Process Monitoring: UV Spectrophotometry as a Practical Tool

Chapter 4

Process Monitoring: UV Spectrophotometry as a Practical Tool M . Bortolotti, G. T. Viola, and A. Gurnari

Downloaded by UNIV OF IOWA on September 3, 2016 | http://pubs.acs.org Publication Date: June 30, 1998 | doi: 10.1021/bk-1998-0696.ch004

EniChem Elastomeri, R&D Center, via Baiona 107/111, 48100 Ravenna, Italy Real time process control techniques permit consistent product quality improvement. It is therefore important to take advantage of on-line analytical facilities even for consolidated production process like living anionic polymerization of SBS and SIS. Although U V spectroscopy was extensively used in the laboratory in early studies on anionic polymerization, U V monitoring of industrial processes was postulated but no further communications appeared about the feasibility of such an analytical tool. We present in this communication results of work covering the monitoring of pilot plant production of typical block copolymers (styrene-butadiene and styrene-isoprene) under conventional solution polymerization conditions (10-15% solids). Information obtained obviously permits control of the most important molecular parameters related to product performance (basically M W of arm for linear/radial SBS and linear SIS); furthermore this gives on-line data that is relevant to process parameters, i.e. solvent or monomer purity, abnormal kinetics, etc. Another useful feature offered by on-line U V spectroscopy is the detection of abnormal concentrations of batches. This gives warning of high concentration which may lead to dramatic run-away reactions. On line measurements take an important role in the improvement of quality of production and in the increase of economics of operations. It is therefore of primary interest, even for consolidated production processes like styrene-diene block copolymerization through living anionic polymerization, to take advantage of on line U V spectroscopy, a powerful tool, for monitoring anionic polymerization. Currently, on line measurements carried out in the polymerization step are mainly physical process relevant parameters (i.e. flow rates, reactor temperature and pressure, agitator power). Finished product analysis significant to product relevant parameters (i.e. rheological measurements like Melt Indexes) are possible. The only drawback is that these analysis can be done some time after the material has come out from the reactor. Possible correction are not taken in real time. Moreover, the complexity of the relationship between viscoelastic response of elastomers in respect of their molecular parameters can not lead to straightforward correction steps. 50

©1998 American Chemical Society

Quirk; Applications of Anionic Polymerization Research ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

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U V spectroscopy has been extensively used since '60s in many laboratories . This has been done mainly on high vacuum equipped glass reactors. We took the challenge to bring this powerful tool also to common 1 I glass reactor and finally to the pilot plant. U V spectroscopy for polymerization monitoring in industrial processes was postulated many years ago, but no further communication has appeared about the feasibility of this analytical tool. In this paper monitoring of pilot plant production of different kinds of polymers is reviewed and advantages and limitations discussed. Potential data gained from on line U V spectroscopy are really impressive and are summarized here. It is not necessary to emphasize their relevant importance for industrial process control: - molecular weight of base (before any coupling reaction) copolymer - molecular weight of first block and therefore efficiency of propagation from first to second block - conversion during styrene polymerization - direct evaluation of efficiency of linking reactions (reacting polydienyllithium with polyfunctional electrophiles, i.e. SiCl , PhSiCl , etc.) - direct monitoring of deactivation of living polymers during addition of terminating agents, (i.e. ethanol or water). This information obviously permits control of the most important molecular parameters related to product performance (basically M W of arm for linear/radial SBS and linear SIS), because of the close correlation existing between molecular weights and the architecture of polymers and the technological performances . Furthermore, this gives on-line data that are relevant to process parameters, i.e. solvent or monomer purity, abnormal kinetics, etc. With these data any possible process problem can be correctly addressed. Another useful feature offered by on-line U V spectroscopy is the detection of abnormal concentrations of batches. This can give warning of high concentrations potentially leading to dramatic run-away reactions. Also impressive is the versatility of U V spectroscopy in terms of monitoring batch reaction of different products (only considering EniChem Elastomeri products by anionic route): -Thermoplastic elastomers (SBS, SIS) -Multiblock copolymer (SBS, tapered-block) -Diblocks (SB) copolymers, pure and tapered -Random styrene-butadiene copolymers (S-SBR) -Low cis polybutadiene (PBDE). We present in this communication results of work covering the monitoring of pilot plant production of typical block copolymers (styrene-butadiene and styrene-isoprene), tapered diblocks and random styrene-butadiene rubbers under conventional solution polymerization conditions (10-15% solids).


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EXPERIMENTAL The system utilized in the pilot plant consists of a photometer equipped with a flow through-cell in which a solution of living polymer in hydrocarbon solvent is continuously pumped from and returned to the reactor. For process control, it was decided to abdicate to sensitivity and selectivity offered by typical laboratory photometer, for such technical requirements as long term stability, ruggedness, ease of maintenance and use. Therefore a process photometer was used (Perkin Elmer Fagos 100: technical most relevant data are collected in Table I) that enables continuous monitoring at different wavelengths. Cells (optical length ranging from 0.5-1.5 mm) are connected via fiber optics to the Quirk; Applications of Anionic Polymerization Research ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

52 photometer which is located in a flame-proof cabinet. Signals from the photometer are sent to a PC which is configured for alarms, possibly giving on-line active lithium concentrations for process control.


Table I: Perkin Elmer Fagos 100, technical relevant data Xenon Flashlamp Light Source Interference filters

1 to 18 (spectral width

Process Monitoring: UV Spectrophotometry as a Practical Tool

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