Biomass-derived Activated Carbon for Energy Storage Applications

Abstract

Activated carbon is a porous carbon material with a broad range of applications as adsorbents in liquid and gas treatment, as well as in catalytic applications. The need for activated carbons is continuing to expand, because environmental pollution is an increasingly serious issue. Activated carbons’ (ACs) specific properties are determined by the properties of the starting materials and the activation methods utilised. Practically, the principal sources of commercial ACs are coal, wood and coconut shells. Given their low cost, sustainability and ready availability, various agricultural and forest by-products have recently gained considerable attention as alternative feedstock for the production of ACs. Accordingly, a major goal of this thesis is to explore and discover the synthesis conditions for generating highly porous materials from starting materials with little to no value, for example waste biomass. We employed (sawdust, SD), date seed (Phoenix dactylifera) and CNL carbon (from accidental and uncontrolled burning of wood under fierce fire conditions of the first Carbon Neutral Laboratory, CNL, building at Nottingham) as feedstock, in order to prepare the activated carbon. The principal objectives are to identify and investigate synthesis conditions for producing highly porous activated carbon for sustainable energy applications. The first chapter presents an overview of the climate change issue, positing some strategies towards reducing the harmful effects of atmospheric pollution. Furthermore, it describes the several types of porous materials used for gas adsorption, for instance MOFs, zeolites and porous carbon. Description of porous materials is a main focus of this chapter, which also covers pore classifications according to size, shape and type of the pores, as well as methods used to prepare activated carbons, and the use of the carbons in gas storage. In the second chapter, the techniques adopted to analyse porous carbons are briefly discussed, with Brunauer, Emmett and Teller (BET) theory and CO2 adsorption using gravimetric analysis methods using a XEMIS instrument being notable. The chapter also described the techniques that may be used to probe the nature of porous materials and includes description of Thermal Gravimetric Analysis (TGA), powder X-Ray Diffraction (XRD), Scanning Electron Microscopy Analysis (SEM), Transmission Electron Microscopy (TEM) and Elemental Analysis. In the third chapter, date seed (Phoenix dactylifera) is used as an example of how biomass with a low O/C ratio can be used to prepare activated carbons in a targeted manner. The chapter describes how the choice of carbonisation mode may be adopted to produce activated carbons with optimised porosity for methane storage. The elemental composition of the biomass precursor, specifically, a low O/C atomic ratio, can be used as a universal predictor of the nature of porosity generated for activated carbon prepared via KOH activation. The carbons can be tailored to have a mix of microporosity/mesoporosity, with high surface area density, high volumetric surface area, in addition to a high packing density. The activated carbons produced are highly microporous with surface area of 995 – 2609 m2 g-1, pore volume of 0.43 – 1.10 cm3 g-1 and high packing density. The resulting carbons had pores of size 8 – 12 Å, which are suitable for methane uptake. At 25 ̊C and 35 bar, the carbons have an excess and total methane uptake of up to 196 cm3 (STP) cm-3 and 222 cm3 (STP) cm-3, respectively, which is superior to any previously reported carbon and comparable to the best MOFs. In the fourth chapter, potassium oxalate (PO) and KOH were employed as activating agents to prepare activated carbons from date seed derived carbonaceous matter designated as ACDS (air-carbonised date seed). Previously, the action of the two activating agents has been compared b