US2272372A - Process of selectively refining petroleum oils - Google Patents

Description

Patented F eb. 10, 1942 Incense OF QSELECTIVELY REFINING {PETROLEUM OILS v Arthur W. H-ixson, Lenma, .N. J., and Ralph Miller,:New 1ork, N. Y., assignors to The Chemical Foundation, Incorporated, a corporation of Delaware N Drawing. Original application December 17, l'93'6fserial N0.'116,348. 'Divided-and this' application-April 23, 1940, Serial'N 0. 331,158

LThisinven tion relates to the frajc'tionation of oils, :more .particularly to the separation of petroleum .oil 'into a series-of desirable, valuable fractions :by -a sp'ecial system of fractional extraction. V V

Petroleumoil, as is known, comprises essentially acomplexmix-ture: of different homologous series or groups of hydrocarbons-such as paratfinic', naphthenic, and aromatic constituents. When petroleum oil is separated into thecom- 'mercially useful fractions, such-for example as the gas foil, lubricating-oil; and'iul oil fractions, the *same general complexity still obtains, although "the respective percentages of the different groups in such commercialfractions may vary. Thus a typical, relatively high boiling range distillate, having the characteristics of' lubricating toil, contains' p'araifinc, naphthenic and aromatic constituents and some -"asphalt. "The respective proportions of 1 such i constituents Y I dependupo'n the type or source'of the crud oil. Thus Pennsylvania oil contains little or no asphalt "and a relatively small amount of aromatics. :Ifhe Coastal(oilgconversely, has a relatively high percentage of asphalt and aromatics.

l\/l-id-Continent"oiltis approximately an interme-.

possesses the *best lubricating properties and itaefi iisrfonthisreason thatl'the Pennsylvania base oil constitutes the accepted standard.

It is also well recognized that T the parafiinicity .of a givenlubricating .oillfrac'tion may be in- :creased' by treating Jsuch ffractio'n to remove;

Such processes consist essentially;

the paraffinic constituents of the starting mate- 515 lrial. The two 'fra'ctions "are then *subj'ected'to distillation to remove the contained solvent. Modifications of such extraction processes include the use of dual solvents,'theiretreatment"or the raffinate with the original solvent or ,a spe- -cifically different solvent to further -refine it, and the like. The desideratum in all such prior -methods, however, has been to enhance the selectivity of the fractionation "for thepurpose or securing the maximum yield of the high viscosity index parafiinic fraction.

To render such processes commercially feasible it is necessary-to separate and recover the solvent which is employed. This is usually done, as noted, by vacuum distillation. 'The residual 'naphthenic oil or extract is thus more naphthenic than the original oil which was-subjected to the treatment. "This extract howeve'r, because of the relatively large p'ercentage or contained asphalt, is a viscous, tacky, black, tar-like product. The quantity of the asphalt in 'a given extract will, of courseyvary dependin'g -u pon the type of lubricating 'oil stock treated. It is greatest-in the extract iproduced from the asphaltic base oils. Such extract, although relativelylfree from parafi'mic constituents, does contain an appreciable quariti'ty of potentially valuable oil. However, due :td' the large percentage of asphalt contained in the "extract, such'ira'ction is practically useful only as a cracking tstock .since it is too difiicult "and expensive to separate the oil from a fraction .of "a 'high asphaltconcentration.

If the oil which to :be treated is not ideasphalted and ,contains'an appreciable amount of asphalt, solvent refining will I not remove the as- 'phalt'from the paraffin fractions, although such asphalt 'will be concentrated, to a considerable degree, in the extract layer. It is of course :possible to "remove the asphalt from the 'oil prior to solvent extraction. If the oil is deasphaltedto'a certain extent, selective solvents will then dissolve the "residual'asphalt, the "color :bodies, the aromatic and 'naphthenic "constituents, but will not ad-issolv'e the iparaflinic hydrocarbons.

The" typical process of solvent extraction'is, in effect, amethod of separating various constituents present in the oil. If, 'as is usually the case, the extraction process is foperated 'to produce a 'raffinate':of "high viscosity index from an initial v:or starting materialhaving but a small percentage of 'high viscosity index oil, it is clear that the-yield of theparaflinic fraction must necessarily be low. In thes circumstances, be- -cause of the characteristics :of the extract, 'the .properties. tion would constitute a marketable lubricating remainder of the oil is employable only for cracking purposes.

The present invention, as will more fully appear, is based on the concept of recovering the maximum values from a given petroleum stock by not only extracting a valuable high viscosity index raflinate, but also by effectively utilizing the phenomenon of preferential solubility for the recovery of a more valuable secondary fraction than has been possible heretofore.

If the oil constituents of the extract could effectively and economically be separated from the associated asphalt, then a number of major advantages would obtain. Thus, from a given starting material, such for example as a Mid- Continent lubricating oil fraction, there could be obtained two substantially asphalt-free lubricating oil fractions and a residuum of a high asphalt concentration. The first lubricating oil fraction would comprise a valuable, high viscosity index rafiinate of excellent lubricating The second novel, recoverable fracoil fraction of lower viscosity index, comprised largely of naphthenic and aromatic hydrocarbons substantially free from asphalt. Finally,

the third fraction would comprise an oil of a high asphalt concentration which, being less refractory than the extract, constitutes a good low temperature cracking stock. Again this third fraction may suitably be treated, by methods known to those skilled in the art, to produce valuable products, such as road oils, binders, mastics, and the like.

It has been found that such advantages may be attained and the enumerated novel results secured by a method which is not only simple and effective but which also may readily be correlated with present methods of solvent extraction.

A major object of the present invention is to devise a method of producing commercially valuable fractions from petroleum oils.

Another object is to provide a method of separating and recovering the more valuable constituents of the naphthenic-like extracts from the less valuable constituents.

Yet another object is to product a novel type of petroleum cracking stock.

An additional object is to devise an eiiective method of selectively extracting parafiinic and naphthenic fractions from an asphalt-containing oil.

With these and other equally important and related objects in view, the invention comprehends the concept of subjecting a natural or pyrogenetically produced petroleum oil fraction to a special type of sequential, selective solvent extraction to recover therefrom a fraction of higher paraifinicity than the original oil, a second oil fraction of higher naphthenicity than the original oil, and a residual fraction in which the asphalt of the starting material is largely concentrated. In sharp contradistinction to prior art methods, in which the original oil was separated into a raflinate and a cracking stock of low value, the present method insures the recovery of a number of valuable fractions. Thus operating under the present method there is produced an excellent lubricating fraction of optimum parafiinicity, a valuable naphthenic lubricant substantially free from tarry matter, and a viscous residual oil of high asphalt concentration.

sion of the discovery explained in application Serial No. 60,634, on which Patent No. 2,143,145 was granted January 10, 1939, and to this degree the present application is a continuation in part of the prior application. As explained in that application, a certain class of solvents possesses a striking preferential solvent action on the non-parafi'inic constituents of a mixed oil The present invention is, in a sense, an extenbase. It was further explained that the high selectivity of these solvents is due to the unequal distribution of the electronic charges of the molecule, i. e. its polar characteristics, and that the effective index of selectivity of a solvent is its dipole moment. It was additionally pointed out that solvents which were characterized by a high dipole moment and which also possessed the other desirable characteristics, such as low melting point, miscibility at elevated temperatures, immiscibility at lower temperatures, etc., served most effectively as single solvents for the separation and recovery of raffinate.

It is now found that this characteristic of optimum selectivity of certain solvents for the non-paraflinic constituents renders them peculiarly useful for the production of substantially asphalt-free naphthenic-like oil fractions. This result can be achieved by treating a solution of the non-paraflinic constituents in a highly selective solvent with a second solvent which functions to extract a certain percentage of the lighter oil from the selective solvent, leaving in the selective solvent phase the heavier asphalt constituents.

In the preferred embodiment of the present invention the first solvent is preferably one which is characterized by a high selectivity and relatively low solubility, such for example as ortho-nitroanisole and ortho-methoxybenzonitrile. As will appear more fully hereinafter, however, the present invention is not limited to these particular solvents but is available for employment with any solvent which possesses a marked selectivity for the naphthenic fractions and which is immiscible with the clarifying solvent.

In order to insure the improved results mentioned it will be appreciated that the second or clarifying solvent must possess certain characteristics. It must be a solvent for oil although, as will be understood, it need not be selective with respect to paraflinic and naphthenic oils.

It must of course be immiscible with the selective naphthenic solvent at the temperature at which stratification is to be effected, and preferably should be immiscible with the selective solvent even at relatively elevated temperatures. It must be amenable to use with the particular selective naphthenic solvent employed. The clarifying solvent should also be of such a character as to be employable without the use of expensive equipment.

A typical illustrative solvent of this type which eifectively fulfills the enumerated prerequisites is tri-amylamine. This alkyl amine is insoluble in water; it has a marked solubility for oil at any temperature; it has a distillation range of 230 C. to 260 C., and a specific gravity of .7937 at 20 C. It dissolves ortho-nitroanisole, one of the preferred solvents, only very slightly at room temperature and is completely miscible with ortho-nitroanisole at C. This, as will be appreciated, is a wide permissive operating range. Since the clarifying solvent may be contacted with the selective solvent-naphthenic oil phase agerzaam at any temperature below this miscibility temperature, the solubility of the tri-amy'laminefor the oil bodies can be modified to a considerable degree to thus controlthe amount and/or quality of the oil removed from the selective solvent phase.

As will be seen more fully hereinafter, the major desirable characteristics of the selective solvent are maximum selectivity and relatively low solubility. The salient characteristics upon which the choice of the clarifying solvent is based are, as noted, a marked solubility for oil bodies at any temperature, relatively low selectivity and a high temperature of miscibility with the selective solvent.

Tri-amylamine is peculiarly effective for the purposes of the present invention and serves Well to illustrate the principles involved, as is shown by the following treatment.

A given quantity of a mixed base oil was treated with 246% by weight of ortho-nitroanisole in a continuous, countercurrent extraction system. The mass was heated to the miscibility temperature, as explained in the application referred to, Serial No. 60,634, and the temperature at the solvent outlet of the system was'held at approximately C. Under these circumstances, upon analysis it was found that 29% of the original oil was removed in the solvent phase, the remainder constituting a high viscosity index raffinate. The solvent phase was then treated with tri-arnylamine in the same countercurrent system in which the temperature of the mass was maintained at substantially 26 C. The amount of tri-amylamine used was 83% by'weight of the original oil. The tri-amylamine fraction was segregated from the ortho-nitroanisole fraction and was subjected to vacuum distillation. It was found that a small amount of ortho-nitroanisole was recovered in the distillate. Upon analysis it was found that 56% of'the oil originally dissolved in the ortho-nitroanisole was solubilized and extracted by the tri-amylamine.

The residual fraction, 1. e. the ortho-nitroanisole and its dissolved oil, was then subjected to vacuum distillation to recover the solvent. It was found, similarly, that a slight amount of the tri-amylamine was contained in the ortho-nitroanisole condensate. The extract remaining after the distillation and removal of the selective solvent was a highly viscous, tacky, tarry mass.

Under the conditions of the treatment, therefore, the original oil was fractionated into a typical rafiinate, a second clarified fraction, 1. e. the extract from the tri-amylamine phase, and a highly viscous residue. The rafiinate constituted approximately 71% of the original charge; the

clarified tri-amylamine extract substantially 16% of the original charge, while but approximately 12% was recovered in the viscous residue.

The effectiveness of the treatment in separating the constituents of the original oil is seen from a comparison of the tri-amylamine extract and the ortho-nitroanisole extract. The original oil had a viscosity of 265 Saybolt seconds at 100 F. and 46.6 Saybolt seconds at 210 F. The tri-amylamine extract had a viscosity of 555 Saybolt seconds at 100 F. and 55.3 Saybolt seconds at 210 F., and a viscosity index of 9. The heavy residuum, on the other hand, had a viscosity of 115 Saybolt seconds at 210 F.

It is to be observed that the clarified naphthenic fraction, or tri-amylamine extract, although of a low viscosity index, is nevertheless a commercially useful fraction and employable,

for example, -asa medium quality light lubricant.

The essential features of the improved method of "fractional separation of oil therefore comprises, extracting agiven mixed base oil fraction with-a solvent which has -a preferential affinity forthe non-paraffinic bodies, then further treating the solvent phase with a clarifying oil solvent, at any temperature at which the two solvents will not form a homogeneous liquid phase so --a's to establish stratification of the respective solvents and their dissolved constituents. The second extraction, as will be appreciated may be carried out at any'temperature below the miscibility temperature of the two solvents chosen. Other things being equal, the higher the miscibility temperature of the two solvents and the greater the selectivity of the selective solvent,

the greater willbe the permissive thermal operative range and the greater will be the corresponding permissivevariation of the characteristics of the clarified extract. Again, as will be understood, the lower the solubility of a solvent of given selectivity, the greater will be the quantity of oil extracted by the clarifying solvent.

The choice of the selective and clarifying solvents, as is understood by those skilled in the art,will'be determined by a number of factors, such as: the character'of the stock to be treated, the quantity of and characteristics desired in the ultimate fractions, the type of plant equipment available, and the like.

The process is, of course, operable with a relatively wide range ofselective solvents, that is to say, t*he-invention is-by no means limited to the use of-the highly selective solvents enumerated. Thus, for the selective solvent utilized for the preliminary extraction there may be employed, in addition to ortho-nitroanisole and orthomethoxybenzonitrile, other solvents of marked selectivity, such as furfural, aniline and the like. As explained, the particular clarifying solvent which ischosens'houldbe correlated with the selective solventfand upon the basis of-the factors given the optimum clarifying solvent for any given operation can readily be determined.

With highly selective solvents, such as orthonitroanisole, th quality of rafiinate that may be produced, when utilizing a given oil-solvent ratio, depends essentially on the oil outlet temperature of the system. Similarly, the yield or quantity of the raffinate depends essentially on the solvent outlet temperature. The characteristics of the second fraction, for any given clarifying solvent and operating conditions, will thus be governed to a considerable degree by th extraction conditions obtaining in the first refining stage.

When refining a Mid-Continent oil, for example, by solvent extraction with selective solvents, a relatively large sacrifice in yield must be made inorder to secur a small increase in viscosity index when the viscosity index of the raflinate is about 90. Generally when a single selective solvent is employed for the fractionation, it is not usually economical to make too great a sacrifice in yield in order to obtain the highest viscosity index oil. The operations conducted heretofore have, therefore, necessarily been a compromise between these factors. It will readily be appreciated that under the present method, assuring as it does the production of a second Valuable product, this sacrifice in yield can more readily be made, thus insuring recovery of the optimum quality of lubricating stock, coupled with the maximum recovery of valuable oil fractions.

It is to be understood that the operations described herein need not be carried out under conditions controlled to insure a substantially quantitative separation of the parafiinic constituents in the first extraction stage. If the selective solvent extract does contain some amount of parafl'inic oil, upon the addition of the second solvent which is immiscible with the selective solvent, the residual paraifinic constituent will largely be taken up in the second solvent because of the greater afiinity of the selective solvent for the naphthenic constituents. In other words, the second solvent displaces the remaining paraffinic constituents from the selective solvent phase.

The principles of the invention may be effected by a number of specifically different methods and by utilizing different types of apparatus. In a typical commercial embodiment, for example, a given oil fraction may be contacted with the selective solvent, such as orthonitroanisole, in a suitable batch or continuous countercurrent system, as more particularly explained in application Serial No. 60,634. If a light oil is to' be refined, the first extraction step may be operated with an oil outlet temperature in the approximate range of from about 115 C. to 120 C. more or less. The solvent outlet temperature may be maintained at approximately 60 C. These temperatures, as is known, will be controlled depending upon the quality and yield of raflinate desired. After stratification and separation of the raffinate in any suitable manner, the solvent phase may, if desired, be cooled further to insure the separation of an additional quantity of the raffinate.

The cold solvent phase may then be contacted with a suitable second solvent, such as tri-amylamine, in a second batch or countercurrent system. In this manner the immiscible second solvent extracts from the selective solvent-oil phase a considerable fraction of the dissolved oil. The temperature at which the second extraction is efiected may be controlled at any degree below the miscibility temperature of the selective solvent and the clarifying solvent. The yield and quality of oil removed in the clarifying solvent phase can therefore be controlled within relatively wide ranges.

The viscous, residual fraction produced in the system may be utilized as a cracking stock. Since this stock contains a relatively high percentage of the heavy hydrocarbons, cracking may be carried out at relatively low temperatures. This fraction may also be suitably processed as by steam distillation, air blowing and the like, to produce valuable, marketable asphaltic products.

While th improved method of treating petroleum oil has been described as being particularly applicable to the refining of lubricating oil fractions, it is to be understood that it is not limited to this particular stock. The principles of the invention may be invoked in any circumstances where it is desired to secure the selective recovery of similar petroleum oil constituents from any initial mixtures thereof. Hence, while preferred modifications of the invention have been described, it is to be understood that these are given to illustrate the principles involved and not as defining the exclusive methods of effectuating these principles.

We claim:

A process of refining petroleum hydrocarbons which comprises, contacting a mixed base petroleum oil with furfural at a temperature above the miscibility temperature of the oil and the solvent; stratifying the mass into an oil phase and a solvent phase; separating the solvent phase with its dissolved naphthenic constituents from the oil phase; cooling the solventphase to remove additional quantities of oil therefrom, and then treating the solvent phase, at relatively low temperatures, with triamylamine which is characterized by a substantial immiscibility with furfural at said temperature.

ARTHUR W. HIXSON. RALPH MILLER.