Abstract: An object is to provide a method for producing a ketene derivative that decreases the consumption quantity of phosphorus compounds, and the discharge quantity of the phosphorus compounds into the environment. A method for producing a ketene derivative includes a step (i) of conducting thermal decomposition reaction of acetic acid in a presence of a phosphorus-containing catalyst in a reactor to produce a thermal decomposition gas containing ketene, a step (ii) of cooling the thermal decomposition gas to be separated into a gaseous component containing ketene, and a condensed liquid containing a phosphorus compound (a), and a step (iii) of causing the ketene to react with a different organic compound to produce a ketene derivative. The step (i) includes conducting the thermal decomposition reaction while supplying, into the reactor, the condensed liquid containing the phosphorus compound (a) or a concentrated liquid of the condensed liquid.

Abstract: In extracting a solute from an aqueous solution using a mixer-settler extractor and an organic extractant comprising a mixture of a tertiary amine and an organic diluent, the extractor is operated while the liquid phase inside the mixer thereof is kept in a state of solvent dispersion. Thus, the mixer-settler extractor can be operated efficiently.

Abstract: In extracting object material from its aqueous solution by using an organic solvent, a mixer-settler extractor is employed as the extractor and operated while a solvent dispersion is maintained in the mixer, and part of the aqueous phase discharged from the settler is recycled to the mixer so that the organic solvent phase in the mixer is stably maintained as the disperse phase.