Isothermal pyrolysis

Montaudo and co-workers have used direct pyrolysis mass spectrometry (DPMS) to analyse the high-temperature (>500°C) pyrolysis compounds evolved from several condensation polymers, including poly(bisphenol-A-carbonate) [69], poly(ether sulfone) (PES) and poly(phenylene oxide) (PPO) [72] and poly(phenylene sulfide) (PPS) [73]. Additionally, in order to obtain data on the involatile charred residue formed during the isothermal pyrolysis process, the pyrolysis residue was subjected to aminolysis, and then the aminolyzed residue analysed using fast atom bombardment (FAB) MS. During the DPMS measurements, EI-MS scans were made every 3 s continuously over the mass range 10-1,000 Da with an interscan time of 3 s. 

These results are quite different from others which have been reported in the literature concerning the high temperature (>600° C) thermal and thermal oxidative degradation of DBDPO, in which >90% degradation was reported (28). We confirmed that temperature was the principal cause for these different observations, by reproducing the 600° C isothermal pyrolysis of DBDPO in which less than 10% unreactive DBDPO was recovered. 

Char Preparatioa Chars were prepared both by isothermal pyrolysis of 5 g samples of resin in a quartz boat heated in an atmosphere of flowing (0.5 SCFM) N2 in a quartz tube oven (N2 pyrolysis chars) and by open combustion of 1 g samples of resin exposed to 2.8 watts/cm2 of radiant energy from an electric heating panel (4-5) (combustion or burn chars). All chars were finely ground with a glass mortar and pestle prior to analysis. 

The TGA system was a Perkin-Elmer TGS-2 thermobalance with System 4 controller. Sample mass was 2 to 4 mgs with a N2 flow of 30 cc/min. Samples were initially held at 110°C for 10 minutes to remove moisture and residual air, then heated at a rate of 150°C/min to the desired temperature set by the controller. TGA data from the initial four minutes once the target pyrolysis temperature was reached was not used to calculate rate constants in order to avoid temperature lag complications. Reaction temperature remained steady and was within 2°C of the desired temperature. The actual observed pyrolysis temperature was used to calculate activation parameters. The dimensionless "weight/mass" Me was calculated using Equation 1. Instead of calculating Mr by extrapolation of the isothermal plot to infinity, Mr was determined by heating each sample/additive to 550°C under N2. This method was used because cellulose TGA rates have been shown to follow Arrhenius plots (4,8,10-12,15,16,19,23,26,31). Thus, Mr at infinity should be the same regardless of the isothermal pyrolysis temperature. A few duplicate runs were made to insure that the results were reproducible and not affected by sample size and/or mass. The Me values were calculated at 4-minute intervals to give 14 data points per run. These values were then used to... 

The isothermal pyrolysis in the presence of air proceeds at a much faster rate and higher weight losses are obtained as compared to vacuum pyrolysis at the same temperature. The first order rate constant obtained is linearly related to the expression [%LOR + o-(% crystallinity)]//o with a degree of correlation r = 0.923, where a is the accessible surface fraction of the crystalline regions according to Tyler and Wooding [501], and / is the orientation factor. No correlation could be found with DP due to very rapid depolymerization. The fact that the rate is inversely proportional to the orientation and that it decreases with the increase in the thickness of the fibers indicates that the rate of the diffusion of the oxygen into the fibers controls the kinetics and that oxidation is the predominant process in air pyrolysis. 

Final temperature (Tf) The final (steady-state) temperature which is attained by a pyrolyser. (The terms equilibrium temperature and pyrolysis temperature may be used when referring to an isothermal pyrolysis they are not recommended for use with a non-isothermal pyrolysis, however.)... 

Isothermal pyrolysis A pyrolysis during which the temperature is essentially constant. 

Table V. Elemental Composition of Starting Material and Its Char Prepared by the Isothermal Pyrolysis for 5 Min at the Temperatures Noted...

Note Char prepared by isothermal pyrolysis for 5 min at the temperatures noted. By difference Contains 1.2% sulfur Contains 0.6% sulfur... 

Commonly, analytical pyrolysis is performed as flash pyrolysis. This is defined as a pyrolysis that is carried out with a fast rate of temperature increase, of the order of 10,000° K/s. After the final pyrolysis temperature is attained, the temperature is maintained essentially constant (isothermal pyrolysis). Special types of analytical pyrolysis are also known. One example is fractionated pyrolysis in which the same sample is pyrolysed at different temperatures for different times in order to study special fractions of the sample. Another special type is stepwise pyrolysis in which the sample temperature is raised stepwise and the pyrolysis products are analyzed between each step. Temperature-programmed pyrolysis in which the sample is heated at a controlled rate within a temperature range is another special type. 

Other polymeric terpenes are also known in nature. One such material is the resin called dammar (recent or fossil), generated by the trees from the family Dipterocarpaceae. Pyrolytic studies were performed on this polymer [16] after separation in two fractions, one soluble in CH2CI2 and the other insoluble. Three different pyrolysis techniques were used to obtain information on the insoluble polymer, flash pyrolysis, open isothermal furnace pyrolysis and closed system isothermal pyrolysis. Several compounds separated and identified in pyrolysates by GC/MS are shown below ... 

An important effort in this investigation was the thermal decomposition study of the shales. Considerable effort has been made to find a simple kinetic model which will accurately describe the weight loss curves for non-isothermal pyrolysis at various heating rates. In the past, many researchers have proposed and tested theoretical kinetic models for this reaction Q-4), however, most attempts at finding a suitable model have been focused on finding a very accurate fit to experimental data. Successive studies have increasingly emphasized microscopic details (i.e., diffusion models, exact chemical composition, etc.) in an attempt to find a precise model to fit the weight loss curves. In this... 

Microfurnaces provide a constantly heated, isothermal pyrolysis zone into which solid samples are introduced. 

As a starting point for the tuning of our multi-component kinetic model we used kinetic data from closed-system non-isothermal pyrolysis experiments which describe the generation of oil and gas from a marine Type II source rock (Dieckmann et al. 1998). The frequency factors (A), activation energy ( ) distributions and hydrocarbon potentials of primary oil and gas generation of Dieckmann et al. (1998) were used as the framework for our model (Figure... 

A compositional kinetic model of hydrocarbon generation for a marine Type II source rock was developed based on data from closed-system non-isothermal pyrolysis experiments. The model predictions were tuned to a natural maturity sequence. The compositional data format chosen is compatible with the compositional resolution used in reservoir engineering, and allows a direct comparison of predicted compositions and phase behaviour to PVT data of natural fluids. 

Fig. 14. Carbon conversion and aromatization of oil shales and coals during isothermal pyrolysis at 425°C for 60 min.

The kinetics of the reaction steps are represented by DSC-derived rate constants for oil shale samples (steps 1 and 2), and TGA-deiived rate constants for bitumen samples (steps 3,4, and 5). The rate constant for the coking process (step 6) was taken from the literature. The stoichiometric coefficients/j to/j were determined for each oil shale sample, giving cumulative effects which are in agreement with the experimentally determined conversions at particular temperature intervals. The coefficients for the coking processand/j were taken from the literature [4-56]. The mathematical model of non-isothermal pyrolysis at a constant heating rate of P= dT/dt and based on the reaction scheme consists of the system of twelve equations 4-7 to 4-18 (Table 4-154). 

Table 4-154 Reaction equations of the non-isothermal pyrolysis according to [4-49].

Fig. 4-118 Non-isothermal Pyrolysis of Korean Oil Shale (Sample KOR) Heating Rate j3 5 K/min...

Fig. 4-119 Non-isothermal Pyrolysis of Jugoslavian Oil Shale Knjazevac (Sample K) Heating Rate p 10 K/min...

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