GB2097014A - Ultrasonic extraction of vegetable oil - Google Patents

Abstract

Enhanced recovery of vegetable oil, (e.g. palm oil) from oil bearing vegetal material is achieved by subjecting vegetal material immersed in a solvent (209) to a plurality of intersecting acoustic fields distributed longitudinally and transversely through a vessel (20) for said solvent and vegetal material, said acoustic fields being generated by a plurality of ultrasonic transducers (202) arranged longitudinally and circumferentially of said vessel (20). <IMAGE>

Description

SPECIFICATION Ultrasonic extraction of vegetable oil The process which is described relates to extraction of vegetable oil from oil-bearing vegetal material, and particularly to the extraction of residual oil contained in fibres after fruit and bunches of the oil bearing palm have been processed in a palm oil mill by known conventional methods.

After pressing, fibres have conventionally been used as fuel to raise steam employed in the process for initial sterilisation of oil-bearing material. Fibres thus burned contain as much as 8 to 12% of oil by dry weight of fibres, and the method described below is particularly suitable for extracting this oil, although it is not restricted to such secondary extrnction. The first extraction, e.g. by a conventional method, may be called primary extraction. After secondary extraction, the fibre is burned as previously to generate steam.

Existing systems using ultrasonics have been directed at different types of oil or fat bearing vegetal matters and have concentrated on the primary extraction of these oils and fats.

For instance, U.S. Patent No. 2601635 describes a process in which oils are extracted from a variety of materials, e.g. citrus fruits, flowers, seeds or beans, by subjecting the materials, in a liquid medium, to ultrasonic vibrations at a frequency of at least 19,000 sec-1.

U.S. Patent No.2717768 describes a process for extracting vegetable oils by passing oil-bearing material through a tube by means of an Archimedean screw while subjecting it to ultrasonic vibrations.

In these patents, neither the level of extraction, nor the amount of energy required to extract oils and fats, nor residence times, have been quantified.

Other previously proposed ultrasonic processes involve passing oil-bearing material through a short tube surrounded by radially acting transducers, concentrating the sound energy in a very limited area.

The process of the present invention makes use of sound waves which tend to influence a much larger zone than has been employed in prior art processes, by developing a near-constant energy field, in order to reach as large as possible a volume of matter to be processed. This is achieved by creating a crossfield of sound waves, intersecting at right angles through the length of the vessel in which the ultrasonic extraction takes place.

The present invention provides a method for the extraction of vegetable oil from oil-bearing vegetal material which comprises immersing said vegetal material in a solvent for said vegetable oil, subjecting said vegetal material and solvent to ultrasonic vibration whereby to extract oil from the vegetal material into the solvent, separating a solution of oil in solvent from the vegetal material, and separating oil from the solution, wherein the ultrasonic vibration is provided by a plurality of transducers generating acoustic waves arranged longitudinally and circumferentially of a vessel for said vegetal material and solvent, thereby generating intersecting acoustic fields distributed transversely and longitudinally of said vessel.

A preferred embodiment of the present invention, wherein the process of this invention is employed for the secondary recovery of palm oil from fibres which have already been partially depleted of oil by a conventional primary extraction process, is described below by reference to the accompanying Drawings, in which: Fig. 1 shows an apparatus for carrying out the process, with recovery and recycling of solvent; and Fig. 2 is a cross section along the line X-X of Fig. 1.

Referring now to the accompanying Drawings, oil bearing fibres are introduced through opening 101 into a variable pitch screw-conveyor 10, driven by motor 104.

The variable pitch screw 102, gradually compresses fibre to form a plug in area 103, which is not airtight but prevents free flow of air between the ambient atmosphere and zone 201, which is normally filled with an inert gas, e.g. CO2 at a pressure slightly above atmospheric, so as to prevent any ingress of air into the chamber 201 and contact with solvent.

The inert gas is supplied from source 30, being fed into chamber 201 by pipe 301. Pressure is controlled by means of a pressure sensor 302 controlling a valve 303.

Extraction vessel 20 is a closed trough, which is lower at the middle than at its ends. It is conveniently rectangular or circular in section (prismatic section). On the upper, lower and side faces of the trough (see Fig. 2), is mounted a series of transducers 202 facing one another across the space between two parallel or opposite faces or sides.

The lower part of trough 20 is filled with a solvent, 2cur9, e.g. an aliphatic hydrocarbon, such as hexane, or halohydrocarbon, such as methylene chloride, or any other solvent compatible with the oil to be extracted. The boiling point of the solvent should be lower than that of the oil. Trough 20 contains the solvent up to level 203 which is above the level of the highest transducer.

Trough 20 is connected to a float control chamber 204 where is set level control electrode 205, which controls level 203, by sending signals to 3-way valve 702, opening flow of solvent from tank 70 through pump 701.

Inside trough 20, fibre is carried by belt conveyor 206 of an open web design driven by pulley 207, through the lower part of 20 and through solvent 209. While passing through the zone of sound energy produced by tranducers 202, fibre is freed from residual oil, which immediately goes into solution in the solvent.

The level of sound energy required is a function of the mass of the fibre subjected to the sound wave action and the residency time in the energy field.

It is independent of the frequency, and normal frequency ranges such as 20 KHz to 60 KHz are satisfactory.

Residency times can conveniently vary between 5 and 30 seconds. At 10 seconds residency, one can observe large separation of oil from fibre. In some instances, 60% separation is achieved with 10 seconds. Longer residency times do not necessarily entail high extraction rates, since waxes are present and are much more difficult to remove, requiring residency times of several minutes. Higher extraction rates have to be weighed against economic return.

Energy requirements are usually in the range of 1 KWH (3.6x 106 Joules) per 1500--2000 g. oil extracted, but may differ from this.

Another critical design feature is the weight ratio of solids (fibres) to solvent, which lies between 1:10 and 1:40 for optimum results.

It has also been noted that preheating of the solvent to somewhat below its boiling point BP (Hexane BP=650C) enhances extraction rate and reduces residency time.

When solvents with a higher boiling point, such as methylene chloride, are used, the efficiency seems to peak off at 700C with little improvement beyond that temperature.

The solvent-oil solution is left to concentrate to about 1 weight % oil content before being let off from 20 by pipe 208.

Pipe 208 takes the solution to sump 80 from where it is pumped by pump 801, through filters 802 (in parallel, so that one can always be cleaned without stopping the process), to oil stripping tower 50 after passing through meter 804. The flow is continuously controlled by monitor switch 501 which controls valve 803, so that when level in header 502 is too high, valve 803 shuts off supply and bypasses solution back to sump 80.

Stripping tower 50 comprises one or more inner tubes 503 dimensioned to give optimum ratio of evaporation rate of solvent to length of tube to residency time, and of an outer shell 504, thermally insulated to form a jacket around bundle of tubes 503. Within this jacket is circulated steam, which is passed through relief valve 152, and pressure gauge 1 54 and is injected inside jacket through pipe 1 51. After pressure relief 1 52 is installed safety valve 1 53.

Before valve 152, a branch pipe 155 takes steam to coil 90 to preheat fresh solvent before it is passed into trough 20. The temperature of the solvent is controlled by thermostat 901, which activates valve 902, thus by-passing warming coil 90 and taking steam direct to fibre solvent stripping tower 40, if solvent temperature is too high. Normally all steam is returned to tower 40.

However, should there be an excess steam, this can be by-passed to waste by activating valve 403 and wasting to 903.

After passing through header 502, the oilsolvent solution overflows into inner tubes 503 through holes 511 and spreads over the inside faces of tubes 503 in a thin film which runs down the length of the vertical tubes. Heat transferred from steam jacket 504 to inner tubes 503, evaporates the solvent whose vapours rise to top of tower 50 into space 505, and are then led away by pipe 506 to condenser 601. Cooling water is let into condensers 60 and flows out at 603. Solvent condensate flows by gravity into solvent storage tank 70, from where it is pumped back to 20 by pump 701 and through control valve 702 and finally distributed over fibre leaving trough 20 through spray ramp 210.

In the oil stripping tower 50, oil is gradually freed from solvent as it evaporates and oil is collected in sump 507 and tapped through pipe 508.

There remains the extraction and recovery of solvent carried by fibres as they leave bath 209.

The solution-iaden fibre falls onto screw conveyor 401 which has the same characteristics as conveyor 10, and feeds fibre into a solventstripping tower 40. Fibre drops into a hot water bath 404, fed by the condensation of return steam from 90-902, through lines 403 and 405 and from the oil stripping tower 50 after passing through steam trap 509 and pipe 510.

When in contact with hot water, solvent evaporates and rises to the top of tower 40 in zone 406 and is drawn by pipe 407 to condenser 602 by the slight vacuum developed by condensation of solvent vapours. Some oil is liberated in the process and floats at level 408 from which it can be skimmed or drained by drain cock 409, and further separated from water by decantation.

Fibre, being heavier than water, settles at the bottom of tower 40, and is removed from tower 40 by screw conveyor 410, suitably inclined so as to lift fibre well above free water level inside tower 40, thus forming a seal. Fibre is ejected through orifice 411.

Level 408 in tower 40 is maintained by level monitor 412 which sends signals to electric valve 409 controlling drain cock 409.

Claims (11)

Claims

1. A method for the extraction of vegetable oil from oil-bearing vegetal material which comprises immersing said vegetal material in a solvent for said vegetable oil, subjecting said vegetal material and solvent to ultrasonic vibration whereby to extract oil from the vegetal material into the solvent, separating a solution of oil in solvent from the vegetal material, and separating oil from the solution, wherein the ultrasonic vibration is provided by a plurality of transducers generating acoustic waves arranged longitudinally and circumferentially of a vessel for said vegetal material and solvent, thereby generating intersecting acoustic fields distributed transversely and longitudinally of said vessel.

2. A method as claimed in Claim 1 wherein said vegetal material is palm oil bearing material.

3. A method as claimed in Claim 2 wherein the palm oil bearing material has been partially depleted of oil by primary recovery of oil.

4. A method as claimed in Claim 2 or 3 wherein the solvent is an aliphatic hydrocarbon or halohydrocarbon.

5. A method as claimed in Claim 4 wherein the solvent is hexane or methylene chloride.

6. A method as claimed in any preceding Claim wherein the solvent is preheated to a temperature below its boiling point.

7. A method as claimed in any preceding Claims wherein solvent is employed in an amount providing a weight ratio of solids:solvent of between 1:10 and 1:40.

8. A method as claimed in any preceding Claim wherein the oil is separated from solvent by evaporating the solvent.

9. A method as claimed in Claim 8 wherein evaporated solvent is condensed and recycled.

10. A method as claimed in Claim 1 and substantially as hereinbefore described with reference to the accompanying Drawings.

11. Vegetable oil when extracted by a method as claimed in any of the preceding Claims.