(2016) Energy_Enhanced thermal cracking of VOCs evolved from the thermal degradation of lignin using CO₂

Kim J., Kim K.-H., Kwon E.E.

(Elsevier Ltd) Energy ISSN: 3605442 Vol.100 Issue. Article No. DOI: 10.1016/j.energy.2016.01.075

This work offers a mechanistic investigation of the thermal degradation of lignin in the recovery of energy from biomass waste (i.e., lignin). Particularly, this work describes the influence of CO₂ in the pyrolysis process since pyrolysis process has been known as an intermediate step for gasification. This work experimentally justifies the effectiveness of the influence of CO₂ in pyrolysis of lignin at temperatures higher than ~550 °C. Our GC/TOF-MS analysis of pyrolytic oil obtained at temperature lower than ~500 °C indicated the thermal degradation of lignin via the thermal bond dissociation of phenolic compounds from the macromolecule of lignin: these phenolic compounds identified in the N₂ and CO₂ environment were nearly identical. The unknown reaction induced by CO₂ at temperatures higher than ~550 °C simultaneously and independently occurred with dehydrogenation of VOCs (volatile organic carbons), which significantly enhanced the generation of CO via providing the additional source of C and O. Thus, this work shows that the ratio of CO to H₂ was significantly enhanced in the presence of CO₂, the enhancement of which reached up to ~1000% at 650 °C as compared to the case in N₂. In order to enhance the identified influence of CO₂, the porous material (i.e., activated alumina) was used in pyrolysis of lignin. Our experimental work shows that employing the porous material was indeed effective to enhance the generation of syngas. This observation indirectly implied not only that employing porous materials could enhance the generation of pyrolytic gases, but also that the reaction rate induced by CO₂ would be very fast. In summary, this study experimentally justifies the fact that exploiting CO₂ as reaction medium enhances not only the thermal efficiency of the thermo-chemical process, but also the sustainability of biomass-derived fuel via achieving the virtuous circle of carbon. © 2016 Elsevier Ltd.

This work was supported by a National Research Foundation of Korea (NRF) Grant funded by the Korean Government (MSIP) (No. 2014RA1A004893 ). The second author acknowledges partial support made by a grant from the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (MEST) (No. 2009-0093848 ).