Behavior of Ion Exchange Resins in Solvents Other Than Water SWELLING AND EXCHANGE CHARACTERISTICS GEORGE W. BODAMER AND ROBERT KUNIN Rohm & Haas Co., Philadelphia, Pa.
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HE use of ion exchange resins in such applications as solvent purification and catalysis of organic reactions has attracted increasing attention in the past few years. Wider use of resins in these fields has perhaps not been made because of a lack of general information on the behavior of such materials in nonaqueous media. In order to obtain a better understanding of such systems, two important properties-swelling and exchange capacity-of typical resinous exchangers were determined in a variety of solvents. PREPARATION O F MATERIALS
The resins were converted to the desired acid, base, or salt form by passing a large excess of the suitable reagent in aqueous solution through a bed of the resin contained in a column. Ten per cent hydrochloric acid was used to convert cation exchange resins to the hydrogen form and anion exchangers t o the chloride form, and 4% sodium hydroxide was used to convert cation exchangers to the sodium form and anion exchangers t o the hydroxide form. The resin bed was then rinsed with deionized water until one drop of 0.1 N base or acid, whichever was appropriate, added to 25 ml. of effluent sufficed to cause a color change with the appropriate indicator-phenolphthalein or methyl orange. Cation exchange resins in the sodium form were dried for 8 hours a t 100" C . All other resins were spread in thin layers and air-dried for 24 to 48 hours a t room temperature (average 21" C.) and 78% relative humidity.
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The resins used were as follows: Amberlite IR-120 = a sulfonated, cross-linked polystyrene resin; a strong acid type Amberlite IR-112 = analogous to Amberlite IR-120, but less highly cross-linked-i.e. more porous Amberlite IR-105 = a sulfonated phenol-formaldehyde resin; a strong acid type Amberlite IRC-50 = a cross-linked polymer containing carboxylic groups; a weak acid type Porous Amberlite IRC-50 = an analog of Amberlite IRC-50, but less highly cross-linked Amberlite IRA-400 = a cross-linked polystyrene polymer containing strongly basic quaternary ammonium groups Amberlite XE-75 = a more porous analog of Amberlite IRA400 Amberlite IRA-410 = a slightly less basic resin of the Amberlite IRA-400 type Amberlite IR-4B = a weakly basic phenol-formaldehyde resin containing primary and secondary amino groups Amberlite IR-45 = a weakly basic, cross-linked polystyrene resin Amberlite XE-76 = A less highly cross-linked analog of Amberlite IR-45 The suffixes appended to the names of the resins have the following significance: H = the free acid, or hydrogen, form of cation exchangers such as Amberlite IR-120 or Amberlite IRC-50 Na = the sodium salt form of cation exchangers OH = the free base, or hydroxide, form of anion exchangers such as Amberlite IRA-400 or Amberlite IR-4B C1 = the chloride form of anion exchangers In conducting such a study a decision had to be made as to the manner of preconditioning the resins. If absolutely anhydrous
conditions were to be investigated, they could probably have been attained by vacuum-drying the resins. On the other hand, data so obtained would be useful only to those who were able to treat resins in a similar manner, and this might be a difficult process on a large scale. It was therefore decided to oven-dry a t atmospheric pressure those resins that would not decompose under such conditions-in this work, the sodium form of cation exchange resins. All other resins were simply air-dried. Resins treated in the latter manner are free flowing and appear dry. However, it has been shown (1,8 ) and confirmed by the authors that such resins may vary widely in moisture content depending on the ambient temperature and humidity. Thus Amberlite IR-120 Na contains about 18% moisture a t a relative humidity of 50% and about 32% moisture a t 90%. It can thus correctly be argued that much of the work described here was not done in a strictly moisture-free system. Nevertheless, it was believed that the drying procedure employed was more likely to be used in actual large-scale practice than a specialized technique such as vacuumdrying. Because of different moisture contents of different resins, rigorous comparisons of swelling of different resins in the same solvent are not possible on the basis of the work described here. However, comparisons of swelling of the same resin in different solvents should be valid. ' As long as there is some moisture present it is believed that the equilibrium exchange capacities of the different resins found in this study are reasonably comparable. While the transfer of ions from one liquid phase to another is probably an important rate controlling step in many of the exchanges examined, the absolute quantity of water present should not greatly affect the final results in static tests. Swelling data have been reproduced, within the expected accuracy of the test, at intervals of as much as 2 years, when the resins were dried under the Conditions indicated. The solvents used were those available in this laboratory without purification, with the following exceptions: ethanol, 200 proof; acetone, dried and distilled; benzene, thiophene free; petroleum ether, boiling point 90' to 100' C; mineral oil, Atreol 34. Gulf Oil 361 is a light lube oil stock consisting of paraffinic and naphthenic hydrocarbons. SWELLING OF AMBERLITE RESINS
It is not necessary for a resin to swell in a solvent in order to exhibit appreciable ion exchange capacity. Many resins are sufficiently porous t o permit ready access of solvents and ions without undergoing a great deal of swelling. Nevertheless, there are cases in which a resin must swell in order to accommodate very large ions. Furthermore, the amount of resin swelling is always an important consideration in designing equipment. Per cent swelling was determined b y placing the dried resin in a graduated cylinder, measuring its volume, adding an excess of solvent, and measuring the volume again after the resin had ceased to swell. Different techniques of conducting this test gave varying results. The use of a small diameter graduated cylinder did not give the same per cent resin swelling as did the 2571
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TABLE I. SWELLING OF CATIONEXCHANGERS FROM DRYTO WET STATE Swelling, % Sulfonic IR-lZO(1-I) IR-120Na IR-112 Ka IR-lOB(H) IR-105Na Carboxylic IRC-BO(H) IRC-5ONa Porous IRC-SO(H)
Eater 43 73 264 107
Ethanol 38 0 0
Glycerol 24 5
99
0
120 5
48 202
98 0
S 6
100
Acetone 18 0 0 73
Aoetio acid 8 0
Benzene 0 0
7
55 7
0
8
0 1
R
0
0 3
5
Petroleum ether 0
0 7 2 2
0 1
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because of little or no density difference, the rebins were distributed throughout the liauid Dhase. I n mixed solvents many of the resins examined showed greater sxelling than in either of the solvents alone. Tables I11 and IV illustrate this effect for mixtures of ethanol-water and ethanolbenzene. Similar results were obtained with acetone-water and dioxane-water mixtures.
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EXCHANGE CAPACITIES IN NONAQUEOUS MEDIA
The work reported here %-ascarried out in static rather than flon.ing systems. One gram of resin was allowed t o stand with occasional shaking in T A B L E 11. SWELLING O F ANIONEXCHANGERS F R O M DIty T O WET STATE contact with 50 ml. of solution containing (when Swelling, % Petroleum solubility permitted) a known excess of the Quaternary Water Ethanol Acetone Pyridine Benzene ether material to be adsorbed. It was a t first assumed IRA-400 O H 37 63 25 20 18 5 that equilibrium mas attained in 1 week, a t which 45 63 20 28 11 6 IRA-400 C1 XE-75 OH 220 140 40 20 7 5 time the solutions and, in some cases, the resins XE-75 C1 200 130 23 32 3 3 IRA-410 OH 25 55 38 50 10 were analyzed. It should be pointed out that there were probably a number of instances where Primary and secondary equilibrium was not reached in the allotted time. IR-4B OH 23 18 0 3 3 3 Thus, some low capacities may reflect plow PYC1 73 5 0 3 3 0 IR-4B 52 40 IR-45 OH 31 50 35 15 change rates rather than an actual inability of IR-45 C1 45 30 10 25 0 0 the resin to effect the exchange. XE-76 OH 35 78 45 55 20 Tables V and VI present data on the adsorption of a strong base, triethylamine, and a weak base, p-yi-idine, from a variety of solvents, by the use of a larger diameter cylinder. When the dry resin was alhydrogen form of cation exchange resins. For these experilowed to fall freely into the cylinder, its volume was generally ments, 7.3 to 7.9 meq. of triethylamine or 6.0 to 7.0 meq. of slightly less than when i t was subsequently shaken or tapped. pyridine were added per gram of resin. In both cases, t,he For these reasons, an arbitrary procedure was used for all measurestrongly acidic resin, Amberlite IR-120, shows capacities in the ments so that the results are believed to be consistent among nonaqueous solutions that are nearly as high as its capacity in themselves and to represent the relative degree of swelling fairly water. reliably. Most resins attained their maximum volumes in 1 A true case of cation exchange was examined using strontium petronate, the strontium salt of a sulfonated aliphatic hydrohour or less, and nearly all resins reached this stage within the carbon, and the hydrogen form of cation exchangers. The limfirst 24 hours. However, the resins were allowed to stand in the ited solubility of strontium petronate in the solvents employed solvents for 120 hours before the final reading was taken. In the standardized procedure, 30 to 40 ml. of the dried resin were poured into a 100-ml. graduated cylinder without shaking or tapping, and the initial volume was read to the nearest 0.5 ml. OF CATIONEXCHANGERS-€I FoRx I N The resin was then covered with the solvent to the 100-ml. mark. TABLE111. SWELLING MIXEDSOLVENTS After 120 hours the volume wa8 again read. Per cent swelling Swelling, % was calculated as 100 times the ratio of the final volume minus Ethanol-Water IR-105 IR-120 IRC-50 the initial volume divided by the initial volume. The method 100- 0 80 40 140 gives results which may vary as much as 10 to 20% in check 95- 5 110 110 160 120 100 190 90- 10 determinations. 140 110 2 10 80- 20 Table I gives the values obtained with cation exchange resins. 0-100 100 40 100 I n this table, S indicates that the hydrogen form of Amberlite Ethanol-Benzene IRC-50 swelled greatly in glycerol and, being of nearly the same 100- 0 80 40 140 90- 10 100 120 130 specific gravity as the solvent, was suspended so as to fill the entire 70- 30 120 130 130 volume of the cylinder. I n the same table, R indicates that the 50- 50 120 140 130 80 120 110 30- 70 sodium form of Amberlite IRC-50 reacted with glacial acetic 10- 90 60 100 90 acid to form sodium acetate and the hydrogen form of the resin. 0-100 0 0 15 I n general Table I shows that the more polar solvents cause greater swelling than the nonpolar hydrocarbons, and the more TABLEIV. SWELLINGOF ANION EXCHANGERS-OH FORM IN MIXEDSOLVENTS porous resins swell more than their less porous analogs. Swelling, % As has been pointed out, comparisons of swelling of different resins in the same solvent are not warranted because of moisture 1R-4B 1R-45 XE-75 40 110 80 40 100- 0 0 variations. Thus Table I shows that -4mberlite IR-120 Na, which 95- 5 40 60 80 80 60 70 70 80 40 90- 10 60 was dried to a greater extent, swells more than Amberlite IR-120 80- 20 50 60 60 40 70 H, which was less thoroughly dried. When both forms are dried 0-100 40 40 80 80 40 to the same extent, Amberlite IR-120 H swells most. Ethanol-Benzene Table I1 shows similar data for anion exchangers. Here, polar 100- 0 0 40 110 80 40 90- 10 40 50 100 70 60 solvents cause more swelling than nonpolar solvents, and porous 30 50 80 50 60 70- 30 resins swell more than more highly cross-linked analogs. The 50- 50 30 60 80 20 50 30- 70 40 50 60 20 40 anion exchange resins swell somewhat more in hydrocarbons than 10- 90 40 50 40 10 40 20 40 20 20 20 0-100 do the cation exchangers. Glycerol, not shown here, produces considerable swelling of most anion exchangers, and in some cases, 60
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Even higher capacities were observed whan a solution of acetic acid in Gulf Oil-benzene mixture was passed through columns containing Amberlite XE-75 or Amberlite XE-76 to exhaustion Meq. Adsorbed per Gram of Resin of the resin bed. In these cases, as much as four molecules of Solvent IR-105 IR-120 IRC-50 acetic acid were adsorbed per functional group. Even the as8.68 3.65 4.21 Water sumption of the existence of dimers or trimers of acetic acid in 3.32 2.61 3.39 Ethanol 0.28 3.52 0.59 Acetone such solvents could not account for such high capacities. 1 . 3 6 0 . 7 5 3 . 8 0 Dioxane L. P. Hammett of the Department of Chemistry of Columbia 0.38 0.19 3.80 Benzene 0.18 0.29 2 80 Gulf Oil 361 University in a private communication suggested that this situation might be pictured as a clustering of the polar acetic acid molecules about the polar functional groups without actually having TABLE VI. ADSORPTION OF PYRIDINE FROM VARIOUS SOLVENTS the usual ionic bonds established. Meq. Absorbed per Gram of Resin It is of further interest that a resin which has adsorbed such an Solvent IR-105 IR-120 IRC-50 excess of acetic acid can be regenerated in part by passing polar 3.22 3.14 3.93 Water solvents through the resin bed. Rinsing with ethanol or 50:50 1.16 2.76 3.97 Ethanol 0.18 0.71 3.62 Acetone ethanol-benzene solution removes 80 to 90% of the adsorbed 0.74 0.79 3.80 Dioxaae acetic acid, leaving less than one molecule of acetic acid per 0.24 3.87 0.86 Benzene 0 00 2.20 0.00 Gulf Oil 361 functional group. Subsequent passage of the hydrocarbon solution of acetic acid through the resin then resulted in adsorption of acetic acid to the previous high degree. TABLE VII. STRONTIUM-HYDROGEN EXCHANGE Table X shows the adsorption of some higher molecular weight (Strontium petronate in nonaqueous solvents) organic acids from a few solvents. The limited solubility of these acids reduced the number of solvents that could be employed. M ~ ~Meq. , Adsorbed per Gram of Resin Solvent ddded IR-105 IR-120 IRC-50 The octadecanoic acid used here was a highly branched isomer. 161 0 00 1 08 1 69 Ethanol With these large molecules the advantage of the porous resins, 0 53 0 00 0 27 Acetone 0 59 0 00 0 00 1 26 Dioxane 1 85 iimberlites XE-76 and XE-75, over their more tightly linked 0 008 0 04 1 49 2 22 Benzene analogs, Amberlites IR-45 and IRA-400, respectively, was pro0 00 0 00 0 39 Gulf Oil 361 2 20 nounced. An unexpected situation arose in experiments with metal salts of naphthenic acids. The compounds used in this work were TABLE VIII. Sr-H EXCH.4XGE WITH IR-120 the commercially available Nuodexes. They were dissolved in (Correlation of acid liberated with metal adsorbed) benzene and in Gulf Oil 361. The amount of metal adsorbed Meq. Adsorbed per Gram of Resin was determined by ashing the resin in the presence of sulfuric Solvent Meq. Added Volumetric Gravimetric acid and weighing as the sulfate, in calcium and lead, or as the
TABLEV.
ADSORPTIONOF TRIETHYLAMINE FROM VARIOUS SOLVENTS
Ethanol Acetone Dioxane Benzene Gulf Oil 361
1 69 0 59 185
2 22 2 20
1 61 0 53
1 26 1 49 0 39
171 0 51 1 69 1 74 0 83
precluded the use of an excess of this compound. Thus it was not possible to determine the maximum capacity of a resin for effecting this exchange, but only the fraction of added material exchanged. The extent of exchange was determined by titrating the liberated sulfonic acid. Table VI1 shows the amount of strontium adsorbed in 1 week. Amberlite IR-120exhibited a high capacity in all solvents except Gulf Oil 361. The Amberlite IR-120 tests were allowed to stand for an additional 10 days in contact with the solutions, and a t the end of that time the resin was rinsed and ashed and the strontiuin determined gravimetrically as the sulfate. The results are shown in Table VIII. Here i t is seen that there has been additional adsorption of strontium during the 10-day period from the dioxane, benzene, and Gulf Oil 361 solutions. Apparently the rate of exchange in Gulf Oil 361 is particularly slow. Table I X gives the data for the adsorption of acetic acid from a number of solvents by anion exchange resins in the hydroxide form. The normal total capacity for these resins, determined by exhaustion with aqueous mineral acids, is given a t the bottom of each column. The more porous Amberlite XE-76 shows higher capacity (or faster rate) for acetic acid adsorption than the less porous Amberlite IR-45 in most solvents. On the other hand, Amberlite IRA-400 seems to possess sufficient porosity, with respect to the size of the acetic acid molecule, that there is no advantage in employing the still more porous analog, Amberlite XE-75. The most interesting feature of these data is the higher capacity exhibited by a11 the resins except Amberlite IR-4B in benzene and Gulf Oil 361 than they normally display when exhausted with mineral acids in water.
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TABLE IX. ACETICACIDADSORPTION FROM VARIOUS SOLVENTS Meq. Solvent Added Water 7 35 7 43 Ethanol Acetone 7 50 Dioxane 7 71 Benzene 9.65 Gulf011361 7 37 Total oapacity
Meq. Adsorbed per Gram of Resin IR-45 XE-76 IRA-400 XE-75 3 81 4 91 2 70 2 50 3 13 4.75 2 69 2 58 3 08 4 10 3 01 2 52 2 79 4 06 2 12 1 94 7 05 8 58 5 30 5 13 6 52 6 86 6 40 6 07 6 60 2.8 3.0 10.0 5.8 6.0
IR-4B 3 87 2 70 0 33 0 49 7 94
TABLE X. FATTY ACID ADSORPTION FROM NONAQUEOUS SOLVENTS
Meq. Added 8.25 8.24
Stearic Dioxane Bensene
Octadecanoio Ethanol 7 03 Benzene 7 03 GulfOil361 6 55
Mea. Adsorbed per Gram of Resin IR-4B IR-45 XE-76 IRA-400 XE-75 0 05 1 16 1.41 0 46 2 34 0 83 0.00 5 23 0 84 1 13 0 47
0 00 0 00
1 10 0 58 0 53
2 52
1 13 0 27 0 00
1 46
0 62 0 83
TABLE XI. METAL-HYDROGEN EXCHANGE (Metal naphthenates in hydrocarbons) Benrene Solution Calcium Lead Cobalt Gulf Oil 361 Calcium Lead Manganese
Iron
Cobalt
Meq.
Added 7.48
5.36 4.29
6.40 6.81 7.61 6.40 4.09
Meq. Adsorbed per Gram of Resin IR-105 IR-120 IRC-50 3.68 0.11 0 03 4.00 0.06 0 00 1.78 0.12 0.04 0 :02
..
2.64 2.92 0.57 0.19 0.31
0:04
..
.. ..
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TABLE XII. ADSORPTION OF METALNAPHTHENATES B Y ANION EXCHALI'GE RESINS Benzene Solution Manganese Iron Cobalt
Gulf Oil 361
Manganwe lron Cobalt
Meq. Added 7.54 8.71 5.55 7.60 8.35 3.97
IMeq. Adsorbed per Gram of Resin IR-45 IRA-400 XE-75 0.22 0.80 0.67 0.14 0.37 0.33 0.05 0.17 0.02 0.28 0.73 0.06
0.00 0.00 0.00 ~~
0.54 0.02
0.00
~~
oxide in cobalt, iron, and manganese. The results obtained with cation exchange resins are shown in Table XI. The exchange of calcium or lead for hydrogen ion proceeded to a considerable extent with Amberlite IR-120, but adsorption of cobalt, iron, and manganese occurred to a much smaller degree, particularly in Gulf Oil 361 solutions. Since the latter metals have in common the ability to exist as anionic complexes, the adsorption of these compounds by anion exchangers was examined. Table XI1 shows that exchange did, indeed, occur, in some cases to as great an extent as when cation exchange resins were used.
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present in the resin and to the porosity or the degree of cross linking. Although there are certain specific effects, the following conclusions may be drawn: Ion exchange can occur in nonaqueous media, just as in water solutions. Rates of exchange are generally slower than in aqueous media, necessitating slower flow rates in column operation. Ion exchange occurs to a greater extent, or more rapidly, in polar solvents than in nonpolar solvents. It is not necessary for a resin to swell greatly in a solvent for exchange to occur, provided its porosity is sufficient to accommodate the ion being adsorbed. However, it seems significant that the solvents that cause the greatest swelling are polar solvents and that these are the solvents in which exchange occurs moat rapidly. ACKNOWLEDGMENT
Acknowledgment is made to the experimental work carried out by Marie Arndt, Martin G. Chasanov, Edward D. Keyser, and Charles F. Ryan and to the assistance of Louis P. Hammett in the interpretation of many of the experimental data. LITERATURE CITED
(1) Glueckhauf, Endeavor, 10, 43 (1951). (2) Pepper, J. A p p l . Chem. (London), 1, 128 (1951).
CONCLUSIONS
In general, the behavior of ion exchange resins in nonaqueous systems is closely related to the nature of hydrocarbon chains
RECEIVED for review January 24, 1953. .ACCEPTED September 2, 1953. Presented before the Division of Colloid Chemistry at the 122nd Meeting, AMERICAN CHEMICAL SOCIETY, Atlantic City, N . J., 1952
Vapor-Liquid Equilibria BINARY SY STEM NITROMETHANE-NITROETHANE AT SUBATMOSPHERIC PRESSURE ALDO CANTONI' AND JULIAN FELDMAW Bureau of Mines, S y n t h e t i c Fuels Research Branch, Ci. S . D e p a r t m e n t of t h e Interior, Bruceton, P a .
N
ITROMETHANE is not manufactured by direct vaporphase nitration of methane because of low yields and high reaction temperatures. The principal raw materials are ethane, propane, or a mixture of light paraffins from which nitromethane is produced along with other mononitroparaffis. This study was made to discover the optimum conditions for the separation of nitromethane from nitroethane. Because of the thermal instability of the nitroparaffins, fractional distillation under vacuum is necessary. Data at subatmospheric pressures were therefore obtained on the vapor-liquid equilibria for t,he system nitromethane-nitroethane. MATERIALS
Nitromethane and nitroethane, purchased from Eastman Kodak Co., were distilled under vacuum in a 40-plate Oldershaw column at a reflux ratio of 15 to 1. The heart cuts were used in this work. Prolonged heating of distillation residues of nitroethane at atmospheric pressures leads to violent explosions. These can be avojtded by keeping temperatures a t lower levels (under 100' C.); vacuum distillations are therefore recommended. The physical properties of the purified liquids are compared with published values in Table I. 1 Present address, Laboratories of the Scientific Department, Ministry of Defense, Haifa, Israel. 2 Present address, Sational Distillers Products Co., Research Div., Cincinnati, Ohio.
TABLE
I.
PROPERTIES O F PURE NITROMETHBNE A X D NITROETH.4NE
Refractive index, nZg Density, d i o
Nitromethane Exptl. Lit.
Nitroethane Exptl. Lit.
1,3821 1.1358
1,3924 1.0431
1.38195 (12) 1.1379 (12)
1.3917 (8) 1.0413 (at 25' C . ) (8)
ANALYSIS
Because the difference between the densities of the two components is much larger than the difference between their refraotive indices, density measurements a t 20.00' i 0.05" C. in a 1.00-mI. Lipkin pycnometer (9) were used for analysis after a calibration curve had been prepared from known mixtures. The nitroparaffins are unusually active solvents, so that samples had to be transferred in the vapor phase to clean tubes. Samples were placed in a test tube having a ground-glass joint and connected to a similar tube by a U-tube. The sample tube was immersed in a dry ice-acetone bath, and the apparatus was evacuated through a st,opcock connected by a T-tube to the [:-tube. After evacuation the stopcock was closed, the ice bath transferred to the other tube, and the sample tube immersed in warm water. This precaution eliminated contamination by
