Adsorption of N,N,N',N'-Tetraoctyl Diglycolamide on Hypercrosslinked Polysterene from a Supercritical Carbon Dioxide Medium.

Mikhail Kostenko,Olga Parenago

doi:10.3390/molecules27010031

Abstract

The work considers for the first time the preparation of sorbents based on hypercrosslinked polysterene (HCP) and chelating agent N,N,N′,N′-tetraoctyl diglycolamide (TODGA) by impregnation in the supercritical (SC) CO2 medium. Such sorbents can be applied for further isolation and separation of lanthanides, actinides and other metals. They are usually prepared by impregnation in toxic organic solvents (e.g., methanol, dichloromethane). Our study shows that application of SC CO2 instead of organic solvents can significantly speed up the impregnation, perfom it in one stage and make the process more eco-friendly. At the same time, the obtained sorbents are close in their parameters to the classical ones. This article presents the results of measuring the TODGA adsorption isotherms on two HCP sorbents (MN202 and MN270) on a wide range of SC fluid parameters. Adsorption measurements were carried out using on-line supercritical fluid chromatography and gravimetry. Based on the sorption capacity parameter, MN202 sorbent was selected as the better carrier for TODGA. An impregnation temperature increase within the range 313–343 K in isochoric conditions (ρ = 0.780 g/mL) reduces the maximum of TODGA adsorption from ~0.68 mmol/g to ~0.49 mmol/g.

Highlights

Metal extraction from aqueous solutions is a common task both in laboratory practice and in industrial production
The present work studied the adsorption of tetraoctyl diglycolamide (TODGA), a common chelating agent, on hypercrosslinked polysterene (HCP) in an SC CO2 medium
Isotherms of TODGA adsorption on the MN202 and MN270 sorbents were measured at 313 K and 20 MPa

Summary

Introduction

Metal extraction from aqueous solutions is a common task both in laboratory practice and in industrial production. The role of carrier matrices in production of sorbents of this type can be played by materials of different kinds, such as silica gels modified by polymers [7], graphene aerogels [13], hypercrosslinked polystyrene (HCP) [1,14], etc Such carriers are commonly impregnated with TODGA solutions in volatile solvents (methanol, dichloromethane, etc.). The solvents are removed by evaporation (reaching complete deposition of the chelating agent on the carrier) [1,6,8,10,11,12] or the carrier with a certain amount of the adsorbed chelating agent is filtered out of the solution residue [7,13] Such approaches to impregnation require volatile toxic organic solvents and, in addition, are rather labor- and time-consuming, which encourages us to use more environmentally friendly and cheaper solvents such as supercritical (SC) CO2

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