April, 1931
I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
(2) Speed of filtration is affected by the size and character of the particles which in the case of hardwoods quickly plug the pores of the alundum crucible. (3) In drying, the hardwood lignin, already closely packed, forms a dense, hard cake at the bottom of the crucible.
Literature Cited (1) Bray, PaPer Trade J . , 87, 59 (1928). (2) Freudenberg, Zocher, and Durr, Ber., 1, 1814 (1929).
421
(3) Harlow, “Contributions t o the Chemistry of the Plant Cell Wall11,” New York State College of Forestry, 1928. (4) Hawley and Wise, “Chemistry of Wood,” p. 163, Chemical Catalog, 1926. ( 5 ) Klason, “Bericht der Vereins der Papier- und Zellstoffchemiker,” p. 52 (1908). (6) Mahood and Cable, J. IND. ENG.CHEM.,14, 933 (1922). (7) Ritter, Zbid., 17, 1194 (1925). ( 8 ) Ritter, J . Forestry, as, 534 (1930).
Filterability of Raw Cane Sugars’ I-Effect of Various Factors Prior to Pan-Boilingz J. C. Keane and H. G. Hill CARBOHYDRATE DIVISION,BUREAUOF CHEMISTRY AND SOILS, WASHINGTON, D. C.
v
has long been considered desirable to find a method by which sugars can be evaluated a s to their filtering properties without making a filtration test. Several methods for colloid determination have been tried, a s well a s a method for the determination of suspended solids. While in general there was a correlation between the results of some of these methods and filterability of the sugars, none of these tests gave uniformly reliable results. That suspended material was to some extent responsible for poor filtration tests was shown by t h e prefiltration of defecated juice. Sirup made from prefiltered defecated juice had a filtration rate twice t h a t not prefiltered. That the presence of suspended solids in the raw sugar affects the filtration rate was demonstrated when pulverizing six representative samples was found to increase the average filterability 54 per cent. It was found t h a t increasing the Pa0s content from 0.016 to 0.027 gram per 100 cc. brought about a 56 per cent increase in the filtration rate of the resulting sirups. On
a factory scale over a 4-day period, the addition of PzOr equivalent to 0.008 gram per 100 cc. of juice added to the raw juice materially increased lime consumption. Progressive beneficial effects were immediately apparent throughout the factory and the averages showed a n increase of over 100 per cent in the filtration rate of the sirup and approximately 50 per cent in t h a t of the sugar produced. Analysis of the original juice from this factory showed it to contain 0.028 gram per 100 cc. total P206, but apparently it was not in available form, since increasing it only slightly allowed the use of considerably more lime. Later laboratory tests on a large number of other juices from which sirups were made clearly indicated t h a t the total PnOscontent of the raw juices is not necessarily a criterion of how a juice will defecate. I t is very desirable t h a t a method be found to indicate the amount of available P z 0 6 present in raw cane juice.
HE filterability of raw cane sugars in connection with the refining operation has been given much attention by various investigators during the past few years. Although filterability of the raw sugar is by no means the only index of its quality, it is one of the most tangible and definite criteria, and probably for that reason has been used, often unconsciously and by implication, as an approximate measure of other, less tangible characteristics of’ quality of raw sugar. It has long been considered desirable to evaluate the filtering properties of raw sugar without an actual filtration test. Moreover, if correlation could be found between filterability arid other physical or chemical characteristics, the tracing of the cause or causes of poor filterability would be greatly facilitated. The routine tests ordinarily applied to raw sugar have been found tjo be in no manner indicative of‘ its filtering qualities. The significance of colloid content was first considered as it is known that raw sugar contains varying quantities of colloidal material and also that certain colloids may affect filtration rates (8, 9,10, 11, l S , 14, 15’). An approximate determination of the content of colloidal material in raw sugar was made, by means of the dye test (3, l o ) , on a series of selected samples of measured filterability. Utra-filtration through collodion membranes according to the method
of the late L. E. Dawson of this division was also used as a means of approximate quantitative separation of colloids. Although on the whole there was a definite correlation in many instances between filterability and content of colloids as determined by the dye test, especially in sugars from the same factory, yet there were certain exceptions; and it is with these exceptions that this investigation is chiefly concerned. The weight of suspended material removed by ultrafiltration also was not found to be a satisfactory index of the filterability of raw-sugar solutions, owing, in part at least, to the varying quantities of suspended material removed by filtration prior to ultra-filtration. I n addition to determining the approximate percentage of total colloids, their solubility in acetone, alcohol, and water was studied from the standpoint of the presence of cane wax constituents. The results of these tests, however, were in no way enlightening. Precipitation by alcohol ( 2 ) with a quantitative separation of the sugar-free precipitate was next considered. A modified method in which tared Gooch crucibles were used to retain the precipitate gave good check results. This alcohol precipitation method was given a thorough trial and found t o afford little, if any, correlation with respect to filterability. The ash content of all the raw sugar samples was determined as well as the CaO content of the ash. hreither of these methods gave any conclusive indication of the filtering qualities of raw sugar solutions. As no definite correlation was found by such methods of
T
1 Received February 21, 1931. Presented before the Division of Sugar Chemistry a t the 80th Meeting of the American Chamical Society, Cincinnati, Ohio, September S t o 12, 1930. Contribution No. 103 from Carbohydrate Division, Bureaii of Chemistry and Soils, U. S. Department of Agriculture.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
422
examination, the filter cakes resulting from the filtration of various samples-that is, the Hy-Flo Super-Cel with retained suspended material and a portion of the sugar solution-were dried, and the weight of alcohol precipitate obtained from a water dispersion of the cakes was determined. These data were somewhat indicative of the filtering properties of the sugars, but were by no means conclusive. Pulverization of Raw Sugars I n order to obtain some information as to what effect possible contamination with cane wax (4) might have on the rate of filtration, several samples of raw sugar were extracted with pure acetone. Sugars of known filterability were pulverized, dried, and thoroughly mixed with acetone. The acetone was filtered off through filter paper, the sugar was again dried, and the filtration rate determined (7'). As a control, a portion of the pulverized sample was tested for filterability without treatment with acetone. It was found that pulverizing alone caused a decided improvement in filterability, but the net result of the acetone treatment alone was very slight. Since pulverization produced such an unexpected result, it was repeated with several additional samples of sugar; without exception a decided improvement was noted, the greatest improvement being obtained with the poorer filtering sugars. Table I-Effect
of Pulverizing on Filterability of Raw Sugar
ORIGINAL FILTBRARILITY
% 104.8 77.7 64.7 52.3 47.2 27.9 Av. 62.4
FILTERABILITY AFTER PULVERIZING
INCREASEIN FILTERABILITY
% 133.0 113.0 99.5 79.0 82.0 55.0 93.6
% 26.9 45.4 53.8 51.0 93.6 98.5 61.5
All filtration tests were made with the pressure filter designed by L. E. Dawson. The filtration of both sirups and sugars was conducted a t 85" C. under 20 pounds (1.5 kg. per sq. cm.) pressure. Hy-Flo Super-Cel was used as a filter medium, 0.25 per cent for sugars and 2.0 per cent for sirups, calculated on the basis of solids. Filtrations were made through a filter leaf of 1 square inch (6.45 sq. cm.) area, a twill filter cloth being used in all tests. All filtrations were made a t 50" Brix and extended over 30-minute periods. The filtrate obtained during the first minute was discarded, and the total filtrate of the remaining 29 minutes was weighed. The percentage filterability was calculated from the figure obtained. For sugars, the weight of filtrate in grams obtained in 29 minutes divided by 1100 equals percentage filterability; for sirups, the weight of filtrate in grams for the same period divided by 1500 equals percentage filterability. The results are shown in Table I. A possible explanation of this phenomenon is that pulverization so changed the physical character of some of the extraneous material in the raw sugar as to allow it to pass through the filter in a much more finely divided condition. This subject is being further investigated. Determination of Suspended Solids
A study of methods of determination of the suspended solids in a solution of the raw sugar was therefore undertaken. The following method devised by R. T. Balch of this division was adopted: A sample of raw sugar was dissolved in water and diluted to exactly 50' Brix. This solution was filtered through a 250-mesh copper cloth in order to remove coarse suspended material which had been found to have no effect on filtration. Forty grams of this solution, equivalent to 20 grams of solids, were weighed into a tared
Vol. 23, No. 4
beaker. Exactly 1 gram of Hy-Flo Super-Cel was added and allowed to stand in the presence of the sugar solution for '/z hour before filtering on a tared Gooch crucible. The filter cake in the crucible was then washed with 150 cc. of cold water, care being taken that the cake did not dry a t any time during the filtering or washing procedure. The crucible and contents were dried a t 105" C. overnight and weighed. Percentage of ash and organic material by difference was obtained. Control tests were made with HyFlo Super-Cel and a solution of pure sugar. The percentage of suspended solids determined by this method on a large number of raw sugars also failed to indicate their filtering qualities. This lack of correlation is apparently due either to inability to separate definitely material which affects filtration from that which does not or to the removal of suspended material upon dilution. When this method was applied to sirups of known filterability, however, the degree of correlation was much better, but even in these cases the differences were not considered sufficiently pronounced to permit evaluation of a sirup with respectato filterability. Study of Sirups from Various Factory Juices Since the sirups showed such a difference in filterability, as well ac.1 in suspended material, a study was conducted on each of the various juices from which factory sirup is made. In a raw-sugar factory using open defecators the sirup is usually composed of the juice from the defecators, the juice decanted from the mud-resettling tanks, and the filter-press juice. The various juice samples selected were produced under average working conditions. These juices were evaporated a t atmospheric pressure for 15 minutes and then concentrated to approximately 60" Brix in vacuo in the laboratory. They were all diluted to exactly 50" Brix for the filtration test. The concentrated defecated juice gave a sirup with a filterability approximately equal to that of the factory sirup; the sirup made from decanted mud-tank juice had a slower filtration rate, whereas that made from filter-press juice had a very good filtration rate. Since the filterability of the sirup from the filter-press juice was so much better than the others it was decided to prefilter defecated and mud-tank juices prior to concentration to determine to what extent the filterability of the resulting sirups would be increased. The prefiltration was conducted a t approximately 60" C., with a vacuum leaf and Hy-Flo Super-Cel as a filter medium. The filtrate in all cases was free of visible suspended material. However, in some instances the filtrate was decidedly less brilliant than in others, and this was especially true of mudtank juices. Prefiltration of the defecated juices causes a decided improvement (9) in the filterability of the resulting sirups, the average filterability being about twice that of sirups made from non-filtered defecated juices. I n the mud-tank juices very little improvement resulted from prefiltration. I n the defecated juices evidently a large percentage of the detrimental suspended material was removed by Hy-Flo Super-Cel filtration, whereas in the decanted mud-tank juices the flocculated mud particles are probably so disintegrated and dispersed by agitation and reheating that they are not retained by Hy-Flo Super-Cel filtration, thus causing lack of brilliancy in the filtered juices and possibly later flocculation upon concentration. The sirup made from filter-press juice had a filtration rate about four times that of sirup made from mud-tank juice, owing no doubt to the more thorough removal of suspended material during filtration. A great percentage of the very finely suspended solids which may pass through Hy-Flo SuperCel in the preliminary filtration as conducted is undoubtedly
retained by the mat of cachaza in the filter presses. Since the presence of suspended matter was shown to affect the filterability of sirup, a study of juice defecation was undertaken, in which the filterability of the resulting sirups was used as a criterion of clarification efficiency. Relation of Added Phosphate to Filterability of Resulting Sirup
It has long been recognized that the presence of phosphoric acid (1, 5, 6, 8, 11, 12) in raw juice in available form is an aid t o defecation. It would be expected that in the clarified juice of high phosphate content the quantity of suspended material would be less and the filteratiility of the resulting sirup would consequently be increased. The following experiments were made to determine the effect of phosphate added to the juice on the filterability of the sirup. A number of samples of juice obtained from sugar canes of known origin as t o variety and soil on which they were grown were divided into two portions of 10 gallons (45.4 liters) each and placed in experimental defecators similar in design to those used in factory practice. One portion was limed to pH 8.5; to the other a small amount of phosphate was added in the form of phosphoric acid solution, the acid being thoroughly mixed with the raw juice. 'This portion also was limed to 8.5 pH. The percentage c'f phosphate was determined in both the untreated and the treated samples. These two portions were heated simultaneously and brought t o the boiling temperature in the same period of time. They were allowed to defecate for 1 hour and 15 minutes, after which the clear, supernatant juice was drawn off each sample and evaporated to sirup in the szme manner. The filterability and the CaO content of each of the sirups were determined. The results of thif series of experiments are given in Table 11. As will be seen from this table, the filterability of the sirup is increased decidedly by the addition cf phosphoric acid, which is what ~voulclbe expected in view of the comparative brilliancy noted in the respective defecated juices. Table 11--Effect of Adding Phosphoric Acid t o Cane Juice o n Filterability of t h e R e s u l t i n e Sirup
I
ORIGINAL JUICE
pzo' Gram/ 100 cc. 0.014 0,022 0.016 0.015 0.014 0.012 .tv, 0 . 0 1 6
423
I-I-DUSTRIAL A-VD ESGI-VEERING CHELIIISTRY
April, 1931
I
-l -I
SIRUP
CaO per
1
II
SAME
PLUS PHOSPHORIC
Filterahility
1OOo Brix
L-/o
Gram
Gram/ 100 cc.
29.5 37.5 29.9 22.2 31.2 24.2 29.1
0.2858 0.2858 0 2730 0.3208 0.3532 0.2985 0.3029
0.025 0.031 0,024 0.025 0.031 0.027 0.027
''O'
ACID
SIRUP
TWICE
Filt,erability
47 51 31 46 53 44 45
6 0 1 2 8 3 7
CaO per
100' Brix
Gram 0 2821 0.2912 0.2912 0.3149 0.3204 0.2912 0,2985
The net result of the large-scale laborator) experiments was so satisfactory that it was deemed advisable to try addition of phosphate to juice on a factory scale t o determine its effect on the filterability of the sugar made. I n a factory which was having clifficulty in making a good filtering sugar it was found that the sirup was very low in filterability. This factory was grinding a large percentage of Uba cane, and the juice clarification was not satisfactory. After several changes in methods had failed to improve the filterability of the sirup, a 4-day experiment on the effect of adding phosphate to the raw juice was undertaken. A good grade of commercial phosphoric acid was double-diluted, and a 500-cc. portion was added to each tank of raw juice, the whole being thoroughly mixed with air before being limed to a pH of 8.5 when cold. This amount of phosphoric acid was equivalent to approximately 0.008 gram Pz05 per
100 cc. of juice. With this increase of Pzos in the raw juice was necessary to increase materially the amount of 10" 136. lime in order to maintain the same pH value in the coldlimed juice. A marked improvement in the general appearance of the defecated juice was noted. The filterability of the sirup and sugar was decidedly improved, as will be seen by the following data showing average filterability for 4-day periods: it
FIRST SUGAR
SIRUP
Before using PlOs During use of PlOr
SECOND
TOTAI OIJTPLT
SUGAR
%
R
70
%
9 9
48 1 73 5
38 8 62 2
45 2 68 4
20 6
The results of this factory experiment confirmed our laboratory tests and showed clearly that the resulting sugar is likewise benefited by the improved clarification due to the added P20;. Availability of Phosphate Content of Raw Juice
Because of the great difference in the amount of lime required after the addition of this small percentage of Pz0s it was assumed that the phosphate content of the original juice was very low. Analyses of the juice from this factory did not show this to be the case. A 100-cc. portion of the original dilute juice was ashed and found to contain 0.028 gram PSOSper 100 cc. of juice. Since the addition of 0.008 gram of PzOb per 100 cc. necessitated such an increase in lime to maintain the same pH in the cold-limed juice, it would appear that a large percentage of the PzOjin the original juice was not in available form. I n previous observations it was noted that, in general, dilute juice from Uba cane is high in phosphate content yet it is very difficult to clarify (6). It is not definitely known whether this is a characteristic of the cane variety itself or of the type of soil on which it is grown. Neither can it be definitely stated that the difficulties experienced in defecating juices from Uba canes are due to a lack of available phosphate rather than to the nature of the impurities in the cane itself. However, the results of this experiment strongly indicate that the availability of the phosphate is an important factor. This was further demonstrated by the data on the sirups made in the laboratory from juices obtained from two widely separated sections of the cane-growing area. As the cane was of the same variety-namely, BH 10-12-apparently the variations in the juice are due to soil or climatic conditions. Table I11 gives another illustration of filterability of sirups made from juices of approximately the same total P20scontent. Table 111-Comparative
I
Filtration Rates of Sirups
I
JUICE
p20'
II
R
Gram/lOO cc.
16.5
84.6
16.6
84.7
0.014 0.011 0.009 0,024
Brix CP0T-D 1
-. ....
-
16.7 l5,7 15 8 16.5 Av. 16 1 6 .22
1
I
84.7 84.3 82.3 86.0 84.3
1
II
1
0.015
I
0.022 16 0 . 0016
I
0.012 0.014
SIRUP
Filterabilitv
70
CaO per 100' Brix
Gyam
22.2 15.0 19.4 25.3
0.3208 0.3168 0.2394 0.3'49
40.5 33.7 39.5 49.5 4 0 . 88 40
0.2821 0.3685 0,4296 0.298.5 0.2985 0.3446
This table shows that the two groups have practically the same total phosphate content. Although the juice of group 1 has a higher average purity, the average filterability of the resulting sirup of group 2 is about twice that of group 1.
424
INDUSTRIAL A N D ENGINEERING CHEMISTRY
The same procedure of defecation and evaporation to sirup was followed in each case. I n general, the filterability of the sirups made from various areas correlated well with the phosphate content found in the raw juice, but other exceptions noted substantiate the belief that in many cases the phosphate present is not in available form. The question of the availability of the phosphate present is important, and it is our present plan to continue work on this phase of the problem. It is desirable to use some analytical method by which the amount of available phosphate may be determined, as obviously the total P20soften gives misleading information. Again, i t is important to ascertain how this factor is affected by cane varieties, and soil and climatic conditions, as well as by fertilization. Conclusion These data indicate that filterability of sirup and sugars is influenced primarily by iinely suspended material, part of which is probably in the upper range of colloid size and the remainder is probably somewhat above the upper limit of colloid dimensions. A large portion of this material may be eliminated by good defecation and proper handling of the muds. That suspended matter is a factor in the filtration rate of sugars was confirmed by the effect of pulverizing, For good defecation it is necessary to have effective manipulation of the proper equipment, and also to have a raw juice containing sufficient available phosphate to form a flocculent precipitate with the lime. The muds should be carefully filtered, and if any juice is decanted from the mud tanks before filter-pressing, this juice should be further treated and not sent direct to the evaporators. However, judging from the good filterability of filter-press juice, it would seem ad-
Vol. 23, No. 4
visable to send this directly to the evaporators whenever good filtration gives a brilliant juice. The addition of phosphate to the raw juice in the form of phosphoric acid will aid defecation and in turn improve the filterability of the resulting sugar when this constituent is deficient in available form. The advisability of its use from an economic, as well as an operating] standpoint] must be decided by each factory. Acknowledgment The authors wish to acknowledge the assistance rendered by Harvey W. Saylor, formerly of this division, in obtaining some of the results reported in this article. They also wish to express their appreciation of the cooperation extended by the Fajardo Sugar Company of Porto Rico, as well as several other centrals in Porto Rico. Literature Cited (1) Anon., Intern. Sugar J., 27, 304-8 (1926). (2) Badollet, Facts About Sugar, 28, 923 (1928),abstract. (3) Badollet a n d Paine, Intern. Sugar J . , 28, 23, 97, 137, 497 (1928). (4) Bardorf, IND. ENQ.CHBM., 20, 258-82 (1928). (6) Bird, Intern. Sugar J . , 80, 798-7 (1928). (6) Bond, Planter Sugar Mfr., 74, 408 (1925). (7) Dawson, Facts About Sugar, 20, 370 (1926),abstract. (8) Farnell, J. SOC.Chcm. I n d . , 46, 343-7 (1928). (9) McAllep e t al., Proc. 46th Annual Meeting Hawaiian Sugar Planters Assocn., Sect. X I , Corn. Repts., 96-119 (1927). (10) Paine and Balch, Reference Book of Sugar Industry o f the World (published by Planter Sugar Mfr.). 6, 47-60 (1928). (11) Paine a n d Keane, Planter Sugar M f r . , 78, 188 (1927). (12) Smith, Sugar, 28, 124-7, 184 (1926). (13) Smith, Facts About Sugar, 20, 1138-47 (1927). (14) Walker, Intern. Sugar J., 27, 54 (1925),abstract. (15) Wayne, Planter Sugar M f r . , 77, 247-50 (1928).
11-Eff ect of Pan-Boiling Operations' While good filtering sirup is a requisite for the making of good filtering raw sugar, the data clearly show t h a t faulty pan construction and operation may cause poor circulation and be responsible for the production of poor filtering sugar from good filtering sirup. This harmful effect was especially noted in the case of second sugars. A large sample of sirup was taken from each of five factories and the filtration rate determined. From these sirups strikes were boiled in the laboratory glass vacuum pans under standardized conditions. Two of these factories had poor filtering sirup and were producing sugars with a low filterability; another with a good sirup was producing a good filtering sugar. The remaining factories had good filtering sirups, but the sugar produced had a low filtration rate. In view of the laboratory boiling experiments on sirups, it was strongly indicated that a t these factories pan operations were largely a t fault. The filterability of second sugars was investigated a t
two factories having good filtering sirup, one of which was making good and the other a poor filtering product. The factory making good sugar produced a second sugar with a filtration rate about three times that of the other. Investigation of individual pans a t the latter factory showed that, of four pans making second sugar from the same molasses, two of the pans produced a sugar having a n average filterability only one-tenth that of the other two. Although the employment of various boiling systems may influence the filtering quality of the total output of sugar, investigation of the products of individual pans shows that variations in design or method of operation of pans may cause a decided difference in the filtering quality of the resulting sugar. The question of pan circulation, design, and operation should be investigated further from the standpoint, not only of raw-sugar filtration, but of crystallization in general.
T HAS long been recognized that good clarification is a prerequisite for making raw sugars of excellent filtering quality, The data obtained in this phase of our investigation clearly confirm the belief (1, 2, 3, 6 to 1.2) that the more brilliant the clarified juice, and the freer it is from finely divided suspended material, the better are the filtering qualities of the resulting factory sirup. Although good filterability of the sirup is essential, our past observation has indicated that it is not the only requisite for the production of raw sugar of satisfactory filtering quality.
During the season of 1930 in Porto Rico, it was decided to consider filterability of raw sugar not only from the standpoint of juice clarification, but also from that of producing sugar from sirup, including the operations of pan-boiling and centrifuging. Two factories grinding similar canes and apparently having good juice clarification were chosen for a study of boiling operations. One factory, hereafter referred to as No. 1, was making a very good filtering raw sugar, whereas the product of the other factory, No. 2, was considerably lower in filterability. A systematic investigation of the various sugar end products from the two factories was undertaken. Two-day
I
8 Contribution No. 104 from Carbohydrate Division, Bureau of Chemistry a n d Soils, U. S. Department of Agriculture.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
April, 1931
composite samples of first and second sugars were tested for filterability. Also, in order to determine whether or not the wide variation in the filtering quality of the final products was caused by poor clarification a t factory No. 2, a 12-hour composite sample and a catch sample of sirup from each factory were examined every other day. This series of samples was studied for a sufficient period to obtain definite information regarding the filtering qualities of the various products. The time required was about one month. During this period consistent results were obtained. All filtration tests were made by the procedure described in Part I (5). Relation of Filterability of Sirup to Corresponding Sugar
The first consideration was the filterability of the factory sirups. It might be expected that the sirup from factory 1 would be of superior filtering quality, as the sugar from this factory was consistently better in this respect than that from factory 2. The results, however, did not show this to be the case. For the duration of these experiments the average filterability of the sirup from factory 2 was 29.3 per cent, whereas that from factory 1 was only 21.2 per cent. If the subsequent procedures of pan-boiling and centrifugal work a t the two factories were identical, these results would indicate that the sugar from factory 2 should be better or a t least equal in filterability to that from factory 1. Both factories used the same type of threeboiling system, both grained on sirup, and both cut this grain for footings for both second and third sugars. The average filterabilities of the first and second sugars from the two factories for this period were as follows: FACTORY 1 2
FIRSI SUGAR
SECOND SUGAR
WEEKLY COMPOSITE OF OUTPUT
%
%
70
123.9
123.5 39.0
118.7 67.0
88.1
These results show clearly that, contrary to what would be expected from the sirup filtration rates, the sugars from factory 2 are decidedly lower in filterability than those from factory 1. A decided difference may be noted in the filtering quality of the first sugars from the two factories. This variation is attributed to the low filterability of the sugars obtained from strikes to which first molasses had been added. The straight sirup strikes gave for the most part a filterability over 100 per cent. At factory 2 the relative difference in filterability between straight sirup strikes and those to which first molasses had been added was greater than at factory 1 or in the experimental laboratory vacuum pans; in operating the latter sufficient first molasses could be added to lower the purity of the strike three to four points without greatly affecting the filtration quality of the resulting sugar. The drop in filterability of first sugars from mixed pans was found to be more pronounced when the molasses was added before cutting. It should be noted, however, that in the experimental laboratory pans only virgin molasses from the previous laboratory straight sirup strike was used, and in factory 1 it is a routine procedure to use only virgin molasses for topping off first strikes. It cannot be stated definitely whether this difference in filtering quality of the sugars made from straight sirup strikes as compared with those made from strikes to which molasses had been added is due to the quality of molasses or to the pan work a t factory 2. I n the second sugars the difference in filterability is much greater than that between first sugars; the filtration rate of second sugar from factory 1 is more than three times that of the second sugar from factory 2.
425
Boiling Experiments in Laboratory Pans
The foregoing data indicate that either the design or the operation of certain vacuum pans in factory 2 was, in a measure a t least, responsible for the poor-filtering sugars. I n order to test this conclusion, a series of sugar-boiling experiments was conducted with glass laboratory coil vacuum pans. It was possible in this way to ascertain whether or not poor circulation in the factory pans was a factor in the production of sugar of poor filtering quality. Several samples of sirup from factory 2 were boiled to massecuite in the laboratory pans. I n some instances first molasses from one laboratory strike was used to top off the contents of the next pan. I n all cases these massecuites were spun in the laboratory centrifuge, no wash water being used on first sugars. A large sample of sirup was obtained from factory 1, and from it two laboratory strikes were boiled, one being a straight sirup strike and the other topped off with the molasses from the first. I n order to check the operation of the pans used for second sugars a t factory 2, three samples of factory 2 first molasses were boiled into second strikes in the laboratory pans, sirup being used for footing in each case. The average filterability of the sugars from the series of laboratory experiments was as follows: FACTORY
FIRSTSUGAR
1 2
SECONDSUGAR
%
%
131.4 123.1
si:5
It will be noted that sirup from factory 1 yielded a first sugar in the laboratory pans that checked very well with the filterability of the factory sugar and that the filterability of the first sugar from factory 2 was somewhat better than that of the corresponding factory sugar. But it should be remembered that the laboratory series contained a greater percentage of straight sirup strikes. The most notable difference, however, is seen in the second sugars of factory 2, since three strikes with an average purity of 70.2 yielded sugar with an average filterability about two and one-half times that of the factory second sugar produced from the same materials during the same period. Table I-Comparative FACTORY
Filterability of Factory a n d Laboratory Sugars
FILTERABILITY ~~~~~~~~R OF FACTORY BOILEDIX SIRUP LABORATORY PANS
F;;E~AB;;~ OUTPUT
%
%
70
26.5 27.6 28.5 17.8 15.1
131.4 125.6 123.7 55.9 42.6
120.0 51.2 62.2
...
46.0
As a further study of pan work and its bearing on filterability of the resulting sugar, a large sample of sirup was obtained from each of several factories and boiled in the laboratory pans. The filterability of the sirup was first determined, and then two strikes were boiled from each lot, one being a straight strike and the other being topped off with molasses spun from the preceding strike. The filtration data given in the third column of Table I represent averages for the sugars yielded by these two strikes. The figures given in the fourth column represent the filterability of the sugar produced in each factory during the period when the sirup samples were obtained. From this table it will be seen that in general the filterability of the sugar increases with the filterability of the sirup from which it is made, assuming that the pan work is equally good in all cases. There is a possibility that a sirup might filter well a t a concentration of 50' Brix, for
INDUSTRIAL AND ENGINEERING CHEMISTRY
426
'
Vol. 23, No. 4
instance, and yet contain very finely divided suspended material which might undergo aggregation and precipitation at higher concentrations, thus affecting the filterability of the resulting sugar, but such cases are believed to be rather exceptional. I n factory 1 we have what may be called ideal conditions. The clarification was such as to produce a good filtering sirup, from which, owing to satisfactory pan operation a t the factory, a sugar having a high filtration rate was produced. I n factories 2 and 3 a good filtering sirup was obtained, from which it was possible to make a good filtering sugar, as can be seen by the results of the laboratory boiling, but owing to faulty pan work the sugar produced by these factories was much lower in filterability than anticipated. I n factories 4 and 5 the sirup was not of good filtering quality, owing no doubt to inferior clarification and, as would be expected, the corresponding factory sugars were lower in filterability. The sugars made in the laboratory pans also had a low filtration rate, showing that in these factories pan operations were not at fault. No filtration rate was determined for the sugar produced a t factory 4 a t the time of conducting the tests, but it was known to be of inferior filtering quality. In factories 2 and 3 we have an example of unsatisfactory pan-boiling as a cause of poor filtering sugars, and in factories 4 and 5 an example of poor juice clarification as a cause.
crystallization factor Table I11 gives the results of these tests, the massecuites being tabulated according to the pans in which they were boiled.
Filterability of Second Sugars as Affected by Pan Operation
Table 111-Comparative
I n the belief that pan operation, particularly circulation in the various pans, was an important factor, a series of filtration tests was made on second sugars a t one of these factories, the samples having been spun from strikes boiled in four different factory pans. The results of these tests are shown in Table 11. The pans designated as C and D are coil pans; B is a calandria pan with one coil below the calandria and two above it; and E is a calandria pan, a duplicate of the B pan but without coils. The figures were obtained over a period of about 6 weeks and do not necessarily represent consecutive boilings in each pan. Table 11-Filterability B
% 30.3 20.7 13.1 31 2 22.9 25.0 36.5 22.5 16.7 16.3 15.8 Av. 2 2 . 8
in which the massecuites were purged might be partly responsible for these variations. I n order to evaluate the pan operations from several points of view, it was deemed advisable to take samples of massecuites boiled in the various pans as they were being discharged from the crystallizers and purge them under standard conditions in a laboratory centrifuge. In each instance the basket of the centrifuge was filled and allowed to spin for 15 minutes a t a definite rate. At the end of the first 5 minutes 100 cc. of water a t room temperature were sprayed on the massecuite by means of a small wash bottle. The resulting sugars were polarized, and the filterability was determined. The total molasses was collected, including the quantity resulting from the 100 cc. of wash water; this was thoroughly mixed and the apparent purity was determined. From the apparent purity of the massecuites as obtained by previous analyses and the apparent purity of the runoff molasses, a crystallization factor for each sample was calculated according to the following formula:
-
D
APPARENT PURITY Massecuite Molasses
%
%
%
97.8 95.1 147.8 89.0 90.3
...
...
61.7
104.0
5.6 2.7 15.7 10.0 7.7 10.0 13.4 9.3 19.8 4.0 1.6 9.1
...
. . I
... ... ...
Comparison of the filterabilities of the second sugars produced by boiling in the several pans shows that the coil pans yield a sugar with decidedly superior filterability. The E pan consistently yielded sugars with such low filterability that, since it was used exclusively for second sugars and was in almost constant use, it would appear to be an important factor in the poor filtering quality characteristic of sugar from this factory, The time and amount of water used in purging are dependent very largely on the quality of the massecuite from each individual crystallizer. During these experiments the second molasses produced varied decidedly in purity from one crystallizer to another. It was difficult to determine whether or not this was an inherent quality of a particular strike, as the molasses was often a mixture from one or more crystallizers. Also, the manner
';EA","FILTERABILITY SUGAR OF
v.
%
R
%
Av.
50.4 49.9 49.8 47.4 52.8 50.1
40.5 41.3 38.6 42.2 40.5 40.6
94.4 96.1 97.0 95.1 97.3 96.0
3.5 8.7 21.3 2.4 9.2 9.0
43.5 44.7 45.3 45.0 47.4 49.4 47.4 46.1
44.6 47.7 43.5 41.8 39.2 41.5 41.5 42.8
96.6 96.6 96.2 97.5 97.6 97.9 97.4 97.1
41.5 66.2 43.9 64.4
100.0
Av.
68.7 70.1 69.1 68.0 67.9 70.4 69.3 69.1
Av.
67.9 68.5 69.5 67.5 69.7 69.7 70.8 68.8 69.1
41.9 44.8 47.7 45.1 44.9 49.3 46.2 45.9 45.7
44.7 42.9 41.7 40.8 45.0 40.2 45.7 42.3 43.0
96.7 96.5 97.0 97.0 97.2 97.5 97.7 96.4 97.0
54.8 58.5 68.2 48.5 59.2 53.5 113.7 30.9 60.9
69.7 70.1 69.0 70.4 68.2 69.6 68.0 69.3 AV. 6 9 . 3
50.1 49.7 48.1 50.7 50.6 48.3 52.6 49.8 50.0
39.3 40.4 40.6 40.0 35.8 41.2 32.5 38.8 38.6
93.8 95 6 95 8 93 4 94.6 94.3 94 3 95.8 94.7
3.7 4.1 4.6 1.7 3.6 8.1 0 2.6 3.6
C
D
E
G::E'f",Z
70:5 70.7 69.2 69.7 71.9 70.4
B
E
40.0 54.4 80.0 74.2 114.4 30.0 74.1 55.6 55.7 38.2
-
Data o n Second Sugars Boiled i n Different Pans (Massecuites taken from crystallizers and spun in laboratory centrifuge under standard conditions, adding 100 cc. wash water)
of Sugars Boiled in Different Pans
c
-
100 (purity of massecuite purity of molasses) 100 purity of molasses
%
79.6 40.7 62.3
It will be seen from this table that the coil pans gave d e cidedly better filtering sugars with higher polarization than either of the calandria pans and, as in the preceding series, the E pan yielded the poorest filtering sugars and likewise sugars of the lowest polarization. I n factory practice it would be necessary to use additional wash water in order to increase the polarization of these sugars, thus tending to increase further the purity of the molasses and to lower further the crystallization factor, which is already appreciably below that of products from the coil pans. The results of these experiments are indicative of pan work alone,
INDUSTRIAL AND ENGINEERING CHEMISTRY
April, 1931
since the centrifuging operation was standardized, and any slight variations in crystallizer operation would be equalized. The question naturally presents itself as to whether these pan difficulties are due to methods of operation or to some fault in the construction or heat distribution of the pans themselves. The data and observations are insiifficient to vindicate entirely the sugar boilers with respect to the o p eration of the calandria pans boiling second sugtrs, since it was possible to make satisfactory grain from sirup in the E pan, this material often being used for footing in other pans yielding a good sugar. This would imply that the circulation of the pan was efficient while sirup was being used. According to the operators, the difficulty was encountered when molasses was added, a false grain appearing unless a high temperature was maintained. However, these sugar boilers stated that at different times they had tried boiling this pan in every possible manner known to them, and they were convinced that the method they employed gave the best results obtainable with this equipment. Also, the sugar boilers were able to make a superior massecuite from the same molasses by using the coil pans. Thus we may assume that, although some improvement might possibly be made in the operation of these pans, the pans themselves are a definite source of the difficulty which is causing poor filtering sugar and deficient crystallization. Relation between Percentage Crystallization and Filterability
I n connection with the average filterability of the rawsugar outputs from factories 1 and 2 for the season of 1930, which were 112.6 and 48.7 per cent, respectively, it may be of interest to note the various average pan and molasses purities, together with the corresponding calculated crystallization factors. These are shown in Table IV. The purity figures represent crop averages for each factory. T a b l e IV-Average P u r i t y of Massecuites a n d Molasses, a n d Crystalllz a t i o n Factor, Factorles 1 a n d 2, for 1930
-~
PURITYOF PURITYOF MASSECUITES ~ I O L A S S E S
FACToRY
CRISTALLIZATION
FACTOR
%
%
70
1 2
1
81.9 82.4
62.8 65.3
51.4 49.3
1 2
2
69.3 69.2
44.3 47.7
44.9 41.1
1 2
3
58.4 57.1
28.8 32.5
41.6 36.5
427
Conclusions
The results of this investigation show that: (1) a good filtering sirup is necessary in order to make a sugar of good filterability; and (2) a poor filtering sugar may result from a good filtering sirup when pan construction or operation is faulty. The effect of inefficient pan work is more pronounced in the case of second sugars. Other investigators (6) have found that variations in systems of boiling affect the filterability of the raw sugar produced. This investigation deals, however, with the individual pans. Although the data given here show that the coil pans which were under observation yielded a decidedly better sugar than that obtained from the calandria pans, this behavior does not necessarily apply to calandria pans in general, as it is very probably due to defects in design or operation of the particular calandria pans investigated. Either of these factors may influence the quality of the resulting sugar, and it is the writers' opinion that the adverse results are largely due to deficient pan circulation. Pan circulation does not refer merely to time of boiling or rate of evaporation but primarily to the manner in which the total mass of crystals is kept in constant motion, bringing individual crystals continually in contact with supersaturated mother liquor and thus producing more complete sucrose crystallization and probably reducing contamination of the sugar crystals. Thc specific effect that various conditions of boiling may have on the resulting sugar is to he studied further, not only from the standpoint of filterability of raw sugar, but also from the standpoint of crystallization in general. The results of these experiments on filtration rates show that there are two prevalent and distinct causes of poor filtration of raw cane sugar: one is poor juice clarification and the other is faulty sugar-boiling operations. Each of these in turn involves a number of different factors. Literature Cited Anon., Sugar, 27, 168-70 (1925). Anon., Intern. Sugar J.. 27, 304-8 (1925). Anon., Platzter Sugar Mfr., 76, 10-12 (1926). Bomonti and McAllep, Proc. 45th Annual Meeting Hawaiian Sugar Planters Assocn., 232-42 (1926). ( 5 ) Ddwson. F a d s A b o u f Sugar, 20, 370 (1925), abstract. (6) Btheridge, Louisiana Planter Sugar M f r . , 70, 408 (1923). (7) King, Planter Sugar M j r . , 79, 221 (1929). (8) Kopke, F a d s About Sugar, 21, 301 (1026). (9) Paine, Reference Book of Sugar Industry of the World, 4, No. 4, 40-3 (1926). (10) Smith, Intern. Suear J., 26, 266 (1924). (11) Walker and Greenfield, Zbrd., 26, 648-52 (1924). (12) Wayne, Planter Sugar Mfr., 77, 247-50 (1926). (1) (2) (3) (4)
Heats of Wetting and of Adsorption on Zinc Oxide'" Warren W. Ewing LEHIGH UNIVERSITY, BETHLEHEM, P A .
z
TSC oxide is used extensively in paint as a pigment, in rubber as an activator for organic accelerators and as a reenforcing pigment, in various medicinal pyeparations, in ceramics, and in numerous other ways. This product exists as a white powder, the particle size varying with the conditions under which it is produced. The average size of the finest oxide is about 0.15 micron, while the warser oxides may 1 Recrived Decembei 23, 1030. Presented under the title "Heat of Adaorptinn of Zinc Oxide" before the Division of Physical Chemistry at the 70th hleeting of the American Chemical Society, Atlanta, Ga.. April 7 t o 11, 1030. Preliminary work on this problem was carried out at the laboratory of tha Research Division, T h e New Jersey Zinc C o . , Paimerton, Pa. f
average as high as 0.7 niicron. This offers, especially in the finer sizes, an extremely large specific surface, and consequently a fruitful field for adsorption phenomena. Various investigators have observed that the nature of the adsorbed material affects markedly the pigment properties of the oxide when used as a raw material for preparing other substances. For example, when two paints are made up under apparently identical conditions except for humidity, the consistencies of the two paints may show pronounced differences which are due to an adsorbed film of moisture. The data presented in this article have been accumulated during the investigation of the nature and effect of adsorbed
