A method for manufacturing an isocyanate compound represented by formula (2) (2) wherein R1 represents a methyl group, an ethyl group, a cyclopropyl group, a chlorine atom, a bromine atom, or a methoxy group; and R2 represents an alkyl group having 1 to 6 carbon atoms, comprising reacting an aniline compound represented by formula (1) (1) wherein R1 and R2 are defined as above with a phosgene compound at a temperature of from 40° C. to the boiling point of the inert solvent in at least one kind of inert solvent.

A method for manufacturing an isocyanate compound represented by formula (2) (2) wherein R1 represents a methyl group, an ethyl group, a cyclopropyl group, a chlorine atom, a bromine atom, or a methoxy group; and R2 represents an alkyl group having 1 to 6 carbon atoms, comprising reacting an aniline compound represented by formula (1) (1) wherein R1 and R2 are defined as above with a phosgene compound at a temperature of from 40° C. to the boiling point of the inert solvent in at least one kind of inert solvent.

A method for manufacturing an isocyanate compound represented by formula (2) (2) wherein R1 represents a methyl group, an ethyl group, a cyclopropyl group, a chlorine atom, a bromine atom, or a methoxy group; and R2 represents an alkyl group having 1 to 6 carbon atoms, comprising reacting an aniline compound represented by formula (1) (1) wherein R1 and R2 are defined as above with a phosgene compound at a temperature of from 40° C. to the boiling point of the inert solvent in at least one kind of inert solvent.

The invention relates to a method for producing di- and polyisocyanates of the diphenylmethane series, in which (i) the liquid product flow created in the phosgenation, (ii) the reaction mixture present in an optionally provided reactor for carbamic acid chloride cleaving, (ii) the liquid product flow leaving such an optionally provided reactor for carbamic acid chloride cleaving, (iv) the reaction mixture present in the dephosgenation, or (v) the liquid product flow created in the dephosgenation, is treated with a gaseous hydrogen chloride flow in one stage in a bubble column or in a plate column within a contact time of 1 min to less than 30 min. The product flow treated din this way or in the reaction mixture treated in this way is fed directly (i.e. in particular without further treatment with an inert gas) to the next step of the reaction or workup.

The invention relates to a method for producing di- and polyisocyanates of the diphenylmethane series, in which (i) the liquid product flow created in the phosgenation, (ii) the reaction mixture present in an optionally provided reactor for carbamic acid chloride cleaving, (ii) the liquid product flow leaving such an optionally provided reactor for carbamic acid chloride cleaving, (iv) the reaction mixture present in the dephosgenation, or (v) the liquid product flow created in the dephosgenation, is treated with a gaseous hydrogen chloride flow in one stage in a bubble column or in a plate column within a contact time of 1 min to less than 30 min. The product flow treated din this way or in the reaction mixture treated in this way is fed directly (i.e. in particular without further treatment with an inert gas) to the next step of the reaction or workup.

The invention relates to a method for producing di- and polyisocyanates of the diphenylmethane series, in which (i) the liquid product flow created in the phosgenation, (ii) the reaction mixture present in an optionally provided reactor for carbamic acid chloride cleaving, (ii) the liquid product flow leaving such an optionally provided reactor for carbamic acid chloride cleaving, (iv) the reaction mixture present in the dephosgenation, or (v) the liquid product flow created in the dephosgenation, is treated with a gaseous hydrogen chloride flow in one stage in a bubble column or in a plate column within a contact time of 1 min to less than 30 min. The product flow treated din this way or in the reaction mixture treated in this way is fed directly (i.e. in particular without further treatment with an inert gas) to the next step of the reaction or workup.

According to an embodiment, the pH of a diisocyanate composition and a diamine hydrochloride composition used in the preparation of an optical lens is adjusted to a specific range, whereby it is possible to enhance not only the yield and purity of the diisocyanate composition but also the optical characteristics of the final optical lens by suppressing the striae and cloudiness. Specifically, according to the process of the embodiment, the amount of an aqueous hydrochloric acid solution introduced to the reaction may be adjusted to control the pH of the diisocyanate composition to a desired range, thereby enhancing the yield and purity. Accordingly, the process for preparing a diisocyanate composition according to the embodiment can be applied to the preparation of a plastic optical lens of high quality.

According to an embodiment, the pH of a diisocyanate composition and a diamine hydrochloride composition used in the preparation of an optical lens is adjusted to a specific range, whereby it is possible to enhance not only the yield and purity of the diisocyanate composition but also the optical characteristics of the final optical lens by suppressing the striae and cloudiness. Specifically, according to the process of the embodiment, the amount of an aqueous hydrochloric acid solution introduced to the reaction may be adjusted to control the pH of the diisocyanate composition to a desired range, thereby enhancing the yield and purity. Accordingly, the process for preparing a diisocyanate composition according to the embodiment can be applied to the preparation of a plastic optical lens of high quality.

According to an embodiment, the pH of a diisocyanate composition and a diamine hydrochloride composition used in the preparation of an optical lens is adjusted to a specific range, whereby it is possible to enhance not only the yield and purity of the diisocyanate composition but also the optical characteristics of the final optical lens by suppressing the striae and cloudiness. Specifically, according to the process of the embodiment, the amount of an aqueous hydrochloric acid solution introduced to the reaction may be adjusted to control the pH of the diisocyanate composition to a desired range, thereby enhancing the yield and purity. Accordingly, the process for preparing a diisocyanate composition according to the embodiment can be applied to the preparation of a plastic optical lens of high quality.

The present invention relates to a method for operating a plant for continuous production of an isocyanate by converting a primary amine A with phosgene P whilst maintaining, based on the amino groups of the primary amine, a stoichiometric excess of phosgene in the presence of a solvent L in the liquid phase, using a first, adiabatically operated reaction chamber and a second, isothermally operated reaction chamber. The method is characterised in that a combination of measures, in particular the maintenance of a sufficiently high starting pressure and a sufficiently high starting temperature, is applied in order to bring the plant back into the target state, standard operation, starting from a state of interruption to production.