Lignocellulosic Biomass Derived Activated Carbon for Energy Storage and Adsorption

Lignocellulosic biomass has been converted to hierarchical porous carbon materials which possess macro-, meso- and micro-pores. The natural structure of porous lignocellulosic structure was preserved during activation with further developed porosity by the activation. The activated carbon can be well applied to electrochemical double layer capacitor for transportation storage of ions as well as adsorbent materials for metal ion removal from wastewater. The first chapter of this dissertation presents an introduction of biomass derived carbon and its applications. In the second chapter, both direct and indirect activation methods using carbon dioxide were adopted in this study. The results show that the carbon in both cases have a mixture of Type I and II isotherm which refers to a dominant microporous structure along with minor larger pores. The morphology reveals tortuous porous structure preserved after activation. The capacitances of 80.9 F/g and 92.7 F/g at current density 100 mA/g have been achieved in optimized carbon from direct and indirect activation, respectively. The surface chemistry study found that the surface functional groups also play a determinant role in capacitance besides the porosity of activated carbons. In the third chapter, activated carbons from two different routes of KOH carbonization of biomass have been successfully fabricated. The yield study showed that the direct KOH carbonization has a higher yield than indirect carbonization. The porosity parameters of both activated carbon such as specific surface area, total pore volume and microporous volume are relatively higher in direct KOH activation sample. The Barium adsorption test showed that both activated carbons can be used to adsorb Ba from actual shale gas flowback water. The activated carbon from direct KOH carbonization has a higher reduction rate which is 11.3% at a relatively low carbon loading (carbon to water mass ratio at 1:38). In the fourth chapter, four lignocellulose biomasses were treated with mediate oxidative torrefaction with air flow at different heating rates. The yield study showed that when applying lower heating rates, the resulted weight of char decreases. The thermal degradation curves revealed that as the heating rates slows down, the peak of the decomposition process of all lignocellulose biomasses have shifted to lower temperatures. The elemental analysis indicated that the lower heating rates could decrease the H/C ratio. The infrared spectroscopy displayed a decreasing holocellulose intensity along with the decreasing heating rates. SEM images of all treated samples showed porosity have been created in most of the biomasses even at mediate level of torrefaction. The oxidative torrefaction could be used as feedstock improvement for biomass conversion to biochar and activated carbon. In the last chapter, four species of lignocellulosic biomass have been converted to activated carbon materials with an intermediate pyrolysis process. Two pyrolysis temperatures were applied in this very process at 450 and 1000 °C to study the differences of resulted biochar and activated carbon materials. Nitrogen adsorption and desorption test, scanning electron microscope as well as Raman spectroscopy have been used to characterize the samples. The results showed that the samples from all species showed a higher specific surface area and a better porosity development at 450 °C than at 1000 °C. The SEM showed that there is sign that intermediate pyrolysis of 1000 °C could lead to the observed collapse of the pore development. The increased ID/IG ratios from Raman spectra of both biochar and activated carbon samples indicated that the higher pyrolysis temperature could result in the increase of amorphous portion in the carbon rich materials and the decrease of graphitization degree. Finally, Chapter 6 summarizes the major findings and results of this dissertation