**3.2. Analysis of reference samples**

Determination of true CO<sup>2</sup> concentration (CO2 loading) in alkanolamine samples was carried out by the *BaCl<sup>2</sup> titration-precipitation method*. 0.1 M Sodium hydroxide (NaOH), 0.1 M HCl, 1 M HCl, barium chloride (BaCl<sup>2</sup> ) purchased from Merck (99%) and the titrator Mettler Toledo T50 were used for the experiment. The titration procedure is discussed in [22]. This titration is popular and a well-established method to analyze CO<sup>2</sup> loading in absorption processes both in laboratory and industrial applications. However, the method needs extensive chemical preparation; and it takes more than 2 h to analyze one sample and needs expertise and tedious manual work. The accuracy of the PLSR models is strongly affected by the accuracy and results of this analysis. All the sampling errors during sample extraction from stock solution, chemical preparation, weighing, transferring samples, dilution, filtering and titration were identified using a fish-bone analysis and addressed based on the knowledge from *Theory of Sampling* [16].

### **3.3. Raman spectroscopy**

The Raman spectroscopy is a process analytical technique which can be used for batch-wise experiments where measurements are taken manually such as in laboratory tests, or for continuous operations such as in process plants where measurements can be taken continuously in each time interval. The instrument output is called a Raman spectrum which is a plot of intensity of scattered light (called Raman intensity) versus energy difference (given by wavenumber in cm−1). If the objective is to measure the concentration of a chemical sample using Raman spectroscopy, then the peaks and their intensity in a Raman spectrum indicate information about the type of chemicals and their composition respectively for the measured sample. Kaiser RXN2 Analyzer (as shown in **Figure 2a**) with 785 nm laser wavelength, 400 mW laser power and 100–3425 cm−1 spectral range was the Raman spectrometer used in this experiment. An immersion optic probe was connected to the RXN2 Analyzer via a fiber optic cable (refer **Figure 2b**). During each measurement, the immersion probe was positioned vertically into the 10 mL glass reactor using a stand. The glass reactor was covered by a black box and aluminum foil to avoid interaction with fluorescence from external light sources (as shown in **Figure 2c**). Each scan was acquired as an average of six scans with 10 s over a total exposure time of 60 s to get a good signal-to-noise ratio.

calibration results in poor correlation between property to be predicted and measured. The RXN2 analyzer was used to generate a data matrix of n × p where n is number of objects (e.g., different samples or measurements with time) and p is 3326 of Raman wavenumbers. This data matrix contains the chemical fingerprints of the objects and typically different types of noise. This noise comes from interference of other chemical components, laser input varia-

loaded amine solutions.

**Figure 2.** RXN2 analyzer; (a) Raman analyzer with exciting source and detector; (b) Raman immersion probe; (c) sample is in an enclosed sample compartment (black box) and probe, which is mounted vertically, takes measurements.

of Raman spectra are visible such as baseline shifts, scattering and peak overlaps. These features avoid the raw spectra to be used directly for the calibration model. Preprocessing of

loaded amines where normal features

Process Analytical Technology for CO2 Capture http://dx.doi.org/10.5772/intechopen.76176 195

tions, noise from fiber optic cable or inadequate path length for the laser.

**Figure 3** shows some raw spectra for four types of CO<sup>2</sup>

**Figure 3.** Unprocessed Raman spectrum for four types of CO<sup>2</sup>
