Production of ammonia from plasma-catalytic decomposition of urea: Effects of carrier gas composition

Abstract

Effects of carrier gas composition (N2/air) on NH3 production, energy efficiency regarding NH3 production and byproducts formation from plasma-catalytic decomposition of urea were systematically investigated using an Al2O3-packed dielectric barrier discharge (DBD) reactor at room temperature. Results show that the presence of O2 in the carrier gas accelerates the conversion of urea but leads to less generation of NH3. The final yield of NH3 in the gas phase decreased from 70.5%, 78.7%, 66.6% and 67.2% to 54.1%, 51.7%, 49.6% and 53.4% for applied voltages of 17, 19, 21 and 23kV, respectively when air was used as the carrier gas instead of N2. From the viewpoint of energy savings, however, air carrier gas is better than N2 due to reduced energy consumption and increased energy efficiency for decomposition of a fixed amount of urea. Carrier gas composition has little influence on the major decomposition pathways of urea under the synergetic effects of plasma and Al2O3 catalyst to give NH3 and CO2 as the main products. Compared to a small amount of N2O formed with N2 as the carrier gas, however, more byproducts including N2O and NO2 in the gas phase and NH4NO3 in solid deposits were produced with air as the carrier gas, probably due to the unproductive consumption of NH3, the possible intermediate HNCO and even urea by the abundant active oxygen species and nitrogen oxides generated in air-DBD plasma.