DESALTING SEA WATER..
.. .
A Practical Chemical Method H. L. Tigeri, S . Sussnian', _M.Lanei, and V. J. Calise THE PERMUTIT COXlPANY, NEW YORK 18. N. Y.
T h e tremendous increase in transocean flying during the recent war made critically important the development of a suitable method for making potable water from sea water. This paper reviews the various methods suggested and describes the chemical method finally adopted by the armed forces. This method is based upon the reduction of the chloride content of sea water by means of a silver
zeolite which is aided by silver oxide to the extent permitted by pH considerations. Sulfate reduction, when required, is achieved by barium hydrate, Ba(OH)I.SH20. The special requirements of this emergency process induced numerous problems in the design of desalting equipment and in the mechanical processing of the desalting mixture; these factors are also discussed in this paper.
T
bags for rain water. Fishing tackle was included in the emergency equipment with the thought that the flier could augment his water intake by chewing pieces of raw fish, but later physiological studies indicated that, in the absence of an adequate water supply, this procedure could be harmful. During the war improved distillation equipment was developed for producing larger volumes of fresh water from sea water where facilities were available for transporting the distilling equipment and the necessary fuel. For example, our landing ships usually carried such portable stills for invasion purposes. However, such devices were still too complicated and bulky for practical operation on a rubber life raft a t sea. Even the smallest still developed weighed almost 30 pounds without fuel, and it was out of the question to burden the individual pilot of a fighter plane, or even the larger group of fliers in a bomber, with such additionai bulk and weight. Another type developed was the body still which required a significant expenditure of muscular energy and body heat, in addition to having several mechanical disadvantages (IO) Solar stills underwent considerable development during the course of the war. Although useful for minimum water requirements under ideal conditions, solar stills are dependent upon t h e weather. Prior to 1942, a t the request of British authorities, the Permutit Company Ltd. and the Water Pollution Research Board, of the British Department of Scientific and Industrial Research, began experimental work on the development of a method for desalting sea water for fliers forced down a t sea A t this time the various chemical methods under investigation suffered from two major handicaps: (a)The volume of desalted water produced was not substantially greater than the volume of the chemical itself, and ( b ) no practical foolproof method had been suggested for applying the chemicals to sea water under life-raft conditions, With the entry of this country into the war, further experimental work took place both here and abroad with the ultimate
H E problem of rendering sea water p o t a b l e s problem as old as the art of sailing-became critically important with the tremendous increase in transocean flying during the recent war. On shipboard sea water is desalted by distillation. Improved distillation equipment has even been taken on lifeboats, although more often fresh water is carried in sealed containers; but the water supply problem of a fier forced down a t sea could not be met adequately by any of the existing methods because of the limited space available for emergency equipment. The wartime urgency of this problem led to an intensive search for a satisfactory method of making sea water potable. I n attempting to provide an adequate emergency drinking water supply for fliers, both physical and chemical approaches were used. Initially the emergency water supply consisted of one or more 1-pint cans of distilled water R-hich, to allow for expansion during freezing, contained only 0.7 pint of water. Thla was later supplemented by plastic collecting sheets and storage 1 Present addresq, Liquld Conditioning Corporation, 423 West 126th Street, Xeir Tork 27, Y P
Desalting K i t with Contents Removed from Container Operating instructions are printed directly on the durable Vinylite desalting bag. A special cotton filter is sealed in a plastic ring at the hase of the bag, and a quick-opening outlel plug is attached to the tube to prevent Loea. Briquets are faetened together and attached to the necketring to prevent loss. Each briquet is double-wrapped in heat-sealed waterproof wraqpings. Mending tape is provided on a plaatic card for repair of holes developed accidentally in the desalting bae.
1130
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development o i t I\ u dexiltiiig procezses, similar iii I'uiiClmitJiit:L chemical ie:ictions but differing in numerous features u i q u i p ment and npplicntion. The process finslly adopted by thts British has been described elsen-here (I, 16). This paper describes the developmcnt of the desalting equirjment adopted by the Vnited States S n r y Bureau of .%eron:?iitic*$ (52) and the Army Air Forces ( J ) . Pupular dcscriprioii; of tlii, equipment have been give11 elwr-kcre (?). REQUIRE.lIESTS FOR DES.iLTISG KITS
.
The most restrictive requirement aEecting this ii.vvstiut iuu tvas that tlie completed desalting kit must have t1.c s : m e size and shape AS the existing 1-pint emergency water cnn (1.75 X 3.88 X 4.00 inclies). This restriction \vas iinpc.scd by t1.e military nutliuritie~in order t o avuid the necessity fur r&sigiiii,g existing emergency equipment. It was &o necessary t o obtniii a substantial inm 0.7 pint oi drinkin'g water formerly obtained frl-ni space. .is shown Ister, ratios of wnter output ttj ?l:c.niic.nl :ipproximating 10 to 11 \\'ere required in order to ubtain w'ely n ratio such thlit the six \\.rapped briquets (formed by comprclisioii of the dcwlting chemical mixture) and des..ltiiig b i g n.oiild ti1 into the pint can and give tlie flier G pints of treated water ttr more than eight times the volume of drinking water he formrrly obtained from the same size eniergcncy water can. Wr:ippiiig and packaging specifications (3, 22) were desiyiietl to protect adequately the contents of the desalting kit under the extremes uf temperature, pressure, and cxpoeurc to sea water espected under service conditions. The establishment of requirements fur the chemical composition of desalted sea \vater was complicated by severd factors. In the first place, the relative composition of the vsrious constituents of sea water is reasonably constant throughout the world, but the total concentration of salts in sea water \wit.+ considerably (25'). Aiter due consideration of the areis i n i\.liic.li desaltiiig kits were most likely to be used, the arnicd furg.cs adopted :is standard a sea watcr of the following compositiuii: Catiorie Sa
7
\re+-
Ca-* Total 0
\lilliequi\slenrs,'Liter" 43 1
so, - -
96 17
544
?rIilliequi~alents/literX 50
Anions c'1-
HCOa-
-
~Iilliequi\.nlenrs.Li,er 495
47
-2 544
p . p . m . a 3 CaCOa.
Although this standard artificial sea water omits the numerous minor constituents of natural sea water, it was felt' that tlicsc constituents could safely be neglected ior the purposes of this investigation and of evaluating the performancc of desalting equipment. The second complicating factor was the difficulty of obtaining agreement among various physiological authorities on the nmsimum permissible salt content oi desalted se11 water and on the distribution of the various ions in this desalted vater. As finally adopted the Army ( 3 ) and S a v y (22) specifications for dcsalted sea water were in substantial agreement on the total salt content, but differed iii that the Army specifiwtion required suliatc reduction whereas thc srrvy specification did i i o t . Table I presents both specifications for desnlted 3ea water, together with the performancc of the desalting briquete under service conditions. t
The Picture nt the Top Shows a Briquet of Desnlting Chemical. Sext the Briquet I s Dropped iiito the Plastic Desalting Rag Filled with Sea Water to the Marked Line. In the Third Photo the Hard Briquet Disrupts Spontaneously, and Water and Chemical Are Thoroughly l l i x e d by Knending. .ifter about an Hour Clenr Water Is Sucked through the Filter at the Bottom of tlie nag.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
1132 CHEMiCAL PROCESSING
logically satisfactory xater. I-Iowxver, the physical manipulations required by two precipitations and filtrations were too complex for use under life-raft conditions, arid many observers found the tasie of the treated water object,ionable.
h l E C H 4 N I C A L PROCESSING
x ISODIUM A L U M I N O
sea n-s.ter with a mixture of phenyl mercuric gluconate or glutamate arid .I trace of uric acid. This pi ocess suffers from the serious handicap that use of the recommended dosage in diluted sea waters n-odd not be safe because the treating chemicals are someu hat soluble. Another precipitation method, proposed by Frisch ( 1 2 ) treats the sea water n ith a mixture of lead fluoride and aluminum or iron fluoride according to the following equations:
I 0RlqUETTlNG PRESS
PLATE-AND-FRAMi FILTRATE
I
WRAPPING MACHINE (CELLOPHANE)
1 1
WRAPPING MACHINE
1
DRIER
(FOIL)
DEMINER-
VlNYLlTE
CRLSHER
c*ys
+ PbF2 + N a g + PbFCl 3NaF + AlF, + Sa3AIFe
KIT
NaCl
A S S E M BLI
j
1 IMPREGNATION
TEST ~
I
TANK
+ 2PbF2+CaF2 + 2PbFCI MgCl2 + 2PbF2 +MgF2 + 2PbFCI CaC12
S H 1 PMENT
I
Figure 1.
Flow- Sheet of Sea Water Desalting Kit
Sumeroub experiments have shown that the desalting mixtures exert a po.iT-erfu1sterilizing action, probably because of the oligodynamic action of the silver compounds contained in them. Earlier investigators ieported such action on the part of similar compounds ( I 7 , 17). However, the desalting mixtures have not been recommended as a substitute for sterilization in treating contaminated sea water and, as far as emergency use on life rafts is concerned, this question does not arise as the danger of pollution at long distances from land areas is very remote. CHEMICAL DESALTING METHODS
As eaily as 1909 Gans (13) proposed the use of a silver aluminosilicate (silver zeolite) for the removal of soluble chlorides from solutions; he did not specifically mention the preparation of a potable wd,er from sea water, Jeanprost (18) later made this suggestion. The numerous chemical methods which have since been proposed for desalting sea water are based upon three operating principles-namely, precipitation, ion exchange, and combined 1011 exchange and precipitation by a supplementary chemical. PRECIPITATION. Goetz (14) proposed the production of potable water by adding silver oxide to sea water to precipitate chlorides followed by neutralization of the sodium hydroxide with citric acid:
+ 2SaCl + H20 + 2AgC1 + 2SaOH 3NaOH + H3(C,H60,) +3H,O + Sa3(C6H507) Ag20
+ H2(CjH2S4O3)--+ SaH(CjH2S403)+ H r O
(4) (5)
(6)
(7)
.4s far as m-e know, no physiological tests have been made on sea water treated by this process, nor has it been applied in actual use. ION EXCHASGE. In a review published in 1942, Parker (24) mentioned successive cation and anion exchange as a possible means for producing potable water from seawater. This two-step method of demineralizing had already been in use for some years for removing the relatively small amounts of dissolved salts in the usual fresh water supplies. A modification of this method, using a mixed cation-anion evchanger bed, &-as described in a British patent (26). However, Tiger and Sussman (30) shoned that this process was impractical for treating sea water because the volume of useful effluent obtained n-as too small compared to the volume of the materials used in the process. ' Specific data were presented by Ingleson (16) who by this method was able to obtain a volume of drinking water equal only to 1.5 times the volume of the exchange materials used. As previously mentioned, Gans (13) and Jeanprost (18) had proposed silver zeolites for removing soluble chlorides from sea water in order to make it drinkable, Austerxeil and Jeanprost (6) mentioned the desalting of sea water by either lead or silver zeolites. I n view of the toxicity of lzad salts and the relatively great water solubility of lead chloride, the dangers of using a lead zeolite for the preparation of a potable water a'e obvious. The use of a silver zeolite prepared from an organic cation exchanger is mentioned in a French patent ( 2 3 ) .
(1) (2)
This method was tested by the Kava1 Medical Research Institute and rejected because the treated water induced alkalosis and dehydration (11) as a result of the sodium citrate left in solution in the treated water. Spealman (27, 28) sought to overcome the objection to this method by neutralizing with uric acid the sodium hydroxide formed by the reaction of silver oxide and sea water: SaOH
Vol. 38, No. 11
(3)
The limited solubility of sodium hydrogen urate reduced the actual solids content of the treated water and gave a physio-
CATION AND
INITIAL
ANION ~
o
1
SILVER ZEOLITE [POWDER] C
HIGH
CAPACITY
SILVER ZEOLITE f 0~W D E R]
HIGH
1
CAPACITY I
SIL~ER
i
H'GH
CA?ACITY
SILVER
ZEOLITE 4ND ZEOLITE AND ~ ~ E S I L V E R ~OXIDE SILVE9 OXID [POWDER] 1 EBRIQUEg
Figure 2. Ratio of Delivered Water Voliime to Zeolite Volume for Five RIaterials, Each of Which Reduces the Chloride Content of Sea Water to 40 RIilliequivalents per Liter
INDUSTRIAL AND ENGINEERING CHEMISTRY
November, 1946
Whereas the silver zeolite processes mentioned above remove only chlorides in accordance with Equations 8, 9, and 10, the inclusion of a barium zeolite ( I ) in the desalting mixture permitted the removal of sulfates as well (Equations 11, 12, and 13):
+ 2SaC1 +Xa2Z + 2AgC1 AgzZ + CaClz +CaZ + 2AgC1 AgzZ + MgC1z +MgZ + 2AgC1 BaZ + NazS04+NazZ + BaS04 BaZ + Cas04 +CaZ + BaS04 BaZ + MgS04 -+- MgZ + Bas04 AgzZ
REQUIREMEKTS TABLE I. CHEIIICBL DESALTING
Army (3) Max. Typical per- performquirement mitted ance ~ v re-.
Cations, meq./liter Na +
1\1g++
(10)
Ca++ Ag Ba'+ Total Anions, meq./liter +
(11)
(12) (13)
c1so4--
Alkalinity lIethyl orange Phenolphthaloin Total
ION EXCHANGE AKD PRECIPITATION BY SCPPLEMENTARY CHEMICAL.An early proposal of this type was that of Austerf%ivered weil (4) who proposed treatment of sea water successively with a copper zeolite and with white lead:
+ 2SaC1 +CuClz + XazZ (14) CuC12 + Pb(OH)z*PbCOa +Cu(0H)z + PbClz.PbC03 (15) CuZ
A more recent patent of Meincke (21) suggests desalting sea water by treatment with phenyl mercuric hydroxide and an acid-regenerated cation exchanger, a process which is severely handicapped by the relatively low capacities of available cation exchangers : CsHsHgOH HnZ
+ K'aC1+
+
CaH6HgCl KaOH
+ 2K'aOH +Sa2Z + 2H20
(16)
(17)
While many of the above alternate chemical desalting methods were submitted to the armed forces, none proved to be adequatp for solution of the emergency drinking water problem. CHEMlSTRY OF PERMUTIT PROCESS
In the accepted process, the bulk of the solids reduction is,accomplished by the use of silver zeolite in accordance nrith Equations 8, 9, and 10. Because of its greater density and lower equivalent Feight which permitted a higher volume ratio of treated water to chemicals, silver oxide was included for supplementary chloride reduction according t o Equation 1. Where sulfate reduction was also required, barium hydroxide was included in the desalting mixture. The chemistry of this reaction is indicated by the following equation: Ba(OH)2
+ NazSOl --+
Bas04
+ 2SaOH
(18)
The means of avoiding excess causticity as a result of reactions 1 and 18are discussed in a later section. Minor constituents of the desalting mixture included activated carbon for taste improvement, a disruptor for breaking up the briquetted chemicals spontaneously upon contact with water, and a briquetting mold lubricant. The manufacture of the desalting kits can be considered in two divisions : chemical processing and mechanical processing. The various steps in the manufacturing process are outlined in Figure 1. The chemical processing consisted of the preparation of a sodium aluminosilicate and its conversion to a silver aluminosilicate. Mechanical processing steps included weighing and blending of the constituents of the desalting mixture, briquetting, briquet wrapping, and final assembly and packaging. SILVER ZEOLITE FOR CHLORIDE REDUCTION
PREPARATION OF SILVER ALUMINOSILICATE. Synthetic geltype sodium aluminosilicate cation exchangers n-ere prepared by reacting solutions of sodium silicate with solutions of aluminum salts according to the methods commonly used in the prepara-
AND
PERFORM AKCE
(8)
(9)
1133
water, mLn Ratio, vol. water delivered pe? briquet/ vol. of briquet a b
72.3 4.7
82.8 6.2
0.0 0.0 77.0
0.0
0.0 89.0
48.0 24.0 5.0 2.6 77.0
4 i i '(rnin.) (8.6)b
Xavy (22) T y ical perPormance
;\lax. permitted
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