Organic acid modified activated carbon filter media for removal of isopropanol in the cleanroom

Abstract

Isopropyl alcohol (IPA) is commonly used for process cleaning. Expensive chemical filters are installed in cleanrooms to remove high concentrations of IPA contamination. We firstly use organic acid to modify coal-based activated carbon (AC) as a starting point for preparation of filtration media for IPA removal. AC was characterized before and after this modification using BET, SEM, thermogravimetric analysis (TGA), FTIR, and temperature programmed decomposition (TPD), comparing results with those obtained from the same tests applied to commercial coconut AC. These tests found that the specific surface area of coal-based AC, modified by the oxalic acid, was not as large as that of commercial AC, but there was a significant increase in surface area following surface modification. As can be seen from the SEM images, following modification, the surface roughness of the AC increases, with additional precipitation of oxalic acid particles. Besides the deposition of oxalic acid functional groups on the AC surface, modification also reduces the presence of basic groups and increases the number of acidic groups, as quantified by TPD with TGA. The adsorption isotherms of IPA adsorption are well fitted by both Langmuir and Freundlich isotherm models. Breakthrough times of 590, 413, and 380 days were observed for modified coal-based AC at 1 ppb initial IPA concentration and 0.3, 0.4, and 0.5 m s−1 face velocity, respectively. The adsorption kinetics are best described by a Pseudo-Second order kinetics model and also could be predicted by the intraparticle diffusion and membrane diffusion models.