A process for producing an aliphatic isocyanate from an aliphatic primary amine comprising a carbonylation step in which an aliphatic primary amine is allowed to react with carbon monoxide at a temperature of about 100-250°C in the presence of an aromatic hydroxyl compound having a pKa value of not more than about 11, molecular oxigen and a catalyst system comprising at least one member selected from palladium and rhodium metals and components thereof and at least one member selected from iodine and bromine and compounds thereof and a combined separation and recovery step comprising a pyrolysis-distillation reaction in which the mixture of carbonylated products is heated to a temperature of from about 100 to 300°C.