Recovery Of N-Butanol By Muti-Stage Cross-Flow Solvent Extraction After Silica Azeotropic Distillation

In the production process of silica, the azeotropic distillation method was used to remove the moisture from SiO2 wet silica gels, making use of the characteristic that n-butanol and water can form binary azeotrope. In the azeotropic distillation process, azeotrope was distilled out, and the mass fraction of n-butanol was 55.5%. The distilled azeotrope would form two phases at room temperature. The upper n-butanol-rich phase could be recycled directly to the azeotropic distillation process, and the n-butanol in the lower water-rich phase required recycle.In order to find a more efficient and economical method to recycle n-butanol, octanol was selected as extraction solvent and multi-stage cross-flow extraction method was used to separate the n-butanol-water mixture in the present work. The liquid-liquid equilibrium of octanol-n-butanol-water ternary system was studied in this article. The three-stage cross-flow extraction process was simulated using Aspen Plus software, and the three-stage cross-flow extraction process was compared with double-column distillation process, in order to obtain a more suitable separation method. The main contents and conclusions were as follows:1. According to the selection criteria and empirical prediction, octanol was selected as extraction solvent to extract n-butanol from n-butanol-water mixture. Experimental results showed that the distribution coefficient, selectivity coefficient and extractability were large when octanol was used as the extraction solvent.2. The liquid-liquid equilibrium of octanol-n-butanol-water ternary system was studied. Experimental results showed that using octanol to separate n-butanol-water mixture was feasible. Among the experimental temperature r=25℃,40℃,50℃, when the temperature was 40℃,the area of two-phase region and the selectivity of n-butanol were the largest, and the separation effect was the best.3. Multi-stage cross-flow extraction process was studied with experiments. Experimental results showed that the multi-stage cross-flow extraction process greatly improved the extraction efficiency. With the increase of the extraction stage, extractability of n-butanol increased. When the total amounts of extraction solvents were same, it was obviously that the higher the extraction stage, the better the extraction efficiency. All things considered, the optimized conditions of multi-stage cross-flow extraction process were:three-stage extraction, extraction ratio R= 0.3, extraction temperature at 40℃.4. The three-stage cross-flow extraction process was simulated with Aspen Plus software. The simulation results agreed well with the experimental results. The three-stage cross-flow extraction process was compared with double-column distillation process, and the results showed that the mass fraction of n-butanol in aqueous phase which was discharged from the three-stage cross-flow extraction process was lower. At the same time, the power consumption of three-stage cross-flow extraction process was lower, and this process was friendlier to the environment. Therefore, compared with double-column distillation process, the proposed process was more suitable to recycle n-butanol after silica azeotropic distillation.