Microwave-Assisted Lignin Conversion to Liquid Products in the Presence of Iron and Nickel
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owave-Assisted Lignin Conversion to Liquid Products in the Presence of Iron and Nickel O. V. Arapovaa, *, A. V. Chistyakova, T. A. Palankoeva, G. N. Bondarenkoa, and M. V. Tsodikova aTopchiev
Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, 119071 Russia *e-mail: [email protected] Received May 5, 2020; revised May 10, 2020; accepted May 12, 2020
Abstract—Results of the microwave-assisted catalytic pyrolysis of lignin have been described. It has been shown that, in a medium of an inert gas (argon) and a hydrogen–argon mixture, the following maximum liquid yield is achieved: 33 and 36% for iron-containing catalyst samples and 45% for nickel-containing catalysts. The gas chromatography–mass spectrometry (GC/MS) method has been used to determine the qualitative composition of the liquid product fraction, which is mostly represented by phenol and anisol, i.e., derivatives of the monomeric units of lignin (coumaryl and coniferyl alcohols). Probable sites of interaction of the functional groups of the lignin surface with nanosized particles of nickel- and iron-containing catalysts have been studied by IR spectroscopy. Keywords: lignin, microwave radiation, microwave-assisted pyrolysis DOI: 10.1134/S0965544120090029
Lignin is a substance constituting the woody walls of plant cells; it is a complex polymer compound of plant origin that is contained in the cells of trees and some other plants [1]. In wood processing and the pulp and paper industry, lignin accumulates as waste, the annual amount of which is estimated at 150 million tons [2, 3]. Lignin processing is complicated by the stability of the structure, which is represented by crosslinked polyaromatic chains [4, 5]. At the same time, lignin contains up to 5% of hydrogen and up to 50% of carbon; this fact is responsible for interest in developing effective approaches to producing energy carriers. A large number of studies are focused on the catalytic conversion of lignin [6–13]; the emphasis is put on the hydrolysis of lignocellulosic feedstocks in the presence of acid and base catalysts [14, 15]. This conversion method is mostly used to produce cellulose as a feedstock for the production of polysaccharides [14] and furfural [14, 15]. Extensive studies on lignin conversion to liquid products by liquid-phase hydrogenation in a hydrogen-donating solvent medium are being conducted [16, 17]. The process is run in the presence of a Pt/γ-Al2O3 catalyst using ethanol, glycerol, and sorbitol as liquid solvents. In a two-stage process, liquid-phase hydrogenation is typically used to produce aromatic hydrocarbons (HCs) [18, 19]. Lignin conversion is commonly conducted by pyrolysis [20–22]. During pyrolysis in the presence of catalytic additives, the С–С bond undergoes cracking to form resinous compounds and a small amount of HCs [20–22]. Lig-
nin gasification processes to produce hydrogen and synthesis gas are being quite vigorously developed. Particular attention is paid to gasification in water under supercritical pressure [23–25]. Recently, in the
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