ABSTRACT
Torrefaction treatment improves biomass grindability by transforming the fibrous herbaceous to a more brittle and lighter coal-like material. Microwave-assisted torrefaction is a promising technology for biomass conversion into energy, fuels, and chemicals. The study applied microwave absorbers in the torrefaction process to improve the thermochemical characteristics and grindability of switchgrass. Switchgrass in two particle sizes was torrefied in a microwave reactor with biochar added as a microwave absorber under inert conditions. After torrefaction, the geometric mean particle and size distribution and selected physical characteristics were evaluated, and the grindability of the torrefied ground and chopped with and without biochar were compared with those of untreated switchgrass. The geometric diameter results decreased, and the specific energy required for grinding torrefied switchgrass with biochar was significantly reduced with extended residence times and at a torrefaction temperature of 300 °C. After grinding, the lowest grinding energy of 32.82 kJ at 300 °C/20 min was recorded with torrefied ground switchgrass/biochar. The 10% biochar added/250 °C resulted in deep cell wall disarrangement, whereas at a torrefaction temperature of 300 °C, large surface deformation and carbonized weight fractions were observed.
ABSTRACT
The effects of microwave-assisted alkali pre-treatment on pellets' characteristics and enzymatic saccharification for bioethanol production using lignocellulosic biomass of canola straw and oat hull were investigated. The ground canola straw and oat hull were immersed in distilled water, sodium hydroxide and potassium hydroxide solutions at two concentrations (0.75% and 1.5% w/v) and exposed to microwave radiation at power level 713 W and three residence times (6, 12 and 18 min). Bulk and particle densities of ground biomass samples were determined. Alkaline-microwave pre-treated and untreated samples were subjected to single pelleting test in an Instron universal machine, pre-set to a load of 4000 N. The measured parameters, pellet density, tensile strength and dimensional stability were evaluated and the results showed that the microwave-assisted alkali pre-treated pellets had a significantly higher density and tensile strength compared to samples that were untreated or pre-treated by microwave alone. The chemical composition analysis showed that microwave-assisted alkali pre-treatment was able to disrupt and break down the lignocellulosic structure of the samples, creating an area of cellulose accessible to cellulase reactivity. The best enzymatic saccharification results gave a high glucose yield of 110.05 mg/g dry sample for canola straw ground in a 1.6 mm screen hammer mill and pre-treated with 1.5% NaOH for 18 min, and a 99.10 mg/g dry sample for oat hull ground in a 1.6 mm screen hammer mill and pre-treated with 0.75% NaOH for 18 min microwave-assisted alkali pre-treatments. The effects of pre-treatment results were supported by SEM analysis. Overall, it was found that microwave-assisted alkali pre-treatment of canola straw and oat hull at a short residence time enhanced glucose yield.