The kinetics of propane cracking at high pressure were measured to evaluate its suitability as a heat-transfer fluid, in either a closed loop or directly injected into the formation, to retort oil shale in situ. Rate constants were measured in batch reactors at isothermal temperatures from 450 to 540°C and at constant heating rates of 1.5 and 3.6°C/min. Rate constants were also measured in a flow loop for isothermal temperatures ranging from 440 to 473°C. The lowest temperatures in the batch autoclave experiments showed evidence of autocatalytic kinetic behavior, but the higher temperature batch experiments and the flow loop were more nearly first-order. The overall rate constants were consistent with an extrapolation of results from higher temperature measurements. Product selectivity changed as a function of conversion, with low conversion products rich in C 4+ products and high conversion products predominantly methane. A combination of the propane kinetics with simple heat balance calculations shows that more than enough propane is supplied by the retorting operation to balance the consumption by cracking, making the use of propane for the heat-transfer fluid self-sustaining. ■ INTRODUCTIONA variety of true in situ oil shale retorting processes are being researched, 1−3 including various methods of delivering or generating the heat of retorting down into the oil-shale formation. Heat delivery methods include resistive electrical circuits, closed-loop hot pipes immersed in a boiling oil pool, and hot gas injected into heating wells. The initial permeability of the oil shale is usually negligible; therefore, a base case is to heat the formation by thermal conduction from the heater wells. However, 20−30% porosity and associated permeability is generated by kerogen removal, which might provide for significant convective heat transfer into the formation.The advent of super-insulation materials 4 makes generation of heat on the surface and injection underground more attractive than previously. To carry that heat to the retort in either a closed loop or direct injection, a heat-transfer fluid with both a high heat capacity and high thermal stability is desired. One proposal by EGL Resources 5 initially used steam because of its high latent heat and then switched to an industrial heattransfer fluid, such as Therminol VP-1 (Solutia-Eastman) or Dowtherm A (Dow Chemical), to raise the formation to a pyrolysis temperature of 350°C. Given that the driving force for heat deposition is proportional to how much hotter than 350°C the heat transfer fluid is, it is highly advantageous to use a heat-transfer fluid above 450°C, which is above the working temperature of all currently available industrial heating fluids (with the exception of molten salts).Although steam, N 2 , and CO 2 are very stable, they have relatively low sensible molar heat capacities compared to light hydrocarbons. Ethane is about 50% greater; propane is twice as large; and butane is nearly 3 times higher. However, a preliminary screening indicated that th...