Hydrothermal liquefaction of soy protein – differences between batch and continuous reactors

Hydrothermal liquefaction (HTL) presents itself as a promising waste management and biofuel production technology. The majority of studies are batch reactors while the technology demands continuous production to be a feasible option. Soy protein was subjected to hydrothermal liquefaction in both batch and continuous reactor at three temperatures (250 °C, 300 °C and 350 °C) for residence times ranging from 5 to 30 min. The renewable crude oil yield, Fourier transform infrared spectroscopy, thermogravimetric analysis and elemental analysis were used to make comparisons between the oils produced. The largest yields obtained were 16.8 wt.% in the continuous reactor (350 °C and 5 min) and 31.3 wt.% in the batch (300 °C and 10 min). Batch HTL produces a renewable crude oil with a larger proportion of low boiling point (80–300 °C) compounds than continuous given the same reaction conditions. FTIR spectra show batch HTL has several larger peak absorbances relating to oxygenated compounds, suggesting a larger proportion of compounds containing carbonyl functional groups. Carbon concentrations in renewable crude oil produced from continuous HTL were larger (>70 wt.%) than batch at the same conditions (60–65 wt.%). Oxygen concentration in the continuous (6–10 wt.%) is significantly lower than that of the batch (17–22 wt.%), which agrees with FTIR data.