Solvent impregnated resin

Figure 1 to the right explains the basic principle, in which the organic extractant E is contained inside the pores of a porous particle.

Also, the impregnation step decreases the solvent loss into the aqueous phase compared to liquid-liquid extraction.

Depending on the pore size of the used particles, capillary forces may also play a role in retaining the extractant.

Otherwise, van-der-Waals forces, pi-pi-interactions or hydrophobic interactions might stabilize the extractant inside the particle pores.

Nonetheless, SIRs have a significant advantage over e.g. custom made ion-exchange resins with chemically bonded ligands.

SIRs can be reused for different separation tasks by just rinsing one complexing agent out and re-impregnating them with another more suitable extractant.

Finally, by filling the whole volume of the particle pores with an extractant (complexing agent), a higher capacity for solutes can be achieved than with ordinary adsorption or ion exchange resins, where only the surface area is available.

However, there are possible drawbacks of SIR technology, such as leaching of the extractant or clogging of a fixed bed by attrition of the particles.

[6] In order to remove or recover the extracted solute, SIR particles can be regenerated using low pressure steam stripping,[7] which is particularly effective for the recovery of volatile hydrocarbons.

During wet impregnation, the porous particles are dissolved in the extractant and allowed to soak with the respective fluid.

[12] In such an application, where the SIR particles are contained in a packed bed, flow rates from 0.5 m3 h−1 upward without maximum flow restrictions can apparently be treated cost competitive to air stripping/activated carbon, steam stripping and bio treatment systems, according to the technology developer.

Also, the application of SIRs for the separation of more polar solutes, such as for instance ethers and phenols, has been investigated in the group of A.B.

One approach by C. van den Berg et al. focuses on the use of impregnated particles for in situ recovery of phenol from Pseudomonas putida fermentations using ionic liquids.

The interior is completely filled with extractant and thus increases the impregnation capacity as compared to classical SIRs.

A completely new approach of using SIRs for the separation or purification of biotechnological products such as proteins is based on the concept of impregnating porous particles with aqueous polymer solutions developed by B. Burghoff.

The setup would consist of a packed column or a fluidized bed rather than liquid-liquid extraction equipment with additional phase separation steps.

Schematic depiction of the extraction principle using a solvent impregnated resin
Figure 1: Basic principle of extraction with SIR.
Comparison of emulsification using LLE and SIRs
Figure 2: Comparison of emulsification during liquid-liquid extraction and with SIR particles.
Photo of SIR particles in water and enlarged SEM picture of impregnated particle surface
Figure 3: SIR particles prepared with the wet impregnation method, dispersed in water. Cut-out section shows enlarged segment of SIR particle surface.