Tree barks are among the most important under-valorized biomass types. They constitute approximately 15% of the log volume and usually treated as a waste stream except certain barks such as the outer bark of cork oak (Quercus suber L.) which is utilized for production of cork stoppers and various different cork materials (joints, composites, adsorbents, etc.).
In the recent years the biorefinery concept, where biomass conversion processes and equipment are integrated, has gained importance to produce materials, heat and power and chemicals. In line with the increasing interest several studies were carried out for valorization of lignocellulosic wastes.
Thermochemical methods (pyrolysis, gasification, hydrothermal liquefaction, etc) have already shown their efficiency in biomass conversion. Among these methods, particularly fast pyrolysis method is a promising method in valorization of lignocellulosic wastes because the method allows to obtain high bio-oil yields from biomass in a relatively short time.
Although cork is obtained from the outer bark of cork oak, certain other tree barks also contain important amounts of cork in their bark mixed with ash-rich phloem portions. These trees are unconventional cork providers and include Turkey oak (Q. cerris L.), ponytail palm (Beaucarnea recurvate Lem.), pau-santo (Kielmeyera coriacea Mart.), etc. In valorization of these barks, usually a trituration is necessary to separate cork and non-cork (phloem) portions. After the trituration and sieving, cork and phloem portions with certain degree of purity is obtained.
The current study aims to find enhanced valorization routes for cork and phloem wastes of Q. cerris bark through fast pyrolysis. The biomass wastes used in this study are low-grade cork and phloem portions that are not suitable for cork stoppers production. The results of this study will also be expanded to cork industry wastes and bark wastes of forestry industry. Cork industry uses cork wastes to compensate its energy consumption by conventional burning. Fast pyrolysis bio-oil (FPBO) may present an alternative fuel for cork industry because it is easier to store and transport than cork powder. The huge amount of bark wastes produced globally each year are composed mainly of phloem. Therefore, finding an attractive application for tree barks may be possible after fast pyrolysis study.
The fast pyrolysis unit of Karlsruhe Institute of Technology (KIT) is a part of Bioliq® project where agricultural wastes are converted to high quality fuels by fast pyrolysis followed by gasification. The process is particularly suitable for ash-rich agricultural wastes such as wheat straw.
The results of the fast pyrolysis tests carried at KIT Germany are currently being analyzed. Detailed analyses of pyrolysis products, specifically the obtained condensate samples, are currently under way. Results will be included in the Master Thesis and a follow up publication is under consideration. From the raw results, it may be concluded that it is possible to obtain approximately 52% bio-oil as total condensate and 16% char (as received base) from phloem. This yield is indeed promising for executing further analyses (moisture content, ash content, elemental composition, etc of raw bark, bio char and bio-oil) followed by carrying a techno economic analysis for development of a feasible biorefinery scale up.