Hydrogen from scrap tyre oil via steam reforming and chemical looping in a packed bed reactor

The production of hydrogen from scrap tyre pyrolysis oil (STPO) was investigated using catalytic steam reforming. STPO is difficult to upgrade to cleaner fuels due to its high sulphur content, complex organic composition, acidity and viscosity, which contribute to catalyst deactivation. The effects of temperature and steam to carbon ratio were investigated through thermodynamic equilibrium calculations of the main aromatic, aliphatic and hetero-N and -S compounds known to be present in STPO. The optimum operating conditions in a packed bed reactor with a Ni/Al2O3 catalyst at atmospheric pressure and molar steam to carbon ratio of 4:1 were 750 °C at a WHSV of 0.82 h−1. The maximum hydrogen yield was 26.4 wt% of the STPO feedstock, corresponding to 67% of the maximum theoretical yield, compared to 79.4% predicted at equilibrium for a model mixture of 22 STPO compounds in the same conditions. The selectivity to the H-containing products was 98% H2 and 2% CH4, respectively, indicating little undesirable by-product formation, and comparable to equilibrium values. The potential to optimize the process to enhance further the H2 yield was explored via feasibility tests of chemical looping reforming (CLR) aimed at lowering the heating and purification costs of the hydrogen production from STPO. However, the hydrogen yield decreased with each cycle of CLR. Analysis of the catalyst indicated this was most likely due to deactivation by carbon accumulation and sulphur originally present in the oil, and possibly also by trace elements (Ca, Na). The NiO particles in the catalyst were also shown to have grown after CLR of STPO. Hence further development would require pre-treating the oil for removal of sulphur, and use of a catalyst more tolerant to carbon formation.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights▸ Steam reforming of scrap tyre pyrolysis oil demonstrated with Ni catalyst. ▸ Highest hydrogen yield reported on basis on scrap tyre feedstock (11.8 wt%). ▸ Optimum conditions at 750 °C, molar steam to carbon ratio of 4. ▸ Deactivation during chemical looping reforming by C, S deposits and Ni crystal growth. ▸ Potentially higher H2 yield if desulphurisation of oil and controlled steam addition.