Abstract
In recent years, there has been a surge of interest in char production from lignocellulosic biomass due to the fact of char’s interesting technological properties. Global char production in 2019 reached 53.6 million tons. Barks are among the most important and understudied lignocellulosic feedstocks that have a large potential for exploitation, given bark global production which is estimated to be as high as 400 million cubic meters per year. Chars can be produced from barks; however, in order to obtain the desired char yields and for simulation of the pyrolysis process, it is important to understand the differences between barks and woods and other lignocellulosic materials in addition to selecting a proper thermochemical method for bark-based char production. In this state-of-the-art review, after analyzing the main char production methods, barks were characterized for their chemical composition and compared with other important lignocellulosic materials. Following these steps, previous bark-based char production studies were analyzed, and different barks and process types were evaluated for the first time to guide future char production process designs based on bark feedstock. The dry and wet pyrolysis and gasification results of barks revealed that application of different particle sizes, heating rates, and solid residence times resulted in highly variable char yields between the temperature range of 220 °C and 600 °C. Bark-based char production should be primarily performed via a slow pyrolysis route, considering the superior surface properties of slow pyrolysis chars.
Highlights
Biomass is defined by the Food and Agriculture Organization (FAO) as a biological material of non-fossilized origin [1]
After having analyzed the different char production process conditions and properAfter analyzed the different charofproduction process conditions andthermochemical propertieshaving of the barks, a critical evaluation bark as a feedstock material for ties of the barks, a was critical evaluation bark as a feedstock material for thermochemical conversion performed for of guiding future char productions considering the described conversion performed for guiding future char productions the described charwas production methods, the chemical composition of considering bark compared to other lignocelchar production methods, thethe chemical of bark compared to other lignocellulosic materials, and studiescomposition involving bark pyrolysis processes
Lignocellulosic charcoals are materials with interesting technological properties that may be used in different areas, in fuel, soil amendment, and adsorption
Summary
Biomass is defined by the Food and Agriculture Organization (FAO) as a biological material of non-fossilized origin [1]. A global bark production as high as 400 million cubic meters per year may be estimated based on FAO wood production figures [6] Despite their abundance, tree barks are rarely used at a large scale, and most of the waste bark is either left in the forest or used for heating by local communities or as fuel in forest industries [7]. High carbohydrate and low-ash containing wood, energy crops, and agricultural wastes could be valorized via fast pyrolysis and gasification, because high yields of bio-oil or gas are likely to be obtained [18,19]. 53.6 million tons in 2019 according to FAO statistics with wood being the main biomass material for charcoal production These data suggest that other lignocellulosic feedstocks, namely, under valorized materials, such as bark residues, may be processed to produce charcoals [29,30,31,32,33,34]. The objectives of this review were to present the current state of-the-art charcoal production methods and processes, to determine the current knowledge gaps, and to present a critical review for developing a feasible pyrolysis process using bark
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