Synthesis Of Rice Husk Ash-Based Silica Nanofluids For Reinforcement Of CO₂ Absorption

The capture and storage of greenhouse gas,CO₂,draws great attention in recent years,since China's CO₂ emissions have exceed 8 billion tons per year.Solvent absorption is one of the most popular techniques used for the separation of CO₂.Currently,the cost of CO₂ capture is as high as 30-70$/t CO₂.By using process intensification techniques,the cost of CO₂ capture may be effectively reduced.Nanofluid is a new media for process intensification,which greatly enhances the mass transfer rate between gas and liquid,and broadens a new horizon for CO₂ capture.Rice husks are important agricultural residues in China,with an annual output about 40 million tons,which accounting for nearly half of the world's total.Presently,rice husks are mainly burned for power generation,with a tremendous amount of rice husk ash produced simultaneously,which,however,is very difficult to directly use.The vast majority of the ash has been discarded as waste and caused serious environmental problems.In this paper,SiO₂ nanoparticles had been extracted from the rice husk ash and were applied for SiO₂ nanofluid synthesis.The SiO₂ nanofluid obtained was applied to enhancement of CO₂ absorption.The effects of types and concentration of surfactant on the size and morphology of silica nanoparticles had been studied.The influences by preparation conditions on the dispersion and stability of nanofluids had been investigated.Besides,the effects of nanofluids on capacity and rate of CO₂ absorption had also been explored.The results were listed as follows:1)In the process of silicon dioxide extraction,adding 1wt% SDBS could effectively control the particle size of silica.The particle size of SiO₂ about 40-50 nm could be achieved.2)Some factors,such as ultrasonic time,types and concentrations of dispersant,the concentration of SiO₂ particles,pH of aqueous solution have a significant influence on the nanofluids' dispersion and stability.When the ultrasonic time was 2h,with 1wt% SDBS as dispersion agent,the concentration of SiO₂ 1wt%,pH = 9¹0,the prepared nanofluid had good dispersion and stability.3)In the experimental study of absorbing CO₂,nanofluids significantly contributed to absorption rate of CO₂ rather than increased the CO₂ absorption compared with pure water.When the absorbent temperature is 4?,the pressure is 550 kPa and the concentration of SiO₂ is 0.5wt%,the optimal absorption rate of CO₂ was about 0.032mol·kg^-1·min^-1.Under the same experimental conditions,absorption rate of CO₂ in pure water is only 0.024mol·kg^-1·min^-1,the absorption rate increased by 33%.