US2475828A - Recovery of naphthene hydrocarbons - Google Patents

Description

Patented July 12, 1949 RECOVERY oF NAPHTHENE HYDRooARBoNs Adalbert Farkas and Arthur F. Stribley, Jr., Long Beach, Calif., assignors to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application March 5, 1945, Serial No. 581,162

(Cl. 26o-666) Claims.

The invention relates to a process and apparatus for the recovery of na'phthene hydrocarbons from petroleum hydrocarbon fractions. More particularly the invention contemplates preparation of pure naphthene hydrocarbons from petroleum fractions or from mixtures of isomeric naphthene hydrocarbons.

The process of preparing pure components from complex hydrocarbon fractions by isolating said components from the fraction is well known. There are many methods by which this type of separation has been accomplished as for example fractional distillation, azeotropic distillation, extractive distillation, solvent extraction, selective adsorption, acid treatment and the like. O'f these processes, fractional distillation is probably the most generally employed for the separation of naphthene hydrocarbons from petroleum mixtures. However, in a large number of cases naphthenic and paraflinic hydrocarbons as found together in petroleum mixtures, have such close boiling points that their separation by distillation becomes impracticable. Further, because of the similarity in the properties of the naphthenic and paraiflnic hydrocarbon no successful method has been found to date for effecting their separation by azeotroly; solvent extraction or the like. These latter processes depend upon variations of the physical properties of the components of a mixture in order to separate one or the other by effecting a, change in the vapor pressure equilibria or by depending upon a differential solubility of the components of the mixture in a solvent employed in solvent extraction. Very little success has resulted from experiments in the separation of the paraiiins and naphthenes by 'az'eotropy' or solvent extraction because of 'this' similarity in their properties andthe lack of azeotrope farmers or solvent to selectively change their boiling points or to separate thernby selective solubility.

It is an Object of our invention therefore t0 recover naphthenic hydrocarbons in substantially pure form from complex petroleum hydrocarbon ini'xtures in which they 'are contained.

It is a, further object of our invention to separate napnthenic and paraiiinic hydrocarbons from mixtures in 4which `they are contained. i

Another object of our invention vis directed to the Y.preparation of certain specific naphthene isomers in substantially pure form from complex hydrocarbon mixtures.

It is a further object of our invention to prepare pure paraflin hydrocarbons by removal of naphthene hydrocarbons from mixtures thereof.

Other objects and advantages of our invention will become apparent to those skilled in the art as the description thereof proceeds.

Briefly, we have found that by a suitable coinbination of fractional 4distillation and catalytic isomerization it is possible to separate naphthene hydrocarbons from petroleum fractions contain= ing as well parafn hydrocarbons. Specically the invention comprises in isolating a narrow boiling fraction containing naphthenic and paraflinic hydrocarbons, which fraction may also contain other hydrocarbons, subjecting the fraction to a catalytic isomerization to effect the isomerization of the naphthene hydrocarbons in the fraction thus bringing about a substantial change in the boiling point of the naphthene hydrocarbons and subsequently separating these isomers by ordinary fractional distillation. In this regard various isomerization mechanisms may be employed. Mixtures or fractions containing polyalkylated naphthenes for example may be separated by isolation of a specific fraction containing only one of the geometrical isomers of the polyalkylated naphthene, then subjecting this fraction to an isomerization reaction thereby converting the particular isomer to another geometrical form having a boiling point appreciably different from that of the fraction in which it is contained and subsequently fractionating the isomerized product to separate the isomers from the original fraction.

For example in the 'separation of dimethylcyclohexanes or dimethyleyclopentanes from a petroleum fraction, the fraction is subjected to a controlled distillation to isolate that portion of the fraction which contains the lower boiling or trans isomers and that portion of the fraction which contains the higher boiling or cis isomers. These narrow boiling cuts are subsequently isomerized to convert the trans isomers in the one case to the cis isomers, and the cis isomers in the other case to the trans isomers. Such an isomerization elfects a change in boiling point of the naphthenes of about 5 C. to about 8 C. and permits their 3 separation from the respective fractions by controlled distillation.

In a similar manner other isomerzation mechanisms may be utilized to effect the change in the boiling point of the naphthenic hydrocarbons in any petroleum fraction, such isomerization reactions including:

1. Change of the relative position of the alkyl group in the naphthene ring.

Change in the naphthene ring structure; that is, conversion of a C5 ring to a Cs ring, or of a Cs ring to a C5 ring and the like.

3. Isomerization of the parafnic side chain attached to the naphthene group such as conversion of a propyl group to an isopropyl group and the like.

4. Disproportionation of the alkyl groups in the side chains such as conversion of two methyl groups to one ethyl group or conversion of two ethyl groups to a methyl group and a propyl group and the like.

We have found that by effecting an isomerization reaction of one of the types described we are able to effect the separation of any naphthene from a narrow boiling hydrocarbon mixture in which it is contained. It is understood that the thermodynamic equilibrium in these cases is not complete and as a result only partial conversion to an isomeric form is possible in a one step operation. As a result it may be necessary to employ two or more stages or a continuous isomerization to effect the substantially complete removal of the naphthenic hydrocarbons by our process.

It is within the scope of our invention to effect the isomerization of the naphthenes in the presence of any desirable isomerization catalyst. We have found that such metallic catalysts as iron, copper, platinum, palladium, reduced nickel, Raney nickel, cobalt and others having hydrogenating activity; metallic oxides, such as alumina, titenia, chormie, zinc oxides, molybdenum oxide or other oxides having dehydrogenating activity; acid materials such as phosphoric acid, acid phosphates, sulfuric acid, acid sulfates, acid halides such as aluminum chloride or bromide, acid suldes such as cobalt sulfide, molybdenum sulfide and the like are effective catalysts for our process. All of these catalysts may be employed in the pure state or in combination with various activators or carriers. Generally speaking the aluminum halides will cause isomerization under the mildest condition, that is at the lowest temperatures, while the acidic isomerization catalysts, hydrogenation catalysts and the dehydrogenation catalysts will require higher temperatures for the isomerization in the order given.

When typical dehydrogenation or hydrogenation catalysts are used the temperatures to be employed will range from room temperatures up to about 300 C. depending upon the nature and activity of the catalyst, although higher temperatures may be employed if desired.

As the isomerization reaction is an equilibrium reaction in which the equilibrium concentration of the reactants is dependent on the temperature, the isomerization has to be carried out at such a temperature as to obtain favorable conversion. Thus, if the desired reaction is geometrical isomerization we have found that the trans isomers, the lower boiling isomers, are the stable form at lower temperatures and isomerization of cis isomers to the trans isomers should be carried out at the lowest practical temperature. Conversely at higher temperatures the cis-trans equilibrium is shifted towards the less stable cis isomers and thus in isomerization of a fraction rich in the trans isomer higher isomerization temperatures will favor the formation of the cis isomer.

We have found that hydrogenation or dehydrogenation catalysts will not cause appreciable dehydrogenation of the -membered ring naphthene hydrocarbons such as for example the cyclopentane homologs and lower naphthenes at the temperatures required for carrying out the isomerization. On the other hand dehydrogenation may occur when employing catalysts of these types in the isomerization of the G-membered ring naphthene hydrocarbons such as cyclohexane, its homologs and the higher naphthenes. In order to repress any undesirable dehydrogenation of these latter naphthenes on hydrogenation-dehydrogenation catalysts the isomerization is carried out at the lowest possible temperature in the presence of suicient hydrogen to shift the hydrogenation-dehydrogenation equilibrium between the naphthene homologs and aromatic homologs in favor of the naphthene homologs. Alsofwe have found that the presence of a small amount of hydrogen in carrying out the isomerization of the -membered ring naphthenes on hydrogenation or dehydrogenation catalysts has a favorable effect even though in this case its role is not necessarily the prevention of dehydrogenation.

The process of our invention may be better understood by reference to the accompanying drawing which exemplifies one modification of the separation procedure 0f our invention. For the sake of clarity the drawing will be described with reference to the separation of pure dimethylcyclopentane from a petroleum hydrocarbon fraction but we do not in any way mean to limit our invention to this separation or this method of procedure.

The majority of petroleum stocks contain dimethylcyclopentanes, the trans isomers (boiling point 90.7 C. and 91.8 C.) being present in most cases in larger proportions than are the cis isomers (boiling point 97 C. and 99.2 C.) However, these isomers are both present to a certain extent and their separation from the petroleum fractions are rendered virtually impossible by the presence of such parain hydrocarbons as 2- methylhexane, (boiling point 89.7 C.) S-methylhexane, (boiling point 91.8 C.) S-ethylpentane, (boiling point 93.3 C.) n-heptane (boiling point 98.4 C.) and 2,2,4-trimethylpentane (boiling point 99.3 C.). Although all of these parafiins may not be present in all petroleum stocks the presence therein of any one or combination of these will render the preparation of substantially pure dimethylcyclopentanes virtually impossible by ordinary fractional distillation.

In employing our process a fraction boiling between about 89 C. and about 100 C. is employed and with reference to the drawing such a fraction is withdrawn from the hydrocarbon feed tank I0 through line I I controlledbyvalve I2 andpumped by pump 3 via line I 4 into fractionating column I6. In fractionating column I6 conditions are so controlled as to give an overhead fraction boiling between the initial boiling point of the feed or about 89 C. and about 92 C. to 93 C. This fraction containing substantially all of the trans isomers of 1,2-dimethylcyclopentane and 1,3-dimethyl-v cyclopentane which were present in the hydrocarbon feed, and also such paraffin hydrocarbons as 2-methylhexane, S-methylhexane, and 3- ethylpentane is taken overhead via. linel I1 con trolled by vaslfve t8. passing therefrom via line I9' into condenser 20 from which it drawn into collecting tank 2 I. The condensate is. withdrawn from condensing tank 2l and is pumped by pump 22 into line 23 controlled by valvesy 24 and 25 and a. part thereof may be returned via line 25 to fractionating column t6 to serve as refluxl the distillation, the remaining portion being passed Vial'ne 2T through heater 28 and' line 2.9- into reactor 30. In one modication of our invention as exemplified by the drawing, reactor 3D is divided into two portions, the'l upper pore tion of which consists of an isomerization cata@ l'yst, which maybe any desired catalyst', and the lower portion contains packing or trays as de# In reactor 3B a temperature' equilibrium is maintained so that theffeed boiling between about 89 and about 93 C". is' maintained in the upper or catalysty portion of the reactor. isomer'- ization takes place therein converting the trans isomer of dimethylcyclopentane to the higherboiling cis isomers which upon formation, because of their higher boiling point, drop to the' bottom portion of the reactor and may be withdrawn theree from continuoushr through line 3|` controlled by valve 32 and pumped by pump 33 vialine 34 to Storagetank 35. By operation of reactor 39 in this mane rier` the equilibrium concentrations of the cis and trans isomers is being continually destroyed by removal of the cis isomers as they are formed and substantially complete isomerioation of the trans isomers may be had. The overhead fraction froni` reactor illicornprising substantially naphthene free hydrocarbons is withdrawn via' line 36` controlled by valve 31 passing therefrom through lin-e 38- into condenser 40 the condensate being collected in collecting tank 4f. The sub-Y stantlally naphthene free lcondensate is withdrawn from collecting tank 4i, is' pumped by pumpv 42 into line 43', a part thereof may be reA turned through valve 4'4- and line 4'5 to the cata@ lyst section of the' reactor 30' in order to further insure substantially complete isomerizati'on of the trans dimethylcyclopentanes in the fraction'. The remainder of the condensate passesvfrom` line 43 through valve 6G and lines 4T and 48 into the gasoline-storage tank 50.

Returning to fractionating column Hi a bot-, toms productV is obtained comprising that part of the initial feed boiling above about 93 C., this' product isy withdrawn from column I't by line 5l controlled byA valve 52 and is pumped by'npump 53' via line 54" into fractionating4 column titi. In fractionating column 5'64 an essentially naphthene free heart cut boiling between about 93 C. and about 96 C. or 97" C. is obtained as an overhead product and is withdrawn from the column through line 5l, controlled by valve 58 through I line 59 into condenser 6U from which the corid'ensate passes to collecting tank 6l'. The con-A densate is withdrawn from collecting tank 61 and is pumped by pump E2 into line 453' a part thereof may be returned through valve 64' and line166 to' fractionating columnv vSii to serve as reflux in the distillation, the remainder passing through valve 6-5 lines 61 and 4'8 to the gasoline storage tank' 5U..

The bottoms; fraction from the fractionating column comprising a fraction boiling in the. range of about 97 C; to about 100' C. and containingsubstantially all of cis isomers of LZ-dimethylcyclopentane and 1`,3-dimethylcyclopen tane present in the initial hydrocarbon feed, is withdrawn rr'om column `5t through line 6% con-l.' trolled by valve 69I and is by pump 1'0" through liner 'H into heater 12 passingv therefrom through line. lf3 into reactor 14. Because of the nature of the isomerization reaction in this case, reactor 14 represents the direct opposite of reactor 3'0. The isomerization of the cis isomers resulting in the formation of the lower boiling trans isomers necessitates the presence of a catalyst the lower portion of reactor 14. In this manner the unconverted cis isomers remain in contactV the catalyst in the lower portion of the reactor while the trans isomers, which are formed the reaction pass upward therefrom intoy the fractionati-ng. section of the reactor con-JV taining packing or conventional trays and are taken overhead therefrom. These reactors are constructed in this manner to prevent a further contact of the desired isomers, formed in the reaction., with. the catalyst inasmuch as such contact would lead to they undesirable isomerization ofi these isomers; back to the isomers as contained` in the feed to thev reactor and prevent the continued isomerization of the naphthene in the feed The section of the reactor not containing catalyst serves as: a, fractionating column and separates the isomers formed from other hydrocarbons which may be carried along therewith from the. catalyst section of the reactor causing said hydror'zarbonV of different boiling point to be returned to the catalyst section and permittingv the removal from ther reactor of the pure iso-S meric dim'ethylcyclopen'taries.v From reactor 'N' the trans dimethylcyclopentanes are obtained as overhead products and are withdrawn from the reactor via.- line T5, controlled by valve 1B pass'-` ing through lin'e 'l1v into condenser 18 passing therefrom to collecting tank 19; The condensate is withdrawn. from collecting tarrk 19 and pumped by pump' 80 into line 8l'- and a part thereof may be returnedby valver 82 through line 84 into the reactor 'I4 to serve as reflux in the distillation taking piace in the upper part of reactor 14. The remainder of the 'condensate passes from line 8i through valve 83v and line 85 into the storage tank 855.l The bottoms product from column 'M comprising essentially naphthene free hydrocarbon isy withdrawn from reactor 14' via line 81 controlled b-y valve 88 and is pumped by Dump 89 through line into the gasoline storage tank 50.

In this manner we are able to obtain from a narrow boiling petroleum fraction containing4 the Various isomeric. formsl of dimethylcyclopentane essentially paraflin free dimethylcyclopen tane and essentially naphthene free paraiiins. Providing; the hydrocarbon feed is a straight ruri' feed we: are this manner able to obtain notonly substantially pure` naphthenes but also sub stantiall-y pure paraflins. Such a process as de a scribed isd ecrually applicable tothe separation of other `napl'ithencs'. such as for example dimethyl-v cyclohexaries; Further, it is desired to sepa rate naphthenic hydrocarbons which do not occur in both cis and trans" forme, that is by an isomerization reaction in which -geom'ertic isomerica tion is. not involved the process' may be similar to only one stage in the above description, that is the fraction containing the naphthenic hydro'-v carbon may be fed directly to a column suchy asA column 30 or Mr as described above in which the:

catalyst occupies one half of the reactor and thev frfactionatingl zone. occupies the other half, the placements of these two being dependent solely on the type of isomer formed from the naphthener i'r the hydrocarbon feed. Thus, if a lower boilingA isomer is formedv the reaction the; catalyst, section should bein the lower part of the reactor and the fractionating section in the upper and conversely if the isomer is higher boiling the catalyst should Ibe in the upper section of the reactor and the packing in the lower section. As pointed out above the catalyst placement is made with the idea in mind of preventing any subsequent contact between the catalyst and the isomerized naphthene and further to prevent the establishment of an equilibrium therein and the consequent cessation of the isomerization reaction.

The process as described is only illustrative of our invention inasmuch as many procedural modifcations are possible and will occur to those skilled in the art. For example a single catalytic reactor may be employed through which the entire hydrocarbon feed is passed to effect the partial isomerization of the naphthene contained in the fraction which reactor may be followed by a distillation column to effect the removal of the isomerized product and a portion of the unisomerized product may be recycled to the reactor.

Examples of other isomerization reactions may further clarify the process of our invention. In addition to the geometric isomerization as described above we may bring about a change in the relative positions of the alkyl group. Thus, if a hydrocarbon mixture containing 1,4-dimethylcyclohexane trans (boiling point 119.3 C.) methylheptanes (boiling point 117.6 to 118.9 C.) 3-ethyl hexane, (boiling point 118.5 C.) 3,4- dimethylhexane, (boiling point 117.7 C.) is isomerized in the presence of aluminum chloride at 50 C. to 100 C. the 1,4-dimethylcyclohexane is partially converted to trans- 1,3 and 1,2-dimethylcyclohexane, (boiling point 120.7 C. to 123.4 C.) and to 1,4-, 1,3- and 1,2-dimethylcyclohexane-cis (boiling point 124.3 C. to 129.8 C.). These isomerized dimethylcyclohexanes are readily separable by distillation from the parain hydrocarbons which are essentially unchanged.

Further it is possible to effect the naphtheneparamn separation by the isomerization of the napthene hydrocarbon in such a manner as to change the ring configuration thereof. For example if a mixture of cyclohexane (boiling point 80.7 C.) and 2,4-dimethylpentane, (boiling point 80.5 C.) is treated with aluminum chloride and anhydrous hydrogen chloride at the boiling point of the mixture the cyclohexane will isomerize to methylcyclopentane (boiling point 71.8 C.) and may be readily separated from the mixture by distillation. In such a case as this wherein a lower boiling naphthenic isomer is formed in the isomerization it is necessary in a continuous process, as pointed out above, to place the catalyst in the lower portion of the reactor and the packing or trays in the upper portion of the reactor in order to minimize any continued contact between the catalyst and the naphthene isomer as it is formed, the lower boiling isomer passing upward in the column into the distillation section. The description of reactor '14 of the accompanying drawing exemplies this type of operation. Cyclohexane may be converted to methylcyclopentane by numerous other catalysts as for example molybdenum sulfide-cobalt sulde at 500 C. Other naphthenic hydrocarbons are susceptible to what may be classified as ring isomerization and We do not Wish to be limited by the example above. For example methylcyclohexane may be isomerized to dimethylcyclopentane over molybdenum sulde-cobalt sulfide catalyst at 500 C. to effect a reduction of the boiling point and permit the separation thereof from parans boiling in the neighborhood of C. by distillation. In operations of this type it is apparent that those isomerzations in which the number of carbon atoms in the ring structure are increased will result in a higher boiling naphthene isomer, and conversely those in which the number of nuclear carbon atoms is decreased will result in an isomer of lower boiling point. It is therefore necessary to control the various operational factors such as catalyst placement, type of distillation and the like accordingly.

Another type of isomerization which may be utilized according to the process of our invention involves the disproportionation of the alkyl groups in the side chains of naphthenic hydrocarbons. Thus ethylcyclopentane (boiling point 103.4 C.) may be separated from 2,2-dimethylhexane (boiling point 107 C.) by subjecting the mixture to the isomerizing action of aluminum chloride or other catalysts whereby the ethylcyclopentane is isomerized to dimethylcyclopentanes (boiling point 91 C. to 92 C.) which dimethylcyclopentanes may be readily separated from the dimethylhexane by ordinary distillation. In similar manner propylcyclohexane (boiling point 155 C.) may be isomerized over aluminum chloride at C. to 145 C. to yield 1,3,5-trimethylcyclohexane (boiling point C.) representing a drop in boiling point of 15 degrees permitting ready separation from paran hydrocarbons in the original mixture by distillation.

In many cases it may be desired to recover a specic naphthene hydrocarbon or hydrocarbon group. If such be the case there are different methods of operation by which the desired end may be accomplished. The specific naphthene or group of naphthenes may be obtained by selecting a petroleum fraction containing a naphthene different from the desired naphthene which may readily be isomerized to such naphthene and separated as such from the petroleum fraction. Thus for example if substantially pure dimethylcyclopentanes are the desired product We may isolate a narrow boiling hydrocarbon fraction rich in methylcyclohexane, subject such fraction to an isomerzation converting the methylcyclohexane to dimethylcyclopentanes which are subsequently recovered from the mixture by distillation. In a similar manner other pure naphthenes may be obtained such as for example methylcyclopentane by the isomerization of cyclohexane rich fraction, 1,2-dimethylcyclohexane from the isomerization of a hydrocarbon mixture rich in ethylcyclohexane, dlmethylcyclohexanes from propylcyclopentane and the like.

For another method of operation to obtain specific naphthene hydrocarbons, we may utilize a fraction containing the naphthene and by isomerizing this naphthene convert it to an isomer of suflciently different boiling point to permit its separation from the original fraction by distillation, and subsequently subject the separated isomer to a second isomerization at conditions which favor the reverse equilibrium to convert it back to the naphthene sought. For example in order to obtain pure trans-dimethylcyclopentanes we may employ a hydrocarbon fraction rich in trans-dimethylcyclopentanes, subject this fraction to an isomerization wherein the trans isomers are isomerized to the cis forms, separating the cis-dimethylcyclopentanes and subjecting these to an isomerization to effect a return to the trans form. In such an instance the isomerizing conditions are chosen in each case to favor the equilibrium in regards the isomeric form sought. Such an operation may be conveniently carried out continuously ,by a method similar to that described above. Such a secondary or reverse isomerization may be employed to obtain specic naphthenes whenever the equilibrium concentration of the isomerc forms may be suitably adjusted by changes in temperature, pressure, contact time or the like.

Having described our invention and realizing that many modifications thereof may occur to those skilled in the art without departing from the underlying principles set forth for the recovery of pure naphthenic hydrocarbons from complex hydrocarbon mixtures, we claim:

1. A process for separating substantially pure dialkylated naphthenes from a hydrocarbon mixture containing dialkylated naphthenes and paramn hydrocarbons boiling in the same temperature range as the dialkylated naphthenes which mixture is diiiicult to separate by means of ordinary distillation because of the closeness of the boiling points of the components in said mixture, the process comprising fractionating the mixture to obtain a narrow boiling fraction containing essentially only the cis type of geometric isomer of said dialkylated naphthenic hydrocarbon together with parain hydrocarbons and a second narrow boiling fraction containing essentially only the trans type of geometric isomer of said dialkylated naphthenic hydrocarbon together with paraiiin hydrocarbons, isomerizing one of said narrow boiling fractions to convert the naphthenes contained therein from said geometric isomer to the other geometric isomer thereby effecting a change in the boiling point of said naphthenes, and distilling the isomerized product to separate the geometric isomer formed in the isomerization from the paraiin hydrocarbons in the mixture.

2. A process according to claim 1 in which said dialkylated naphthenes are dimethylcyclopentanes.

3. A process according to claim 1 in which said dialkylated naphthenes are dimethylcyclohexanes.

4. A process for separating substantially pure dimethylcyclopentanes from a hydrocarbon mixture containing dimethylcyclopentanes and parailin hydrocarbons boiling in the same temperature range as said dimethylcyclopentanes, which dimethylcyclopentanes are difcult to separate by means of -ordinary fractional distillation because of the closeness of the boiling points of said dimethylcyclopentanes with the boiling point of parain hydrocarbons contained in said mixture which comprises fractionating said mixture to obtain a narrow boiling fraction rich in the trans isomers of dimethylcyclopentane and the second fraction rich in the cis isomers of the dimethylcyclopentane, isomerizing each of these fractions separately to effect the iscmerization of the trans isomers in the one fraction to the ciis-omers and the cis isomers in the other fraction to the trans isomers thereby effecting a change in the boiling points of the dimethylcyclopentanes in each fraction, and separately distilling the products from the isomerizations to remove therefrom the isomerized dimethylcyclopentanes.

5. A process for separating substantially pure dimethylcyclohexanes from a hydrocarbon mixture containing dimethylcyclohexanes and paraiiin hydrocarbons boiling in the same temperature range as said dimethylcyclohexanes, which dimethylcyclohexanes are difficult to separate by means of ordinary fractional distillation because of the closeness of the boiling points of said dimethylcyclohexanes with the boiling point of parafn hydrocarbons contained in said mixture which comprises fractionating said mixture to obtain a narrow boiling fraction rich in the trans isomers of dimethylcyclohexane and the second fraction rich in the cis isomers of the dimethylcyclohexane, isomerizing each of these fractions separately to effect the isomerization of the trans isomers in the one fraction to the cis isomers and the cis isomers in t-he other fraction to the trans isomers thereby effecting a change in the boiling points of the dimethylcyclohexanes in each fraction, and separately distilling the products from the isomerizations to remove therefrom the isomerized dimethylcyclohexanes.

ADALBERT FARKAS. ARTHUR F. STRIBLEY, J R.

REFERENCES CITED The follorwing referenlces are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Egloi et al.: Isomerization of Pure Hydrocarbons, A. C. S., Monograph Series, No. 88 (1942), Reinhold Pub. Co. (N. Y. City), pages 91 to 107.

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