Pyrolysis and CO2 gasification of barley straw: Effect of particle size distribution and chemical composition

We evaluate how the heterogeneity of the precursor may affect pyrolysis and CO2 gasification behavior aimed at activated carbon applications. Barley straw, ground and classified into five size ranges, is characterized by non-isothermal thermogravimetry tests at various heating rates. Fixed carbon and volatile matter contents decrease with particle size. Also, the finest fraction is enriched in minerals by exogenous contamination and accumulation of silicon-rich leaves. Faster pyrolysis kinetics are found for small sizes, caused by their higher alkali contents and heat-mass transfer rates. Char-CO2 gasification conversion rates show an unexpected behavior, not previously reported. Higher reactivity is found for the finest fraction, decreasing significantly at temperatures beyond 750 degrees C. The high alkali content of the finest fraction promotes the catalytic effect of minerals on gasification reactivity at lower temperatures, hindering the reaction at higher temperatures by forming low-melting-point potassium silicates. Results help improve pretreatment strategies to enhance activated carbon quality.