Isocyanate residue purification

A process for isolating aliphatic diisocyanate monomers and forming a polymeric isocyanate solid residue from a crude residue mixture containing the aliphatic diisocyanate monomers, said process comprising the steps of:

• (a) introducing said crude residue mixture containing aliphatic diisocyanate monomers selected from the group consisting of isophorone diisocyanate (IPDI), 1,6-diisocyanatohexane (HDI), saturated 4,40-diphenyl methane diisocyanate (H.sub.12 MDI), and combinations thereof into a heating zone of a dispersing evaporative dryer;
• (b) heating said crude residue mixture to cause at least a portion of said aliphatic diisocyanate monomers in said crude residue mixture to evaporate, thus forming a gaseous stream of aliphatic diisocyanate monomers and a molten stream of polymeric isocyanate residue;
• and
• (c) moving said molten stream of substantially aliphatic diisocyanate monomer-free residue from said heating zone to a cooling zone of said dispersing evaporative dryer, and cooling said molten stream to solidify said polymeric isocyanate residue as a dry solid residue having an isocyanate monomer content of less than 1% by weight.

A process for isolating aliphatic isocyanate monomers and forming a solid residue from a crude residue mixture containing the aliphatic isocyanate monomers, said process comprising the steps of:

• (a) introducing said crude residue mixture into a thermal evaporative dryer selected from the group consisting of a wiped film evaporative dryer and a thin film evaporative dryer, said thermal evaporative dryer evaporating a first portion of said isocyanate monomers to form a first gaseous stream of isocyanate monomers and a molten stream of crude residue comprising a second portion of said isocyanate monomers;
• (b) introducing said molten stream of crude residue into the heating zone of a dispersing evaporative dryer;
• (c) heating said molten stream of crude residue to cause at least a portion of said second portion of said isocyanate monomers to evaporate from said crude residue thus forming a second gaseous stream of isocyanate monomers and a molten stream of polymeric isocyanate residue;
• and
• (d) moving said molten stream of polymeric isocyanate residue from said heating zone to a cooling zone of said dispersing evaporative dryer, and cooling said molten stream to cause said molten stream to solidify as a solid polymeric isocyanate residue having an isocyanate monomer content of less than 1% by weight.

A process for isolating diisocyanate monomers and forming a solid residue from a crude residue mixture containing the diisocyanate monomers, said process comprising the steps of:

• (a) introducing said crude residue mixture containing diisocyanate monomers selected from the group consisting of toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), 1,6-diisocyanatohexane (HDI), saturated 4,4'-diphenyl methane diisocyanate (H12MDI), and combinations thereof into a thermal evaporative dryer selected from the group consisting of a wiped film evaporative dryer and a thin film evaporative dryer, said thermal evaporative dryer evaporating a first portion of said diisocyanate monomers to form a first gaseous stream of diisocyanate monomers and a molten stream of crude residue comprising a second portion of said diisocyanate monomers;
• (b) introducing said molten stream of crude residue into the heating zone of a dispersing evaporative dryer;
• (c) heating said molten stream to cause at least a portion of said second portion of said diisocyanate monomers to evaporate from said crude residue, thus forming a second gaseous stream of diisocyanate monomers and a molten stream of polymeric isocyanate residue;
• and
• (d) moving said molten stream of polymeric isocyanate residue from said heating zone to a cooling zone of said dispersing evaporative dryer, and cooling said molten stream of polymeric isocyanate residue to cause said molten stream to solidify as a solid residue having an isocyanate monomer content of less than 1% by weight.