| Biomass fly ash is a solid waste produced by biomass power plants,which has a large output and lacks large-scale utilization methods.The commonly used treatment methods are backfilling mines or direct landfill.In this paper,the biomass fly ash produced by a biomass power plant in Heilongjiang Province is taken as the research object.The fly ash is produced by burning biomass consisting of 60%rice husk,20%straw and 20%undergrowth in a circulating fluidized bed.Its silica content is as high as 75%,which is an ideal raw material for preparing silicon-based products with high added value.Silica aerogels are widely concerned because of their excellent properties such as high specific surface area,low thermal conductivity and high porosity.The preparation of silica aerogels from biomass fly ash can not only realize high added value utilization of biomass fly ash,but also reduce environmental pollution.Therefore,in this paper,a series of researches have been made on the process of preparing silica aerogel from biomass ash,in order to provide some theoretical and experimental reference for the large-scale utilization of biomass ash.It mainly includes the following four aspects:Using biomass fly ash to prepare sodium silicate,from single factor experimental design to orthogonal experimental design,the influences of Na OH concentration,reaction time,reaction temperature,solid-liquid ratio and other factors on the modulus of sodium silicate and the dissolution rate of silica were comprehensively explored,and the preparation parameters were optimized.It is determined that under the conditions of Na OH concentration of 1mol/L,solid-liquid ratio of 1:4,reaction time of 4 hours and reaction temperature of120℃,the dissolution rate of silica and modulus of sodium silicate are the best,which are55.8%and 2.47 respectively.In order to shorten the process time,silica aerogel was prepared with self-made water glass as silicon source and trimethylchlorosilane(TMCS)as modifier.The effects of four preparation methods and modification time on the structure and properties of silica aerogel were investigated.Considering the time cost and aerogel performance,the best preparation method is determined as follows:Silica aerogel was prepared by gelling water glass with cation exchange resin,replacing with alcohol,modifying and drying.With this preparation method,when the modification time reaches 16h,the hydrophobic modification of the alcohol-gel is basically completed,and the prepared silica aerogel has a specific surface area of532.4m~2/g,a pore volume of 2.262cm~3/g,a contact angle of 143,a thermal stability temperature of 393℃,and good hydrophobicity and thermal stability.Silica aerogels were prepared with ethyl orthosilicate,self-made water glass and commercial water glass as silicon sources,respectively.The effects of silicon sources on the properties of silica aerogels were investigated.The results showed that:Silica aerogel prepared with tetraethoxysilane as silicon source has the best performance,with a specific surface area of 769 m~2/g,a pore volume of 1.939cm~3/g,high thermal stability before 450℃,and a contact angle of 152,which is a super-hydrophobic material.The performance of silica aerogels prepared with self-made water glass and commercial water glass as silicon sources is similar,the specific surface area is kept at 535-545 m~2/g,the contact angle is kept at about145,the hydrophobic performance is similar,and they all keep high thermal stability before400℃.It is proved that there is no obvious difference between the silica aerogel prepared from fly biomass and the silica aerogel prepared from commercial water glass.The physical and chemical analysis of waste residue and waste liquid from the process of preparing silica aerogel from biomass ash was carried out,and according to its physical and chemical properties,the further treatment and utilization scheme was put forward by consulting the literature. |
