(679a) Research On Technology for Recovering Ethanol, n-Propanol and Isobutanol From Alcohols-Water System

As alcohols-water azeotropes and mixtures of ethanol and n-propanol which have similar structure and chemical properties are difficult to separate, the technology for recovering ethanol, n-propanol and isobutanol from alcohols-water system becomes one of industrial difficult problems. Take industrial alcohols-water system as an example, it is composed by water (20%, mass), ethanol (40%), n-propanol (30%) and isobutanol (10%). After this mixture is treated by extractive distillation with salt and azeotropic distillation, their existing problems are introduced respectively: in distillates, high pure ethanol product and n-propanol product can’t be obtained, and water content is not less than 8%; large dosage of azeotropic agent is required, causing high energy consumption.

This paper proposes a new technology of saline extraction combining with azeotropic distillation and vacuum distillation to separate alcohols-water system. In saline extraction process, Adding extracting agent and inorganic salt alters distribution coefficients of alcohols and water in solution and makes solution layered. Extraction phase containing less water content than the mixture inflows into subsequent azeotropic distillation column, which makes the energy consumption of technology reduced greatly. In azeotropic distillation process, extracting agent of saline extraction process shows the same effect as azeotropic agent, and formation of ternary azeotrope of extracting agent, ethanol and water can overcome the difficult that ethanol and n-propanol are not easy to separate. Separation of n-propanol and isobutanol by vacuum distillation can increase their relative volatility and product purities. The product purity of ethanol, n-propanol and isobutanol could reach 95%, 99% and 97% correspondingly by using this technology. Compared with other separation techniques, this technology is applicable to separating alcohols-water system with high water content. This paper also studies the effect of kinds of inorganic salts and extracting agents, different mass ratios of inorganic salt to extracting agent and PH on distribution coefficients of alcohols and water in saline extraction process, energy consumption of technology and product purities through a series of contrast experiments. The optimal technology parameters are determined, which provides basis for industrialized production of alcohols-water system separation.