An integrated approach of membrane and resin for processing highly toxic and corrosive tetramethylammonium hydroxide alkali to ultrahigh purity. Issue 5 (October 2021) - Govardhan, Bapanipally
Abstract: There is a great demand for ultrapure grade tetramethyl ammonium hydroxide (TMAH) for the production of semiconductors and to remove the photoresist layer from the surface of electronic circuits. Electronic grade TMAH accounts for levels, and hence various elements present in ppb levels in technical grade TMAH are marked as impurities. In the present research work, a simplified integrated membrane-adsorption process is described to remove sub-ppm metallic impurities from technical grade TMAH. The pressure-based Nanofiltration (NF) process works effectively to hinder the diffusion of metal ion contaminants in ultrapure TMAH. It is employed in double stage mode along with resin-based post treatment for achieving desired purity levels. The hydrophilized polyamide nanofiltration (HPA-NF) membrane was synthesized in the laboratory using interfacial polymerization technique. The membrane and mixed bed resin were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectra (FTIR), atomic fluorescence spectroscopy (AFM), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC), and energy-dispersive fluorescence spectroscopy (EDXRF) to determine the morphological, structural, thermal, and elemental analysis, respectively. A contact angle of 66.2o revealed that the prepared membrane was successfully hydrophilized. The maximum metal ion rejection was achieved to be 90% and 95% with a TMAH recovery of 80% and 85% for stage 1 and stage 2 NF treatment whereas the post treatment by resin ensured 99% metal ion rejection producing ultrapure TMAH. Cost estimation showed the hybrid process to be an economical route to purify the TMAH for semiconductor applications with feasibility for scale up. Graphical Abstract: ga1 Highlights: Production of TMAH of ultrahigh purity for electronic industry by hybrid membrane-adsorption process. Purification of TMAH with hydrophilized polyamide nanofiltration membrane to remove 90% of ionic contaminants. Optimization of experimental parameters including operating time and feed pressure on membrane flux and % rejection. Resin-based post treatment to achieve 99% ion removal efficiency. Economic estimation of the indigenously developed hybrid process.