US2218514A - Method and apparatus for separating wax from oil - Google Patents

Description

Och-22,1940. v u. B. BRAY 2,218,514

METHOD AND APPARATUS FOR SEPARATING WAX FROM OIL Filed July '7, 1950 INVENTOR. Ulric B Bray ATTORNEY.

perature.

Patented Oct. 22, 1940 METHOD AND APPARATUS FOR, SEPARAT- ING WAX FROM OIL Ulric B. Bray, Palos Verdes Estates, Califi, as-

signor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application July '7, 1930, Serial No. 466,189 26 Claims. (01. 196-18) This invention relates to a method and apparatus for treating petroleum to produce lubricating oil, and also, a novel lubricating oil.

This invention will be better understood by reference to the accompanying drawing which is a schematic flow sheet of the process.

I find that the process is best carried out by the use of hydrocarbons which are normally in the vapor state at atmospheric pressure and tem- Such hydrocarbons include propane, isobutane, butane, ethane, methane and mixtures thereof. These may be obtained by rectification of casinghead'gasoline by the so-called stabilizing method now "conventional in'the natural gas industry. They are the overhead thus obtained. They are liquefied bycompression and cooling in the conventional manner and drawn off into pressure chambers where they'are maintained in the liquid state until they are used. A typical analysis or such a fraction is 6.72% ethane, 22.20%

propane, 19.91% isobutane and 1.17% normal butane and the necessary pressure to maintain the fraction in a liquid state is approximately 125 lbs. per square inch gauge at 73 F.

' The iollowing is a description of a preferred method for treating a mixed base oil, i. e., one containing asphalt and wax, wherein the asphalt is precipitated under conditions such as to leave the wax and oil" in the propane solution. Advantage is taken of the propane solution to permit a continuous acid treatment and alkali treatment of the oil. This is a particular advantage of this process since it permits rapid settling of the sludge. The extremevolatility of the propane is used toact as a refrigerant to cause separation of the wax. The process will be more particularly described by reference to the accompanying drawing.

Referring to the drawing, the crude oil tobe used as a source of lubricating oil such as, for example, a $anta Fe Springs crude of 335 A. P. I.

' gravity is taken from the crude oil storage tank I and sent through coil 2 in furnace 3, whence it is sent to evaporating column 4. The temperature in coils 2 and i9 and the duration of heating in the still system 2, 4, ll, l9 and 22,, is

so regulated that the amount of conversion i. e.,

the destruction .of inherent paraffin base charac- 50 teristics is minimized. As a convenient criterion the temperature should not be raised beyond 600-650 F. I prefer to distil the oil to leave a residue which contains the fractions having a viscosity above 400 to 500 seconds Saybolt Universal 5.5 at 100 F. "In other words, the degree of distillabecause of the danger or injuring the quality of tion should leave a residue such that if it were redistilled the first 'fractions taken overhead would be about 600 to 880 seconds Saybolt Universal at 100 F. These figures are by their very nature approximate since they must overlap and the spread of the cut will be dependent on the percentage taken overhead. The vapors passing through 5, consisting of gas oil, kerosene and gasoline vapors, go to dephlegmator 6 where they are fractionated into gasoline overhead and kerosome and gas oil bottoms, which may be re-run or handled. in any conventional manner. The vapors pass through I, are condensed in 8, condensate, i. e., gasoline, is collected in 9. A part is returned through It), to distributor H, to act as a reflux. The dephlegmator bottoms pass through l2, and are cooled in I3. These consist of gas oil and kerosene. Part is returned as a wash via line l4 and spray IS.

The bottoms from evaporator 4, consisting of oil containing lubricating fractions and asphalt,

pass through the rundown line IE to the hot residuum storage tank H which may serve only as a surge tank in the continuous operation of the process. The hot residuum from tank I1 is passed through pump it which sends the hot residuum through coil [9 in furnace 26, where the residuum is heated to about 625 F. Care is taken at this point not to overheat the residuum the lubricatingoil to be obtained later, i. e., its parafiin base characteristics. The temperature to which the oil may be heated has been adequately described above. The heated residuum passes to fractionatingcolumn 22. Steam, superheated in coil 2|, is introduced in column 22 to aid in the flashing of the volatile oils which are taken off in one or more side streams and as an overhead. The oil is fractionated by fractionating plates 23 and a number of side streams are 4 removed through lines 24 controlled by valves 25, reflux is generated by means of a cooler positioned .at'the top of the column. The various oils pass through valve 26 and are cooled in 2'! and collected in 28. If desired as many tanks as there" are side streams may be employed. The side stream distillate may beprocessed' in any suitable manner to produce desirable products. The overheads from the column pass through line 29, are condensed in condenser 30 and cooled in rundown tank 3!. Uncondensed vapors are removed through 32, condensed oils composed of light lubricating oils are removed through 33 and the toms from column 22 are run through line 35 by means of pump 35a to cooler 36 from which it is delivered to the topped residuum tank 31. The operation of coil I 9 and column 22 is so regulated as to produce the predetermined extent of topping necessary to give the proper viscosity oil in the later extraction with propane.

The topped residuum stored in tank 31 is sent by pump 38, meets liquid propane containing a small amount of oil coming through line 45. The preferred fraction is that obtained as an overhead in the stabilization of natural gas gasoline as previously mentioned. The mixture of propane and residuum pass through mixing coil 39 into decanter 40, where the asphalt in the topped residuum is precipitated and settles rapidly as a slurry. From the bottom of decanter 40, the asphalt slurry is pumped by pump M to meet fresh liquid propane introduced by pump 48 via line 41 from propane storage 48. The asphalt slurry and fresh liquid propane are sent through mixing coil 42 into decanter 43. The asphalt propane slurry from the bottom of decanter 43 is drawn off through line I45, and valve I48 and discharged at a lower pressure into a still, as will be discussed hereafter.

The overflow from decanter 43, containing the oil and wax is sent by pump 44 through line 45 to be mixed with the topped residuum and sent into decanter 40, as explained above. The overflow from decanter 40 consisting of propane and lubricating oil stock in the desired ratio is sent through pump I for the acid and alkali treatment of the extracted lubricating oil stock. The countercurrent washing of the precipitated asphalt illustrated by the above method of operation may be extended to as many steps as desired, but in general two decanters giving two countercurrent washings will be sufficient to produce an asphalt satisfactorily free of wax and oil.

To the propane solution of extracted lubricating stock, acid from tank 52 is added to mixer 55 by means of pump (or acid egg) 53, and the flow is controlled also by valve 54. The propane solution and acid are forced by pumps 5| and 53 through mixing coil 55 into decanter 60 where the acid sludge settles rapidly. The addition of the acid in several dumps without drawing the sludge between dumps may be accomplished by tapping mixing coil 55 at various points and introducing acid at these points. The addition of acid in several dumps with the Withdrawal of sludge between dumps may be accomplished by means of additional mixing coils and acid decanters. The acid treated oil solution from decanter 60 flows continuously through line 62 into decanter 83, where Water is introduced as a spray through line 68 from water storage 64 through pump 55 and valve 61 and acid reaction products are withdrawn through line 56 controlled by valve 51. The water washed oil overflows from decanter 63 and is sent by pump 89 to be treated. Water is withdrawn via line 58 controlled by valve 59. The soda solution contained in tank is introduced by pump 1I through line 12 controlled by valve 13. The mixture of oil solution and aqueous alkali solution is forced through mixing coil 14 into decanter where the caustic solution separates from the propane solution of the oil, and is withdrawn through valved line 16. The overflow from decanter 15 goes through line 11 to decanter 18, where water is introduced through spray 19 by means of pump 65 through valve 86. The separated water Wash is withdrawn through valved line 80. The use of propane as a solvent permits the continuous and rapid treatment of lubricating stock in the manner just described.

The neutralized and water washed oil solution overflowing from decanter 18 is carried by line 8I to tank 82, the latter acting as a reservoir or surge drum between the acid treating and dewaxing operation.

. Treated oil solution in tank 82 is sent through valve 83 and line 84 to line 86 or 92 where it is sent into low pressure column 81 or low pressure column 94 by the proper operation of valves 85 and 93. Considering valves 9I and 93 closed and valves 85 and 90 open, the propane solution flows into loW pressure column 81. Valves 85 and 93 are pressure reducing valves separating the low pressure columns 81 and 94 from the high pressure treating and decanting vessels. In low pressure column 81, sufficient propane vaporizes to reduce the temperature of the remaining material to a predetermined dewaxing temperature. The desired dewaxing temperature is obtained by controlling the pressure in column 81 by the proper operation of valve 90 and propane compressor I03, which is connected to the evaporator by line I02. The pressure to be maintained in column 81, as shown by gauge 89, will be, generally, about 0 1b., gauge which corresponds to a temperature of approximately 4=0 F.

As the propane solution passes through valve 85, its pressure is reduced so that a portion of the propane evaporates in column 81 and the vapors pass out of the top, through mist extractor 81a through line 88 controlled by valve 90. The solution from tank 82 continues to flow into column 81 until a predetermined quantity has accumulated. Valves 85 and 99 are then closed and valve 93 opened. Production then flows into column 94 until the predetermined quantity of solution has passed into the second column. The propane is vaporized, passes through mist extractor 95 through line 96, valve 98 being. controlled so that the proper reading is obtained on gauge 91. In the meantime, the vapor pressure of the propane in column 81 has been reduced to approximately 0 lb. gauge by the operation of valve 90 and propane compressor I03, thereby reducing the temperature of the material remaining in column 81 to approximately 40 F. When this temperature is reach in column 81, valve 9I is opened and the cooled material is passed through line I00, pump I Ill and valve I06 into the gas tight centrifuge I01 in box I09. Motor I08 is for the centrifuge. The centrifuge is of conventional type. The dewaxed propane solution of lubricating oil discharged from the center of the centrifuge through line I2I is sent by pump I22 through valw ed line I23 and heat exchanger I24. In passing through heat exchanger I24, heat is absorbed from the vapors coming from the top of the evaporator I32. The propane solution of dewaxed oil may be passed directly to evaporator I32 through line I28 by the proper operation of valves I21, I26 positioned in lines I25 and I28. If it is desired to supply all or a portion of the heat required for vaporization of the propane by fire rather than by steam, the propane solution may be passed through coil I29 in furnace I30 by the proper manipulation of valves I26, I21 and I3I into evaporator I32. Open steam is introduced into evaporator through I33 to complete the vaporization of the propane and to reduce the oil to satisfactory flash and fire specifications. In general, however, the function of the steam will be {to complete thevaporizationof the propane.

light oil removed from evaporator "I32 passinto separator v I 36 with the uncondensed propane vapors. :e un'condensed propane'v-apors leave the separator I35 through line I 39 andpass to line hit tr'om which they enter thesuctionof -propane compressor IM to be compressed and sent through "line 104 to propane .cooler I05 wherethe propane vap'orsare liquefied and returned to propane melt-the wax in the waxdischarge line from the centrifuge, as will be later described. Leaving heat exchanger I42, the treatedand'dewaxed oil into storage tank I43. 1

The wax discharged from thecentrifuge through line I ill is mixed with warm water, at about 140? The melted wax and water pass into separator III. and the wax-.iis withdrawn, through line 1 I2 to wax storage 41-3 The water from separator I II is passedthroughline H4 to watt-3rstorage tankerIlfi and then through line H 6, pump Ill and line I I8 to heat exchanger ccil I I8 where it is heated by'the bottoms from evaporator .l32, as explained above. :The warm watertleaving .heat exchanger coil II9is passed through line IN .to line III to complete the cycle. The vapors from thetop of separator-III, consisting of propane discharged with the wax from the centrifuge, are conserved .by compressing and returning to high pressure propane line I04 going to propane cooler I05 by passing through line I I2a interline I40Yand compressors I44. The vapor sp 'ein the gas tight centrifuge should be con-- .1 "eoted with the-suction of a propane compressor discharging into the high pressure propane system. Provision forthis latter conservation of propane is made by connecting either thedewaxed oilldischarge line I ZI or the wax discharge line litll with the gas space in the centrifuge, as will be und'erstood'by those skilled in the art.-

The asphalt -materia-l from separator 43 is passed through line I45, flashed through valve 4% and heating coil 44] in furnace M8 and pressure reduction valve I49 into evaporator I5I, which operates at a lower pressure. Steam superheated incoil I-50is introduced into I5I tosupply additional-heat and to reduce the asphalt to "proper specifications,generally only as regards and fire'points. The asphalt is taken from the bottomof'the evaporator I 5| and sent through the valved rundown line I59 to asphalt storage its} The overhead fromevaporator I'5I passing through mist extractor I52 issen-t through line Ili3;to cooler 1 54, and then'to separator155. The

uncondensed propane from separator I55 is sent through line I51 to line 140 tot'hesuction'of propane contpressor M4 wherei-ts pressure is raised to that in the high pressure system and then sent toiine IiM to propane cooler I05 where it liquefies and downinto propane storage tank-48. Any condensedlight oil is withdrawn through line I56 I and condensed water through line- I58.

. JFrointhe standpoint of convenience and eporation, it-m'ay be desira bletoconnect all of the Leaving heat-exchanger co-11435, the condensed steam and any high pressure vessels containing liquid propane to a pressure equalizing line 49 controlled by valve 50, as shown in the drawing. Without provision for equalizing the pressure in the different vessels, flow of liquid will be controlled entirely by pump pressure.

In the operation of the centrifuges, it is desirable to maintain a higher pressure upon the propane, oil, wax mixture than corresponds to the vapor pressure of the mixture at that temperature. The reason for this increased pressure is to prevent foaming or gas evolution in the liquid. This pressure is applied by pump IOI. If it is desirable to operate the centrifuge at atmospheric pressure or at only slightly increased pressure, the pressure maintained in cool ing column 81 or-94 before the liquid in that column is sent to the centrifuge should be less than atmospheric pressure, so that when the pressure is raised to atmospheric before passage through the centrifuge, the liquid may-warm up several degrees without boiling or foaming.

Evaporator I32 may be operated at a sufficiently high pressure to cause liquefaction of the propane vapors when cooled, and in this manner eliminate the use of a compressor on the vapors from the top ofseparator I3 3. When operating column I132 at high pressure, pump it! is operated at a higher discharge pressure and heat exchanger 42!! is operated so as to cause condensation ofonly steam and oil vapors.

I claim: 1. A process for separating. wax from a wax- 'oil'rnixture which comprises forming a chilled mixture of separated wax and oil diluted with liquefied normally gaseous hydrocarbon diluent mixture.

5. A process according toclaim 1 in which the pressure on said chilled mixture is increased priortosai'd removal of said Wax from the diluted oil. Y

6. A process according to claim 1 in which the having an average molecular weight greater than wax is removed from the diluted oil in a centrifuge. V i y '7. A method of removing wax from petroleum oils which comprises diluting an oil-wax ture with a liquefied hydrocarbon diluent which has a vapor pressure higher than that of butane and lower than that of ethane, chilling the mixture to precipitate wax and removing the precipitated wax from the chilled mixture.

8. A method of separating wax from a waxbearing oilwhich comprises mixing said oil with a hydrocarbon diluent composed chiefly of propane and having a vapor pressure substantially equal to. that of propane, chilling the mixture to precipitate wax and removing the precipitated wax from the, chilled mixture.

9. A method for dewaxing oil, comprising diluting a wax-bearing oil with, and cooling said oil in the presence of, a normally gaseous liquefled hydrocarbon diluent heavier than ethane but lighter than butane, to solidify wax contained in said oil, and separating the solidified wax from the diluted oil.

10. In a method of removing wax from oil, the steps of commingling the waxy oil with a normally gaseous hydrocarbon liquid diluent having an average molecular Weight greater than that of ethane and at least as low as that of butane, chilling the, mixture to separate solidified wax, and separating the wax from the diluted oil.

11. A method for the separation of wax from a wax-bearing .oil which comprises commingling said oil with a liquefied normally gaseous hydrocarbon diluent consisting chiefly of propane, chilling the mixture to separate wax and removing the wax from the chilled oil and liquefied normally gaseous hydrocarbon.

12. The method of removing wax from oils which comprises adding a light, low-boiling, nonviscous hydrocarbon diluent having a vapor pressure lower than that of ethane and at least as high as that of butane to the mixture of oil and wax, evaporating a portion of said hydrocarbon diluent in direct contact with the oil whereby the oil is chilled to solidify the wax, and separating the wax from the diluted oil.

13. The method of removing wax from petroleum oils which comprises diluting an oil-wax mix ture with a liquefied hydrocarbon diluent which has a vapor pressure higher than that of butane and lower than that of ethane, removing liquefied hydrocarbon therefrom in regulated amounts whereby the mixture is refrigerated and the wax is solidified, and mechanically separating the wax from the oil diluted with said liquefied hydrocarbon.

14. The method of removing wax from oils which comprises adding a light, low-boiling nonviscous hydrocarbon diluent consisting chiefly of propane to the mixture of oil and wax, evaporating a portion of said hydrocarbon diluent in direct contact with the oil whereby the oil is chilled to solidify the wax, and separating the wax from the diluted oil.

15. The method of removing wax from oil which comprises diluting a waxy oil with a mixture of liquefied light hydrocarbons having a vapor pressure lower than that of ethane and higher than that of butane, vaporizing a portion of said mixture to cause refrigeration whereby wax crystals are formed in the remaining mixture of the liquefied light hydrocarbons and oil, mechanically separating said crystals from said diluted oil mixture, compressing, condensing and returning said vaporized portion to the system, separating the oil from the remaining light hydrocarbon diluent, and returning said diluent to the system.

16. The method of claim wherein light hydrocarbon diluent is separated from the oil at a sufficient pressure to allow its condensation without further compression.

17. In a process of dewaxing hydrocarbon lubricating oils the steps which comprise adding suflicient liquefied normally gaseous hydrocarbon diluent having a vapor pressure lower than that of ethane and at least as high as that of butane to said oil under pressure to both reduce its viscosity to permit ready separation of wax at dewaxing temperatures, and to provide the necessary refrigeration to bring the mixture to such temperature, reducing the pressure on said mixture to reduce the temperature by evaporation of the liquefied hydrocarbon to precipitate the wax,

mechanically removing the wax, and recovering liquefied hydrocarbon from the dewaxed oil.

18. A process according to claim 17 in which the liquefied normally gaseous hydrocarbon diluent consists essentially of liquid propane.

. 19. A process according to claim 17 in which the liquefied normally gaseous hydrocarbon diluent consists essentially of liquid butane.

20. A process according to claim 17 in which the pressure on the solution of oil and diluent and precipitated wax is increased before the wax is mechanically removed from the solution of oil and diluent.

21. A method for dewaxing mineral oils comprising adding to a mineral oil under pressure a hydrocarbon solvent which is preponderantly liquid propane in quantity sufiicient both to reduce the viscosity of the oil to permit ready separation of wax at dewaxing temperatures and to provide necessary refrigeration to produce such temperature, evaporating only a portion of said hydrocarbon solvent to produce said dewaxing temperatures and precipitate the wax while retaining suflicient of said hydrocarbon solvent in liquid form to permit ready separation of the wax, mechanically removing the wax, and separating the hydrocarbon liquid from the dewaxed oil.

22. A method for dewaxing mineral oils comprising adding to a mineral oil under pressure a normally gaseous hydrocarbon solvent liquid which is preponderantly butane in quantity sufficient both to reduce the viscosity of the oil to permit ready separation of Wax at dewaxing temperatures and to provide necessary refrigeration to produce such temperature, evaporating only a portion of said hydrocarbon solvent to produce said dewaxing temperatures and precipitate the wax while retaining sufficient of said hydrocarbon solvent in liquid form to permit ready separation of the wax, mechanically removing the wax, and separating the hydrocarbon liquid from the dewaxed oil.

23. In apparatus of the class described, a closed chill chamber, a closed wax separator, a closed receiver for wax-free liquid, connections whereby a liquid comprising a liquefied refrigerant may be passed into said chill chamber, thence to said wax separator, and thence into said receiver, means for compressing and condensing refrigerant vapors, and refrigerant vapor collecting means for collecting vapors from said chill chamber, separator and receiver and conducting them to said compressing and condensing means whereby low temperature in various parts of the system may be maintained by vaporization of refrigerant therein.

24. A process for the treatment of oil containing wax which comprises diluting said oil with a liquefied normally gaseous hydrocarbon solvent, acid treating the oil dissolved in said solvent, removing the acid reaction products from the oil dissolved in solvent, chilling the solvent solution of oil substantially free of acid reaction products to separate wax, removing the wax from the oil solvent solution and removing the solvent from the substantially wax free oil.

25. A process for the treatment of oil containing wax which comprises diluting said oil with a liquefied normally gaseous hydrocarbon solvent, acid treating the oil dissolved in said solvent, removing the acid reaction products from the oil dissolved in solvent, vaporizing a portion of the solvent from the solvent solution of acid treated oil to chill the oil and separate wax, removing the wax from the oil solvent solution propane-oil solution, substantially free of acid reaction products, to separate wax, removing the wax from the propane solution of oil and removing the propane from the substantially waxfree oil.

ULRIC B. BRAY.

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