(674f) Catalytic Decomposition of Tricyclodecane at High Temperature and Pressure

The catalytic decomposition of exo-tricyclo[5.2.1.0^2,6]decane (tricyclodecane) used as fuel was investigated. Fuel goes through high temperature around 400 °C and high pressure about 50 bar before combustion. In this severe condition, the fuel can be decomposed to lead formation of carbon deposit (coking). This coking decreases the thermal conductivity of system made of metal to lose subrole of fuel as a coolant. It would also plug the nozzle. Therefore either knowledge of properties about coking of metals or the selection of metal used for systems is important. The goal of this study is to investigate the effect of metal such as titanium(Ti), stainless steel 304 (SS304) and stainless steel 316 (SS316) for catalytic decomposition of tricyclodecane.

Catalytic decomposition of tricyclodecane was carried out in a batch-type reactor of 50 ml. The quartz flask was inserted inside the reactor made of SS304 to remove a catalytic role of wall inside the reactor. Chemical composition of product was determined by GC/MSD(Agilent 7890A Series GC Custom, 5975C inert MSD Standard Turbo EI). The total amount of coking ot metal surface was determined by Elementy Analyzer. The morphology of coking was determined by Scanning electron microscpe (SEM).

The Conversion of tricyclodecane was 5% in quartz flask for 3 h at 410 °C, 38 bar. Conversions of tricyclodecane were each 7%, 10%, 12% for Ti, SS304, SS316 inserted into a quartz flask at same reaction conditions above. SEM image shows ball-shaped carbon on the surface of Ti although filament carbon grew on both SS304 and SS316. They were each 8% (Ti), 15% (SS304), 19% (SS316) at reaction time of 5 h. Ti had almost the same conversion for both 3 h and 5 h at 410 °C, 38 bar. SEM image shows that the amount of ball-shaped carbon on every surface of Ti, SS304, SS316 is increased. This result indicated that Ti made stable Ti carbide of the ball-shaped surface with deposited carbon while amorphous carbon was grown as the filament shape on both surfaces of stainless steel. Therefore they look similar but their properties are different.

In a supercritical condition of tricyclodecane (435 °C, 38 bar) whose critical point is 428 °C, 36.6 bar, each conversion of tricyclodecane was 9%, 19%, 25% for Ti, SS304, SS316 in the reaction time of 5 h. All of those were increased comparing to a liquid condition. However amounts of coking of all metals in a supercritical condition are lower than those in a liquid condition (410 °C, 38 bar). These results were caused not by change of cracking properties of tricylcodecane in supercritical condition but by a property of supercritical fluid as a role of strongly extractive solvent. Formation of coking is generally increasing along with acidity of catalytic metal. However metal having relatively extremely strong acidity makes stable carbide with deposited carbon on surface of metal to reduce a total amount of coking. Therefore Ti is more suitable for aircraft application using tricyclodecane as its fuel with respect to thermal stability of fuel. SS316 generally known that it has ability of prevention of corrosion, has more amount of coking than SS304. It is demonstrated by increasing of the amount of Ni in SS316 comparing to SS304, whose d orbital is 3d8 to be catalytic metal. The conversion of tricyclodecane in a supercritical condition was higher than that in a liquid condition with all kind of metals (Ti, SS304, SS316). But the amount of deposited carbon is reduced. These results could be from property of strong extraction of supercritical fluid.