Study On The Preparation Of Silica Nanoparticles And Hydrophobic Aerogels From Oil Shale Ash

With the increasing demand on the energy all over the world, the development of the global economy has been constrained by the shortage of oil resources. Oil shale is an important supplementary energy resource for oil and gas. At present, one of the main technologies available for utilizing oil shale resources is retorting oil shale to produce shale oil and gas, and the other is burning oil shale to generate electricity. Both of them produce a huge amount of residue. It can not only cause serious environmental pollution, but also lead to enormous waste of the other available elements. These problems limit the development of oil shale industry. So, to effectively utilize oil shale ash (OSA) becomes an important issue. In this paper, the sodium silicate solution was produced using Huadian OSA as silica source, and then the silica white, spherical silica nanoparticles and hydrophobic aerogels using the prepared sodium silicate solution. This method developed a new way for the comprehensive utilization of OSA. The samples were characterized by SEM,TEM,BET,FT-IR,XRD和TG-DTA. At present, there is little available information about silica series chemical products such as silica white, silica nanoparticles and aerogels from OSA.The water glass was produced through alkali extraction with OSA calcined and leached by acid. Box-Behnken statistical design was firstly used to optimize the factors affecting the extraction efficiency of the silica such as the sodium hydroxide concentration, the reaction time and the reaction temperature, to explore the interaction of the factors and to determine the optimum conditions for the extraction process. Multiple regression analyses showed that the extraction efficiency was in an agreement with the generated model and the experimental results. It was observed that the extraction efficiency of silica was increased by increasing the concentration of sodium hydroxide, the reaction time and the reaction temperature. At the optimum condition of reaction time 5 h, reaction temperature 100℃, and the concentration of sodium hydroxide 40 wt.%, the extraction efficiency reached 73±0.50%.The silica white was successfully synthesized using water glass prepared, and hot air drying simulating fluidized bed drying was employed for drying precipitation at an ambient pressure. The effects of the silica concentration, sulfuric acid concentration, temperature, pH value and aging time on the value of DBP adsorption and the BET specific surface of silica had been investigated. The optimum conditions were determined, such as the silica concentration 8.0 wt.%, sulfuric acid concentration 1.5mol/L, temperature 70-80℃, pH value 8 and aging time 8h. The microstructure analysis showed that the shape of silica white is sphere with an average size of about 50nm.The spherical silica nanoparticles were firstly synthesized using water glass as silica source and polyethylene glycol (PEG) as the surfactant via ultrasonic technique followed by azeotropic distillation. The results showed that the addition of PEG could effectively prevent the aggregation of silica nanoparticles and change the particle size, and the particle size and distribution depend on the PEG concentration. When the PEG concentration and molecular weight was 3wt.% and 10000, respectively, the silica particles with average diameter of 10 nm were uniformly distributed. The results indicated that ultrasonic is a key factor to the formation of small, uniform nanoparticles and an optimum hydrolysis-condensation period and powder of the ultrasonic cavitation is 0.5 h and is 70 W, respectively. The azeotropic distillation evidently restrains agglomerating. Possible mechanism of azeotropic distillation can be explained by the following facts. Firstly, the excess n-butanol molecules can not draw particles together through the formation of hydrogen bonds. Secondly, during the following solvent removal process, no hydrogen bond can be formed among neighboring particles because the hydroxyl groups on the particle surface are replaced by butoxy ones. Thirdly, the butoxy group has steric hindrance that can prevent the approach of particles. As a result, the azeotropic distillation dramatically reduces the possibility of the formation of chemical bonds and prevents the formation of hard agglomerates. The FT-IR spectra showed C-H peaks 3132 and 1402 cm-1, clearly indicating the organic modification of the nanoparticles surface. The hydrophobic silica aerogels were prepared using sodium silicate solution based on OSA via ambient pressure drying by improved method of solvent exchange-surface modification for the hydrogel. The influences of the kind of surface modification agents, SiO2 concentration, the pH value of sol and heat-treated temperature on properties of the aerogel were investigated. The results indicated that all the silica aerogels prepared under different conditions were nanoporous material with the meshwork structure, the BET surface area of 800-980 cm2/g, tapping density of 0.084-0.11 g/cm3, pore diameter of 9.38-10.10 nm. In the process of heat-treatment between 180 and 300℃, it was very hard for the gas to escape because of the heat expansion and low-permeability of the gas inside the aerogel. The gas compressed the framework of aerogel so as to enlarge the surface aera and pore size of silica aerogel. With the increasing of the temperature,-CH3 which was on the surface of the silica aerogel burned to decompose and became hydrophilic gradually.The aerogel with large specific surface area of 1360 cm2/g and big pore diameter of 12.4 nm was firstly synthesized by microwave heating technique. This method compensated for the shortcomings of oven drying of the temperature gradient, shortened drying time and reduced the agglomeration of the powders, so the aerogels maintained the original pore structure as much as possible.In summary, the silica series chemical products such as silica white, nanoparticles and aerogels, had been firstly synthesized using OSA as a new silica source. This method developed a new way for the comprehensive utilization of OSA and had important social and economic significance.