US2261724A - Process for dewaxing hydrocarbon oils - Google Patents

Description

Nov. 4, 1941. C, F, HQLM 2,261,724

PROCESS 'FOR DEWAXING HYDHOCARBON OILS Filed April 2l, 1939 Patented Nov. 4, 1941 UNlTED STATES sorrise asesinar Paocsss Foa DEWAIXISNG HYDROCARBON Application April 21, 1939, Serial No. 269,158

In Sweden May 17, 1938 4 Claims. 196-19) In the removal of wax from hydrocarbon oils, their distillation and transformation products and the like, it is well known to add to the waxbearing oil a diluent which is a preferential solvent for the oil and which may be lighter or heavier than the oil, ychill the solution to precipitate the wax, and sub-ject the mixture of wax and oil-diluent solution to centrifugation in such manner as to separate a substantially wax-free oil-diluent solution from a wax or petrolatum mixed with a considerable quantity of the .oildiluent solution. Owing to the comparatively viscous character of the wax, it is usually necessary to provide means for heating the separated wax either while in the bowl oron its way out of the bowl or at the dischargefrom the bowl, one common expedient being to discharge Yhot water into the wax near or at its outlet from the bowl. The separated wax, rather rich in oil as above stated, is then subjected, usually after addition of a fresh quantity of solvent, to a second-stage centrifugation, wherein wax carrying with it but little oil in solution with the diluent is separated from the bulk of the oil-diluent solution, which latter, consisting mainly of the diluent, may be employed as a diluent for preparing the oil for the rst stage centrifugal operation. If, to facilitate the discharge of the viscous wax in the rst stage operation, hot water has been added to the wax either while it is flowing toward theoutlet or as it leaves the bowl outlet, the wax, before the second stage centrifugal operation, must be dehydrated, and in any case the partly de-oiled wax must be pumped from the first stage separator to the second stage separator and in the course of its flow must be diluted with a further quantity of solvent and must usually be rechilled.

The process above described involves the use of quite expensive equipment and great care in the execution of the process and especially in the handling of the wax between the two centrifugal separation stages.

The object of my invention is to simplify the known process by eliminating all necessity for any special treatment of the wax between the two separating operations. sible to perform the two separating operations successively in a single separator with addition of added diluent between the two stages and to avoid the necessity of heating the partly de-oiled wax separated in the first stage operation, thereby performing the whole de-waxing process in a single separator or in a single set of separators,

dispensing with the equipment heretofore required to treat the waxI between the two stages, and rendering the process simpler and more economical.

The process may be practiced in separators of various constructions. The accompanying drawing shows diagrammatically, in vertical section, simplified forms of centrifuge in which the process may be practiced when a diluent, such as naphtha, lighter than the oil, is used as an oil solvent. Fig.v 1 illustrates a separator adapted to carry out the process in two stages. Fig. 2 illustrates a separator adapted to carry out the process in three stages.

The practice of the process in the centrifuge of Fig. l'will rst be described.

The chilled mixture of wax and cil-naphtha solution is .fed through a pipe l into the supply chamber 3 of the centrifugal bowl 2 whence it Y ows through channels 4 into the separating I have found it-pos- The separating chamber other. -The mixture is fed into the lower compartment, which is preferably equippedwith a set of discs 6, between which,`under the action of centrifugal force, the mixture is separated into an oil-naphtha solution free of wax and wax containing a substantial quantity of the oilnaphtha solution. The separated oil-naphtha solution, which is'of lower specific gravity,V flows inwardly through the space 8 and channel 9 to an outlet I6, whence it is thrown out into a collecting vessel l l. The wax, with the oil-naphtha solution that has not been separated therefrom, ows upwardly through the opening l, between the two compartments, into the upper separating compartment.

On itsway to the upper separating compartA ment additional naphtha is supplied to the Wax. lIhis may be done, for instance, by flowing the naphtha through an axial channel lliv bored in the bowl spindle l5 and thence through a channel I4 to an outlet I3 positioned adjacent to the opening l, s o that the wax entering the upper compartment is mixed with a fresh quantity of f naphtha. The naphtha may be at the same tem.

perature as the wax, but it maybe at a lower or higher temperature to thereby establish in the upper compartment any desired temperature different from that in the lower compartment. In the upper compartment, which may be equipped with a set of discs Il, wax, containing but little oil, ylout considerable naphtha, is separated from the bulk of the oil-naphtha solution. The latter, which is of lower specic gravity, iiowsA inward through the space I8 and thence through a channel I9 to an outlet 20, whence it is thrown out into a collecting vessel 2|. The wax, poor in oil, flows outward through the space I2 and thence through a channel 22 and over a regulating disc 24 into a collecting vessel 25.

In the channel 22 the viscosity of the wax may be reduced by heating the same in some known manner, as, for example, with steam, hot air or the like discharged, through a channel 26, upon the top of the bowl hood.

The strongly diluted oil solution discharged through the outlet 20 may be used for diluting the oil prior to the first centrifuging stage. It

may be added at any convenient temperature either before or during or after the chilling of the oil, either at one point only or at various points atdifferent temperatures.

It will be understood that, instead of naphtha, any known liquid may be used as a diluent. If it is desired to provide an oil solution of distinctly lower specific gravity than the wax, it is preferable to use as a diluent a light hydrocarbon. If it is desired to provide an oil solution distinctly heavier than the wax, it is preferable to use as a diluent a chlorinated hydrocarbon, such as trichlorethylene or dichlorethane. If, however, a heavy diluent is used, the additional diluent supplied to the centrifugal bowl must, of course, be 'added on a radius smaller than that of the two separating compartments of the bowl, since, in such case, the separated oil-diluent solution is displaced toward the periphery and the wax toward the center.

The practice of the process is not limited to the use of a centrifuge of the construction shown. There are many different known types of centrifuges such as those having inlets and outlets closed to the atmosphere and popularly called closed centrifuges and centrifuges equipped with peripheral outlets for the discharge of the heaviest constituent. 'I'he adaptation of other types of centrifuges to the practice of the process is within the skill of those familiar with the designing or operation of centrifuges.

While the process described involves a simple two-stage operation, it may be conducted in three stages by providing the bowl with an additional separating chamber.

In Fig. 2 is shown a centrifuge adapted to carry out a three-stage operation, which is preferable if it is desired to produce a practically oil-free wax. The chilled mixture of oil-diluent and wax is introduced to the lower compartment 3B in which substantially the same separation occurs as in the lower compartment of the centrifuge of Fig. l. That is, an oil-naphtha solution, free of wax, is separated from wax carrying a substantial quantity of oil and naphtha. For example, there may be discharged through the channel 9 into the receiving vessel II a 33% oil-67% naphtha solution, while a mixture of wax 25%, oil 25% and naphtha 50% is discharged from the lower compartment into the intermediate compartment 40. In this intermediate compartment a4 10% oil-90% naphtha solution is separated from a mixture of Wax 50%, oil 5% and naphtha 45%. The oil-naphtha solution escapes through a channel I9 into a receiving vessel 2l, while the wax mixture is discharged from the intermediate compartment 40 to an upper compartment 50. In the upper compartment a 2% oil-98% naphtha solution is separated from a mixture of wax 49%, oil 1% and naphtha 50%. The naphtha, containing this very small percentage of oil, escapes through a channel I into a receiving vessel 52, while the wax, mixed with naphtha and a substantially negligible percentage of oil, is discharged from the upper compartment 5U through a channel 22 into a receiving vessel 25.

Added quantities of naphtha are added to the wax mixture, through the channel I4, between the second and third separating stages as well as between the first and second separating stages.

It will be understood that the specified proportions of wax, naphtha and oil in the three-stage process just described are merely illustrative and would be subject to more or less variation in actual practice.

In either of the two processes it is practicable to make the wax in the discharge channel 22 less viscous by prolonging the channel I4 so that its Vextremity opens into the lower end of the channel 22. Sufficient diluent is fed to channel I4 to feedthe necessary quantity thereof to the upper compartment or compartments and also to dilute the wax discharged from the upper compartment. Such dilution of the-wax may be a substitute for the application of heat to the outer wall of the channel 22, or may be used concurrently therewith.

From the foregoing description it is clear that the process affords great economies as compared with the known oil-dewaxing processes. Aside from the fact that there is employed only one centrifuge (or one set of centrifuges) it is unnecessary to facilitate the expulsion of the wax from the lower compartment of the separating bowl by applying heat thereto, which is customarily done by adding `hot water at the outlet of the rst stage separator. This in turn necessitates subsequent dehydration of the wax and re-chilling. The cost of installation is much reduced, since the necessity of equipping the system with additional tanks, pumps and piping is altogether avoided and the secondary cooling system is greatly simplified.

One feature of the process is of value regardless of whether the two or more separating stages are practiced in a single centrifuge. This feature v is the addition of diluent (either fresh diluent or the oil-diluent solution poor in oil that is a product of the later or last centrifugal stage) to the wax discharging from any of the stages. This expedient is therefore applicable to the known process of dewaxing in two or more Successive centrifuges. The addition of such diluent as described should not be confused with the known process of adding a fresh quantity of diluent after the first stage de-waxing and preparatory to the second stage de-waxing step, my improvement involving the addition of the diluent to the wax as it discharges and not subsequent to its discharge. It is of especial value when applied to the stage or stages preceding the last stage, it being important to avoid, in order to facilitate the expulsion of the wax, either heating or the addition of water. Heating causes a certain remelting of the wax crystals, which, in order to make the wax separable in the next centrifugal operation, necessitates rechilling; while the presence of water in the mixture undergoing separation in such next stage is obviously unobjectionable. The addition of diluent is also of value when applied (preferably in the form of fresh diluent) to the substantially oil-free wax discharging from the last centrifuge, whereat the viscosity of the nearly completely de-oiled wax is most pronounced and troublesome. A still further reduction in viscosity inthe substantially oil-free Wax discharging from the last centrifuge may be secured by increasing the temperature of the wax as it is so discharging. This may be done by adding the diluent at a comparatively high temperature, or by the application of heat to the outer wall of the discharge channel as hereinbefore described. Raising the temperature of the outgoing wax in the last stage is not objectionable (since the wax must go to the still for recovery of the solvent), the heating, in fact, being of some advantage.

What I claim and desire to protect by Letters Patent is:

l. The process of dewaxing hydrocarbon oil to which has been added a diluent that is a preferential solvent for the oil and which has been chilled to precipitate the Wax, which comprises subjecting the mixture to the multistage centrifugal operation hereinafter defined in each stage of which a substantially wax-free oil-diluent solution containing the major part of the oil treated in that stage is separated from all the wax and some diluent and a minor part of the oil treated in that stage, only the separated material containing all the Wax being subjected to treatment in the stage or stages following the rst stage, applying the centrifugal force continuously and without interruption between the stages, supplying added diluent to the separated material containing all the wax as it flows, without interruption of the centrifugal force, from one stage to the next to thereby substantially reduce the proportion of oil in the oil-diluent solution so as to obtain in the last stage a separated diluent containing a substantially negligible proand diluent containing only a negligible proportion of oil, continuously and simultaneously discharging from the loci of centrifugal force the Wax-free solution and the substantially oil-free and wax-free diluent separated in the different stages and the substantially oil free mixture of wax and diluent separated in the last stage, thereby separating substantially all the wax from all the oil and obtaining substantially oil-free and wax-free diluent Without recirculating any of the wax and without necessarily recirculating any of the oil. v

2. The process set forth in claim 1 in which the substantially oil-free and waxfree diluent separated in the last stage is utilized for addition to the wax and oil-diluent solution preparatory to the first stage separation.

3. The process set forth in claim l in which the substantially oil-free and wax-free solution CURT F. HOLM.

portion of oil and no Wax and a mixture of wax CERTIFICATE 0R CORRECTION. Patent No. 2,261,721 I November t, 19in.

GURI R. HoLM.

It is hereby certified that error appears in the above numbered patent requiring correction as follows: In the grant, line 6, title of' invention, for "REWAXING" read DEWAXING; and that the said `Letters Patent should be read with this correction thereinthat the -same may conform to the record of the ease in the Patent Office.

signed and sealed this 16th day `of December, A. D. 19ML.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

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