Pyrolysis of volatile aromatic hydrocarbons and n-heptane over calcium oxide and quartz

Abstract

Benzene, toluene, 1-methylnaphthalene, and n-heptane pyrolysis was studied over the temperature range 550-950 OC, by passing the vapor of the pure compound (initial concentration 2.4-3.9 mol % in helium) through -5.5 cm deep packed beds of calcium oxide/quartz mixtures, or of quartz in control experiments. The total pressure was -1 atm, and contact times were 0.9-1.3 s. The calcium oxide significantly increased the rates and extents of pyrolysis of the aromatics, reducing the temperature for a given percentage conversion by around 140, 140, and 170 OC for benzene, toluene, and 1-methylnaphthalene, respectively. In contrast, CaO decreased the comparable temperature for the aliphatic n-heptane by only -40 'C. Coke was the major product from pyrolysis of the aromatics over both beds. Minor amounts of coke deposition slightly increased the CaO activity for benzene and toluene pyrolysis, but continued coking produced a strong acthmy decay that was fitted to an Elovich model. Oxygen burn-off regenerated 75% and 100% of the initial CaO activity for these two compounds, respectively. A generic stone chemical property, rather than specific BET surface area, is believed responsible for the CaO pyrolysis activity.A shortcut procedure to evaluate the minimum vapor flows in distillation columns with a sidestream stripping section is presented. The method Is simple and highly accurate for relatively ideal mixtures. The case of a ternary mixture is discussed, but the algorithm readily extends to mixtures with any number of components. Also, the approach can be generalized to other types of complex columns as well.

The influence of abundant calcium oxide addition on oil sand pyrolysis

“…However, thiophenic species, which predominantly were alkyl substituted benzo[b]thiophene, shared the greatest proportion of aromatic fraction. Possibly attributed to the dehydrogenation by CaO [28], the relative amount of polycyclic aromatic hydrocarbons (PAHs) got an obvious increase when pyrolyzed with abundant CaO additives. As expected, acidic compounds in resin (e.g.…”

“…But additives of CaO are amorphous with surface area less than 5 m 2 /g. The inhibition are more likely coming from the absorption by the strong basic sites on the CaO surface [28].…”

Evaluation of different oxygen carriers for biomass tar reforming (I): Carbon deposition in experiments with toluene

“…Because of the complex composition of real tar, several researchers have studied tar decomposition reactions using biomass tar model compounds such as: anthracene [25], benzene [25][26][27][28][29][30][31], cyclohexane [32], 1-methyl-naphthalene [26,33], naphthalene [25,27,28,[34][35][36][37][38][39][40][41][42][43][44][45], n-heptane [26,[46][47][48], phenol [49], pyrene [25] and toluene [10, 11, 25-28, 31, 50-57].…”

Thermal removal of pyrene contamination from soil: basic studies and environmental health implications.

“…Literature on the pyrolysis of pyrene and other aromatic hydrocarbons gives guidance on chemical reactions that may impact the yields, compositions, and toxicologic activity of tars and other products from thermal decontamination of PAH-polluted soils. Pyrolysis of aromatic compounds in the presence of CaO at 400 to 800°C produces solid carbon (38,39). If these or other carbonforming reactions occur before the PAH exits the soil, i.e., if the relevant chemistry is fast compared to pyrene mass transfer from the soil, solid carbon will deposit on the soil, leading to lower weight loss than if all the contaminants had escaped the soil as volatile substances.…”