预处理稻壳流化床燃烧制备纳米SiO_2的小试实验

Experimental study on pretreated rice husk combustion in bench-scale fluidized bed for the production of nanosilica

为研究预处理稻壳在流化床中燃烧制备纳米SiO_2工艺可行性,在小型流化床试验台上进行预处理稻壳的燃烧试验,并得到活性稻壳灰样品.采用扫描电镜仪(SEM)、能谱仪(EDS)、透射电镜(TEM)、X射线荧光光谱仪和比表面积及孔径分析仪等设备表征床料和稻壳灰的微观结构和理化特性,深入研究酸预处理对稻壳流化床燃烧状态和稻壳灰性能的改善.结果表明:预处理稻壳在流化床内燃烧状况良好,床料无粘结现象,避免了高温下流化床的团聚问题;所得稻壳灰理化特性大幅提高,稻壳灰由15～50 nm的纳米颗粒聚集而成,并具有丰富的约4 nm的介孔孔隙、≥98%的SiO_2纯度以及≤0.08%的超低残炭质量分数;低温条件下酸预处理可以大幅度消除燃烧温度对稻壳灰性能的制约,但高于800℃时温度制约逐渐显现.酸预处理稻壳流化床燃烧可实现制备高纯高活性稻壳灰的目的,且硫酸预处理效果优于柠檬酸.

To investigate the feasibility of industrial preparation of nano-silica process by pretreated rice husk combustion in fluidized bed, the combustion test of pretreated rice husk was carried out in a bench-scale fluidized bed and active rice husk ash ( RHA) samples were obtained. Scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, X-ray fluorescence spectrometer and specific surface area and pore size analyzer were used to characterize the microstructure and physicochemical properties of bed material and RHA, and then the effects of acid pretreatment on the combustion state of rice husk in fluidized bed and the performance of RHA were deeply studied. The results showed that the pretreated rice husk burned well in the bench-scale fluidized bed and the bed material's agglomeration was not happened. The obtained RHA consisted of 15-50 nm nanoparticles and had abundant mesoporous pores of about 4 nm, SiO2 purity of higher than 98 wt.% and ultra-low residual carbon content of less than 0.08wt.%. Acid pretreatment greatly eliminated the limitation of combustion temperature on RHA properties under low temperature condition, however, the temperature constraints gradually appeared when temperature above 800 ℃. In brief, the fluidized bed combustion of acid-pretreated rice husk could achieve the purpose of preparing high purity and high active RHA, and the pretreatment effect of sulfuric acid was better than citric acid.