US2102334A - Process for dewaxing hydrocarbon oils - Google Patents

Description

Dec. E4, 937. E. PETTY PRocEss FOR DEWAXING .HYDRocARBoN OILS Filed April 14, 1.933

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Patented Dec. 14, 1937 UNITED STATES PATENT OFFICE Earl letty, Hempstead, N. Y., assignor, by mesne assignments, to Sun Oil Company, Philadelphia, Pa., a. corporation cf New Jersey Y Application April 14, 1933, Serial No. 666,099

6 Claims.

My invention relates to a process for dewaxing hydrocarbon oils and more particularly to a process of dewaxing in which pressablewax crystals are produced by chilling wax-bearing-distillates from crude oil.

This application is a continuation in part of my co-pending application entitled Process of xligzvsaxing oil, Serial No. 624,968, filed July 27,

Heretofore, to produce pressable wax distillates from crude oil it required a high degree of fractionation and a very careful selection of the pressing fraction. 'I'his pressing fraction usually had a boiling range of from 450 F. to 675 F. 10 m/m Hg. absolute pressure.

One object of my invention is to provide a methodv of dewaxing hydrocarbon oils in which the fractions which can be dewaxed by pressing are extended to include oils of a boiling range up to '725 F. to '750 F. 10 m/m Hg. absolute pressure.

Another object of my invention is to provide a method of chilling hydrocarbon oils which will greatly improve the formation of pressable wax therein. Y

Another object is to produce a more oil-free wax crystal by improving the conditions under which crystallization is conducted.

Other and further objects of my invention will 30 appear from the following description. f

'Ihe accompanying figure, which is to be read in conjunction with the instant specification and which forms part thereof, shows a diagrammatic view of an apparatus capable of carrying out my invention.

In general, my invention consists of blending, under pressure, a predetermined amount of hydrocarbon such as propane with the wax bearing oil. It is to be understood that throughout this 40 specification by propane is meant any of the low boiling hydrocarbons which may exist in a liquid state in the normal temperature range by the imposition of super-atmospheric pressure.

Commercial propane, for example, is liquid within 45 the normal temperature rangeat pressures between 80 and 120 pounds per square inch and contains at least 60% of pure Cal-Ia. At atmospheric pressure it boils at approximately 45 F.

and solidies at about -300 F. These later 50 characteristics indicate another contributory and complimentary characteristic of this diluent, viz a low viscosity. The viscosity of gasoline or naphtha normally used as a diluent in connection with Adewaxing at temperature of C. is an average of .00690 C, G. S, unit., whereas propane has a viscosity at the same temperature of .00125 C. G. S. unit. This low viscosity indicates high freedom of movement and velocity of the molecular structure and has definitely proven to be very advantageous to crystallization, when it is present as a diluent. The other characteristic of low temperature of boiling makes it possible to remove the propane as the crystallizationprogresses. The removal of this diluent has the effect of accelerating crystallization by concentrating the amount of oil in the mother solution. In other words, the crystal is formed and cul-V tured during the first part of the cooling bythe dilution and low viscosity effect of the propane. Then the increased concentration of the oil and incidental refrigeration eiect produced by allowing the propane to evaporate produces the final Wax crystal. These above complementary and contributory physical eiects are accomplished by the following chilling procedure. The blend is made at approximately 80 to 100? F. The chilling is divided into two stages, viz, 1st, in- `direct heat exchange to approximately 30 F., and

2nd, by evaporation of the propane and the incidental reduction of temperature to as/low as -30 F. In the first stage the blended mixture is passed under pressure through precoolers in order to chill the same by indirect heat exchange.

The precooled mixture is then passed into theV evaporator-crystallizer for concentration by the removal and evaporation of the propane and incidental refrigeration or cooling. This is accomplished by reducing the pressure on the evaporator and results in the evaporation and removal of substantially all the propane. The effect of the propane upon the wax during the pre-cooling is as a diluent to reduce the viscosity ofthe solution and accelerate the crystallization. The final chilling, incidental to evaporating the propane, is such that a desirable wax crystal is developed due to increased concentration of the oil in the solution, producing a wax of improved filtering quality. (See co-pending patent application 632,- 278, Sept. 9, 1932.) This effect enables me, by the practice of my process, to extend the range of pressable wax bearing oils, or to increase the rate of filtration, and reduce the oil content ofY the wax. The propane from the evaporator isV recovered for re-use. The chilled oil containing the wax crystals and substantially freeoi:` propane is then passed to a CO2 stripper tower 50 where CO2 vapors are expanded into tower lilly counterflow to the chilled wax ydistillate before4 it is passed to lter press. In the tower 50, by the vstripping step, the final traces of propane are removed and replaced with CO2 vapors. The oil which Vis recovered from the pressing operation, at a very low temperature, is passed in heat exchange with the incoming mixture as the cooling medium although it is understood that any other suitable refrigerant may be employed for the indirect heat exchange step. The oil is then passed to a pressure evaporator to insure the complete-removalof"propane andl CO2 therefrom, nally stripped by steam to remove 'the last trace of any of the volatile products, and then passed to storage and further processing.

If desired, the processbouldbe modifiedby combining the steps performed in the stripping tower .and evaporator by passing C052 vapors directly into the oil transfer line yfro eX- changer to the evaporator, indirect into the evaporator, thereby eliminating 'the stripping v the blending tank *4, inlfwhich a'thor'ou'gh mixture ofthe bill-tobe dewaxed with'the" propane, is

effected'' It" is: toV be-'understood 'that suitable agitatin'g means maybe vprovided in 'theblending tank. -The nri'xtur'e' orVV solution is" pumped throughf valved line" 9 by pufmpilll, through heat exchangersHf These-hein;VVVV exchangers may be of any suitable type. The'drawirigillustrates a diagrammatic viewof scraped surf ace heat ex changers.A -The "solutionlisfchilled in r heat exchangers andlpasses Ithrough line`V |2 into the evaporatory crystallizenil 3,'ingwhich the pressure is 'reduced to fallowthe propane to* evaporate to l secure' additionarand" runner smiling;- AIf, uesired, propane Ymay be passed through line |'4 and pumped "by I5y through line" I@ iht'o the to secure additional and evaporato'r crystallizer further cooling." 'f

-The Igaseousl propane leaves lthe evaporator crystallizer I 3f through line V| 1 `and""'pressure reducing valve H1 and mayvv be recovered by Vany suitable means.'-" Separator I8 is providedto in surethat'n'doil is"'carried'outv of the system, the oil freturningthroughlie |9.l Pump |5is adapted to takesuction"'throughf'valve :1ine20jfor reing pressable wax'erystals is Ywithdrawn'`from evaporator Vcrystalliz'er*|3through valved; line 2'! by pump 55,*valv`e |-'22 being? closedgandpas'ses through line |l2| into "CO2 strippen 50.5; CO2 vapors from cylidersSl vor" 52Y are passed: into this stripper through'pipe |75| 'andpipe |52 controlled by valves v|53 and |54iand dueto the partial 'pressure effecttheremainder ofthe propane is removed?" Thepropanev7 andVCOz vapors are taken'of :throughvapo'iline 53 and pump 54'to be compress'edan'd recovered.- The chilled stripped liquid' is with'drawn irm" the tower 50'Y through line'f-Zlq;A by means of pump-*55a by which it is fed'tothe iilterV or pressing system. (It is not intended'tofusethe COzasa refrigerant at this stag'L-'flfhe' tower would fbelcarefully' insulated nd'the 'amoun't' of CO2 vapors used 'would not remove heat, and rthe effect of these vapors wduldffbefto remove the 'entraihed propane and thereby give slight refrigeration effect from evaporation of propane, due to partial vapor pressure eiect.) are arranged in parallel.

The Wax leaves the lter presses through lines 28, 29 and 30 andpasses into wax receiver 3| which is provided with a tting 32 through which a reduced pressure may be placed on the Wax receiver to evaporate thereiromf all tr-acesiof volatile'propane and/or CO2.` The cold dewaxed oil Yleaves the filter' presses through lines 32, 33 and .3"` through line 35, and is pumped by pump 36 through 'th'e'heat exchangers Il to chill the in.- coming solution. The oil leaves the heat exchangers v|| through line 39 and passes into stean'istripper 45. The dewaxed oil, freed of the solvent, is than pumped by pump 48 into storageltank 48, Recycle with the undewaxed oil may be'practiced'to reduce cold test and thickness of'rnaterial being dewaxed by diverting a portionpf the dewaxed oil in line 39 thro-ugh line 44 by means of pump'45 or through lineMc (or the wax-distillatetmayb 'diiutedfasfonvea tionally practiced, with glas` oil or' kerosene) "The rlter presses I:maybe of the'conv'entional type or may be special .continuous'orjbatch type It will be seen that I have accomplished the objects of/r'nyinvertion. amv enabledt pro'- duce pressable wax from distillates of a greater boiling" range'. By my methodiof' chilling; I 'am Y enabled to producerpres'sa'ble waxfwhereiit" has been -impossible heretofore' tor dq so; 'and' alsoto produce 'ag'greater' amount of pressable wax for' a 'given"fraction, enabling the complete dewaxing thereof. An increased" crystal'ff'formation is achieved by the use of propanefas a 'diluent accompaniedbythe manner inwhi-ch Ichill the solution. I preclude 'the ldanger-:of flirein the pressroom byr keeping itfinan atmosphere of metgas'm. .l y It will be understood that certain features, sub-combinationsand operationsy arei of utility and maybe "employed withutrreference to any other features4 and A'sub=combinations. is contemplated by and is within the scope-of 'my claims. ItY is further obvious that various. changes may be made in detailswithin the'scope of my claims without departing from the spirit of my invention. It' is,Y thereforefto be understood that my'invent'ion isv not to be Ylimited t0- the specific details shown anddescribedi` Filter presses 22, 23 and 24, as shown,

It willbe'un'derstood,further, that', while I ed hydrocarbons expanded to 'chill the oiland Y the wax then removed from the oil, the step of stripping the chilled oil ofr residual normally gas# eous hydrocarbons afterthe expansion 'step byv means-of` an inert gas lower boiling than the normally gaseous hydrocarbons.

'2. A method'of'rdewaxing hydrocarbon oils including'the-steps of mixing the oil to be dewaxed with liquefied normally gaseous hydrocarbons, chilling thevoil by evaporating normally gaseous hydrocarbons mixed therewith, removing the residual hydrocarbons from the chilled oil by stripping with carbon dioxide in a stripping zone, and then dewaxing the oil.

3. A method of dewaxing hydrocarbon oils including the steps of mixing the oil to be dewaxed with liqueed propane, cooling the mixture by indirect heat exchange, chilling the cooled oilV by evaporating the propane, removing'the residual hydrocarbons from the chilled oil in a stripping zone by stripping the oil with a gas lower boiling than the propane and then dewaxing the oil.

4. A process of dewaxing hydrocarbon oils including the steps of adding a low viscosity normally gaseous hydrocarbon diluent to the oil to facilitate crystallization of wax in the oil during a pre-cooling stage, chilling the diluted oil by indirect heat exchange in a rst chilling zone to initiate crystal formation, evaporating substantially all of the low viscosity diluent from the chilled oil in a second zone of chilling to concentrate the amount of cil in the mother solution and secure nal wax crystal development, then removing the residual diluent from the chilled oil by stripping with an inert gas lower boiling than the diluent and mechanically removing the wax from the oil.

5. A method of dewaxing a hydrocarbon distillate of boiling range from 450 F. to 750 F. 10 m/m I-Ig. absolute pressure including diluting the oil with low Viscosity normally gaseous hydrocarbons under pressure and in the liquid phase and in sufficient quantity to serve as an accelerator of crystallization by low viscosity effects during a pre-cooling stage, cooling the diluted oil by indirect heat exchange to approximately 30 F., removing substantially all the diluent from the oil by evaporation which by incidental physical efrects results in cooling and co-incidental concentration of the oil in' the mother solution and produces a further developed wax crystal substantially oil free, carried in oil, then freeing the oil of residual diluent by stripping with a normally gaseous, non-iniiammable' material of a lower boiling range than the diluent, and mechanically removing the wax crystals from the oil.

6. A method of dewaxing hydrocarbon oils including the steps of mixing oil to be dewaxed with a liquefied, normally gaseous hydrocarbonV diluent, then chilling the mixture and increasing the concentration of the oil in the mixture by stripping the diluent hydrocarbon from the oil with a normally gaseous, Ynon-inilammable ma` terial of a lower boiling range than the diluent and removing the wax from the oil.

EARL PET'I'Y.

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