Abstract In a process of pyrolyzing urea in a reactor system through which a stream of inert gas is passed to accelerate the rate of pyrolysis by purging evolved ammonia therefrom, an improved method for recovering unreacted vaporized urea also purged by the gas stream with the ammonia which comprises passing the condensable vapors of an inert compound through the reactor (s), cooling the purged ammonia and urea containing vapor mixture to a temperature low enough to condense the vapors of the inert compound thereby minimizing the concentration of this component in the vapor mixture, but high enough to preclude urea condensation, feeding the resulting concentrated vapor mixture to a gas/liquid contacting column and contacting the same with fresh urea melt feedstock, thereby condensing a substantial amount of the urea vapor contacted, feeding the condensed urea along with the urea melt feedstock to the pyrolysis reactor(s), and passing the urea depleted effluent vapor mixture to a conventional ammonia recovery unit.
A method according to claim 1 wherein the condensable vapors of the inert compounds employed are the vapors of saturated branched- and straight- chain hydrocarbon compounds of the alkane series having from about eight to about 12 carbon atoms or mixtures thereof which are condensable at temperatures above about 120*C.
Claim 2
Dependent Claim
134 words
A method according to claim 1 comprising purging one or more urea pyrolysis reactors with a mixture of the condensable vapors of eight and nine carbon atom isoparaffinic hydrocarbons, cooling the purged hydrocarbon/ammonia/urea vapor mixture in the condensor to a temperature of about 125*C. to condense a substantial amount of the hydrocarbon vapor, passing the resulting concentrated vapor mixture having greatly increased mole fraction concentrations relative to ammonia and urea to a gas/liquid contacting column, separating the urea vapor from the concentrated vapor mixture by contacting countercurrently in said column the concentrated vapor mixture with melt feedstock having a temperature of from about 135* to about 140*C. and an equilibrium vapor phase concentration at or about a minimum thereby condensing and recovering a substantial amount of the urea vapor contacted by said melt feedstock.
Claim 3
Dependent Claim
36 words
A method as claimed in claim 1 wherein the gas/liquid contacting column is substantially vertically disposed above the urea pyrolysis reactor so that the melt feedstock flows therefrom to the reactor under the force of gravity.