ULF PRUESSE AND KLAUS-DIETER VORLOP Institute of Technology and Biosystems Engineering, Federal Agricultural Research Centre, Bundesallee 50, 3SI 16 Braunschweig, Germany - Fax: +49531 5964199 - Email: [email protected]
1. Introduction
Solid particles (pellets, beads) in the size range between /-lm and mm play an important role in various industries like biotechnology, agriculture, chemical, pharmaceutical and food industry. Thus, plenty of particle production technologies exist and their further development is of major interest both from the economic and scientific point of view.
Generally, single and discrete solid particles may be produced by three different approaches: • From larger solid entities by grinding, • from smaller solid entities by agglomeration, granulation, pressing or tabletting
- small fluid entities may also be used if in-situ drying is applied -, or • from fluid entities in the same size range in addition with an immediate
physical or chemical solidification step. Despite the necessity to be produced in industrial amounts, in recent years, solid particles are more and more required to have an ideal spherical shape as such beads are much easier to dose, pose less danger to humans and equipment during manufacturing (less respirable dust resulting from abrasion and lower explosion risk) and last but not least, look much nicer from an aesthetic point of view, which is very important if the beads are part of a final product.
From the three different approaches named above, the third one, in principle, is best suited for the production of ideal spherical beads, since only by this approach the solid bead has been a more or less equally sized liquid droplet - which is perfectly round due to the surface tension - directly prior to its solidification. Correspondingly, numerous different techniques exist which use the principle of generating a droplet which immediately afterwards is solidified to a spherical bead by physical means, e.g. cooling or heating, or chemical means, e.g. gelation, precipitation or polymerisation. These techniques include emulsion techniques, simple dropping, electrostatic-enhanced dropping, jet break-up (vibration) or rotating disc and rotating nozzle processes. Some of them, e.g. dropping and vibrational techniques are especially useful for lab-scale applications, whereas others, e.g. rotating disc and nozzle techniques and to some extent also the vibration technique, may also be used for large-scale applications. Anyway, all
techniques have in common that the fluids , which are processable, have to be low in viscosity. Further, these techniques either allow monodisperse beads to be produced in small quantities or beads with an undesired broad size range to be produced in large quantities, but none of these processes enables the production of monodisperse beads in large quantities.
A new and simple technology for bead production that meets the requirement of producing monodisperse beads with a high production rate is the JetCutter technology. This technique is especially capable of processing medium and highly viscous fluids up to viscosities of several thousands mPas. Monodisperse beads originating from solutions, melts or dispersions in the size range from approx. 200 11m up to several millimetres are accessible. Therefore, the JetCutter is not only a valuable completion to the palette of bead production technologies but might even have a great potential to replace existing technologies.
2. Principle of function
For bead production by the JetCutter the fluid is pressed with a high velocity out of a nozzle as a solid jet. Directly underneath the nozzle the jet is cut into cylindrical segments by a rotating cutting tool made of small wires fixed in a holder. Driven by the surface tension the cut cylindrical segments form spherical beads while falling further down, where they finally can be gathered (Figure 1).
Bead generation by JetCutting is based on a mechanical impact of the cutting wire on the liquid jet. This impact leads to the cut together with a cutting loss, which, in a first approach, can be regarded as a cylindrical segment with the height of the diameter of the cutting wire. This segment is pushed out of the jet and slung aside where it can be gathered and recycled. The losses will be described in detail later.
Figure 1. Scheme of the cutting process, simplified model.
As only a mechanical cut and the subsequent bead shaping driven by the surface tension are responsible for bead generation, the viscosity of the fluid has no direct influence on
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the bead formation itself. Thus, the JetCutter technology is capable to process fluids with viscosities up to several thousands mPas.
The size of the beads can be adjusted within a range of between approx. 200 /lm up to several millimetres. The main parameters are the nozzle diameter, the flow rate through the nozzle, the number of cutting wires and the rotation speed of the cutting tool. In order to get narrowly distributed beads one has to take care of a steady flow through the nozzle and an uniform rotation speed of the cutting tool.
3. Description of the JetCntter device
3.1. GENERAL EQUIPMENT
A JetCutter device consists of five central elements: • Pump or pressure vessel, • solid jet nozzle, • cutting tool, • motor, • spraying shield. The first element is related to fluid feeding. This may be achieved either by using a pressurised vessel or a simple storage tank connected to a pulsation-free pump, e.g. a screw pump, and the necessary tubes ending up inside the nozzle. Special attention has to be paid to ensure a steady flow through the nozzle.
A major requirement for the JetCutter is that a solid jet is formed. Therefore, special solid jet nozzles have to be applied which are commercially available. Not the whole particle size range (200 /lm up to several millimetres) is accessible with only one single nozzle diameter. Thus, nozzle diameters ranging from some tens of microns up to a few millimetres have to be applied to cover the whole size range. Even if solid jet nozzles are used, the liquid jet disintegrates after a certain length. This length depends on the viscosity and velocity of the fluid. In order to ensure a perfectly shaped jet at the point where it is cut by the wires, the cutting tool should not be too far away from the nozzle outlet, e.g. only a few millimetres (Figure 2, left).
The cutting tool itself is the major part of the whole JetCutter device. It is very important that the cutting wires are equally distributed around the tool in order to produce beads of the same size. This is best achieved by a circular stabilisation of the wires on the outer perimeter (Figure 2, right). This circular stabilisation is even essential if the wire diameter is reduced in order to decrease the cutting losses. Therewith, the diameter of the cutting wire may be decreased down to 30 /lm. Usually, stainless steel wires are used but the application of polymer fibres is also practicable.
A circular stabilisation of the wires is not necessary for cutting wire diameters larger than 300 /lm. Such large wire diameters seem to be detrimental as far as the losses are concerned but, nevertheless, are necessary for the production of larger beads. As a rule of thumb it can be said that small wires are to be used for the production of small beads, as they cause only small losses and do not transfer such a large impulse to the liquid jet than thicker wires would do, which would lead to a serious deflection of the beads. Thick wires have to be used for the production of larger beads, as smaller ones are not
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able to cut a thick liquid jet into separate segments, since, in this case, the liquid jet flows together again after the wire has passed it.
Figure 2. Arrangement of nozzle and cutting tool (left); cutting tool with 48 stainless steel wires (0 = 50 j1m) and circular stabilisation (right); 0 = diameter.
Another central part of the JetCutter device is the motor, to which the cutting tool is mounted. No special care has to be taken concerning the motor unless it is capable to maintain a constant rotation speed. Usually between 3000 and 12000 rpm (rotations per minute) are used for bead production. The motor with the cutting tool may be inclined up to 70° with regard to the nozzle in order to reduce the losses (see section 4).
The spraying shield surrounds the cutting tool. Its task is to collect the losses, which were slung aside by the cutting tool. If necessary, the losses may be recycled through a drain inside the spraying shield's channel. The shield also covers the rotating cutting too\, which is important for safety reasons.
3.2. SPECIAL EQUIPMENT
The general equipment described before is sufficient for the production of beads from a broad variety of fluids, like polymer solutions, sols and dispersions. Nevertheless, for some applications special equipment is needed, e.g.: • A spraying tunnel for larger beads, • a heating device for melt processing, • a 2-fluid nozzle for simultaneous coating. The high fluid and therefore bead velocity is one of the advantages of the JetCutter, as high throughputs are easily realised. Nevertheless, this high droplet velocity is a problem regarding the collection of beads with a spherical shape, especially for larger beads. If the droplets were collected in a collection bath, e.g. a CaCl2 bath for alginate beads, the droplets may be deformed at the liquid surface when entering the bath. For small droplets the problems are minor even at speeds of up to 30 mls. However, larger droplets, which have such high speeds, will be deformed at the collection bath surface due to their higher weight.
In order to overcome this problem, the droplets have to be pre-gelled prior entering the collection bath. This pre-gelation is achieved by letting the droplets fall through a tunnel (5 m length) equipped with several spraying nozzles (Figure 3, left and middle). The hardening solution from the collection bath is permanently pumped through the spraying nozzles, which generate a fine mist (aerosol) of the hardening solution inside
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the tunnel. During falling, the spherical droplets are covered with the mist and, thus, are pre-gelled maintaining this spherical shape. The pre-gelation hardens the droplets - in fact they are no droplets anymore but capsules - so that they maintain their spherical shape when they enter the collection bath.
spmylng nonle
~Jetcult.r • •
collection bath
Figure 3. Scheme of the 5 m spraying tunnel (leji); photo of the combined spraying/cooling tunnel (middle); photo of the heating device surrounding the JetCutter. the heating device sits on top of the 5 m tunnel.
Another special equipment is needed for the processing of all kinds of hot material, which might be melts, e.g. waxes, or hot solutions, e.g. gelatin solutions. In order to process such materials not only thermostated tanks, vessels, pumps and tubes have to be used but also the nozzle and the cutting tool have to be heated to avoid clogging. Therefore, the JetCutter has to be surrounded by a heating chamber (Figure 3, right).
The heated JetCutter sits on top of the 5 m tunnel, which in this case acts as cooling line. This cooling line is sufficient to harden small beads, which have high velocities. In order to harden also larger beads, the top of the tunnel might be additionally equipped with a device to distribute cold gas inside the tunnel.
For some applications a one-step coating process is desired, in which one substance has to be coated by another and the spherical shape is maintained. Such coated particles can be applied for protection of sensitive substances, for controlled release systems, for taste masking or for the encapsulation of liquids. Common pharmaceutical coating technologies do not cover all applications, e.g., they are not well suited for the encapsulation of liquids. In these cases dropping or vibration techniques with a 2-tluid-nozzle are often applied. These nozzles generally consist of a central cannula which is assigned to the core liquid and that is surrounded regularly by a second annular nozzle, which is assigned to the coating liquid. The Jet Cutter
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technology can also be used for simultaneous coating procedures by using a 2-fluidnozzle (Figure 4, left).
So far, only preliminary experiments have been carried out concerning this topic. As model system the encapsulation of common vegetable oil inside calcium alginate beads has been investigated. For a better visualisation the oil has been coloured with charcoal. The coloured oil has been used as core liquid whereas a 2% sodium alginate solution has been the coating liquid. The beads have been gathered in a 2% calcium chloride solution, where ionotropic gelation of the alginate with the calcium ions has occurred finally leading to calcium alginate coated oil beads (Figure 4, right). Thus, in principle, the JetCutter can be used for one-step coating processes, but due to the small number of experiments carried out so far, no general conclusion can be drawn, yet.
Figure 4. Photo of the 2-jluid nozzle used with the JetCutter (left); Ca-alginate coated vegetable oil beads produced with the JetCutter (right). the oil has been coloured with charcoal.
4. Model of the cutting process
Bead generation by JetCutting is achieved by the cutting wires, which cut the liquid jet coming out of a nozzle. Each cut leads to a cylinder, which afterwards becomes a bead, and a cutting loss (Figure 1). The cutting losses, although minor in their extent as it will be shown later, serve very well as a parameter to discuss the whole cutting process.
Usually, beads of a definite diameter are required. Such beads may be produced with plenty of different sets of parameters, which are the nozzle diameter, the cutting wire diameter, the number of cutting wires in the cutting tool, its rotation speed and the flow rate through the nozzle. In a first simple geometrical approach the influence of the nozzle and the cutting wire diameter shall be discussed.
Beads of a definite diameter can be produced by JetCutting with different nozzle diameters. This means that either short and thick or long and thin cylinders are cut from the jet. By adjusting the right parameters both cylinders have the same volume and, thus, the resulting beads have the same diameter. Obviously, these different ways of cutting, i.e. the nozzle diameter, will have a significant influence on the resulting cutting losses as it is displayed in Figure 5.
Figure 5 clearly demonstrates that the losses dramatically decrease with decreasing nozzle diameter, i.e. if longer and thinner cylinders are cut. Depending of the rheological behaviour of the fluid it is possible to get beads from cut cylinders having a
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length that is up to 30 times their diameter. The diameter to length ratios shown in Figure 5 range from 1 :0.7 (left) to 1: 10 (right).
It is even more obvious that the diameter of the cutting wire has an influence on the cutting loss, which is shown in Figure 6. Unfortunately, it is not possible just to always use very small cutting wires. As already mentioned, very small wires are not able to cut thick liquid jets, because the liquid flows together again after the wire has passed it. As a rule of thumb the diameter of the cutting wire should have at least 1110 of the liquid jet's diameter.
1.1 1.9
37.8% 27.8% 17.8 %
0 1.0
4.2
8.8 %
nozzle
liquid jet
cutting wi re & cutting loss
bead-building volume
losses
resulting bead
Figure 5. Influence of the nozzle diameter on the cutting losses, unless othelWise written the unit for all numbers is mm, cylinder height is displayedfor the bead-building volume.
5.1 % 9.8 % 14.0 %
0 1.0 0 1•0 0 1.0
nozzle
liquid jet
cutting wi re & cutting loss
1.9 bead-building
17.8 %
0 1.0
volume
losses
resulting bead
Figure 6. Influence of the diameter of the cutting wire on the cutting losses. unless othelWise written the unit for all numbers is mm, cylinder height is displayed for the bead-building volume.
At first view the cutting process according to this geometrical model is very simple. Nevertheless, at second view the cutting process is more complicated. As discussed so far the cutting process is idealised and only valid if the velocity of the cutting wire is much higher than the velocity of the liquid jet. Actually, these two velocities are in the same range so that the progressive movement of the liquid jet has to be taken into account for a proper description of the cutting process (Figure 7).
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Figure 7 shows both a locally and temporally resolved scheme of the cutting process. On the very left hand side, the liquid jet and the positions of the cutting wires at the different times t, to ts (cutting plane) in relation to the liquid jet are shown. Further to the right, the progressive movement of the jet is shown at each time (t, -s) as wen as the actual position of the cutting wire at that time (black circle). Blank circles indicate prior and subsequent positions of the wire. The cutting loss that is pushed out of the jet is also displayed.
In case of a vertical nozzle and a horizontal cutting plane (Figure 7 , top) it can be seen that the progressive movement of the liquid jet during the cutting process leads to a diagonal cut through the liquid jet. Accordingly, a proper inclination of the cutting tool should lead to a straight cut through the jet (Figure 7, bottom).
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Figure 7. Locally and temporally resolved schematic representation of the cutting process for a horizontal cutting plane (top) and an inclined cutting plane (bottom), actual position of the cutting wire: black circles, former and future positions of the cutting wires: blank circles, cutting loss: dark grey, liquid j et: bright grey, t = time.
Figure 7 displayed that the progressive movement of the jet during cutting leads to a diagonal cut through the liquid jet. Thus, the cutting loss has a somewhat ellipsoidal shape - and is therefore larger than it is in the idealised model in Figure 5 and 6 - and the cut cylinders are distorted (Figure 8). Further, it is imaginable that the ends of the distorted cylinders might be torn off from the rest of the cylinder and form the so-called additional spraying losses. In that case the overall losses generated by the mechanical cut through the liquid jet would be quite high. Nevertheless, it is also shown in Figure 8 that a proper inclination either of the cutting tool or the nozzle leads to a straight cut through the jet with the 'normal ' cutting loss and no additional spraying losses.
On the basis of this more sophisticated geometrical model a set of equations displayed in Table 1 has been derived which is capable of describing the cutting process both for a perpendicular arrangement of nozzle and cutting plane (horizontal cutting plane) as wen as for an inclined arrangement (inclined cutting plane).
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One of the most important parameters for the JetCutter is the ratio of the velocities of the fluid (Ujluid) and the cutting wire (UlVire)' It determines the cutting angle f3 as well as the proper inclination angle a. It can be taken from Table 1 that for a horizontal cutting plane, the cutting angle not only influences the losses but also the bead diameter, as the bead-building volume is decreased by the additional spraying losses (see also Figure 8). For an inclined cutting plane, the overall losses are the same as the cutting losses, because no additional spraying losses are formed.
o ,~ ,
Figure 8. Possible arrang ments of nozzle and CUlling tool. from leJi to right: perpendicular arrangement, inclined cutting tool, inclined nozzle.
Table 1. Mathematical model for the cutting process (for details see [1-2]); V loss = volume of the cutting loss, V'IOSS = volume of the overall loss, dw;" = CUlling wire diameter, D = nozzle diameter, n = number of rotations. z = number of CUlling wires. dbead = bead diameter; for other abbreviations see text.
Table 2 shows the check-up of the model. Here, the experimental values of the overall losses during the production of PV A beads in dependence of the diameter of the cutting wires used are displayed. Two sets of experiments are shown, one with a horizontal cutting plane (cutting losses and additional spraying losses) and one with a properly inclined cutting plane (only cutting losses). For comparison, the theoretical values according to the equations in Table 1 are also given.
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Table 2. Overall losses .lor horizontal and inclined cutting plane in dependence on the diameter of the cutting wire, Exp. = experimental, Calc. = calculation.
Wire dia l11eter. Overall l o~es, % 111111 Hori zontal clIllinJ!. plane Incl ined culling plane
Table 2 offers three important bits of information: • The losses decrease if a proper inclination is applied. • Experimental and theoretical values are in good agreement, so that the model
is suited to describe the cutting process. • By using small cutting wires and an inclined cutting plane, the losses can be
decreased down to less than 3%, which means that more than 97% of the initial liquid is transformed into monodisperse beads. Such low losses are tolerable; no loss recycling has to be applied.
Anyway, although the model is able to describe the process in terms of losses and also the resulting bead diameter, it is still a model. Thus, it is not really surprising that reality still looks different (Figure 9).
Figure 9. High-speed images of the cutting process during the production of alginate beads, lefl: high wire velocity and low fluid velocity = small beads. right: low wire velocity and high fluid velocity = large beads.
In Figure 9, two photos of the cutting process taken with a high-speed camera are shown. In both cases a horizontal cutting plane has been applied. It is obvious that the cut segments do not really have a cylindrical shape. Nevertheless, these segments are able to form spherical beads after a short way (Figure 9, left). Regarding the losses, there is a bend end of the cut segment at its top, but it is almost still in contact with the cutting wire, which pulls it from the cut segment like if it was molten cheese (Figure 9, right). But still in this case beads are formed after a while. Anyway, these photos clearly indicate that there is still a lot of work to do in order to fully understand the process of bead formation by JetCutting.
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S. Throughput and scale-up
A necessary requirement for bead production in JetCutting is that really a solid jet is pressed out of the nozzle and that this solid jet is maintained until it is cut by the wires. This can be achieved with a combination of special solid jet nozzles and a high fluid velocity (up to 30 m/s), the latter with corresponding high flow rates. Due to the solid jet requirement, the flow rate per nozzle is considerably higher for the JetCutter than for any other bead production technology [3].
The throughput of the JetCutter is best described by the cutting frequency. It determines how often the jet is cut in a definite time period and, thus, how many beads are generated in that time. The cutting frequency is the product of the number of cutting wires in the cutting tool and its rotation speed. Usually, the JetCutter is used with cutting frequencies between 5000 and 10000 Hertz (Hz) (current maximum 14400 Hz), what means that 5000 up to 10000 beads per second are generated. As a rule of thumb it can be said that the higher the viscosity of the fluid is and the smaller the beads size shall be, the higher the cutting frequency might be.
The production rates of a single nozzle JetCutter device for common cutting frequencies are shown in Table 3. The rates are given in terms of L/(h·nozzle). Table 3 indicates that, depending on the desired particle size, even with a single nozzle JetCutter device and common cutting frequencies, the production rate per day can range between a kilogram and several tons of beads.
Table 3. Theoretical throughput of the JetCutter in U(h·nozzle) for different bead diameters and cutting frequencies (5000. 7500 and 10000 Hz).
Figure 10. Scheme ofa multi nozzle JetCutter operating without additional spraying losses.
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Anyway, sometimes these throughputs might not be sufficient, so that a further scale-up is necessary. Generally, for the JetCutter technology two ways of scaling-up are possible. First, a multi-nozzle JetCutting device can be applied, in which the nozzles are staggered near the perimeter of the cutting tool [3]. In this case, special attention has to be paid to avoid additional spraying losses. If a horizontal cutting tool is used with vertically arranged nozzles considerable amounts of additional spraying losses will be obtained, which, of course, is undesirable. The application of an inclined cutting tool, although perfectly suited for a single-nozzle system, is not much better since the additional spraying losses can only be avoided at one single site on the circuit, whereas on the opposite side of the circuit these losses would be even higher than usual. The problem can be solved only if properly inclined nozzles are used together with a horizontal cutting tool. With this arrangement the additional spraying losses can be avoided at any site on the cutting tool's circuit (Figure 10).
The second way for a JetCutter scale-up is the increase of the cutting frequency. A further enhancement of the cutting frequency will be achieved when a motor drive with a higher rotation speed and a cutting tool with more wires are used. Cutting frequencies of up to 25000 Hz are within range. This approach needs not only higher rotations speeds but also a higher throughput per nozzle, which means a higher velocity of the jet and the beads. As already mentioned, the high speed of the beads might cause problems, as they might be deformed when they enter a collection bath. Thus, this approach might only be successful for some special applications.
6. Applications
Since spherical beads are intermediates or products in different industrial sections, e.g. pharmaceutical, chemical and food industry, biotechnology, agriculture, many applications exist for the JetCutter technology. Generally, each application field has its own requirements and restrictions concerning the materials to be encapsulated, the type and viscosity of the fluid, the desired particle size or the medium in which the beads should be gathered. In this connection it is advantageous that the JetCutter is capable to process all kind of liquid material covering • Solutions (alginate, pectinate, chitosan, cellulose derivatives, polyvinyl alcohol
(PV A), gelatin, carrageenan), • melts (waxes, polymers, sugars, sugar alcohols) and • dispersions (emulsions, suspensions, inorganic sols). Usually, something is encapsulated inside the beads in order to get a formulation of an active agent, a controlled-release system, a protection against impacts from the environment, a taste-masking system or an immobilised catalyst. Such substances might be: • Catalysts (enzymes, bacteria, fungi, chemical catalysts), • active agents (pharmaceuticals, pesticides), • ingredients (vitamins, amino acids, probiotics), • aromas and fragrances, • pigments and dyes, • particles (titanium dioxide, zirconium dioxide, magnetite).
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Some examples of beads of pure polymer solutions as well as some encapsulated substances produced with the JetCutter are displayed in Figure 11.
Figure 11. Photos of different types of beads prepared by Jet CUlling (not in true scale). From top left to bollom right: Ca-alginate (0 = 0.6 mm). bacteria in Ca-alginate. ji"eezedried (0 = 0.3 mm). vitamin in Ca-pectinate (0 = 0.5 mm). chitosan (0 = 0.5 mm). gelatin (0 = 0.8 mm). wax (0 = 0.7 mm). PVA (0 = 0.5 mm). 20 % magnetite in chitosan (0 = 0.8 mm). 40 % Ti02 in alginate (0 = 1.3 mm).
As already mentioned, one of the major advantages of the JetCutter is that the viscosity of the fluid does not limit bead generation. That means that not only the formulation recipes used at the moment can be applied to bead production by JetCutting but also those whose transformation into products failed due to a too high viscosity. For the same reason biological matter can be treated at lower temperatures, i.e. more carefully, with the JetCutter since heating for viscosity reduction is not needed. Further on, encapsulation matrices originating from solutions with a high polymer content and corresponding high viscosities generally form mechanically superior beads. This is especially advantageous for the production of immobilised biocatalysts [4-8]. For this purpose encapsulation matrices based on polyvinyl alcohol (PV A) are particularly suited, as PV A hydrogels are very stable, do not show any abrasion and are not biodegradable. Such beads were also successfully used for the encapsulation of metal catalysts [9].
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7. Summary and prospect
Solid particles (pellets, beads) in the size range between 11m and mm play an important role in various industries like biotechnology, agriculture, chemical, pharmaceutical and food industry. Thus, plenty of particle production technologies exist. Some of them, like simple dropping, electrostatic-enhanced dropping or vibration are especially suited for lab-scale applications, others, like rotating disc and nozzle technologies and to some extent also the vibration technique, are also suited for technical applications.
With all these technologies either monodisperse beads in small amounts or broadly distributed beads in large amounts may be produced and all these technologies are limited concerning the viscosity of the fluids, which can be processed.
The only technology so far, which is able to transform not only low viscosity but also highly viscous solutions into monodisperse beads, is the JetCutter. The bead size, which is accessible by the JetCutter, range between approx. 200 11m up to several millimetres. The throughput is suited both for lab-scale and technical scale applications. The principle of function and the equipment is rather simple, which makes the JetCutter quite attractive for industrial purposes.
A mathematical model of the cutting process exists, which is able to describe very well the bead formation in dependence of the main parameters. Vice versa, suitable parameters can be estimated from this model in order to produce the desired beads.
Bead generation by JetCutting is not possible without the production of losses. Quite a lot has been written about the losses. It is necessary to point out that the reason for that is that the losses are very well suited to describe the whole cutting process and not that the losses are so important. In fact, the losses can be entirely regarded as negligible -less than 2% - if the JetCutter is run in the right way.
The JetCutter technology is of interest for different industries, like pharmaceutical, chemical and food industry, biotechnology or agriculture. As a broad variety of solutions, melts and dispersions are processable, the JetCutter is useful for manifold applications such as the formulation of active agents, the preparation of controlledrelease and taste-masking systems, the encapsulation of ingredients or the immobilisation of (bio-) catalysts [10].
None of the other technologies for bead production shows this sum of advantageous characteristics as the JetCutter does. It is, at least, an alternative and completion to other techniques. Whether it is even more will be seen during the next years. Although the JetCutter is a quite novel technology, the fIrst industrial scale bead production process based on the JetCutter technology has already started in summer 2002.
References
[1] Pruesse, D.; Fox, B.; Kirchhoff, M.; Bruske, F.; Breford, J. and Vorlop, K-D. (1998) New process (JetCutting method) for the production of spherical beads from highly viscous polymer solutions. Chern. Eng. Technol. 21: 29-33.
[2] Pruesse, D.; Bruske, F.; Breford, J. and Vorlop, K-D. (1998) Improvement of the JetCutting method for the preparation of spherical particles from viscous polymer solutions. Chern. Eng. Technol. 21: 153-157.
[3] Pruesse, D.; Dalluhn, J.; Breford, J. and Vorlop, K-D. (2000) Production of spherical beads by JetCutting, Chern. Eng. Technol. 23: 1105-1110.
[4] Pruesse, D.; Fox, B.; Kirchhoff, M.; Bruske, F.; Breford, J. and Vorlop, K-D. (1998) The JetCutting method as new immobilisation technique. Biotechnol. Tech. 12: 105-108.
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[5] Muscat, A; Pruesse, D. and Vorlop, K.-D. (1996) Stable support materials for the immobilisation of viable cells. In: Wijffels, R.H.; Buitelaar, R.M.; Bucke, C. and Tramper, 1. (Eds.) 1nunobilized cells: Basics and applications. Elsevier Science, Amsterdam (The Netherlands); pp. 55-61.
[6] Leidig, E.; Pruesse, D.; Vorlop, K.-D. and Winter, J. (1999) Biotransformation of poly R-478 by continuous cultures of PV AL-encapsulated Trametes versicolor under non-sterile conditions. Bioprocess Eng. 21: 5-12.
[7] Reimann, C.; Pruesse, D.; Welter, K.; Willke, Th. and Vorlop, K.-D. (1997) Stoffkonversion nachwachsender Rohstoffe durch einschlussimmobilisierte Biokatalysatoren (in German). VDI-Berichte 1356: 211-214.
[8] Jahnz, u.; Wittlich, P.; Pruesse, D. and Vorlop, K.-D. (2001) New matrices and bioencapsulation processes. In: Hofman, M. and Thonart, P. (Eds.) Engineering and manufacturing for biotechnology, Volume 4; Hofman, M. and Anne, J. (Ser. Eds.) Focus on biotechnology. Kluwer Academic Publishers BV, Dordrecht (The Netherlands); pp. 293-307.
[9] Pruesse, D.; Morawsky, V.; Dierich, A; Vaccaro, A and Vorlop, K.-D. (1998) Encapsulation of microscopic catalysts in polyvinyl alcohol hydrogel beads. In: Delmon, B.; Jacobs, P.A; Maggi, R.; Martens, J.A; Grange, P. and Poncelet, G. (Eds.) Studies in Surface Science and Catalysis, Volume 118, Preparation of Catalysts VII. Elsevier Science, Amsterdam (The Netherlands); pp. 137-146.
[10] Pruesse, D.; Jalmz, D.; Wittlich, P.; Breford, J. and Vorlop, K.-D. (2002) Bead production with JetCutting and rotating disc/nozzle technologies. Landbauforsch. Volkenrode SH 241: 1-10.
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