Pyrolysis, pressurized operating conditions

During pyrolysis, the yield of gaseous and liquid products can vary from 25 to 70 percent by weight, depending on a number of variables, such as coal type, type and composition of the atmosphere present, final pyrolysis temperature, time-temperature path, and pressure. Although certain operating conditions may lead to increased product yield, achieving these conditions may result in increased costs. 

Operation conditions. A specially designed oxygen mixer and the interlock system assure safe operation outside tbe flammability envelope. Simple design and high quality material specifications result in two to three year intervals between major turnarounds and on stream times as high as 98+% over one year. The heat of reaction is recovered as high-pressure steam (18+ barg), which can be used by other parts of tbe VCM process (e.g., pyrolysis). Wastewater does not contain suspended catalyst fines therefore, there is no need to settle them and then dispose as a hazardous waste. Copper levels in fixed-bed effluents are below 0.3 ppm thus, no treatment is required. 

This screening approach is not a stand-alone technique, however, and bench-scale experimentation is needed to provide data for parameters which the screening approach does not adequately address isolation and confirmation of isomers of products, product mass balance, long-term studies in accessing catalyst life, and the variation of certain reactor operating conditions which have limited ranges at this scale, such as feed partial pressure. The catalytic conversion of wood pyrolysis products will be discussed in a screening context in this paper. 

This reaction has been studied using batch reactors, perfectly stirred continuous reactors, tubular continuous reactors, BENSON type reactors, wall-less reactors and shock tubes. The reaction has been carried out at temperatures between 700 and 1300 K, at pressures of 0.1 Pa to 10 Pa and at reaction times of 10 s to 10 s. The effects of the nature and of the area of the reactor walls as well as those of various additives have also been studied. The diversity of the studies carried out by a dozen teams throughout the world, the particularly widespread range of operating conditions (600 K for the temperature, which represents 11 orders of magnitude for the rate of initiation, 8 orders of magnitude for the pressure and reaction duration) make the pyrolysis of neopentane into a model radical reaction. 

The pyrolysis of isopentane has been studied in a batch reactor at constant volume at the temperature T = 480 at an initial isopentane pressure of p = 25 mmHg. Figure 2 shows the variation of the partial pressures of the products formed as a fimction of the reaction time. Very different results are observed according to the operating conditions. 

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. 

The stmcture of residual char particles after devolatilization depends on the nature of the coal and the pyrolysis conditions such as heating rate, peak temperature, soak time at the peak temperature, gaseous environment, and the pressure of the system (72). The oxidation rate of the chat is primarily influenced by the physical and chemical nature of the chat, the rate of diffusion and the nature of the reactant and product gases, and the temperature and pressure of the operating system. The physical and chemical characteristics that influence the rate of oxidation ate chemical stmctural variations, such as the... 

The recent use of the transmission electron microscopy of high resolu tion at the in situ condition at large enough pressure of methane resulted in the direct observation of the metal nanoparticle liquefaction at the cata lytic methane pyrolysis. Thus, the formation of carbon fibers and nano tubes often results from fluidization of the catalyticaUy active phase via its oversaturation with carbon at the catalyst operation. This may happen to a variety of processes when the deposition of graphitized carbon is pre ceded by the primary atomic or another energy saturated carbon species formed on the surface of the catalyticaUy active metals (see Figure 5.2). Supposedly, the formation of the very specific structures of the carbon fil ament, like the so caUed fishbone structure (see Figure 5.3B), may be... 

In ideal conditions, a furnace operating on naphtha can run for 90 days without decoking However, the run length is always shorter due to the inevitable fouling of the quench boiler. Progressive coke deposition in the pyrolysis tubes results in an increase in their metal skin temperature, connected with the growing inefficiency of heat transfer, and in an increase in the pressure drop caused by the reduction of the open cross-section of the tube. 

Pyrolysis of scrap rubber may be conducted under significantly varied conditions of time, temperature, and pressure. It may be effected under reductive or oxidative conditions which in turn could be catalytic or noncatalytic. In considering scale-up, engineering alternatives are more important than in most chemical processes. For example, product yield and quality would be expected to be different in batch operation from that in continuous operation. 

J.E. BLAKEMORE et al. (12) recently studied the pyrolysis of n-butane in the presence of trace quantities of oxygen, using a gold microreactor operated under plug-flow conditions, at 530-600 C and atmospheric pressure. For a given initial concentration of n-butane, increasingly larger fractions of 1- and 2-butenes,... 

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