1. A process for extracting pyrethrins from a pyrethrin containing material, which process comprises the steps of:
2. A process according to claim 1 including cooling said second solvent, after evaporation, and removing wax thrown out of solution before said back-extraction step.
3. A process according to claim 1 including, after partially evaporating said second solvent and before back-extracting, the steps of:
4. A process according to claim 3 in which the amount of water in said second solution is 6 to 12% by volume.
5. A process according to claim 1 in which the first solvent is a low boiling petroleum fraction.
6. A process according to claim 1 in which the first solvent is commercial isohexane or n-hexane.
7. A process for extracting pyrethrins from a pyrethrum containing material comprising the steps of:
8. A process according to claim 7 in which the step of extraction into the second solvent is carried out at ambient temperature to 50°C.
9. A process according to claim 8 in which the said extraction is carried out at 35° to 45°C.
10. A process according to claim 7 in which the evaporation is carried out under reduced pressure.
11. A process according to claim 7 including, after partially evaporating said second solvent and before back-extracting, the steps of:
12. A process according to claim 7 in which said methanol is evaporated to about half volume.
13. A process for extracting pyrethrins from a pyrethrin containing material, which process comprises the steps of:
This invention relates to the extraction of pyrethrins from a pyrethrum material, e.g. oleoresins or pyrethrum flowers. By the term "pyrethrins" is meant the active constituents of the insecticide derived from the pyrethrum flower, whilst "non-pyrethrins" are inactive constituents.
Pyrethrins extracts are used in aerosol insect sprays. Such an extract needs to be sufficiently refined as to be light in colour and therefore non-staining in domestic use and also to be non-clogging in relation to aerosol nozzles. We have found an advantageous process for producing a pyrethrins extract which can be operated to produce a light-coloured extract of the above-mentioned type using commercially acceptable, economical amounts of liquids in a relatively small number of steps, an overall economic process thus resulting.
According to the invention a process of extracting pyrethrins from a pyrethrum material comprises extracting the pyrethrins from a solution of the material in a first organic solvent into a second organic solvent containing water and back-extracting the pyrethrins from the second organic solvent containing water into first organic solvent, the partition coefficients of the pyrethrins and non-pyrethrins being adjusted for the back-extraction step so that the pyrethrins are extracted preferentially into the first organic solvent, the second solvent being miscible with water, and the first solvent forming a separate phase with a mixture of the second solvent and water.
The first solvent used in the back-extraction can be the same or different first solvent used in the forward extraction step. Both first and second solvents are, of course, solvents for pyrethrins. The second solvent need not necessarily be miscible in all proportions with water.
The first solvent is a low boiling hydrocarbon solvent with 4 to 8 C atoms and especially a low boiling petroleum fraction e.g., commercial isohexane or n-hexane.
The second solvent is preferably ethanol or methanol. When used, methanol preferably contains 3 to 15% by volume of water and more desirably 6 to 12%. When ethanol is used, it preferably contains somewhat more water than those amounts for methanol.
With methanol as the second solvent and isohexane or n-hexane as the first, a water content for the methanol of less than 5% renders the methanol with water too miscible with the first solvent to effect a good phase separation of the solvents and if the water content is greater than 15% an excessive uneconomic amount of methanol is needed for the forward extraction step.
The invention includes a process in which, as a first step, a solution is made up of the pyrethrum material in the first solvent.
In the invention the said alteration of the partition coefficients permits an economic process to be achieved. The partition coefficients can be altered by evaporation to increase the ratio of water to second organic solvent and/or by cooling. In order to avoid degradation of the pyrethrins it is desirable that the evaporation takes place under reduced pressure. At some stage dewaxing must be carried out. This is most conveniently brought about by the evaporation and/or cooling to alter the partition coefficients and the wax, thrown out of solution, is removed. Dewaxing can, alternatively or in addition, be carried out on making up a solution of pyrethrum material in the first solvent or as a step carried out after the back-extraction. When evaporation is followed by cooling, the evaporation is desirably continued until just above the point at which pyrethrins or wax precipitate. The ensuing cooling will then readily bring about precipitation of the wax. It is convenient to adjust the volumes of solvents used so that reduction to half volume by evaporation represents reaching just above the said point. Water can be added to alter the partition coefficients in addition to evaporation.
A preferable process according to the invention of extracting pyrethrins from a pyrethrum material comprises making a solution of the material in commercial isohexane, counter-current extracting the pyrethrins from the hydrocarbon solution into methanol containing at most 15% water, increasing the concentration of the pyrethrins by evaporation of the methanol, lowering the temperature of the methanol solution and filtering to remove solid materials thrown out of solution, and extracting the pyrethrins into a further quantity of commercial isohexane.
In one aspect of extracting pyrethrins, given by way of example, pyrethrum flowers are extracted into isohexane; if the pyrethrum is available as oleoresins, then these resins are dissolved in the isohexane. The solution is filtered to remove any coarse particles of insoluble matter and is then counter-current extracted with nearly dry (i.e., containing 3 to 15% water) methanol to produce a pyrethrum extract in the methanol layer. After this partitioning has been effected finely divided insolubles and brown colouring matter are left in the isohexane, and the methanol layer which has a clear yellow colour contains practically all of the pyrethrins. The partitioning is carried out at about 40°C.
The temperature for the step of extracting of the pyrethrins from the first solvent into the second solvent can be from ambient to 50°C, and the more preferred range is 35° to 45°C.
The methanol extract from the partitioning is evaporated to about half volume, the evaporation taking place under reduced pressure. As a result, the concentration in the methanol solution of the pyrethrins and the water is doubled, the composition of the methanol layer being changed from about 90% methanol and 10% water to about 80% methanol and 20% water. The concentrated solution is now cooled slowly to about 0°C to crystallise out a clean, almost white wax which contains only a small proportion of pyrethrins. The methanol solution is filtered in order to remove the wax, and the resulting clear methanol solution is then extracted cold with clean isohexane to give a clear, high purity, pale and dewaxed pyrethrins solution which, when evaporated under reduced pressure, yields a dewaxed pyrethrins extract of high strength.
In one form of the process, the methanol solution, after evaporation, is allowed to cool only slightly to crystallise out a very small amount of wax. The warm solution is filtered to remove the wax which is dark coloured and which contains a significant quantity of pyrethrins. The concentrated solution of pyrethrins in 80% methanol is now cooled slowly to about 0°C to crystallise out a further crop of clean white wax which has a negligible pyrethrins content. The methanol solution is again filtered in order to remove the wax and the resultant clear methanol solution is then extracted as before.
The advantage of removing the wax in two stages as described above is that the pyrethrins-containing impurities are removed with the first impure crop of wax crystals, and the pyrethrum content of the wax removed in the first stage is at a sufficiently high concentration to make the recovery of the contained pyrethrins worth while. The second crop of wax crystals is comparatively pure and of such a low pyrethrins content that pyrethrins recovoery is uneconomic, the wax being sold or otherwise disposed of, for further treatment.
The invention will now be further described by way of specific examples.
In a typical process, a dewaxed oleoresin at 33.7% pyrethrins content was dissolved in isohexane to make a 15% solution of the oleoresin in the solvent. This was extracted with four times its own volume of a solution of methanol containing 10% by volume of water, at a temperature of 40°C. The resulting methanol extract contained 56.8% pyrethrins and 43.2% non-pyrethrins in solution and left a residue of 7.3% pyrethrins and 92.8% non-pyrethrins in the isohexane. The methanol solution was evaporated to approximately half volume and cooled to throw down a wax which contained 74.4% waxes and 25.6% pyrethrins. The cold methanol solution was filtered and then extracted with two volumes of isohexane. The isohexane solution was then evaporated under reduced pressure to give a clear yellow extract containing 83% pyrethrins and 17% non-pyrethrins.
In a similar experiment the methanol solution after evaporation was allowed to cool until a pale green wax separated. This was filtered off and found to contain 15.1% pyrethrins. The solution was then further cooled to 0°C when a further crop of white wax was separated and this was filtered off and found to contain only 0.3% pyrethrins.
The step of evaporating the methanol solution is of importance because the increase in the concentration of the pyrethrins in the methanol allows the recovery of an isohexane solution of the pyrethrins of increased strength. Furthermore, the change in the methanol composition resulting from the evaporation alters the partition coefficient of pyrethrins between methanol and isohexane, and causes the extraction of the pyrethrins into the isohexane to take place readily. This is particularly true when the extraction from methanol to isohexane to performed cold. The increased concentration of the methanol extract and its increased water content further permits an efficient and easy dewaxing to be performed with a minimum loss of pyrethrins. It is found that the wax crystals thrown out of the methanol solution on cooling are better formed and easier to remove by filtering, with lower losses of pyrethrins, than the dewaxing achieved by cooling a solution of pyrethrum in isohexane. It is a subsidiary advantage that the wax is free of resinous impurities and has a potential commercial value.
The invention will now be further described, again by way of example, with reference to the accompanying drawing which is a flow sheet of a process of extracting pyrethrins from pyrethrum.
In the drawing pyrethrum in isohexane (as first solvent) is mixed in an extractor 1 with methanol (as second solvent) containing water, and pyrethrins are extracted into the methanol, the temperature being maintained at 40°C. The ratio of the phases is 4:1 by volume of 90% methanol: isohexane. After allowing the two phases to separate, isohexane now containing residue material is withdrawn through line 2 from the extractor and returned to the extraction plant (not shown), whilst the 90% methanol containing pyrethrins is withdrawn through a line 3 to a vacuum still 4.
Here, some of the methanol is vaporised to increase the water content to 20%. The vaporised methanol is condensed in a condenser 5 and is used as a pure methanol feed as is explained below.
The 80% methanol solution of pyrethrins is withdrawn from the still 4 to be cooled to 0°C in a cooler 6 where a coloured waxy residue containing 25.6% pyrethrins in relation to non-pyrethrins precipitates and is separated by a filter 7. The filtrate is a two volume 80% methanol solution and this is fed to a second extractor 8 operating at 20°C to which four volumes of isohexane solution are introduced.
After separation of the phases the isohexane containing 83% pyrethrins in relation to non-pyrethrins is passed to a second vacuum still 9 and the other phase consisting of 80% methanol is recycled being mixed with pure methanol from the condenser 5 to produce the 90% methanol fed to the extractor 1.
Isohexane vaporised in the still 9 is recovered in a condenser 10 and thereafter supplied as a feed to the extractor 8. Product refined pyrethrum extract is withdrawn from the still 9.