April, 1928
I N D U S T R I S L A S D EXGINEERISG CHEMISTRY
differs from oxycellulose in that it is soluble in sulfite and yields no furfural. 3-Most of the carbon-dioxide-yielding material is formed during the first chlorination, when 56.6 per cent of the unstable pentosans are rendered soluble in sodium sulfite.
373
4-Carbon dioxide equivalent to 0.86 per cent is liberated from the original wood by boiling hydrochloric acid. 5-There is no danger of forming oxycellulose during the analytical procedure for determining cellulose by the chlorination method.
Effect of pH on Lime Salts and Character of Colloids i n Filtered Juice from Cane Muds' J. C. Keane, M . A. McCalip, and H. S. Paine CARBOHYDRATE DIVISION,BUREAU OF CHEMISTRY AND
SOILS, WASHINGTON, D. C.
T
H E handling of the muds formed during cane-juice It is the usual practice to add lime to the diluted mud prior clarification presents a problem of importance in raw- to resettling, but this procedure was not followed because sugar manufacture. It has usually been approached lime did not increase the settling rate of the muds in question from the standpoint of expediting the disposition of the muds nor did it improve the quality of the mud-tank juice. Howwith as low a sucrose content as possible. One of two general ever, after resettling and decanting the supernatant liquid, procedures is followed, namely-filtration or return of the the mud was treated with a quantity of lime, heated, and muds to the mill. The former is the one more widely em- pumped to a separate filter press. A number of experiments ployed and with which this paper is concerned. The methods were made in which this procedure was repeated with the most frequently followed are thcse that permit rapid filtra- exception of varying the quantity of lime added to the mud. tion and yield a press cake of relatively low sucrose content, Composite samples of each lot of juice mere taken as follows a t the various stages of the but they give less consideraprocedure: (1) d e f e c a t e d tion to the effect that lime j u i c e , f r o m t h e draw-off may have on the filtered The filtration of muds formed by the defecation of valves of the four defecators; juice (which is r e t u r n e d cane juice is an important step in the manufacture of (2) resettled mud-tank juice, either to the raw or the raw sugar. In the effort to obtain a good filtration from the side ~ a l v eof the defecated juice). rate by the addition of excess quantities of milk of mud tanks; and (3) filtered The physical character of lime to the muds, the fact that the percentage of harmjuice, from the press during muds resulting from defecaful impurities-namely, lime salts and colloids-will be the period of filtration. tion varies greatly in pracincreased in the filtered juice by this practice is freThe following determinatice. For instance, some quently overlooked. Considering all factors, it was tions were made on each of muds are quite readily filterconcluded that the muds should be limed to a pH the above samples: Brix, able and form a firm press value not exceeding 7.8, and that the properly filtered purity, pH, CaO, and colcake with the addition of juice may be added to the clarified juice without de:loids by the dye test; in little or no lime, while others rimental effect and sent directly to the evaporators. some instances the quantity are gummy and difficult to of colloidal material was also f i l t e r unless considerable determined by ultra-filtralime or other filter aid is added. This difference in the character of the muds is depend- tion. A quinhydrone electrode, in conjunction with a saturated , ~ used for measent upon variation in certain characteristics of the juice as calomel half-cell as described by D a ~ s o nwas well as in procedure. Although addition of lime to the mud uring p H values. For estimating colloids the dye m e t h ~ d , ~ improves its filterability by altering the physical character specifying the basic dye night blue, was used. This method is of the press cake, it was suspected that certain 'adverse effects based upon the mutual neutralization of the electric charges on result, especially when addition of lime is not properly con- the colloid and dye particles, the end point being determined by trolled. The lack of information on this phase of factory means of an ultra-microscopic cataphoresis apparatus. The operation led the authors to conduct a series of laboratory quantity of dye required t o neutralize exactly the electric and factory experiments relative t o the effect produced on charge on the colloid particles is taken as a measure of the colthe filtered juice by treating the muds in various ways. Atten- loids present. CaO was determined in the ash from 100-cc. tion was also given to the two customary methods of return- portions of juice by the volumetric oxalate method, 0.1 N ing the filtered juice to the process for the purpose of deter- potassium permanganate solution being used for titration. In order to ascertain the relative proportions of the irremining which is the better procedure. versible and reversible types of colloids present in the liquors Methods of Analysis and Procedure a t different stages of the mud-treating process, some of the With the codperation of the factory staff2 four consecu- samples of defecated juice and the corresponding samples tively filled defecators were selected and so segregated that of filtered juice were subjected to ultra-filtration under careafter the defecated juice had been drawn off the muds were fully controlled conditions. The following procedure was dropped into two specially prepared mud tanks as a unit. used: A known weight of juice, containing approximately This mud was diluted with water, heated, and resettled. 200 grams of solids, was filtered with the aid of vacuum through standard collodion membranes. Toluene was used Presented before the Division of Sugar Chemistry a t the 74th Meeting of the American Chemical Society, Detroit, Mich., September 5 t o 10, 1927. The authors desire to express their appreciation of the hearty cooperation received from the officials and operating staff of Central Fajardo, Fajardo Sugar Company of Porto Rico, Fajardo, P. R.
3
Sugav, 28, 211, 262, 310, 369 (1926).
4
Badollet and Paine, Intern. Sugar
J.,
28, 23, 97, 137, 497 (1926),
Planter Sugar M f r , 79, 121 (1927). 6 The technic of preparing these ultra-filters will be described in a forthcoming paper by .I E Dawson, formerly of this division.
INDUSTRIAL AND ENGI NEERING CHEMISTRY
374
as a preservative. When the original volume of juice was reduced to approximately 250 cc., washing was started automatically; maintaining this volume, the liquid above the collodion membrane was washed practically free of crystalloids with 4.5 liters of distilled water. The material remaining on the ultra-filter was then transferred to a suitable vessel and evaporated to approximately 100 cc. on a steam
.CJ I
,Z5 .35
.f5
.55
.65
.75
.85
.95
/05
//5
/25
Cu 0 P€E /00 BX. Figure 1
GRAMS
bath. At this stage 2 grams of specially prepared diatomaceous earth were added, and the liquid was filtered through an asbestos pad in a tared Gooch crucible to separate the irreversible colloids (which had flocculated during ultrafiltration). After washing, the crucible and contents were dried to constant weight in a vacuum oven a t 80" C. After correcting for the diatomaceous earth added, this weight represented the irreversible colloids. The filtrate (containing the reversible colloid fraction) was transferred to a tared silica dish and evaporated to dryness and to constant weight under similar conditions. The sum of the irreversible and reversible portions was recorded as the total colloid content as estimated by ultra-filtration. Single Filtration of Muds
I n factory operation either single or double pressing of muds is practiced, and the considerations involved in adopting one of these methods are (1) the capacity of the filter station, and (2) the relation between the estimated cost of the additional filtration and the sucrose recovered, little or no attention being paid to the impurities returned in the filtered liquors. rlnalyses were made of the juices following both of these procedures. Although the filterability of muds is improved by the addition of lime, it was found that large quantities of lime salts were simultaneously formed. These are detrimental constituents in themselves and, in addition, they were found to be accompanied by a n increased quantity of reversible colloids in the filtered juice, as may be seen from an inspection of the results given in Table I. The relation between reversible colloids (as determined by ultra-filtration of the defecated and filtered juices) and CaO is shown in Figure 1. This increase in reversible colloids which accompanies an increase in lime salts in the filtered juice is attributed to peptization of certain constituents of the mud a t the higher p H values and the formation of small quantities of colloidal lime compounds. The relation of CaO to reversible colloids in defecated juice is different from that in filtered juice, as is shown by the slope of the curves A and B in Figure 1. This might possibly indicate that the smaller excess of lime in the defecatej juice has the greater peptizing effect, due, conceivably
Vol. 20, No. 4
to the presence of a greater quantity of colloids or colloidforming substances in raw juice that had not previously been in contact with excess lime. I n the case of addition of lime to the mud, certain constituents of the juice presumably have already been neutralized and a greater proportion of the dissolved lime remains in free condition, greatly increasing the CaO content of the filtered juice. However, the quantity of reversible colloids formed is relatively smaller than in defecated juice, since a large portion of the material on which the lime may act probably has already been either peptized or firmly enveloped in the precipitated mud. No doubt the temperature and time of contact of the lime in both the defecated and filtered juice influence the relation between the lime salts and reversible colloid contents of the juice. Considering individual samples as recorded in Table I, a considerable variation is to be noted in the analytical data. In the case of the defecated juice the CaO and colloid contents are influenced by the percentage of P205 in the raw juice and the p H to which it is limed. The analysis of resettled mud-tank liquor varies approximately in proportion to that of the corresponding defecated juice, but with slightly higher CaO and colloid values, owing possibly to solution (peptization) of some of the mud caused by lowering of the p H value on standing. It has been established that a portion of the increased acidity is due to decomposition of the Ca3(PO+ of the mud into a soluble acid salt and an insoluble basic phosphate.6 This transformation is accompanied by a slow decomposition of other constituents into compounds with an acid reaction. The CaO and colloid contents of the filtered juice varied more than in defecated juice, being dependent to a great extent on the quantity of lime added to the muds previous to filtration. Table I-Single
Filtration of M u d s
IRREVRR-
DATE
BRIX (2OOC.)
DYE PURITY
P H
VALUE
CaO G./lOOO
Brix
DEFECATED
Feb. 2 3 24 24 25 26 28 Mar. 1 3 7 10 15 26 26 Average
13.40 13.65 13.80 12.45 13.00 14.60 12.85 13.55 14.70 13.65 14.50 14.00 11.40 13.68
80.60 80.44 82.10 80.72 79.08 80.14 77.66 84.13 81.15 80.44 82.69 81.57 82.20 80.89
7.06 7.08 7.08 7.34 7.24 7.24 7.34 7.08 7.10 7.18 7.28 7.40 6.94 7.20
SIBLE COLLOIDS
REVER. SIBLE COGLOIDS
TOTAL COLLOIDS
Grams ger looo B r i x
IUICE
0.451 0.615 0,595 0,624 0.505
1000
0.3573 0.227 0.331 0 . 5 5 8
MUD-TANK JUICE
Feb. 23 24 24 25 26 2s Mar. 1 3 7 10 I5 0 - I 26 Average
11.95 11.40 12.20 10.85 11.10 12.20 11.20 12.95 12.40 11.60 12.50 11.40 11.80
Feb. 23 24 25 26 28 Mar. 1 3 7 10 15 26 Average
11.25 9.05 11.40 11.50 11.65 10.45 12.10 11.15 10.55 12.45 11.75 11.21
a
998 80.68 6 . 7 2 7 9 . 3 0 6 . 8 0 1090 0:3533 6 . 8 6 101.5 82.50 8 1 . 2 0 7 . 1 0 1055 0:3983 885 78.55 6 . 9 5 7 7 . 6 4 6 . 9 2 1484 0:4i30 7 . 0 7 1153 0.5260 77.59 8 1 . 9 3 6 . 8 8 1192 0 . 3 8 6 8 8 0 . 6 4 6 . 7 8 1036 0 . 3 7 3 4 914 0 . 3 3 4 2 79.74 6 . 9 0 8 1 . 0 4 6.00 1181 0 . 3 6 8 2 8 2 . 2 0 6 . 9 4 1133 0 . 3 8 5 1 8 0 . 2 5 6 . 9 0 1095 0 . 3 9 6 4 FILTERED IUICE. FIRST PRESS . ~ - ~ . 7 8 . 5 8 7 . 9 4 IS71 7 7 . 5 7 8.00 1983 1 . 1 9 6 1,449 78,50 8.21 7 7 . 3 9 8 . 1 8 1830 . . . . . 7 6 , 9 0 8 . 0 4 1886 1 . 3 4 0 7 6 . 5 5 8 . 8 8 1745 1 . 5 2 5 7 9 . 5 8 8 . 5 0 1813 1 . 2 3 0 7 9 . 4 6 8 . 8 1 1631 1 . 2 3 0 7 8 . 1 9 7 . 8 2 1592 0 . 7 8 2 7 9 . 6 6 8 . 3 5 1336 0.7430 8 0 . 6 0 8 . 2 4 1381 1 . 0 4 9 7 8 . 4 6 8 . 2 7 . 1707 1.172
....
0.053 0.131 0.122 0.100 0.027 0.087
0.548 0.545 0.427 0.394 0.513 0.485
0.601 0.676 0.549 0.494O 0.540 0.572
Diatomaceous earth used as filter aid.
Paine and Balch, Planter Sugar M f v . , 78, 127, 148 (1927); Farnell, J. SOC.Chem. I n d . , 45, 3431' (1926). 1
INDUSTRIAL A N D ENGINEERING CHEMISTRY
April, 1928
I n general, the colloids by dye test varied in a manner corresponding to the ultra-filtration data. A 6-hour composite sample of factory-run filtered juices, the pH value of which was below 7.7, showed a CaO content of 0.856 gram per 100" Brix and a dye value of 1053, both of which values are considerably below the average, substantiating the conclusion that low liming of muds causes a decrease in the content of both the CaO and reversible colloids in filtered juice. Double Filtration of Muds
In order to reduce further the sucrose content, double filtration of the mud is practiced in many rawsugar factories. To prevent the second-press juice from becoming too acid, and to assist filtration, it is necessary to relime .the muds again just previous to filtering the second time. The data given in Table I1 are average analyses of six 6-hour factory composite samples obtained on 4 separate days while operating by this method. It may be noted that the average purity of second-press juice is approximately 9 points below that of the corresponding first-press juice, while the CaO content is almost doubled and is seven times greater than that of the corresponding defecated juice. Unfortunately, it was impossible to obtain a measure of the colloid content of the second-press juice, owing to lack of time for the ultra-filtration of the diluted liquors and the apparent inapplicability of the dye test to this type of juice. However, it seems probable that the relation between CaO and reversible colloids established from data on first-press juice applies as well to second-press juice, and a further increase in reversible colloids when double pressing of muds is practiced would be expected. It is therefore debatable whether the additional recovery of sugar offsets the deterimental effect of the impurities that enter the process during double filtration. As shown previously, the increase in lime salts is accompanied by an increase in reversible colloids, both of which cause additional difficulty in working the low-grade sugar products. DATE
Table 11-Double Filtration of M u d s PURITY PH D Y E V A L U E CaO
BRIX (200 C.)
C./lOO" Brix FIRST PRESS IUIC&
Feb.26 Feb.28 March 1 March4 Average
11.35 10.95 10 90 11.35 11.14
Feb. 26 Feb. 28 March 1 March 4 Average
2.95 3.40 2.10 2.30 2.69
79.90 80.00 76.70 77.88 78.62
7.80 8.14 7.70 8.40 8.01
SECOND PRESS IUICB
69.20 69.10 73.00 68.70 70.00
7.80 8.27 7.95 9.20 8.31
2360 2469 2637 2444 2478
1.33 1 30 1.45 1 64 1.43
..
2.60 2.30 2.47 2.53 2 48
.. ,.
.. ..
Filter Aid in Mud Filtration
Having shown the deleterious effect of the action of lime on the muds, the advantage to be gained by decreasing the quantity of lime used a t this station is evident. An experiment has shown that diatomaceous earth has possibilities as a substitute for a large portion of the lime required to obtain a satisfactory rate of filtration. Filtered juices from muds treated with diatomaceous earth and a little lime were analyzed and found to be comparatively low in lime salts, reversible colloids (by ultra-filtration), and total colloids by the dye test. Calculating the data pertaining to the sample of March 15 (Table I) on the basis of 100" Brix, it will be noted that the content of CaO was 0.743 gram and that of the reversible colloids was 0.394 gram, compared with an average CaO content of 1.225 grams and an average content of reversible colloids of 0.508 gram in juices from muds limed in the usual manner and having approximately the same rate
375
of filtration, but to which no diatomaceous earth had been added. Further investigation of this procedure is necessary, however, in order to determine whether greater ease of handling the sugar end products and any increased yield would justify the additional cost of the filter-aid required. Method of Returning Filtered Juice to the Process
Having shown that excess lime added t o the muds increases the quantity of CaO and reversible colloids in the filtered juice, the question arises whether these detrimental substances can be eliminated to any material extent in cases where the filtered juice is added to the raw juice and redefecated. This procedure, which is followed in many rawsugar factories, was duplicated in a number of laboratory experiments. In order to reproduce as nearly as possible the procedure of returning filtered juice to the raw juice and redefecating, 15 parts by volume of a previously analyzed filtered juice were added to 85 parts by volume of an analyzed raw juice. This mixture was defecated simultaneously with another portion of the same raw juice which contained no filtered juice, both samples having been limed to the same pH value. The theoretical analysis of the mixture before liming was calculated from the analyses of the filtered and raw juices. The resulting defecated juices were likewise analyzed, in order to make a comparison of the relative efficiency of the two methods of returning the filtered juice to the process. The results indicated that about 20 per cent of the CaO present in the filtered juice reacted with the constituents of the raw juice and thus decreased somewhat the quantity of lime required to bring the latter to a given p H value, while 80 per cent remained in solution during defecation and increased accordingly the CaO content of the resulting defecated juice. Comparing the two procedures from the standpoint of lime salts-i. e., one allowing the filtered juice t o pass directly to the evaporators and the other returning the filtered juice to the raw juice and redefecating-calculations showed that the CaO content of the juice entering the evaporators was reduced about 7.5 per cent by redefecating the filtered juice. This redefecation does not, however, cause a decrease in the quantity of colloidal material, since the calculated quantity entering the evaporators is practically the same in both procedures. This lack of improvement is also noted in the apparent purity, there being no change. These results indicate that colloidal material produced in filtered juice by the action of lime on the mud is not removed by further lime defecation. General Conclusions and Summary
The nature of the settled mud from the defecation of most cane juices is such that its filtration presents a difficult factory problem. The filterability varies greatly, and the addition of lime as an aid to filtration is almost universally practiced. It has been shown that certain objectionable substances-namely, lime salts and reversible colloids-are produced in the resulting filtered juice approximately in proportion to the quantity of lime used. Because these substances affect adversely the boiling-house efficiency, their prevention so far as possible is of importance in raw-sugar manufacture. Therefore, it is advantageous to use only sufficient lime to obtain an acceptable rate of filtration, and to add this amount after resettling the muds previous to filtration. This necessitates the exercise of a close control of the liming of the muds. An hourly determination of the pH of the filtered juice might suffice, but an occasional determination of CaO in composite samples of filtered juice should be made to serve as a check on the indirect method. Since reducing the quantity of lime decreases the rate
INDUSTRIAL A N D ENGINEERING CHEMISTRY
3 76
of filtration, it is necessary to establish a practical mean between a poor filtration rate and excessive formation of objectionable substances. It is believed that with the proper supervision most muds can be filtered with a resulting juice having a p H value not exceeding 7.8, and with many muds even less lime can be used. It has also been pointed out that double pressing of muds further increases the impurities entering the process. However, calculated on a solids basis, the quantity of material that may be redissolved in the second filtration is so much less than in the first that the benefits to be derived by careful handling of the muds a t the first press station can be readily seen.
VOl. 20, No. 4
Likewise, the data indicate that, while a portion of the lime is utilized when the filtered juice is returned to the raw juice, the colloidal material (reversible colloids) formed in the filtered juice is not eliminated during redefecation. The quantity of filtered juice is about 15 per cent of the total juice; therefore, when the filtrate is returned to the raw juice the defecation capacity is, of necessity, reduced, and it is a question whether the benefits derived are sufficient to offset this loss in capacity. When, however, with good filtration, the resulting juice is maintained a t a p H near that of the defecated juice, its addition to the defecated juice appears to be the better practice.
Viscosity and the Ice-Cream Mix’ G . D. Turnbow and K. W. Nielson UNIVERSITY O F CALIFORNII, D - ~ v r sCALIF. ,
I
T HAS been considered desirable that an ice cream mix show a viscosity between certain limits and much has been written concerning the proper processing, aging, and methods of handling in order that it should possess and retain this viscosity. Obviously, a certain amount of true viscosity will be derived from the components in solution in the mix, which would affect viscosity only from the points of temperature and concentration. The true viscosity depends largely upon the composition of the mix.
milk solids-not-fat, 15.5 per cent sugar, and 0.35 per cent gelatin. The mixes were pasteurized in a glass-lined vat a t 63” C. and homogenized a t the same temperature and a t a pressure of approximately 1133 kg. per sq. cm. The pressure was varied slightly with the acidity, in order to obtain for a uniform composition a uniform viscosity for the fresh mix. ACIDITY P e r cent
Development of Apparent Viscosity
Present standard procedure calls for the aging of the mix from 24 to 48 hours a t 1.1’ to 4.4” C. There develops during this period a colloidal viscosity due to the formation of a gel structure known as “apparent viscosity.” Ice-cream manufacturers believe that this apparent viscosity is necessary for proper yield and smoothness of texture. The apparent viscosity of the mix depends somewhat upon the processing, the amount and quality of gelatin used, and the time a n l temperature that the mix is held in the aging vat. If the mix is held too long it becomes difficult to incorporate air into it during the freezing period, and mixes held for a long time may be quite viscous. It has been assumed, therefore, that the long period allowed for aging led to the development of too great viscosity, making it difficult to incorporate air. Leighton and Williams2 processed a standard mix in the usual way, and found the true viscosity in the fresh mix t o be, for example, 9.11 centipoises; upon aging approximately 24 hours the mix had an apparent viscosity of 50 centipoises. I n this experiment a 6-gallon brine-cooled freezer TI a: fillel with mix, agitated a t 175 r. p. m., and the destruction of the apparent viscosity measured with an Oswald viscometer. After 60 minutes there remained a basic or constant viscosity of 36.31 centipoises. The authors of this paper have obtained repeatedly a much lower basic-viscosity figure-in fact, so low as to indicate that the apparent viscosity developed during the aging period is completely destroyed by agitation -this basic viscosity being equal to the true viscosity in the original mix prior to aging. Reduction of Apparent Viscosity
The mixes were divided into three lots; one was homogenized once, another twice, and the third three times. The average composition was 11 per cent fat, 10.5 per cent 1
2
Received October 31, 1927. .I. P h y s . Chem., S 1 , 596 (1927)
of Acidity to H o m o g e n i z a t i o n Pressure, Viscosity Being Constanta PRESSURE ACIDITY PRESSURE K g . / s q . cm. P e r cent Kg./sq. cm. 0.16 1582 0.24 1133 0.18 1474 0.26 1020 0.20 1361 0.28 907 0.22 1246 0.30 816 Turnbow and Milner, unpublished data.
Table I-Relation
a
Viscosity determinations were made immediately after the mix left the cooler, and then a t 5-, 24-, 48-, and 72-hour periods. The measurements were made with a MacMichael viscometer using standard methods. The viscosity of the fresh mix processed once was 0.7921 poise, and the same mix after 5 hours had developed an apparent viscosity of 3.3884 poises (Table 11). The standard commercial mixes when taken from the cooler were drawn into glass containers of uniform size and held a t a constant temperature. At the end of the 5-hour period one of these containers was placed on a shaker in a room of constant temperature and shaken 1400 oscillations, a t the end of which a constant viscosity was obtained. This viscosity was 0.7481 poise, a figure slightly lower than the viscosity of the fresh mix taken directly from the cooler. This slight variation can be explained by experimental error and by the fact that it is impossible to obtain a true temperature of the fre;jh mix. If time were allowe I for the tempering of the sample, a colloidal structure would have started to develop. The mix processed two and three times decreased in apparent viscosity with each processing. The viscosity developed during the aging period regardless of the number of times processed, though the same relationship tends to hold. One fact largely responsible for the decrease in viscosity usually caused by homogenizing two and three times is that there is less clustering of the butter fat. An increased dispersion of the butter-fat clusters was noticed by homogenizing three times instead of twice. An ice-cream mix homogenized once showed marked formation of fat clusters, but these clusters were largely destroyed during the first few minutes in the freezer. The data presented in Table I1 were checked by preparing standard mixes as previously described and determining
