Preparation of activated carbon from autohydrolysed mixed southern hardwood

• Hemicellulose in the raw precursor was substantially reduced by autohydrolysis.
• Autohydrolysis changed the decomposition mechanism of the AC precursors below 400 °C.
• Autohydrolysis of hardwood increased the surface area of activated carbons produced.
• Mesopore rich activated carbons were made with pore volumes between 1.3 and 1.5 cc/g.
• Activated carbons with 90% total pore volume in pores ≤6 nm were produced.

Activated carbons have been prepared from raw mixed southern hardwood (MSH), extracted raw material (EF-MSH) and autohydrolysed extracted raw material (A-EF-MSH) precursors. The temperature of autohydrolysis ranged from 130 to 170 °C. The mixture of phosphoric acid and precursor primarily treated with microwave energy in a microwave oven was activated/carbonised in a rotary reactor at 450 °C under an inert nitrogen atmosphere. The activated carbons were characterised in terms of the surface area (BET) and pore volume. Extraction and autohydrolysis of the raw material resulted in a slight increase in the surface area and pore volume of the final product. The activated carbon prepared from the sample autohydrolysed at 150 °C gave the highest BET surface area and pore volume; 2143 m2/g and 1.474 cc/g, respectively. Autohydrolysis in this temperature range decreased the hemicellulose content of the sample. The mixed southern hardwood and solids obtained from its extraction and autohydrolysis are potential precursors to produce high quality activated carbons. Thermogravimetric analysis (TGA) revealed the raw, extract free and autohydrolysed samples mainly decomposed in the range 225–390 °C. However, TGA weight losses of the autohydrolysed precursors were lower than the raw and extract free samples in this temperature range.