Features of Lignin Destruction in Wood under the Action of Ozone
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ICAL KINETICS AND CATALYSIS
Features of Lignin Destruction in Wood under the Action of Ozone N. A. Mamleevaa,*, A. N. Kharlanova, and V. V. Lunina a Faculty
of Chemistry, Moscow State University, Moscow, 119991 Russia *e-mail: [email protected]
Received November 2, 2019; revised November 2, 2019; accepted November 12, 2019
Abstract—Samples of pine wood ozonated with different contents of water are studied via UV diffuse reflectance spectroscopy. It is shown that polyaromatic and stilbene structures, guaiacyl derivatives, and carbonyland carboxyl-containing aromatic structures of lignin are destroyed during ozonation of pine wood. The destruction of aromatic structures proceeds efficiently in wood with a moisture content of more than 60–65% in the 2–3 mmol/g range of ozone consumption. When the moisture content is below 40%, ozone treatment of pine wood at low ozone consumption allows us to obtain different modifications of oxygen-containing aromatic and polyaromatic structures on surfaces of lignocellulosic material (LCM). IR absorption spectra of dioxane lignin obtained from the initial and ozonated wood samples confirm the different direction of lignin transformations, depending on the content of moisture in the wood. Keywords: wood, lignin, ozone, UV diffuse reflectance spectroscopy, IR spectra of dioxane lignin DOI: 10.1134/S0036024420090186
INTRODUCTION Ozone is an effective oxidizing agent for aromatic compounds [1, 2] and is used in processes of residual lignin removal in paper pulp production at the stage of paper pulp bleaching [3, 4]. The delignification of plant biomass by ozone is considered as pretreatment that allows us to increase the yield of monosaccharides during the subsequent enzymatic hydrolysis of lignocellulosic material (LCM) [5–8]. This approach is also of interest for the production of cellulose, since the destruction of cellulose during LCM ozonation is relatively low [9, 10]. The use of wood as the initial material for ozone treatment is of interest due to the considerable amount of industrial waste that can serve as a raw material for further chemical processing [3, 4, 10, 11]. The promise of these studies is also due to the high content of cellulose in wood characterized by a high degree of polymerization [9]. It is known that the presence of water in the structure of a sample is a necessary condition for biomass delignification during ozone treatment; the amount of consumed ozone and the depth of biomass delignification depends on the amount of water, and the optimum amount of water is different for different types of plant substrates [5–10]. In studying ozone consumption and determining the residual lignin content in ozonated wood samples, it has been shown that a moisture content of 60–63% is optimum for the processing of pine wood when a degree of wood delignification of 40% is achieved [9, 12]. The products of lignin ozonolysis that form during the ozonation of pine
wood are glyoxalic, formic, and oxalic acids, which also participate in oxidation with ozone [9, 12]. The results
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