Off-line pyrolysis

It is necessary to point out that our off-line pyrolysis data with GC/MS analysis of the resultant pyrolysates showed no interconversion between catechol and hydroquinone, and each dihydroxybenzene gave the corresponding benzoquinone. In addition, the analysis confirmed that the peak found at m/z 132 was indeed indanone (CgHs O). Nevertheless, the identities of other products should be confirmed by off-line experiments. This should be applied also to the following discussion. 

Analytical pyrolysis requires heating of the sample at a temperature significantly higher than ambient, commonly between 500° C and 800° C. For special purposes this temperature can be higher. The pyrolytic process is done in a pyrolysis unit (pyrolyser) which commonly interfaces with an analytical instrument (see Section 1.2). The analytical instrument is used for the measurement of the pyrolysis products. It is also possible to perform "off line pyrolysis (no direct interface to an analytical instrument), followed by the analytical measurement. The pyrolysers have a source of heat where the sample is pyrolysed. The pyrolysis products are usually swept by a flow of gas from the pyrolyser into the analytical instrument. 

In this separation, a 10-mL sample (large volume) containing a solution in tert-butyl methyl ether (tBME) of the pyrolysate of 1 mg cellulose obtained at 600° C was injected (off-line pyrolysis). The PTV injector was programmed at 20° C initial temperature for 2 min. and ramped with 10° C/min at 250° C and kept at this temperature for 1 min. Then the injector was further heated at 300° C. The split vent purge time was 2.5 min. The oven temperature for the first dimension separation was kept at 35° C for 2.5 min. then heated with 30° C/min. at 55° C and further heated with 3° C/min. to 240° C. The detector used in the first dimension was an MS system, which allowed the identification of a series of compounds from this chromatogram. The peak identification is given in Table 5.2.2. 

The TIC obtained using off-line pyrolysis of CMC (D.S. 1.2) done at 590° C followed by derivatization with BSTFA and separation on a non-polar column is shown in Figure 7.3.4. 

Besides derivatization or selective analysis using SPME, off-line pyrolysis before a chromatographic analysis can be used for various other purposes. One such purpose is the use in the pyrolyzer of larger samples, which would not be appropriate to send directly into a GC instrument. Larger sample must be used in specific applications, for example in the analysis of trace components in pyrolysates. Another application of offline systems Is found when a dedicated GC or GC-MS instrument cannot be afforded only for pyrolysate analysis. 

Off-line pyrolysis of a poly(4-vinylphenol) sample followed by the silylation using N,0-bis(trimethylsilyl)-trifluoroacetamide (BSTFA) of the pyrolysate and GC/MS analysis with separation on a DB5 column (30 m length. 0.32 mm i d., 0.32 pm film thickness) is shown in Figure 6.6.2. The identification of the compounds in the silylated pyrolysate was done using MS library searches and is given in Table 6.6.3... 

Figure 6.6.2. Result fora off-line pyrolysis of a poly(4-vinylphenol) M = 8000 followed by silylation and GC/MS analysis. Pyrolysis done at BOCP C in He, with the separation on a 5% phenyl methylsilicone column.

One of the methods of studying the composition of macromolecular sedimentary organic matter in more detail is the molecular analysis of pyrolysis products. For this purpose, the pyrolysis products are transferred to a gas chromatographic column and analyzed as described for extractable organic matter in Sect. 4.5.5, with or without the combination with a mass spectrometer. Both flash pyrolysis (Curie-point pyrolysis samples are heated on a magnetic wire by electrical induction almost instantaneously, e.g., to 610°C) or off-line pyrolysis at various heating rates have been applied to geological samples (see Larter and Horsfield 1993 for an overview of various pyrolysis techniques). 

In 1948, the first reports on the off-line pyrolysis-MS (Py-MS) of polymers were published by Madorsky and Straus/ and Wall. In 1953, Bradt et al. described on-line Py-MS for which pyrolysis of polymer samples was effected within the instrument in vacuo. Thus valuable structural information about the samples became obtainable. 

Ishiguro et al. [846] have used off-line pyrolysis-infrared spectroscopy for the analysis of polymers in various kinds of plastic materials. The pyrolysis products were obtained by heating small amounts of the plastic samples on a gas burner in middle size test tubes the IR spectra of the pyrolysates were measured by a KBr sandwich method. This method was found to be simple, speedy and usefiil for the analysis of complex mixtures consisting of polymers and various kinds of additives in plastic materials. Washall et al. [834] used direct PyFTIR for polymer analysis. 

The use of HMDS as a derivatization reagent in the analysis of triterpenoid resins has been less explored. The TMS derivatives of triterpenoids bearing hydroxyl groups [a-amyrine, p-amyrine and hop-22(29)-en-3p-ol] have been identified in the triterpenic fraction of Burseraceae resins, thus demonstrating that HMDS combined with Py-GC/MS is effective in the derivatization of triterpenoid compounds [59]. However, the range of structures that can be fully derivatized and detected must be extended and, in order to get comprehensive results comparable with those coming from the well assessed off-line GC/MS procedures, general improvements in the on-line trimethylsilylation-pyrolysis method are needed. 

Sulfates are precipitated as BaS04, and then reduced with carbon at 1,000°C to produce CO2 and CO. The CO is either measured directly or converted to CO2 by electrical discharge between platinum electrodes (LonginelU and Craig 1967). Total pyrolysis by continuous flow methods has made the analysis of sulfate oxygen more precise and less time-consuming than the off-line methods. Bao and Thiemens (2000) have used a C02-laser fluorination system to liberate oxygen from barium sulfate. 

Hua, G. and D. A. Reckhow. 2006. Determination of TOC1, TOBr and TOI in drinking water by pyrolysis and off-line ion chromatography. Anal. Bioanal. Chem. 384 495-504. 

McKinney, D.E., Carson, D.M., Clifford, D.J., Minard, R.D., and Hatcher, P.G (1995) Off-line thermochemolysis versus flash pyrolysis for the in situ methylation of lignin is pyrolysis necessary J. Anal. Appl. Pyrol. 34, 41-46. 

Quantification of Pyrolysis Products. The pyrolysis must be performed separately ( off-line approach, see Fig. 4.7.5), and the products are trapped completely so that an internal standard can be added. Accurate quantification of the pyrolysis products is achieved using a gas chromatograph equipped with a flame ionization detector (Faix et al. 1987). Fluoranthene is a suitable internal standard as it elutes from the column after the last detectable lignin pyrolysis product (trans-sinapyl alcohol). 

Laboratory-scale pyrolysers can be used for producing oils for analytical purposes. Many scientific and technical publications report on the pyrolysis of well-characterized polymers in open or closed reaction vessels, furnace-heated tubes, fixed-bed and fluidized-bed reactors. The pyrolysis products are generally analysed off-line, being condensed in cooled traps. 

Sealed vessel pyrolysis is another pyrolysis type that is performed in furnace type pyrolysers. In this type of pyrolysis, the sample is heated for a relatively long period of time, in a sealed vessel, generally at relatively low temperature (below 350° C). The pyrolysis products are further analyzed, commonly by off-line procedures (GC, GC/MS, FTIR, etc). The technique allows the pyrolysis to be performed for as long as months and to use different atmospheres (inert or reactive) [17a]. The procedure is not used only as an analytical tool, and it can be seen as a preparative pyrolysis technique. 

Historically, pyrolysis-mass spectrometry (Py-MS) was applied to the analysis of biopolymers before Py-GC [45]. However, the first application utilized an off-line setup. In time, several on-line procedures were developed and they became more common. In Py-MS the pyrolysate is directly transferred to the mass spectrometer and analyzed, generating a complex spectrum (sometimes also called a pyrogram, although this should not be confused with the chromatogram of a pyrolysate, also called pyrogram). The ionization process that takes place in the ion source of the mass spectrometer can... 

As indicated previously (see Section 1.2) pyrolysis must be associated with an analytical technique in order to provide information on a sample. Several common analytical techniques such as GC, GC/MS or GC/FTIR have been utilized either hyphenated with pyrolysis or off-line and were described previously. Less frequently, techniques such as HPLC, preparative LC, TLC, SFE/SFC, or NMR also have been used for the analysis of pyrolysates. These types of techniques are commonly applied off-line. They are used mainly for obtaining information on that part of the pyrolysate that is difficult to transfer directly to an analytical system such as a GC or for the analysis of materials associated with the char. However, the analysis of the non-volatile part of pyrolysates is frequently neglected, although this leads to an incomplete picture regarding the chemical composition of pyrolysates. 

Cellulose pyrolysis has been studied in detail from a variety of points of view mainly related to chemical utilization of wood pyrolysis products or to fire related problems. Analytical pyrolysis of cellulose is not often used as a tool for cellulose detection, but it is a common procedure for studying the pyrolysis products. A variety of analytical procedures have been applied for this study, pyrolysis/gas chromatography/mass spectrometry (Py-GC/MS) being the most common [11-16]. Besides Py-GC/MS, other analytical procedures also have been utilized, such as Py-MS [17,18], Py-IR [19], and off-line Py followed by HPLC [20]. The Py-MS spectrum of cellulose was shown in Figure 5.4.1 (B). Some procedures applied GC/MS on derivatized pyrolysis products (off-line), the derivatization being done by silylation [21], permethylation, perbenzoylation [22], etc. Information about cellulose also has been obtained from the analysis of pyrolysis products of several cellulose derivatives, such as O-substituted cellulose [23]. Also the study of cellulose crystalline structure with X-ray during pyrolysis has been used [23a] to generate information about the pyrolysis mechanism. 

In order to identify less volatile compounds, the pyrolysis of cellulose acetate sample (at 590° C) can be followed by an off-line derivatization with bis-(trimethylsilyl)-trifluoroacetamide (BSTFA). Typically the derivatized pyrolysate is analyzed by GC/MS on a non-polar column. The results of this type of analysis (separation on a 60 m DB-5 column 0.32 mm i.d. and 0.25 p film thickness) is shown in Figure 7.3.2 and the peak identification is given in Table 7.3.3. 

Some less volatile compounds formed in starch pyrolysis at 590° C were seen, as expected, only in the trimethylsilylated pyrolysate. Figure 7.4.2 shows the chromatogram of a starch pyrolysate performed at 590° C off-line, followed by trimethylsilylation (with BSTFA) and separated on a DB5 column (60 m long, 0.32 mm i.d. and 0.25 n film thickness). 

The same polymer was also analyzed for less volatile components by performing the pyrolysis off line at 600 C in a filament system followed by off-line derivatization with BSTFA. The silylated pyrolysate was analyzed by GC/MS on a DB-5 column (60 m long, 0.32 mm i.d., 0.25 urn film thickness). For this analysis the GC separation was done using a temperature gradient between 50° C and 300° C. The chromatogram is shown in Figure 11.3.2. 

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