Formation characteristics of PCDD and PCDF during pyrolysis processes

Area of Science:

• Environmental Chemistry
• Chemical Engineering
• Waste Management Technologies

Background:

• Pyrolysis is emerging as an industrial-scale alternative to waste combustion.
• Limited data exists on polychlorinated dibenzodioxins and dibenzofurans (PCDD/Fs) formation during pyrolysis.
• Shredder fractions like industrial light shredder (ILS) and refrigerators (REF) contain high chlorine and copper, relevant precursors for PCDD/F formation.

Purpose of the Study:

• To investigate PCDD/F formation characteristics during the pyrolysis of specific waste streams.
• To compare PCDD/F profiles from pyrolysis with those from conventional waste incineration.
• To identify the dominant PCDD/F congeners and their distribution within different fractions.

Main Methods:

• Pyrolysis of ILS and REF fractions in a pilot plant (100 kg/h capacity).
• Controlled conditions with oxygen concentrations below 2% and temperatures between 430-470°C.
• Analysis of PCDD/F formation, distribution, and congener patterns in different product fractions (oil, gas, solid).

Main Results:

• Considerable PCDD/F formation observed under investigated pyrolysis conditions.
• Over 90% of the total toxic equivalent (TEQ) was found in the oil fraction (gas phase).
• PCDD/PCDF ratios and homologue patterns differed significantly from waste incineration, with up to 400 times more PCDF than PCDD, favoring low-chlorinated congeners.

Conclusions:

• Pyrolysis conditions studied generate significant PCDD/Fs, predominantly in the oil fraction.
• The formation characteristics, particularly the high PCDF proportion and preference for low-chlorinated congeners, distinguish pyrolysis from waste incineration.
• Despite differences in formation patterns, the isomer distribution suggests similar fundamental formation mechanisms for PCDD/Fs in both processes.