Abstract: A refined dihydroxyaryl compound, for example, catechol, having a high degree of purity and a very low metal content is produced by evaporating a starting dihydroxyaryl compound in a distillation column, condensing the vapor fraction in a condenser connected to a top outlet of the distillation column, and collecting the condensed fraction from the condenser into a storage tank through a conduit, wherein the condenser and optionally the conduit and/or the storage tank have inside surfaces thereof formed from a metal material containing at least 25% by weight of nickel, and the condensed dihydroxyaryl compound fraction is brought into contact with the specific nickel (25% or more)-containing metal inside surface.

Abstract: A mixed liquid of two or more components different in boiling temperature from each other and soluble in or compatible with each other is evaporated into a mixed vapor having a similar composition to that of the mixed liquid by using an apparatus having a thin film evaporator (1) having a feed inlet (1a) and a delivery outlet (1b), while forcedly circulating the non-evaporated portion of the mixed multi-component liquid by withdrawing the non-evaporated mixed liquid portion from the delivery side end portion of the evaporator and returning the mixed liquid portion into the feed side end portion of the evaporator through a circulating line (3), and the resultant mixed multi-component vapor can be used as a mixed material vapor for a gas phase catalytic reaction for producing, for example, a mono and/or a di-alkylether of an aromatic dihydroxy compound.

Abstract: A mixed liquid of two or more components different in boiling temperature from each other and soluble in or compatible with each other is evaporated into a mixed vapor having a similar composition to that of the mixed liquid by using an apparatus having a thin film evaporator (1) having a feed inlet (1a) and a delivery outlet (1b), while forcedly circulating the non-evaporated portion of the mixed multi-component liquid by withdrawing the non-evaporated mixed liquid portion from the delivery side end portion of the evaporator and returning the mixed liquid portion into the feed side end portion of the evaporator through a circulating line (3), and the resultant mixed multi-component vapor can be used as a mixed material vapor for a gas phase catalytic reaction for producing, for example, a mono and/or a di-alkylether of an aromatic dihydroxy compound.

Abstract: A heat-deteriorative compound contained in a liquid mixture is refined by a distillation procedure using a distillation column in which a vapor fraction and a liquid fraction containing the heat-deteriorative compound are generated from the liquid mixture, and a liquid film-falling reboiler in which the liquid fraction falls in the form of liquid films along inner surfaces of a plurality of vertical heat-conductive pipes at a Reynolds number (Re) of 700 to 10,000 and heated to a temperature lower than the heat-deterioration temperature of the heat deteriorative compound to such an extent that 1 to 15% by weight of the liquid fraction is evaporated per pass through the reboiler, the heated liquid fraction being returned into the distillation column to generate the vapor fraction from the liquid mixture fed into the distillation column.

Abstract: A dihydric phenolic compound is produced, with a high selectivity thereof, by a plurality of oxidation reactors connected to each other in series, by (1) feeding a monohydric phenolic compound with a temperature of 30 to 100° C.