Field of the invention

The invention relates to an improved process for the ultrasound-assisted extraction of valuable components, particularly hardly-extractable components, with organic solvents from solid plant material, for example pitch from wood raw material, bioactive substances from roots, pits, kernels, seeds, shells, peelings. Also the invention relates to a system for extraction.

Background of the invention

Despite the rapid development of the production process of the synthetic food flavors, flavoring substances, nutraceuticals and pharmaceuticals, many bioactive compounds are still isolated from natural plant material. Extraction is an important method in isolation of compound groups or individual substances from plant material. However the conventional extraction methods such as maceration, re-maceration, percolation, re-percolation, Soxhlet extraction technique, circulation take hours, days and even weeks particularly for hardly-extractable components.

Also extraction process is very important to overcome the pitch problems during papermaking and wood working. It is clear that such continuous processes require very short operating time of extraction, low organic chemical consumption and high yield. The problem of removal of pitch and volatile organic compounds exists in the process of saccharification of wood raw material.

It is known that the extraction rate depends on the diffusion process on the phase interface between the solvent and particles of plant material. There are different techniques to improve the contact between the material and the extraction agent and provide mass transfer intensification.

Intensification of the extraction process can be achieved through vibration motion of solid-liquid system in the sound and ultrasound range. It leads to changes of hydrodynamic process environment and the particles of the plant material are subjected to mechanical and hydrodynamic shocks that improve capillary effect, the internal and external diffusion.

The fundamentals of the ultrasound-assisted extraction are different from those of conventional methods since the extraction occurs because of changes in the cell structure caused by sound waves. Depending on the parameters and environment high power ultrasound can improve an extraction process through the phenomenon of cavitation, break down the plant cell walls, releasing their content. Moreover, by the milling effect on the bulk plant material, much more plant surface is in contact with extracting solvent and, therefore, a better extraction of plant components can occur. Dispersion of the material and particle size reduction is other possible effects of ultrasound that may improve extraction. Ultrasound is able to promote a better penetration of solvent into the plant cells and a resulting benefit in extraction yield.

There have been different attempts to improve the extraction process for solid plant material by using ultrasound.

WO 05/087338 discloses a process for extraction of diterpenes and triterpenes from plant material comprising the step of submitting wood meal, branches, bark in organic solvent to ultrasound waves with a frequency of 10 kHz to 20 kHz during 20 to 90 minutes at temperature between -20 to 40 ⁰ C. The ultrasonic probe with a tip diameter of 0.5 inches is used in the experiments of the invention.

RU 2104733 discloses method of extraction of bioactive compounds from solid plant material (e.g. leaves and roots of Panax ginseng), the method consists of grinding plant material with subsequent action by ultrasound with an intensity of 1 to 70 W/cm ² , a frequency of 22 kHz for 60-420 sec in ethanol. The cone nozzle of the ultrasound piezoelectric generator is used in the extraction process.

EP 0583200 discloses a process for continuous extraction of evening primrose seeds with a solvent combined with ultrasonic treatment. The process is carried out in an extraction column with attached ultrasonic transducers. Plant material is brought into contact with solvent in countercurrent.

WO 08/074072 discloses a method of liquid phase extraction of chemical compounds from solid material (e.g. grape seeds) using high energy ultrasound with intensities of between 0.01 - 1000 W/cm ² . The liquid phase can be a supercritical liquid. Also the invention relates to an apparatus for extracting chemical compounds from a solid material including an extractor body, a conduit for directing a flow of liquid extraction phase around the material; at least one ultrasonic generator connected to at least one sonotrode, the sonotrode is in contact with the liquid phase.

RU 2261103 discloses method of extraction of Echinacea purpurea L. with ethanol wherein the raw material is subjected periodically to ultrasonic waves with the frequency of 22 kHz and a power of 0.4-4 kW. The ultrasound interaction time is 6-10 hours. The process is carried out in an extractor equipped with an ultrasonic transducer.

RU 2218204 discloses an extractor for solid-liquid system including an extractor body, devices for feeding solvent and extract discharging, a feeder for raw material and a device for discharging extracted material, mixing element in the form of a frame and ultrasonic transducers mounted on the side surface of the extractor body. The ultrasonic transducers are made from n units with m transducers, where n and m are integral numbers.

However these methods and systems do not provide high rate of the mass transfer, the extraction process lasts quite long period of time and either high recovery ratio is not achieved. Summarizing the aforesaid, a need exists for an improved process and a system for extraction of bioactive compounds, particularly hardly-extractable components, from solid plant material, for example pitch from wood, bioactive substances from roots, pits, kernels, seeds, shells, peelings.

Brief summary of the invention

In accordance with the present invention, there is provided a process for extraction of bioactive compounds from a solid plant material with organic solvents by subjecting the pretreated plant material to ultrasound wherein the process is carried out in few stages: at the first stage - in the low frequency ultrasonic field, in the mode of the broadband radiation with the power density at least 0.05 Wt/cm ³ ; at the second - in the low frequency ultrasonic field, in the mode of the resonance action with the power density at least 0.5 Wt/cm ³ . In one embodiment a hydrodynamic generator is used to obtain the low frequency ultrasonic field with the broadband radiation. In another embodiment piezoelectric or magnetostrictive transducers are used to obtain the low frequency ultrasonic field with the resonance action. Additionally the extracted plant material is washed with organic solvent in countercurrent. In one embodiment pretreated solid plant material has particles of size no more than 0.2 cm and humidity no more than 20%. The preferred solvent - plant material ratio is from 8:1 to 15:1. The organic solvent is selected from the group consisting of acetone, ethanol, butanol, tetrachlormethane, petroleum- ether. In one preferred embodiment the plant material is coniferous wood chips.

In accordance with the present invention, there is provided also a system for extraction of bioactive compounds from a solid plant material including a system body and devices for feeding solvent and discharging extract, a feeder for raw plant material and a device for discharging the extracted material, moreover the body is divided into chambers, the first chamber is equipped with a hydrodynamic generator and configured to saturate the particles of the plant material with solvent in the acoustic field; the second chamber is in the axial alignment (coaxial) with the first chamber and is configured to carry out further ultrasonic treatment of the saturated particles; the second chamber has electromechanical transducers mounted on its side surface; and the last chamber is configured to the final extraction of the plant material. Preferably electromechanical transducers are piezoelectric or magnetostrictive transducers and the last chamber is inclined at an angle to the first and the second chambers and is equipped with an internal screw. Brief description of the drawings

FIG. 1 is a schematic representation of a system for extraction of the present invention.

Description of the preferred embodiments

In accordance with the present invention, the process for extraction of bioactive compounds is provided.

Preferably, the pretreatment of plant material includes the following steps: drying and grinding. Drying can be effected by air blowing to the humidity of about 20%. The particle size are about 0.2 cm. Smaller particles present higher ratios of surface area to volume, which enhance the contact between solvent and solid matrix and diminish the diffusion path of the particle to reach the surface, resulting in a faster extraction rate.

At the first stage a hydrodynamic generator is used to obtain the low frequency ultrasonic field with the broadband radiation. For example such hydrodynamic generator is a liquid whistle. The heterogeneous mixture of plant material and solvent is forced under pressure generated by a powerful pump through an orifice from which it emerges, as a jet. The jet impacts upon a thin steel blade which is caused to vibrate and thereby produce mixing of the process material flowing over it. The whistle relies on mechanical generation of ultrasonic power; the device derives its power from medium (by mechanical flow across the blade) rather than by transfer of energy from an external source to the medium.

At the second stage electromechanical transducers are used to obtain the low frequency ultrasonic field with the resonance action. The two main types of electromechanical transducers are based on either piezoelectric or the magnetostrictive effect. Piezoelectric transducers are constructed with a piezoelectric material such as quartz and based on an electric field. Magnetostrictive transducers are based on a magnetic field and constructed with materials like nickel alloys.

The modes of the first and second stages are defined by the acoustic power density. The methods of the power density definition are known from the prior art (e.g. see Akopyan V.B., Ershov Y.A., The fundamentals of ultrasound interaction with biological objects, Moscow, publisher of BMSTU, 2005, p.224).

Preferably, the mass ratio of solvent to plant material is in the range of from about 8:1 to about 15:1, more preferably 10:1.

According to the invention, the preferred solvent for the pitch extraction is exemplified by the group consisting of acetone, ethanol, butanol, tetrachlormethane, petroleum-ether. Other solvents may also be useful. Acetone is the most preferred solvent for pitch extraction since it is miscible with water, forms a minimal azeotrope with water, boils at about 56 ⁰ C, and has a high affinity wood. Preferably, the solvent used in the extraction process of the invention is of a type that can be recycled for reuse in the process.

Without wishing to be bound by theory of operation mechanism of the combined ultrasonic action can be the following:

1. The dry particle of the plant material that has bubbles of air capable expand and collapse, comes into the ultrasound field of a hydrodynamic generator with broad line of frequencies. The own frequency of the particle that depends on its size and air content coincides with one of the frequencies generated by the hydrodynamic generator. High-amplitude resonance pulsations of the particle cause increasing the diffusion rate and the surface of solvent-particle contact. During this operation solvent surrounds and penetrates the particles dissolving and leaching bioactive compounds, e.g., pitch from the structure of wood chips.

2. The particle saturated by solvent comes to the zone of high power density produced by the piezoelectric or magnetostrictive transducers that are in the resonance mode. The high density facilitates diffusion of the bioactive components to the outer zone, which is the limiting step of mass transfer.

3. Further the ultrasound treated particles are washed with solvent by countercurrent operation, therefore, a better extraction of plant components can occur. The solvent washes last traces of soluble matter from the extracted plant material.

For ease of understanding the process of the invention, the system for extraction is illustrated in FIG.1.

The system has a chamber 1 configured to saturate the particles of plant material with solvent in the acoustic field; a chamber 2 configured to carry out further ultrasonic treatment of the saturated particles; and a chamber 3 configured to the final extraction of the plant material. The chamber 1 is in the axial alignment (coaxial) with the chamber 2. The extraction system has a flow circuit 4.

The chamber 1 is equipped with a hydrodynamic generator (e.g. liquid whistle); the chamber 2 has the electromechanical transducers 6 mounted on its side surface. Transducers are piezoelectric, constructed with a piezoelectric material such as quartz and based on an electric field, or magnetostrictive, based on a magnetic field and constructed with material like nickel alloys.

The flow circuit 4 has an inlet conduit 7 for solvent injection through the hydrodynamic generator into the chamber 1, a conduit 8 for solvent injection and output of the extract from the chamber 1, a pump 9 and a locking control valve 10. The chamber 3 is equipped with an internal screw 11 that is inclined at an angle to the chambers 1 and 2. The system is supplied with a feeder 12 for raw material, a device 13 for discharging the extracted material and a device 14 for feeding solvent and extract discharging.

The system for extraction operates as follows:

Solvent enters into the flow circuit 14 through the device 14 when the valve 10 is opened. Moreover a high-pressure jet stream of solvent falls into the chamber 1 through the hydrodynamic generator 5 by the pump 9. Also solvent enters into the chamber 1 through the conduit 8 when the valve 10 is opened.

Previously milled and dried plant material is fed by the feeder 12 into the chamber 1. The solvent level in the extraction system is constant. The suspension of the plant material and solvent is subjected to the pretreatment by the acoustic field of low-frequency sound oscillations produced by high-pressure jet stream of solvent through the hydrodynamic generator 5.

Then the saturated particles of the plant material falls into the chamber 2 wherein the transducers 6 connected the ultrasonic generator (not shown) produce the acoustic field with high density energy. It provides the efficient transport of the bioactive components to the outer zone.

Further the extracted material falls into the bottom of the chamber 3 and the internal screw rotates by a drive motor (not shown) to move particles of plant material held up between the screw threads. Fresh (recycled) solvent is injected in the inner conduit into the chamber 3. Thus as fresh solvent goes down, moving against the internal screw, it encounters the particles that have already undergone extraction. Consequently, the chips with the lowest concentration of bioactive compounds come into contact with fresh solvent. This provides optimum driving force for the final extraction. The extracted plant material is removed through the device 13. The chamber 3 is inclined at an angle to the chambers 1 and 2; it provides that the solvent containing the bioactive components falls toward the bottom of the chamber 2. The extract is removed by the device 14 and the conduit 8. Then solvent is evaporated and therefore the complex of bioactive compounds is obtained. Preferably, the solvent used in the extraction process can be recycled for reuse in the process.

The invention may be further understood by the following non-limiting examples.

Example 1:

The known method of extraction

1 kg of air-dried Echinacea purpurea L. herb (the particle size is 2.5 mm, humidity 8- 10%) is placed in extraction apparatus (e.g. Soxhlet). The extraction is carried out with 10 1 of a suitable solvent, e.g. ethanol for 6 hours. Then the solvent is evaporated to near-dryness and

26 g of complex of bioactive compounds is obtained. The extraction yield is 2.6 %. Example 2: The known method of extraction

10 kg of air-dried pine sawdust (the particle size is 1 mm, humidity 8%) is placed in extraction apparatus (e.g. Soxhlet). The extraction is carried out with 100 1 of a suitable solvent, e.g. acetone for 6 hours. Then the solvent is evaporated to near-dryness and 200 g of pitch is obtained. The extraction yield is 2 %.

Example 3

Suspension of 1 kg of air-dried Echinacea purpurea L. herb (the particle size is 2.5 mm, humidity 8-10%) and ethanol (the mass ratio is 1 :8) is subjected to the treatment by the acoustic field of low-frequency sound oscillations produced by high-pressure jet stream of solvent through the hydrodynamic generator (e.g. a liquid whistle). It facilitates solvent penetration into the solid particles of the plant material. The power density of the acoustic field is 0.1 W/cm ³ . The frequency is 22 kHz. Then the solvent is evaporated to near-dryness and 35 g of complex of bioactive compounds is obtained. The extraction yield is 3.5%. The extraction time is 20 seconds.

Example 4

Suspension of 100 kg of air-dried pine sawdust (the particle size is 1 mm, humidity 8%) and acetone (the mass ratio sawdust: solvent is 1:10) is subjected to the treatment by the acoustic field of low-frequency sound oscillations produced by high-pressure jet stream of solvent through the hydrodynamic generator (e.g. a liquid whistle). It facilitates solvent penetration into the solid particles of the plant material. The power density of the acoustic field is 0.05 W/cm . The frequency is 22 kHz. Then the solvent is evaporated to near-dryness and 100 g of pitch is obtained. The extraction yield is 0.1%. The extraction time is 20 seconds.

Example 5

Suspension of 100 kg of air-dried pine sawdust (the particle size is 1 mm, humidity 8%) and acetone (the mass ratio sawdust: solvent is 1:10) is subjected to the treatment by the acoustic field of low-frequency sound oscillations produced by high-pressure jet stream of solvent through the hydrodynamic generator (e.g. a liquid whistle). It facilitates solvent penetration into the solid particles of the plant material. The power density of the acoustic field is 0.05 W/cm . The frequency of the field is 22 kHz. Then the saturated particles of the plant material falls into the chamber wherein the piezoelectric transducers connected the ultrasonic generator produce the acoustic field with high power density. It provides the efficient transport of the bioactive components to the outer zone. Then the solvent is evaporated to near-dryness and 2.8 kg of pitch is obtained. The extraction yield is 2.8%. The extraction time is 30 seconds.

Example 6

Suspension of 100 kg of air-dried pine sawdust (the particle size is 1 mm, humidity 8%) and acetone (the mass ratio sawdust: solvent is 1:10) is subjected to the treatment by the acoustic field of low-frequency sound oscillations produced by high-pressure jet stream of solvent through the hydrodynamic generator (e.g. a liquid whistle). It facilitates solvent penetration into the solid particles of the plant material. The power density of the acoustic field is 0.05 W/cm ³ . The frequency of the field is 22 kHz. Then the saturated particles of the plant material falls into the chamber wherein the piezoelectric transducers connected the ultrasonic generator produce the acoustic field with high power density. It provides the efficient transport of the bioactive components to the outer zone. Further the extracted material falls into the bottom of the extraction tank and the internal screw rotates by a drive motor to move the particles held up between the screw threads. Fresh (recycled) solvent is injected into the extraction tank. Thus as fresh solvent goes down, moving against the internal screw, it encounters the particles that have already undergone extraction. Consequently, the particles with the lowest concentration of bioactive compounds come into contact with fresh solvent. This provides optimum driving force for the final extraction. Then the extracted plant material is removed from the extraction tank, solvent is evaporated and 3.5 kg of pitch is obtained. The extraction yield is 3.5%. The extraction time is 50 seconds.

Some results of the examples with pine sawdust as plant material are reported in the accompanying Table 1.

TABLE l

These results indicate that the combination of the acoustic fields produced by hydrodynamic generator and electromechanical transducers gives option to decrease dramatically the operating time of the extraction process. Particularly, the present invention provides for the high extraction rate and recovery ratio of pitch from wood raw material in wood working processes.