Abstract: Isocyanates are produced by a) reacting at least one amine with phosgene, optionally in the presence of a solvent to produce the corresponding isocyanate and a stream containing hydrogen chloride, phosgene and optionally solvent, low-boiling compounds and inert substances is obtained, b) separating the stream containing hydrogen chloride, phosgene and optionally solvent, low-boiling compounds and inert substances in an at least two-stage sequence of absorption steps that includes (1) at least one isothermal absorption step and (2) at least one adiabatic absorption step, to obtain (i) a hydrogen chloride stream containing phosgene in concentrations of at most 0.5 wt. % (based on the weight of the hydrogen chloride stream) and (ii) a liquid phosgene stream, and c) recycling the liquid phosgene stream (ii) to the reaction of amine with phosgene.

Abstract: Isocyanates, preferably diisocyanates and polyisocyanates of the diphenylmethane series (MDI), are produced by reaction of amines dissolved in a solvent with phosgene in the same solvent to form the corresponding isocyanates. Hydrogen chloride and excess phosgene are subsequently removed from the reaction mixture to obtain a crude isocyanate-containing solution. Subsequently, the crude isocyanate-containing solution is separated by distillation into isocyanates and solvent. The solvent is recycled and used for the production of solutions of the amines and of phosgene. The solvent being recycled is treated to reduce the phosgene and diisocyanate contents before being used for the production of the solution of the amine.

Abstract: Isocyanates are produced by a) reacting at least one amine with phosgene, optionally in the presence of a solvent to produce the corresponding isocyanate and a stream containing hydrogen chloride, phosgene and optionally solvent, low-boiling compounds and inert substances is obtained, b) separating the stream containing hydrogen chloride, phosgene and optionally solvent, low-boiling compounds and inert substances in an at least two-stage sequence of absorption steps that includes (1) at least one isothermal absorption step and (2) at least one adiabatic absorption step, to obtain (i) a hydrogen chloride stream containing phosgene in concentrations of at most 0.5 wt. % (based on the weight of the hydrogen chloride stream) and (ii) a liquid phosgene stream, and c) recycling the liquid phosgene stream (ii) to the reaction of amine with phosgene.

Abstract: In a method for detecting an offset drift in a resistive Wheatstone measuring bridge, a switch is made between a measuring mode and a testing mode without interfering in the internal structure of the measuring bridge. In testing mode, two sensor resistors that act in the same way and lie in different bridge arms in the measuring mode are connected in series, and a voltage level occurring in the connection of these sensor resistors is compared with a reference voltage. Preferably the sensor resistor that acts in a different way and lies between the two series-connected sensor resistors acting in the same way is bridged. The reference voltage is advantageously formed by resistive division of the voltage applied to the series connection of the sensor resistors. The testing mode may expediently be switched in such a way that the two pairs of sensor resistors acting in the same way are respectively tested in succession.

Abstract: In a method for detecting an offset drift in a resistive Wheatstone measuring bridge, a switch is made between a measuring mode and a testing mode without intervening in the internal structure of the measuring bridge. To this end, in testing mode two sensor resistors which act in the same way and lie in different bridge arms in the measuring mode, are connected in series and a voltage level occurring in the connection of these sensor resistors is compared with a reference voltage. Preferably the sensor resistor which acts in a different way and lies between the two series-connected sensor resistors acting in the same way is bridged. The reference voltage is advantageously formed by resistive division of the voltage applied to the series connection of the sensor resistors. The testing mode may expediently be switched in such a way that the two pairs of sensor resistors respectively acting in the same way are tested in succession.