Conditioning the volatile stream from biomass fast pyrolysis for the attenuation of steam reforming catalyst deactivation

Abstract

The fast deactivation of the reforming catalyst greatly conditions H2 production from biomass. In order to alleviate this problem, use of conditioning catalysts in a previous conditioning step has been proposed to modify the pyrolysis volatile stream reaching the reforming catalyst. The experimental runs have been conducted in a two-step reactor system, which includes a conical spouted bed reactor for the continuous pinewood sawdust pyrolysis and an in-line fixed bed reactor made up of two sections: the conditioning and the reforming steps. Biomass fast pyrolysis was conducted at 500 °C and the reforming step at 600 °C. Different conditioning beds (inert sand, γ-Al2O3, spent fluid catalytic cracking (FCC) catalyst and olivine) were used for the conditioning of biomass pyrolysis volatiles and the influence their composition has on the performance and deactivation of a commercial Ni/Al2O3 reforming catalyst has been analyzed.

Considerable differences were noticed between the conditioning catalysts, with the reforming catalyst stability decreasing as follows depending on the type of material used: γ-Al2O3 > olivine > inert sand ≈ no guard bed > spent FCC catalyst.

The high acidity of γ-Al2O3 (with a high density of weak acid centers) is suitable for the selective cracking of phenolic compounds (mainly guaiacol and catechol), which are the main precursors of the coke deposited on the Ni active sites. Although H2 production is initially lower, the reforming catalyst stability is enhanced. These results are of uttermost significance in order to step further in the scaling up of the in-line pyrolysis-reforming strategy for the direct production of H2 from biomass.