Technical Field

The present invention relates to an oxidant activator and a method of oxidising organic molecules using the oxidant activator.

Background

Hydrogen peroxide is an environmentally friendly oxidant because only oxygen and water are released as end products. It has been widely used in many industrial applications. Most industrial applications involve organic solvent systems.

Even though hydrogen peroxide is a strong oxidant, it is very stable at room temperature. Thus, reaction rates of oxidation reactions involving hydrogen peroxide are too slow under ambient conditions. At high temperatures such as > 90°C, however, hydrogen peroxide can self-decompose to release oxygen and water quickly, leading to a low molecular efficiency. Thus, the amount of hydrogen peroxide used in these processes has to be increased. Because of the large amounts hydrogen peroxide used in the process, the products of the oxidation reactions are contaminated with hydrogen peroxide and water. These have to be removed by using heat and vacuum for a long time, thereby adding to cost as well as making the entire process very energy intensive and tedious.

Accordingly, hydrogen peroxide activators have been used in oxidation reactions, in which the activators can react with hydrogen peroxide to form highly reactive species which are able to oxidize organic molecules quickly at room temperature. An example of a known hydrogen peroxide activators is iron-tetraamidomacrocyclic complex (Fe- TAML). A combination of hydrogen peroxide and Fe-TAML works very well in aqueous solutions. However, generally a combination of hydrogen peroxide and a hydrogen peroxide activator does not work well in organic solvents. In the case where the hydrogen peroxide activator is Fe-TAML, since hydrogen peroxide is not soluble in many organic solvents, it forms a two-phase system. Further, Fe-TAML has a poor solubility in most organic solvents and cannot be dispersed uniformly inside an organic phase. Recovery of the hydrogen peroxide activator is also difficult from the organic solvent. As a result, following oxidation, final products may be contaminated by the hydrogen peroxide activator. This is especially problematic for food and pharmaceutical industries as Fe-TAML is highly toxic and non-biodegradable.

There is therefore a need for an improved oxidant activator.

Summary of the invention

The present invention seeks to address these problems, and/or to provide an improved oxidant activator, as well as a method of oxidising organic molecules using the oxidant activator.

In general terms, the invention relates to an oxidant activator specifically suitable for use in organic solvent systems and which may be used with suitable oxidants, such as hydrogen peroxide, in organic solvents for various applications. These applications may include bleaching vegetable and fuel oils, bleaching food and pharmaceutical products, wastewater treatment processes, decontamination of polluted sites, etc. In particular, the oxidant activator may allow reduction of the amount of oxidant used. For example, the oxidant activator enables very little or no residual hydrogen peroxide to be left after the end of the oxidation process. Since the oxidant activator of the present invention is made of non-toxic materials and is fully compatible with food and pharmaceutical products, its use in oxidation processes is advantageous, particularly those processes in the food, pharmaceutical and automobile industries. This makes the oxidation processes using the oxidation activator of the present invention green and cost-effective.

According to a first aspect, the present invention provides an oxidant activator comprising a macrocyclic tetraamide metal complex (MTMC) encapsulated in a hydrophilic hydrogel.

The hydrophilic hydrogel may be any suitable hydrogel. For example, the hydrophilic hydrogel may comprise a polymeric hydrogel, peptide-derived hydrogel or a combination thereof.

The polymeric hydrogel may be any suitable polymeric hydrogel. For example, the polymeric hydrogel may comprise: calcium alginate, carrageenans, polyvinyl alcohol, sodium polyacrylate, polyethylene glycol (PEG), hyaluronan, agarose, polyacrylic acid, polyhydroxyethyl methacrylate, polymethacrylic acid, polyacrylamide, elastin, hyaluronic acid, gelatin, chitosan, collagen, fibrin or a combination thereof.

According to a particular aspect, the hydrophilic hydrogel may be porous.

The oxidant activator may have any suitable size. For example, the oxidation activator may have an average diameter of 1 μηι - 30 mm.

The MTMC comprised in the oxidant activator may be any suitable MTMC. In particular, the MTMC may have a general formula (I):

wherein: each X is independently selected from the group consisting of: H or CI; each R is independently selected from the group consisting of: alkyl groups, carbonyl groups or other substituents;

M is a transition metal;

B is selected from the group consisting of: N-(CH ₃ ) or C-(CH ₃ ) ₂ ;

L is an optional substituent selected from the group consisting of: H ₂ 0 or COO ^" ; and

Q is a counterion selected from the group consisting of sodium or potassium, for balancing the charge of the compound on a stoichiometric basis.

According to a particular aspect, M may be iron (Fe) or copper (Cu). In particular, the MTMC may be: iron-tetraamidomacrocyclic complex (Fe-TAML), iron-phthalocyanine, copper-peptide complex, iron porphyrins, tetraacetyleihy!enediamine (TAED), acetamide, dicyandiamide or a combination thereof. The oxidant activator may have a suitable working temperature. According to a particular aspect, the oxidant activator may have a working temperature of -40-100°C.

In particular, the oxidant activator may be used as an oxidant activator for oxidation in organic systems or in aqueous systems comprising organic solvents.

According to a second aspect, there is provided a method of oxidising organic molecules, the method comprising adding an oxidant and the oxidant activator according to the first aspect for activating the oxidant.

The oxidant may be any suitable oxidant. For example, the oxidant, may be, but not limited to, hydrogen peroxide (H ₂ 0 ₂ ), organic peroxide, organic hydroperoxide, peroxy acid, hypochlorite, ozone, or a combination thereof.

The method may be performed under suitable conditions. For example, the method may be performed at a suitable temperature. According to a particular aspect, the method may be performed at a temperature of -40-100°C.

The method may further comprise recovering the oxidant activator. The recovered oxidant activators may be reused in the method of the present invention. According to a particular aspect, the method may further comprise mixing the recovered oxidant activators with polar organic solvents prior to the reusing.

Brief Description of the Drawings

In order that the invention may be fully understood and readily put into practical effect there shall now be described by way of non-limitative example only exemplary embodiments, the description being with reference to the accompanying illustrative drawings. In the drawings:

Figure 1 shows the general scheme by which the oxidant activator according to one embodiment of the present invention is formed; and

Figure 2 shows the bleaching kinetics of β-carotene as represented by the absorbance of β-carotene. Bleaching with hydrogen peroxide assisted by oxidant activator beads according to one embodiment of the present invention ( A ) is conducted in total 4 cycles by reusing the beads when the previous cycle is completed. The control experiment comprised β-carotene supplemented with only hydrogen peroxide (·) without any oxidant activator beads.

Detailed Description

As explained above, there is a need for an improved oxidant activator which is particularly suitable for use in organic solvent systems. Many industrial processes are carried out in organic solvents instead of aqueous solutions. For example, organic synthesis, extraction and column chromatography often require organic solvents. Many commercial products such as paints, also contain organic solvents. Unfortunately, many oxidants such as hydrogen peroxide do not work well in the organic solvents due to poor solubility in organic solvents and therefore forms a two-phase systems.

In general terms, the present invention therefore provides an oxidation system comprising an oxidant activator which is suitable for use in organic solvent systems. There is also provided a green oxidation process which may be applied to many industrial processes in which hydrogen peroxide may be used as an oxidant and the oxidant activator may be used as a catalyst. The oxidation process according to the present invention may be used in manufacturing of chemicals and/or bleaching food products. It may also be used in a dry cleaning process, or wastewater treatment process.

In particular, the present invention provides an oxidant activator which comprises an oxidant activator, such as hydrogen peroxide activators, encapsulated in a hydrogel. The hydrogel encapsulated oxidant activators may enable one to perform green oxidation in organic solvents by using a suitable oxidant such as hydrogen peroxide. The encapsulated oxidant activators may prevent the leaching of activators and may be easily recovered and therefore, reused.

According to a first aspect, the present invention provides an oxidant activator comprising a macrocyclic tetraamide metal complex (MTMC) encapsulated in a hydrophilic hydrogel.

The hydrophilic hydrogel may be any suitable hydrogel. The hydrogel may act as a non-active carrier for the MTMC, which is the active catalyst. The hydrogel enables the active catalyst to be recoverable and be reused for multiple cycles of oxidation. For example, the hydrophilic hydrogel may comprise a polymeric hydrogel, peptide- derived hydrogel or a combination thereof.

The polymeric hydrogel may be any suitable polymeric hydrogel. For example, the polymeric hydrogel may comprise: calcium alginate, carrageenans, polyvinyl alcohol, sodium polyacrylate, polyethylene glycol (PEG), hyaluronan, agarose, polyacrylic acid, polyhydroxyethyl methacrylate, polymethacrylic acid, polyacrylamide, elastin, hyaluronic acid, gelatin, chitosan, collagen, fibrin, or a combination thereof. In particular, the polymeric hydrogel may be calcium alginate.

The peptide-derived hydrogel may be any suitable peptide-derived hydrogel.

According to a particular aspect, the hydrophilic hydrogel may contain more than 95% water and less than 5% polymer. The polymer network may be used to encapsulate the MTMC and disperse the MTMC uniformly inside the hydrogel. In this way, the MTMC do not aggregate together. Water inside the hydrogel may provide a reaction medium for the oxidant and oxidation reaction when the oxidation activator is in use in the oxidation reaction. The hydrogel, being hydrophilic, does not dissolve in organic solvents. This makes the oxidant activator suitable for use in oxidation processes of organic solvent systems or in aqueous systems containing organic solvents.

According to a particular aspect, the hydrophilic hydrogel may be porous. In this way, the oxidant may be allowed to react with the MTMC and become activated to enable the oxidation reaction to take place without the oxidant getting affected in the organic solvent system. In particular, when the oxidant is hydrogen peroxide, the porous hydrophilic hydrogel may act as the hydrogen peroxide reservoirs when the hydrogel is dispersed in an organic solvent system. The hydrogen peroxide may diffuse into the hydrogel and react with the MTMC, thereby getting activated.

The oxidant activator may be of any suitable form. For example, the oxidation activator may be in the form of, but not limited to, beads, membrane, film, or fibre. In particular, the oxidation activator may be in the form of a bead, wherein the MTMC is encapsulated in a hydrogel bead.

According to a particular aspect, the oxidant activator in the form of a bead may have any suitable size. For example, the bead may have an average diameter of 1 μηι - 30 mm. In particular, the bead may have an average diameter of 1-3 mm. The size of the bead may depend on the process used in the formation of the hydrogel. For example, the hydrogel beads may be prepared using a syringe with a needle or a pipette. Smaller hydrogel beads may be prepared using a specialized extrusion device with a vibrating nozzle. The properties of the hydrogel beads (dimensions, rigidity and stability) formed may be adjusted by altering several factors known to a person skilled in the art.

The MTMC comprised in the oxidant activator may be any suitable MTMC. In particular, the MTMC may have a general formula (I):

wherein: each X is independently selected from the group consisting of: H or CI; each R is independently selected from the group consisting of: alkyl groups, carbonyl groups, or other substituents;

M is a transition metal;

B is selected from the group consisting of: N-(CH ₃ ) or C-(CH ₃ ) ₂ ;

L is an optional substituent selected from the group consisting of: H ₂ 0 or COO ^" ; and

Q is a counterion selected from the group consisting of sodium or potassium, for balancing the charge of the compound on a stoichiometric basis.

According to a particular aspect, M may be iron (Fe) or copper (Cu). Even more in particular, M may be iron. In particular, the MTMC may be: iron-tetraamidomacrocyclic complex (Fe-TAML), iron- phthalocyanine, copper-peptide complex, iron porphyrin, tetraacetylethylenediamine (TAED), acetamide, dicyandiamide or a combination thereof.

According to a particular aspect, the oxidant activator may have a working temperature of -40-100°C. In particular, the temperature may be 0-100°C, 10-90°C, 20-80°C, 30- 70°C, 40-60°C, 50-55°C. Even more in particular, the temperature may be≤ 50°C, preferably about 50°C. It would be clear to a person skilled in the art that the oxidant activator activates an oxidant such as hydrogen peroxide at a lower temperature. For example, when the oxidant is hydrogen peroxide, in the absence of the oxidant activator of the present invention, the hydrogen peroxide is generally activated only at temperatures≥ 90°C. However, in the presence of the oxidant activator of the present invention, the temperature at which the hydrogen peroxide may be activated may be lowered to about 50°C.

As explained above, the oxidant activator of the present invention may be suitable for use as an oxidant activator for oxidation in organic systems. This is because the oxidant activator does not have the problems with oxidant activators of the prior art associated with aggregation, solubility, etc.

The oxidant activator of the present invention may be formed according to any suitable method. For example, the oxidant activator may be formed by a method involving extrusion.

According to a particular embodiment, the hydrogel may be calcium alginate. Figure 1 shows the general reaction scheme by which the oxidant activator of the present invention may be formed. In particular, fabrication of the oxidant activator may involve preparation of an aqueous solution containing an MTMC and sodium alginate. Alginate is a copolymer consisting of mannuronic and guluronic acid residues. When the solution contacts a calcium chloride solution, ion exchange occurs between the sodium and calcium ions. The alginate copolymer chains are then cross-linked by the divalent calcium ions. The alginate then solidifies and traps the MTMC molecules within the alginate, as shown in Figure 1. Accordingly, the active catalyst of the oxidant activator may be blended into the hydrogel solution before they solidify. By dripping the hydrogel solution on to a solid surface and cross-linking the droplets, for example by UV, or dripping the hydrogel solution into a calcium chloride solution (in the case of calcium alginate), beads of hydrogels of various diameters may be formed. In particular, calcium alginate may be made into bead form by extruding the sodium alginate solution through a needle into a solution containing the calcium ions.

The hydrogel beads may be strengthened in organic solvents. For example, porous solid materials such as silica gel, fume silica or activated carbon may be added. In particular, up to 5 wt% of porous solid materials may be added. The hydrogel beads may be further cross-linked with suitable solvents such as dipicolylamine (DPA) and glutaraldehyde (GA) to increase their resistance to organic solvents.

According to a second aspect, there is provided a method of oxidising organic molecules, the method comprising adding an oxidant and the oxidant activator according to the first aspect for activating the oxidant.

The oxidant may be any suitable oxidant. For example, the oxidant may be, but not limited to: hydrogen peroxide (H ₂ 0 ₂ ); organic peroxide such as, but not limited to, benzoyl peroxide; organic hydroperoxide; peroxy acid; hypochlorite; ozone; or a combination thereof. In particular, the oxidant may be hydrogen peroxide.

The method may be performed under suitable conditions. For example, the method may be performed at a suitable temperature. According to a particular aspect, the method may be performed at a temperature of -40-100°C. In particular, the temperature may be 0-100°C, 10-90°C, 20-80°C, 30-70°C, 40-60°C, 50-55°C. Even more in particular, the temperature may be≤ 50°C, preferably about 50°C.

The method may further comprise recovering the oxidant activator. The recovered oxidant activators may be reused in the method of the present invention. According to a particular aspect, the method may further comprise mixing the recovered oxidant activators with polar solvents prior to the reusing. For example, the polar solvent may be a polar organic solvent, such as, but not limited to, acetone, acetonitrile, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), short chain alcohols, or a combination thereof.

According to a particular aspect, the mixing may comprise mixing the recovered oxidant activator with non-polar organic solvents prior to the reusing. For example, the non-polar organic solvent may be hexane. If a non-polar organic solvent is used, a phase-transfer catalyst may be further required.

The method of the present invention may be applied to various industrial applications. For example, the applications may include, but are not limited to, bleaching vegetable oils to reduce their colour, bleaching food and pharmaceutical products, decontamination of polluted sites, treatment of recycled motor and lubricant oils, treatment of pharmaceutical and industrial wastewater, and the like.

The method of the present invention may be performed in any suitable reactor. For example, the method may be performed in a packed-bed column. According to one embodiment, the oxidant activator according to the first aspect may be put inside a packed-bed column. Organic solvents may be mixed with an oxidant such as hydrogen peroxide and poured from the top of the column. In this manner, the method of oxidising may be performed in a continuous manner.

Having now generally described the invention, the same will be more readily understood through reference to the following embodiment which is provided by way of illustration, and is not intended to be limiting.

Example

Materials

MTMC used for the example, hereafter referred to as MTMC1 has a formula (I):

wherein: each X is H; each R is CH ₃ ; M is Fe(lll); B is C-(CH ₃ ) ₂ ; L is H ₂ 0; and Q is Na ⁺ . The macrocyclic ligand was synthesized based on the protocol outlined in US 6,011 , 152 A with some modifications. The formation of MTMC1 was modified based on methods described by C Panda et al {Chem Commun, 2011, vol. 47(28):8016-8). In brief, n-butyllithium in THF and hexane were added to the resulting macrocyclic ligand under argon gas. Anhydrous FeCI ₂ was added into the mixture which was then incubated for 12 hours under room temperature to obtain MTMC1. MTMC1 has the following structure:

Fabrication of oxidant activator

Fabrication of the oxidant activator started by preparing an aqueous solution containing 0.1 g/L of MTMC1 and 40 g/L of sodium alginate. When the solution was in contact with 50 g/L calcium chloride solution, ion exchange occurred between sodium and calcium ions. The alginate copolymer chains were then cross-linked by the divalent calcium ions. The alginate then solidified and trapped the MTMC1 molecules within the alginate.

Calcium alginate was made into bead form by extruding the sodium alginate solution through a needle into a solution containing the calcium ions. In particular, the alginate solution was pumped into a manifold with multiple openings. Each opening was regulated by a valve and was connected to a 21 gauge needle at the end. The alginate solution was then extruded dropwise into a calcium chloride bath and the oxidant activator beads were formed in the mildly-agitated bath. This set-up was suitable for both small and large-scale fabrication and required minimal human operation. The resulting beads were spherical and had an average size of 2.02±0.04 mm.

Application and reusability of the oxidant activator in bleaching applications (i) β-carotene β-carotene was used as the model bleaching target to evaluate the performance of the oxidant activator beads, β-carotene is naturally present in most vegetable oils and is one of the compounds giving rise to the colour of the oils, β-carotene solution was prepared by dissolving 50 mg/L of β-carotene into acetone which appeared yellow before bleaching. To bleach β-carotene, oxidant activator beads were added into the β- carotene with a loading of 80 g/L. Hydrogen peroxide solution was then added to a final concentration of 0.6 g/L. After 30 minutes bleaching at 40°C, the colour of the β- carotene faded and gradually became completely colourless. In contrast, in a control experiment in which bleaching was performed using the same hydrogen peroxide concentration but without oxidant activator beads, no change in colour was observed even after 6 hours.

The colour of the β-carotene solutions may also be characterized by their absorbance values. Figure 2 presents the absorbance profiles of β-carotene solutions (at 450 nm) during the bleaching process. When both hydrogen peroxide and oxidant activator beads were present, the absorbance value of β-carotene decreased from an initial value of 0.71 to 0.19 within 30 minutes of bleaching. The absorbance decreased gradually thereafter to 0.12 after an additional 240 minutes. On the other hand, the absorbance value observed in the control experiment only decreased slightly to 0.69 after 450 minutes. The difference in absorbance values corroborates the colour difference of β-carotene described earlier. This observation clearly shows that the oxidant activator beads enhance the bleaching of β-carotene significantly despite the low hydrogen peroxide concentration (0.6 g/L). At such a low hydrogen peroxide concentration, β-carotene was not bleached by hydrogen peroxide alone when no oxidant activator beads were used at relatively low temperature (40-45°C).

For reusability studies, used oxidant activator beads were collected at the end of a bleaching process and were then washed with acetone. To initiate the next cycle of bleaching, the recovered oxidant activator beads were then added into a fresh β- carotene solution containing the same concentration of hydrogen peroxide. The absorbance time profile of β-carotene for each cycle of reuse was similarly plotted in Figure 2. When the oxidant activator beads were reused for the next 3 cycles of bleaching, the absorbance values (at 450 nm) of β-carotene decreased by around 87- 90% to a range of 0.07-0.09 within 30 minutes of bleaching in each cycle. It also took significantly shorter time (30 minutes) for the second bleaching cycle and beyond to achieve the same final absorbance value compared to the time taken during first cycle (> 270 minutes).

This clearly show that the oxidant activator beads could be reused for at least 3 additional cycles of bleaching. Interestingly, the bleaching rates using reused oxidant activator beads were higher than those of the fresh ones. This shows that the bleaching rates is improved when the oxidant activator beads were incubated in acetone prior to bleaching. For confirmation, bleaching was repeated by using fresh oxidant activator beads pre-incubated in acetone and a bleaching rate similar to the one with reused oxidant activator beads was observed. The trapping of acetone within the alginate beads facilitates the migration of β-carotene molecules into the beads since β-carotene is more soluble in acetone than water.

(ii) Soybean oil

The soybean oil by-product during the processing of soybean lecithin is usually discarded or sold cheaply due to the low quality of the oil. This is due to the dark colour of the oil and is aggravated when the oil is exposed to high temperatures (> 100°C). By utilizing the oxidant activator beads, the soybean oil was bleached. This may increase the market value of the soybean oil by improving the colour and thermal stability of the oil. The process consisted of three stages and crude soy lecithin (CSL) was used as the starting raw material.

The first stage separated the hexane-insoluble fraction from the lecithin. CSL was first dissolved in hexane in a volume ratio of 1 :2.5. The solution was then spun in a centrifuge under 18,500xg for 10 minutes. Compounds which were insoluble in hexane such as biomolecules (including soy protein and DNA) were pelletized at the bottom and could be separated. The hexane was then evaporated off to recover the lecithin. The second stage separated the oil from lecithin. The hexane-treated lecithin from the previous stage was dissolved in acetone in a volume ratio of 1 : 10. Lecithin, a phospholipid, was insoluble in acetone and was therefore precipitated while the oil was extracted to the acetone phase. The oil extract was filtered after removing the lecithin solid.

The third stage of the process was to bleach the oil extract in acetone. To prepare for bleaching, oxidant activator beads were incubated in acetone for about 90 minutes. The oxidant activator beads were then added into the oil extract with a loading of 80 g/L. Bleaching started when hydrogen peroxide was added into the oil extract to a final concentration of 6 g/L. Bleaching was conducted at 40-45°C under 250 rpm of shaking. The oil extract turned colourless after 6-7 hours of bleaching. Acetone may be evaporated off if the colourless oil is to be recovered. For comparison, a control experiment was conducted in which oxidant activator were not added. No colour change was observed on the oil extract after the same period of bleaching.

The objective of the first stage of the process was to remove soy proteins and amino acids from the oil. This is because soy proteins and amino acids can react with the reducing sugars naturally present in oil via Maillard reaction. The reaction usually takes place at elevated temperature (140-160°C) and leads to colour darkening of the oil. Thus, it is necessary to remove the proteins and amino acids prior to bleaching to prevent colour darkening when the bleached oil is exposed to high temperature during downstream refining processes.

After extracting the oil from lecithin during the second stage, the oil extract was ready to be bleached in the third stage. To prepare for bleaching, the oxidant activator beads were first incubated in acetone so that the water originally trapped inside the beads was exchanged with acetone. The present experiment showed that the presence of oxidant activator beads improved the bleaching rate by using relatively low concentration of hydrogen peroxide (6 g/L). At such a low hydrogen peroxide concentration, oil extract was not bleached in the absence of oxidant activator beads. This result also showed that the oxidant activator beads could be used in actual oil samples which have a more complex composition than β-carotene solution.

The bleaching process transformed the oil originally in yellow into a colourless liquid with enhanced thermal stability. Only a low amount of hydrogen peroxide was required which also minimized the contamination of oil by hydrogen peroxide. In addition, the bleaching was conducted under a relatively mild temperature (< 50°C) and it was also possible to reuse the solvents (hexane and acetone). Therefore, the soybean oil was bleached in a green and safe way.

Optimisation of oxidant activator bead loading in bleaching of soybean oil extract

To reduce the amount of oxidant activator beads required for bleaching oil extracts, the bead loading used during bleaching was varied from 5 to 80 g/L. The appearance of oil extracts from lecithin with various bead loadings was observed after certain period of bleaching. After 12 hours of bleaching, oil extract samples with 40 g/L of bead loading and above were completely bleached. The oil extract samples with 20-30 g/L of bead loading were partially bleached while those with 10 g/L and below were not bleached. Samples with 20 g/L and 10 g/L bead loadings were bleached completely after 24 hours and 42 hours of bleaching, respectively. However, sample with 5 g/L bead loading still appeared pale yellow after 42 hours of bleaching and was not bleached completely when bleaching was extended for another 36 hours.

These results show that bleaching rate increases with bead loading. Nevertheless, the difference observed among samples with 40 g/L bead loading and above was not significant. Therefore, for comparable bleaching efficiency, the bead loading can be reduced from 80 g/L to 40 g/L. On the other hand, below a certain bead loading (5 g/L in this case), the oil extract was only partially bleached even after an extended period of bleaching (> 75 hours). This proves that a minimum amount of oxidant activator beads needs to be present to completely bleach the oil extract.

Whilst the foregoing description has described exemplary embodiments, it will be understood by those skilled in the technology concerned that many variations may be made without departing from the present invention.