730
INDUSTRIAL AND ENGINEERING CHEMISTRY
in which the temperature of the catalyst bed was measured by a movable thermocouple in a well through the center of the bed. In one experiment the catalyst v-as placed on &earn a t a temperature of 350’ and a space velocity of 250 grams of propylene oxide per liter of catalyst space per hour. I n 7 minutes the temperature a t the top of the catalyst bed rose to 410” with an increase in the production of propionaldehyde a t the expense of allyl alcohol for a short period of time. When the reaction was allowed to continue under t>heseconditions, the “hot spot’’ moved slowly down through the catalyst bed and diminished in intensity. Simultaneously, allyl alcohol production became the major reaction. On the other hand, an attempt t o blow the hot spot out by a greatly increased feed rate resulted in a rapid rise in the temperature of the hot spot accompanied by an increase in the proportion of propionaldehyde in the product. I n extreme cases considerable decomposition to gaseous product,s occurred. Thus, the results shown in Table I1 represent experiments carried out under conditions such t h a t the temperature of the catalyst bed was not excessive, except in experiment 7 in which the space velocity was 1100 grams per liter per hour. In this case, the temperature of the catalyst bed increased to the point where propionaldehyde became the major product. An at,temptto modify the activity of the catalyst by heating it to 880” C. in air for 1 hour caused a change in its appearance from the normal shiny black to a dull green. Simultaneously the x-ray diffraction pattern changed from amorphous t o that corresponding t o crystalline chromic oxide (CrpOs). Little change was observed in the ratio of allyl alcohol t o propionaldehyde in the products, but the quantity of propylene oxide reacted was decreased markedly (compare experiments l to 3 with 8 to 10). The age of the catalyst appeared to exert an effect on the ratio of allyl alcohol t o propionaldehyde as shown by a comparison of experiments 11 and 12. During the first 6 hours’ operation with a fresh sample of catalyst the ratio of allyl alcohol to propionaldehyde \?as 1.53. This run was continued until the activity of the catalyst was negligible a t the end of 98 hours of operat’ion. After reactivation by heating in a slow air stream a t 450” the catalyst was placed on stream again under similar conditions to the preceding run. The initial 6-hour sample of products gave a ratio of allyl alcohol to propionaldehyde of 2.10 and this higher ratio appeared to be maint,ained in succeeding cycles.
Vol. 43, No. 3
Although total yields from 89 to 95% of combined allvl alcohol and propionaldehyde were readily obtained, the ratio of allyl alcohol to propionaldehyde could not be increased above 2.10. The presence of minor amounts of acetone and 1-propanol \\as shown by infrared anal) sis. hcetone comprised about 4y0 of the carbonylic product and 1-propanol as present in an amount approximating 10% of the alljl alcohol. Acrolein could not be detected either by infrared or b r chemical means. Acetone presumably resulted from the direct isomerization of propylene oxide. The presence of 1-propanol can be explained by the hydrogenation of either propionaldehyde or allyl alcohol with hydrogen released by a dehydrogenation reaction occurring on the chromic oxide catalyst. It is improbable that the direct leduction of propylene oxide occurred, inasmuch as 2-propanol, which should also have been formed if this were the case, x-as not detected. ACKNOW LEDGMEUT
The authors are indebted to Edward Boettner aiid I,clla Trafelet of these laboratories for the infrared and chemical analyses, respectively. They are also indebted to Boettner for the x-ray diffraction patterns of the catalysts. LITERATURE CITED
(1) Am. Soc. Testing Materials, Method D 875-46T. (2) Baur, U. S.P a t e n t 1,906,833 ( M a y 2, 1933). (3) Ibid., 2,031,200 ( F e b . 18, 1936). (4) Dunbar, J . OTQ.Chem., 10, 501 (1945). (5) Fowler and Fitapatrick, U. 8. P a t e n t 2,426,264 (Aug:. 26, 1947). (6) Grolle and Hearne, Ibid., 2,106,347 (Jan. 25, 1938). (7) Grosse and Ipatieff, IND. EKG.C H m i . , 32, 288 (1940). (8) Ipatieff, “Catalytic Reactions a t High Temperatures and Pressures,’’ p. 162, Xew York, Macmillan Co., 1936. (9) Ipatieff and Leontovitch, Ber., 36, 2016 (1903). (10) Krassusky, Chem. Zentr., 11, 1095 (1902). (11) Law and M c S a m e e , U. S. P a t e n t 2,159,507 ( M a y 23, 1939). (12) Sabetay, Bull. SOC. chirn., 5 [5], 1419 (1938). (13) Sauer and Adkins, J . Am. Chem. Soc., 59, 1 (1937). (14) Turkevitch, Fohrer, and Taylor, Ibid., 63, 1129 (1941). (15) Young and Law, U. S.Patent) 1,917,179 ( J u l y 4 , 1933).
RECEIVED >ray
io, 1950.
EngFnFring Process development
A. C. REENTS
AND
F. H. KAHLER
ILLINOIS W A T E R T R E A T M E N T CO., ROCKFORD, ILL,
A study of operating techniques of mixed-bed deionization was undertaken to project previously reported work from the laboratory to plant scale equipment and to determine whether comparable results could be obtained. The study indicates that w-ith properly designed equipment and appropriate operating procedures a treated
water with resistivity approaching theoretical, and a uniform, neutral pH can be produced on a commercial scale. For the first time, water is available in any required volume or f l o w rate with a dissolved impurity content below 1 p.p.m.
S
been steadily improved. The sulfonated coals contain carboxylic, phenolic, and sulfonic acid groups. The sulfonated phenol-formaldehyde resins contain phenolic and sulfonic groups, while the styrene-type resins are unifunctional, containing only the sulfonic acid group. Because the styrene resins contain only the sulfonic acid groups, they are the strongest acids, and give the most uniform operation. During the same period of time, the anion exchange materials developed from the aromatic amine-formaldehyde resins ( 1 ) to
I N C E the work of Adams and Holmes ( 1 ) the system of deionization by ion exchange has been an accepted method for the purification of water. The principal field of endeavor has been in the developinent of better exchange materials. The cation exchange materials have progressed through the sulfonated natural materials (Q), such as coal, through the sulfonated phenol-formaldehyde resins ( 2 ) to the sulfonated styrene-divinyl benzene resin ( 3 ) . During this time the capacity per unit volume and the stability and resistance to oxidizing agents have
March 1951
I N D U S T R I A L A N D E N G I N E E R ING C H E M I S T R Y
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the aliphatic amine-formaldehyde resins of improved chemical resistance and higher basicity (IO). Within the past 2 years the “strong base” type of anion exchanger has been developed ( 7 ) . The last type of exchanger contains the strongly basic quaternary ammonium group. These quaternary ammonium-type resins have available hydroxyl ions for exchange and act as true anion exchangers. They are strong bases and will exchange a hydroxyl ion for anions of even very weakly ionized acids, such as carbonic or bilicic. THEORY OF MIXED BED DEIONIZATION
i
Until the advent of anion resins with lower densities and uniform particle size, practical operation of deionizing equipment on a regenerable basis necessitated housing the cation and anion exchange materials in separate vessels and passing the fluid in series through the two reaction vessels. Deionization could be accomplished by intimately mixing the exchange materials in a single vessel, but no practical method was available for separation and separate regeneration. The advent of the strong base anion exchange resins with low density has made mixed-bed deionization practical on a cyclic basis. The relatively great difference in density between the cation exchanger and strong base anion exchanger allows ready separation by hydraulic classification. hlixed-bed deionization involves passage of a fluid through an intimate mixture of an anion exchanger and a cation exchanger. There have recently been developed weakly basic anion exchange resins and weakly acidic cation exchange resins with suitable physical properties t o permit their use in mixed-bed operation. The various possible combinations of all types of exchangers and the quality of water that may be produced by each have been reported (8). A mixed bed of these regenerated resins may be visualized as a multiple pass deionizing system containing alternate layers of cation and anion exchange resins. The exchange resins used in this work have an average particle diameter of 0.5 mm.
Figure 1.
Industrial Mixed-Bed Deionizer
system located a t the interface of the resins when they are separated. When the resistance of the treated water fell below 1,OQ0,000 ohms per cubic centimeter the unit was taken out of service and regenerated by one of the methods outlined below. The regenerant solutions were drawn into the reactor vessels by means of hard rubber ejectors or by gravity feed. After regeneration, the unit was rinsed until the resistance reached 1,000,000 ohms per cubic centimeter, a t which time the unit was returned t o service. Included as accessories were a water meter, a resistivity meter, and a p H meter.
I n a bed of mixed resins 24 inches deep, consider a column 0.5 mm. in diameter. The column will contain 1219+ resin particles, each 0.5 mm. in diameter. With perfect distribution or mixing, there will be 609 cation and anion pairs in this column. The entire bed of mixed resins may be considered as a series of such columns, with cation and anion resin particles appearing as alternate layers. With perfect distribution there will then be the equivalent of 609 deionizing units operating in series a t the beginning of any cycle.
Throughout each operation cycle continuous readings were taken of the resistivity and p H of the effluent and solids content was determined at various points throyghout the run as well as on the composite sample obtained. The method of regeneration of mixed-bed units is of extreme importance. Several methods of regeneration were used.
Because ion exchange is a mass action phenomenon, passage of a fluid through a cation exchanger, followed by passage through an anion exchanger, will leave some residual ionized materials in the fluid. In mixed-bed deionization with the large number of theoretical deionizers, the residual of ionizable impurities remaining is reduced further by each successive pass and finally t o an almost unmeasurable quantity.
anion and cation exchanger. C. Dilute caustic (4%) regeneration downflow through anion exchanger, simultaneous with sulfuric acid ( 5 % ) upflow regeneration of cation exchanger. D. Rinse. E. Mix resins with air. METHOD11. A. Separate resins by backwash with water. B. Sulfuric acid (1%) scavenging rinse downflow through both anion and cation exchanger. C. Sulfuric acid ( 5 % ) regeneration downflow through cation and anion exchanger. D. Dilute caustic (4%) regeneration downflow through anion exchanger. E. Rinse. F. Mix resins with air. METHOD 111. A. Dilute sulfuric acid ( 1yo)domxflow through unit, resins still in mixed state. B. Dilute sulfuric acid ( 5 % ) downflow through mixed bed, C. Rinae. D. Separate by backwash with water. E. Caustic regenerant (4%) downflow through anion resin, at same time rinsing upflow through cation exchanger bed t o prevent contamination of acid regenerated cation exchanger with sodium salts. F. Rinse G. Mix resins with air. METHODIV. A. Separate resins by backwash with water. R. Dilute caustic (4%) downflow through both anion exchanger and cation exchanger. C. Rinse.
OPERATIONAL PROCEDURE
The operational data shown in this report were obtained from mixed-bed deionizers 4 inches in diameter by 60 inches high, 12 inches in diameter by 7 2 inches high, 14 inches in diameter by 72 inches high, and 30 inches in diameter by 96 inches high. Each was charged with a mixture of strongly acidic cation resin and strongly basic anion resin. Figure 1 shows a typical industrial type of mixed-bed deionizer. With the exception of the smallest unit, these units were piped with saran and hard rubber piping and control was by means of saran bodied diaphragm valves. The external piping and valves were arranged t o provide the required directions of flow for all phases of regeneration. I n all operations during service the water entered the top of the unit through a distribution system and passed downward through the bed of mixed resin. I n the bottom of the unit there was a collection system, which also served as a distributor during the regeneration when the direction of flow- was upward. There was also a distribution and collection
METHODI. A. Separate resins by backwash with water. B. Sulfuric acid (1%)scavenging rinse downflow through both
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 43, No. 3
are undoubtedly even more significant in the removal of ionizable materials from solutions of organic, nonionized materials. The quality of the effluent is improved by mixed-bed deionization. As water is the fluid most frequently deionized, a comparison is given here of the analyses of water produced b>-various systems of deionization. Table I gives the raw water and average effluent analyses when Rockford city water is deionized by four different methods, and shows the average analysis of the effluent water produced by the same methods of treatment, using as an influent a synthetic water made by adding sodium chloride to single deioniecd, aerated water obtained from a two-bed unit using a weak base anion exchanger. These data were taken from units with same cross-sectional bed area, operated in each case a t a flow rate of approximately 5 gallons per minute per square foot of bed area. All resin bed depths were a minimum of 24 inches and not grrater than 36
PER CENT OF CYCLE
Figure 2.
Relationship between Specific Resistance and Per Cent of Cycle
Dilute sulfuric acid ( 2 to 5y0)downflow or upflow through exchanger bed only. Rinse. Mix resins with air. METHOD V. A. Separate resins by backwash with water. B. Dilute caustic (4%) downflow through anion exchanger, simultaneous with C. C. Dilute sulfuric acid (2% t o 5y0)upflow through cation exchanger. D. Rinse resins simultaneously. E. Mix resins with air. METHODVI. A. Dilute caustic ( 4 % ) downflow through both anion exchanger and cation exchanger. R. Rinqe. C. Separate resins by backwash with water. D. Dilute sulfuric acid (2y0 to 5%) downflow or upflow through cation exchanger bed only E. Rinse. F. Mix resins with air. Any strong mineral acid can be used instead of sulfuric acid. Wherever backwash or rinse with water is indicated, soft water is recommended. Satisfactory operation can be carried out with hard water, but the treated water will have a lower average specific resistance.
D. cation E. F.
Oi
30
Figure 3.
Ca
2 HCOa c1 NO8 OH Free COz Si02 Fe COS--
%%istivity (average)
The greatest field of application of deionizing equipment has been in the treatment of water. The advantages indicated below have been observed in the treatment of water, but several of these
60
70 80 90 TEMPERATURE ’F
100
I
110
120
I
130
Variation in Specific Resistance of Pure Water with Temperature
(Parts per million) Two-Bed Mixed-Bed Weak Weak base base Raw anion Strong anion Strong Water exchanger base exchanger base after anion after anion (Rockford aeration exchanger aeration exchanger City) 0.5 0.5 0.2
