Chemical and Biomolecular Engineering
Pyrolytic Remediation of Soils: The Catalytic Role of Clays and Metals
Lowering the Pyrolysis
Very high TPH conversions achieved with 10% Fe-bentonite amendment at the very low temperature of 300 oC.
H2 intensities from TG-MS pyrolysis of (A) unamended contaminated soil and (D) contaminated soil amended with 10%wt Fe-bentonite. The temperature shift provides strong evidence of the catalytic effect of Fe.
Pyrolytic treatment offers great potential for rapid remediation of soils contaminated with petroleum crudes without destroying soil fertility and with lower energy requirements than incineration. In a recent study, we show that clays impregnated with non-toxic transition metals (iron or copper) can be used as an amendment to decrease the required pyrolytic treatment temperature and time.
Amending a weathered crude-oil-contaminated soil with 10% (by weight) of bentonite modified via ion exchange with Fe or Cu, achieved 99% removal of residual total petroleum hydrocarbons (TPH) at a pyrolysis temperature of 370°C with a 15-min contact time. Pyrolytic treatment of amended soils at the unprecedentedly low pyrolysis temperature of 300°C resulted in 87% TPH removal efficiency with Cu-bentonite and 93% with Fe-bentonite.
We postulate that the transition metals catalyzed the pyrolysis reactions at lower onset temperatures. This hypothesis is supported by thermogravimetric analysis coupled with mass spectrometry, which revealed the release of hydrogen, methyl, and propyl ion fragments (markers of pyrolytic degradation products of crude oil) at lower temperatures than those observed for unamended soil.
Overall, these results provide proof of concept that natural or metal-impregnated clays can be used as amendments for rapid pyro-catalytic treatment of soils contaminated with petroleum crudes. We are already working to better understand the catalytic reaction mechanisms and to determine the pyrolysis kinetics so that we can design optimal pyrolysis processes for contaminated soils with specific properties.
Read our group’s publications…