Basic Research Of Supcritical Carbon Dioxide Extraction Of Low-concentration Ethanol From Aqueous Solutions

Organic compounds at low concentration in water samples mainly include trace organic pollutants in water and stimulants taken by athletes. And they have the similar point:the organic compounds are at low concentration in aqueous. It is difficult to achieve the lowest detection limit of analytical instruments; therefore, we need pre-treatment of water sample by enrichment and separation. This work focuses on the process intensification of the separation of low-concentration ethanol from aqueous solutions with supercritical CO2, linking the separation technology in chemical engineering and sample detection in the pretreatment process.The system of ethanol and water was selected because they are the most difficult to be separated in the stimulant and wastewater samples. The influence of operating conditions, e.g. the initial aqueous ethanol mass fraction, phase volume ratio, temperature, pressure and the kinds of salts added on the extraction process was investigated in this work. The salting effect was investigated on the SC CO2extraction by adding some inorganic solid salts and ionic liquids. This work also tries to identify the relationship between molecular structure of the salts and separation performance by comparison of the experimental and predicted results. It was found that for inorganic solid salts, the salting effect follows the order of KHCO3> KAc> NaCl≈NaBr> Nal which conforms to the Hofmeister series, while it follows the order of [BMIM]+[Ac]->[OMIM]+[Ac]->[EMIM]+[BF4]->[BMIM]+[BF4]-for ionic liquids. It was found that KHCO3is the best among all of the salts investigated, and a suitable mass fraction of the addition should be above25wt%.The separation mechanism was explored by means of the combination of Fourier Transform Infrared (FTIR) and Density Functional Theory (DFT), and the results coming from experiment, calculation and theoretical analysis are consistent.