US2411492A - Method for treating waxy stocks - Google Patents

Description

Nov. 19, 1946. B. F. wlNGRovE METHOD FOR TREATING WAXY STOCKS Filed March 9, 1945 w3 .i kwh.

kw w EQU INVENTOR BJI/mv fr wwe/iwf Patented Nov. 19, 1946 METHOD FOR TREATING WAXY STOCKS Byron F. Wingrove, Beaumont, Tex., assignor to Socony-Vacuum Oil Company, Incorporated, New York, N. Y., a corporation of New York Application March 9, 1945, Serial No. 581,923

11 Claims.

This invention is directed to certain improvements to solvent dewaxing processes for the preparation of substantially pure wax or petrolatum and of low pour point lubricating oils. It is specifically directed to a novel and economical method Within such solvent dewaxing processes for the removal of ash-forming constituents from the wax or petrolatum product. Such ash-forming constituents are those non -carbonaceous constituents found in the residue from a batch distillation to dryness of a petroleum oil, The ash generally consists of metal salts and oxides such as those of sodium, calcium and magnesium and may also contain certain other inorganic constituents. It is in this sense that the terms ash-forming constituents will be used herein both in describing and in claiming this invention. The solvent dewaxing processes may involve the use of a single solvent such as petroleum naphtha or more generally the use of a mixture of f solvents such as benzol ketones, benzol-acetone and toluol ketone mixtures. It is well known, for example, that if a waxy petroleum stock be dissolved in a mixture of benzol and methyl-ethyl ketone and then chilled to suitably low temper-` atures, waxy constituents will crystallize in such form as to permit their removal from the mixture by filtering in a suitable filter. The separated wax is then washed with additional solvent and then introduced into suitable distillation equipment for the removal of contained solvent.

Ii the waxy stocks so processed bear high ash contents, the resulting wax will contain a large proportion of said ash and as a result will be unt for most oi the commercial wax products. Moreover, serious ash deposition results in the distillation equipment used for separation of solvent from the pressed wax. Such ash deposition causes severe loss in the heat transfer rates in the distillation and cooling systems as well as substantial equipment corrosion. Attempts to wash the pressed wax as normally charged to distillation equipment or attempts to wash the wax product Jfrom such distillation with water result in serious emulsion dilculties and resultant negligible ash removal. As a consequence, at the present state of the art, high ash bearing waxy stocks are generally avoided in dewaxing operations; and, if used,l the wax product is generally useful for nothing more than a low grade cracking stock. i

It is an object of this invention to provide an economical and practical method for removal of ash forming constituents from separated waxy materials. Y

It is a further object of this invention to provide removal of ash-bearing constituents from separated wax in solvent dewaxing processes before the subjection of the solvent containing separated wax to distillation conditions. These and other objects of this invention will become apparent from the following description thereof, The separated wax after washing in solvent dewaxing processes contains small quantities of solvent and possibly some ice. It has now been found that by proper dilution of this wax cake with additional quantities of the same solvent or with at least one of the constituents of that solvent, followed by heating to controlled temperatures,` the ash-forming constituents may then be removed from the mixture by mixing therewith a relatively small proportion of water, which dissolves the ash-forming constituents, and by a subsequent separation of the water by settling.

This invention may be more readily understood by reference to the single drawing, Figure 1 at tached hereto, wherein is shown in highly diagrammatic form a flow plan of a solvent dewaxing process modified according to this invention.

Turning now to Figure l, a waxy charge stock which may contain wax or petrolatum and which contains ash-forming constituents is pumped by charge pump I0 through pipe Il wherein it is mixed with a suitable solvent which passes from solvent tank i2 through pipe I3, pump I4 and pipe l5 into pipe il. The solvent may consist of a single solvent capable of dissolving t-he waxyV stock or it may consist of a mixture of solvents, for example, benzol and methyl-ethyl ketone. Suitable means for providing thorough mixing of the solvent and waxy stock may be provided in pipe Il, such as a series of venturis. The solvent-waxy stock mixture then passes through cooler I and chiller Vl, wherein it is chilled to the desired temperature, for example 0 degrees Fahrenheit. The chilled mixture then passes through pipe i8 to surge tank I9 from which it is withdrawn through pipe 20, and pump 2| and charged through pipe 22 into the lter 23. The lter may be any of a number of types either of the plate and frame variety or of the continuous rotary vacuum type variety such as an Oliver lilter. The crystallized waxy material is pressed on the filter 23 and washed by means of additional solvent introduced through pipe 24. The wax cake containing some solvent and ash-forming constituents is withdrawn from filter 23 through screw conveyor 25 which pumps it into a pumpablemixture which passes through pipe 2.6, pump 2'! and pipe 28 to heat exchanger 25. Additional solvent is added to the wax cake at some location before the exchanger 29, such as within pipe 25, into which it is introduced through pipe 30. The volume of solvent sc added should be substantially in excess of the volume of the wax cake. The solvent wax cake mixture is heated in exchanger Z5 to a suitable temperature, for example, 120 to 150 degrees Fahrenheit and is then passed through pipe 52 into mixing tank 33. Water amounting to a small proportion of the wax-solvent mixture is added to the mixer 33 through pipe 3l and thoroughly mixed with said mixture; whereby the ash-forming constituents therein are dissolved in the added Water. It will be understood that the mixing tank 33 may be of any conventional construction suited for its purpose and may consist only of a series of venturis or oriiices within a section of conduit. The mixture then passes from the mixer 33 through pipe 34, pump 35, and pipe 35 into a settling tank 31 wherein the mixture stratii'les into an upper layer containing solvent and waxy material and a lower layer containing Water, ash-forming constituents and a small quantity of solvent. The settling tank 3l may be of any conventional construction well known to the art, and while only one is shown in the drawing, several may be used alternately to provide continuity to the process. The material in the wax-solvent layer is then passed through pipe 38, pump 39, and pipe 40 to heater lil wherein it is heated to a suitable temperature and then charged ,through pipe 42 into fractionator 43 wherein the wax and solvent are separated by fractionation.A The waxy material is discharged from the lower section of iractionator i3 through pipe 44 and passes as a substantially ash free wax either to storage or to further refining equipment. The recovered solvent passes overhead through pipe 45 and condenser i6 to pump 41 from which it is forced in part through pipes 48 and 49 to the upper section of tower i3 as reflux and in part through pipes 48 and 50 and 5l to the solvent tank l2. Alternately this latter fraction of solvent instead of passing through pipe 5| into tank l2 may pass through pipes 52 and 30 into pipe 25 as dilution solvent for the wax cake as hereinabove described or it may pass through pipes 52 and 53 to the nlter 23 as wash solvent. On the other hand, if desired, solvent may be drawn from tank i2, through pipe i3, pump M, pipe I5 and pipe 55 into pipe 52 for use for washing or dilution purposesl The water containing ash-forming constituents and small amounts of solvent passes from settling tank 37 through pipe 55, pump 55, heater 5l' and pipe 58 to the water-solvent fractionator 59. Water is drained from the bottom of tower 5S through pipe 50 to the sewer and the solvent overhead passes through pipe Si, condenser 52, to pump 63 from which it passes through pipe 54 partly through pipe 55 to tower 59 as reiiux and partly through pipes 55, 50 and 5! to solvent'tank I2.

Returning to lter 23, the dewaxed oil produced therein dissolved in solvent passes there-- from through pipe 5l to pump 58 from which it passes through pipe 59 to the flash tower 10. Most ofthe solvent passes overhead from tower 'I0 through pipe il, and condenser T2 to pump 13 from which it passes in part through pipes 'M and 'i5 to the upper section of tower as reflux and in part through pipes i4, 'i6 and 5| to solvent tank l2. The oil stillcontaining some solvent passes from the bottom of tower 'i0 through pipe 71, pump 'i8 and pipe 'i9 to the steam stripping tower B. Solvent and steam pass overhead from this tower through pipe 8| into the Water- 5 solvent fractionator 59, from which dewaxed lubricating oil is withdrawn from the bottom of tower Bil through pipe 82.

It should be understood that no novelty is claimed herein in the solvent dewaxing process as such, but novelty is claimed in the practical incorporation into such'solvent dewaxing processes of the hereinabove described practical and economical method for removing ash-forming constituents from the wax cake. The ltered wax cake obtained from filter 23 in conventional solvent dewaxing processes will contain certain amounts of solvent and frozen water as well as the ash-forming constituents. The method of this invention employing additional quantities 0f the same solvent and of water to effect the removal of ash-forming constituents, requires the addition of no constituents to the dewaxing process other than those that were already present. This is of substantial practical importance as it means no particular increase or change in the fractionation equipment already existing in the solvent dewaxing plant, and makes highly practical the solvent dewaxing of ash bearing waxy stocks for the production of substantially ash free wax products as well as low pour point lubricants. It will be readily recognized by those skilled in the art that various modifications in the equipment, equipment arrangement and flow streams are employed in various solvent dewaxing processes which modifications will differ somewhat from the highly diagrammatic flow plan shown in Figure 1. It will be understood that the specific arrangement shown in Figure 1 is intended merely as exemplary and it is not intended that the scope of this invention be limited thereto.

The amount of solvent mixed with the waxy charge stock will vary depending upon the particular stock and process involved. As an ex- 45 ample, in the solvent dewaxing of an acid treated and caustic neutralized mixed base residuum of approximately 160 S. U. V. at 210 F., the

solvent to waxy stock ratio is of the order of 5.0

to 1. The amount of solvent required to adequately dilute the filtered wax-solvent mixture discharged from lter 23 will also vary with the solvent used, and the stock involved. Inany case the volume of the solvent should greatly exceed the volume of the wax cake. In general the volumetric ratio of solvent to wax cake in the mixture should be at least 8 to 1. As an example, in the processing of the wax cake from the above mentioned mixed base residuum, suilicient solvent should be added to provide a mixture con- 50 taining approximately `8 to 10 volumes of solvent per volume of pressed wax cake. The solvent used in that example consisted of a mixture containing about 60% benzol and 40% methyl-ethyl ketone. When the solvent dewaxing process involves the use of mixed solvents, it is not entirely necessary that the solvent constituents be of the same ratio in the solvent mixture used for dissolving the waxy oil charge stockv and in the solvent mixture used for diluting the wax-cakesolvent mixture. In the latter case, it may often be desirable to use either one or the other of the solvents involved in substantially pure form depending upon the process. It will be understood that in the claiming of this invention the word '15. solvent is used in a sense suiliciently broad to.

cover a `single solvent material or a mixture thereof.

The temperature to which the solvent-wax cake mixture should be heated before addition of water is torsome extent dependent upon the materials involved. In general, it should be above about 12o degrees Fahrenheit and below the boiling points of the solvent and of water at the existing pressure conditions of the heating. The preferable temperature range is from about 120 10 to about 150 F.

The amount of water required to remove the ash-forming constituents will depend in part on the amount of such constituents present. In general the quantity of water required is a small proportion of the total mixture and preferably should be of the order of 5 to 10 percent by volume of said mixture.

I claim:

l. In a solvent-dewaxing process wherein waxy material is separated at suitably low temperatures from a waxy petroleum stock, mixed with a suitable composite solvent, the method for removing ash-forming constituents from the separated wax cake which comprises: adding at least one constituent of the solvent involved in said dewaxing process to said wax cake in an amount substantially in excess of the volume of said Vwax cake, heating the mixture to a temperature above about 120 degrees Fahrenheit but below a temperature sufficient to substantially boil said solvent and water, mixing with said mixture a relatively small proportion by volume of water, whereby the ashforming constituents contained in said `wax cake will be dissolved in said added water, and substantially separating the water containing said ash-forming constituents from said solvent-wax mixture.

2. In a solvent dewaxing process wherein waxy material is `separated `at suitably low temperatures from a waxy petroleum stock, mixed with a suitable solvent, the method for removing ashforming constituents from the separated wax cake which comprises: adding at least one constituent of the solvent involved in said dewaxing process iff to said wax `cake in an amount sufficient to pro, vide a mixture containing about 8 to l0 volumes of solventper volume of wax cake, heating the mixture to a temperature above about 120 degrees Fahrenheit but below a temperature sui- 5U` cient to substantially boil said solvent and water, mixing with said mixture about 5 to l0 per cent by volume of water, whereby theash--forming constituents contained in said wax cake will be dissolved in said added water, and substantially separating the water containing said ashforming constituents from said solvent-wax mixture.

3.` In a solvent dewaxing processwherein waxy material is separated at suitably low .temperatures 5o from a waxy petroleumstock, mixed with a solvent having a substantially greater solubility for the non-waxymaterial .than for the waxy material contained in saidstock `at said low ternperatures, the method for removing ashfforming constituents from the separated waxy material which comprises: adding to said separated waxy material, before removal of any contained solvent therefrom, an additional amount of said solvent sufficient to provide a waxy material- `solvent mixture containing at least 8 volumes of said Solvent per volume of waxy material, heating said mixture to a temperature at least above 120 degrees Fahrenheit and below the boiling point of water and of said solvent atV the conditions of heating, thoroughly mixing atleast 5 per cent by volume water to said heated mixture, thereby accomplishing the solution of said ash-forming material in said water, and substantially separating the water containing said ash-forming material from said mixture of solvent and waxy material by settling.

4. In a solvent dewaxing process wherein waxy material is separated at suitably low temperatures from a waxy petroleum stock, mixed with liquid solvent having a substantially greater solubility for the non-waxy material than for the waxy material contained in said stock at saidlow temperatures, the method for removing ash-forming constituents from the separated waxy material which comprises: adding to said separated waxy material, before removal of any contained solvent therefrom, an additional amount of said solvent sufcient to provide a waxy materialsolvent mixture containing at least 8 volumes of said solvent per volume of waxy material, heating said mixture to a temperature at least above l2() degrees Fahrenheit and below the boiling point ofwater and of said solvent at the conditions of heating, thoroughly mixing at least 5 per cent by volume water to said heated mixture, thereby accomplishing the solution of said ashforming material in said water, maintaining the resulting mixture in a settling chamber wherein the water containing said ash-forming constituents substantiaily separates from said mixture of waxy-material and solvent by stratification,

separately removing the stratied materials from said chamber and effecting the separation 0f said purified waxy materials from said solvent.

5. The method for producing a substantially ash-free wax from a wax-containing petroleum stock which method comprises: dissolving said wax-containing stock in a `solvent having a low `viscosity relative to said stock and a substantially greater solubility for the non-waxy constituents of said stock than for said waxy constituents at reduced temperatures, chilling the mixture to a suitable temperature substantially below the freezing point of water, whereby the waxy constituents crystallize, ltering the wax from the oilsolvent solution, to effect separation therefrom, adding sufficient solvent to said separated wax to provide a mixture` containingat least 8 volumes of solvent per volume of wax, heating said wax-solvent mixture to a temperature above about degrees Fahrenheitand below the boiling point of water and of said solvent, thoroughly mixing at least lper cent by volume of water with said mixture to effect solution of said ash-forming constituents therein, maintaining the resulting mixture in a settling chamber wherein said water containing said ash-forming constituents is separated from said wax-solvent mixture by stratification, separately withdrawing the wax-solvent layer from said chamber, effecting the separation of said puried wax from said solvent, and recovering dissolved solvent from said separated water.

6. The method for producing a substantially ash-free wax `from a wax-containing petroleum stock which method comprises: dissolving said" wax-containing stock in a composite solvent having a low viscosity relative to said stock and a substantially greater solubility for the non-waxy constituents of said stock than for said waxy constituents at reduced temperatures, chilling the mixture to a suitable temperature substantially below the freezing point of water, whereby the waxy constituents crystallize, filtering the wax 7 from theI oil-solvent solution to obtain a substantiallywax-free oil stock and a wax cake containing some residual solvent, substantially diluting the wax-solvent mixture `with an additional quantity of at least one constituent of said solvent to raise its solvent content, heating the mixture to a temperature above about 120 degrees Fahrenheit and below the boiling point of said solvent and of water under the: pressure conditions of heating, thoroughly mixing arelatively small proportion of water with said heated mixture toefiect solution' of said ash-forming censtituents therein, maintaining the resultingmixture in a settling chamber wherein said water containing said ashforming constituents is s eparted from said waxsolvent mixture by stratication, separately withdrawing the wax-solvent layer from said chamber, effecting the separation of said puried wax from said solvent. l

7. lIn a solvent dewaxing process wherein waxy material is ltered at suitably low temperatures Vmixing at least V per cent by volume water to said heated mixture, thereby accomplishing the solution of said ash-forming material in said water. and substantially separating the water containing said ash-forming material from said,

mixture of solvent and waxy material by settling.

8. In a solvent dewaxing process wherein waxy material is filtered from a benzol, methyl-ethyl ketone solvent mixture with a vwaxy petroleum stock at suitably reduced temperatures the method for removing ash-forming constituents Afrom the ltered waxy material which comprises: adding a suicient quantity of at least one constituent of said solvent mixture to said filtered waxy material to provide a mixture containing about 8 to 10 volumes of said solvent to one volume of waxy material, heating the resultant Vmixture to a temperature within the range about 120 to 150 degrees Fahrenheit, thoroughly mixing about 5 to 10 per cent by volume of water with said mixture whereby said ash-forming constituents are dissolved in said water and eecting the separationof said water from said solvent-wax mixture byV settling.v y A I 9. The method of obtaining a substantially ashfree wax from a wax-containing petroleum stock which method comprises: ldissolving said waxcontaining stock in a solvent containing a mixtureV of a fatty ketone having aliphatic groups containing within. therange l to 4 carbon atoms and of material selected from the group consisting of benzol, toluol and -xylene and aliphatic substituted derivatives thereof, chilling the mixture to a suitable temperature substantially betweend 32 degrees Fahrenheit, filtering the wax from the oil-solvent solution, to eiiect separation therefrom, adding suicient solvent to said ltered wax to provide a mixture containing at least 8 volumes of solvent per volume of wax, heating said wax-solvent mixture to a temperature above about 120 degrees Fahrenheit and below the boiling poi-nt of water and of said solvent, thoroughly mixing at least 5 perv cent by volume of water with said mixture to effect soluvfrom a waxy stock mixed with a suitable solvent tion oi?v said ash-forming constituents therein, maintaining the resulting mixture in a settling chamber wherein said water containing said ashforming constituents is separated from said waxsolvent mixture by stratification, separately withdrawing the Wax-solvent layer from said chamber, elTecting the separation of said purified wax from said solvent, and recovering dissolved solvent from said separated` water.

l0,A The method of obtaining a substantially ash-free wax from a waxy petroleum stock which method comprises: dissolving said waxy stock in a solvent consisting of benzol. methyl-ethvl ketone mixture, chilling said solution to a temperature below zero degrees Fahrenheit. whereby the wax constituents are crystallized, filtering said chilled mixture to effect separation of waxy Vmaterial from non-waxy petroleum oil, adding a quantity of at least kone constituent of said solvent mixture tosaid iiltered waxy material to form a mixture containing, about 8 to 10 volumes of solvent per volume of waxy material, heating said'mixture to a temperature within the range to 150 degrees Fahrenheit, thoroughly mixing about 5 to 1'0 per cent by volume of water with said heated mixture whereby the ash-forming constituent in said waxy material are dissolved in said added water, separating said water from said mixture by settling and eiecting a lseparation of said waxy material from said solvent by distillation.

11. In a solvent dewaxing process wherein waxy material is ltered at suitably low temperatures from 'a waxy petroleum stock mixed withV a solvent mixture having a substantially greater solubility `for the non-waxy material lthan for4 the waxy material 'contained in said V'stock at said low temperatures, the method for removing ashforming constituents from the filtered waxy material which comprises: adding to said ltered waxy material, before removal of any contained solvent therefrom, an additional amount of at least one constituent of said solvent mixture sufcientto provide a waxy material-solvent mixture containing at least 8 volumes of said solvent per .volume of waxy material, heating said mixture to a temperature at least above Y120 degrees Fahrenheit and below the boiling point of water and of said solvent at the conditions of heating, thoroughly mixing at least 5 per cent by "volume water to said heated mixture, thereby accomplishing the solution of said ash-forming material in said water, and substantially separating the water containing said ash-forming material from said mixture of solvent and waxy material r by settling. Y v

BYRON F. WINGROVE.

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