Catalytic fast pyrolysis of Millettia (Pongamia) pinnata waste using zeolite Y

- De-oiled Pongamia pinnata waste (PPW) was evaluated as a pyrolysis feedstock.
- With no catalyst, oxygenated compounds, especially oleic acid, were the main products.
- Pyrolysis temperature was important at a 1:1 but not a 1:5 PPW: USY catalyst ratio.
- Smaller PPW particle sizes favored oxygenated compounds at lower temperatures.
- Highest hydrocarbon yield (99.0%) was with 125-425 μm PPW, 500 °C and 1:5 PPW: USY ratio.

De-oiled Millettia (Pongamia) pinnata seed waste (PPW) is produced in large amounts after the oil extraction process, but still contains 20% (w/w) oil residues. These raw wastes are of no value and consist of toxic compounds, such as karanjin and di-ketone pongamol, with an overall composition of 45-51% carbon and 5-7% hydrogen and 91% combustible compounds, including fixed carbon and volatile matter. The conversion of PPW to biofuel via pyrolysis is one potential use. Fast pyrolysis of PPW was performed at 400, 500 and 600 °C in a micro-batch pyrolyzer interfaced with gas chromatography-mass spectrometry (Py-GC/MS). However, the pyrolytic products contained a high level of oxygenated- (34.1-66.5%) and nitrogenated-compounds, giving poor fuel properties, such as a high acidity and viscosity. Oxygenated compounds were mainly carboxylic acids, ketones, alcohols and esters.The introduction of the zeolite (USY) catalyst into the pyrolysis of PPW improve the pyrolytic liquid properties. The oxygenated compounds underwent undergoing decarbonylation, decarboxylation and dehydration reactions and further conversion to aliphatic and aromatic hydrocarbons. Pyrolysis at 500 °C of small sized PPW particles (125-425 μm) at a PPW: USY ratio of 1:5 gave the highest hydrocarbon yield (99.0%). The selectivity for monocyclic aromatic hydrocarbons at 500 °C was increased from 4.7-17.4% to 52.5-56.5% when the biomass: catalyst ratio was increased from 1:1 to 1:5. Moreover, the USY catalyst promoted carbon chain scission producing shorter hydrocarbons (C5-12), which was enhanced by the decarboxylation and dealkylation of the alkylated oxygenated compounds.