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March 19, 1963 A, c, McK'INNlS 3,082,270 SOLVENT EXTRACTION METHOD Filed July 31, 1961 woA/Aeo/wl 7765 ‘£245; 440/144 77:5 401/5005 A4455 £XTEACT 1 SOLVE/VT ,4QUEOU5 A4455 ART INVENTOR. :3 44¢ K/A/M/S BY )JLN'W United States Patent 3,082,270 nee Patented Mar. 19, 1963 1 3,082,270 Art C. McKinnis, North Long Beach, Calif, assignor'to SOLVENT EXTRACTION METHOD Union Oil Company of California, Los Angeles, Cairn, a corporation of California Filed July 31, 1961, Ser. No. 128,244 20 Claims. (Cl. 260-674) This invention relates to. a solvent extraction method 2 pl-oying a particular type of amine-acid solvent by means of which componential segregation ‘of aromatics is read ily 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 nonaro matics of like boiling ranges. There are many such mix tures, exemplary of which are those petroleum fractions known to contain monoaromatics such as polyalkyl ben for separating hydrocarbons of greater aromaticity from 10 zenes boiling within the range from about 400° to about hydrocarbons of lesser aromaticity in admixture there 450° F. as well as nonaromatics such as parat?ns and with. More speci?cally, the invention relates to such a method in which mixtures of ammonia and/ or amines and thiocyanic and/ or cyanic acid are employed as selective naphthenes of the same boiling range. solvents for the hydrocarbons of greater aromaticity. The invention has particular utility 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 sired separation and the solvent extraction method of this invention furnishes a simple and practical solution benzenes or the like. There are a number of known solvent extraction pro cedures 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, furfural, di ethylene glycol, nitriles, organic bases, etc. Such solvent Here again, as in the case of the like ‘boiling aromatics, fractional distilla tion fails as a practical means of accomplishing the de to the problem. I ' It is thus a principal object ofrthis invention to provide an improved solvent extraction method by means of which 20 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 nonar'omatic com pounds in admixture therewith. A more speci?c object of the invention is to provide extraction procedures have been attempted with varying an economical solvent extraction method by means of degrees of success on mixtures of aromatic and nonaro which diaromatic compounds are readily separable from like boiling mon-oaromatic compounds in admixture there with. ‘Other objects and advantages of the invention will matic hydrocarbons for purposes of extracting all of the aromatics therefrom, but heretofore it has not been pos sible to bring about any kind of effective fractional sep~ matic components of differing degrees of aromaticity can be economically and effectively fractionated. There are many hydrocarbon mixtures, as, for example, be apparent from the complete description thereof which follows. The degrees of aromaticity of organic compounds of roughly equivalent boiling points depend upon the num ber of aromatic rings (benzene nuclei) in their respective molecules, the higher the number of such rings the greater thearomaticity of a given compound. Thus diaromatic compounds, those having two aromatic rings per mole various petroleum processing fractions, which contain substantial proportions of diaromatic hydrocarbons such ticity'than the monoaromatic compounds which have as naphthalene and its alkyl and polyalkyl derivatives, molecular structures containing only one such ring. It makes little difference, insofar as degree of aromaticity aration of the aromatic components from each other by solvent extraction means. 1 have now discovered an improved method of solvent extraction for use on hydrocarbon mixtures whereby aro— and also monoaromatic hydrocarbons which can be mono cule, are considered to have a greater degree of aroma is concerned, whether polyarom-atic compounds have alkyl t'etralins, alkyl indanes, alkyl indenes and the like 45 individual or condensed ring systems. Thus, diaromatics of individual ring systems such as hiphenyl, diphenyl which boil within the same boiling range as the diaro cyclic, such as alkyl benzenes, and/or bicyclic, such as methane, etc., are considered to have roughly the same matics. The boiling range of the diaromatics in hydro degree of aromaticity as the dinuclear aromatics (di carbon mixtures of this ‘type is typically from about 400° aromatics having condensed ring systems), such as naph~ to about 450° F. A speci?c example of such a hydro carbon mixture is the heavy reformate fraction obtained 50 thalene, etc., at least insofar as this invention is con cerned. in the catalytic reforming of naphthenes. This fraction The method of this invention is not limited to the normally boils above about 400° F. and contains from treatment of organic mixtures in which the aromatics about 40 to about 80 percent by weight naphthalene and methyl naphthalenes, the remainder being largely made up of monoaromatic compounds such as alkyl benzenes, tetralins, indanes, indenes, and the like, or of such mono aromatics plus a signi?cant proportion of nonaromatics such as naphthenes, para?ins, etc. Many other fractions of highest possible degree of aromaticity are diaromatics, and mixtures containing higher polyaromatic compounds are also amenable to separation by said method. For example, it is within the scope of the invention to sub~ ject hydrocarbon mixtures containing triaromatic com pounds, such as anthracene and phenanthrene, and di~ conversion operations, such as catalytic cracking, thermal 60 aromatic compounds of roughly the same boiling range to solvent extraction as taught herein, to separate the cracking, catalytic reforming, catalytic cycle oil, etc. oper triaromatics from the diaromatics. ations, also ?t the above described category. The method of this invention is not limited in appli Hydrocarbon mixtures such as those described are di?i cation to the treatment of organic mixtures having clear cult of separation into their componential fractions, i.e., ly obvious differences in the degree of aromaticity among fractions containing separate or like components Within its various components. There are many organic mix the ‘diaromatic, monoaromatic, etc., categories by conven tures containing aromatic components not sharply dis tional fractionation means. For one thing, the like boil tinguishable from others present in degree of aromaticity ing point ranges of the diaromatics and monoaromatics and the treatment of such “grey area” mixtures, either for normally found ‘in such mixtures precludes the possibility of getting effective separation between these two classes of 70 the separation of the aromatics in toto or for further obtained in the practice of petroleum fractionating and materials by fractional distillation techniques. The pres separation of said aromatics into fractions of varying ent invention comprises a method of solvent extraction em degrees of aromaticity, lies within the purview of my in 3,082,270 4 3 vention. It is more difficult to separate such “grey area” aromatics into distinct fractions than it is to separate more sharply “black” and “white" aromatics, such as diaro~ matics and monoaromatics of roughly the same boiling range, but such separations are possible and hence within the scope of my invention. Among the above noted peratures 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 tempera ture in either direction are undesirable in solvent ex “grey area” aromatic compounds of intermediate de traction operations. grees of aromaticity may be mentioned those substituted aromatics containing functional groups of such nature the operating temperature below a certain level are not However, the effects of lowering necessarily all bad since such lowering frequently re sults in an increase of solvent selectivity. Furthermore, not all of the effects of an excessive elevation of tem the aromaticity of their unsubstituted counterparts. It perature are necessarily deleterious, since such elevation will be clear that a wide variety of feed mixtures can normally brings about a shortening of the time required be resolved by the method taught herein. for phase separation as well as an improvement in the Attention is now directed to the accompanying draw ing which schematically illustrates a preferred process for 15 solvent power of selective solvents. It will be apparent from the above-noted considerations that the selection of the practice of my invention. ‘an optimum temperature range for solvent extraction pur Referring speci?cally to the drawing, there is shown a poses depends on many factors and entails a balancing continuous countercurrent solvent extraction process em of the advantages and disadvantages inherent in various ploying a solvent of the type described more fully here after, such as for example, triethylammonium thiocyanate, 20 temperature adjustments, taking into consideration the as to have a signi?cant effect of one sort or another on the reaction product of stoichiometric quantities of tri ethylamine and thiocyanic acid. While it is possible to characteristics of the components present in the system, prepare triethylammonium thiocyanate timum operating pressures for solvent extraction opera tions is subject to the consideration of other factors of the operating pressures, etc. So too, the selection of op 25 an in?uencing nature. Thus operating pressures can vary by simply mixing equivalent molar amounts of triethyl amine and thiocyanic acid, my preferred way of pre paring that material is to mix equimolar proportions of triethylamine and NH4SCN and then fractionate off the NH;;: My reasons for preferring ammonium thiocyanate to from subatmospheric, through atmospheric, to superat mospheric ranges depending upon the peculiarities of the given system. Returning now to the discussion of the drawing, I have 30 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 from about 20° to about thiocyanic acid as a starting material for the prepara 150° C.,, the preferred temperature range being from tion of my amine-thiocyanic acid solvent mixtures are the 35 about 30° to about 60° C. cheapness, greater availability and relative stability of the former by comparison with the latter. The yield and purity of the ra?inate and extract prod ucts, identi?ed infra, from column 1 are, as previously A feed stream containing both aromatic and non indicated, partially dependent upon the number of ex aromatic hydrocarbons of like boiling ranges such as traction stages in said column. It is, as a general rule, a heavy reformate petroleum fraction containing diaro 40 true that the greater the number of stages in a solvent matics (naphthalene, alkylated naphthalenes, etc.,); extraction column, the greater will be the yield and monoarornatics (alkyl benzenes, alkyl tetralins, alkyl purity of a product of the column. However, as those indanes, etc.,); and nonaromatics (naphthenes and paraf skilled in the solvent extraction art will appreciate, the ?ns) is continuously fed into the bottom of a counter selection of an optimum number of stages is a matter of current solvent extraction column 1 through line 3 as economics since as the number is increased a point of shown. There simultaneously, solvent is recycled into 45 diminishing returns is reached beyond which the relatively the top of column 1 through line 5, from a source here small improvement per additional stage makes it imprac inafter disclosed. Solvent extraction column 1 is so tical to proceed. I have found that solvent extraction designed and the conditions of operation so ?xed and column 1 is operatively effective for use in processes of controlled as to result in the extraction of substantially the contemplated type when it has from about 2 to about all of the aromatic components from the feedstock as it 15, and preferably from 7 to 11, stages. circulates upward in countercurrent contact with the sol Referring again to the drawing, an extract phase is vent in said column. withdrawn from the bottom of solvent extraction column As those skilled in the art realized, there are gen 1 through line 7 and a raf?nate phase is withdrawn from erally four important things to be considered in the 55 the top of the column through line 9 as shown. When practice of countercurrent solvent extraction, namely: column 1 is designed and operated according to the pre (1) the operating temperature; (2) the operating pres ferred precepts and conditions set forth above, aromatic sures; (3) the number of extraction stages; and (4) the hydrocarbon yields of from about 85 to about 99 percent solvent/feed ratio. Careful selection and control of op by weight and purities of from about 90 to about 99 per erating conditions in the above four areas is important in 60 cent by weight are attainable in the extract phase. The order to achieve optimum phase separation, selectivity, extract phase contains most of the solvent passing through and solvent power, all of which have a bearing on prod column 1, in addition to that portion of the feedstock uct yield and purity. which the solvent has extracted in its travel within the The operating temperature level is important in solvent column. The ra?’inate phase from column 1, under pre extraction operations since in the usual case too low a ferred conditions of operation, typically contains between 65 temperature results in an inordinately high feed vis about 90 and about 99.5 percent, by weight, nonaromatic cosity which in turn results in unnecessarily long phase separation periods. Additionally, too low a temperature hydrocarbons, the remainder being solvent. other hand, excessively high temperatures are undesirable since they usually have the effect of reducing solvent through valve 11, with valve 13 closed, without further selectivity and tend to make the extract and ra?inate ent extraction column 17 through line 15, as shown on the drawing, for removal of traces of the amine-acid solvent The ra?inate phase from column 1, as the drawing is undesirable in that it normally has a detrimental ef shows, is subject to an alternate choice of disposition. fect on the solvent power of selective solvents. On the 70 Thus, the raf?nate can be withdrawn from the process phases mutually miscible. Where solvent extraction is treatment, or it can be circulated to countercurrent solv carried out at atmospheric pressure, the operating tem 76 picked up in column 1, using water as ‘the solvent. Ob 3,082,270 6 5 wherein the amine-acid solvent ‘(being water soluble, as pointed out supra) is selectively extracted therefrom With water. The extraction. of the solvent from the extract to remove amine-acid solvent therefrom is possible be phase is not limited to the use of water as the extracting cause the solvent, as will be emphasized later, is quite agent and any other material which is a relatively stable soluble in water. liquid under the conditions-of service, and in which the For ease of illustration, and simplicity of explanation, amine-acid solvent is substantially miscible, may be em the process shown on the drawing and described here is ployed for the purpose if desired. It is, of course, ob depicted as one yielding a recovery of all feedstock aro vious that the chosen material must also be substantially matics in one pass through column 1. However, it is to be understood that, as explained above, my method of 10 immiscible with the hydrocarbon, or hydrocarbons, in the extract phase. solvent extraction is equally applicable to the separation The products from column 25 are an aqueous solution of aromatics into fractions dilfering as to degree of aro of the amine-acid solvent (aqueous phase) which is with maticity, such as for example the recovery of diaromatics drawn from the bottom of the column through line 27, from a feedstock comprising both diaromatic and mono aromatic components. To accomplish this type of sepa 15 and the hydrocarbon product consisting of the aromatic fraction of the feedstock in substantially pure form, which ration it is only necessary to assure the proper number is withdrawn through line 29 to storage or other dis of stages in column 1 and the proper operating conditions position. ' to accomplish the purpose. The determination of opti The aqueous solution of solvent from column 25 is mum plate plurality and operating conditions to achieve passed through line127 ‘to a distillation column 33 in this, or any other result Within the‘ scope of my inven which the water is separated from the solvent, the water tion, is a relatively simple matter to those skilled in the passing off through line 31 as an overhead and the solvent solvent extraction art, in the light of the teachings here Ibeing withdrawn through line 5 as a ‘bottoms product. in, requiring at most a minimum amount of routine ex viously, valve 13 is kept open and valve 11 closed in the latter event. Water extraction of the column 1 ra?inate perimentation. Primarily, the achievement of maximum separating et?cacy among compounds of varying degrees of aro maticity is a matter of having a su?iciently high number of extraction stages in column 1. In this respect it is pointed out that more stages are required for such selec The water overhead from column 33 is condensed in condenser 35 and then recirculated to solvent extraction column 25 through line 37 as shown on the‘ drawing. The solvent bottoms product from column 33 is recycled through line 5 to solvent extraction column '1.‘ Column 25 is shown schematically as a countercurrent tive extraction, all other things being equal, than for 30 solvent extraction column and the preferred technique for practicing the subject process is by continuous operation mere separation of a mixture into aromatic and nonaro matic fractions. of that unit as well as all other units in the process. How ever, it is possible to replace column 25 by batch ap paratus ‘for solvent extraction if desired. It is also pos from a mixture containing both aromatics of differing aromaticities and nonaromatics, the subject process can 35 sible to modify the process in other ways obvious to those skilled in the art without substantial alteration by relatively simple modi?cation be made to accommo of its purpose or accomplishments. One such modi?ca date this requirement. One Way of accomplishing this is If it is desired to obtain two or more aromatic fractions to add one or more additional solvent extraction columns tion is, for example, the incorporation of puri?cation techniques for the treatment of one or more of the prod similar to column 1 to the process, with appropriate lines, ?ttings, and other equipment, where needed, to handle 40 ucts of separation from solvent extraction column 25 as well as distillation column 33'. Makeup amine-acid the various streams in the system. For example, if it is solvent is introduced into the system through line 39‘ and desired to separate a diaromatic fraction and a monoaro valve 441 as needed. ' ‘ ' matic fraction from a feedstock containing diaromatics, There are a number of things to consider in the selec monoaromatics and nonaromatics, this can be done by in corporating an additional solvent extraction column in 45 tion of solvents for solvent extraction purposes, among which are: (1) the stability of the candidate material series with column 1; using column 1 to extract the .diaromatics from the feedstock; and utilizing the addi tional column to separate the monoaromatics from the nonaromatics in the raffinate phase from column 1. While the instant method is preferably practiced as a continuous or ?ow process, and that aspect of operation is stressed in this description, it functions equally well as a batch process provided column 1 is considered to repre sent suitable apparatus for batch extraction, countercur rent batch extraction, or the like, purposes. To continue with the detailed description of the process shown on the drawing, in the event the raflinate phase from column 1 is routed to solvent extraction 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 a 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 towards 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 column 17, it is there countercurrently contacted with water which is introduced into said column through line 60 that mixtures of ammonia and/or amines and cyanic and/ or thiocyanic acids varying widely as to component 19. The water extracts substantially all of the solvent proportions satisfy all of the requirements inherent in contaminant from the ra?inate phase which is then With the above points of consideration to qualify as excellent drawn through line 21 to storage, or other disposition. solvents for the selective extraction of aromatic hydro~ The aqueous phase from the extraction operation is with carbons from organic mixtures of the type previously dis drawn from column 17 through line 23 as shown and closed. I have further found that, in addition to having either discarded, recycled for reuse in column 17, or other an extraordinary selectivity for aromatic hydrocarbons in wise disposed of. The amount of amine-acid solvent general, such amine-acid mixtures have relatively greater picked up by the water passing through column 17 is so selectivities for aromatics of relatively greater degrees of slight as to rule out the practicality, in most cases, of aromaticity, thus making the separation of aromatics by any attempt to recover amine-acid solvent from said degree, as discussed in detail supra, possible by solvent aqueous phase. Any other liquid having properties suit able for the purpose may be substituted for the Water em extraction means. ployed in column 17, if desired. The extract phase from solvent extraction column 1 is passed into solvent extraction column 25, through line '7, for use in my invention must, of necessity, be liquid under the service conditions of my solvent extraction method. The amine-acid mixtures suitable as selective solvents 3,082,270 8 N-methylpiperidine N-methylmorpholine N,N'-dimethylpiperazine The term “amine-acid,” without further modi?cation, is used throughout this speci?cation to refer to the unique solvent mixtures of this invention. It is, of course, to be understood that the amine-acid ingredient combinations thereby contemplated are those combinations within the scope of this invention as de?ned and exempli?ed here Pyridine N-ethylpiperidine Methylethylisobutylamine Triethylenediamine in. Triphenylarnine The amines of most e?ectiveness as solvent ingredients Dimethylaniline Methyldiphenylamine l-methylpyrrole 1,3-dimethylpyrrole l-dimethylamino-B-butene for purposes of this invention are those amines having from about 1 to about 15, and preferably from about 1 to about 9, molecular carbon atoms. The amines may be wholly or predominantly of aromatic, aliphatic or heteroeyclic 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 15 otherwise suitable, having substituent groups of a sub stantially neutral character with respect to other com~ ponents in the system can be employed for my purpose if desired. The amine-acid solvents of this invention are not 20 amides but merely, in effect, mixtures of ammonia and/ or amines and acids. Such mixtures are sometimes referred to as salts. However, the term “salts” has been, to a large extent, avoided herein to diminish the possibility of misunderstanding as to its meaning. Although as in 25 dicated above, my class of amine-acid solvents is ex— elusive of amides, this poses no particular problem in the selection of suitable amines as solvent ingredients a-Pieoline 3 ,5 -lutidine 2,4,6-collidine ,e-Picoline Quinoline Quinaldine Isoquinoline Conyrine Conine Tropane Tripropylamine N-benzylideneaniline N- l-ethylbutylidine-p-toluidine Examples of secondary amines which can be employed as solvent ingredients for purposes of this invention are given below. Here again, as in the ease of the tertiary since, insofar as I am aware, no amines form amides with the acids of this invention. Any mixture of eyanie acid, 30 amines, the list is exemplary only and not exhaustive. thiocyanic acid or a combination of those acids, and ammonia, any amine, combination of amines, or am monia-amine combination which is liquid under the serv ice conditions of my solvent extraction method, is a use ful solvent for purposes of, and within the scope of, this 35 Diethylamine Ethyl-sec-butylamine Di-isopropylamine Dimethylamine invention. Primary, secondary and tertiary amines, and Diethanolamine mixtures thereof, are all suitable amine ingredients for my solvent mixtures. Although, for the reason given above, I have de emphasized use of the term “salts” in connection with my 40 amine-acid solvents. I have found that a stoichiometric proportion of ammonia or amine to acid, which results in a high salt content solvent, is optimum for purposes of this invention. I attribute the superiority of stoiehi ometrically balanced solvent mixtures to the fact that Acetylisobutylamine Piperizine Diphenylamine Monomethylaniline Dibenzylamine Benzylaniline Butylaniline Methylaniline cyanic and thioeyanic acids are‘substantially less stable The following list is, as in the case of the tertiary and the secondary amines, exemplary only. Z-aminopropane 2-amino-Z-methylpropane Ethylarnine Methylarnine Aniline tively stable by comparison with eyanic or thiocyanic acid). A list of tertiary amines useful as solvent ingredients 60 for purposes of this invention appears below. It should be emphasized that this list is merely representative, and not lirnitative of the class of tertiary amines suitable for my purpose. - Diethyloctylamine Diethylpropylamine N,N,N’,N’-tetramethylethylenediamine N-ethylpyrrolidine N-methylpyrrolidine Examples of primary amines suitable as solvent in~ gredients for purposes of this invention are listed below. than their ammonium and substituted ammonium salts. While it is preferable not to have large excesses of cyanic or thiocyanic acid present in my solvent mixtures, because of the tendency of those acids toward instability, it is nevertheless within the scope of this invention to employ amine2acid molar ratios other than the stoiehi ometric ratio (1:1). In this connection, I have deter~ mined that the preferred range of molar ratios is from about 0.5 :1 to about 2:1, although ratios outside of this range are also operative, particularly in those cases in which the amine is present in excess (amines being rela Triethylamine Trimethylamine Methyldibutylamine Dimethylbutylamine Ethylmethylpropylamine Ethyldipropylamine Morpholine n-Propylamine n-Butylamine Sec-butylamine Tert-butylamine Isobutylamine n-Amylamine n-Hexylamine Ethylenediamine Tetramethylenediamine Pentamethylenediamine Ethanolamine Diethylenetriamine Putreseine Cadaverine Aniline 70 Benzylamine ?-Phenylethylamine p-Bromoanaline p-Aminophenyl p-Phenylencdiamine As already indicated, my novel amine-acid solvents are 3,082,270 10 limited acid-wise to the inclusion of cyanic or thiocyanic acid vor mixtures of those two acids. One method of preparing the solvents is to simply mix the appropriate amine and acid starting materials by stirring or other means. However, for previously indicated reasons, a preferred method, in many cases, of preparing my sol vents is to react a suitable acid derivative with the chosen that the incorporation of a dialkylamine, such as diethyl amine, thereinto, results in an increase in product purity, with no sacri?ce of recovery, when such mixtures are employed for the d-i?icult extraction of naphthalene from hydrocarbon mixtures containing, in major proportion, monoaromatics rand nonaromatics. The use of a dialkyl amine in conjunction with a trialkylarnine in the manner A suitable acid derivative for such purpose, is suggested has an additional advantage in that it normally one which reacts with the amine in such fashion as to results in a solvent ‘which is liquid at room temperature, amine. yield an amine-acid product of substantially the same type 10 whereas without the dialkylamine the solvent would ordi narily have a melting point higher than room temperature (e.'g., where the ingredients are thiocyanic acid and tri et-hylamine, the melting point of the solvent, in its pre ferred formulation, is about 30° C.). ‘An important ‘factor in arriving at optimum conditions excellent acid derivatives for the purpose since the am 15 of operation in solvent extraction processes is the rapid monia by-product is readily eliminated as a gas and does ity with which the r-af?nate phase separates from the ex not contaminate the solvent. tract phase under various circumstances. Relatively Another reason for the excellence of the ammonium rapid separation of these two bases takes place when using salts of cyanic and thiocyanic acid as starting materials for the preparation of my amine-acid solvent mixtures 20 the novel amine-acid solvents of my invention at room as that resulting from a straight mixture of the same amine with the acid corresponding to the derivative. Thus, ammonium salts of cyanic and thiocyanic acids (ammonium cyanate and ammonium thiocyanate) are temperature. At higher temperatures, phase separation is the fact that those salts are themselves solvents within is faster and the solvent power of the amine-acid solvent the scope of this invention. Thus, excesses of ammonium is greater, but temperature increases have-an adverse ef cyanate or ammonium thiocyanate present in my amine fect on selectivity of the solvent towards aromatics. The .acid solvents are not present as contaminants but as sol ,vent of an ammonia-acid rather than an amine-acid type. 25 previously recommended temperature ranges for the prac tice of my invention (about 20° to about 150° C., prefer Solvent mixtures such as the instant one, as Well as mix ably from about 30° to‘about 60° C.) were determined by tures of any of the nitrogen base compounds (ammonia taking the aforesaid factors into consideration. and amines) and acids disclosed herein, are all within The solvents of this invention are relatively non-toxic the scope of my invention. As already made clear, my amine-acid solvent must 30 at standard, as well as operating, conditions. Also, these solvents are miscible with water, as previously indicated, be liquid under the service conditions of my solvent ex~ traction method. This does not mean that the amine-acid thus making it an easy matter to recover them from ex tract phases, \as well as raf?nate phases, by water extrac solvent must be liquid at standard temperature and pres tion, for recycling or other purposes. In addition, the sure conditions although such is frequently the case. It is within the scope of my invention to employ amine and/ 35 solvents of this invention are unreactive with the feed stock components throughout the temperature range to ,or acid (or acid salt) starting materials which are solid, or form solid or semisolid mixtures, at standard con which they are subjected in service. . The solvent extraction process of my invention can be ditions, so long as the resulting amine~acid mixtures are carried out in various ways, the most common mode of liquid under the operating conditions contemplated. . In the preparation of solvent mixtures according to 40 operation comprising the use of a spray, packed, or bub ble plate tower wherein the hydrocarbon feed mixture is this invention, if theingredients are all liquid at room temperature simple stirring is usually suf?cient to effect rapid homogenity of the mix. Where not all of the in~ gredients are liquid at the temperature of preparation it might be necessary to use more rigorous means of achiev ing 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. As ‘emphasized previously, .the amine-acid mixtures of contacted by the stream of amine-acid solvent ?owing, 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 without colorable modi?cation of those sol vent properties necessary to the proper functioning of the process. For example, where'it is proposed to subject .a mixture of hydrocarbons of varying degrees of aromat icity to solvent extraction according to my method, and this invention exhibit extraordinary powers of selectivity 50 the hydrocarbons are all extremely soluble in the chosen solvent, the incorporation of a minor amount of water into toward aromatics when used as solvents in this invention. the solvent, prior to or during the extraction operation, In addition to being highly selective toward aromatic hy to assure the rapid and distinct formation of two liquid drocarbons, the amine-acid solvents of this invention also phases is within the spirit and scope of my invention. exhibit high solvent power, i.e., relatively small quan tities of solvent dissolve relatively large quantities of aro 55 When water is added for such purpose, the proportion used should normally not exceed about 20% of the weight matics. In striking illustration of this, I have found that of the solvent ‘and preferably fall within the range from a stoichiometrically proportioned mixture of triethyl about 2 to about 5% of the solvent weight. amine and thiocyanic acid exhibits a solvent power with If desired, my process cm be carried out by distilling respect to u-methylnaphtalene, an aromatic hydrocarbon, in the presence of decalin, of 23.8 by comparison with a 60 the hydrocarbon \feed mixture in the presence of an amine-acid solvent, of the type disclosed herein, as an ex solvent power of 8.0, under the same circumstances, for tractive distillation process. In the practice of extractive 'phenol, a known solvent for aromatic hydrocarbons. distillation,.the feed mixture to be separated is distilled These solvent power values were arrived at by multiply in the presence of a selective solvent which has a substan ing the difference in a-methylnaphthalene concentration tial-1y lower volatility than any of the components of said between the solvent~free extract and the feedstock times vmixture, as a result of which an overhead enriched in 'the percent a-methylnaphthalene recovery in the extract that portion of the feed mixture not selectively extracted times 10—2. The trialkylamines are particularly suitable is removed, leaving behind a bottoms product which com for use as amine ingredients in my novel solvents. prises a solution of solvent and selectively extracted ma , While the amine~acid mixtures of this invention, and 70 terial. particularly the stoichiometrically balanced trialkylamine thiocyanic or cyanic acid mixtures, are highly selective for aromatics (as will be illustrated in an example to .follow, showing a recovery of 97%, of 93% naphthalene, from a 40% naphthalene feedstock), I have discovered It is pointed out, however, that a number of my amine-acid solvents tend toward instability at elevated temperatures and therefore when considering the desir ability of a particular solvent for an extractive distilla tion operation attention must be paid to the nature of the 75 material to be separated in order to avoid those tempera 3,082,270 12 11 Example IV tur'es potentially destructive of the solvent. One possible way of avoiding this di?iculty, where the separation of high boiling mixtures is contemplated, is the use of re duced pressures during the operation. 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 m1. of methylnaphthalene vwith 16 m1. of triethyl amine-thiocyanic acid solvent (approximately 68% thio cyanic acid) at a weight ratio of solvent to hydrocarbon feed mixture of approximately 1.821. The solvent-hy drocarbon mixture is moderately agitated and a solvent rich extract phase is separated therefrom. The solvent rich extract phase is washed with pentane, Still another way in which my process can be carried out is to employ an antisolvent 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 ant-isolvents for purposes of this invention are para?ins such as pentane, heptane, octane, isooctane, and the like; water; etc. In order to more fully illustrate the invention the fol~ as an antisolvent, to selectively extract dodecane which lowing examples are set forth. These examples are to be is dissolved therein as a contaminant. As a result of considered as illustrative only and not limitative of the 15 the washing operation, two phases (a pentane rich phase scope of the invention. containing dodecane and a solvent rich phase containing methylnaphthalene) are formed. The two phases are Example I separated ‘and the solvent rich phase is subjected to water extraction treatment to remove the triethylamine-thio~ cyanic acid mixture as a solvent in the method of my 20 cyanic acid solvent therefrom and recover the methyl invention. naphthalene as an extract product. This example illustrates the use of a triethylaminethio A 100 gram hydrocarbon feed sample comprising Example V paramns, naphthenes, alkyl indanes, alkyl indenes, alkyl tetralins, and the like, in the amount of 67%, and methyl~ This example illustrates the use of a tributylamine naphthalene in the amount of 33% was treated with 67 25 cyanic acid mixture as a solvent in the method of my in g. of a triethylamine-thiocyanic ‘acid mixture, in which vention. the acid and amine components were present in stoichi A 100 g. hydrocarbon feed sample comprising paraf?ns, ometric proportions, having a density of 0.998, in a one naphthenes, alkyl indanes, alkyl indenes, and alkyl tetra stage solvent extraction process. After separation of the lins, in the amount of 67% by weight, and methylnaph phases it was found that the hydrocarbon portion of the 30 thalene in the amount of 33% by Weight is treated with extract phase contained approximately 45% of the methyl 100 ‘grams of a stoichiometrically proportioned tributyl naphthalene in the feed sample and had a purity of ap amine-cyanic acid mixture in a one stage solvent extrac The solvent was most effective as tion operation. The solvent-hydrocarbon feed mixture is evidenced by the yield and purity of the methylnaphtha moderately agitated and a solvent rich extract phase is 35 sepanated therefrom. lene extract product. The solvent rich extract phase is subjected ‘to a water Example II ‘extraction treatment whereby its tributylamine-cyanic acid This example serves to illustrate the e?Fect of increasing solvent portion is selectively extracted by the water. The the number of operating stages and the ratio of solvent to remaining hydrocarbon portion is enriched in methyl proximately 90%. feed in my solvent extraction method. 40 A hydrocarbon dealkylation product containing 40% naphthalene. Example VI naphthalene and 60% alkylated monoaromatics and non~ aromatics such as naphthenes, alkyl indanes, alkyl in This example illustrates the use of an aniline-thiocyanic denes, alkyl tetralins, and the like, was subjected to acid mixture as a solvent in the method of my invention. solvent extraction treatment according to the method of 45 A 100 g. hydrocarbon feed sample comprising paral?ns, this invention utilizing the same solvent as that employed naphthenes, alkyl indenes, alkyl indanes and alkyl tetralins in Example I. Five theoretical operating stages were in the amount of 67 % by weight, and methylnaphthalene in the amount of 33 % by weight, is treated with 100 grams employed and the solventfeed ratio was 1.25. An ‘analysis of the extract phase showed a recovery of of a stoichiometrically proportioned mixture of aniline naphthalene of approximately 97% and a purity of ap and thiocyanic acid in a one stage solvent extraction proximately 93%. A comparison of these results with operation. The solvent-hydrocarbon feed mixture is those of Example I, in which the weight ratio of solvent moderately agitated and a solvent rich extract phase is separated therefrom. to feed was little more than half that here, and in which only one stage, rather than ?ve, was employed, sharply The extract phase from the solvent extraction opera points up the bene?cial effects on recovery and purity, 55 tion is subjected to a water extraction treatment whereby its aniline-thiocyanic acid solvent portion is selectively and particularly the ‘former, of an increase in solvent:feed ratio and number of solvent extraction stages. extracted by the water. The remaining hydrocarbon Example III 60 This example illustrates the use of a triethylamine cyanic acid mixture as a solvent in the method of my in. vention. A 100 g. hydrocarbon feed sample comprising para?’ins, naphthenes, alkyl indanes, alkyl indenes, and alkyl tetralins, in the amount of 67% ‘by weight, and methyl naphthalene in the amount of 33% by weight, is treated with 100 grams of a stoichiometrically proportioned tri portion is enriched in methylnaphthalene. Example VII This example illustrates the use of a Z-aminopropane cyanic acid mixture as a solvent in the method of my in vention. A 100 g. hydrocarbon feed sample comprising para?ins, naphthenes, alkyl indanes, alkyl indenes, and alkyl tetra lins, in the amount of 67% by weight, and methyl naph thalene in the amount of 33% by weight is treated with 100 grams of a Z-amino-propane-cyanic acid mixture (in which the acid and amine ingredients are present in ethylamine-cyanic acid mixture in a l-stage solvent ex traction process. 70 stoichiometric proportions) in a one stage solvent extrac The extract phase from the solvent extraction process tion operation. The solvent-hydrocarbon feed mixture is subjected to a water extraction treatment whereby its is moderately agitated and a solvent rich extract phase is triethylamiue-cyanic acid solvent portion is selectively extracted by the water. The remaining hydrocarbon por tion of the extract phase is enriched in methylnaphthalene. separated therefrom. The extract phase from the solvent extraction opera tion is subjected to a Water extraction treatment whereby 3,082,276 13 7 its Z-amino-propane-cyanic acid solvent portion is selec tively extracted by the water. The remaining hydrocar bon portion is enriched in methylnaphthalene. It will be apparent that many modi?cations of my proc ess can be practiced simply by varying the permissible solvent components, feed materials, and operating tech niques within the limits taught herein. All percentage data in the above examples and elsewhere in this disclo _ . . 14 . t , tract phase by extracting the amine-‘acid solvent from that phase with water. 6. A method of extracting hydrocarbon material of greater aromaticity from a mixture thereof with hydro carbon material of lesser aromaticity which comprises: (1) contacting said mixture-with a substantially amide free mixture of a material selected from the group con sisting of ammonia and amines and an acid material se sure are on a weight basis unless otherwise speci?ed. The present invention is not limited to the use of water ex lected from the group consisting of thiocyanic acid, cyanic acid and mixtures of thiocyanic and cyanic acids, to form traction for recovery of the hydrocarbon portion of the extract phase, and any other means known to those skilled in the art to accomplish this purpose may be employed if desired. For example, it is possible, in some cases at least, to recover the hydrocarbon portion of the extract phase by distillation techniques. The success of such tech niques depends in many instances on the use of reduced pressures to avoid destruction of the solvent, if it is of a type substantially unstable at elevated temperatures. an extract phase containing hydrocarbon material rich in said hydrocarbon material of greater aromaticity and a minor amount of said hydrocarbon material of lesser aromaticity, and a raf?nate phase; (2) treating the ex tract phase with an antisolvent to extract said hydrocarbon material of lesser aromaticity therefrom; and (3) recov ering, substantially all of the hydrocarbon material of greater aromaticity from the extract phase. 7. The method of extracting diaromatic hydrocarbons The preferred solvent: hydrocarbon feedstock weight 20 from a feedstock containing diaromatic, monoaromatic and non-aromatic hydrocarbons comprising: (1) continu ously contacting said feedstock, in countercurrent relation ratios for purposes of this invention are from about 0.25 :1 to about 3.0:1. However, my process is not limited to this range of ratios and the ratio may vary within wide limits. within the scope of the invention. ship, with a solvent consisting essentially of a mixture of thiocyanic acid and a trialkylamine at a molar ratio of The present process is particularly well adapted to pre 25 the former to the latter of from about 120.5 to about 1:2, paring feedstocks for dealkylation processes. Thus, a heavy reformate fraction containing alkyl naphthalenes and non-naphthalenic ,materialspcan be treated in accord ance with the invention to obtain an alkylnaphthalene concentrate which is thereafter dealkylated to form naph thalene by any of the conventional catalytic or thermal dealkylation processes. I claim: whereby an extract phase rich in said solvent and con taining a portion of the feedstock enriched in diaromatic hydrocarbons and a ra?inate phase containing substantial ly 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 water extraction to form an aqueous phase containing water and substantially all of the solvent in said extract phase, and a hydrocarbon phase 1. A method of separating hydrocarbon material of greater aromaticity from a mixture thereof with hydro containing substantially all of the diaromatic hydrocarbons from said extract phase; (3) subjecting the aqueous phase carbon material of lesser aromaticity which comprises from step (2) to fractional distillation to form an over head product of substantially pure Water and a bottoms contacting said mixture with a substantially amide-free mixture of a material selected from the group consisting of ammonia and amines and an acid material selected product of substantially pure solvent; ( 4) recycling the sol vent bottoms product from step (3) to solvent extraction from the group consisting of thiocyanic acid, cyanic acid 40 step (1); (5) condensing the overhead water product from step (3); and (6) recycling the condensed water from step and mixtures of thiocyanic and cyanic acids. (5) to water extraction step (3). 2. A method of separating hydrocarbon material of 8. The method of claim 7 in which the trialkylamine greater aromaticity from a mixture thereof with hydro is triethylamine. carbon material of lesser aromaticity but roughly the same boiling point which comprises subjecting said mixture to 45 9. The method of claim 7 in which the acid and amine extractive distillation in the presence of a substantially amide-free mixture of a material selected from the group ingredients of the solvent are present in stoichiometric pro portions. 10. The method of claim 7 in which the ra?inate phase from step 1 is subjected to water extraction treatment to selected from the group consisting of thiocyanic acid, remove substantially all of the solvent therefrom and to cyanic acid and mixtures of thiocyanic and cyanic acids. 3. A method of extracting hydrocarbon material of 50 obtain a substantially solvent free ra?inate hydrocarbon consisting of ammonia and amines and an acid material greater aromaticity from a mixture thereof with hydro carbon material of lesser aromaticity which comprises con product. ' 11. The method of claim 7 in which step 1 is conducted ‘at atmospheric pressure and at a temperature Within the tacting said mixture With a solvent comprising a substan range from about 20° to about 150° C. tially amide-free mixture of a material selected from the 12. The method of claim 7 in which the ratio of solvent group consisting of ammonia and amines and an acid 55 to hydrocarbon feedstock in step 1 is from about 0.25 to about 3.0 parts by weight of the former to about 1 part by weight of the latter. acids, to form an extract phase containing hydrocarbon 13. The method of extracting diaromatic hydrocarbon material rich in said hydrocarbon material of greater 60 material from a mixture comprising said diaromatic hy aromaticity, and a rai?nate phase. drocarbon material and monoaromatic hydrocarbon ma 4. A method of extracting hydrocarbon material of greater aromaticity from a mixture thereof with hydro terial which comprises: (1) contacting said mixture with a mixture of va tertiary amine and thiocyanic acid, whereby carbon material of lesser aromaticity which comprises: (1) an extract phase containing hydrocarbon material rich in contacting said mixture with a substantially amide-free mixture of a material selected from the group consisting 65 said diaromatic hydrocarbon material and a ra?inate phase, are formed and (2) subjecting said extract phase of ammonia and amines and an acid material selected from the group consisting of thiocyanic acid, cyanic acid to water extraction treatment whereby substantially all and mixtures of thiocyanic and cyanic acids, to form an of the amine-acid mixture is removed therefrom leaving extract phase containing hydrocarbon material rich in substantially all of the diaromatic hydrocarbon material as said hydrocarbon material of greater aromaticity, and a 70 the extract product of the process. material selected from the group consisting of thiocyanic acid, cyanic acid and mixtures of thiocyanic and cyanic raf?nate phase and (2) recovering substantially all of the 14. A method of extracting hydrocarbon material of greater aromaticity from a mixture thereof with hydro tract phase. carbon material of lesser aromaticity which comprises: 5. The method of claim 4 in which the hydrocarbon ( 1) contacting said mixture with a solvent comprising a material of greater aromaticity is recovered from the ex 75 substantially amide-free mixture of a material selected hydrocarbon material of greater aromaticity from said ex 3,082,270 16 15 for the aromatic hydrocarbon material is a stoichiomet from the group consisting of ammonia and amines and an acid material selected from the group consisting of thio rically proportioned mixture of triethylamine and thio cyanic acid, cyanic acid and mixtures of thiocyanic and cyanic acid. 20. A method of extracting naphthalene and alkyl cyanic acids, and containing a minor amount of water, to form an extract phase containing hydrocarbon material rich in said hydrocarbon material of greater aromaticity naphthalenes from a feedstock containing these compounds and close-boiling mono-aromatic hydrocarbons compris ing: (1) continuously contacting said feedstock, in coun and a raf?nate phase. 15. The method of claim 14 in Which the water is pres tercurrent relationship, with a solvent consisting of a stoichiometrically proportioned mixture of thiocyanic acid by weight thereof. 10 and triethylamine, whereby an extract phase rich in said solvent and containing a portion of the feedstock enriched 16. In the method of extracting aromatic hydrocarbon in naphthalene and alkylnaphthalenes, and a ra?inate material from a mixture thereof with nonaromatic hydro phase containing susbtantially all of the remaining por carbon material which comprises contacting said mixture ent in the solvent in an amount from about 2 to about 5% with a solvent for the aromatic hydrocarbon material to tion of the feedstock and a minor amount of said solvent, form an extract phase containing hydrocarbon material rich in said aromatic hydrocarbon material, and a ra?inate phase; the improvement which comprises employing a sub to water extraction to form an aqueous phase containing are obtained; (2) subjecting the extract phase from step 1 water and substantially all of the solvent in said extract phase, and a hydrocarbon phase containing substantially all of the naphthalene and alkylnaphthalenes from said material selected from the group consisting of thiocyanic 20 extract phase; (3) subjecting the aqueous phase from step 2 to fractional distillation to form an overhead prod acid, cyanic acid and mixtures of thiocyanic and cyanic stantially amide-free mixture of -a material selected from the group consisting of ammonia and amines and an acid uct of substantially pure water and a bottoms product of acids, as the solvent for the aromatic hydrocarbon material. 17. The improvement of claim 16 in which the solvent for the aromatic hydrocarbon material is a mixture of a. tertiary amine and thiocyanic acid. 18. The improvement of claim 16 in which the solvent for the aromatic hydrocarbon material is a mixture of a 25 substantially pure solvent; (4) recycling the solvent bot toms product from step 3 to solvent extraction step 1; (5) condensing the overhead water product from step 3; and (6) recycling the condensed water from step 5 to water ex traction step 3. trialkylamine and thiocyanic acid. 19. The improvement of claim 16 in which the solvent No references cited.