Membranes impregnated with bis(2-ethylhexyl) phthalate for enhanced VOC/N2 separation

This work deals with the separation of volatile organic compounds (VOCs) from nitrogen using membranes impregnated with bis(2-ethylhexyl) phthalate (DEHP). Instead of immobilizing the DEHP oil in a microporous support as in the supported liquid membrane approach, we attempted in this study to impregnate DEHP into a nonporous organophilic poly(ether-b-amide) (PEBA) matrix in order to enhance the membrane permselectivity and stability. DEHP was chosen because of its high-boiling, VOC-philic and plasticizing characteristics, and its excellent affinity to PEBA so that the DEHP oil impregnated in the membrane was retained by the PEBA matrix to form oleogel-like composite membranes. The membrane could have a DEHP content as high as 74 wt% while still maintaining sufficient mechanical strength. The DEHP-impregnated oleo-gel membranes were tested for the separation of various VOCs (including alcohols, alkanes, and aromatic hydrocarbons) from nitrogen. The results showed that the VOC permeability could be increased by 2–5 times by impregnating the membrane with DEHP, and the oleo-gel membrane was particularly effective for non-polar VOC compounds due to their favorable solubility in the membrane. The membrane stability for VOC/N2 separation was confirmed by subjecting the membrane to various VOC/N2 mixtures over a 30-day test.