Liquid-Liquid Extraction on a Tonnage Scale For some uses, sodium hydroxide must he free of sodium chloride and sodium rhlorate which are normally present in causric soda produced in thc diaphragm cell' to thvextent of 0.9-1.1% and 0.05-0.10%, respectively. A process has been developed by PPG Industries2 to extract 50% caustic with liquid ammonia (at superatmospheric pressure) and thereby reduce the content of the salts present. In an extraction column, the heavier caustic solution is introduced a t the top and withdrawn at the bottom while the lighter liquid ammonia rises from the bottom and is withdrawn at the top. The ratio of the liquid ammonia to caustic determines the extent of removal of salts, but in plant practice the purified product has about 0.08% NaCl and 0.0002% NaC103. These are recovered by distilling the ammonia for reuse. Residual ammonia is removed from the caustic solution by submitting it to reduced pressure upon withdrawal from the extraction column. The product caustic meets the most stringent requirements (such as those for the manufacture of rayon) and the process introduced no mercury into the environment.
' Leddy, J. L., J. CHEM.EDUC, 57(9), 640 (1980).
Twiehaus, H. C., and Ehlers, N. J., Chem. Ind., 63, 230 (1948).
W. Conard Fernelius
768
Journal of Chemical Education
Increase in Low-Pressure Processes Help Save Energy ~ew-catalysts for three commercial syntheses not only save energy by lowering operating conditions hut also in plant .construction. The three processes are: 1) The classical synthesis of methanol from carbon monoxide and hydrogen can now he carried out a t pressures as low as 50 atm and temperatures of 220°C. In the ICI process a new copper catalyst is wed that allows for energy savings of a t least 25%. 2) Union Carbide says its new low pressure process (catalyst not stated) for low density polyethylene cuts capital costs by as much as 50% and energy requirements by 75%. 3) Union Carbide and Mitsubishi state that the use of triphenylphosphine modified rhodium catalyst for the O X 0 reaction reduces operating pressures to 200-400 psi from 1000-5000 psi needed by the older cobalt catalyzed system. This low pressure process yields a 10:l ratio of n-butyraldehyde to isohutyraldehyde instead of the usual 4:l ratio. Shell, a major integrated O X 0 alcohol producer, seems to he staying with the cobalt catalyst system (Chemical Week, March 5, 1980, pp. 33-34). Kenneth E. Kolb
