Lignoselüloziklerden biyo-kökenli poröz karbon materyalin üretilmesi

Fossil resources are directing the economy today. The limited reserves of fossil resources, environmental pollution and greenhouse gas emissions caused by the use of fossil fuels, and the desire of countries to decrease the dependence of crude oil have led to a search for alternatives. Bio-based economy, which bases on producing value-added products (including bio-based chemicals, functional materials and biofuels) from biomass, has a great impact on reducing the dependency on fossil fuels. Moreover, adapting bio-based economy increases resource efficiency, reduces emissions and accelerates rural development. Among the biomass sources, lignocellulosic biomass such as agricultural residues/wastes and forestry residues/wastes require special attention. There are several conversion methods to produce different platform molecules, which can be used directly as an end-product or an intermediate product to produce the desired product. Hydrothermal carbonization (HTC) is among the thermochemical conversion methods, which gives opportunity to produce different value-added products including bio-based chemicals, carbon-rich materials and fuels with higher energy densities. This thesis presents hydrothermal carbonization as a method a) to obtain solid fuels with better properties compared to their original feedstock, b) to obtain a precursor for producing bio-based activated carbon. Therefore, this study comprises two parts: 1) producing hydrochars of selected lignocellulosics, and comparing the fuel properties of the lignocellulosics with their corresponding hydrochars, 2) activation of those hydrochars with KOH to produce porous activated carbons, and assessment of porous structure based on the type of lignocellulosic feedstock. Wood dust, walnut shell, tea stalk, olive pomace, apricot seed and hazelnut husk were used as lignocellulosic biowastes, which were hydrothermally carbonized at 220°C for 90 min. Hydrochars of those lignocellulosics were activated by chemical activation with KOH at 600°C. As the wood dust, walnut shell, tea stalk, olive pomace, apricot seed and hazelnut husk biomass samples and their corresponding hydrochar were compared, the improvement of the fuel quality after HTC was remarkable. All hydrochars represented lower volatile matter content and hydrogen content. Fixed carbon content of all hydrochars were higher than their original raw sample, resulting higher net calorific values. The percentage increase in heating values were ranked between 30% (olive pomace) and 14% (wood dust). Among the hydrochars, olive pomace presented the best improvement in terms of high heating value (6106 cal/g) and low ash percentage (5.5%). All of the hydrochars had the heating values as high as bituminous coal. Activated hydrochars demonstrated BET surface areas of between 308.9 m2/g and 666.7 m2/g (activated hydrochar of wood dust and tea stalk), and total pore volumes of between 0.25 cm3/g and 0.73 cm3/g (activated hydrochar of olive pomace and wood dust). The average pore size distribution of the activated hydrochars was ranging between 1.05 nm (olive pomace) and 4.74 nm (wood dust). All agricultural based activated hydrochars had similar average pore size distribution of between 1.05 nm and 1.25 nm, which fell in the range of microporous structure. With the average pore size of 4.74 nm, activated hydrochar of wood dust was classified under the mesoporous structure. This thesis clearly points out that: - The type of lignocellulosic biomass affects the amount and characteristics of its corresponding hydrochar. - HTC is a very effective method to decrease the moisture and volatile matter content of lignocellulosics. - HTC is a very effective method to increase the fixed carbon content and heating value of the lignocellulosics. - After HTC, all hydrochars represent similar pyrolysis and combustion profile, the only difference is the shifting of the characteristic temperatures (the temperatures of maximum mass loss rate, ignition temperature and burnout temperature) to higher values. - HTC is a very effective method to enhance the fuel properties of the lignocellulosics. - HTC, alone, also produces hydrochars with higher porous structure compared to their raw feedstock. - Activating HTC with KOH dramatically affects the microporous structure formation. - The type of lignocellulosic material (mainly the structure of lignin) has a great impact on porous structure.