Alkaline catalytic liquefaction of pig manure fermentation residue in ethanol solvent for the production of high-quality biocrude oil

Abstract

The widespread application of biogas projects generates substantial amounts of waste fermentation residue. Further treatment of fermentation residues facilitates resource utilization, ensures safe disposal, and is anticipated to enhance the economic returns of biogas projects. Herein, catalytic liquefaction of pig manure fermentation residue to produce biocrude oil was investigated using various alkaline catalysts at 340 ℃ with ethanol as the solvent. Biocrude oils were analyzed by elemental analysis, gas chromatography-mass spectrometry (GC–MS), thermogravimetric analysis, and kinetic analysis. The maximum biocrude oil yield (45.24 wt%) was obtained with the KOH catalyst. Additionally, the biocrude oil produced by the catalysis of CaO exhibited the maximum higher heating value at 44.18 MJ/kg. GC–MS results showed that KOH and K₂CO₃ considerably increased the content of phenols and hydrocarbons in the biocrude while reducing nitrogenous compounds. All alkaline catalysts effectively reduced the activation energy of biocrude oil compared to biocrude oil without catalyst. The maximum reduction in activation energy (18.73 %) was achieved with the addition of Na₂CO₃. More importantly, adding CaO not only increased the yield and higher heating value of biocrude oil but also reduced nitrogenous compounds and activation energy, improving the overall yield and quality. Overall, this work provides an effective and promising method to convert pig manure fermentation residue into green high-quality biocrude oil, simultaneously providing an economical and environmentally friendly waste management strategy for the fermentation industry.