A method is provided for collecting a compound of formula (III) (in which R31 is a monovalent to trivalent organic group and n31 is an integer of 1 to 3) from a liquid phase component that is formed as a by-product in a method for producing a compound of general formula (I) (in which R11 is a monovalent to trivalent organic group and n 11 is an integer of 1 to 3), wherein the collection method contains steps (1) to (3) or steps (A) and (B), and step (4). Step (1): a step for reacting the liquid phase component with at least one active hydrogen-containing compound in a reactor. Step (2): a step for returning a condensed liquid obtained by cooling gas phase components in the reactor to the reactor. Step (3): a step for discharging gas phase components that are not condensed in the step (2) to the outside of the reactor. Step (A): a step for mixing the liquid phase component, water, and a compound of general formula (III). Step (B): a step for reacting the liquid phase component with water inside the reactor. Step (4): a step for discharging, as a liquid phase component inside the reactor, the reaction liquid containing the compound of general formula (III) to the outside of the reactor.
R.sup.11NCO).sub.n11  (I)
R.sup.31NH.sub.2).sub.n31  (III)

A method is provided for collecting a compound of formula (III) (in which R31 is a monovalent to trivalent organic group and n31 is an integer of 1 to 3) from a liquid phase component that is formed as a by-product in a method for producing a compound of general formula (I) (in which R11 is a monovalent to trivalent organic group and n 11 is an integer of 1 to 3), wherein the collection method contains steps (1) to (3) or steps (A) and (B), and step (4). Step (1): a step for reacting the liquid phase component with at least one active hydrogen-containing compound in a reactor. Step (2): a step for returning a condensed liquid obtained by cooling gas phase components in the reactor to the reactor. Step (3): a step for discharging gas phase components that are not condensed in the step (2) to the outside of the reactor. Step (A): a step for mixing the liquid phase component, water, and a compound of general formula (III). Step (B): a step for reacting the liquid phase component with water inside the reactor. Step (4): a step for discharging, as a liquid phase component inside the reactor, the reaction liquid containing the compound of general formula (III) to the outside of the reactor.
R.sup.11NCO).sub.n11  (I)
R.sup.31NH.sub.2).sub.n31  (III)

A method is provided for collecting a compound of formula (III) (in which R31 is a monovalent to trivalent organic group and n31 is an integer of 1 to 3) from a liquid phase component that is formed as a by-product in a method for producing a compound of general formula (I) (in which R11 is a monovalent to trivalent organic group and n 11 is an integer of 1 to 3), wherein the collection method contains steps (1) to (3) or steps (A) and (B), and step (4). Step (1): a step for reacting the liquid phase component with at least one active hydrogen-containing compound in a reactor. Step (2): a step for returning a condensed liquid obtained by cooling gas phase components in the reactor to the reactor. Step (3): a step for discharging gas phase components that are not condensed in the step (2) to the outside of the reactor. Step (A): a step for mixing the liquid phase component, water, and a compound of general formula (III). Step (B): a step for reacting the liquid phase component with water inside the reactor. Step (4): a step for discharging, as a liquid phase component inside the reactor, the reaction liquid containing the compound of general formula (III) to the outside of the reactor.
R.sup.11NCO).sub.n11  (I)
R.sup.31NH.sub.2).sub.n31  (III)

A process for producing EDA from a mixture comprising water (H2O), ethylenediamine (EDA) and N-methylethylenediamine (NMEDA) by feeding the mixture into a rectification column, wherein the rectification column is operated at the top pressure in the range of 5.0 to 7.5 bar.

A process for producing EDA from a mixture comprising water (H2O), ethylenediamine (EDA) and N-methylethylenediamine (NMEDA) by feeding the mixture into a rectification column, wherein the rectification column is operated at the top pressure in the range of 5.0 to 7.5 bar.

A process for producing EDA from a mixture comprising water (H2O), ethylenediamine (EDA) and N-methylethylenediamine (NMEDA) by feeding the mixture into a rectification column, wherein the rectification column is operated at the top pressure in the range of 5.0 to 7.5 bar.

Catalytic activity of a spent precious metal-iron catalyst is restored by combining the spent catalyst with an iron (III) compound. This can be performed by adding the iron (III) compound into a chemical reaction that contains the spent precious metal-iron catalyst. It is unnecessary to add more of the precious metal. The process is especially useful in a continuous process for converting a nitro compound such as nitrobenzene to the corresponding amine.

Catalytic activity of a spent precious metal-iron catalyst is restored by combining the spent catalyst with an iron (III) compound. This can be performed by adding the iron (III) compound into a chemical reaction that contains the spent precious metal-iron catalyst. It is unnecessary to add more of the precious metal. The process is especially useful in a continuous process for converting a nitro compound such as nitrobenzene to the corresponding amine.

The present invention provides a method for operating a rectification column (1000) for separating a mixture (S) containing a component A and a component B having a boiling point higher than that of the component A at an operating pressure of the rectification column (1000) which is lower than ambient pressure, wherein the method comprises a step for controlling the mass fraction of the component B in the product stream of the component A (P1) to a value within a first target range from 0.1% to 5.0% and the mass fraction of the component A in the product stream of the component B (P2) to a value within a second target range from 0.1% to 5.0%, wherein the control is carried out as a function of a controlling temperature (TC) for which a setpoint TC.sub.setpoint is calculated according to the equation TC.sub.setpoint=T2+F.Math.(T1−T2), where F is a factor which is in the range from 0.1 to 0.9 and T1 and T2 are reference temperatures, wherein in the case of a deviation in the measured control temperature (TC) from its setpoint TC.sub.setpoint being found the control temperature (TC) is readjusted to the setpoint TC.sub.setpoint by varying one or more of the following actuating variables: (i) heating of the column bottom (130) by the evaporator (200), (ii) the mass flow {dot over (m)}.sub.A42 of the reflux (A42) fed back into the rectification column, (iii) the mass flow {dot over (m)}.sub.P2 of the product stream P2 and (iv) the mass flow {dot over (m)}.sub.P1 of the product stream P1.

The present invention provides a method for operating a rectification column (1000) for separating a mixture (S) containing a component A and a component B having a boiling point higher than that of the component A at an operating pressure of the rectification column (1000) which is lower than ambient pressure, wherein the method comprises a step for controlling the mass fraction of the component B in the product stream of the component A (P1) to a value within a first target range from 0.1% to 5.0% and the mass fraction of the component A in the product stream of the component B (P2) to a value within a second target range from 0.1% to 5.0%, wherein the control is carried out as a function of a controlling temperature (TC) for which a setpoint TC.sub.setpoint is calculated according to the equation TC.sub.setpoint=T2+F.Math.(T1−T2), where F is a factor which is in the range from 0.1 to 0.9 and T1 and T2 are reference temperatures, wherein in the case of a deviation in the measured control temperature (TC) from its setpoint TC.sub.setpoint being found the control temperature (TC) is readjusted to the setpoint TC.sub.setpoint by varying one or more of the following actuating variables: (i) heating of the column bottom (130) by the evaporator (200), (ii) the mass flow {dot over (m)}.sub.A42 of the reflux (A42) fed back into the rectification column, (iii) the mass flow {dot over (m)}.sub.P2 of the product stream P2 and (iv) the mass flow {dot over (m)}.sub.P1 of the product stream P1.