Effects of Pb on pyrolysis behavior of water hyacinth

• The concentration of H2 significantly increased with presence of Pb.
• The yields of bio-oil significantly increased with presence of Pb.
• The high heating values of bio-oil decreased slightly with presence of Pb.
• More than 82% of Pb was enriched in the char in the form of PbO and PbS.

Heavy metal contaminated biomass derived from biosorption is widespread and the disposal of the biomass needs to be paid more attention to avoiding second pollution. In this study, pyrolysis of Pb contaminated water hyacinth (Pb-WH) in a fixed-bed was investigated. The results indicated that the presence of Pb could increase the yield of pyrolytic bio-oil maximumly by 56% with only 0.6% lower of high heating value (HHV), while decreased the char and gas yield with a little higher concentration of H2. The increased amount of carboxylic acids and decreased aromatics were responsible for the slightly decrease of HHV. The remained char was analyzed by flame atomic absorption spectrometry and X-ray diffraction analysis, showing that more than 82% of the Pb in the Pb-WH was kept in the char in the form of PbO and PbS. It is proposed that Pb2+ stabilized the carboxyl or carbonyl groups and changed the position of chemical bond scission of aliphatic components formed via depolymerization of hemicellulose and NDS rather than decarboxylation at initial stage, thus forming more fatty acids by decreasing CO2 concentration and promoting H2 to release.