Addition Of Phenyl Research Articles

Influence of aliphatic side chains of aromatic hydrocarbons on soot formation: Experimental and numerical investigation

The effect of aliphatic side chains in the feedstock on soot formation was studied with experimental and numerical simulation. Feedstocks of ethylbenzene, xylene, toluene, and benzene were pyrolyzed at different residence times and temperatures, and the particle size distribution (PSD) of the formed soot was measured. The initial nucleation rates of soot during ethylbenzene or toluene pyrolysis was high. However, after a long residence time, the amount of soot produced from benzene pyrolysis became higher than for these feedstocks. This result suggests that at long residence times, the growth rate of soot from benzene is higher than those of ethylbenzene and toluene. Numerical simulation for the pyrolysis of ethylbenzene, toluene, and benzene was conducted with the KAUST PAH Mechanism 2 (KM2) model, and the prediction accuracy was improved by adding some new reactions. The simulations were performed at two conditions similar to the experimental ones: The production rate of polycyclic aromatic hydrocarbons (PAHs) was very high at the beginning of reactions of ethylbenzene and toluene, indicating high rates of soot nuclei generation. In benzene pyrolysis, modification of the KM2 model led to a higher predicted PAH concentration than that with the original KM2. Most of the reactions we added to the KM2 model are those of PAH growth by phenyl addition (PA). Therefore, the PA mechanism would be an important reaction pathway for PAH growth in the pyrolysis of benzene.

Experimental Study of Gas-Phase Pyrolysis Reaction of Benzene to Investigate the Early Stage of Coke Formation

Gas phase pyrolysis of benzene was performed at 1,123, 1,173, and 1,223 K using a flow type reactor to examine the mechanism of the initial stage of coke (poly-aromatic hydrocarbons; PAHs) formation. The pyrolysis products including hydrogen, tar, and coke were quantified as the function of benzene residence time using gas chromatography, gas chromatography-mass spectrometry, LDI-TOFMS, and elemental analysis to establish the carbon balance within 95 to 105% for all of the experiments. Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) was applied to determine individual components in coke. Main tar components quantified were biphenyl (C12H10), terphenyl isomers (C18H14), quaterphenyl isomers (C24H18), phenanthrene (C14H10), and triphenylene (C18H12). Phenanthrene was found to be formed by the H-abstraction-C2H2-addition (HACA) mechanism and the other components were judged to be formed by the phenyl addition (PA) and the phenyl addition/cyclization (PAC) mechanisms. One of the smallest molecules identified within the coke was dibenzo[fg,op]naphthacene (C24H14) that is formed from triphenylene by the PAC mechanism. Larger molecules formed by the PAC mechanism and the HACA mechanism were also identified as coke components at the initial stage of pyrolysis. The phenyl addition to PAHs by the PAC mechanism and the HACA mechanism were judged to be main pathways to form larger PAHs. Main reaction mechanisms at the early stage of coke formation were suggested based on the detailed experimental data.