Application Of High Shear Mixer In Preparation Of Nanomaterials

High shear mixers?HSMs?,a new type of process intensification equipment,have advantages in gas-liquid system,liquid-liquid system and quickly micro-mixing,and are advantageous to the preparation of small nanoparticles with uniform particle size distribution.Thus,the preparation of nanomaterials by HSMs will be one of the important technologies in the future.Firstly,the preparation of aragonite CaCO₃ nanoparticles was studied in an in-line high shear mixer?HSM?-aided crystallizer between CO₂ gas and the aqueous slurry of Ca?OH?₂.The effects of the HSM rotor speed,reaction temperature,CO₂flow rate,concentration of H₃PO₄ and polyacrylamide?PAM?on polymorph and particle size were investigated,and then these conditions were optimized as 1.0�10⁴rpm,83 ^oC,200 mL/min,11.2 g/L and 0.5 g/L respectively.Under the conditions,aragonite CaCO₃ with the average width of 50 nm were obtained.And the reaction time in the HSM was less than 1/3 of the reaction time in stirred tank.HSMs generate sufficient micro-mixing level in the reactive crystallization,beneficial to the formation of metastable aragonite CaCO₃.H₃PO₄ reacted rapidly with Ca?OH?₂to form very fine and needle-like hydroxyapatite?HAP?,which served as heterogeneous nuclei.PAM could absorb onto the surface parallel to the c-axis of the needle-like aragonite CaCO₃,which inhibited of the crystal growth in the radial direction.Secondly,dispersed uniformly Ru nanoparticles with average diameter of 50nm were prepared in HSM reducing RuCl₃ precursor with NaBH₄,and the Ru nanoparticles existed mainly in Ru⁰.Then the obtained Ru nanoparticles were loaded on coconut activated carbon by impregnation method to form catalyst Ru⁰-HSM/AC,and the activity in acetylene hydrochlorination reaction was studied.We found that Ru⁰-HSM/AC showed higher activity than that prepared in stirred tank,with the acetylene conversion of 97.8%and the selectivity to VCM of 99.9%after 48 h at the reaction conditions of V?HCl?:V?C₂H₂?=1.1,GHSV?C₂H₂?=180h^-1,170�C.The characterization results show that Ru⁰-HSM/AC catalyst could maintain small size and high dispersion during the acetylene hydrochlorination reaction and have stronger ability to adsorb reactant HCl,which can improve the activity and stability of catalyst.