THE JOURNAL OF INDUSTRIAL AND ENGINEERING CHEJfISTRY
946
Vol. 14, No. 10
The Precipitate Formed in Sugarhouse Sirups' By J. F. Brewster and W. G. Raines, Jr. LOUISIANA S U G A R EXPERIMENT STATION, NEW
OATES and Slater2in 1916 published a study of the precipitate that forms when clarified cane juice has been evaporated to sirup and allowed to stand. These authors examined two lots of precipitate obtained from two different Louisiana sugarhouses, where plantation white sugar was being manufactured by the sulfitation process. Of the organic constituents of their precipitates Coates and Slater isolated cane wax and found to be present a levorotatory substance which was not sugar. The percentages of ash in their precipitates were 58.0 and 75.6, respectively. The constituents of the ash reported were copper, oxides of iron, aluminium, calcium and magnesium, silica, sulfur trioxide, and phosphorus pentoxide. Coates and Slater conclude that, although the precipitate is made up of substances insoluble in the ordinary sense, it is held in colloidal solution by the heavy sirup, from which it flocculates on standing, particularly when kept hot. Last year the present writers8 analyzed a sirup precipitate resulting after cane juice had been treated with Filter-Cel and Norit. The ash analysis showed the presence of manganese in addition to the constituents found by Coates and Slater. A thorough study of a similar precipitate has been published very recently by B i r ~ k n e r ,who ~ reported the presence of zinc in addition to the ash constituents enumerated above. The fact that precipitation invariably occurs in sirup from cane, no matter how brilliant the clarified juice may appear before evaporation, and the fact that it is impossible to obtain high-grade white sugar unless the precipitate is removed, thus forming a distinct step in the process, makes its study important. The source of the inorganic part of the precipitate-forming substances seems to be an open question. Coates and Slater conclude that the character of the precipitate varied
C
ORLEANS, L O U r S I A N A
possible to remove precipitate-forming substances or to reduce the amount of precipitate formed. Cane juice in 10-liter lots was clarified, filtered by means of the laboratory press, and evaporated in vacuo to 30' BB. while warm. The sirup was allowed to stand, and when the precipitate had settled the clear sirup was drawn off by suction and the residue stirred with water and centrifuged. The precipitate was washed three times by centrifuging with water, then thrown upon a filter and washed in the ordinary way until free from soluble matter. It was then dried a t 100" and analyzed. As the methods of clarification differed, no refinements in analytical methods were attempted. The dried samples were ashed and after obtaining the weight of ash the latter was fused with sodium carbonate and the methods of silicate analysis applied. No attempt was made to separate the constituents of the ammonia precipitate, which may have contained some phosphates and members of the dkali earth groups. The results for determination of total precipitate and ash are shown in the following table. The methods of clarification in the first column should be be explained. Under the head "sulfur-lime" in Expt. 1, is meant that the raw juice was treated with sulfur dioxide to an acidity of 5.0 cc. and limed back to neutrality against phenol red. The mixture was heated to the boiling point and filtered. The brilliantly clear filtrate was immediately evaporated. In Expt. 2 filter-paper pulp was mixed with the juice, heated, and pumped through the press. The paper proved to be a poor filtering medium when used in this way, the filtrate being cloudy. Norit alone was used in Expt. 3, giving a slightly cloudy filtrate. I n Expt. 4, 2 per cent of freshly precipitated and thoroughly washed calcium carbonate was mixed with the juice, heated as in the other experiments, and filtered. The filtrate was brilliant and it
PRECIPITATES FROM SIRUP Expt. No. 1
2 3 4 5 6 7
Clarification Method Sulfur-lime Paper Norit CaCOs Lime Filter-Cel Lime Filter-Cel-Norit
Ppt. G.
4.1936 3,4916
....
....
0.3370 0.8243 1.6118
---Ash--
G.
3.7121 2.2161 0.5808 0.0838 0.1627 0.5315 1.1260
Per cent
87.32 63.46
.... ....
48.28 64.48 74.47
according to the method of clarification. Bircher believes this t o be true to a certain extent, particularly in those methods of clarification in which lime is dsed. The latter author, however, believes that in view of the occurrence of the precipitate in sirups resulting from treatment of juice with kieselguhr and Norit, that is, from treatment without the use of chemicals, it is doubtful whether the precipitate can be attributed, in its main features, to factors not inherent in the cane juice itself. In making some small-scale clarification experiments, we had as one object to determine whether it would be 1 Presented before the Division of Sugar Chemistry at the 63rd Meeting of the American Chemical Society, Birmingham, Ala., April 3 to 7, 1922. 2 THISJOURNAL, 8 (1916),789. 3 Ibzd., 13 (1921),923. 4 Louisiana Planter., 68 (1922), 285.
SiOe
23.23 9.99 26.12 53.58 37.95 60.82 43.47
--Analysis of Ash, Per centAmmonia Ppt. CaO MgO 1.11 32.02 None 4.13 38.28 None
35.97 0.24 25.47 8.10 2.94
SOa
14.94 40.57 26.35
None None
42.00 34.09 1.67 6.67 1.63
22.72
None
27.48
....
1.92
....
....
PrOr
0.46 0.73 12.71 3.34 None
None
....
was found that the acidity of the juice had been reduced about 50 per cent. Calcium carbonate is an excellent filtering medium and can be used in much less quantity than we employed here. Its use was suggested to us by Dr. Sauer, of the Norit Co., who had tried it previously as a possibility for direct manufacture of white sugar in conjunction with Norit. Expt. 5 was limed to neutrality (phenol red), 0.5 per cent of Filter-Cel added, heated, and filtered. The filtrate was clear. Expt. 6 represents juice limed to neutrality, heated, and filtered. I n spite of difficulty in fiItering, this mixture was all put through the press, although the filtrate was slightly cloudy. Expt. 7 was a precipitate obtained from the sugarhouse sirup tanks. This jnice had been clarified with Filter-Gel, then decolorized with Norit in the presence of a small amount of added phosphoric acid which was neutralized with lime just before filtering. It
