of A1 C-kLF'IN CAL&fON AND 6. P. sI1$IOxl Research Laboratory, T h e P e r m u t i t Co., Birmingham, S. J . EHRNAN and Gustafson ( 2 ] >in their study of the eff'ect of waters of low pH on the capacit,y and stability of siliceous zeolites, observed that, the pH of softened Chicago tap water varied during the course of the Poftening process and that the
TABLE 11. I-OLULIE ~ N DOSAGE D OF REGESERAST SOLUTIOY
regenerant effluent, had a lower pH than the initial regenerant solution. T o explain their observations, t,hey assumed that the reactions involved hydrolysis or hydrat,ion of the siliceous exchangers, and that the lower capacity of these exchangers wit'h low pH waters was due to equilibrium conditions determined by t,he pH of the influent. King and Smith ( 4 ) , on determining the quantity of acid required to neutralize the alkalinity (alkalinity A or methyl orange alkalinity) of a zeolit,e-softened water prior to its use as boiler feed, observed that the alkalinity and carbon dioxide contents varied during the course of the run, and that the degree of variation of the carbon dioxide content was inversely proportional to the variation in alkalinity. I n their study, King and Smith used two types of waters, one containing i p.p,rn. of carbon dioxide and the other 15 p.p.m. With these they showed that the degree of variation in the alkalinity depended on the amount of carbon dioxide in t'he influent water. They explained their observations on the basis of formation of a hydrogen exchanger. The presence of exchangeable hydrogen in t,he greensand exchanger was shown experimentally by passing a wat,er containing alkalinity through the bed which had been treated previously with dist,illed water containing carbon dioxide. A portion of the alkalinity vias convrrted to carbon dioxide. As high methyl orange alkalinity in boiler water causes return line corrosion, due to high carbon dioxide formation, low total alkalinity in the feed water is desirable. A study was, t'herefore, made on the alkalinity variation of the effluents of the new t,ypes of cation exchangers iyhich have appeared on the market since the publication of the work of the previous investigators. EXPEKI3I ENTA L
The cation exchangers chosen for this CATIONEXCHANGERS. work are typical of the commercial types used for water softening. Properties as well as functional groups and the trade niimes of t,he produck employed are given in Table I.
Exchanger S a t u r a l siliceous
Regenerant. 411 Q/200-l\ll Bed 81 260 202 FOB 606
Lh Salt/ Cu. Ft Bed 1.26 4.0.5 3 15 9,45 9 .43 15.0
goo
a 5 % salt solution
TABLE111. CHEMICAL COMPOSITIOS OF IKFLUENTS P.P.RZ,
Calcium Rlagnesium E odi u r n Bicarbonate Sulfate Chloiide
as CaCOa 286 142 6 117 20 296
Silica as Si01 Iron as Fe Carbon dioxide a6 C O Q Water A Water B
p.P.ni 1.5 0.1 0-2 26-30
generant used in these tests depended on the capacity of the CYchangerh and are given in Table 11. The contact time of the regenerant with the bed as 15 minutes. The rinse volumr. 300 i d . of the water, was passed through a t the same rate a? the regenerant. The start of the run was taken when 5 drop3 of B (9: B soap (5)in 40 ml. of the effluent gave a permanent lather The softening rate was 50 ml. per minute and the end point of the softening run was taken when the effluent appeared hard to 8 drops of B R: B soap. This soap content is equivalent to approvimately 13 p.p.m. of total hardness expressed as calcium carbonate. The chemical composition of the waters used is given In Table 111. T h e two waters varied only in carbon dioxidc content. Water A had 0 to 2 p.p.m. of carbon dioxide and water B had 26 to 30 p.p.m. Av ILYTIC IL METHODS.The alkalinities and carbon dioxide were determined according to standard methods ( I ) , the pEI was measured n i t h a Beckman pH meter, and the sodium content was determined with a Perkin-Elmer flame photometer. RESULTS
TABLE
I.
Trade name Functional groups
Satural siliceous Zeo-Dur A1-0-Na. SO-Ka 1300
Density, g./liter wet resin Total capacity, meq./g. ., Softening operating capacity, kilograin8 as CaCO!/cu. from ft. wet Swelling dry,exchanger 70 03
Synthetic siliceous Decalso .Il-O-Na, SiO-ha 120 3.1
Sulfonated Sulfonated phenolic coal Zeo-Ihrb Zeo-Rex SOaH, COOH, SOaH. OH
310OH 2.0
300 3 5
010-14
8 56
13 106
OPERATING COSDITIONS.The runs were made with 200-ml. beds in tubes of 23-mm. diameter. The regeneration was carried out 'iTith a 5% sodium chloride solution. The volumes of re1
Present address, Brookhaven Xational Laboratory, Upton, N. 1 ' .
ALKALISlTY
Figures 1 to 5 show the methyl orange alkalinity of the effluents from five cation eschangers for the two types 01 n+ater used in these te 200 440 3.5 4.6 The curves for the natural siliceous material are similar 16 25-35 to the curves in Figure 3 (6). 78 100 T h e first five ion exchangers (Table 1 1 ) show a variat,ion i n t h e a l k a l i n i t , y of t,hrir effluents, depending on the carbon dioxide content of the influent. In the initial part of the run of the water high in carbon dioxide, the alkalinity is greater than in the influent, and, toward the end of the runs, it is less than that of the infiuent. I n thc
PROPERTIES O F c.%TION EXCHANGERS USED IiX S T U D Y O F
Type of exchange
2404
w-Sulfonated phenolic Experimental SOaH, OH
YARIATIOS
Sulionated polystyrene Permutit Q SOaH
INDUSTRIAL AND ENGINEERING CHEMISTRY
November 1954
2405
I 0
0
I t - E N D OF SOFT E F F L U E N T
v %I60
5 2
I20
-
.,
--.
WATER-A
d 0
i
"
INFLUENT ALKALINITY>
"
Y
0
2
4
6
8
10
12
14 FFFLliENT VOLUME, LITERS
EFFLUENT VOLUME, LITERS
Figtire
Figure 1. Variations of Alkalinity in Cation Exchange Effluents
2. Variations of Alkalinity i n Cation Exchange Effluents Carbonaceous cation exchanger (Zeo-Karb)
Synthetic siliceous exchanger (Decalso)
case of the sulfonated polystyrene exchanger, the variation in the alkalinity was very slight for both waters. Figure 6 shows the pH of the regenerant and rinse effluents from a natural siliceous cation exchanger. The lowering of the pEI during the regeneration depended on the carbon dioxide content of the influent prior to the rcgeneration. T!ie sodium content of an effluent from the natural siliceous cation exchanger when a water of high carbon dioxide content was treated, was higher than the total metallic cations of the influent, indicating that sodium was released in excess of thP calcium and magnesium exchanged. This is due to the exchangP of the sodium of the exchanger for hydrogen.
+I-
END
OF
SOFT EFFLUENT
\\
160 \'
DISCUSSIOI\I \\*ATER .4,Low CARBON DIOXIDE CON TEN^^. Figures 1,3, and 4 for the effluents of the mater of low carbon dioxide content show a slight increase of the methyl orange alkalinity at the start of the run and a decrease as the run proceeds. Figures 2 and 5 fihoiv that the alkalinity curves for water A are slightly below the alkalinity of the influent I n view of the carbonate found in the former curves, the indication is that hydrolysis is taking place in theye exchangers. The reaction is given hy the equation:
NaR
+ H+
-,HR
+ D;a+
(1)
whwe R is the anionic portion of the cation exchanger. The sodium hydroxide formed reacts with tlie bicarbonate to form carbonate, which gives a phenolphthalein alkalinity and caiiscs the total alkalinity to increase owing to the change from the monovalent HC03- t o the divalent co~--.
HCOE-
+ OH-
Cog--
+ €It0
(2)
The hydrolysis in siliceous, phenolic, and carbonaceous exchangers was shown b y the appearance of phenolphthalein alkalinity in boiled distilled water n.hen passed through the freshly regenerated cation exchange beds. N o phenolphthalein alkalinity was found in the effluent (boiled distilled water) of the sulfonated polystyrene exchanger (Permutit Q). Toward the end of the softening run, the calcium and inagnesiuni of the influent replace the hydrogen from the hydrogen exchanger formed, thus neutralizing the hydrolysis effect of the IoLver portion of the bed and also reacting with the bicarbonate in the influent to form carbonic acid.
Cat+ M ~ + + ) -t 2HR HCOa-
+ H+
-L.
-
IIzCOq
+
+ 2H+ HzO + CO,
(3) (4)
When most of the bed has been converted to the calcium and magnesium state, nearly all of the hydrogen is gone, so that the
80 0
Fiputw 3.
I
i
5
IO 15 E F F L U E Y T VOLUME
I
I
I
20
25
LITERS
Variations of Alkalinity i n Cation Exchange Effluents Sulfonated phenolic rosin (Zeo-Rex)
methyl orange alkalinity of t,hc effluent hegins to increase until the original alkalinity of the inHuent is reached. In order to explain the lowering of the alkalinity in Figures 2 and 5 , a study was made of the rinse, after the regeneration and the initial part of the softening run. No increase in the methyl ormge alkalinity as found, but thcre wits a trace of phenolphthalein allralinit~yindicating some carbonate formation which would imply the formation of a hydrogen exchanger at the end of the regeneration. l 1 7 ' a13, ~ IIIGIf ~ ~ CARBOX I~IoX11)li:
