Preparation Of Rice Husk Ash-derived Silica Nanoparticles By High-gravity Technology And Its Application For Reinfororcement Of CO₂ Absorption

As the global warming has become an increasingly serious issue,more and more researchers focus on the capture and storage of greenhouse gas such as CO₂.Solvent absorption is an important technology for capturing CO₂,which has the advantages of good separation effect and technical maturity.However,the cost of this technology is too high for large-scale CO₂ process.The process intensification can improve the absorption rate and can reduce the cost of CO₂ absorption.The addition of nanoparticles in the absorption solution can effectively increase the mass transfer rate between gas and liquid.It has received much more attention in strengthening CO₂ absorption in recent years.Rice husk as a byproduct of rice cultivation,which China produces about 40 million tons per year.Rice husk is mainly burned for power generation due to its high calorific value,thus generating a significant volume of rice husk ash（RHA）.If the RHA is improperly handled,it will become tremendous waste and can potentially pollute the environment.In this paper,the rice husk ash was used as a raw material to prepare SiO₂ nanoparticles by sulfuric acid precipitation in a high gravity rotating packed bed.The as-prepared SiO₂ nanoparticles were applied to enhance the CO₂ absorption.The main works and results are listed as follows:1.Rice husk ash-derived SiO₂ nanoparticles were prepared by high-gravity rotating packed bed.The effects of several factors,such as the flow rate of sodium silicate,rotating speed,types and content of surfactants on the specific surface area,particle size and morphology of SiO₂ were investigated.The results showed that the flow rate of sodium silicate has little effect on the specific surface area of SiO₂ nanoparticles.At the rotating speed of 1250 rpm and with 1% wt SDBS,SiO₂ nanoparticles with the size of 10-20 nm and BET surface area of 600 m2/g could be obtained.Compared with SiO₂ nanoparticles without surfactant,the addition of SDBS make the specific surface area increased by 70 m2/g.2.The effect of nanoparticles on gas-liquid mass transfer in high-gravity rotating packed bed was investigated.By using chemical absorption method（CO₂-NaOH）and physical absorption method（CO₂-air-water）,the effective specific surface area a,liquid-mass transfer coefficient kL,overall mass transfer coefficient kLa,and the surface renew frequency S were measured.The results showed that the addition of nanoparticles can enhance the gas-liquid mass transfer and there was an optimal SiO₂ content（2.0 g/L）for the strengthening of a,kL,kLa and S;The a,k L,kLa,S increased with the increase of liquid flow rate and gas flow rate;The a,k L,k La,S increased firstly and then decreased with the increase of rotating speed.The intensification of nano-particles on gas-liquid mass transfer was indicated mainly by the increase of a,kL,and S.3.The effect of Si O₂ nanoparticles on the CO₂ absorption with ethanolamine（MEA）solution in high gravity rotating bed was investigated.The result showed that the absorption rate of CO₂ was 0.00458 mol/s,when the solid content was 1.5 g/L,the MEA concentration was 10% wt,the flow rate was 120 L/h,the mixed gas flow rate was 4000 L/h,and the rotating speed was 1200 rpm.The absorption rate increased up to 16.7% compared with MEA solution without nanoparticles.In summary,by using rice husk ash as raw material,SiO₂ nanoparticles prepared via high-gravity techniquecan effectively enhance the gas-liquid mass transfer.