INDUSTRIAL AND ENGINEERING CHEMISTRY
744
Comparison of Tables I and I1 shows that the rate of reduction in flow with additions of P205 is substantially the same with washed sugar as with distilled water where both have been defecated and limed to the same point. It would appear, then, that the principal effect in reducing flow comes from phosphoric acid and lime floc, and not from the bodies or elements it may remove from the sugar liquor. There has been some feeling that if the flocs formed by the phosphoric acid and lime defecation could be handled without breaking, easier filtration would result, but this is not true in the light of our experience. The amount and character of filter aid required depends upon the amount and character of suspended slimes t o be removed. This is a standard rule. The filter aid functions to keep the cake from sliming over, and to accomplish this, the surface area of the filter aid must predominate over the surface area of the slimes being removed.
Affination Liquors To get the same color removal on affination liquors as on washed sugar, it is necessary to use about eight times as much P205as on the washed sugar liquors. Although this liquor is harder t o filter and requires more filter aid, it is still a reasonable-cost operation.
Whole Raw Sugar Filtration and Defecation Additional runs were made on whole raw sugar filtration in view of the increased interest in filtering whole liquors as compared with washed liquors. The data presented here show that it is economically feasible t o filter, or defecate and filter, whole sugar juice without washing. Whether this procedure can be used in a refinery t o advantage is beyond the scope of the paper, but if it can be used, costs will be reduced.
Vol. 34, No. 6
Using raw sugar 219 and filtering whole sugar liquor at 63' Brix and SO" C. with 10 pounds of precoat per 100 square feet of filter area, with a defecation cycl'e of 4 hours and a pH of 7.4, the following results were obtained: Run No. 1 2
Speedex %Iter Aid
% PlOa
0.50
None 0.01
3 4 5
0.50 0.55 0.60 1.00
0.03 0.05 0.03
Bleach,
%
None 24
Flow Rate Gal./'Sq. Ft./kr. 12.7 3.3
0.7 0.6
40
47
0.8
40
Clarity Very good Exoellent Excellent Excellent Exoellent
On sugar 234 a t 63' Brix on a 4-hour cycle, using 10 pounds of filter aid per 100 square feet of filter area for precoating, limed to a pH of 7.4 the following results were obtained on a flowrate with a bleach of 42 per cent: Run No. 1 2 3
% Speedex Filter Aid 0.5 0.5
% PsOa None
0.038 0.038
1.0
Flow Rate Gal./&. Ft./hr, 15 1.2 1.4
The drop-off in flow rate is higher with sugar 219 than with sugar 234, but again the ratio is not far from that for water or for washed sugar liquor. However, it is obvious that whole sugar liquors can be economically filtered with or without defecation with phosphoric acid.
Procedure for Adding P,Os Better results, lower filter aid consumption, and better bleaches are obtained by adding the PZOS substantially ahead of liming. Further tests are being made to determine whether 3 minutes is sufficient time. At present we believe that the longer the interval is between Pz06addition and lime addition, the better the result will be, PRESENTED in a group of papere on Filtration and Cla,rifiostion before the Division of Sugar Chemistry and Teohnology at the 102nd iMeeting of the AMERICAN CHEMICAL SOCIETY, Atlantio City, N . J .
DECOLORIZING FILTER AIDS ROBERT BOYD British Columbia Sugar Relining Company, Ltd., Vancouver, B. C., Canada
I
N RECEXT years a number of organic compounds have
been discovered which are capable of extracting mineral constituents from aqueous solutions; these compounds fall into two general classes according to whether they depress or raise the hydrogen-ion concentration of the solution with which they are brought into contact-in other words, whether they absorb cations or anions. These compounds are finding use in the softening of hard waters, and their use has been suggested in the purification of sugar solutions. Some of these compounds not only absorb ions from solution but exert a remarkable decolorizing power in removing colored organic substances associated with sugar in factory juices and in refinery liquors. The response of these compounds to change in the pH of the surrounding medium renders their regeneration possible both with respect t o ions absorbed and to the organic nonsugar. In applying ionic absorbents to the sugar industry, a number of factors are t o be taken into consideration which appear not a t all or only to a limited extent in water softening; factors such as temperature, viscosity, concentration of specific ions and of organic nonsugars, relative concentration of ions, and economic considerations are of prime importance, so that
R. W. SCHMIDT The Dicalite Company, Torrance, Calif.
a material which is satisfactory in a water softening plant may be unsuitable for the sugar industry. In sugar refining in particular, where high-density and highviscosity liquors must be handled, the problem is aggravated; to meet the exacting conditions a new product, Kyrite, waa developed a t the refinery of the British Columbia Sugar Refining Company, where a large-scale process has been in active operation during the past three years. This material remains in the process and is continuously regenerated without loss in activity. A second material, M-23, with somewhat similar properties, was developed a t The Dicalite Company's plant. This product is nonregenerative and is used on a throwaway basis.
ICyrite Kyrite is produced in the form of a filter aid so that it can be used in standard refinery filter presses and readily handled by those familiar with industrial sugar practices. It consists of a very active absorbent resin deposited upon a diatomaceous base; in this way a large active surface is presented to the liquor to be treated and, as the layer of resin on the diatoms is thin, the viscosity and time factors are largely discounted.
June, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
745
be removed from such soluThe resin used has special tions. In such circumstances properties in regard to the Two new decolorizing a t e r aids have been the possibility of removing absorption of iron and calcium ions, and is active in absorbing developed recently for the sugar industry. iron by a base exchanger is organic nonsugars; it thus proThe product Kyrite (British Columbia . particularly attractive* vides the sugar refiner with a Sugar-Refinery) is a cation-absorbing resin new purifying agent. This new Source of Iron in Sugar deposited on a high-grade diatomaceous agent does not displace standLiquors filter aid, and possesses unique decolorizing ard refining practices. Bone In the beet sugar industry char and activated carbons and iron absorption properties. Sugar reiron in the juice as it is prochave definite places to fill, but finery liquors treated with Kyrite yield soft essed appears to be derived whereas these agents find their sugars with excellent bloom, and Kyrite has entirely from corrosion of iron highest and (in the case of been in commercial use for some years for equipment; beet juice leaving activated carbons) their chief the carbonation station is this purpose. It is handled on standard economic use in the treatment practically iron-free, but subseof high-purity materials, Kyfiltration equipment and is regenerated quently iron is picked up by rite is of special value for the after use. corrosion and dark-colored purification of low-grade prodM-23 represents a second type of decolorisproductsare formed. This has ucts such as affination and ing filter aid with good filtrability, good been noticed in marked degree granulated sirups. It may at the thin-juice sulfur station. clarification, and high decolorizing value. therefore be regarded as comI n the cane sugar refining inplementary to bone char and The tremendous surface area of the diadustry iron compounds enter activated carbon in a process tomaceous silica filter aids is first carbonthe refinery in the raw sugar for the complete refining of coated and then activated. M-23 used in and are augmented by corraw sugar. the sugar refinery will not only yield brilrosion at a number of points as Reference has been made to the sugar is processed. Iron in liantly clarified filtrates but will also parthe iron-ion absorptive propraw sugar received for refining erty of Kyrite, and the use of tially decolorize the liquor and thus reduce varies from 3 to 80 p. p. m. It the Kyrite process for the rethe load on the char. 'The material is is not known whether this iron moval of iron is of special interintended to be used on a throwaway basis. is derived from the cane juice est to sugar refiners producing or is largely the result of corsoft sugars. It is important rosion in the raw sugar factory. that soft sugars varying in color When the raw sugar is from cream to golden yellow a f i e d , the greater partof the and to brown should be attraciron compounds pms into the a f i a t i o n sirup. Cloth filtration tive in appearance and have a good bloom. The production with the aid of a diatomaoeous filter aid such as Speedflow of sugars with these qualities has been difficult; when soft removes from 20 to 40 per cent of the iron present. Presugars are made from regular refinery liquors, they invariably sumably part of the iron present in raw sugar is in combinahave a disagreeable gray tone, and many attempts have been tion with, or absorbed by, colloidal compounds, and theremade to overcome this. At one time the sugars were washed fore this portion is easily removed by simple filtration. A with a yellow dye to mask the gray, and some refiners used further portion of the iron compounds may be removed by sulfur dioxide as a bleach. Neither of these expedients wm defecation with lime and phosphoric acid followed by filtrasatisfactory. If a mineral acid, such as phosphoric, is added tion, but the filtrate still contains iron in such a state of comto the sugar, the gray color disappears but a pungent odor of bination as to render its removal impossible with any standacetic acid appears; while the sugar is improved in appearard refinery procedure. The action of bone char and acance at first, the color is not stable but turns dark in storage tivated carbons was investigated, and the results indicate and red tones appear, so that after some time the sugar is markedly different from what it wm when newly produced. that only small amounts of iron may be removed by such agents. I n some cases the bone char filtration process actually The gray color is due to the presence of iron, and if the iron increased the iron content of the liquor treated. This inis removed, the sugar has the bloom so much desired by r e crease may be due to solution of iron from the cast-iron cistern finers. This has been found true of sugars derived from raw sugar from a number of sources, and there is no remon to beused to hold the char and also to iron present in the char itself. lieve it is not generally true of all raw sugars. . This latter effect was demonstrated when the walls of the cistern had been sandblasted and painted; a decrease of iron It has long been known that the presence of iron in sugar in the effluent from the char was obtained. juices and sirups leads to the formation of dark-colored bodies In view of the marked effect which iron has on the color of due chiefly to combination with organic substances of a polyphenal character occurring in plant juices, but it is questionsugar products and the dficulty experienced in removing it able if the subject has received the attention it deserves. from solution, the rate of solution of iron in sugar solutions becomes of interest. Iron and steel are largely used for tanks, This may be due to the comparatively small amounts of iron pump casings, filter presses, char filters, vacuum pans, and involved and also to the practical difficulties encountered in attempts to remove the iron from sugar solutions. The charmany other types of equipment found in sugar refineries, so that the sugar in solution is more or less in contact with iron acter of the problem will be better understood when it is stated that in the case of a soft sugar of a light fancy grade, throughout the whole refining process. Hitherto the rate of corrosion has been regarded primarily from the point of view iron will produce a distinct gray tone if present in amount of cost of replacement without much regard to the action of greater than 2 p. p. m. With darker grades the tolerance is somewhat higher. Refinery liquors contain varying amounts the iron on the sugar products. No figures are available to of iron up to 100 or 200 p. p. m. of sugar solids. In the presshow what proportion of the iron found in the final refinery ence of large amounts of sugar the common precipitants of products is derived from the raw sugar, but that an appreiron fail, and no chemical method is known whereby iron can ciable amount comes from corrosion of equipment may be
INDUSTRIAL AND ENGINEERING CHEMISTRY
746
assumed from considerations to be discussed. The rate of solution of iron in dense sugar solution with an alkaline reaction in the cold is appreciable as shown by the following data: Equal volumes (150 ml. each) of granulated sirup were adjusted to various reactions ranging from pH 6.6 to 7.5, and t o each one was exposed a clean iron surface, 71 sq. cm. in area, a t 26" C. for 72 hours. The iron content of the sirup was determined before and after the exposure in each case. The results obtained were: P 1-I
6.6
7.0 7.2 7.5
,--
Before
0.00053 0.00083 0.00053 0.00053
Iron,
Yoon Solids Aft8r
Differenoe
0.01840 n.oifi70 n. 01130
0.01787 0.01617 0.01077 0.00837
o.oos9o
These figures were obtained a t 26" C. In the refinery high temperatures prevail, and the solution rate will be much greater. The effect of the solution of iron may be noted in the refinery after a shutdown. During the shutdown, m a t e rials in process are held in iron or steel tanks which afford ample opportunity for heavy contamination to take place. On starting up after such a period, the refinery liquors are much darker in color than usual, and color and chemical analysis confirm the presence of excess iron. The corrosion of iron equipment is heavy where acid sweet waters occur-for example, a t the char cisterns, evaporator supply tanks, etc.-but these points are obvious and do not need special comment. Our experience is that the greater part of the color of refinery-concentrated sweet water is due to iron; the effect of the removal of this constituent is striking.
Vol. 34, No. 6
to the Kyrite slurry, and the mixture agitated for a few minutes. The agitator is stopped when the regenerated Kyrite settles rapidly t o the bottom of the tank; it is drawn off t o an Oliver vacuum filter on which the Kyrite cake is washed t o a low acid content. The acid solution is run to the sewer and the regenerated Kyrite returned to treat a fresh batch of liquor. Three 1000-pound batches of Kyrite are required to keep the station operating Eiteadily; the material can be regenerated an indefinite number of times, and from time to time some new material is added to compensate for mechanical loss in the operations. The three grades of soft sugar produced are known as Best Brown, Golden Yellow, and Fancy Soft, respectively. For the manufacture of Best Brown, affination sirup and molasses are used. Both materials are cloth-filtered with Ilicalite Speedflow as a filter aid and then treated with Kyrite. The molasses is high in iron and receives a double treatment. The massecuite for Best Brown sugar should contain about 10 p. p. m. iron in order to yield a sugar with lesri than 8 p. p. m. For Golden Yellow sugar the base materials are granulated sirup of suitable purity and soft sirup spun off a previous soft sugar strike. Both materials are cloth-filtered and then Kyritetreated. Fancy Soft is made from a light colored char liquor and soft sirup. It is unnecessary to cloth filter the char liquor before the Kyrite treatment. Golden Yellow should have an iron content not greater than 3 p. p. m. (Figure l), and Fancy Soft, not more than 2 p. p. m. Sugars with less amounts of iron may be obtained by the Xyrite process, but there seems no need for working to lower limits as the effect of the iron at these levels is not apparent to the eye. It may also be added that the accurate determination of one part iron per million of sugar solids in a routine control laboratory is not an easy task.
Kyrite Process While Kyrite does absorb cations in general, the process as used a t present in the Vancouver refinery is employed solely for the removal of iron ions and organic coloring matter in liquors used for soft sugars, although provision has been made to permit the expansion necessary to treat all affination sirup produced. Regenerated Kyrite from a previous cycle is added to the liquor to be treated in an Everdur tank equipped with mechanical agitation. The amount of Kyrite added to each batch is held constant, but the size of the batch of liquor is varied according to the iron content. The mixture of Kyrite and liquor is kept a t 75-80" C. for about 10 minutes. The addition of the Kyrite causes the pH of the solution to fall, due to ion absorption; therefore milk of lime or soda ash is added to adjust the final pH t o 6.8. The liquor is then fltered through one of the two Kelly filters; the design of these filters was modified so that the leaves are at right angles to the central axis of the shell and the filtering area is increased to 976 square feet. The clear filtrate is sent directly to pan storage tanks to be boiled to one of the three grades of soft sugar normally produced. It is not allowed t o come into contact with iron; all piping used is copper, the pan is copper and brass, and the storage tanks which are disused bone char cisterns have been painted inside with a Bakelite paint and varnish. The Kyrite cake on the Kelly leaves is partially sweetened off by pumping thin sweet water produced a t other refinery stations; it is then hosed of€ with thin sweet water, and the resultant slurry is pumped to two No. 9 Sweetland presses in which the cake is washed sugarfree with hot water. Washing with hot water is continued for about 30 minutes to remove coloring matter absorbed by the Kyrite from the liquor; then the Kyrite is transferred in the form of a slurry to the acid regenerating tank. This tank is lined with acid-resisting brick and cement, and equipped with mechanical agitation. Sulfuric acid is added
7
FIGURB 1. UNTREATED SUGAR (Zejt) CONTAINING 50.2 P. P. M. IRON AND GOLDION YELLOWSUGAR(right) CONTAININQ 2.2 P. P. M. IRON AFTER TREATMENT WITH KYRITE
The application of the Kyrite process t o the purification of beet juice has been studied and a 'large-scale experimental run made, but provision has not yet been made for continuous operation. The action of the Kyrite on the beet juice is to remove practically all the calcium ions present as lime salts and a portion of the potassium ions. This is accomplished by treating the thin beet juice leaving the second carbonation filtration station with Kyrite. The absorption of calcium and potassium ions reduces the alkaliinity and liberates carbon dioxide. The filtrate from the Kyrite process goes directly t o the evaporator where the carbon dioxide is removed and the alkalinity of the juice rises. The amount of Kyrite used is regulated to give a pH value of 7.4 in the first body of the evaporator. With juice from good beets treated with 5 per cent of Kyrite on solids, a remarkable purification is obtained. The ash content is reduced from 10 t o 15 per cent, the depth of color is reduced by half, lime salts are largely eliminated, and a limpid fast-boiling juice results. The need for sulfuring the juice is eliminated by this process.
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
'June, 1942
747
Dicalite M-23 M-23 is not regenerated but is used on a throwaway basis. This material shows the properties of a valuable filtering agent or filter aid, and in addition has powerful decolorizing properties. M-23 can be described as diatomaceous earth substantially coated with active carbon in which the decolorizing power of the carbon present is materially enhanced m compared with that per unit of carbon made from the same raw materid. A natural. grade of diatomaceous filter aid withexcellentspicular structure is mixed with a oarbomeous material, sawdust or wood shavings. No particular typeof organic material is necessary for the productionof M-23; however, pine or redwood shavings are equal if not FIQ~E 2. DIFFERENCE IN COLOR REMOVAL AFTER FILTRATION WITH si;&ly superior to the other materials from DICALITE FILTDR AID AND WITH DICALITE M-23 which carbons have been produced. Same liquor 81Unfiltered Same liquor filIn the preparation of diatomaceous filter tered with final sugar tered with filter aids to be used as such, the natural diatoliquor aid B product A maceous powder is frequently calcined to improve the surface condition, which results in an that the decolorization produced by a mixture of equal parts improvement in the flow mte. In the preparation of M-23 would be more than half that produced by a dose of carbon this calcination step is not necessary, for in the carbonizaequal to the combined weights. It is well known that the retion of the organic material the diatomaceous earth is heated moval of unit-color from solutions containing color bodies beto ca,loimtism temperature. comes increasingly difficult as the concentration of these bodies decreases. It seems reasonable to anticipate, however, Properties of Final Product that the decolorizing effebt of a 2 per cent dose of a mixture with its In I the proprties Of M-23 are containing one half decolorizing and one half nondecolorizdiatomaceous and carbonaceous both 'lone ing material would be substantially equal to that of the 1 per and in simple admixture, and with certain representative cent decolorant which it contains, commercial sugardecolorizing carbons. These various matern the case of the this expectation w ~ realized, s rials were separateiy applied to the decolorization and clariwithin the h i t s of accuracy of the test, but the M-23 prodfieation of StaIKh'd raw sugar solutions in the used uct, A , has & decolorizing value far in excess of the equivalent in the industry. The sugar was raw Hawaiian cane and the of its weight contentof charcoal; in the tests on which the w&9 made up to The temperature Of the following data are based, the dosage of carbon alone is unidecolorizing test Was 80" C. The determbatiom of color formly 1 per cent of the weight of sugar in the test solution, reduction and clarity were made on the filtrates from the while the dosage of the mixtures and of product A is uniformly flow rate tests, a single solution being used for all the tests. 2 per cent, half of which (1per cent) is carbon: Since the standard for measuring reduction in color reads Deoolorizing Decolorizing in per cent of the total original color, it would be expected Carbon Value, % Mixture Value, %
, TABLEI. PROPERTIES OF DECOLORIZINQ CARBONS Filter Aid0
Carbon,
%
Ash, '
%
Dose,
%
Decolorizing Value,
%
Flow Rate
Clarity
:f P
1 I 1% c
50 55 40 50 2% final product A
45
50 40 45 70
Product A has a decolorizing value over one and a half timem as great as that of an equivalent simple mixture of its components. Flow Rate and Clarity Relations As explained above, the decolorizing carbons have only a
60
G
G J
77.8 77.8 38.9
22.2 22.2 01.1
2
H H K
96.5 96.5 48.1
3.5
8.5
2 1
70 55
51.9
2
, 50
I
1
2
60
45
0.12 0.04 0.42
Fair Fair Fair
0.14 0.10 0.28
Fair Poor Brilliant
4.1 2 60 90.9 0.16 Fair 96.9 4.1 1 40 0.08 Poor 47.9 52.1 2 40 0.82 Brilliant 0 A is an example of the M-23 produot. B was prepared by heating the same natural diatomaceous earth to 900' C. without the addition of carbonaceous matter or of any chemical or fluxing agent. C is & wood charcoal grepared by carbonizing and activating the wood flour used in making A ut without addition of diatomaoeous material. it was reduced to the fineness necessary to develo its decolorizing vaiue properly. D is a mechanical mixture of B and ni!( about equal proportlons so as to give substantially the same ratio of carbon to ash as found in product A . after the constituents had been finished and cooled they were intimatkly mixed. Q H and I are commercial sugar decolori.6nh carbons of well-known brands ded'in the condition in which they were received. J , F, and L are intimat; mixtures of G. H, and I,respectively. with an equal weight of filter aid B .
I L
slight effect in promoting filtration and, because of their extreme fineness, are difficult to retain on the filter cloth and give an improperly clarified, cloudy filtrate. For these reasons it is customary, in decolorizing sugar solutions, to use a filter aid along with the carbon. In such mixtures the carboni is solely for decoloriaing while the filter aid removes colloidal suspensoids existing in the raw sugar or, if these suspensoids have been removed by a previous clarification, to assist ia removing the spent carbon from the solution. In view of these properties it seems reasonable t o anticipate that a mixture of carbon with filter aid will have a flow rate lower than that of the filter aid alone but greater than that of the carbon alone. Also, the clarity of the filtrate produced by the mixture may be lower than that of the filtrate from the filter aid alone, but it will be much better than that of the filtrate from the carbon alone.
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
748
For the same reasons, if the final product were assumed to be a mere mixture of carbon and filter aid rather than the composite substance we believe it to be, the flow rate and clarity produced by a unit dose of final product A should be substantially identical with the flow rate and clarity produced by the same dose of an equivalent mechanical mixture, D, These predictions were fully realized for the mixtures but not for product A: -1% TreatmentFlow rate Clarity Brilliant Filter aid 5 1.00 Fair Carbon U 0.04 Poor Carbon H 0.10 Poor Carbon I 0.08 Poor Charcoal C 0.10 Brilliant Final product A 0.75
-2% TreatmentFlow rate Clarity Filter aid B 1.20 Brilliant Mixture J 0.42 Fair Mixture K 0.28 Brilliant Brilliant Mixture L 0.82 Brilliant Mixture D 0.42 Final product A 0.90 Brilliant
On a 2 per cent basis the flow rate of the final product is more thandouble that of the correspondingmixture and substantially the same as the flow rate of the 1 per cent filter aid addition, while the clarity of the filtrate from the product is substantially identical with that of the filtrate from the filter aid alone. The advantage in flow rate of final product A on a 1 per cent dosage is even more apparent if this material is compared to equal percentages of carbons C, G, H , and I . These carbons, however, are not used by themselves as a general rule, and the better comparison is furnished on the mixture basis. Figure 2 illustrates the results of filtration with filter aid B and with final product A . It appears evident that this new product is in no sense a mixture of decolorizing carbon with diatomaceous filter aid but is, on the contrary, a substance having properties entirely different from and more valuable than those of the corresponding mixture.
M-23 in the Sugar Factory Raw cane sugar liquors contain certain percentages of suspended, insoluble, finely divided solids that are ordinarily removed by filtration using diatomaceous silica filter aids.
Vol. 34, No. 6
I n addition to the suspended solids there is a small percentage of dissolved impurities and the sirup is fairly dark. The color as well as some of the dissolved impurities are removed in char filters, When M-23 is used in the sugarhouse, it is proposed that this product be substituted for the diatomaceous filter aid ordinarily employed. Since M-23 product has equal filter aid efficiency, it will effectively remove the suspended solids by the normal filtration steps and in addition will show a good decolorizing effect on the plant liquors. This treatment will give results comparable to bone char and will permit simplified handling. A considerable proportion of the load on the char houses is thus removed and a considerable saving in the refining process results. In plants not employing a char house for decolorization of their washed sugar liquors, this step can be accomplished by the use of M-23. I n these plants effective and efficient treatment of the washed sugar liquor ii3 obtained by a threestage countercurrent decolorizing step. The sugar liquor is decolorized in large mechanically agitated tanks, and the M23 is removed by filtration in a pressure flter. M-23 does not require additional filter aid to obtain satisfactory filtration of the bleached sugar liquor. The results are considerable saving in the decreased amount of solids to be handled, less press labor, less wash water, and fewer sugar losses. Small-scale tests indicate that as little as 6.0 pounds of M-23 per ton of sugar solids yields a decolorized washed sugar liquor of excellent quality, and a filtration rate of 10 to 20 gallons per square foot per hour is obtained. Another advantage obtained on the hI-23 material is the comparative ease of wetting. The product does not require the long stirring period usually associated with the use of vegetable carbons but instead wets itself readily with a minimum of labor and dusting. PREBENTID in a group of papers on Decolorizing Carbons and Analysis before the Division of Sugar Chemistry and Technology a t the 102nd Meeting of the AMERICAN CHEXICAL SOCIETY~ Atlantic Cily, N. J.
Corrosion of Steel by issolved Carbon Dioxide and Qxygen G . T. SIWERDAS' AND H. H. UHLIG2 Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Mass. NEXPECTED corrosion difficulties have been found in parts of the condensate return lines of central steam heating systems. The condensates carried by these return lines are essentially dilute solutions of carbon dioxide and oxygen. As a result, the problem of steel corrosion in solutions of carbon dioxide and oxygen and the relative importance of each gas has received renewed interest and is the subject of the present study. The major factors to be considered in this problem are temperature, dissolved carbon dioxide and oxygen concentrations, pH, circulation of corroding medium, metal composition, and duration of attack. Present address, The M. W. Kellogg Company, New York. N. Y. N. Y.
I Present address, General Electria Comprtny, Sahenectady,
Previous Investigations
h number of incidental experiments bearing on the effect of carbon dioxide and oxygen on the corrosion of iron and steel have been reported. Rhodes and Clark (8)reported that up to 200 pounds per square inch, corrosion a t 22" C. increases rapidly with carbon dioxide pressure but reaches a constant value a t about 300 pound:; per square inch, further increase in pressure having no eflect. Whitman, Russell, and Altieri (14) found that dissolved carbon dioxide increased corrosion as the pH was lowered, and that a t a given pH more corrosion was caused by carbon dioxide than by hydrochloric acid. Girard (4) confirmed these results, as did Groesbeck and Waldron (6) who investigated a wide range of
