USE OF UTRASOUND AND ACOUSTICS TO CONTROL CRYSTALLISATION

Abstract

The use of ultrasound or acoustics applied at a level below that which causes cavitation to control the energy balance between particles and the liquid phase in a metastable liquid.

Claims

1. A process for the control of crystal formation comprising applying ultrasound or acoustics at a level below that which causes cavitation, including stable cavitation and transient cavitation, to a metastable liquid to thereby control the energy, mass balance, or both between particles and a liquid phase in the metastable liquid.

2. The process according to claim 1, wherein the level of ultrasound or acoustic frequency, power and duration is tailored to promote or supress crystal formation.

3. The process according to claim 1, wherein the ultrasound is employed at an MI level of 0.08 or less.

4. The process according to claim 1, wherein the rate of nucleation, crystallisation, dissolution, or a combination thereof is controlled.

5. The process according to claim 1, wherein a morphology of the crystals formed from the metastable liquid is controlled.

6. The process according to claim 1, wherein a habit of the crystals formed from the metastable liquid is controlled.

7. The process according to claim 1, in which the ultrasound or acoustics is of intensity such that a hydrophone, when detecting sound radiated from the ultrasound or acoustics exposed liquid, shows a signal pattern which is free from broad-band cavitation noise.

8. The process according to claim 7, wherein the ultrasound or acoustics intensity is at a level that a hydrophone when detecting sound radiated from the ultrasound exposed liquid, shows a view with a main signal corresponding with a main radiation frequency and a further signal corresponding with a first subharmonic frequency where an intensity peaks ratio of the further signal and the main signal, AS/AF, is <0.5.

9.-10. (canceled)

11. The process according to claim 1, wherein the ultrasound or acoustics are in a frequency range between f=500/10=50 Hz (Acoustics) and f=3000×5/(100×10−6)=150 MHz (Ultrasound).

12. The process according to claim 1, wherein the ultrasound or acoustics are of peak power flux below 5 kWm.sup.−2.

13. The process according to claim 1, wherein the ultrasound or acoustics are of average power flux below 5 kWm.sup.−2.

14. The process according to claim 1, comprising controlling the crystallisation of triglyceride fats, triglyceride oils, or a combination thereof.

15. (canceled)

16. The process according to claim 14, in which the triglyceride oil is of vegetable origin or animal oil and is selected from the group consisting of animal oils, rapeseed oil, corn oil, soybean oil, cottonseed oil, linseed oil, and olive oil.

17. A process for fractionating a triglyceride fat or oil, which comprises the steps of: a. when the triglyceride fat or triglyceride oil is solid, heating the triglyceride fat or triglyceride oil until no substantial amount of solid triglyceride fat is present in the triglyceride oil, b. allowing the triglyceride oil to cool and to crystallize and controlling the crystallisation by exposing the cooling fat to selective ultrasound or acoustics resulting in a solid fraction,

18. The process according to claim 17 for the preparation of edible emulsion spreads.

19.-20. (canceled)

21. The process according to claim 1 comprising tempering of chocolate.

22. A process comprising de-tempering of chocolate melt during re-work by the application of ultrasound or acoustics power which melts crystal nuclei produced in the tempering operation without heating a liquid oil suspending phase.

23. The process according to claim 1, comprising processing of hydrocarbon liquids selected from fuels, lubricants and waxes.

24.-26. (canceled)

27. A fuel system such as a fuel tank, a fuel tank take-off chamber, or a fuel delivery line close to a location of a feed of fuel to a diesel engine or a heating boiler containing a source of ultrasound.

28.-29. (canceled)

30. The process according to claim 1, for the crystallisation of materials selected from pharmaceutical materials, energetic materials, agrochemicals, semiconductor materials, personal care products, and inorganic materials such as TiO.sub.2 and CaCO.sub.3.

31.-32. (canceled)

33. The process according to claim 1, to control polymer crystallisation from a melt of a material that is being extruded, coated or moulded.

34.-40. (canceled)

Description

[0057] The clustering of molecules in the Metastable Zone is illustrated in FIG. 1 and FIG. 2 illustrates the Metastable Zone Width.

[0058] FIG. 1 shows in Zone 8 solute molecules in solution and shows how the molecules (9) form clusters (10) in the liquid medium (11) which subsequently convert to crystals (12) once a critical nucleus (13) is formed.

[0059] FIG. 2 is a plot of the concentration of a solution against temperature and shows a solution (18) and the metastable zone (19) between kinetic crystallisation [curve 14/15] and thermodynamic dissolution [curve 16, 17] and it is in this zone (19) that ultrasound is applied according to this invention resulting in the control of the number of crystals formed, the size and habit of the crystals and perhaps their morphology,

[0060] The invention is illustrated by reference to the following Example.

[0061] The apparatus used in this Example is shown in the accompanying Figures.

[0062] FIG. 3 is a schematic drawing of the apparatus in which [0063] A Circulating cooling bath [0064] B Sample cell (see detailed figure) [0065] C Clear lid [0066] D Sample under investigation [0067] E Stand (allowing coolant circulation) and magnetic stirrer plate [0068] F 4 wire resistive temperature device (PT-100) [0069] G Ultrasound transducer [0070] H Coolant [0071] J Temperature display and logging [0072] K Amplifier [0073] L Waveform synthesiser [0074] M Magnetic stirrer

[0075] FIG. 4 shows the ultrasound cell B of FIG. 3.

[0076] FIG. 5 is a diagrammatic illustration of the internals of the ultrasound cell showing the cell wall (1) provided with an ultrasound transducer (2) which generates the ultrasound wave (3). The cell is equipped with a magnetic stirrer (4), a temperature probe (5) and means (6) and (7) for the transmission of details of operation of the cell to a data recorder system comprising the temperature display and logging a wave from generator and as shown in FIG. 3 amplifier.

[0077] The sample cell (B) was made of stainless steel and had a RTD centred 15 mm from the top (under the top level of the liquid) and the 2 MHz highly damped ultrasound transducer centred 37.5 mm from the bottom. The thermocouple and the ultrasound transducer were vertically aligned.

[0078] The sample cell dimensions are: [0079] Height: 75 mm [0080] Outside diameter: 66 mm [0081] Inside diameter: 40 mm

[0082] Two sample cells were placed in the same cooling bath, one was connected to the continuous excitation source (waveform generator plus amplifier). The other was not sonicated. The equipment also has the ability to measure the speed and attenuation of sound in the sample and thereby monitor the crystal nucleation process.

[0083] A 15% (w/v) solution of eicosane (99% pure) was made up in a Heptane/Toluene mixture (80/20 v/v), (both 99% pure). Two samples were used in the experiment. Sample 1 was sonicated and Sample 2 was not.

[0084] The samples were stirred using magnetic “flea” stirrers set in reverse mode every 7 seconds.

[0085] The experiment investigated the impact of ultrasound on both the inhibition of crystal nucleation and the “reversing” of the process to dissolve the newly formed crystals. Hence the power levels were adjusted up and down as the sample was cooled.

[0086] The crystallisation or dissolution was observed optically. Qualitative observations were made regarding the crystal sizes and viscosity of the media.

[0087] The samples were cooled from 30° C. to 0° C. at 0.35° C./min. Cooling from 0° C. to −3.5° C. was at 0.15° C./min.

[0088] Observations were made at intervals or when there was a change in sample appearance such as crystal change and/or viscosity change.

TABLE-US-00001 Sample 1 Sample 2 Temp Frequency Power Qualitative Frequency Power Qualitative (° C.) (MHz) (W) Crystals Appearance Viscosity (MHz) (W) Crystals Appearance Viscosity 10.0 — — — Clear Fluid — — — Clear Fluid  8.0 2 1 — Clear Fluid — — — Clear Fluid  7.0 2 1 — Clear Fluid — — large crystals Cloudy Fluid  6.0 2 1 v small crystals Slightly cloudy Fluid — — large crystals V cloudy, opaque Gel  5.8 2 20 — Clear Fluid — — large crystals V cloudy, opaque Gel  4.8 2 20 — Clear Fluid — — large crystals V cloudy, opaque Gel  4.0 2 10 — Clear Fluid — — large crystals V cloudy, opaque Gel  4.0 2 5 — Clear Fluid — — large crystals V cloudy, opaque Gel  3.7 2 4 — Clear Fluid — — large crystals V cloudy, opaque Gel  2.3 2 3 v small crystals Slightly cloudy Fluid — — large crystals V cloudy, opaque Gel  1.5 2 3 v small crystals Slightly cloudy Fluid — — large crystals V cloudy, opaque Gel  1.0 2 5 — Clear Fluid — — large crystals V cloudy, opaque Gel  0.5 2 5 — Clear Fluid — — large crystals V cloudy, opaque Gel  0.0 2 2 v small crystals Slightly cloudy Fluid — — large crystals V cloudy, opaque Gel −0.7 2 5 — Clear Fluid — — large crystals V cloudy, opaque Gel −0.8 2 4 — Clear Fluid — — large crystals V cloudy, opaque Gel −1.2 2 4 — Clear Fluid — — large crystals V cloudy, opaque Gel −1.4 2 3 — Clear Fluid — — large crystals V cloudy, opaque Gel −1.7 2 3 v small crystals Slightly cloudy Fluid — — large crystals V cloudy, opaque Gel −1.7 2 4 — Clear Fluid — — large crystals V cloudy, opaque Gel −2.0 2 3 — Clear Fluid — — large crystals V cloudy, opaque Gel −2.3 2 2 v small crystals Slightly cloudy Fluid — — large crystals V cloudy, opaque Gel −2.5 2 2 v small crystals Slightly cloudy Fluid — — large crystals V cloudy, opaque Gel −2.5 — — v small crystals Slightly cloudy Fluid — — large crystals V cloudy, opaque Gel −2.0 — — v small crystals Slightly cloudy Fluid — — large crystals V cloudy, opaque Gel −0.5 — — v small crystals Slightly cloudy Fluid — — large crystals V cloudy, opaque Gel  1.1 — — v small crystals Slightly cloudy Fluid — — large crystals V cloudy, opaque Gel  1.7 — — v small crystals Slightly cloudy Fluid — — large crystals V cloudy, opaque Gel  2.2 — — v small crystals Slightly cloudy Fluid — — large crystals V cloudy, opaque Gel  3.3 — — v small crystals Slightly cloudy Fluid — — large crystals V cloudy, opaque Gel  3.8 — — — Clear Fluid — — large crystals V cloudy, opaque Gel  4.0 — — — Clear Fluid — — large crystals V cloudy, opaque Starting to move  5.5 — — — Clear Fluid — — large crystals Cloudy, opaque Fluid  7.8 — — — Clear Fluid — — small crystals Almost clear Fluid  9.7 — — — Clear Fluid — — — Clear Fluid

[0089] The following table summarises the observations.

[0090] It should ne noted that the sonicating equipment or cell can be of any desired shape and size to optimise the ultrasound propagation for the particular application. For example, it may be flat, cylindrical or any other shape to provide the best effect. It should also be noted that the liquid my be quiescent, vibrated, stirred or flowed.

Conclusions:

[0091]

TABLE-US-00002 (Sonicated) Not Sonicated) indicates data missing or illegible when filed [0092] 1. Viscosity and crystal size: The visible nature of the crystals were very different. The crystals were qualitatively much smaller in the sonicated Sample 1. The sonicated sample remained completely fluid down to (at least) the lowest test temperature (−2.5° C.). Whereas Sample 2 gelled 1° C. below the Wax Appearance Temperature (WAT) of 7° C. and did not revert to a fluid state until warmed to 5.5° C. Thus the sonicated Sample 1 remained fluid and moveable at least 9.5° C. lower than the non-sonicated Sample 2. It is anticipated that Sample 1 will remain fluid to a much lower temperature. [0093] 2. Inhibition of crystal nucleation: At power levels above 3 watts (W), the selected ultrasound frequency is capable of inhibiting the nucleation of Eicosane in solution as shown by the fact that without sonication the Wax Appearance Temperature (WAT)=7° C. Whereas with sonication it was WAT≤−2.0° C. This gives a Delta-WAT between the samples of 9° C. [0094] 3. Dissolution of crystals: Without sonication: The Wax Disappearance Temperature (WDT) is observed between 7.8° C. and 9.7° C. With sonication the WDT=3.8° C. This gives a Delta-WDT of between 4 and 5° C.

[0095] These results shows that the use of ultrasound at below cavitation frequency can be used to control many aspects of crystallisation from liquids.

[0096] FIG. 6 shows how the invention may be applied to an extruder for the processing of molten thermoplastic materials and shows the end section of an extruder comprising a barrel (25) a screw or screws (20) several extruderzones (21 & 22) and an extrude die (23) provided with an ultrasound transducer (24) at the die which may be cooled.

[0097] In a further embodiment the invention therefore provides an extruder provided with an ultrasound transducer at or close to the extrusion die A transducer may be provided on other moulding equipment such as injection moulding machines and the invention further provides such plastic moulding, coating or film forming equipment provided with ultrasound transducers.