Environmental and Safety Aspects of Spent Hydroprocessing Catalysts - Spent Hydroprocessing Catalysts - page 107

Table 5.3: Hazardous characteristics [From ref. 306 . Reprinted with permission].
Explosive
Flammable
Liable to spontaneous combustion
Corrosive
Toxic
Liberation of toxic gases in contact with air and water
Capable, by any means, after disposal, of yielding another material
the test ignitability (40 CFR 261.21), corrosivity (40 CFR 261.22), reactivity (cyanide and
sulfide, 40 CFR 261.23), and toxicity characteristics leaching procedure (Toxicity
Characteristic Leaching Procedure [TCLP], 40 CFR 261.24) [280] . The EPA added spent
hydrotreating catalyst (K171) and spent hydrorefining catalyst (K172) to its hazardous waste
list in August 1998 [16] because of their self-heating behavior and toxic chemicals content.
The spent hydrocracking catalysts from the dual hydroprocessing operations were added to the
list in 1999 [16-18] .
It is evident from the hazardous characteristics listed in Table 5.3 [306] , that hazardous nature
of spent catalysts is always associated with the potential release of toxic species on the
exposure either only to air or a combined exposure to air and water. The characteristics, such
as explosive, flammable, and liable to spontaneous combustion dictate that all precautions are
taken to minimize the contact with air particularly in the case of spent catalyst that was not
adequately de-oiled and dried. Toxic species may be released either to atmosphere or to
ground water causing harm to humans on exposure. Special regulations and regulatory affairs,
which have been in effect to deal with all stages of handling spent catalysts, e.g., unloading,
storage, transportation, disposal, etc., were discussed above.
The analytical methods used for determining hazardous characteristics were discussed by
McKenna and Pickering [330] . For example, corrosivity can be simply determined by
measuring the pH of soils. For cyanide reactivity test, samples are held in a hermetic system
and acidified to a pH of 2. The generated gases are scrubbed and analyzed. For sulfide
reactivity, samples are acidified in an enclosed system. The generated gases are scrubbed and
analyzed. The objective of the cyanide and sulfide reactivity tests is to determine the potential
release of HCN and H 2 S.
The ignitability of spent catalysts can be determined using the Pensky-Martens method, which
has been used widely in petroleum refining for determining the flammability of fuels.
According to this method, a sample is heated while being exposed to the atmosphere directly
above the sample, to an open flame. The lowest temperature, at which the vapor above the