Experimental Study On Preparation Of Mercury Adsorbent By Hydrothermal Carbonization Of Bamboo And Bromine Flame Retardant

At present,global mercury pollution is serious,and China is the world’s largest mercury emitter.Mercury emission from the flue of coal-fired power stations is one of the main factors for mercury emission in China.The activated carbon injection method is a commonly used technology for mercury emission control in the flue of coal-fired power plants,but the traditional activated carbon has a poor removal effect of Hg~0,and the C/Hg ratio during the injection process is high.The development of cheap,environmentally friendly and efficient mercury sorbents is a current research hotspot.This article proposes a new idea for the preparation of bromine-containing waste-derived mercury adsorbents.Bamboo powder and tetrabromobisphenol A are used as raw materials,KOH is used as an additive,and the adsorbent is prepared by hydrothermal carbonization and pyrolysis activation methods.Mercury removal performance was studied.First,raw material composition analysis,infrared analysis,and thermogravimetric analysis were performed to provide basic data for the preparation experiments of adsorbents.Studies have shown that bamboo is a typical fibrous plant.The main chemical components include cellulose,hemicellulose,lignin,and trace elements such as Na and K.The main thermal weight loss intervals of bamboo powder and tetrabromobisphenol A are between220～400℃and 220～380℃,respectively.The thermal weight loss intervals of the two are highly coincident.Secondly,experiments were conducted on the effects of preparation conditions such as hydrothermal temperature,material ratio,and pyrolysis temperature on the physicochemical properties of hydrothermal char and adsorbents.The study found that after hydrothermal reaction,the alcohol and phenolic substances in the raw materials decreased and the degree of carbonization increased.Increasing the hydrothermal temperature is conducive to optimizing the pore structure of the adsorbent,increasing the specific surface area,enhancing the effect of bromine fixation,reducing the yield of hydrothermal char and the pyrolysis loss rate.Increasing the proportion of tetrabromobisphenol A will increase the pore structure block of the adsorbent.At the same time,pyrolysis temperature is also an important influencing factor for forming a good pore structure and improving the effect of fixing bromine.At 320℃of hydrothermal temperature,2:1 of bamboo powder:TBBPA ratio,800℃of pyrolysis temperature and 140℃of adsorption temperature,the removal efficiency of elemental mercury can reach 99%.Finally,XPS analysis and adsorption kinetics fitting methods were used to study the adsorption mechanism.It was found that the adsorption process of elemental mercury by the adsorbent accorded with the quasi-secondary adsorption kinetics dominated by chemical adsorption.The main chemical and adsorption reactions are as follows:Tetrabromobisphenol A is debrominated to form HBr,and then reacted with KOH to form KBr.The C-Br bond formed by the combination of C radicals and bromine ions oxidizes Hg~0 to a stable oxidation state and adsorbs on the surface of the adsorbent.