Drying of Difficult Materials
Figure 1: Foaming and very high viscosities make it difficult to recover TDI from distillation residue. LIST KneaderReactor technology handles the viscous and pasty residue with ease, recovering all the TDI and discharging a free-flowing dry product.

A Single Solution for Multi-Phase Drying

Using conventional solutions, the drying of multi-phase material is both costly and imperfect. The limitations of the technology require that the material be transferred to different pieces of equipment as it transitions from phase to phase during the drying process: from thin to viscous to powdery. Each phase requires a different machine.

As a result, process engineers face high capital investment, high operating costs, and large space requirements.

At LIST, our kneader reactor solutions are designed to tackle this problem head-on.  With the unique ability to handle all phases in the drying process, a single LIST kneader reactor can help processors significantly lower their investment and operating costs while delivering a consistent, high-quality product.

Other Benefits

Other key benefits of the innovative LIST technology include:

  • Robust construction capable of handling especially sticky, viscous material.
  • Self-cleaning design that eliminates dead spots, product build-up, and stagnant areas.
  • Customized residence times ranging from 10 minutes to several hours.
  • Narrow residence time distribution for a more consistent, higher-quality end product.

Beyond Multi-Phase Drying

LIST kneader reactor technology is remarkable not only for its ability to handle multi-phase drying in a single machine; it provides a single solution for mixing, kneading, devolatilization and more. The forward-looking, field-proven design is in use in a wide variety of processing application around the world; delivering more value, better product quality and a healthier bottom line.   

LIST’s Dry Processing Kneader Reactor Technology ensures:

  • Quick return on investment
  • Low operating costs
  • Competitive advantage

An example of drying of difficult materials is the continuous evaporation and drying of toluene di-isocyanate (TDI), a raw material for polyurethanes. In a standard TDI plant, pure TDI from the main process stream accounts for a little over 90 % of the total output. The remainder is recovered from a distillation residue containing 30 – 70 wt% TDI.

Evaporating TDI from the residue is difficult. The mixture tends to foam, and as the TDI content falls, the remaining material becomes first viscous, and then pasty. Finally, at a free TDI content of 15 wt%, the residue solidifies into hard deposits. LIST KneaderReactor technology allows complete recovery of up to 6,000 t/y of TDI in a single unit. Operating continuously and under vacuum, the KneaderReactor copes easily with the viscous and pasty phases generated by the evaporation process. The final products are crude TDI and a free-fl owing granular residue containing just a few parts per million of TDI.