• Energy Research

Interactions of cellulose- and lignin-derived intermediates have been well documented during pyrolysis of lignocellulosic biomass. The reaction network for the interactions is rather complex, as cellulose-derived volatiles could interact/react with not only lignin-derived volatiles but also lignin-derived char and vice versa. To probe specifically the impacts of cellulose-derived volatiles on the lignin-derived char or the opposite, herein the sequential pyrolysis was performed by arranging cellulose in the upper bed with lignin in the lower bed or lignin above with cellulose below at 350 and 650 °C, respectively. The results indicated that the sequential pyrolysis of cellulose→lignin or lignin→cellulose at 350 °C induced increased char yield from formation of carbonaceous deposits via volatiles-char interactions. Compared with the lignin-derived volatiles, the cellulose-derived volatiles, especially aldehyde fractions, were more reactive towards the lignin-derived char at 350 °C, forming oxygen-rich lignin-derived char with a higher yield, an abundance of aliphatic structures and consequently lower thermal stability. In sequential pyrolysis of lignin→cellulose, more aromatics-rich species were deposited on cellulose-derived char, but the lignin-derived volatiles were less reactive for enhancing the char yield. At 650 °C, instead of polymerisation of the volatiles on the char, either the cellulose- or lignin-derived char catalyzed the cracking of the counterpart volatiles to remove the aliphatic functionalities, which made the char more aromatic and thermally more stable.

Abstract Reaction atmosphere is one of the principle parameters affecting pyrolysis characteristics of biomass. In this study, instead of feeding reactive gases, methanol was co-fed in the pyrolysis of saw dust, aiming to understand the impacts of methanol on evolution of functionalities/structures of the major pyrolysis products. The results showed that at low pyrolysis temperature of 350 °C, methanol did not affect much on the charring reactions but promoted the formation of the heavier organics. At 500 or 650 °C, the co-feeding of methanol enhanced the yields of both char and the heavy components of bio-oil, resulting from the reaction of methanol or its derivatives with the organic components on surface of biochar via recombination/condensation reactions. In addition, methanol enhanced evolution of the organics with π-conjugated structures. The co-feeding of methanol also enhanced crystallinity and sizes of the crystal carbon in the biochar, but led to their lower thermal stability. The in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) characterization of saw dust pyrolysis indicated that methanol promoted the aliphatic structures formation on surface of the biochar, leading to the low thermal stability.

CaO captures CO2 from pyrolysis, forming CaCO3 that activates biochar via decomposition.

The interaction between volatiles and homologous and/or heterologous char is almost inevitable during the transfer or diffusion of volatiles from inner core to outer surface of a biomass particle in pyrolysis. This shapes both composition of volatiles (bio-oil) and property of char. In this study, the potential interaction of lignin- and cellulose-derived volatiles with char of varied origin was investigated at 500 °C. The results indicated that both the lignin- and cellulose-char promoted polymerization of the lignin-derived phenolics, enhancing production of bio-oil by ca. 20%-30%, generating more heavy tar but suppressing gases formation, especially over cellulose-char. Conversely, the char catalysts, especially the heterologous lignin-char, promoted cracking of the cellulose-derivatives, producing more gases while less bio-oil and heavy organics. Additionally, the volatiles-char interaction also led to gasification of some organics and also aromatization of some organics on surface of char, resulting in enhanced crystallinity and thermostability of the used char catalyst, especially for the lignin-char. Moreover, the substance exchange and formation of carbon deposit also blocked pores and formed fragmented surface dotted with particulate matters in the used char catalysts.

Abstract Co-pyrolysis of coke bottle (CB) with sawdust/cellulose/lignin was conducted at 700 °C in this study, aiming to understand the potential influence of interactions of the volatiles of the varied origins on properties of the char. The results indicated that the interaction of volatiles from CB with that from biomass enhanced cross-polymerization of the volatiles, decreasing the formation of gases while enhanced the formation of both char and oil. The cross-interactions of the intermediates also diminished the formation of π-conjugated organics. In addition, the varied volatiles from the pyrolysis of cellulose, lignin, or sawdust interacted with that from CB and affected the properties of char in different ways. The char from the co-pyrolysis of sawdust/CB was more aliphatic, and had a higher oxygen content (7.3%) and higher polarity but lower thermal stability. Additionally, the thermal stability, crystallinity as well as the evolution of functionalities of char versus increasing temperature were also significantly affected by the cross-interactions of the volatiles.