| According to the"China Blue Book on Climate Change（2020）",the global warming trend continues.As the main greenhouse gas,the global average concentration of CO2 has increased by nearly 0.5 times in recent 268 years.Therefore,it is extremely urgent to pay attention to and realize the further development of CO2 emission reduction technology.Post-combustion carbon capture can be used to solve this problem.As a high-temperature solid adsorbent,Li4SiO4 is expected to be used in this technology.However,the adsorption performance of Li4SiO4 still needs to be improved in order to realize industrial application.Dry-milling has been proven to be an effective way to optimizate adsorption performance of Li4SiO4 through reducing particle size with crushing.However,when the milling time is too long,cold welding will occur and the modification effect will be weakened.Therefore,a mechanochemical activation method was used to modificate Li4SiO4-based adsorbents in this thesis.The physicochemical properties and adsorption performance of the mechanochemical activated adsorbent and the dry-milled modified adsorbent were compared and the modification mechanism of mechanochemical activation was summarized.Through orthogonal experiment,the influence of the activation facters including water/material ratio,rotating speed,ball/material ratio and time on the performance of the adsorbent was explored and the optimal condition was found.Combined with the changes in physicochemical properties of adsorbents,the influence of water/material ratio on adsorption performance was analyzed.Comparing the activated sample with the dry-milled sample,the results showed that the mechanochemical activation performs better in increasing surface area,reducing the particle size and optimizing the microstructure,so the adsorption performance was significantly enhanced.After 72 minutes of activation,the CO2 adsorption capacity of the adsorbent was increased to more than 6 times,which was about 2 times of the dry milled sample.Modification mechanism of the mechanochemical activation process:（1）water can take away the positive and negative charges generated during milling,inhibit cold welding,and promote the crushing of the adsorbent;（2）the smaller particles can promote hydration（Li4SiO4+H2O?Li2SiO3+2Li OH）,so as to optimizate surface morphology and increase surface area by producing porous layered Li OH.Orthogonal experiment results of comprehensive comparison of mechanochemical activation conditions showed:the order of the influence of activation facters is:water/material ratio>rotation speed>ball/material ratio>time.The optimal activation condition is water/material ratio of 1.75:1,speed of 350r/m,ball/-material ratio of 20:1,time of 72 min.The adsorption capacity of the adsorbent activated under the optimal condition reached 0.152g CO2/g adsorbent in 30 minutes,and the surface area of which increased by 34 times.With the increase of water/material ratio,there were two obvious trends:（1）from 0.25:1 to 1:1,the adsorption capacity increased sharply;（2）when the water/material ratio was less than 1.75:1,increasing the water/material ratio improved the performance of the adsorbent,but when the water/material ratio exceeded 1.75:1,continuing to increase the water/material ratio led to a downtrend of adsorption performance.The reasons can be summarized as follows:if the water/material ratio is too small,the insufficient water environment will lead to an insufficient fragmentation and less porous Li OH,leading to remarkable surface area.So an appropriate increase of the proportion of water can enhance the effect of water on the milling action and obtain smaller adsorbent particles.However,when the water/material ratio is bigger than 1.75:1,there will be excess water,which forms buffers between the grinding balls and the adsorbents,making the contact and collision between them difficult.Therefore,the adsorbent particles will be crushed uncompletely.As a result,the effect of activation will diminish. |
