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 Ludwigshafen .
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 Leverkusen ,
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.
More
information
For more
information visit the F3 Factory Project website or contact Dr. Achim Stammer at BASF.
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