Developing hierarchically ultra-micro/mesoporous biocarbons for highly selective carbon dioxide adsorption

Wei Herng Tan,Hao Liu,Wenlong Wang,Chenggong Sun,Colin Snape,Xin Liu

doi:10.1016/j.cej.2018.11.062

Wei Herng Tan, Hao Liu + Show 4 more

Open Access

https://doi.org/10.1016/j.cej.2018.11.062

Copy DOI

Abstract

Activated carbons represent one of the important categories of the adsorbent materials for CO2 capture currently under development. However, the low adsorption capacity and selectivity at low CO2 partial pressure and/or relatively high flue gas temperatures is the main barrier for carbons to be applied in post-combustion CO2 capture under practical conditions. Here, we report the successful preparation of hierarchical ultra-micro/mesoporous bio-carbons from using a facile one-step method with a low-grade biomass waste as the feedstock. The bio-carbons exhibit high adsorption capacities (1.90 mmol/g) and record-high Henry’s law CO2/N2 selectivities up to 212 at ambient temperature and low CO2 partial pressure. Unlike conventional chemical activation process for manufacturing carbon materials, the integrated compaction-carbonization-activation method proposed endows the biowaste-derived carbons with unique hierarchical bio-modal pore structures, which are highly characterised by their high mesoporosity and high ultra-microporosity with narrow pore size distributions. The results demonstrated that the unique surface textural properties along with the enhanced surface chemistry due to the simultaneously achieved potassium intercalation created favourable conditions for CO2 adsorption with high CO2/N2 selectivity at low CO2 partial pressures, whilst the presence of mesoporosity greatly increased the CO2 adsorption kinetics. Measurements of CO2 adsorption heat confirmed the strong surface affinity of the prepared bio-carbons to CO2 molecules.

Highlights

IntroductionCutting greenhouse carbon emissions those from large stationary sources has widely been recognised as being one of the essential measures to combat global climate change, whilst carbon capture and storage (CCS) has increasingly become the only technology
Cutting greenhouse carbon emissions those from large stationary sources has widely been recognised as being one of the essential measures to combat global climate change, whilst carbon capture and storage (CCS) has increasingly become the only technologyChemical Engineering Journal 361 (2019) 199–208 option that is able to achieve the climate change target without compromising the energy security due to the continual dominance of fossil energy in any foreseeable futures [1,2,3,4]
Differing from the carbons prepared without compaction, those prepared with compaction all showed H3 type adsorption isotherms, with the mesoporosity dominated by slitshaped mesopores which were believed to be formed by the aggregation of plate-like particles, which occurred clearly as a result of the applied compaction before activation [45]

Summary

Introduction

Cutting greenhouse carbon emissions those from large stationary sources has widely been recognised as being one of the essential measures to combat global climate change, whilst carbon capture and storage (CCS) has increasingly become the only technology. Numerous solid adsorbents have been investigated, including carbon materials, metal organic frameworks (MOFs), zeolites, zeolitic imidazolate frameworks (ZIFs), grafted and impregnated polyamine adsorbents [8,9,10,11] Of these candidate adsorbent materials aforementioned, activated carbon is gaining increasing attention, thanks to their low-cost, fast adsorption kinetics, lower regeneration temperature and especially their novel thermal and chemical stability in hostile flue gas conditions [12,13]. Among many low-density biomass wastes, the hard-to-burn puffy agricultural waste of rice husk, which is produced at a scale of 140 million tonnes per annum [43], could potentially be an excellent candidate precursor for preparing high performance carbon materials for CO2 capture, due to its unique silicon-dominated mineral composition that can contribute to the development of desirable ultra-microporosity for enhanced CO2 adsorption at low CO2 partial pressures [44]. A compaction combined chemical activation protocol was investigated as a means to manufacture high performance CO2 adsorbent materials from puffy rice husk wastes

Synthesis of porous carbon

Characterization

CO2 adsorption performance

Characterization of the rice husk derived carbons

Selectivity and heat of CO2 adsorption

Conclusions