Question

For the extraction of oil from soybean either leaching using conventional organic solvent or supercritical carbon dioxide can be used. For answering the following questions, please cite your text and indicate all the references at the end of your text. You need to use reliable references such as journal articles to support your answer. a) describe the fundamental reason for separation of oil from soybean in the cases of leaching and supercritical carbon dioxide extraction. b) describe the operating principles of leaching and supercritical carbon dioxide extraction of oil from soybean. Sketch a simple diagram to supplement the process description and show all the streams.

Answer 1

Leaching is process of mass transfer that occurs by a substance from solid that comes in contact with a liquid. The liquid is very important in the leaching process to remove the given substance from solid matrix. Leaching can be done in batch, semi-batch or continuocs process at elevated temperature to increase the solubility of the solute in solvent. Feed to a leaching system is typically a solid, consisting of an insoluble carrier material and soluble compound. The feed in prepared by chopping or grinding. It is then mixed with a liquid solvent. The desired material dissolves and leaves the liquid as overflow. Soybean oil is a vegetable oil extracted from the seeds of the soybean (Glycine max). It is one of the most widely consumed cooking oils. Soybean oil can be considered a healthy oil, provided that it's not been hydrogenated and provided that it's certified organic. The bottom line with soy oil—and with all components of your diet—is that it is important to determine what's best matched for your individual health needs and cooking plan and then insisting on the highest quality food to meet those needs. There are two methods of soybean oil production, one is mechanical way, which is a traditional method that use screw press machine to squeeze oil out from seeds and kernels; the other way is chemical method that extract oil with solvents. Both two oil production methods have advantages and disadvantages. The previous one is natural and healthy but the oil yield is much lower, however, oil yield of the solvent extraction method is much more higher. You can choose one according to the capacity and your oil making needs, or you can use the two together. To produce soybean oil, the soybeans are cracked, adjusted for moisture content, heated to between 60 and 88 ºC (140–190 °F), rolled into flakes, and solvent-extracted with hexanes. The oil is then refined, blended for different applications, and sometimes hydrogenated.

Cleaning Section of Soybean Oil Production: The soybeans are first cleaned, dried and dehulled prior to oil extraction. The soybean hulls needs to be removed because they absorb oil and give a lower yield. This de-hulling is done by cracking the soybeans and a mechanical separation of the hulls and cracked soybeans. Magnets are used to separate any iron from the soybeans.
The soybeans are also heated to about 75°C to coagulate the soy proteins to make the oil extraction easier.

Extraction Section of Soybean Oil Production: First the soybeans are cut in flakes which are put in a percolation extractors and immerged with a solvent, normally hexane. Counterflow is used as extraction system because it gives the highest yield. After removing the hexane, the extracted flakes only contain about 1% of soybean oil and is used as livestock meal or to produce food products such as soy protein. The hexane is separated from the soybean oil in evaporators. The evaporated hexane is recovered and returned to the extraction process. The hexane free crude soybean oil is then further purified.

Purification Section of Soybean Oil Production: The crude soybean oil still contains many oil-insoluble and oil-soluble impurities that needs to be removed. The oil-insoluble material are removed with filtration and the soluble materials is removed with different processes including degumming (removing of phosphatides), oil refining (washing with alkaline solution to remove free fatty acids, colorants, insoluble matter and gums) and bleaching (with activated earth or activated carbon to remove colour and other impurities.

The extraction of soy oil from soybean flakes in industry requires large amounts of hexane solvent and results in significant losses and energy consumption during the distillative removal of the solvent. Hexanes and related hydrocarbon extractants are also becoming an environmental and health concern. A new method for extraction of the oil is sought, that would require neither hexane nor distillative removal of solvent. This article presents a preliminary assessment of several new methods for soy oil extraction and subsequent solvent removal from the oil. The most promising are (a) extraction by an amidine switchable solvent that can then be removed from the soy oil by carbonated water and (b) extraction by a moderately hydrophilic solvent that can then be removed from the oil by water.

(a) The content of omega-3 in soybean oil is important in the development of infants and is an alternative for the omega-3 in fish oils. The investigation of extraction of soybean oil is needed to obtain the bioactive compound in the extract. Supercritical carbon dioxide extraction is modern and green technology to extract herbs and plants to obtain high quality extract due to high diffusivity and solubility of the solvent. The aim of this study was to obtain the optimum condition of soybean oil extraction by modified supercritical carbon dioxide. The soybean oil is extracted by using modified supercritical carbon dioxide (SC-CO2) under the temperatures of 40, 60, 80 °C, pressures of 150, 250, 350 Bar, and constant flow-rate of 10 g/min as the parameters of extraction processes. An experimental design was performed in order to optimize three important parameters of SC-CO2 extraction which are pressure (X1), temperature (X2) to achieve optimum yields of soybean oil. From the optimization process, the optimum condition of extraction of soybean oil was obtained at pressure 338 Bar and temperature 80 °C with oil yield of 2.713 g. Effect of pressure is significant on the extraction of soybean oil by modified supercritical carbon dioxide. Increasing of pressure will increase the oil yield of soybean oil.

(b) Operating Principle:

Plant Material
The sun-dried soybean was powdered using dry-mill grinder with the aim of increasing the samples’ surface area. The dried powdered plants were then sieved by using sieve trays with particle size of 300 μm. The chosen size was made based on the preliminary result which showed that particle size of 300 μm was the optimum size for extraction process. At the end of this stage, the material’s powder was put inside the sealed plastic bag and stored in a refrigerator at temperature −20 °C to maintain the freshness of samples before being used for extraction.

Modified Supercritical Carbon Dioxide Extraction
To begin with, the collection vials were prepared, labelled and weighted. Meanwhile, the oven and chiller were turned on. The chiller and heater temperature were set at 5 °C and 50 °C, respectively. Next, 15 g of powdered soybean that has been processed through the sampling process was placed into the vessel. The extraction vessel was then fixed properly in the oven. The investigated values of pressure and temperature conducted in this experiment were: pressure of 150, 250 and 350 bar; temperature: 40, 60, and 80 °C and each set of extraction processes were run for 3 hours. Then, the back pressure regulator (Tescom 10000) had been controlled while the temperature was adjusted by setting the oven (France Etuves H555) temperature. Next, the CO2 gas was pumped into the system continuously with supercritical pump (Separex Piston Pump P200GP50) at flow rate of 10 g/min while ethanol as modifier was pumped into the system at flow rate of 0.5 g/min. The extract was collected for every 15 minutes of the extraction process. The extract oil obtained was placed in the collection vials, sealed and stored in the chiller at 2.7 °C to prevent any possible degradation of the product.

Reference:

• "Optimization of Soybean Oil by Modified Supercritical Carbon Dioxide" By N. R. Putra, A. H. Abdul Aziz, A. S. Zaini, Z. Idham, F. Idrus, M. Z. Bin Zullyadini, M. A. Che Yunus.
• http://www.oilmillmachinery.net/Soybean-Oil-Production.html