Fumed Silica The Flow Characteristics And Deacidification Mechanism

In this paper flow characteristics of different surface area deacidification fumed silica in self-made fluidized bed equipment have been studied. Research results show that at a certain gas velocity range which can regard as the initial fluid state stage, secondary aggregates size is relative to gas velocity, when the second aggregates stop growing up, the gas velocity is the "real initial flow velocity", according to the analysis of bed pressure drop curve, bed expansion curve and observe of microscope the size of secondary aggregates. Combining Davidson's pressure distribution in emulsified phase around single bubble and this paper's model have Deduced bed axial pressure drop formula which coincides with the experimental results, it indicates that unit distance of bed pressure drop is Associated with number of bubble. Bed pressure drop and bed expansion data have been used to monitor slight change of channel width:if pressure drop values decreased, the channel must become wider; if pressure drop values increased, there is little change in channel width. In both cases, the value of bed height may be increased or reduced, but as long as the bed height decreases, channel become wider significantly.Deacidification diffusion model and Influence on weight loss, the number of surface hydroxyl groups, and the relationship between H2O desorption volume and desorption HCl volume on fumed silica at different treating temperature have been studied. The conclusion is that HCl volume of not deacidification fumed silica samples is far less than the H2O volume, and larger of specific surface area, the more hydroxyl groups and water the sample has; Room temperature to 250℃scope in which the main desorption is physical Adsorbed Water, with the treating temperature increases, the sample weight loss quickly result in greater than 70% at 250℃While the weight loss that is chemical Adsorbed Water and including a small amount of hydroxyl generated by condensation of water is very slow as the temperature increases from 250℃. Hydroxyl number rises at about 150℃result from desorption of chemical Adsorbed Water combining with adjacent hydroxyls which desorption energy is very low. At 150-400℃, hydroxyl condensation reaction happen mainly, it's reactant are generated adjacent hydroxyls and some hydroxyls not combined with H2O, so the number of hydroxyl reduce. But in this stage, desorption of surplus chemical Adsorbed Water combining with adjacent hydroxyls which desorption energy is very high is more difficult. After deacidification 30min in the scope form room temperature to 250℃, the desorption volume of H2O and HCl swap into a certain proportion, and HCl and physical Adsorbed Water are desorpted off almost simultaneously at 250℃250-400℃, fumed silica have small changes in pH value result from different surface structure of fumed silica at different temperature. With the treatment time increases, HCl volume of unit mass of fumed silica reduce rapidly at the beginning and reduce speed become more and more slower later. Time-content curve's shape comply with the function a [1+exp (-βt)] (a>0,β>0).Based on the truth that solid surface heterogeneity and different adsorption energy of adsorbed molecules in the same adsorption lay, combining with Polanyi theory, statistical thermodynamics and the probability of knowledge have deduced the adsorption isotherm, but the reasonableness and the accuracy must confirmed through a large number of experiments that this is outside the scope of the profession and insufficient time. To be in the follow-up research work in its perfect authentication.