Processes for custom-made powders
Although Hosokawa Micron B.V. is particularly well known for its mixing and drying systems, it actually offers much more technology for making custom-made powders. The company develops complete processes which enable customers to give their end products the desired properties directly.
Doetinchem-based Hosokawa Micron has a long-standing reputation for a wide range of mixing and drying systems based on the Nauta® conical screw mixer. These systems have earned their stripes over the past decades in a multitude of applications in numerous industrial sectors. Hence, the company has built up a wealth of experience in the processing of almost every raw material imaginable. This has resulted in a strategy of product diversification, with the company developing technology for a whole host of new applications.
Hosokawa Micron’s current product range facilitates the setup of complete factories so that customers can give their end products the desired properties directly. In these production lines, the raw materials and products are not only subjected to mechanical and/or physical treatment (such as mixing, drying and impregnation), but are also exposed to chemical processes (such as high-temperature reactions or polymerization).
Polymerization, metal coating and crystallization are just a few examples of high-temperature processes. Hosokawa Micron has responded to market demand for these kinds of processes by developing various processing equipment including the conical paddle mixer (CPM) and the conical paddle dryer (CPD). Just like the Nauta mixers, all these pieces of equipment have a wide range of uses and the product can be discharged quickly, efficiently and completely. However, what makes the CPM and CPD different from the conventional Nauta mixer is that they only have one drive unit. This reduces the construction complexity of the high-temperature systems. As a result, models are available with useful volumes of up to 10,000 liters for product temperatures of up to 325°C. Apart from the double-walled versions, the CPM and CPD can be adapted for specific applications, irrespective of whether atmospheric, overpressure or vacuum processes are required. Construction materials, bearings, gaskets and seals can be aligned with the process requirements.
In view of the strong market growth for both biodegradable polymers and strong fibers, Hosokawa Micron is increasingly being asked to provide solutions for the polymerization process. Polymers are commonly synthesized in a mixer in which liquids react with one another. This often means that the resulting polymer (a solid substance) has to be dried. A Nauta vacuum dryer is an excellent solution, especially when the liquid (the monomer) can be reused and its boiling point is higher than the polymer’s melting point. This enables the monomer, which is usually toxic and highly flammable, to be separated off and then recovered in a condenser without loss of quality. Hosokawa Micron has already supplied various 16m³ vacuum dryers for polymerization processes of this kind. If higher capacities are required in continuous processes, the disc dryer can be used.
A single system
It is sometimes essential that the polymers being produced have a consistent quality and are completely free of contamination. In such cases, it is a significant advantage if the consecutive process steps can be performed in a single system, i.e. without having to be moved to a different machine. Hosokawa Micron has achieved such a process for a certain customer in a vacuum dryer with a special rotor. During synthesis of the polymer in question, an alcohol forms which is rinsed away using a liquid chemical. Furthermore, the mixer contains other liquids in addition to the synthesized polymer. These liquids (80% of the mixture) are heated under vacuum to evaporate them. At the end of this process, the product temperature is raised gradually which not only removes the remaining liquid but also ‘cures’ the product.
Hosokawa Micron processing equipment is also used for the production of heterogeneous catalysts, which are support materials or carriers impregnated with active compounds. Molecules temporarily adhere to these compounds and hence become reactive. Once the molecules have reacted, the catalyst remains behind. Theoretically it is unchanged, but in practice catalysts slowly become contaminated with reactants, meaning that they have to be replaced regularly. Typical process steps for the production of a heterogeneous catalyst include the preparation of the support material, the impregnation of the carrier with ‘active groups’ and the regeneration of the catalyst.
The catalyst support is usually a solid substance with a high surface area. Typical support materials include zeolites and carbon, aluminum or silicon compounds. The production of these substances involves mixing, drying and homogenization. For example, an alumina catalyst (for refining oil) is dried using a spray dryer. This entails feeding in the material in slurry form, which requires a lot of vaporization heat. However, it is also possible to use the Hosokawa Micron DMR-H flash dryer instead of a spray dryer. This system can be fed with slurries but also with pastes or filter cakes. Therefore the slurry can be mechanically dewatered first, making this approach much more energy efficient than thermal drying.
The actual catalytic compound (the ‘active groups’) is applied to the support material. In many cases this is a solution of a metal salt derived from vanadium, cobalt, platinum or nickel. The impregnation of the support material with these solutions utilizes mixing and drying processes, and Nauta mixers and vacuum dryers achieve excellent results. The solution is injected into the support material directly in front of the mixing screw to ensure that the active ingredient is homogeneously distributed on the carrier. The product can then be dried and the solvent can be recovered. This process is performed gently so as not to damage the product and to leave both the activity and the selectivity of the catalyst intact. Other options in these processes include the calcination of the catalyst, drying under inert atmosphere and the addition of oxygen to passivate the metals on the carrier.