Recovery of valuable biopolymers from thermo-mechanical process waste streams

Abstract

Thermomechanical process waste streams contain significant amount of valuable bio polymers such as lignin and hemicelluloses. These biopolymers have beneficial applications in everyday life, thus, their recovery from thermo-mechanical process effluent is vital. In this thesis, ultrafiltration was experimented on two thermo-mechanical process effluents from a wood processing mill for a cost-effective separation of lignin and hemicelluloses. RC70PP, a regenerated cellulose membrane with cut-off value of 10 kDa was used during the membrane filtrations. Dead end membrane filtration and cross flow membrane filtration were both conducted at the temperature of 50 °C and 2 bar pressure until the volume reduction factor (VRF) of 58 –82 % was achieved. Process water with total solid content of 4.1 % was easily concentrated with both dead end and cross-flow filtration. Whereas for concentrated process water with total solid content of 49.2 %, dead end filtration was not possible to be conducted due to zero flux from the beginning of the filtration, cross flow filtration was possible with a volume reduction factor of 40 % in 5 hours of filtration.

Although the ultrafiltration worked well in concentrating the effluent, separation of lignin and hemicellulose was unsuccessful because both lignin and hemicellulose had similar retentions. Similar molecular weight and covalent bonding between these two components might have resulted in unsuccessful separation. Precipitation experiments with ethanol were also conducted to isolate lignin and hemicellulose from the effluents. The supernatants/dissolved solutions after centrifugation were analysed with ultraviolet visible spectroscopy (UV-VIS) analysis whereas, the precipitates were analysed with Fourier-transform infrared spectroscopy (FTIR) analysis. The UV result showed the decrease in the concentration of the lignin in which samples after what? whereas the FTIR peaks had traces of lignin and hemicellulose.