Bull. Spec. CORESTA Congress, Brighton, 1998, p. 178, ST31
Novel technologies for the abatement of phosphine
Philip Morris USA, Research Center, Richmond, VA, USA
The program to implement effective phosphine abatement after tobacco warehouse fumigation has led us to develop two technologies for the purpose, replacing Ag/C. The first was a liquid scrubber system based on H2O2 to convert PH3 to H3PO4. Silver (I) efficiently captured phosphine from air, and initiated its oxidation, being reduced to Ag(0) in the process. Ag(0) was efficiently recycled by H2O2 and H+, in the presence of co-catalysts. Of these, tungsten (VI) was by far the best, followed by vanadium (V), molybdenum (VI), titanium (IV) or iron (III). An optimized medium consisted of 0.05 M AgNO3, 1 M HNO3, 0.01 M Na2WO4, and 2 M H2O2. This was able to maintain the silver content in soluble form while in use. In the field, a 25 gpm counterflow through a standard packed bed completely removed phosphine of fumigation concentrations from 1000 cfm of airflow. The second technology, and the one chosen for implementation, was based on activated carbon. Certain coal-based carbons are intrinsically active for the catalytic oxidation of phosphine, in the presence of water. However, these show induction periods that require reduced air-flow until the catalyst becomes fully active, to provide complete phosphine removal. Calgon Corporation’s CENTAUR→ Carbon was first applied to phosphine abatement in 1994 at PM. A more economical carbon, NORIT AMERICA’s Vapure 610, shows very similar behavior, and was successfully tested in the field in 1997. It was found that the induction period of either carbon could be eliminated by the addition of certain acidified reducing agents. These included H3PO2, NaHSO3, H2SO3, and H2SO4 acidified solutions of SnSO4, Ti2(SO4)3, or FeSO4. It was also found that H2SO4 sufficed to eliminate the induction period in Vapure. Philip Morris has assisted NORIT in developing an acid-activated version of NORIT Vapure for the abatement of PH3 and H2S, and is actively evaluating the material.