Thermochemical conversion of animal by-products and rendering products

This paper presents a preliminary study of the characterization of real waste from slaughterhouses as well as their rendering products (protein and fat) through different pyrolytic techniques: thermogravimetric analysis (TG), analytical pyrolysis in a pyroprobe equipment and hydrothermal liquefaction process (HTL). The experiments have allowed a deeper knowledge about the thermal behavior of these wastes under different conditions: slow pyrolysis up to 800 °C (TG), flash pyrolysis at 500 °C and room pressure (pyroprobe) and slow pyrolysis at 290 °C and 110-130 bar (HTL batch reactor). Experiments with each one of the materials (real waste, PAP and fat) as well as some mixtures have been performed. Gas chromatography and mass spectrometry techniques were used to identify the pyrolytic products obtained. The results indicate that fatty acids and fatty esters are the major group obtained in the pyrolysis of fat samples, followed by aliphatic hydrocarbons. In the case of PAP pyrolysis, heterocyclic aromatic compounds, which includes typical products coming from protein degradation, is the major group obtained. Oxygenated aliphatics are also obtained in high amounts. In the case of the HTL experiments, significant glycerine amounts were detected in the aqueous phase. The yield of biocrude obtained under HTL conditions is about 30%, with a high proportion of nitrogenated compounds (amides, pyrrole and pyridine derivatives). Generation of amides is much higher under HTL conditions than in the analytical pyrolysis runs while the proportion of acids is reduced.