Study On Simultaneous Removal Of SO₂,NO_x And Hg⁰ In Acid Production Tail Gas By Corn Straw-based Activated Carbon Catalyst

Low-concentration sulfur dioxide（SO₂）,ntrogen oxides（NO_x）and zero-valent mercury（Hg⁰）contained in the acid-making tail gas of the lead-zinc smelting flue gas are often emitted directly into the atmosphere.As China implements ultra-low emissions（SO₂,NO_x and Hg⁰emission concentrations are below 35 mg/m3,50mg/m3,and 30μg/m3,respectively）and energy-saving retrofit.It is necessary to develop a purification material for the simultaneous and efficient removal of multiple pollutants.And further purify the low concentration SO₂,NO_x and Hg⁰after lead and zinc smelting flue gas to make acid,and explore the reaction mechanism.It provides a theoretical basis for the synergistic purification of SO₂,NO_x and Hg⁰in acid production tail gas from lead-zinc smelting,and promote the green development of the non-ferrous metal industry.This study will combine the three technologies of adsorption oxidation desulfurization,SCR denitrification,and catalytic oxidation demercuration to achieve the synergistic purification of SO₂,NO_x and Hg⁰gaseous pollutants in the acid tail gas from lead-zinc smelting flue gas.First,screening and optimization of the best preparation conditions for corn straw-based activated carbon catalyst catalysts,including carbonization temperature,types and contents of activators,activation temperature,types and loadings of metal active components,metal precursors,and calcination temperature.Then,screening and optimizing the optimal reaction conditions for catalysts,including reaction space velocity,O₂content,ammonia-nitrogen ratio,and inlet concentration.Investigate the effects of different preparation and reaction process conditions on simultaneous desulfurization,denitrification and mercury removal;In addition,the structure and surface characteristics of the materials were analyzed by means of BET,XRD,TG/DTA,XPS,CO₂-TPD and FTIR,and the possible reaction mechanism of the catalytic removal of the catalyst was explored.The effects of the preparation conditions on the simultaneous desulfurization,denitrification and mercury removal by corn straw-based activated carbon catalyst at low temperature were investigated.The reaction conditions are as follows:200 ppm SO₂,300 ppm NO,100μg/m³Hg⁰,600 ppm NH₃,3%O₂,N₂as the equilibrium gas,the flow rate is 450 m L/min,and the space velocity（GHSV）is 5000h^-1.The reaction temperature gradient is 100-150-200-250-300-350°C,and it stays at each temperature for 40 min.The optimal preparation conditions are as follows:carbonization temperature is 700°C,activator is KOH,activator content is alkali-carbon ratio=3:1,activation temperature is 700°C,10%CuCl₂is loaded,and roasting temperature is400°C.Under optimal conditions,the prepared corn straw based activated carbon showed a good aromatization structure,with a high specific surface area（1259m²/g）,a pore volume（0.56cm³/g）,rich active functional groups,and good copper dispersibility.The maximum removal rates of SO₂,NO_x and Hg⁰at 100-350°C under catalyst are 100%,99%and 95%,respectively.The effect of catalyst on simultaneous desulfurization,denitrification and mercury removal at different reaction conditions at low temperature was studied.The reaction conditions include space velocity and flue gas components.Studies have shown that the optimal reaction conditions are as follows:the reaction space velocity is 5000 h^-1,the optimal oxygen content is 3%,the optimal ammonia-nitrogen ratio is2:1,and the optimal inlet concentration is 200ppm SO₂,300ppm NO and 100ppm Hg⁰.Under this reaction condition,the best removal rate of removing ntrogen oxides,sulfur dioxide and zero-valent mercury using corn straw-based activated carbon catalyst under low temperature conditions is 100%desulfurization rate,99%denitration rate and 95%mercury removal rate.In the range of 100-250℃,N₂O was hardly observed and 35ppm and 85ppm N₂O were generated at 300-350℃,with selectivity of 76%and 43%,respectively.The possible reaction mechanism of corn straw-based activated carbon catalyst for the removal of SO₂,NO and Hg⁰at low temperature was studied by using in durability and pure adsorption experiments,transient response and XPS characterization.Studies have shown that the simultaneous desulfurization,denitrification and mercury removal by activated carbon catalyst includes adsorption removal reaction and catalytic removal reaction.Adsorption removal is the main method at 100℃,and catalytic removal is the main method at 200℃.In addition,SO₂in flue gas forms sulfate and sulfite under the condition containing NH₃.At the same time,NH₃adsorbed on the catalyst reacts with NO in the gas phase to form N₂and H₂O;and the Hg⁰in the flue gas reacts with O₂to generate Hg O,so as to achieve the purpose of removing SO₂,NO_x and Hg⁰.