November 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
Figure 12. Photomicrograph near Edge of Inside Surface of Cooling Coil Tube Seven Inches from Weld
is columbium or molybdenum. Type 317 steel is the least affected, structurally. It shows carbide precipitation in the grain boundaries of the core. This was caused by the temperature to which it was exposed. It shows this change in structure when held a t 426" to 815 O C. a t atmospheric pressure. Types 321 and 347 show a new phase in the corners between grains. This is a very fast etching material, and it is distributed throughout the core. No evidence of carbide precipitation can be seen, even a t high magnifications, so evidently the titanium and columbium are still effective as stabilizers of the carbon. The new phase appears t o be much like the unknown phase described by Clark and Freeman ( 2 ) . It appears to be similar to that obtained by them in Types 347, 309, and 310 stainless steels when exposed to temperatures of 538" to 982" C. in air for 24 hours or more. Clark and Freeman ( 2 )show that apparently this phase markedly reduces the strength of these alloys a t high temperatures. CONCLUSIONS
The effect of hydrogen and nitrogen from 13,000 to 15,000 pounds per square inch pressures and at temperatures of 204' to 593" C. has been studied on various steels. The more carbon the steels originally contained the more they were attacked.
2521
The carbon was removed and voids were left in the steels throughout their cross sections. The more carbon the steels originally contained the more nitrogen they absorbed. Nickel in amounts of 1.75 to 3.47y0 added to low carbon steel does not give the steel any additional resistance. The small amount of molybdenum in the 1.75% nickel steel seems to have incieased the attack. The chromium steels show decreased attack with increased chromium content. The addition of the carbide-forming elements to a 5% chromium steel did not prevent attack as reported previously by investigators using lower pressures. The austenitic chromium-nickel steels were the least attacked of any studied, and although they contained the carbide-forming elements molybdenum, titanium, and columbium, they showed a thin high nitrogen case on exposure. All of these steels showed changes in the core structure, probably because of the temperatures to which they were exposed. Therefore, it is believed that although the austenitic chromiumnickel stainless steels are the best for use a t high pressures of hydrogen and nitrogen, care should be taken in the design of high pressure vessels for such use. Samples of these steels should be removed after periods of operation to determine whether the attack has been progressive. , ACKNOWLEDGMENT
The writer wishes to thank J. H. Shapleigh of the engineering department 'of Hercules Powder Company for arranging for t h e exposure of the samples in the ammofiia synthesis plant and for the data of the conditions of this exposure. He also wishes t o thank William Harding and Walter Dickinson of the Globe Steel Tubes Co. laboratories for the chemical analyses and metallography. LITERATURE CITED (1) Bartz, M. H., and Rawlins, C. E., Corrosion, 4 , 'No. 5 , 201 (1948). (2) Clark, C. L., and Freeman, J. W., Trans. Am. SOC.Metals, 38, 148-79 (1947). (3) Evans. T. C., Mech. Ena.. 70. 414-16 (1948). (4) Naumann, F. K., Tech. Mitteilungen KTUPP, A. Forschungaberichte9 1, No. 12,223-34 (1948). (5) Schuyten, J., Corrosion and Muterial Protect., 4, No. 5 , 13-18 (1947).
RECEIVED March 21,1949. j
Color Removal in Sugar Liquors bv Svnthetic Resins J
J
I. M. ABRAMS AND B. N. DICKINSON
'
Chemical Process Company, Redwood City, Calq. Ion exchange treatment of industrial sugar liquors is always accompanied by decolorization. Experience has shown that color removal is more effective on the anion than on the resinous-type cation exchanger. Considerable circumstantial evidence has indicated that decolorization and deionization are frequently independent of each other. Concurrent pH and color-removal curves obtained with two types of anion exchange resins and with both a beet sugar liquor and a corn sugar liquor serve to illustrate both a parallelism and a lack of correlation between the two phenomena. A new type of adsorptive resin which effectively removes color without influencing pH is described.
T
HE use of synthetic ion exchange resins in refining crude
sugar solutions is becoming an increasingly important tool. The separation of ionic impurities from the nonionic sugar generally consists of passing the crude juice downflow through a pair of cylindrical resin beds in series. The cation resin serves to exchange inorganic cations and nitrogenous bases or amphoteric compounds for hydrogen ions, whereas the anion exchanger generally adsorbs mineral and organic acids produced by the cation bed. The reader is referred to a number of recent publications for a more complete discussion of the general aspects of ion exchange in the sugar industry (1-8). One of the commercially important aspects of the ion exchange sugar process, however, lies in the ability of these adsorbents to
INDUSTRIAL AND ENGINEERING CHEMISTRY
2522
remove color. The extent to which the brown color, normally found in all crude sugar juices, is removed is subject to considerable variation. This phenomenon is poorly understood, The experiments in this report constitute an attempt to determine the nature of the color-removal process and to study the reIationship between color removal and deionization.
Vol. 41, No. 11
Different resins showing very similar exchange capacities give widely different color-removing capacities. Different solutions on the same resin will also bchavc differently. Another striking phenomenon frequently observed with some anion exchangers is that a resin which is completely exhausted with various acids can still effectively decolorize a solution percolated through it. All of this seemingly confusing evidence pointed to the necessity for the prescnt study. The data presented here will illustrate a case in which color removal parallels acid removal; one in which no correlation appears to exist; and one in which color removal is obtained with an essentially nonionic resinous adsorbent. EXPERIMENTAL
2 I
b
I)
RESIN
II
RLSiN
,
,
4
/ 9
I
I
24
28
A E
,
I
,
I2
20
16
3z
VOLUMES CFFLUENT PER VOLUME RESIN
It has been the authors' experience that in general color is rcmoved to a greater extent by anion exchangers than by cation exchangers of the synthetic resinous typo. This might lead one to believe that the chromophoric constituents reside in the anion portion of the molecules. It is well known also that crude sugar juices are more highly colored in alkaline than in acid solution. Wndoubtedly, then, some of the color is due to the presence of the mionic form of weak organic acids. ILowever, evidence indicates that a t least part of the color remains unaltwed by changes in pH. This may well be due to nonionic constituents.
The procedure followed was that generally employed in imi cxchange experiments. As a preliminary to ail runs the variouE sugar solutions used were passed downflow through a bed of an acid-regenerated cation exchange resin. The decationized solutions were then passed through approximately 90-ml. beds of anion exchange resins in 1-inch cylindrical glass tubes at a rate of 8 to 10 volumes per hour (1.0 to 1.25 gallons per cubic foot per minute), except where noted in the text. The anion resins were all preeonditioned by cycling at least twice with an excess of sodium hydroxidc and hydrochloric acid. Prior to the actual runs the resins m r c upflovved for a 5-minute period and then regenerated downflow with a n excess of 6 hi sodium hydroxide The excess alkali was washed out unt,il the effluent reached a pR of 9 to 10. The effluents from the anion exchange columns were collected in beakers calibrated to give volumes equal to the volumes of resin in the tubes. As each volume was collected, pH and coloi inrasurrments were made, pH being determined with a Reckman Model M meter. All color comparisons wcre made with a KlettSummcrson photoelectric colorimeter, using the influent as thf standard. I n order to eliminate pH effects on the color, the color of the influent vas determined at the same pH as the effluent The run was eontinued at least to the p H break-through (normally 6.8).
The influent solution used in the first experiment was a second carbonation thin juice (13.4" Brix). The effluent from one large cation exchange bed was blended before use and had a pH of 1.6 rind a total acidity of 0.06 N . The color was a deep amber. I n the second experiment the influent was a diluted corn sugar molasses. The thick syrup, known as Hydrol, was diluted to about 3.5 O Brix then decationized before passage through the anion exchangers. (This degree of dilution was necessary in order to bring the color range on t o the photoelectric colorimeter scale.! The total acidity of this solution was 0.03 N and the pH 2.1, bun thv color was a very deep reddish brown. DISCUSSION O F RESULTS 6
I2
18
e4
30
36
42
48
31
60
VOLUMES EFFLUWT PER Y O W M E RESIN
I n working on the purification of these crude sugar solutions by means of ion exchange, a number of observations were made with anion exchangers which indicated that the decolorization by this procws involved phenomena other than ion exchange. The following is offered as evidence: .in ammonia regenerant tends to maintain acid-adsorptive capacity better than it does color-refining capacity. Sodium hydroxide usually maintains both equally well and at a higher icvel than ammonia. Thus it may be inferred that caustic is more efficacious in preventing the blockage or poisoning of nonionic adsorptive centers. It has been the experience in this laboratory that cBolor capacity can nlwayh be rcstorcd by rinsing with mineral acid or alkali.
The results of the second carbonation juice run are shown i f h Figure 1. Two different types of anion exchangers designated a? resin A and rcsin B were run simultaneously. Both resins arc' synthetic polyamine exchangers of types currently being manufactured commercially. Resin A is a nonporous, transluccnt, geltype material, whereas resin B is a highly porous, opaque product The two resins do not differ very markedly in their effects on second carbonation juice. Resin A has a somewhat higher acid capacity whereas resin B has a slightly higher color capacity. The similarity in the S-shape of both the color curves and the pR curves indicates that a close relationship must exist between colot removal and acid removal, a t least with the exchangers and solutions used. Although the color break-through is not nearly N U sharp as the pH break-through, the changes in slope occur at nearly the same pH values. Whether or not the dips in the coloi
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
November 1949
a*t
COLOR
REMOVAL WITH HON IONIC
DUOLITE
RESIN,
4.0
5-50
L P I
B
2
m
VOLUMES
EFFLUENT
PER VOLUME RESIN
curves are real is not certain, but the fact that this phenomenon was observed with both resins seems significant. Complcte intcrpretation of these phenomena is difficult)because of the lack of specific information on the nature of the coloring matter, Some insight into the problem may be obtained by a closer examination of the curves and from a consideration of the nature of the exchange groups involved. Both resins are essentially weakly basic exchangers and hence they have a limited capacity for extremely weak acids, The decline in pH is thus due to a leakage of weak acids, and since the color leakage occurs concomitantly it may be assumed that at least part of the color is due to a weak acid type of solute. The fact that the degree of color removed levels off at about 50% would indicate either that the color constituents are strong acids or that they are being removed by an adsorption not involving primary valence forces. In view of what is known about the nature of chromophoric constituents in natural products, thc latter explanation seems more likely. The results of the Hydrol experiments with resins A and B are shown in Figure 2. I n this case, the two exchangers behave quite differently. With Resin E3 the parallel again exists between color removal and acid removal, as with second carbonation juice. However, the loss in color-refining capacity of resin A is quite rapid, although deacidification remains nearly constant. This experiment was run at a very low flow rate, only 6 volumes per hour. By using a still slower rate, the color-refining capacity can be somewhat improved, but if the rate is increased to 12 volumes per hour, the resin begins to throw color into the effluent well before the acid break-through. These variations were not observed with resin R. The differences recorded in Figure 2 serve to illustrate the differences in the activity of gel-type and porous-type exchange adsorbents. In the latter case, the fact that color and acid breakthroughs coincide would indicate the acidic nature of a t least some of the coloring matter. It is apparent, however, that the basic groups (as indicated by the high pH of the effluent) of the gel adsorbent are not readily accessible to the acidic coloring agents. NONIONIC ADSORPTION
The results in Figure 3 were obtained with an essentially nonionic type resin, Duolite $30. It is a specially activated, granular, phenolic-type resin recently developed in this laboribtory and contains groups which are not normally considered as active ion exchange radicals. It is a porous material and has proved rather effective as an adsorbent for colors occurring in various aqueous solutions. The resin is completely reversible in its activity and can be regenerated with small quantities of dilute alkali followed by a brief acid rinse. As little as 1 pound of caustic per cubio foot of Duolite 530 can be effective and only a fraction of this quantity of acid is needed for neutralization following a water rinse. The amount of acid to be used can be determined by watching the color change in the resin,
2523
The solutions used in these experiments were the two described above-namely, a decationized second carbonation juice and a decationized Hydrol. In both instances there is from 99.5%down to 80% color removal with virtually no change in pH. The evidence here points specifically to a nonionic adsorption. If ion exchange were involved one would expect some change in pK, p’articularly in the virtually unbuffered Hydrol. Duolite 5-30 can undergo some cation exchange in alkaline solutions because of the presence of some weakly acid phenolic groups. I n contact with a second carbonation juice a t pH 8.7, sufficient exchange occurred to lower the pH to 7.8 at equilibrium. However, it can be shown that cationic exchange or deashing in such solutions is not accompanied.by color removal. For example, by passing this same solution through one of the commercially available phenol-sulfonic acid-type cation exchangers, the p H waa reduced to 1.7, indicating a relativcly complete ash removal, without materially affecting the color. Further evidence of the nonionic nature of Duolite 8 3 0 is given by the fact that no pH change is incurred when the resin is contacted with an excess of a saturated sodium chloride solution. Three types of color bodies found in factory sugar juices are described by Zerban (9). These are caramel bodies, melanoidin compounds (produced by the interaction of reducing sugars with amino acids), and polyphenols (tannins). All three of these were tried on Duolite 5-30 (the nonionic adsorbent) and it was found that the color of the f i s t two (synthetic preparations) was effectively removed. Removal of an iron-tannin-type color was materially less efficient. The activity of Duolite S-30has been ascribed to three principal factors: the presence of hydrophilic groups which in turn give rise to secondary valence forces; a large surface area; and a derangement or strain in the crystal lattice of the resin polymer. The new resin described here offers a number of advantages not only for commercial applications but for academic study as well. The fact that it can be used in column operations and that it is reversible in its activity renders it a convenient adjunct to ion exchange processes. It may be attractive to the pure scientist in that its physical and chemical characteristics are somewhat better defined than those of carbon- and clay-type adsorbents. The principal conclusion to be reached as a result of this study is that the use of ion exchange resins involves phenomena other than simple ion exchange, It is hoped that this paper has given some insight into the general problem of decolorizing by resinous granular materials. Studies are prescntly being made on the adsorption of acid and basic dyes from aqueous solution. These results will be the subject of a future communication.
.
ACKNOWLEDGMENT
The authors are grateful to J. A. Ratekin of Holly Sugar Corporation, Alvarado, Calif., and to J. B. Gottfried of Corn Products Refining Company, Argo, Ill., for their generous supplies of second carbonation juice and Hydrol, respectively. LITERATURE CITED
Benin, G. S.,and Shnaider, E. E., S a & m y a
P r m . , 20, No.6, 9 (1947). Block, E., and Ritchie, R. J., Im. ENG.CHEM., 39,1581 (1947). Dickinson, B. N.,Chem. Eng., 55, 114 (1948). Ellison, H.E.,and Porter, L. B., Sugar, 43,30 (1948). Handleman, M.,and Rogge, R. H., C h . Progress, 44,583 (1948). MaoAdam, W. T., Food Packer, 28, No. 10, 34, 30 (1947). Porter, L.B.,Sugar, 42, 22 (1947). Smit, P., Chena. Weekblad, 43, 42 (1947). Zerban, F.W.,Sugar Resaarch Foundatian ( N . Y.),Technol.R&. SET.NO,2,pp. 1-9 (1947).
&.
RECEIVED November 18, 1948. Preeented before the Division of Cdloid CHEMICAL 8001mr, Chemistry at the 114th Meeting of the AMERICAN Portland, Ore.
