Evaluating the products of low power, sealed vessel microwave pyrolysis of microalgae

The products of low power, sealed vessel microwave pyrolysis of a proprietary microalga, ALG01, similar to Eustigmatophyceae, were evaluated at fixed power (50 W, 100 W and 150 W). The afforded biochars were characterised by CHNS, ATR-IR, SS 13C NMR, TGA and SEM, whilst the bio-oils were characterised by CHNS, 1H and 13C NMR, GC-MS/FID and ATR-IR. The bio-oils were all rich in fatty acids, although with increased microwave power, these long chain fatty acids experienced cracking. The higher heating values (HHVs) of the bio-oils was calculated, with the 50 W bio-oil attaining the highest HHV (35.04 ± 2.40 MJ/kg). Preliminary copper(II) adsorption studies were performed on the biochars, with activated carbon (AC) used as a control. The biochar produced at 150 W adsorbed the highest amount of copper(II) when dosed at both 1 mg/mL and 10 mg/mL of biochar (110.00 ± 4.83 and 31.26 ± 2.63 mg/g, respectively). Thus, the use of low power as opposed to high power and/or high temperature conventional pyrolysis yields interesting products that can be used as potential platform chemicals, adsorbents for critical element recovery and as a potential solid biofuel. However, the latter application is limited because the HHV is similar to that of low-grade coal and has a relatively high ash content.