Preparation of high surface area porous carbons using methane as the carbonaceous feedstock

Abstract

Research has recently focused on the adaptation of environmentally benign routes for porous materials synthesis. Porous carbon materials have found applications on gas storage, water purification, catalyst supports, and electrodes for electrochemical double-layer capacitors nd fuel cells. Various methods using various carbon precursors have been used to synthesise porous carbon materials. Aim of this study is to develop solid carbons i.e., Templated carbons, MOF derived carbons and carbon nanotubes, using methane (CH4) from biogas as a carbon precursor. Biogas, a product of anaerobic digestion, is an attractive renewable energy source due to its continuous production and use cycle. Recently there has been great interests on value addition of biogas, concerning the utilisation of the main component methane (CH4). In this work we focused on utilisation of simulated biogas (CH4 and CO2 mixture) and pure CH4 for preparation of zeolite templated carbons (ZTC). ZTCs are known to have attractive properties such as high surface area, uniform pores and large pore volumes, and have found applications n gas storage and gas separation. When methane was utilised on both one-step and two-step process, the obtained ZTCs had higher surface area and hydrogen (H2) adsorption as compared to the simulated biogas feedstock. The high surface area obtained was 2974 m²/g while the best H2 storage capacity at 1 bar was 2.77 %wt. Structural (XRD) and morphological SEM and TEM) characterisation were found to be almost similar to the samples obtained when ethylene was used as a carbon source. The study has proven that sustainable source of eedstock in ZTCs production can be utilised to create value added products. Metal organic frameworks (MOF) have great properties as porous materials; however, most types are known to have very low thermal stability which can be shortcoming for various pplications. Carbonisation strategy can be employed to enhance thermal stability of this porous materials. Two MOFs types (MIL-88B & MIL-101) derived from acid mine drainage waters (AMD) were carbonised to generate carbons which were then tested for hydrogen adsorption and further used to grow carbon nanotubes (CNTs). For the growth of CNTs, CH4 was used as carbon precursor. The obtained results shown that the MOF structures were completely carbonised and multiwalled carbon nanotubes (MWCNTs) were prepared. Surface rea of MOF-derived carbons (MDC-88B and -101) was found to be 267 and 272 m²/g with hydrogen adsorption of 0.58 wt% and 0.54 wt% respectively. The MWCNTs had a reasonable degree of graphitisation (IG/ID = 1). This study confirms that AMD derived MOFs can be used s catalyst for synthesis of CNTs and their derived carbons can be used for H2 adsorption.