(644c) Tuning Polyimide Thin Film Composite Membranes for Organic Solvent Reverse Osmosis Separations Via Boc Protected Amine Solid-State Crosslinking

Organic solvent separations are energy intensive yet ubiquitous in the chemical, petrochemical, and pharmaceutical industries. Membrane technology can reduce the energy, carbon, and water intensity required in these separations significantly. However, these molecular separations often involve highly similar molecules, which reduces the efficacy of the membrane-based process. Some polymers used in organic solvent reverse osmosis (OSRO) have been known to suffer from plasticization, making them inefficient for these molecular separations. One method to avoid such effects is crosslinking the polymer. Here, we develop a method to uniformly crosslink a selective layer for a thin film composite (TFC) membrane to improve stability in organic solvents and tune separation performance. Traditional crosslinking methods are hindered by the diffusion of crosslinking agents into the polymer matrix, and this effect becomes more pronounced as crosslinking agents become bulkier. We have developed a method to introduce larger crosslinking agents that impart additional free volume to the membrane while overcoming diffusional limitations during the crosslinking infusion step. We utilize the commercial polymer Matrimid® 5218 and three crosslinking agents: para-xylylene diamine, 4,4’-biphenyldicarbontrile, and triptycene. We introduce a Boc protection method to the amines before dissolving into the membrane casting solution. After casting, the amines within the membrane are thermally deprotected to induce a solid-state crosslinking reaction. The resulting membranes were characterized by FT-IR, gel fraction, helium pycnometry, and TGA. The separations performance was tested in a crossflow OSRO permeation system for a toluene/triisopropyl benzene system and a multicomponent organic solvent mixture. The crosslinked TFC membranes showed excellent stability in organic solvents and tunable separation characteristics based on crosslinking agent and concentration of the crosslinking agent.