Ethylene selectivity, naphtha pyrolysis

Figure 9. Ethylene yield selectivity, naphtha pyrolysis. (--------------) Prediction.

Toluene. The sources of toluene lie primarily in the catalytic reforming of selected petroleum fractions rich in naphthenes or in the recovery of toluene contained in aromatic concentrate (pyrolysis gasoline) produced as a byproduct of ethylene manufacture—mostly from naphtha/gas oil cracking. U.S. production and pricing for benzene and the aromatics discussed in Sections... 

Figure 1. Each sloped line represents the loci of all possible combinations of average residence times and hydrocarbon partial pressures which are consistent with a fixed pyrolysis yield pattern, i.e., constant pyrolysis selectivity lines. For liquid feedstocks, the methane-to-ethylene ratio found in the pyrolysis reactor effluent has been used as a good overall indicator of pyrolysis reactor selectivity. Low methane-to-ethylene ratios correspond to a high total yield of ethylene, propylene, butadiene and butylenes. Consequently, the yields of methane, ethane, aromatics and fuel oil are reduced. TL refore, each constant pyrolysis selectivity line shown in Figure 1 is identified with a fixed methane-to-ethylene ratio. This specific selectivity chart applies to a Kuwait heavy naphtha which is pyrolyzed to achieve a constant degree of feedstock dehydrogenation, i.e., a constant hydrogen content in the effluent liquid products, which in this case corresponds to the limiting cracking severity.

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