Abstract
The hydrothermal liquefaction reactions (HTL) in subcritical conditions of a lignin residue has been studied on a lab scale. The starting material was a lignin rich residue co-produced by an industrial plant situated in Northern Italy producing lignocellulosic bioethanol. The reactions were carried out in batch mode using stainless steel autoclaves. The experiments were under the following operating conditions: two different temperatures (300–350 °C), the presence of basis catalysts (NaOH, and NH4OH) in different concentrations and the presence/absence of capping agent 2,6-bis-(1,1-dimethylethyl)-4-methylphenol (BHT). Lignin residue and reaction products were characterized by analytical and spectroscopic techniques such as CHN-S, TGA, GC–MS, EPR, and 1H-NMR with (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (T.E.M.P.O.). The addition of BHT did not significantly affect the yield of char which is formed by radical way. Spectroscopic analysis indicated that the level of radicals during the reaction was negligible. Therefore, the results obtained experimentally suggest that the reaction takes place via an ionic route while radical species would play a minor role.
Highlights
The hydrothermal liquefaction reactions (HTL) in subcritical conditions of a lignin residue has been studied on a lab scale
Amongst the different technologies being proposed for the depolymerisation of lignin, hydrothermal liquefaction (HTL) has been gaining increasing interest[7]
The EPR and 1H-NMR spectroscopic analyses did not show a relevant presence of radicals
Summary
The hydrothermal liquefaction reactions (HTL) in subcritical conditions of a lignin residue has been studied on a lab scale. The main use of by-product lignin is in energy enhancement in thermal cogeneration plants This entails the loss of important aromatic resources that could be used for the production of chemicals or biofuels but, in the case of incomplete combustion, the occurrence of serious environmental pollution problems[6]. When water is heated and compressed up to the supercritical state, the dielectric constant drops to the typical values of a non-polar solvent, for example at 400 °C and 25 MPa, ε ⁓ 69. This value is comparable to that of 1-dodecanol[10]. For these reasons supercritical water is an excellent solvent for non-polar substances such as organic compounds including lignocellulosic m aterials[11]
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