Study On The Effect Of Microbubbles On The Preparation Of Precipitated Silica By Carbonization

Hydrated silica is a general term for amorphous white powdered s ilicic acid and silicate products.It is often used to replace the conventional carbon black in the reinforcement process,so it is also called white carbon black,including fumed silica and precipitated silica.Because of its superior chemical stability,thixotropy,reinforcing and thickening effects,it is widely used in rubber,tire,paint,toothpaste,paper and many other industrial fields.The preparation of silica by precipitation is the main method of producing silica in China.The products are mainl y used in silicone rubber and rubber products.The preparation of precipitated silica by carbonization can make full use of carbon containing flue gas such as lime kiln gas and reduce production cost of silica,which is an important way of CO2 resource utilization.The carbonization process of silica is a complex three-phase reaction process,which is affected by many factors,such as reaction temperature,concentration,ripening temperature,etc.In addition,the gas-liquid mass transfer of CO2 is an important factor to limit the carbonization reaction rate,and will further affect the quality of precipitated silica products.Improving the gas-liquid mass transfer process is the key to increase the carbonization reaction rate and acquire high-quality silica products.In this paper,a new method of preparing silica by microbubble carbonization is proposed and compared with the traditional method of bubbling.The effect of microbubbles on the mass transfer process of carbonization and the quality of silica products is studied by experiment and theoretical analysis.In this paper,the carbonizations of silica were carried out on the microbubble / bubbling experimental equipments respectively.By comparing the specific surface area,DBP oil absorption value and particle size of silica products,the effects of reaction temperature,concentration,aging temperature and bubble conditions on the product quality were explored;and the enhancement of mass transfer by microbubbles was explored by calculating and analyzing the p H change of solution in the carbonization process.In the experiment,the p H change of solution was measured on-line by a p H meter,silica products were dried and ground,and the basic morphology and properties of the products were determined by SEM and X-ray diffraction;the specific surface area,DBP oil absorption value and particle size of silica products were measured by N2 physical adsorption,manual method and laser diffraction method respectively.The experimental and analytical results of bubbling condition show that with the increased of temperature,the specific surface area of silica decreased,the oil absorption value increased,and the particle size decreased;with the increase of reaction solution concentration,the specific surface are a of silica decreased,the oil absorption value decreased slightly,the changes particle size were not obvious;with the increase of aging temperature,the specific surface area decreased,and the oil absorption value increased,but the particle size decreases.The change trend of the quality of microbubble silica with temperature and aging temperature was the same as that of bubbling conditions,and the particle size of microbubble silica was larger;the effect of microbubble on the quality of silica was different with the change of the concentration of reaction solution.When the total concentration of solution was higher(?0.5M),with the increase of concentration,the introduction of microbubble made the specific surface area increase,and the oil absorption value decrease initially and then increases.The first and second order reactions of carbonation process under the condition of low concentration bubbling at room temperat ure are calculated,and the results of the second order reactions are more consistent with the theoretical values,so it can be concluded that this process is a second order reaction process.The introduction of microbubbles(the average diameter of mic robubbles was about 50 ? m)can increase the CO2 utilization rate and the volume mass transfer coefficient by two to four times,while the liquid mass transfer coefficient decreases,which shows that the enhancing mass transfer process of microbubbles was mainly achieved by significantly increasing gas-liquid interfacial area.