Time scales pyrolysis

Both quadricyclane and norbornadiene are high-energy isomers of C7H8, and it is interesting to compare their thermal behavior. Figures 4.5 and 4.6 show the pyrolysis breakdown behavior for norbornadiene and quadricyclane, respectively, extracted as described above. As shown, norbornadiene (NBD) is stable on the available time scale for temperatures up to 600 K. (The small apparent decrease in NBD contribution in the 400-600 K range is within the uncertainty of the fitting process — no product species are observed.) Above 600 K decomposition... 

The pyrolysis breakdown behavior for cubane is plotted in Fig. 4.7. Cubane is found to be stable on the millisecond time scale for temperatures up to 500 K. Minor decomposition was found between 500 and 700 K, and above that point decomposition is faster than the flow tube residence time. By 800 K there is essentially no remaining cubane. The dominant product channel is loss of C2H2, delding benzene. Some rearrangement to COT was observed above 650 K, and a small amount of styrene was found at high temperatures. The decomposition lifetimes corresponding to these breakdown curves are given in Table 4.2. 

The properties of wood(7,14) were used to analyze time scales of physical and chemical processes during wood pyrolysis as done in Russel, et al (15) for coal. Even at combustion level heat fluxes, intraparticle heat transfer is one to two orders of magnitude slower than mass transfer (volatiles outflow) or chemical reaction. A mathematical model reflecting these facts is briefly presented here and detailed elsewhere(16). It predicts volatiles release rate and composition as a function of particle physical properties, and simulates the experiments described herein in order to determine adequate kinetic models for individual product formation rates. 

The product yields of the laboratory scale pyrolysis of fibre sludge are differing badly in comparison to the PDU scale results. The oil yield of the PDU scale pyrolysis is 3 times lower than the laboratory scale pyrolysis. In fact the PDU scale data are the more reliable ones. Yields of 8.4 wt.% bio-oil and 25,8 wt.% charcoal formed by fibre sludge pyrolysis can be also found in earlier studies [18]. 

The purpose of this study is to maximize the fraction of arsenic in wood charcoal while minimizing mass reduction of the bio-oil. Lab-scale pyrolysis was conducted in order to determine mass balances of yield and percentage of arsenic over the total system The experimental set-up was built to examine the influence of process parameters such as pyrolysis temperature and total pyrolysis time. The optimum combination of temperature and total pyrolysis time, at which the amount of arsenic retained in the wood charcoal is maximized and that in oil is minimized, was tried to be found. 

Experiments with peanut shell pyrolysis vapor reforming duplicated the 5-cm bench-scale unit results with the aqueous fraction of wood pyrolysis oil. This is the first time whole pyrolysis vapors have been processed in the fluid bed reforming process. 

The time-scale of DPMS and Py-GC/MS is quite different and, in the case of thermally labile pyrolysis products the two techniques may detect different compounds. ... 

The time-scale of the two pyrolysis techniques is quite different, and owing to the thermal lability of the sulfur-containing primary products, significantly different compounds were detected by the two methods. However, the results... 

The effects of decreasing contact time and increasing temperatures on product yields and feedstock conversions in the steam pyrolysis of a wide range naphtha and a kerosene were studied in the laboratory bench scale pyrolysis unit and in the Millisecond Pyrolysis Pilot Plant. The laboratory studies covered wide ranges of operating variables such as reactor outlet temperature [1400-1750 F (760 to 954 C)], contact... 

The proper design of commercial pyrolysis reactors requires a suitable expression for the intrinsic rate of the reactions. As intrinsic rate equations cannot yet be predicted, especially for the ultrapyrolysis regime, experimental data is required. This data is best obtained from bench-scale laboratory reactors, rather than from pilot plants or commercial-scale units. In laboratory scale pyrolysis reactors, the design and operating conditions can be chosen to reduce or eliminate the effects of mass and heat transfer, contaminants and catalytic surfaces from the observed measurements, thus allowing for the development of accurate expressions. It is most advantageous if the laboratory reactor is operated isothermally (in space and time), so that the temperature can be considered as an independent variable. Also, the pressure should be ideally kept constant. 

Pulsed electronic transition chemical laser operation appears to be possible in a much wider class of reaction systems than those defined by the foregoing considerations. Reaction initiation in premixed reagents by pulsed techniques can provide population inversions on time scales short compared with fluid mixing times and relaxation times for lower laser states. Such techniques include photolysis, laser-induced dissociation, electrical discharge production of atoms or metastables, and shock-induced dissociation and pyrolysis. Such lasers are subject to the pumping rate condition of Figure 3.21 which is much less restrictive than the condition for diffusive mixing... 

Decaborane is the most studied of all the polyhedral boranes and at one time (mid-1950s) was manufactured on a multitonne scale in the USA as a potential high-energy fuel. It is now obtainable in research quantities by the pyrolysis of B2H9 at 100-200°C in the presence of catalytic amounts of Lewis bases such as Me20. B10H14 is a colourless, volatile, crystalline solid (see Table 6.2, p. 163) which... 

The performance of a novel microwave-induced pyrolysis process was evaluated by studying the degradation of HDPE and aluminiutn/polymer laminates in a semibatch bench-scale apparatus. The relationship between temperature, residence time of the pyrolytic products in the reactor, and the chemical composition of the hydrocarbon fraction produced was investigated. 28 refs. 

The high temperature pyrolysis of PE, PP and mixtures of these polymers was studied in a novel bench-scale rotating eone reaetor to identify the optimal operating eonditions for this reaetor. It was shown that the effect of the sand or reaetor temperature on the product spectrum obtained was large eompared with the effect of other parameters, e.g. residenee time. 15 refs. 

The application of a selective pyrolysis process to the recovery of chemicals from waste PU foam is described. The reaction conditions are controlled so that target products can be collected directly from the waste stream in high yields. Molecular beam mass spectrometry is used in small-scale experiments to analyse the reaction products in real time, enabling the effects of process parameters such as temperature, catalysts and co-reagents to be quickly screened. Fixed bed and fluidised bed reactors are used to provide products for conventional chemical analysis to determine material balances and to test the concept under larger scale conditions. Results are presented for the recycling of PU foams from vehicle seats and refrigerators. 12 refs. 

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