US2172320A - Method of dewaxing hydrocarbon oils - Google Patents

Description

Patented Sept. 5, 1939 UNETED STATES FATENT QFFlCE METHOD OF DEWAXING HYDROCARBON OILS poration of Delaware Application November 27, 1933, Serial No. 699,918

9 Claims.

The present invention relates to the removal of wax from hydrocarbon oils and is particularly concerned with the dewaxing of petroleum oil lubricating stock in such a manner as to remove the major portion of the wax from such stock and thereby produce a lubricating oil of desirably low cold test while substantially completely avoiding loss of oil by precipitation and separation with the removed wax.

In current refinery practice wax is ordinarily removed from oil by filter pressing or by the use of Sharples continuous Super-Centrifuges in accordance with the method described in the patent to P. T. Sharples No. 1,351,265 of August 31, 1920, depending upon the nature of the wax to be removed. The wax contained in the petroleum fraction known as wax distillate is removed by chilling such distillate and passing it through filter presses to efiect removal of precipitated wax, while the wax in the heavier distillates and residues is removed by the Sharples centrifugal process. The crystalline nature of the wax precipitated from the lighter fractions and from heavier fractions which have been subjected to cracking distillation renders difiicult the discharge of such wax continuously from a -centrifugal separator and the amorphous nature of the major portion of the wax precipitated from other heavier fractions precludes the separation of wax contained in these heavier fractions by filtration. Prior art practice has accordingly entailed the inconvenience inherent in careful fractionation to obtain a fraction which may be dewaxed by filter pressing and a heavier fraction which may be 35 centrifugally dewaxed and it has also entailed the necessity of observing numerous other precautions in the treatment of the stock to be deva axed in order to facilitate adequate wax removal by these methods.

The present invention has had as its principal object the practice of a process by which petroleum fractions containing substantial proportions of both crystalline and amorphous wax may be dewa'xed in single operation. In view of the 45 fact t it is applicable to stocks containing both crystalline and amorphous wax, the invention may be practiced without resort to the elaborate precautions heretofore necessary in the production of fractions of which the wax content 50 consisted almost exclusively of crystalline and amorphous wax, actively. It involves a method of operation by which a stock which may contain both of these types of wax is first diluted and chilled and the wax is thereafter removed from the oil by a process of subsidence separation whereby the individual precipitated wax particles are gathered into a cake during the removal of the major portion of the oil and the residual oil may thereafter be removed from the wax cake by drainage or straining through a 5 suitable filter surface such as a pervious screen. In the preferred operation, both the step of removing the major portion of the oil by subsidence and separation and the step of removing the residual oil from the wax cake are performed in 10 a single operating cycle in a centrifugal bowl of the extractor type, provided with a filter medium or screen for separating oil from the wax cake resulting from the gathering of wax during the subsidence separation. In connection with these operations, I prefer to use a centrifugal separator of the general type indicated in 2 of the patent to L. P. Sharples No. 1,761,593 of June 3, 1930. In the use of such a separator, the stock to be dewaxed is first diluted with a solvent or mixture of solvents adapted to maintain substantially all of the oil of the stock in a liquid state at a temperature sufiiciently low to cause substantially all of the wax to be precipitated in solid state. The solvent 2 used should be of different specific gravity than the oil or wax of the stock under treatment and in the preferred embodiment should be of higher specific gravity than these ingredients. The stock is preferably diluted at a temperature at which both oil and wax are soluble in the solvent and the mixture is thereafter chilled to a temperature sufficiently low to efiectively precipitate the wax from the solution. The nature of the particular solvent mixture used for dilution of the oil has an important bearing upon the efficiency of operation. In the preferred embodiment of the invention, it is important that the solvent mixture have such a high solvent action upon all of the oil constituents of the stock that substantially all of the oil is retained in solution at the dewaxing temperature. An important feature of the invention resides in the discovery that a mixture of a chlorinated hydrocarbon solvent of relatively high specific gravity with a hydrocarbon diluent such as petroleum naphtha or a benzene homologue has an important effect in increasing the solubility of certain portions of the oil under treatment in the solvent mixture when such hydrocarbon is added to the chlorinated solvent in substantial proportions. Another important feature of the invention consists in the discovery that the addition of substantial proportions of one or more homologues of benzene to a chlorinated hydrocarbon solvent of the type indicated above facilitates the precipitation of wax from the solution in such solvent of hydro- .carbon oil, in a form adapted to produce, upon gathering of the wax, a porous wax cake well adapted for separation from residual oil by drainage or straining of the oil from the cake.

Other important features and advantages of the invention will be apparent from a'reading of the sub-joined specification in the light of the attached drawing, in which:

The single figure represents a central longitudinal section of portions of a centrifugal machine adapted to be used in the practice of the invention.

Referring to the drawing by reference characters, the numeral l0 indicates an imperforate centrifugal bowl which is mounted for rotation upon a shaft II that is supported for rotation in bearings I2 and is provided with a pulley l3 or other similar driving element. Within the bowl I!) and co-axial therewith is a perforate or pervious partition or screen l4 adapted to effect retention of wax while allowing the oil solution to flow therethrough, this partition or screen being spaced from the inner wall of the bowl l0 and held in spaced relation with respect thereto by a spacing member I5 which may be a coarse woven wire screen or grid adapted to permit free flow of liquid between the screen l4 and the inner circumference of the bowl l0. Within the bowl l0 and spaced from the outer end thereof is a disc l6 that extends radially inward from partition I4 and forms with the radially extending outer end of the bowl a liquid compartmentlB.

The hub 20 of the bowl is surrounded by a disc aliording a feed channel for liquid to be admitted a sage 24 into the bowl proper.

to the bowl. The conically and radially extending portions 2| and 22 of this channel are provided with wings 25 and these wings act to accelerate liquid introduced into the bowl through the supplyhozzle 23 and passage 24 in order that this liquid may attain substantially the'speed of the bowl by the time it passes from the supply pas The supply passage 24 leads into the main separating compartment 26 of the bowl. An adjustable skimming nozzle 28 is introduced into the compartment l8 of the bowl and this skimming nozzle acts to remove from the compartment l8 liquid which passes through the filter surface and under the dividing wall l6 into the compartment I8. By adjusting the position of the skimming nozzle the depth of liquid in the compartments 2!? and I8 may be controlled. The bowl is surrounded by a casing. 29 which supports the bearings l2. Conventional scraper and discharge mechanisms are used in effecting release and discharge of accumulated solids, the scraper mechanism being indicated generally at 3| and the discharge chute at 32.

In the use of a centrifugal separator of the type illustrated in the dewaxing of a hydrocarbon oil stock, the stock is first dissolved in a chlorinated hydrocarbon solvent having a specific gravity very considerably higher than that of any constituent of the stock to be dewaxed. In this connection,

best results have been obtained by the use of ethylene dichloride, although other chlorinated hydrocarbons such as methylene dichloride, propylene dichloride, dichlor ethylene or trichlor ethylene may be substituted for the ethylene dichloride. When compounds of this type are I used alone and the solution is chilled'to a temperature adapted to efiect separation of wax from oil, a certain degree of extraction of naphthenic if possible. An important feature of the present invention resides in the discovery that the loss of parafiin oil by reason of the solvent extraction effect of the heavy chlorinated solvent can be substantially completely avoided by the addition to such heavy chlorinated solvent of a substantial proportion of a solvent for the parafiinic constituents of the oil and such solvent should preferably be of relatively low viscosity. Thus, by the addition of amounts of naphtha or benzene constituting 25% or more of the volume of chlorinated solvent used, the solvent extraction efiect of the chlorinated solvent in separating naphthenic from parafiinic oil is almost completely avoided.

Since the preferred practice of the invention involves an ultimate separation of oil from wax by a process by which the oil passes through a V pervious surface by which the wax is retained, it is desirable that the solvent be of such a nature as to permit the precipitation of wax in a form r in which it may not clog the screen. To this end it is necessary that a substantial proportion of the wax be of a sufiiciently crystalline nature to avoid clogging of the pervious surface. An important feature of the invention consists in the discovery that the use of a homologue of benzene in conjunction with a chlorinated solvent of the typediscussed above results in the precipitation of a substantial proportion of the wax in crystalline form' and produces, upon gathering of the wax during separation of the major portion of the oil by subsidence, a coherent wax cake'of sufliciently crystalline nature to be separated from the residual oil by drainage upon discontinuance of the subsidence separation operation and of sufiiciently porous nature to permit it to be effectively washed after drainage. In the preferred practice of the invention a solyent mixture is therefore utilized which consists of 75% or less by volume of a heavy chlorinated hydrocarbon such as methylene dichloride and 25% or more of a benzene homologue.

The stock to be dewaxed is first diluted with a quantity of the solvent mixture discussed above amounting to between 2 and 4 times the volume of the stock under treatment at a temperature of approximately 100 F. The solution is thereafter chilled to a temperature of about 20 F. and is fed to the rotating centrifugal bowl l0 through the feed nozzle 23 and the supply passage. 24. The skimming nozzle 28 is adjusted to position A during this stage of the cycle of operations. During continued feed of the solution to thecentrifugal bowl, thissolution will accumulate in the bowl until it extends radially in-' ward in compartments 2B and'l8 to the position occupied by the skimming nozzle l8. In view of the fact that liquid flows under the dividing wall [5 from compartment 26 to compartment IS, the liquid in these two compartments will be at the same level. V

The precipitated wax which is suspended in the oil fed through the supply passage 24 to the centrifugal bowl, being of lower specific gravity than the oil solution, will pass radially inwardly through the body of oil in the compartment 26 and form a coherent porous cake of wax at the inner surface of the body of oil rotating in that compartment. In view of the adjustment of the skimming nozzle to the position A, the layer of liquid in the compartments 26 and I8 is of substantial depth during this stage of the operation and the accumulated layer of wax is accordingly maintained out of contact with the pervious surface id and has no tendency to clog this surface. After the feed of oil through the passage 24 and the removal of oil through the skimming nozzle A has taken place until the accumulation of a substantial quantity of wax at the inner surface of the body of oil rotating in the compartment 26, the feed is discontinued and the skimming nozzle 28 is moved radially outwardly to the position indicated at B. This adjustment of the skimming nozzle effects removal of the residual oil in the compartments 26 and IB and the wax cake accordingly moves radially outwardly against the straining or filter surface I4.

The wax cake lying against the filter surface id is thereafter washed by spraying on the wax an additional quantity of solvent mixture. This solvent mixture may be of the same character as that originally used in dilution of the oil and penetrates the wax cake and removes therefrom residual paraffmic oil constitutents which may have been retained in the wax cake by reason of the solvent extraction effect of the chlorinated hydrocarbon solvents. Other impurities are also removed during this washing operation. At the conclusion of the washing operation the wax cake may be removed by manipulation of the scraper tool 3! in conventional manner and the machine is thereafter ready for a repetition of the cycle of operations. It will be evident from the above discussion that, by the practice of the process of the invention, it is possible to effect removal of wax from an oil-wax mixture containing wax of both the crystalline and amorphous types and that the removal of wax from such a mixture can be continued for a substantial period of time by utilization of a heavy solvent in connection with a centrifugal separator of the type illustrated because of the fact that the primary separation of wax from oil is a separation by subsidence and that the precipitated wax is kept clear of the filter surface during this primary separation.

t will be further obvious that the use of the particular combination of solvents discussed above renders such a mode of operation feasible and facilitates performance of the process by reason of the fact that the separation of paraffinic from naphthenic hydrocarbons is minimized in connection with the use of such a mixture. It will be further evident that a further important advantage is attained in utilizing a mixture of solvents adapted to cause precipitation of a substantial proportion of the wax in crystalline form and that the utilization of this same mixture in the subsequent washing of the wax filtered from the oil effects removal of any parafiinic hydrocarbon oil constituents which may have become enmeshed in the wax.

While the invention has been described by reference to particular apparatus, it will be evident that certain broad aspects of the invention are applicable to treatment of hydrocarbon oils in other types of apparatus. Oil may be separated from wax, for example, by a combination of subsidence and filtering or straining operations in a centrifugal bowl of simpler design having but a single separating compartment through which oil is projected through a peripherally arranged filter surface directly from the bowl, provided the rate of feed of oil to the bowl is maintained at a sufiicient speed to maintain a body of oil within the bowl and thus avoid accumula tion of wax upon the filter surface during the primary separation by subsidence. In case a simpler bowl of such type is used, the rate of feed of oil may be diminished or the feed may be discontinued after the accumulation of a sub stantial cake of'wax. Such decrease or discontinuance of feed will result in movement of the wax cake against the surface and the residual oil will be removed from the wax by filtration as in the case of separation by subsidence and filtration involving use of the apparatus of the prefered embodiment of the present invention.

Other modifications which may or may not involve the use of the specific apparatus described above fall within the spirit of the invention. It is possible, for example, toinitially chlute the stock to be dewaxed by means of a solvent mixture of higher specific gravity than the stock, effect the primary separation of the major portion of the wax from oil in the manner above indicated and feed additional solvent mixture into the compartment 25 without changing the position of the discharge nozzle 28 until after the washing operation. In connection with an oper ation of this type, the solution used. for the purpose of removing impurities from the wax penetrates the wax by reason of the fact that it possesses a higher specific gravity than the wax and this washing solution is discharged by the skimming nozzle 28 from the zone A of the auxiliary compartment it. At the conclusion of the washing operation, the nozzle 28 may be adjusted from the position A to position B in order to effect removal of residual solvent and subsidence of the porous wax cake against the member Hi from which it is thereafter removed, as above described. In connection with an operation of this type, the wax may be removed from the washing solution without first adjusting the nozzle 28 from the position A to position B, if desired, or, as a still further alternative, the wax and washing solution or residual oil may be discharged together from the bowl and thereafter separated from each other.

The invention includes still other modifications of the specific procedure described above, provided the primary separation of wax from oil is attained by a process of subsidence and the secondary separation involves separation of residual oil from wax by a process of draining or filtration, or subsidence. It also includes all embodiments in which a primary separation of wax from oil is atta ned by a process of subsidence in a centrifugal bowl and a purification of the wax is attained by a washing operation in the same bowl by passage of a washing liquid through the wax separated from the main body of oil by the subsidence separation.

Still further modifications will be obvious to those skilled in the art and I do not, therefore, wish to be limited except by the scope of my subjoined claims.

I claim:

1. The method of dewaxing a hydrocarbon oil stock which comprises diluting such stock with a solvent consisting of a low boiling liquid chlorine derivative of an aliphatic hydrocarbon having a higher specific gravity than the oil stock and with a hydrocarbon diluent of relatively low visc'osity in a proportionof at least 25% by volume of hydrocarbon diluent to 75% by volume of normally liquid chlorine derivative diluent, feedingv the mixture so formed to a centrifugal bowl provided with a circumferentially extending filter surface'at a temperature sufficiently low to effectprecipitation of the major portion of the wax from the solution, separating the major portion of the wax from the solution by centrifugal subsidence while maintaining within the bowl a suflicient volume of oil to avoid accumulation of substantial quantities of wax upon the filter surface, and finally discharging residual oil from the bowl and thereby projecting precipitated wax against the filter surface and separating said wax from such'residual oil by filtration.

2. The method of dewaxing a hydrocarbon oil stock which comprises diluting such stock with a solvent consisting of a low boiling liquid chlorine derivative of an aliphatic hydrocarbon having a higher specific gravity than the oil stock and with a hydrocarbon diluent chosen from the group consisting ofpetroleum naphtha and benzene in a proportion of at least 25% by volume of hydrocarbon diluent to 75% by volume of normally liquid chlorine derivative diluent,

' feeding the mixture so formed to, a centrifugal bowl provided with a circumferentially extending filter surface at a temperature sufilciently low to effect precipitation of' the major portion of the wax from the solution, separating the major portion of the wax from the solution by centrifugal subsidence while maintaining within the bowl a suflicient volume of oil to avoid accumulation of substantial quantities of wax upon the filter surface, and finally discharging residual oil from the bowland thereby projecting precipitated wax against the filter surface and separating said wax from such residual oil by filtration.

3. The method of dewaxing a hydrocarbon oil stock which comprises diluting suchfstock with a solvent consisting of a low boiling liquid chlorine derivative of an aliphatic hydrocarbon having a higher specific gravity than the oil stock and with a hydrocarbon diluent consisting of benzene in a proportion of at least 25% by volume of hydrocarbon diluent to 75% by volume of normally liquid chlorine derivative diluent, feeding the mixture so formed to a centrifugal bowl provided with a'circumferentially extending filter surface at a temperature sufiiciently low to 7 effect precipitation of the major'portion of the wax from the solution, separating the major'portion of the wax from the solution by centrifugal subsidence while maintaining'within the bowl a suffi'cient volumeof oil to avoid accumulation of substantial quantities of wax upon the filter surface, and finally discharging residual oil from the bowl and thereby projecting precipitated wax against the filter surface and separating said wax from such residual oil by filtration.

4. The method of dewaxing a hydrocarbon oil stock which comprises diluting such stock with a solvent of "substantially higher'specific gravity than said stock, feeding the mixture of oil and wax, at a temperature sufficiently low to effect precipitation of the major portion of the wax from the solution, to a centrifugal bowl proj vided with a circumferentially extending filter surface, maintaining a substantial quantity of oil within the bowl under a condition of liquid balance during the subsidence of wax to the inner zone'of thev body of material within the bowl, and finally withdrawing the 'oil from the bowl and thereby projecting precipitated wax against the filter surface and separating wax from residual oil by a process of filtration. V

5. The method-of dewaxing a hydrocarbon 011 stock which comprises diluting such stock with a solvent of substantially higher specific gravity than said stock, feeding the mixture of oil and Wax, at a temperature sufiiciently low to effect precipitation of the major portion. of the wax from the solution, to a centrifugal bowl provided with a circumferentially extending filter surface, maintaining a substantial quantity of oil within the bowl under a condition of liquid balance during the subsidence of wax to the inner zone of the body of material within the bowl, withdrawing the oil from the bowl and thereafter passing a solvent through wax projected against said filter surface to remove residual impurities therefrom. a

6. The method of dewaxing a hydrocarbon oil stock which comprises diluting such stock with a solvent of substantially higher specific gravity than said stock,'feeding the mixture of oil and wax, at a temperature sufficiently low to effect precipitation of the major portion of the wax from the solution, to a centrifugal bowl provided with a circumferentially extending filter surface, maintaining a substantial quantity of oil within the bowl under a condition of liquid balance during thesubsidence of wax to the inner zone of the body of material within the bowl, withdrawing the oil from the bowl and thereafter passing a solvent through wax projected against said filter surface to remove residual impurities therefrom, the solvent used in connection with the removal of residual impurities being of the same composition as that used in connection with the initial dilution of the oil.

7. The method of dewaxing a hydrocarbon oil stock which comprises diluting such stock with a solvent consisting of a low boiling liquid chlorine derivative of an aliphatic hydrocarbon having a higher specific gravity than the oil stock and with a hydrocarbon diluent of relatively low low to effect precipitation of the major portion of the wax from the solution, separating the major portion of the wax from the solution by centrifugal subsidence while maintaining within the bowl a sufiicient'volume of oil to avoid accumulation of substantial quantities of wax upon the filter surface, and finally discharging residual oil from the bowl and. thereby projecting precipitated wax against .the filter surface and separating said wax from such residual oil by drainage.

8. The method of dewaxing a hydrocarbon oil stock which comprises diluting such stock with a solvent of substantially higher specific gravity than said stock, feeding the mixture of oil and wax, at a temperature sufficiently low to effect precipitation of the major portion of the wax from the solution, to a centrifugal bowl, maintaining 'a substantial quantity of oil Within the bowl under a condition of liquid balance during the subsidence of wax to the inner circum ference of the body of oil within the bowl and the removal of the major portion of the oil fed to the bowl from the wax, and finally separating residual oil from wax by a process of drainage.

9. The method of dewaxing a hydrocarbon oil 75 stock which comprises diluting such stock with a solvent of substantially higher specific gravity than said stock, feeding the mixture of oil and Wax, at a temperature sufiiciently low to effect precipitation of the major portion of the wax from the solution, to a centrifugal bowl provided with a circumferentially extending filter surface, maintaining a substantial quantity of oil within the bowl during the subsidence of 10 wax to the inner circumference of the body of oil within the bowl, feeding a washing solution of higher specific gravity than the wax to the bowl and passing said solution through the precipitated and subsided wax within the bowl while maintaining said wax clear of the filter surface and finally withdrawing residual liquid by straining and thereby effecting projection of precipitated wax against the filter surface.

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