US2723941A - Wax fractionation process - Google Patents

Description

Nov. 15, 1955 R. L. wr-:EKs ET AL WAX FRACTIONATION PROCESS Filed March 26, 1952 United States Patent O 2,723,941 WAX FRACTIONTION PROCESS Robert L. Weeks, Union, and Chester L. Read, Westfield,

N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware Application March 26, 1952, Serial No. 278,676

7 Claims. (Cl. 196-17) The present invention is 'concerned with an improved process for segregating waxes of different melting points. In accordance with the present invention a wax is segregated from a petroleum waxy oil utilizing dewaxing solvents. The wax is repulped with an added aromatic type solvent to dissolve high melting point wax fractions. The aromatic type solvent is separated from the undissolved wax constituents and the high melting point wax fraction segregated therefrom.

In the refining of hydrocarbon oils such as petroleum oils, it is known to segregate paraflin waxes from so called paratn distillates, waxy lubes and the like. The segregation of these waxes is secured by a number of processes. For example, it is known to chill the selected wax containing oil fraction in order to secure crystallization of the Wax `and to filter or centrifuge the wax crystals from the oil. It is also known to use various dewaxing solvents such as liquid normally gaseous hydrocarbons, such as propane and other low boiling hydrocarbons, as well as other solvents such as methylethyl ketone and the like. In these dewaxing operations, it is also known to use various filter aids, de- Waxing aids and other agents in order to render the dewaxing and filtering operations more efficient. The wax segregated from the hydrocarbon oil, usually termed, slack wax contains from about 10% to 40% of oil. The oil content and melting point range of this wax may be reduced if desirable by means of a distillation operation. The slack wax is handled usually by sweating in a manner to reduce the oil content to less than about 4% by weight. This, crude scale wax, generally has an oil content of about 2.5% by weight. In order to further remove the oil from the crude scale wax and to produce a refined wax having an oil content below about .5%, usually below about .3% various procedures have been proposed and employed.

As pointed out, it is known to employ dewaxing solvent mixtures wherein one solvent comprises an antiwax solvent while the other comprises a solvent having a high solubility for oil. y A solvent mixture of this `character for example comprises about 60% by volume t kof a ketone such as methyl-ethyl ketone and about 40% by volume of an aromatic solvent such as toluene. When utilizing a mixture of this character it has been the practice to add the mixture incrementally to the waxy distillate as it is being chilled.

In accordance with the` present invention the wax cake segregated by various dewaxing procedures is repulped at substantially the same temperature with an additional quantity of an aromatic solvent. This aromatic solvent containing the relatively high melting point wax constituents is segregated and the wax recovered therefrom. The proces-s of the present invention may be more readily understood by reference to the drawing illustrating one embodiment of the same.

."NReferring specifically to the drawing, waxy ydistillate is introduced `into the system by means of line 1. 'The ice waxy distillate is mixed with a dewaxing solvent which is introduced into line 1 by means of' line 3. For the purpose of illustration it i-s assumed that the solvent comprises an anti-wax solvent and an oil solvent. The antiwax solvent, for purposes of description, comprises methyl-ethyl ketone `and the aromatic solvent having a high solubility for the` oil comprises toluene. Approximately l to 4, preferably about 31/2 volumes of solvent mixture per volume of oil is utilized. The oil and solvent mixture is passed through a heating zone 2 wherein the temperature is raised to a temperature in the range from about F. to 140 F. The waxy distillate fiows serially through a plurality of chilling zones 4 and 5 which may comprise one or more stages. A typical op eration is to introduce the feed oil into an initial chilling zone at a temperature of about 130 F.; to introduce the feed oil into a second chilling zone at a temperature of about F.; to introduce the waxy distillate to a third chilling zone at a temperature of about 60 F.; to introduce the feed oil to a fourth chilling zone at a temperature of about 25 F. and to chill the same in a final chilling zone to a filtering temperature in the range of from about *10 to +l0 F. The number of the respective chilling stages as well as their arrangement may be varied appreciably and either direct or indirect chilling means utilized.

The entire chilled mixture comprising oily constituents, crystallized wax constituents, toluene and methyl-` ethyl ketone is held at the filtering temperature and passed to filtering zone 18 wherein the solid wax particles are segregated from the oily` constituents by any suitable filtering or separation means. The filtering zone may comprise plate and frame presses, centrifuges or equivalent suitable equipment for the separation of the precipitated waxy constituents from the oily constituents. The oil and a portion of the solvent mixture is removed from zone 18 by means of line 19. The wax cake is washed with a wash solvent introduced into filtering zone 1S by means of line 20. The washed wax cake is removed from zone 18 by means of line 21. The oilsolvent mixture removed from filtering zone 18 by means of line` 19 is introduced into distillation zone 26 wherein a separation is made between the oily constituents and the solvent mixture. The oil is removed from zone 26 by means of line 27 while the solvent mixture is removed gt); means of line 28 and recycled to solvent storage zone In accordance with the present invention the Wax cake removed from zone 18 by means of line 211 is mixed with.

additional aromatic solvent withdrawn from zone 22 by means of line 23. This mixture is passed toV mixer or repulper 10. These operations are carried out at substantially the same temperatures as those existing in filtering zone 18. The repulped mixture is withdrawn from zone 10 by means of line 11 and introduced into a secondary filtering zone 12. The secondary filtrate containing dissolved low melting point waxes is removed from zone 12 by means of line 13 and passed to a secondary distillation zone 14 wherein the aromatic solven't,.the anti-Wax solvent and the low melting point wax constituents are segregated. The low melting point Wax is removed from zone 14 by means of line l5 while the toluene is segregated by means of line 16 and recycled to zone 22. The anti-wax solvent is removed from zone 14 by means of i line 17 and recycled to solvent storage zone 30.

The wax cake comprising relatively high boiling wax y constituents in secondary filtering zone 12 is washed with additional aromatic solvent. This washing solvent is withdrawn from zone 22 by means of line 31, cooled in zone 32 and is introduced into zone 12 by means of line 33. The washing solvent is passed to zone 14 by means of line 13.

The high melting point wax is removed from filtering zone 12 by means of line 34 and passed to distillation zone 35. Temperature and pressure conditions in zone 35 are adjusted to segregate the 'solvent and the high melt-v ingk point wax which is removed from the system by means f line 35, The toluene solvent is segregated by means of line 36 and passed to storage zone 22, while the antiwax solvent is removed by means of line 37 and passed to solvent storage zone 30. Solvent used as a washing solvent'in zone 18 is withdrawn from zone 30 by means of line 40, cooled in zone 41 and introduced into zone 18 by means of line 20.

' The invention is broadly concerned with a dewaxing operation utilizing two solvents, one of which is characterized by being an anti-wax solvent, while the other is characterized by having a relatively high solubility Afor oily constituents. Solvents of the anti-wax characteristic, for example, comprise methyl-ethyl ketone, methyl-propyl ketone, acetone and the like, while solvents having a relatively high solubility for oily lconstituents .comprise benzene, toluene and other aromatic solvents. General operating conditions may be varied appreciably. For example, the concentration of the anti-wax solvent may vary from about 50% to 70% by volume while the concentration of the aromatic oil solvent may vary from 5,0% to 30% by volume. The amount of solvent mixture utilized may vary from about .5 to 8 volumes per volume of oil being dewaxed. Preferred ratios are from 1 to 5 volumes of solvent mixture per volume of oil being dewaxed. e

In accordance with the present invention, after the wax cake has been substantially freed of oily constituents by conventional procedures, an additional quantity of the aromatic solvent is added at substantially the same temperatures existing in the filtering zone. It is preferred that the temperature not vary more than 5 F. and inV no instance shouldy the temperature vary more than about to 20 F.

The amount of additional aromatic solvent added to the wax cake which is preferably characterized by havingy less than 2.5% weight of oily constituents and preferably having below about 5% of oily constituents may vary appreciably depending upon the range of low melting point waxes it is desired to segregate from the relatively higher melting point waxes. In general, it is preferred to add from .5 to 3 volumes of aromatic solvent such as toluene and to yrepulp the wax` cake. After the removal of the secondary filtrate, it is then preferable to wash the wax cake with an additional .5 to 3 volumes of toluene based upon the quantity of original wax-bearing oil.

The process of the present invention may be more fully understood by the following example illustrating the same:

Example A wax-bearing distillate oil of the following inspections:

Gravity, API 31.7 Flash, COC, F 400 Viscosity, SSU 210 F 40.9 Pour point, F 120 Dry wax content, wt. percent 1 49 Boiling range, F 710-925 1 For 40 F. pour dewaxed oil.

tional 3 volumes of toluene (based on original waxy distillate feed to the dewaxing operations) at 20 F. The

resulting slurry was reiiltered at 20 F. and the wax cake` washed with one volume of toluene based on waxy distillate feed to the original dewaxing step.

The filtrate and wax fractions were then stripped of solvent and inspected. The filtrate contained 20% of the wax charged to the repulping operation. This wax had a melting point of 106 F. The wax from the repulping operation constituted of the feed to repulping. Thls wax had a melting point of 136 F.

From the above it is apparent that a low melting point wax fraction can be efficiently separated from a wax product obtained in dewaxing without resorting to recrystallization or reheating in accordance with the process of the present invention.

What is claimed is:

1. Improved process for the `segregation of relatively low melting point ywaxes. from relatively high melting point waxes comprising the steps of precipitating a mixture of high and low melting point waves from a hydrocarbon mixture, filtering the wax mixture so formed in a first filtering zone to form a wax cake, re-mixing said wax cake with a solvent consisting essentiallyof a compound from the group consisting of benzene and toluene at substantially the same temperature existing in said filtering Zone, passing the mixture so formed to a separation zone, separating said mixture in said separation zone at a temperature substantially the same as the tem- V perature existing in said filtering zone to form a second wax cake comprising relatively highV melting wax and a mixture containing solvent and low melting wax, and separating said solvent from said low melting wax.

2. Process as defined by claim 1 wherein said solvent comprises toluene.

3. Process as defined by claim 2 wherein said solvent is added to said wax cake at a'temperature in the range from about 10 F. to -l-30 F.

4. Process as defined by claim l wherein the amount of solvent added is in the range from about 1 volume to 6 volumes based upon the quantity of waxy distillate from which said wax cake is segregated 5. Improved process for the segregation of relatively high and relatively low melting point waxes from a waxy distillate which comprises adding to said waxy distillate a solvent mixture comprising an anti-wax solvent and an aromatic solvent selected from theV class consisting of benzene and toluene having a high solubility for oil constituents, chilling the mixture to precipitate a mixture of relatively high and relatively low melting point waxes, separating said mixture -of waxes from said solvent mixture, further processingsaid mixture of waxes to reduce the Voil content thereof below about 2%, thereafter adding to said mixture of waxes additional aromatic solvent substantially free of said anti-wax solvent at substantially the temperature at which said mixture of wax was separatedY from said solvent mixture, filtering the product o f the addition of said additional aromatic solvent at substantially the sametemperature at which bsaid additionalv aromatic solvent was added to form a filter cake containing relatively highrmelting pointvwax anda filtrate containing aromatic solvent and relatively low melting pointV wax,rand removing said relatively low melting p oint wax from said aromatic solvent. e'

6. Process as defined by claim 5 wherein the aromatic solvent is added to said wax cake at a'temperature in the range from about *10 F. to +30 F. l

7. Process as defined by claim 6 wherein saidV aromatic solvent'comprises toluene. i

Referencesy Cited in the file of this patent f UNITED srA'rEs PATENTS 2,46345 v Backlund et al. Mar.v 8, 1949 '2,486,014 Evans Oct. y25, 1,949 2,625,502 VBaelclund et al. Jan. 13, 1953

Claims (1)

1. IMPROVED PROCESS FOR THE SEGREGATION OF RELATIVELY LOW MELTING POINT WAXES FROM RELATIVELY HIGH MELTING POINT WAXES COMPRISING THE STEPS OF PRECIPITATING A MIXTURE OF HIGH AND LOW MELTING POINT WAVES FROM A HYDROCARBON MIXTURE, FILTERING THE WAX MIXTURE SO FORMED IN A FIRST FILTERING ZONE TO FORM A WAX CAKE, RE-MIXING SAID WAX CAKE WITH A SOLVENT CONSISTING ESSENTIALLY OF A COMPOUND FROM THE GROUP CONSISTING OF BENZENE AND TOLUENE AT SUBSTANTIALLY THE SAME TEMPERATURE EXISTING IN SAID FILTERING ZONE, PASSING THE MIXTURE SO FORMED TO A SEPARATION ZONE, SEPARATING SAID MIXTURE IN SAID SEPARATION ZONE AT A TEMPERATURE SUBSTANTIALLY THE SAME AS THE TEMPERATURE EXISTING IN SAID FILTERING ZONE TO FORM A SECOND WAX CAKE COMPRISING RELATIVELY HIGH MELTING WAX AND A MIXTURE CONTAINING SOLVENT AND LOW MELTING WAX, AND SEPARATING SAID SOLVENT FROM SAID LOW MELTING WAX.

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