Pyrolysis cracking

Oil Shale Oil shale is nonporous rock containing organic kero-gen. Raw shale oil is extracted from mined rock by pyrolysis in a surface retort, or in situ by steam injection after breaking up the rock with explosives. Pyrolysis cracks the kerogen, yielding raw shale oil... 

Most ethylene is produeed by the pyrolysis cracking of heavier hydrocarbons such as naphtha. Figure 2.2 illustrates the key thermodynamie features using heptane as a proxy for the feedstock. 

The LPG stream produced by pyrolysis cracking contains all possible C3 and C4 molecules. As well as olefins, prominent are highly unsaturated materials such as acetylenes and dienes. 

Naphtha is also produced from natural gas condensate by distillation. In many condensates there exists a long high boiling tail which makes it unsuitable for pyrolysis cracking. Further, the relatively lower value (in mass terms) of condensate relative to naphtha makes it... 

A number of petrochemical processes produce significant volumes of hydrogen as a by-product, including pyrolysis cracking. This can be used as a fuel oil substitute, but this greatly undervalues hydrogen, and alternative use in other chemical processes is the better option and generally pursued by successful operations. 

More olefins are produced by routes which convert the coal into an intermediate product which is subsequently converted into olefins. This could be a liquid, which is then subject to pyrolysis cracking. Most interest focuses on the gasification of coal into carbon monoxide and hydrogen, commonly known as synthesis gas. From synthesis gas olefins can be produced directly or via further intermediates, such as naphtha or methanol. 

The coefficients of the Arrhenius equation determined in this manner, are the basic data for the calculation of the kinetics of pyrolysis (crack) reactions and therefore also the basis for the choice of process conditions, such as pre-setting of reactor temperatures, residence times etc. in thermal conversion processes. 

The peak maximum temperatures of the pyrolysis (cracking) reaction (450-485 °C) differ so little that for each heating rate a coefficient of variation V = 1.08 % of the corresponding mean has been calculated. Calculation of the kinetic coefficients using ASTM E 698-79 gives the following average values ... 

The start temperature of the cracking process was ascertained according to Adony [4-14], A mean x = 414 °C ( V=4.2 %) has been found independent of the provenance of the samples. The empirical detennination of 400 °C as the end of the evaporation range and the start of the pyrolysis (cracking) range, is thus justfied. 

Arrhenius equation gives the best description of the dependence of the reaction rate upon the temperature, for pyrolysis (cracking) and oxidation reactions. It is possible to extrapolate the reaction rate constant and the half life time to higher or lower temperatures. Therefore the coefficients of the Arrhenius equation, (activation energy E and the frequency (pre-exponential) factor A) were determined using the method according to ASTM E... 

Fig. 8. Photographs of C/C composites after the first carbonization with decreasing amounts of matrix pyrolysis cracks, due to decreasing cross-sectional shrinkage of the matrix precursor and decreasing adhesion between fibre and matrix precursor.

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