US2446514A - Separation of hydrocarbon mixtures - Google Patents

Description

Aug. 3, 1948. I H. STEWART ET AL.

SEPARATION OF HYDROCABBON MIXTURES Filed Sept 16, 1944 V mi mm m ww m mm m HAH A m m m .m m

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1 "1' ROCARBON MIXTURES Hall Stewart, Oakland, and August A Schaerer,

El Cerrito, Calm, asslgnors to Shell Development Company, San Francisco, ,Calif., a corporation oil Delaware Application September 16, 1944, Serial No. 554,486 14 Claims. (01. lac-14.48)

This invention involves a process for separating oils of different degrees of aromaticity and paraiilnicity from a liquid hydrocarbon mixture.

More particularly, it deals with a process for producing a 'high viscosity index oil fom lubricating oils.

The process is based upon the discovery that when lubricating oil containing solid wax and high and low viscosity index oil components in a solution of a solvent for aromatic hydrocarbons is gradually chilled, it will become thicker and thicker, forming a gelatinous slurry until all at once a temperature is reached where a granular solid precipitate is produced of substantially all the non-aromatic hydrocarbons.

It is a purpose of this invention to simply, economically, and effectively separate liquid nonaromatic hydrocarbons from liquid aromatic hydrocarbons in a mixture thereof heavier than kerosene. Another purpose is to produce high viscosity index oils from lubricating oil of lower viscosity index. Another purpose is to produce a highly refined high viscosity index oil in a simple and effective manner. Another purpose is to simply, economically and emci'ently separate crystalline and amorphous waxes (petrolatum) from each other. Other purposes are to fractionate solid waxes, separate straight chain type paraffins from naphthenes and branched chain type hydrocarbons, etc.

Generally speaking this invention comprises mixing a hydrocarbon oil having an average mo-;j

lecular weight above that of kerosene, comprising aromatic and non-aromatic hydrocarbons and containing between about 5% and 25% normally solid wax with a solvent selective for aromatic hydrocarbons, chilling the resulting mixture to solidify relatively non-aromatic hydrocarbons (parafiinic and/or naphthenic oil and wax) as a filterable precipitate, and filtering this precipitate from the resulting liquid solvent containing step may be removed from the oils by any suita ble means, such as distillation, and re-used in the process.

The terms aromatics vs. non-aromatics and parafilns and/or naphthenes vs. aromatics as used herein are all relative to. each other, de-

pending upon the composition or the 011 being treated.

The presence of normally solid paramn wax in the oil-solvent mixture is necessary to enable precipitation of the major portion or the non-aromatic hydrocarbons in an easily fllterable iorm, thereby making possible an easy and eiiective washing of the filter cake. When chilling a lubricating oil in solution of selective solvent to a very low temperature and a portion of the oil begins to precipitate, the mixture becomes thick and jellylike. As the temperature is further reduced, this condition becomes more aggravated. However, if solid wax is present, a sudden break occurs at a certain temperature: the gelatinous slurry suddenly becoming readily filterable. This break does not occur it solid wax is substantially absent. If the gelatinous slurry falls to break, the mixture filters only with difllculty and the cake retains large amounts of aromatic oil. It follows that, for a given yield of dewaxed parafilnic oil, a higher viscosity index is realized when carrying out the separation in the presence of paraffin wax rather than in its absence. In other words, the sequence of the separation should be: first separating aromatics from non-aromatics in the presence of wax and then dewaxing the non-aromatics to produce the high viscosity index dewaxed oil. 1

The break of the gelatinous slurry causes a sudden drop in the viscosity of the mixture as a result of which it becomes quite fluid. The temperature at which this break occurs and the precipitate becomes readily filterable is as a rule about -50 C. or below, although it varies somewhat with different oils and solvents. For example, for most lubricating oil distillates using methyl ethyl ketone as the solvent, this temperature is between about -50 and C. The break is probably due to a change in the crystalline forms of iso and cyclic paramns in the mixture, and as indicated results in an abrupt reduction of the viscosity.

Washing of the filter cake is an important step where good separation is desired. It is because of this that filtration is superior to centrifuging as a. separating method, because the wax separated by centrifuging cannot be washed as readily and economically.

Hydrocarbon oils which may be treated by the process of this invention should have, an initial boiling temperature above about 200 0., and major portions should consist of components having at least 12 and preferably 15 or more carbon atoms per molecule. As indicated the oils must contain dissolved at least 5% and not over 25%. preferably between and 20%. of a normally solid wax, i. e. one which is solid at room temperature (20 0.). Since the wax acts only as a nucleus upon which the non-aromatic hydrocarbon oil may crystallize it is immaterial from what source it is derived. It may even be a natural wax ester such as a vegetable wax or an animal wax, provided it has a crystalline structure (micro-crystalline or otherwise). If the oil is deficient in wax, wax must be added. If it contains too much wax, it should be partially dewaxed to within the above limit, because such a large amount of wax serves no useful purpose in the oil and needlessly increases the volume of the filter cake and the cooling requirements. The oil must be substantially free from asphalts wh ch stay in the oil when chilled because they inhibit the formation of filterable crystals by forming a gel. Hard asphalts, however, which remain in the wax when chilled may be tolerated or even mav be added as a filter aid although they contaminate the wax. Nevertheless, it is desirable that the o" be deasnhaltized prior to its separation by chillina by this process.

Suitable hydrocarbon oils may be derived from any crude containing aromatic and non-aromatic hydrocarbons. that is high and low viscosity index components. Distillate oils are easier to treat by this method than residual oils. In fact the latter may be very diiiicult to handle unless special means are employed. The narrower the fraction treated the closer the separation. Although wide lubricating oil fractions also may be treated with success, separation can be made between compositions having substantially the same or identical boiling temperatures. Pure crystalline waxes that contain compounds difiering in not more than two carbon atoms per molecule may be produced by this process.

The solvent must be a polar solvent more selective for aromatic than for parafilnic hydrocarbons, that is, must have a greater solvency for aromatics than for parafilns. It must be stable and liquid at the temperatures employed in the process and must not become too viscous when chilled to temperatures near its freezing point. Preferably, the solvent is an organic solvent, since it must be completely miscible at room temperature with the hydrocarbon oils treated, It should be easily separated from the oils, say by distillation, that is, have a boiling temperature at least 10 C. outside the boiling range of the oils. It may consist of and/or comprise several liquids. The more selective the solvent for aromatic hydrocarbons the lower its solvent power for the wax and high viscosity index oil components. This results in the formation of a filterable preclpitate of the non-aromatic and wax at a higher temperature, the formation of harder wax crystals, and easier filterability.

Some examples of suitable solvents are chlorinated hydrocarbons such. as methyl chloride, ethylene dichloride, chloroform. etc.; alcohols such a isopropyl alcohol, secondary butyl alcohol, etc.; ketones such as acetone, methyl ethyl ketone, methyl nand iso-propyl ketone, diisopropyl ketone, methyl isobutyl ketone, etc.; esters such as methyl and ethyl formates, acetates, propionates, etc. Ketones of 4-7 carbon atoms are preferred. The outstanding solvents are methyl ethyl ketone, methyl isopropyl ketone and methyl isobutyl ketone. Methyl ethyl ketone is the most fall short of solvent power. The addition of a minor proportion of benzene, toluene, xylenes. etc. will raise its solvent power. Methyl isobutyl ketone on the other hand has plenty of solvent power even at the lowest practical temperatures but is somewhat less selective. Therefore, methyl isobutyl ketone is often used in admixture with acetone or methyl ethyl ketone to increase its selectivity. Methyl isopropyl ketone stands between. methyl ethyl ketone and methyl isobutyl ketone.

It is desirable to wash the filter cake with a polar solvent of the true just described, and preferably with the same solvent that is used in forming the precipitate. Fresh solvent may be used'for the washing, and the wash liquor may then be used to eifect the precipitation, after which the solvent may be recovered and recycled. The same or different solvents may be used in each separation and chilling operation, as desired.

The accompanying drawing shows a simplified fiow diagram of one embodiment of this invention. Its description is divided into the following sections: (1) Separation of low viscosity index components, (2) Separation of high viscosity index components and (3) Separation of amorphous and crystalline waxes.

1'. Separation of low viscosity index components Referring to the drawing, the oil to be treated, which contains dissolved a solid wax content between about 5% and 25% by volume and both high and low viscosity index components, is fed through line i and admixed with solvent from line 2 in mixer 3. The resulting mixture is passed through line 4 to chillers 5 wherein it is a itated and chilled to a temperature \sufiicient to cause the break in the viscosity of the mixture, i. e. a temperature of -50 C. or below. The chilled solution then passes through line 6 to the filter l0 which, for convenience, has been shown as a vacuum rotating drum filter containing compartments so that the precipitate is sucked onto the porous drum surface H from the trough l2 and the filtrate (or liquid phase containing the solvent and low viscosity index components) is removed through line l3. The filter cake of precipitate comprising the waxes and the high viscosity index components rotates with the drum in the direction of the arrow and is washed with fresh or regenerated solvent pre-chilled in cooler 15 to the temperature of said cake by spraying it on the cake through lines it. The spent wash solvent may be separately drawn from the center of the drum through line IE, or joined with the filtrate in line l3 either by elimination of the partition H in the drum or through valved line l8. Preferably, the spent wash solvent is passed through line I9 to line 2 and is used for admixing with the feed oil in line i The filtrate and possibly the spent wash solvent, each of which contains som low viscosity index oil components, may be treated to remove the solvent, such as by distillation, in still 20 from which fresh solvent may be returned to line M through line 2 i, or to line 2 or other parts of the system (through lines not shown). The low viscosity index components are withdrawn as low viscosity index oil products through line 22. Fresh solvent may be introduced into this first separation step through line I joining line 2, or through line 23 joining line 14 as desired. The washed wax cake on drum II is scraped oif and passed through line 24 to the next step in the Ii. Separation of high viscosity indew components The cold wax cake from line 20 is admixed with more solvent introduced through line 3i into mixer 30. The resulting mixture is then passed through line 32 into heat exchangers 33 wherein it is continuously agitated and heated (or cooled, as required) to a temperature, above that employed in chillers 0, and dependent upon the pour point of the high viscosity index oil to be produced. The higher this temperature, th higher the pour point of the high viscosity in-dex oil due to the presence of dissolved waxes; while the lower this temperature, the lower the pour point (and the viscosity index) of the high viscosity index oil due to the absence of dissolved waxes. For economy, the solvent and/or 011 introduced in the first separation step I may be pre-cooled by heat exchange in exchangers 33. The resulting mixture, which contains a liquid phase of solvent and high viscosity index oil components and a solid phase of precipitated solid waxes, is then separated on a filter 34 and washed similarly to that described above in step I. Also, the solvent may be similarly recovered in still 35 and separated from the high viscosity index oil components which are withdrawn through line 36. The solid waxes may be removed through valved line 31 as product, recycled to blend with oil feed to make its wax content within the above limits, or further separated as described in the next step. The high viscosity index oils produced are highly refined and usually white, They are unstable to oxidation, but have good inhibitor susceptibllities.

, Alternatively. this step II may comprise merely further washing the precipitated wax formed in step I with a warmer solvent than that used in the first step to dissolve the high viscosity index oil components from the normallysolid waxes. However, this alternative method does not give as complete a separation as that described above.

III. Separation of amorphous and crystalline waxes The solid waxes from filter 34 are admixed with more solvent introduced through line ll into mixer 40. The resulting mixture is continuously agitated in heat exchangers 43 until a temperature is reached which is higherthan that in step II and which depends upon the melting point of the waxes desired. The higher melting or crystalline waxes are precipitated and the lower melting or amphorous waxes are dissolved in the solvent. The suspended solids are separated by such as filtering and washing on filter 44 and the crystalline wax is scraped off as a final product at 61. The amorphous wax is separated from the solvent in still 05 and withdrawn through line 46, while the recovered solvent may be recycled.

The described apparatus is merely illustrative of what may be employed in this process. For example, the chillers and heat exchangers may be of the Carbondale type and the filters may be of the Oliver, leaf, or other type, or they may be replaced by centrifuges or other suitable means to separate suspended solids from a liquid.

- Many of the necessary pipes, valves, tanks, pumps, heat exchangers, and the like are not shown in the drawing but their proper placement is within the knowledge of anyone skilled in the art.

The temperatures and solvent-to-feed ratios employed in each step of theprocess may vary with the type of solvent employed and the properties of the products to be produced. However. the temperature of the separation in step I is the lowest reached in the process, while the temperature in each succeeding step is progressively higher. The more selective the solvent is for aromatics and low viscosity index components, the higher may be the temperature in order to obtain the filterable precipitate required in step I. If low viscosity index oil, high viscosity index oil, amorphours waxes and crystalline waxes are the products, the temperaturefor step I is below about --50 (3.; for step II is between about -30 C. and 0 0.; and for step III is between about 0 C. and 20 C.

The solvent-to-oil ratiosvvary with the type of solvent. For example in step I, the ratio ranges from about 1:1 to 10:1,and preferably from 2:1 to 5:1. In steps II and III the ratios vary from between 2:1 to 8:1 for solvents of relatively high solvent power such as methyl isobutyl ketone to from about 8:1 to 20:1 for solvents of relatively low solvent power such as methyl ethyl ketone. If the solvent power of a low solvency solvent is raised, as by the addition of toluene, the desired ratio may be reduced to below 8:1.

For washing the cakes amounts of solvent normally vary between /2:1 to 3:1 times its volume.

and preferably about 2:1.

We claim as our invention:

1. A process for separating liquid non-aromatic hydrocarbons from liquid aromatic hydrocarbons in a mixture thereof having an initial boiling point of above about 200 C. and containing dissolved between about 5% and 25% by volume of normally solid wax. comprising treating said mixture with at least about an equal volume of a first polar solvent having a preferential solubility for aromatic hydrocarbons, cooling the resulting mixture to a temperature below about wax phase and a second liquid phase comprising said liquid non-aromatic hydrocarbons and said second polar solvent, and separating said second solid wax phase from said second liquid phase.

2. The process of claim 1, where in said second polar solvent is the same as said first polar solvent.

3. A process for separating low viscosity index oil from high viscosity index oil in a petroleum distillate having an initial boiling temperature above about 200 C. and containing dissolved between about 5 and 25% by volume of a normally solid wax, comprising treating said distillate with at least about an equal volume of a selective solvent for said low viscosity index components, cooling the resulting mixture to atemperature below about -50 C. to produce a solid phase comprising at least a major portion of said high viscosity index components and wax and a liquid phase comprising saidselective solvent and said low viscosity index components, separating said phases, treating the separated solid phase with a polar solvent at a temperature higher than that employed in producing the first solid phase but below about C. to produce a second solid phase and a second liquid phase comprising the high viscosity 'index components of said distillate, and separating said second solid phase from said high viscosity index components.

4. A process for separating liquid non-aromatic hydrocarbons from liquid aromatic hydrocarbons in a mixture thereof having an initial boiling temperature above about 200 C. comprising treating said mixture inthe presence of between about and 25% by volume of a normally solid wax dissolved therein, with at least about an equal volume of a ketone having a preferential solubility for aromatic hydrocarbons, cooling the resulting mixture to a temperature below about -50 C. to produce a solid phase comprising at least a major portion of the non-aromatic hydrocarbons and wax and a liquid phase comprising said ketone and said aromatic hydrocarbons, separating said phases, treating said separated solid phase with a solvent at a temperature higher than that used in obtaining the first solid phase but below about 0 C. to produce a second solid wax phase and a second liquid phase comprising said liquid non-aromatic hydrocarbons and said solvent, and separating said second solid wax phase from said second liquid phase.

5. A process for separating liquid nonaromatic hydrocarbons from liquid aromatic hydrocarbons in a mixture thereof having an initial boilin temperature of above about 200 C. and containing dissolved between about 5 and 25% by volume of a normally solid wax comprising treating said mixture with at least about an equal volume of a polar solvent having a preferential solubility for aromatic hydrocarbons and thereby forming a resulting mixture which upon cooling sufiiciently yields a gelatinous mass which increases in viscosity as the temperature is lowered progressively until a critical low temperature is reached at which the viscosity of the resulting mixture decreases, cooling the resulting mixture to a temperature at least as low as said critical low temperature and producing a solid phase comprising said wax and at least a major portion of the non-aromatic hydrocarbons and a liquid phase comprising said solvent and said aromatic hydrocarbons, separating said phases, treating said separated solid phase with a second solvent at a temperature higher than that in the first cooling stage to produce a second solid wax phase and a second liquid phase comprising said liquid non-aromatic hydrocarbons and said second solvent, and separating said second solid wax phase from said second liquid phase.

6. A process for obtaining crystalline wax from a mixture of liquid non-aromatic hydrocarbons, substantially devoid of aromatic hydrocarbons, which mixture possesses an initial boiling temperature above about 200 C. and contains at least 5% by volume of a normally solid wax dissolved therein comprising treating said mixture with at least an equal volume of a solvent comprising a ketone and an aromatic hydrocarbon and thereby forming a resulting mixture which upon cooling sufliciently yields a gelatinous mass which increases in viscosity as the temperature is lowered progressively until a critical low temperature is reached at which the viscosity of the resulting mixture decreases, cooling the resulting mixture to a temperature at least as low as said critical low temperature and producing a liquid phase and a solid phase, separating the two phases and treating said separated solid phase at a higher temperature with at least an equal volume of a ketone containing solvent to produce a solid phase essentially containing crystalline wax and a liquid phase essentially containing said solvent and amorphous wax dissolved therein and separating these latter two phases.

7. A process for separating a liquid hydrocarbon mixture having an initial boiling temperature above about 200 C. and containing aromatic hydrocarbons and non-aromatic hydrocarbons including amorphous Wax, comprising treating said mixture in the presence of at least 5% by volume of a normally solid crystalline wax dissolved therein with at least about an equal volume of a first solvent which has a selective solubility for aromatic hydrocarbons and thereby forming a resulting mixture which upon cooling sufficiently yields a gelatinous mass which increases in viscosity as the temperature is lowered progressively until a critical low temperature is reached at which the viscosity of the resulting mixture decreases, cooling the resulting mixture toa temperature at least as low as said critical low temperature and producing a first liquid phase containing said first solvent and said aromatics and a first solid phase containing said non-aromatics and said waxes, separating said phases, treating said separated first solid phase at a substantially higher temperature with at least an equal volume of a second solvent to produce a second liquid phase containing said second solvent and said non-aromatic hydrocarbons and a second solid phase containing said waxes, separating said second phases, treating said separated second solid phase at a still higher temperature with at least an equal volume of a third solvent to produce a third liquid phase containing said third solvent and said amorphous wax and a third solid phase containing said normally solid crystalline wax, and separating said third phases. .1

8. The process of claim '7, wherein said first,

'said second and said third solvents are the same.

9. The process of claim 7, wherein said first, said second and said third solvents contain a ketone.

10. The process of claim 3 wherein said selective solvent and said polar solvent are the same.

11. A process for separating non-aromatic hydrocarbons from aromatic hydrocarbons in a liquid mixture thereof having an initial boiling temperature of above about 200 C. and containing dissolved therein at least about 5% by volume of a normally solid wax comprising treating said mixture with a solvent having a, preferential solubility for aromatic hydrocarbons and thereby forming a resulting mixture which upon cooling sufficiently yields a gelatinous mass which increases in viscosity as the temperature is lowered progressively until a critical low temperature is reached at which the viscosity of the resulting mixture decreases, cooling the resulting mixture to a temperature at least as low as said critical low temperature and producin a solid phase comprising said wax and at least a major portion of the non-aromatic hydrocarbons and a liquid phase comprising said solvent and said aromatic hydrocarbons, separating said phases, treating said separated solid phase with a second solvent at a temperature higher than that in the first and a second liquid phase comprising said liquid non-aromatic hydrocarbons and said second solvent, and, separating said second solid wax hase from'said second liquid phase.

12. A process for separating components of a liquid hydrocarbon mixture having an initial boiling temperature above about 200 C. and containing aromatic hydrocarbons and non-aromatic hydrocarbons including amorphous wax, comprising treating said mixture in the presence of at least by volume of a normally solid crystalline wax dissolved therein with a first solvent havinga preferential solubility for aromatic hydrocarbons and thereby forming a resulting mixture which upon cooling sufficiently yields a gelatinous mass which increases in viscosity as the temperature is lowered progressively until a critical low temperature is reached at which the viscosity of the resulting mixture decreases, cooling the resulting mixture to a temperature at least as low as said critical low temperature and producing a first liquid phase containing said first solvent and said aromatics and a first solid phase containing said non-aromatics and said waxes, separating said phases, treating said separated first solid phase at a substantially higher temperature with a second solvent to produce a second liquid phase containing said second solvent and said non-aromatic hydrocarbons and a second solid phase containing said waxes, separating said second phases, treating said separated second solid phase at a still higher temperature with containing said-third solvent and said amorphous wax and a third solid phase containing said normally solid crystalline wax, and separating said third phasesl,

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS "Number I Name 1 Date 1,669,151 Wagner May 8, 1928 1,951,780 Voorhees Mar. 20, 1934 1,980,649 Voorhees et ai Nov. 13, 1934 2,108,629 Van Wijk Feb. 15, 1938 2,161,569 Gross June 6, 1939 2,164,013 Jenkins June 27, 1939 2,180,763 Nederbragt Nov. 21, 1939 2,193,767 Manley et a1. Mar. 12, 1940 2,198,576 Govers Apr. 23, 1940 2,234,916 Jones Mar. '11, 1941 2,246,982 Nederbragt June 24, 1941 FOREIGN PATENTS Number Country Date 441,104 Great Britain Jan. 13, 1936

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