Process Development for Deep Temperature Emulsion Polymerization Baldur Schroeter 1, Sven Bettermann 1, Timo Melchin 2, Werner Pauer 1, Hans-Ulrich Moritz 1 1 University of Hamburg, Institute for Technical and Macromolecular Chemistry, Bundesstr. 45, 20146 Hamburg, Germany 2 Wacker Chemie AG, Johannes-Hess-Strasse 24, 84489 Burghausen, Germany Department of Chemistry .
1 INTRODUCTION The speed of radical polymerization is limited by the radical generation rate of the initiator. In this work, kinetic investigations on redox initiator systems containing ascorbic acid (AsAc), iron ions and a variable peroxide component are presented. These systems o!er an applicability in a broad temperature range, a short induction period and a high degree of "exibility in terms of radical generation rate. The decomposition rates of the components were determined by UV/Vis-, Ramanand electron paramagnetic resonance (EPR) spectroscopy in aqueous solution. This combination of spectroscopic methods covers a broad concentration range and provides comprehensive insights into the kinetics of the systems. It is possible to control the reaction speed of polymerization processes for various material systems in a broad temperature range, just by customizing the ratios of the redox components. Due to the comprehensive kinetic knowledge, emulsion copolymerization processes in 3D-printed continuous reactor systems are realized.
2 S P E C T R O S CO P Y R E D OX I N I T I ATO R S YST E M S
3 R E D OX
2.1 UV/ V I S
b)
3.1 S C R E E N I N G B ATC H
d)
Figure 5: Conversion patterns of emulsion copolymerization (VAc/ VeoVa10™, 20 wt% mon. content and emulsi#er PVA). The amount of catalyst was varied at a constant AsAc/TBHP ratio (1 : 1). Reactions were carried out at di!erent jacket temperatures Tj and operation modes of the reactor. Reactions at Tj = 70 °C were carried out in isotherm mode. At Tj = 10 °C, isoperibole operation mode was chosen. Control of conversion speed is achieved due to changes of Fe-cat. content. Development of redox systems for continuous processes is based on data of screening in batch mode.
a)
Figure 2: a) UV/Vis spectra of AsAc decomposition b) Exemplary kinetic evaluation of decomposition rates with #rst order and Weibull model c) Arrhenius-Plot for a redox system with molar ratios of the redox initiator system components AsAc/TBHP/Fe3+ 1 : 1 : 0.003 (three fold determination at each c) temperature). d) In"uence of AsAc ratio on EA and ln A0. Each Arrhenius evaluation consists of measurements at #ve temperatures. Lowering the AsAc content results in faster redox systems. Variation of the Fe-cat. content and peroxide component were also investigated.
2.2 R A M A N
Figure 1: Reaction scheme of redox initiator systems. The peroxide component is reduced and radicals are produced. Monitoring of the kinetics is carried out by a combination of UV/Vis-, Raman- and EPR spectroscopy.
I N I T I AT E D
P O LYM E R I Z AT I O N P R O C E S S E S
3.2 D E E P T E M P E R AT U R E E M U LS I O N C O P O LYM E R I Z AT I O N
Figure 3: The signal of the TBHP (OO) bond at 883 cm-1 at the beginning and the end of the reaction. AsAc is also Raman active (lactone vibr. at 1692 cm-1). Therefore, simultaneous determination of the decomposition rates as well as quanti#cation of the components conversions are possible. Both components show similar decomposition rates. At a molar ratio of AsAc/TBHP = 1 : 2, the peroxide conversion is 63%, while AsAc decomposes completely. At ratios of 1 : 1 and 1 : 0.5, quantitative conversion of the peroxide component is achieved. Ramanspectroscopic results allow for optimization of AsAc/TBHP ratios in polymerization processes.
Particle size (DLS) Redox system works even at -1.3 °C Max. ΔT = 15 K Total GC conversion 95%
Figure 6: Experimental setup and data: Deep temperature emulsion copolymerization Vac/VeoVa10™.
2.3 EPR
3.3 C O N T I N U O U S A I R C O O L E D 3D-P R I N T E D R E AC TO R
Figure 4: EPR signal of the redox system AsAc/TBHP/Fe3+ in aqueous solution at g = 2.0072. At the beginning of the measurement, a fast decomposition is detected. The in"uence on the decomposition kinetics due to variations of AsAc and Fe-cat. are in accordance with UV/Vis spectroscopic data. Experiments in presence and absence of dissolved oxygen showed the same results.
Figure 7: Thermal image of a polymerization process in a 3D-printed continuous, air cooled tubular and biodegradable reactor. Copolymerizations of two di!erent systems (VAc/VeoVa10™ and S/BA) were carried out. Tailor made redox initiator systems were used to provide high conversions (> 90%) in short retention times from 15 to 30 min at room temperature for di!erent momoner contents (20 wt%, 40 wt%). The linear temperature pro#le indicates, that the redox system provides a constant radical to monomer concentration throughout the whole length of the reactor.
The start intensity of the signal varies linear with the amount of Fe-cat. Therefore, it can be assigned to an iron-ion species. The observed kinetics indicates, that this species is catalytically active.
4 S U M M A RY -
Process development for 3D-Printed tubular reactor: 1. Determination of redox initiator kinetics 2. Screening of reaction rates emulsion copolymerization (batch) 3. From batch to conti
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Control of emulsion copolymerization reaction rates in temperature range -1.3 °C - 70 °C.
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Comprehensive determination of redox initiator kinetics by means of UV/ Vis-, Raman- and EPR-spectroscopy.
C O N TAC T
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