US2130126A - Hydrocarbon oil treatment - Google Patents

Description

Patented Sept. 13, 1938 STATE PATENT OFFICE 1 E TREATMENT 1 No Drawing. Application February 28, 1933,

Serial No. 658,979

The present invention relates to the art of mineral oil refining, and has particular reference to the separation of crude petroleum or petroleum products into fractions of difierent chemical com- 5 positions while of approximately thev same distillation range.

In accordance withmy invention, crude petroleum or petroleum products, particularly oils of substantial viscosity, are separated into various fractions by means of fractional extraction with cresylic acid, or a mixture of solvents containing substantial amount of cresylic acid. The term cresyl'ic acid" as used herein comprehends one or a mixture of two or more of the isomeric cresols, or such mixtures as are sold commercially under the name cresylic acid and which may contain considerable proportions of the xylenols and high homologues.

It is recognized in the art that mineral oils, such as petroleum, comprise essentially a mixture of hydrocarbons of various groups or homologous series of compounds, such, for example, as paraffins of the general formula CnH2n+2, olefines of the general formula CHI-Ian, hydroaromatlcs and polymethylenes of the same empirical formula, and various other series of compounds of chain and/or ring structures in which the hydrogen to carbon ratio is less than in the foregoing series. A large number of -individual compounds of each series and of differing boiling points are present in petroleum.

The various types of crude petroleum, which are generally classified into three groups, namely, parafllnic base, naphthenic or asphaltic base, and mixed base, contain the various series of hydrocarbons mentioned heretofore in different proportions. For example, in the paraffin base crude oils, such as those obtained from the oil fields of Pennsylvania there is a relativelyhigh pro- 40 ture and a high hydrogen to carbon ratio, whereas in the naphthenic or asphaltic bas'e crude oils, there is a relativelylarge proportion of hydrocarbons having ring structures and a low hydrogen to carbon ratio. Mixed base crude oils, such as are obtained from the Mid-Continentv oil fields, contain hydrocarbons in proportions intermediate these two extremes.

The variance in the proportion of the different series of hydrocarbons in parafi'inic, naphthenic, and mixed base oils in evidenced by the physical properties of the various oils and particularly by the relationship of the specific gravity to the viscosity of one 011 as compared with another. For example, oils derived from a Pennsylvania crude portion of hydrocarbons having a chain struc-,

and having a viscosity of 400 seconds Saybolt universal at 100 F., will show a specific gravity at'60 F., of about 0.878, whereas an oil of corre-- spending viscosity produced from a napht'henic crude, such as one from the Gulf Coast area, will show a specific gravity of about 0.933 at F. The relationship between the viscosity and gravity indicates the degree of paraflinicity or naphthenicity of the oil, and such relationship may be expressed by .theviscosity-gravity constant as hereinafter described.

If a given crude petroleum be distilled into successive fractions" and the specific gravities and viscosities of the several viscous fractions be determined, it will be found that they conform to the "general relationship expressed by the formulaeor G=0.24+0.755a+0.022 log (V'35.5), in which G" is the specific gravity at 60 F., V and V' are respectively Saybolt universal viscosities at F. and 210 F., and a is a constant known as the viscosity-gravity constant. Viscous fractions from each of the difierent types of crude have different viscosity-gravity constants. While, in general, viscous fractions from a single crude have substantially the same viscosity-gravity constant, such constant is lower for fractions of the parafiinic crudes than is the constant for fractions ofthe naphthenic crudes. An article entitled The viscosity-gravity constant of petroleum lubricating oils, by J. B. Hill and H. B. Coats. which will be found in volume 20, page 641 et seq., Industrial and Engineering Chemistry for June, 1928, explains ,thedetermination of such constant for several typical oils.

The viscosity-gravity constant is, therefore, an index of the paraffinicity or naphthenicity of viscous oils, since when a given crude is distilled, the fractions thereof collected, and the specific gravity and the viscosity of each of the viscous fractions determined, such specific gravities and .viscosities substituted in the formula,'and the viscosity-gravity constants of the fractions calculated, it will be found that such constants are substantially the same.

The viscosity-gravity constants of the viscous fractions for some of the typical crudes are as follows: I

Milltown (Pennsylvania) 0.8067 Burbank (Mid-Continent) 0.8367 Guadalupe (Gulf Coast) 0.8635

Mirando (Gulf Coast) 0.9025

While the above figures indicate the viscositygravity' constants of specific oils from several types of crudes, it is to be understood that for any particular type of crude such constant may be within a range between values above and below the constant of the typical crude given. For example, viscous oils resulting from the distillation of Mid-Continent crudes have viscosity gravity constants ranging from about .835 to about .855, whereas the viscous fractions resulting from the distillation of Pennsylvania type crudes range from about .805 to about .828, and in most instances, are below .820. Oils are increasingly parafiinic as their viscosity-gravity constants decrease.

My invention is based upon the discovery that oils containing both the paraflinic series of hydrocarbons and the various naphthenic series may be fractionally extracted with cresylic acid as defined hereinabove. The various series of hydrocarbons possess a differential solubility in such solvent, the naphthenic hydrocarbons being much more soluble therein than the paraflinic hydrocarbons. By means of extraction with such solvent, it is therefore possible to effect a partial separation of the naphthenic hydrocarbons from the parafiinic, and to obtain from an oil containing both classes of hydrocarbons, an oil which is much more paraflinic than the original oil and one which is much more naphthenic. By my invention, for example, it is possible to produce an oil of the quality normally obtained from Appalachian crudes, from crudes of the mixed base type from the Mid-Continent area, and, conversely, to obtain oils from mixed base crudes such as are normally obtained from the naphthenic oils of. the Gulf Coast area. In general, from oils from any source there may be obtained by my process, oils which are respectively more 'paraffinic and more naphthenic than the oils normally obtained from such source by distillation.

In accordance with my invention I first mix the oil to be treated with a suitable proportion of the solvent at a temperature such that complete solution is effected and a homogeneous liquid obtained. I then cool the mixture to a temperature at which separation of the liquid into a two-layer system will take place. The upper layer will contain a relatively small amount of the solvent dissolved in the paraflinic portion of the oil while the lower layer will contain the more naphthenic portion of the oil dissolved in the solvent. Or, I may agitate the mixture of solvent and oil at temperatures at which the liquids are only partially miscible, and thereby effect solution of the naphthenic portion of. the oil in the solvent. In either of the above procedures I may take advantage of the principles of countercurrent extraction.

After the extraction proper, I efiect separation of the two layers which form, by any suitable procedure, as for example, by decantation. I then remove from each of the separated layers, the portion of. solvent which each contains, by suitable procedure, such as-by vacuum distillation, thereby to obtain two oils of similar distillation ranges but of different chemical compositions and different physical characteristics.

Before removing the solvent from the upper and more paraifinic layer, I may add a further quantity of solvent and repeat the extraction, thereby to remove additional naphthenic constituents from said layer. The extraction step may be repeated any desired number of times,

each repetition producing an oil of higher paraffinicity as evidenced by its lower viscositygravity constant.

Where substantial quantities of waxy hydrocarbons belonging to the true paraflin series (CnHzMz) are present, such hydrocarbons remain in the upper or more paraffinic layer and may cause such layer to be solid or semi-solid. Such layer may be separated into solid and liquid hydrocarbons by any of the well-known dewaxing processes such as by cold-settling or by centrifuging. In many instances it may be advantageous to dewax the oil prior to extraction. However, it is to be understood that in accordance with my invention, dewaxing may be effected either prior or subsequent to extraction.

My invention will be further understood from the following specific examples:

100 parts of a previously untreated distillate obtained from a Gulf Coast crude oil and having a viscosity of 612 seconds Saybolt universal at 100 F., a specific gravity at 60 F. of 0.9303, and a consequent viscosity-gravity constant of. 0.874 was mixed with 175 parts of cresylic acid. The mixture was heated to slightly above the temperature of complete miscibility, which was approximately 62 F. The homogeneous liquid which resulted was cooled with agitation, to approximately 23 F., and allowed to settle, whereupon a two-layer system formed, which consisted of an upper undissolved oil layer comprising 42.2 parts of the mixture, and a lower layer of oil dissolved in cresylic acid comprising 232.8 parts of the mixture. The layers were separated by decantation. After separation each of the layers was freed from the solvent by vacuum distillation. The upper layer yielded 7.5 parts of cresylic acid and 34.7 parts of oil, while the lower layer yielded 167.5 parts of cresylic acid and 65.3 parts of oil. The oil from theupper layer had a Saybolt universal viscosity at 100 F. of 382 seconds, a specific gravity of. 0.8961, and a viscosity-gravity constant of 0.836. The oil from the lower layer had a Saybolt universal viscosity of 210 F. of 64 seconds, a specific gravity of 0.9509, and a viscosity-gravity constant of 0.899.

As a further illustration, 100 parts of a Mid- Continent distillate having a Saybolt universal viscosity at 100 F. of 305 seconds, a specific gravity at 60 F. of. 0.9088, and a viscosity-gravity constant of 0.853, was treated as above described, with 300 parts of cresylic acid. The resulting undissolved oil fraction comprising 44.7% of the original stock, had a Saybolt universal viscosity at 100 F. of 210 seconds, a specific gravity of 0.8772, and a viscosity-gravity constant of 0.821, while the dissolved fraction comprising 55.3% of the stock, had a Saybolt universal viscosity at 100 F., of. 403 seconds, a specific gravity of 0.9279, and a viscosity-gravity constant of 0.878.

From the above examples it will be noted that by extraction of an oil with cresylic acid, there may be obtained oil fractions which are respectively more paraflinic and more naphthenic than the original oil. By repetition of theextraction process upon the undissolved fraction, oils of even greater paraflinicity .will result.

My process is practically independent of the particular nature or source of the crude oil or oil fraction to be extracted. There may be produced by my process oil products of desired characteristics from oils which by distillation will not produce such products.

Hereinabove, mixtures of solvents have been referred to. It is to be understood that in such mixtures the constituents will not react with one another nor with the oil upon which they are to be used, and that such mixtures will contain substantial amounts of cresylic acid.

For brevity, in the appended claims cresylic 'acid" is employed in a generic sense to include one or a mixture of two or more of the isomeric cresols, or such mixtures as are sold. commercially under the name of cresylic acid" and which may contain considerable proportions of the xylenols and higher homologues; or amixture of solvents containing substantial amounts of cresylic acid or of one or more of the components thereof.

Also, where herein and in the appended claims, oil is specifically referred to as being visc0us". it is to be understood that the oil is of substantial viscosity, 1. e., of the order of 50 seconds Saybolt universal at 100 F. or more.

What I claim is:

1. The method of producing a viscous lubricating fraction of petroleum having a relatively low viscosity-gravity constant from a viscous traction of petroleum oil whose viscosity-gravity constant is at least .015 higher than the viscosity-gravity constant of said viscous lubricating fraction, which comprises bringing said viscous fraction of petroleum oil into contact with an amount in excess of one and a half times its volume of cresylic acid under such temperature conditions that at least one quarter of the viscous fraction will dissolve in the cresylic acid, and removing cresylic acid and the portion of the oil so dissolved .from the portion of the oil that remains undissolved; thereby to efiect separation of said viscous fraction into two liquid viscous portions of substantially higher and lower viscosity-gravity constants respectively.

,2. The method of producing irom a. viscous fraction 01' petroleum oil having a viscosity-gravity constant between substantially 0.805 and 0.875, a viscous lubricating fraction of petroleum having a viscosity-gravity constant at least'0.015 lower than that of said viscous fraction of petroleum" oil, which comprises bringing the viscous fraction of petroleum oil into contact with at least one and three quarters times its volume of oreviscosity-gravity constant from a viscous fraction of petroleum oil whose viscosity-gravity constant is at least .015 higher than that of said viscous lubricating fraction, which comprises bringing said viscous fraction of petroleum oil into contact three times'its volume of cresylic acid under such temperature conditions that more than a quarter of said fraction will dissolve in the cresylic acid, and removing cresylic acid and the portion of the oil so dissolved from the portion of the oil that remains undisso lved, thereby to effect separation of the viscous oil fraction into two liquid viscous portions of substantially higher and lower viscosity-gravity constants respectively.

SEYMOUR W. FERRIS.

with from about one and three quarters to about a