Solvent impregnated resins are a liquid coordination compound that is spread uniformly in a solid polymeric medium referred to as support resins. They have ion exchange and solvent extraction advantages which include rapid rate of mass transfer, high selectivity among other advantages. Macroporous adsorbent resins, which have stable physical and chemical properties, elevated specific surface area and plentiful pores, are known to be favorable supports for the preparation of solvent impregnated resins.
It is widely accepted that physical adsorption is the most important way for the adhesion of extractant into the macroporous adsorbent resin pores, whereby the adhesion strength can be varied as a result of support properties which include specific surface area, pore structure and matrix.
Wuhan University of Technology researchers in China investigated the time of impregnation equilibrium and the quantity of solvent impregnated resin extractant in relation to the preparation process, as well as the extractant utilization efficiency and the stability of these resins in relation to the adsorption performance of their support properties. The authors used 5 macroporous absorbent resin types. The work is now published in Reactive and Functional Polymers.
The authors observed a sharp increase in nitrogen uptake with an increase in relative pressure which proved micropore structures exist and the presence of hysteresis loops showed the presence of mesoporous structures in the resins.
The resins SD300 and L493 had more micropores, smaller average pore diameter and total volume, but larger specific surface area as compared with the XAD series resins. Due to the abundant micropores which have the smallest diameters, the SD300 achieved the fastest impregnation equilibrium and this reduced progressively from the L493 to the XAD series resins as a result of the changing number and diameter of pores.
It was observed that the SD300 resin had the best stability effected by the reduced adsorbing capacity as a result of the high number of micropores. For the XAD-7HP resin, its adsorbing capacity initially reduced then became stable achieving the highest adsorbing capacity which indicated that the elevated affinity between the extractant and matrix has a major function in the solvent impregnated resin stability.
The research team concluded that the resins with a large pore volume and few micropores can be preferentially considered in preparing solvent impregnated resins and drawbacks such as reduced stability can be overcome by using a matrix with a high affinity for the extractant.
Yongping Tang, Shenxu Bao, Yimin Zhang, Liang Liang. Effect of support properties on preparation process and adsorption performances of solvent impregnated resins. Reactive and Functional Polymers 113 (2017) 50-57.Go To Reactive and Functional Polymers