(356d) CO2 Assisted Mechanical Expression of Fat from Rendered Materials on the Laboratory and Pilot Plant Scale

This work employs liquid and supercritical carbon dioxide for the enhanced expression of fat from rendered materials, specifically a finished poultry meal. Current industrial rendering processes use continuous screw presses or expellers to remove fats from rendered materials; however, this process can leave 10 to 15% residual fat. The higher economic value for the fat and emerging markets for low fat rendered protein meals makes enhanced fat recovery desirable.  Results from this work demonstrate the use of CO₂ assisted mechanical expression where the rendered material is pressed in the presence of pressurized CO₂.  The fat content of the poultry meal was reduced from an initial 12.1% down to 2.3% after pressing. The optimal conditions for a maximum expression were on the order of 40°C, 210 bar of CO₂, and 500 bar of effective mechanical pressure. An optimum effective mechanical pressure was observed at around 500 bar, which can be attributed to a reduced permeability of the CO₂-fat mixture through the protein matrix at high mechanical pressures, as described by Darcy’s law. At CO₂ pressures greater than 172 bar, expression enhancement is negligible, likely due to a plateau reached for the viscosity of the oil-CO₂ mixture beyond such pressure. The primary mechanisms governing the enhanced expression were the reduced viscosity of the fat with CO₂ dissolution; which increases the drainage of fat through the cake, and the confinement rupture due to swelling upon CO₂ dissolution. Overall, it was demonstrated that high expression yields can be achieved when conducting a gas-assisted mechanical expression of rendered materials, utilizing only a fraction of the amount of CO₂ used for CO₂-only extractions. Furthermore, the optimum operating conditions are suitable for application in screw presses or expellers currently used on industrial scales which were explored on a 1 ton per hour scale with the HIPLEX system at the Crown Iron Works Pilot Plant Facility in Roseville MN.