A Review of Urea Pyrolysis to Produce NH₃ Used for NO_x Removal

Table 2

Condensed-phase kinetic scheme for urea thermal decomposition.

Reaction	Ai (s^−1)	Ei (kJ mol^−1)
(1) Urea ⟶ NH4^+ + NCO^−	8.50 × 10^6	84
(2) NH4^+ ⟶ NH3(g) + H^+	1.50 × 10^2	40
(3) NCO^− + H^+ ⟶ HNCO(g)	6.57 × 10^2	10
(4) Urea + NCO^− + H^+ ⟶ biuret	7.87 × 10^14	115
(5) Biuret ⟶ urea + NCO^− + H^+	1.50 × 10^24	250
(6) Biuret + NCO^− + H^+ ⟶ CYA + NH3(g)	2.81 × 10^18	150
(7) CYA ⟶ 3NCO^− + 3 H^+	1.50 × 10^19	260
(8) CYA + NCO^− + H^+ ⟶ ammelide + CO2	3.48 × 10^5	35
(9) Ammelide ⟶ 2NCO^− + 2H^+ + HCN(g) + NH(g)	6.00 × 10^14	220
(10) Urea(aq) ⟶ NH4^+ + NCO^-	1.20 × 10^8	84
(11) NCO^− + H^+ + H2O(aq) ⟶ NH3 + CO2(g)	5.62 × 10^9	59
(12) Urea(aq) + NCO^− + H^+ ⟶ biuret	3.93 × 10^14	115

(g): gaseous; (aq): aqueous.