Abstract
A comparative study among different pretreatment methods used for the fractionation of the birch outer bark components, including steam explosion, hydrothermal and organosolv treatments based on the use of ethanol/water media, is reported. The residual solid fractions have been characterized by ATR-FTIR, 13C-solid-state NMR and morphological alterations after pretreatment were detected by scanning electron microscopy. The general chemical composition of the untreated and treated bark including determination of extractives, suberin, lignin and monosaccharides was also studied. Composition of the residual solid fraction and relative proportions of different components, as a function of the processing conditions, could be established. Organosolv treatment produces a suberin-rich solid fraction, while during hydrothermal and steam explosion treatment cleavage of polysaccharide bonds occurs. This work will provide a deeper fundamental knowledge of the bark chemical composition, thus increasing the utilization efficiency of birch outer bark and may create possibilities to up-scale the fractionation processes.
Highlights
Efficient bioconversion of lignocellulosic materials to ethanol and value-added biochemicals represents a challenging proposition from both energy and environmental viewpoints
The highest yield of dissolved substances in uncatalyzed treatments was obtained with organososlv treatment, with a ratio of 80:20 of ethanol–water mixture
The solid fractions obtained present different characteristics depending on the specific process conditions
Summary
Efficient bioconversion of lignocellulosic materials to ethanol and value-added biochemicals represents a challenging proposition from both energy and environmental viewpoints. Apart from polysaccharides, multiple biomass feedstocks, including cork and outer bark residues, are rich in natural waxes, such as triterpenes, and insoluble polyesters (suberin) that serve as structural components of the outer barriers of plants. Degradation products, some of which are found almost exclusively in the suberized plant cell walls, may be of considerable value as sources of oleochemicals [1,2,3]. Silver birch (Betula pendula) is widely distributed in the northern hemisphere, in boreal climates, and is of great commercial significance as it constitutes the dominant hardwood tree species used for pulp production in Northern European countries. The total production of market pulp in Sweden amounts to approximately 3.8 million tons annually, according to The Swedish Forest
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