Preparation of activated carbon from biomass and its application in gas adsorption

Preparation of activated carbon from biomass and its application in gas adsorption

Biomass is an abundantly available and sustainable resource, which is widely utilized as precursor for producing activated carbons.

In this thesis, hemp hurd and retted hemp hurd, the by-products of hemp fibre industry, were used as precursors for the preparation of activated carbon by chemical activation with ZnCl2 and physical activation with CO2. Then, activated carbons were prepared from bamboo fibre and hemp fibre in the similar conditions for comparison. The influence of the carbonization temperature and the impregnation ratio was studied on morphology, porosity, chemical property, and activation mechanism of the activated carbons. The gas capture performance of the synthesized activated carbons was evaluated in CO2 adsorption.

Key findings include an understanding of the structure, morphology, and characteristics of hemp hurd and retted hemp hurd, and the influence of retting process on the obtained activated carbons. In addition, a systematic comparison of the effect of ZnCl2 chemical activation and CO2 physical activation on the properties of activated carbons, and a comprehensive review of the activated carbons derived from hemp hurd, retted hemp hurd, bamboo fibre, and hemp fibre was realised. The effect of carbonization temperature and the impregnation ratio, and the influence of precursor on activated carbon properties was also analysed.

Experimental results showed that hemp hurd possesses a unique structure, which consists of two types of macropore channels of different sizes. Activated carbons from hemp hurd after HCl washing retains the original appearance of the hemp hurd with increased porosity of the inner walls. ZnCl2 activation was deemed advantageous for synthesis of high surface area of porous carbon from biomass, and the derived activated carbons using this method exhibited larger surface areas compared with those using the CO2 activation. The pore development was strongly dependent on the impregnation ratio of activation reagent and the subsequent carbonization temperature. HCl washing further increased the porosity of activated carbon. Activated carbons from retted hemp hurd and bamboo fibre were highly microporous materials. Activated carbons from hemp fibre possessed mixtures of micropores and mesopores. The optimized Brunauer-Emmett-Teller (BET) specific surface area of the activated carbon from retted hemp hurd reached 1781 m2/g and total pore volume reached 1.023 cm3/g. Activated carbon from retted hemp hurd by ZnCl2 activation showed the highest CO2 adsorption capacity of 142 cm3/g STP at 273 K.

This thesis contributes to the field of biomass-based activated carbon production and application in gas adsorption. This investigation reinforces the understanding of activation mechanisms as well, and the potential of obtained activated carbons and the future work are discussed.