US2642377A - Dewaxing process - Google Patents

Description

June 16, 1953 L. C. FETTERLY DEWAXING PROCESS Filed Oct. 27. 1947 ,2.6: .IGM

:E200 @SD :E200 +oGL+xm By His A'H'orney:

expense.

Patented .une 16, 1953 UNITED STATES PATENT OFFICE DEWAXING PROCESS Lloyd o. Family, seattle, wasn., assignor to shell Development Company, San Francisco, Calif., a corporation of Delaware Application October 27, 1947, Serial No. `782,450

Claims. (Cl. 196-17) l This inventionrelates to an improved process for the dewaxing of oils. I' More particularly it relates to a process for Vthe separation of waxy c onstituents from petroleum' oils Without the necesnsity for resorting to excessive refrigeration. The

process is particularly directed to the separation of wax from petroleum products having a low Wax ,content and to the isolation of waxes which are difficult to remove by the processes known to the prior art. t

Pressing to remove paraiiin wax from distlllates and sweating the resultant slack wax to produce substantially oil free wax are two of the oldest processes in the petroleum industry. 'I heyare applicable, however, only to the wax d1st1llates of relatively low boiling range. Newer processes such 'as centrifuging and solvent dewaxing have been used successfully to dewax higher boiling distillates. While also capable of handling the low boiling distillates, these last two methods have not replaced to any extent the processes of pressing and sweating. VRegardless of the Wealth of experience gained, endless difculties have .arisen in the practice of these various methods.

The process of pressing, for example, may give a lhard dry cake with one distillate while lanother .oil may result in -a salvy mushy cake. Furthermore, the slack wax from the latter type of cake almost invariably behaves in an unsatisfactory method when sweated.

The use of such modern processes as solvent dewaxing partially remedies these shortcomings but only at considerable economic disadvantage. It has been estimated that the cost of refrigeration in most solvent dewaxing procedures constitutes approximately 60% of the total dewaxlng It is'immediately apparent that any method eliminating the necessity for the use of excessively low temperatures, such as are required by solvent deWaxing methods, would be an 1mmediate and substantial advance in the fart Aof The dewaxing of'petroleum fractions having a. low Wax 'content is highly ineicient in that a high proportion of'the wax removed mustl-be recycled to the system prior to the separation l this invention to provide a area in order that a filter cake having satisfactory ous theories have beenadvanced considering the Atype ofhydrocarbons present which cause these poor v crystal characteristics. paraflin waxes have a substantially straight chain configuration has been supplanted within recent years by the postulation that petroleum waxes are mixtures containing, not only normal parafns, but also substantial'quantities fof isoparafns and cyclic hydrocarbons. A summary of the evidence confirming thisjtheory has Abeen presented by Ferris and Coles,.Industrial EngineeringChemistry, Volume 37, pages 1054-62 (1945) In other fields of 'activity the preparation of crystalline complexes between agents such as ureawith other organic compounds has been recently investigated. Ithas been determined that urea is highly selective in that it crystallizes substantially exclusively with hydrocarbons of straight chain configuration, crystalline complexes neverbeing known to form 'between urea 'and hydrocarbons having Ybr-anched chains or 'cyclic structures. It has been believed up to the present time that this characteristic was invariable and that complexes Would not form with or- It is `an object of this invention tot provide an..l

improved process for the dewaxing of oils, particularly petroleum oils.

It is another object of process for the dewaxing of oils which avoids the necessity of using refrigeration. vIt is a third object of this invention to provide a process for the dewaxing of oils which avoids the necessity 'for processing'waxes of poor iiltration characteristics. It is a further object of this invention to provide new types 0f The theory that 3 complexes formed between urea and certain high molecular weight hydrocarbons. Other objects will become apparent during the following discussion.

Now, in accordance with this invention it has been found that crystalline complexes may be formed between urea and the waxy constituents of oils regardless of the structure of the waxes. Still in Iaccordance with this invention, it has been found that oils may be dewaxed by treating them with urea, thus allowing the formation of crystalline complexes with waxy constituents which are present, and subsequently separating the complexes from the main body of the oil. While the process may be applied to the separation of animal and vegetable waxes from their oils, it is particularly suitable for the dewaxing of petroleum fractions. The fact that urea reacts with lall types of waxes regardless of their structural configuration is entirely unexpected in view of the selective reactivity which urea..ex hibits with organic compounds having lower molecular weight. As will be pointed out hereinafter, the use of this process is particularly valuable -for the avoidance of excessive refrigeration 'costs and for the dewaxing-or petroleum fractions having low wax content, as well as for the removal of the so-called micro-crystalline or amorphous waxes from oil fractions containing them.

The term amorphous wax as employed herein includes not only the' amorphous waxes per se but also mixtures containing an amount of hydrocarbon waxes having sufficient branching and/or cycloaliphatic groups so that ,the wax fraction has the familiar amorphous character. Straight chain para'in waxes may ybe present in an amorphous petroleum wax as long asb the blend retains the I amorphous character` shows its distinguishing and` characteristicbrittle, non-plastic property.

Amorphous petroleum wax essentially contains branched (i. e. side chain alkyl groups) and/or cycloaliphatic groups. Many such waxes commonly employed in industry have a melting point range of between about C. and` about 88 C., which is higher than many of the melting points of the normal paraffin waxesused commercially. An amorphous petroleum wax usually has about the same boiling point for a given'V molecular weight as the non-amorphous `normal paran wax, in which casethe melting point of the amorphous wax is usually much lower than that of the normal parafiin wax. Amorphous petroleum waxes are further distinguished by the fact that they cannot be separated from petroleum lubricating oils by the familiar sweating process used to separate straight chain paraiiin. waxes from the oil.

The term paraffin wax is understood to refer to those hydrocarbon waxes which are capable of having a plate-like crystalline structure. Amorphous waxes do not have this property. Another property of the paraffin waxes istheir relatively greater brittleness and their consequent ease of fracture. This kind of wax consists of aliphatic straight chain structures and is substantially free from hydrocarbon waxes having suicient branching to cause the so-called mal-crystalline form referred to in the paper by Ferris and Coles.

Amorphous petroleum wax and paraffin wax are normally separately obtained during the process of refining lubricating oils derived from petroleum. Paraihn wax is obtained from the wax containing lubricating oil distillate fraction and is separated by oil removal methods such as chilling and subsequent refining operations such as sweating. Most amorphous petroleum waxes on the other hand are obtained from the residuum although such waxes are also available in the waxy oil distillate fractions. Usually the amorphous wax is separated by adding petroleum naphtha to the residuum and then centrifuging or using filter processes. The wax obtained by such a process may contain up to about 35% or more of oil and may be further de-oiled by dispersi'ng in naphtha and repeating the previous treatments.v The wax thus obtained generally contains. about 5% of the heavy lubricating oil fraetionl This Wax may be further cie-oiled by further treating it at about 10 C. with a solvent' solutionsuch. as a mixture of methyl ethyl ketone, toluene and benzene.

The process of the present invention comprises essentially the contacting of waxy oils with urea, whereby crystalline complexes are formed between the waxes present and'urea. These waxes may be separated from the main bodyy of the oil by conventional methods such as filtration' or centrifuging. Where lightl distillates are involved and wax content is relatively low this operation is simple, since a fluid slurry results and the low viscosity oil does not tend to contaminate the filter cake. If the oil contains a substantially higher proportion of wax; the amount of complexes may be such that a substantially non-fluid mass results which has poor filtration properties and other disadvantages of handling. Furthermore, in the treatment of high viscosity fractions the oil may be of suchl a character that it is highly absorbed on the surface of the crystalline complexes, orV at least does not flow freely awa-y therefrom, thus causing excessive contamination of the crystals. In these cases it is preferable to employ a diluent which should be one having a high solvent power for the oil and which is relatively non-solvent with respect to the crystalline complexes. Furthermore, any solvent which is chosen should be substantially inert toward urea and any other material whichV may be present. Preferred solvents include the ketones, such as methyl ethyl ketone and particularly methyl isobutyl ketone, as well as other well known solvent materials. The proportion of the diluent to be used will depend upon the relative .bulk of the crystalline complexes and the viscosity of the oil fraction being treated. Under normal circumstances equal volumes of the dilnent and oil give satisfactory results, although higher or lower proportions of the diluent may be used to suit particular processes and mixtures. Non-polar diluents, such as isopentane, may be used in place ofr or inaddition to the polar solvents if desired.

The urea may be employed in either solid or dissolved form, although the latter is preferred. Water is a satisfactory solvent, but methyl alcohol or other lower alcohols may be employed either alone or in conjunction with other solvents. For example, aqueous alcoholic solutions of urea are particularly effective. For complete lremoval of` all the waxy constituents present-the solution of urea should be substantiallysaturated and it is evenA preferable to employ a saturated solution having excess 'solid urea ysuspended therein. The reaction may be conducted in a vmulti-phase system or in a single-phase system as desired. A reaction mixture comprising oil dissolved in methyl isobutyl ketone and urea dissolved in water has been found to have particular advantages in the rate of crystal formation `and in thev crystalline character of the complexes formed. ,Y n Y Therparticular advantage gainedl by the present process is the elimination of the necessityfor refrigeration and the consequent freedom from refrigerating equipment and refrigeratingoperation costs. In forming complexes between waxes and urea it is possible to operateat normal room temperatures or even attemperatures somewhat above room temperature, for example, 2560 C. At these temperatures as y'well asiat lower temperatures the crystalline complexes form readily and may be easilyvsepas complexes by heating the latter.

rated from the oil by such methods as filtration. It will be apparent that in utilizing room temperatures the vis-cosity of the oils present will be considerably less than when the ytemperatures present during a refrigeration operation are em-- ployed. This is particularly important Yin improving ltration rates and in raising the purity and yield of both the waxes and the oils. A preferred process comprises .formation `of a satu-` rated solution of urea,`warm`ing itto approximately 40 C. and mixing it with the wax-bearing oil which has previously been warmed to the same temperature. The mixtureis allowed to react at this temperature and then cooled to approximately 22 C. at which time the crystalline complexes formed may be readily separated from the other componentsof the reaction mixture.

With some types of Ywaxesand oilsit is advantageous to form the complexes in the absence of an oil solvent and then to add such `asolvent immediately' prior to filtration. 'This operation allows the optimum crystalfstructure to grow and at the same time enables ready filtration of theprodu-ct. j

It will be apparent that anumber kof process variations may be employed to suit'aparticular feed'ora particular set of refinery'equipment. Thus the contacting of urea with the wax-bearing oilmay be carried out by the following means:

1. Concurrent fluid processes, whereby a solu-I tion of urea is introduced into the-hydrocarbon feed line.

2..Countercurrent fluid processes, whereby a 7 .solution of urea is introduced into the hydrgcarbon flow near the exit.r l

3. Fluid x'ed bed'processes,whereby the hydro- A carbon is passed through av stationary column n of urea solution.

4. Moving bed processes, whereby solid urea proi ceeds tomove countercurrentlyto the hydro.- carbon feed- Y, 5. Slurry processes, whereby a .mixtureof solid urea and urea solution Vmoves concurrently or countercurrentlyv with thev hydrocarbon feed. 6. Emulsion processes, whereby solutions vof urea are emulsified, at least'momentarily with the hydrocarbon feed. y

7V. Fixed bed processes-wherebythe hydrocarbon feed ispassed through a bed of urea.

' The complexes formed by any of the above processes must be subsequently separated from eration.

the main body vof the'oil such as by settling, cen- .trifuging or filtration. -In order to remove-oil loccluclecl on the surface of the crystals it is preferable to vwash the latter with .an oil solvent such as propane or pentane. Subsequent to this operation the waxes may be recovered from their This causes the decomposition of the complexes and results inthe regeneration of urea and wax therefrom. The heating may be carried out in an inert atmosphere or by passing the hot dry gas or steam through the complexes, by the application of a urea solvent such as water together with heat or by the application of a wax solvent'while heating. A preferred means comprises heating the complexes in the presence of water to a Vtemperature vof approximately 50 F. higher than the temperature ofr reaction sothat the complexes decompose and the urea dissolves in the water while the waxes form a melted separate layer which may be separated from the aqueous urea s solution.

crystallization means, preferably without refrigyAlternatively evaporation technique may be employed.

In order to more fully describe the process of this invention. reference will now be madev to the drawing illustrating a parti-cular embodiment of the dewaxing process. 1

A wax-bearing oil and a solvent (methyl isobutyl ketone) are mixed together with a saturated solution of urea, the reaction mixture entering a reactor l, containing Va stirrer having fins or blades throughout its length. The complexes formed therein between urea and wax move together with the oil out of the crystallizer at the top and `into a filter 2 wherein the crystalline complexes are separated from the dewaxed and diluted oil. The'crystals are then transferred from the filter usually after a washing operation, toa separator 3 containing a urea solvent, such as water, heated to a temperature whereat the complexes are decomposed and the urea dissolves in the water, while the waxes may be removed in their melted state to a storage point 1. The Vliquid. components passing out of the filter 2 comprise oil, oil solvent and dilute aqueous urea solution; This mixture may be passed to a settling area 8 wherein the diluted oil Vis separated from the aqueous urea. The former as heatingnashing or distillation. The solvent is returned to original storage, while the dewaxed, Legrainate, oil is sent tothe storage area l0. The dilute aqueous urea solution obtained in the settler 8 may be 'passed to the separator 3 to actV as the aqueous medium present during decompositiony of the complexes. The following examples are presented as specific embodiments of the invention:

' s'One"hundredseventy-one parts by weight of wax-'containing lubricating oil were mixed with an equal volume of methyl isobutyl ketone, and ve hundred parts of Water having dissolved therein six hundred'parts urea. The mixture was initially reacted at F. and was shaken for onehalf hour. A voluminous mass of white crystalline complexes formed during this period. The reaction'mixture was allowed to stand for V30 minutes atnroom temperature, following which, the complexes were removed' by filtration.

` amasar The filter cake was washed with; methyl iso butyl lretone and wasthen heated to 145 F; until it decomposed, the urea dissolving in the water and the melted wax regenerated from the complex forming ya layer containing residual methyl isobutyl ketone from the washing operation. The two phases were separated and the ketone evaporated from the wax to yield the products described in the table below.

The filtrate from which the crystalline complexes had been removed separated into two phases, one being t-he residual aqueous urea, the other being the dewaxed oil and methyl isobutyl ketone. The ketone was evaporated, from the latter layer in order to isolate the dewaxed oil.

Starting with the original wax-containing lubricating oil, conventional solvent dewfaxing procedure was carried out, using methyl ethyl ketone as the solvent, in :1 ratio with the oil, at C. Three stocks were dewaxed by these two procedures. Properties of the waxes and oils produced are given in the following table:

a; temperature between 25 andv 60 C., whereby crystalline molecular complexes are formed between urea and substantially all the waxy components present in said oil, and separating said complexes from the dewaxed lubricating oil.

4. The process for dewaxing lubricating oils whichk comprises contacting aqueous alcoholic urea solution with a lubricating oil fraction containing minor amounts of both microcrystalline and normal parafne waxes, at a temperature between 25 and 60 C'.,` whereby crystalline molecular complexes are formed between urea and substantially all. the; waxy components present in said oil', and separating said complexes from the dewaxed lubricatingfoil.

5'. The process for dewaxing lubricating oils which comprises contacting urea withV a petroleum'oil fractioncontaining minor amounts of both microcrystalline and normal paraine waxes, at-:a temperature between 25 and 60` C., whereby crystalline molecular complexes are formed between urea and substantially all the Properties of Wax- Properties ol- Oil Yield A 'Dewaxme v Source Grad@ Method .Pertent Meir ser. Yield, Pour Ref. Pt., Ind., Percent Pt., Ind., G. 70 C. wt'.v F. ,30 C

Crude Med. Lubestock.. Complex.- f 8.3' 43 1.43'17 84-.5 l5 1.5095r do S01vent 9.5 44 1.4306 90.5 -13 n 1. 5100 Complex.. l0 46 11.4350 78 -l5- A l. i913 do l Solvent--- v 6 49.5-V 1.433l 94 6' 1.4952 Crude Hvy.Lubestock Complex` Y 5.5 64 1.4365 94 0 1.4948 do Solvent-.- 5.0 56 1:4375 94.3- 0 l 1.4998' A particular advantage of the present process comprises the possibility of fnactionating waxes by various expedients. For example, the temperature may be controlled to an extent where one type of wax forms a complex while the formation of complexes of other waxes is repressed. Furthermore, the present process may be combined with normal solventV dewaxing procedures so as to effect fractionation. -In the latter case, the wax-bearing oil may be diluted, for example, with benzene and methyl ethyl ketone, cooled to the point whereat normal paraffin waxes separate, filtering oil the wax crystals, then adding urea and forming complexes of the micro-crystallin and amorphous waxes which remain` I claim as my invention:

l. The process for dewaxing lubricating oils which comprises contacting aqueous urea.A solution with a petroleum oil fraction containing minor amounts of both microcrystalline` and normal paraine waxes, at a temperature between 25 and 60 C., whereby crystalline molecular complexes are formed. between 'ureav and, substantially all the waxy components present in said oil, and separating said complexes from the dewaxed lubricating oil.

2. The process for dewaxing lubricating oils which comprises contacting aqueous urea solution with a lubricating oil fraction containingV minor amounts of both rnicrocrystalline 'and'normlal paraftine waxes, at a temperature of. about- 32 C., whereby crystalline molecular'complexes are formed between urea and substantially lall of the waxy components present in said oil, and separating said complexes from the dewaxed lubrieating oil.

3. The process for dewaxing lubricating oils which comprises contacting a substantially saturated aqueous urea solution with a lubricating oil fraction containing minor amounts of both microcrystalline and normal parane waxes, lat

waxy components present-in said oil, and separating said complexes from the dewaxed lubricating oil.

6. The process for dewaxing lubricating oils which comprises contacting. solid urea with a petroleum oil fraction containing minor amounts of both microcrystalline and` normal parafline waxes, at fa temperature between 25 and 60 C., whereby crystalline molecular complexes are formed between urea and substantially all the waxy components present in said oil, and separating said complexes from the dewaxed lubricating oil.

7, The process for dewaxing. lubricating oils which ,comprises contacting aqueous urea solution with a. petroleum oil fraction containing minor amountsv of. both microcrystalline and normal parane waxes, at a temperature between 25 and: 60 C., whereby crystalline molecular complexes areformed: between urea and substantially all the waxy components present in said oil, separating.l said complexes from vthe dewaxed lubricating. oil, and regenerating waxes and 'urea therefrom.

81 The4 process forY dewaxing lubricating oils which comprises: contacting aqueous urea solution with :a petroleum lubricating oil fraction containing minor amounts of. both micro'crystalline Aandmormal. paraffin. waxes at a temperature between 25 and 60 C., whereby crystalline complexesare formed betweenk urea and both micro'- crystallinez'and paraffin. waxes and separating saidcomplexes fromv the dewaxed. lubricating oil.

9. The` process' for dewaxing lubricating oils which comprisescontacting ureawith apetroleum lubricating oil fraction containing minor amounts ofbothL microcrystalline andi normal paraffin waxes at atemperature between 25'and 609' C., whereby molecular complexes are formed between the urea and substantially all the types of waxy components present in said oil and separating said complexes from the dewaxed lubricating oil.

10. The process for dewaxing lubricating oils which comprises contacting aqueous urea solution with a petroleum oil fraction containing minor amounts of both microcrystalline and normal paraffin waxes at a temperature between 25 and 60 C., whereby crystalline complexes are.

formed between urea and both microcrystalline and paran waxes and separating said complexes from the dewaxed lubricating oil.

LLOYD C. FETTERLY.

10 References Cited in the iile of this patent UNITED STATES PATENTS Number Name Date 2,229,658 Jenkins Jan. 28, 1941 2,246,257 Kohn June 17, 1941 2,397,868 Jenkins Apr. 2, 1946 OTHER REFERENCES Technical Oil Mission, Reel 143, 6 pagetranslation of German patent application No. B 190,197, deposited in the Library of Congress May 22, 1946.

Claims (1)

1. 5. THE PROCESS FOR DEWAXING LUBRICATING OILS WHICH COMPRISES CONTACTING UREA WITH A PETROLEUM OIL FRACTION CONTAINING MINOR AMOUNTS OF BOTH MICROCRYSTALLINE AND NORMAL PARAFFINE WAXES, AT A TEMPERATURE BETWEEN 25 AND 60* C., WHEREBY CRYSTALLINE MOLECULAR COMPLEXES ARE FORMED BETWEEN UREA AND SUBSTANTIALLY ALL THE WAXY COMPONENTS PRESENT IN SAID OIL, AND SEPARATING SAID COMPLEXES FROM THE DEWAXED LUBRICATING OIL.

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