I
RICHARD C. GLOGAU,'
DAVID 0. HALVORSON, and W. JOHN SLOANZ
Repauno Development Laboratory, Explosives Department, E. I. du Pont de Nemours & Co., Inc., Gibbstown, N. 1.
Separate Sulfonic and Sulfuric Acids with an Ion Exchange Resin This process permits the separation of two strong acids of differing molecular size by the screening effect of a highly cross-linked ion exchange resin, and requires only water for regeneration
SULFONIC
ACIDS are prepared by reaction of a n organic compound with fuming sulfuric acid or sulfur trioxide. An excess of sulfonating agent is usually required, and on a commercial scale, the excess sulfate is often precipitated with limestone to form CaS04. A more complete removal of sulfate may be obtained by using a barium salt; but i n either case, the calcium o r barium sulfate is difficult to filter, and the filter cake must be washed thoroughly to remove product. I n order to avoid the filtration of Cas04 o r BaS04, the use of a n ion exchange resin was investigated. Anderson, Bauman, and Harrington (7) developed a method by which a strong acid, such as sulfuric acid, could be separated from a weak acid, a n organic material, or certain salts by taking advantage of the sulfate-bisulfate equilibrium on anion exchange resins. In this method, sulfuric acid is picked u p from a n aqueous two-component solution by a column of resin such as Dowex 1-X8 in the sulfate form by means of the following reaction :
RzS04
+ H+ + HSOI-
2RHS04
T h e other component passes through the column, thus effecting the separation. T h e resin is regenerated to the sulfate form simply by washing with water: 2RHS04
RzSOd
+ 2H+ + SO*-
By substituting a more highly crosslinked resin for Dowex 1-X8, two strong acids may be separated, provided they differ in molecular size, since the adsorption of the larger acid will be hindered. By using highly concentrated acid solutions. physical adsorption of undissociated sulfuric acid becomes important and aids in the separation. T h e separations of sulfuric acid from 5-sulfoisophthalic acid, from benzenesulfonic acid, and from $-toluene sulfonic acid were studied. Most of the work Present address, Explosives Department, E. I. du Pont de Nemours & Co., Inc., Wilmington, Del. 2 Present address, Engineering Service Division, Engineering Department, E. I. du Pont de Nemours & Co., Inc., Wilmington, Del.
,
was done with 5-sulfoisophthalic acid (SIPA) a n d Dowex 1-Xl6. Experiments were carried out by batch techniques, in fixed-bed columns, and in a moving-bed system. This scheme offers a n interesting method for separating two strong acids, particularly sulfonic and sulfuric acids. Because of the large volume of sulfonic acids manufactured, this process has definite industrial potential, since expensive chemical regeneration of the resin is unnecessary.
Experimental
Batch Capacity Tests. -4 measured volume of regenerated sulfate-form resin was suction filtered to remove interstitial water, then the resin was transferred to a beaker, and an equal volume of feed solution was weighed and added. The feed solution was a diluted sulfonation mixture which usually contained from 8 to 10% H,SO4 and from 25 to 5Oy0sulfoisophthalic acid. The mixture was swirled in a constant temperature bath (usually at 70" C.) for 30 minutes for standard tests, and longer for adsorption rate studies. Then the mixture was suction filtered and washed rapidly with two eaual volumes of cold water. The feed so1;tion and the weighed filtrate-including the washes-were analyzed for HzS04 and SIPA as follows. Total acidity was measured by titration with base, then HzSO4 was determined by adding a sample to a large excess of aniline to precipitate aniline sulfate, which was filtered and titrated with base. Then the amounts of each acid retained by the resin were calculated. Fixed-Bed System. Most of the fixedbed work was carried out in a semiworks system consisting of four jacketed glass columns, two inches in diameter and 22 feet in height, filled with 20 feet of Dowex 1-X16 sulfate-form resin. Feed solution containing 10% HQS04 and 50% SIPA was pumped upflow through two columns in series, while the other two columns were rinsed and regenerated with water. When sulfuric acid breakthrough occurred in the effluent from the second column in the series, the first column was replaced by the second column, and the second column was replaced by a regenerated column. In a typical cycle, 30 pounds of feed solution were fed at 70 O C . , and 10 pounds of product solution containing a low concentration of H2S04 were obtained. The feed solution in the exhausted column was rinsed out downflow with a rapid flow of hot water, and the rinse effluent was concentrated for reuse as feed solution. The rinsed column was then regenerated with
a prolonged slow flow of water. This cycle took 7 to 10 hours, and was repeated for the duration of the run. Moving-Bed System. The moving-bed system was a semicontinuous pulsed-bed unit of the type described by Higgins and Roberts (2) and was constructed of 1-inch glass pipe plus the necessary pumps and valves. I t also contained Dowex 1-X16, sulfate-form resin. As originally designed, the system consisted of loading, rinse, and regeneration sections separated by plug valves. The separating valves were closed while the liquids were flowing. When HzS04 breakthrough occurred in the proauct effluent, the feed, rinse, and regeneration flows were stopped; the separating valves were opened; and the resin bed'was moved a few inches hydraulically in a direction opposite to that of the liquid flow. This caused regenerated resin to move into the loading section, exhausted resin to move into the rinsing section, and rinsed resin to move into the regenerating section. Then the separating valves were closed and the liquid flows were resumed until HzS04 breakthrough occurred again. I n practice, however, difficulty with resin movement was experienced because of the resin swelling (3 to 5%) which occurred as the resin passed from the loading section to the rinsing and regenerating sections. Free resin movement was obtained, however, in a system in which the regeneration section was separated from the other sections. The dimensions of the loading, rinsing, and regenerating sections were 16, 1.5, and 16 feet, respectively. The resin was moved 5 to 12 inches every 5 to t 0 minutes. The feed CONTACT TIME 4
30 MIN
l
1
-TI
1
I
>
t
a u
%
S I P A IN TEED SOLUTION
Figure 1. SIPA cdpacity decreased while HzS04 capacity increased with increasing SIPA concentration VOL. 53, NO. 4
APRIL 1961
275
solution was 10% HzS04 .~ and 44% SIPA. and feed rates of-1 to 4 gPm/sq. of bed area cross-section were used successhlly. The attrition of resin particles in the course of their travel in the moving-bed unit was studied. Although a local concentration of fines was occasionally found in the resin valves, no appreciable change in the screen size of the resin was noted over a period of 17 cycles-375 operating hours.
fc
Acid Capacity Decreased with Increasing Crosslinkage and in Several Cases the SlPA Was Virtually Excluded Feed Solution 10% H?SOI
10% HzSO4,
50% SIPA Acid Capacity. Acid Capacity, Lb./Cu. Ft. Lb./Cu. Ft. Hi304 SIPA HnSO; SIPA
30% SIPA
~~~i~ (Sulfate
1 1 1 1
Results a n d Discussion Effect of Resin Crosslinkage. T h e results of batch capacity . tests performed on samples of Dowex 1 manufactured
Form) - X7.5 - X16 - X18 - X20
- x22 1 - X24
3.3 2.3 2.0 2.3 1.3
1.8 1.5 1.8 1.0
...
...
3.3 3.1 3.7
0.5 1.8 0.9
. ..
0.8
0.0
o.l
. ..
o.l
TEMPERATURE: 7 0 4 C . SIPA CONCENTRATION: 4 5 %
t-r---
,
% H 2SO4
Figure 2. Sulfuric acid capacity of 1 - X 1 6 is roughly proportional to H2S04 concentration in the feed F E E D : 10% H 2 S O 4 , 5 0 % S l P A --C
2 " x 20' COLUMN
--&-
1/2" x 4 ' C O L U M N
EXTRAPOLATIONS
8
6
HEIGHT
IO
12
OF EXCHANGE ZONE ( f t . )
Figure 3. The exchange zone height reached a minimum value of very low flow rates
5
feet for
---e
3
4
5
6
BED VOLUMES O F
7
9
IC
EFFLUENT
Figure 4. The shape o f the curves indicates that the SlPA adsorption rate i s controlled b y diffusion within the resin particle, while the HzS04 adsorption i s primarily controlled b y film diffusion
276
INDUSTRIAL AND ENGINEERING CHEMISTRY
with 7.5 to 24y0 divinylbenzene crosslinking agent are shown in the table. Most of the work described from here on was done with Dowex 1-XI6 because 1-X16 excluded SIPA satisfactorily under certain conditions and resins of higher crosslinkage were not commercially available. Effect of Feed Composition. As shown in the table, sulfuric acid capacity of all of the resins was increased by using a feed solution containing a higher concentrarion of SIPA. This effect is shown more clearly for Dowex 1 - X l 6 in Figure 1. Here the HzS04 concentration in the feed was held constant a t loyo,while the SIPA concentration was varied from 30 to 50%. T h e effect of varying HzS04 concentration lrhile holding SIPA concentration constant is shown in Figure 2. Effect of Temperature. An increase in temperature from 2 5 " to 50" C. caused the sulfuric acid capacity to increase from 1.6 to 3.0 pounds per cubic foot. This temperature effect was also borne out a t 70 to 90 C. by semiworks data, which indicated that the average resin loading increased from 1.8 to 2.2 pounds per cubic feet as the operating temperature was increased from 70 to 90' C. Effect of Flow Rate. T h e exchange zone height, hB, was determined in the semiworks fixed beds for difTerent flow rates by the method of Moison ( 3 ) > and was found to reach a minimum value of 5 feet for verylow flow rates (Figure 3). Mechanism of H2S04Adsorption. A typical concentration-volume curve is shown in Figure 4. Sulfuric acid is considerably undissociated at high acid concentrations ( 4 ) . For this reason, it is believed that physical adsorption of undissociated sulfuric acid by the resin matrix plays a n important role in the process described here, in addition to the simple ion exchange pick-up of bisulfate ion. Observations to support this theory are : Acid concentration affects sulfuric acid capacity of the resin as shown in Figures 1 and 2. As total acid concentration increases, the H2S04 capacity increases. This seems to be a direct result of the increase in the amount of undissociated HZSOa with increasing acid concentration. An increase in temperature causes an increase in HzS04 capacity. For a simple ion exchange mechanism, an increase in temperature may cause an increase in the rate of adsorption, but not in the total capacity. I n simple ion exchange processes, the exchange zone height is usually considerably less than the 5 to 10 feet shown in Figure 3. The sulfuric acid capacitj of fresh, unused resin was almost twice the theoretical ion exchange capacity, indicating that another mechanism was operating.
SULFONIC A N D SULFURIC A C I D S E P A R A T I O N Physical adsorption of H2S04 is not the sole operating mechanism, however, since complete removal of sulfuric acid from SIPA was accomplished several times with the moving-bed system. This would not be possible unless ionexchange adsorption of HS04- ion were also occurring, since HSO4- ion exists to a large degree even at very high acid concentrations (4). Rinsing the Resin. Because the resin column was filled with a concentrated solution of valuable product after H&04 breakthrough, efficient rinse techniques were necessary to recover the solution for recycle. A rinse method found feasible was to flow fresh water through the exhausted bed at a high flow rate at 70' C. (Figures 5 a n d 6). Regeneration. After .the resin was rinsed rapidly, the water flow rate was decreased and the regeneration was allowed to proceed. Two t o four bed volumes of water were usually employed over a 2-hour period for regeneration. Figure 7 shows the effects of regeneration conditions on resin capacity. Fixed-Bed Operation. T h e integrated operation of feed, rinse, and regeneration steps was carried out in the fixed-bed system. For a continuous operating period of over 400 hours (51 feed cycles), the average sulfuric acid removal was 95%. T h e average product solution contained 4570 SIPA and less than 0.570 HzS04. The resin loading averaged 1.5 pounds of H2S04 per cubic foot of resin, and the yield of SIPA over the separation process averaged 79%. Moving-Bed Operation. Operation of the moving-bed system for 137 hours, during which time the regeneration section was separated from the other sections, resulted in an average sulfuric acid removal of 99%. T h e average product contained 4170 SIPA and 0.1% HzS04, and the average resin loading was 1.05 pounds of HaS04 per cubic foot of resin, although loadings as high as 1.8 pounds of H 2 S 0 4per cubic foot were attained. Resin Life. T h e resin loadings of 1.5 to 1.8 pounds of H2S04 per cubic foot obtained in the fixed- and moving-bed units were lower than had been obtained in laboratory capacity tests. This was because the resin capacity fell off rapidly after a few cycles of operation, then nearly leveled off, as shown in Figure 8. The cycles indicated in Figure 8 were of short duration. T o determine whether capacity drop was a function of the number of loadingregeneration cycles or of the length of contact time with the feed solution, unused Dowex 1-Xl6, sulfate form, was soaked in SIPA-HzSOI feed solutions for periods of 1 hour and 24 hours. After regeneration with water, capacity
DOWEX I-X16, UPFLOW
MESH RESIN
20-50
10% H z S 0 4 , 50 % SIPA
OF
TOTAL
53LUTION
HEAD L O S S
( PSIG/FT
RESIN
OF
BED )
Figure 5. The flow rate-limiting factor was the high pressure drop resulting from the concentrated viscous feed solution and from the 3 to 5% increase in resin volume that occurs as the resin is rinsed
20-50 15.0,
,
l
05
,
MESH
,
I O
RESIN
,
,
,
15
20
i
l
I
l
25
l
l 30
TOTAL HEAD LOSS ( PSIG/FT.
OF
RESIN
BED )
Figure 6. After the feed solution was pushed out with water, the head loss dropped to values approaching normal
R E S I N RINSED WITH ONE BED VOLUME OF WATER A L L OPERATIONS CARRIED O U T AT 7OoC. F E E D SOLUTION:
50 % S I P A , 9 %
HzS04
BED VOLUMES OF REGENERATION WATER
Figure 7. Excellent regeneration was obtained with only 0.5 bed volume of water applied over a 6-hour period, indicating that sufficient regeneration time is more critical than the amount of water used
tests showed that the 24-hour sample had a sulfuric acid capacity of 1.6 pounds per cubic foot whereas the 1-hour sample had a capacity of 3.3 pounds per cubic foot indicating that as milch capacity
drop occurred in one lengthy cycle as in 100 short cycles. Figure 9 shows the results of tests in which Dowex 1-X16 was allowed to remain in contact with feed solution for VOL. 53, NO. 4
o
APRIL 1961
277
-
TEMPERATURE
FEED
d'
IO
Figure 8.
20
SOLUTION
30
25'C
-
20
10% H p S 0 4
,b
'
,
4 5 % SlPb
70
60
80
90
'
Id,
No OF LOADINGS ( c y c l e s )
The capacity drop was due to adsorption of SIPA
varying periods of time, after which the amount of each acid adsorbed by the resin was measured. With a feed solution containing only 30% SIPA and 1070 HzSO?, the sulfuric acid was almost completely displaced by the SIPA after 24 hours contact time. T h e resin has a higher selectivity for SIPA than H2S04, and this selectivity is enhanced at low acid concentrations. T h e semiworks fixed-bed columns rapidly became fouled when low feed concentrations and long contact times were used, both of which encourage SIPA adsorption. T h e wet resin contained 25 to 30$& SIPA even after prolonged regeneration with water, and its HzS04 capacity was only 0.3 pound per cubic foot. Kormal HzS04 capacity was restored, however, by treatment with 57, KNO, solution a t 70' C. followed
by reconversion to the sulfate form. This reduced the SIPA content to 470 although the resin again picked u p SIPA slowly during use. Most lots of Dowex l-X16 behaved satisfactorily in standard capacity tests except for one lot which picked u p more SIPA than HzS04. Since this lot had met all specifications, the crosslinkage specification proposed for this separation is believed to be borderline; that is, the pore size of Dowex 1-X16 is very near the size of the SIPA molecule, so that small variations in resin composition and other variables could cause large differences in the amount of acid adsorption. Highly Cross-linked Resins. Since Dowex I-X16 has a high selectivity for SIPA under certain conditions, it was desirable to use an even more highly
cross-linked resin to exclude SIPA better, even though a workable process was developed using Dowex l -X16, Therefore, Dowex 1-Xl8,1-X20, and 1-X22, made especially for us by the Dow Chemical Company, were tested in the sulfate form by contacting these resins with SIPA-HzSO4 feed solution for various periods. All of the resins except Dowex 1-X22 adsorbed appreciable amounts of SIPA in 6 hours, and the use of less concentrated feed solutions resulted in increased SIP.4 adsorption. However, Dowex 1-X22 adsorbed less than ' 1 2 pound of SIPA per cubic foot in 6 hours, no matter which feed concentration was used. Dowex 1-X22 attained maximum H2SO4 adsorption (2 pounds per cubic foot) more slowly than Dowex 1-X16, but the HzS04 adsorption remained at this level for 6 hours without decreasing when 50% SIPA, 10% Has04 feed \vas used. Thus, it appears that Dowex 1-X22 would be a much better resin than Dowex l-XI6 for this particular separation. This work terminated before we could put Dowex 1-X22 to an actual test, however. Other Sulfonic Acids. Two experiments were done to show that other sulfonic acids could be separated from sulfuric acid in this manner: An aqueous solution of benzenesulfonic acid and sulfuric acid was passed through a short column of Dowex 1-X16 in the sulfate form. '4 maximum of 8970 of the sulfuric acid was removed from the effluent sulfonic acid sTlution. Over 95% of the benzenesulfonic acid was recovered by rinsing the resin with water. When an aqueous solution of p-toluenesulfonic acid and sulfuric acid was treated in a similar manner, a maximum of 6870 removal of HtS04 was attained, and again, over 95y0of the sulfonic acid was recovered by rinsing.
Acknowledgment Many of the personnel in the Chemical Section and the Development Section a t the laboratory workcd as a team on the development of this process.
Literature Cited (1) Anderson, R . E., Bauman, W. C., Harrington, D. F., IND.ENG.CHEY.47, 1620 (1955). (2) Higgins, I. R . , Roberts, J. T . , C.hern. &g. Progr. Symp. Series 50, 87 (1954). ( 3 ) Moison, R . L., "Ion Exchangc Kinetics," A.1.Ch.E. Meeting, Scptember 1957. (4) Young, T. F., Blatz, L. A . , Chem. Rev. 44, 102 (1949). RECEIVED for review October 10, 1960 A C C E P T E D January 25, 1961 CONTACT TIME
-
HOURS
Figure 9. Maximum sulfuric acid adsorption occurred in one-half hour, after which time the HzS04 was gradually displaced b y SIPA
278
INDUSTRIAL AND ENGINEERING CHEMISTRY
Presented at Twelfth Delaware Science Symposium, Wilmington, Del.: January 13, 1960, and at Division of Industrial and Engineering Chemistry, 138th Meeting, ACS, New York,, N. Y., September 1960.
