Development of a Regenerable System Employing Silica-Titania Composites for the Recovery of Mercury from End-Box Exhaust at a Chlor-Alkali Facility

Abstract

The release of mercury to the environment is of particular concern because of its volatility, persistence, and tendency to bioaccumulate. The recovery of mercury from end-box exhaust at chlor-alkali facilities is important to prevent release into the environment and reduce emissions as required by NESHAP (National Emission Standards for Hazardous Air Pollutants). A pilot-scale photocatalytic reactor packed with silica-titania composite (STC) pellets was tested at a chloralkali facility over a 3-month period. This pilot reactor treated up to 10 ft3/min (ACFM) of end-box exhaust and achieved 95% removal. The pilot reactor was able to maintain excellent removal efficiency even with large fluctuations in influent mercury concentration (400-1600 microg/ft3). The STC pellets were regenerated ex situ by regeneration with hydrochloric acid and performed similarly to virgin STC pellets when returned to service. On the basis of these promising results, two full-scale reactors with in situ regeneration capabilities were installed and operated. After optimization, these reactors performed similarly to the pilot reactor. A cost analysis was performed comparing the treatment costs (i.e., cost per pound of mercury removed) for sulfur-impregnated activated carbon and the STC system. The STC proved to be both technologically and economically feasible for this installation.

Characterization of HF-catalyzed silica gels doped with Degussa P25 titanium dioxide

“…The combined material is herein referred to as a silica-titania composite (STC). This material has been studied for use in a variety of photocatalytic applications such as mercury removal from flue gas [7,8], mercury recovery from caustic exhaust emitted from the chlor-alkali industry [9], and the degradation of volatile organic compounds in gas emitted from pulp and paper mills [10]. While optimal material conformations were found for the applications listed, it was not well-understood how the material characteristics changed with HF concentration and TiO 2 loading.…”

Role of Activated Carbon Precursor for Mercury Oxidation and Removal: Oxidized Surface and Carbene Site Interaction

“…In fact, the breakthrough curve for GH HT continues to improve over time. A potential layering effect (nucleation), whereby oxidized and adsorbed mercury is participating in the removal of the influent Hg 0 has been seen in other works employing silica-titania composites can begin to explain these results [59].…”

A pilot-scale TiO2 photocatalytic system for removing gas-phase elemental mercury at Hg-emitting facilities

“…Numerous studies have previously reported that the presence of UV (regardless of the intensity) at the initial stage is essential to trigger the photocatalytic reaction by TiO 2 [11][12][13][14][15][16]23,24]. As shown in Fig.…”