988
INDUSTRIAL AND ENGINEERING CHEMISTRY
Time
lSOo F.
0 5 10 15
100 99 96 96
Room Temp. 100
97 97 96
Time 30 45 60
Room Temp.
.''081 93 94 93
93 93 89
Then, instead of air, it would seem desirable to use something that would aid instead of deteriorate color. Possibly even waste gases from the boiler house could be utilized if their composition was suitable. ACCORDING to these results, companies using air agitation in the blowups or storage tanks are paying a penalty of additional cost for removing color. How much that cost is will depend upon the time and amount of air in contact with the sugar liquor and the temperature a t the time of contact, and money can be saved by changing the method of agitation from air to mechanical means. The amount of air used in conjunction with the modified Williamson clarifier undoubtedly accounts for the need for larger amounts of phosphoric acid to obtain 40 per cent bleach than are required when these defecated liquors are
Vol. 34, No. 8
handled on a pressure filter where no air agitation is used in the blowups. The work on this subject is being continued to determine the following factors: 1. Is this deterioration in color with air agitation due to further oxidation of iron salts, organic matter, or sugar? 2. Is the air oxidation taking place at the blowups due t o air agitation an aid to easier removal of color at the char? 3. Is there any loss of sugar due t o air agitation?
We believe that the effect of the air is to increase color due to further oxidation of the iron. We are not convinced that any sugar is lost due to air agitation. It seems, however, that the bad effect air agitation has on color is sufficient to justify prompt change to mechanical agitation of a suitable type. If paddle or mechanical agitation is adopted, it should be designed to give the degree of agitation required for best results from a uniform and rapid dispersion standpoint. PRESENTED before the Division of Sugar Chemistry and Technology at the 103rd Meeting of the AXERICANCHEXICAL SOCIETY, Memphis, Tenn.
Adjustment of the pH of Sugar Solutions with Attapulgus Clay W. A. LA LANDE, JR., J. B. SANBORN, 0. T. AEPLI, AND W. S . W. MCCARTER Porocel Corporation, Philadelphia, Penna.
0 AVOID excessive losses from inversion and decomposition, it is necessary to prevent or to correct the acidity which develops a t various stages of the sugar refining process. The refiner uses lime or sodium carbonate for the purpose. The method is objectionable because ashforming constituents are added, the color of the solution is darkened, and some sucrose is lost to the final sirup (many inorganic compounds are melassigenic). I n early experiments with mineral adsorbents as sugar refining media, it was observed that Attapulgus clay invariably produced a filtrate pH of 7.0 or above, although it was inferior to bauxite and char as a refining adsorbent. The ability to raise the pH of an acid sugar solution was not possessed by other common types of argillaceous or baseexchanging minerals. Filtration through fuller's earth as a preliminary step in the processing of a sugar solution is ineffectual in ultimate pH adjustment, since a solution so treated appears to be more susceptible to pH lowering during the subsequent adsorbent refining operation than one which has not been clay-treated. But by immediately repercolating acid bauxite and char filtrates through the properly calcined earth, it is possible to produce an extraordinarily high yield of filtrate with satisfactory pH; in many cases a slight further refining action is also obtained. The purpose of this paper is to report the results of a systematic laboratory investigation of this effect.
T
Materials and Operating Technique The Georgia fuller's earth used is a hydrated magnesium aluminum silicate known commercially as Attapulgus clay. In this report it will be referred to by this term or as clay, earth, or fuller's earth. Kerr considers Attapulgus clay to be a member of the montmorillonite group (8). Lapparent (4, 6) and Bradley (1) published data to support the view that the earth is a distinct mineral species to which the former worker gave the name "attapulgite". The clay was calcined before use a t the specified temperatures for 30 minutes in a gas-fired rotary furnace. After heating under these conditions a t 900" F. Attapulgus clay has a settled volume weight of about 32 pounds per cubic foot and a volatile matter content of 3.0 per cent. For the contacting experiments, weighed quantities of the sugar solution (usually 300 grams) and adsorbent were mixed a t 165" F. and agitated a t this temperature for 10 minutes. The suspension was separated by filtration through paper. The percolation experiments were run according to the technique described in an earlier publication ( 3 ) . All filtrations were made a t 165" F. * 2". The filters were run a t a rate proportional to 12.5 ml. per minute per 1000 ml. of clay, unless otherwise specified, to a given yield or throughput or to a given pH. The filtrates were collected in measured fractions. The pH of each fraction was determined immediately (electrometrically). Progressive composite filtrates were made by combining successive fractions. In the tabulated data the throughput a t any given time is the total quantity of sugar solids, expressed as pounds of sugar solids per pound of clay, which has passed through the filter up to that time. The various sugar solutions were analyzed by standard
,
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INDUSTRIAJL A N D E N G I N E E R I N G CHEMISTRY
methods. Unless otherwise noted the results are reported on the dry basis.
989
are unnecessary and undesirable, since the color of the solution darkens slightly as the pH is increased, although if the filters are run until the composite filtrate pH approaches Capacity Of Attapd@s 'lay for pH Adjustment 7.0, the degree of darkening is very small. Experiments Clay capacity is defined as the throughput when the pH of 5 and 6 (Table I) in which the filters were run to high yields, the total composite filtrate reaches 7.0. show that the clay which had been calcined at the highest temperature had the greatest capacity. These results were All our data show that the highest pH is obtained during the early stages of the filtration. The pH of successive fracconfirmed in every respect in the contacting method. EFFECT OF CONTACT TIME. tions decreases as the filtration continues, slowly a t first I n the percolation treatment and then more rapidly as the The"perco1ation of acid sugar liquors and contact time is varied by sirups through heat-treated Attapulgus regulating the filtration rate. throughput mounts. The clay produces filtrates with a pH of 7.0 or (With the contacting method pH of a given composite filtrate will therefore be higher it has been observed that the above. The filtrate pH increases as the calthan the pH of the last fracmaximum change in pH is cination temperature of the adsorbent is produced during the first tion added to it. EFFECT OF CLAYCALCINAraised (up to about 1500' F.). The action minutes.) Five filters were TION TEMPERATUR AE . of the earth is practically independent of charged with equal amounts the initial pH and the filtration rate. of fuller's earth which had quantity of 10-30 mesh fuller's earth was divided into been calcined a t 1100" F. A With washed sugar liquors, yields of 100five batches which were ther64" Brix char-refined washed mally activated as shown in 230 pounds of sugar solids per pound of adsugar liquor having a pH of Table I. (Uncalcined fuller's sorbent per cycle are obtained. The proc6.2 was filtered through the earth cannot be used in the essing of wash sirups results in yields of clay a t rates varying between 20-38 pounds of sugar solids per pound of 0.4 and 4 times the standard filtration method because, unrate. The results of this exder the conditions Of Operaearth. At these yields the clay shows only a tion, the clay granules disperiment appear in Table 11. integrate and form an almost slight effect on the ash and invert contents of The maximum pH attained, impervious mass; in 36 hours the solutions, while the color is very slightly the fraction pH a t a given a washed sugar liquor penedarkened. The earth used in this type of throughput, and the ultimate service can be thermally regenerated. capacity of the clay are all trated a 14-inch column of uncalcined clay to a depth of practically independent of only 5 inches.) Raw, bauxitethe flow rate in the treatment of washed sugar liquor. refined, and char-refined washed sugar liquor and charrefined wash sirup were then percolated through the clays When a 54" Brix wash sirup (char-refined) having a pH of 6.2 was filtered a t various rates through fuller's earth which at the standard temperature and filter rate. A number of filtrate fractions was collected from each filter. had been calcined a t 1100" F., the results given in Table I11 Clay calcined at 700" F. increases the pH slightly but were obtained. During the early stages of the filtration (maximum pH), definitely; however, it is incapable of producing a neutral or the longer the contact time (i. e., the slower the filtration slightly basic solution. Earths calcined a t 1300" and 1500" E'. are only slightly more effective than one calcined a t 1100" F. rate), the greater is the rise in pH. It was noted that these Other percolation experiments have shown that granular differences largely disappeared as the process continued. The effect of filtration rate on clay capacity is slight in thz clay which has been heated to 1800" F. has little or no effect upon the pH of liquor filtered through it. The high pH processing of wash sirups. values produced by the clays activated at 1300" and 1500" F, INFLUENCE OF TYPEOF SUQAR SOLUTION ON pH ADJUSTMENT. It is important to note that the concentration of sucrose in the solution probably has no effect per se on the pH changes inTEMPERATURE OF FULLER'S EARTHON TABLE-I. EFFECTOF CALCINATION duced by the adsorbent, and that three varipH RISE AND CAPACITY ables change in passing from a washed sugar Composite Filtrate pH at Calcinaliquor to a wash sirup; i. e., the contents of Throughput, tion Temp. of: Expt. Solution Initial Pounds er 700O 900° 1100" 1300" 1500° ash, invert sugar, and nonsaccharin matter all No. Processed PH Pound' F. F. F. F. F. increase. 1 Raw washed sugar 6.6 1.0 ... 6.9 7.7 8.1 8.1 The data already presented indicate that with liquor 2.0 ... 7 . 2 7 . 7 8 . 2 8 . 2 3.1 ... 7 . 2 7 . 7 8.0 8 . 1 a high-purity solution-i. e., one having a 4.1 ... 7.1 7.9 8.1 8.1 polarization of about 96 per cent or higher2 Bauxite-refined washed 6 . 1 1.1 6.5 7.1 7.9 8.0 7.9 a capacity of at least 100 pounds of sugar per sugar liquor 2.2 6.4 7.1 7.8 8.0 7.9 3.3 6.4 7.1 7.8 8.0 7.9 pound of clay (usually between 150 and 200 4.4 6.4 7.1 7.8 8.0 7.9 pounds per cycle may be expected. With low3 Char-refined washed 6.2 2.3 ... 7.8 8.0 8.1 ... purity solutions such as wash sirups, consugar liquor 6.8 ... 7 . 5 8 . 0 8 . 1 . . . siderably lower capacities have been ob30.9 ... 7.4 7.9 8.2 . . . 64.0 ... 7.5 7.8 8.2 ... served. It is estimated that the maximum 4 Char-refined wash sirup 6 . 2 4.5 ... 7.1 7.7 8.1 ... yields from the 1100" and the 1300" F. clays 11.3 ... 6 . 9 7 . 4 7 . 7 ... would be of the order of 30 and 38 pounds of 5 Char-refined washed 6.3 123.0 ... 7.3 7.4 7.9 ... sugar solids per pound of clay, respectively. sugar liquor These yields are between only about one fifth 6 Char-refined washed 6.3 106.0 .... . . 6.. 9. 7. . 0. . . . .. .. .. .. .. to one tenth of those obtained with highsugar liquor 230.0 . 230.0 . . . . . . . . . . 7.3 ... purity liquors, but are several times higher than the yields from a refining filter.
INDUSTRIAL AND ENGINEERING
990
HEMISTRY C
TABLE11. EFFECTOF FILTRATION RATEON pH RISE IN CHARREFINEDUT^^^^^ SUGAR LIQUOR Throughput Lb. Sugar Solids/ Lb. Clay 4.2 29.4 62.8 79.6 105.0 130.0 155.0
Fiaction Sumber 1
7 15 19 25 31 37 T-4BLE
p H of Fractions a t Percolation Rate of: Ml./min./kg. d a g 10 25 50 75 100 Gal./hr./ton clay 144 360 720 1080 1440 7.8 7.9 7.8 7.6 7.7 7.8 7.6 7.6 7.8 7.7 7.6 7.4 7.4 7.4 7.6 7.4 7.3 7.3 7.4 7.5 7.1 7.3 7.3 7.3 7.3 7.0 7.2 7.2 7.1 7.0 ... 6.9 6.9 7 .O 6.9
111. EFFECTO F FILTRATION RATE ON CAPACITY
: : : :1:: 0
..i n . . . , . . .
., .,
C
OF
CHAR-REFINED WASHSIRUP
Filter Rate Gal./Hr./' Ton Clay 144 360 720 1080
Throughput, Lb. Sugar/Lb. Clay Running t o Last Fraction 13.5 15.2 15.2 15.2
p H of Last Fraction Taken 6.8 6.9 7.0 6.9
p H of Tota! Composite 7.0 7.3 7.2 7.0
>I.~px.pH during Run 7.7 7.6 7.4 7.3
The contacting data show that a dosage of about 0.32 per cent of clay calcined a t the optimum temperature (1400" F.) will raise the pH of a 60" Brix washed liquor from 6.2 to 7.0. This dosage corresponds to about 312 pounds of sugar solids per pound of clay. EFFECT OF INITIAL pH. Six filters were each charged with earth which had been calcined a t 900" F.; and six batches of washed sugar liquor, taken a t successive intervals (i. e., to obtain a series of decreasing pH1 from a plant char filter, were filtered through the adsorbents. Four equal fractions were taken from each filter (total yields, 4 pounds sugar solids per pound clay). Table IV shows the pH of each fraction. The data indicate that in the range studied, the pH of the filtrate is independent of the initial pH of the washed liquor processed.
Regeneration Spent adsorbent materials may frequently be reactivated by solvent extraction or thermal treatment or both. Similarly, Attapulgus clay which has been used until it is no longer capable of raising the pH may be regenerated and re-used as a pH-adjusting agent through several cycles. The data in Table V were obtained with washed sugar liquor. In runs 1 to 5, inclusive, the clay was regenerated by a-ashTABLEIV. EFFECTOF INITIAL pH Initial p H p H of Fraction No. 1 2 3 4
UPON
6 7 8 9 10 11
Method of Regeneration
6.9
6.5
6.2
6.1
6.0
7.6 7.5 7.6 7.6
7.4 7.6 7.6
7.6
7.6 7.5 7.6 7.7
7.7 7.7 7.8 7.5
7.7 7.6 7.7 7.6
7.7 7.6 7.7 7.6
Washing steaming: air-blowing Calcination a t : 900' F. l l O O o F. 1300' F. 1300' F. 1300' F. 1300' F.
p H of Washed Liquor Charged 6.3 6.3 6.3 6.2 6.3
Maximum p H during Run 7.7 7.3 6.9 6.6 6.8
6.2 6.3 6.3 6.3 6.2 6.1
6.6 7.0 8.3 7.9 8.1 8.0
p H of Total Composite Filtrate 7.4 7.0 6.8
Throughput, Lb. Sugar Solids/Lb. Clay 60.4a 59.1 31.3
...
... ...
... ...
6.9 7.5 7.4
3
.. 0N. .. .. .. ., (0
, ,
., .. .. $. n
.. .. .$. . . m .. .. .. .. w .. .. .N . . m
..
..
"5 .re
. . N
.. ..
.. .. .. ..
pH RISE
7.0
OF FULLER'S EARTH TABLEV. REGENERATION
Run So. 1 2 3 4 a
i
:1
...
32.4 64.3a 106.80 ... 86.30 7.4 93.7Q Total 534.3Q a O n the basis of the composite p H values, these figures must be considered 8 6 only a fraction of the actual capacity of the clay.
Vol. 34, No. 8
ing, steaming, and air blowing. This procedure was folloffed until the clay was no longer capable of producing a filtrate having a pH of 7.0 or higher. The capacity of the clay decreased appreciably with each successive use. The efficiency of the adsorbent which had been processed t o exhaustion in this way was regenerated by recalcining the clay a t a t e m p e r a t u r e higher (run 7 ) than the initial a c t i v a t i n g temperature. Reheating a t the oiiginal t e m p e r a t u r e (run 6) was ineffec,tive in restoring the pHraising property. Runs 8 t o 11, inclusive, show the effect of further regenerations a t 1300" F. Other work has shown that an increase of 50-100" F. is sufficient to restore the pH-regulating property of a spent clay. Additional yields of sugar solution of adjusted pH could have been obtained with t h e clays by calcining a t l O O O " , 1200", and 1400" F., etc. If the clay is to be regene r a t e d b y w a s h i ng , steaming, air drying, and recalcining a t a fixed temperature (instead of a t progressively higher temperat u r e s ) t h e d a t a in Table V indicate that a temperature of 1300O F . provides the greatest life capacity. Clays which have been spent in petroleum d e c olo r i z a t i 011 service are effective in raising the pH of sugar s o l u t i o n s . F o r example, a clay which had been used and regenerated sixteen times a t a b o u t 1 2 0 0 " F. raised the pH of a bauxite-refined washed sugar liquor from 6.1 to 7.3 a t a throughput of 4 pounds of sugar per pound of clay.
August, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
991
amounts of dolomite and calcite contained in the gangue. An increase in the pH of an acid sugar soluColorClay Filter ,tion brought into contact with clay could occur Filtrates from Clay Filtersb Sample Refining Throu hput, Liquor through the direct neutralization of acids by the No. Adsorbent Lb.hb. Charged A B C Washed Sugar Liquor calcium and magnesium carbonates in the earth or by the oxides resulting from the thermal decomposition of the carbonates. An exactly similar effect would be obtained if the acidic components acted directly on the silicate to replace cations with hydrogen. If the neutralizaWash Sirup tion products were insoluble or completely 25.8 4 . 7 (6.2) ... 6 . 1 (7.3) S Char 31.4 4 . 7 (6.2) ... 6.2'(7.3) 9 Char adsorbed by the clay, the ash content of the 10 Char 10.2 8.4(6.2) 11.4'(?.1) ... sugar solution would be decreased by the clay 11 Char 13.5 8.4 (6.2) .. . lO.i'C7.3) 12 Char 15.2 8 . 4 (6.2) ... , .. 10.6'(7.2) treatment. Against an explanation based on Numbers in parentheses are p H values. the presence i f carbonates- is our observation b A B and C refer to calcination temperatures of 900°, 1100°, and 1300' F., respectively, that the carbonate content of the clay has very excepd in'the oase of sample 6 where the letters refer to percolation through clay calcined a t l l O O o F. atrates of 720, 1080, and 1440 gal./hr/ ton, respectively, and samples. 10,11, and 12 little effectupon the capacity of the clay or where they refer to percolation rates of 144, 360, and 720 gal./hr./ton, respectlvely. upon the maximum pH produced. A quantity of clay was ground to pass a 200-mesh screen. A portion was then reconverted to 10-30 mesh granular form by moistening with water, extruding the plastic Refining Action in Adsorbent-Refined Sugar mass, and drying, crushing, and screening the extruded forms. Solutions Another portion was digested with 2 per cent hydrochloric acid The literature cites numerous instances of the use of fuller's to remove carbonate, washed free of chloride, dried to about earth or other claylike minerals for the purification of sugar 52 per cent volatile matter, extruded, dried, and'reduced to solutions. In every case this treatment relied upon the 10-30 mesh granules. Other portions of the acid-extracted flocculating action of a raw clay. Calcination destroys this clay were intimately mixed with 1.5 and 3.0 per cent of particular property of clay, and no reference has been found calcite (through 200 mesh) and converted into the granular to the refining action of a calcined clay. For this reason our form. These materials were then calcined a t 1100" F. and observations on the refining action of Attapulgus clay are used for the percolation treatment of a washed sugar liquor here summarized. having a pH of 6.1. The data indicated that the pH-adASH REMOVAL.Table VI illustrates the variation in the justing factor survives acid washing and that the capacity of ash content of fuller's earth filtrates during the course of excalcined acid-washed, carbonate-fortified clay is substantially haustive percolations. The data were obtained by deterthe same as that of the calcined acid-washed clay to which mining the ash content of arbitrarily chosen fractions from no carbonate was added. the different filters. The ash of the charge solution is sharply When the clay is first calcined and then treated with water decreased during the early stages of filtration through clay; or dilute hydrochloric acid, the subsequent ability of the clay i t then increases as the percolation progresses, tending to to raise the pH of a sugar solution is appreciably diminished; approximate that of the charge. The reaction of the ashi. e., the pH-raising factor of the clay is present only after forming constituents in the sugar solution to clay treatment heating. Calcination apparently produces a water- and is independent of filter rate and clay calcination temperature. acid-soluble factor which in neutralizing (1) the acidity of a DECOLORIZATION. In filtering light-colored adsorbent-resugar solution forms an insoluble derivative, or a compound fined washed sugar liquors through fuller's earth, the color that is strongly adsorbed by the clay. remains either substantially the same or increases slightly. A base-exchanging medium in contact with a sugar solution I n the case of refined wash sirups there is usually an increase could increase the pH of the solution by providing cations in color. The results in Table VI1 are typical. which formed salts with the anions involved more alkaline When a low-pH-refined liquor or sirup is limed to 7.0 or than those present in the unprocessed liquor. An increase above, there is a marked darkening in color. In no case did in pH would occur also if the clay preferentially adsorbed pH adjustment by clay produce darkening equal to that acid or acid salt molecules or hydrogen ions from the mixture caused by liming to the same pH. of compounds present in a raw or partially refined sugar ADSORPTIONOF INVERT SUQAR AND NONSACCHARIN solution. Further work on the mechanism of pH adjustORGANICMATTER. Practically without exception, fuller's ment with clay is in progress. earth filtration decreases the invert sugar content of the washed sugar liquors or wash sirups treated. The data Acknowledgment obtained show no relation between the decrease in invert and the original invert content. It is a pleasure to record our appreciation of the collaboraA reduction in the amount of nonsaccharin organic matter i ~ in the early tion of our former co~league,D. ~ l l Neunherz, was effected by clay filtration in all but a few cases. stages of the work on which this paper is based.
OF FULLER'S EARTHTREATMENT ON COLOR OF REFINED TABLE VII. EFFECT WASHED SUGAR LIQUORS
-
0
Possible Mechanisms of pH Adjustment by Attapulgus Clay Raw and intermediately refined sugar solutions contain, in addition to the carbohydrate components, inorganic and organic Salts, organic acids, and possibly small m m ~ n t sof inorganic acids. Calcination of the clay, especially at the in an higher temperatures used in Our work, in the clay mineral and a partial decomposition of the small
Literature Cited (1) Bradley, W. F., Am. Mineral., 25, 405-10 (1940). (2) Kerr, Ibid., 22, 634-50 (1937).
i2i
~ ~ (5) Lapparent, J. de,
~
~
~'253-83~ (1938). ~
conzpt. rend., 201,481-3 (1925).
P R E S E N Tbefore ~ D the Division of Sugar Chemistry and Technology a t the 103rd Meeting of the AMERICAN CHEMICAL SOCIETY, Memphis, Tenn.
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