March 26, 1957 W, T, NELSON 2,786,804 DISTILLATION SEPARATION OF ALIPHATIC AND NAPHTHENIC HYDROCARBONS EMPLOYING HALIDES Filed Sepì. 28, 1954 __ 2,786,804 United States Patent O 1C@ Patented Mar. 26, 1957

1 2 Gardner C. Ray discloses and claims the use of a dialkyl sulfate as a solvent for the separation of phosphorus 2,786,804 halides from hydrocarbons. The improved azeotropic DISTILLATION SEPARATION 0F ALIPHATIC AND distillation process of this invention provides a means NAPHTHENIC HYDROCARBONS EMPLOYING whereby naphthenic hydrocarbons of increased purity PHOSPHORUS HALIDES can be separated from parailinic hydrocarbons differing but little in boiling point from the naphthenic hydrocar William T. Nelson, Bartlesville, Okla., assignor to Phillips bons. Petroleum Company, a corporation of Delaware The drawing illustrates in ñow sheet manner an em Application September 28, 1954, Serial No. 458,979 10 bodiment of the inventionin which phosphorus trichlo ride is employed to separate 2,4-dimethylpentane from` 13 Claims. (Cl. 202-42) cyclohexane which is recovered in substantially purified form. The entrainer >of this invention comprises a phosphorus This invention relates to the separation of close-boiling 15 halide; and phosphorus tn'bromide hydrocarbons employing for the purpose a phosphorus . are specific-phosphorus halides which are now preferred: halide. In one of its aspects, the invention relates to the and phosphorus pentañuoride are separation of a mixture containing aliphatic and naph not very useful inY the separation processes of this inven thenic hydrocarbons which have closely similar boiling tion since the boiling points of these phosphorus halides points and/or which form azeotropes. In another aspect 20 are so much lower than the boiling points of the com of the invention the separationof close-boiling naphthenic ponents of the hydrocarbon mixtures which are now and paratiinic hydrocarbons, employing a phosphorus ordinarily separated. Phosphorus dichloride is very un halide, is accomplished. In a specific embodiment of stable and for'this reason is not now considered to be ai the invention the purification of cyclohexane, a product very satisfactory entrainer. Some of the physical'prop-~' of increasing and presently great importance in the chem 25 erties of phosphorus trichloride and phosphorus tribro ical arts, is accomplished employing phosphorus trichlo ì mide aregiven in Table I. ride. TABLE I` The several objects, other aspects and the advantages of the invention are apparent from this disclosure and Physical properties of phosphorus halides the claims appended thereto. 30 Phosphorus Phosphorus In the various ways of processing hydrocarbons, there Trichloride Tribromide will frequently be encountered mixtures of hydrocarbons which are difficult to separate into specific components Molecular weight ______._ 137.35 Boiling point, C ______75. 3 by ordinary fractional distillation procedures because of Boiling point, F- ______167. 5 small differences in boiling points.v For example, cyclo C _111.8 Melting point F _169. 2 hexane, which has a boiling point of 177.3° F., is not Specific gravity, 60/ 1. 585 readily separated from a mixture comprising, 2,2-dimeth Specific gravity, 15/4. ______. ylpentane, 2,4-dimethylpentane, and/or 2,2,3-trimethyl Density, lbs/gal ______._ 13. 2 butane, which have boiling points of 174.6, 176.9, and Heat of hydrolysis, kcaL/mol ______177.6° F., respectively. Commonly employed processes 40 The azeotropic distillation process of this invention is for separating such close boiling components are azeo particularly useful in separating a naphthenic hydrocar tropic distillation or extractive distillation. In these proc bon such >as cyclohexane from a parañinic hydrocarbon esses, the hydrocarbon mixture is distilled in the presence such as 2,2-dimethylpentane, 2,4-dimethylpentane, or of an added substance-which has a preferential affinity 2,2,3-trimethylbutane; however, it is also useful for Vpro for one of the hydrocarbon components in the fraction ducing dimethylcyclopentane, >n-hexane and 2,3-dimethyl and thereby changes the relative volatilities of the hy pentane in a high degree of purity from close boiling drocarbons. to such an extent that separation by frac naphthenic-parañinic fractions. Cyclohexane in a purity tional distillation is feasible. Heretofore, benzene has exceeding 95 volume percent can be separated in a distil been used as an entrainer for separating cyclohexane from lation column from a commercial cyclohexane fraction 50 a mixture of paraflinic hydrocarbons comprising 2,2-.di containing 88 volume percent cyclohexane and one or methylpentane, 2,4-dimethylpentane, and 2,2,3-trimeth more than one of the parafñnic hydrocarbons comprising ylbutane in an azeotropic distillation process; however, 2,2-dimethylpentane, 2,4-dimethylpentane, or 2,2,3-tri the use of an improved entrainer which would result in methylbutane. i a more effective separation process is desirable. 55 The separation process of this invention can also be According to the present invention, there is provided performed as an extractive distillation process to elfect an improved entrainer for effecting the separation of ali the separation of close-boiling naphthenic and parañ‘inic phatic and naphthenic hydrocarbons from paraflinic hy hydrocarbons which do not azeotrope with the phos drocarbons having small differences in boiling point by phorus halide entrainer. For example, a cyclopentane an azeotropic distillation process, said entrainer com neohexane mixture can be separated in an extractive dis prising a phosphorus halide. According to one embodi 60 tillation process inrwhich phosphorus trichloride is used ment of the present invention, a hydrocarbon mixture of as the solvent and cyclopentane is recovered as the kettle naphthenic hydrocarbons and paraiîinic hydrocarbons is product. distilled in an azeotropic distillation process using a phos The distillation process of this invention can be per phorus halide as an entrainer so that substantially pure formed as a batch process; however, it is usually carried 65 naphthenic hydrocarbon is recovered as the residual frac out as a continuous process with the phosphorus halide; tion and substantially all the other constituents of the after separation from the para?’inic hydrocarbons, being mixture, including the entrainer and some naphthenic continuously recycled to the distillation column. The hydrocarbon, distill overhead. The phosphorus halide proportion of phosphorus halide in the naphthenic-paraf is recovered and a substantially pure paratlinic hydrocar ñnic feed to the distillation column will vary considerably bon fraction is obtained from this overhead stream by a 70 and depends to some extent on the concentration or subsequent separation step such as solvent extraction. nature of the parafiinic hydrocarbons in the hydrocarbon Serial Number 477,840, ñled December 27, 1954, by mixture, the purity desired in the naphthenic fraction re 2,786,804 « " ~ - " I ‘ 3 covered, andthe design and operation of the distillation EXAMPLE III column. The choice of the Aparticular phosphorus halide A commercial cyclohexane ystream containing 88.2 employed for the distillation process will depend upon volume percent cyclohexane was subjected to azeotropic the Íboiling range of the hydrocarbon mixture to be sepa. distillation using phosphorus trichloride as the azeotrope ated.'A For example, in the azeotropic •distillation‘process former in phosphorus trichloride-hydrocarbon volume of ~the invention the boiling range of the hydrocarbon ratios of 0.6 and 1.0. The data for these azeotropic dis mixture should be Within at least 60° F., and preferably tillations as well as a comparative separation employing Within 30° F., of the boiling point of phosphorus halide. simplerdistillation aregiven in Table V. The yield of ‘ EXAMPLE I kettle product was ‘87.4, 87.3 and 84.2 volume percent A blend of 96.2 volume percent cyclohexane and 3.8 10 by simple distillation, azeotropic distillation using phos volume percent 2,4-dirnethylpentane Was subjected to phorus trichloride in a phosphorus trichloridefhydrocarbon separation processes of simple fractional distillation and volume ratio of 0.6 `and azeotropic distillation using azeotropic distillation using phosphorus trichloride as an _ phosphorus trichloride in a phosphorus trichloride-hydro azeotrope former. A comparison of the results of .these carbon volume ratio of 1.0,4 respectively. " separations is shown in Table II. l5 n TABLE V'

_ TABLE Ir Y Dìstillation of commercial cyclohexane Dìstìllation of 96.2% cyclohexane-3.8% 2,4-dìmethyl ­ pen'tane Composition of Kettle Product, Vol. Percent 20 Normal Compo Charge, ml. Overhead Composi ' Bolling sitlonpf s ' Hydro- tion of Component Point, Vol. _ 0.6 Vol 1.0 Vol. carbon Kettle F. Percent No. PC15- PC13 Azeo- Over- Product, PCl| Vol. Vol. Azeotrope Hydro- Azeo- trope head Vol. Hydro- Hydro Former carbons trope Former, Temp.;l °F. Vol. Percent carbon carbon Former Vol. Percent Cyclo ' Percent hexane Methylcyclopentane. _ 161. 3 0. 1 b 0. 0 2,2-Dimethylpentane.. 174. 6 2. 3 0. 3 Nunen-.__ 50 0 0 176. 2 21 b 97.0 2,4-Dimethy1pentane__ 176. 9 6. 5 1. 1 PCI; ____ _. 50 15 ~75 166. 1-168. 3 ° 8 ‘1 97.9 Cyclohexane ...... __ 177. 3 88.2 ß 95.6 3,3­Dimethylpentane._ 186. 9 O. 7 ...... __ 1. 2 1,1-Dimethylcyclopen lCorrected to 760 mln. 30 hBased on refractive index. 114,20 curve based on mi“ of feed, kettle tane ______190. 1 0.8 ...... __ 1. 0 product of azeotropie distillation and of 100%J cyclohexane (lit. value). 2,3-Dimethylpentane.- 193. 6 0. 9 ...... __ 0. 6 °By difference. 2~Methylhexane ..... _. 194. 1 0.5 ______0.2 dBy freezing point. EXAMPLE [[I 100.0 100.0 A blend of 90 volume percent cyclohexane and 10 h Average of two infrared analyses. volume percent 2,4-dimethylpentane was subjected to sim b Infrared analyses. n ple distillation and azeotropic distillation using phos-V ß Freezing point, 33.1 F., which corresponds to 97.6 mol percent purity. phorus trichloride as the azeotrope former. A compari~ d Freezing point, 35.6 F., which corresponds to 98.1 mol percent purity son of these data is given in Table III. In this example, A partial list of binary azeotropes of phosphorus tri the composition of the kettle product was determined chloride is given in Table VI: from the distillation data given in Table IV. 40 TABLE VI Y y p »l TABLE III List of PCls binary ozeotrûpes Dístillatíon of 90% cyclohexane-10% 2,4-dimethyl pentane Normal . Vol. Per 45 Boillng Bolling Percent Charge, ml. Overhead Composi System Point of Point of Hydro Hydro- tlonb of Hydro- Azeotrope, carbon in carbon Kettle carbon, ° F. Distillate Azeo- Over- Product, ° F. Azeotrope Hydro­ Azeo- trope head Vol. Former carbons trope Former, Te1np.,\` °F. Vol. Percent Former Vol. Percent Cyclo PCla~n~hexane ______. 155. 7 155. 5 92 Percent _ hexane 50 PClß-2,4•dimethylpentane__ _ 176. 9 165. 6 27 I’ Cla-2,2,3-trimethylbutane- _ 177. 6 166. 1 26 POh-2,3~dìmethylpentane_ _ _ . 193. 6 166. 1 1. 2 None--." 100 0 0 174. 9­­176. 4 7.8 91.3 PG13-2,2-dimethylpentane l ______174. 6 1 (165) l 35) PCI; ______100 50 78-87 166. 2­-166. 6 7.8 97.2 1 Calculated using Skohiik method for correlation ol azcotropcs. lCorrected to 760 mm. L hCalculated from data in Table IV. Reasonable variation and modiíìcation are possible within the scope of the foregoing disclosure andthe ap TABLE IV pended claims to the invention, the essence of which is Data for distillation of 90% cyclohexane-I0% 2,4-di that phosphorus halides, especially phosphorus, trichlo methylpentane ride and have been provided as 60 distillation aids in the separation by distillation of aliphatic Approximate Cumulative Vol. Cumula- Cyclohexane percent of 2,4 and naphthenic hydrocarbons, more particularly the dis tlve Vol. Concentration in Dimethylpentane tillation separation of cyclohexane from dimethylpentanes, percent of Cutß Volume Removed Hydrocar- Percent as described. Cut bon PG13 Charge I claim: No Azeo- No PG13 65 l. The distillation of a mixture of an aliphatic and a trope Azeo- (Azeo- j No Azeo close-boiling naphthenic hydrocarbon which comprises Former trope trope trope PCI; Former Former- Former distilling the mixture in the presence of at least one of Free) phosphorus trichloride and phosphorus tribromide. .2. A distillation according to claim l in which the 3. 4 3. 4 61 6 12. 5 34 70 phosphorus halide is phosphorus trichloride. 5.3 5.3 70 14 18 51 7.8 7. 8 73 20 24 73 3. The distillation of a mixture comprising a parañinic 11.8 11.8 75 b 77 34 b 82 hydrocarbon and a naphthenic hydrocarbon which corn 100. 0v 100. 0 92V 98. 1 ______prises admixing said mixture with at least one of phos e Based on refractive index. .phorus trichloride and phosphorus -tribromide and sub ‘ß' P013 Vin column was depleted during this cut.' 75 jeçting'the admixture to distillation. 2,786,804

4. A distillation according to claim 3 wherein the phos mixture which comprises admixing therewith at least one phorus halide is phosphorus trichloride. of phosphorus tríchloride and phosphorus tribromide 5. The distillation of a mixture containing cyclohexane entrainer and then subjecting the mixture thus obtained and at least one dimethylpentane which comprises adm_ix to distillation. ing with said admixture at least one of phosphorus tri« 1l. The distillation of a mixture of 2,4-dimethylpentane chloride and phosphorus tribromide and subjecting the and a close-boiling naphthenic hydrocarbon which com mixture thus obtained to distillation under conditions so prises admixing with said mixture at least one of phos as to recover cyclohexanes with increased purity as bot phorus trichloride and phosphorus tribromide and sub toms from said distillation. ` jecting the admixture thus obtained to distillation. 6. A distillation according to claim 5 wherein said 12. The distillation of a mixture containing cyclo phosphorus halide is phosphorus trichloride. hexane and a-t least one of the following hydrocarbons: 7. A distillation according to claim 6 wherein the cyclo methylcyclopentane; 2,2-dimethylpentane; lli-dimethyl hexane is present in said admixture in a preponderant pro pentane; 3,3-dimethylpentane; 1,1-dimethylcyclopentane; portion and wherein the ratio of phosphorus trichloride to 2,3-dimethylpentane; and 2-methylhexane; which corn the hydrocarbon on a volume basis is at least approxi prises admixing with said mixture at least one of phos mately 0.6. phorus trichloride and phosphorus tribromide and sub 8. The distillation of a mixture of dimethylcyclopentane jecting the admixture thus obtained to distillation to re from a close-boiling paraflìnic hydrocarbon-containing cover as bottoms a product containing a higher per mixture which comprises admixing therewith at least one centage of cyclohexane than was contained in the original of phosphorus trichloride and phosphorus tribrornide mixture. entrainer and then subjecting the mixture >thus obtained 13. A distillation according to claim l2 wherein the to distillation. said phosphorus halide is phosphorus trichloride, the 9. The distillation of a mixture of normal-hexane from cyclohexane is present in said mixture in a preponderant a close-boiling naphthenic hydrocarbon-containing mix proportion and wherein the volume ratio of phosphorus ture which comprises admixing therewith at least one of 25 trichloride to hydrocarbon is at least approximately 0.6. phosphorus trichloride and phosphorus tribromide en trainer and then subjecting the mixture thus obtained to References Cited in the tile of this patent distillation. UNITED STATES PATENTS 10. The distillation of a mixture of 2,3-dimethylpentane from a close-boiling naphthenic hydrocarbon-containing 30 2,463,919 Stribley et al. ______Mar. 8, 1949