Removal Of Thiophene From Waste Gas By Heterogeneous Fenton Process Supported By ZSM-5 Molecular Sieve Nanosized Zero-valent Iron

Thiophene is one of the main sulfur compounds,widely used in the synthesis of pesticides,medicine,biological products,dyes,etc.Like many VOCs,thiophene is easily released into the atmosphere,causing serious environmental pollution.Heterogeneous Fenton process is an effective advanced oxidation technology to remove VOCs in the atmosphere,which has been widely concerned and studied by scholars at home and abroad in recent years.Therefore,ZSM-5/n ZVI heterogeneous Fenton catalyst was prepared by chemical impregnation method.A wet scrubber（500 m L）was used to combined with heterogeneous Fenton catalyst to remove gaseous thiophene.The catalytic performance and stability of the catalyst were investigated,the influence of different factors on heterogeneous Fenton catalytic system was studied,and the mechanism of catalytic degradation of thiophene was explored.First,X-ray diffraction（XRD）,scanning electron microscopy（SEM）,specific surface area test（BET）and other characterization results showed that n ZVI was uniformly loaded on ZSM-5 zeolite,and the catalyst mainly contained Fe,Si and O elements.The content of Fe element was17.73%,and the specific surface area was 97.39 m²/g.The pore volume was 0.041 cm³/g and the pore size was 1.49 nm.Then,with 60 mg/L H₂O₂as the research object,the catalytic decomposition rate of H₂O₂by ZSM-5/n ZVI reaches 93%at p H 3.EPR determination results show that·OH is the main reactive oxygen species produced by ZSM-5/n ZVI heterogeneous Fenton system.Secondly,with 500 mg/L thiophene as the research object,the maximum thiophene removal rate of ZSM-5/n ZVI heterogeneous Fenton system is 81.7%at 5 min,and the removal rate is still 48.7%after 3 h.The removal rate of catalyst is still more than 40%after 5 times of reuse.The leaching amount of Fe ion was lower than 26 mg/L under different conditions.In general,ZSM-5/n ZVI heterogeneous Fenton system has good catalytic degradation ability and stability.Then,the effects of ZSM-5/n ZVI heterogeneous catalyst dosage,initial concentration of H₂O₂,initial p H of solution,initial concentration of thiophene and gas flow rate on thiophene degradation efficiency were studied.The results showed that the removal rate of thiophene was positively correlated with the amount of ZSM-5/n ZVI heterogeneous catalyst and the initial concentration of H₂O₂,and negatively correlated with the increase of the initial p H of solution,the initial concentration of thiophene and the increase of gas flow.RSM was used to optimize the influencing factors.The results showed that when the initial thiophene concentration was 500mg/L,ZSM-5/n ZVI heterogeneous catalyst dosage was 2.93 g/L,H₂O₂initial concentration was 81.3 mg/L,p H was 4.52,and gas flow rate was129.2 m L/min.The thiophene removal rate was 67.9%after 3 hours.Finally,the reaction kinetics and mechanism of heterogeneous Fenton system are studied.The results showed that the reaction order of catalyst dosage,H₂O₂initial concentration and thiophene initial concentration were 0.3703,0.335 and 0.9956,respectively.The pre-exponential factor and activation energy of the reaction were 1.442mol^-1·s^-1and 1.33×104 J/mol,respectively.NZVI in the catalyst as the active site,and H₂O₂in solution on the surface of the catalyst,reaction and produce·OH reactive oxygen species,thiophene and·OH addition reaction,C₄H₅SO,C₄H₄SO,C₄H₄SO₂,then C₄H₅SO,C₄H₄SO₂oxidation by·OH,The pyrolysis reaction produces acetic acid and glycolic acid,in which the acetic acid can be further mineralized into CO₂ and H₂O.