The Effect of Chlorine on PAH, Soot, and Tar Yields From a Jet Stirred/Plug Flow Reactor System

Abstract

The effect of Cl on polycyclic aromatic hydrocarbon (PAH), soot, and tar yields from fuel rich combustion is studied using a jet-stirred reactor close-coupled with a plug flow reactor system (JSR/PFR). The JSR provides input to the PFR from the fuel rich (φ_JSR = 2.2) combustion of C₂H₄/O₂/N₂, and chlorine is introduced into this stream at the PFR inlet via addition of CH₃Cl (φ_PFR = 2.3). This experimental condition is compared to second condition where C₂H₄ is added (φ_PFR = 2.3) to the PFR in lieu of CH₃Cl. PAH yields are seen to increase under both conditions at early PFR residence limes, while coming to an equilibrium value, or even decreasing in concentration at the end of the PFR. However, the yield of cyclopenta(cd)pyrene, a major human and bacterial cell mutagen, is suppressed with Cl present by as much as 90% near the end of the PFR, while benzo(a)pyrene, a major human carcinogen, shows a decrease in yield of about 25%. Tar (defined as total CH₂Cl₂ soluble material) is split into a low molecular weight fraction (128 amu to 226 amu), and a high molecular weight fraction (greater than 226 amu). The low molecular weight fraction shows behavior similar to representative individual PAH from that fraction, whereas twice as much high molecular weight tar is produced in the CH₃,Cl injection case. While soot production increases with time for both cases, accelerated soot growth occurred when CH₃Cl was added. These data indicate an increase in the ability of soot to capture high molecular weight PAH when Cl is present.

Key Words:

• PAH
• tar
• soot
• chlorine
• CH₃Cl
• mutagens.