February, 1943
INDUSTRIAL AND ENGINEERING CHEMISTRY
Summary and Conclusions The types of wheat best suited for alcohol production are White or Soft Red Winter, Red Winter subclass. Durum and Hard Red Spring wheats are generally not suitable for alcohol production, owing to the lower starch content and resultant low yield of alcohol. Hard Red Winter wheat falls between the above two groups. The location of the White wheat and the limited supply of the Soft Red Winter wheat make it imperative that the Hard Red Winter be used. The starch content of wheat is a reliable index of the anticipated yield of alcohol. Alcohol yields from wheat are generally lower than yields from corn; the difference is about 0.2 proof gallon per bushel. Higher yields of alcohol can be obtained from wheat, either by pressure cooking (batch or continuous processes) or by atmospheric mashing a t 155" F. Mixed grain bills comprised of over 50 per cent corn, 35-40 per cent wheat, and the remainder distiller's barley malt can be successfully handled in a grain distillery and produce yields only slightly lower than those obtained from corn. The most suitable method of processing for any given plant necessarily depends on the existing equipment. The minimum concentration of barley malt required for corn mashing may be reduced by 50 per cent through the
137
utilization of wheat-barley malt mixtures as the conversion agent. This is successful if the mash is allowed to ferment for 72 hours. The dried grain yield is 2-3 pounds per bushel lower when recovering spent wheat grains from high percentage (80-90 per cent) wheat mashes. This and other problems incidental to the utilization of wheat in alcohol production are discussed. These problems vary with the equipment of each individual plant. Further research must be done to utilize wheat efficiently as a raw material for alcohol production and to minimize the operating problems.
Acknowledgment The authors gratefully acknowledge the technical assistance of the following members of the Research and Development Department: R. S.Mather, G. A. Snyder, J. S. Hudson, and Luella Shehan.
Literature Cited (1) Gallagher, F. H., Bilford, H. R., Stark, W. H., and Kolachov, Paul, IND. ENQ.CHEM.,34,1395 (1942). (2) Unger, E. D., Thesis, Case School of Applied Soienco. PRE~ENTE before D the Division of Agricultural and Food Chemistry at the 104th Meeting of the AMERICAN CHEMICAL SOCIETY, Buffalo, N. Y .
Solubilitv of Melamine in Water J
R. P. CHAPMAN, P. R. AVERELL, AND R. R. HARRIS Stamford Research Laboratories, American Cyanamid Company, Stamford, Conn.
The solubility of melamine has been determined at several temperatures over the range 20-100° C. Independent determinations starting from unsaturated and supersaturated solutions yielded values which were in satisfactory agreement. The points thus obtained, when plotted on semilogarithmic paper, coincided closely with a strhtght line
T
H E purpose of this paper is to present data on the solubility of melamine in water over the range 0-100" C. In his review of the chemistry of melamine, McClellan ( 3 ) showed that there was a discrepancy between the solubility found by Christmann and Foster (1) in this laboratory and that reported by Lemoult (2) many years earlier. The Christmann and Foster data were the result of a few rough determinations made for immediate practical use in the crystallization of melamine-dicyandiamide mixtures. Present day interest in melamine and its rapidly growing commercial importance, particularly in the field of amino plastics, made it seem desirable to redetermine in an exact way the solubility-temperature relation of the melamine-water system.
Experimental MATERIAL.Several pounds of the purest melamine available were recrystallized four times from water, air-dried, and micropulverized. APPARATUS.The Walton-Sudd apparatus, diagrammed and described in Scott's book (4)was adopted with a few additions and modifications; Figure 1 shows the modified apparatus. The outer vessel is a 1000-ml. tall-form beaker
representing the Clausius-Clapeyron relationship. The equation of this line is as follows: log (solubility) = -1642 X 1 / T
+ 5.101
By means of the equation reasonably reliable extrapolated values can be obtained down to 0' C.
without a spout, the inner sampling vessel an ordinary 25 ml. weighing bottle. The small thistle a t the lower end of the filter tube is covered with No. 44 Whatman filter paper, reinforced by a piece of strong, white, soluble-free cotton cloth; the filter paper and cloth are tied tightly over the flange of the thistle with thread. The outer vessel, held in a specially designed clamp, is immersed as deeply as possible in an electrically controlled constant-temperature oil bath maintained within 0.1 " C. of the equilibrium temperature. PROCEDURE. Two separate sets of apparatus were used to run simultaneous determinations starting from unsaturation and supersaturation, respectively. Each beaker contained 750 ml. of water and enough melamine to provide a 3-5 gram excess over the necessary amount. Before being placed in position in the bath, one beaker was raised to about 5" C. below the bath temperature, the other 5-10" above the bath temperature, and held there until supersaturated with respect to bath temperature. The two vessels were then lowered into position in the bath and allowed to reach equilibrium. When the time for sampling arrived, the sampling device (previously raised to bath temperature) was inserted, and the necessary amount of sample allowed to siphon into the sample
INDUSTRIAL AND ENGINEERING CHEMISTRY
138
bottle. A simple periscope device and a tubular electric light bulb immersed beside the beaker furnished a means of o b s e r v i n g when the required amount of solution had passed over. After removal from the solution, the sampling devicewas rinsed off and dried. The stopper carrying the thistle was replaced by the ground glass stopper, and the sample weighed. The melamine content of the solution was then FIGURE1. MODIFIED WALTOX-JUDD determined by SOLUBILITY APPARATUS suitable means. (A direct m e t h o d developed in this laboratory was used. This method has not yet been published, and its dcscription is outside the scope of this paper. In some instances check determinations were made by evaporating the solution to dryness and weighing the residue. Agreement between the two methods was very good.) The solubility was calculated as follows: 100
x
grams
Vol. 35, No. 2
site sides of equilibrium were remarkably close, thus boxing in the true equilibrium value within a satisfactory range. The values obtained are plotted in the usual manner in Figure 2 and given in the following table: Soly., G. Melamine/100 G. HsO-From From unsatn. supersatn. Mean
7 -
Temp.,
O
19.9 34.9 49.8 64.1 74.5 83.5 94.8 99.0
C.
0.324 0.321 0.590 0.590 1.040 1.040 1.W 1.69 2.34 2.35 3.15 3.14 4.56 4.58 4.63 5.03 5.07
0.324 0.326 0.591 0.590 1.048 1.051 1.75 1.69 2.43 2.35 3.17 3.15 4.63 4.64 4.60
0.324 0.590 1.045 1.70 2.37 3.15 4.59
.. .
5~05
I
Since melamine is relatively not very soluble, .particularly a t lower temperatures, its change of solubility with temperature should obey the Clausius-Clapeyron equation reasonably closely. The integrated equation, assuming constant AH over the range studied, was employed here. A plot of log (solubility) against the reciprocal of the absolute temperature should therefore exhibit a straight-line relation. The experimental data, plotted in this manner and shown in Figure 3, were found t o be remarkably close t o a straight line whose equation, constructed from the two points a t 34.9' and 83.5" C., is as follows: log (solubility) = -1642 X 1/T 5.101. Solubility is expressed in the conventional unit, grams per 100 grams of solvent, and T i s the absolute temperature.
+
melamine/(grams sample - grams melamine) = grams melamine/100 grams HzO
At suitable intervals the sampling was repeated until the unsaturated and supersaturated solutions arrived a t the same concentration or were close enough to give satisfactory precision. Data At each temperature investigated, a t least two runs were made from each side of equilibrium, with the exception of 99" C. where it was practically impossible to get a supersaturated solution. The limiting values obtained from oppo-
1 01'
9'7
30
104x
i/r
I ABS.
36
us. THE RECIPROCAL OF FIGURE3. PLOTOF LOGSOLUBILITY ABSOLUTETEMPERATURE
The higher values show some tendency to deviate from the straight line. This might possibly be expected from theoretical considerations, since melamine solutions saturated near the boiling point might be classed as fairly concentrated solutions. At lower temperatures the Clausius-Clapeyron equation should be quite valid, so that extrapolation of the curve to 0" C. should be justifiable. The extrapolated value thus calculated is 0.12 gram melamine per 100 grams water a t 0" C.
5
P0 . 4 8
a2
% 3
Literature Cited
61
IO
20
30
40
50 TEMP ('C)
BO
70
80
80
FIGURE2. SOLUBILITY OF MELAMINE
100
(1) Christmann and Foster, U. S. Patent 2,203,880(1940). (2) Lemoult, P.,Ann. chim. p h y s . , [7]16,410 (1899). (3) McClellan, P.,IND.ENQ.CHEM.,32, 1181-6 (1940). (4) Scott, W.W.,"Standard Methods of Chemical Analysis", 6th ed., Vol. 2, p. 2575 (1939).
