Gases, analysis using FTIR

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. 

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. 

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. 

C/min and secondly a ramp from 100 - 300°C at 20°C/min was used. Injector and detector temperatures were maintained at 270°C and 300°C respectively. GLC-FID/FPD analysis was performed on a Varian 3400 gas chromatograph using the same chromatographic conditions as used in the GC-MS runs. FTIR spectroscopy was performed on a Nicolet instrument using the thin film on sodium chloride plates technique for liquids and the potassium bromide pellet technique for solids. 

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]. 

FTIR spectroscopy to a particular pesticide, the methods have general applications to numerous compounds. Most of these utilize the high sensitivity of FTIR, and the data manipulation capability of the system. In several of the gas evolution studies, spectra were acquired at less than one-minute intervals. While this is not really "rapid scanning," the high resolution required for vapor phase spectra would not have been possible with a normal dispersive instrument. Several other techniques using FTIR show promise in the area of pesticide analysis. 

Apparatus Use a Fourier transform infrared spectrometer (FTIR), with its associated computer and peripherals, capable of measuring from 4500 to 500 cm-1 and of acquiring data with a resolution of at least 2 cm-1. The optics of the instmment must be sealed and desiccated, or, like the sample chamber, must be under continuous dry air or nitrogen gas purge. The spectrometer is equipped with software capable of multicomponent analysis using the partial least squares method (PLS-1, or equivalent). This software is commercially available as an accessory to the spectrometer or as an external software package. 

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. ... 

The concentrations of hydrocarbon at the inlet and outlet of the reactor were measured using FTIR (Nicolet) with a meicury-calcium-telluride (MCT) detector, which was cooled by liquid nitrogen and gas cell (Infrared Analysis), and with 16 scans and a resolution of 2 cm. The concentrations were also checked using GC (HP3890plus) with FID (flame ionization detector) and HP plot column. The vapor pressures of the hydrocarbons were calculated by using Reid equation [6]. 

The analysis of the produced LCV gas is performed directly behind the ceramic candle filter by means of continuous on-line O2 (paramagnetic), CO- and CO2 (NDIR) analysers. In addition, H2, CO, CH4 and N2 concentrations are measured off-line by means of a gas chromatograph. An FTIR is used for measurement of NHj, HCN, CO, COj, CH4, C2H4, C2H2, HCl, COS and HjO. 

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]. 

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. 

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