The transfer of multi-product batch polymerisation of high temperature thermoplastics in organic solvent to a solvent-free process is a challenging task and has so far prevented producers from developing solvent-free processes.
Without reducing viscosity by applying very large amounts of solvents, “difficult processes” like solvent-free polymerisation cannot be carried out in standard mixers. The focus of this F³ Factory case study therefore concentrated on the development of intensified, high-strength mixing equipment. To succeed this approach needed to guarantee material integrity and enable effective supplementary mixing as well as devolatilisation and solidification. Performance at long residence times in continuous mode also needed to be assured.
A new twin-shaft, high-torque kneader reactor developed by Buss-SMS-Canzler (pictured below) was shown to meet the key requirements of strength and operational flexibility and led to a step-change improvement in viscosity handling up to 10 000 Pascal seconds.
Modular construction and many standardised parts also allow for flexible adaptation to different products and processes, with the ability to switch rapidly between different mixing rotor assemblies.
To realise the full potential of this intensified kneader reactor, its complex geometry required focus on several key durability issues. Their examination has been a classic model of F³ Factory project partnerships.
The University of Paderborn (UPB) investigated the mechanical integrity; modelling of unit processes; radial and axial mixing; micro/macro mixing and axial dispersion. Investigations confirmed the ecological and economic advantages of the kneader from its fast radial mixing and minor back mixing plus well-developed devolatilisation based on reactor partial-fill operation.
Numerical simulations using CFD analysis were performed by Technical University Eindhoven to calculate the velocity and pressure fields within the kneaded material, leading to rotor strength and fatigue computations by Buss-SMS-Cransler (SMS). Online measurement techniques for the high-torque kneaders were then developed by BASF, with technology transfer to UPB and SMS.
BTS derived a mass-balance for the intensified kneader reactor design, providing the liquid filling level as a function of viscosity, throughput and rotational speed. Following validation of the new reactor technology at lab-scale and successful polymerisation trials, the modular plant concept was designed by BTS and demonstrated successfully at the INVITE facility.
Excellent progress on the integration of process and equipment design enabled illustration of the plant concept and contributed to the design and construction of a pilot facility at BASF’s site in
The new solvent-free process was subsequently validated with a continuous
lab-scale kneader reactor.
The intensified process was then transferred to the F³ Factory modular, continuous plant concept with design of a demonstrator Process Equipment Container and respective Process Equipment Assemblies.
By eliminating the use of solvents, the process has been intensified significantly. It has reduced complexity, energy consumption and facilitated the successful transfer from batch to continuous polymerisation.
The case study was demonstrated successfully at the INVITE facility in
over an extended processing time, confirming both the strength and integrity of
the kneader reactor.
In addition to the technological advancement achieved in this project, the transfer from batch to continuous of a new solvent-free polymerisation process has demonstrated both cost (30% reduction in energy demand) and environmental benefits (100% solvent reduction) for the continuous production of high viscous polymers.