US2031210A - Process and apparatus for dewaxing oil - Google Patents

Description

Feb. 18, 1936. 1.. DILLON ET AL PROCESS AND APPARATUS FOR DEWAXING OIL Filed Sept. 19, 1933 I). A I n I I III :\5 6! cifllllllllliilll I. .III II 1 11: VI 1 I miwmuwm .7 fqsqfi mm mm mm. M m

INVENTORS ZJZeDzY/on QT Claudefiffi'mff A'TTORNEY.

Patented Feb. 18, 1936 UNITED STATES PATENT OFFICE PROCESS AND APPARATUS FOR DEWAXING OIL Application September 19, 1933, Serial No. 690,094

6 Claims.

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

When the temperature of lubricating oil containing wax or paraflln is sufficiently lowered wax or paraifin'is found to begin to be precipitated from solution in the form of a colloidal suspension and as the temperature is further lowered, more wax is precipitated until the oil and wax mixture finally co-ngeals to a semi-plastic or even solid mass. Oils containing a large quantity of wax will have relatively high congealing temperatures and oils containing a small quantity of wax will correspondingly have low congealing temperatures. Thus it is apparent that the presence of wax limits the minimum temperature at which lubricating oils containing it can be used, by congeallng or solidifying at low temperatures. The pour point of a lubricating oil is that temperature 5 F. above the temperature at which the oil, under certain specified test conditions, congeals or ceases to flow and it is apparent that the presence of wax or paraffin in lubricating oil greatly influences this characteristic of the oil. Therefore, in

the production of lubricating oil it is necessary to remove a large proportion of the wax or paraifin present therein in order to lower its pour point and therebyv extend'the lower range of temperatures at which it retains its lubricating qualities.

Wax has been separated from oil by a number of processes, three of which are the cold settling process, cold pressing process and the recently developed electrical process. In the separation of wax from waxbearing oils by the electrical process the wax-bearing oils are mixed with suitable diluents, the solution of oil and diluent chilled to a temperature at which the wax precipitates from solution and the resulting mixture of waxbearing oil, diluent and the suspension of precipitated wax subjected to an electric field between electrodes submerged in said solution. A

major portion of the chilled precipitated wax suspension under the influence of the electric field is separated from the oil-diluent solution in the form of a deposit upon the electrodes between which the said treating field is maintained. The oil-diluent solution thus freed from wax is then distilled to recover the diluent and the wax free oil.

After a short period of electrical treating to remove precipitated wax from the chilled waxbearing oil according to the hereinbefore described process the electrodes upon which the wax is deposited become thickly coated with the deposited wax and it is necessary that this Wax be continuously removed in order to maintain the apparatus in operative condition. If the wax is allowed to accumulate to an appreciable thickness 5 on the electrodes it decreases the effectiveness of the electrical precipitating and depositing action and reduces the cross sectional area of the passage between the electrodes through which the oil undergoing treatment flows. This reduction in lo cross sectional area of treating space results in an increase in velocity in the wax-bearing oil undergoing treatment and a consequent decrease in time during which the oil remains in the treating field and thus the capacity of the treater is 15 eiiher reduced or the thoroughness of the treating impaired by allowing an accumulation of wax on the electrodes. Furthermore, the wax may in time accumulate to the extent that the entire treating space between the electrodes is filled with 0 it and the wax-bearing oil either forced to channel its way through the wax or be entirely stopped from flowing. The means heretofore employed for removing deposited wax from the electrodes have been in the form of scrapers which returned 5 ihe wax accumulations to the oil-diluent solution from which they were formerly deposited. Subsequent settling of the thus removed wax in the treated oil was thereby made necessary to accomplish final separation.

Apparatus for the electrical deposition of wax from oil may be constructed to operate over long periods of time without attention by providing said apparatus with a large area of electrode surface and suitable mechanical means for main- 35 taining this surface reasonably free from deposited wax. Moreover the wax may be positively removed from the electrode surface out of contact with the wax-bearing oil and directly disposed of without recontacting or being returned to the oil.

Objects of this invention, therefore, are to provide an apparatus for dewaxing oil which will be efiicient, of high capacity and capable of operating for long periods of time Without attention. Other objects are to provide an electric treater for dewaxing oil in which the completeness of the separation of precipitated wax from the waxbearing oil will be a maximum; in which the electric treating zone will be continuously maintained in operative condition by mechanical removal therefrom of accumulated wax, and in which the said mechanical removal of accumulated wax is positively accomplished out of contact with the wax-bearing oil and positively removed from the treater without recontacting the said wax-bearing oil or the dewaxed oil.

In general these objects are attained according to the invention by providing an electric treater structure incorporating a large movable electrode surface area adapted to be removed from the wax-bearing oil after a wax deposit has been formed thereon and suitable mechanical scraper means for periodically or continuously freeing said electrode surfaces from said accumulated deposited wax while removed from and out of contact with either the said wax-bearing or dewaxed oil. These objects are also attained according to the invention by providing suitable mechanical means for positively removing the wax from the electric treater without recontacting either the wax-bearing oil or the dewaxed oil from which said wax was deposited.

The invention broadly stated includes a process and apparatus for removing wax from waxbearing oil wherein a movable electrode is placed in contact with the wax-bearing oil and wherein said electrode receives a layer of electrically deposited wax on its surface while in contact with said oil and wherein after said deposition of wax, the surface of said movable electrode carrying the layer of deposited wax is removed from contact with the wax-bearing oil and the said deposited wax layer mechanically removed therefrom while out of contact with said wax-bearing oil.

The invention more specifically resides in a.

process and an apparatus adapted to carry on the process wherein a continuously moving electrode surface is maintained in partial contact with oil to be dewaxed, and wherein a mechanical scraper is provided for removing deposited wax from the moving surface of said movable electrode, said removal of deposited wax being accomplished by said scraper while out of contact with the oil and wherein provision is made to positively eject said wax from the treater without recontacting said oil and without necessitating subsequent settling for separation and wherein means is provided to wash adhering oil from the deposited wax surface prior to its removal by the scraping means and wherein oil circulation means is provided to accomplish a continuous circulation of substantially dewaxed oil through the treater and through the electrical field therein and wherein provision is made for constantly withdrawing a portion of the dewaxed oil from the said circulating body of oil and wherein pro.- vislon is made for constantly adding an equal quantity of wax-bearing oil to said circulating body of oil, and wherein local refrigeration of the wax-bearing oil at the surface of the electrode is provided for and wherein suitable means is provided for imposing a high electrical potential upon the said 011 at the said electrode.

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

The accompanying drawing illustrates one embodiment of the invention in which Figure 1 is a sectional elevation through the axis of the treater, Figure 2 is a cross section through the treater taken at line 2-2 in Figure 1, Figure 3 is a section through wax collecting trough on line 33 and Figure 4 is a similar section through the wax collecting trough illustrating an optional arrangement of means for disposal of wax.

The treater unit illustrated in Figures 1 and 2 is provided with a rectangular enclosure or tank l3, inside of which a hollow, cylindrical drum electrode II is centrally, coaxially and rotatably supported onbearings I3 and i4. Blowrotatiou ofsaiddrum ll isacoomplishedbymeansofan electricmotor I3 drivingsaiddrumthroughshaft l1whichextendsintotank l3 throughstuiilng box l3 andontheend ofwhichislocatedaworm pinion 23 whichmesheswithworm gear2l which isinturnsolidlyfastenedtodrumll through drum shaft 22. p

A segmental cylindrical electrode 23 is coaxially positioned below said drum electrode II, by insulating support 21 with a short free space therebetween as shown at 23.

The insulator 21 in addition to being a support for electrode 23 is hollow and forms an inlet between the outside of the treater unit enclosure I 3 and the space 23 between the electrodes. A pump 33 driven by an electric motor 3| is provided for circulating oil from the space surrounding the electrode 23 in the enclosure I3 to and through said space 23 between the said electrodes. Oil from said space in the container l3 outside of electrode 23 is withdrawn through two outlets 32 and 33 through valves 34 and 33 and suction lines 33 and 31 to pump 33 from which it is discharged through valve 33 and inlet connection 41 through the insulator 21 to the space 23 between the electrodes and flows therebetween in a substantially axial direction with respect to drum I i to return to the before mentioned space in container II. A T 33 is provided between the discharge of the pump 33 and the valve 33 to which a line 42 is connected and through which a portion of the circulating oil may be continuously withdrawn. A T 44 is provided between valve 33 and inlet connection 4| to which a line 43 is connected and through which a quantity of the wax-bearing oil may be continuously introduced to the circulating system. A valve 43 in the oil inlet line 43 limits the quantity of oil introduced into the system and it is regulated by a liquid level float control 43 in order to maintain a liquid level in the treater inside of container l3 approximately as shown by liquid level line 33.

A scraper 32 and trough 33 extend along and make contact with the full length of drum electrode II. A heater element 34 shown in Figure 3 is located near the bottom of the trough 33 and extends throughout its length. Electrical connection is made to the element through conductor 33 and insulator 33 and the circuit completed through the ground. A bracket 31 supports the grounded end of the heater element under tension in its proper position near the trough bottom. The purpose of this heater element is to heat and melt the wax shavings in the bottom of trough 33 after they are removed from the drum electrode by scraper 32. An outlet pipe 33 with valve 33 makes connection with the end of the trough 33 through the wall ll of the treater unit container and serves to drain melted wax from said trough and from said treater. A wax screw mechanism may in some cases be employed in the trough to eject the solid wax from the treater as shown in Figure 4. Here a screw 33 is employed to move the wax along the trough bottom to a depression 3i where it is allowed to accumulate in suflicient quantity to be withdrawn by means of a wax pump 32.

A spray connection 33 carrying spray head 33 which extends along the length of the drum ll enters the treater unit at 31 above the upward moving side of said drum II.

A vapor outlet pipe 13 in the top of the treater unit container i3 serves, through valve 1|, to

exhaust gases and regulate pressures and temperatures in container l0.

A high tension lead-in insulator I3 is provided in the top of the treater unit through which electrical connection is made between a high voltage generator 14 and the electrode 25 by way of conductors I5 and I6. The electrical return circuit to the generator 14 is completed by way of the drum electrode H, the ground and ground connection H.

A pipe extends into the hollow drum electrode H through the hollow drum shaft 22 and.

through flange 8!. Flange 6| closes the end of a side outlet connection 82 which is placed coaxial with the drum I! on the end of the treater unit container l0 and into which shaft 22 projects through a stufling box 83. The hollow shaft 22 is open ended and connects the inside of the drum II with the space 84 inside of the side outlet connection 82. A vapor outlet pipe connects with said side outlet connection and serves to vent drum ll of gases by way of hollow shaft 22 and space 84. Spacer rings 81 and 88 attached to the inside of the container opposite the ends of the drum electrode it serve to shield the said endsthereof from contact with waxy oil and thus prevent wax accumulation where no provision is made for its removal. Slight clearance is allowed between the rings and drum. A liquid refrigerant, such as a normally gaseous hydrocarbon may be introduced into drum l I through pipe 80 which extends therethrough. The normal liquid level of the thus introduced refrigerant is maintained approximately as shown by liquid level line 86.

The operation is as follows: A body of substantially wax free oil or an oil having a pour point which is practically that which is desired in the finished product is established in the treater unit within the container or tank I I], filling approximately the lower half thereof and the space between the drum electrode I and the segmental cylindrical drum 25 to a liquid level as shown at line 50. Circulation of this oil is established and maintained between the said electrodes II and 25 by means of a pump 3|] driven by a motor 3i. Pump 30 takes suction from the body of oil in the treater through outlet connections 32 and 33 on either side of the insulating support 27 through valves 34 and 35 and lines 36 and 31 and discharges the thus withdrawn oil through valve 39 and inlet connection 4| and through hollow insulating support 21 into the said space between the electrodes H and 25. The oil thus forced into the space between electrodes H and 25 flows in a longitudinal and substantially horizontal path therebetween to the ends of the said electrodes where it returns to the body of oil from which it was withdrawn, thus completing the cycle of circulation. A portion of this circulated oil is withdrawn continuously through the withdrawal line 42 as the finished product while accomplished by chilling the hollow drum electrode from the inside and this refrigeration is accomplished preferably by introducing a normally gaseous hydrocarbon, such as propane through line 80 into the inside of the drum II to establish a liquid level therein approximately as shown at 86. Evaporation of this liquid inside of drum II provides the necessary refrigeration and the resulting vapors are allowed to escape therefrom through the hollow shaft 22, side outlet connection 84 and the vapor vent pipe 85. Heat exchange with the oil undergoing treatment takes place through the walls of the drum ll between the refrigerant inside thereof and the film of oil contacting the outside surface of said drum. The thus cooled film of oil which extends over the contacted area of the drum throughout the space between said drum electrode I i and said segmental cylindrical electrode 25 is cooled sumciently to precipitate wax from solution. The wax thus precipitated from solution lies in a region very close to the surface of the outside under surface of the drum H, and under the influence of the electrical potential established through the oil between electrode 25 and the surface of drum electrode ll readily attaches itself to said submerged surface of said drum Ii. Just enough wax-bearing oil is introduced into the circulating oil passing between the electrodes to form this wax precipitate at the temperature maintained at the surface of the drum ill while the bulk of the circulated oil in the treater. outside of the space between the electrodes is sufllciently wax free to besubstantially free from wax precipitate at the slightly higher temperature maintained therein. In other words, the wax concentration is so adjusted that at the electrode surface temperature only local precipitation of wax occurs in the treating zone between the electrodes and this only in a film of limited thickness close to the surface of said refrigerated electrode surface H.

The drum electrode ii is slowly rotated at approximately twoR. P. M. by means of'electric motor I6 through worm pinion 20 and worm gear 2 l, as explained hereinbefore, said rotation being at a suitable speed to allow the accumulation of deposited wax on the surface of the drum-ii while in contact with the liquid. As the drum rotates, as shown, in a counterclockwise direction, the surface of the wax coating which was previously in contact with the oil is constantly withdrawn from the liquid into the gas space thereabove. As the rotation of the drum continues that wax film which was deposited in contact with the liquid is removed from the surface of the electrode H by means of scraper 51 which makes contact along the length thereof and the thus removed wax moves down the inclined surface of the said scraper to the bottom of the trough 53 where it comes in contact with a heating element 54. Sufficient heat is imparted through element 54 to the wax shavings in trough 53 to melt them and the resultant liquid wax is withdrawn from the end of the trough through an outlet pipe 58 and a valve 59.

The deposited layer of wax adhering to the drum surface as it is withdrawn from the oil by rotation, may be washed by a spray of a suitable solvent to remove adhering oil and this is provided for through a spray head 66, the supply for which enters the treater through pipe 65 and inlet connection 61.

During operation a unidirectional high electric potential gradient in the region of 45,000 to 60,000 volts per inch is maintained between the electrodes and this high potential is supplied from a high tension generator or other suitable source through conductor 15, lead-insulator bushing 13 and conductor 16 to the electrode 25.

The return circuit is completed from drum ll through the ground and ground connection 11 to the said generator.

When it is desired to dissolve the wax-bearing oil in a suitable diluent before treating to maintain the desired fluidity at low temperatures this dilution may be effected before introduction of the resulting solution into the treater through line 49. Under some conditions of operation it is desirable to employ a normally gaseous hydrocarbon diluent, such as propane, in solution with the oil in the treater, to accomplish either partial or complete refrigeration. As described hereinabove, this diluent may be added to the flowing stream of wax-bearing oil under pressure and evaporation of the thus added diluent allowed to take place inside of the treater at reduced pressure. The pressure inside of the treater and thus the temperature of the contents of the treater is regulated by the vapor outlet valve H.

In normal operation the bulk of the oil in the treater is maintained at a temperature only slightly above the cloud point and, as described hereinabove, wax precipitation caused to take place only within the film of oil contacting and lying close to the refrigerated drum electrode sur-- face. This precipitation is caused by the local ized chilling of the said film of oil, through heat exchange with the cold electrode surface, to a temperature below its cloud point. Regulation of the temperature of the surface of the drum electrode to the proper degree may be accomplished by varying the pressure upon the liquid refrigerant therein in a manner similar to that described for the refrigeration of the bulk of the oil in the treater. The temperature of the contents of the drum electrode may vary from 20 to 40 F.

Instead of employingnormally gaseous diluents in the wax-bearing oil for refrigeration, it is sometimes desirable to cool the oil, either prior to introduction into the treater or during recirculation thereof, by indirect heat exchange with a refrigerant. Cooling of the oil either by external indirect heat exchange means or by indirect heat exchange through the refrigerated drum electrode, is desirable where the oils undergoing treatment are sufficiently fluid at the low temperatures to be treated without diluents or where heavy diluents, such as dewaxed lubricating oil, kerosene, gas oil and the like are employed. The reduced solubility of wax in heavy diluents as compared to light diluents makes the employment of heavy diluents desirable in the herein described process and apparatus. It is especially desirable to employ a portion of the previously dewaxed oil product as a diluent since subsequent separation of oil and diluent is then unnecessary. Recirculation of treated oil as described hereinbefore provides a method of operation in which the circulated dewaxed oil serves as the diluent for the added wax-bearing oil.

It has been found that the wax particles in most suspensions of precipitated wax resulting from chilling of wax-bearing oil are negatively charged. Therefore, by providing for a positive polarity on the movable drum electrode surface, the deposition of a major portion of the wax on the said surface is insured and it is unnecessary to provide means for cleaning the negative stationary electrode. Where the charges on the precipitated wax particles are found to differ from this the polarities of the electrodes may, obviously, be reversed as required to cause the deposition to take place on the electrode which is provided with means for wax removal.

It has been observed that a cold surface in contact with a wax-bearing oil tends to collect a film of precipitated wax. It is, therefore, an advantage to combine this function with that of the electric field by cooling the electrode on which the precipitated wax is electrically deposited.-,It is-also an advantage to cause the wax, by localized chilling, to be precipitated in a region which is very close to the surface upon which it is electrically deposited.

The 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 or 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 the invention is not limited thereby but may include any apparatus which accomplishes the same within the scope of the invention.

We claim:

1. A process for the separation of wax from wax-bearing oil which comprises circulating a body of substantially wax-free oil in a continuous path between electrodes charged to a high electric potential difference, introducing a wax-bearing oil to be dewaxed into said first mentioned oil, depositing wax on one of said electrodes and removing oil from which wax has been removed from said path.

2. A process for the separation of wax from wax-bearing oil which comprises commingling said wax-bearing oil with substantially wax-free oil, contacting said mixture with a cold surface and precipitating wax from the mixture, passing said mixture in a continuous path between electrodes charged to a high electric potential difference to deposit wax on one of said electrodes, removing wax deposited upon said electrode and withdrawing wax-free oil from said path.

3. A process for removing wax from wax-bearing oil comprising circulating a body of relatively wax-free oil in a continuous path between electrodes charged to a high electric potential difference, adding wax-bearing oil to said path, maintaining a portion of said circulating body of oil at a temperature at which wax is precipitated from said added wax-bearing oil, removing wax from said path and removing relatively wax-free oil from said path.

4. Apparatus for dewaxing oil comprising a pair of electrodes, means to maintain one of said electrodes at a low dewaxing temperature, means to impress an electric potential between said electrodes, a reservoir for containing a quantity of oil and means to circulate oil from said reservoir through the space between said electrodes and return to said reservoir.

5. An apparatus according to claim 4 and means for adding a wax-bearing oil to oil circulated from said reservoir.

6. An apparatus according to claim 4 in which one of said electrodes is a rotatable drum.

LYLE DILLON. CLAUDE E. SWIFT.

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