Benefits of microwave heating method in production of activated carbon

Abstract

This work investigates the chemical activation of a biochar sample using microwaves with KOH and NaOH. The activation of char samples was carried out in a microwave oven operating at 2.45 GHz with a power input of 1200 W. The specific surface area (SSA), yield (%), and pore size distribution were studied for microwave activation with KOH and NaOH. In microwave‐assisted activation, the activation yields for NaOH and KOH activation were in the ranges of 40–70 % and 60–80 %, respectively. The NaOH‐activation takes 1.5 h in a furnace to fabricate an activated carbon with a SSA of 2600 m2 · g−1. However, in microwave activation, a 5 min activation with a power of 1200 W results in activated carbon with a SSA of 1900 m2 g−1. The activation yield and SSA are mainly controlled by impregnation ratio in microwave‐assisted activation because KOH and NaOH were the sources of heat for the activation reaction. In this work, the microwave activation increased the reaction rate by 15 times compared to the furnace activation. Microwaves have a “non‐thermal effect” on the kinetic parameters of chemical activation reactions. This effect was more evident in the case of NaOH microwave activation, probably because it is a more reactive compound compared to KOH.

Optimizing Microwave-Assisted Pyrolysis of Phosphoric Acid-Activated Biomass: Impact of Concentration on Heating Rate and Carbonization Time

“…8,10 Recent studies employing microwave energy as the mode of heating in carbonization step of AC production from biomass proved that heating time is significantly reduced compared to that in conventional furnaces. Namazi et al (2016) produced chemically activated carbon out of biochar from pulp mill sludge with similar surface area in 2 h under 600 °C conventional heating and in 5 min under 1200 W microwave. 12 A similar study produced comparable textural properties of activated carbon from sewage sludge heated in a 500 °C furnace in 15 min and in a 980 W microwave in 12 min.…”

“…Namazi et al (2016) produced chemically activated carbon out of biochar from pulp mill sludge with similar surface area in 2 h under 600 °C conventional heating and in 5 min under 1200 W microwave. 12 A similar study produced comparable textural properties of activated carbon from sewage sludge heated in a 500 °C furnace in 15 min and in a 980 W microwave in 12 min. 13 Activated carbon derived from raw bamboo chemically activated by H 3 PO 4 was observed to have a faster activation rate and higher yield under microwave heating.…”

Advances in Microwave Synthesis of Nanoporous Materials

“…[ 64 ] Therefore, employing alternative energy sources such as microwave irradiation can reduce the energy usage and other negative environmental impacts of synthesis processes, which is of high importance. In literature, there are many papers devoted to pyrolysis, [ 65–74 ] activation, [ 75–98 ] and even regeneration of spent carbons [ 99–106 ] under microwave radiation. Recently, excellent reviews were reported to summarize the main accomplishments in the microwave‐assisted synthesis of biomass‐derived porous carbons.…”

“…Porous carbons obtained via microwave‐assisted methods with their SSA values and potential applications are summarized in Table 4 . [ 65–122 ]…”

Rapid Preparation of Activated Carbon Fiber Felt under Microwaves: Pore Structures, Adsorption of Tetracycline in Water, and Mechanism

“…However, because of the selective heating of the microwave, many precursors cannot be carbonized by microwave heating. Similarly, in the study of Namazi et al 6 and Duan et al, 7 sludge and cotton were adopted to make activated carbon, and the samples were activated with the assistance of microwaves. At present, the so-called "microwave-assisted" actually refers to the use of microwaves during the activation part.…”