September, 1928
IXDUSTRIAL A N D ENGINEERING CHEMISTRY
933
Some Adsorption Properties of Bone Char' T. B. Wayne IMPERIAL SUGAR Co., S U G A R LAND,TEXAS
Experiments have been conducted t o show t h a t , while t h e seat of t h e ash-adsorbing powers of bone c h a r may be regarded a s i n t h e mineral skeleton, a n adsorbed layer of alkaline substances within t h e c h a r exerts a very great influence on adsorption of a s h f r o m sugar solutions a n d solutions of calcium acetate. Chars t h a t have been washed prior t o testing absorb less a s h t h a n chars t h a t have been burned t o s u c h temperatures t h a t a layer of alkaline substances is formed a t t h e interfaces of t h e c h a r a n d becomes available for exchange reactions which undoubtedly occur during adsorption. I t h a s been shown t h a t on increasing t h e alkalinity of chars, within certain limits, a n d t h e n extracting t h e m with successive portions of distilled water under conditions which allow t h e c h a r a n d extract t o remain together a n d establish a n adsorption equilibrium, they will yield filtrates having higher pH values b u t lower conductivity. On t h e other h a n d , if t h e chars are severely overburned, b o t h t h e pH a n d conductivity of t h e distilled water extracts will increase. Chars having insufficient alkalinity will adsorb less a s h a n d also yield acid filtrates. T h e l a t t e r is suggestive of a f o r m of hydrolytic adsorption a n d occurs o n all sugar solutions a n d calcium acetate solutions. Lowering of t h e pH by s u c h chars occurs regardless of their calcium carbonate content, a n d t h e alleged buffer action of t h e char carbonates c a n n o t be depended upon t o neutralize t h e acidity so formed. F r o m t h e d a t a presented, t h e con-
clusion may be drawn t h a t i n actual refinery practice one may expect a s h adsorption t o be increased t h r o u g h revivification of chars a t t h e highest temperature t h a t is consistent with certain other considerations, notably t h e relation between pH a n d decolorization or t h e subseq u e n t darkening of granulated sirups. I n a t t e m p t i n g t o evaluate t h e comparative ash-adsorbing powers of chars, if pH is not considered or if t h e chars are washed before using, very erroneous.results are liable to be obtained. The same may be said of a t t e m p t s to compare t h e reactions of liquors which are treated by various chars. The results for bone char of Van der Zwet [Centr. Zuckerind., 34, 1119 (1926); C. A., 21, 1563 (1927)l which have been extensively advertised by t h e manufacturer of a well-known vegetable carbon, may be explained on t h i s basis. I n t h e actual char-filtration experiments described, there is considerable invert sugar disappearance a t t h e beginning of t h e filter cycle while t h e char is fresh a n d highly alkaline, Less invert sugar appears i n t h e filtrates from t h e more alkaline chars, b u t t h e d a t a are insufficient to indicate whether this apparent disappearance is due to adsorption, invert sugar destruction, or analytical error caused by a n alteration of t h e copper-reducing powers. However, there is considerable evidence t h a t invert sugar is released by char as soon a s t h e density changes i n "sweetening off" t h e char.
.. . . . . DSORPTIOK by activated carbons has been a favorite subject of many investigators during recent years. Most of this work has been in connection with decolorizing efficiencies and methods of evaluation, and although much confusion of methods, data, and interpretations still exists, some very enlightening papers have been published during the past two years. Peters and Phelps2 have studied colorimetry as applied to sugar products and supplied methods which are satisfactory for research purposes if certain physicochemical factors are observed, and which with certain modifications may be applied to routine determinations. Lunden, in various papersj3 has covered the same subject in detail. Blowski and Bon4have also given a detailed discussion of the subject and emphasized the vital factors to be observed in evaluating carbons; and recently Hauge and Willaman5 stressed the importance of pH in such determinations and showed the reasons for the discrepancies in the results of various investigators. While it is true that a better understanding of decolorization principles has resulted from these fundamental investigations, very little concrete information is available on the adsorption of other substances, notably ash and invert sugar, from sugar solutions. WijnbergJ6 Zerban and Taggart,' Wein-
A
1 Presented before the Division of Sugar Chemistry a t the 75th Meeting of the American Chemical Society, St. Louis, Mo., April 16 to 19, 1928. 2 Sugar, 27, 223 (1925); Bur. Standards, Tech. Paper 338. 8 Centr. Zuckerind., 33, 1341 (1935); 34, 468 (1926); 36, 219 (1927); Z . Vev. deuf. Zuckerind., 7 6 , 780 (1926); 77, 709 (1927). 4 IND.'ENG. CHEM.,18, 32 (1926). 6 Ibid., 19, 943 (1927). 8 Intern. Sugar J . . 18, 194 (1916). 7 La. State Expt. Sta., Bull. 161.
rich,* S a ~ e rAvot,lo ,~ and others discussed adsorption of other substances, in most cases ash, and in some instances made comparisons between vegetable carbons and bone char. Hornel' concluded that vegetable chars adsorbed no ash and conducted experiments to prove that the ash-adsorbing property of bone char is confined to the mineral skeleton. Horton and Sengson12made comparisons of the ash adsorbed by bone char and a vegetable char and decided that when equal weights of the chars are compared under certain conditions the vegetable char examined is as effective as bone char. These investigators conducted tests by heating the chars with dilute test liquors, and considered the increase in ash content of the chars after washing free from adhering sirup, as the ash adsorbed. This procedure will be discussed later. Blowski and Bon4 compared bone char with several vegetable chars and found that all chars exhibited ash-removal powers, some being decidedly superior to bone char. They stated that other investigators who had concluded that vegetable chars possessed no ash-removal powers had probably failed to remove soluble ash from the carbons prior to testing and concluded that the mineral skeleton of the char is mainly responsible for the aeh-adsorptive properties. K n ~ w l e s 'called ~ attention to the selective action of char in the removal of inorganic matter from sugar solutions. Infern. Sugar J , 20, 424 (1918). Ibid., 2 0 , 24 (1918). 'OIbid., 26, 196 (1923). l1 J. INL). EXG.CHEM.,14, 1134 (1922). 12 Ibid., 16, 165 (1924). 18 Ibid , 19, 222 (1927). 8
934
INDUSTRIAL AND ENGINEERING CHEMISTRY
H e also indicated that adsorption of inorganic salts is accompanied by an exchange of bases, presumably lime derived from the calcium carbonate of the char. Rice and Murray14 presented additional data in this connection and indicated that exchange adsorption occurred between the solutes and the char. Data on invert sugar adsorption by bone char are meager and, a t best, contradictory. Kolthoff l 5 states that charcoal adsorbs various sugars and that in clarifying certain physiological products, if the charcoal is used cautiously in just sufficient amount to decolorize, the glucose is retained quantitatively. The so-called “bone-black error” in clarifying sugar solutions for polariscopic test is well known. Knowles16 shows in tables the analytical changes occurring in a refinery char filter and, while large adsorption of coloring matter, ash, and non-sugar is indicated, the glucose ratio is not materially lowered except in a few instances which the author cites as instances of invert sugar destruction. Rice and Murray14 percolated a sugar solution containing reversion products through bone char and obtained maximum adsorption in the first portions followed by an increased invert sugar content in succeeding fractions of the effluent liquor. Their data do not indicate whether this disappearance of invert sugar is due to adsorption or destruction. Later, these same investigators’’ published a continuation of their work wherein washed and unwashed chars were compared under identical conditions, and no appreciable differences were noted. Since the alkalinity of the char has undoubtedly been largely removed by washing, their results are not suggestive of invert sugar destruction. The purpose of this paper is to present some data on the adsorption of ash and invert sugar by bone char. Although a discussion of the data will be made to indicate the writer’s viewpoint, interpretations of these data will be left to the reader. There are certain factors which exert powerful influences on the adsorptive processes. In addition, there is a possible correlation between the reaction of the original char, the amount of adsorption, and the reaction of the treated liquor. The last factor is influenced by what is believed to be a form of hydrolytic adsorption. Analytical Methods
Bone-char filtration processes, as used in refinery practice, involve successive filtrations of liquors and sirups of decreasing purity until a point is reached where the char is sufficiently “loaded” with impurities to require regeneration. They may reach a condition of equilibrium with the constituents of the first liquor used, and then be made to do more work by substitution of a second liquor of lower purity, and so on. The final equilibrium is disturbed when water is run on the filter during the “sweetening off” period, and the sugars are selectively washed out followed by the impurities. Some of these sugars are never washed out, and remain to be destroyed in the char kilns. The ease with which these adsorption equilibria are disturbed indicates the fallacy of attempting to evaluate the ash-adsorbing properties of chars by washing them free from sugar and determining the increase in ash content of the original char. In the case of bone char, the ash so adsorbed and determined would represent only a part of the ash really held in a state of adsorption t o the interfaces of the char. Therefore, the data which follow are all based on analytical changes in the liquors after char treatment. Ash determinations were made on all original liquors and sirups used by incineration with sulfuric acid a t 750” C. in IND.ENG.CHEM.,19, 214 (1927); 20, 276 (1928). Biochem. Z., 168, 122 (1926); C. A , , 20, 1641 (1926). 16 IND.ENG. CHEM.,17, 1151 (1925). 17 I b i d . , 20, 276 (1928).
Vol. 20, No. 9
an electric muffle, and conductometric methods were used on all filtrates except those especially noted. A ratio between the specific conductance and ash content (sulfated ash less 10 per cent) was established on the original liquor and this ratio used in calculating the ash and salt percentages from the conductivity measurements on the char-treated solutions. While it is quite possible that char treatment alters this conductivity-ash ratio, this is immaterial in the present instance since we are interested in the trend of the adsorption rather than absolute values. Moreover, the data are satisfactory for comparative purposes, as all chars received identical treatment under the conditions of each experiment. No corrections were made for the conductance of the distilled water used, as it was found that water freshly obtained from a Barnstead still which had been in operation several hours did not introduce appreciable error. Invert sugar determinations were made by a modification of the Lane and Eynon methodIs using carefully selected methylene blue as an inside indicator. The copper solution was standardized against standard solutions of invert sugar and sucrose in about the proportions in which these constituents occurred in the liquors under examination. The results were in good agreement with the original tables. I n making the determinations on the liquors and sirups, both before and after char treatment, 50 grams of the liquor at 50’ Brix were dissolved in water and diluted to 100 ml. p H determinations were made by a colorimetric method. Distilled water of 6.9-7.0, prepared by the method of Daw~ 0 x 1 ,was ~ ~ used in all dilutions and the indicator solutions of bromothymol blue and phenol red used’ were adjusted to show exactly p H 7.0 on this water to prevent errors when testing the slightly buffered char liquors and sirups. The other indicators of higher and lower ranges were standardized against standard buffer solutions. Chars Used
Six chars were used in the experimental work. Each char was then used in several modifications. Descriptions of the chars and their modifications are as follows: Char A , a service char taken from the wet char hoppers in the refinery and burned a t 480’ C. in a laboratory char kiln. The caustic test was “good” and the pH of the char 8.2. This char was then repeatedly washed with distilled water, dried a t 200’ C., and screened on a 48-mesh screen. Char B , new char which had been washed and burned in the factory equipment. No liquor had ever been on this char. It was again washed with tap water and reburned in the laboratory kiln, then again washed with distilled water and reburned in the laboratory kiln a t 200” C. and screened. This repeated washing and burning was to remove the excess of ammonium compounds. Char C, char B which had been partially decarbonized by heating a t 500’ C. in the presence of air until the whole assumed a grayish appearance. After repeatedly washing for days with distilled water, it was dried a t 200” C. and screened. Char D, char B completely ashed a t low redness in a muffle furnace, repeatedly washed for weeks with distilled water, dried at 200” C., and screened. Char E, char B, powdered and screened through 100 mesh, then repeatedly extracted with 25 per cent hydrochloric acid to remove soluble ash, The char carbon was washed for weeks with distilled water, then with 0.1 per cent sodium hydroxide, and finally with distilled water until free from chlorides. However, for some reason it was never possible to wash this char to a reaction of pH 7.0, although recently boiled distilled water was used and indicators were standardized to indicate pH 7.0 with this same water. Nevertheless, the char persistently tested pH 6.2. Perhaps the explanation for this lies in the observations of Miller and Bandemerz0 and Parks and BartletLZ1 The char carbon was then dried a t 200’ C. and screened through 100 mesh.
16
1s
15
19 20 9’
J . Soc. Chem. I n d . , 42, 32 (1923). J . Phys. Chem., 29, 551 (1925). J. A m . Chem. Soc., 49, 1686 (1927). I b i d . , 49, 1698 (1927).
I,YDUSTRIAL AND ENGINEERING CHEMISTRY
September, 1928
933
PHYSICALANALYSIS CH.4R
55.3 41.5 40.9
B
C
' ~
0.884 0.664 0.654
...
CHEMICAL ANALYSIS MESH
Relative On
14
On 16
On 20
%
%
%
36.3 10.6 44:O 20.0 8.0 36.3 22 0 7.0 31.0 23.0 8.1 Through 100 mesh Through 100 mesh
On 28
On 35
%
%
7c
%
%
%
1 6 1.0 0 2 0 0
2.71 6.48 6.80 2.96
9 89 9 29 3.24 05 93.05 9.29
89.77 90.34 96.34 99 44 .37 90.34
0.34 .37 .42
6:48
A-1, B-1, and C-1 prepared by heating chars A, B, and C, respectively, in a closed retort a t 480" C. for 3 hours. A-2, B-2, and C-2 prepared by heating chars A, B, and C, respectively, in a closed retort a t 620" C. for 3 hours. D-1, prepared by grinding char D and sifting through 100-mesh screen. E-2, prepared by treating char E with 0.04 N limewater for 3 hours, then filtering with aid of suction on a Hirsch funnel, washing once with distilled water, and drying at 200" C. E-1, prepared by heating char E a t 620" C. in a closed retort for 3 hours. E-3, prepared by heating char 8 - 2 a t 620" C. in a closed retort for 3 hours.
Since the object in heating these chars was to increase their pH, the reactions of all chars are summarized in Table 11. of H e a t i n g a n d p H of Chars
DRSCRIPTION
TEMPERATUREPH" O
A A- 1 A-2 B B- 1 B-2 C c-1 c-2 D D-l E E-1 E-2
E-3 F
Washed service char Same Same Washed new char Same Same Decarbonized new char Same Same Char ash, washed Same, ground, sifted Char carbon Same Same, limed, washed Same as E-2 New char, powdered
c.
200 480 620 200 480 620 200 480 620 200 200 200 620 200 620 200
6.9 8.2
9.6
7.4 9.6f 9.6f 7.6 9.6+
9.6+
7.6 7.9 6.2 7.0 7.5 8.6 7.6
a pH values outside of the range of thymol blue (alkaline range) are marked 9 . 6 f . In view of the properties of these overburned chars as shown later, it is unfortunate that it was impossible to locate their exact pH value with the indicators available.
Test Liquor
A raw sugar solution of approximately 50" Brix was prepared and filtered with the aid of standard Super-Cel. This solution analyzed as follows: Total solids, 20°/4' C. (refractometer), 50.0 per cent Apparent purity, 97.2, ash, 0.24 per cent Specific conductance, 272.1 X Table 111-Ash CHAR
a
DESCRIPTION
Original sirup, no char Check, test sirup heated, no char B New char, washed F Char B , ground, washed D Char ash, granular D-1 Char ash, ground E Char carbon E-1 Char carbon, heated E-2 Char carbon, limed E-3 Char E - 2 , heated 620' C. Percentages marked show increase.
+
CHAR PH
... ...
7.4 7.6 7.6 7.9 6.2 7.0 7.5 8.6
Acidinsoluble ash
7.7 1.5 2.5 3.1
Analyses of these chars are given in Table I. The following modifications of the above chars were prepared as follows:
CHAR
Acidsoluble ash
%
Char F, char B powdered, screened through 100 mesh, repeatedly washed with distilled water, dried a t 200' C., and screened through 100 meih.
Table 11-Degree
Carbon
16.5 4.5 7.5 8.3
% 27.3 21.0 24 5 26.5
CaC03
On Through 48 48
Extract pH
6.9 7.4 7.6 7.6 6.2 7 6
.51 6.58
.37
Method of Tests
The following method was used in making all tests reported in Tables I11 to VIII, inclusive: Fifty grams of char were added to 200 ml. of test liquor and the mixture was thoroughly shaken. The flasks were then connected with reflux condensers and placed in a water bath which was thermostatically controlled a t 80" C. All flasks were thoroughly shaken for 30 seconds a t 15-minute intervals, and after 1 hour removed from the bath. The test liquor was then immediately poured off the char while still a t 80" C. or as near thereto as possible, and filtered through filter paper on small Bilchner funnels. The filtered liquors were then tightly corked and allowed to cool. A blank sample of liquor without char was likewise treated as a check. The liquors were then analyzed electrometrically for ash and total solids were determined with a refractometer. pH determinations were run on the liquors, except in the case of the crystallizer remelt sirups, which were run on the solutions prepared for the conductance measurements. Seat of Ash Adsorption Power
Each of the chars listed iri Table I11 was treated with 50" Brix raw sugar liquor as described above. The results indicate that adsorption by char ash is very high. The impure char carbon was practically freed from adsorbed materials by the continuous washing it received, and adsorbed no ash. However, if this same carbon is heated, some impurities are probably rendered available, and some ash adsorption is shown. Furthermore, if a base is added artificially to this carbon to raise its pH and provide some soluble ash, some ash adsorption is indicated. However, if this carbon is heated to 620" C. its alkalinity rises to p H 8.6, and negative adsorption is indicated by the conductometric method used. It is possible that the pH of the solution affected the results in a liquor of such low ash content, but the agreement of the pH of char and filtrate. differing in this respect from the other chars studied, indicates that little or no adsorption occurred. Nevertheless, the data do indicate in a general way that the seat of the ash-adsorbing powers is in the mineral structure of the char, and whatever ash adsorption is shown by the carbon is probably due to the presence of mineral salts and alkalies which become available for the exchange adsorp tion reactions which undoubtedly figure in these adsorption phenomena. The influences of inorganic salts, acids, and bases on adsorption have been the subject of much investigation in connection with adsorption studies on pure carbons, mainly
Adsorption b y Various Chars FILTRATE
PH
SPECIFIC CONDUCTANCE
ASH
% 7.2 7.0 6.8 6.8 7.3 7.6 6.4 6.8 7.4 8.6
272.1 272.3 200.1 141.9 192.3 185.9 282.2 225.8 256.4 295.3
0.240 0.240 0.176 0.125 0.170 0.164 0,249 0.199 0.226 0.260
TOTAL SOLIDS ASH ASH (20°/4' C.) TOTAL SOLIDS REMOVED"
so
50.0 49.8 50.0 49.7 49.8 49.9 49.8 49.8 49.8 49.9
0,480 0.482 0.352 0.252 0.341 0.329 0.500 0.400 0.454 0.621
% ... ...
+ +
26.7 47.5 29.0 31.5 4.2 16.7 5.4 s.5
INDUSTRIAL AND ENGINEERlNG CHEMISTRY
936
sugar charcoal. Many of the contradictory data on the adsorbent properties of charcoals may be traceable to the influence of impurities in the charcoals used by the different investigators.22 It is generally agreed, however, that the presence of an adsorbed layer of electrolytes on the surface of charcoal greatly influences the type of adsorption occurring, and largely determines whether it will be positive or negative for bases or acids, and molecular or ionic in the case of neutral salts. That some of these principles are also applicable to adsorption by bone char will be evident later in this discussion. Tests on Calcium Acetate Solution
The writer has observed during his refinery experience t h a t tests made on revivified bone char with 1.0 per cent calcium acetate solutions will accurately detect any tendency toward lowering the pH of the sugar liquors by the char under observation. It is well known that bone char which has not been properly revivified will give off acid liquors, especially toward the end of the liquor cycle, owing to what is believed to be a form of hydrolytic adsorption. This property of bone char was first noted in refinery practice when filtering washed sugar liquors, and at first was attributed to acid substances adsorbed within the structure of the revivified char through incomplete burning, or possibly fermentation or the action of excessive temperatures within the char filter. This lowering of the pH occurred even with new char, and when filtering over chars which gave colorless tests by the conventional caustic soda test. The trouble was remedied by improving the mechanical condition of the kilns so that higher revivification temperatures could be used, but the experience prompted the present investigation into the properties of revivified chars. T a b l e IV-Calcium
-~
Acetate Adsorption b y Various C h a r s
~
CHAR
DESCRIPTION OF CHAR^
yg
FII- SPECIFIC
T R A ~ CONPH DUCTANCB
CaAc CaAc
R&MOVED
..
Original solution Check. heated A Service char distilled-water washed, hlated at ZOOo C. A-1 Same, heated a t 480' C. A-2 Same, heated a t 620' C. B New char, washed, heated at 200' C. B-1 Same heated a t 480' C. B-2 Same: heated a t 620' C. C Decarbonized new char, washed heatedat200'C. C-1 Same heLted a t 480' C. P-9 Sernel heated a t 620' C.
7.2 7.3
472.8 472.4
1.000
1,'OOO
.. ..
6.9 8.2 9.6
6.0 7.0 8.4
411.8 408.6 400.8
0.871 0.864 0.847
12.9 13.6 15.3
7.4 9.6+ 9.6+
6.4 7.8 8.7
369.4 359.1 374.1
0.781 0.780 0.791
21.9 24.0 20.9
7.6 9,6+ 9.6+
6.6 8.5 8.7
364.2 371.7 407.5
0.770 0.786 0.862
23.0 21.4 13.8
a Detailed descriptions are given previously in Tables I and I1 and supplementary descriptions.
The calcium acetate test is very sensitive to hydrolytic adsorption owing to the liberation of an acid of higher activity than the usual acids thus liberated from the salts in sugar liquors, while on the alkaline side of pH 7.0 the reaction of the filtrate closely parallels that of sugar liquors of the higher purity ranges after treatment with the same char under similar conditions. This will be apparent later. PROCEDURE-Ten grams of calcium acetate [c. P. (Cenco) Ca(CzH802)2.H20]were dissolved in distilled water and diluted to 1 liter. The pH of the solution was adjusted to 7.2 by the addition of two drops of glacial acetic acid, and the whole filtered. The specific conductivity of this solution was determined by diluting 10 ml. t o 200 ml. It was found that the specific conductance of this solution increases approximately 2.44 per cent per degree above 20' C., up to 26" C., and as the measurements were made a t 23-24' C. the results were corrected to a basis of 20"
c.
Miller, J . A m . Chem. Soc., 47, 1270 (1925); Bartell and Miller, J . Phys. Chem., 28, 992 (1924); Miller, Ibid., 81, 1197 (1927); Kolthoff, Rec. trav. chim., 46, 549 (1927), C. A . , 22, 339 (1928); Proc. Acad. Sci. Amsterdam, 27, 742 (1924), C. A , , 19, 1976 (1925). 22
Vol. 20, No. 9
Fifty grams of char were treated with 200 ml. of this solution a t 80' C., as previously described, and the conductance of the filtrates was determined on solutions containing 10 ml. diluted to 200 ml. pH determinations were made on the original undiluted filtrates.
Results are shown in Table IV. Crystallizer Remelt Sirup
Crystallizer remelt sugar of about 90 per cent purity was dissolved in hot water, limed to approximately pH 7.2, filtered, and the density adjusted to approximately 50" Brix. The sirup was then analyzed. Total solids, 20"/4" C. (refractometer), 50.36 per cent Apparent purity, 89.7 Sulfated ash less 10 per cent, 0.89 per cent Ash per total solids, 1.767 Specific conductance, 10 grams to 100 ml., 924.6 X
Table V shows the results of treating 50 grams of each of the chars listed with 200 ml. of this solution under the usual experimental conditions. Ash adsorption increases regularly with increasing alkalinity of the char provided this alkalinity is not too high. I n factory practice i t is hardly probable that chars would ever be overburned to the extent shown for chars B-2, C-1, and C-2. A surprising increase in ash adsorption is shown by the decarbonized new char over what the new char itself adsorbed. Effect of Varying pH
The effect of varying the pH of the char is indicated in Table V. Varying the pH of the sirup also affects the results and should be taken into consideration in evaluating the ash-adsorbing properties of chars. The same crystallizer remelt sirup was used. One portion was adjusted to pH 6.3 by addition of a few drops of glacial acetic acid, and another to pH 8.2 with limewater. A third portion was used in its original state at pH 7.2. The results on chars B and B-2, the latter being an overburned B char, are shown in Table VI. The original analysis of the remelt sirup shown above Table V was used as the basis of the calculations in Table VI; hence the slight discrepancies in the analyses of the sirup noted as pH 7.2. Acidifying the sugar sirup with acetic acid causes a material increase in its specific conductivity. On the other hand, increasing the alkalinity to pH 8.2 did not so greatly affect the conductance of the solution. The results indicate that increasing the alkalinity of the sirup increases the ash adsorption by char B, but does not thus affect the results from the highly alkaline char B-2. This is what should be expected, judging from the preceding data. However, it should not be inferred from the pH values obtained under the conditions of these experiments that in actual refinery practice the pH of the filtered sirups from char may be increased by increasing the alkalinity of the original sirup. This point will be discussed more fully in a later section. Raw Sugar Solution
The raw sugar solution previously described was used with 20-, 40-, 60-, and 80-gram portions of chars A and A-1, under the same experimental conditions. Results are shown in Table VII. For every proportion of char to liquor, the pH value remains the same for each char, and ash adsorption increases as the proportion of char is increased. In every instance char A-1 adsorbed more ash than the same original char before burning to higher alkalinity. It was not considered advisable to continue conductometric measurements on the filtrates obtained from this sirup
ISD CSTRIAL A-VD ENGINEERING CHEMISTRY
September, 1928
of p H of C h a r o n Ash Adsorption
T a b l e V-Effect
CHAR
FILTRATE SPECIFIC TOTAL SOLIDS
CHAR
DESCRIPTION OF CHAR'
CONDUCTANCE (20°/40
PH
PH
Original sirup Check, heated A Service char, distilled-water washed, heated a t 200' C. Same, heated a t 480' C. A-1 Same, heated at 620' C . A-2 B New char, distilled-water washed, heated a t 200' C . B-1 Same, heated a t 480' C. B-2 Same. heated a t 620' C. C c Decarbonized new char. char, washed,' distilled-water washed, heated at 200' C. C-l Same, heated a t 480' C. C-2 Same, heated a t 620' C.
ASH ASH TOTAL SOLIDS R E M O V E D ~
70
%
7.2 6.9
924.6 928.5
50.36 50.13
0.890 0.893
1.767 1.781
+ 618
6.9 8.2 9.6
6.5 6.9 7.6
828.5 824.6 807.0
49.15 49.15 49.00
0.798 0,794 0.777
1.624 1.615 1.586
8.1 8.6 10.3
7.4 9.6.t 9.64-
6.8 7.5 7.7
789.5 794.9 806.2
49.70 49.80 50.08
0.760 0.765 0.776
1,529 1.536 1.550
13.6 13.1 12.3
7 . 66 9 6-l9.6-l9.6,9.6--
7.0 7.8 8.0
760 7 6 0 .88 788.8 811.1
50.10 50.15 50.13
0.732 0 732 0.759 0.781
1.461 1.5 513 13 1 . 5558 58
17.3 14.4 11.8
'
5%
+.
b
of p H of Sirup on Ash Adsorption b y C h a r
T a b l e VI-Effect
ORIGINAL FIL-
CHAR
pH
DESCRIPTION OF CHARa
CHAR
SIRUP
TRATE
PH
6.3
Sirup, acidified Same. heated Original sirup Same, heated Sirup, limed Same, heated B
7.2
New char, distilled-water washed, heated a t 200' C.
-
of Varying P r o p o r t i o n s of C h a r on p H and Adsorption
FIL- SPRCIFIC
TyF CON-
ML. L I Q U O R
ASH
DUCTANCE
TOTAL Asir
A: : : :_-
SOLIDS (20°/40 C . )
%
Grams CHAR A-PH
ASH
RE-
MOVED
%
20 40 60. Original liquor Check, heated 80
247.6 228.0 210.7 272.1 272.3 200.6
6.4 6.4 6.4 7.2 7.0 6.4
49.90 49.82 49.94 50.00 49.80 49.90
0.218 0.201 0.184 0.240 0.240 0.177
0.437 0.403 0.372 0.480 0.482 0.355
9.0 16.0 22.50
..
2610
S A M E . S E R V I C E CHAR. 8.2 ((SAME, CHAR, H E A T E D A T 481' C . )
A-1-PH
~~~~~
~~
7.0 7.0 7.0 7.0
20 40 60 80
T a b l e VIII-Effect
ASH M$:Db
0.9i5 0.925 0.895 0,897 0.893
50.35 51.16 50.50 50.55 49.70
1.817 1.808 1.772 1.775 1.797
++ 22:s. 3 + 0.3 + + 01 .. 55
821.5 791.6 770.9 822.3 806.0 802.2
0.791 0.762 0.742 0.792 0,776 0,771
50.90 50.72 49.75 51.00 50.60 49.70
1.554 1.502 1.491 1.553 1.534 1.551
12.1 15.0 15.6 12.1 13.2 12.2
%
5%
%
6.5 6.8 7.2 7.2 8.2 8.3
I
~
242.6 221.0 202.0
199.7
49.79 50.00 49.91 49.95
0.215 0.195 0.178 0.176
0.432 0.390 0.357 0.352
10.0 18 8 25.6 26.8
of p H of C h a r s on R e a c t i o n of Various Solutions" P H OF FILTRATE FROM:
CHAR DESCRIPTION OF C H A R
Checks, no char 4 Servire char, distilledwater washed, heated a t 200' C. '4.1 Same, heated a t 480' C . A-2 Same, heatedat 6 2 0 ' C . B ?;ew char, distilledw a t e r washed, heated a t 200° C. B-1 Same heatcd a t 48OOC. B-2 Same: heated a t 620' C . C Decarbonized new char, d i s t i 11 e d-wa t e r washed, heated at
zona c.
Same, h e a t e d a t 4SOOC. Same, heated a t 620' C. ~
~
F';
6 9 8 2 9 6
;$,
Raw sugar sirup
Washed sugar liquor
7.0
7.1
6.9
6.4 7 0 8.2
6.3 7.0 8.3
6.5 6.9 7.6
6.0 7.0 8.4
6.7
6.8 7.5 7.7
6.4 7.8 8.7
7.0 7.8 8.0
6.6 8.5 8.7
7 4 9.6+ 9.6+
8.2
6.8
8.2
7 6 9.6+ 9.6+
7.1 8.7 8.9
7.0
8.7
8.7
8.1
8.9
r:izit
See Table V.
after treatment with other chars, as the high pH in the presence of small quantities of ash may lead to erroneous results. However, the p H of these filtrates are tabulated in the first column of Table VIII. Washed Sugar Liquors
%
6.g (SERVICE CHAR, DISTILLED H20 W A S H E D , DRIEIl A T ZOOo C . )
P WAR CHAR
TOTAL SoLxns
950.2 961.2 930.0 931.5 928.0
...
Detailed description in Tables I and 11, and appended data. b Ash removal figures based on analysis of original crystallizer remelt sirup.
C H A R IN
ToTAL
SOLIDS
...
7.0
6.3 7.2 8.2 6.3 7.2 8.2
7.4 7.4 7.4 9.6+ 9.6+ 9.6s
a
200
ASH ASH
(k X 10-6)
Sample lost
Same, heated a t 620' C.
T a b l e VII-Effect
SPECIFIC CONDUCTANCE
PH
6.3
8 2
B B B-2 B-2 B-2
~~~
ASH
C.)
Detailed descriptions are given previously in Tables I and I1 and supplementary descriptions. Indicated ash increase over original solution is indicated by
a
C-1 C-2
937
acetate soh.
7 3
~~
Reaction of each solution was pH 7.2 prior to heating wizh char.
Washed sugar liquors were used in connection with each of the chars listed in Table VIII, the method and proportions being the same as usual. pH determinations were made and are reported in Table VIII. The results from previous experiments are also tabulated for convenience in comparing these values. The pH values for the crystallizer remelt sirups treated with the more alkaline chars are lower than those of the other solutions from the same chars. It is probable that some destruction of invert sugar has occurred and that the acid products thus formed removed some of the excess alkalinity from the solution. The ash content of washed sugar liquors is very small and difficult to determine by chemical methods. Likewise, when working with chars which impart either an acid or alkaline reaction to such liquors, the pH may appreciably affect the accuracy of the ash figures calculated from specific conductance. However, as some data should be presented to show the relationships between pH of chars and the p H and ash content of the filtered liquors therefrom, i t was decided to conduct some experiments in an automatic charfiltration apparatus which the writer had available. Another object in conducting these further tests was to obtain results that would be representative of what actually occurs in refinery char-filtration practice, the principle of which is quite different from the batch experiments previously described, which are more representative of the methods in which decolorizing carbons of vegetable origin are employed.
INDUSTRIAL AND ENGINEERING CHEMISTRY
938
Table IX-Effect
COMPOSITE No.
of PHof Char A on Adsorution f r o m Washed Sugar Liquor
CHAR TOTAL S O L ~ SSUCROSE INVERT
TIXE
COEFFICIENTS-PER
ASH^
Sucrose
Hours Liquor No. 1 Liquor No. 2 0 tor4 I
1 2 3 1 2 3 1 2 3 1 2
5 to 8
I1
9 t o 12
I11
13 t o 16
IV
3
V
17 to 20
VI
21 t o 24
VI1
25 to 28
1 2 3 1 2 3 1 2 3 1 2
29 to 32
VI11
% 60.64 61.84 61.12 60,42 61.12 60.66 61.52 61.17 61.72 61.42 61.52 62.19 61.27 62,02 62.82 61.42 62.19
Vol. 20, No. 9
% 60.20 60.90 60.65 60.20 60.65
...
... ...
61.10 61.05 61.05
... ...
... 62.10 60.80 61.60
% 0.241 0,392 0.157 0.119 0.095 0.189 0.142 0.139 0,240 0.184 0.182 0,265 0.215 0.215 0.310 0.265 0.256
%
98.86 98.99 99.06
% 0.27 0.29 0.16 0.12 0.12 0.15 0.12 0.13 0.16 0.13 0.13 0.16 0.15 0.14 0.18 0.15 0.14
0.46 0.43 0.39
99,51
99.23
... ...
...
0.100 0.080
99,oo 99.40 99.24
0.080
...
0.100 0.090 0,085 0.110 0.095 0,090
%
0.40 0.63 0.26 0.20 0.16 0.32 0.23 0.23 0.39 0.30 0.30 0.43 0.35 0.35 0.50 0.43 0.41
99.11 98.48 99.23
0.080
CENT OF TOTAL SOLIDS FILTRATE PH Asha Non-sugar
70
%
0.165 0.180 0.095 0.075 0.075 0.090 0.075
Invert
... ...
0.22 0.60 0.35 0.17 0.49
.. .. ..
0.45 0.17 0.33
.. .. ..
N o tests except p H
62.84 62.09 62.37
62,OO 61.30 61.75
0.384 0.384 0.350
0.120
0.110 0.100
98,67 98.73 99.01
0.61 0.62 0.56
0.19 0.18 0.16
0.53 0.47 0.27
No tests except p H
3
33 t o 36
IX
X
37 to 40 (in sweet water)
Xl
41 t o 44
XI1
45 to 48
1 2 3 1
62,08 46.81 47,62 10.26
61.20 45.80 47.00 9.43
0.468 0.553 0.367 0.480
0.120 0.160 0.150 0.300
98.59 97.85 98.70 91.92
0.75 1.18 0.77 4.68
0.19 0.34 0.32 2.92
0.47 0.63 0.21 0.48
2 3 1 2 3 1 2 3
1.80 2.13 0.33 0.32 0.32 0.30 0.30 0.25
0.41 0.81 0.08
0.366 0.050
0,208 0.142
22.80 38.03
22.78 2.35
11.56 6.67
42.84 52.95
None None None None None
None None None None None None
6.6 6.6 6.5 7.1 8.4 6.4 6.8 8.3 6.3 6.7 8.3 6.2 6.5 8.0
6.2 6.4 7.8 6.2 6.4 6.8 6.2 6.4 6.6 6.2 6.4 6.7 6.2 5.8 6.2
Filter No, 1 free of sugar after 41st hour, or 13 hours on water. This filter slightly behind Filter No. 2 free of sugar after 39th hour, or 11 hours on water. Filter No. 3 free of sugar after 39th hour, or 11 hours on water. a Ash determinations b y conductivity method on all composites to I X , inclusive; others by sulfated ash less 10 per cent; variations in total solids of composited liquors due t o evaporation while running into receivers; results were calculated to coefficients to make strictly comparable.
This char-filtration apparatus consisted of an automatic char kiln wherein char could be dried on a regular char drier, burned in retorts of conventional design, cooled in cooler pipes, and then drawn from these pipes on a predetermined schedule. The char so prepared was then run into small char filters of usual design holding about 5600 cc. of char, and fitted with a pressure head and constant-level device to insure a constant feed of liquor t o the filter. The rate of char-burning, settling, and running of t h e filters, as well as the temperatures, could be closely regulated t o conform to standard practice. A large sample of char A was run through the automatic kiln. 'The first portion for filter No. 1 was burned a t 482" C., a second portion for filter No. 2 a t 538" C., and a third at 620" C. for &filterNo. 3. The draw from the retorts was regulated to allow the char t o be heated 3 hours in the retorts and then remain 3 hours in the cooler pipes. After a sufficient quantity of char for N o . 1 filter was obtained the temperature of the kiln was raised to burn the char for the next filter, and raised again for the third. The char run through the kiln between these temperature .adjustments was discarded, this being possible by timing the draw. This procedure was repeated on the B char. The first batch 'was burned at 616" C., and the second batch was run after shutting off the fires almost entirely, the object being to run .the char through a t about 200' C. to dry it thoroughly without .any oxidafion. These chars were then run into their respective filters, which 'were then placed in a water bath a t 80" C. The same hot water surrounding the filters was adapted to circulation around t h e supply tank and feeding devices to insure constant rate of flow to the filter from the constant head pressure employed. The entire operation was practically automatic. All filters were .then settled by running the liquor on the dry char according to a predetermined rate, and a t completion of the liquor cycle water was introduced st the head of the filters and run a t approximately haIf .the.liquor late. .FILTER
TEMPERATURE BURNED
CAUSTIC TEST
PH
Good Good Colorless
7.0 8.4 9.3
c. '1
.2 3
482 538 620
TESTSWITH CHAR A (WASHED SERVICE CHAR)-oWing to an accident to the liquor supply shortly after starting the test, the filters were started on one liquor and then switched to another 3'/2 hours after the filters had started running. Analyses of the liquors are shown in Table IX. Most of the liquor cycle was on the liquor No. 2, and although there are some slight differences in composition, from what has been shown previously concerning adsorption equilibria occurring in chars, these differences would not be expected to show in the filtrates. Both liquors had been filtered through the factory Sweetlands. TESTSWITH CHARB (WASHEDNEW CHAR)-The work was repeated in considerably less detail on char B to ascertain whether the same general principles apply to new char which had been freed from excess ammonium compounds but which had never filtered any liquor. While the lowering of the pH by underburned char previously noted in the batch experiments had been confirmed when working under char filtration conditions with the variously burned char A, it could be contended that adsorbed organic acids from incomplete burning of the organic matter in this service char could account for this phenomenon. Therefore, it was considered necessary to repeat the work with the new char. Table X shows that the result of underburning is similar in every respect for this char. FILTER 1
2
TEMPERATURE BURNED
CAUSTIC TE~T
PH
Colorless Colorless
9 6482
c. 616 200
Tables I X and X confirm the sitme general principles which have been described in connection with the previous batch tests reported in Tables I11 to VIII, inclusive. Briefly, these are: 1-Service chars may be burned to a satisfactory or even "colorless" caustic test, and yet be underburned to an extent that acid liquors may result. 2-Ash adsorption increases with increased alkalinity of the char within the limits to which service chars are likely to be burned in practice.
IXDUSTRIAL A N D ENGINEERING CHEMISTRY
September, 1928
Table X-Effect Composite no.
I
Ash coe5cient
0.19 8.9
0.19 7.2
of p H of Char B on Adsorption f r o m Washed Sugar Liquor
I11
IV
0.18 8.8 0.62
0.17 8.7
0.16 8.4
0.19 7.1 0.76
0.18 6.9
019 6 7
I1
v
VI
CHAR BURNED AT 616'
fnHvert coefficient
0.15 8.0
0.16 7.6
VI1
f z e r t coefficient
Table XI-Effect
I
1
?i
2
