Phase Quilibriume And Mass Transfer Kinetics Study Of Extraction Of Phenol From Model Oils Via Forming Deep Eutectic Solvents

Phenols are valuable raw materials in organic chemical industry, which are widely applied in the synthesis of pesticides, spices, medicine, synthetic fiber, disinfectant, preservative, phenolic resin and other chemical products and intermediates. It has been reported in the literature that coal tar and coal liquefaction oil possesses are rich in phenols, so extraction of high value-added phenols from coal tar and coal liquefaction oil is of great significance. Up to now, the only way applied in the industry to separate phenols from oil is extraction by aqueous alkaline solutions. The process includes the alkaline washing and acid washing. The process needs a large amount of inorganic acid and alkali solutions, and produces lots of waste water containing phenols, which is difficult to treat with. Hence, a new way is expected to separate phenols from oil and avoid the above disadvantages.To solve the above problems, our group has found that a series of quaternary ammonium salts can extract phenols from oils by forming deep eutectic solvents (DESs). This approach has many advantages, such as simple operation, low-cost extraction solvent, non-toxicity, and recyclability. The method has excellent industrial application prospects. As we all know, the application of new technology requires a lot of basic data of thermodynamics and kinetics. In this paper, phase equilibrium and mass transfer kinetics of extraction of phenol from model oils via forming DES have been carried out. The main results of this work are presented as following:1. This work investigated the effect of temperature and concentration of quaternary ammonium salts on phase equilibrium of the separation process for the first time. The results show that the distribution coefficient and selectivity of phenol decrease with the increase of temperature, which is unfavorable to separation process. The increase of temperature results in elevating the quantity of quaternary ammonium salts after reaching equilibrium, which is not conducive to reverse extraction of quaternary ammonium salt from DES. Under a fixed temperature, phase equilibrium composition does not change after a certain amount of quaternary ammonium salts during extraction.2. The presence of hydrogen bonding between phenol and ChCl in DES was demonstrated by FTIR and 1H NMR.3. The influence of temperature and phenol content on the solubilities of ChCl, TMAC, TEAC, BmimCl and EmimCl in toluene was investigated. The results indicate that the higher the temperature, the more the solubilities. Among the salts, TEAC and ChCl show minimal solubility in toluene. At 25 ℃, the solubilities of ChCl, TMAC, TEAC, BmimCl and EmimCl in toluene are very small in a concentration range of 20-50 μg/mL. Phenol concentration has a great influence on the solubilities. The greater the concentration of phenol, the more the solubility of salts.4. In order to deeply understand the dynamic characteristics of separation of phenols from oils via forming DESs under the extraction process, the extraction kinetics of phenol with ChCl was studied using a constant-interface cell method. The mass transfer migrate coefficient of phenol on the interface of model oil/DES was determined and the effects of stirring speed, temperature, specific area, salt content, quaternary ammonium salt on the extraction were investigated. The experimental results reveal that the extraction rate of phenol increases with the increase of stirring speed. The mass transfer resistance in the model oil phase is lower than that in the DES phase, i.e. the diffusion of phenol to DES phase is the rate determined step of the extraction. With increasing temperature, the extraction rate of phenol is improved. In this system, the apparent active energy is 8.9 kJ·mol-1. The separation of phenol is a diffusion-controlled process. The interfacial mass transfer coefficient of phenol does not change with two-phase specific area and salt content, but the mass flux of phenol increases with the rise of specific area. The kinds of quaternary ammonium salts play a role in mass transfer coefficient and the extraction rate. The smaller the viscosity of DES of quaternary ammonium salt and phenol, the more efficient the mass transfer process.