Patented Sept. 27, 1949 2,483,246

UNITED STATES PATENT OFFICE 2,483,246 SEPARATION OF PRIMARY, SECONDARY, AND TERTARY BY AWAEO TROPC DISTILLATION Josephine M. Stribley, Long Beach, Calif., as signor to Union Oil Company of California, Los Angeles, Calif., a corporation of California No Drawing. Application April 16, 1945, Serial No. 588, 17 9 Claims. (C. 202-42) 2 This invention relates to a process of azeotropic creasing molecular weight may boil within a few distillation to prepare pure alcohols from Com degrees centigrade of each other. For example, plex organic fractions which are difficult to sepa ethyl , , and tertiary butyl rate by means of ordinary fractional distillation alcohol boil in a range of 4.3° C. and similarly due to small differences in the boiling points ex normal propyl alcohol, secondary butyl alcohol isting between the components in the fraction. and tertiary boil within a range of More particularly the invention relates to a proc 4.6° C. Because of this small difference in boil ess of azeotropic distillation for separating con ing points such alcoholic mixtures are virtually plex alcohol mixtures which are difficult to sepa impossible to separate by fractional distillation. rate by means of ordinary fractional distillation 10 Complex alcoholic mixtures result in many due to small differences in the boiling points of cases in conventional preparation methods. Thus the alcohols in the mixture. in the hydration of mixed olefins, fermentation The process of separating one component from of starch, chlorination and hydrolysis of aliphatic another component of substantially the same boil hydrocarbons and the destructive distillation of ing point contained in a complex organic fraction 5 wood, methods commonly employed for the prep by azeotropic distillation is well kown. This proc aration of alcohols, complex mixtures often oc ess consists of distilling the fraction in the pres Cur, depending upon the type of operation, which ence of an extraneous substance which has a contain varying proportions of primary, second preferential affinity for one of the components ary and tertiary alcohols. contained in the fraction thus causing a disturb 20 It is a primary object of my invention to further ance in the vapor pressure equilibrium that for the progress in the art of the separation of alco merly existed in the fraction in such a manner hols by the process of azeotropic distillation which that the partial vapor pressure or fugacity of at is simpler and more efficient than ordinary chem least one component within the fraction is ical separation methods. changed sufficiently to permit its separation by 25 It is a further object of my invention to sepa controlled fractional distillation. Such an azeo rate primary, Secondary, and tertiary alcohols troping process has found widespread usage in which are difficult to separate by means of ordi the treatment of hydrocarbon fractions, alcohol nary fractional distillation due to small differ ketone mixtures, and the like for the purpose of ences existing in their boiling points and due fur separating components of one structural type 30 from components of another structural type. In ther to deviation from ideal solution properties such operation the azeotrope former employed which may be exhibited by such alcohol mixtures. has the effect of increasing the vapor pressure of It is another object of the present invention to the components of one structural type in the frac effect the separation of the primary, secondary tion, thus permitting their removal from the frac and tertiary alcohols when such alcohols are con tion as an overhead distillate together with the taminated with other organic compounds such as azeotrope former. In the present description of ketones, , and the like. my invention, the aforesaid type of distillation A more specific object of my invention is to per will hereinafter be referred to as “azeotropic dis-, form the separation of alcohols of small boiling tillation' and the overhead product or products point differences by means of azeotropic distilla consisting of the azeotrope former together with 40 tion. the component or components most effected by Other objects and advantages will occur to said azeotrope former will be hereinafter referred proceeds.those skilled in the art as the description thereof to as the “azeotropic distillate' while the residue I have discovered that it is possible by employ remaining as bottoms in the azeotropic distilla ing the azeotrope formers as hereinafter dis tion referred to as “azeotropic bottoms.' closed to improve the separation of the primary, The process of azeotropic distillation for the Secondary and tertiary alcohols. As azeotrope separation of compounds within a series of com formers for this separation I have found hydro pounds is of considerable importance. For ex carbons, organic esters and ketones to be par ample, in complex mixtures of alcohols there are, 50 ticularly effective in the order mentioned. These in many cases, alcohols within the mixture hav compounds when boiling within certain limits ing such small boiling point differences that their of the alcoholic mixture were found to form separation by conventional fractional distillation azeotropes with each of these types of alcohols, is extremely difficult. Thus, it is found that the the azeotropic mixtures boiling farther apart primary, secondary and tertiary alcohols of in 55 than the alcohols themselves. In this regard it 2,488,246 3 4. appears that the azeotropic drop, that is, the dif of normal propyl alcohol, secondary butyl alcohol, ference in the boiling points of the azeotrope and tertiary amyl alcohol, boiling in the range and of the lower boiling component or com of 9 C. to 102° C. I may employ those azeotrope ponents of a complex mixture is of greater sig formers conforming to the boiling point limita nificance than might be expected. It has been tions hereinbefore given such as for example, reported in the literature and is confirmed by toluene, xylene, 2,5-dimethylhexane, normal my investigation that azeotropes of a given boil Octane, 1 - chloropentane, 1 - bronobutane, 1 ing point spread are in many cases more readily bromopentane, normal butyl formate, normal separated by fractional distillation than are the amyl nitrite, diethyl ketone, ethyl isopropyl ke components of the same boiling point Spread. In O tone, and the like. this manner an azeotrope with a given alcohol In like manner other close boiling mixtures of boiling only slightly below an azeotrope with a primary and secondary alcohols, primary and ter second alcohol is considerably more readily Sep tiary alcohols, secondary and tertiary alcohols arated from the second azeotrope than are the or primary, secondary and tertiary alcohols may alcohols themselves. Thus I have found that s be separated by the use of azeotrope formers se by forming azeotropes with the alcohols in a lected from the aromatic hydrocarbons boiling narrow boiling mixture of primary, Secondary in the range of 20° C. below to 40° C. above the and tertiary alcohols that the ease of separation average boiling point of the mixture; the aliphatic is greatly increased although the spread in boil hydrocarbons boiling within the range of 25 C. ing point of the azeotropes thus formed is only 20 below to 50° C. above the mixture; halogenides slightly greater than the spread of boiling point and oxygen esters boiling in the range of 20' C. below to 20° C. above the average boiling point of the alcohols themselves. For example in a of the mixtures; and the ketones boiling in the mixture of ethyl alcohol, boiling point 78.5' C., range of 15° C. below to 15° C. above the mixture. isopropyl alcohol, boiling point 82.3° C., and ter 25 In employing these azeotrope formers in the tiary butyl alcohol, boiling point 82.8 C., the dif separation of a binary or ternary alcohol mixture, ference in boiling points between the primary and the amount of azeotrope former employed will be secondary alcohol is 3.8° C., between the sec a function of the desired separation. Thus in ondary and tertiary is 0.5 C., and between the a mixture of close boiling primary, secondary and primary and tertiary alcohol is 4.3° C. By dis 30 tertiary alcohols it may be desired to separate tilling these alcohols in the presence of a hydro therefrom only the primary alcohols in which carbon such as for example normal heptane form case an amount of azeotrope former must be ing an azeotrope between normal heptane and employed at least sufficient to form an azeotrope the ethyl alcohol, boiling at 70.9 C., between the with the primary alcohol. In most cases the normal heptane and the isopropyl alcohol boil 35 ratio of the alcohol to the azeotrope former in ing at 76.3° C. and between the normal heptane the ultimate azeotrope is in the range of 50% and tertiary butyl alcohol boiling at 78.0° C. the or more alcohol to less than 50% of azeotrope ease of separation of these alcohols is increased former. This very desirable ratio is particularly over and above what might be expected by the apparent in the case of the hydrocarbon azeo comparatively small increase in the spread of 40 trope formers and in some instances may be as their boiling point. This increase in the ex high as 75% alcohol to 25% azeotrope former. ample given being less than 3' C. in each case. It should be pointed out, however, that the pres We have found this effect to be con ence in such a ternary mixture of only a suff sistent throughout the range of alcoholic mix cient amount of azeotrope former to distill over tures when employing the azeotrope formers dis 45 head, the primary alcohol will not effect a tem closed. perature spread within the mixture equivalent For the purposes of the separation of these to the difference in the boiling point of the azeo alcohols I may employ as azeotrope formers the trope formed with the primary alcohol and the hydrocarbons such as the aromatic hydrocarbons boiling point of the secondary and tertiary alco boiling not more than 20° C. below or 40 C. 50 hol inasmuch as while the azeotrope former is above the average boiling point of the alcohol present in the mixture the effective boiling point mixture and the aliphatic hydrocarbons boiling Spread is equivalent only to the boiling point not more than 25° C. below or 50° C. above the Spread of the azeotropes formed with each of the average boiling point of the alcohol mixture, the alcohols in the mixture. esters of the organic and inorganic acids, which The presence of any azeotrope former in the may be divided into oxygen containing esters and 55 mixture capable of forming azeotropes with two halogenides, which esters in order to be effective or more of the alcohols present will result in a azeotrope formers must boil not more than 20 maximum boiling point difference corresponding C. below or 20° C. above the alcohol mixture and to the difference in the boiling points of the azeo the ketones boiling within the range of 15 C. 60 tropes formed between the azeotrope former and below to 15° C. above the average boiling point these alcohols until all of said azeotrope former of the alcohol mixture. Thus in the separation has been taken overhead with the primary alco of ethyl alcohol, isopropyl alcohol, and tertiary hol. However, this phenomena does not interfere butyl alcohol boiling within the range of 78° C. to with the effectiveness of my invention inasmuch 83° C. I may employ such aromatic azeotrope 65 as I am able to obtain improved separation by the formers as benzene or toluene, aliphatic hydro formation of the azeotropes as hereinbefore de carbons such as hexane, heptane, 2,5-dimethyl Scribed even in those cases where sufficient azeo hexane, 2-methylheptane, and the like; hal trope former is present to form azeotropes with ogenides, such as isobutyl chloride, chloroform, all of the alcohols in the mixture. iodoethane, isopropyl iodide, carbon tetrachlo It is within the scope of my invention to use ride, and the like; oxygen esters such as methyl 70 borate, ethyl nitrate, normal propyl formate, any manner of separation of the azeotrope former methyl acetate, methyl propionate, methyl car from the alcohol azeotrope obtained in the azeo bonate, and the like; ketones such as methyl trope distillate such as for example secondary ethyl ketone, methyl isopropyl ketone, and the azeotropic distillation, solvent extraction, ex like. Similarly in the separation of a mixture 75 tractive distillation or the like. The particular 2,488,246 5 6 method employed for separating or breaking the 92.3° C. and 95.3° C. comprising 5.9% of the orig azeotrope is a function of the individual aeo inal charge contained 8 volumes of normal propyl trope formers, of the availability of the solvent, or alcohol, 7 volumes of secondary butyl alcohol and secondary ozeotrope formers and of the equip 13 volumes of toluene. A third fraction com mentof my available invention. and is not peculiar to the process 5 prising a binary azeotrope of secondary butyl alcohol and toluene in the ratio of approximately The preferred azeotrope formers for the sepa 55% of the alcohol and 45% toluene was ob ration of these alcohols are the hydrocarbons in tained at a vapor temperature of 95.3 C. and cluding the aromatic and aliphatic hydrocarbons represented 33.2% of the original charge. The which hydrocarbons are preferred primarily be () transition fraction between this azeotrope and cause of their availability, the ease of breaking the azeotrope of tertiary amyl alcohol and tolu the azeotropes formed, by simple water wash ene represented 4.5% of the original charge and ing and subsequent distillation of the water-alco was obtained at a vapor temperature of 95.3' C. hol extract, and also of the greater azeotropic to 100 C, and comprised 27.9% of secondary spread resulting by the use of these hydrocar 5 butyl alcohol, 25.6% of tertiary amyl alcohol and bons. It is, however, to be understood that al 46.5% of toluene. The bottoms from this dis though the hydrocarbons are the preferred azeo tillation representing. 20.2% of the original trope formers for the above reasons, the esters charge were comprised of 94.5 volumes of tertiary and ketones are also effective for the separation amyl alcohol and 3 volumes of toluene. In each tion.and constitute an essential part of this inven 20 of these examples the amount of the azeotrope former employed was only slightly in excess of The following example of my process will serve that required to form azeotropes with the pri advantagesto illustrate accruing the effectiveness from its usage: thereof and the mary and secondary alcohol. As pointed out above if it were desired to only separate the pri Eacample I 25 mary alcohol from these mixtures a Smaller A mixture of 100 volumes of ethyl alcohol, boil amount of azeotrope former could be employed ing point 78.5° C., 100 volumes of isopropyl alco and conversely if desired to separate each of hol, boiling point 82.3° C., and 100 volumes of these alcohols from a complex mixture contain tertiary butyl alcohol, boiling point 82.8 C. Was ing other organic compounds, a greater amount distilled in the presence of 140 volumes of 2,5-di 30 of azeotrope former could be employed in order methylhexane, boiling point 109.0° C., in a frac to form azeotropes with each of the alcohols. The usage of these azeotrope formers and the tionating column of approximately 30 theoretical quantities employed will be a function of the mix withplates the with following an internal results: reflux ratio of 20 to 1 ture to be separated and of the azeotrope former An initial fraction was taken overhead amount employed and must be determined under each ing to 34.9% of the original charge comprising set of conditions. 90 volumes of ethyl alcohol and 63 volumes of It is to be understood that my invention is not dimethylhexane at a vapor temperature of 73.6 limited to the separation of ternary mixtures C. A transition fraction was obtained boiling be of primary, secondary and tertiary alcohol inas tween 73.6° C. and 79° C. representing 7.7% of much as a binary mixture of any two of these the original charge and comprising 10 volumes of alcohols may be separated by the same means. ethyl alcohol, 11 volumes of isopropyl alcohol and Many variations and modifications of my inven 13 volumes of dimethylhexane. A third fraction tion may occur to those skilled in the art with was obtained comprising the azeotrope of iso out departing from the spirit and scope of the propyl alcohol and dimethylhexane boiling at 79 following claims: C. and representing 29.3% of the original charge. claim: This fraction consisted of 62% isopropyl alcohol 1. A process for the treatment of a mixture of and 38% dimethylhexane. A second transition primary, secondary and tertiary alcohols boiling fraction boiling between 79° C. and 81.5 C. and in the same temperature range to separate said comprising 6.6% of the original charge was ob 50 mixture into its constituent parts which com tained containing 31% isopropyl alcohol, 34.5% prises azeotropically distilling said mixture in tertiary butyl alcohol, 34.5% dimethylhexane. the presence of a sufficient amount of an azeo The bottoms from this distillation amounted to trope former comprising an oxygen ester selected 21.5% of the original charge and comprised 90 from the group consisting of alkanol nitrates, volumes of tertiary butyl alcohol and 5 volumes 55 nitrites, borates, carbonates, formates, acetates, of dimethylhexane. and propionates, said ester having a boiling point not more than 20° C. below and not more than Eacample II 20 C. above the average boiling point of said Another azeotropic distillation was performed mixture of alcohols, Said azeotrope former hav employing toluene as the azeotrope former for 60 ing the effect of forming minimum boiling azeo the separation of normal propyl alcohol, sec tropes with the primary, secondary and tertiary ondary butyl alcohol and tertiary amyl alcohol. alcohols in the mixture in such a manner that In this distillation 100 volumes of each of these the difference in boiling points of the azeotropes alcohols boiling at 97.2° C., 99.8° C. and 101.8 thus formed is greater than the difference in C. respectively, was distilled in the presence of 65 boiling points of the alcohols whereby the pri 180 volumes of toluene, boiling point 110.7° C., mary, secondary and tertiary alcohols may be in a fractionating column of approximately 30 separated from each other. theoretical plates with an internal reflux ratio 2. A process according to claim 1 wherein the of 21 to 1. The initial fraction from this dis azetrope former is an alkanol formate. tillation representing 36.2% of the original 70 3. A process according to claim 1 wherein the charge was obtained at a vapor temperature of azeotrope former is an alkanol acetate. w 92.3° C. and was comprised of 92 volumes of nor 4. The process of claim 1 wherein the azeo mal propyl alcohol and 82 volumes of toluene. A trope former is an alkanol propionate. second or transition fraction, boiling between 5. A process for the treatment of a mixture of 75 a primary and secondary alcohols boiling in the 2,483,848 8 7 from the group consisting of alkanol nitrates, same temperature range to separate the primary nitrites, borates, carbonates, formates, acetates, alcohol from the secondary alcohol which con and propionates, said ester having a boiling point prises azeotropically distilling said mixture in not more than 20° C. below and not more than the presence of a sufficient amount of an azeo 20° C. above the average boiling point of said trope former comprising an oxygen ester Selected 5 mixture of alcohols, said azeotrope former having from the group consisting of alkanol nitrates, the effect of forming minimum boiling azeotropes nitrites, borates, carbonates, formates, acetates, with Said secondary and said tertiary alcohols and propionates, said ester having a boiling point whereby the lower boiling secondary alcohol not more than 20° C. below and not more than 20 azeotrope is obtained in the azeotropic distillate C. above the average boiling point of Said mixture and the higher boiling tertiary alcohol remains of alcohols, said azeotrope former having the in the azeotropic bottoms. effect of forming minimum boiling azetropes 8. A process according to claim 1 in which th with said primary and said Secondary alcohols mixture of alcohols comprises ethyl alcohol, iso whereby the lower boiling primary alcohol azeo propyl alcohol and tertiary butyl alcohol. trope is obtained in the azeotropic distillate and 9. A process according to claim 1 in which the the higher boiling secondary alcohol remains in mixture of alcohols comprises in-propyl alcohol, the azeotropic bottoms. isbutyl alcohol and tertiary amyl alcohol. 6. A process for the treatment of a mixture of a primary and tertiary alcohols boiling in the JOSEPHINE M. STRIBLEY. same temperature range to separate the primary 20 REFERENCES CTED alcohol from the tertiary alcohol which Com prises azeotropically distilling said mixture in the The following references are of record in the presence of a sufficient amount of an azeotrope file of this patent: former comprising an oxygen ester selected from UNITED STATES PATENTS the group consisting of alkanol nitrates, nitrites, borates, carbonates, formates, actetates, and Number Name Date propionates, said ester having a boiling point 2,392,534 Won Keussler ------Jan. 8, 1946 not more than 20 C. below and not more than OTHER REFERENCES 20° C. above the average boiling point of said Rose et al., Bureau of Standards Journal of mixture of alcohols, said azeotrope former hav ing the effect of forming minimum boiling azeo Research, vol. 21, page 183, (1938), copy in Sci. tropes with said primary and said tertiary alco Lib.Keyes, Industrial & Engineering Chem, vol. hols whereby the lower boiling primary alcohol 33, pp. 1019-1021 (1949), copy in Sci. Lib. azeotrope is obtained in the azeotropic distillate Mair et al., Bureau of Standards Journal of and the higher boiling tertiary alcohol remains 35 Research, vol. 27, pp. 39 to 63 (1941), copy in in the azeotropic bottoms. Sci. Lib. 7. A process for the treatment of a mixture of Ewell, Industrial and Engineering Chem. vol. a secondary and tertiary alcohols boiling in the 36, pp. 871-874 (Oct. 1944), copy in Sci. Lib. Same temperature range to separate the sec Horsely "Table of Azeotropes and Nonazeo ondary alcohol from the tertiary alcohol which 40 comprises azeotropically distilling said mixture tropes,' Analytical Chemistry, Fol. 19, pp. 508 in the presence of a Sufficient amount of an azeo 600 Aug. 1947 (pp. 530-531 relied on) copy in trope former comprising an oxygen ester selected Sci. Lib,