Microwave assisted and conventional pyrolysis of MDF – Characterization of the produced biochars

Two different heat treatments for MDF, microwave assisted pyrolysis (MWP) and conventional pyrolysis (CPS), are investigated. The influence of different microwave absorbers (activated carbon (AC) and K2CO3) and different microwave powers in MWP and different temperatures in CPS on the characteristics of biochar is reviewed. Morphology and chemical properties of the obtained biochars are evaluated comparing biochar yield, ultimate analysis, proximate analysis, biochar stability test, FTIR spectroscopy and solid-state 13C CP/MAS NMR spectroscopy. The resulting biochars of both processes are compared to find the best production method. An increasing microwave power without the use of MWA, leads to a higher degree of aromaticity. The addition of increasing amounts of AC at low microwave power (300 W) leads to higher pyrolysis temperatures and more aromatic biochars. At 400 W a more aromatic biochar with a more open surface is achieved compared to 300 W. However, the addition of an increasing amount of AC as a MWA at 400 W induces a lower pyrolysis temperature with increasing biochar yields and decreasing aromaticity. K2CO3 is more effective as a MWA and produces more aromatic biochar at lower microwave power than when using AC. In general MWP yields a biochar with a higher degree of aromaticity at lower temperatures than CPS. Both CPS and MWP are viable options for transforming MDF into a value added biochar.