Triboelectric effects of continuity additives and a silica catalyst support on polyethylene fluidized bed wall fouling

Abstract

In commercial polyethylene gas-phase reactors, continuity additives (CAs) are periodically fed into the reactor to tackle reactor sheeting. In dry feeding of CAs, they are pneumatically conveyed into the reactor separately or doped on the catalyst support. This work investigated the role of five materials reported to act as CA (aluminum-distearate, AS-990, calcium-stearate, zinc-stearate, and CHIMASSORB-944) along with a catalyst support (amorphous silica) on the polyethylene fluidized-bed fouling degree. Powders were conveyed into a 0.1-m diameter stainless-steel atmospheric fluidization column containing polyethylene using a pneumatic conveying line of similar material (SS316) and diameter (4.75 × 10−3 m) to those used in commercial processes. The bed bulk net specific charge and the extent of wall fouling were directly proportional. The degree of bed charge and wall fouling varied by the type/concentration of the CA, emphasizing the importance of CAs surface chemistry. An optimum CA-to-silica ratio was proposed to minimize the wall fouling.