Study Of SO₂ Poisoning And Regeneration Of Manganese-based Denitration Catalysts

NH3-selective catalytic reduction(NH3-SCR)is the most effective flue gas denitrification method,which is widely used in the flue gas denitration of coal-fired flue gas and industrial coke oven.Catalystic performance,especially the temperature window,is a central factor in the NH3-SCR denitrification technology.In the non-electricity field,the flue gas temperature of most industrial devices is low,which is not suitable for the traditional medium-high temperature SCR denitrification technology.Therefore,there is an urgent need to develop and apply SCR denitration technologies which are suitable for middle and low temperature regions,especially catalysts with low temperature denitrification activity.In recent years,it has been found that the manganese-based catalyst has good low-temperature denitrification SCR activity,which has received more attention However,SO2 at low concentration in flue gas has a serious poisoning effect on manganese-based catalysts,which will lead to the deactivation of catalysts,reduce the service life of the catalyst and increase the cost of denitrification.Therefore,it is greatly significant study the SO2 poisoning mechanism and regeneration technology of catalysts for improving the recycling of catalysts,reducing the cost of denitrification,reducing the environmental pollution and waste of resources.In this paper,the attapulgite-supported manganese(Mnx/PG)catalysts developed in the earlier stage of the research group were studied.The denitration performance of catalysts at low temperature,SO2 poisoning and regeneration of deactivated catalyst were mainly studied.The results show that the Mn8/PG catalyst has good denitrification performance at low temperature,and the activity of denitrification reaches 86%at 200 ?.When 400ppm SO2 in flue gas is introduced,the activity of catalysts decreases sharply.When the catalyst is completely poisoned,the activity of denitrification decreases to 24%at 200 ?.The deactivated catalyst was regenerated by thermal regeneration and water-washing regeneration.It was found that thermal regeneration could only partially recover the activity of deactivated catalysts;however,water washing can fully restore the activity of the catalyst.Through characterization of fresh,poisoned and regenerated Mng/PG catalysts,ammonium sulfate and ammonium bisulfate generated after the SO2 poisoning,it deposited on the surface of the catalyst,and blocked the catalyst pore,resulted in the deactivation of the catalyst.These ammonium sulfate salts have good thermal stability and are very difficult to completely remove by heat treatment;however,they can be effectively removed by water washing and can not wash off the active ingredient manganese.Mnx-V2O5-WO3/TiO2 catalyst was prepared by impregnation method using commercial V2O5-WO3/TiO2 as the matrix.The effect of preparation parameters(Mn loading and calcination temperature),SO2 poisoning and regeneration of deactivated catalyst were studied.The results showed that when the loading of Mn was 8%and the calcination temperature was 500? the activity of denitrification was the best.When the temperature was above 200 ?,the activity of denitrification was nearly 100%.However,when the catalyst was completely poisoned in the sulfur atmosphere(400ppm SO2),it dropped to 35.6%.After thermal regeneration,the denitrification activity of the catalyst decreased further,it decreased from 16.5%to 9.7%at 150?.After water washing,the denitrification activity of the catalyst could be completely recovered.Through the characterization of fresh,poisoned and regenerated Mn8-V2O5-WO3/TiO2 catalysts,it is known that the deactivation of the catalyst in the sulfur-containing atmosphere causes:on the one hand,ammonium sulfate is deposited on the surface of the catalyst and covers the pore structure of the catalyst.This is the common cause of sulfur poisoning on all SCR catalysts;on the other hand,the active component manganese combines with the sulfur in flue gas to form an intermediate like manganese sulfate,which occupied the active center of the catalyst,which was resulting in more severe poisoning.The ammonium sulfate salt can be removed by thermal decomposition,but the sulfur dioxide produced by the decomposition is further oxidized by the vanadium in the catalyst,and combined active ingredient manganese,so the activity is further decreasing.Washing regeneration can remove the ammonium sulfate salt on the surfae of catalysts,it can also destroy the structure of intermediates,remove the sulfate and can not wash away the active ingredient manganese,so the denitrification activity can return to fresh level.In this paper,we studied the process of sulfur poisoning and regeneration of two manganese-based catalysts.And discovered the common cause of sulfur poisoning in all SCR catalysts:The ammonium sulfate salt deposited on the surface of catalysts covered the pore structure of the catalysts,and it also leads to different performances in catalysts of sulfur poisoning and regeneration because of the different carrier:the sulfur-poisoned Mnx/PG catalyst is regenerated by heat,the activity of denitrification can be partially recovered;and the sulfur-poisoned Mnx-V2O5-WO3/TiO2 catalyst is regenerated by heat,the activity of denitrification further decreased.It reveals the basic laws of sulfur poisoning and regeneration processes for two manganese-based catalysts.