INDUSTRIAL AND ENGINEERING CHEMISTRY
954
Vol. 23, No. 8
Cane-Juice Liming and Clarification' R. H. King SUGARTECHNOLOGY DIVISION, COLLEGE OF AGRICULTURE, UNIVERSITY OF
THE
PHILIPPINES, LAGUNA, P. I.
Single Lime Defecation Investigations have been conducted and the literature HE liming of the sugarreviewed in order that a rational system of cane-juice cane juices expressed I n t h e single-defecation clarification could be formulated. by m o d e r n m i l l i n g process of cane-juice clarifiSucrose is destroyed by inversion or decomposition plants is a considerable probcation lime in suspension is at all temperatures and pH's. High temperatures lem which is complicated by added to the juice before or and low pH's result in large losses. Purity increase the widely varying characafter heating to temperatures is a function of the substances that can be eliminated. teristics of the raw juices and slightlyabove 100" C. The Phosphates and silicates are not completely removed the amounts of non-sugars treated juice is allowed to with moderate liming. Sulfates are very soluble; that can be r e m o v e d b y settle and the clear juice demagnesium is eliminated at high alkalinity; iron defecation. Notwithstanding canted. The settlings are and aluminum are removed with low liming. the wide variation in the conpassed to a filter press or reGlucose is destroyed by lime and heat. Cane fiber stituents, the liming station settled. is decomposed in alkaline solutions, colloidal elimimust function without any By this method only one nation, as given by the dye test, varies from 6 to 35 predetermined information as treatment of lime is given the per cent. t o the behavior of the limed juice and no effort is made to The settling rate of treated juices depends upon the juice during and after setcorrect a deficiency or an reaction. Careful, routine control of liming, together tling. The analyses of fairly excess in contrast to the with settling rates and purity determinations, will representative s u g a r - c a n e double-defecation, carbonaresult in a higher sucrose recovery. juices shown in Table I give tion, and sulfitation processes, The optimum reaction for clarification must be but a mere indication of the wherein the excess lime is redetermined for a particular juice; historical evidence variations encountered in the moved. Since the single defeaids only in furnishing a probable liming point. average liming station. cation is used in most rawThrough the formation of acids by high liming, matter s u g a r factories, it will be It is generally agreed that previously precipitated is brought back into the juice. considered in this discussion. the efficiency of the entire A n automatic, continuous liming device has been I n this process the expressed sugar-recovery unit depends described which completely meets the lime control juice is treated with a susupon the thoroughness of the requirement. pension of lime without reclarification (7, 9, I S , 25, 29, gard to its original aciditv. 33, 38, 39, 4S), but there is little general information as to what efficient clarification is. the impurities, and the matter capable of precipgation. T i e Some investigators have considered good clarification to be variation in acidity is considerable, as seen from the data in measured by the clearness of the limed, heated, and settled juice. Table 11, which shows the average acidities and pH's of 1728 These investigators consider the removal of suspensions only. juices analyzed during a 6-week period. With this variation Others (18,20,21,22,40,42) define it as the result of the maxi- possible the amount of lime to be added is determined by an mum increase in purity of the solution. It has been main- unskilled attendant from his reaction to a certain predetertained that good clarification will result if the juice is limed to mined tint or color of some indicator. Recent research (2, 7, 29) has advanced the liming operaa definite hydrogen-ion concentration (21, 23, 35, 42, 44). Then there are those who advocate liming to a so-called iso- tion in that the reaction of the cold-limed juice or other juices electric point, which they believe exists for all juices, the iso- can be expressed in grams of hydrogen ion per liter. This electric point being defined as that hydrogen-ion concentra- end point may be determined either by potentiometric methtion a t which a minimum solubility exists (2, 3, 4, 16, 25, 37). ods with the hydrogen electrode or with the quinhydrone
T
Table I-Analysis
SAMPLE ~~1~~
I 2 3
4.9 5.1 5 3 5.1 5.8
4 5
of Representative High- and Low-Purity Mixed Juices f r o m an Eighteen-Roller Milling Plant
A;g:F
~~
%
%
14.36 14 7 5 13.61 12.57 18.70 17.84
81 18 84.24 81.11 73.76 86.10 81 75
GLUCOSE
% 0 426 0 376 0 274 0 719 0 581 0 324
Pz01
% 0.044 0.049 0.038 0.065 0.064 0.050
so4
CaO
SiOn
AlrOa
FerOa
MgO
%
7%
%
%
%
%
%
0 146
0.546 0.312 0.405 0.398 0.505 0 629
0,025
0.036 0,022 0.020 0.023 0.015 0.018
0.058 0.058 0.073 0.036 0.023 0.026
0.004 0.005 0.006 0.006 0.007 0.005
0.083
0.0iS 0.206 0.017 0 082 0,009
There are numerous objections to all these theories. It appears that, in general, their advocates have neglected the extreme comp1exit.y of the problem. The advice given and the experimental evidence presented by these investigators are worthy of careful consideration, but practice in various manufacturing units has shown that no one has arrived a t a standard method of liming or defecation which can be followed in raw sugar factories using a single defecation method of clarification. 1
ASH
Received December 15, 1930; revised paper received June 2, 1931.
0.026 0.027 0.024 0.016 0.015
0.111 0.166 0.150 0.070 0.178
half-cell. The juice so limed is then heated to varying temperatures. Many practical heater and settling-tank operators believe that the juice must be heated to more than 105" C., so that the "flash point" will be reached and the scums will break up in the flash tank and thus avoid accumulation on top of the juice. This belief is not supported by facts. In general, temperatures around 100" to 105" C. are used; 120" C. has been suggested upon the supposition that the silica in the juice would be dehydrated and precipitated. The treated juice is allowed to settle in large insulated tanks or
August, 1931
INDUSTRIAL AND ENGINEERING CHEMISTRY
defecated in continuous settlers. Insulation is necessary for the prevention of convection currents and for heat economy. Table 11-Acidity
of Crusher a n d Mixed Juices
PHB Y POTENTIOMETER
TITRABLE ACIDITY
Gram H
+
per liter
C R U S H E R JUICE
Minimum Maximum Average
5.26 5.57 5.39
0.01161 0.01762 0.01508
MIXED JUICE
Minimum Maximum
Averase
5.23 5.65 5.40
0.01249 0.01928 0.01575
By such a treatment the juice is maintained a t a high temperature a t a more or less alkaline reaction in tbe presence of the coagulated or settled impurity for an indefinite period. Investigators have recorded an increase in hydrogen-ion concentration during this settling period (SO, SS, 34) which may amount to as much as 1.1 pH and as little as 0.3 pH. This increase in hydrogen ions certainly indicates the formation of acids and suggests the re-solution of precipitated matter with the formation of soluble lime salts. Paine (34) believes that the hydrogen-ion increase is due to the formation of calcium phosphate with the liberation of hydrogen ions. Experimental evidence obtained in the writer’s laboratory indicates a variance. The data in Chart 1, which are based on data obtained from 325 juice analyses, show that hydrogen ion is developed during clarification. This development is peculiar in that the drop in pH is small a t low pH’s of coldlimed juice and reaches a maximum a t higher pH’s and then shows a decrease with much higher liming. I n view of this evidence, we believe that this maximum increase in hydrogen ion is due to a maximum destruction of reducing sugars under the particular treatment. Other data obtained on the destruction of reducing sugar substantiate this conclusion.
955
the phosphate content of the clarified juice and the drop in p H does not appear to be a function of the phosphoric acid present, but seems to be related to the amount of lime in the juice. Additional data given in Table I11 indicate that juices high in phosphates show a small drop in pH during clarification. Table 111-Average P2Os Content of Mixed and Clarified Juice when Mixed Juice Was Limed t o pH 8.0 a n d the Drop i n pH Associated with Various Average PSOSContents Pros
IN
MIXEDJUICE
PnOs I N CLARIFIED JUICE
%
%
0.147 0.197 0.292 0.304 0.356 0.459 0.492
0 0191 0.0212 0 0256 0 0392 0 0433 0 0604 0 0695
DROPI N PH
1 4 1 2
0 9 0.8 0 6 0 4 0 3
This drop in pH during clarification is important. If through the addition of large amounts of lime acids are formed, then the attempt to obtain an alkaline juice in order to prevent inversion during evaporation and boiling is useless.
..Y
r
104
mr
SO
t
Chart 1-Drop i n pH from Cold-Limed Juice t o Clarified Juice a n d Lime Required for Average pH’s
The data in Chart 2 were obtained from a series of experiments on juices of equal phosphoric acid content which were limed to various alkalinities. The drop in pH of the settled juices from the pH of the cold-limed juice is interesting. It is seen that the greater the drop in pH the greater was the amount of lime present, whereas the phosphate content of the clarified juice varied but slightly. The relationship between
Chart %Lime a n d Phosphate Content of Raw-Limed Juice a n d Drop in pH during Clarification
It is the writer’s experience that this drop in pH seems to be closely related to the formation of titrable acidity. Chart 3 gives the average relationships between titrable acidity and pH present in the raw, unlimed juice and that formed during heating, settling, and reheating. The greatest acidity was found in the raw juice, although considerable acid was formed after neutralization during the short interval of heating. Low-purity juices gave the greatest acid formation during clarification. These low-purity juices contained large amounts of reducing sugars. No quarrel is desired with the advocates of the various systems of liming and settling. Inspections of various liming stations have clearly demonstrated the failure of a constant liming point. The thousands of milling plants throughout the world present individual problems of clarification which must be met locally. The results obtained by individual investigators cannot be applied to other conditions without investigation. The problem of clarification is complicated by the fertility of the soil, the elements taken up by the various canes, the kind of cane milled, the time of harvest, and the time intervening between harvesting and milling and the extraction. All the investigators may be correct when they have followed standard methods of analysis and procedure. However, as a result of a series of investigations and a careful study of the data available, the writer is of the opinion that no constant predetermined liming will produce results most advantageous to the recovery.
956
INDUSTRIAL AiVD ENGINEERING CHEMISTRY
Vol. 23, No. 8
Purity of juice is no criterion of the method of clarification. A low purity may be due to B large amount of inorganic impurities, which can be eliminated, or it may be due to invert sugar. A low-purity juice containing a large amount of glucose will not show a great increase in purity from clarification, but on the contrary will show a decrease if limed high. This decrease will be due to the formation of acids and the solution of lime salts. The clarification of cane juice is believed to be obtained in the following distinct, though correlated, stages: (1) flocculation of colloids by change in hydrogen-ion concentration, (2) flocculation of colloids by heat, (3) formation of insoluble lime salts, and (4) formation of soluble lime salts. These reactions may or may not result in the maximum elimination of non-sugars, a minimum loss of sucrose by inversion, a complete removal of colloids with a rapid settling of impurities, or a maximum recovery- of sucrose. Chart +Average Titrable Acidity in Representative Cane Juices from Different Portions of The problems involved are numerous, Cane. Acidity Increase during Heating a n d Clarification, a n d ~ l s ofor a 3-Hour Period of Digestion but a consideration of the evidence avail(The acidity increase has been correlated with pH and shows the drop during the 4-hour period of able in the literature and that obtained treatment) in this series of investigations will aid in A constant predetermined liming pH implies the existence formulating a procedure by which the individual operator can of an isoelectric point for the precipitation of all impurities. devise a rational method of cane-juice liming. Published data indicate that all impurities are removed a t The questions that the investigator or control operator a certain hydrogen-ion concentration (29, 35, do, 2.4). The must ask himself can be summarized as follows: writer's investigations lead him to believe that the advocates (1) Can a maximum elimination of non-sugars be accomof high liming have not balanced the effect of soluble lime plished with the settling tanks, Dorr clarifiers, and resettling salts and the re-solution of matter insoluble a t lower hydrogen- tanks available without seriously interfering with the capacity ion concentrations, and particularly the destruction of of the factory? reducing sugars in alkaline solutions. High liming (above ( 2 ) Will the available filter presses accommodate the prep H 8.0) should be permitted only in exceptional circum- cipitate obtained as a result of the maximum elimination of stances. Low liming (below pH 7.0) should be advocated non-sugars ? (3) Will the management provide additional equipment t o only when the phosphate content of the juice is low. If the obtain a maximum clarification after experimental data have impurities in the juice are not sufficient to eliminate the cal- been obtained? cium ion, then alkalinity should not be gained a t an expense (4) What will be the calcium oxide content of the clarified of calcium ion increase. The entire question of high or low juice due to a maximum removal of non-sugars from the mixed liming can be answered by balancing the possible inversion juice? ( 5 ) A t what point will the increased p H affect the greatest loss by boiling acid juices and the loss due to the introduction increase in purity? of non-sugars and the formation of soluble lime salts. (6) Does heavy liming in order to provide an alkaline juice Clarification Problem Defined
Sugar-cane juices, as a result of heavy milling, hot or cold maceration, age of cane, soil and moisture conditions, contain a variable amount of soluble silicates, phosphates, and ferric, aluminum, calcium, and magnesium ions; a certain amount of sulfates, chlorides, nitrogen compounds, and colloidal matter accompanies these bases. Upon the addition of calcium hydroxide the acids present in the juice are neutralized and insoluble phosphates, sulfates, etc., are formed with the calcium ion. Experimental evidence (25) indicates that sugar-cane juices follow the classical laws of chemical precipitation. If the solutions are made sufficiently alkaline, the ferric, aluminum, and phosphate ions are precipitated. Colloidal matter is absorbed by these precipitated ions resulting in a clear juice. The silicate content of the juice varies, but the removal of this impurity is very desirable as it comprises the greatest amount of inorganic non-sugar. The complete removal of silicates has presented a considerable problem which has not yet been solved.
that will retard inversion in later products counterbalance the effect of an increased calcium content? (7) What is the effect of a high alkalinity on the decomposition products of impure sugar solutions? Do the decomposition products affect the recovery? (8) I n what manner should lime be applied and when? Should the juice be heated before or after liming? ( 9 ) Is a better refining commercial raw sugar produced when the clarification is carefully studied and continually investigated? (10) What is the best method of adding lime to the juice so that an intimate mixture occurs without local overliming?
Methods of Introducing Lime into Juice
The most important factors in cane-juice clarification are the method of lime introduction and the amount to be added. These two phases of clarification are closely related, but for the sake of clearness they will be considered separately. Good clarification is, in general, a direct result of careful tempering of the juice and the allowance of sufficient time for settling. Batch liming usually results in poor clarification. Before
INDUSTRIAL A N D ENGINEERING CHEMISTRY
August, 1931 Table IV-Analysis
957
of Juice Obtained from Sugar Canes a t Different Stages of Growth and from Various Portions of Stalk Together with Analysis of Inorganic Constituents Expressed as Percentage Dry Matter
it!&$-GLUCOSEGKAVMOISITY
og
AGE
czEs
IN JUICE
IN
TURE IN
ASH IN DRS
PVRITY CANE MATTER
Si02
Po06
NarO
Kz0
FerOa
Ah01
CaO
MgO
SO8
%
%
%
%
0.065 0.051 0.025 0.036 0.043
0.036 0.035 0.037 0.025 0.039
0.015 0.053 0.053 0.046 0.042
0.093 0.110 0.073 0.062 0.079
0.091 0.379 0.302 0.258 0.017 0.193 0.012 0.196
0.032 0.034 0.017 0.042 0.046
0.045 0.031 0.027 0.031 0.043
0.083 0.081 0.083 0.067 0.092
~
~~
Months
%
%
%
%
%
%
%
%
%
%
%
NEGROS PURPLE
9
10
17.69 18.32 17.82 17.06 14.56
14.84 15.36 14.99 14.28 12.11
0.313 0.471 0.626 0.746 1.180
93 64 94 92 93 29 92.16 86.66
66.04 67.41 69.61 68.31 67.15
3.79 2.93 1.98 1.95 1.96
2.455 1.671 1.098 1.024 1.069
Bottom 18.35 Upper bottom 17.59 16.95 Middle 16.82 Lower top 15.72 TOP
15.38 14.78 14.24 14.09 13.12
0.144 0.168 0.240 0.399 0.637
94.34 93.31 92.52 91.81 89.72
70.29 73.84 75.30 72.32 74.12
2.51 2.17 1.83 2.09 2.22
1.381 0.224 1.116 0.204 1.073 0.222 0,911 0.241 0.982 0.239
Upper bottom Middle Lower top TOP
18.32 15.21 17.72 14.73 17.29 14.36 16.27 13.43 17.72 14.75
0.628 0.752 0.895 1.202 0.806
92.19 91.48 90.61 89.00 91.90
Bottom Upper bottom Middle Lower top TOP
19.12 19.57 18.89 17.41 14.89
17.23 17.56 16.99 15.71 13.08
0.226 0.378 0.530 0.890 1.210
94.98 95.32 94.35 91.05 86.97
75.56 3.24 1.602 0.369 0.469 0.427 0,380 0.380 0.046 0.062 0.185 72.20 3.66 2.033 0.338 0.684 0,609 0,313 0.313 0,082 0.054 0.166 70.26 3.11 1.520 0.258 0.397 0.339 0.244 0,244 0.029 0.041 0.151 71.62 2.88 1.392 0.359 0.537 0,511 0.204 0.204 0.072 0.045 0.080 71.76 2.88 1.468 0.267 0.520 0.480 0.190 0.190 0.079 0.C87 0.088 M-1900 68.33 4.11 2.913 0.180 0.241 0.261 0,041 0,507 0.146 0.120 0.055 70.17 2.01 1.070 0.178 0,117 0.273 0.056 0.276 0.106 0.092 0.077 69.33 2.21 1.052 0.216 0.138 0,312 0.074 0.324 0.097 0.106 0.073 70.60 2.42 1.030 0,234 0,175 0,453 0.108 0.354 0.114 0.151 0.097 72.71 3.75 1.638 0.318 0.308 0.792 0.084 0.491 0.154 0.224 0.188
Bottom Upper bottom Middle Lower top TOP
18.09 17.58 17.59 17.25 16.13
16.16 15.84 15.86 15.52 14.36
0.141 0.167 0.313 0.398 0.647
93.72 95.12 94.16 92.89 90.21
71.48 73.76 74.36 74.28 73.40
3.56 2.027 0.228 0.234 2158 i:i94 0.269 1.95 0.834 0.155 2.28 0.541 0.215
0.372 0.412 0.547 0.431 0.528
0.126 0.076 0.084 0.048 0.040
0.122 0.115 0.096 0.083 0.130
18.97 16.61 16.82
18.01 18.90
17.06 14.75 15.09 16.25 17.03
0,361 0,567 0.544 0,454 0.433
93.21 90.96 91.11 92.45 93.61
72.32 70.50 70.20 69.48 71.46
2.58 3.78 3.16 2.64 2.57
0.383 0,323 0,037 0.261 . . . 0.016 0.415 o:ii4 o:4i9 o:5& 0.012 0.336 o:Oii 0.102 0.644 0.355 0.012 0.205 0.071 0.125 0.803 0.438 0.012 0.191 0.053 0.115
0.097 0.166 0.133 0.132 0.105
18.91 19.32 19.42 17.72 14.55
16.93 0.371 17.29 0,471 17.30 0.790 15.70 1.130 12.81 1.780
95.50 92.62 93.99 89.68 82.37
68.71 69.47 70.11 69.87 71.82
1.01 2.048 0.103 0.107 0.244 0.013 2.06 1.439 0.093 0.081 0.255 0.012 1.95 1.148 0.116 0.137 0 379 0.011 1.88 1.087 0.133 0.140 0.397 0 . 0 0 8 2.37 0.978 0,169 0.283 0.727 0.009
15.18 15.95 15.60 15.27 14.51
0.215 0.298 0.483 1.020 1.420
92.85 93.21 92.65 89.26 87.72
70.54 72.34 71.32 73.14 74.30
3.20 2.344 2.37 1.478 2.01 1.577 2.19 1.647 2.50 0,891
18.75 16.67 19.28 17.04 19.76 17.50 20.68 18.39 20.79 18.40
0.652 0,887 0.689 0.669 0,703
94.84 94.65 95.59 94.90 94.50
68.01 2.12 67.63 68.93 1.'86 66.30 1.78 68.00 1.76
TOP
15.72 14.02 16.11 14.38 15.77 14.01 19.79 13.99 13.93 12.30
0.127 0.331 0,483 0.644 0.889
90.92 90.72 89.03 84.65 86.32
Bottom Upper bottom Middle Lower top TOP
11.29 10.01 10.69 11.76 11.47
10.17 8.95 9.51 10.54 10.22
0.274 0.301 0.331 0.318 0.469
15.56 12.71 14.05 15.31 15 81
13.84 11.30 12.51 13.62 14.12
0.604 0.861 0.558 0.398 0.239
Bottom Upper bottom Middle Lower top TOP
12 mo. 13 days Bottom
9
lo
12 mo. 12 days Bottom
Upper bottom Middle Lower top TOP
1.502 1.802 1.661 1.328 1.177
0.161 0.174 0.164 0,190 0.144 0.148 0.140 0.149 0.128 0.147
0.249 0,275 0.285 0.284 0.318
0.039 0.065 0.489 0.041 0.329 0,029 0,073 0,027 0.385 0,021
0,341 0,364 0,379 0.362 0 479 0.510 0.451 0.463 0.576 0.424
0.389 0.363 0.343 0.438 0.545
0,020 0.010
0.052 0.026 0.019 0.014 0.013
0.667 0.391 0.375 0.341 0.403
0.096 0.083 0.089 0.032 0.047
BADILLA
9
lo
Bottom Upper bottom Middle Lower top TOP
17.01 Bottom Upper bottom 17.71 Middle 17.51 16.96 Lower top 16.14 TOP
12 mo. 11 days Bottom Upper bottom Middle Lower top TOP
0.295 0.047 0.045 0.025 0.095
0.011 0.017 0.032 0,010 0.018 0.039 0.009 0.015 0.045 0.006 0.019 0.039 0.016 0.031 0 083
0.146 0,143 0.138 0.188 0.229
0.259 0.258 0.280 0.392 0.398
0,260 0.257 0.250 0.422 0.470
0.051 0.335 0.010 0.017 0.023 0.039 0.013 0.253 0:002 O:O20 0.032 0.014 0.225 0.009 0.008 0.032 0.015 0,215 0,009 0.014 0.035
0.133 0.109 0.141 0.178 0.191
0,223 0.212 0.269 0.300 0.439
0.195 0.184 0.235 0.263 0.421
0.013 0,010 0.014 0,011 0.009
0.184 0.073 0.062 0.085 0.050
0.031 0.033 0.033 0.031 0.024
0.040 0.036 0.011 0.062 0.008 0.041 0.012 0.067 0.020 0.112
67.30 65.97 71.21 70.50 73.43
4.22 1.776 0.098 4.27 1.557 0.106 3.67 1.878 0.172 3.20 0.828 0.104 3.07 1.475 0.211
0.285 0.167 0.574 0.150 0.292
0.287 0.321 0.909 0.299 0.746
0.0.73 0.165 0.084 0.441 0.076 0.530 0.019 0.161 0.039 0.292
0.102 0.059 0.085 0.046 0.094
0.079 0.053 0.077 0.056 0.113
0.047 0.091 0.116 0.052 0.082
87.52 84.68 86.07 86.98 85.15
69.68 73.72 73.52 72.60 '73.28
5.74 5.16 4.76 4.17 4.30
3.667 3.071 2.675 2.502 0,980
0.234 0.348 0.347 0,252 0,239
0.536 0.541 0.734 0.615 0,624
0.592 0.559 0.789 0,390 0,391
0.051
0.092 0.069 0 . 0 6 0 0:025 0.063 0.083 0.036 0.015 0.050 0.057 0.014 0.042 0.040 0.012 0.052 0.045 0:043
0.142 0.172 0.175 0.196 0,175
89.22 88.01 89.26 89.86 89.12
70.01 74.53 70.65 70.74 69.35
3.01 3.10 2.71 2.46 2.87
1.940 1.700 1.424 1.373 1.591
0.160 0.151 0.170 0.164 0.189
0.648 0,763 0,669 0,635 0 647
0.751 0.020 0,746 0.019 0,647 0.006 0,548 0.008 0.506 0.006
0.108 0.071 0.058 0.157 0.101 0.061 0.048 0.164
1.503 1.291 1.222 1.097 0.882
0 . 0 2 8 0.241
LUZON WHITE
9
lo
Bottom Upper bottom Middle Lower top
12 mo. 10 days Bottom
Upper bottom Middle Lower top TOD
the advent of semi-automatic liming devices the contents of a scale tank were tempered by the addition of small quantities of a lime suspension and, after stirring by hand or with steam or compressed air, the reaction to litmus or phenolphthalein was taken. If the desired end point had not been reached, more lime was added. If the end point had been passed nothing could be done to reduce the alkalinity and the juice was discharged to the heater. This method of liming resulted in irregular precipitation when the juice reached the settling tanks. However, under careful control, even though tedious, batch liming produced excellent results; under an indifferent control no clarification was possible. FLEENER LIMEMETER-An advance over the batch system of liming was made possible by the Fleener lime meter (Figure 1). This device must be classed, however, as semi-automatic
0.310 0.066 0.027 0.115 0.254 0.054 0.039 0.090 0.147 0.078 0.066 0.530
and not as a continuous liming device, for it does not give continuous liming to a constant reaction when the volume of juice fluctuates. Moreover, it permits considerable overliming of the juice used for testing, which is used to wash the milk of lime being added to the raw juice. Owing to the use of the previously limed juice as a carrier for the great amount of lime to be added, this juice is also greatly overlimed for a short period, causing the development of color adverse to the production of a good refining sugar. The device is not flexible. If the volume of juice being limed fluctuates and the volume of lime suspension being added is not changed, the previously determined settling will not give the desired reaction. Moreover, the device permits the introduction of a large amount of air through the use of the centrifugal pump to pump the juice t o the heaters. When the
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
958
lime suspension and the returned juice is not sufficient to fill the pipe completely, air will be drawn into the line and passed into the heaters. Factories using this device should have an attendant specially assigned to its operation. Changes in maceration water and changes in the grinding rate, and therefore in the volume of raw juice being limed, necessitate a quick change in the amount of lime being added.
Vol. 23, KO.8
and an outlet, 9, and is divided into three compartments, 13, 14, and 15. Partition 10 is set up from the bottom of the tank and the chamber 13 is provided with a sloping baffle so that there is no obstacle to the continuous flow of juice through the passage 16 and no juice remains pocketed in the tank. The gradual rise in chamber 14 raises the float, 62, which regulates the amount of lime to be added to a given volume of juice. Partition 12 acts as a weir and has a Vshaped overflow, 17, whereby juice from compartment 14 flows into chamber 15. Drains are provided for periodic cleaning. The juice and lime mix a t this overflow. The volume of juice flowing over the V weir determines the volume of lime added and an intimate mixture is obtained. A small portion of the limed juice is returned by the pump to the liming station for testing the reaction. The hot clarified juice is also returned for settling tests at this station and is returned with the limed mixed juice. The amount of lime to be added is regulated by the adjustment of the sleeve 45, which is directly connected to the float. This regulation prevents a flow of lime into the juicereceiving tank after the sugar-cane juice has ceased to flow. Semi-automatic devices do not permit such a control, but allow lime solution to flow into the juice tank owing to the carelessness of the attendant. A decrease in the overflow through the sleeve raises the level of lime in the overflow tank and allows a greater quantity of lime solution per unit of juice to flow over the V weir of the lime box. Amount of Lime to Be Added
1 Figure 1-Fleener
f n \
I
Liming Device
The device consists-ofitwo boxes, one stationary and the other movable. The stationary box is divided by a partition. A pipe which connects with the lime-supply tank from one side of this box returns the surplus milk of lime. Another pipe carries the lime and the juice discharged from the testing pipe from the liming side of the box into the mixed supply line. The movable box is mounted on an arrangement which corresponds in principle to a crossfeed of a lathe. By turning a screw,the milk of lime overflow is regulated. AUTOMATICCONTINUOUS LrMrNG-The essentials of an automatic continuous liming device are: (1) automatic addition of a constant amount of available calcium hydroxide per unit of juice, (2) adaptability to change in quality of juice, and (3) immediate change in the amount of lime added when the volume of juice changes. The Fleener and Petrie-Dorr devices do not meet these requirements. As a result of this need a continuous, automatic liming device was invented and successfully operated a t the central of the Pampanga Sugar Development Company, in the Philippine Islands, during the 1929-30 grinding season. With this apparatus (Figures 2 to 7 ) a continuous supply of lime was added according to the rate of flow of the juice and the amount was constantly checked by colorimetric standards; settling rates were determined and immediate changes in the amount of lime being added were possible. This is very important for even liming, Once the amount is determined, within practical limits, any fluctuation in the juice flow produces a corresponding variation in the lime flow. The limed juice which is returned for testing is mixed with the large volume of unlimed juice so that no overliming is possible. The principal part of the liming device is the mixing tank, 7 , which is provided with a sloping conical bottom so that no juice remains in any compartment. This tank has an inlet, 8,
The research of the past six years has advanced the knowledge of clarification to a point where the principles are fairly well understood (7, is,29,38,39). However, the general belief is that liming to certain predetermined pH’s is necessary. Advocates of liming to as high as pH 8.3 believe that such gives the best possible clarification; others working with different juices believe that a juice limed to around pH 7.6 is the most satisfactory. It is now definitely established that, if there are present no substances capable of reacting with the calcium ion, there will be no precipitation. However, certain colloids present in the juice can be coagulated by heat and can be precipitated at certain hydrogen-ion concentrations. The titration of a juice with a standard alkali will give the amount of hydroxyl ions necessary for the neutralization of the acids present and the amount necessary to produce a given concentration of alkalinity. Any determination of hydrogen-ion concentration after liming gives only the end reaction. The colorimetric method of determining hydrogen-ion concentration is the most simple and is thoroughly satisfactory in the hands of a worker sensitive to color changes (27). It is essential, however, that the color standards be replaced each season. Clarke (IO), however, gives detailed instructions for the preparation of standard buffer solutions to which standard dyes can be added and color tubes can be prepared weekly or monthly so that the error due to fading can be practically eliminated. No satisfactory commercial operation of a potentiometric method of determining hydrogen-ion concentration is known to the writer. All the suggested electrodes either poison or become coated or polarized during actual factory operation. It is believed that radical changes will be necessary before a satisfactory continuous, automatic, recording, potentiometric device can be used at the liming station. Published work indicates that the quantity of lime to be added depends upon the phosphate content of the juice. This dependency has limitations, since the calcium precipi-
August, 1931
INDUSTRIAL A N D ENGINEERING CHEMISTRY
959
31
( 7 ) Mixing tank (8) Juice inlet pipe (9) Juice outlet pipe (10, 11,'12) Partitions (13) Chamber (14, 15) Compartments (16) Passage from compartment (17) V weir juice overflow (18) Drain from compartment 14 (19) Drain from compartment 15 ( 2 0 ) Lime-meter box (21) Platform (22) Brackets (23) Partitions spaced from bottom (24) Weir for lime box ( 2 5 ) Passage (26, 27) Lime compartments (28) V-shaped overflow between compartments 26 and 27 (29) Pipe which drains chamber 27 of lime-meter box and empties into chamber 15 (30) Lime-supply tank (31) Pump line (32) Motor for lime solution (33) Stub pipe for lime solution (34) Lime-supply pipe ascending
Zitkowski Continuous Automatic Lime Meter
(38) Vent (39) Lime-supply pipe for 2 5 (40) Valve for controlling outgoing lime (41) Milk of lime spreader (42) Spreader supports (43) Lime-overflow pipe (44) Collar on lime overflow (45) Adjustable sleeve on lime (46) Overflow (47) Bail for sleeve 45 (48) Sleeve supporting rod (49) Support for rod and sleeve (50) Support for sleeve bar (51) Bearings for sleeve bar (52) Slide rod for sleeve adjustment (53) Adjusting screw (54, 55) ,Adjustable heads on lime adjusting screws (56) Wheel for regulating screw (57) Treaded opening (58) Pointer attached to 54 (59) Graduated scale (60) Lever for lime adjustment (61) 4 r m for lime adjuster (62) Float for lime regulator (63) Rod for float
INDUSTRIAL A N D ENGINEERING CHEMISTRY
960
Vol. 23, No. 8
data are based upon the work of McAllep and co-workers ($1). Chart 5, for example, shows that at 87.78' C. at pH 7.2less than 0.2 kg. of sucrose is destroyed. If the pH drops considerably and the juice is held for 1 hour a t pH 6.2, a loss of 1.2 kg. per ton of sucrose is to be expected. According to Chart 6 at pH 7.0 juices held below 82.22' C. show a loss of less than 0.2 kg. of sucrose per hour while if the temperature is increased to 98.89' C. the loss closely approaches 1kg. per ton of sucrose per hour. At lower pH's and higher temperatures the loss increases. A careful study of these charts will give information as to the economical limit of liming and temperature. The lime-station operator must carefully weigh the loss by inversion and decomposition with the possible influence of l i e salts upon the recovery of sucrose from the low-grade products.
90t
Rote
Chart &Relationship between Temperature and Rate of Decomposition and Inversion of Sucrose i n Pure Solution and T i m e Required for Formation of a Standard Amount of Caramel (Bur. Standards, Circ. 44, Table 28)
4OL
tates not only the phosphates but also the silicates, which by far exceed the phosphates in the precipitate found in the absence of cane fiber. Sucrose Loss by Inversion and Decomposition
Liming eliminates non-sugars to a certain degree, increases the calcium in the juice, and introduces a certain variable amount of alkalinity as a preventive measure against inversion due to the acidity in the juice. However, the excess calcium results in a catalytic destruction of invert sugar with an increase in acidity, and the higher the alkalinity the more rapid is the acid formation. The net result is an inferior juice. Sucrose solutions immediately begin to deteriorate as a result of the enzymes present in the juice, the acidity present or developed, and the heat treatment. The decomposition through heat is shown in curve a, Chart 4. Curves b and c show the inversion of sucrose in a pure solution at different temperatures as compared with standards of 0" and 15" C. For example, the rate of inversion a t 62" C. would be 30,000 as compared with the rate a t 15" C., while an increase in temperature to 76" C. would result in an increase in the rate to 100,000. The destruction of sucrose by inversion and decomposition is influenced by the degree of acidity and the duration of treatment. In Charts 5 and 6 are curves showing, respectively, the sucrose destroyed by both temperature and inversion in 1 hour a t various temperatures and pH's. (These
I 500-
*
%
0.20
of0
060
K/os Chart 6-Sucrose
ago
/osr
per
100
/.20
/40
660
/on ~ u c r o s c
Lost a t Various Hydrogen-Ion Concentrations by 1 Hour
mo 0
010
OLO
060
024
,m
K ~ O/om J p r ton
I
I
1
126
/""
,GO
I
La*
l 100
O Y C ~ Y *
Chart 5-Sucrose Lost by Heating t o Various Temperatures for 1 Hour a t Certain Hydrogen-Ion Concentrations
Role of Added Calcium in Juice
If the lime added to the juice is not precipitated, calcium and alkalinity accumulate and acidity is reduced. Table IV gives average analyses of five varieties of cane at different ages of growth, in order to show the possible variation in substances which can be eliminated during clarification of juices expressed from canes of different maturities. Mill juices contain invert sugar. If the invert sugar is decomposed, non-sugars are formed and the ratio of sucrose to Brix solids is decreased; that is, there is a lowering of the purity. A series of fifteen juices of high and low purity were treated with milk of lime to different hydrogen-ion concentrations and heated to 100' C. for equal intervals of time. Chart 7 shows that glucose is destroyed a t all pH's but that above pH 9 the destruction is exceedingly rapid. The same juices were heavily limed and then $ ; treated with acetic acid to different hydrogen/ ion concentrations in order to have a variation in the calcium content. They were then heated to 100' C. and settled. It is seen in Chart 7 that there was greater destruction when calcium was present at the same pH. At pH 7 when a large amount of calcium was not present, the destruction of invert sugar was around 2.5 per cent of that originally present in the juice, while in samples of the same juice that has been overlimed and the pH reduced with acetic acid, the destruction amounted to 17.5 per cent. This effect was observed at all hydrogen-ion concentrations. These data clearly demonstrate the catalytic 180 2.00 influence of the calcium ion upon the decomposition of invert sugar with heat. It was also Heating for observed that rapid decomposition of pure in-
August , 1931
INDUSTRIAL A N D ENGINEERING CHEMISTRY
961
vert sugar in solution took place in the presence of calcium salts without heat.
cation and poor filtrability of raw sugar, found that a low phosphate content of a juice and a large amount of h e suspended matter coming from the return of the second mud to Table V-Filtration Rate, Polarization a n d Clarity of Commercial the mill were the responsible factors. By increasing the Raw Sugars Produced by Limidg of Raw Cane Juice phosphoric acid content of the primary juice to 0.01-0.015 HOTLIMING 1 COMPOUND LIMING COLDLIMING per cent, the filtration rate of the sugar and the clarity of the juice improved considerably. The amount of phosphate Filtra- PolariFiltra- polariFiltration zation Clarity tion zation Clarity tion C1arit.S present in juice when sufficient calcium ion is provided seems rate rate rate - to be the general limiting factor in clarification. However, 34 65.89 96.9 the role of the soluble silicate has been neglected. 31 71.27 9 7 . 2 ~~
I
~~
64.64 66.73 67.18 70.55 68.84 70.63 69.14 67.72 73.55 69.82 66.63 66.86 69.80 65.84 70.72 71.50 69.32 68.83
Av. 4 5 . 4 6 9 7 . 3
38
32 33 32 34 36 34 35 35 35 35 36 35 57 58 58 57 57 57
97.2 97.3 97.4 97.3 97.4 97.0 97.0 96.9 97.2 97.2 97.3 97.3 97.0 97.3 97.2 97.4 97.3 97.2
68.77 9 7 . 2
45
1
65.38 9 7 . 3
41
Precipitation of Soluble Silicates
The juices used in the above experiments were analyzed for silica both before and after heating, liming, and settling. Juices to which excess lime to pH 10 had been added were treated with acetic acid in order to reduce the pH. They were then also analyzed for silica. The control juice was filtered in order to exclude silica from fiber. The data obtained are plotted in Chart 8, curves c and d. These curves give the average per cent removal from thirty-two juice experiments in liming.
Precipitation of Phosphates
The juices used in the above series of experiments were further analyzed for Pn05both before and after treatment. The average results of thirty-two tests are given. Analyses were made on juices which, after liming to pH 9.5 or 10, were treated with acetic acid in order to reduce the alkalinity to determine the re-solution of precipitated matter and the influence of excess calcium ion. Curve a, Chart 8, gives the average per cent elimination of phosphates in the juices after liming to pH 10 and decreasing the pH a t which heating and settling took place. It is seen in comparison with curve b that there is a greater elimination a t a particular pH when excess calcium ion is present. Curve b shows the per cent elimination through gradual addition of lime. Below pH 7.5 there is a rapid re-solution of phosphates. From this graph of averages it is seen that, if a juice is limed to a high alkalinity and the pH drops during heating and settling, the phosphates will redissolve if the precipitate is not removed. Individual juices manifested greater or less re-solution than this average curve. The precipitation of phosphates seems to be a function of both the hydrogen-ion concentration and the amount of calcium ion. It appears that both the mass law and the solubility constants apply in this precipitation. When an excess of calcium was present a greater precipitation occurred, but in no case was there a complete elimination. In juices where the calcium ion was low there was less removal for a given pH. In juices deficient in both calcium and phosphate the per cent removal was low. In juices of low phosphate but high calcium content there was a greater removal of phosphates. It appears that the economical limit for the precipitation of phosphates is approximately 7.6 pH. Fries (17) found that the addition of approximately 0.68 pound of double superphosphate per ton of cane or approximately 0.03-0.035 per cent P105 on juice gave clearer juices, higher sirup purity, and a better refining sugar. The data given by him indicate that, by liming juices with this amount of phosphates to a pH 8, a 36 per cent increase in clarity and a 0.7 per cent increase in the recovery of commercial raw sugar were obtained. He estimated that, through the use of soluble phosphates with liming to pH 8, 16 additional pounds of sugar were recovered at a cost of 15 cents per ton of cane. Bomonti (j), working in Hawaii on the cause of poor clarifi-
~
I
5
6
7
8
I
I
9
I
IO
11
PH Chart 7-Destruction of Glucose in Juice during Clarification a t Various pH's in Presence of Calcium
The data are rather conficting. I n general it appears that not all of the silica is removed. At a pH as high as 10 only 70 per cent was removed, while at pH 8 only approximately 35 per cent was eliminated from the juice. There is a greater re-solution of the silica through the addition of acid, as shown in curve d. The plotted average per cent elimination as shown in curve d indicates that there is a much smaller elimination of silica a t a given pH when the pH is below 8. Better filtration of commercial sugar and less scale in the boiling and heating equipment will result through a greater removal of silica. Additional work aimed to secure a greater elimination of silica is under way in this laboratory. Precipitation of Magnesium
The removal of magnesium is found to be a function of the alkalinity. The greatest removal occurred in the neighborhood of pH 9. The elimination at lower pH's is small and the curve of elimination rises sharply between pH 8.5 and 9. Additional work now under way will give more information. Removal of Iron and Aluminum Sulfates
Nearly complete removal of iron and aluminum occurszat pH 8. Below pH 7 there is an average of about 50 per cent removal of iron and approximately 30 per cent of aluminum. The removal of iron seems to be associated with the amount of phosphate present. When the phosphate was considerable
962
INDUSTRIAL 9 X D ENGINEERING CHEMISTRY
(0.06 per cent of the juice) nearly all of the iron was eliminated below pH 7.5, whereas when the phosphate was low (0.01 per cent) the juices had to be limed to pH 8 before 95 per cent of the iron was eliminated. The re-solution of iron followed the drop in pH. I n other words, if juices become acid in the presence of the precipitated matter, a re-solution of iron takes place. In general, the aluminum precipitation followed that of the iron. u 0
Vol. 23. No. 8
of these juices. The immature portion of the stalk contained a considerable amount of protein. I n the more mature portions the nitrogen content was practically constant. A series of experiments on the nitrogen content of canes of different ages showed the same trend. Juices expressed from young cane contained a large amount of nitrogen, while old cane contained much less. The comparison was made on millable cane and the “tops” were excluded. The clarification of the young canes and also of the upper portions of old canes gave considerable trouble. Liming to pH 8 did not produce a satisfactory clarification based upon the rate of settling, increase in purity, and clarity of the clarified juice. On liming to lower pH’s better clarikation was obtained. The greatest elimination of nitrogen was obtained at a pH of 6.5 and where the nitrogen content was high, owing to immaturity of the cane, the best clarification was obtained below pH 7 . The data obtained on the nitrogen elimination seem to point to an isoelectric point below pH 7 and above pH 6.5. It was impossible to establish a definite isoelectric point in these clarification studies on account of the variation in coagulable matter which contained a considerable amount of the nitrogen present in the juice. Without heat coagulation the greatest elimination of nitrogen occurred a t pH 6.2. However, individual juices deviated from this pH. The writer believes that in the clarification of young canes high liming will not give the best results.
Chart &Precipitation of Phosphate, Soluble Silicates and Removal of Sulfate on Liming, Together with Calcium Content of Clarified Juice
Colloid Content and Elimination
Sulfates are quite soluble in sugar-cane juices. I n many of the juices examined there was no removal of sulfates. However, when the sulfate content was appreciable there was a greater elimination. Curve e shows the sulfate elimination for juices high in sulfate content which were limed to as high as pH 10. Increasing amounts of calcium ion seemed to aid in the precipitation.
The investigations of Bond (8), Paine and co-workers ( I , 2, g4, 54,Monsalud (SI),and King (25) indicate that no absolute generalizations on the colloid content or its elimination during clarification can be made. There are no adequate methods for the estimation of colloid content. The suspensions present in the juice may be reversible, irreversible, or capable of neutralization with night blue. Bond estimated
Calcium Content of Clarified Juice
The average data obtained in this series of investigations are given in Chart 8. The cross-hatched columns show the per cent increase in calcium oxide by liming the juice to pH 10 and decreasing the pH through the addition of acetic acid, in order to obtain conditions similar to those existing when the juice is heavily limed and pH drops during heating and settling in the presence of the precipitate. The dark columns are for the data obtained by liming, heating, and settling. The analysis of the clarified juice was used in plotting these increases. It is seen that the calcium content of the clarified juice increases tremendously when acids are either developed or added. There is also a gradual increase in the calcium content from pH 5.5, but at no time is the calcium oxide content equal to that obtained from acid development. Liming to around pH 8 resulted in approximately a 200 per cent increase over that of the raw juice, but liming to pH 7 gave less than a 100 per cent increase. Protein Content, Its Elimination, and the Isoelectric Point
One of the minor precipitating agents in the clarification is the albumin present in the juice, The quantity varies with the variety and age of the cane. Thirty-five stalks of the same age and approximately the same number of joints were divided into joints and these joints were milled separately. Nitrogen determinations were made on these separate juices. The analyses in Chart 9 show the increase in nitrogen content
Chart %Nitrogen in Juice Expressed from Different Joints of Sugar-Cane Stalks
the colloid content of juices by dialysis through collodian bags; Paine and co-workers used the ultramicroscope for the estimation of colloids neutralized by the dye. Monsalud, Sitchon, and the writer have estimated the colloid content by neutralization with night blue, and have found conflicting results. It must be remembered that any sugar solution will shorn a Tyndall cone. The turbidity in impure sugar solutions is generally due to suspensions. These suspensions may be positively charged or they may or may not be capable of dialysis through semi-permeable membranes. For these reasons a direct estimation of the actual suspension content of a particular juice is difficult. Monsalud, working in the Philippines, found that from 15.5 to 30 per cent of the colloids, as determined by the dye test, were eliminated during clarification. Paine, working in Cuba, found that the elimination as indicated by the same
August, 1931
INDUSTRIAL AIVD BNGINEERIiVG CHEMISTRY
test varied from 6.56 to 39.67 Der cent. He also investigated the irreversible colloid conteit and concluded that thue reversible colloids varied from a minimum of 0.191 gram per 100’ Brix solids to a maximum of 0.589, while the irreversible colloids varied from 0.008 to 0.267 gram. After a series of investigations on the relation of mill juices to the milling process, Bond (8) concluded that colloids are formed from the cane fiber during the milling and that the low purity of the last mill juice is the direct result of the milling upon the fiber. He also found that during dry crushing the colloid content of the last juice from milling units consisting of a crusher and an eighteen-roller milling plant was considerably less than when maceration was applied to the last mill and the juices returned to the mills. A summary of his work is given in Chart 10. Monsalud (32), working on the colloids, as determined by the dye test, expressed by the various mills with varying amounts of maceration found that little reliance could be put on grab or occasional samples. Through the average compositing of samples and routine determination of dye value, data were obtained which are given in graphical form in Chart 10. These average figures are the result of a 6 weeks’ investigation and indicate the amount of colloids in the various mill juices with a normal maceration of 12 per cent and less. It is seen that the addition of water increased the dye value. While the average increase was small individual tests with 20 per cent maceration showed a considerable increase. The colloidal content increases from mill to mill and is greatest in the last mill juice; that of the mixed juice was approximately 20 per cent greater than that of the crusher juice. Effect of Cane Fiber on Clarification
Settling is aided by fine particles of cane fiber. The filtration of the settled mud is rapid when bagacillo is present in the mud, but the hot, alkaline digestion of the bagasse results in the solution of substances which have an ill effect upon the recovery. When juices are passed through a 200-mesh screen before defecation, the rate of settling is retarded and the juice is not so clear and limpid as when cane fiber is present. The general practice in the Philippines is to screen both the mixed juice and the clarified juice thoroughly. The screenings from the clarified juice are added to the mud before pressing. Bond ( 8 ) ,Bomonti and McAllep (6), and Conklin (11) have studied the effect of finely divided cane bagasse upon clarification. Conklin found that with high liming, when the juice was not thoroughly screened, a considerable amount of matter was made soluble. Bomonti and McAllep stated that the drop in purity during clarification was due to solution of impurities in the cush-cush through the combined action of lime and heat. They also believed that the greater the amount of cush-cush the greater was the drop in purity. The solution of the material and the drop in purity, however, were irregular for increasing amounts of lime. Experiments conducted by the writer (25) show that non-sugars are obtained from the alkaline digestion of bagasse and that a considerable amount of soluble silicates and colored organic non-sugars is introduced in the juice a t high alkalinities. These substances seriously interfere with the production of a good filtering raw-sugar solution. The heavy liming of settlings which contain a large amount of cush-cush generally results in the lowering of the purity of the press juice, and when the press is sweetened off there is a gradual lowering of the purity of the washings through the re-solution of the precipitate and the solution of products formed from a hot, alkaline digestion. Bomonti and McAllep found a drop in purity of 1.83 when 25 grams of cush-cush with 60 per cent fiber were added to a liter of juice in an alkaline reaction.
963
Rate of Settling of Limed and Heated Juice
Untreated juices are extremely turbid. Heat causes a settling by coagulating the albuminoid matter present; the resulting precipitate is very high in nitrogen (25). However, such a heated juice does not present a clear, sparkling appearance, and the rise in purity is small. One of the most striking characteristics of the suspensions present in cane juices is that under certain conditions the particles remain finely divided, whereas under others they unite to form larger particles. In the first case the rate of settling is exceedingly slow, whereas in the second the particles settle rapidly. If sufficient time is allowed, the amount of precipitate may be the same. This peculiarity is of great importance to the operator desiring to deliver well-clarified juice to the evaporator. W O L
c
P pi Chart 1 G C o l l o i d Content of Mill Juices Obtained from a n 18Roller Milling Plant under Dry Crushing a n d w i t h Application of Water with Return of Dilute Juices ( 8 ) Dye value content of a 14-roller milling plant juices with a normal maceration of 12 per cent and with 4 per cent and the return of dilute juices in simple imbibition (32)
A suspension undergoing flocculation presents a definite series of changes. At first, if the reaction is satisfactory, the individual particles cannot be seen without a microscope and their appearance is manifested by a Tyndall cone. Large particles gradually make their appearance, usually as discrete clumps. More or less rapid settling of these larger particles now occurs and in the course of time the solid matter forms a precipitate in the lower portions of the tank. Defecation therefore consists of three distinct steps: first, the changing of the medium so that optimum conditions are a t hand; second, the collection of small particles into large aggregates; and third, the gradual settling of these larger particles. Any disturbance of these three phases will result in poor settling. It has been observed that when two oppositely charged suspensions are brought together in equal amounts a precipitation occurs; if either suspension is in excess the suspensions will remain stable and no precipitation will occur. Clarification cannot be accurately controlled by liming to an arbitrary pH. The control must be based upon the pH a t which a maximum amount of material is eliminated with a rapid growth of the fine particles and a rapid settling of these larger particles. The only measure of clarification that is economically possible in raw-sugar manufacture is that of the addition of lime. If it were practicable to settle the cane juice in fractions, excellent clarification would be possible; and if the juices could be defecated from the settled material and again limed to a higher alkalinity, a t which most of the inorganic material would be precipitated and again defecated after being saturated with carbon dioxide to remove the large amount ofJime, excellent clarification would he realized. The settling rates of juices so treated would vary. hom-ever.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
964
Table VI-Comparison
of L i m i n g before Heating, L i m i n e a f t e r Heating, and Double L i m i n g
COLDLIMING MIXED JUICE
cL;$:FD %
% 85.5 85.4 83.2 86.1 84.9 85.6 84.6 84.2 85.7 85.5 86.1 84.1 81.4 84.9 83.1 84.6 84.2 82.3 85.2 83.1 84.5
I
1133 1148 1155 1204 1159 1108 1333 1201 1181 1129 1026 1129 1265 1058 1170 1129 1137 1173 1192 1199 1161
86.6 87.2 84.9 85.7 86.9 88.1 83.7 86.2 87.5 88.0 87.6 84.9 82.9 86.1 86.9 86.3 84.1 82.4 86.5 83.1 85.8
929 1102 1022 926 1056 897 1072 994 959 908 811 902 1025 848 852 858 1004 943 931 964 9502
Vol. 23, No. 8
HOTLIMING :ise in Colloid ,urity elimina tion
%
%
+1.3 +1.8 +1.7 -0.4 +2.0 +2.5 -0.9 472.0 +1.8 +2.5 $1.5
18.00 18.25 11.52 23.09 8.89 19.04 19.07 17.23 18.80 19.57 20.96 20.11 18.97 19.85 27.18 24.00 11.52 19.61 21.90 19.60 18.9
+0.8 $1.5 4-1.2 +3.8 +1.7 -0.1 +O.l $1.3
+i:o
MIXED JUICR
Purity
c:
%
DOUBLE LIMING
CL;E:iEDRise in purity
Purity
DNyoe
%
Experiments conducted in this laboratory on the rate of settling of variously limed juices indicate that if juices are underlimed the rate of settling is extremely slow and, on the other hand, if overlimed the rate of settling is retarded. If a rapid settling juice is desired, the liming must be controlled irrespective of the pH for maximum increase in purity. I n some juices the optimum clarification pH corresponds to the pH of most rapid settling. However, such points must be constantly determined. Change in Purity during Liming and Clarification
Owing to the combined action of the lime as a precipitating agent, the coagulation brought about heat, and the removal of suspensions, the ratio of sucrose to solid changes. With the removal of non-sugar the ratio increases-that is, the purity is increased. With the destruction of sucrose during clarification or through the introduction of lime which is not removed, the ratio decreases and a drop in purity results.
C h a r t 11-Relationship between P u r i t y of J u i c e and p H Juices of high, medium, and low purity were limed t o various pH's and analyzed after clarification. Analyses are shown by the continuous curves. These juices were limed to the maximum p H and the p H reduced with acetic acid; average analyses are shown by the broken lines.
In order to investigate these purity changes, fifteen juices of varying purity were treated with lime to various hydrogen-ion concentrations, heated to 100" C., and allowed to settle. The same juices were also limed to pH 10, and the pH was decreased by the addition of acetic acid so that the purity change could be evaluated as the juice became acid. The analyses of these juices after such treatment are given in Chart 11. The continuous lines show that the maximum
% 1245 1188 1417 1326 1419 1301 1191 1086 1318 1377 1246 1320 1114 989 1054 1030 1032 981 1054 1074 1323
+2.7 +0.4 -0.3 -0.8 4-0.4 $0.9 $1.4 -0.4 +1.5 +1.5 +0.2 4-1.4 fO.2 +0.6 +0.2 -0.2 4-2.8 +0.8 $0.7 $0.2 $1.0
Colloid elimination
MIXED JUICE
Purity
%
%
22.38 19.58 19.49 17.69 16.28 17.29 26.02 27.07 23.59 15.88 14.07 15.49 21.60 25.41 22.43 17.99 25.75 25.51 23.01 22.34 20.93
85.6 84.9 86.3 85.3 86.0 85.4 86.2 86.6 86.8 85.7 84.1 88.1 86.2 85.3 86.3 86.8 87.1 87.2 86.6 85.7 86.1
ge %. 1576 1423 1385 1845 1534 1357 1392 1427 1472 1520 1537 1354 1565 1619 1808 1724 1624 1835 1719 1784 1575
86.4 86.5 86.4 86.7 88.2 86.7 88.6
86.7
87.7 86.2 87.0 88.1 87.6 86.4 87.3 86.0 87.6 87.6 87.2 87.3 87.1
% 1155 1203 1099 1249 1097 1135 1136 1056 1000 1287 1252 1177 1239 1392 1358 1397 1339 1397 1397 1450 1240
+0.8 +1.6 4-0.1 +1.4 +2.2 +1.3 +2.4 fl.0 +0.9 +0.5 +2.9 fO.0
f1.4 +1.1 +1.0 +0.8 +0.5 +0.4 +0.6 +l.6 C1.3
% 26.71 15.46 20.65 31.93 28.49 16.37 18.39 26.00 32.07 16.64 18.54 18.94 20.83 14.02 24.89 18.97 17.55 23.87 18.73 18.72 21.39
increase in purity is not obtained at the same pH. Some juices showed an increase in purity of 2.5 points, while others showed but 0.7 a t the same hydrogen-ion concentration. It appears that the low-purity juices do not, in general, respond to clarification so well as high-purity juices. After obtaining an increase in purity, on further addition of lime the purity decreases. The data obtained from the analysis of the juices heavily limed and treated with acetic acid are given in the discontinuous curves. The acid brought into solution substances which lowered the sucrose-solid ratio considerably. It is believed that the formation of acids during heating and settling will produce identical results. Heating before or after Liming-Double
Liming
Experiments in clariiication of juices a t the university sugar mill by heating before and after liming indicate no advantage in either method from the standpoint of increase or removal of non-sugars. It has been claimed that more silica is removed by heating to 120" C. before liming; no such evidence has been obtained by the writer. The only advantage was less lime scale formation in the heater, but this advantage was to a large extent offset by an increase in reducing sugar, Inversion took place during the heating, and when juices below pH 5 were so treated the inversion was appreciable. When these juices were limed the increased glucose content aided in producing a very dark colored clarified juice. During the past season a series of comparative factory runs was made to determine the effect of (1) liming the juice in the cold to pH 7.8-8.0 and heating to 104.5" C.; (2) heating to 105" C. and liming the hot juice to pH 7.6-7.8; (3) liming to pH 6.2-6.4 heating to 104" C., and liming the heated juice to pH 7.6-7.8. Comparative analyses of the juices and sugar resulting from the three methods of clarification are given in Table V. The rate of settling was practically the same for all treatments at the same pH. The volume of mud varied according to the amount of lime applied to the unsettled juice. Twenty runs of the first treatment showed a slight reduction in the reducing sugar content. The average of twenty tests of the second treatment showed an average increase in reducing sugar content of 25 per cent, while individual tests showed more than an 80 per cent increase, These tests demonstrated that heating before liming results in a large increase in the reducing-sugar content of the clarified juice. The average of
August, 1931
INDUSTRIAL A N D ENGINEERING CHEMISTRY
twenty tests with the third treatment showed a considerable reduction in the amount of invert sugar formed. The average increase amounted to 8 per cent, while individual tests showed a maximum increase in reducing sugars of approximately 15 per cent. r, The data given in Table VI indicate that colloid elimination, as given by the dye test, varied from 8.89 per cent to 27.18 per cent; the increase in purity varied from 2.5 to practically no increase; the filtration rate of the sugar varied from 31.62 to 57.70, with an average of 45.46, when the juice was limed cold and then heated. When the juice was heated to 105’ C. and then limed, the increase in purity varied from a minus 0.8 to a plus 2.8; the dye value elimination varied from a minimum of 14.07 to a maximum of 27.07 per cent, with an average elimination of 20.93 per cent. The filtration rate of the commercial sugar varied from 65.84 to 73.55 with an average of twenty runs of 68.77. The clarity of the sugar varied from 37 to 53 with an average figure of 45. These increases mere advantageous in that a better refining sugar was produced, but the increase in reducing-sugar content of the clarified juice was a loss to the sugar factory. By liming the juice in the cold to pH 6.2-6.4, heating to 105’ C., and again adding lime to pH 7.6-7.8, the clarified juice showed a maximum increase in purity of 2.9; the clarity improved and the dye value elimination varied from 14.02 to 31.93 per cent with an average of 21.39 per cent. The fltration rate of the sugar varied from 55.14 to 74.32 with an average of 65.38. The clarity of the sugar varied from 31 to 58 with an average of twenty runs of 41. During these factory runs it was noted that with the hot liming the growth of Leuconostoc in the liming tanks and pipe lines was eliminated. The heaters scaled but slightly during these runs. There was but little advantage in the cold liming and the double liming in this respect. The heaters scaled badly and the Leuconostoc contamination was severe when the juice was limed before heating. Literature Cited (1) Badollet, M. S., and Paine, H. S., Intern. Sugar J., 29, 23-8, 97-103, 137-40 (1928). (2) Balch, R . T., and Paine, H. S., IND. ENG.CHEM.,20, 348-53 (1928). (3) Bird, M., Louisiana Planter. 69, 61 (1922).
965
Bird, M., Facts About Sugar, 16, 12 (1923). Bomonti, H. F., Hawaiian Planters’ Record, 36, 49-57 (1931). Bomonti, H. F., and McAllep, W. R., Ibid., 25, 124-31 (1921). Bomonti, H. F., and McAllep, W. R . , Ibid., 28, 559-83 (1924). Bond, J. D . , Ibid., 28, 152-61 (1924). Brewster, J. F., Planter Sugar Reference Book, No. 2. 55-7 (1924). Clarke, W. hl., “Determination of Hydrogen Ions,” Williams and Wilkins, 1925. Conklin, D. G., 3rd Annual Meeting, Hawaiian Sugar Technologists, 1924. Cook, H. A,, and McCleery, W. L., 4th Annual Meeting, Hawaiian Sugar Technologists, 1927. Coop, E. M . , Facts About Sugar, 26, 338 (1930). Deerr, Noel, Intern. Sugar J . , 18, 502 (1916). Deomano, F., Philippine Agr., 20 (1931), in press. Farnell, R . G. A,, Intern. Sugar J., 26, 359-63 (1924). Fries, A,, Hawaiian Planters’ Record, S6, 17-9 (1931). Geerligs, H. C., “Cane Sugar and Its Manufacture,” pp. 145-65, Horman Rodger, 1924. Gomez, F., Philippine Agr., 19, 609-34 (1931). Hadfield, H. F . , Facts About Sugar, 15, 480 (1922). Hazewinkel, J. J., Arch. Suikerind., 2S, 654-71 (1915). Hazewinkel, J. J., I b i d . , 24, 913-22 (1916). Horne, W. D., Planter Sugar Mfr., 72, 11 (1924). Keane, J. C., McCalip, M. A., and Paine, H. S., Ibtd., 80, 640-63 (1928). King, R . H., Ibid., 74, 12 (1927). King, R. H., Sugar News, 11, 499-515 (1930). King, R. H., and Guanzon, G. A,, Planter, 89, 222 (1929). McAllep, W. R., Rept. Committee on Manufacturing Machinery, Hawaiian Sugar Planters’ Assocn., pp. 6-8 (1923). McAllep, W. R . , Hawaiian Sugar Planters’ Record, 29, 34-9 (1925). McAllep, W. R . , and Cook, H. A., Hawaiian Planters‘ Record, Sa, 294-307 (1928). McAllep, W. R., Cook, H. A., and Bomonti, H. F., Hawaiian Sugar Planters’ Assocn., Spec. Bull. (1926). Monsalud, M. R., Philippine Agr., 20 (1931), in press. Orth, W. K., Hawaiian Sugar Planters’ Record, SO, 126-33 (1926). Paine, H. S., Keane, J. C., and McCalip, M. A., IND. ENG. CHEM., 20, 262-7 (1928). Peck, S. S., Intern. Sugar J . , 21, 60-2 (1923). Petric Liming Device, Rept. Committee on Manufacturing Machinery, Hawaiian Sugar Planters’ Assocn., pp. 6-8 (1922). Roxas, M. L., Sugar News, 1, 13-4 (1922). Roxas, M. L., and Africa, R., 1st Annual Meeting, Philippine Sugar Assocn., 1923. Smith, W. E., Hawaiian Sugar Planfers’ Record, SO, 113-25 (1926). Spencer-Meade, “Cane Sugar Handbook,” pp. 45-62, Wiley, 1930. Tingson, W., Philippine Agr., 20 (1931), in press. Walker, H. S., Compilation of Committee Repts., Philippine Sugar Assocn., 98-101 (1928). Zerban, F . , Planter Sugar Mfr., SS, 171-3 (1915). Zerban, F., Louisiana Agr. Expt. Sta., Bull. 173 (1920).
Canadian Chemical Industry Of the chemicals consumed in Canada last year over 85 per cent were manufactured by Canadian chemical industries. This statement is based upon an official preliminary report which sets forth the status of the industry in 1930. The output value of the chemical and allied industries of Canada last year is placed at $122,266,852. The imports of chemicals and allied products during the same period amounted to $36,785,050, and the exports to $16,320,506. Of the imports of chemicals into Canada about 65 per cent were from the United States, 13 per cent from the United Kingdom, 10 per cent from Germany, and 4 per cent from France. Of exports of Canadian chemicals over 55 per cent went to the United States and 20 per cent to the United Kingdom. The chemical industries of the Dominion in 1930 did not reach the high point attained in 1929-the record year since the war. They showed, however, in spite of the adverse conditions so generally felt, a range of activity greater on the average than that of the previous five years, which had been a period of rapid growth. The production of the Canadian chemical industries in 1926 was valued a t $108,500,933. It advanced by approximately $3,000,000 in the next year; in 1928, by $11,000,000; and in 1929, by nearly $15,000,000 additional. I n the lastnamed year the value of the output was $138,545,221. From 1926 to 1930 the increase in production was about 13 per cent, and in the same period the increase in capital investment was approximately 27 per cent-from $133,407,891 to $169,982,605.
The chemical industry in Canada centers to a large extent in Ontario and Quebec. I n 1930 there were 312 establishments in Ontario and the output value in that province was $71,353,476, while in Quebec there were 175 works with an aggregate production worth $38,083,773. British Columbia was third in importance, with 39 plants in operation and an output valued a t $4,919,955. Manitoba came next, with 31 factories and a total production of $3,762,385. Nova Scotia’s 13 establishments produced $2,296,867 worth of chemical products. Seven plants in New Brunswick made goods worth $1,009,897, and Saskatchewan and Alberta together were represented by 13 plants, which had a combined output of $840,499. Several new ventures of importance have recently been made in the manufacture of chemicals in the Dominion. The most recent of these is the construction of a plant a t Toronto for the manufacture of phenol. Quite recently a sulfuric acid and niter cake plant commenced operation a t Sudbury in close association with the nickel-copper industry, while plants designed for the production of fertilizers have been constructed near Montreal and a t Trail, British Columbia. The plant a t Trail is designed to make use of the by-products of the smelter which have previously gone to waste. The sulfuric acid and niter cake plant a t Sudbury carries with it the development of a valuable natural resource in the Province of Saskatchewan. This is the sulfate mine of the Horseshoe Lake Mining Company.
