Patterns of the Ozone Pretreatment of Lignocellulosic Biomass for Subsequent Fermentation into Sugars
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HYSICAL CHEMISTRY
Patterns of the Ozone Pretreatment of Lignocellulosic Biomass for Subsequent Fermentation into Sugars E. M. Ben’koa,* and V. V. Lunina a Department
of Chemistry, Moscow State University, Moscow, 119991 Russia *е-mail: [email protected]
Received December 11, 2019; revised December 11, 2019; accepted January 21, 2020
Abstract—General patterns of ozone pretreatment for subsequent fermentation into sugars are found, based on samples of different types of plant biomass. It is shown that the reactivity of plant substrates pretreated with ozone is determined by the amount of consumed ozone, and the rate of ozone consumption depends on the content of water in a sample. Optimum values of moisture (~2FSP) and ozone consumption (2–3 mol O3/C9PPU lignin) are found. Keywords: ozone, lignin, plant biomass, moisture content, wood, straw, pretreatment, sugars DOI: 10.1134/S0036024420090034
INTRODUCTION Ozonation has been studied for several decades as way of pretreating lignocellulosic raw materials to increase their reactivity during subsequent fermentation into sugars and alcohols [1–3]. It has been found that ozone mainly reacts with lignin, promotes the destruction of lignocellulosic material and its delignification, and thus facilitates the release of sugars during hydrolysis by cellulolytic enzymes [2, 4]. Ozone treatment is characterized by high efficiency, mild conditions, and the environmental safety of the process [4]. The need to use large amounts of ozone restrained the practical application of ozone technologies for some time, making the technique economically unbeneficial. In recent years, considerable progress has been made in the field of ozone synthesis, allowing the cost of ozone to be brought down substantially, and interest in the ozone pretreatment has grown. This is apparent from the large number of works devoted to the problem. However, the question of the optimum conditions for ozonation that allow us to reduce ozone consumption and increase the yield of target products in the bioconversion of plant materials, remains open. To solve it, we must understand the physicochemical patterns of the ozonation of plant biomass, and determine and separate the role of the process’s operating parameters. The experimental material we have accumulated and the extensive literature database allow us to make certain generalizations and assumptions regarding the optimum conditions for the ozone pretreatment of plant biomass.
EXPERIMENTAL Samples of wood and annual plants were provided and characterized at Altai State University (Barnaul, Russia) according to the standard procedures [5]. Table 1 presents characteristics of some of the lignocellulosic materials that were used: the content of main components, the composition of lignin, and the average molecular weight of the phenylpropanoic structural subunits (PPUs) of lignin. Prior to treatment with ozone, the samples were moistened by adding the required amount of distilled water and kept in a closed container for several days. The moisture content of
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