| For it will form binary azeotrope with water, n-butanol can be used to remove moisture in the SiO2and other nano-powder. Compared with common drying method, azeotropic distillation can weaken the agglomeration between the particles successfully and enhance properties of powder. So azeotropic distillation with n-butanol has proved to be an ascendant drying method by some literatures. After azeotropic distillation, alcohol-water mixture which contains57.5%n-butanol will be produced. Under room temperature, the mixture can form two phase obviously after standing and stratification. The n-butanol phase can be recycled and used in azeotropic distillation dehydration directly, while the lower aqueous solution with7.7%n-butanol needs to be separated and recycled.In this paper, separation methods of alcohol-water system were introduced, such as special distillation, extraction, membrane distillation, pervaporation, and some composite separation technologies. By comparison, extraction was supposed to be the better method for this system, for its simple devices, high yield, convenient operation, mature industrialization, and low energy consumption. In this research, the optimum operation conditions of salting-out extraction and liquid-liquid extraction were determined by experimental research. Then process simulation of this two processes was conducted by the Aspen Plus software, and energy consumption was compared.The main contents and conclusions of this paper are as the followings:1. The experimental research of salting-out extraction indicated that inorganic salt solution could extract n-butanol from its aqueous and extractability increased with increasing salt concentration. At20℃, when extraction ratio R=1.5, the extractability was up to95%with60%K2CO3solution. The organic phase, in which the mass fraction of salt was less than10-4after extraction twice, could be recycled and used in azeotropic distillation. The evaporation times of K2CO3solution had little effect on the extraction.2. The experimental research of liquid-liquid extraction indicated that n-hexanol and n-octanol were the appropriate extractant when considering the solubility, boiling point, density, toxicity, price and other parameters of organic solvents. Indeed, distribution coefficients of n-butanol in n-hexanol or n-octanol were both high. Under room temperature, R=0.8was supposed to be the best extraction ratio for it can balance both technology and economic benefits. When extraction ratio R=0.8, the extractability of n-butanol with n-octanol and n-hexanol could reach90.46%and92.7%respectively. Considering both extraction effect and economic factors, n-octanol was the better extractant. And50-60℃was the appropriate extraction temperature when having an overall consideration of extraction effect, split-phase velocity, and solvent loss.3. The results of aspen simulation showed that n-butanol could be concentrated to93.54%and69.40%respectively from the feed of100kg/h n-butanol-water mixture by salt extraction and solvent extraction, which meaned salt extraction had a better extraction effect. However, solvent extraction was energy saving compared to salt extraction. As a result, salting-out extraction and solvent extraction could be used to separate n-butanol-water system in the industry. |
