398
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 34, No. 4
TABLEV. FILTRATION OF DIFFICULT-FILTERING RAWSUGAR I WITH DIFFEREKT TYPES AND PERCENTAGES OF FILTER AID Standard Super-Cel0.60 0.80 1.00
c
7 %
Time, hfin.
0.40
1.40
0.40
0.60
% Hyflo 0.80
1.00
1.40
0.40
0.60
21.24 18.49 15.48 11.87 16.77
21.93 20.21 18 06 15.65 18.96
10.15 18 92 12.90 8.17 12.53
28.44 17.95 15.63 15.28
26.55 18.37 16.37 16.37
63.68 33.42 22.08 15.45
% Celite 503 0.80
1.00
1.40
22.79 25.46 17 46 11.44 19.28
28.81 27 95 21.24 15.48 23.37
31.39 32.94 26 40 19.95 27.67
32.42 34 66 34.40 30.96 33.11
51.76 26.55 17.54 13.61
44.06 20.61 17.54 15.10
43.05 23.66 19.23 16.94
38.37 24.21 20.14 18.79
Filtration Rate, Gallons per Square Foot per Hour 15-30 30-45 45-60
0-60
0.43 2.32 6.71 4.30 3.44
6.28 8.00 6.02 4.30 6.15
6.97 8.86 8.43 5.50 7.14
10.05 9.63 8.43 6.71 8.71
10.75 10.49 9.29 7.74 9.57
0-15 15-30 30-45 45-60
54.20 31.19 18.37 11.59
25.35 13.30 11.32 10.54
22.59 13.30 11.32 11.07
20.61 13.30 11.59 11.59
18.37 13.30 12.13 11.86
0-15
6.88
8 43
6.54 4.56 6.60
14.79 15.48 11.61 8.60 11.97
16.60 16.51 13.33 9.98 14.10
Clarity, Foot-Candles 43.05 18.37 13.94 12.13
open, because of their higher ratios of diatomaceous particles to entrapped gelatinous impurities. The results were increased total filtrates but somewhat lower clarities than for some lower percentage of filter aid (0.6 per cent), at which point the filter cakes had maximum clarifying capacity a t the sacrifice of some rate of flow. This condition shows the advantage to be gained by carrying out for different sugars tests in which different filter aids are tried in varying percentages. An indication may be obtained for operating conditions such as (a) optimum balance between rate of flow and degree of clarification, (b) maximum throughput which can be secured
34.99 17.54 13.61 11.86
30.83 17.54 14.93 14.59
for a desired clarity, (c) best clarity obtainable for a given rate of flow, and ( d ) the most economic amount of filter aid to meet these conditions, etc.
Literature Cited (1) Cummina, A. B., and Badollet, M. S., IND. ENG.CHEM., ANAL. ED., 5, 328-32 (1933). ( 2 ) Cummins, A. B., and Miller, M. C., Am. Chem. SOC. Meeting, N e w York, 1935. PRBSENTED before the Division of Sugar Chemistry and Technology a t the CHEMICAL N SOCIBTY, Detroit, Mich. 100th Meeting of the A M ~ R I C A
Calcium Phosphate in the Filtration of Sugar Liquors A. B. CUMMINS Johns-Manville Research Laboratories, Manville, N. J.
HE use of calcium phosphate as a defecant in the refining of sugars is an old practice. I n cane sugar refining, calcium phosphate was employed generally for several decades in conjunction with Taylor bag filters of different designs and is still so used to minor extent. The Williamson process of defecation is also based on the use of a flocculent calcium phosphate precipitate which is formed and handled under certain prescribed conditions. As a general procedure, the use of calcium phosphate with diatomaceous silica filter aids has not been practiced satisfactorily up to the present time for reasons given below. As employed previously, phosphoric acid (as orthophosphoric acid or one of the acid calcium phosphates of varying degrees of purity) is first added to the impure sugar solution. Calcium hydroxide is then added as milk of lime in amount sufficient to neutralize the phosphoric acid and precipitate it as tricalcium phosphate. This comes down as a voluminous flocculent precipitate which occludes, entraps, or otherwise serves t o remove some of the colloidal or finely divided impurities characteristic of unrefined sugars. The combined floc of calcium phosphate and impurities must then be separated from the defecated sugar solution by mechanical
T
methods, such as settling, flotation, or filtration. The calcium phosphate floc is removed with considerable difficulty since the precipitate has troublesome physical characteristics. It frequently passes somewhat readily through most filter media a t the start of filtration, t o give a turbid filtrate and incomplete removal of impurities. As filtration progresses, the rate of flow becomes slower and slower. When brilliant filtrates are obtained, the rate of filtration is generally unsatisfactory. Factors such as inversion losses, bacterial growths, etc. , frequently become troublesome. Thus, the calcium phosphate method for handling washed raw sugar in American refineries has been supplanted largely by other processes. The use of diatomaceous silica as a filter aid for washed raw sugar liquor has been usually carried out with lime alone as the defecating agent. Attempts to use lime, “phosphate paste”, and filter aids with the conventional filter equipment have not been considered satisfactory. The difficulty has generally been that the calcium phosphate floc plugs the pores and openings in the diatomaceous filter cake, with consequent low rate of flow. I n 1938 data were presented (1) t o show the possibilities of treating affination sirup with phosphoric acid and lime and
April, 1942
399
INDUSTRIAL AND ENGINEERING CHEMISTRY
Use of calcium phosphate defecation in conjunction with diatomaceous filter-aid atration of washed raw sugar has not previously been found advantageous. New experimental data are presented showing that, under suitable conditions, washed raw sugar can be processed by calcium phosphate treatment combined with filtration by one of the newer type, fast flow rate, diatomaceous filter aids. The treatment described offers the ad-
of filtering with the Oliver precoat filter. The apparent advantages found for afEnation sirup were not so pronounced for washed raw sugar. However, since combinations of phosphoric acid, lime, and diatomaceous silica offer attractive theoretical possibilities for a high degree of clarification together with some removal of color, it was considered worth while t o work out a method to solve the low rate of filtration problem that has held back the use of calcium phosphate with diatomaceous a t e r aids. Recently laboratory tests have been made which appear to be of sufficient interest t o warrant consideration by sugar refiners. Plant runs in two refineries confim the results. The tests show that the use of phosphoric acid with filter aids which have become standardized for the sugar industry, such as Filter-Cel, Standard Super-Cel, and Hyflo Super-Gel, is not to be recommended; the phosphate floc slows down the filtration rate with these filter aids to an undesirable extent, without sufficient advantages to make the practice attractive. On the other hand, a treatment with calcium phosphate can be prescribed with one of the more recently developed, faster flow rate filter aids such as Celite 503 or Celite 545 (which have not generally given fully satisfactory clarity for sugar refining by present day practice); at least for some types of sugars this treatment will give filter rates comparable with the older type filter aids, and with the advantages of both better degree of clarification and removal of some color from the raw sugar liquor. These advantages are not obtained with the lower flow rate filter aids without phosphoric acid. Similarly, a better rate of flow with equal clarity can be obtained in some instances, as well as some color removal. The better clarification and color removal should result in lower bone coal costs per ton of melt. It is believed that this saving will be substantial under many practical conditions. Against this will be the cost of phosphoric acid and possibly some increased consumption of filter aid. It is also likely that the proposed procedure will entail some additional expense for process control since several factors appear to be important in obtaining the full advantages of combinations of phosphate and fast-flow-rate filter aid.
Experimental Methods Unless otherwise stated, the filtration studies re orted were carried out with a four-bomb filter assembly (2). Cfmity determinations were made with the apparatus and method outlined (2). Color measurements were made on the Leifo colorimeter with No. 64 filter. This ap aratus is of good accuracy and. has proved satisfactory for gtermining the color of sugar solutions.
vantages of improved clarification or increased filtration rate or both, combined with removal at low cost of a portion of the raw sugar color. Effective treatment is accomplishedwithextremelysmall amounts of phosphate. The indicated advantages of the process, particularly the possible saving in char filter cost, are believed to be of sufficient interest to warrant consideration by sugar refiners.
All tests were made with 65" Brix washed raw sugar solutions, the temperatures bein held constant at 80' C. Precoats corresponding to 0.1 pouncfof filter aid per square foot of filter area were applied from clear liquor at a pressure of 3 pounds per square foot. The amount of filter aid in the batch was 0.3 er cent on the weight of sugar qolids. No. 07&DR cotton d e r cloth (Filter Medm Corporation) was employed for all tests reported here. Monel metal cloth was shown by other tests to be equally satisfactory. The method followed in the phosphate treatment of the liquors was to add the calculated amount of c. P. orthophosphoric acid diluted to a volume corresponding t o 20 cc. per pound of sugar in the batch. The sugar liquor was first heated to 70" C., and the diluted. phosphoric acid solution was added slowly with constant agitation. Three minutes after the final addition of phosphoric acid, a lime suspension containing 3.33 grams of calcium hydroxide per liter was slowly added with agitation until the pH was raised to the desired value. The density of the solution was adjusted to 65" Brix, the tem erature quickly raised to 80" C., the liquor transferred t o the d e r , and the test started without delay.
TABLE I. COMPARISON OF FILTRATION PERFORMANCE^ OF CELITE 545 WITH PHOSPHATE AND CELITE 536 WITHOUT PHOSPHATE Time, Min. 0-30 30-60 60-90 90-120 120-150 150-180 180-210 2 10-240
Filtration with C-11902 3-6.5 6.5-13 13-20 20-28 28-36 36-40 9 15) 40 b : 4 ) 40 6.70)
Min. to 40 Ib.
Co?F2Zoval, % 0-30 30-60 60-90 90-120 120-150 150-180 180-210 210-240
Celite 536, No Phosphate Filtration Clarity, pressure footlb./sq. in'. candles
161 0
Filtration with C-10533 3-7 7-13 13-21 21-28 28-37 37-46 46-60 9 5) 50 k 1 7 )
Min. to max. pressure Ratio, cycle length to max. pressure, % Color removal, yo
Celite 545, 0.0045'% PnOr Filtration Clarity, footlr?E:%. candles
Washed Raw Sugar S o h . 6.59 3-7 5.36 7-13 5.00 13-20 4.72 20-29 4.51 29-36 4.41 36-45 4.41 45-50 (8.95) 4.36 50 (7.56)
4.16 2.91 2.78 2.72 2.72 2.72 2.72 2.69
160 31 Washed Raw Sugar Soh. 9.00 3-5.5 6.98 5.5-12 6.37 12-18 5.94 18-25 5.74 25-32 5.68 32-39 5.61 39-47 5.61 47-50 (9.89)
189
219
100 0
116 34
5.81 3.62 3.34 3.19 3.19 3.19 3.19 3.19
a Constant rate at 10 gal./sq. ft./hr., except where noted otherwise in parentheses.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 34, No. 4
cent color removal, and a 16 per cent longer time period to reach t h e m a x i m u m p r e s s u r e of 50 pounds per square inch.
Regular Pressure Cycle (Series 11) The filtrations were conducted for 4-hour periods with a gradual and regular pressure-increase cycle beginning a t the precoat pressure of 3 up t o 50 pounds per square inch at the end of 3 hours, which was maintained constant for the last hour. Excellent pressure control during these tests was maintained with an automatic Foxboro pressure-time regulator (9). As in series I, the liquors were 65' Brix washed raw sugars limed to initial pH values of 7.1. Additions of calcium phosphate were variable (Tables I1 and 111); 0.3 per cent filter aid on weight of sugar solids was added. Precoats A TYPICAL FILTER STATION IN AN AMERICAN SUGAR REFINERY of the same filter aids used in the batches were applied in amounts corresponding to 0.1 pound per Constant Filtration Rate (Series I) square foot of filtering area. Two washed raw sugars were used: c-11902 as employed in series 1, and c-14027, a Tests were made with Celite 545 filter aid and calcium phossomewhat more difficultly filterable, washed raw product phate in comparison with Celite 536 filter aid without phosobtained from the Pennsylvania Sugar Refining Company, phate. Celite 545 has a coarse particle size and gives very Filter rates and clarities for 30-minute periods are given fast flow, but has inadequate clarifying capacity for sugar for each test condition. The percentage of filter aid used, solutions. Celite 536 is of the Hyflo Super-Cel type, but has both in the precoat and the batch are the same for each test. superior clarifying capacity and slightly lower flow rate. It As a basis for comparison, Standard Super-Cel and Celite 536 is a commercial filter aid employed by refineries desiring a without phosphate were selected. With the c-11902 sugar, flow rate faster than Standard Super-Cel and a clarity better Standard Super-Cel gave an average flow of 5.5 gallons per than Hyflo. The tests were conducted on a constant-volume square foot per hour for the 4-hour period, whereas Celite basis; that is, the filtering pressure was regulated by manual 536 gave 11.4. The clarity of the Standard Super-Cel filtrate manipulation of the air pressure valve so that a filtration rate of 10 gallons per square foot per hour was maintained. The tests were continued for 4 hours. When the maximum pressures O F SUQAR C-11902 WITH ST.4NDABD TABLE 11. COMPARISON O F FILTRATIONS of 40 and 50 pounds per square inch had FILTER AIDSAND WITH FAST-FLOW-RATE FILTERAIDS AXD ADDEDCALCIUM been reached, these pressures were mainPHOSPHATE tained constant and the rates of flow re0.3% corded. Two different washed raw sugars Celite 545 0.370 0.3,% c 0.37' Celite 503 , + were employed. Results of the test runs are Time, Standard Celite 0.002%Q 0.00357, 0.0045% 0.000% 0.008% 0.004.5% hlin. Super-Cel 536 PnOa Pa06 PzOa PzOs PL)s PiOs given in Table I. With sugar C-11902 the pressure cycles Filtration Rate, Galiona/Square Faot/Hour are much the same, and the filtration rate 7 52 16.70 13.46 9.80 1.5.70 15.62 18.92 0-30 6.92 5 85 13.34 of 10 gallons per square foot per hour was 7.74 9.89 14.36 11.83 6.78 13.42 30-60 5.;M 11.78 7 05 10.45 8.85 12.26 6.06 11.84 60-90 maintained for 2 hours 40 minutes for both 5 . 4 0 11.66 8 . 5 1 6 6' 2 9.89 11.18 11.27 90-120 5.80 5 I(i 11.0'2 8.08 6 06 9.12 10.33 11.96 120-150 5.33 tests. With the phosphate-Celite 545 com5 10 11 6 1 7.95 5.76 12.70 8.81 10,58 150-180 5.03 5.16 4 (io 10 15 bination, hon-ever, the clarity was definitely 7.74 7.56 8 55 9.S8 180-210 4.43 4.39 4.04 8 42 6.92 6.96 6.45 9.11 210-240 3.87 better from the start t o the end of the 40-240 5.82 11.42 11.95 9.96 8.90 6.58 540 11.83 hour period. In addition, the phosphate Clarity, Foot-Candles liquor was partially decolorized, the color 3.54 2 88 4.56 3.30 2.81 6.67 8.11 0-30 4.78 of the filtrate being 31 per cent less than 3 01 2 66 4 R1 2.56 3.16 2.75 5 48 4.06 30-60 2 00 2 91 2 . 6 6 2.RR in the Celite 536 filtrate. Thus, two im2 . 9 1 3 . 8 8 4 . 8 3 3.58 60-90 2 81 2 5'1 2.51 2.88 2.59 3.75 4.56 3.42 90-120 portant benefits are obtained with Celite 2 .io 2 81 2.59 2.45 2.81 3.93 4.41 3.30 120-150 2.81 2 5Y 2.42 2 88 2.86 3.93 4.31 3.30 150-180 545 and an addition of 0.0045 per cent 2.81 2.59 2.66 2.45 2.88 2.91 4.16 3.30 180-210
P206.
With the C-10533 sugar the clarities obtained were not so good as with the C-11902 sugar, but here the Celite 545 plus 0.0045 per cent P205gave superior clarity, 34 per
210-240 0-240
3.25 3.70
4.02
0
0
5.14
2.81 4.36
2.88 3.25
2.66 2.78
2.45 2.68
2 59 2 67
2.81 2.98
Calor Removal, Per Cent 17
20
27
29
a3
27
April, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
40 1
0.0045 per cent PZO5, Celite 503 gave the excellent clarity of TABLE 111. COMPARISON OF FILTRATIONS OF SUGAR C-14027 4.4 foot-candles with a flow rate of 4.74 gallons. With Celite WITH STANDARD FILTERAIDS AND WITH FAST-FLOW-RATE ,545and 0.0045 per cent PZOSit was possible to obtain an averFILTER AIDS AND ADDED CALCIUM PHOSPHATE age clarity of 4.5 foot-candles and a flow rate of 8.95 gallons. n2 ~ " Color removal was 24 per cent with Celite 503 and 26 per cent ~eiite'ki 0.3F 0.3p -0.3% Celite 503+ with Celite 545. 0.002% 0.0045% 0.008% 0.0045% Time, Stan ard Cehte The results of series I and I1 show that, under the condiMin. Super-Gel 536 Pa06 Pi08 PzOa PaOs tions of testing described, there are substantial advantages in Filtration Rate, Gallons/Square Foot/Hour the use of small amounts of calcium phosphate with the 9.93 10.10 7.91 5.68 13.75 0-30 5.59 faster flow rate filter aids of the types employed. Filtration 7.44 5.72 30-60 4.60 7.91 4.00 10.32 6.62 7.01 5.03 3.53 8.94 60-90 4.04 with a monte-jus press of the type employed and the tech6.10 6.36 4.64 3.23 8.76 90-120 3.70 nique followed in making these tests are believed to be favorable 4.26 5.71 5.85 2.88 8.29 3.57 120-150 5.63 5.3s 3.91 2.62 8.12 3.31 150-1 80 for the formation of the calcium phosphate floc in a condi5.25 4.73 3.44 2.37 7.39 180-2 10 3.05 4.39 4.17 3.01 2.02 6.10 2.71 210-240 tion advantageous for use with filter aids in pressure filtration. 6.38 6.44 4.74 3.29 8.95 3.82 0-240 It should not be assumed without further confirmation that Clarity, Foot-Candles these highly favorable conditions will always be obtained in practical refinery operations. As the result of much addi6.82 5.01 4.72 4.51 5.30 0-30 6.08 4.46 5.68 5.00 4.57 4.31 30-60 5.55 tional work it was found that the phosphate floc is sensitive 5.24 4.89 4.41 4.21 4.31 60-90 5.24 5.24 4.78 4.31 4.11 4.31 to many conditions and that it may be converted into forms 90-120 5.12 4.7s 4.31 4.06 4.26 5.24 5.12 120-150 which may give poor clarities or low flow rates, or both. The 5.24 4.78 4.31 4.11 4.26 5.24 150- 180 5.24 4.78 4.21 4.06 4.21 5.24 180-2 10 use of too much phosphate is not satisfactory, and the correct 5.24 4.67 4.21 4.06 4.21 5.24 210-240 5.62 4.99 4.43 4.25 4.49 5.41 0-240 amount to use varies with different sugars. pH control is highly important. Long standing of the phosphate floc in Color Removal, Per Cent the sugar liquor is to be avoided. Excessive agitation of the 0 0 15 24 33 26 sugar liquor after the floc is formed is unfavorable for best results. Some tests made by passing the phosphate-treated liquor through a piston pump, with excessive recirculation so was superior, averaging 3.7 foot-candles as compared to 5.1 for Celite 536. Celite 503 without phosphate had a flow rate four to six times as fast as Standard Super-Cel, the ratio depending upon the conditions of application, type of sugar liquor, etc. The addition of very small amounts of calcium phosphate to Celite 503 had a pronounced effect in lowering the flow rate but, under the test conditions described, materially improved the clarity. With the C-11902 sugar, Celite gave a n average flow rate of 11.95 503 with 0.002 per cent P20s gallons per square foot per hour with an average clarity of 4.35 foot-candles. This flow rate is about the same as that obtained with Celite 536. The clarities of the Celite 503 with 0.002 per cent PZ0sliquors, however, are better than those of the Celite 536 liquor. With 0.002 per cent P206the Celite 503 clarity did not equal that of Standard Super-Cel, but , Celite 503 gave clarities of high with 0.0035 per cent P z O ~the brilliancy which were equal to or a little better than the corresponding clarities for Standard Super-Cel. Celite 503 with 0.0035 per cent Pz06flow rate was 9.96 gallons as compared with 5.52 for Standard Super-Cel. This constitutes a substantial advantage for the faster flow rate filter aid with phosphate. In addition there was 20 per cent color removal for the phosphate liquor. With still higher percentages of Pz05 the flow rate with Celite 503 was further decreased with corresponding clarity improvement until about 0.006 per cent Pz05 was reached. From this point additional clarity improvement was not found, and with P206 in amounts greater than 0.01 per cent the flow rate dropped off substantially. I n a test with Celite 545, 0.0045 per cent PzOagave a flow rate of 11.8 gallons per square foot per hour and an average clarity of 3.0 foot-candles, which is superior to Standard Super-Cel in both volume and quality of filtrate. The results with the C-14027 washed raw sugar confirm the findings with C-11902. The C-14027 sugar was more difficultly filterable than C-11902 and is believed to represent about an average washed raw. Standard Super-Cel (Table 111)gave an average flow rate of 3.82 gallons with an average clarity of 5.4 foot-candles. Celite 503 with 0.002 per cent P20s gave a flow rate of 6.44 gallons and an average clarity of 5.0 foot-candles. Color removal was 15 per cent. With
TABLEIV. EFFECTOF pH IN THE FILTRATION OF WASHED RAWSOOAR WITH CELITE503 AND PHOSPHATE Initial p H Filtration rate, gal./sq. ft./hr. 0-30 m!i. 210-240 m p . 0-240 min. Filtration rate based on DH 7.2 as 100 Clarity, foot-candles 0-30 min. 210-240 mjn. 0-240 min. Final p H Color removal, %
6.6
7.2
7.6
7.9
8.89 3.94 6.04
7.23 3.61 6.34
6.62 2.58 4.39
6.01 2.62 4.11
113
82
100
2.72 2.45 2.51 6.3 41
3.23 2.81 2.99
3.75 3.34 3.56
7.0 30
7.5 27
77 3.93 3.42 3.67 7.7 21
RESULTS OF DIRECT CENTRIFUGAL PUMP
TABLE V.
FILTRATIONS5
Celite 503
Time, Min.
+ 0.006% P90,
Monte-jus bomb press, no pum (Table If)
Test liquor pumped to filter with excessive action
Standard Super-Cel. No Phosphate Trst liquor Monte-jus pumped t o bomb press, filter with cn${yf) excessive action
Filtration Rate, Pounds per Square Inch 0-30 60-90 120-150 210-240 0-240
9.80 7.05 6.06 4.39 6.58
6.32 4.21 3.25 1.78 3.52
6.92 6.06 5 33 3.87 5.52
3.31 4.81 4.90 2.98 4.14
... ...
4.67 4.51
Clarity, Foot-Candles 0-10 10-30 0-30 60-90 120-150 210-240 0-240
Color removal, yo a 0.3%
... 2: il 2.56 2.45 2.45 2.58
7.1 6.5 29
6.59 4.16
... 2.91
2.91 2.88 3.36 7.2 6.8 35
filter aid, washed raw sugar C-11902.
...
4.78 3.58 3.30 3.23 3.70
3.93 3.79 3.75 3.95
7.1 6.6 0
7.2 6.9 0
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 34, No. 4
necessity of using pump equipment which may tend to break up the -0.00457 PzO6phosphate floc. In earlier tests it was Reg& procedure found that while specially favorexcept 0.006770 P ~ O P able results could be obtained in pro19 min. Regular 30-min 5 miu. 30 min. O . O O G O ~ o 0 . 0 0 8 0 ~ o lon ed through proprothrough through P~OS PzOs, phosphate filtration in the bomb press Regular s t a n k g Westco oedure peller Westco Westco Reg& Regular Time probefore pump and agitapump pump ProProor with a slow-speed Viking rotary Min.' cedure test (-3OX) standing tion ( = 3 X ) ( = 3 0 X ) cedure cedure pump without recirculation, satisFiltration Rate, Pounds per Square Inch factory operation was not obtained 0-30 13.46 9.75 6.36 9.02 5.85 5.50 with a recirculating plunger pump 4.66 9.80 7.52 60-90 8.85 7.82 5.94 5.46 5.07 4.81 3.61 7.05 5.38 system where excessive recirculation 120-150 8.08 6.80 5.42 4.73 4.39 3.78 3.18 6.06 5.16 210-240 6.92 4.90 3.35 4.12 2.23 2.41 2.15 4.39 4.04 and passing through the pump were 0-240 8.90 7.10 5.79 4.93 4.60 4.15 3.25 6.58 5.40 deliberately used. The test results Clarity, Foot-Candles obtained in a further study of the 0-30 3.30 3.38 5.74 3.12 3.05 3.27 6.52 2.81 2.88 effect of agitation are shown in Tables 60-90 2.66 2.98 2.91 2.66 2.72 2.78 2.72 2.56 2.66 2.66 2.72 120-150 2.59 2.84 2.81 2.72 2.59 V and VI. 2.45 2.59 210-240 2.66 2.84 2.59 2.78 2.66 2.66 2.59 2.45 2.59 The data in Table VI indicate that 0-240 2.78 2.98 3.43 2.74 2.79 2.85 3.34 2.58 2.67 7.1 7.1 30-minute vigorous propeller agitaInitialpH 7.1 7.1 7.1 7.2 7.2 7.2 7.2 Final pH 6.5 .. . ... 6 . 7 6 . 6 6.6 6 . 6 6 . 5 6 . 5 tion had only a small effect on the Color re29 33 filtering character of the phosphate moval, % 27 32 32 33 33 33 33 floc suspension; it had no-effect on a Liquors and hosphate subjected t o ,pump action or propeller agitation and then filtered in clarity and caused a flow rate decrease monte-jus bomb Bters; 0.3% Celite 503 in washed raw sugar C-11902. of only 7 per cent in subsequent bomb press filtration. Five-minute circulation of the liquor through the Westco pump a t 40 pounds pressure that much of the liquor passed through the pump many times (equivalent to passing three times through the pump) reduring the course of the filtration, gave results in which the duced the flow rate 16 per cent but did not affect the clarity. flow rate advantage of the phosphate plus fast-flow-rate filter A longer period of circulation through the pump (equivaaid was lost, and in some cases definitely poorer flow rates lent to passing thirty times through the pump at 40 pounds were obtained. In addition, excessive pump action gave pressure) had the effect of reducing the flow rate 34 per cent extremely poor clarities. Severe pump action seems to break with the 0.0067 per cent PzO6 treatment and 18 per cent up the phosphate floc to such an extent that it is difficult to with the 0.0045 per cent PZOs in subsequent Celite 503 hold in the filter cake. The very fine phosphate particles bomb press filtration. Initial clarity was lowered by this may be in a colloidal or semicolloidal condition and thus give pump treatment, but after the first 30 minutes clarity was dirty filtrates or plugged cakes or both. Any treatment not affected. which tends to peptize or disperse the phosphate floc is to be The results in Table V indicate that successful direct filavoided; it should be retained in the physical state obtained, tration of phosphate-treated liquor which had been cirwhen the procedures described are followed, as closely as culated through a centrifugal pump should be possible. possible under operating conditions. I n this series filtrations were successfully carried out on phosphate-treated sugar which had been subjected to pump action believed to be more severe than would ordiEffect o f pH in Forming Phosphate Floc narily be encountered in practice. Comparison was made with Standard Super-Cel filtration of untreated sugar. The importance of using the correct amount of lime in Pumping directly to a filter chamber provided with 0.20 neutralizing the added phosphoric acid is shown by the data square foot of leaf filter area, the filtration rate with in Table IV. C-11902 washed raw sugar (65' Brix) was Celite 503 and 0.0060 per cent Pi05 was 85 per cent of employed. Filtrations were for 4 hours with the bomb press that obtained with Standard Super-Cel, under comparable assembly and under the same pressure cycle and operating conditions and with superior clarity for the phosphate run conditions as the tests of series 11. A precoat application of after the first few minutes of operation. 0.1 pound per square foot of Celite 503 was made a t 3 pounds The net conclusion to be drawn from the tests with pump per square inch pressure; 0.3 per cent Celite 503 was used filtration and with the liquors in which the phosphate floc in the batch, and 0.006 per cent PzOj was added. Additions had been agitated is that, while pump action is unfavorable of lime were made in variable amounts to obtain the pH to the optimum benefits that may be attainable with combinavalues reported. At a p H of 6.6 the best flow rates and claritions of fast flow rate filter aids and small amounts of phosties were obtained. The calcium phosphate floc is believed phate, this detrimental effect may not be expected to be so to be completely formed a t this pH, and the results show great as to vitiate the method for practical application. On favorable results for operating on the acid side; but most the other hand, the benefits of a pressure filtration with phosrefiners prefer to operate a t neutrality or slightly on the phate and Celite 503 or 545 are indicated t o be sufficient to alkaline side because of possible inversion losses a t the lower warrant careful consideration by refiners. pH. Initial pH values of 7.6 and 7.9, however, are too far on the alkaline side for optimum results, and show a definite decrease in both flow rate and clarity as compared with tests Literature Cited a t pH 7 . 2 . TABLEVI. EFFECT OF AGITATION ON SUBSEQUENT BOMBFILTRATION^
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Effect of Pumping and Agitation The effect of agitation on the filtering qualities of the phosphate floc was studied because of the usual practical
(1) Cummins, A. B., and Morris, D. C., Facts About Sugar, 33, 23-7 (1938). (2) Cummina, A. B., and Weymouth, L. E., IND.ENQ.CUEM.,34, 392 (1942).
PRESENTED before the Division of Sugar Chemistry and Technology a t the CHEXICAL SocImu, Detroit, Mich. 100th Meeting of the AMERICAN
