Research On The Preparation Process Regularity Of High-quality Nano-SiO₂ From Rice Husk Ash

Rice husk ash derived from rice husk is an important biomass raw material,which can be used to produce high value-added silica and carbon materials with various uses.At present,most of the technologies for preparing silica from rice husk ash have practical problems such as using inorganic acid as precipitant,difficulty in post-treatment of waste liquid,inability to recover structure regulator and low product quality.In this paper,an improved clean chemical precipitation had been developed that features the recycling of the by-products and structure modifiers.The morphology,structure and physico-chemical properties of the samples were characterized and confirmed by XRD,FT-IR,BET,SEM and SEM-EDS.The main work and achievements are as follows:（1）The mixed alkali solution of Na₂CO₃ and Na OH was used as the extractant to convert the silica in the rice husk ash into Na₂SiO₃ with high extraction yield.The optimal process conditions were as follows:the concentration of Na₂CO₃ solution was 24.0%,the mass ratio of Na OH to Na₂CO₃ was 0.2:1,the liquid-solid ratio was 5:1,the alkali dissolution temperature was 100℃,the alkali dissolution time was 3 h,the extraction yield of silica was 99.4%.（2）With the prepared Na₂SiO₃ solution as raw material,dodecyltrimethylammonium bromide（DTAB）as structure regulator,and CO₂ as precipitant,nano-silica with high specific surface area was successfully prepared.The optimal process conditions for the preparation were as follows:the dosage of DTAB was 5.0%,the CO₂ acidification temperature was 50℃,the CO₂ flow rate was 4 L/h,the aging time was 3 h,the calcination time was 3 h,the temperature was 550℃,and the heating rate was 5℃/min.The yield of silica was 99.3%,the specific surface area was 818 m²/g,the pore size was 2.5nm,and the average particle size was 200 nm.After the by-product solution was treated,it was reused with the structure modifier in the solution,which has little effect on the silica extraction yield and specific surface area.（3）With the prepared Na₂SiO₃ solution as raw material,switch-type surfactant N,N-dimethyldodecylamine（DDA）as structure regulator,and CO₂ as precipitant,nano-silica was successfully prepared.The optimal preparation parameters were:the dosage of N,N-dimethyldodecylamine was 0.9%,the CO₂ acidification temperature was 60℃,the CO₂flow rate was 5 L/h,and the aging time was 3 h.The silica yield was 99.3%,the specific surface area was 462 m²/g,the pore diameter was 21.6 nm,and the average particle size was 200 nm.After the by-product solution was reused 5 times,the silica extraction yield reached 99.1%,the recovery yield of DDA reached 95.3%,and the specific surface area of silica was about 460 m²/g.（4）The coupling-modified nano-silica was prepared by mechano-chemical method.The best modification process conditions silane coupling agent was KH172,the dosage was 2.0%of the mass of silica,the ball milling time was 2.5 h,the ball milling speed was600 r/min and the ball-to-material ratio was 7:1.At this time,the oil absorption value of the product was 3.10 m L/g.（5）The modified SiO₂ filled styrene-butadiene rubber（SBR）and the mixed rubber of styrene-butadiene and natural rubber（SBR/NR）were prepared.It is determined that the optimal modified SiO₂ filling amount of the modified SiO₂-SBR composite material was30.0%,the tensile strength of the obtained composite material was 13.0 MPa,and the elongation at break was 825%;the optimum modified SiO₂ filling amount of the SiO₂-SBR/NR composite was 35.0%,and the tensile strength of the composite was 16.6MPa and the elongation at break was 758%.