Catalysis by Acid-Regenerated Cation Exchangers Slln EY s 1-sSill AN I The P e r m u t i t Company, Birmingham. 11. J .
,kcid-regenerated cation exchangera, long used for M ater treatment and related ion exchange processes, are applied as catalysts for esterification, acetal synthesis, ester alcoholysis, acetal alcoholysis, alcohol dehydration, ester hydrolysis, and sucrose intersion. Several types of organic. cation exchangers +I ere used, and their continued re-use was demonstrated. These catalysts permit simplified procedures for reactions involving high boiling and tiscour compounds, because the catalysts can be separated from the reaction products by simple filtration. Compoundwhich polymerize in the presenre of arids hate been esterified directly by the use of these ration exchangers.
E”””
in 1941 an investigation uf the use of acid-regenerated cation exchangers as catalysts for organic reactions n-nundertaken in this laboratory. The preliminary results n - e w promising and, during the intervening years, the method ha6 becm used for an esterification process in this country. Hon.ever, the pressure of war research forced postponement of further work oii this problem. We have been led t u publish our inconiplete pt’tliminary results a t this time by the recent publication of a German technical report on t,he use of Wofatit, a cation exchange resin, as a catalyst for certain esterification, ester. interchangc., ant1 hydrolysis reactions ( 2 ) . The literature disclosed two references \vtlic11, at, f i r s t glancc, appear to report the use of ion exchangers as cat,alysts. Cheeb ham (1) catalyzed the condensation of certain resins by adding tx) the reaction mixture an acid-regenerated entioil exchange resin and a salt. I n t,his case it is quite probable that the cation exchange resin reacted with the salt,, producing an equivalent amount of mineral acid which, in turn, was the actual catalyst. Likewise, Spurlin (6) employed a met,hylated anion exchange. resin, together with sodium chloride, as a substitut,e for calcium oxide in the synthesis of pentaerythritol. Here also it is probable that the anion exchanger reacted 7vith the salt to yield wdiuni hydroxide, which was the actual rondensat,ioii catalyst. I n this work the author found that acid-regenerated cat,ioii exchangers, in the absence of any ionizable salt, may be used a i catalysts for a wide variety of reactions normally carried out with acid catalysts. Some degree of suc(’es‘:\vas achieved in the, catalysis of esterification, acetal synthezi3, ester alcolrol tal alcoholysis, alcohol dehydration, ester hydl.ci1 inversion. Several other reactions !\-ere tried without success, although the experiments were too few to definitely rule out cafion exchangers as catalysts in these cases. Cation exchangers of different,types \\-ere u ~ t buc:cessfully i catalysts. Although most of the experimental work reported in this paper was carried out with Zeo-Narb H, a sulfonated coal type of cation exchanger (9) , a few experiments were successfully carried out witE phenol-formaldehyde types of resins containing sulfonic acid groups ( 5 ) . Still, anot,her cation exchaiiye resin n-as employed in the German work ($). Apparent,ly the nature of the cation exchanger is of relatively minor importanye as long as it contains strongly acidic groups. 1 Present address, Liquid Condirioning Corporation, 423 West 126th Btreet, New York 27, N. Y.
The author also derrioiistritted that, the catalyst in rated from the reaction products by filtration and 511bsequent esterification without’ regeneration or othe tn one such series of experiment? a single portion of cation vx13 hanger was used for five successive esterifications without a])parent deterioration of the mtalyst. Fixed bed experiments were planned, but not carried out, i n such a m y that the catalyst n-as retained in a tube ~-lii(:11 wuld be maintained a t the desired reaction te~nperat~ure whik the reactants were allowed to pass through the tube. According t o Dierichs (2) such a ,process as actually employed a,hrosid on a sizable scale. .ilthough for one-time m e cation exchangers are more exl)rn,Give than the mlfuric, hydrochloric, or sulfonic acids ordinwit! employed as catalysts iu reactions of the type described, catalj l)y these granular, insoluble materials greatly simplifies iiiaii> I)roduct purification problems, especially with high 1)oiling viscous compounds. The removal of the usual acid ratat! train such conipvunds ofteii involves a trouldrsonie risuti,ali . tion and filtration procedure. Failure to remove the acid cata!:,.-t. completely generally results in excessive decomposition (1iii.iiiy t,he separation or purification of the reaction products. Thr iiw of cation exchangers as catalyst. makes it possible to remove the vatalg-sts by decantat,ion or siniple filtration without harm to the rtwrtioii products. I n some cases it Tvas even possible to dibtili tht! products directly in the prewnre of the cation exchangrt~ catalyst without apparent harm. Cse of acid-regenerated cation exchangers permitted the direct cnsterification of acid-sensitive compounds which resinify wheii contacted with the acids normally used as esterification catalyst.. Despit,e their higher initial cost, cation exchangers are competitive with the usual acid catalysts in the cases mentioned because of the special advantages they offer. They might well br. compet,itive for most acid-catalyzed reactions in view of their demonstrated continued activity during a series of success actions. The ability to be used in fixed bed operations them especially attractive for continuous processes. CATALYST PREPARATION
I r r t,he preserit, invest,igatiori the catioii exchangers ir-err usrii
usual particle Fize provided for via,ter treatment-namely . iipproximately through 10 oii 50 mesh. Minus 50 mebh material has been used for an industrial process in which the catalyst a a s su.;pended in the liquid reactants. For the fixed bed technique inentioned, larger particale size; vould be d lia~ been reported briefly ( 2 ) . Preparation of the catiori exi.Ii:~igersfor use as catalg volved conversion to the hydrogen condition by treatment witJi hulfurir acid. About 900 ml. of 0.4 A‘ siilfuric acid n-erc, u s i d t o regenerate 100 grain* of cation exchanger; t,his rotre,*pcinded to ii regenerant dosage of 1210 inilliequivalent~per liter. ’L’he catiriii exchanger was placed in a tube, and the acid solut,ioii wag allon-rti to flow through the bed of cation exchanger in accordancr wit’ti the usual ion exchange tube technique ( 8 ) . After the acid trciitment the exchanger \va:: rinsed with demineralized water until the effluent rinstl hati a ]JHl r c 4 u . r ~6~a n d 7 . sampl?s p r t 7 1 i : i r i a t ~ i i r the
1228
December, 1946
INDUSTRIAL A N D ENGINEERING CHEMISTRY
in this manner contained little, if any, residual free soluble acid. When 1 gram of air-dried cation exchanger was placed in 100 ml. of distilled water a t room temperature for 24 hours, or at 75' C. for 4 hours, the solution contained less than 1 part per million acidity to methyl orange. The cation exchanger was generally air-dried before use. The moisture content of the air-dried material was usually 15-30%. ESTERIFICATION
In this preliminary survey esterification reactions were studied more completely than any other type. In addition to experiments on establishing the catalytic activity of several different cation exchangers, esterifications were used for experiments involving acid-sensitive and high boiling compounds and for experiments establishing the fact that the catalyst could be re-used in a number of successive syntheses without regeneration or other treatment. This latter information is particularly valuable in view of the relatively high cost of cation exchangers as compared with sulfuric acid, hydrochloric acid, and the various sulfonic acids. Re-use of the cation exchanger catalysts cuts the catalyst cost ppr unit of product to a value which may not be out of line with that for the usual acid catalysts. CaTALYST RE-USE. The synthesis of n-butyl oleate was used for demonstration of the fact that the catalyst could be used for at least five successive runs without special treatment between runs. I n this series of experiments 52.8 grams (0.25 mole) of U.S.P. oleic acid and 74 grams (1.0 mole) of n-butanol were the reactants, the latter acting also in the capacity of water carrier. In the first run of this series 15 grams of Zeo-Karb H (12.4% water) were added and the mixture was refluxed; the water formed during the esterification was removed as the lower layer of the nbutanol-water azeotrope. Refluxing was continued until water evolution virtually stppped. The catalyst was removed by filtration and washed with several 20-ml. portions of n-butanol, which were then combined with the filtrate. The solvent wap removed under reduced pressure; it left an ester residue of dark straw color. Vacuum distillation of this residue yielded ~ 6 butyl oleate (saponification equivalent: theory, 338 grams pel equivalent; found, 334 grams per equivalent). The catalyst removed from this run by filtration was added to the same amounts of oleic acid and n-butanol, and the procesb was repeated. The same portion of Zeo-Karb H was then used for three additional esterifications; excellent yields were obtained during all three. There was a tendency toward a slower rate of reaction during the later cycles, although the trend was not consistent. Although the literature contains numerous cases of esterification of high boiling materials (3, T , I O , I I ) and such esterifications are used industrially with good yields, a control run carried out in the absence of catalyst failed to give any indication of ester formation after 5-hour refluxing. Possibly the experimental conditions were too mild for noncatalyzed esterification, but, in any event, the effect of the cation exchanger catalyst is clear. I t is unlikely that the catalytic effect could have resulted from a reaction between the cation exchanger and salts present in the reactants ( I ) in view of the low ash content of the latter (oleic acid, 0.003%; n-butanol, 0.0046%). In view of the results of Table I it seems possible that the cation exchangers will retain their catalytic activity for many cycles and that additional fresh catalyst will be required only to make up mechanical losses. EFFECTOF CATIONEXCHANGER TYPE. In addition to the sulfonated coal type of cation exchanger (Zeo-Karb H) used in the foregoing and most of the subsequent experiments, the catalytic activity of two different resinous cation exchangers was also demonstrated. Both of these resinous exchangers were phenolformaldehyde types of resins containing sulfonic acid groups (6). The n-butyl oleate synthesis was used in these experiments.
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Single runs were made with the same amounts of reactants a+ were used above, except that the Zeo-Karb H was replaced by the same weight (dry basis) of each of the two resinous cation exchangers in turn. Using resin I, water evolution was complete in about 4 hourb. The yield of n-butyl oleate was 99%, but the color of the product was about 2.5 times the color of that obtained with Zeo-Karb H a8 the catalyst. This enhanced color may have been caused by leaching of partially condensed material from the resin by the organic reactants. Resin I1 gave a much slower rate of reaction. After 4-hour I Pfluxing, esterification was incomplete. At this point the product contained 13.6 grams of oleic acid and 68.6 grams of n-butyl olate; it corresponded to an 81% yiel: of the ester. The color of the ester prepared with resin I1 was about the same as that obtained with Zeo-Karb H as a catalyst and distinctly better than that obtained with resin I.
CAT.4LYS'I' TABLEI. RE-USEO F ESTERIPICATION
Run Blank
A B C D E
!homKarb Time,
G. 0 15 (15) (15)
Source
(15)
D
(15)
*.
..
A B C
Hr. 6 2 2.25 3
6.5 4.5
Product, G Oleic n-Butyl acid oleate 72.8 0 0.66 84.6 81.3 1.3 1.5 84.2 1.1 83.2
0.8
81.7
Eater Yield, 70 0 99.5 95.8 99.0 97.8
96.1
The direct esterification of furACID-SENSITIVE REACTANTS. furyl alcohol has been virtually unknown because of the great sensitivity of this alcohbl t o the strongly acidic catalysts normally used for esterification. Contact with these catalysts generally results in resinification of the furfuryl alcohol. Using Zeo-Karb H as the catalyst the author directly esterified furfuryl alcohol with acetic acid without any evidence of resin formation. However, yields were small-from 10 to 21 % in the three experiments carried out. In a typical experiment 19.6 grams (0.2 mole) of furfuryl alcwhol, 24 grams (0.4 mole) of acetic acid, 74 ml. of benzene, and 20 grams of Zeo-Karb H were refluxed for 1 hour, with decanting of the lower layer of the azeotrope. At the end of this time the rate of evolution of water was extremely low. The catalyst was removed by filtration and washed with 40 ml. of benzene in several portions. The benzene was combined with the reaction products and distilled under reduced pressure. The yield (21%) was 6 grams of furfuryl acetate. No trace of resinification was apparent in the still residue. HIGH BOILINGREACTANTS.I n addition to n-butyl oleate, several other high boiling esters were prepared using Zeo-Karb H as the catalyst. Triacetin was prepared from 92 grams ( 1 mole) of glycerol, 180 grams (3 moles) of acetic acid, 100 ml. of benzene, and 5 grams of Zeo-Karb H (air-dried) by refluxing on a water bath and decanting the lower layer of the benzene-water azeotrope. The reaction was continued until the distillate, corrected for the entrained acetic acid, was equivalent to 54 grams (3 moles) of water. Because of the small amount of catalyst used, a total reflux time of 24 hours was necessary. The reaction mixture was filtered to remove the catalyst, and the benzene and a small amount of acetic acid were removed by distillation. Acid and ester equivalents of the product showed that it had the following composition: 94.3% triacetin, 4.66% glycerol, and 1.04% acetic acid. The total yield of this product was 173 grams (75%). Glycol diacetate was prepared from 62 grams (1mole) of ethylene glycol, 135 grams (2.25 moles) of acetic acid, 100 ml. of benzene, and 9 grams of Zeo-Karb H (air-dried) by refluxing on a
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INDUSTRIAL AND ENGINEERING CHEMISTRY
water bath and decanting the lower lafer of the distillate until the evolution of lower layer had practically ceased. The reaction mixture was then filtered and distilled. The fraction boiling a t 183-188 O C. was further purified by dissolving in ether and washing with sodium bicarbonate solution. Sfter removal of the solvent and drying, 70 grams of glycol diacetate were obtained (saponification equivalent: theory, 73 grams per equivalent; found, 75 grams per equivalent). The yield was 480j0. Ethyl chloroacetate was prepared in a similar manner by refluxing 69 grams (1.5 moles) of ethyl alcohol, 94.5 grams (1 mole) of chloroacetic acid, 100 ml. of benzene, and 33.7 grams of ZeoKarb H (25.9% water) and decanting the lower layer of the azeotrope as formed. After 7 hours the benzene and excess alcohol were removed by distillation, and the catalyst was removed by filtration. The undistilled residue ivas clear and had only a light yellow color. This residue had an acid number of 35.9 and an ester number of 352; this corresponded to an 87.5y0 yield of ethyl chloroacetate. ESTER ALCOHOLYSIS
Methyl acetate was prepared by gently refluxing 65 grams (0.5 mole) of amyl acetate, 64 grams (2 moles) of methanol, and 5 grams of Zeo-Karb H (air-dried) under an 8-inch packed column and taking off the methanol-methyl acetate azeotrope (boiling point, 54" C.) as formed. The reaction rate was relatively slo~v, but after 27 hours a yield of 74.5% methyl acetate was obtained. The residue in the reaction flask was identified as being mostly amyl alcohol. The slow reaction rate apparently reaulted from low catalyst dosage in terms of the available acidity. 9 parallel experiment, tn which the catalyst was an amount of sulfuric acid equivalent to the hydrogen exchange capacity of that Zeo-Karb H used in the initial ester alcoholysis experiment, gave almost exactly the same rate of reaction. ESTER HYDROLYSIS
Attempts to hydrolyze esters, including fats, using Zeo-Karb H a catalyst were less successful than the other reactions reported here. I t is believed that the difficulty resulted from the poor contact attainable in the three-phase system ester-watercation exchanger. The one experiment in which a mutual solvent was employed was partially successful. In this case 20 grams of n-butyl oleate, 100 ml. of water, 150 ml. of ethanol, and 100 grams of Zeo-Karb H were refluxed for 7 hours. The catalyst was removed by filtration and the reaction mixture distilled to remove the solvent and water. Analysis of the residue indicated a 9% yield of oleic acid. 6s
ACETAL FORMATION
Mixed glycerol formals were formed by heating 46 grams (0.5 mole) of glycerol, 15 grams (0.5 mole) of p-formaldehyde, and 6 grams of Zeo-Karb H (air-dried) in a 120-130" C. bath and taking off water as formed. Water evolution ceased after 4 hours. The &-aw-colored liquid in the reaction flask was cooled and filtered to remove the catalyst. Upon distillation 90% of the product boiled a t 190-194" C. Van Loon ( 4 ) reported 193-194" C. as the boiling point of mixed 01,a'-and a ,&glycerol formals. Di(n-butoxy)-methane was prepared by heating 74 grams (1 mole) of n-butanol, 15 grams (0.5 mole) of p-formaldehyde, and 9 grams of Zeo-Karb H (air-dried) and taking off water as formed. The product was then distilled and the cut boiling a t 177-179 C. was separated. Upon redistillation more than 90% of this cut distilled a t 179" (3.;' this corresponded t o the recorded boiling point of di(n-butoxy)-methane. This fraction weighed 76.7 grams (96% yield of the acetal). In this experiment the product was distilled directly from the reaction flaqk without separating the Zeo-Karb catalyst. There was no charring or discoloration apparent in the flask or in the product.
Vol. 38, No. 12
ACETAL ALCOHOLYSIS
Methylal was formed from 56 grams (0.35 mole) of di(7~butoxy)methane by refluxing under a column with 45 grams (1.4 mole) of methanol and 10 grams of Zeo-Karb H (air-dried) and taking off the methanol-methylal azeotrope (b.p., 42" C.) ap formed. The reaction rate was rather slow, and, when the experiment ivas shut down after 16 hours of refluxing, a total of 20 grame of the methanol-methylal azeotrope iyas obtained. On the basis of the published composition of this azeotrope (92% methylal), the yield was 69%. DEHYDRATION O F ALCOHOLS
Isobutylene mas readily produced by heating 7.4 grams (0.1 mole) of t-butanol in 50 ml. of xylene with 0.54 gram of Zeo-Karb H (air-dried). The flask was connected through a reflux condenser with a calibrated receiver inverted in a water bath. When the flask was gently Tvarmed, regular gas evolution developed without boiling. In three hours 1250 ml. of gas identified as isobutylene were evolved; this corresponded to 52% of theory. Some evidence of Zeo-Karb H-catalyzed castor oil dehydration was obtained, although the reaction temperature was so high that decomposition of the catalyst was evident. Seventy-five grams of castor oil and 28.2 grams Zeo-Karb H (47% water) were heated in a 180-200" C. bath for 3 hours, cooled, and filtered During the heating period there was some evalution of sulfur dioxide, probably as a result of partial decomposition of the cation exchanger a t this high temperature. Analysis of the product by the Wijs method indicated that the iodine number of the castor oil had been increased from 66 t o 80. SUCROSE INVERSION
Sucrose inversion was tested qualitatively a t 25 O , 50 ', and 90 'C by treating 45-ml. samples of 33% sucrose solution with 1 gram each of air-dried Zeo-Karb H, and testing with Fehling solution a t intervals. The results of this experiment are given in the following table, in which a minus sign indicates a negative test and plus signs indicate positive tests ranging from a trace reaction tm a very strongly positive reaction. 0 min.
Blank (no catalyst)
c. 900 c. 250 50' C.
--
Sucrose Inversion at Reaction Time of: 2 min. 4 min. 8 min. 10 min. 30 min.
-
-
+
-
-
-
+ ++t ++ + ++ ++ +++ ++++
LITERATURE CITED Cheetham, U. S. Patent 2,334,904 (Nov. 23, 1943). Dierichs, Report P B 866, Office of Technical Services, Dept. of Commerce, Washington, 1945. Dutt, J . Chem. SOC.,123,2714 (1923). Loon, van, Rec. trau. chem., 48, 173-90 (1929). Myers, Eastes, and Myers. IND. ENQ.CHEM., 33, 697-706 (1941) Spurlin, U. S. Patent 2,364,925 (Dec. 12, 1944). Thompson and Leuck. J . Am. Chem. SOC.,44, 2894 (1922). Tiger, J . Am. Water W o r k s Assoc., 26, 357-67 (1934). Tiger, Trans. Am. SOC.Mech. Engrs.. 60, 315-25 (1938). Van Schaack, U. S.Patent 1,697,295(Jan. 1, 1929). Zimmerli, U. S. Patent 1,708,404 (Apr. 9, 1929).
Correlating Equilibrium Constants-Correction Attention has been called to the folloq-ing mistakes in drafting of Figures 2 and 4 of this article by D. F. Othmer and A. H. Luley in the April, 1946, issue. In Figure 2, page 408, the temperature Tines should eachobe labeled 100" C. higher, and will then read 700°, 800", 900 , llOO", 1300" C. In Figure 4 the 450" C. line should be approximately inch to the right of its present location. This relocation also moves to the right the uppermost points on curves (1) and (2) so that they fall closer t o their respective lines.
