US2047826A - Dewaxing mineral hydrocarbon oils - Google Patents

Description

- bility of the solid wax in the oil.

Patented July 14, 1936;

UNITED STATES PATENT OFFICE to Shell Development Company, San 0alii., a corporation of Delaware Francisco,

No Drawing. Application A sust 17, 1935, Serial No. 38,717

18 Claims. 01'. 196-19) This invention relates to a process for separating from mineral oils various waxy substances occurring therein. More particularly it pertains to a diluent for decreasing the viscosity of the oil and the solubility of the wax, whereby the wax and oil may be readily separated when the oilsolvent mixture is chilled to solidify the wax.

Mineral oils, such, as petroleum hydrocarbon products and tars, naturally contain varying amounts of waxy paraihns or petrolatum, for convenience hereinafter designated as waxes, which at normal or elevated temperatures are dissolved in the oil or are present in the liquid state. but which tend to solidify or become very viscous at low temperatures, causing the oil to resist flow or to have a cloudy appearance.

The removal of wax from oil, and more particularly the removal of mineral wax from mineral oil, has heretofore been accomplished by diluting the waxy oil with a suitable diluent or diluent mixture, chilling the solution so formed to precipitate or solidify the wax, and separating the solidified wax by some suitable means, such as filter pressing, centrifuging, or cold settling. The functionof the diluent was to reduce the viscosity of the chilled mixture, whereby the separation of the wax was facilitated. I

' More recently it was proposed to improve the separation of the wax by employing diluents or diluent mixtures which exercise a selective solvent action between the solid wax and the oil. For example, it'is known to effect the separation of these waxes from hydrocarbon oils by diluting the oil with mixtures of two liquids, one of which is a good solvent for hydrocarbons, and the other a poor solvent for solid param'n wax. Thus, a mixture of benzol and acetone has been used for dewaxing lubricating oils.

In such selective dewaxing mixtures the function of the selective solvent is to lower the solu- These selective solvents are, however, not suiiiciently miscible with the oil at the dewaxing temperature, and it is often necessary to add another liquid which is miscible with the oil and with the selective solvent. This latter liquid is commonly known as the solubility enhancing agent.

According to the present invention'it was found that particularly good results are obtained by dewaxing mineral oils in the presence of a selective dewaxing mixture containing low boiling hydrocarbon oil extract or recycled kerosene extract as the solubility enhancing agent. This extract may be obtained by extracting a low boiling hydrocarbon distillate, which may, for. exam-.

' as examples:

ple, be the portion of petroleum oils which is commonly known as kerosene distillate, and which boils substantially within the range 150 C. to 300 0., with a selective solvent for aromatics, i. e., with a solvent having the selective solvent characteristics of liquid sulfur dioxide. any solvent of this type may be used, particularly the following, which are disclosed here merely Furfural (furfuraldehyde) nitrobenzene, pp dichlorethyl ether, cresol, and phenol. The term "kerosene" as used in the present specification and claims is used to designate any hydrocarbon oil distillate boiling substantially between 150 C. and 300 (3., although its actual boiling temperature range includes but a portion of the stated range, and might for this reason be known to the art by other names.

The hydrocarbon extract may be obtained by any process which is effective in subjecting a hydrocarbon distillate to the extractive action of such a selective solvent. For example, a kerosene or lower boiling oil distillate may be mixed with the solvent in an agitator or mixer, the resulting mixture allowed to stratify into two liquid layers, the layers separated, and the solvent layer or extract phase distilled or otherwise treated to separate it into solvent and hydrocarbon portions. This treatment may be conducted also in a packed tower, or in a multi-stage countercurrent' treater, as is well known in the art.

The kerosene or similar hydrocarbon distillate extract may also be produced incidentally to the extraction of another hydrocarbon fraction. For example, in the extraction of lubricating oil, gas oil, Diesel fuel, or gasoline, kerosene distillate is sometimes mixed with the oil or introduced in some other manner into the extraction zone to improve the extraction. In such extractions the produced extract will be a mixture or a solution of the aromatic portions of both the kerosene and the particular oil. The kerosene extract may be recovered from such extracts by simple or fractional distillation.

In such extraction processes employing low boiling hydrocarbon distillate or kerosene diluents, the hydrocarbon distillate may be partially or entirely replaced by a hydrocarbon distillate extract,- derived from the same process (asby recycling a portion of the distillate extract recovered as described in the preceding paragraph from a prior operation) or from a separate extraction operation. In such processes which employ hydrocarbon distillate extract as a diluent, .the distillate extract which is recovered from the extract phase will be substantially richer in aromatic hydrocarbons, and will be more suitable for use as the solubility enhancing agent, and is in the present specification and claims designated as recycled hydrocarbon extract. Although this recycled hydrocarbon extract is most conveniently produced in conjunction with the extraction of another hydrocarbon oil, it should be noted .that it may also be produced by repeatedly extracting hydrocarbon distillate without the simultaneous extraction of other hydrocarbon fractions, to obtain a highly aromatic extract. The term recycled hydrocarbon extract is, therefore, to be taken to include any hydrocarbon distillate extract which has been subjected to repeated treatments which concentrate its aromatic components, as defined below.

In general, it was found that the hydrocarbon distillate or kerosene extract to be employed as the solubility enhancing agent should possess the following properties:

Boiling within the range 150 C. to 300 C. Gravity from A. P. 1... 8 to 32 Total aromatics, by volume 60-100% Materlally improved results, are, however, obtained by using recycled kerosene extract. Such extracts should have the following properties:

Boiling within the range 180 C. to 300 C. Gravity from ....A. P. I.-- 8 to 25 Total aromatics, by volume 90-l00% Although I have indicated 180 C. as the lower limit of the boiling range of my preferred recycled kerosene extract, it should be noted that my invention may also be practiced with similar distillates having even lower initial boiling points, particularly when operating at lower dewaxing temperatures. For example, a recycled distillate with an initial boiling point of 150 C. may be suitable.

The selective solvent component which is used in my dewaxing mixtures may be any polar compound which has the property of creating a condition in the oil-wax-solvent system under which the wax has-a minimum solubility in the liquid phases containing the oil. Among such compounds, may be mentioned the following: Sym- 'metrical and unsymmetrical aliphatic ketones,

aliphatic esters, aliphatic acids, hydroxy or ketoaliphatic acids, anhydrides of aliphatic acids, aliphatic alcohols, aliphatic carbonates, preferably containing not more than five carbon atoms in the molecule, as well as oxy-cyclic and nitrocyclic compounds, and halogen substituted oxyaliphatic compounds. Specific examples of these groups are: Acetone, ethyl methyl ketone, diacetone alcohol, methyl formate, methyl acetate, ethyl acetate, acetic acid, butyric acid, lactic acid, acetic anhydride, methyl carbonate, ethyl 'formate, butyl alcohol, quinoline, iso-quinoline,

pyrrol, pp dichloroethyl ether, chloracetic acid, triethanol amine and aniline. Although I have enumerated a number of selective solvents which may be used with the hydrocarbon distillate extract in my dewaxing mixture, my invention is not limited thereto, but may be employed in connection with other analogousselective solvents.

The constituents of the dewaxing mixture may be mixed in any desired proportion, depending upon the amount of wax to be separated, upon the dilution ratio, and upon the separation temperature. It is essential that the mixture have a high solvent power for the liquid hydrocarbons and a low solvent power for the solid hydrocarbons at the temperature at which the separation of the solid from the liquid hydrocarbons occurs. The low solubility selective solvents, of which the ketones and the quinolines form the preferred group, are effective for separating solid and liquid oil components, due to the difference in solubility of such oil components in these solvents, but this action is limited by their low solubility in the oil at the low or moderate temperatures of the dewaxing operation. The hydrocarbon extract increases the solubility of the oily components, and aids the action of the selective solvents, as will be seen from the examples hereinafter presented. Under certain condition the hydrocarbon extract, has the further effect of reducing the viscosity of the oil to aid in the separation of the liquid and solid phases.

Suitablemixtures may, for example, consist of 50 parts of hydrocarbon extract, or recycled kerosene extract, and 50 parts of acetone or equivalent selective solvent, although 75/25 or 25/75 or other ratios may be employed, according as the nature of the oil is more parafllnic or more aromatic, and according as the other factors, heretofore discussed, affect the solvent characteristics. It will, in general, be more advantageous to use the minimum quantity of extract which is required to cause the dewaxing diluent and the oil to form a homogeneous liquid phase, at the temperature at which the separation occurs, although it is possible to use even smaller amounts of extract, thereby permitting 'two liquid phases to be formed in the system. Actual dewaxing with selective solvent mixtures has shown that most efficient dewaxing takes place at or near the composition of the dewaxing diluent which corresponds to the transition between the one liquid phase and the two liquid phase conditions. Eflicient is used here as implying most desirable combinations of pour point and yield. When larger concentrations of solubility enhancing agent are employed in the dewaxing mixture, oil yields are higher, but the pour points are usually only slightly below the dewaxing temperature. When smaller concentrations of solubility enhancing agent are used, yields drop off very sharply, and the pour point may be as much as 25 F. below the temperature at which the solid wax is separated from the oil. By working with compositions which produce at the dewaxing temperature a single liquid phase, but are near the two liquid phase composition, a better yield may be obtained with but a small sacrifice of the pour point, which is often between F. and 10 F. below the separation temperature. With these eifects in mind it becomes possible to operate so as to cause either a high yield, or a very low pour point, or any desired intermediate result, and

to determine the proper ratio empirically in each particular case.

It is often desirable to use a eutectic mixture of these constituents. This is of particular advantage when dewaxing at very low temperatures. It was found that hydrocarbon extract and recycled hydrocarbon extract were distinctly superior to benzol in operations of this type because the extracts remained liquid at temperatures. at which benzol, when used in a corresponding concentration, crystallized. It was found that excellent results were obtained when dewaxing at extremely low temperatures, such as 20 C. and lower, but using hydrocarbon ex-.

tracts and particularly recycled hydrocarbon extracts boiling between 150 C. and 240 C.

2,047,826 Thedilution ratio, i. e., the volume ratio of oil to dewaxing mixture is determined by the viscosity needed at the filtration or settling temperature and may vary with the character of the oil and the viscosity of the diluents employed, but can be readily determined by those skilled in the art.

The process may be operated by dissolving the wax-bearing oil, such as parafllnous petroleum residues, paraflinous lubricating oils, lignite tars, shale oils, low temperature tars, and fuel oils in the selective dewaxing mixture, after which the paraiiin wax is caused to separate out in a crystalline or amorphous state at a lower temperature, such as, for example, 0 0., depending on the desired pour point of the oil and the desired melting point of the wax. Theseparation may be carried out inany desired manner, al-

though I have found filtration methods to be' the best for my solvents. centrifuging and cold settling may, however, often be employed, especially when the specific gravity of the selective solvent is such as to cause a sufiicient difierence between the densities of the oil phase and the precipitated wax crystals. I have found that my dewaxing mixture is efiective to cause the pour point of the dewaxed oil to be often somewhat below the temperature at which the wax is separated. After the separation of the wax the dewaxing solvents may be removed from the oil and from the "wax by ordinary or vacuum distillation, or by any other method, such as washing with a suitable selective solvent, such as ethyl alcohol, to dissolve the selective solvent .component of the dewaxing mixture, and then distilling'the oil or wax to recover the kerosene or similar distillate extract and/or other selective solvent remaining therein. The dewaxing may be conducted either according to a continuous or a batch method.

It is desirable, but not essential, to produce a homogeneous oil-solvent system before chilling the oil to precipitate the wax. To achieve this, the dewaxing diluent may be added to the oil at an elevated temperature, or the mixture of oil and diluent may, after mixing, be heated. It is,

moreover, often advantageous to heat the mixture to a temperature between 65 0. and 100 C. before chilling to condition the wax, and'thereby improve the filter rate.

Under certain conditions, as when a moderately high pour point is permissible, and/or when,

in a multiple stage process, it is desired to obtain high melting wax in the first stage, the precipitation of the wax may be eifected at temperatures which are the same as or only slightly below normal. In this manner a relatively highmelting wax may be produced. The oil filtrate may, after further addition of dewaxing diluent, be further chilled to separate additional quantities of wax. g

It is not necessary to mix all of the components of the solvent mixture before dissolving them in the oil. Thus, the hydrocarbon extract or recycled hydrocarbon extract may be added first, or may be present in the oil as aresult of its use as a diluent in a prior solvent extraction. step, and the requisite amount of the selective solvent or a solution of low boiling hydrocarbon distillate extract having a high concentration of the selective solvent may be added separately to the oil.

The effect of using low boiling hydrocarbon extract as the solubility enhancing agent will be seen from the following examples:

Example I.-Seve'ral portions of a lubricating oil distillate derived from a-Ventura crude, and

.having a pour point of 95 were each diluted with four parts by volume of solvent mixtures of the composition shown in the following table,

heated for half an hour to raise the temperature to between C. and C., chilled for about ten hours to lower the temperature to 0 (3., and filtered at temperatures between 0 C. and 1 C. The results are shown in the table:

Diluent Filtration Dewaxed oil 1% R cl d Y 1a P o. ecy 0 1e our Acetone kerosene X 5 g volume point extract percent F.

Example Ill-Several portions of the same Venture. distillate were similarly treated, except that the chilling was more drastic, so that in 8 /2 hours the mixture was chilled to 20 0., and the chilled mixture was filtered at temperatures between -l9 C. and 20 C. The results are shown in the following table:

Diluent Filtration Dewaxed oil 1 R 1 d Y ld P o. ecyc e 1e our Acetone kerosene X 5 2 3 volume point extract percent F.

My invention is not restricted to the operating conditions, nor to the concentrations and dilution ratios, nor to the specific selective solvent de scribed in the preceding examples, because it may be practiced under widely varying conditions and with many other selective solvents.

I claim as my invention:

1. A process for dewaxing oil by mixing waxbearing mineral oil with a liquid dewaxing-agent having a high solvent power for the oily components of the wax-bearing oil but low solubility for its waxy components, chilling the resulting mixture to precipitate waxy components, and separating the precipitated wax from the liquid, characterized by the use of hydrocarbon extract boiling substantially below 300 C. and having an A. P. I. gravity not substantially over 32, and a selective solvent having a low solvent power for oil and miscible with kerosene extract as the dewaxing agent.

2. A process for dewaxing oil by mixing waxbearing mineral oil with a liquid dewaxing agent having a high solvent power for the oily components of the wax-bearing oil but low solubility for its waxy components, chilling the resulting mixture to precipitate waxy components, and separating the precipitated wax from the liquid, characterized by the use of recycled hydrocarhon extract boiling substantially below 300 C. and having an A. P. I. gravity not substantially over 25", and a selective solvent having a low solvent power for oil and miscible with recycled kerosene extract, as the dewaxing agent.

3. A process for dewaxing oil'by mixing waxbearing mineral oil with a liquid dewaxing agent having a high solvent power for the oil components of the wax-bearing oil but low solubility for its waxy components, chilling the resulting mixture to precipitate waxy components, and separating the precipitated wax from the liquid, characterized by the use of kerosene extract having a boiling range substantially between 150 C. and 300 C. and an A. P. I. gravity not substantially over 32, and a selective solvent from the group consisting of iurfural, aniline, nitrocyclic compounds, aliphatic acids, hydroxy aliphatic acids, aliphatic esters, aliphatic alcohols, aliphatic ketones, and aliphatic carbonates, said aliphatic compounds having less than six carbon atoms in the molecules, as the dewaxing agent.

4. A process for dewaxing oil by mixing waxbearing mineral oil with a liquid dewaxing agent having a high solvent power for the oily components of the wax-bearing oil but low'solubility forits waxy components, chilling the resulting mixture to precipitate waxy components, and sepmating the precipitated wax from the liquid, characterized by the use of kerosene extract having aboiling range substantially between 150 and 300 C. and an A. P. I. gravity not substantially over 32, and an aliphatic ketone having not more than five carbon atoms in the molecule,

as the dewaxing agent.

5. A process for dewaxing oil by mixing waxbearing mineral oil with a liquid dewaxing agent having a high solvent power for the oil components of the wax-bearing oil but low solubility for its waxy components, chilling the resulting mixture to precipitate waxy components, and separating the precipitated wax from the liquid, characterized'by the use of recycled kerosene extract having a; boiling range substantially between 150 and 300 C. and an A. P. I. gravity not substantially over 25, and an aliphatic ketone having not more than five carbon atoms in the molecule, as the dewaxing agent.

6. A process for dewaxing oil by mixing waxbearing mineral oil with a liquid dewaxing agent having a high solvent power for the oil components of the wax-bearing oil but lowsolubility for its waxy components, chilling the resulting mixture to precipitate waxy components, and separating the precipitated wax from the liquid, characterized by the use of kerosene extract having a boiling range substantially between 150 and 300 C. and an A. P. I. gravity not substantially over 32", and acetone, as the dewaxing agent.

'7. A process of dewaxing mineral lubricating oil comprising the steps of mixing a wax-bearing mineral oil with an effective quantity of a substance from the group consisting of furfural, aniline, nitrocyclic compounds, aliphatic acids, hydroxy aliphatic acids, aliphatic esters, aliphatic alcohols, aliphatic ketones, and aliphatic carbonates, said aliphatic compounds having less than six carbon atoms in the molecules, precipitating wax from the resulting mixture at a suitable temperature at which at least a portion of the wax is solidified in the presence of kerosene extract having a boiling range substantially between 150 and 300 C., and an A. P. I. gravity not substantially over 32, the quantity of said kerosene extract being s'ufllcient to prevent the separation of substantial amounts of oil from the oil-solvent mixture during the precipitation, and mechanically separating the precipitated wax from the solution.

8. A process of dewaxing mineral lubricating oil comprising the steps'of mixing a wax-bearing mineral oil with an effective quantity of a substance from the group consisting of furfural, aniline, nitrocyclic compounds, aliphatic acids, hydroxy aliphatic acids, aliphatic esters, aliphatic alcohols, aliphatic ketones, and aliphatic carbonates, said aliphatic compounds having less than six carbon atoms in the molecule, precipitating wax from the resulting mixture at a suitable temperature at which at least a portion of the wax is solidified, in the presence of recycled kerosene extract having a boiling range substantially between 150 and 300 C., and an A. P. I. gravity not substantially over 25, the quantity of said recycled kerosene extract being sufilcient to prevent the separation of substantial amounts of oil fromthe oil-solvent mixture during the precipitation, and mechanically separating the precipitated wax from the solution.

9. A process of dewaxing mineral lubricating oil comprising the step of mixing a wax-bearing mineral oil with an effective quantity of an aliphatic ketone having not more than 5 carbon atoms in the molecule, precipitating wax from the resulting mixture at a suitable temperature at which at least a portion of the wax is solidified, in the presence of kerosene extract having a boiling range substantially between 150 and 300 C., and an A. P. I. gravity not substantially over 32, the quantity of said kerosene extract being suflicient to prevent the separation of substantial amounts of oil from the oil-solvent mixture during the precipitation, and mechanically separating the precipitated wax from the solution.

10. A process for dewaxing mineral oil, comprising the steps of mixing a mineral wax-bearing oil with a selective solvent having a low solvent power for oil and being miscible with kerosene extract, subsequently described, precipitating wax from the resulting mixture at a low temperature in the presence of a quantity of kerosene extract having a boiling range substantially between 150 and 300 C., and an A. P. I. gravity not substantially over 32, and mechanically separating the precipitated wax from the solution, the quantity of kerosene extract being suflicient to cause the oil and -diluents to exist as a single liquid phase at the temperature of said separation.

11. A process for dewaxing mineral oil, comprising the steps of mixing a mineral wax-bearing oil with a selective solvent having a low solvent power for oil and being miscible with recycled keroseneextract, subsequently described, precipiting wax from the resulting mixture at a low temperature in the presence of a quantity of recycled kerosene extract having a boiling range substantially between 150 and 300 C., and an A. P. I. gravity not substantially over 25, and mechanically separating the precipitated wax from the solution, the quantity of recycled kerosene extract being suflicient to cause the oil and diluents to exist as a single liquid phase at the temperature of said separation.

. 12. The process according to claim 11 in which the quantity of recycled kerosene extract is not substantially greater than required to cause the oil and the diluents to exist as'a single liquid phase.

13. A process for producing low pour point mineral oils, comprising the steps of mixing a mineral wax-bearing oil with a selective solvent tially between and 240 C., and an A. P. I. 73

Ill

acaaeec I; l

gravity not substantially over 25", chilling the resulting mixture to a temperature below -20 C. to precipitate wax from the solution, and mechanically separating the precipitated wax from the solution at a temperature below --20 C.

14. The process according to claim 13 in which the selective solvent is acetone.

15. A process for dewaxing mineral oil, comprising the steps of mixing a mineral wax-bearing oil with a selective solvent having a low solvent power for oil and being miscible with kerosene extract having a boiling range substantially between 150 and 300 (1., and an A. P. I. gravity not substantially over 32, precipitating wax from the mixture in the presence of said kerosene'extract at a temperature at which the mixture of said selective solvent, kerosene extract, and oil remains liquid, and at which benzene crystallizes from a mixture of the same composition but containing benzene instead of kerosene extract, and

mechanically separating the precipitated wax from the solution of oil, selective solvent and kerosene extract.

16. A process for dewaxing mineral oil, comprising the steps of mixing a mineral wax-bearing oil with a selective solvent having a low solvent power for oil and being miscible with recycled kerosene extract having a boiling range substantially between 150 C. and 300 C., and an A. P. I.

gravity not substantially over 25, precipitating from the solution of oil, selective solvent and recycled kerosene extract. 17. A process for dewaxing mineral oil, comprising the steps of mixing a mineral wax-bearing oil with a selective solvent having a low solvent power for oil and being miscible with recycled hydrocarbon extract boiling substantially below 240 C., and having an A. P. I. gravity not substantially over 25, precipitating wax from the mixture inthe presence of said recycled kerosene extract at a temperature at which the mixture of said selective solvent, recycled kerosene extract, and oil remains liquid, and at which benzene crystallizes from a mixture of the sanie composition but containing benzene instead of recycled kerosene extract, and mechanically separating the precipitated wax from the solution of oil, selective solvent and recycled kerosene extract.

18. A process for dewaxing mineral oil, comprising the steps of mixing a mineral wax-bearing oil with a selective solvent having a low solvent power for oil and being miscible with recycled kerosene extract having a boiling range substantially between 150 and 240 C., and having an 2 A. P. I. gravity not substantially over precipitating wax from the mixture in the plesence of said recycled kerosene extract at a temperature at which the mixturepf said selective solvent, recycled kerosene extract, and oil remains liquid, and at which benzene crystallizes from a mixture ofthe same composition but containing benzene instead of recycled kerosene extract, and mechanically separating the precipitated wax from the solution of oil, selective solvent and recycled kerosene extract.

CHEVER M. KELLOGG.