Methane adsorption on KOH microwave treated porous carbon from sustainable coconut solid waste material

Abstract

The shorter driving range is the challenge of compressed natural gas (CNG) as a vehicular fuel. In this study, adsorbent is prepared from coconut shells using KOH microwave activation to overcome the challenge of CNG storage system. The CNG storage system has some disadvantages which include high-pressure operation with less safety guard, and heavy storage cylinders. The adsorbent is used as a potential Sorbent for methane (CH4) storage at different pressures. The coconut shell was carbonized from ambient temperature to 700 ± 20 °C at 10°C min-1 heating rate with 1 L min-1 N2 flow rate. The carbonization temperature of the precursor was determined using thermo-gravimetric and derivative thermogravimetric (TG/DTG) analysis. The activation was achieved with well modified microwave equipment operated at 500W and 5 minutes. The CH4 adsorption characteristics were conducted using volumetric adsorption equipment at an ambient temperature and pressures of 4, 5 and 7 bar. The CH4 uptake achieved at 4, 5 and 7 bar are 2.9707, 3.0559 and 3.6685 mmol g-1. The experimental data simulated using two common adsorption models: Langmuir and Freundlich. The experimental data was also evaluated using the common adsorption kinetic namely pseudo-first order, pseudosecond, order kinetics and Elovich. For the three initial pressures of 4, 5 and 7 bar, CH4 adsorption show more fits to pseudo-second order with R2> 0.967, R2 > 0.967 and R2> 0.960. The results reveal that coconut shell is a viable and sustainable material for synthesizing of the adsorbents for methane adsorption.