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Ind. Eng. Chem. Process Des. Dev., Vol. 18, No. 3, 1979
Pyrolysis of Western Kentucky Heavy Oil Using a Transfer Line Reactor S. Krishnamurthy and Y. T. Shah* Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 1526 1
G. J. Stiegel Process Sciences Division, Pittsburgh Energy Technology Center, U S . Department
of Energy, Pittsburgh, Pennsylvania 75213
The pyrolysis of a heavy fraction of the COED Western Kentucky coal oil was studied using a transfer line reactor at temperatures ranging from 600 to 750 OC, with pressures of essentially 1 atm and residence times up to 0.1 s. Results indicate the preferential pyrolysis of the saturates fraction in the oil. The main gas products are hydrogen, methane, and ethylene whose formation is favored by increasing temperatures and residence times. The formation of polycyclic aromatics is evident in the liquid pyrolysate at high temperatures and long residence times. The rate of cracking of the heavy oil was found to follow first-order kinetics with an activation energy of 16 947 cal/g-mol. A comparison is made with the results reported earlier for the pyrolysis of a light fraction of the COED Western Kentucky coal oil (Krishnamurthy et al., 1979). The light oil, due to its lower boiling range and higher saturates content, yields more gaseous hydrocarbons and appears to be less susceptible to polymerization than the heavy oil under similar conditions.
Introduction There is currently a dearth of literature on the pyrolysis of coal liquids. Recently Peters (1977) has reported results from hydrocracking of coal liquids obtained by the SYNTHOIL, HRIH-coal, SRC, and COED processes. Pyrolysis studies on model compounds are extensively reported in the literature. They include studies made on single hydrocarbons as well as hydrocarbon mixtures. The reported studies also include the effect of reactor surface on the product distribution. One of the earlier studies on the pyrolysis of model aromatic compounds was performed by Kinney and DelBel (1954). Results from their study on the pyrolysis of benzene, diphenyl, naphthalene, chrysene, and anthracene at 1atm and 800-1000 " C indicate that destabilization of the aromatic ring is the rate-determining step. Madgwick et al. (1959) have reported results from the pyrolysis of crude oil in a fluidized bed reactor. Their study indicates that for residence times greater than 1 s, equilibrium could be approximated for the ethane-ethylene-hydrogen system. They also observed an increase in the aromatics yield with temperature. Kunugi et al. (1970a,b) have detected the formation of cyclic compounds during pyrolysis of ethylene and propylene. Virk et al. (1974) have reported that hydrogen to hydrocarbon ratios of less than 6.6 favor the formation of aromatic molecules during pyrolysis of paraffinic and olefinic hydrocarbons. These trends have also been observed to be more pronounced at higher temperatures. Sakai et al. (1976) have postulated that the formation of aromatics during pyrolysis of paraffinic hydrocarbons could be due to Diels-Alder reactions between butadiene and olefins. In another study, Kunugi et al. (1976) have reported results from the pyrolysis of different crude oils in a bench scale fluidized bed of carbon particles. Some of the recent studies on the effect of reactor surface during pyrolysis include those of Frech et al. (1976), Dunkelman and Albright (1976),and Brown and Albright (1976). 0019-7882/79/1118-0466$01.00/0
In a previous paper (Krishnamurthy et al., 1979) we reported results from the pyrolysis of a hydrotreated light fraction of the COED Process (Parsons Co., 1975; Scotti et al., 1975) Western Kentucky coal oil in a transfer line reactor. In this paper we extend our previous study to the case of a hydrotreated heavy fraction of the same coal oil.
Experimental Apparatus The experimental apparatus used in the present study has been described in detail by Krishnamurthy et al. (1979). This unit, shown in Figure 1,consisted essentially of a transfer line reactor 76 cm long and 0.61 cm in diameter with inlets for the fluidizing gas, coal derived liquid, and an alumina powder. The gas, liquid, and solid were preheated before being fed into the reactor. The purpose of the alumina was to provide part of the heat required for, and to remove any coke formed, during pyrolysis. Alumina possesses low abrasiveness and was therefore an obvious choice in this study. However, there have been some questions regarding its catalytic activity. In view of the fact that pyrolysis reactions are mainly of the free radical type (Rennard, 1979) and that the temperatures examined in this study are akin to pyrolysis conditions, the alumina was not considered to have any major catalytic effect. The reaction products leaving the reactor are separated from the alumina powder in a tank where the powder settles by gravity. The product gases then pass through a condenser unit where the condensables are separated. The noncondensables are metered and vented. The reactor and the separator tank were alonized in order to eliminate undesirable reactions promoted by the stainless steel surface. This technique has been applied by Frech et al. (1976) and has been found to be fairly effective in passivating the reactor surface. Efforts were made to maintain a truly isothermal reactor by using independent heating sections. As a result the temperature along the length of the reactor could be @ 1979 American Chemical Society
Ind. Eng. Chem. Process Des. Dev., Vol. 18, No. 3, 1979
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STC
9 /j--'-T C o r r i e r gas
STC
-Skin thermocouple
NP NP
Figure 1. Experimental apparatus. Table I. Comparison of Hydrotreated COED Western Kentucky Light and Heavy Oils light oil flash point (ASTM D92), F specific gravity (ASTM D287) kinematic viscosity (ASTM D2170), cSt % carbon % hydrogen % oxygen heating value, kcal / kg FIA analysis % recovery aromatics (assuming diolefins absent) % olefins % saturates
77 0.818 0.78 86.38 12.5
-
10717
heavy oil
HYOROCEN 0 COEO LO 7 4 0 C COEO LO 7 8 8 C CI COED HO 6 9 8 C
COED HO 750 C
165 0.906 2.5 85.5 11.6 2.8 10531.1
95 26.1
61 48
