Thermal degradation of crab shell biomass, a nitrogen-containing carbon precursor

Waste and low-cost lignocellulosic biomasses are well studied and widely used as raw materials for porous carbon adsorbents. Much less attention is given to the exploration of the potential of marine biomasses, though these materials contain also nitrogen, which—if preserved during the processing—has a beneficial influence on the sorption properties of the porous carbon obtained. Here, we report a multi-technique investigation into the conversion of crab shell to porous carbon adsorbent. Thermogravimetry and pyrolysis-GC/MS studies were used to reveal the thermal degradation of this natural polymer and follow the decomposition process through the identification of the products. Almost 40 various volatile degradation products were distinguished released at 500 °C pyrolysis temperature. Based on the TGA/DTG results, two temperatures, 350 and 500 °C, were selected to obtain pyrolytic samples in macroscopic quantities in order to characterize the morphology and surface chemistry of the solid fraction. More than 50% of the nitrogen atoms were still in the carbonaceous matrix after the 500 °C pyrolysis in the C–N=C, C–NH and 3C–N-type bonds. The ash content < 1% included hydroxylapatite-type crystalline matter. Based on these results, we may conclude that crab shells have a high potential as precursor of nitrogen-containing biochar.