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Microwave drying offers a cost-effective means of recovering delicate, high-value powder products from liquid slurries. Solvents are fully recoverable, too. |  ong drying times, low product yields and high capital and running costs plague many production processes in the fine chemical industry. In addition, batch production constrains throughput and increases the risk of exposing operators to hazardous substances.
In the past decade, manufacturers of microwave equipment have tried but failed to address these problems. A wide range of professional engineering skills, a knowledge of the industrial processes and a committed post-installation support service are all required. Collaboration between specialist companies from a number of different disciplines, including expertise beyond that of simple microwave technology, was needed to address issues such as pressure vessel construction and sophisticated computer control.
Only recently has this large-scale challenge been taken up in a CRAFT project(1) by Pro-C-epT, a Belgian company which manufactures and supplies equipment for the powder processing industry.
Powder puff
As well as providing technical expertise, Pro-C-epT co-ordinated the project team of researchers and equipment manufacturers. From the start, the partners recognised that close collaboration between the groups was essential. Using technology and equipment supplied by small specialist firms such as Solvay Duphar, Busch and Sri, scientists at the University of Paris performed tests on small quantities of pigments or food additives dissolved in solvents to characterise the effects of microwaves. The final marketing stage was left to Comber, a leading filter dryer manufacturer with an extensive sales and distribution network.
The partners expect this revolutionary new drying system to attract attention quickly. Pro-C-epT's Managing Director, Marc De Wit, emphasises the need for new technology in liquid product separation. "Many specialised products such as pigments and pharmaceuticals are difficult to process in the conventional way," he says. "We needed to look for innovative methods to overcome the numerous shortcomings of the traditional process." Rapid processing at low temperatures would be particularly valuable for volatile or high-value products, such as pharmaceutical drugs, whose delicate molecular structures are easily damaged.
Microwave drying soon appeared to be a viable option. It was combined with vacuum technology, which allows the process to be conducted in an inert atmosphere, eliminating oxidation and explosion hazard. "The new process also allows for 100% recovery of solvents", De Wit adds, "so they can be fully recycled."
Energy efficiency
Conventional methods rely on a conductive heat source to transfer energy through a container to the slurry - a mixture of product and solvent. By contrast, the new process heats each batch of slurry directly, using microwaves. Energy is specifically and directly applied to the vaporisation of the solvent, leading to significant energy savings and allowing the material to be much more delicately handled. Drying occurs not only on the surface but also within the slurry, considerably reducing the formation of films and crusts. High energy efficiency also makes the recovery of useful materials from many industrial sludges economic for the first time.
Several models have been developed to suit all scales of production. The Mini Microwave Processor (Mi-Mi-Pro) is a lab-scale dryer capable of processing up to three litres of material. Large-scale production requires the Magnetron Nütsche filter dryer (Tro-N-uT) which can deal with up to 400 litres. Software developed by Pro-C-epT not only offers the operator a control interface, but also gathers process data during each batch run.
Perhaps surprisingly, for such a complex development, there were no major setbacks. "We were very
lucky," admits De Wit. "It took two and a half years to develop the first prototype, but everything went smoothly. The biggest difficulty we had was maintaining regular communication between all the different partners." Even patents have not presented a problem - both the Mi-Mi-Pro and Tro-N-uT technology have been patented in several European Union Member States, and Pro-C-epT plans to apply for world-wide patents in the next year. Future prospects
The market potential for a product like this is enormous. "I believe it could win up to 25% of the current world-wide market of $200 million," says De Wit. "It is a specialised niche market, but we certainly foresee great potential." However, he does not expect adoption of such a radically new technology to occur overnight. "It may take years to encourage companies to convert their production processes. Many are understandably conservative, and tend to avoid rapid change."
Nevertheless, the technology is now available when needed, and Pro-C-epT has lived up to its full name - Processing Concept Ltd - by providing the knowledge to develop the world's first microwave drying technology.
(1) CRAFT project CR1460-91 - Drying powders from slurries using microwaves in a single closed vessel.
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