Characterization of high acid value waste cottonseed oil by temperature programmed pyrolysis in a batch reactor

• Temperature programmed pyrolysis combined with gravimetric analysis is shown to be a useful approach to characterizing the oils’ properties and to producing pyrolytic oil in a batch type reactor.
• Using the isoconversional method, the activation energies, determined for the WCO pyrolysis process, were higher than those for virgin cottonseed oil.
• Quantification and analyses of the pyrolytic products including: gases, liquids and solids, is used to provide useful information that helps us to optimize the heating program.
• The low molecular weight pyrolytic oils obtained using heating rates <3 °C min−1, are able to meet biodiesel requirements after esterification with methanol.
• The use of slower heating rates produces greater amounts of lower boiling point compounds in the resulting pyrolytic oil.

Temperature programmed pyrolysis of high acid value waste cottonseed oil (WCO) was carried out in a batch type reactor. A thermogravimetric analysis (TGA) method, which did not require a carrier gas, was used to study the properties of oil products. Weight loss data were obtained at heating rates (from 5 to 15 °C min−1) and used to estimate the pyrolysis activation energy. A systematic study of the molecular weight distribution was made for the pyrolysis of WCO and virgin cottonseed oil at different heating rates. The yields of the products including: gases, liquids (collected pyrolytic oil), and solids (residual char) were quantified in this work. The production of pyrolysis gas was estimated during heating. The weight loss results indicated that the optimum pyrolysis rate occurred between 400 and 450 °C at a heating rate of 10 °C min−1 from room temperature to 600 °C. Our work indicated that high acid value WCO yields comparatively greater volumes of gases and masses of residual products when compared to virgin cottonseed oil. After the temperature programmed pyrolysis of WCO (acid value 8.66 mg KOH g−1), at a heating rate of 10 °C min−1, the average boiling point of the pyrolytic oil was ∼349 °C, which is significantly lower than that of the unprocessed WCO (456 °C). The pyrolytic oil produced in this process after esterification with methanol, was found to comply with biofuel specification requirements.