June 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
medium containing about three parts of alkali t o one of coal at around 270' c. and total pressures of approximately 1000 pounds per square inch gage and the organic acids are recovered by acidification of the reaction mixture with sulfuric acid followed by solvent extraction. The nitric acid process, working a t lower temperatures and pressures and yielding an acid solution as the end product, would appear to be simpler. However, there would be the problems of good separation and recovery of the nitricacid and of corrosion of the equipment. Also, judging from earlier work, it appears that the content of crystalline aromatic acids is higher in the product from the alkaline process, and the presence ofnitrogen-containing functional groups in the acids from the nitric acid reaction might prove disadvantageous in a number of fields of utilization.
1411
LITERATURE CITED
Bone, W. A., Parsons, L. G. B., Sapiro, R. H., and Groocook, C. M., Proc. Roy. Soc. (London),148A, 521 (1935). (2) Franke, N. w., and Kiebler, M. w.9 Chem. I n d s . , 58, 580 (1946). (3) Horn, O., Brennst0.f-Chern., 10, 362 (1929). (4) Howard, H. c., llChemistry of coal Utilization,'i H. H. L ~ ed., pp. 358-63, New York, John Wiley & Sons, Inc., 1945. (1)
(5) Ibid.9 PP.3 7 3 - 4 ,
c.,and Howard, H c.,J . Am. Chem. SOC.,
( 6 ) Juettner, Be,Smith, R.
57, 2322 (1935). (7) Ibid,, 59, 236 (1937).
(8) Petrick, A. J., and Groenewoud, P., J . Chem. Minzng SOC.S
Africa, 38, 370 (1938). ACCEPTED January 17, 1852. for review August 1, 1Q51. Presented before the Division of Gas and Fuel Chemistry at the 118th MeetCHEMICAL SOCIETY, Chicago, Ill., September 1850. ing of the AMERICAN
RECEIVED
Ion Exchange Resins in Sugar Cane Juice Processing PRACTICAL LIFE AND CAPACITY J. rI. PAYNE, H. P. IIORTSCHAK, AND R. F. GILL, JR.' Experiment Station, Hawaiian Sugar Planters' Association and Research Laboratory, Pacisc Chemical and Fertiliaer Co.,Honolulu, T . H .
T
HE choice of ion exchange resins for commercial scale purification of solutions depends not so much upon the initial cost and capacity as upon the useful life in a particular application as measured by capacity losses. Unfortunately, manufacturers' data on the capacity for inorganic ions and stability in any one application, usually water treatment, is not a dependable guide for the selection of a resin for deionizing a material such as sugar cane juice in a raw sugar factory. A testing procedure for determining the practical life and capacity of resins was, therefore, developed and applied to a study of cane juice. A noncritical review of a large part of the published work on the application of ion exchange to sugar processing is given by Nachod (4). Yearly reviews of ion exchange as a unit operation have been made by Kunin (13). Tompkins (6) recently presented an excellent discussion of the properties of ion exchange materials and the mechanism of ion exchange separations. Thompson and Roberts ( 5 ) give valuable information on the capacity and operating characteristics of commercial ion exchange resins, although the resins are not identified. These references provide access to the rapidly growing literature on ion exchange. TESTING PROCEDURE
The testing procedure consisted of preparing the standard resin samples, measuring volume and dry matter, determining capacity for inorganic ions and for clarified sugar cane juice, and cycling the resins in a semiautomatic apparatus which carried them any desired number of times through the normal cycle of exhaustion with cane juice, rinse, backwash, regeneration, and rinse. At several stages the samples were removed quantitatively from the apparatus and the volume9 and capacities were redetermined. PREPARATION OF RESINS
Representative samples of new resin were taken from commercial production materials. Those received in the dry form were soaked in distilled water until the initial swelling had taken place. The resins were then regenerated in beakers with an excess of the 1 Present
address, Hawaiian Pineapple Co., Honolulu, T. H.
same regenerant used in other phases of the tests. The samples were washed with distilled water by decantation, the anion exchange resins being washed down to p H 8 and the cation exchange resins up to p H 4. The washing was completed immediately after regeneration and any subsequent changes in p H of the water on standing were disregarded. The next steps were taken as soon as possible, minimizing the period of standing in the regenerated state before making volume measurements. The samples were gently but thoroughly wet-screened, discarding all fines passing 40 mesh. Subsequent screening of the resin samples, at the several stages of the stability tests, was carried out by repeated flotation and decantation through 52-mesh platinum screen, so that accumulated mud and dirt were removed along with developed fines. VOLUME AND DRY MATTER DETERMINATIONS
Although prices and capdcities are usually referred to a unit volume rather than a unit weight of dry resin, preliminary work showed that volume measurements were closely reproducible only when a standardized procedure was followed. A further complication is the continued swelling of the resins over a large number of cycles, which masks any physical loss. Therefore, in these st,udies,the dry weight was measured initially upon separate samples, and upon the used samples a t the end of the tests. The volumes of the resin samples were measured in a special buret. The buret was constructed of 25-mm. borosilicate glass tubing with a 52-mesh screen shielding the bottom. The bottom outlet tube was provided with B side arm connected by flexible tubing to a distilled water bottle operating with a 5-foot static head. The buret was calibrated against known water volumes, taking a line midway between the upper and lower meniscuses as the mark corresponding to the flat upper surface of a resin column. The buret was marked to 350 ml. a t 5-ml. intervals. A ruler-type gage was made for estimation of resin volumes to the nearest 0.1 ml. between markings. Resin samples larger than 150 ml. were measured in two or more roughly equal increments. The measure ment procedure was as follows:
~
1412
INDUSTRIAL AND ENGINEERING CHEMISTRY
The liquid was drained to a level several millimeters above the top of the resin bed, then backwashed rapidly to double the volume. Holding the volume at this point by adjusting the flow rate through the side arm, 50 ml. of water were allowed to flow upward through the resin. The flow was stopped and the resin allowed to settle. The liquid mas then drained a t a flow rate of 60 to 100 ml. per minute, stopping several millimeters above the resin bed surface. This process was repeated several times until the classification was essentially complete and the volume nearly constant. These preliminary volume readings were rejected, then a series of measurements, at least seven if the readings varied by more than 0.2 ml., were made. From the series of values the mean volume and the standard deviation were determined. Care was taken that the buret was not jarred or vibrated during the settling or draining. Some resins when classified in the buret form stable columns, while others are subject to collapse when shocked. X tendency was noted toward a decrease in the standard deviation in volume measurements with certain of the resins after use. This is believed to be due to increased cohesion between the particles coated with matter from the cane juice. About 300 ml. of the cation and 125 ml. of the anion exchange resins were taken. These volumes were roughly matched in capacity for cane juice. The dry matter in a separate sample of about 50 ml. of each resin, prepared and measured as above, was determined by drying to constant weight in an oven a t 105" to 110' C. Since the oven drying was not in an inert atmosphere, some resins were found to gain weight slowly after prolonged periods of heating. I n such cases, the minimum weight was taken. I n conjunction with the dry matter determinations, each of these resin samples was first weighed with sufficient water t o make a total volume of 100.0 ml. in order to calculate the volume of water in each standard sample of resin. Thus the correction for the amount of water in the resin bed at the beginning of each capacity test could be made. The same volume correction was used a t all stages of the tests, disregarding the small effect caused by swelling and the physical loss of resin. DETERMINATION OF CAPACITY
APPARATUS.The apparatus in which the capacities of the resins were measured was of conventional design, consisting of a series of borosilicate glass tubes, having an outside diameter of 38 mm. and a length of 4 feet, closed a t either end with rubber stoppers, each carrying the appropriate number of outlets and inlets. The resin was supported in the tube by a rubber stopper with a l/Z-inch hole covered with a sheet of hard multipore rubber. The top outlet was covered with 52-mesh platinum screen. Calibration marks were placed on the tubes a t levels corresponding to 175 and 350 ml. above the support plate. PROCEDURE. Each sample, prepared and measured as indicated, was placed in a tube of the apparatus described and backwashed (300 ml. per minute) until the tube was full, then with a 1500-ml. excess. The resin was allowed to settle and liquid was drained to the appropriate mark (175 or 350 ml.) at 50 ml. per minute. Juice capacity tests were made before the salt or acid tests, except for measurements of the new resin, in order to eliminate a detergent effect by which the juice capacity is temporarily increased. All tests were repeated until successive runs gave the same results. The capacity values obtained were not strictly comparable to large scale operation, since the bed depths were less than in commercial installations and since excess regenerant rather than the minimum economic amount was used. CATIONEXCHAXGE RESINS. These resins were regenerated with 1500 ml. of sulfuric acid (2.00 grams per 100ml.) at 25 ml. per minute. (To provide excess regenerant, the volume was doubled for resins Duolite C-3J6 and Dowex 50.) The tube was filled t o remove regenerant from the sides and drained to the 350-ml. mark; the rinse was continued to a total of 2000 ml. at 50 ml. per minute.
Vol. 44, No. 6
To determine the neutral salt capacity, water 'Ivas run at 25 ml. per minute until the effluent was above p H 4.0 and the conductivity below 10-4 mhos. Adjusting the liquid level to the mark with as little interruption of the flow as possible, neutral sodium chloride solution (0.500 gram per 100 ml.) was run a t 25 ml. per minute until the effluent p H was 2.0. The first few milliliters of effluent were caught in a p H meter cup and the remainder was collected in a calibrated 100-ml. graduate. The p H sample was returned to the graduate before the first 100 ml. of effluent were collected. The effluent was collected in 100-ml. increments in this manner during the course of the run, the p H being measured on the first few milliliters of each and conductivity upon each whole increment. A sufficient number of the 100-ml. samples was titrated to give a curve of the hydrogen ions liberated during the run. To complete the run, the resin was rinsed with 500 ml. of water a t 50 ml. per minute. To determine the capacity for cane juice, fresh clarified cane juice (screened commercial product), cooled to 25" C., was run at 25 ml. per minute in the same manner as sodium chloride solution, except that the run was discontinued when the effluent pH was 4.0, and the rinse was 1000 ml. of water. The ash (grams per 100 ml.) was determined in the untreated, clarified juice on a sufficient number of 100-ml. increments of the effluent to provide points for plotting a curve of ash removal during the run. The juice, being highly colored, was titrated with the glass electrode to pH 8.0. The difference between the titers of the sample and the original juicc was a mcasure of the acid produced and equivalent to the cations removed. ASION E X C H ~ S G E RESIUS. These resins were regenerated with 1000 ml. of sodium hydroxide (1.00 gram per 100 ml.). (To provide excess regenerant the volume was doubled for Amberlite IR-4B and Duolite A-2J6.) After filling the tube with water, it was drained to the 175-m1. mark and rinsed to a total of 5000 ml. The acid capacity was determined by running water a t 25 ml. per minute until the effluent was no longer over pH 10 and the conductivity was below 10-3 mhos. Adjusting the liquid level, n-ith minimum interruption of the flow, hydrochloric acid or sulfuric acid (0.250 gram per 100 ml.) was run at 25 mi. per minute until the conductivity was above 0.025 mho. The run was completed with 500 ml. of rinse water. Collecting the effluent in the same manner as in the cation exchange capacity tests, the p H and conductivity were measured and enough samples of the effluent were titrated to plot a curve of hydrogen ions removed. To determine the capacity of cane juice, clarified cane juice was run through a n 800-ml. column of freshly regenerated, high capacity cation exchange resin a t 50 ml. per minute until 1500 ml. were collected and discarded. (The column was sufficient to supply enough cation-exchanged juice of practically constant composition for the standard sample of any anion exchange resin.) During this time the anion exchange resin sample in an adjacent tube was rinsed as in the step preliminary to the acid capacity test. The flow of cation-exchanged juice was diverted into the anion exchange resin column and the run continued as in the acid capacity test, except that the run was discontinued when the pH values reached the minimum plateau and the rinse was 1000 ml. of water. A continuous drip sample (about 2.5 ml. per minute) was collected from the cation exchange resin effluent during the run, and pH, conductivity, and titration values were determined on the composite. The ash in the untreated, clarified juice was determined. The calculations provide corrections of the CALCULATIONS. effluent volumes for variations of the initial cation and anion exchange resin volumes (initial volume was used throughout the calculations, since most of the resins increased unpredictably in volume during the tests) from the adopted standards of 300 ml. and 125 ml., respectively, for the water in each resin sample, for variations in the concentration of the solutions, and for fluctua-
June 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
1413
tion in the ash content of the juices used. (In 128 samples of juice used the ash varied from 0.335 to 0.688 gram per 100 ml., averaging 0.480, as compared with the adopted standard of 0.500.) Correction for fluctuation in the ash content is not entirely satisfactory, because the concentration of organic ions is not considered and some of the ash is either nonionic or suspended inaoluhle matter. The corrected effluent volume was found by using the equation
(E - W)CaV,
Corrected volume = ~C,V,
(1)
For calculating ion removal for the cation exchange sodium chloride runs, the equation Sodium removed, % = T
N _b N,
(2)
was used, while for the cation exchange juice runs the equation used w'as
T-B
Cations removed, % = S ___ T, - B
(3)
The percentage of ash removed was found by Au - At Ash removed, % = 100 ___
A"
(4)
For the anion exchange acid runs, the equation
N Anions removed, % = 100 - T -b N,
Figure 1. Resin Stability Apparatus
(5)
was used for determining the percentage of anions removed, while for the anion exchange juice runs this value was found by
T, - T TC
Anions removed, % ' = 100 -__
(6)
I n the cation exchange cane juice capacity tests there is no direct method for determination of the cations initially present. An approximation (Equation 3) is based upon the assumption that a t the same stage of the tests, the maximum values for removal of sodium ions (during sodium chloride runs) and of all cations (during juice runs) are equal. STABILITY CYCLING OPERATIONS
In subjecting the standard resin samples to repeated cycling, an effort was made to approximate the conditions of actual service. The individual cycle was complete, each phase being similar to average operations anticipated for a commercial installation. For resins of satisfactory behavior, it was planned to carry the
tests to a t least 1500 cycles, as roughly representative of the amount of service a resin unit might encounter in one season. Unfortunately, it was not possible to do this with all of the resins. The apparatus for repeated cycling was constructed so that six hand levers served to operate the 38 valves in the proper arrangements and sequence. The apparatus is shown in Figure 1. Groups of four cation and four anion exchange resin samples were cycled simultaneously. Clarified cane juice was passed first through the four cation exchange units in parallel, and on leaving these cells was mixed and divided between the four anion exchange cells. The cells were borosilicate glass tubes, 3 inches in diameter and closed a t both ends with rubber stoppers. The resin was supported on a sheet of hard multipore rubber and the backwash outlets were screened with 52-mesh platinum gauze. The treated juice was discarded. The phases of the cycle were controlled by time, with occasional adjustment of the flow rates during operation, so that 1900 ml. of screened, clarified cane juice entered each cation exchange cell (100 ml. per minute). Of this about 1400 ml. passed on to the anion exchange cells, since the cation exchange cells were full a t the end of this phase, and in the following rinse (1000 ml. at 100
TABLEI. STANDARD SAMPLE DATA01' I O NEXCHANGE RE SINS^ Source Class Amberlite IR-1 Resinous Products & Chemjcal Co. Sulfonated phenolic Amberlite IR-100 Resinous Products & Cheqical Co. Sulfonated phenolic Infilco, Inc. Catex Sulfonated carbonaceous Dowex 30 Dow Chemical Co. Sulfonated phenolic Dow Chemical Co. Dowex 50 Sulfonated polystyrene Chemical Process Co. Duolite C-1 Sulfonated phenolic Chemical Process Co. Duolite C-3 Sulfonated phenolic Chemical Process Co. Duolite C-3J6C Sulfonated phenolic Ionac C-284 American Cyanamid Co. Sulfonated phenolic Permutit Co. ZeoKarb-H Sulfonated carbonaceous Amberlite IR-4 Resinous Products & Chemjcal Co. Aldehyde-aromatic polyamine Amberlite IR-4B Resinous Products & Chemical Co. Aldehyde-aromatic polyamine Deacidite Permutit Co. Aldehyde-nonaromatic polyamine Chemical Process Co. Duolite A-2 Aldehyde-nonaromatic polyamine Chemical Process Co. Duolite A-3 Aldehyde-nonaromatic polyamine Duolite A-2J6C Chemical Process Co. Aldehyde-nonaromatic polyamine American Cyanamid Co. Ionac A-293 Aldehyde-guanidine All resins received from manufacturers in 1944 except IR-4B (1945), and Dowex 50, C-3J6, 6 Total water in sample plus water t o 350 or 175 ml. E Improved" resins, manufacturer's designation, A-2 and C-3, not changed.
Initial Init. Dry Weight correotiona, Dilution Volume, MI. Grams/100 ml. Lb./cu. f t . h41. 308.1 z t 0 . 3 26.0010.05 16.3 307 300.610.2 30.98zt0.12 19.4 290 304.2zt0.4 25.68f0.05 16.1 302 301.5 f 0 . 8 39.96 f 0 . 1 6 25.0 280 304.610.3 46.15 k O . 0 9 28.8 268 301.9 f 1 . 3 14.06 z t 0 . 0 3 8.8 326 302.41t0.2 32.7610.07 20.5 288 300.0 1 0 . 1 33.69 A 0 . 0 7 21.0 319 314.6zt0.9 26.64zt0.21 16.7 301 303.2 f O . 4 36.70 z t O . 0 0 22.9 282 126.610.5 31.0810.00 19.4 146 120.2 f 0 . 5 28.50 dzO.00 17.8 149 123.7 10 . 3 14.74 10 . 0 9 9.2 162 131.0 f 0 . 4 21.92 f 0.00 13.6 154 124.7 z t O . 1 21.86 10.10 13.7 156 124.0 f O . 1 27.21 It 0 . 0 0 17.0 154 125.6 f O . 7 40.14f0.08 25.1 146 and A-2J6 (1946).
1414
INDUSTRIAL AND ENGINEERING CHEMISTRY
ml. p-r minute), each cell was washrd separately. The backvash phase n a s continued for 5 minutes a t a rate (not less than 200 ml. per minute) sufficient to lift and churn the resin. The following regeneration and rinse phases were 6 and 2.5 minutes, respectively, at the same flow rate, using the same regenerants employed in the capacity tests. Tap water was used in the rinsing. The volume of juice was adequatetoexhaust completely the standard samples of all the resins available a t the beginning of the study, but not severaI received later. The resins tested are shown in Table I ,411 were materials available commercially and were used as received, except for the preliminary screening treatment. At the end of 50, 150, 300,500, 1000, and 1500 cycles the resins mere removed from the apparatus and tested. Graphs were prepared from the cation exchange resin test data as follows: The effluent volume was plotted versus conductivity and versus pH for both the juice and the sodium chloride capacity te5ts. For the juice capacity tests, the effluent volume was also plotted against the per cent of ash removed and the per
IO0
90
00 !-
z
W
*
70
(L
W
a
I
60
a W
>
0
H
W
50
(z
E
40
0 CT)
30
20
IO
1.0
0
2.0
6.0
3.0
VOLUME - LITERS Figure 2.
Vol. 44, No. 6
t 3 Amberlite IR-I
Sodium Removed-Volume Relationship for Cation Exchange Salt
Amberlite PR-100 Catex 0 Dowex 30 Q Dowex 50
0
Runs
500-cycle stage
Q Dixolite C-1
A Duolitc C-3 V Duolite C-3J6 X Ionac C-284 @ ZeoICarh H
TABLE11. CAPACITYOF CATIONEXCHANGE RESIXS Standai d Cane Juice Capacity, Gallons/Cu. Ft. Times Cycled Original 50 150 300 500 1000 1500
- - Original .-
7
Amberlite IR-1 Amberlite IR-100 Catex Dowex 30 Dowex 50 Duolite C-1 Duolite C-3 Duolite C-3J6 Ionac C-284 ZeoKrtrb H
43 41 28 55
41 35 26 51
39 33 24 56
28
28 43
37 39
26 36 49 35 29
52 55 41 63
54 46 36 62
54 39 35 59
51 41 33 66
29 45 57 49 45
31 44
24 41 53 51 39
31 45 ., 50 41
60 60 49 70 93 31
66 51 48 66
65
61
43 48 28 55 82 26
40 51 38 38
90
50 60
59 55
38
..
48 48
..
34 53 .. 59 59
..
..
42 30
..
45 46 63
46 42 69
.. 31 44 55 63 50
.. 34 51 .. 58 52
35 36 19 48 68 26 34 33 38 30 48 43 30 60 93 30 48 45 49 39 63 48 40 65 98 31 51 49 60 48
2Q ,
.
40
,.
32 30 38 23
.. 35 .. 54 .. .. 45 51 35
42
..
60
.. 48 50
64
46
AT 90% . _ REMOVAL .. 8,800 7,900 24 3,300 13,900 43 34,600 8,200
.. "
36
..
31 0
14,200 17,500 8,300 5,000
Sodium Chloride Capacity, Grains/Cu. Ft. as CaCOa Times Cycled 150 300 500 1000 50
7,300 7,200 3,800 14,600 6;400
6,400 6,600 3,100 12,900 6;500
5,800 5,600 2,800 11,800 6;400
13,400
10 800
10,900
7;500 4,900
153000 7,200 3,100
7;iOO 3,500
AT 50Y0 REMOVAL 11,000 9,300 9,900 8,900 29 ,. 5,700 5,400 16,600 17,500 53 38,600 9,400 7,'300 16,000 14,800 43 20,500 12,200 l0;960 44 31 7,000 7,000
8,400 8,200 5,000 15,900
7,800 7,500 4,500 14,800
7;iOO 12,400 17,900 10,700 5,500
7;000 12,200
AT 25% REMOVAL .. 11,400 10,300 35 .. 6,600 58 17 39: 400 600 .. 9,700 16,400 46 21,100 13,300 53 40 7,900
9,000 8,700 5,600 16,700 7;600 12,800 18 500 11:700 6,700
8,400 8,000 5,000 15,400 7:300 12,600
.. ..
.. ..
9,800 9,400 6,100 18,400 7;600 15,100 12;OOO 7,900
l0;iOO 5,700
1l;ZOO 6,500
5,800 5,800 2,800
4:iOo
9,200 32,200 6,300
8;660
9,200 14,000 6,800 3,100
11;300 11,800 7,000 2,600
7,800 7,700 4,300 12,100 36,200 7,100 10,800 17,100 10,000 5,100 8,300 8,300 4,900 12,900 37,200 7,500 11,400 17,600 10,800 5,680
..I
._ T
1500
4:iio l O : .%.O. ll:560
5:bi)O 0
6:700
6:ObO
12;500
...
14;iOO
13:200 14,800 9,200 4,600
13;?00
...
8;400 3,000
7;200
6;500
131600 ...
15;200 ...
13:600 15,300 10,100 5,500
14:200 9:300 3,600
INDUSTRIAL AND ENGINEERING CHEMISTRY
June 1952
1415
6.0
cent of cations removed, while in the sodium chloride capacity tests it was plotted against the per cent of sodium removed. The data from the anion exchange resin tests were used to plot effluent volume us. conductivity, pH, and per cent of anions removed for both the juice and acid capacity runs. Capacities were measured by the areas under the curves effluent volume us. ions removed. Where the maxima on the curves were significantly under 100~o removal, a horizontal line was drawn from the point of maximum ion removal to the corresponding level on the percentage removal axis. The area under this modified curve was then taken. When developing the procedure, it was thought that increasing percentage of removal during a run was a dilution effect. It is now realized that this is not always true, and this correction is not recommended. In the estimation of juice capacity, the capacity values are given only as volumes of effluent collected. For salt and acid tests, total equivalents removed were determined.
5.0
I a 4.0
3.0
2.0
RESULTS
1.c Figures 2 to 9 show graphically the 0 1 .o 2.0 3.0 4.0 data obtained a t the 500-cycle stage. VOLUME LITERS Data a t the other stages were plotted Figure 3. pH-Volume Relationship for Cation Exchange Juice Runs in a similar manner. 500-cycle stage Total capacities of the resins up to the See Figure 2 for symbols points in each test where the removal of ions had dropped to 90, 50, and 25% are shown in Tables I1 mated from the curves a t the 50% removal point, are shown in and 111. Table IV. These values represent the actual capacity of the Total volume of standard juice treated by the resins, as estisamples, without regard to swelling or loss of resin. The tabulated capacities are not the absolute ones to be anticipated in commercial 16 installations because of the shallow bed depths and the excess regeneration. I n addition, it should be borne in mind 14 that the results are for single-pass treatment only. m
-
0
I 2
STABILITY OF CATION EXCHANGE RESINS
I 5
I t
l o
>.
L
5
8.0
3 0
z
0
*
6.0
4.0
0
I
.o
2.0
VOLUME
Figure 4.
3.0
4.0
LITERS Conductivity-Volume Relationship for Cation Exchange Juice Runs 500-cycle stage See Figure 2 for symbols
SODIUM CHLORIDE CAPACITY.With one exception, there appears to be no loss of efficiency of removal of sodium ions from the salt solution although there is a loss in capacity. The maximum percentage removal thus remained relatively constant throughout the tests, except, for ZeoKarb H a t 1500 cycles. At this stage the capacity of the cation exchange resins for sodium chloride varies from 52 to 81% of the original capacity a t the 90% removal point. I n all cases, except for Catex, there is a rapid initial drop in capacity.
1416
Vol. 44, No. 6
INDUSTRIAL AND ENGINEERING CHEMISTRY
I N 3 3 H3d
- a3AOW38
SNOINV
Y
a
Y n
0 0
$
.C
c
c
June 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
The cause of the apparently sudden drop of capacity in the case of ZeoKarb H is the predictable result of a continued trend. The curve of effluent volume 9.18. per cent of sodium removed for each testing stage can be obtained by shifting the curve obtained at the previous stage to the left. At 1500 cycles, the point on the curve at 90% removal has reached zero on the volume axis, so that there is no longer any capacity above this level. It is probable that the same will eventually occur with other resins. The data at 50 and 25% removal show that there has been only a small (13%) loss in total capacity for the Dowex 30 and Duolite C-3 resins. There was no appreciable loss after the 300-cycle point. The absolute loss in capacity is of the same order of magnitude for all the resins, irrespective of the original capacity. This is true even for the one value available for Dowex 50. At 25% removal at 500 cycles, the Dowex 50 capacity loss is 2400 grains per cubic foot, while Catex, with 1/8 the original capacity, has lost 1700 grains per cubic foot. As a result, the higher capacity resins are much more stable than the lower capacity resins when judged on the basis of per cent of original capacity. Data on total capacity at the 25% removal point are shown in Figure 10. CANEJUICECAPACITY.The data show that it is not possible to predict even the relative order of the resins with regard to capacity for cane juice from the results obtained with sodium chloride. For instance, Duolite C-3J6, exceeded only by Dowex 50 in the salt tests, is not outstanding with juice. Amberlite IR-1, which stands low in salt capacity, is high when tested with cane juice. Dowex 50 was far above the rest. When it is remembered that the correction factors used in calculating these data are relatively high, it is evident that in many cases no substantial loss in capacity for cane juice has been proved, even at 1500 cycles, since a variation of less than 10% is probably not significant. Values given for percentage of removal do not actually represent percentage of removal of cations because they are based on the maximum removal attained in the corresponding salt tests. The loss of efficiency with regard to ash removal is the most serious evidence of deterioration of the cation exchange resins. With the striking exception of Ionac C-284, all resins tested past the 500-cycle stage show a very significant reduction in t h e maximum per cent of the total ash removed from the juice. The contrast between this large loss of efficiency and the constancy found with sodium chloride is remarkable. There is some indirect evidence that any means taken t o reduce the loss in capacity caused by accumulation of calcium not ,removed by sulfuric acid regeneration will also improve ash removal. That this does not restore the resin to its original condition is shown by the poor result for Dowex 30 at 1500 cycles, despite seven sodium chloride treatments and a hydrochloric acid regeneration a t loo0 cycles. The curves for capacity at 90% ash removal (Figure 11)reflect mainly the lowering of the maximum ash removal. As this goes below 90%, the capacity is, of course, zero. At 50 and 25% re-
1417
TABLE 111. CAPACITY OF ANIONEXCHANQE RESINS Standard Cane Juice Capacity, Gallons/Cu. Ft. Times Cycled Original 50 150 300 500 Amberlite IR-4 Amberlite IR-4R Deacidite ' Duolite A-2 Duolite A-2J6 Duolite A-3 Ionac A-293
66 135 54 59
Amberlite IR-4 Amberlite IR-4B Deacidite Duolite A-2 Duolite A-2J6 Duolite A-3 Ionac A-293
156 192
..
72 36
124 126
84
AT 90% REXOVAL 69 42 85 51 78 66 90 72 57 30 8
64 98 58 61
Si
..
..
76 14
AT 50% REMOVAL 147 108 186 135 96 141 123 137 iii io5 90 47
139 173 96 117
lis 50
7
1000
68 114 47 58 48 57 9
66 77 62 59 58 59
126 154 92 108 89
101
124 107 97 113 102 93
234
204
117 154 105 124 116
147
45
1500
66 66 42 52
.
.. .. ..
..
103
93 72 91
..
..
..
.4~25y0 REMOVAL Amberlite IR-4 Amberlite IR-4B Deasidite Duolite A-2 ' Duolite A-2J6 Duolite A-3 Ionac A-293
210 216 150 171
228
150 132
166
168 186
..
174 225 128 168 151 138 94
255 218 155 157 14i 78
170
Sulfuric Acid Capacity, Grains/Cu. Ft. as CaCO, c Times Cycled Original 50 150 300 500 Amberlite IR-4 Amberlite IR-4B Deacidite Duolite A-2 Duolite A-3 lonac A-293
27,000 50 ,700a 12,000" 24,400 23.000 15,000
AT 90% REMOVAL 31,100 30,600 28,800 25,700 38 600 35 900 18,'200 14,'OOO 16,'600 16;ZOO 22,100 21,000 19,600 22:800 21.600 21.000 19.400 11,800 10,400 9,900 7,400
Amberlite IR-4 Amberlite IR-4B Duolite A-2 Deacidite
35,000 54,200 30,000' 28 600 28:OOO" 25,000
AT 50% REMOVAL 35,900 35,900 33,800 43 800 40 000 26;SOO 22:OOO 22:lOO 27,200 25,000 27;500 24,800 23,800 20,700 17,700 17,600
Duolite A-3 Ionac C-293
Amberlite IR-4 Amberlite IR-4B Deacidite Duolite A-2 Duolite A-3 Ionac A-293
;
55 300
.. ..
.. ..
31,400
116 156
..
..
1000
1500
..
..
--. 21,000
14,000 18,200 18;500 16,300 18,500 17,300 18.100 _.
..
27,100
20;700 20:900 23,400 22,400 21,900 21,000 14,400 ..
:: .
Hydrochloric Acid Capacity, Grains/Cu. Ft. a8 CaCOr Times Cycled 7Original 50 150 300 500
90 121
..
AT 25% REMOVAL .. 35,300 32,900 28,600 .. 45;300 41.000 .. 24,400 23,600 21:900 21:600 28 900 26 400 24 600 23 700 26:OOO 24'800 23'100 21:QOO .. 23:lOO 21:OOO .. I
lib
1000
22,200 26,600 19,200 20,000
..
.. 23,400 27,300 19,500 21,200
.. ..
1500
Amberlite IR-4 Amberlite IR-4B Deacidite Duolite A-2 Duolite A-2J6 Duolite A-3 Ionac A-293
AT 90% REMOVAL 13,000 9,500 15,200 14,400 20,100 19,000 13 300 38 ZOO 10;000 9,400 10,300 12'500 23,100 19,600 17,600 16:700 24 200. 22,750 20,300 25,700 19 ;eo0 18,400 17'600 17,000 5 200 5,100 8,300 5,000
Amberlite IR-4 Amberlite IR-4B Deacidite Duolite A-2 Duolite A-2J6 Duolite A-3 Ionac A-293
AT 50% REMOVAL 23,600 18,800 22,300 19.100 18,800 15,800 31 700 29 200 28 100 22 900 21 000 17'700 16'000 16'000 15'400 16'100 15'600 29;QOOb 26:800 22:QOO 21:lOO 19:300 18:500 17:500 23 300 20 600 30,300 26 000 .. 2 l ; k O 20:700 19;iOO 18'600 16:800 .. .. 12,700 9,900 8,600 9,'OOO .. ..
1
; ..
:
15,000 8,500 17,600 15,800 14,400 14,000 15,500 15,000 .. 17,900 .. 15,300
..
..
:
45 800
..
AT 25% REMOVAL .. 35'500 27,100 32 900 Amberlite IR-4 49 300 Arnberlite IR-4B 21'200 19'700 18'600 .. Deacidite 26:700 24:QOO 22:lOO Duoljte A-2 32 io0 Duolite A-2J6 22;600 21:400 27 400 20:400 .. Duolite A-3 ,. 14,400 13,100 Ionac A-293 0 Calculated from conductivity curve. b Calculated from pH curve.
; 1
..
22,200 32 400
21,700 25 400
17,000 21 900
16'900 20:200
17'200
16'000 18:200
21:OOO
24,300 19,300 21,600 17,300 13,300
..
.. .. ..
1418
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 44, No. 6
be due to incomplete regeneration by sulfuric acid following cane juice throughput. It is known that the fully regenerated resin has the smallest volume. With the exception of Duolite C-3, increase in volume is roughly parallel to decrease in capacity. This raises the question as to whether some of the capacity losses are not due to accumulation of substances not removed in normal regeneration, rather than any actual chemical or physical deterioration of the resin. If this is the case, an occasional more drastic regeneration might restore the resin more nearly t o its original condition. This was not attempted here, as it was necessary first t o determine stability without such treatments. As Table VI ~hows,most of the resins gained weight; there was thus no measure of the amount of resin mechanically lost. STABILITY O F Ah-ION EXCHANGE R E S I h S
HYDROCHLORIC ACID CAPACITY.Ambcilite IR-4B shows an abrupt initial loss in capacity. Deacidite does not show appreciable loss except a t the 25% removal stage. The other rrsins show a gradually decreasing loss. SULFURICACID CAPACITY.These niessurements show the original wide differences in capacity becoming progressively smaller (except for Ionac A-293), until at 1500 cycles the differences between the highest and lowest is less than 10°F a t 50 and 25% removal. The very low value for Amberlite IR-4 a t 90% removal indicates that the rapid capacity loss would probably continue at 50 and 25Yc on further testing. 411 resins lose a large fraction of their original capacity. RATIOOF CAPACITIES FOR SCLFURIC ACIDAND HYDROCHLORIC ACID. In view of the fact that the literature shows that the capacity of anion exchange resins for sulfuric acid is much higher
500-cycle s t a g e 0 Amberlite IR-4 8 Duolite A-2 0 Amberlite IR-4B V Duolite A-2J6 0 Deacidite A Duolite A-3 X Ionac A-293
moval, only a moderate drop in capacity-from 10 to 25% a t 1600 cycles-is evident. When evaluating the reliability of these measurements, it is encouraging to note the practical identity of the results of ash and cation removal a t the 50 and 257, points. This is not true, however, a t the 90% removal level (Table V). Table IV shows the sum total volume of standard juice treated by the resins at the 50% ion removal stage. These figures are significant in comparing resins for actual volume of juice that they may be expected t o treat in a given number of cycles. RESINVOLUMES AND WEIGHTS. All resins except Duolite C-3 increased in volume; in most cases the major part of the increase took place during the first 50 cycles. It is possible that this may
TABLE IV.
TOTAL VOLUME OF STANDARD CANEJUICE TREATED
RESINS
BY (50% ion removal)
Juice Treated, Gallons/Cu. Ft. 500 Cycles 1000 Cycles 1500 Cycles Ainberlite IR-1 Amberlite IR-100 Catex Dowex 30 Dowex 50 Duolite C-1 Duolite C-3 Duolite C-3J6 Ionac C-284 ZeoKarb H Amberlite IR-4 Amberlite IR-4B Dertcidite Duolite A-2 Duolite A-3 Duolite A-2J6 Ionac A-293
4 i ,'do0
57;ooo
60 ;000
86;OOO
...
46,'dOO 49,000 50,000 39,000 128,000 153,000 98,000 116,000 105,000 108,000 . . I
...
68,'OOO
74 id00 56,000 185,000 203,000 140,000 168,000
...
CAPACITY OF RESINS TABLE V. ASH REMOVAL Btandard Juice, Gallons/Cu. Ft. Resin ,-Times Cycled Original 50 150 300 500 Amberlite IR-1 Amberlite IR-100 Catex Dowex 30 Dowex 50 Duolite C-1 Duolite C-3 Duolite C-3J6 Ionac (2-284 ZeoKarb H
AT 90% REMOVAL 35 41 38 36 45 38 32 31 26 28 24 25 48 43 45 29 80 .. 24 2 i 26 28 32 37 35 36 51 . . 50 33 35 32 36 34 33 27 25
Amberlite IR-1 Amberlite IR-100 Catex Dowex 30 Dowex 50 Duolite C-1 Duolite C-3 Duolite C-3J6 Ionac C-284 ZeoKarb H
AT 50% REMOVAL 50 55 48 50 52 47 38 40 35 34 34 28 61 57 64 .. .. 87 29 29 .. 31 46 40 47 47 58 57 45 48 46 47 38 47 43 36
Amberlite IR-1 Amberlite IR-100 Catex Dowex 30 Dowex 50 Duolite C-1 Duolite C-3 Duclite C-3J6 Ionac C-284 ZeoKarb H
AT 2 5 % RnnfovaL 58 59 56 55 50 44 40 42 35 .. .. 61 69 91 ,. .. .. .. 33 48 48 44 50 58 59 .. 54 50 56 53 47 53 42 43
..
I .
..
.. .. ..
..
..
32 33
19
46 65
1000
.. ..
-
1500
,
23
0
,.
..
0 ,
0 ._ .
26 34 30 33 0
18 12 34 0
._ 3.5
44 42 28
0 0
33
ii
59
53
.5 0
50
44 45 48 31
91 29 45 46 37
53 46 33 64 96 a1 52
.,
4i
..
.. .
I
..
38
..
59 ,
.
..
..
.. ..
42
io 29
2s .. 56
.. ..
48
44
65
45 32
..
37
..
June 1952
I N D U S T R I A L A N D EN G I N E E R I N G C H E M I S T R Y
1419
cycles and a t 1500 cycles no value exceeds 1.20. In addition, the ratios decrease as the resin becomes more nearly exhausted; at 25% removal no ratio exceeds 1.50, only one being over 1.30. Ionac A-293, from all evidence, is not nearly exhausted at the 25% removal point, which may explain why this resin shows high ratios even at this point. As this resin was tested only to 500 cycles, it is not possible t o evaluate the results of continued use. Thus, the total capacity for sulfuric acid is generally about the same as for hydrochloric acid, and apparently higher capacities merely indicate more efficient removal by the regenerated resin. I n other words, there is more leakage of hydrochloric acid. When these resins are subjected to continued use for the treatment of cane juice, this higher efficiency for sulfuric acid removal appears to be lost. Apparently the power of the resin to removeweakeracids from solution deterioratesmore rapidly thandoesthe effectiveness for strongacids. Because of residual alkalinity from the regeneration of the resins, the first portion of each run is always alkaline. This makes it impossible to determine the maximum removal of acid by titration. The only measure of maximum removal is the conductivity. The consistency of the results with sulfuric acid and hydrochloric acid is remarkable. I n every case, the data show progressively poorer maximum removal with each testing stage. This is shown for hydrochloric acid runs in Figure 12. JUICE CAPACITY. With the exception of AmberliteIR-4B and Ionac A-293 the anion exchange resins suffered no great loss in capacity. Amberlite IR-4B dropped definitely from its original very high capacity to values of the same order of magnitude as the other resins. Ionac A-293 lost a considerable portion of its original low capacity. The data in Table IV show that Amberlite IR4B still had treated the greatest volume of juice -at the 1500-cycle stage. 0 1.0 2.0 3.0 4.0 Figure 13 shows the change in capacity of the VOLUME - LITERS resins at the 90% removal stage. Figure 8. Conductivity-Volume Relationship for Anion Exchange Juice RESINVOLUMES AND WEIGHTS. The volumes Runs of anion exchange resins tested either remain con500-cycle stage stant or increase slowly, except for Duolite A-2J6 See Figure 7 for symbols and Ionac A-293. Results for Duolite A-2J6 would appear to indicate some mechanical loss during the first 150 cycles. Ionac A-293 decreases in volume at than for hydrochloric acid, the results shown here are unexpected. each testing stage; no correlation between volume and capacity The resins may be divided into three groups: Duolites A-2 and A-3, with a nearly constant ratio of sulfuric/hydrochloric acid not far from unity (maxiTABLE VI. RESINVOLUME AND WEIGHTCHANQE mum 1.27); Amberlites IR-4, 1500-Cycle 1000-Cycle 1500-Cycle Orig. Wt., 500-Cyole, Orig. Vol., IR-4B, and Deacidite, where Wt., Grams Vol., MI. Vol., MI. Grams Vol., M1. M1. . the ratio varies widely; and 308.1 366.3 Amberlite IR-1 Amberlite IR-100 300.6 9312 308.6 300: 7 3ib: 6 103.2 Ionac A-293 with a high ratio 804.2 310.6 Crttex Dowex 30 301.5 12016 313.9 3ii:4 3ii:9 120.7 at all times. Dowex 50 304.6 328.6 .. .. If the data for the second 348.8 301.9 Duolite C-1 105:g 2%: 3 Duolite C-3 302.4 99:2 297.5 298:O group are examined, each resin 300.0 100.8 325.3 326.8 97.6a Duolite C-3J6 shows at least one value apIonrtc C-284 314.6 83.7 344.6 350.1 3%: 3 97.0 ZeoKarb H 303.2 111.3 308.1 311.8 313.7 132.7 proximating a ratio of 2 (capac34.4 143.6 157.9 39.4 ity for sulhric acid twice that 35.4 144.0 140.1 34.3 22.3 139.4 147.4 18.2 for hydrochloric acid at the 33.5 159.3 170.0 28.4 32.4" aftme removal point and num... 122.2 33.7 147.5 ... ber of cycles). However, these .. ... ratios decrease as the resins are 5 1000 cycles only. tested after a larger number of
..
...
0
....
...
..
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
1420
Vol. 44, No. 6
was found. As sevrral rcsins gained in lveighi, x decrease dors not measure mrrhanical loss. Development and removal of fines v i t h Amberlite IR4 was observed. CONCLUSIQS S
The results obtained in this study einphasiee the impossibility of judging the useful life of ion eschange resins by any arbitrary nicthod. By choosing a single testing procedure, one can show that cation exchange resins develop little loss in capacity (Figure 10) or that most of them loee all of their capacity (Figure 11); that, some anion PXchange resins are very stable (E'ig,ure 13), or that they deteriorate rapidly (Figure 12). Since the resins tested were inanufact'urcd in thc years 1944-46, t,he refiults cannot be applied directly to resins of the same manufacturers which are currently available. They do, however, shoiv the
t-
z
w
0
a W Q
I D W
>
0
z W a
v)
z
0
z
4
1.0
0
-
CYCLES
LITERS
Figure 9. Anions Removed-Volume Relationship for Anion Exchange Juice Runs 500-cycle stage See Figure 7 for symbols
1500
Figure 10. Cation Exchange Salt R u n s Showing Capacity Change with Use To Z5yc removal point
1 e?vberliie I R I BiQmberlite
.
1000
500
4.0
3.0
2.0
VOLUME
1
1
I
I
1RiOO
i
LL I-
mUeaCI3I
re
e3uol i t e A ?
&Duo1 it: A3 v b c I i :.. A?J6 X l i r a c A293
j6 0
-
J
6
P 40
a46
0
J
500
loo0
c YCLES
Figure 11. Cation Exchange Juice Runs Showing Capacity Change w i t h Use To 90% ash removal point
500
1500
IO00
1500
CYCLES
Figure 12. Anion Exchange Acid Runs Showing M i n i m u m Conductivity Increase with Use With hydrochloric acid
Figure 13. Anion Exchange Juice R u n s Showing Capacity Change with Use To 90 7' removal point
lune 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
wide variation in behavior which can be expected and the necessity of developing criteria of stability which are closely defined by the specific purposes for which the resins are t o be used. For the treatment of cane juice the outstanding cation exchange resin is Dowex 50. Unfortunately it was possible to put this resin through only 500 cycles but a t this point it has more than double the capacity of any other resin in salt runs and more than soy0greater capacity for juice. Of the resins that were tested for 1500 cycles, Dowex 30 maintained the highest capacity for cane juice, followed by Ionac C-284 and Duolike C-3. The salt capacity of Duolite C-3 is approximately the same as Dowex 30 a t this stage. All of the cation resina carried to the 1500-cycle stage appeared to be good for considerably more than 1500 more cycles without extreme decrease in capacity. Ionac C-284 shows a high increase in volume which would be disadvantageous in commercial operation. Amberlite IR-4B maintained the highest capacity for both acid and cane juice through 1500 cycles. Amberlite IR-4 was in second place with regard to juice and Duolite A-2 third. The acid capacity of Duolite A-2 was higher than that of Amberlite IR-4, however. The Amberlites developed considerable fines, giving greater evidence of mechanical disintegration than Duolite A-2. The anion resins appeared to be less stable than the cation resins and it is probable that another 1500 cycles would bring about substantial losses in capacity. Alf of the anion resins showed a marked increase in volume with use.
1421
The work indicates that the better resins, both cation and anion, are suffieiently stable to be of value in the treatment of cane juice. NOMENCLATURE
A, At B
= = = C, = C, = E = N. = Nb =
N, = S
=
T
= =
T,
T,
=
V, = V, = W =
ash from untreated juice, % ash from treated juice, % ' titration value of juice used actual concentration, grams per 100 ml. standard concentration, grams per 100 ml. effluent volume, ml. normality of acid normality of base used in titrations normality of sodium chloride solution maximum value for sodium removed in sodium chloride run a t same stage titration value of sample under consideration, ml. titration value of cation exchange-treated drip sample, m1. maximum value of titration during run, ml. actual initial resin volume, ml. standard resin volume, 125 or 300 ml. volume of water in resin bed, ml. LITERATURE CITED
(1) Kunin, Robert, IND.ENQ.CHEM.,40, 41-5 (1948). (2)Zbid., 41,65-9 (1949). (3)Ibid., 42, 66-70 (1960). (4) Nachod, F. C.,"Ion Exchange Theory and Application," New York. Academic Press. Inc.. 1949. (5) Thompson, R. B.,and Roberts, E. J., C h m . Eng. Progress, 43, 97-102 (1947). (6) Tompkins, E. R., Anal. Chem., 22, 1352-9 (1960). RECEIVED for review May 22, 1951.
ACCEPTED November 26, 1951.
Highly Cross-Linked Polvbutadiene J
PREPARATION AND MECHANICAL BEHAVIOR JOHN A. COFFMAN Locomotive & Car E q u i p m e n t Laboratory, General Electric Co., Erie, P a .
P
OLYBUTADIENE, on being heated for several days a t about 250" C . , changes from a rubber to a hard, rigid material. The formation of such a material was mentioned briefly by hlorton, Patterson, Donovan, and Little (6),and in somewhat more detail by Russian investigators (B), who called it a "thermoebonite." It seems to have been extensively investigated by I. G. Farbenindustrie in Germany, judging by a patent assigned t o that company (7). There are also indications that the Russians have used a material made by thermal treatment of their sodium polymerized polybutadiene in practical applications. However, many of the details of the preparation of thermally cross-linked polybutadiene, and of the varying properties which result from different degrees of cross linking, have not been reported. Furthermore, several points of general theoretical interest have been encountered in investigating the properties of the material, and it seemed desirable to make this information available. PREPARATION
POLYBUTADIENE RUBBER. Most of the material was made by emulsion polymerization, using otassium persulfate as the catalyst, potassium ferricyanide wit! excess caustic as the promoter, dodecyl mercaptan a s the modifying agent, and potassium stearate as the emulsifier. The polymerization temperature was 26" t o 30" C., and the reaction was carried t o 90 t o 95% of completion. The latices were coagulated with hydrochloric aoid after addition of 1t o Zyoof phenyl-2-naphthylamine, and the resulting
rubber was washed and dried under vacuum, I n experiments where the presence of the antioxidant was undesirable, it was removed by acetone extraction of the rubber just rior to use. MOLDING OF SAMPLES AND INITIAL CURE. ?he curing agent used for lightly crowlinking the polybutadiene rubber was ditert-butyl peroxide or 2,2-bis (tert-butylperoxy) butane. Molding conditions were 3 t o 15 minutes a t 180" C., the peroxide being milled into the rubber just prior t o molding. Depending upon the molecular weight of the rubber and whether or not phenyl-2naphthylamine was present, the amount of eroxide needed t o effect a satisfactory cure varied from 1 to 5 g Five per cent of peroxide in the presence of 1% of phenyl-2-naphthylamine was about equivalent in curing action t o 1.5% of peroxide in an extracted sample of rubber. The molded pieces were clear and well knit, with smooth surfaces and sharp corners. They were still rubbery, and had a very high degree of rebound, but the material had much more gel character than ordinary vulcanized rubber. The ultimate elongation was only about 25%, and the tensile and tear strengths were exceedingly low. Molded pieces showed no tendency whatever t o melt down or deform at temperatures up to 300" C., and exhibited no cold flow whatever, when tested by compressing samples t o two thirds of their original height for a period of a month. THERMAL HARDENING.On being baked a t about 250" C. for 1 to 10 days, the molded material gradually changed from a rubbery gel to a harder, tougher resin, and finally became a very hard,
