The invention relates to a method for producing two isocyanates by reacting a first amine with phosgene in a stoichiometric excess in the gas phase to produce a first isocyanate, wherein the excess phosgene is subsequently recovered and recirculated back to react with a second amine to produce a second isocyanate. In another embodiment, both fresh and recycled phosgene may be used in reacting each respective amine to produce an isocyanate. The amine streams may be optimized to contain different concentrations of hydrogen chloride, as required for the production of two different isocyanates.

The invention relates to polyphenyl polymethylene polyisocyanates having an NCO number of at least 29% comprising less than 2% by weight ureas, less than 8% by weight carbodiimides or uretonimines and less than 1000 ppm organic chlorine compounds. The polyphenyl polymethylene polyisocyanates can be prepared according to the invention by reacting (i) polyphenyl polymethylene polyamines with organic carbonates to give the corresponding polyphenyl polymethylene polycarbamates, (ii) by thermally cleaving the polyphenyl polymethylene polycarbamates to give the polyphenyl polymethylene polyisocyanates,
wherein, prior to the thermal cleavage, the free amino groups or urea groups present in the carhamate crude mixture comprising the polyphenyl polymethylene polycarbamates are reacted with a derivatizing reagent to give amide groups or urethane groups. The polyphenyl polymethylene polyisocyanates can further be prepared according to the invention, prior to the thermal cleavage, by removing compounds having free amino groups or urea groups present in the carbamate crude mixture from the carbamate crude mixture by filtration of the carbamate crude mixture comprising the polyphenyl polymethylene polycarbamates over a solid acidic adsorbent in the presence of an acid dissolved in the carbamate crude mixture.

The invention relates to polyphenyl polymethylene polyisocyanates having an NCO number of at least 29% comprising less than 2% by weight ureas, less than 8% by weight carbodiimides or uretonimines and less than 1000 ppm organic chlorine compounds. The polyphenyl polymethylene polyisocyanates can be prepared according to the invention by reacting (i) polyphenyl polymethylene polyamines with organic carbonates to give the corresponding polyphenyl polymethylene polycarbamates, (ii) by thermally cleaving the polyphenyl polymethylene polycarbamates to give the polyphenyl polymethylene polyisocyanates,
wherein, prior to the thermal cleavage, the free amino groups or urea groups present in the carhamate crude mixture comprising the polyphenyl polymethylene polycarbamates are reacted with a derivatizing reagent to give amide groups or urethane groups. The polyphenyl polymethylene polyisocyanates can further be prepared according to the invention, prior to the thermal cleavage, by removing compounds having free amino groups or urea groups present in the carbamate crude mixture from the carbamate crude mixture by filtration of the carbamate crude mixture comprising the polyphenyl polymethylene polycarbamates over a solid acidic adsorbent in the presence of an acid dissolved in the carbamate crude mixture.

The invention relates to polyphenyl polymethylene polyisocyanates having an NCO number of at least 29% comprising less than 2% by weight ureas, less than 8% by weight carbodiimides or uretonimines and less than 1000 ppm organic chlorine compounds. The polyphenyl polymethylene polyisocyanates can be prepared according to the invention by reacting (i) polyphenyl polymethylene polyamines with organic carbonates to give the corresponding polyphenyl polymethylene polycarbamates, (ii) by thermally cleaving the polyphenyl polymethylene polycarbamates to give the polyphenyl polymethylene polyisocyanates,
wherein, prior to the thermal cleavage, the free amino groups or urea groups present in the carhamate crude mixture comprising the polyphenyl polymethylene polycarbamates are reacted with a derivatizing reagent to give amide groups or urethane groups. The polyphenyl polymethylene polyisocyanates can further be prepared according to the invention, prior to the thermal cleavage, by removing compounds having free amino groups or urea groups present in the carbamate crude mixture from the carbamate crude mixture by filtration of the carbamate crude mixture comprising the polyphenyl polymethylene polycarbamates over a solid acidic adsorbent in the presence of an acid dissolved in the carbamate crude mixture.

The present invention is directed to a process for preparing amides or polyamides by replacing isocyanate starting materials of a catalyzed thermal reaction with aromatic carbamates. Through the catalyzed thermal process involving a non-isocyanate precursor of the present invention, efficiency for producing amides or polyamides can be significantly improved, and the impure side products produced from a side reaction of isocyanate can be greatly curtailed. Hence, amides or polyamides of high purity and yield can be achieved. The invention also relates to a process for preparing aromatic carbamates, the new non-isocyanate precursors for amides or polyamides.

The present invention is directed to a process for preparing amides or polyamides by replacing isocyanate starting materials of a catalyzed thermal reaction with aromatic carbamates. Through the catalyzed thermal process involving a non-isocyanate precursor of the present invention, efficiency for producing amides or polyamides can be significantly improved, and the impure side products produced from a side reaction of isocyanate can be greatly curtailed. Hence, amides or polyamides of high purity and yield can be achieved. The invention also relates to a process for preparing aromatic carbamates, the new non-isocyanate precursors for amides or polyamides.

A process for preparing an isocyanate compound is provided. The process includes a step of reacting an amine compound A having at least one primary amino group with CO.sub.2 and an organotin compound S having at least one radical OR.sup.3 attached to the tin atom of the organotin compound to convert at least one of the primary amino groups in the amine compound A into a carbamate group to obtain a carbamate compound C; a step of cleaving the carbamate groups in the obtained carbamate compound C to form the isocyanate compound and an alcohol R.sup.3OH, without separation of the tin compounds; and a step of obtaining the isocyanate compound. The radical R.sup.3 is a C-bound organic radical of 1-30 carbon atoms with 1, 2, or 3 carbon atoms optionally replaced by oxygen or nitrogen.

A process for preparing an isocyanate compound is provided. The process includes a step of reacting an amine compound A having at least one primary amino group with CO.sub.2 and an organotin compound S having at least one radical OR.sup.3 attached to the tin atom of the organotin compound to convert at least one of the primary amino groups in the amine compound A into a carbamate group to obtain a carbamate compound C; a step of cleaving the carbamate groups in the obtained carbamate compound C to form the isocyanate compound and an alcohol R.sup.3OH, without separation of the tin compounds; and a step of obtaining the isocyanate compound. The radical R.sup.3 is a C-bound organic radical of 1-30 carbon atoms with 1, 2, or 3 carbon atoms optionally replaced by oxygen or nitrogen.

A process for preparing an isocyanate compound is provided. The process includes a step of reacting an amine compound A having at least one primary amino group with CO.sub.2 and an organotin compound S having at least one radical OR.sup.3 attached to the tin atom of the organotin compound to convert at least one of the primary amino groups in the amine compound A into a carbamate group to obtain a carbamate compound C; a step of cleaving the carbamate groups in the obtained carbamate compound C to form the isocyanate compound and an alcohol R.sup.3OH, without separation of the tin compounds; and a step of obtaining the isocyanate compound. The radical R.sup.3 is a C-bound organic radical of 1-30 carbon atoms with 1, 2, or 3 carbon atoms optionally replaced by oxygen or nitrogen.

The invention relates to a method for decomposing polyurethane, wherein material containing polyurethane is heated to a temperature from 190? C. to 250? C. under overpressure in the presence of an aqueous solution containing 1 to 45 mass percent urea. It further relates to a liquid process medium obtainable thereby.