Reclaiming of Amine CO2 Solvent Using Extraction of Heat Stable Salts in Liquid-Liquid Membrane Contactor

Amine CO₂ solvents undergo oxidative degradation with the formation of heat stable salts (HSS). These HSS reduce the sorption capacity of amines and lead to intense corrosion of the equipment. In our work, we propose a membrane-supported liquid-liquid extraction of the HSS from alkanolamines. For this purpose, a hollow fiber membrane contactor was used for the first time. A lab-scale extraction system on the basis of a hollow-fiber liquid-liquid membrane contactor with hollow fiber ultrafiltration polyvinylidenefluoride and polysulfone membranes has been studied. The extraction of the HSS-ions from a 30 wt.% solution of monoethanolamine was carried out using a 0.25-1 M solution of OH-modified methyltrioctylammonium chloride in 1-octanol as an extractant. It has been shown that >90% of HSS ions can be extracted from the alkanolamine solvent within 8 h after extraction. The results obtained confirm the possibility of using membrane extraction with a liquid-liquid membrane contactor for the reclaiming of amine CO₂ solvents to increase the general efficiency of carbon dioxide capture.

An Experimental and Theoretical Study on the Unexpected Catalytic Activity of Triethanolamine for the Carboxylative Cyclization of Propargylic Amines with CO2

Chemical conversion of CO₂ under atmospheric pressure and metal-free conditions remains a great challenge. In this work, a series of alkanolamines, low-cost and biodegradable bases, were used to catalyze the carboxylative cyclization of propargylic amines with CO₂ . Among these alkanolamines, triethanolamine (TEOA) was found to be a highly efficient organocatalyst for this important transformation at atmospheric pressure, and a series of desired products were synthesized in good to excellent yields. After the reactions, TEOA could be easily recovered and reused without obvious reduction in the efficiency. DFT studies revealed that TEOA may activate CO₂ to form a ring-shaped carbonate intermediate that plays an important role in the catalysis of the reaction. This finding provides an effective and environmentally friendly alternative route for the production of 2-oxazolidinones.