter 70 is coupled with the increased filtration rates at -mittent pressure filter. By operating> in accord tributable to solvent dewaxing with ',the solvent ance „with the present invention. a filtration ‘ mixtures specifiedabove, and the use of wax rateof from 2.0 to as high as 3.5 gallons per hour crystal modifying materials, a coordinated con- . persquare foot of` filtering surface hasI been ob-' trol of the pick-up or cake .forming time. soas tained,- thus >givingÍa plant `capacity.' of _ about 75 to employ only the highest or peak portion of the four ormore times thatof the intermittent filter. 9,184,381 s At the same time, ~ the dewaxed oil yield is in emerges from the chilled ,mixture after which creased, due to the superior‘washing and drying vthe said cake on theemerged filtering surface is oi' the cake. For example, a dewax'ed oil yield of about 80% to 85% has been regularly obtained continuously washed,'dried `and discharged there from; the` steps ywhich comprise supplying a in practic'ze,l as compared to a dewaxed oil Vyield 6r' around 75% or lower onthe yintermittent pres sure filter.v - ' ~ ' _ - chilled gaseous atmosphere to surround `exposed 5 portions of 'the filtering surface after emergence >from the chilled mixture and tol maintain a pres sure Vslightly ‘in excess ofl atmospheric pressure upon the wax cake during the washing and dry 1 VThe following are examples of results obtained in the dewaxing of oil‘by continuous nltration 10 without the employment of Ai‘llter aid in accord ‘ing operations, Ithe gaseous atmosphere having 10 ance with the present invention: ' A l ~a temperatureapproxim'ating that of the chilled A Mid-Continent distillate oil and an Illinois wax-bearing mixture'being filtered, supplying a l Kentucky distillate oil were employed, these oils .chilled solvent mixture in which the wax is sub-_ having the following tests:` ` - stantially yinsoluble rfor rthe washing operation 14sl ’_ Mid-Con- , _ Kentucky Gravity, "'A. P. I 2l. 7 ~ Fissa-"1F _____ _. ,_ 45o , Fire, °F_-__-. 23.1 46o . 550 vis. @ 21o°F .............. ._ > _ filtering" surface during the washing and drying 550 ;, 7i _Pour test,_°F-'. .......................... _. and applying the said solvent mixture to the wax cake on the filtering surface by-fiowing .the sol vent mixture by gravity onto the wax cake to forma continuousliquid film on the> said cake, and regulating the pressure differential on the Illinois tlnent ` 105 , so operations so as, to maintain said-pressure dif 90 ferentialat less than twenty‘pounds per square inch to avoid compactingfof the wax cake. A selective'solvent mixtureicomposedof ace 2. The method of continuouslyseparating wax tone 35%,- benzol 52% and‘toluol 13% 'was em >from a wax slurry on a rotary Vfilter, element ployed in the’ratio of 4.parts ofv‘solvent to _1 , mounted within a filter casing having an enclos- . part kof ycharge stock.v The oil was> then-,chilled ing cover, which comprises immersing said ele to aA temperature of about _10° F. or slightly ment'in a wax slurry under a pressure differential ulower, and the chilled wax-bearing `_mixture 'I'he lfollowing sumcient to force filtrate through the element and to build-,up a wax cake thereon, removing the >filter cake from the` slurry, washing said filter cake, .drying said cake by means of a stripping gas, continuously removing saidcake from said element, introducing a stripping medium into said casing to provide a chilled gaseous atmos phere therein between said-filter casing with en 30 passed to the continuous filter. tabulation indicates the operations and results obtained: ` - " ' MidCont. 'run #l 35 MidCont. run #2 Filtering temperature, aF ~ Wax dist. mix_-__ _ ` ' -13 -4 -10 -12 -12 cous atmosphere is at a temperature approxi `> mating that of the wax slurry being filtered and ‘ 120 120 120 60 supplies-f‘said‘stripping gas, and regulating the -14_ f Drying stage._«_ 40 30 10 10 Washing stage. Drying stage... 40 40 , 00 30 60 50 60 50 48 4.8 12.6 48 . 4. 8 12. 6 i 35 _ 3. 6 16. 8 9i 2. 7 3.0 82. 9 17. l 82.3 17. 7 85. 6 14. 4 _. 48 4. 8 12.6 _ Cake thickness in inches _________ .-'.._ Filtering rate of dewaxed oil in gai/sq. ft./hr.-.-. ...... _. Dewaxed oil _____ _. .... -Slack wax ........ _; ____ -_ - closing cover and said filter element, which gas -13‘ _ }í-% _ 2.6 Yields percent by weight: . _ 2.5 ` - , 80. 3 19. 7 Solid point °F. of dewaxed 50 K' " y' “m n ' CakeA discharge stage__-._ Total cycle time in minutes . Cycles per hour ____________ __ f 45 ’ -9 ‘ Wash solvent_-.__ Time of filtration in secs. Pick-up stage.- m K " y‘ n 1 oi _______________________ __ -8 -12 -10 -8 Dewaxing differential °F-. _ _ 1 1 3 6 pressure of the said gaseous atmosphere and the pressure differential through said filter element to maintain a pressure differential throughsaid filter element which is less than 20#/sq. in.v to , avoldjobjectionable compression of the said wax 45 _ cairel on the filter‘element.Y _ 3. _'I'he method of. _continuously separating wax froml a wax slurry, on a rotary filter element mounted within a- filter casing having an enclos ing cover, which comprises immersing saidk ele 50 ment in a wax slurry under a pressure difieren-_ ` 'While the invention hasbeen described in con _nection with the separation of’wax from wax bearing oils, it is'to be understood that it is also 55 applicable to the removal of similar types _of solid jmaterials from liquids v‘wherein it is desirableto maintain the resulting cake- of'solids ata tem 60 perature below that at which the solids tend ‘to liquefy and reach a condition where they pen etrate the fabric and ultimately result in plug gms, ‘ _ l , ' ‘i Obviously many modiflcationsand variations of the invention, as hereinbefore set forth, may be made without departing fromfthe spirit and 65 scope thereof, and therefore only such limitations should be imposed as are indicated in the ap pended claims. I claim: _ , , ` ' -l. In the continuous 'process of' dewaxing min 70 eral oil by continuously filtering the chilled wax bearing mixture at temperatures of around 0° F. tial sufiicient to force filtrate through the element _ and‘to build up a wax lcake thereon, removing the filter cake fromthe slurry, washing said filter cake, drying saidcake by means of a stripping 55 gas, continuously removing said cake from said . element, introducing a stripping medium into said >casing toprovide a chilled gaseous atmos phere >therein between said filter casing with en closing cover and lsaid filter element, which gas 50 eous _atmosphere is at a temperature approxi mating that of the wax slurry being filtered and supplies said stripping gas, and regulating the pressure of _ the said gaseous atmosphere and the pressure difîerentialthrough said filter element 65 to maintain a _pressure differential through >said - filter element which is less than 15#/sq. in to avoid Vobjectionable compression of the said wax cake on the filter element. 4. The method of continuously separating wax 70 from` a wax slurry on a rotary filter` element or lower, and wherein a wax ñlter cakeïis'con tinuously formed on a moveable filtering surface -mounted within a filter casing having enclosing which consecutively submerges `within the chilled ment in‘a wax slurry under a pressure differen 75 mixture to deposit a filter cake thereon, and then cover, which comprises immersingthe said ele tial sufl‘lcient to force filtrate throughthe element 75 9,184,881 and to build up a wax cake thereon. removing the ñlter cake from the slurry, washing said ñlter cake with dewaxing solvent chilled to a .5. temperature approximating that of -the wax slurry being filtered by preforming the solvent >as a continuous liquid ñlm and leading this ‘co'ri tinuous i‘llm onto the cake, drying said cake by means of a stripping gas, continuously removing said cake from said element, introducing a strip 10 ping medium into said casing to> provide a chilled gaseous atmosphere therein between said ñlter casing with enclosing cover and said ßlter ele ment, which- gaseous ~atmosphere is at a> tem perature approximating that of the- wax slurry being tlitered. and supplies 'said stripping gas, andv regulating thepressure of the `said gaseous atmosphere and the pressure diiierential through ^ said filter element to maintain a pressure diiïer ential through said illter element which is lesa v than iifteen pounds per square inch to avoid ob Jectionable compression of the said` wax cake on v the nlter'element. O wnmm r». om.