A comparative study on the catalytic effect of H-ZSM5 on upgrading of pyrolysis vapors derived from lignocellulosic and proteinaceous biomass

Abstract

The upgrading of biomass pyrolysis vapors by zeolite cracking over H-ZSM5 (Si/Al 45, biomass:zeolite mass ratio 1:10) was investigated by analytical (Py–GC–MS) and preparative pyrolysis. Pine sawdust, the microalgae Spirulina platensis, seaweed (Ulva sp.), and marine fish discard were selected as representative biomass with different composition, in particular protein content (from <1% to 55%d.w.). Py–GC–MS showed that the relative product distribution from zeolite cracking was dominated by alkylated benzenes, with minor levels of benzene and polycyclic aromatic hydrocarbons (PAHs) for all the samples, while the levels of nitrogen-containing compounds (N-CCs) increased with increasing biomass protein content. Preparative pyrolysis was conducted with a semi-batch system by treating the biomass at 460°C. The evolved vapors were subjected to zeolite cracking at 460°C, the yields of pyrolysis fractions (char, bio-oil, aqueous phase, volatiles, coke and gas) were quantified and compared with those determined in the absence of catalytic treatment (thermal pyrolysis). Due to the reactor configuration the yields of char formed from thermal and catalytic pyrolysis were similar, while the yield of bio-oil decreased considerably after zeolite cracking with a concomitant formation of coke (6–14%), water and volatiles, which was higher for the proteinaceous biomass. However, the bio-oils from catalytic pyrolysis were characterized by lower levels of nitrogen and oxygen, a higher carbon content and a GC–MS composition dominated by monoaromatic hydrocarbons (>60%), followed by PAHs (mostly naphthalene). The relative abundance of N-CCs in catalytic bio-oil was lower in comparison to Py–GC–MS suggesting that a fraction was distributed into the aqueous phase. In general, HZSM-5 exhibited a significant dehydration, deoxygenation and denitrogenation effect favoring the formation of a “gasoline-like” bio-oil even from a highly proteinaceous biomass. However, it also induced the formation of nitrogen-containing polyaromatic compounds, like carbazoles.