Abstract
Gasification with supercritical water is an efficient process that can be used for the valorization of biomass. Lignin is the second most abundant biopolymer in biomass and its conversion is fundamental for future energy and value-added chemicals. In this paper, the supercritical water gasification process of lignin by employing reactive force field molecular dynamics simulations (ReaxFF MD) was investigated. Guaiacyl glycerol-β-guaiacyl ether (GGE) was considered as a lignin model to evaluate the reaction mechanism and identify the components at different temperatures from 1000 K to 5000 K. The obtained results revealed that the reactions and breaking of the lignin model started at 2000 K. At the primary stage of the reaction at 2000 K the β-O-4 bond tends to break into several compounds, forming mainly guaiacol and 1,3-benzodioxole. In particular, 1,3-benzodioxole undergoes dissociation and forms cyclopentene-based ketones. Afterward, dealkylation reaction occurred through hydroxyl radicals of water to form methanol, formaldehyde and methane. Above 2500 K, H2, CO and CO2 are predominantly formed in which water molecules contributed hydrogen and oxygen for their formation. Understanding the detailed reactive mechanism of lignin’s gasification is important for efficient energy conversion of biomass.
Highlights
Biomass is a complex mixture of carbon-based organic molecules containing hydrogen, oxygen, often nitrogen and small quantities of other atoms
Before applying a higher temperature for lignin gasification, two simulations were investigated with the temperature of 1000 K and 1500 K to study initial reactions potentially occurring at low temperature
The number of molecules such as water and lignin model were analyzed and it was predicted that water molecules and lignin models remain almost the same for about 1 ns
Summary
Biomass is a complex mixture of carbon-based organic molecules containing hydrogen, oxygen, often nitrogen and small quantities of other atoms. Gasification is a hightemperature thermochemical conversion process focused on the production of combustible gas, instead of heat This is achieved through the partial combustion of the biomass material in a restricted supply of air or oxygen, usually in a high-temperature environment. One of the most promising methods for thermochemical conversion of biomass into hydrogen-rich gas is the gasification of lignin in supercritical water [12,13,14]. In this method, wet biomass can be converted into hydrogen-rich syngas at lower and higher temperatures with different catalysts. This study investigates the lignin model from temperature 1000 K to 5000 K to elaborate step-by-step evolution of products in supercritical water
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