A
General Utility Laboratory Distillation Column W. M. LANGDON AND G. M. O'BRIEN, JR.',
M
ANY articles have been written on the design of laboratory distillation columns, but the construction details of a practical column, suitable for general distillation operations, are not easily available to those not familiar with this field. The column described in this paper is believed to embody most of
University of Illinois, Urbenr, 111.
the characteristics desirable for general utility. It is easily constructed of commonly available materials, suitable for most distillation operations over a wide temperature range, and free from mechanical or thermal strains. The essential feature is a glass heating jacket in which any desired distillation tube up to 45-mm. outside diameter may be inserted. There is also shown (Figure 1) a still head which is suitable for almost every type of distillation operation encountered in the laboratory. I t s applications are discussed briefly. CONSTRUCTION JACKET. The jacket, which is electricall heated, is made up of two concentric glass tubes, G 55 and $ 70 mm. in outside diameter, held in lace loosely by grooves cut in the two 3/4-inch transite disis, B . These disks are bolted rigidly to a framework of three */8-inch steel pipes, so that there is no mechanical strain on the glass. This arrangement allows both tubes to expand or contract independently of each other upon heating and cooling. The pipe framework is made rigid by means of two transite collars, C, fastened intermediate to the disks by setscrews. The inner glass tube is wound with two double-spiral, 20-ohm heating elements, D, so that the temperature of the upper and lower halves of the jacket may be adjusted independently. The heating elements are wound directly on the glass and held in place by moistened alundum cement. The ends of the elements are fastened securely by wire bands. The temperature of the jacket is measured by two thermocouples, E , placed inside the 55-mm. tube with the hot junctions located one fourth and three fourths of the distance along the jacket. The thermocouples are preferably strung as single strands running the length of the jacket. The elecfrical connections are made to the inner surfaces of the two end disks and the wires strung through the pipe framework. DISTILLATION TUBES.The distillation tubes, which may be as large as 45 mm. in outside diameter, are inserted through the opening in the upper transite disk and rest upon the tapered openin4 of the bottom disk. The tubes smaller than 45 mm. in outside diameter are centered in the upper disk by means of split transite collars, J , and are provided with a ring of glass a t the loner end if they are smaller than the bottom openin (As an alternative arrangement the top of the distillation tu%e may be provided with a ring of glass which rests on the upper opening.) This arrangement, intended for use with standard-taper joints, allows the tube assembly to rise and,pivot about the top when the bottom accessories are being attached. Breakage is thus prevented when the pieces are not correctly aligned. The distillation flasks are joined to the column by suspending them in a clamp attached a t A , so as to raise the tube off the tapered opening in the bottom disk. This allows the tube to seat itself in the flask by its own weight. STILLHEAD. A still head, which has been found suitable for many operations, is constructed so that it may be inserted in the top of the distillation tube without clamping, thus facilitating the assembling of the bottom accessories. The head is constructed of a straight tube 25 mm. in outside diameter and is provided with vapor, 0, and liquid, L , sampling lines and also a line, K , for returning liquid to the column. The inner tube of sample condenser in the vapor line should be constructed of 8-mm. tubing in order to prevent a liquid leg from forming in the condenser. The vapor line, together with its stopcock, and that portion of the head below the sampling lines are provided with a 30-ohm heating element. The windings on the vapor line and stopcock are wound over asbestos paper and coated with moistened nlundum cement. The rest of the windings are wound directly on the glass. A thermocouple is wound around the barrel of the stopcock to measure the temperature a t that point. A capillary thermocouple well, M , extending through the still head and, in the case of a packed column, down through the packing, may be used to measure the temperature at all points in the column.
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S E C T I O N H-H
DISCUSSION
A
The column described above may be used for practically all types of distillation operations which are condurted above
S S E M B LY Figure 1.
Dirgrem of Column
1
639
Present addreaa, U. S. Navy.
640
INDUSTRIAL AND ENGINEERING CHEMISTRY
room temperature and a t pressures varying from a few millimeters of mercury absolute to several pounds per square inch gage. I t is suitable for the analogous operations of absorption and extraction and may also be used as a reaction tube. In the latter case, the reaction tube should be provided with an additional heating element. While the design of this column is best suited for operations above room temperature, it may also be used for low-temperature work where it is necessary to observe the column action. I n this operation, the cooling fluid would be circulated in the annular space between the 55- and 70-mm. jacket tubes. If the fluid was introduced several inches below the upper disk, only the lower end of the jacket would have to be sealed by a gasket. The still head shown in the figure is a composite of several types used by the authors. The thermocouple well extending down through the packing is useful where the temperature is a criterion of the product compositions. While the thermocouple well will decrease the efficiency of the packing, this is in many cases compensated for by the gain in operability of the column. It enables the optimum reflux ratio to be set with a minimum of trial and error and the future course of batch distillations to be predicted without frequent readings of the temperature. The vapor sampling line, 0, is used where it is necessary to maintain a high reflux ratio and low holdup, as in the case of analytical distillations. Reflux ratios of 20/1 ( O / P ) are readily
Vol. 16, No. 10
and accurately obtained by adjusting the stopcock and then applying a slight pressure to the column (or vacuum to the receiver). The take-off rate is closely proportional to the square root of the pressure applied. Other advantages of vapor sampling are that it minimize8 contamination of the sample by the stopcock grease and allows accurate sampling of distillates which give two liquid phases upon condensation. A simple method of attaching accessories to the still head ie illustratecLin the figure for operation a t total reflux with product holdup. The receiver is suspended in a clamp, so that line L may be connected to it. The receiver is then rotated on its own axis until line K may be connected. The connecting lines have sufficient flexibility to allow them to be slid emily.into place at the same time providing tight seals for vacuum work. The connections illustrated are pieces of rolled rubber tubing to provide flexibility. In the case of high-boilin organic solvents, standardtaper joints may be used a t points and K. The capacity of the receiver may be varied by the use of return lines of different lengths. This same receiver, by closing the stopcock in return line K , may be used for automatically discontinuing the removal of product in batch distillations.
k
The applications of this still head to the various types of azeotropic distillations with two-phase condensate are similar to the above and do not require description.
Method For Detecting Inadequately Heated Soybean Oil Meal C. D. CASKEY,
JR.,
AND
FRANCES C. KNAPP
Southern States Laboratories, Baltimore, Md.
Editor's Note. Since receipt of this p p e r , a subcommittoe of the Animal Nutrition Committee of the National Research Council has been appointed to study tests which might be applied to soybean oil meals to indicate the degree of heat treatment and to correlate i t with biological efficiency. The committee is carrying on collaborative work with additional samples in order to check further the validity of the urease test.
Since the over-all processing conditions of temperature, time, and moisture content favorable for protein denaturation would also be favorable for the inactivation of enzymes, a test based upon the enzymatic activity of the finished product was indicated. Urease was selected because of its unusually high concentration in soybeans and the ease with which its presence can
T
Table
HE high nutritive value of soybean oil meal for poultry
and swine depends considerably upon the heat treatment used in its preparation. Adequate heat treatment improves the biological value .of the proteins (8, 3, 4) and simultaneously inactivates the enzymes present (6). The enzyme lipoxidase if left active in the meal could readily cause the destruction of vitamin A or its precursors with which it comes in contact in the digestive tract of animals. The contemplated use of urea in feed mixtures for ruminants makes it important that the soybean oil meal used in such mixtures be heated sufficiently to inactivate urease. Mixtures of inadequately heated soybean meals or raw soybeans and urea develop the highly characteristic odor of ammonia and, hence, become unpalatable. It hm been reported by Bird and co-workers ( 1 ) that commercially produced meals differ markedly in their nutritive values when used as the principal source of protein in the chick ration. Some of the poor results obtained were attributed to the use of insufficiently heated meals. With the enormously increased production of soybeans and their subsequent conversion into meal by plants having no previous experience with this commodity, the need for a rapid test for determining adequacy of heat treatment is apparent.
1. Growth Response and Results of Tests on Samples of M e a l Receiving Different Heat Treatments Average Chick Weight at 9 Weeks. Grams0
Treatment
Results on Test Solution, PH
Experiment I Raw beans 143O F 11.6 minutq 173' F:: 16.5 minutes 175' F., 105 minutes 217' F., 42 minutes Solvent meal Hydraulic meal B
476 528 586 572 669 798 637
8.9 8.8 8.6 8.7 7.6 7.1 8.9
664 728 733 784
8.4 7.1 7.1 7.1
317 494 483 443 494
8.6 7.1 7.1 7.1 7.1
Experiment I1
Experiment Raw meal Autoclaved 2.5 minutes at 20 pounds Autoclaved 7.5 minutes at 20 pounds Autoclaved 12.5 minutes at 20 pounds Autoclaved 60 minutes at 5 pounds 5
b e
Growth data from ( 1 ) .
Producer's designation. Weights given for 7th week.
IIIC
