Optimal design of an efficient polyphenols extraction process for high concentrated phenols wastewater

Abstract The export phenols concentration of the current process is as high as 500–700 mg/L. Most of them are polyphenols which easily lead to the broken down of the following biochemical treatment process due to its high toxicity for biochemical bacterial. This paper analyzes the drawback of the current process. The solvent used in the current process has a weak selectivity on polyphenols. Meanwhile, the pH value of the wastewater is in the range 7.5–8.5 before extraction. Polyphenols are partly dissociated into ionic state which limits the extraction efficiency. Therefore, intensification and improvement of the phenols extraction process is carried out in this paper from the aspect of new solvent development and process innovation. The framework for this work design includes solvent development, extraction experiment, process synthesis, modeling and simulation. A compound solvent with 95% MIBK and 5% toluene for polyphenols removal is developed. Process synthesis of CO 2 acidification and extraction is carried to develop a new polyphenols extraction process. Modeling and simulation of the process are conducted to determine the operation parameters. 400 kg/h CO 2 is used to reduce the pH value of the wastewater to 5–6. Theoretical extraction stage number is set to 4 for the new solvent and the solvent/water ratio is 1:5.5 (volume). After the treatment of the new process, the polyphenols in raffinate could be reduced to 88 mg/L. The removal efficiency of polyphenols reaches 96.5%.