Still, Othmer

Comparison of columns 3 and 7 of Table II shows, as expected, that for all systems except the first, the sample deviations of total pressure are reduced after temperature smoothing. At this point in time no clearcut explanation can be given for the unexpected result for the potassium nitrate system (8). However, the paper reveals that an Othmer still was used to give x and y values only, and these data were subjected to smoothing. The boiling points of synthetic liquid measures were determined separately in a three-necked flask under total reflux. With the other systems of Table II all data were measured in a modified Othmer still. 

Isothermal vapor-liquid equilibrium data at 75°, 50° and 25° C for the system of 2-propanol-water-lithium perchlorate were obtained by using a modified Othmer still. In the 2-propanol-rich region 2-propanol was salted out from the aqueous solution by addition of lithium perchlorate, but in the water-rich region 2-propanol was salted in. It is suggested from the experimental data that the simple electrostatic theory cannot account for the salt effect parameter of this system. 

The thermodynamic excess functions for the 2-propanol-water mixture and the effects of lithium chloride, lithium bromide, and calcium chloride on the phase equilibrium for this binary system have been studied in previous papers (2, 3). In this paper, the effects of lithium perchlorate on the vapor-liquid equilibrium at 75°, 50°, and 25°C for the 2-propanol-water system have been obtained by using a dynamic method with a modified Othmer still. This system was selected because lithium perchlorate may be more soluble in alcohol than in water (4). 

Apparatus. All vapor-liquid equilibrium measurements were made by using a modified Othmer still provided with an external electric heater. Total volume of the still was about 500 cm3, of which about 300 cm3 was occupied by liquid. The liquid loaded in the condensate receiver was about 7 cm3. Details of the still are described in a previous paper (5). 

Salt concentrations were obtained by the addition of known weights of dried salt to the solvent mixture. The compositions of the condensed equilibrium vapor samples and the previously prepared ethanol-water charges to the still were determined as previously outlined. The mole fractions of the salt, ethanol, and water charged to the Othmer still were thus accurately determined by mass balance calculations. 

Dimensional analysis is simply a mathematical tool. In all cases, it will reduce the number of experimental variables to be correlated, and often it will point out the best experimental approach to a problem. It will not give quantitative information, howev.er experiments must still be performed (Ref 3) Refs 1) D.Q. Kern, "Dimensional. Analysis , PP 133—41 in Kirk 8r Othmer s, Vol 5(1950)... 

Vapor-liquid equilibrium experiments were performed with an improved Othmer recirculation still as modified by Johnson and Furter (2). Temperatures were measured with Fisher thermometers calibrated against boiling points of known solutions. Equilibrium compositions were determined with a vapor fractometer using a type W column and a thermal conductivity detector. The liquid samples were distilled to remove the salt before analysis with the gas chromatograph the amount of salt present was calculated from the molality and the amount of solvent 2 present. Temperature measurements were accurate to 0.2°C while compositions were found to be accurate to 1% over most of the composition range. The system pressure was maintained at 1 atm. 1 mm... 

The data were obtained by means of an improved Othmer recirculation still (34), as modified for salt effect studies by Johnson and Furter (22,35). Thermal energy was applied to the still by means of a heating mantle controlled by a rheostat in order that the boiling rate could be adjusted effectively. Suppression of bumping of the solution and both thermal and physical homogeneity were maintained by means of a magnetic stirring mechanism. 

Experimental measurement of relative volatility. Rank candidate solvents by the increase in relative volatility caused by the addition of the solvent. One technique is to experimentally measure the relative volatility of a fixed-composition, key component + solvent mixture (often a 1/1 ratio of each key, with a 1/1 to 3/1 solvent/key ratio) for various solvents [Carlson et al., Ind. Eng. Chem., 46, 350 (1954)]. The Othmer equilibrium still is the apparatus of choice for these measurements [Zudkevitch, Chem. Eng. Comm., 116, 41 (1992)]. 

Donald F. Othmer while at Eastman Kodak during the 1920 s experimented using salts to concentrate acetic acid (14). He also developed an industrial process for distilling acetone from its azeotrope with methanol by passing a concentrated calcium chloride brine down the rectification column (15). Pure acetone was condensed overhead, and acetone-free methanol was recovered in a separate still from the brine which was then recycled. The improved Othmer recirculation still (16) has been the apparatus generally favored by investigators who have studied the effects of salts on vapor-liquid equilibrium. 

The apparatus used—the improved Othmer recirculation still modified for salt effect studies—was described previously (1,7), as were the analytical techniques, specifications on the purity and treatment of the solvents, and details of surface tension and solubility measurements (4). 

FIGURE 59. Chemist at a still from the Liber Minerdium Alberti Magni, a 1518 text attributed to Albert The Great note the poem above the figure (from The Roy G. Neville Historical Chemical Library, a collection in the Othmer Library, CHF). 

FIGURE 99. Title page (hand-colored see color plates) from Liber de Arte Distillandi (Heironymous Brunschwig, 1512), depicting a double-still in which the central tower contains cooling water that is continuously replenished. Come to think of it, this apparatus evokes an image of the caduceus two serpents entwined about the staff of Hermes where the loops symbolize couplings. (From the Othmer Library, CHF.)... 

FIGURE 100. Distillation employing rosenhuts (air-cooled still heads) in Brun-schwig s 1512 Liber de Arte Distillandi (from the Othmer Library, CHF). 

Many model studies dealt with models involving feedback control of enzymatic activities (e.g. Morales McKay, 1967 Hunding, 1974 Hastings et al., 1977 Tyson Othmer, 1978 Berding Harbich, 1984). Furthermore, the interpretation of periodic and aperiodic phenomena in biochemical systems is still an open topic. 

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