Production of edible or inedible vegetable oils for human consumption, lubricants, cosmetics, pharmaceutical, or biofuels purposes refers to removal of the available oil contained in seeds or beans by using mechanical extraction or chemical extraction. Oilseed are divided into two sub-groups, low oil content seeds which are those having up to 20% oil content and high oil content seed which have up to 60% oil or more.
This was the first method invented by Egyptians around (1650 B.C.) which extracted oil from olives by using wooden pestles and stone mortars. Around 1795 the pressing was done in England by using vertical hydraulic presses. It was not until 1900 when mechanical extraction was adopted as an industry standard with the invention the continuous expeller screw press. Mechanical extraction refers to the crushing process of oilseeds where the available oil is removed from the seeds by using expeller presses to squeeze the oil and leave the cake or meal with 5-7% residual oil. This method was called full pressing (for low capacity) and has been used for many years in the oilseed industry. Low oil content seeds have been processed using one-pass full pressing, while high oil content seeds have been processed by implementing a two-pass step called pre-pressing to remove about one half of the available oil. and then go to a second press to remove as much as possible of the remaining oil.
Today, single screw expanders are an integral part of many crushing plants since they replaced the old fashioned stack cookers used for many years and eliminate the use of required steam to cook or condition the seeds prior expelling process. Expanders for mechanical extraction are called dry expanders (meaning, “without steam”) and the temperature is crated only by frictional heat produced into the expander barrel. This new technology develops temperatures up to 280-310ºF and creates an efficient oil cell shearing, preparing the mash to be squeezed by the expeller, which allows us to use an expeller press with a low pressure. Main worms shaft and faster gear ratios and main worm speeds to achieve much higher capacities (we can easily triple or more the normal capacity of an Anderson Duo 33 or Duo 55 expeller with this process). Preparation equipment is required prior to the expelling process such as cleaning, cracking and dehulling (optional).
This is a fairly new technology started in France around 1855 where the first experiments were conducted by using carbon disulfide to dissolve olive oil retained in spent olive cakes. In 1870 the first batch solvent extraction plants were installed in France and Italy. In the early 1920’s, with the availability of petroleum-based solvents, German inventor Hildebrandt invented the continuous countercurrent immersion extractor and German inventor Bollman invented the continuous two-stage percolation extractor. The first commercial scale continuous solvent extraction plants were installed in Germany in the late 1920’s. The removal of the available oil takes place in the extractor (percolator) buy using Hexane as the solvent which will extract the oil from the meal having a specific retention time in the extractor and a specific usage of hexane per ton of meal processed. The final meal will have 1% or less residual oil compared against mechanical extraction which leave the meal with 5-7% residual oil. Solvent extraction demands extremely high capacity if compared with mechanical extraction, big solvent extraction plants can process up to 5000-6000 MTPD or more. Expanders also play a very important part of this process, wet expanders (using steam) and producing “collets” are used extensively in this industry prior the extractor to improve porosity and percolation in the meal and improving the hexane percolation in the extractor which results in less retention time, higher capacity and lower hexane and steam consumption per ton processed. Preparation equipment is required as well as equipment to desolventize-toaste-dry and cool the meal and to recovery the hexane to be used again in the process.