FTIR gas analysis

Two final examples of the sensitivity and general applicability of the FTIR gas analysis technique are illustrated in Fig. 8. Trace (A) shows the spectrum obtained from an ultra-air filled 70 liter sampling bag into which had been injected, 18 hours previously, 4.8 microliters of TDI, toluene diisocyanate. On the basis of the single feature at 2273 cm l, it is estimated that 50 ppb TDI could be detected. The lower Trace (B), shows the spectrum of nickel carbonyl. This highly toxic but unstable gas was found to decay rapidly at ppm concentrations in ultra air (50% lifetime 15 minutes). Calibration of its spectrum was established by recording successive spectra at ten minute intervals and by attributing the increase in carbon monoxide concentration (calibration known) to an equivalent but four times slower decrease in nickel carbonyl concentration. The spectrum shown represents 0.6 ppm of the material. Note the extraordinary absorption strength. The detection limit is thus less than 10 ppb. 

Fourier transform infrared (FTIR) gas analysis spectroscopy... 

The use of FTIR (Fourier transform infrared) spectrometers as a continuous monitoring technique overcomes many of the problems associated in analyses of hot fire gases. FTIR offers an opportunity to set up a calibration and prediction method for each gas showing a characteristic spectral band in the infrared region of the spectrum. A European project, SAFTR, aims to further develop the FTIR gas analysis of smoke gases to be an applicable and reliable method for the determination of toxic components in combustion gases related to fire test... 

Applications Transportable FTIR analyzers have been used in monitoring applications such as continuous emissions monitoring, process gas analysis, and car exhaust and industrial air hygiene. 

The use of IR pulse technique was reported for the first time around the year 2000 in order to study a catalytic reaction by transient mode [126-131], A little amount of reactant can be quickly added on the continuous flow using an injection loop and then introduce a transient perturbation to the system. Figure 4.10 illustrates the experimental system used for transient pulse reaction. It generally consists in (1) the gas flow system with mass flow controllers, (2) the six-ports valve with the injection loop, (3) the in situ IR reactor cell with self-supporting catalyst wafer, (4) the analysis section with a FTIR spectrometer for recording spectra of adsorbed species and (5) a quadruple MS for the gas analysis of reactants and products. 

The ability of the new precursors to decompose thermally to yield singlephase CIS was investigated by powder XRD analysis and EDS on the nonvolatile solids from the TGA experiments of selected compounds. Furthermore, using TGA-evolved gas analysis (EGA), the volatile components from the degradation of the SSPs could be analyzed via real-time fourier transform infrared (FTIR) and mass spectrometry (MS), thus providing information for the decomposition mechanism.3 The real-time FTIR spectrum for 7 and 8 shows absorptions at approximately 3000,1460,1390,1300, and 1250 cm-1 (see Fig. 6.7). 

Several methods have been developed to estimate the exposure to such emissions. Most methods are based on either ambient air quality surveys or emission modeling. Exposure to other components of diesel emissions, such as PAHs, is also higher in occupational settings than it is in ambient environments. The principles of the techniques most often used in exhaust gas analysis include infrared (NDIR and FTIR), chemiluminescence, flame ionization detector (FID and fast FID), and paramagnetic methods. 

The applications of simultaneous TG-FTIR to elastomeric materials have been reviewed in the past. Manley [32] has described thermal methods of analysis of rubbers and plastics, including TGA, DTA, DSC, TMA, Thermal volatilisation analysis (TVA), TG-FTIR and TG-MS and has indicated vulcanisation as an important application. Carangelo and coworkers [31] have reviewed the applications of the combination of TG and evolved gas analysis by FTIR. The authors report TG-FTIR analysis of evolved products (C02, NH3, CHjCOOH and olefins) from a polyethylene with rubber additive. The TG-FTIR system performs quantitative measurements, and preserves and monitors very high molecular weight condensibles. The technique has proven useful for many applications (Table 1.6). Mittleman and co-workers [30] have addressed the role of TG-FTIR in the determination of polymer degradation pathways. 

Some general applications of TG-FTIR are evolved gas analysis, identification of polymeric materials, additive analysis, determination of residual solvents, degradation of polymers, sulphur components from oil shale and rubber, contaminants in catalysts, hydrocarbons in source rock, nitrogen species from waste oil, aldehydes in wood and lignins, nicotine in tobacco and related products, moisture in pharmaceuticals, characterisation of minerals and coal, determination of kinetic parameters and solid fuel analysis. 

The cure of PMR-15 and its model compound 4,4 -methylene dianiline bi-snadimide (MDA, BNI) has been studied by simultaneous reaction monitoring and evolved gas analysis (SIRMEGA) using a FTIR with a mercury-cadmium telluride detector. The system allows the observation of the variation in IR spectra correlated to the gas evolution during the curing. The data show that the cy-clopentadiene evolution involves only minor modifications in the spectrum [39]. 

A recent study on the stability of various indium alkyl derivatives has been performed using differential scanning calorimetry (DSC), which provides a comprehensive thermal fingerprint of the compounds. In addition, when this method of thermal analyses is used in conjunction with thermogravimetric analysis coupled to FTIR and/or GCMS evolved gas analysis, it can provide a complete mechanism for the decomposition pathway of prospective compounds. ... 

S. Li et al. Real-time evolved gas analysis by FTIR method an experimental study of cellulose pyrolysis. Fuel, 80, 1809-1817 (2001). 

Fourier Transform Infra Red (FTIR) Spectroscopy is a promising and versatile technique for gas analysis which lately has moved from the laboratory to industrial applications such as emission monitoring of combustion and gasification plants [2]. The single most important advantage of the FTIR is its capability to analyse in-situ virtually all gas species of interest in flue and fuel gas applications. In this way potential sampling artefacts can be avoided. 

Pyrolysis results are very important for coal characterization, as all conversion processes of coal such as combustion, liquefaction, and gasification start with a pyrolytic step. For this reason, pyrolysis was frequently used for the analysis of coals [17,18). Pyrolysis data were correlated with coal composition, coal characterization and ranking [18a], prediction of coal reactivity as well as of other properties related to coal utilization. Techniques such as Py-MS, Py-GC/MS with different ionization modes, Py-FTIR, or evolved gas analysis (EGA) [19] were described for coal analysis. Programmed temperature pyrolysis is another technique that has been proposed [17] for a complete evaluation of the two types of molecules present in coal. 

Infrared (IR) techniques are reported in literature to be used in combination with different thermal experiments as a convenient tool of analysis. For example, IR-EGA (infrared evolved gas analysis) was used for obtaining information on different thermal and combustion processes [19]. A simple IR attachment where the sample can be pyrolyzed close to the IR beam is also commercially available (Pyroscan/IR from CDS Analytical). Although the IR detectors are by far not as popular as the MS, pyrolysis-gas chromatography/Fourier transform IR (Py-GC/FTIR) occasionally has been used in polymer analysis. Such applications have been commonly related to the analysis of certain gases such as CO2, CO, CH4, NH3, etc., where the MS analysis is less successful [20, 21]. 

TGA experiments on polymeric systems often show complex TGA mass/temperature curves in which multiple decomposition products correspond with the weight change observed (see, for example, Figure 2.10). TGA has thus proven to be an excellent quantitative technique but less suitable for specification. This drawback can be eliminated if the components which are causing the mass losses detected, are also analysed simultaneously, the so-called evolved gas analysis (EGA). Several TGA-EGA systems are described in literature, analysing the evolved gases with different techniques i.e. thermal conductivity, cold-trapping followed by GC, mass spectrometry (MS) and infrared (FTIR). MS and FTIR have proven to be the most powerful techniques [3, 10]. 

The main decomposition products of the tested 7 VOCs were CO and CO2. Formic acid was the common intermediate from the decomposition of aromatic compounds, but its yield was much lower than those of CO and CO2- No other ring-cleavage or ring-retaining products were detected from the gas analysis using the FTIR. Figure 20 shows the carbon balance data as a function of SIE. Carbon balance was simply calculated from the sum of CO, CO2 and HCOOH, which were the only measurable gaseous products. 

The combination of polymer analysis and evolved gas analysis certainly provides considerable and complementary information about the degradation process, but in many cases pyrolysis-evolved gas - FTIR analysis alone is very useful, and generally simpler. This technique was pioneered by Griffiths (10) but developed to a high level by Lephardt and Fenner (11-13) we have found it to be very useful for characterisation work. In recent years it has been coupled with TGA (TGA-FTIR) but this does not yet appear to be widely used. The manufacturers data so far suggest that the pyrolysis chamber/gas cell relationship has not yet been optimised. 

This chapter is devoted to the description of an easy and efficient method based on the application of gas phase Flow FTIR spectroscopy analysis for determination of adsorption characteristics of volatile organic compounds. As adsorbent beds are usually operated under dynamic conditions, the adopted analytical approach is based on gas phase composition monitoring at reactor outlet during adsorption/ desorption experiments carried out under dynamic regime. This method permits further simultaneous detection of new IR bands that may originate from adsorbate dissociation during adsorption or desorption. 

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