Microporous carbon from cashew nutshell pyrolytic biochar and its potential application as CO 2 adsorbent
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ORIGINAL ARTICLE
Microporous carbon from cashew nutshell pyrolytic biochar and its potential application as CO2 adsorbent Sonal Garg 1 & Piyali Das 2 Received: 10 April 2019 / Revised: 19 August 2019 / Accepted: 21 August 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract Cashew nutshell (CNS)–based biochar is obtained as a by-product in a pilot scale (20 kg/h) gas-fired auger pyrolysis reactor at 500 °C during bio oil production. This pyrolytic biochar has low BET surface area (BET SA 0.80 m2/g) and poor porosity as the fast pyrolysis conditions are set to augment the bio oil yield over other products. To value add to this carbon, downstream activation is performed in an externally heated lab scale reactor. Formation of activated carbon with BET SA between 300 and 700 m2/g with moderate improvement in porosity ensued from CO2 and steam activation, while chemical activation with K2CO3 enhanced the BET SA to 1225 m2/g and Langmuir surface area to 1707 m2/g in addition to significant enhancement of porosity. CNS-based activated carbons predominantly possess narrow pore size distribution with small-sized micropores and ultra-micropores limiting the presence of mesopores. The effect of equilibrium time (10 s and 45 s) on N2 adsorption is extensively studied, and it is found to have a significant role in detection of ultra-micropores below 0.8 nm (at very low pressures). The CO2 absorptivity of K2CO3activated CNS carbon is found to be between 4.16 and 6.22 mmol/g (i.e. 183.04–273.6 mg/g) at atmospheric pressure and 0 °C. These activated CNS carbons possess ultra-micropores between 0.46 and 0.8 nm suitable for CO2 uptake. This study shows the sustainable path of making CO2 adsorbent from a low-cost renewable biomass precursor like CNS. Keywords Cashew nutshell . Pyrolytic biochar . Activated carbon . K2CO3 activation . CO2 adsorption . DR plot
1 Introduction Globally, India ranks 1 in terms of production, processing and export of cashews, Anacardium occidentale Linn, which was originally brought during 1400 by Portuguese missionaries. Later, its commercial cultivation in India started in 1960s. Cashew tree that was originally native to Central and South America is now widely spread throughout the tropics, particularly in Africa and Asia [1]. In India, 1.03 million hectares which cover almost the entire coastal region is under cashew cultivation, producing over 0.67 million metric tons of raw cashew nuts annually [2]. The cashew processing industries generates large quantities of shell, which is about 50–65% of raw nuts. * Piyali Das [email protected] Sonal Garg [email protected] 1
Department of Energy and Environment, TERI School of Advanced Studies, 10 Institutional Area, Vasant Kunj, New Delhi 110070, India
2
The Energy and Resource Institute (TERI), Lodhi Road, IHC, New Delhi 110003, India
The cashew nutshell (CNS) is about 0.125 in. thickness, with a soft honeycomb structure inside, containing a dark reddish brown viscous liquid known as cashew nutshell liquid (CNSL) which find
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