FIELD OF INVENTION

The present invention relates to the extraction of oil and other matter from starting materials using dimethyl ether. The present invention has particular but not exclusive application for extracting from biological material. By way of example only, reference will be made to the extraction of oil from biological material.

PRIOR ART A number of processes exist for extracting oils from oil-bearing material. Most oil seeds are initially processed to extract the oil by either cold crushing or expeller processing. While expeller processing is slightly more efficient at extracting oil, both of these processes leave about 10% oil (by weight) in the residual meal. Solvent extraction has been used to extract oil from the residual meal and reduce the oil content to about 1%. Extraction solvents which have been used include hexane, methyl acetate, ethyl acetate, acetone, ethanol and methanol.

Although solvent extraction processes are used on a commercial scale, the solvents that are currently used in these processes are often not satisfactory because of their high boiling points. The solvent that is currently most effective and most widely used is hexane, but extensive clean-up is required to reduce the residual hexane content in the meal to acceptable levels. The solvent extraction of essential oils (flavoured or aromatic oils which are used in the food, cosmetic, pharmaceutical, aromatherapy and chemical industries) requires that the resultant liquor be distilled to remove these high boiling solvents from the extracted material. The essential oils contained in plants are complex substances and contain a large

number of individual compounds. Some of these compounds are relatively volatile or relatively thermally unstable. High distillation temperatures can result in product loss either through co-evaporation of the volatile compounds with the extraction solvent or degradation of the thermally unstable compounds.

OBJECT OF THE INVENTION

It is an object of the present invention to provide an alternative method of extracting oil from biological material using a solvent extraction method that overcomes one or more of the aforementioned problems.

SUMMARY OF THE INVENTION

The present invention results from the identification that dimethyl ether (DME) has several properties that make it suitable for use as an extraction solvent and the development of a method that makes the commercial use of DME viable. DME has not been commercially used as an extraction solvent because it is expensive to produce and difficult to use and store safely.

The present invention uses DME or a DME solvent mixture for extracting oil and other compounds from oil-bearing materials. DME is gaseous under standard atmospheric conditions. It can be readily liquefied by cooling to below -25°C at atmospheric pressure or by compression to approximately 5 atmospheres or above at room temperature. Liquefied DME can mix with most oils and also with about 6.3% by weight of water at 20 ⁰ C. It has a specific gravity of 0.661 g/ cm ³ and a latent heat of vaporisation (at -20 ⁰ C) of 410 kj/kg. DME has a small size (about 5 angstroms in diameter, molecular weight of 46 Daltons) and appears capable of permeating most materials. DME has a low viscosity and appears not to be

hazardous to human health. This combination of properties is not shared with other organic solvents such as diethyl ether, hexane and petroleum ether.

In one aspect the present invention broadly resides in an extraction method including subjecting material for extraction to liquid dimethyl ether solvent; separation of the solvent liquor containing the extractants from the residual matter; separation of the solvent from the extractants from the solvent liquor; and reclamation of the dimethyl ether for use with further extractions, wherein dimethyl ether separates from the extractants by vaporisation and condenses for reuse.

The material may be any suitable matter including biological material such as foliage, nuts and seeds, microorganisms, and cartilage and tissues from invertebrate and higher animals or inorganic materials such as rock and shale, sand, and plastics. For example, oil from soya beans, corn, cotton seeds, olives, peanuts, linseed, coconuts, sunflower seeds, sesame seeds and flax can be extracted using the above mentioned method. Biologically active compounds such as pyrethroids, alkaloids and antibiotics may be selectively extracted from the raw material. Reusable compounds from recyclable products such as some plastics can also be extracted.

The DME solvent used for extraction may be a mixture of DME with other solvents to enhance the extraction of desired compounds from a particular material. The DME solvent preferably comprises 30-100% DME. Preferably the DME solvent has 50% DME or more. In a preferred embodiment, the DME extraction solvent is substantially 100% DME.

The material is preferably subjected to DME for up to 30 minutes but more preferably between 30 seconds and 15 minutes.

The range of temperatures for the extraction may vary between -25 ⁰ C and 8O ⁰ C and the pressure may vary between 1 and 10 atmospheres. Preferably, the extraction occurs between O ⁰ C and 4O ⁰ C. In one preferred embodiment, the extraction is carried out conditions of 25 ⁰ C and 5 atmospheres.

The material is preferably pretreated to increase the surface area and provide greater exposure of the material to the DME solvent. Pretreatment may include grinding, milling or chopping of the material to a powder or other small particulate form.

DME is able to extract oil such as triglycerides, fat-soluble compounds such as vitamins and alkaloids and some water-soluble compounds from starting material. The DME extraction method is also able to reduce the water content in extracted materials. The same material may be subjected to two or more extractions to achieve maximum extraction from the material.

The extraction method may be a batch process were the bio-mass material is exposed to the liquid DME solvent in distinct batches or continuous were liquid DME solvent is continuously cycled through the starting material. In a further aspect the invention broadly resides in an extraction system for using the above mentioned extraction method, including a collection chamber for the collection and storage of the DME solvent, said collection chamber is operatively associated with a compressor for compressing and condensing the DME solvent from gas to liquid form; a reaction chamber wherein the material is extracted with the DME solvent; and

an evaporation chamber wherein the DME solvent evaporates from the separated solvent liquor and is compressed in the collection chamber for reuse, wherein the evaporation chamber, reaction chamber and collection chamber are operatively connected with each other. The reaction chamber is preferably cooled to ensure that the maximum liquid volume fills the chamber. The evaporation chamber is preferably heated to facilitate maximum extraction and vaporisation of the DME solvent. The temperature in the reaction and evaporation chambers are preferably controlled by means of water baths. Preferably the chambers are interconnected by pipework, which can be opened and closed by taps or one-way valves.

The compressor can compress the gaseous DME solvent and preferably evacuate the reaction and evaporation chambers. Preferably the reaction and evaporation chambers are evacuated to form at least a partial vacuum prior to introducing the DME solvent to the reaction chamber. Preferably the compressor is an oil-free compressor. Preferably, heat exchangers are used to keep the compressed solvent cool.

The system can be operated as a batch process using one reaction chamber or a continuous batch process using two or more reaction chambers operating alternately or in tandem in a controlled system.

Where the extraction method is a continuous batch process, the method preferably uses a filter arranged at the bottom of the reaction chamber to filter particulates from the solvent liquor prior to its entry into the evaporation chamber. Other types of filters may be installed in-line between the reaction chamber and the evaporation chamber and between the evaporation chamber and the collection chamber.

Preferably there is also a bleed valve associated with the collection chamber to allow removal of compressed air.

Preferably there is a water filter to remove water vapour from the vapourised DME solvent. The water filter is preferably located in-line between the evaporation and collection chambers and more preferably inline between the two chambers.

In a preferred embodiment the starting material is placed in a filter bag and then positioned in a tapered mesh basket before it is placed in the reaction chamber. The shape of the tapered basket facilitates the removal of the extracted material. The use of baskets allows the possibility of loading raw material off-line. In a preferred embodiment, the basket has a riser tube in the middle to assist with improved diffusion of the liquid DME into the bulk of the starting material in the basket and to facilitate removal of the dissolved material in the DME.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT By way of example, the method of extracting oil from Jojoba seeds is described. Jojoba is pretreated by grinding them to powder to increase the amount of material exposed to DME. The powdered Jojoba (Jojoba meal) are placed in a filter bag and positioned in a tapered basket that has a central channel for allowing DME to reach material in the centre. The reaction and evaporation vessels are connected by a pipe with a tap (the evacuation tap) to isolate one vessel from the other. The basket is then loaded into the reaction vessel. With the evacuation tap open, the compressor (or a vacuum pump) evacuates the reaction and evaporation vessels producing a partial vacuum. The evacuation tap is then closed. Liquid 100% DME is introduced into the reaction vessel covering the Jojoba meal. The Jojoba meal is incubated at 3O ⁰ C for 15

minutes. With incubation, oil and oil-soluble compounds are extracted from the meal. After 15 minutes has elapsed, the evaporation tap is opened and the solvent liquor passes out of the reaction vessel, through a filter and into the evaporation vessel. A tap in the pipe between the evaporation and collection vessels (the collection tap) is opened and the compressor is turned on, thereby driving the reaction to the production of gaseous DME in the evaporation chamber and the collection of liquid DME in the collection vessel. The extracted material (Jojoba oil) is only soluble in the liquid phase and when the DME vaporises, the extracted material collects at the bottom of the evaporation vessel. The extracted material, which comprises mostly Jojoba oil and oil-soluble compounds, is then passaged through an opening and an in-line filter and collected in the collection vessel.

DME is held in liquid state under pressure in the collection vessel ready for reuse.

The extraction process is repeated until the desired levels of extraction have been achieved.

ADVANTAGES The advantages of the present invention include:

• The commercial use of DME as an extraction solvent by reclaiming, recycling and reusing DME.

• DME is able to extract a wide range of fats and fat-soluble material and some hydrophilic compounds.

• DME is easily removed from the product (as it boils at about -25°C) leaving the products residue-free.

• DME can be used for extraction at comparatively low temperatures (0-50 ⁰ C), decreasing the risk of damage to thermolabile compounds.

• The extraction process occurs in a substantially oxygen-free environment, thereby avoiding problems of oxidation of extracted products.

• The apparatus can be constructed so that the extracted material remains in a sterile environment, thereby offering possibilities of meeting regulatory requirements (DME has also shown to act as a sterilising agent for some biological materials).

• Variations in the extraction conditions, including temperature, exposure time, pressure and co-solvents can allow tailoring of the extraction method for the maximum extraction of desired components.

• The DME extraction method allows removal of lipids, fats, water and non-polar and some polar products. Residual oil in extracted materials can be 1 % or less. Removal of oil to these levels can result in a more freely flowing matrix which can reduce milling costs and overcome subsequent handling issues such as bridging in hoppers and pipes. Some systems such as supercritical CO ₂ cannot remove water as it freezes in the pipes, thus blocking the extraction.

• The DME extraction method can remove chlorophylls, polyphenols and other colourants in biological matter, producing a matrix with reduced colouration.

This can value-add to the matrix material (e.g. produce a whiter purer looking flour).

• Besides oils and lipids from seed and legume products, the process may be applied to other biological applications such as removal of taxol from hazelnut timber and nuts and lipranol from the green-lipped mussel.

• The DME extraction method may be used in non-biological applications, including cleaning of oil covered components, removal of oil from sand/dirt in contaminated sites or the extraction of oils from shales, sand and other geological formations, and recycling of plastics, particularly foamed polystyrene and other thermoplastics.

VARIATIONS

It will of course be realised that while the foregoing has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as is herein set forth. Throughout the description and claims of this specification, the word

"comprise" and variations of that word such as "comprises" and "comprising", are not intended to exclude other additives, components, integers or steps.