Purification of Sugar Be t Juices CONTINUOUS CARBONATION AND CLARIFICATION
I
X T H E manufacture of Some of the factors are imestigated which underlie thr obtain n thin juice with niirusucrose ‘from beets, an system of continuous carbonation and clarification, of mal concentrations of 1im1 aqueous extract of sugar sugar beet juices commonly employed in this country. balts and colloidal and colorThe optimum end point for thin juice quality in first and some associated impuriing matter. The result5 of carbonation is determined for both saccharate milk and ties is obtained from the sliced studieq on two phaseb ~ ) f milk of lime defecation. The effects of temperature, roots by a process of menithe process, carbonation auil alkalinity and pH, and juice density on the optimum end brane diffusion. The resultclarification, are reported I I ing “diffusion juice” is defpoint are investigated. Clarification is not economically this paper. There is practiecated with lime and carbon possible at this end point. However, a study of the settling cally no literature on thii characteristics of first carbonation mud gives informadioxide to remove impurities bubject. Much work has betw that would interfere with the tion which may enable operators to approach more nearlj puhlirhed on European mefhconcentration of the juice the optimum end point. Retention time between first ods which, however, involv~ and the crystallization of and second carbonation is found to degrade thin juice batch rathei than continuou~ pure sucrose from it. After quality. When it is not possible to control temperature of carbonation. The ha+ i v first carbonation closely, pOH is a more suitable control being treated with a small nctioni are probably iderii I measure than pH. Alkalinity determined by titration amount of sulfur dioxide, tal in both cases, and tht is the most reliable measure of the correct end point. the defecated “thin juice” is mechani5m of defecation h d i concentrated in evaporators been studied to a certaii and the sugar crystallized extent by Dedek (4) an11 from it in vacuum pans. K. S. SKAARI -4ND R. A. MCGINNIS otheri. Since no publiihcvi Since the lime-carbon diSpreckeIs Sugar Company, Woodland, Calif. descii1)tions have been found oxide defecation is normally of labolatory methods I O I the major purification process studying cwntinuous vsrh bto which the diffusion iuice . . nation, these are described in some detail. is subjected, it is important that the operation of this process he as efficient as possible. The results of incomplete defecation CARBONATION include a thin juice containing excessive quantities of lime salts, For the study of variables which dill FIRST CARBOXATIOX. coloring matter, and other nonsugars. The presence of large riot involve material with characteristic settling rates, carbon:iamounts of lime salts leads to excessive evaporator scaling and tion in batches was found satisfactory. Lime was added t,)) to poor juice-boiling qualities. The quality of the final sugar diffusion juice, preheated to the required temperature, rinti 1 the p H corresponding to the desired end point was reached. Thi, is also strongly affected, since its color and turbidity in solution remaining lime was added slowly from a separatory funnel, thf, are dependent on the quality of the t’hinjuice. mixture was carbonated simultaneously, and the pH was held ai The factory of this company at Woodland, together with the constant as possible. This method produced a material similar to the factory product in all respects except’the settling charact,r%rmajority of the beet sugar factories of the nation, uses a system of istics of the mud. Continuous defecation and clarification2. I n brief, the process For studies in which the settling characteristics were iinporinvolves the continuous addition of lime in the form of milk of tant, a miniature, fully continuous, first carbonation apparatus foi lime or saccharate milk, diffusion juice, and carbon dioxide gas to bench scale te& simulated factory-scale equipment (Figure 1) a first carbonation apparatus. The effluent, which has a pH of This apparatus made a clarifier feed which was similar to thi. factory product in a11 respects. The product of first carbonatioii about 10 (measured at the operating temperature of 80” C.) was stored in a water bath a t the first Carbonation temperatun flows to a Dorr multitray clarifier. The clear overflow is heated for 2.5 hours. The retention time in the Dorr clarifier was deto 100’ C. and is again treated with carbon dioxide (second carsigned to be 2 hours. This somewhat longer interval was mad(. necessary by practical considerations but does not seriousl: bonation) to remove as much as possible of the dissolved lime. alter the test results. The treated juice is filtered in Kelly or similar filters. The SECOND CAxBoh-ArrIoN. The batch method was used. The, filtrate is called “thin juice”. The mud from the D o n darifier liquid removed from the hot water bath storage was quickl: underflow contains about 20% solid phase, which is separated filtered under vacuum in a Biichner funnel through Reeve-Angd KO. 226 filter paper precoated with diatomaceous earth. ‘Thi from the liquid phase by continuous vacuum filters. This filfirst 100-150 ml. of filtrate were discarded, and the remainder trate, including wash water, is termed “sweet water” and is rewas rapidly heated in a Pyrex beaker to 95” 6.while stirring. turned to first carbonation in the milk of lime or saccharate milk. The juice v a s carbonated to the desired p H in slightly less thaii 1.0 minutes, boiled for exactly 2 minutes, and vacuum-filterel! Lime is introduced into the process in the form of saccharate through Whatman No. 40 paper. The first I50 ml. of filt,rilti‘ milk only in those factories incorporating the Steffen process for were discarded, and the remainder was cooled and analyzed a b removing sugar from molasses. rapidly as possible. The correct carbonation end point had pmviously been found by determining the p H a t which the juirc A laboratory study was undert,a,ken of the chief variables contained a minimum of dissolved lime salts. When milk of iinderlying this process to determine conditions necessary to lime was used as defecant, it was necessary to redetermine thca correct end point for every juice, the optimum pH varying from 1 Present address, Basic Magnesium, Inc., Las Vegas, Nevada. 7.8 to 8.7 a t 95” C. When saccharate milk was used, tho 2 Essential features of this process are covered by patents controlled by point was found t o be more constant at 7.5-7.6 pH a,t 95” C. l’etree and Dorr Enpineers, I n c . c t n r l
574
INDUSTRIAL AND ENGINEERING CHEMISTRY
June, 1944
CLARIFICATION
Tests of the Yettling characteristics of the first carbonation mud were based on the method of Coe and Clevenger (8). By this procedure laboratory-scale tests can be made which predict rather accurately the behavior of the material in full-scale equipment. Later work (5, 6) showed that this procedure will lead to error when a compressible mud is involved. However, the zone of compression is never reached, a t least in the Woodland rlarifier, and thickening in the ordinary sense never occurs. I n any vessel used for settling there will be found layers of mud of every consistency between that of the feed and that of the discharge, although some of the layers may be infinitely shallow. The maximum capacity of the clarifier may be expressed by:
C
=
WR/(F - G)
(1)
where C = capacity, lb. solids/sq. ft./hr. W = weight of clear juice, lb./cu. ft. F = weight ratio of fluid (solid-free liquid) to suspended solids in layer considered G = weight ratio of fluid to solids in underflow discharge required R = rate of settling of mixture of consistency F, ft./hr. The capacity of the clarifier for any material will be the smallest value of C obtained by applying this formula to a series of tests made on mud ranging in consistency from that of the feed to that of the underflow discharge, a t a fixed value of G. The detailed test procedure follows: A 1-liter cylinder of the material is placed in a constant-temperature air bath equipped with a glass door. Holes in the bath permit stirring, withdrawal of liquid by suction, etc., without opening the door. Close control of temperature ( =t1O C.) is necessary to minimize convection currents which disturb settling. The mixture is stirred thoroughly with a large rubber stopper on the end of a glass rod. After the solids have settled about l/g inch, the precise level is noted and an interval timer started. At the end of 2 minutes the height of the solids layer is again measured, and 400 ml. of clear solution are withdrawn from the cylinder. The remaining material is stirred and again observed while settling for a 2-minute interval. Then 200 ml. of clear solution are withdrawn, and settling is again observed for 2 minutes; 125 ml. of clear solution are withdrawn, and settling is observed for 3 minutes. A pyc-
575
nometer density determination is now made at 20" C. on'the original mixture, the contents of the pycnometer are filtered through an asbestos pad in a Gooch crucible and the solids are dried a t 110" C. for 1.5 hours and weighed.. The R:D.S. (% refractometer dry substance) of the clear juice is determined. The following terminology is used in the calculations: e = sp. gr. of clear juice a t 20/20° C. (7) d = sp. gr. of feed liquor (from pycnometer determination) s = suspended solids in feed (from pycnometer and gravimetric analysis), % j = sp. gr. of suspended solids, determined from:
j
1OOe
- ddes(100 - s)
The terminology for volumes and weights of suspended solids and juice in 1 liter of feed a t the experimental temperature (80" C.) is: g = volume factor for juice, 20-80" C. (8) m = volume of liquid phase, given by:
m= 1000
-
g j (1 s / l O O ) 1000 g j (1 - s/lOO) (se/100)
+
-
m = volume of solids em/g = weight of juice nj = weight of solids
The percentage of suspencledrsolids and ratio of fluid to soli& in each of the settling mixtures are then readily calculated The rate of fall in each case is converted to feet per hour, and formula 1is applied. For more practical comparisons the weight of dry mud to be handled (pounds per hour) may be divided by C to give the square feet of clarifier area required. The final test results are customarily shown by plotting a curve of t h e clarifier area required against F . By this test ( a ) comparisons may be made of the settling characteristics of various classifier feed materials; (b) the clarifier area required to clarify a given material may be calculated, for a given amount of solids to be handled and a fixed discharge ratio; ( c ) the discharge mud ratio to give satisfactory clarification under fixed conditions of clarifier area and amount of solids may be calculated; ( d ) the amount of suspended solids that can be handled satisfactorily by the clarifier under fixed conditions of area and discharge ratio may be calculated. PREPARATION O F REAGENTS
LIME FEEDER
DIFFUSION JUICE. During the operating season the juice was obtained from the factory, filtered through cloth, and cooled to room temperature by pouring through a heat exchanger. No apprec i a b l e deterioration w a s noticed within 2.5 hours a t t h i s t e m p e r a t u r e . When k e p t for slightly longer periods, itwas cooled to 10' C. When the factory was not operating, diffusion juice was prepared from dehydrated beets with a miniature diffusion battery. It was found inadvisable to aerate the juice unnecessarily, since lowercolored thin juice is obtained under such circumstances (6). If one sample is aerated more than another, the results may be misleading. S A C C H A R A T EM I L K .
Figure 1. Bench Scale Apparatus for +perimental Work on Continuous Carbonation
Weighed amounts of saccharate cake and sweet water were mixed. Saccharate cake was made by mixing 1 part of cake from the hot stage of the Steffen process
INDUSTRIAL AND ENGINEERING CHEMISTRY
5'26
O F .kLKALIXIl'Y TABLEI. INFLUENCE
ASD
FIRSTC A R B O N h T I o N
,-l a c carbonation
R.D.S., diff. juioe
E a l i n i ty Thin Juice .4lkalinity R.D.S. Lime sit1t.s
pH O f F I R S T ' C A R B O N A T I O N dL' # r U I C L n ITH SACCHARATE: MILK
AT
13.8 9.90 0.067
13.8 10.12 0.093
13.8 10.27 0,139
0.009 14.1 0.115
0.009 14.2 0.088
0.008 14.55 0.051
13.8 10.37 0.151 0.006
14.25 O.OS4
Test No, 1
R.D.S., diff. juice PH Alkalinity Thin juice Alkalinity K.D.S. Lime salts Color (-log Tbi
c., l . S - H R .
13.8 13.8 13.8 13.8 9.78 9.02 10.05 10.13 0.062 0.085 0.114 0.163
12.0 10.23 0.146
0.014 12.9 0.054
12.75 0.055
0.013
14.5
0.378
PH Alkalinity Thin juice Alkalinity R.D.S. Lime salt5
14.4 9.68 0.082
...
15.2 0.143
1' 80'
11.2 14.75 0.098 U.136 . _ . 0.372 0 . 4 1 2 .
I -
0.011
0.012
13.95 0.046
13.2 0.035
0.012 13.35 0.102
13.6 10.09 0.108
0.014
0.011 13.7 0.072
IIBBOHE S E C O N I ) CARBOXATION
so,3--"-.
No 4.-
_"_
-
13.7 1 3 . 7 13.i 9.92 10.02 10.08 0.116 0.169 0.181
13.2 13.2 13.2 13.2 9.80 9.93 10.03 10.12 0.095 0.119 0.143 0.181
0.009 0.008 0.009 13.7; 13.9 13.4 0.070 0.075 0.077 0.2'39 0.304 0.341
0.015 0.015 0.013 0.013 13.6 13.4 13.0 13.2 0.076 0,053 0.046 0.065 0.364 0.336 0.303 o ,7411
!JO"
IIIFOBE
--
, /
SECUND CARBONATION
--.
14.4 9.71 0.106
14.4 9.82 0.154
14.4 9.94 0.279
13.3 9.54 0.080
13.3 9.66 0.110
13.3 9.77 0.145
13.3 9.84 0.188
0.012 15.35
0.013 1 4.8 0.102
0.013 14.95 0.173
0,013 13.95 0.081
0.013 13.9 0.060
0.015 13.8 0.061
0.015 13.6 0.097
0.111
13.6 10.35 0.308
13.6 9.99 0.077
.- l e s t Nu.2
' ~ ' I u B ; .\'I
13.6 10.19 0.141
12.0 10.60 0.277
Test
0 013
. , ...
-
Twt Nu. 8----
*
12.4 0.088
_-
.-
. . . 0,013
-
1 1
R.D.S., diff. juice
12.6
0.060
TI>!*: .3
REPENTION
FIRSTC A X B O N A ~ I,\r ON 80" C., 2.5-HR. XwrmvrIox lat carbonation
0.014
0.015
No 2 .
0.105
---
BEFORY: S E C O N D C A R B O N A T I O N
12.0 10.39 0.212
14.6 14.6 14.6 34.t; 9.86 9.97 10.10 10.17 0,101 0.128 0.176 0 . 3 1 0
0.012 0.014 0.014 0.014 14.4 14.8 14.25 14.00 0.104 0.081 0.057 0.057 0.423 0.426 0.364 0.3:O
l e s t No. 1
70'
Tect No. 2
12.0 10.08 0.114
,--'rest
90" C. ONLIME SALTS JLVD COLOR OF THIN
AND
DEFECATION
T I V E 4T
7 -
FIRST~ . 4 X < B U X ~ \ T I O AX T 80" -_.-
1st carbonation
c., 2.5-HR R E T E N T I O X
70'
Test No. l-------
70°, 80",
Yol. 36, No. 6
._ T
~
12.6
~ J No. , 3.
. ..
9.63 0.087
12.6 9.74 0.111
12.6 9.80 0.118
0.012 13.1 0.111
0.011 12.6 0.093
0.012
13.1 0.089
~~
12.6
9.84 0.164 0.011 12.25 0.134
CARBONATION WITH SAME SOURCBOF MATERIALS AT 7 0 ° , SOo,A N D 90' C., FOLLOWID BY 1.6-HR. RETENTION TIbrZ A T S A M E TIMP. A 8 FIRST CARBONATION -----Teat
1st carbonation R.D.S., diff. juice Temp., C . Ealinity 'Thin juice Blkalinity
R,.D.S.
Lime salts
Color
12.0 70 10.40 0.132 0.014 12.35 0.066 0,352
No. 1--I. 12.0 80
---.
___ Test NO. 2-----
0.134
10.06
12.5 70 10.38 0.139
12.5 80 9~93 0.136
12.5 90 9.78 0.133
0.014 12.65 0,080 0.364
0.012 12.65 0.120 0.412
0.013 13.1 0.023 0.280
0,012 12.9 0.037 0.296
0.013 12.8 0.043 0.342
w t h 5.6 parts of cake from the cold stage. The two cakes were made into a slurry with a minimum amount of water, mixed thoroughly, and filtered under vacuum. The resulting cake was mixed with sweet water immediately before use in such proportion as to give 9.3% CaO in the saccharate milk. MILK OF LIME. Burned lime rock was slaked and made up t o a 30' Brix suspension with water. CARBONATING GAS. Pure carbon dioxide was used instead of the 35% kiln gas utilized in factory-scale operation. Many types of laboratory gas distributors have been tried, the one preferred consisting of a b/ie-inch rubber tube plugged at one end. Year this end about forty holes were made with a No. 100 needle. Two of these distributors were w e d in first, and one in second carbonation. ANALYSES
ALKALINITY. Carbonation end points were measured by alkalinity as well as pH. First carbonation juice was filtered for exactly 1 minute by gravity through Reeve-Angel KO. 226 filter paper, and 20 ml. of the filtrate were titrated with 0.0357 N
TABLE 11. INFLUENCE OF ALKALINTYAND pH c--I_
I a t carbonation
!iEalinity Thin iuice .iKaiinit).
R.D.S.
Limesalt& Color
--
-
12.0 90 9.75 0.133
sulfuric acid to a phenolphthalein end point. Thr number of milliliters of acid divided by 200 gives the alkalinity in grams CaO per 100 ml. of filtrate. The alkalinity of second carbonation was determined by titrating 20 ml. of the thin juice. LIME SALTS. 50 ml. of thin juice, cooled to 20' C. and made alkaline if necessary with dilute ammonia, were titrated with standard soap solution. After a blank correction was made, the following formula was used:
ml. soap solution 5d (R.D.S.) where d = density at 20' C.
- % CaO 011 I
R.ll.8
COLO~Z. 115 a measure of color the negativc logsridhm oi the transmittancy, Tb, of blue-green light through 5 em. of a 10 R.D.S. solut,ion was used. The filter was Corning No. 428, 3.4 mm. thick. Double distilled water was used as a standard. The 10 R.D.S. thin juice samples were freed irom turbidity by filtration through specially prepared asbestos (1). HYDROGEN-ION CONCENTRATION. For measurements at high temperatures, a Beckman apparatus (National Technical Laboratories) was used. A glass electrode No. 8990 and a saturated calomel electrode KO.8970 were placed in the carbonation liquors. The readings obtained from a Model F laboratory pH meter with temperature compensator set at 25" C. were corrected to pH a t the working temperature with the aid of a nomograph (9). The electrodes were checked with a 7.0 pH buffer solution. It was found necessary to preheat the eleclrodes before use to minimize error due to hysteresis of the calomel electrode The values reported here are estimated to have a
FIRST CARBONATION AT 80' C. O N LIXE SALTS AND COLOR OF THIKJUICE WHEN DIFFUSION JUICE R.D.S.IS VARIED&
OF
12 X.D.S. Diffusion'Juice, 12.7% CaO on R.D.S,b--Continuous Carbonation
Simultaneous liming and carbonation in batches
l___--ll_l_ll___.
-24 R.D.S. Diffusion Juice, 12.7% CaO on &.!>.S.b-Simultaneous liming and
Continuous carbonation
carbonation in batch-
_ S _ l _ _ -
9.71 10.00 9.96 9.88 10.00 10.09 0.046 0.071 0.0840.089 0.107 0.125
9.82 9.97 10.08 10.1410.19 0.051 0.0780,1140.122 0 . 155
9.52 9.60 9.68 9.80 0.085 0.086 0.090 0.140
9.52 U.79 9.92 9.96 0 . W 4 0.092 0.1380.162
0.011 0.012 0.010 0.011 0.010 0.011 12.0 11.65 11.5 12.2 11.6 11.6 0.069 0,0080.018 0.006 0.008 0.020 0.656 0.429 0.334 0.278 0.237 0.307
0.012 o.011 0.011 0.011 0.010 12.1 11.9 11.9 11.9 11.8 0.011 0,0080.015 0.016 0.029 0.611 0.308 0.286 0 . 3 1 2 0.407
0.018 0.0180.017 0.017 20.6 20.9 22.3 22.35 0.010 0.006 0.004 0.007 0.592 0.568 0.533 0.251
0.016 0.017 0.015 0.016 2 0 . 8 20.6 20.5 20.3 0.004 0.004 0.003 0.004 0.7540.4180.199 0.198
Dried cossettes were used as a source of diffusion juice. In form of milk of lime used for defecation.
INDUSTRIAL AND ENGINEERING CHEMISTRY
June, 1944
total error not greater than 0.1 pH, due to some hysteresis and alkali-metal-ion error; the latter is approximately constant a t -0.06 unit. Error due to hysteresi8 may be of the order of 10.05.
RESULTS. Among the factors affecting the quality of the defecated juice are: concentration and composition of diffusion juice, amount and composition of defecating agent, pH and alkalinity, temperature, and retention time in the system. I n this work the lime addition was based on the R.D.S. of the diffusion juice. When saccharate milk was used, 18% CaO on R.D.S. of diffusion juice was added; this is about 3.5% CaO on beets. When milk of lime waa used, the addition was held to 12.7% CaO, which is closely equivalent to 2.5% CaO on beets.
S?7
The relation between color of thin juice and'alkalinity of first carbonation a t 80" C. is illustrate$ by Figure 3. The plot of experimental values was made in the manner described above. The optimum alkalinity appears to be slightly higher than for lime salts. These data indicate that factories normally holding first carbonation between 0.070 and 0,080 alkalinity could reduce thin juice lime salts about 50% and color 20-25% by operating a t the optimum alkalinity, assuming that settling and filtration vere possible.
.Sob
Lz
o TEMP I S T C A R B . 8 0 2 . APPR. CURVE SO'
--
0:
FIRST CARBONATION
OPTIMUMCONDITIONS WITH S A C C H A RMILK. A ~ For maximum lime salts and color elimination, a higher first carbonation pH and alkalinity is required than is practical with the usual operating equipment. At 80" C. the optimum pH is about 10.0 (alkalinity about 0.130). This alkalinity is too high for satisfactory settling in a factory clarifier of the usual size. The optimum pH varied with every juice tested, whereas a surprisingly constant optimum alkalinity was found near 0.130.
.080 .I20 .I60 ALKALINITY OF FIRST CARB.
Figure 3. Effect of First Carbonation Alkalinity and Temerature on Thin Juice Color Saceharate Milk Defecation)
P
OPTIMUM CONDITIONS WITR MILKOF LIME. The work using milk of lime as a defecating agent is less complete. For juices of normal density the optimum alkalinity for lowest retained lime salts and color is about 0.100 a t 80" C. Figure 4 and Table I1 illustrate typical relations between alkalinity, lime salts, and color. Also shown is the effect when the concentration of the solids is increased in carbonation. Lime salts are more completely eliminated by increasing the diffusion juice concentration, and elimination is influenced less by the alkalinity of firstzcarbonation. The optimum point for maximum color removal is increased from approximately 0.100 to about 0.135 alkalinity]eby increasing the dissolved solids in carbonation from 11.5 to 20.0%.
I I
c
1 x 1
I
I
I
I
I
I
I
1
1 ALKALINITY
OF FIRST CARBONATION
.Figure 2. Effect of First Carbonation Alkalinity and Temperature on Thin Juice Lime Salts (Saccharate Milk Defecation)
i
I
--
THIN JUICE R.D.S. 0 12 x 24
Figure 2 and Table I illustrate the effect of f i s t carbonation alkalinity upon thin juice lime salts. For clarity the curves from several tests are superimposed so that the minimum points are brought to the same lime salts values. Straight lines drawn through the points on either side of the optimum intersected near 0.130 alkalinity. The original points were multiplied by factors which would give these points of intersection lime salts values of 0.045,0.059,and 0.082 for first carbonation temperatures of 70", 80°, and 90" C., respectively. These values were experimentally determined by carbonating one juice as close to the optimum alkalinity as possible at the temperatures given. Increase in temperature from 70" C. increased the lime salts content of the thin juice considerably. The same effect is noted with color. Unfortunately clarification and filtration are more difficult a t lower temperatures.
ALKALINITY OF FIRST CARBONATION
Figure 4. Relations between First Carbonation Alkalinity and Thin Juice Color and Lime Salts (Milk of Lime Defecation at 80" C.)
1
INDUSTRIAL AND ENGINEERING CHEMISTRY
578
Vol. 36, No. 6
CLARIFICATIOY
L)ECR DATION OF JUICE BY TIim IN CLAHIBWH('larifier feed samples, defecated with paceharate milk, were beparated into seveial parts. One part was taken through second carbonation immediately; the others were held for increasing intervals before second carbonation. A plot of lime salts and color increases in thin juice against retention time is presented in Figure 6. The alkalinities of the feed samples varied from 0.078 to 0.107 with an average of 0.089. More complete data are given in Table 111. Increases of approximately 7% in color and 0.010 in lime salts per hour are indicated for juice defecated with saccharate milk. Some of the feed samples were filtered before storage and others were not. Xo apparent difference in tht, rate of lime salts and color increase resulted. I t is possible to give a percentage increase in color but not in lime salts. The increase in lime salts was independent of the total amount present in the control sample and, apparently, is chiefly the result of reactions between lime and materials introduced in the saccharate milk. It is obvious from low values in Table I1 and Figure 4 that the lime salts content of normal juice defecated with milk of lime had not increased much in the rlarifier.
10.5
6 10.3 b-
9
0 ffi
CL Q 10.1 (J
+ a:
9.9
1;
r, 9.7
.I20
,080
'
"
"
00'
"
"
"
SO'
.I60
e9
28
om
E
2.6
.BO.
240
.ZOO X
=
4
0 0
1
TEMP IST CARB.70'C.
V
b10
a: iL
2.4
1; r
X
2.2
.OB0
I
I
I
1
I
1
I
I
.I60 -200 .240 ALK4LINITY OF FIRST CARBONATION
'I
.I20
I .280
Figure 5. Kelation between pH or pOH and Alkalinity of First Carbonation at Various Temperatures (Saccharate Milk Defecation)
CONTROL. Changes in temperature of first carbonation shift the optimum pH by an amount equal, within the limits of error, to ilpK,/At, where pK, is the negative logarithm of the dissociation constant of water. Beet sugar factories controlling carbonation by p B and having fluctuating temperatures probably would have a more satisfactory control if their instruments were calibrated to read pOH and were equipped Rith appropriate temperature compensators. Plots of first carbonation alkalinitp and pH and of alkalinity and pOH (Figure 5 ) illustrate the advantage. High-temperature glnbs electrode5 have given the sugar illdustry its most reliable means for measuring pH. However, ignoring the influence of temperature, in the factory they cannot he relied on to be more accurate than 0.1 without excessive atttirition being paid t o the equlpment. This rorrespondi to 0.020 alkxhniiy in the normal operating range. Thus alkalinity must be regarded ab the niost reliable ciitenon tor control of first carbonation. Alkalinity determinations can be used in conjunction riith pH control in many fnctories t o good advantage
TAB1.F
111.
I 2 3 VOURS RETENTION TiME AT 8 O Z . B E T W E N
FIRST AND SECOND CARBONATION
Figure 6. Effect of Time irr Clarifier on Thin Juice Qualit?
EFmcr OF A L ~ C ~ L I N Iox T YSETILING. The clarifier teed* used in thehe tekts ueie prepared in the coiititiuous carbonation apparatub. Saccharate milk was used for defecation. Ln the calculation of the required clarifier areas, it is assumed that 14,000 pounds of mud were handled per hour, with a ratio of underflow fluid t o solid of 4.36 (42.5' Hlix at 80" C.1. Dattt are shox ii in Figure 7 . Similar effects are 3hown lor milk of lime defec.ation (Figure 7) I n there tests it is assumed the clarifier handles 8900 pounds of mud per hour, with a n unclerflow ratin of 5 5 (37.5' Brix a1 soo C.).
l N C E E A S X 1iS T~lIvlb: SAI,TS AND COLOR O F THINJCICEC A U S E D BY RETENTION AT 80" C ~ R B O N< n o s WHENDEFECITIN(: WITH SACCHARATE MILK
Test No. Retention time. Iir. i s t carbonation
,-.---1---0
r--Z-.--
1.55
Ealinitg o.Osi 0.082 Alkalinityjust before2ndrarbonstion 0.082 0.073 Thin juice Alkalinity 0.014 0.011 R.D.S. 13.9 13.4 Lime salts 0.045 0.063 Color 0.355 0.394
n
o.Oii
0.091
,--
1 0,oii 0.080
0,014 0.011 13.75 13.7 0.038 0,049 0.332 0.344
0
o.Os8 0.088
___ 2.47
3 1.67
--.-4.~.~.----
"
o
FIRSTANI) .
fhCONI>
----. 1.63
j.
0
0.93
2.48
9.99 0.107
9.99
0.105
0.107 0.103
0.678 0.678
0.013 0 , 0 1 3 13.9 13.9 0.031 0.035 0 . 2 7 1 0.304
0.010 13.85 0.044 0.299
0.012 0.011 0.010 0.011 12.7 12.8 12.8 12 8 0.279 0 . 2 8 8 0.294 0.321 0.392 0.418 0.436 0.480
9.90
9.90
0.088
0.088
9.99 0.107
0.082
0.074
0.107
0.012 0.009 0.009 14.1 14.2 13.3 0.034 0.047 0.054 0.291 0.334 0 355
c. B E T W E E N
0.078
0.83
0.074
3.62
0.078 0.078 0.070 0.070
INDUSTRIAL AND ENGINEERING CHEMISTRY
lune, 1944
579
P
I
2 2 .-
18
.-
14
.-
I
I
I
-ALKALINITY .072 __-' .os0
I
1'
-
IO.
-
I .
6.
I 100
300
900
700
500 SQUARE
FEET
1100
1300
1500
100
1700
Saccharate Milk Defecation
I
I
I
I
-
I
I
I
1 I
___
I
I
I I -
I
i
r
I I I
1
MILK ADDED TO MIXTURE BEFORE SETTLING
-
-
\
b\
-
\
-
\
-
ALKALINITY \O .076
0
ALKALINITY .I03
100
Figure 8.
300
500 100 500 700 900 SQUARE FEET CLARIFIER AREA REPUIRED
.
added. . The most satisfactory reagent is cow's milk. For practical large-scale use, dried skim milk is low in cost and very effective. It is put into solution and added to the clarifier feed in the proportion of 1 pound dry skim milk to 4500 gallons of clarifier feed. Alkaline solutions of casein have a similar but much less marked effect. The effect of adding cow's milk is showa clearly in Figure 8. When the settling curve is type A , the clarifier area required is greatly decreased. With a type C curve there is no decrease. The effect is almost entirely on the settling rates i n the materials with the high ratios of fluid to solid. Since with type A curves these rates control the area required, the use of milk gives a striking result. I n it type C curve the rates in the high ratio materials are similarly decreased; but since the required area is determined by the rates in the materials having the lower ratios, there is no beneficial effect. Since the clarifier area requirements of materials having type A settling curves are generally
YI
'\
500
REQUIRED
type C curve. Thus the over-all effect of increming the alkalinity is at first an increase in required area, followed by a slight decrease during the type B section and finally by a strong increase. I n general, it seems that, with saccharate milk defecation, under 0.073 alkalinity the type A curves are found; between 0.073 and 0.085, type B; and over 0.085, type C, although these limits cannot be fmed with any precision. As the R.D.S. of the diffusion juice is increased from 12, these limits are raised and are likewise found to vary with juice type. From these and other data not given here, the conclusions have been reached that (n) the relative alkalinity determines the shape of the settling curve; (b) the absolute-alkalinity required to give any curve shape is a function of such variables as the juice type and the juice R.D.S.; and (c) while in general the clarifier area required increases with the alkalinity, this does not hold strictly true while the curve is in the transitional type B stage. MODIFICATION OF SETTLING CURVES. If it is desired to improve the settling of materials having type A settling curves,
0
0
-
I
400
Milk of Lime Defeaation
Effect of Alkalinity on Settling Curves
These two sets of data illubtrate the effect of alkalinity on the Jettling curve. At the lower alkalinities the clarifier area required is determined by the initial rate, or by the rate of clarification of the feed material with its original ratio of fluid to solids. For convenience this type of curve is termed A . With high alkalinities the clarifier area required is determined by the mixtures with the lower ratios of fluid to solid. This type of curve is termed C. At intermediate values of alkalinity the curves are of a transition type termed B, where the clarifier area required may be determined either by the initial rates or by the rates in the mixtures haying the lower ratios of fluid to solid. If the settling curves of a series of samples carbonated to increasing alkalinities are compared as to clarifier area required, a t the lowest alkalinities type A curves prevail, with low clarifier area requirements. As the alkalinity is increased, the whole curve starts to pivot around a central point. The higher-ratio area requirements decrease and the lower-ratio area requirements increase until the type B curve is encountered. At still higher alkalinities the lower-ratio area requirements predominate in the
1
300
SQUARE FEE T CLARIFIER AREA
CLARIFIER AREA R E W I R E D
Figure 7.
200
1100
Effect of Adding Cow's Milk to Clarifier Feed on Type .4 and C Settling Curves
580
INDUSTRIAL AND ENGINEERING CHEMISTRY
low, there is w u d y no use for such a reagent unless the clarifier is operated greatly over capacity. No reagents have been found which have a similar effect on the settling rates in mixtures with low ratios. The pSesence of grits, or sandlike material, has a slightly beneficial effect. IN FLUE KC^ OF CLOUDYOVIRFLOW. Within the limits of experimental error, lime salts and color in the thin juice increased in proportion to the amount of suspended solids in the second carbonation feed. With 0.1% suspended solids, there was a p proximately 0.005 increase in lime salts and 6% increase in color. This amount of suspended solids corresponds to a Kopke clarity reading of about 3. A slightly cloudy clarifier overflow will probably do much less damage to the thin juice than will carbonation a t a lower alkalinity than neoessary. This is substantially in agreement with the results of Stanek and Pavlas (10). CONCLUSIONS FROM EXPERLMENTS
The conclusions apply particularly to California beet juices and to the type of continuous defecation and clari6cation under study: 1. In first carbonation with saccharate milk defecation, the best quality thin juice, as judged by lime salts and color content, is obtained a t low temperatures (at least 70" C.) and at a n alkalinity of 0.130. 2. The lime salts content of the thin juice is increased about 0.010 per hour and the color content about 7% per hour by retention a t 80" C. between first and second carbonation. 3. Titratable alkalinity is the most reliable end point measurement in first carbonation control. The optimum alkalinity for best thin juice quality was found to be nearly constant a t 0.130 in saccharate milk defecation. This value was practically unaffected by such variables as type and concentration of juice or carbonation temperature (at least in the range 70-90" C.). Clarification is not economically possible at this alkalinity. The measurement of pOH should be superior to pH in controlling first carbonation in that errors caused by the pH temperature coefficient are avoided. 4. When defecating with milk of lime, the optimum alkalinity in first carbonation is about 0.100 at 80" C. Increasing the concentration of the diffusion juice raises the optimum alkalinity. 5. The difficulty of settling the first carbonation mud increases, in general, with the alkalinity. 6. Under certain conditions, the settling characteristics of clarifier feeds can be improved by the addition of reagents. 7. Lime salts and color in thin juice increase proportionally to the amount of suspended solids in the clarifier overflow.
PRACTICAL OPERATION
With the continuous carbonation system studied, it, is tipparent that in plant-scale practice some sacrifice in thin j u i c ~ quality must be made for clarification and filtration to be performed satisfactorily. While the juice quality is improved by high alkalinities and low temperatures, clarification and filtration are made more difficult. It is apparent that a compromise must be made. At Woodland a medium temperature (SO' C.) ifi cai ried, and alkalinities are kept as high as possible without, preventing clarification. This system of continuous defecation is apparently still capable of improvement. The most complete> defecation will not be obtained until a system is perfected which will permit carbonation at the optimum alkalinity, and still allow satisfactory separation and washing of the carbonation mud. For end point control, the Woodland factory uses an automatic carbon dioxide controller operated by high-temperature glass electrodes. However, frequent alkalinity determination+ are made, and the pH control point is readjusted to give ihe alkalinity desired. Second carbonation control is similar. The recognition of the three types of settling curves for materials in the clarifier enables somewhat more intelligent operation With a known type C curve, the clarification may be greatly improved by lowering the density of the underflow. There is little advantage in this procedure for a type A curve. The advantages of using cow's milk for enhancing settling wlth type A curves were discussed above. ACKNOWLEDGMENT
The helpful supervision of P. W. Alston is gratefully rtcknowledged. LITERATURE CITED
(1) Brewster, J. F., and Phelps, F. P., IND.ENG.CHEM.,ANAL.ED.. 2. 373 (1930). (2) Coe, H.S.,and Clevenger, G. H., Trans. Am. Inst. Mining M r i Engrs., 55,356(1916). (3) Comings, E. w., IND.ENG.CHEM.,32,663(1940). (4) Dedek, J., Facts About Sugar, 34, (Nov.) 42-4, (Dec.) 38 41 (1939). ( 5 ) Kammermeyer, K., IND.ENG.CHEM.,33,1484 (1941). (6) Komers, K., and Coker, K., French Patent 648,450(1928). (7) National Bur. of Standards, Circ. C440, Table 109 (1942). (8) Ibid., Table 119. (9) National Tech. Lab., Circ. 58-4011 (1943). (10) Stanek, V.,and Pavlas, P., L b t y Cukrovar., 52, 313-17 (1934) ,
I
HYDROCARBON GASES. EDWARD G. SCHEIBEL' AND DONALD F. OTHMER Polytechnic Institute, Brooklyn, N. Y .
e
e
Specific Heats and Power Requirements for Compression
T
HE ratio, 7 , of the specific heat a t constant pressure to the specific heat a t constant volume is an important thermodynamic property of a gas, necessary in calculations of its adiabatic compression and expansion. Edmister ( 2 ) calculated the variation of the isobaric specific heat of hydrocarbons by the use of the residual volume quantity which is defined as the deviation of the actual volume from that given by the perfect gas laws. He expressed the thermodynamic equation for the value of the difference between the isobaric and the isometric specific h a t s in terms of the residual volume function (9). I
Vol. 36, No. 6
Present addresr, Hydrocarbon Research, Ino., New York, N. I'.
This ratio is used to calculate the isentropic work of comprehsion or expansion of a perfect gas, for which the ratio is constant with temperature and pressure variations. York (6) showed that, for actual gases, the correlation gives a n increase of y with increasing temperature and pressure; and the use of a mean valnc would increase the calculated power requirement, whereas the work of compression of an attual gas is less than that for a perfect gas. He pointed out that the use of the average y value based on an actual gas cannot be applied to an equation derived for a perfect gas, since all the other thermodynamic properties of the system will also deviate from those of a perfect gas and may
