Microwave-synthesised hydrothermal co-pyrolysis of oil palm empty fruit bunch with plastic wastes from Nigeria

Microwave-assisted hydrothermal co-pyrolysis of biomass (oil palm empty fruit bunch) and plastic waste from sachet-water (widely available in Nigeria) was studied to improve the yield and quality of bio-oil. The experiment was carried out in a customised microwave system under a maximum microwave power of 300 W, using a coconut shell-based susceptor. Further, the hydrothermal process was optimised using Box–Behnken design. The optimum conditions at which the highest bio-oil yield (66.7 wt%) was obtained were determined to be a temperature of about 380 °C, a sachet-water plastic ratio of 49 wt%, and a carrier gas flow rate of 1500 mL/min. Major chemical compounds found (by gas chromatography–mass spectrometry) in the aqueous phase of the bio-oil were alkane (decane), 3.7% and phenol, 84.9% with methoxyphenyl, 2.5% and ethanone, 8.9%. Aliphatic hydrocarbons (22.7%), monoaromatic (15.3%) and polycyclic (9.16%) aromatic hydrocarbons, linear oxygenates (2.1%), furan derivatives (2.3%), phenol derivatives (15.84%) and other compounds such as derivatives of cyclopentanones and pyran were found in the organic phase of the bio-oil which constituted 39.7% of the bio-oil fraction. Aqueous pre-treatment of the sample with deionised water under microwaves enhanced selectivity and produced bio-oil with optimum phenolic compounds (84.9%) in the aqueous bio-oil.