US2086666A - Process for dewaxing oil - Google Patents

Description

I BY 4O ATTORNEY.

H. F. FISHER PROCESS FOR DEWAXING OIL Filed Aug. 21, 1953 a 7 m .5 m 1; 8 w w y 8 w I: a 1 5 6 8 w v A R6 .0 k C/ 1v H v 0 Y- D o m 8 L m 5 1 f 55 g a M 4 4 B, "m.

July 13, 1937.

I e N O W 0 IEIRQNR m A 7 5 3 m w m 5 E0: QEM kkbw Patented July I I 13, 1937 PATENT OFFICE I 2,086,666 Paoouss Fon DEWAXING on.

Harmon F. Fisher, Los Angelos, Calif., assignor to Union Oil Company of. California, Los Angeles, Calif., a corporation of California Application August 21, 1933; Serial No. 686,015

6 Claims.

This invention relates to wax separation from wax-bearing oil. The invention relates more particularly to the separation of precipitated wax from suspensions-in oil.

Many crude oils from which lubricating oil is produced contain paraflin or wax. It is found associated with lubricating oil fractions of paraffin base crude oil, asphalt base crude oil and the mixtures or blends of lubricating oil fractions of both paraflin and asphalt base crude oils. The wax is not only of limited lubricating value but limits the minimum temperature at which lubricating oils containing it can be used, by congealing at low temperatures. Therefore, in the production of lubricating oil from petroleum frac. tions containing wax and paraflin, it is customary to remove a substantial portion of the wax and 'paraflin present in the oils in order to lower its poulr point and the temperature at which it congea s.

The separation of wax from wax-bearing lubricating oil fractions has been accomplished by several processes in the past. The most common and oldest of which are the cold settling process and the "cold pressing process".

In the cold settling process" the wax-bearing oil is first diluted with a quantity of a light hydrocarbon fraction, such as naphtha, gasoline'or kerosene. The diluted wax-bearing oil is then slowly chilled by suitable refrigerating means for a period of from twenty 'to fifty hours until a temperature is reached at which a substantial portion of the wax is precipitated. The chilled oil and precipitate mixture is, then allowed to stand for a period of several weeks to allow the wax to settle to the bottom of the chilling tank. Objections to this process are the cost of refrigeration for the necessary long periods of time, the large capacity of refrigeration and storage equipment necessary and the poor separation of v wax and oil obtained.

in the cold pressing process the wax-bearing oil is chilled slowly, as in the above described cold settling process. The chilled mixture of precipitated wax and oil is then pumped through a filter press at a high pressure. The wax is collected upon the filter and the oil is removed as a pressed distillate relatively free from wax. This process has found commercial application only in conjunction with oil having wax present in a crystalline form. The other forms of wax, such as amorphous and micro-crystalline -wax have been found extremely diflicult and impracticable to separate by filtration methods.

It has been found that" the enumerated disadvantages and other disadvantages inherent in the common methods'f'of wax separation methods may be overcome by the process which will be, described hereafter.

It has been discovered that wax can be readily the precipitated wax from the oil.

separated from wax-bearing oils by mixing thewax-bearingoils with suitable diluents, chilling the solution to a temperature at whichthe ,wax

precipitates from solution and the resulting mixture of wax-bearing oil, diluent and precipitated wax, subjected to an electric field. A major portion of the precipitated wax acted upon by the electric field is separated from the mixture in the form of a deposit on the electrodes between whichthe said treating field is established. That portion of the precipitated wax which is not removed from the mixture in the form of a deposit is agglomerated orotherwise conditioned tomore readily separate from the mixture by settling. The diluent may be recovered by distillation subsequent to the separation of the wax from the solution and recycled through the system, according to the processdescribed above.

Diluents are usually employed during dewaxing by these methods to render the waxy oil fiuid at the temperatures at which the wax is precipitated out of solution. However, thepresence of a large quantity of diluent in the wax-bearing oil is always detrimental by reason of its solvent action upon the wax. Even at the lower temperatures many diluents retain an appreciable amount of wax in solution. Therefore, when large quantities of diluent are employed during dewaxlng a relatively higher pour point is obtained in the final product due to the wax retained in solution in the diluent. Furthermore, it is undesirable to use large quantities of diluent because of the added cost in recovering these materials from the dewaxed oil product.

Therefore, it is desirable to employ a minimum quantity of diluent in the wax-bearing oil while subjecting it to treatment for the removal of wax according .to the methods described hereinbefore. Moreover, it is desirable when the characteristics of the lubricating oil permit, to treat the oil according to the hereinbefore described methods without the use of diluents. v

The preferred method according to this invention comprises treating the undiluted wax-bearing oil in a number of stages of successively lower temperatures as follows: The wax-bearing oil is chilled in the first stage-of treatment to a temperature at which wax is precipitated from solution. Following this the mixture of wax-bearing oil and wax precipitate thus formed is treated by an electric field to deposit and otherwise remove Then the oil from which the precipitated wax has thus been removed in the first 'st'ageof treatment is fur- A ther cooled in asecond stage of treatment to precipitate additionalwax from the oil. The wax-bearing oil, wax precipitate mixture thus formed in the second stage of treatment is again subjected to an electric field, as in the first stage, to remove additional precipitated wax. These of stages of treatment, the precipitated wax being removed electrically in each stage, inthe manner described for the first and second stages, until the temperature at which wax will precipitate from solution is reduced to the desired pour point temperature of the oil. I

It has been found that wax-bearing oil can be dewaxed by this method in many cases without theu se of diluents. Some undiluted wax-bearing oils are solid at ordinary temperatures and when this condition obtains the said wax-bearing oil' is heated in the initial stage or stages of treatment to a temperature at which the wax-bearing oil .is sufiiciently fluidyet contains precipitated wax. Thus each stage of treatment is carried on at a suitable temperature between the cloud point temperature and the congealing temperature of the wax-bear ing oil where the fluidity of the re-. suiting mixture of wax-bearing oil and wax, precipitate is suitable for efiicient electrical treatment and deposition of the precipitated wax. When it is desired to operate the various stages of treatment at a lowerrange of temperatures than is possible with undiluted oil, the wax- ,bearing oil is dissolved in a suitable quantity of diluent before being subjected to the said, stages of treatment.

- ing the refrigerated wax-bearing oil from con-- The addition of certain electrolytes to the wax bearing oil or the wax-bearing oil-diluent solution prior to or during refrigeration and electrical treatment has been found to aid in theseparation of precipitated wax from the oil 'by.

electrical treatment. The electrolyte'in solution is also beneficial in obtaining thorough andeflicient separation of the undeposited precipitated wax from the solution by settling. Electrolytes which have been found suitable in aiding sepa- .ration are: inorganic acids, such as sulphuric, hydrogen chloride;.organic acids, such as formic, acetic, oleic-,rstearic, naphthenic and palmetic;

vmetallic halides, such as aluminium chloride, ierric chloride, stannic chloride and zinc chloride.

settling, agglomeration and deposition of theprecipitated wax and these substances may be mixed with the wax-bearing oil. or the diluent prior to their introduction to the stages of treatment.

In some cases it is advantageous to introduce simultaneously finely divided solids and electrolytes into the wax-,bearing oil, or into the waxbearing oil-diluent solutions. which are undergoing treatment. Finely divided materials which I have discovered to be applicable to this process are iron, aluminium, lead, zinc, tin, litharge, graphite, iron oxide, carbons, such as lamp-black or gas-black, asphalt, diatomaceous earth, clay, sawdust or wood flour. The wax-bearing oil may be dissolvedin a diluent prior to refrigeration according to the process described above for the purpose of preventgealing and to maintain the mixture sufliciently fluid to allow the precipitated wax to be readily separated from the mixture. Diluents which I have found suitable forthis purpose are propane,

V aoeaeco steps are repeated through any desired number' pentane, butane, petroleum ether,- naphtha, gasoline, kerosene, acetone, benzol, mixtures of acetone and benzol, methylchloride and halogenated 'hydrocarbonsfsuch as monochlorodifluorometh'ane, dichlorodifluoromethane and 'dichloroethylene and trichloroethylene, ethers, alcohols-and various mixtures thereof. ber of these solvents, such as propane, butane and methylchloride. are normally gaseous and may;by-a reduction of pressure, he made to serve as refrigerants as will be described hereinafter.

Refrigeration of. the. wax-bearing oil-diluent solution is accomplished either by means of external indirect heat exchange with a refrigerant, internal indirect heat. exchange by means of a refrigerant circulated through cooling coils or by direct cooling by ineans of evaporation of a normally gaseous liquid diluent from the waxbearlng oil solution. It has also been found possible to cool the-rcontents of the electrical treater chambers by evaporation therein of liquid sulphur dioxide, carbon dioxide or ammonia.

The currents and/orpotenti'als preferably employed in treating the refrigerated wax-bearing -oil or solution of wax-bearing oil and diluent, .contaming precipitated wax, are either continuous direct current or interrupted direct current.

When direct current either continuous or interrupted is employed, deposition ofa portionof v the precipitated wax on the electrodes immersed in the mixture takes placeand the remainder wise eflected, so that it is readiiy'settled from of the precipitated wax is agglomerated, or other;

the solution. Analternating potential may also I be imposed upon the solution containing precipitated wax to agglomerate the wax and render, it more readily separated by settling. Potential gradients of 5,000 to 60,000 volts per inch through the solution containing precipitated-wax have been foundmost eflective for deposition and agglomeration. Some precipitates exhibit a definite negative charge and are, therefore, de-

posited in greatestquantity on the positive electrode.

Materials which have been effectively used for electrodes are iron, aluminium, copper, zinc and- 'lead.

Objects of this invention are to overcome th enumerated. disadvantages and other disadvantages of the common wax separation methods and to provide a novel process for separating wax y from oil which will be efficient, economical, of high capacity and less costly in time and equipment than the processes heretofore employed.

Other objects are to provide a process, for the separation of precipitated wax from.wax-bearing oil which will be complete, inwhich the time of separation of the wax is greatly reduced and in,

which the time and'energy consumption of refrigeration is a minimum and by which fine preeipitates both crystalline and amorphous can be effectively separated; "Another object of this in-' vention is to provide a process for the separation of wax from wax-bearing oil in "stages-6f successively lowered temperatures. Another object of the invention is to provide a process for dewaxing oil in which the quantity of diluent employed in connection therewith. can be minimized or entirely eliminated. Another object of this invention is to provide a method for. separating wax which has been precipitated by quickly cooling or shock chilling. the wax-bearing oil. 7 J I In general these objects are attained according to this invention through treating the mixture of oil'and precipitated wax by an-electrical treatment by. chemicals and/or finely divided solid materials and electrical treatment in stages at successively lower temperatures.

The invention, broadly stated, comprises a method of separating wax from wax-bearing oil electrically in a plurality of stages, these stages being at successively lower temperatures. The invention more specifically stated comprises a multi-stage process for treating either'undiluted wax-bearing oil or wax-bearing oil dissolved in a diluent, by an electric field or current to separate wax therefrom by agglomeration, settling and/or deposition, each stage comprising cooling the wax-bearing oil to precipitate wax, subjecting the thus formed wax-bearing oil-wax .precipitate mixture to an electric field and removing the precipitated wax from the oil. The invention also comprises the combined method of treating wax-bearing oil with chemicals and/or finely divided solid materials and an electric field or current in a plurality of stages at successively lower temperatures to aid in separation of the wax therefrom. The invention specifically stated consists of a process for removing wax from waxbearing oil comprising adjusting the temperature of the wax-bearing oil to precipitate wax from solution, subjecting the mixture of waxbearing oil and precipitated wax to an electric field, separating the precipitated wax from the oil, reducing the temperature of the wax-bearing oil from which the wax has been separated to precipitate additional wax,. subjecting the mixture of the saidw'ax-bearihg oil and additionally precipitated wax to an electric field, separating addithe treater.

tionally precipitated wax from the oil and soon,

repeating the above described steps through anyrequired number of stages, each at reduced temperature for the removal of sufiicient wax to obtain the desired pour point oil..

Other objects, advantages and features of the invention will be evident hereafter.

The preferred structure of each electrical treater unit comprises a gas tight, vertical cylinder having an upper spherical head and an inverted conical bottom with a cylindrical electrode situated axially.within the electrical treater shell and supported by and electrically connected through a high tension lead-in insulator extending through the center -of the said top spherical head. The electric treating potential is maintained between said cylindrical electrode and the wall of the treater shell by means of a high voltage generator or transformer through suitable electrical connections. The p'recipltated wax which settles out of the wax-bearing oil and the wax which is removed from the treater walls and electrodesurfaces moves downward toward the apex of the inverted conical bottom of the electrical treater shell where it enters a pump by means of which it is ejected from the system. Refrigeration of the contents of the electrical treater units may in. some cases be directly attained by evaporation of a normally gaseous liquid from solution with the waxy oil undergoing treatment in structed towithstandthe pressures associated with The treater shellis, therefore, con-.

provided in the inside of the electrical treater shell through which a refrigerant may be circulated for the purpose of cooling the treater contents or maintaining its temperature constant. The wax-bearing oil or wax-bearing oildiluent solution is introduced at a pointin the of the electrical treater and directing it to the 6 outlet in the conical bottom. A periodic reversal of the polarity of the electric potential impressed upon the electrodes in the treaters has been found efiective in many cases in removing deposited wax. Upon reversal of polarity the deposited wax -is observed to be suddenly broken away in large pieces and momentarily repelled from the electrode, after which redeposition and continued deposition of the wax immediately takes place.

The deposited wax particles thus re- H moved from the electrode'surfaces, if allowed a short settling period without imposition of electrical potential thereupon, rapidly settle through the oil to the bottom of the treating chamber from which they are readily removed. In some cases where mechanical or other means for removing wax from the treaterwalls and electrodes are not used it has been found satisfactory to utilize a battery of two or more treaters in parallel so that they can be operated intermittently or alternately allowing the ones not in operation to be entered and the accumulated wax removed.

The accompanying drawing illustrates one embodiment of the invention in which:

Figure 1 is a diagram of apparatus by means of which the process of multi-stage dewaxing can be carried on.

Figure 2 is a graph showing the physical states for a given wax-bearing lubricating oil under varying conditions of temperature and wax percentage.

Wax-bearing oil at a temperature'above its congealing point is stored in tank' III. This waxbearing oil is withdrawn from tank III by pump H and forced through line l2, valve l3, mixing valve I4, line i5, refrigerator l6 and valve l'l' into the first stage treater unit A. The waxbearing oil is chilled in refrigerator l6 to a temperature suificiently low to cause precipitation of .a portion of the wax from the oil yet to a tem-' perature insufliciently low to cause the mixture to congeal or to cause the mixtu'res fluidity ,to be materially reduced. The chilled oil containing precipitated wax, in treater unit A, is subjected to an electric field between the treater wall and the electrode 20, resulting in. a major portion of the wax precipitate being removed from the oil and deposited on the electrical treating chamber wall and. electrode. with other wax which settles, is removed from the interior surf aces of the electrical treater chamberA and withdrawn from the conical bottom thereof by means of pump 2|. A high potential'electric field is established through the oil containing precipitated wax in the electric treater A between the central electrode 20 and the treater wall by means of a high voltage supplied by a generator through requisite electrical connec- 65 This deposited wax, along ,tions comprisingconductor 26; switch 21 and treater lead-in insulator bushing 28; The electrical return circuit from the treater shell is com pleted' through the ground and the generator ground connection 30. The electrically treated 0nd stage electric treater unit B. The said waxbearing oil from treater A is-again reduced in temperature while passing through refrigerator bottom by means of pump 4!.

36 to a point where additionalwax is precipitated from solution but to a temperature insuificient, as in the first stage of cooling, to materially reduce the fiuidity of the mixture. Here, as in the 1 first'stage of treatment, the wax-bearing oil con- 'talning precipitated wax is subjected to an electric field between the treater wall and. the electrode 40 where precipitated wax is removed from the saidwax-bearing oil by deposition and settling. The deposited wax removed from the treater wall and electrode 40 of unit B along with that which settles, is removed from the conical The high potential electric field established through the solution containing precipitated wax: in the treater unit B between the wall of the electrode 40 is supplied by the generator 25 through electrical connection. 26, switch 42 and lead-in insulator bushr ing". ,The electrical'return circuit from the treater shell is completed through the ground and ground connection 30. The wax-bearing oil from which a portion of the wax has been removed in the first and second stages of treatment in treater units A and B is withdrawn from the second stage treater B through line 45 and introduced through refrigerator 46 and valve 41 into the third stage electric treater unit' C. The wax-bearing ol, as in the first and second stages, is again reduced in temperature by refrigerator 46 to a point where additional wax is precipitated from solution 'yet'to a temperature insufflcient to materially decrease the fluidity of the resulting mixture of wax-bearing oil and precipitate. The wax-bearing oil containing the said precipitate is again subjected to a high'potential electric field between .the central electrode 50 and the wall of the treater unit C, as in the first and second stages. Wax removed from the oil by deposition and settling is ejected from the system by meansof pump 5|. The high poten-. tial electric field between the wall of treater C and the central electrode is also supplied by means of a high voltage generator 25 through connecting conductor 26, switch 51 and lead-in insulating bushing 58. The electrical return circuit from the treater shell, as in treater units A and B, is completed through the ground and ground connection 30.

The oil from which wax has been removed in the first, second and third stages of treatment in treater units A, B and C, respectively, is withdrawn from treater unit C through line 65, valve 68 and lines 69 and T0 to the dewaxed oil storage tank 12. In some cases the characteristics of the oil treated are such that in the latter stages of treatment the viscosity of the said oil becomes. so great that continued treatmentof the oil in additional stages is impossible without dilution. .In this case a suitable diluent is supplied to any one of the stages of treatment frorh diluent storage tank'l5 through suitable connections, such as shown in the drawing by line 16, valve 11 and aoeaeee line 19;;The diluent in line I9 joins and mixes with the wax-containing ofl withdrawn from any one of the treater units, such as'unitB, through line 45.. The wax-bearing oil-diluent solution resulting from the mixture of the'diluent from line 19 and the wax-bearing oil from line 45 proceeds through refrigerator 46 and valve 41 into 'the next stage of the treatmentaccording to the process described herei'nbefore. In some cases the characteristics ofthe wax-bearing oil undergoing treatment'are such that dilution thereof is necessary in the initial treating stage in order to maintain" sumcient fluidity and in this case the diluent from diluent storage tank 15 after flow- I ing through line J6 and-valve 89 is mixed withthe wax-bearing oil in mixing valve l4. The solution of the diluent'andyvax-bearing oil resulting from said mixture in mixing talve l4 proceeds through line l5, refrigerator l6 and valvel1 into the initial stage of treatment in treater unit A, as

described'hereinbefore.

When diluents are employed in any of the stages .of treatment, it lsnecessary to separate said diluents from the final dewaxed oil product and this is accomplished .by means of distillation in a still 85. The dewaxed oil containing diluent in solution is withdrawn from the final treater C through line 65, valve 66 and introduced through,

line 61 into still '85. Heat is indirectly supplied to still by means of heatingcoil 86.- The bottoms from the still 85 comprising the dewaxed oil 1 from which the diluent has been stripped is withdrawn through bottom outlet'8l, valve 88, cooler 89 and run through line 10 to the dewaxe'd oil storage'tank 12'. i I I The diluent vapors removed from the dewaxed oil arewithdrawn from still 85 through vapor line 90 and, where the diluent employed is normally liquid, the vapors arecondensedln cooler 9| and returned by means of pump 92 through line 94!.

to the diluent storage tank 15. Where the diluent used is normally gaseous the vapors from the still are cooled in cooler 9|, compressed in compressor 92, condensed in cooler 93 and the condensate returned through line 94 to the diluent storage tank 15.

When coolingv or refrigeration of the waxbearing oil in the treater unit A, B or C is accomplished directly, wholly or in part, by evaporation of a normally gaseous diluent the vapors are withdrawn from the tops of said treater units through vapor outlet connections 96, 91,- 98 and pressure regulating valves 99, I00 and I0 I respectively, and the said vapors compressed by means of compressor I02, cooled and condensed in cooler 93 and the condensate, as hereinbefore described,

returned through line 94 to the diluent storag tank ,15.

When it is advantageous to use electrolytes.

and/or finely divided solid materials in conjunction with the refrigeration and electrical treatment, according to the process of this invention, these materials may be mixed or dissolved in the diluent in storage tank 15 or in the wax-bearing oil in storage tank l0 priorto their introduction into the following treating stages.

' quent steps of treatment carried on at successivea given degree of dilution of the said lubricating oil fraction is determinedby means of a typical graph as shown in Figure 2. This graph comprises lines showing the cloud point and congealing point for a given wax-bearing lubricating-oil fraction said lines being obtained by plotting wax percentage abscissa against oil solution temperature as ordinates, for the stated conditions. The cloud point line indicates the temperatures at which given concentrations of wax will start forming wax precipitates from solution. The

solid line indicates the temperatures for given plastic line.

' concentrations of wax at which the entire solution will solidify. The semi-plastic line between the cloud pointline and the solid line indicates a region in which the mixture of oil and wax precipitate changes from a fluid to a semi-plastic state.

Multi-stage treatment must be confined to steps of refrigeration in which the temperature steps are such that the characteristics of the resulting mixture of wax-bearingoil and precipitate will lie chiefly in the region represented on the graph of Figure 2 between the cloud line and the semi- E, F, G, H and I show diagrammatically what may be expected and how many stages will be necessary for a multi-stage treatment-of a given lubricating oil fraction. The horizontal portions of the said stepped line in the graph of Figure 2 represent the points during the stage and treatment of the lubricating oil fraction where the wax precipitate is. electrically removed from the oil. The vertical portions of the said stepped line indicate the point in the multi-stage treatment where the temperature of the lubricating oil fraction is reduced following each of said pointsof removal of precipitated wax. Therefore,each pair of 'horizontal and vertical portions of the said stepped line represents the operations of one stage of treatment.

For example, starting with a 30% wax concentration in a solution of oil as represented in-the graph of Figure 2, the first dewaxing stage would remove all dispersed solid wax precipitateparticles at a temperature of 70 F. as indicated by the horizontal path AB. The temperature of the fluid mass following this removal of wax would then be dropped to approximately 42 F.

as indicated by the vertical path 3-0, at which temperature, additional wax would be forced from I solution into the solid phase and the mixture in this manner through four stages, as represent-' ture of the waxy oil is mospheric temperature, it will be necessary to would again appear as a semi-fluid, semi-plastic mass. At this temperature the next dewaxing stage is carried out in which the additionally precipitated wax is removed as indicated by the horizontal path C-D. The process is continued apply heat to the mixture undergoing treatment in the initial'step of the. process with the subseapparatus which accomplishes the The steps, or arrows, A, B, C, D,

1y lowered temperatures. When such heating of the oil prior to the initial stage of the electrical dewaxing process is necessary, such heat may be introduced by suitable heating means in the wax-bearing oil storage tank 10.

The process and apparatus is not to. be limited to the treatment of oils for the removal of wax but is applicable to the treatment of similar substances for the removal. of asphalt, asphaltines, petrolatum, sludges and other substances and impurities both solid and plastic.

The foregoing is merely illustrative of one apparatus and method and the invention is not limited thereby, but may include any method and same within the scopeof the invention.

I claim: i

1. A process for separating wax from waxbearing oil comprising heating the wax-bearing oil-wax mixture to a temperature at which it is a fluid containing wax precipitate, subjecting the thus heated mixture to an electric field and separating wax from the oil.

2. A process for separating wax from waxbearing oil comprising heating the wax-bearing oil-wax mixture to a temperature at which it is a fluid containing wax precipitate, subjecting the thus heated mixtureto an electric field and sepj .arating wax from the oil, cooling the said oil from which wax has been removed to precipitate additional wax from solution, subjecting the oil containing the additionally precipitated wax to an electric field and separating additional wax from the oil.-

3. In a process for separating war: from waxbearing oil comprising cooling the wax-bearing oil to precipitate wax from solution, electrically depositing said wax precipitate on electrodes immersed in said wax-bearing oil, intermittently reversing the polarity of said electrodes to dislodge deposited wax and allowing said dislodged wax to settle out of the oil.

4. A process for separating wax from wax-bearing oil which is congealed at ordinary temperatures comprising heating the wax-bearing oil to a temperature above its congealing point but below its cloud point, subjecting the thus heated mixture containing precipitated wax to an electric field and separating wax from the oil.-

5. A process for separating wax from waxbearing oil comprising heating. the waxbearing oil in the absence of a. diluent, adjusting the temperature of the thus heated wax-bearing oil to a value at which it is a fluid containing wax precipitate, subjecting the thus treated mixture to an electric field and separating wax from the oil.

6. A process for separating wax from waxbearing oil comprising heating the wax-bearing oil in the absence of a diluent to a temperature above its pour point, subjecting the said oil to an electric field to separate a portion of the waxy from the oil, adjusting the temperature 'of the said oil from which a portion of the wax has been thus removed to precipitate additional wax from the oil, adding a diluent to the said oil from which a portion of the wax has been removed, subjecting the diluted partially dewaxed oil containing precipitated wax to an electric field and separating additional ,wax from the oil.

HARMON F. FISHER.

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