Patented Nov. 19,’ 1946 2,411,346 ‘ ,UNi-TED STATES PATENT ‘OFFICE John W. Teter and Walter J. Merwln, Chicago,Iil., ‘ assignors to Sinclair Re?ning Company, New " York, N. Y., a corporation of Maine No Drawing. Application October 6, 1943, Serial No. 505,196‘ , 3 Claims. 1 This invention ‘relates to the re?ning of nitriles and relates more particularly to an im proved method. of separating hydrocarbon im purities from nitriles of three to four carbon atoms per molecule, 1. e. propionitrile and butyro nitriles. ' ‘ These nitriles may with advantage be pre pared by the amination of ole?nic hydrocarbon (Cl. 202-42) carbon impurity from the other nitriles noted ' may be readily effected by distillation. Utilizing this peculiarity of acetonitrile and the hydrocarbon contaminant to form a readily separable azeotrope in the presence of propio nitrile and butyronitriles', the processing of our_ presentinventlon comprises adding acetonitrlle the nitrile-hydrocarbon mixture and, frac at an elevated-temperature. The crude, stabi- ' to tionally distilling the mixture to separate the lized nitrile product of such amination isusually 10 acetonitrlle-hydrocarbon azeotrope from ‘the composed primarily of a mixture of propionitrile, ‘ other nitriles. The optimum proportion of aceto iso-butyronitrile, and normalibutyronitrile and nitrlle to be added will depend primarily upon frequently contains hydrocarbon impurities. the proportion of the hydrocarbon contaminant These nitriles may be isolated by close fractional distillation of the crude product. However, the 15 Most of the hydrocarbon readily separates present. thus isolated nitriles are frequently contaminated , by hydrocarbons which distill off within the same temperature range as the nitrile and which pass . > fromthe acetonitrlle constituent of the azeotrope ' fraction as an upper layer uponvcooling the frac tion to room temperature and more may be re over with the respective nitriles from the frac moved by chilling. The lower acetoni'trile layer tionating operation in varying amounts, as an 20 will contain most, if not all, of any propionitrile azeotrope. ‘ , carried over with the azeotrope fraction and may The complete separation of such hydrocarbon be recycled with the decanted acetonitrlle to'the impurities from these nitriles by direct fractional nitrile puri?cation tower. The upper hydrocar distillation has heretofore been extremely di?i- , bon layer will usually contain about 1.5% of dis cult, if not impossible. , ,- solved acetonitrlle, at room temperature. This Our present invention provides a method acetonitrlle may be recovered by water washing, whereby substantial complete removal of these hydrocarbon, impurities from these nitriles. may be effected by direct fractional distillation. dried and returned to the nitrile purification tower. ‘ ' The invention has also been found to be ap We have discovered that the hydrocarbon con 30 plicable to the direct puri?cation of a stabilized taminant of the nitrile fractions forms an azeo mixed nitrile product resulting, for instance, trope with acetonitrile in the presence of the from the catalytic amination of propylene. This otherrespective nitriles, which azeotrope'has a product, as previously noted,_ usually contains boiling point substantially below that of these various nitriles along with hydrocarbon im other nitriles and may be separated therefrom 35 purities and sometimes contains small amounts by fractional distillation without substantial loss of acetonitrile. In accordance with this aspect of the other nitriles. ’ of my invention the hydrocarbon impurities may The boiling point of pure propionitrile, for ex be removed directly from the nitrile mixture ample, is approximately 97° _C. and that of pure prior to isolation of the respective nitriles. Usu- - acetonitrile is 82° C. The azeotrope formed by 40 illy the amount of acetonitrile present, if any, is , acetronitrile and the hydrocarbon contaminants insu?‘icient to carry o?’ completely the hydrocar has been found to boil slightly below 82° C.. at atmospheric pressure. ’ bon impurities. Accordingly it is usually neces , sary to add to the mixture acetonitrlle from an ‘ Further, theacetontrile has been found not to extraneous source. However, wev have found that form binary azeotropes with anymaterial quan 45 the proportion of acetonitrile in the stabilized product can be regulated somewhat by the choice tity of either of the other nitriles previously noted of the catalyst used and other operating condi herein, or ternary azeotropes with these nitriles tions of the amination process. By this applica and the hydrocarbon impurities, to any substan¢ tion of my invention the hydrocarbon impurities tial extent. A small amount of propionitrile may be carried over with ‘the acetonitrlle “but this v50 are distilled from the mixture with the aceto amount is so small as to have little aifect on the \ nitrile and thereafter propionitrile and the e?iciency of the operationeven if not subse-, . butyronitriles substantially free from hydrocar bon impurities may be directly obtained. quently recovered. Thus substantially complete Our present invention contemplates either' removal of the added acetontrile and the hydro 65 batch or continuous operation. In either type of 2,411,846 3 4 an equal volume of acetonitrlle, no extraneous ' operation, the acetonitrlle layer of the azeotrope ' bottoms being added. The acetonitrlle-hydro 'carbon fraction came o? at a temperature of 4 fraction is with advantage recycled to the nitrile puri?cation zone to carry off further hydrocar bons. In this way the acetonitrlle requirement 80.5-81° C., the temperature remaining substan tially constant until about 50% of the charge was distilled off and then rapidly rising to 101° C. and ?nally gradually rising to 102° C. There 'fractive index of‘ the acetonitrlle-hydrocarbon is considerably reduced. Intermediate fractions may [also be recycled for further puri?cation. In small scale operation, particularly, we have found it frequently desirable to add, in addition fraction at 20° C. was 1.3462 but toward-the end to the acetonitrlle, ‘a portion of astable higher boiling liquid to constitute a residual liquid in 10 of the cut dropped to 1.3441, approximating that of pure acetonitrile and indicating that the hy ' the still, which will not be decomposed or dis drocarbon impurities of the mixture had become tilled off at the distillation temperature of the nitriles or of the azeotrope. and which will not _ exhausted and that - more than the required amount of acetonitrlle had been added. The niinterfere with separation of the acetonitrile-hy- _ drocarbon azeotrope from the mixture. We have 15 trogen content of the iso-butyronitrile fraction foundcapronitrile, for instance, to be satisfac tory for this purpose. By-its use, danger of poly merizing and coking of the nitrile being distilled is substantially avoided and a more complete re covery of the nitrile is made possible. However, 20 was-19.3% and its refractive index was 1.3731, substantially that of pure iso-butyronitrile, indi-. cating complete removalof the hydrocarbon im purities therefrom. About 820 cc. of the pure iso butyronitrile was thus obtained, Its speci?c ' gravity was found to be 0.7712. it will be understood that the use of such ex traneous bottoms material is not essential to our ' puri?cation process. > The invention will be illustrated by the follow ing specific examples: ' - Example IV , , 25. To 100 cc. of a’ crude stabilized mixed nitrile product, resulted from the direct amination‘of propylene there, there was added 50 cc. of aceto nitrile, The ‘mixture was then subjected to frac Example I A synthetic mixture was prepared from 20 cc. tional distillation in‘ a 9.5 millimeter Stedman of pure propionitrile, having a refractive index ‘ of 1.3662 at 20° C., and 2.8 cc. of hydrocarbons 30 column. Approximately 44 volume percent of the mix- separated from hydrocarbon-contaminated pro pionitrile by chilling it. To this mixture there ture distilled off at?a temperature below 82° 0., was added 50 cc. of acetonitrile and the entire mixture was subjected to fractional‘distillation in a 9.5 millimeter Stedman column. The aceto nitrile-hydrocarbon‘ fraction distilled off-at a substantially constant temperature beginning at 78° C. and ?nally rising to about 81°C., indicat 29 volume percent of the charge was distilled off, the distillate separated into two layers upon cool ing to room temperature. The refractive index ' of the upper layer at 20° C. rose ‘from 1.412 to ing‘exhaustion of the hydrocarbon contaminant. ‘ 1.420. including 7.5% of material distilling oif below _ 75° C. Between the point where 7.5 to that where ‘ Thereafter the distillate no longer sepa The propionitrile fraction distilled off at about 40 rated upon cooling to room temperature and the refractive index of the distillate fraction dropped 96°v C. and was foundlto ‘be substantially free sharply to ‘1.351 and ?nally to 1.3450 at a tem from hydrocarbon impurities as indicated by a perature of 82° C., indicating that the hydrocar nitrogen content of 24.6% and a refractive index bon impurities, originally present in, the mixture, of 1.366‘ at 20° C., which is substantially that of the propionitrile used in the preparation of the 4: had been substantially exhausted and relatively pure acetonitrlle was being distilled off. synthetic mixture. After about 44 volume .per cent had been‘ dis Example II ‘ tilled off the temperature rose sharply to 94° C. and at 94 to 96° C. a fraction was obtained hav 4160 cc. of a normal butyronitrile'product, con-4 taminated with hydrocarbons and having a re 5'0 ing a refractive index‘ of .l.3655'and a, nitrogen content of 24.1%, indicating that it was rela fractive index at 20° C. of _ 1.3850 and a nitrogen tively pure propionitrile. Finally at 116.5° C. a content of 19.3%, was subjected to fractional dis fraction was obtained having a refractive index tillation in a two inch Stedman column with an at 20° C. of 1.3840 and containing 19.4% nitro equal volume of acetonitrile. In this distillation, 1930 cc. of capronitrile also was added toact as 5 gen, indicating that it was substantially pure normal butyronitrile. Thus, ‘by our improved an extraneous bottoms. The acetonitrlle-hy process, the respective nitriles, uncontaminated drocarbon fraction distilled off at a temperature of 80 to 81° C.,‘ the temperature ?nally rising by hydrocarbons may be obtained directly from a crude mixture of the nitriles containing hydro gradually to 82° C. for a brief period indicating exhaustion of the hydrocarbon impurity. from the 60 carbons. ' rose The hydrocarbon contaminant normally pres . sharply to 114° C. and then gradually to 118° C. ' ent in these nitrile products has been found by .1 mixture. Thereafter the temperature analysis to consist of about 12.6% paramns, 64% 40% of the charge, excluding the extraneous bot ole?ns, 20.6 naphthenes, and " 2.8% aromatics. ~ toms, was obtained andv this fraction was found 65 The identity and composition of the hydrocarbon ‘ to contain approximately 20% nitrogen and to contaminants may vary somewhat. However, we have a refractive index of 20° C. of 113840, indi have consistently found them to be substan cating itjto be substantially pure normal butyr tially completely removable from propionitrile or ' In this last mentioned temperature range over onitrile. ‘Example III . - ‘ 1390 cc. of an iso-butyronitrileproduct, con taminated with hydrocarbon and‘ having a re . fractive index ‘at 20° C. of 1.3737 and containing I 19.9% nitrogen, was subjected to fractional dis tillation in van one inch Stedman column with ‘ the butyronitriles or mixtures thereof by out im-" ’ 70 proved distillation process. ‘ ' > The invention is speci?cally illustrated in the - ' foregoing examples by ‘complete fractional dis tillations of the mixture. It will be understood. however, that the invention also contemplates 75 an operation wherein the distillation proceeds 2,411,846 5 , only to the point where the acetonitrile-hydro carbon fraction has been distilled oil’. We claim: 1. In a process for removing from nitriles of the class consisting ‘of propionitrile, normal butyronitrile, and isosbutyronitrile, hydrocarbon impurities having boiling points. such that in mix tures with said nitriles they normally distil in approximately the same temperature, range as said 6 7 said nitriles, the improvement which comprises adding acetonitrile to the hydrocarbon-contam inated nitrile and distilling oi‘! the hydrocarbon contaminant and acetonitrile as an azeotrope. 3. In a process for removing from nitriles 0'! the class consisting of propionitrile, normal butyronitrile and iso-butyronitrile, hydrocarbon impurities having boiling points such that in mix tures withis'ai'd nitriles they normally distil in nitriles, the improvement which comprises sub 10 approximately the same temperature range as jecting the hydrocarbon-contaminated nitrile said nitriles, the improvement which. comprises product to fractional distillation in admixture subjecting the hydrocarbon-contaminated nitrile with acetonitrile and distilling oil! the hydrocar product to fractional distillation in admixture‘ bon-contaminant and acetonitrile as an azeo with acetonitrile, distilling oil a fraction compris— trope. ' 0 ing acetonitrile and the hydrocarbon-contami 2. In a process for removing from nitriles of nant, cooling said traction; whereby the distillate the class consisting of propionitrile, normal is separated into an upper hydrocarbon layer and butyronitrile and iso-butyronitrile, hydrocarbon a lower acetonitrile layer and returning the lower impurities having boiling points such that in layer to the zone of fractional distillation. mixtures with said nitriles they normally distil in '20 _ > JOHN W. TETER. approximately the same temperature range as WALTER J. MERWIN.