Inline Measurements

The previous experiment was also inline monitored by photometric measurements. The pulse laser photometer used is well suited to characterize physical properties of emulsions like dispersed phase content or average droplet size [33]. The following results demonstrate that the pulse laser can not only be used in laboratory experiments but also for monitoring continuous emulsification processes. 

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The visible to near-infrared spectral region (375-740 or 680-1080 nm, resolution < 10 nm) is the domain of a micro spectrometer presented by the Institut fur Mikrotechnik Mainz [121]. This device (overall dimensions 16 x 28 x 38 mm) is commercially available but not yet adapted to direct inline measurements in a plant (Figure 4.72). 

A micro gas chromatograph, as small as a check card (dimensions 91 x 59 x 27 mm), was presented by SLS MICRO TECHNOLOGY GmbH [122], This device is one of the first commercial products of micro system technology and it possesses sufficient robustness to withstand chemical and thermal stress. Hence, it should be ideal for inline measurements in a plant. 

The inline measurement of the water vapour pressure makes it possible to monitor its progress in the course of the reaction. The water vapour pressure does not stay constant but slowly decreases until a very low value is reached. In the absence of the enzyme however no such decrease was detected (Figure 6). We believe that the enzymatically catalyzed hydrolysis of isopropenyl acetate is responsible for this decrease in water content. The hydrolysis occurs as a parallel reaction to the transesterification of isopropenyl acetate to menthyl acetate. It is not yet clear how significant the contribution of this parallel reaction to the overall decrease in (transesterification)reactivity is. If we assume that the rate constants for the hydrolytic reaction are of the same order of magnitude as those for the transesterification such a parallel reaction would lead to a significant decrease in the rate of transesterification as the water activity rises. At low water activities the hydrolytic reaction might be responsible for the observed decrease in reactivity. Very likely however the accumulation of water around the enzyme... 

There are two different methods for obtaining metrology measurements on a CMP chemical supply system—bottle sample with subsequent bench-top analysis and inline measurement directiy on the system. The advantage of bench-top analysis generally is higher accuracy while the advantage of in-line measurement is real-time measurement for faster response to concentration changes in the system. 

The supersaturation before the addition of seeds should be adjusted according to the solubility curve and the supersolubility curve (cf. Figure 10.2). Typically, seeding at 4—5 K below saturation temperature is fine. Of course, the metastable zone width has to be considered here and the seeding point should be closer to the solubility curve than to the supersolubility curve. It should be kept in mind that the metastable zone width is not thermodynamically determined, but strongly depends on plant properties and process parameters, such as cooling rate. If the metastable zone width is very narrow, for the sake of process robustness temperature control has to be improved or even an inline measurement of the supersaturation (e.g., by NIR) may have to be used to detect supersaturation close to the solubility curve and to avoid spontaneous nudeation or unwanted dissolving of the seed crystals. In such cases, special care has to be taken that no crystals are present in the crystallizer from the previous batch. 

Membrane emulsification processes can be directly visualized by microscope as vell as by the use of high-speed cameras. In this case, information can be obtained about droplet disruption [10, 11] and fouling of the membrane. An indirect characterization method is the (inline) measurement of the emulsion characteristics. The emulsion is mainly characterized by its droplet size and droplet size distribution [2]. These infiuence important product characteristics like structure, mouthfeel, color and appearance, texture and viscosity [12, 13]. 

The effect of repeating process can also be monitored by inline measurement, as shown in Figure 13.17. An o/w emulsion with 10% dispersed phase and 2% Tween 80 and Sauter diameter X32 = 13 pm was pressed three times by 12 bar through a membrane with a mean pore size of 0.45 pm. 

Dannigkeit, F., Steinke, L., Ripperger, S. (2012). Basic preexaminations of inline measurements of droplet size distributions by statistical extinction method. In 12th Triennial International Conference on Liquid Atomization and Spray Systems, September 2-6, 2012, Heidelberg, Germany. 

Wei, T. Han, Y. Li, Y. Tsai, H. L. Xiao, H., Temperature insensitive miniaturized fiber inline Fabry Perot interferometer for highly sensitive refractive index measurement, Opt. Express 2008, 16, 5764 5769... 

To measure the internal flow velocity in the duct, dust sampling was taken at various points along the vertical diameter. A pitot static tube and magnehelic gauge, shown in Figure 1, was the equipment used for these measurements. The duct humidity, tempertaure, and static pressure were measured to calculate the gas density. In determining the humidity, the wet and dry bulb temperature of a continuous sample stream was used. To prevent dust buildup on the wet bulb thermometer, an inline metal filter was inserted into the line. 

In some manufacturing process analysis applications the analyte requires sample preparation (dilution, derivatization, etc.) to afford a suitable analytical method. Derivatization, emission enhancement, and other extrinsic fluorescent approaches described previously are examples of such methods. On-line methods, in particular those requiring chemical reaction, are often reserved for unique cases where other PAT techniques (e.g., UV-vis, NIR, etc.) are insufficient (e.g., very low concentrations) and real-time process control is imperative. That is, there are several complexities to address with these types of on-line solutions to realize a robust process analysis method such as post reaction cleanup, filtering of reaction byproducts, etc. Nevertheless, real-time sample preparation is achieved via an on-line sample conditioning system. These systems can also address harsh process stream conditions (flow, pressure, temperature, etc.) that are either not appropriate for the desired measurement accuracy or precision or the mechanical limitations of the inline insertion probe or flow cell. This section summarizes some of the common LIF monitoring applications across various sectors. 

Even once a method is standardized, erroneous results can still be generated. As a result, it is critical to have robust quality control procedures in place. Here, careful attention should be paid to identify opportunity for in-process control measures such as internal standards, calibration, control plates, replicates and so on as opposed to post-processing data review steps. Inline QC approaches allow sources of error to be identified and remedied much more rapidly and help limit costly re-tests, or the possibility of erroneous data leaving the laboratory. 

Three types of inline HPLC detector have been used to measure fat-soluble vitamin concentrations in food sample extracts absorbance, fluorescence, and electrochemical detectors. Each of these detectors provides a continuous electrical output that is a function of the concentration of solute in the column effluent passing through the flow cell. 

R 18] [A 1] Each module is equipped with a heater (H3-H8) and a fluidic cooling (C03-C06). Temperature sensors integrated in the modules deliver the sensor signals for the heater control. Fluidic data such as flow and pressure are measured integrally outside the micro structured devices by laboratory-made flow sensors manufactured by silicon machining. The micro structured pressure sensor can tolerate up to 10 bar at 200 °C with a small dead volume of only 0.5 pi. The micro structured mass flow sensor relies on the Coriolis principle and is positioned behind the pumps in Figure 4.59 (FIC). For more detailed information about the product quality it was recommended to use optical flow cells inline with the chemical process combined with an NIR analytic or a Raman spectrometer. 

Inline UV/Vis absorption measurements to monitor photochemical reactions in microfluidic chips are described in [116,117]. 

Figure 4.71 Micro spectrometer (2000-14 000 nm) for inline mid-infrared measurements [119]...

The S abundance has been studied in stellar optical spectra, usually inline transitions of the neutral S atom. Unfortunately, these sulfur lines are dominated by 32S, so that little is known about the galactic chemical evolution of 33S and 34S except through theoretical calculations. It is important that techniques be developed to measure 34S itself in stars. 

From the general point of view, ultrasound has advantages regarding the measurement of dairy product quality in that it may be implemented inline, non-invasively and even using non-contacting techniques such as laser excitation and detection (Mulet et al, 1999). Ultrasound can also be safe, hygienic and economic in implementation, all characteristics desirable for any technique for the measurement of food quality (Povey, 1997a). Moreover, it can reveal aspects of the quality of dairy products which are not measurable by current techniques. An example is the extraordinary capability of ultrasound to detect crystal nucleation (Povey et al., 2001 Hindle et al., 2002). 

In this work we used an aluminium oxide humidity sensor to measure inline the water vapour pressure. We investigated the partitioning of water between SC-CO2 and the enzyme preparation and we determined the influence of water activity on the initial reaction velocity. 

The schematic of the experimental apparatus is shown in Fig. 1. It consists of a supply tank, variable speed gear pump, filter, preheater, flowmeter, test section, and return tank. The supply tank is provided with a preheater (1.5 kW). The return tank is provided with cooling coils and is mounted above the supply tank and is coimected to the supply tank by a valve. An inline filter and an additional inline preheater (700 W) are provided downstream of the pump. The liquid flow rate is measured using the flowmeter provided upstream of the test section. 

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