I
DONALD S. SEITZ, F. L. MINNEAR, and R. E. DUNBAR School of Chemical Technology, North Dakota Agricultural College, Fargo, N. D
Ion Exchange Resins from lignite Coal Air-dried, heated, and sulfonated lignite provides a cation resin suitable for hard water treatment that compares favorably with available commercial products BEcnvsE of its low cost and natural ion exchange properties coal, and particularly lignite, is promising as an organic base for making ion exchangers. Considerable work has been done to find a way of using coal for this purpose, and methods of treatment have included heating, phosphonation, chlorosulfonation, and sulfonation (7, 3-8). However, the general opinion seems to prevail that treatment with sulfuric acid yields the best product. Hard coals such as anthracite wlfonate readily and yield a product that is granular. The resulting coal-based resins can be exhausted and regenerated without noticeable particle disintegration. Lignite and similar soft coals, however, do disintegrate, and this has been a major objection to their use as a base for ion exchange resins. But the process described here yields a product from lignite that can be adapted to practical use if and when economics dictate. The lignite as received from the mine has some ion exchange capacity which is increased both by heat treatment and by sulfonation for 1 hour. Sulfonation for longer periods increased the capacity little if any; however, heat treatment for 1 hour a t 100" to 110" C. followed by sulfonation for 8 hours produced the best ion exchanger. Phosphonation increased the capacity more than heating alone but less than sulfonation.
when needed, to maintain the reaction temperature between 90" and looo C. After the reaction had been continued for the desired length of time, distilled water was added cautiously; the lignite was then washed with distilled water until the effluent gave a pH between 4 and 6. The same general method was used for phosphonating the coal, except that 85% phosphoric acid was used. The samples of raw, dried, and treated lignite were exhausted with standard hard water by an equilibrium method. In this procedure the exchanger was
Table 1.
11.20 36.09 43.76 8.95 100.00
Experimental The lignite coal (Table I), obtained from the Baukol-Noonan Mine at Noonan, N. D., was shipped and stored in air tight, 5-gallon pails until actually used. The lignite was subjected to 17 different treatments that might be expected to test or enhance its exchange properties. These included testing the coal, as received in several mesh sizes, by heating a t 100' to l l O o C. for various time intervals, sulfonation for different periods of time, phosphonation, and combinations of the above (Table 11). The method of acid treatment consisted of placing a known amount of lignite into a flask equipped with stirrer, reflux condenser, and thermometer, and adding enough 20% fuming sulfuric acid to cover the sample. Heat was applied,
As Received
Moisture Free
Moisture
Proximate analysis, % 34.12 26.78 40.64 32.46 49.28 6.64 10.08 100.00 100.00
+ Ash Free
45.20 54.80 100.00
Ultimate analysis, % 5.31 5.10 6.81 4.58 58.81 73.65 43.63 66.23 1.00 0.74 1.13 1.25 19.21 25.30 41.71 17.27 0 2 0.79 0.63 S 0.47 0.71 8.95 Ash 6.64 10.08 100.00 100.00 100.00 100.00 Total a Air-dry loss, 25.81%. Moisture determined by xylene method was 35.0%
Hz C N
Table II. P
Analysis of Baukol-Noonan Lignite"
Air Dried Moisture* Volatile Matter Fixed C Ash Total
weighed out in duplicate samples of 5, 10, 15, and 20 grams. These were placed in 500-ml. Erlenmeyer flasks, and a 100ml. portion of standard hard water was added to each of the flasks. This particular hard water had 5486 p.p.m. equivalent of calcium acetate or 1.250 grams of calcium ion per liter. The stoppered flasks were placed on a mechanical shaker and gently agitated for several hours. They were then allowed to stand several hours until the small particles in the solution settled. A 10-ml. aliquot of the solution was then pipetted
Resin Capacities from Equilibria Studies
Heat treatment for 1 hour followed by sulfonation for 8 hours produced the best exchanger Capacities for Varying Sample Sizes, Mg./Gram Exchanger 20-gram 15-gram 10-gram 5-gram As received, 12- to 25-mesh 3.90 4.53 5.20 6.20 3.95 4.60 As received, 40- to 60-mesh 5.50 6.80 As received, 60- to 80-mesh 3.80 4.53 5.40 6.40 Heat-treated 1 hr., 12- to 25-mesh 4.05 4.67 5.50 6.80 Heat-treated 1 hr., 25- to 40-mesh 4.15 5.13 5.60 7.60 4.30 5.07 Heat-treated 4 hr. 6.10 7.60 Heat-treated 8 hr. 4.40 5.20 6.40 8.40 Heat-treated 25 hi. 4.10 5.07 6.40 8.40 As received, sulfonated 1 hr. 23.40 6.10 8.07 11.90 12.30 As received, sulfonated 1 hi., regenerated 23.80 6.15 8.20 As received, sulfonated 8 hr. 12.00 23.20 6.05 8.07 Heat-treated 1 hr., sulfonated 1 hr. 10.80 18.60 6.00 7.87 10.80 19.20 Heat-treated 1 hr., sulfonated 4 hr. 5.50 7.27 18.70 36.00 Heat-treated 1 hr., sulfonated 8 hr. 8.70 12.00 12.20 24.20 Heat-treated 20 hr., sulfonated 8 hr. 6.10 8.13 As received, phosphonated 1 hr. 7.50 10.20 5.15 6.13 7.90 As received, phosphonated 8 hr. 10.40 5.20 6.33 12.10 Cullexa 6.10 8.13 24.00 11.60 Cullitea 7.87 19.40 5.95 0 Commercial water softeners (Cdligan, Inc.,Northbrook, Ill.).
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APRIL 1960
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from each flask and titrated by the Versene method (2). T h e equilibrium reaction was maintained at room temperature and varied from 25’ to 26’ C. The Versene (sometimes called Versenate) method for the determination of water hardness involves the titration of an unknown water sample with standard Versene solution (2). The 10-ml. aliquot was diluted with 100-ml. of distilled water, and 0.3 to 0.4 gram of the indicator and 8 to 10 ml. of approximately 8 N potassium hydroxide was added to the solution. A magnetic stirrer was used to agitate the mixture slowly during the titration. The regeneration procedure was similar to traditional treatment. T h e asreceived lignite, which had been sulfonated for 1 hour, was regenerated with a saturated sodium chloride solution for 0.5 hour. The lignite was then washed with distilled water until it tested free of chloride ions with a silver nitrate solution. A 100-gram portion of the regenerated lignite, dried overnight at 55” to 65’ C., was exhausted with standard hard water. Results and Discussion
T h e original, as-received lignite coal displayed some ion-exchange or watersoftening capacity. There appeared to be no significant difference with particle size. Heat treatment of the lignite generally increased the ion-exchange capacity with a maximum improvement at the end of approximately 8 hours, which may be associated with oxidation. The lignite, when sulfonated for 1 to 8 hours, increased in exchange capacity noticeably over the as-received lignite. Regeneration increased the capacity
again slightly as compared to the original 1-hour sulfonated coal. Sulfonation for 8 hours, however, did not produce better results than the corresponding 1-hour treatment on as-received coal. Combining the heat treatment with the sulfonation might be expected to increase the ion exchange capacity greatly as each procedure alone produced noticeable improvement. However, the lignite which was heat-treated for 1 hour and sulfonated for 1 hour actually had lower exchange capacities for all sample weights than the corresponding as-received lignite which was merely sulfonated for 1 hour. T h e same was true of the lignite heat-treated for 1 hour and sulfonated for 4 hours. Actually, the maximum exchange capacity wasachieved when lignite was dried for 1 hour and then sulfonated for 8 hours. Subsequently, a sample of lignite was heated for 20 hours at 185’ C. and then sulfonated for 8 hours to see if this more drastic heat and sulfonation treatment would increase the exchange capacity of the lignite. A significant decrease occurred. When as-received lignite was phosphonated for 1 hour with 85% phosphoric acid. an inferior product was obtained compared with the sulfuric acidtreated product. Similar treatment for 8 hours with phosphoric acid did little to increase the ion-exchange capacity over similar treatment for 1 hour. Both phosphonations did, however, produce exchangers with higher capacities than those in which heat treatment alone was used. The lignites treated with phosphoric acid, however, appeared to have a better physical structure than coals receiving similar treatment with sulfuric acid.
There is no inconsistency in the exchange capacities as reported in Table I1 for the 5-, lo-, 15-, and 20-gram samples. These findings are based on an equilibrium study involving the distribution of calcium ions between a fixed but excessive volume of hard water and a variable amount of exchange lignite resin. The capacities in milligrams per gram naturally respond consistently with the changing ratio of volume to weight. Two commercial synthetic water softeners wereexhausted in thesame manner for purposes of comparison. Acknowledgment
Thanks are extended to the BaukolNoonan Mining Co., Noonan: N. D., for the samples of lignite, and to the Minneapolis-Honeywell Regulator Co., of Minneapolis, Minn., for financial support of the project. Literature Cited (1) Behrman, A. S. (to Infilco, Inc.), U. S. Patent 2,376,896(May 29, 1945).
(2) Bersworth Chemical Co., Framingham, Mass., “The Versenes for Exacting Control of Cations in Solution,” Tech. Bull. No. 1, Sect. 3, p. 5 (1952). (3) Broderick, S. J., Bogard, D., IND.END. CHEM.33,1291 (1941). (4) Crosfield, J.; & Sons, Ltd., Furness, R , , Wellington, R., Brit. Patent 547,580 (Sept. 2,1942). (5) Dean, J. G., Heiligman, R., Riley, R. (to Permutit Co.), Can. Patent 420,270 ( M a y 16, 1944). (6) Furness, R., Crosfield, J., & Sons, Ltd., Brit. Patent 486,471 ( J u n e 3, 1938). (7) Gordon, I. L., Teplo-Silovoe Khoz 1941, p. 29. (8) Grigorov, 0. N.: Volf, I. V., Teoriya i Prakt. PrimEnen Ionoobmen Sbornik State i 1955, p. 82.
Materialou,
RECEIVED for review May 15, 1959 ACCEPTED January 4, 1960
The authors comment Critics may question two major points in the above report, distintegration tendency and batch equilibration. Both complications were recognized early in the study and realistically faced. The choice between batch equilibration vs. column technique was adopted only after dozens, if not hundreds, of preliminary trials. The first, and incidentally major, objective was to produce the best possible ion exchange resin from lignite coal and to evaluate the effect of different heat, sulfonation, and phosphonation treatments. To make honest comparisons all variables, except the one under consideration, should b e held constant. This i s utterly impossible under traditional column practices. It was difficult, for instance, to control contact time, rate of flow, channeling, volumes, and admixture of resin with solution by the column procedure. With the equilibrium procedure, however, not only were comparable results obtained, but also consistent duplicate values from which honest comparisons between different lignite treatments could be drawn. It i s fully realized that the ultimate value of such a resin will depend upon its behavior in a bed or column. Actually, most of these lignite resins gave surprisingly good results in column studies. However, i t seemed unwise to compromise and settle for good results that were not com-
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INDUSTRIAL AND ENGINEERING CHEMISTRY
parable. The equilibrium approach permitted the change of one variable at a time and selection of the best treatment. It i s generally known that heat treatment and drying of lignite in contact with air produces additional leonardite through oxidation. This change should be of maior interest in evaluating such a product. Hence, the interest in time and extent of drying and heating, as well as variation in sulfonation. The problem of lignite disintegration during storage and drying i s well known to many North Dakota home owners and scientists. However, much progress has already been made leading to stabilization, not only with lignite but with similar products. Techniques include pelletizing, briquetting, and addition of additives, binders, plasticizers, and other adhesives. Such stabilized lignite products are already produced and consumed b y the ton in the state. This i s not considered to be an insurmountable obstacle but probably can be solved by methods already available. This, in fact, is one of the projected future studies. From this study a desirable product has been produced that could be adapted to practical use. The economics involved may dictate when, if ever, such a product will be utilized, but basically the present study involves the best method of producing and evaluating such a lignite resin.
