Abatement of tetrafluoromethane by chemical absorption with molten aluminum

Abstract

Chemical absorption with molten aluminum to abate tetrafluoromethane (CF₄) was investigated in this paper. The experiments were conducted at a series of different temperatures of 973 K, 1003 K, 1103 K, and 1188 K and the abatement rate of CF₄ was calculated. It was found that CF₄ can be adsorbed firstly and then react with molten aluminum automatically. The initial abatement rate of CF₄ in molten aluminum was 3.10 × 10^-2 mol·m^-3·s^-1 at 973 K, while it reached its maximum value of 1.08 × 10^-1 mol·m^-3·s^-1 at the temperature of 1103 K. The highest abatement efficiency was 48.4%, reached at 1003 K. Higher temperatures up to 1188 K did not affect the abatement efficiency, however, they accelerated slightly the initial reaction rate. The products of the chemical absorption are white solid AlF₃ and black graphite powder identified by XRD and SEM-EDS analysis. Due to density differences, solid AlF₃ and graphite powder in the product tend to accumulate on the top of molten aluminum where they form two separate layers. This makes them recover more easily. The gas-liquid reaction process between CF₄ and molten aluminum is accorded with the two-film theory model, diffusion process is considered to be the control step of the whole process.

Keywords: Aluminum electrolysis; Chemical absorption; Greenhouse gas; Tetrafluoromethane; Two-film theory.