Study Of Solvent Sublations: New Applications And Related Theoretical Model

Solvent sublation is a special adsorption bubble separation technique:the surface-active (or hydrophobic) compounds in aqueous phase are adsorbed on the bubble surfaces of an ascending gas stream, and then collected in an organic layer on top of the aqueous phase by some ways (such as dissolution or dissolution after complexation reaction). The technique has many advantages, such as high separation efficiency, high concentration coefficient, low dosage of organic solvent, soft separation process, and simple operation. Thus, this technique has been widely applied in sample pretreatment of instrumental analysis, separation of organic pollutant in wastewater, separation of active component from natural product and so forth. In this dissertation, the application of solvent sublation is extended to environmental analysis of organic pollutant, separation and concentration of active components in natural product, separation and purification of target compounds in fermentation broth; novel separation modes of solvent sublation, "Aqueous Two-Phase Flotation" (ATPF) and "Flotation Complexation Extraction" (FCE), are proposed for the first time; based on the new concepts of "Critical Bubble Radius" and "Mass transfer equilibrium of water droplet", the classical mathematical model of solvent sublation is improved, and another new theoretical model is proposed. The main conclusions are listed as follows:(1) A novel method is developed for separating and concentrating pyrethroid pesticides from vegetables by solvent sublation, and determination of pyrethroids is performed by high-performance liquid chromatography (HPLC). According to the optimal separation conditions of solvent sublation, three kinds of pyrethroid pesticides (fenpropathin, deltamethrin and bifenthrin) are successfully separated and concentrated from the extracts of different vegetables. The HPLC determination results show that the limit of detection values range are form 1.4μg/kg to 4.2μg/kg, the recoveries of spiked vegetable samples are from 85.7% to 110.4%, and relative standard deviation values are from 1.70% to 6.19%.(2) Using solvent sublation, penicillin G is successfully separated and concentrated from Penicilliun Chrysogenum fermentation broth. In the soft separation process, penicillin G can be separated at solution pH 3.5 and room temperature, and the distribution coefficient reaches 9.89. Moreover, the butyl acetate residual rate is reduced to 0.018 wt%, and the strong polar compounds of the fermentation broth were efficiently removed in the separation process.(3) Aqueous two-phase system is used in solvent sublation for the first time, and a new separation mode of solvent sublation, "Aqueous Two-Phase Flotation" (ATPF), is proposed. Because of the good solubility of penicillin G in polyethylene glycol (PEG), penicillin G is successfully separated and concentrated from Penicilliun Chrysogenum fermentation broth. The separation efficiency of ATPF reaches 97%, and the concentration coefficient reaches 19. Another advantages are the low environmental pollution and very soft separation conditions (pH= 6.8, room temperature). The kinetic results show that there are two stages in the separation process of ATPF:(Ⅰ) precipitation flotation and (Ⅱ) molecular adsorption flotation, and both of them follow the first-order kinetics equation. Moreover, the differential spectrum of organic phase shows that penicillin G ion can directly dissolve into PEG phase. This is the reason that the separation conditions of ATPF are very soft, and the separation efficiency of ATPF is significantly higher than that of the traditional extraction techniques.(4) The ATPF technique is used to separate and concentrate some active compounds from extracts of natural products. Under the optimal conditions, puerarin and daidzin are separated and concentrated from the extract of Puerarine. The separation efficiencies of puerarin and Daidzin are 87% and 91%, respectively, and the concentration coefficients reach 29.04 and 30.33. Then the flotation product is purified by high-speed counter-current chromatography (HSCCC), and high purity puerarin is obtained (purity> 95 %). At the same time, ATPF is used to separate and concentrate Baicalin from the extract of Scutellaria Baicalensis Georgi with a series optimal condition, and the separation efficiency is higher than 90%.(5) Combining solvent sublation with complexation extraction, another new separation mode of solvent sublation, flotation complexation extraction (FCE), is proposed. Using di-(2-ethylhexyl) phosphoric acid (P204) as a complexation agent, L-phenylalanine in Escherichia coli fermentation broth is separated and concentrated by FCE, and the distribution coefficient reaches 24～25. After back-extraction and purification of re-crystallization, the white crystal L-phenylalanine can be obtained with high purity (higher than 98%). The primarily research of FCE mechanism shows that the FCE process is mainly controlled by complexation reaction; on the mass transfer interface, the concentration of the target compound is greatly increased by bubble mass transfer process, and it is very beneficial to increase the separation efficiency of the target compound.(6) Some theoretical problems are investigated. Based on the classical theoretical model, the concepts of "Critical Bubble Radius" and "Mass transfer equilibrium of water droplet" are proposed. Using the new concepts, some special phenomena of solvent sublation can be explained very well, and the classical mathematical model is also improved. The simulation results show that the improved mathematical model gives better results to describe the kinetic process and the thermodynamic equilibrium of traditional solvent sublation. According to the separation behavior of solvent sublation, ATPF and FCE, solvent sublation can be considered a special liq-liq extraction, which is greatly strengthened by the bubble concentration effect. The bubble concentration effect effectively increases the sublate concentration of the mass transfer interface. Based on the novel theoretical model, a new mathematical model of solvent sublation is primarily established.