Study On Co₂Absorption Performance Of Lithium Orthosilicates

With the rapid development of modern industry, more and more greenhousegases are emitted into atmosphere. This is the main reason to cause the greenhouseeffect. Carbon dioxide (CO2) as the major greenhouse gas, the emission and controlhas aroused more and more attention. The technologies for CO2capture andseparation is an efficient way to reduce CO2emissions. China is a major country ofcoal, so in our country, the main source of emissions of carbon dioxide is thecombustion of coal. However, the exhaust gas temperature is high, the absorption bythe traditional method must pass before cooling treatment, it will increase the energyconsumption and increase the cost of treatment of carbon dioxide. Sometimes theregeneration of absorbent is easily decomposed or volatile. Based on this, to find away to directly absorb carbon dioxide absorbent at high temperature has importanttheoretical significance and practical value. This thesis mainly consists of two parts asfollows:(1)Li4SiO4to be used as a high temperature absorbent is synthesized by hightemperature solid-state reaction, using commercial Silicon dioxide and lithiumcarbonate as raw materials. The calcining temperature has been initially measured. Inaddition, the effects of different surface structure of SiO2(commercially SiO2andMCM-41) on Li4SiO4were also studied. The synthesized Li4SiO4materials have beencharacterized by several techniques. The influence of different microscopicmorphologies of absorbents which were viewed by sanning electron microscopy(SEM) on the absorption rate of CO2was investigated systematically. The sampleswere characterized by X-ray diffraction (XRD) patterns. The performance of CO2absorption was measured with a thermogravimetric analyzer (DTA-TG). The resultsshow that, the crystal form and better crystallinity of Li4SiO4, which is prepared withcommercial SiO2as a raw material is better than that of using MCM-41. It also has agood CO2absorption performance. After rising rapidly in N2, the absorbed amount ofCO2on the optimized sorbent can reach to an equilibrium amount of35.43%(wt) inCO2at700℃.(2)On the basis of the aforementioned procedure for preparing lithiumorthosilicates (Li4SiO4), we have prepared kaolin-Li4SiO4successfully. With Silicon dioxide made from the waste residue of acid processing coal-kaolin and lithiumcarbonate as raw materials, kaolin-Li4SiO4was prepared by high temperaturesolid-state reaction. An analysis is made on the influence of some acid treatmentconditions of Kaolin, including the amount of acid, acid concentration, reactiontemperature, reaction time, on the CO2-adsorption performance of lithium silicate.The results show that, reaction temperature and reaction time affected it significantly.Also, we compared the the CO2-adsorption performance of lithium silicate (Li4SiO4)and kaolin-lithium. The result indicated that the CO2absorption of kaolin-lithiumsilicate was faster at low temperature than the Li4SiO4that prepared with commercialSiO2as silica source. Although its absorption capacity is its lower than that of Li4SiO4,it also exhibited good ability to absorb CO2, the biggest absorption capacity was up to31.07%(wt).