Physical Preparation of Rapeseed For Mechanical Extraction of Oil

Abstract

The study investigated the preparation treatment of rapeseed for the mechanical extraction of oil. Current mechanical oil extraction processes achieve an extraction efficiency of approximately 85% resulting in a residual oil in the press cake following high pressure pressing of 8 to 10%. The aim was to enhance the extraction efficiency of the process to leave approximately 3% residual oil in the press cake (as specified by the sponsor) by improving the preparation of rapeseed. Enhancing the extraction efficiency of the mechanical extraction process to achieve a residual oil content of 3 % will provide a commercially viable alternative to solvent extraction omitting the use of hazardous chemicals from the oil extraction process. A practical programme_ of work was carried out to investigate the potential of introducing extrusion technology as a replacement preparation treatment to flaking and conditioning currently used in the mechanical extraction process. The experiments were in two major stages. Initial trails were carried out using a laboratory scale Brabender single screw extruder and the second set, with a larger scale Almex single screw extruder. The findings from the investigation indicated that, at the optimum operating conditions, the Brabender extruder was effective in breaking virtually every seed with a high level of cell damage apparent from the analysis of the rapeseed microstructures. The residual oil in cake following extrusion and pressing in a hydraulic ram press was 9.37% and the milling defect, a commercially used indicator of seed preparation efficincy, as low as 0.7. The analysis of the results from the larger scale extrusion experiments revealed that the performance of the extrusion process as a preparation treatment reduced with a scaling up in size of operation. The laboratory scaled extrusion trials revealed a greater percentage of cell structure damage, lower milling defect values and a 26% greater process extraction efficiency, at process optimums, than the larger scale trials. With current extrusion technology the introduction of extrusion to a commercial scale processing plant will not improve the oil yield of the process sufficiently to make the mechanical extraction process commercially competitively against a current solvent extraction plant. The process will only become a viable alternative to solvent extraction if future advancements in large scale extruder design can achieve the preparation efficiency attainable with laboratory scale extrusion. A commercial scale plant with an extrusion preparation treatment, achieving a preparation performance equivalent to that of the small scale Brabender, will increase the extraction efficiency of the process. The increase in extraction efficiency, together with the elimination of the steam requirement from the process, achieved from the elimination of conditioning from the preparation process, will increase the profitability of the mechanical extraction process nearing that of a solvent extraction plant. The net profit would increase from £6.33/t for current mechanical extraction to £10.03/t with the introduction of extrusion, this is still less than £11.19/t achievable with solvent extraction.