US3244761A - Solvent extraction - Google Patents

Description

April 5,1966 A. c. MGKINNIS 3,244,761

` SOLVENT EXTRACTION Filed July 31, 1961 MKE-UP 50A VEA/7' MA KE-u .su mem" A40/warms 59 United States Patent O 3,244,761 SOLVENT EXTRACTION Art C. McKinnis, North Long Beach, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation f California Filed July 31, 1961, Ser. No. 128,243 20 Claims. (Cl. 2643-674) This invention relates to a solvent extraction method Ifor separating hydrocarbons of greater aromaticity from hydrocarbons of lesser aromaticity in admixture therewith. More specifically, the invention relates to such a method in which mixtures of amines and acids are employed as selective solvents for the hydrocarbons of greater aromaticity. The invention has particular futility for the recovery of diaromatic hydrocarbons, such as naphthalene or the like, from mixtures thereof with monoaromatic hydrocarbons of substantially equivalent boiling points, such as alkyl benzenes or the like.

There are a number of known solvent extraction procedu-res for isolating various components of hydrocarbon mixtures and numerous materials have been proposed for use as selective solvents in such procedures, typically representative of which are sulfur dioxide, furfura-l, diethylene glycol, nitriles, organic bases, etc. Such solvent extraction procedures have been attempted with varying deg-rees of success on mixtures of aromatic yand nonaromatic hydrocarbons for purposes of extracting .all of the aromatics therefrom, but heretofore it has not been possible to bring about any kind of effective fractional separation of the aromatic components from each other by solvent extraction means.

I have now discovered an improved method of solvent extraction for use on hydrocarbon mixtures whereby aromatic components of differing degrees of aromaticity can be economically and effectively fractionated.

There are many hydrocarbon mixtures, as, 'for example, various petroleum processing fractions, which contain substantial proportions of diaromatic hydrocarbons such as naphthalene and its alkyl and polyalkyl derivatives, and also monoaromatic hydrocarbons which can be monocyclic, such as alkyl benzenes, and/or bicyclic, such as alkyl tetralins, alkyl indanes, alkyl indenes and the like, which boil Within the same boiling range as the diaromatics. Tlhe boiling range of the diaromatics in hydrocarbon mixtures of this type is typically from about 400 to about 450 F. A speci-fic example of such a hydrocarbon mixture is the heavy reformate Ifraction obtained in the catalytic reforming of naphtha or heavy Agasoline fractions. This fraction normally boils above about 400 F. and contains from about 40 to about 8O percent by weight naphthalene and methyl naphthalenes, the remainder being either la-rgely made up of monoaromatic com-A 3,244,761 Patented Apr. 5, 1.966

in the diaromatic, monoaromatic, etc., categorie-s by conventional fractionation means. For one thing, the like boiling point ranges of the diaromatics and monoaromatics normally found in such mixtures precludes the possibility of getting effective separation between these two classes of materials by fractional distillation techniques. The present invention comprises a method of solvent extraction employing a unique amine-acid solvent by means of which segregation of aromatics of the same degree of aromaticity is readily and economically feasible.

In addition to the problem of separating like boiling aromatics of differing degrees of'aromaticity, there is a parallel problem of separating aromatics from nonaromatics of like Aboiling ranges. There are many such mixtures, exemplary of which are those petroleum fractions known to contain monoaromatics, such as polyalkyl benzenes, boiling within the yrange vfrom about 400 to about 450 F., as well as nonaromatics such as paraflins and naphthenes of the same boiling range. Here again,

as in the case of the like boiling aromatics, fractional distillation fails as a practical means of accomplishing the desired separation and the solvent extraction method of this invention furnishes a simple and practical solution to the problem.

It is thus a principal object of this invention to provide an improved solvent extraction method by means of which componential ,fractions of various aromaticity levels can be segregated from mixtures of such aromatic compounds.

It is another object of the invention to provide a solvent extraction method for readily and economically separating aromatic compounds from like boiling nonaromatic compounds in admixture therewith.

A more specific object of the invention is to provide an economical solvent extraction method by means of which diaromatic compounds are readily separable lfrom like boiling monoaromatic compounds in admixture therewith. Other objects and advantages of the invention will be apparent from the complete description thereof which follows. 7

The degrees of aromaticity of organic compounds of roughly equivalent boiling points depend upon the number of aromatic rings (-benzene nuclei) in their respective" molecules, the higher the number of such rings the greater the aromaticity of a given compound. Thus diaromatic compounds, those having two aromatic rings per molecule, are conside-red to have a greater degree of aromaticity than the monoaromatic compounds which have molecular structures containing only one such ring. It makes little difference, insofar as degree of aromaticity is concerned,

Whether polyaromatic compounds have individual or condensed ring systems. Thus, diaromatics of individual ring systems such as biphenyl, diphenylmethane, etc., are considered to have roughly the same degree of aromaticity as the dinuclear aromatics (diaromatics having condensed ring systems), such as naphthalene, etc., at least insofar as this invention is concerned.

The method of this invention is not limited to the treatment of organic mixtures in which the aromatics of highest possible degree of 4arom-aticity are diaromatics,A

and mixtures containing higher polyaromati-c compounds are also amenable to separation -by said method. For example, it is Within the scope of the invention to subject hydrocarbon mixtures containing triar-omatic com-y pounds, such as vanthracene and pheneanthrene, and diaromatic compounds of roughly the same boiling point level to solvent extraction as taught herein, to separate the triaromatics from `the diaromatics.

The method of this invention is not limited in application to the treatment of organic mixtures having clearly obvious differences in degree of aromaticity among its various components. There are many organic mixtures containing -aromatic components not sharply distinguishable from others present in degree of aromaticity and the treatment of such grey area mixtures either for the separat-ion of the aromatics in toto or for further separation `of said aromatics into fr-actions of varying degrees of aromaticity, lies within the purview of my invention. It is more difficult to separate such grey area aromatics into distinct fractions than 4it is `to separate more sharply black and white aromatics, such as diarom-atics and monoaromatics, but su-ch separations are possible and hence within the scope of my invention. Among the above-noted grey area aromatic compounds of intermediate degrees of aromaticity may be mentioned those substituted aromatios containing functional groups of such nature as to have a :significant effect of one sort or another on the aromatic-ity of their -unsubstituted counterparts. It will be clear that a wide variety of feed mixtures can be resolved by the method taught herein.

Attention is now directed Lto the accompanying drawings which schematically illustrate typical processes for the Ipractice of my invention.

Turning first to FIGURE l, there is shown a continuous countercurrent solvent extraction process employing a solvent of the type described more fully hereinafter, such as for example, an azeo-tropic mixture o-f triethylamine and acetic acid. A feed stream containing both aromatic and nonaromatic hydrocarbons of like boiling ranges such as a heavy reformate petroleum fraction containing diaromatics '(naphthalene, alkylated naphthalenes, ete); monoaromatics (alkyl benzenes, alkyl tetralins, alkyl indanes, etc); and nonaromatics (naphthenes and parans), is continuously fed into the bottom of a countercurrent solvent extraction column .1 through line 3 as shown. Simultaneously, solvent is recycled into the top of column 1 through line 5, from a source hereinafter disclosed. Solvent extraction column 1 is so designed and the conditions of operation so fixed and controlled as lto result in the extraction of substantially all of the aromatic components from the feedstock as it circulates upward in countercurrent contact with the solvent in said column.

As -those skilled in the art realize, there are generally four important things to be considered in the practice of countercurrent solvent extraction, namely: (l) the operating temperature; (2) the operating pressures; (3) the number of extraction stages; and `(4) the solvent/feed ratio. Careful selection and control of operating conditions in the above -four areas is important in order to achieve optimum phase separation, selectivity, and solvent power, all of 'which have a bearing on product yield and purity.

The operating temperature level is important in solvent extraction operations -since in Ithe usual case too low a temperature results in an inordinately high feed viscosity which in turn results in unnecessarily long phase separation periods. Additionally, too low a temperature is undesirable in that it normally has a detrimental effect on the solvent power of selective solvents. On the other hand, excessively high temperatures are undesirable since they u-sually have the effect of reducing solvent selectivity and tend -to make the extract and raffinate phases mutually misc-ible. Where solvent extraction is carried out at atmospheric pressure, the operating temperatures should preferably not exceed `the boiling points of any of the various components present in the system since this would obviously have a deleterious effect on the operation.

Reasons have been given why extremes of temperature in either direction are undesirable in solvent extraction CII operations. However, the effects of lowering the operating te-mperature below a certain level are not necessarily all bad since such lowering frequently results in an increase of solvent selectivity. Furthermore, not all of the effects of an excessive elevation of temperature are necessarily deleterious, since `such elevation normally brings about a shortening of the time required for lphase separation as well as an improvement in the solvent power of selective solvents. It will be apparent from the abovenoted considerations that the selection of an optimum temperature range for solvent extraction purposes depends on many factors and entails a balancing of the advantages and disadvantages inherent in various temperature adjust-ments, taking into consideration the characteristics of the components present in the system, the operating pressures, etc. So too, the selection of optimum operating pressures for solvent extraction operations is subject to the consideration of other factors of an influencing nature. rl`hus operating pressures can vary from subatmospheric, Ithrough atmospheric, to superatrnospheric ranges depending upon the peculiarities of the given system.

Returning now to FIGURE l, I lhave discovered that solvent extraction `column 1 is effectively operative on typical systems of the `type contemplated when maintained at atmospheric pressure and within an operating temperature range of from about 20 to about 150 C., the Ipreferred temperature range being `from about 30 to about C.

The yield and purity of the raffinate and extract products, identified infra, from column 1 are, as previously indicated, partially depen-dent upon the number of extraction stages in said column. It is, as a general rule, true that the greater the num-ber of stages in a solvent extraction column, ythe greater will be the yield and purity of the products of the column. However, as those skilled in the solvent extraction art will appreciate, the selection of an optimum number of stages is a matter of economics since -as the number is increased a point of diminishing returns is lreached beyond which the relatively small improvement per additional .stage `makes it impractical to proceed. I have found that solvent extraction column =1 is operatively effective for use in processes of the contemplated type when it has lfrom about 2 to about l5, and preferably Ifrom 7 to l1, stages.

Referring again to FIGURE 1, an extract phase is withdrawn from the bottom of solven extraction column 1 through line 7 .and a raffinate phase is withdrawn from the top of the column through line 9 as shown. When column 1 is designed and operated according to the preferred precepts and conditions set forth above, aromatic hydrocarbon yields of from about to about 99 percent by weight and purities of from about to about 99 percent by weight are attainable in the extract phase. The extract phase contains most of the solvent passing through column l, in addition to that portion of the feedstock which the solvent has extracted in its travel within the column. The raffinate phase from column 1, under preferred conditions of operation, typically contains 'between `about 90 and about 99.5 percent, by weight, nonaromatic hydrocarbons, the remainder being solvent.

In the FIGURE l process, as the drawing shows, there is an alternate choice of disposition of the raffinate from column l. Thus, the raffinate can be withdrawn from the process through valve 11, with valve 13 closed, without further treatment, or it can be circulated to distillation column 17 through line l5, as shown on the drawing, toy effectuate the recovery of solvent therefrom. Obviously, valve 13 is kept open and valve ll closed in the latter event.

For ease of illustration and simplicity of explanation, the FIGURE l process is shown and described in terms of the recovery of all feedstock aromatics in one pass through' column l. However, it is to be understood that, as explamed above, my method of solvent extraction is equally aas-m61 lapplicable to the separation of aromatics into fractions differing as to degree of aromaticit-y, such as for example the recovery of diaromatics from a feedstock -comprising both diaromatic and monoaromatic components. To. accomplish this type of separation it is only necessary -to lassure the proper number of stages in column 1 and the proper operating conditions to accomplish the purpose. The determination of optimum plate plurality and operating conditions to achieve this, or any other result within thev scope of my invention, is a relatively simple matter to those skilled in the solvent extraction art, 'in the light of the teachings herein, requiring at most a minimum amount of routine experimentation. y

Primarily, the achievement of maximum separating efficacy among compounds of varying degrees of aromaticity is a matter of having a sufficiently high number of extraction stages -in column 1. In this respect, it is pointed out that more stages are required for such selective extraction, all other things being equal, than for mere separation of the mixture into aromatic. and nonaromatic fractions.

If it is desired to obtain two or more aromatic fractions from a mixture containing both aromatics of differing aromaticities and nonaromatics, the FIGURE 1 process can by relatively simple modification be made to accommodate this requirement. One way of .accomplishing this is to add one or more additional solvent extraction columns similar to column 1 to the process, with appropriate lines, fittings and other equipment, Where needed, to handle the various streams in the system. For example, if it is desired to separate a diaromatic fraction and `a monoaromatic fraction from a feedstock containing diaromatics, -monoaromatics and nonaromatics, this can vbe done by incorporating an additional solvent extraction column in series With column 1; using column 1 to extract the diaromatcs from the feedstock; and utilizing the additional column to separate the monoaromatics from the nonaromatics in the raffinate phase from column 1.

While the FIGURE 1 method is preferably practiced as a continuous or flow process, and that aspect of operation is stressed in this description, it functions equally well as la batch process provided column 1 is 4considered to represent suitable apparatus for batch extraction, countercurrent batch extraction, or the like, purposes.

To continue with the detailed description of FIGURE 1, in the event the raffinate phase fromcolumn 1 is routed to distillation column 17, it is fractionated therein into an overhead product of substantially pure solvent which is passed through line 19 into cooler 21, wherein it is condensed, and from thence through line 22 to juncture with line 5 and admixture With the solvent feed to column 1, l

and a bottoms product of nonaromatic raffinate hydrocarbons which is withdrawn to storage or other disposition through line 18. lOther appropriate means for separating the raffinate phase into its solvent and nonaromatic. fractions, such as, for example, ywater extraction of the solvent, can be employed in lieu of the column 1`7 distillation operation, if desired.

The extract phase from solvent extraction column 1, normally containing from about 20 to about 30 percent aromatic hydrocarbons and from about 80 to about 70 percent solvent, is passed` through line 7 and into distillation column 23 wherein it is separated into solvent (overhead) and aromatic hydrocarbon (bottoms) fractions, the former being recirculated to solvent extraction column 1 through condenser 24 and line 5, as shown on the drawing, and the latter (bottoms) being withdrawn .through line 25. None of the components of the extract phase from column 1 decompose at or near their normal boiling points. Furthermore, the boiling points of the extract components are normally of such magnitude and disposition as to permit distillation of the extract phase at atmospheric pressure and, accordingly, distillation column 23 is preferably operated at about that pressure level. At atmospheric pressure, the most effective temperature range for operation of column 23 is, in most instances, from about to about 300 C., the preferred range being from about to about 275 C.

Under certain circumstances, there may be minor quantities of contaminating hydrocarbons present in the extract phase from column 1, the exact amounts of such contaminants depending upon, inter alia, the operating temperatures and pressures of, and the number of stages in, said column. Where such is the case, it is conceivable that the contaminants will, at le-ast to some extent, accompany the solvent overhead from column 23, possibly in the form lof a minimum boiling azeotrope therewith. While the llikelihood of an occurrence of this type producing solvent contamination to any significant extent is remote, it is a relatively simple matter to cure such .an evil by inserting a phase separator in line 5 between condenser 24 and column 1 and routing the solvent phase therefrom t0 column 1. Bottoms product from column 23 is recovered as the Vfinal extract product from the process or it can be circulated to further treatment, not shown, such as additional solvent extraction treatment to break it down into componential aromatic fractions or some form of purification treatment to remove `traces of solvent or other contaminant(s) possibly present. Makeup 4solvent is introduced into the system through line 217 and valve 29 as needed. i v Y Turning next to FIGURE 2, it will be noted that the process there is similar to that -of FIGURE 1 in many respects, differing only in the means of separating the extract phase into its solvent and aromatic hydrocarbon fractions. Thus, in the FIGURE 2 scheme a feed material containing both aromatic and nonaromatic components is introduced through line 31 into the bottom of a -continuous countercurrent solvent extraction column 33 in which it is subjected to countercurrent extraction by a suitable amine-acid solvent. The solvent is continuously fed into the upper portion of solvent extraction column` 33, from a source hereinafter disclosed, .through line 35 as shown on the drawing. The products from column 33 are a raftinate phase which is withdrawn from the top of .the column through line 37 and an extract phase which is withdrawn from the bottom through line 39.

The ranate phase from column 33, lsimilarly to that from solvent extraction column 1 of FIGURE l, is subject to an alternate choice of disposition. either withdrawn through valve 4,1, with valve 43 closed, to storage or with destination not shown or it is routed to distillation column 47 through line 45 by proper manipulation of valves 41 and 43, wherein it is factionally distilled to separate it into an overhead solvent product and a bottoms product of nonaromatic rainate hydrocarbons which is withdrawn through line 49. It should be undertsood that the various alternatives as to technique, apparatus, feed materials, etc., set forth in the description of the FIGURE 1 process have equal significance with respect to those elements of the FIGURE 2 process which are common to both methods of operation.

The solvent overhead from distillation column 47 is routed through line 51 into cooler 53, wherein it is condensed, and from thence through line 55 to juncture with line 35 and admixture with the solvent being'fed to column 33. f

The extract phase from solvent extraction column 33 is` passed into solvent extraction column S7, throughl line 39, wherein the solvent (being Water soluble, as pointed out infra) is selectively extracted therefrom with Water. The extraction of the slovent from the extract phase is not limited to the use of waterl asthe extracting agent and any other material which is a relatively stable liquid under the conditions of service, and in which the amine-acid solvent is substantially miscible, may be employed for the purpose if desired. It is, of course, obvious that the chosen material must also be substantially immiscible with the hydrocarbon, or hydrocarbons, in the extract f phase.

Thus, it is The products from column 57 are an aqueous solution of the amine-acid solvent (aqueous phase) which is withdrawn from the bottom of the column through line 59, and a hydrocarbon product consisting of the aromatic fraction of the feedstock in substantially pure form, which is withdrawn through line 61 to storage or other disposition.

The aqueous solution of solvent from column 57 is passed through line 59 to a distillation column 63 in which the Water is separated from the solvent, the water passing ot through line 65 as an overhead and the solvent being withdrawn through line 3S as a bottoms product. The water overhead from column d is condensed in condenser 69 and then recirculate-d to solvent extraction column 57 through line 71 as shown on the drawing. The solvent bottoms product from column 63 is recycled through line 35 to solvent extraction column 33.

Column 57 is shown schematically as a countercurrent solvent extraction column and the preferred technique for practicing the FIGURE 2 process is by continuous operation of that unit, as well as all other units in the process. However, it is possible to replace `column 57 by batch apparatus for solvent extraction if desired. It is also possible to modify the FGURE 2 process in other ways obvious to those skilled in the art without substantial alteration of its purpose or accomplishments. One such modification is, for example, the incorporation of known purication techniques for the treatment of one or more of the products of separation from solvent extraction column 57, as well as distillation column 63. Makeup solvent is introduced into the FEGURE 2 process through line 67 and valve 73 as needed.

There are a number of things to consider in the selection of solvents for solvent extraction purposes, among which are: (l) the stability of the candidate material under the conditions (heat, pressure, etc.) of service; (2) the selectivity of said material, under service conditions, with respect to the mixture to be extracted; (3) the tendency or lack of such tendency of the material to react chemically with any of the components of systems in which it will be used; (4) its boiling point relative to the boiling points of the `components of the mixtures to be separated; (5) its melting point; (6) its corrosiveness t0- wards the materials of construction of the equipment to be employed; (7) its toxicity (which is important from an operational standpoint); (8) its water solubility; and (9) its density relative to the densities of the components of the mixtures to be separated. I have now discovered that mixtures of amines and acids varying widely as to ingredient composition and component proportions satisfy all of the requirements inherent in the above considerations to qualify as excellent solvents for the selective extraction of aromatic hydrocarbons from organic mixtures of the type previously disclosed. I have further found that, in addition to having an ainity or selectivity for aromatic hydrocarbons in general, such amine-acid mixtures have relatively greater selectivities for aromatics of relatively greater degrees of aromaticity, thus making the separation of aromatics by degree, as discussed in detail supra, possible by solvent extraction means.

The amine-acid mixtures suitable as selective solvents for use in my invention must, of necessity, be liquid under the service conditions of my solvent extraction method. I have determined that best results are usually achieved when molar ratios of acid to amine within the range from about 1:1 to about 6:1 (optimum: from about 2:1 to about 4:1) are employed. It is of interest to note that amines and acids often form maximum boiling azeotropes and, in this connection, I have made the interesting discovery that the preferred acidzamine ratios for purposes of this invention typically correspond to maximum boiling azeotrope compositions.

The amines of most effectiveness for use as taught herein are tertiary amines having from about 3 to about 15, and preferably from about 3 to about 9, molecular carbon atoms. The amines may be wholly or predominantly of aromatic, aliphatic or heterocyclic character, or they may partake, in varying degrees, of the characteristics of compounds in any two, or all three, of those categories. Amines which are otherwise suitable having substituent groups of a substantially neutral character with respect to other components in the system can be employed for my purpose if desired.

The amine-acid solvents of this invention are not amides but merely mixtures of amines and acids. Such mixtures are sometimes referred to as salts. However, the term salts has been deliberately avoided herein to obviate any possibility of misunderstanding as to its meaning. Furthermore, the amine and acid ingredients are not always present in my solvent mixtures in amounts stoichiometrically consistent with salt proportions so the term salts would not be precisely applicable in those cases anyway. Since my class of amine-acid solvents is exclusive of amides, it will be apparent that combinations ot amines and acids which react to form such compounds under the conditions encountered in the practice of my invention are outside of the scope of said invention. Secondary and primary amines generally react with organic acids to yield amides whereas tertiary amines do not so react with those acids. As will be presently made clear, the aci-d ingredients of my amine-acid solvents are organic acids. Hence, only tertiary amines, and not secondary or primary ones, are normally suitable for use as the amine ingredients of my solvent mixtures.

The following tertiary amines are representative of those amines most suitable for use in this invention:

Triethyiamine Triphenylarnine Trimethylamine Dimethylaniline Methyldibutylamine Methyldiphcnylamine Dimethylbutylamine l-methylpyrrole Ethylmethylpropylamine Ethyldipropylaminc Diethyloctylamine Diethlypropylamine N,N-dimethylpiperazine 1,3-dirnethylpyrrole l-dimethyiamino-3-butene ot-Picoline 3 ,S-lutidine 2,4,6-collidine N-ethylpiperidine Methylethylisobutylamine Triethylenediamine N- l -ethylbutylidine-ptoluidine Any organic acid yielding a liquid mixture under service conditions within the reach of this invention when combined with Ian amine, or amines, of proper type is a suitable acid ingredient for my amine-acid solvent. The organic acid can be of any type, such as, for example, an alkanoic, benzoic, etc. acid, and it can be nnsubstituted or substituted. Examples of representative acids are monocarboxylic acids such as formic, acetic, propionic, etc., acids; substituted monocarboxylic acids such as triiiuoroacetic, rnonochloroacetic, diehloroacetic, trichloroacetic, a-bromocaprioic, etc. acids; sulfonic acids such as ethylsulfonic acid, butylsulfonic acid, etc.; unsaturated acids such as acrylic acid, oleic acid, etc.; substituted unsaturated acids such as ,-dibromopropionic acid, etc., hydroxy acids such as glycolic acid, lactic acid, etc.; aldehydic acids s uch as glyoxalic acid, etc.; ketonic acids such as ketoproplonic acid, etc.; amino acids such as lysine, ornithine, etc.; aromatic aminobenzoic acids such as oaminobenzoic acid, etc.; aromatic substituted and unsubstituted acids such as benzoic acid, o-phthalic acid, phenylacetic acid, cinnamic acid, p-nitrobenzoic acid, o-toluic acid, m-toluic acid, p-toluic aci-d, ni-bromobenzoic acid,

p-chlorobenzoic acid, o-sulfobenzoicacid, salicylic acid, gallic acid, mandelic acid, cinnamic acid, etc., alicyclic acids such as cyclopentano-l,2dicarboxylic acid, truxillic acid, truxinic acid, etc.; and heterocyclic acids such as furoic acid, furylacrylic acid, nicotinic acid, barbituric acid, tryptophane, indol--acetic acid, quinolinic acid, cinchophen, 2-phenoxybenzoic acid, tnt-pyridine carboxylic acid, etc.

The method of preparing the amine-acid mixtures lfor use as solvents in this invention is simple, it being only necessary, in most instances, to add the amine to the acid, or vice versa, in the desired amount, normally'such an amount as to yield a final mixture containing azeotr'opic proportions of the two materials where such proportions are possible. y

My invention is not limitedto the use of amine-acid mixtures of azeotropic proportions and other mixtures can be employed if desired. Examples of `such other mixtures are those combinations of azeotrope forming amines and acids in nona'z'eo'tropic proportions and combinations of nonazeotrope forming amines and acids.

The use of mixtures of two or more amines and/or acids, instead of only one lamine and one acid, is within the scope of my invention. AS` indicated previously, the amine-acid solvent must be in liquid form under the conditions of service of my solvent extraction method. This does not mean that the amine acid mixture must be liquid at standard conditions of room temperature and atmospheric pressure, although such is frequently the case. It is within the scope of the invention to employ amines and/ or acids which are solid at standard conditions, or form solid or semi-solid mixtures thereat, so long as the resulting amine-acid mixtures are liquid under the operating conditions to be employed in the solvent extraction systems in which they are to be used. v

In the preparation of solvent mixtures according to this invention, if the ingredients are all liquid at room temperature, simple stirring is usually sufficient to effect rapid homogeneity of the mix. Where not all of the ingredients are liquid at the temperature of preparation, it might be necessary to use more rigorous means of achieving uniformity of mix such as, for example, kneading or the like. In either event, the application of heat to change the viscosity characteristics of the system can be employed if desired.

The preferred solvents for my solvent extractionprocess are those mixtures`of trialkylamines, such as triethylamine, and lower alkanoic acids havingv carbon chain lengths not greater than about 6, such as acetic acid, etc., in which the amine and acid components are present -in their azeotropic proportions.` These mixtures form maximum boiling azeotropes and I have determined that mixtures corresponding in component proportions to such azeotropes are highly selective toward aromatics for purposes of this invention. In addition, the boiling points of these particular mixtures are sufficiently low to permit relatively easy and inexpensive separation of the solvents from their hydrocarbon mixtures by distillation. In addition, the components of these preferred mixtures are 'cheap and readily available. Other amine-acid mixtures worthy of note as outstanding .solvents for use in the present invention are prepared by mixing an l -alkylpyrrolidine, such as N-methylor N-ethylpyrrolidine, with a lower alkanoic acid, such as acetic acid, in az'e'otropic proportions. These mixtures are highly selective solvents for aromatic hydrocarbons and in addition, are possessed of relatively high densities which, as those skilled in the art realize, is highly advantageous in a selective solvent.

It should be emphasized that even though molar excesses of acids are normally used in the preparation of my selective solvents, the corrosivity of the solvents to ward materials vulnerable to acid attack is unexpectedly low, sometimes approaching that of distilled water. This is obviously of major importance from the standpoint of equipment econo-my and simplicity of maintenance. The reason for the surprising lack, or minimization, of corrosivity in my selective `solvents is not understood with certainty. Y

The solvents of this invention, in addition to Ibeing highly selective toward aromatic hydrocarbons, exhibit high solvent power, i.e., relatively small quantities of solvent dissolve relatively large quantities of .aromatics More specifically, solvent proportions of from about 0.25 to about 3.0l parts of solvent' (my preferred proportions) to about l part of hydrocarbon feedstock, on a weight basis will normally manifest a solvent power of from about 5 to about 35. The method of calculating solvent power values forpurposes of this invention is set forth in Example II following.

An important factor in arriving at optimum conditions of operation in solvent extraction processes is the rapidity with which the raffinate phase separates from the extract phase under various circumstances. By using the preferred tertiary amine-acid solvents in the method of my invention, relatively rapid separation takes place between the phases when operating at room temperature. At higher temperatures, phase separation is faster and the solvent power of the amine-acid solvent is greater, but temperature increases have an adverse effect on the selectivity of the solvent towards aromatics. The previously recommended temperature ranges for the practice of my invention (about 20 to about 150 C., preferably from about 30 to about 60 C.) were arrived at by taking the aforesaid factors into consideration. The relatively fast phase separation achievable with my .amineacid solvents is thought to be attributable, at least in part, to the fact that they have high densities, normally in excess of one, compared to hydrocarbon oils.

The solvents of this invention are relatively nontoxic at standard, as well as operating, conditions. Also, these solvents are miscible with water, thus making it an easy matter to recover them from extract phases, by water extraction, for recycling or oit-her purpose. In addition, the solvents are stable at their boiling points and unreactive with the feedstock components at those temperatures, as well as other temperatures to which they are subjected in service. The preferred tertiary amine-acid azeotropic mixtures of this invention have boiling points ranging between about and about 300 C. Those having boiling points within the range from about to about 275 C. have been found most efficacious for use in my process.

The solvent extraction process of my invention can lne carried out in various ways, the most common mode of operation comprising the use of a spray, packed, or bubble plate tower, wherein the hydrocarbon feed mixture is contacted by the stream vof amine-acid solvent iiowing, usually countercurrently, therethrough. It is within the scope of my invention to .add a minor amount of water, or other inert agent, to my amine-acid solvents, where such can .be done with colorable modification of those solvent properties necessary to the proper functioning of my process. -F or example, where it is proposed to subject a mixture of hydrocarbons of varying degrees of aromaticity to solvent extraction according to my method, and the hydrocarbons are all quite soluble in the lchosen solvent, the incorporation of a minor amount of water into the solvent, prior to or during the extraction operation, to assure the rapid and distinct formation of two liquid phases is within the spirit and scope of my invention. When water is added for such purpose, the proportion used should normally not exceed about 20 percent of the weight of the solvent and preferably fall within the range from about 2 to about 5 percent of the solvent weight.

If desired, my process can be carried out by distilling the hydrocarbon feed mixture in the presence of an 1 1l amine-acid solvent, of the type disclosed herein, as an extractive distillation process.

In the practice of extractive distillation, a feed mixture to be separated is -distilled in the presence of a selective solvent which has a substantially lower volatility than any of the components of said mixture as a result of which an overhead enriched in that portion of the feed mixture not selectively extracted is removed, leaving behind a bottoms product which comprises a solution of solvent and selectively extracted materia-l. Since not all of my amine-acid solvents are of lower volatility than all components of those feed mixtures separable by methods taught herein, it is necessary to .be selective in choosing a solvent of proper volatility for the extractive distillation of a given feedstock in accordance with this invention. To illustratean amine-acid solvent suitable for the extractive distillation of a petroleum fraction having a boiling range of from about 400 to about 450 F., such as a heavy refer-mate fraction containing naphthalene, alkyl naphthalenes, alkyl benzenes, tetralins, indanes, etc., must lboil at a temperature level much higher than 450 F. Examples of solvents fitting this category are mixtures of tributylarnine and caproic acid, mixtures of dimethylaniline and benzoic acid, etc.

Still another way in which my process can be carried out is to employ an atisolvent in conjunction with the amine-acid solvent in any manner known to `those skilled in the art. The use of such antisolvents in hydrocarbon solvent extraction processes is `well known and need not be considered in detail here. Typical antisolvents for purposes of this invention are paraflins such as pentane, heptane, octane, isooctane, and the like; water; etc.

In order to more fully illustrate the invention lthe folcarbons and 76.5% by weight solvent, and a rainate phase containing 99.3% by weight hydrocarbons and 0.7% by weight solvent were produced. The solventfree extract was about 73.5% by weight naphthalenes, and the solvent-free raffinate was about 15% by weight naph- -thalenes The solvent was removed from the extract phase, by fractional distillation, which yielded a bottoms product containing 86% by weight naphthalenes. The overall recovery of naphthalenes from the feed was 78%.

This example serves to illustrate the selectivity of my preferred tertiary amine-acid mix-tures as solvents for diaromatics in th-e presence of monoaromatics, as well as the relatively high solvent power of such mixtures towards diaromatics. The use of additional stages in the method of this example results in a substantial increase in extract purity and yield of diaromatics. Thus, recoveries of from about to about 99 percent of the naphthalencs in the feed stock and extract product purities of from about to about 99 percent diaromatics are attained by the use of such additional stages.

EXAMPLE II A number of one-stage tests were conducted using as selective solvents various tertiary amine-acetic acid mixtures. The hydrocarbon-solvent batch was prepared by adrnixing 10 ml. of solvent, 10 ml. of decalin and 5 ml. of ic-methylnaphthalene. The a-methylnaphthalene and decalin represent the feedstock. a-Methylnaphthalene was separated by the solvent as the extract phase. Decalin is a bicyclic paraflin. All solvent mixtures were prepared in azeotropic component proportions. The results appear in Table I, following:

Table I TERTIARY AMINE-ACETIC ACID AZEOTROPES FOR AROMATICS PURIFICATION Weight Percent Percent 13.1. Amine B.P. Percent D 25 C. Naph. Purity Amine, Stability Solvent 1 C.) HAc 1n Recovery 0f Naph C. Power Azeotrope N-cthylpyrrolidiue 170 64 1. 023 47 67. 8 106 Good 16, 2 Triethylamine 163 68 1. 003 44 68. 1 90 Very gooCL.. 15. 4 N-methylpyrr0lidine 168 76 1. 047 34 69. 8 83 Good 12. 4 Methyldibutylamine 161 65. 5 9874 42. 5 60. 0 11. 4 N-methylpipcridine 165 68 l. 047 30 71. 5 11, 5 N,N,N/,N'-tetramethylethyl- 171 64 l. 039 33 67. 8 1l. 4

enediamine.

N,N-dimethylethanolaminc 162 62 1. 062 26 73. 1 10. 4 N-methylmorpholine 152 66 1. 081 27 71. 0 10. 2 N,N'dimetliylpiperazine 168 62 1. 052 36 61. 0 10, 0 Trimethylamine 152 80 1. 035 24 72. 0 9, 3 Pyridine 141 53 1. 039 25 66. 0 S, 2

l Diierence in a-methylnaphthalenc concentration between the solvent-free extract and the feedstock times percent recovery times 1 0-2. lowing examples are set forth. These examples are to be considered as illustrative only and not limitative of the scope of the invention.

EXAMPLE I Using 100 gms. (100 ml.) triethylamine-acetic acid solvent, a simulated continuous solvent extraction in three stages was carried out at atmospheric pressure using 75 gms. (83 ml.) of catalytic cycle oil as feed. Approximately 68% by weight of the solvent was acetic acid and the weight ratio of solvent to feed was 1.33 to 1. The feed was a hydrocarbon fraction which boiled at a range between 445 F. and 500 F. A hydrocarbon type analysis showed the following approximate composition (weight percent):

Parains 17 Naphthenes 2l Monoaromatics 20 Diaromatics 1 42 1 Consisting 'of methylnaphthalenes (14 percent on n total feed Weight basis) and dimethylnaphthalenes (2S percent on a total feed Weight basis).

An extract phase containing 23.5% by weight hydro- Table I provides much valuable information.

The boiling point of the solvent is higher than the boiling point of each of its components considered separately. For instance, the boiling point of acetic acid is about 118 C. The boiling point of N-ethylpyrrolidine is 106 C. (column 6) but the boiling point of the solvent is C. which indicates that the solvent is a maximum boiling azeotrope. This boiling point is sufficiently lower than that of a-methylnaphthalene (244.6 C.) to permit substantially complete separation of high purity solvent from the solvent extraction extract phase by fractional distillation.

Column 2 of Table I indicates the percentage of acid in the solvent. In spite of the high percentages of acid in every case, the corrosivity of the solvent was generally low-in some cases not significantly greater than that of distilled water. v

With one exception (methyldibutylamine), the solvents had a density greater than one, thereby indicating ease of separation between the extract and raffinate phase. Even in the case of the exception (methyldibutylarnine), the density was sufficiently higher than that of the feedstock to assure good phase separation. In this connection, it is i previously indicated, substantial increases in yield and purity. ,Examplel oiers'. evidence ofthis in the'f'act that a `yield of 78% and a purit'yo'f 73.5% was obtained in threustages. Still more stageswould, as'pointed` outpreviously, result in yieldsV and purities representing almost ideal separation of the feed components.

Column 7 gives an indication of the stability vof the liste-d solvents at their boiling points. As column 7 shows, onlythe N,Ndiethanolamine resulted in a -solvent having poorboiling point stability. However, even though that solvent is not particularly stable at .its boiling point, it is a good solvent as evidenced by the .data of columns 4 land 5. It also has -a relatively high boiling point (maxim-um boiling azeotrope). In view of these facts, the relatively poor boiling .pointV stability .of the ance being composed of Arnonoaromatics 4such as those named above. Thus, it can be determined that the ratio of diaromatics to monoarornatics increased from 1.73 in the feed lto 3.67 in the extract.

Theabove results clearly show that there was greater selectivity ofthe *solvent for the diaromatics than for the'mon'oaromatics present in the system.

.EXAMPLE ,IV

This exampleillustrates the utility of various amine- 'acid combinations as selective solvents for diaromatics in the presence. ofmonoaromatics.

' A-hydrocarbon dealkylation product containing 40% naphthalene and 60% alkylatedmonoa-romatics and nonaromatics such as naphthenes, alkyl indanes, alkyl indenes, alkyl .tetralins, and the like, ,was divided into g. samples. Each sample was `mixed with 4125 g. of a separate solvent fro-m thelist in Table II, below. A single stage solvent extraction process for each sample was then carried out at a temperature of 125 C. The results are tabulated in Table II, following.

Table I I Percent Purity of Percent Compound B .1. Diaro- Exact Acid in Solvent Density 1 C.) matics (Percent) Azeotrope Power Recovery 'rriethyimme-fomn Acid Azeotrope 18e 35. 5' s4. 1 e7. 0 1s. 2 1. 0179 Triethylamine-triiluoro-acetic 'Acid Azeotrope 235 4G. 5 76. 8 59. 5 20. 2 1. 1916 Triethylamine-methoxy-acetic Acid Aze- Otlope 2 18 33. 8 79. 0 80. 0 l5. 4 yl. 0743 Diethylcyclohexylarnine-aceticAcidAzeotrope 175 59. 5 55. O 55. 0 12. 9 9789 Nora-All percentages in the above table are on a weight basis.

solvent does not r-ule out its use as a selective solvent for my new -process and there are techniques known to those skilled in the art for recovering the `solvent from ythe extract phase without subjecting'it to temperatur-es 'potentially damaging to its stability. For example, the

extract lphase can be fractionally distilled at reduced pressures to penmit operation at lower temperatures lor it can'be extracted with water to selectively dissolve out the solvent in accordance with the` FIGURE 2 pro- This example illustrates the selectivity of my amineacid solvents Vfor diaromatic hydrocarbons in the presence o-f monoaromati-chydrocarbons.

A 133 ml. lquantity of N-methylpyrrolidine and acetic acid was ad-mixed with 100 ml.` of a hydrocarbonfraction having aboiling range of 430-520 F. The acetic acid comprised 76% by weight of the solvent and the weight ratio of `solvent toy feed was 1.33 to 1.` The hydrocarbon fractionwas compo-sed of 58.3% monoaromatics and diaromatics, including naphthalene, methyland dimethylnaphthal'enes, Valkyl indanes, alkyl indenes, alkyltetralins, and thel like The balance of the hydrocarbon fraction (41.7%) was composed of parans and naphthenes. The ratio of di'aromatics to monoaromatics in the hydrocarbon fraction was 1.73 to 1.

The mixture of solvent and hydrocarbon fraction .was moderately agitated at '25 C. and allowed to settle into a rainate and extract phase. The extract phase after analysis showed an aromatic concentration of 95.2% which was found to be 74.3% diaromati-cs such as naphthalene, and methyland dimethylnaphthalenes, theV balvof this invention.

The rirst two solvents listed in Table II have maximum boiling azeotrope compositions which are unstable at their boiling points. However, here again, as in the case of the N,N-dimethylethanolamine-acetic acid solvent of Example II, and Vfor the same reasons, .the solvents are not thereby rendered ineligi-ble for use in my invention. i

Columns 2 and 3 of Table II list naphtlralene recovery and purity results. It is to be noted that even though the first two listed solvents in Table II decompose at their boiling points they are extremely effective solvents, the recoveries and purities, and particularly the latter,

,attributable to their use being exceptionally high for a one-stage operation.

Column `5 sets forth the solvent powers of the solvents which, it will be observed, `are relatively high, indicating good perfor-mance capability in the solvents for purposes The superiority in solvent power is accented by the rather low ratio of solvent to feed employed in the described procedure.

EXAMPLE V This was an example of a laboratory-scale solvent extraction of rnethylnaphthalene from a mixture of niethylnaphthalene (a diaromatic) and dodecane (a paraffin), using a mixture of triethylamine andv acetic acid as the solvent.

A single stage solvent extraction was carried out at 25 C. by treating a mixture of 14 ml. of dodecane and 6 ml. of methylnaphthalene with 16 rnl. of triethylamineacetic acid solvent. v The weight ratio of solvent to hydrocarbon feed mixture was approximately 0.8 to 1. Approximately 68% of the solvent was acetic acid. The .solventhydrocarbon mass was moderately agitated and a solvent rich phase separated therefrom.. It was determined that approximately 21% of the volume of the This example illustrates the selective extraction of diaromatics from a mixture thereof with monoaromatics according to the method of this invention.

100 grams (100 ml.) of a triethylamine-acetic acid mixture at C. is admixed with 75 g. (83 ml.) of a hydrocarbon fraction composed 60% of dimethyltetralins and dimethylnaphthalenes. 68% of the solvent comprises acetic acid and the ratio of solvent Ito hydrocarbon fraction is 1.33 to 1. A two-phase separation is conducted in which the diaromatics are absorbed in the solvent rich phase.

The solvent rich or extract phase contains about 20% diaromatic hydrocarbons and about V80% solvent and monoaromatic hydrocarbons. The recovery, or yield, of

diaromatic hydrocarbons effected bythe method de-`" scribed in this example is equal to An increase in the number of stages increases the yield and purity of the extract product to between 85-99% and 90-99%, respectively.

i EXAMPLE VII This example illustrates the selective extraction of monoaromatic hydrocarbons from a mixture thereof with nonaromatic hydrocarbons according to the method of this invention.

100 grams (100 ml.) of a mixture of 68% acetic acid and 32% triethylamine is admixed at 25 C. with a hydrocarbon fraction composed of 20% benzene, toluene and xylene and 80% parathns and naphthenes as a result of which an extract phase rich in the monoaromatic hydrocarbons is recovered. The extract phase is composed of about 20% monoaromatic hydrocarbons and 80% solvent and nonaromatic hydrocarbons and contains about 47% of the monoaromatic hydrocarbon content of the feedstock mixture.

Here, as in the case of the other examples, the yield and purity of the extract product is greatly increased by an increase in the number of solvent extraction stages.

EXAMPLE VIII The following example illustrates the use of' a solvent containing a minor amount of .water in the process of my invention.

A selective solvent composed of 32 parts triethylamine, 5 parts water, and 68 parts acetic acid was prepared. 10 ml. of the solvent was admixed with l0 ml. of decalin and 5 ml. of methylnaphthalene and the resulting batch was agitated and allowed to separate into an extract phase and a ratiinate phase. The extract phase was analyzed for its methylnaphthalene content and it was found to contain 27% of the methylnaphthaleneV origi-l nally introduced and to have a purity, solvent-free, of`

The solvent had a density of 1.003 and lboiled at 100- 163 C., the 100 C. being the boiling point of the Water therein.

The solvent was found to be stable over its boiling point range making'fractional distillation of the extract phase to separate solvent from the aromatic hydrocarbon feasible.

EXAMPLE IX This example illustrates the use of a triethylamineethylsulfonic acid mixture as a solvent in the method of methylnaphthalene in the amount of 33 percent by weight, is treated with g. of a triethylamine-ethanesulfonic acid mixture (47.6 percent by weight triethylamine and 52.4 percent by weight ethanesulfonic acid) in a onestage solvent extraction process.

The extract phase from the solvent extraction process is subjected to a water extraction treatment whereby its triethylamine-ethylsulfonic acid solvent portion is selectively extracted by the water. The remaining hydrocarbon portion is enriched in methylnaphthalene.

EXAMPLE X This is an example of the use of an antisolvent in the practice of my invention.

A single stage solvent extraction operation is carried out at 25 C. by treating a mixture of 14 ml. of dodecane and 6 ml. of methylnaphthalene with 16 ml. of triethylamine-acetic acid solvent (approximately 68 percent acetic acid) at a weight ratio of solvent to hydrocarbon feed mixture of approximately 0.8 to 1. The solventhydrocarbon mixture is moderately agitated and a solventrich extract phase is separated therefrom.

V.Thesolvent-richextract phase is Washed'with pentane, as an antisolvent, to selectively extract dodecane which is dissolved therein as a contaminant. As a result of the washing operation, two phases (a pentane rich phase containing dodecane and a solvent-rich phase containing methylnaphthalene) are formed. The two phases are separated'and the solvent-rich phase is distilled to remove the triethylamine-acetic acid solvent as an overhead and recover the methylnaphthalene as a bottoms product.

EXAMPLE XI This example illustrates the use of a tributylaminecaproic acid mixture as a solvent in the method of my invention.

A l0() g. hydrocarbon feed sample comprising paraffins, naphthenes, alkyl indanes, alkyl indenes and alkyl tetralins, in the amount of 67 percent by weight, and methylnaphthalene in the amount of 33 percent by weight is treated with 100 g. of a tributylamine-caproic acid mixture (40 percent by weight tributylamine and 60 perment by weight caproic acid) in a one-stage solvent extraction process. The solvent-hydrocarbon feed mixlture is moderately agitated and a solvent-rich extract phase is separated therefrom.

Thesolvent-rich extract phase is separated by distillation into a solvent fraction and a hydrocarbon extract product rich in methylnaphthalene.

EXAMPLE XII This example illustrates the use of a dimethylanilinebenzoic acid mixture as a solvent in the method of my invention. y

A 100 g. hydrocarbon feed sample comprising paraftins, naphthenes, alkyl indanes, alkyl indenes and alkyl tetralins, in the amount of 67 percent by weight, and methylnaphthalene in the amount of 33 percent by Weight is treated with 100 g. of a dimethylaniline-benzoic acid mixture (35 percent by weight dimethylaniline and 65 percent by weight benzoic acid)A in a one-stage solvent extraction. The` solvent-hydrocarbon feed mixtureis 'Amoderately agitated and a solvent-rich extract phase is separated therefrom.

Thesolvent-rich extract phase is separated by distillation into a solvent fraction andahydrocarbon extract product rich in methylnaphthalene. v

K EXAMPLE XIII This example illustrates the use of a tropane-triuoroacetic acidmixture as a solvent in the method of my invention. v f Y. K l

A 100 g. hydrocarbon feed sample comprising parafiins,

naphthenes, alkyl indanes, alkyl indenes and alkyl tetralins, in the amount of 67% by weight, and methylnaphthalene inthe' amountof 33% by weight is treated 17 with 100 g. of a tropanetriliuoro-a'oetic acid mixture (.30 percent by weight tropane and 70 percent by weight trifluoro acetic acid) in a one-stage solvent extraction process. The solvent-hydrocarbon feed mixture is moderately agitated and a solvent-rich extract phase is separated therefrom.

The solvent-rich extract -phase is separated by distillation into a solvent fraction and a hydrocarbon extract product rich in methylnaphthalene.

It will be apparent that many modifications of my process can be practiced simply by varying the permissible solvent components, feed materials and 'operating techniques Within the limits taught herein. All percentage data in the above examples and elsewhere in this 'disclosure are on a weight basis unless otherwise specified.

The present process is particularly well adapted to preparing feedstocks for dealkylation processes. Thus, a heavy reformate fraction containing alkyl naphthalenes and non-naphthalenic materials can be treated in accordance with the invention to obtain an alkylnaphthalene concentrate which is thereafter dealkylated to form naphthalene by .any of the conventional catalytic or thermal dealkylation processes.

I claim:

1. A method of separating hydrocarbon material of greater aromaticity from a mixture thereof with hydrocarbon material of lesser aromaticity which comprises contacting said mixture with a substantially amide free solvent comprising a mixture of a tertiary amine and an organic acid selected from the group consisting of carboxylic and sulfonic acids.

2. A method of separating hydrocarbon material of greater aromaticity from a mixture thereof with hydrocarbon material of lesser aromaticity but roughly the same boiling point which comprises subjecting said mixture to extractive distillation in the Vpresence of a substantially amide free solvent comprising a mixture of a tertiary amine and an organic acid selected from the group consisting of :carboxylic and sulfonic acids.

3. A method of extracting hydrocarbon material of greater aromaticity from a mixture thereof with hydrocarbon material of lesser aromaticity which comprises contacting said mixture with a solvent comprising a mixture of a tertiary amine and an organic acid selected from the group consisting of carboxylic and sulfonic acids to form an extract phase lcontaining hydrocarbon material rich in said hydrocarbon material of greater aromaticity, and a raffinate phase. v 4. A method of extracting hydrocarbon material of greater aromaticity from a mixture thereof with hydrocarbon material of lesser aromaticity which comprises: (1) contacting said mixture with a solvent comprising a mixture of a tertiary amine and an organic acid selected from the group consisting of carboxylic and sulfonic acids to form an extract phase containing hydrocarbon material rich in said hydrocarbon material of greater aromaticity, and a raffinate phase and (2) recovering substantially all of the hydrocarbon material of greater aromaticity from said extract phase.

5. The method of claim 4 in which the hydrocarbon material of greater aromaticity is recovered from the extract lphase by fractional distillation means.

6. A method of extracting hydrocarbon material'of greater aromaticity from a mixture thereof with hydrocarbon material of lesser aromaticity which compris-es: (1) contacting said mixture with a solvent comprising a mixture of a tertiary amine and an organic acid selected from the group consisting of carboxylic and sulfonic acids to form an extract phase containing hydrocarbon material rich in said hydrocarbon material of greater aromaticity but containing a minor amount of said hydrocarbon material of lesser aromaticity, and a raiiinate phase; (2) treating the extract phase with an antisolvent to extract said hydrocarbon material of lesser aromaticity 18 therefrom; and (3) recovering substantially all of the hydrocarbon material of greater aromaticity from the thus treated extract phase.

7. A method of extracting diaromatic hydrocarbons from a feedstock containing diaromatic, monoaromatic and non-aromatic hydrocarbons comprising: (1) continuously contacting said feedstock, in countercurrent relationship, with a solvent consisting essentially of a mixture of a lower alkanoic acid and a trialkylamine at a molar ratio of the former to the `latter of from about 1:1 to about 6: 1, whereby an extract phase rich in said solvent and containing a portion of the feedstock enriched in diaromatic hydrocarbons and a raiiinate phase containing substantially all of the remaining portion of the feedstock and a minor amount of said solvent, are obtained; (2) subjecting the extract phase from step (l) to fractional distillation to form an overhead product of substantially pure solvent and a hydrocarbon bottoms product enriched in diaromatic hydrocanbons; 3) condensing the overhead solvent product from step (2); and (4) recycling the condensed solvent from step (3) to step (l).

8. A method of extracting diaromatic hydrocarbons from a feedstock containing diaromatic, monoaromatic and nonaromatic hydrocarbons comprising: (l) extractively distilling said feedstock in the presence of an extractive distillation solvent consisting essentially'of a mixture of a lower alkanoic acid and a trialkylamine at a molar ratio of the former to the latter of from about 1:1 to about 6:1, whereby an overhead fraction of the feedstock enriched in monoaromatic and nonaromatic hydrocarbons and a bottoms product containing said solvent and a portion of the hydrocarbon feedstock enriched in said diaromatic hydrocarbons, are obtained; (2) subjecting the bottoms product from step (l) to fractional distillation to form an overhead product of substantially pure solvent and a hydrocarbon bottoms product enriched in diaromatic hydrocarbons; (3) condensing the overhead solvent product from step (2); and (4) recycling the condensed solvent from step (3) to step (l).

'9. The method of claim 7 in which the trialkylamine is tricthylamine and the lower alkanoic acid is acetic acid.

10. The method of claim 7 in which step (1) is conducted at atmospheric pressure and at a temperature within the range from about 20 to about 150 C.

11. The method of claim 7 in which the ratio of solvent to hydrocarbon feedstock in step (l) is from about 0.25 to about 3.0 parts by weight of the former to l part by weight of the latter.

12. The method of extracting diaromatic hydrocarbons from a feedstock containing diaromatic, monoaromatic and non-aromatic hydrocarbons comprising: (1) continuously contacting said feedstock, in lcountercurrent relationship, with a solvent consisting essentially of a mixture of a lofwer alkanoic acid and a trialkylamine at a molar ratio of the former to the latter of from about 1:1 to about 6:1, whereby an extract phase rich in said solvent and containing a portion of the feedstock enriched in diaromatic hydrocarbons and a raflinate phase containing substantially all of the remaining portion of the feedstock and a minor amount of said solvent, are obtained; (2) subjecting the extract phase Vfrom step (l) to water extraction to form an aqueous phase containing substantially all of the water from the water extraction step and substantially all of the solvent in said extract phase and a hydrocarbon phase containing substantially all of the diaromatic hydrocarbons from said extract phase; (3) subjecting the aqueous phase from step (2) to fractional distillation to form an overhead product of substantially pure water and a bottoms product of substantially pure solvent; (4) recycling the solvent bottoms product from step (3) to solvent extraction step (1); (5) condensing the overhead water produ-ct from step (3); and (6) recycling the condensed water from step (5) to water extraction step (3 13. The method of claim -12 in which the trialkylamine is triethylamine and the lower alkanoic acid is acetic acid.

14. The method of claim 12 in which the raflinate phase from step (1) is subjected to fractional distillation to remove solvent therefrom as an overhead product and to obtain a substantially solvent free hydrocarbon bottoms product.

15. The method of claim 12 in which step (1) is conducted at atmospheric pressure and at a temperature within the range from about 20 to about 150 C.

16. A method of extracting diaromatic hydrocarbon material from a mixture comprising said diaromatic hydrocarbon material and monoaromatic hydrocarbon material which comprises: (l) contacting said mixture with a mixture of a tertiary amine and monocarboxylic acid whereby an extract phase containing hydrocarbon material -rich lin said diaromatic hydrocarbon material, and a rainate phase, are formed and (2) fractionally distilling said extract phase whereby substantially all of the tertiary amine-monocarboxylic acid mixture is removed therefrom as an overhead product and substantially all of the diaromatic hydrocarbon material is recovered therefrom as a bottoms product.

17. A method of extracting hydrocarbon material of greater aromaticity from a mixture thereof with hydrocarbon material of lesser aromaticity which comprises: (l) contacting said mixture with a solvent comprising a substantially amide-free mixture of tertiary amine and an organic acid selected from the group consisting of carboxylic and sulfonic acids containing a minor amount of water, to form an extract phase containing hydrocarbon material rich in said hydrocarbon material of greater aromaticity, and a raffinate phase.

18. The method of claim 17 in which the water is present in the solvent in an amount from about 2 to about percent by weight thereof.

19. In the method of extracting aromatic hydrocarbon material from a mixture thereof with nonaromatic hydrocarbon material which comprises contacting said mixture with a solvent for the aromatic hydrocarbon material to form an extract phase containing hydrocarbon material nich in said aromatic hydrocarbon material, and a raffinate phase, the improvement which ycomprises employing a substantially amide-free mixture `of a tertiary amine and an organic acid selected from the group consisting of carboxylic and sulfonic acids as the solvent for the aromatic hydrocarbon material.

20. A method of extracting naphthalene and alkyl naphthalenes from a feedstock containing those compounds and close-boiling mono-aromatic hydrocarbons comprising: (l) continuously contacting said feedstock, in countercurrent relationship, with a solvent consistingof a mixture of acetic acid and triethylamine at a molar ratio of the acid to the amine of from about 1:1 to about 6:1, whereby an extract phase rich in said solvent and. containing a portion of Vthe feedstock enriched in naphthalene and alkylnaphthalenes, and a rainate phase containing substantially all of the remaining portion of the feedstock and a minor amount of said solvent, are obtained', (2) subjecting the extract phase from step (1) to fractional distillation to form an overhead product of substantially pure solvent and a hydrocarbon bottoms product enriched in naphthalene and alkylnaphthalenes; (3) condensinfy the overhead solvent product from step (2); and (4) recycling the condensed solvent from step (3) to step (l).

References Cited by the Examiner UNITED STATES PATENTS 2,035,102 3/1936 Stratford et al, 208-324 2,096,725 10/1937 Andrews et al. 208-331 2,191,767 2/1940 McClure et al. 208-331 2,812,372 11/1957 Walsh et al. 260-674 2,842,484 7/1958 Fleck 208-330 3,082,270 3/1963 MicKinnis 260-674 DELBERT E. GANTZ, Primary Examiner.

MILTON STERMAN, ALPHONSO D. SULLIVAN, Examiners.

I. H. HALL, C. E. SPRESSER, Assistant Examiners.

Claims (1)

1. A METHOD OF SEPARATING HYDROCARBON MATERIAL OF GREATER AROMATICITY FROM A MIXTURE THEREOF WITH HYDROCARBON MATERIAL OF LESSER AROMATICITY WHICH COMPRISES CONTACTING SAID MIXTURE WITH A SUBSTANTIALLY AMIDE FREE SOLVENT COMPRISING A MIXTURE OF A TERTIARY AMINE AND AN ORGANIC ACID SELECTED FROM THE GROUP CONSISTING OF CARBOXYLIC AND SULFONIC ACIDS.

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