Dielectric-Barrier Discharge Plasma Reaction For Conversion Of CO And NH₃

Carbon monoxide and ammonia are cheap and abundant in chemical raw materials. Therefore, the direct synthesis of high value chemicals from carbon monoxide and ammonia have a broad application prospect and a profound scientific significance. In this paper, a dielectric barrier discharge(DBD) has been used to study the CO/NH3 plasma reaction, and some results have been obtained as follows:Firstly, the types of the plasma reactors have significant effects on the CO/NH3 DBD plasma reaction. In the double dielectric barrier discharge (DDBD) reactor with a circulating water grounding electrode or a spiral iron wire grounding electrode, the main products of the CO/NH3 plasma reaction were amides which include formamide, acetamide, and N-methyl formamide. In the DDBD reactor with aluminum foil grounding electrode, urea was mainly obtained from the CO/NH3 plasma reaction. However, in a single dielectric barrier discharge reactor (SDBD) with a circulating water grounding electrode, the CO/NH3 plasma reaction mainly produced hydrazine.Secondly, the reactor structure parameters of the plasma reactor, the discharge parameters and the reaction conditions have significant effects on the results of the CO/NH3 plasma reaction for the synthesis of amides, urea and hydrazine. In the DDBD reactor with a circulating water grounding electrode, the optimum conditions for synthesis of amides were as follows:7 cm discharge zone length,4 mm high voltage electrode diameter,45 W input power,9 kHz discharge frequency,1:1 CO/NH3 feed ratio,20 mL/min total flow rate and 29 ? circulating water,where 4.8% formamide yield has been achieved. In the DDBD reactor with a aluminum foil grounding electrode, the appropriate conditions for the synthesis of urea were as follows:7 cm discharge zone length,4mm high voltage electrode diameter,45 W input power,9 kHz discharge frequency,1:1 CO/NH3 feed ratio,80 mL/min total flow rate, where 7.8% urea yield has been achieved. In the SDBD reactor with a circulating water grounding electrode, optimum conditions for synthesis of hydrazine were as follows:7cm discharge zone length, stainless steel the voltage electrode material,36 W input power,9 kHz discharge frequency,1:5 CO/NH3 feed ratio,60 mL/min total flow rate,29? circulating water, where 0.28 gL-1h-1 hydrazine yield has been obtained.Finally, the CO/NH3 DBD plasma have been diagnosed by optical emission spectrum (OES). The OES results show that, in the CO/NH3 DBD plasma, CO can be activated into electronic and vibrational exited states CO*, NH3 can be activated into NH, NH2 and NH3* species. It can be inferred that the formamide may be generated through the reaction of CO* and NH2 radicals, the urea may be produced through CO* and two NH2 radicals. However, hydrazine may be synthesized through self-coupling of NH2 radicals, where CO molecules might help to generate NH2 radicals by combining with H atoms.