Removal of aromatic organic compounds by silica modified with EO/PO-based block copolymers

Abstract

This work focused on the use of the adsolubilization process to separate toxicants from a disposal stream. The adsorbents used in the experiments were silica and its modified forms with various EO/PO-based block copolymer surfactants having different configurations and HLB (hydrophilic lyophilic balance) values, namely Pluronics L31, Pluronics 17R2, Pluronics P123, Pluronics 25R4, Pluronics L64 and Pluronics 10R5. Firstly, the adsorption of block copolymers onto hydrophilic silica was studied for the tested copolymers which have an HLB in the range of 1-18. Phenol, 2-naphthol, and naphthalene were then used as the model organic contaminants in the subsequent a adsolubilization study. The results showed that block copolymers with HLB values lower than 7 could not appreciably adsorb onto silica due to the small number of EO groups capable of interacting with the silica surface. Thus, the HLB values for the adsorption of EO/PO-based block copolymers onto silica were shown to be in the range of 7-18. The adsorption isotherms of block copolymers illustrate the Langmuir characteristic. HBL value, surfactant configuration, EO/PO ratio, and molecular weight were found to affect the adsorption behavior. In addition, the adsolubilization study revealed that organic compounds such as phenol and 2-naphthol were found to adsolubilize into the adsorbed layer of block copolymer on the modified silica much higher than the amount when using conventional surfactants. The amount of adsolubilized phenol and 2–naphthol appeared to be 50 and 10 times higher in adsorbed layer of copolymers, respectively.