Preparation And CO₂ Capture Of Amine-impregnated Titanium-based Composites

CO2 emission has caused serious environmental concerns,since CO2 is the major contributor to greenhouse gas and its consequent global warming effect.It is reported that the concentration of CO2 in the atmosphere has increased to 406.42 ppmv at February 2017.To mitigate the CO2 emission,different CO2 capture techniques have been explored.Among various CO2 capture techniques,adsorption by sorbents has been proposed as the one of the most effective technologies and the key of this technology is to find sorbents with superior CO2 capture capacity.Due to the strong interaction between-NH2 moiety and CO2 molecules,solid-supported amine sorbents have shown high CO2 sorption capacity,high CO2/N2 selectivity,and good reversibility under the simulated flue gas conditions indicating their great promise in CO2 capture.In this thesis,amine-impregnated titanium-base composites have been prepared and their CO2 adsorption properties have been investigated.The summaries of the results are as follows:1.Porous titanium oxides was synthesized by hydrolysis of titanium(IV)isopropoxide and modified by tetraethylenepentamine(TEPA)to obtain the amine-impregnated composite with 40 wt.%TEPA loading.The CO2 capture performance of the composite sorbent was tested by a fixed-bed reactor equipped with an on-line gas chromatograph.It was found that CO2 uptake capacity of this composite sorbent is 2.23 mmol/g under simulated flue gas conditions(10.0%(v/v)CO2 in N2 at 75 ℃),which is lower than the analogue Si-based amine-impregnated composites.2.To further improve the CO2 uptake of titanium-based amine-impregnated composites,protonated titanate nanotube(PTNT)with large pore size and high pore volume was synthesized by a.hydrothermal method using anatase titanium oxide as the precursor.The resulting sample was modified with different amounts of TEPA through wet impregnation for CO2 adsorption.The as-synthesized adsorbents were characterized by different techniques such as nitrogen adsorption,scanning electron microscopy,transmission electron microscopy,Fourier transform infrared spectroscopy,powder X-ray diffraction,and thermogravimetric analysis.The CO2 capacity of PTNT with 60 wt.%TEPA loading was as high as 4.13 mmol/g under simulated flue gas conditions,which is higher than those achieved with the porous titanium oxides with 40 wt.%TEPA loading,analogue TEPA impregnated SB A-15 and many other previously reported TEPA-impregnated materials.The high CO2 uptake is probably due to the large pore size and high pore volume of PTNT support combined with its special surface characteristics.Cyclic CO2 adsorption-desorption tests demonstrated the excellent regenerability and stability of the PTNT with 60 wt.%TEPA loading.In addition,moisture appears to have a promoting effect on the CO2 sorption capacity of the composite sorbent.3.To find the PTNT-based sorbent with higher CO2 capacity and further understand the CO2 adsorption mechanism for this system,protonated titanate nanotube(PTNT)with different porous textures were synthesized by a hydrothermal method and further modified with different types and amounts of amines including triethylenetetramine(TETA),tetraethylenepentamine(TEPA)and poly ethyl eneimine(PEI)for CO2 adsorption.Equally,PTNT supports or amine composite sorbents were characterized by different techniques and the CO2 adsorption performances of sorbents were also evaluated in a fixed-bed reactor coupled with an on-line gas chromatograph under simulated flue gas conditions.Experimental results revealed that pore volume of PTNT support is the dominant factor that determines the CO2 sorption capacities of the composite sorbents.Furthermore,the CO2 uptake capacities of the PTNT composite decreased as the size of the impregnated amines increased.The highest CO2 sorption performance attained with the sorbents is 4.33 mmol/g for a PTNT with 60 wt.%TETA loading under simulated flue gas condition.It is also found that enhanced contact between CO2 and the impregnated amine was obtained when there was a small space left within the pores of the composite sorbent after amine impregnation,which is beneficial for CO2 adsorption.Besides high capacity for CO2 adsorption,good stability and reusability,the amine-impregnated PTNTs also display positive effect of moisture,further indicating their great potential in CO2 removal from flue gas.