Effects of chromium on pyrolysis characteristic of water hyacinth (Eichornia crassipes)

•The presence of Cr contributes to the increase of bio-oil yield.•Effects of Cr content on the whole pyrolysis products yield were evaluated.•The suggested parameters for pyrolysis of water hyacinth with Cr are provided.•Cr content has a major influence on the decreasing of acid value of bio-oils.•Components of bio-oil was revealed and rupture process of fatty acid suggested.

The chromium polluted water hyacinth was subjected to pyrolysis to understand its pyrolytic characteristic in a fixed bed. The results indicated that chromium has a positive effect on the bio-oil produced, accompanied by a decrease of gas yield and moderate formation of char. The maximum bio-oil yield obtained from Cr-WH pyrolysis reached the maximum of 63.1 wt.%. The acid number and high heating value of the Cr-WH pyrolytic bio-oil were 85.04 mgKOH/g and 26.72 MJ/kg, respectively. GC-MS analysis of the bio-oils showed that the amount of nitrogenous compounds, alcohols and phenols increased, while the number of esters reduced in the Cr-WH pyrolytic bio-oil which indicated that chromium promoted bond rupture of lignin and changed the degradation process of protein. Furthermore, after pyrolysis, Cr may transfer from the toxic state of ions into an amorphous state in the char, which reduce its harm to the environment.