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

Abstract

Hydrogen (H 2) and other gases (CO 2, CO, CH 4, H 2O) 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 H 2 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 H 2 formation. Without added CaO, little H 2 was produced during primary pyrolysis; rather, most H 2 was generated from tar-cracking, reforming, and char-decomposition reactions at higher temperatures. When CaO was added, significant H 2 was produced during primary pyrolysis, as the water-gas shift reaction was driven toward H 2 formation. CaO also increased the formation of H 2 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 H 2 from pine over the course of pyrolysis could be modeled by summing the H 2 evolutions from the separate biomass components in relevant proportions.