Study On Plasma Degradation Process Of Fumigation Residues Of Phosphine In Grain Barn

Phosphine with the characteristics of high efficiency,fast speed and low residue,has been used as a fumigant for a long time in grain storage industry in China.However,phosphine is highly toxic and usually discharged directly into the atmosphere after fumigation,which not only pollutes the surrounding air,but also endangers the health of nearby residents.Therefore,it is urgent to find an efficient method to degrade phosphine fumigation gas.Non-thermal plasma(NTP),as a new degradation technology,received more and more attention from scholars because of its simple equipment,low energy consumption,high efficiency and no residue.In this paper,the degradation effect of phosphine by single NTP and the NTP combined with catalysts were investigated in a coaxial cylinder single dielectric barrier discharge reactor.The degradation mechanism was discussed,and the effects of degradation products on the quality of oat were analyzed.The research results were as follows.1.The results of degradation of PH₃by single NTP showed that,with the prolongation of the discharge time,the discharge state was partially changed,and the discharge voltage and current had no obvious changes.In the process of PH₃degradation,the degradation rate of PH₃decreased gradually and then tended to be stable with the extension of discharge time,which was due to the uneven discharge caused by the gradual accumulation of degradation products.The O₃concentration showed a tend of rising then falling and finally tending to zero with the prolongation of the discharge tine,which was due to the decomposition of O₃caused by the increase of the reaction temperature.The more the power input,the less the gas flowed and the larger the discharge gap was,the higher the degragation rate of PH₃was.2.Phosphoric acid was the main product of degradation of PH₃by single NTP,and there was no obvious gaseous product containing phosphorus.The degradation process may be that the high-energy electrons collided directly with the PH₃molecule,resulting in the chemical bond breaking.High-energy electrons collided with the background gas to produce an active radical,which then acted on PH₃and oxidized it to phosphoric acid.3.The experimental results of NTP combined with carrier showed that the intensity of discharge current pulse in the reactor filled with the carrier was obviously reduced,and there were more times of current pulse,which indicated that the discharge state had changed after the filling material,and the original filamentous discharge had changed to the mixed discharge form of filamentous discharge and surface streamer discharge.The degradation effect of NTP combined with different carriers was as follows:ZSM-5>Zr O₂>Si O₂>Ti O₂>Al₂O₃>Single NTP.After supporting Fe₂O₃,the degradation effect of NTP combined with Fe₂O₃catalysts was as follows:Fe₂O₃/Al₂O₃>Fe₂O₃/ZSM-5>Fe₂O₃/Ti O₂>Fe₂O₃/Si O₂>Fe₂O₃/Zr O₂>Single NTP.As the carrier of catalyst,Al₂O₃could better achieve the effect of NTP combined degradation of phosphine.4.The specific surface area and pore volume of ZSM-5 support,Fe₂O₃/Al₂O₃and Fe₂O₃/ZSM-5catalysts all decreased,and the crystal form remained unchanged.However,the valence states and composition of Fe,P and O on the surface of the two catalysts all changed,and the change of Fe₂O₃/Al₂O₃was small.The degradation mechanism of NTP combined with catalysts was mainly as follows:NTP gas reaction and catalyst surface reaction.Among them,high energy electrons and active radicals in the plasma reacted with PH₃to oxidize and degrade phosphoric acid.The catalyst could adsorb PH₃and its intermediate products,reacted with reactive oxygen species on the catalyst surface,and produced a large number of phosphoric acid products on the catalyst surface.5.The content of soluble protein,starch,malondialdehyde and lipoxygenase activity in oat were adversely affected by NTP degradation of phosphine,and the storage quality of oat was significantly affected.