Hydrogen synthesis from biomass pyrolysis with in situ carbon dioxide capture using calcium oxide

Hydrogen (H2) and other gases (CO2, CO, CH4, H2O) produced during the pyrolysis of cellulose, xylan, lignin and pine (Pinus radiata), with and without added calcium oxide (CaO), were studied using thermogravimetry-mass spectrometry (TG-MS) and thermodynamic modeling. CaO improved the H2 yield from all feedstocks, and had the most significant effect on xylan. The weight loss of and gas evolution from the feedstocks were measured over the temperature range 150–950 °C in order to investigate the principle mechanism(s) of H2 formation. Without added CaO, little H2 was produced during primary pyrolysis; rather, most H2 was generated from tar-cracking, reforming, and char-decomposition reactions at higher temperatures. When CaO was added, significant H2 was produced during primary pyrolysis, as the water-gas shift reaction was driven toward H2 formation. CaO also increased the formation of H2 from reforming and char gasification reactions. Finally, CaO increased the extent of tar cracking and char decomposition, and lowered their onset temperatures. The production of H2 from pine over the course of pyrolysis could be modeled by summing the H2 evolutions from the separate biomass components in relevant proportions.