Solvent Regeneration in Complex Mixture Using Pervaporation

Abstract

This study aims to demonstrate the efficiency of dichloromethane (DCM) regeneration from a methanolic effluent by a combination of distillation and membrane pervaporation process. The presence of an azeotrope (MeOH/DCM/water) makes the regeneration of DCM via distillation alone impossible. A process simulation using ProSim software was carried out in order to evaluate the behavior of the azeotropic mixture. Two secondary treatments aiming to purify the DCM contained in the azeotrope were investigated. The first is the washing of the azeotrope with water. ProSim software was used to target the optimal conditions for washing before the experimental test. Residual water was recovered in the organic phase, meaning that the quality specifications for DCM were not reached. The second process studied for DCM purification was a pervaporation step. The feasibility of this had been proven at laboratory scale. The recovered DCM had the quality of a new solvent, and the whole process (distillation + pervaporation) reached a global DCM regeneration yield of 71.8% before optimization. This yield was limited by the distillation of methylal (also called dimethoxymethane) present in the methanolic effluent at the end of the distillation of the azeotrope, a compound retained by the pervaporation membrane. The pervaporation was performed on a hydrophilic Hybsi membrane letting methanol and water pass through and retaining the DCM (membrane surface = 0.15 m 2 ). Optimization and scaling up were then carried out with a semi-industrial pervaporation pilot (membrane surface = 1.05 m 2 ) which enabled the industrial scale-up. In order to facilitate the steering of the process and to ensure continuous and efficient monitoring of the regeneration operation, online monitoring by near-infrared probe (NIR) had been implemented allowing the composition of the mixture to be determined with an accuracy of ±0.05% on each compound. Finally, an assessment had been conducted of the regeneration pathways for methanol recovery at the bottom of the distillation column, for maximizing the regeneration of methanolic effluents by separating heavy compounds and methylal from methanol.

Pervaporation of dichloromethane‐cyclopentane and methylal‐cyclopentane mixtures through membranes from chloroprene rubber

“…Pervaporation is a membrane separation process, in which a liquid mixture evaporates through a polymer film and the permeate is removed by the stream of a sweep gas or by pumping (vacuum). The key application of pervaporation is the separation of azeotropes, particularly in hybrid devices combining pervaporation units with rectification columns 14–16 . Pervaporation can be used, for instance, for the recovery of the valuable components from feeds containing water, methanol, methylal, and dichloromethane using inorganic membranes preferentially permeable to the hydrophilic compounds (water, methanol) 16 .…”

“…The key application of pervaporation is the separation of azeotropes, particularly in hybrid devices combining pervaporation units with rectification columns 14–16 . Pervaporation can be used, for instance, for the recovery of the valuable components from feeds containing water, methanol, methylal, and dichloromethane using inorganic membranes preferentially permeable to the hydrophilic compounds (water, methanol) 16 . However, the separation of mixtures of organic compounds other than alcohols, which do not markedly differ in their hydrophilicity, remains an issue.…”

“…Thus, the pervaporation of dichloromethane‐cyclopentane (DCM‐CP) and methylal‐cyclopentane (ML‐CP) mixtures through membranes from CR is reported in this work. The studied compounds are common solvents, refrigerants, and blowing agents 16–20 ; ML is also a chemical feedstock and intermediate in the production of synthetic diesel fuel 21,22 . The separation of the above mixtures by distillation appears complicated by the similarity of their normal boiling points, 23 which are 39.9, 42.2, and 49.3°C for DCM, ML, and CP, respectively.…”

Hydrophilic and organophilic pervaporation of industrially important α,β and α,ω-diols

“…In the beginning it was started from the dehydration of various alcohol, now it applied for recovery of bio fuel, 14,28 treatment of effluent treatment in pharmaceutical industries. 29 Therefore, to expand the applications of pervaporation to the production of important raw materials in the cosmetics industry, we examined the potential of PVA-and PDMS-based pervaporation membranes for the removal of excess water from 1,2-HDO (hydrophilic approach) and trace amounts of IPA from 1,5-PDO (organophilic approach), respectively, with low energy consumption. For both hydrophilic and organophilic separation, the synthetic and operating conditions were varied to optimize the pervaporation output of both membranes.…”

Solvent Regeneration by Thermopervaporation in Subsea Natural Gas Dehydration: An Experimental and Simulation Study

“…Pervaporation has been widely applied to liquid−liquid/ vapor−liquid separation with an emphasis on alcohol/water systems, 11−21 bio-oil dehydration, 22 hazardous substances and organic solvent removal from water, 23,24 solvent regeneration from complex mixtures, 25 isomer separation, 26 and glycol dehydration. 27−32 The pervaporation process benefits from the membrane selectivity in addition to the vapor−liquid equilibrium selectivity.…”