Abstract
In order to valorize lignin wastes to produce useful aromatic compounds, the thermal degradation pyrolysis of Kraft lignin in the absence of catalysts has been investigated at 350, 450, and 550 °C. The high content of sulfur in the fresh sample led to the formation of S-containing compounds in products whose evolution in the gas phase was monitored through GC-MS analysis. Pyrolytic gas is rich in CH4, CO, CO2, and H2S with the presence of other sulfur compounds in smaller amounts (i.e., CH3SH, CH3-S-CH3, SO2, COS, and CS2). Biochar morphology and elemental composition have been investigated by means of SEM and EDX. The carbon content reaches ~90% after pyrolysis at 550 °C, while the oxygen content showed a decreasing trend with increasing temperature. From GC-MS analysis, bio-oil resulted rich in alkyl-alkoxy phenols, together with (alkyl)dihydroxy benzenes and minor amounts of hydrocarbons and sulfur compounds. NaOH/H2O and EtOH/H2O extraction were performed with the aim of extracting phenolic-like compounds. Sodium hydroxide solution allowed a better but still incomplete extraction of phenolic compounds, leaving a bio-oil richer in sulfur.
Highlights
Over the last century, the world’s population and energy demands have increased, highlighting the need to find valid renewable alternatives for energy and chemical intermediate production
The commercial Kraft lignin used in this work was purchased from StoraEnso® (LineoTM Classic Lignin, Kotka, Finland), and its chemical characteristics are available at the supplier website
The ergy-dispersive X-ray spectroscopy (EDX) analyses are in rough agreement with the elemental analyses reported for Kraft lignin samples [25,26]
Summary
The world’s population and energy demands have increased, highlighting the need to find valid renewable alternatives for energy and chemical intermediate production. The use of non-renewable materials is no longer sustainable due to their limited availability and their impact on the environment. Gaseous products deriving from the combustion of these materials have been one of the major components responsible for the enhancement of the global warming effect [1]. Biomasses have been deeply studied as one of the most promising sources of hydrocarbons. Despite biomasses having already been adopted in many application fields, their actual contribution is not sufficient to satisfy the global energy demand. Many issues concerning large-scale applications of biomasses must be considered from the life cycle point of view
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