MODELING AND RESPONSE SURFACE ANALYSIS OF SUPERCRITICAL FLUID EXTRACTION OF VEGETABLE OILS

Abstract

Increasing demand of edible oil in India, leads the search towards untapped natural seed materials having potential to produce large quantities of oils after Soyabean, Groundnut, Mustered and Sunflower. The search indicates that Watermelon and Moringa Oleifera seeds have a large quantity of oil which can be used as edible oil. These will increase production and productivity of edible oil in India and will utilize this untapped resource. Commercially, oils are extracted by means of organic solvents mainly hexane. Removal of organic solvent from vegetable oil has mostly been made by distillation - a cost intensive process. Further, in this process it is also difficult to remove solvent completely from the end product. However, due to increased public awareness for health, environmental and safety hazards associated with the use of organic solvents in extraction, supercritical CO2 based extraction has provided the necessary impetus to substitute petroleum based solvent such as hexane, ethers and chloroform, etc..The extraction by supercritical CO2 is beneficial in terms of energy consumption because of the separation is possible only by decompression and the resulting CO2 can be recompressed and reused and thus does not add to increase in greenhouse gases. In the present experimental investigation, the vegetable oils are extracted from Moringa Oleifera, Watermelon and Sunflower oil by the means of supercritical CO2. To perform the experiments, an experimental setup (SFE 1000F) is procured from Thar Technologies Inc., Pittsburgh. To carry out experiments in a methodical way that will help to develop input-output correlation using statistical analysis, design of experiment (DOE) technique is applied to the design and analysis. Analysis of variance (ANOVA) is performed to establish the relative significance of the individual input parameters and their interaction effects. For supercritical fluid extraction of vegetable oils, five input parameters of significance are screened out from eleven input parametersfrom published in literature, and the effect of these input parameters on the cumulative extraction yield (g oil/ gkernel) are identified. An attempt is also made to establish relationships between the input parameters and cumulative extraction yield (g oil/g kernel). Response surface methodology (RSM) of DOE is applied for the optimization of cumulative yield (g oil/g kernel) for Moringa Oleifera, Watermelon and Sunflower oil extraction. After extraction of oils from Moringa Oleifera, Watermelon and Sunflower, the physico-chemical properties, namely,acid value, iodine value, saponification value, un-saponifiable matter, flash and fire points, refractive index and specific gravityof oil samples are determined. ii The composition of oil samples are obtained by gas chromatography (GC). The characteristics of seed kernel are analyses by scanning electron microscopy (SEM), Thermal analysis (TGA/DTA/DSC) and FTIR spectroscopy. Regression analysis of the experimental data for Moringa Oleifera, Watermelon and Sunflower seed oil extraction confirmed that reduced quadratic model is best for the prediction of cumulative extraction yield (g oil/ g kernel) and offers 96.3%, 90.13%and 85.47(predicted R-Square) of the variability in predicting new observations in comparison to approximately 99.72%, 99.6% and 99.98% (R-Square) variability in the original data for Moringa Oleifera, Watermelon and Sunflower oil extraction respectively. Further, from statistical analysis, it is evident that interaction between all the five input parameters exists and pressure is observed to be the most critical parameter followed by co-solvent (%) for all seed kernels.The prediction of cumulative extraction yield (g oil/g kernel) values, through reduced quadratic model, lies within error range of –2.5 to +11.06%, –3.94 to +9.73% and –3.62 % to +3.59 % of experimental values for Moringa Oleifera, watermelon and sunflower oils respectively. The extraction process is modeled by extended lack model proposed by Sovova (1994). A software program has been developed for Box complex optimization method in Matlab environment to find the optimum vales of parameters Z, W and xk of Sovova’s model by minimizing the average absolute relative deviation (AARD) between the amount of extracted oil computed with the model and the actual amount extracted oilfrom experiments .It is found that, at high pressure, the Sovova, (1994) model fits most of the experimental data within the error (AARD) band of 0.55-6.71%, 0.50-6.65% and 0.28-8.88% for Sunflower, Moringa Oleifera and Watermelon seeds respectively, whereas, at low pressure and for larger particle sizes (≥1.00 mm), the Sovova, (1994)model poorly fits the experimental data within an error (AARD) band of 9.98-16.12%. It is observed that, at low pressure, such as 200 bar, Sovova, (1994) model fits the experimental data only for the first extraction period and large deviations are observed for second and third extraction periods. Further, it has been observed in the present case that the mass transfer coefficient in the fluid phase (kYa) is several orders of magnitude greater than that in the solid phase (kXa) for all pressure values investigated.The analysis of all seed kernels though Scanning electron microscopy (SEM) analysis suggested that oils and non-extractable solids are closely interpenetrating and hence, high pressure is required to extract the oil. The FTIR analysis of all seed kernels confirmed the presence of fatty acid, protein and carbohydrates. Gas chromatographic analysis shows that, Moringa Oleifera oil is very rich in cis-oleic acid iii (C18:1 n9c), and Watermelon and Sunflowerseed oil is rich in linoleic (C18:2 n6c ) and cis-oleic acid (C18:1 n9c). Further, physico-chemical analysis of Moringa Oleifera, Watermelon and Sunflower oil such as, refractive index, flash and fire point, specific gravity, saponification value, unsaponification matter along with the Gas chromatographic analysis suggests that, these oils can be used as edible oils.