Online process monitoring

Figure A2.1 Waters ProMonix On-Line HPLC analyzer. The upper compartment door contains a keypad for programming and operation of the analyzer. The upper window allows viewing of indicator lights and a liquid crystal display that provides the operator with analyzer interface, programmed parameters, and instrument status results. The lower chamber contains the pumps, valves, injector, and detector(s) required for the chromatographic separation. The sample conditioning plate for online process monitoring is to the right of the analyzer. This is a typical process HPLC. (From Cotter, R.L. and Li, J.B., Lab Rob Autom., 1, 251,1989. With permission of VCH Publishers.)...

HORIBA Jobin Yvon Inc. [Online], Process Monitoring Control, available http //www.horiba.com/us/en/ scientiflc// Ovly=l, accessed 10 September 2008. 

Joeris K, Frerichs J-G, Konstantinov K, Scheper T (2002), In-situ microscopy online process monitoring of mammalian cell cultures, Cytotechnology 38 129-134. 

From a practical perspective near-real-time measurements are made with online process monitors. These systems utilize sensors in the sample stream with calibration usually performed by moving the sensors into a separate calibration stream. This requires some redundancy in the system if continuous monitoring is needed. Direct measurements can be made in sample streams or in a slip stream, where all the sensing is performed. 

FIA has many features that make it a valuable technique for industrial analysis and for online process monitoring and control. Most FIA techniques used in the laboratory can be adapted to industrial analysis. Sampling is of utmost importance in industrial analysis since very often the analyzed liquids are not homogeneous. FIA cannot directly improve the... 

Figure 1 A single-line FIA analyzer for online process monitoring with automatic calibration. Inset The shape of the output signal from the analyzer.

Table 1 Features of FIA online process monitoring and control ...

Infrared spectroscopy is widely used in industry. The applications range from quality control and quality assurance of raw materials to customer complaints (troubleshooting) to quantitative analysis and online process monitoring and control. Most of the instrumentation is based on a Fourier transform infrared (FTIR) spectrometer but specialist applications use instruments as diverse as a nondispersive infrared detector through to mid-infrared diode lasers. 

NIR-Raman has found applications in the pharmaceutical industry. McCreery and colleagues reported the use of the technique for identification of pharmaceuticals inside amber vials. Even with the signal attenuation through the glass, adequate spectra were obtained for determination of vial content with 1-60 s integration times. Using a library of spectra, identification of the pharmaceuticals in the vials was performed and identification was found to display accuracy between 88% and 96%. This work demonstrated the potential of NIR-Raman for online process monitoring. 

The conventional BOD test has certain benefits such as being a universal method of measuring most wastewater samples, and furthermore, no expensive equipment is needed. It has, however, the limitation of being time consuming, and consequently it is not suitable for online process monitoring. Thus, it is necessary to develop a measurement method that could circumvent the weaknesses of the conventional method. The need for fast, portable, and cost-effective methods for environmental monitoring has stimulated the development of a variety of field analytical tools such as biosensors. Biosensors are... 

The reactive extrusion is a process demanding precise operation by well-trained personnel. The knowledge of the extruder, compounding and mixing principles, design of screw and temperature profile, local residence time distribution, etc., is required. For optimization of the reactive extmsion, in- or online process monitoring, control, and data logging are recommended. This imposes further demands on the extruder operator. 

Investment in laboratory apparatus/equipment which give accurate results in the shortest time is a must. Since the laboratory apparatus/facilities required depend on the individual processing plants, these items should be procured in consultation with the shop floor persormel only. However it is suggested that instruments for online process monitoring should be installed as far as possible so that changes in process conditions can be immediately monitored and control actions initiated early. These instruments are helpful for automatic process control. 

While these instrument designs may appear most suitable for laboratory analysis, some manufacturers have proposed apparatus suitable for real-time online process monitoring. It is the case for spatially resolved spectroscopy. A very good review on the topic on pharmaceutical applications to the separation of absorption and scattering was written by Shi and Anderson [34]. A comprehensive review of those techniques and applications in tissue optics can be found in a review by Wilson [35]. 

The trend has been toward the increased nse of GC in the petrolenm industry. This is due to the relatively low cost of a gas chromatographic system that can provide more detailed analyses as well as the detection of trace components. Gas chromatography has also provided a means for online process monitoring. Future utilization of GC will involve the establishment of basic relationships between composition and performance parameters. This will allow the substitution of this rapid and reliable chromatographic analysis for the empirical methods from the past. 

NIR spectrophotometry is a nondestructive method. This represents a considerable advantage for applications where the analyzed samples must not be altered (e.g., biological and medical applications [6], online process monitoring, etc.). 

The installation of Raman for online process monitoring can either be by immersion optics or in a noncontact fashion through a sapphire or diamond window. The laser excitation source can be hazardous. Low voltage lasers are required to avoid sparks or ignition when hitting black particles and must be located outside of a production area unless well shielded and conforms to safety requirements. Additionally, laser power will deteriorate with time requiring periodic replacement. 

The Raman spectroscopy provides the opportunity to investigate a sample in a noninvasive and nondestructive way. It is as a nonsensitive analytical method towards water and air and can be used for online process monitoring. The intensity of the bands obtained is dependent on the electron density, which makes this method interesting for polymerization reactions where the intensity of the carbon-carbon-double bond decreases over time. 

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