Slow pyrolysis of flax straw biomass produced in Kazakhstan: Characterization of enhanced tar and high-quality biochar

In the present study, local flax straw waste biomass samples were studied for their physical and chemical characteristics using a thermogravimetric analyzer (TGA) and thermal properties. Thermochemical conversion of the flax straw samples was performed in an electrically heated horizontal tube furnace from 400 to 600℃. Thermal analysis of the flax straw biomass showed higher calorific value of 18.2 MJ/kg, cellulose (27.4 wt%) and hemicellulose (24.8 wt%) content and lower lignin content (21.2 wt%). Mass balance of pyrolysis products showed 40.3% for bio-oil fraction at temperature of 500 ℃, which resulted in a notable reduction in the biochar yield by 34.6% compared to biochar yield at temperature of 400 ℃. Pyrolysis of flax straw samples further shows a notable reduction in moisture, ash and fixed carbon by 4.4%, 2.9% and 11.4%, respectively. In addition, it was noted that the tar obtained from flax straw is mostly composed of phenolic components, while XRD analysis confirms the degradation of cellulose in biochar fraction. Due to the higher de-volatilization behavior, calorific value, cellulose and hemicellulose content, also lower lignin and ash content, flax straw biomass can be used as a promising feedstock for bioenergy production.