The Research Of Preparation And CO₂ Adsorption Performance Of Sepiolite-based Adsorbents

Today,the massive CO2 emission has caused many serious environmental issues.It is very important to capture and store CO2 emitted from power plants for they are the resources of more than 40%of CO2 in the atmosphere.In this dissertation,the raw sepiolite from Xiangtan,Hunan was purified,modified and then impregnated with DETA to obtain CO2 adsorbents.And then the morphology,texture and CO2 adsorption performance of as-prepared adsorbents were tested.The raw materials in this dissertation are raw sepiolite and sepiolite industrial products.The physical sedimentation method was selected for sepiolite purification.Under proper conditions(solid-to liquid ratio:1:8,dispersant amount:0.2%of solid amount,stirring period:3 h),the purity of sepiolite can be upgraded from 17%to higher than 85%and 95%after 24 hr and 48 hr sedimentation,respectively.For sepiolite industrial products,stratification method by using tap funnel was used to make sepiolite sedimentation again.At similar conditions,the purity of sepiolite can be upgraded to around 95%.Hereafter,ultrasound-assisted method was developed to accelerate the purification rate.At same conditions,the purification rate of ultrasonic groups is 1.2-1.6 times of groups without ultrasonic treatment.Subsequently,the acid activation of Sepiolite is studied in this paper,and find that the specific surface area of sepiolite increases and then decreases with the activation time in solid-liquid ratio 1:10 and 20%hydrochloric acid,reaching the maximum for 18h activation.The increase is due to the carbonate elimination and hole expansion effect of acid,while the decline at longer activation time is originated from the collapse of the pore structure of sepiolite as the extraction of majority of Mg ions.On the basis of the above experiments,this paper develops the "one-step" method to prepare the sepiolite carrier,and improves the sepiolite specific surface area to 255 m2/g by simply one acid-purification step.Further,DETA was impregnated into the purified sepiolite(DETA/SEP)and acid-activated sepiolite(DETA/SH-18)with different content to obtain CO2 adsorbents.The adsorbents were characterized by N2 adsorption isotherm analysis,XRD,FTIR and TGA,and the adsorption capacity of adsorbent was tested by Thermogravimetric method.The adsorption capacities of DETA/SEP are lower than the capacity of the original sepiolite.This is due to the small pore size of the adsorbent,the addition of amines is easier to completely block the sepiolite pore,preventing the CO2 from reaching the amine adsorption sites in the inside pore.The adsorption capacity of DETA/SH-18 decreases first and then increases,reaches a maximum and then drop again.The first reduction process is due to the adsorption capacity increase caused by the addition of a small amount of amine does not offset the reduction of the capacity caused by the surface area loss.The second reduction was due to the amine starting to load on the surface of the adsorbent and began to gather,preventing the CO2 from entering the adsorption sites.The acid activated Sepiolite with 0.8-DETA loading has the best adsorption capacity at lbar and 35?,with the adsorption capacity of 1.6 mmol/g.With the increase of adsorption temperature,the adsorption capacity of 0.8-DETA/SH-18 first rises and then decreases,and the optimal adsorption temperature is 65?.In order to investigate the kinetics of adsorbent,the experimental adsorption curve was fitted by selecting pseudo first order equation,pseudo second order equation and Avrami equation,and the Avrami equation could fit the experimental data well.Finally,the CCC index,calculating the cost of adsorbent for adsorbing per unit CO2,was established in this paper in order to compare the cost of preparing adsorbent with similar conditions,and the adsorbent prepared in this experiment has the lowest preparation cost under this evaluation system.