Pyrolysis-gas-chromatography/mass spectrometry (Py-GC/MS) was employed to investigate the thermal cracking evolution and thermochemical conversion pathways of the main carbon and oxygen-containing functional groups contained in sewage sludge under different pyrolysis temperatures. The results show that sewage sludge mainly contain carbon-carbon double bonds (C=C)

carboxyl groups (—COOH)

hydroxyl groups (—OH)

aldehyde groups (—CHO) and benzene (π-π*). Pyrolysis temperature has an evident influence on the functional groups evolution. At the stage of the pyrolysis with a temperature lower than 350℃

the increased temperature results in the largest decrease of —COOH content

which is approximately 33%. In the mid-temperature thermal cracking stage (350-550℃)

the production of C=C

—OH

—CHO

and π-π* in pyrolysis product increased significantly

while —COOH show a decreasing trend

but its mass ratio is still the highest. The benzene becomes the main functional groups when the pyrolysis temperature higher than 550℃. In the high temperature pyrolysis stage (>550℃)

due to aliphatic hydrocarbon molecules. The chemical activity is enhanced

mainly due to aromatization polycondensation reaction such as dehydration

decarboxylation

decarbonylation and aldol condensation. In the range of pyrolysis temperature study

carbon-carbon double bonds

aldehyde groups and hydroxyl groups content are lower

but show obvious pyrolysis rules. Further

combining the pyrolysis rules of each functional group

the possible path of the pyrolysis evolution of carbon and oxygen-containing functional groups in sludge is proposed.