Polyolefins manufacturers are confronted with the daunting task of having to develop new polymers with reduced chemical complexity for improved recyclability whilst simultaneously maintaining or improving various physical properties required for end applications.
This represents a difficult balancing act.
1. Industrial Multimodal Polyolefins Synthesis
Multimodal polyolefins play a key part in achieving this goal. Custom tailoring the relative quantities of each mode formed in multistep synthesis allow for optimal combinations of recyclability, processability and mechanical strength.
There are a variety of multistep industrial processes for multimodal polyolefin development. One example is the Borstar Process from Borealis (see Figure-1 for a schematic representation of the Borstar process).
The highly active catalyst first undergoes a mild pre-polymerization step critical to defining good morphology of the final polymer. Loop reactors are often used for these applications which provide excellent surface/volume ratios and high linear flow velocities for improved heat transfer at high monomer concentrations.
Larger loop slurry-phase reactors are used in subsequent steps where additional monomer, co-monomer and hydrogen are added. Solvent is flashed off and the polymer powder is transferred to a fluidized-bed reactor where one or more gas-phase synthesis step takes place. This step is virtually free of mass-transfer and amorphous solubility issues but great care must be taken to prevent local hot-spot formation.
Multistep processes enable the production of a far greater diversity of polyolefins. It is this flexibility in polymer synthesis that will be key to producing recyclable polymers with the desired physical properties for future applications.
2. Multimodal Polymer R&D at the LABORATORY Scale
Laboratory-scale units for polyolefins R&D generally fall into one of 3 reactor types. A brief overview of these is provided below.
2.1. Dynamic Batch Synthesis in a Single Reactor
Dynamic batch synthesis in a single reactor refers to lab-scale synthesis where each of the reaction steps are performed in the same reactor in sequential steps with rapid transitioning between steps.
- Low Price
- Bulk, slurry and gas-phase processes can be performed
- No complicated continuous catalyst addition or polymer transfer from reactor to reactor
- Non-Ideal stirring for both liquid & gas-phase. The stirrer chosen is a compromise allowing various modes to be done in a single reactor but isn’t hydrodynamically optimized for any of them specifically.
- Residence time-effects realized in true, continuous operation are missing.
- Catalyst activation and decay make steady-state operation behavior impossible to observe.
2.2. Stepwise batch-in-series operation
Stepwise batch-in-series operation involves sequential operation with at least 2 batch reactors. The first polymerization step is completed in the first reactor. Solvent is may be flashed or the mixture transported as a slurry directly to a 2nd reactor for the following step.
- Moderate Price
- Same as Dynamic Single-Batch
- Rapid transition can be realized by fast polymer transport from one reactor to the next.
- Same as Dynamic Batch Synthesis
- Transfer of polymer from one reactor to another can be difficult at lab-scale
2.3. Continuous CSTR-in-Series
Continuous CSTR- in-series involves cascaded CSTR’s operated in continuous-flow mode.
- Much more closely simulate the residence-time-effect of the full-scale process
- Catalyst activation/deactivation does not mask data
- Continuous catalyst and polymer transport at very low flowrates resulting from small reactor volumes is difficult without damaging catalyst and/or polymer morphology. Low laminar flowrates easily result in blockage and plugging.
3. High-Throughput Experimentation
High-throughput R&D techniques enable scientists to perform large numbers of experiments in a parallel fashion. Fully automated high-throughput testing enables researchers to test much wider process-parameter spaces or catalyst-compositions in far less time than traditional one-at-a-time experiments.
Most existing high-throughput tools on the market only make 100-200mg quantities of polymer and are not capable of doing rapid transitioning for multimodal synthesis.
Clearly there is a need for a new tool capable of performing multimodal polyolefin synthesis and produce sufficient quantities of material for comprehensive materials testing and polymer characterization.
4. Parallel Dynamic Multistep Batch Synthesis:
A High-Throughput Tool for Multimodal Polymer Synthesis
ILS-Integrated Lab Solutions has developed a novel polymer reaction platform designed specifically for multimodal polyolefin process- and catalyst R&D.
It combines the benefits of high-throughput parallel screening with the scalable results obtained using the dynamic batch synthesis approach described above.
The unit is a scalable, modular platform with reactors arranged in groups of 2 available with volumes from 500ml to 5L. Each reactor operates completely independently with the full functionality shown here. Integration of a slurries handling robot in an inert glovebox make fully automated catalyst and co-catalyst handling and injection under reaction conditions possible.
4.1. Excellent Reproducibility
The high-degree of automation results in reactor-to-reactor yield accuracies of below 5% stdev and molecular weight distributions which accurately mimic full-scale processes (see Figure-3).
4.2. Gas-Phase Composition Control
Gas-phase synthesis require tight control of the gas-phase composition of the reactor. The ILS unit implements fast on-line GC with feedback control to mass-flow controllers controlling H2 and monomer feed rates. Figure-4 shows an example of how the feedback control can be used to realize a user-specified ethylene/H2 ratio. Ethylene or propylene/co-monomer ratios can also be controlled to achieve different compositional variation. H2 capping of polymer chains is critical and can be precisely realized with this approach. Both low H2 concentrations required for metallocene-based systems and higher concentrations for Ziegler-Natta systems can be measured and controlled.
Combining parallel reaction technology with dynamic batch synthesis represents a powerful new R&D approach for multistep polyolefins process optimization.
Webinar from ILS about this Technology:
ILS will be hosting a webinar introducing this technology on Thursday, October 22nd at 2pm Berlin time that can be subscribed to here.