Kinetics of Propane Cracking Related to Its Use as a Heat-Transfer Fluid

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 C₄₊ 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.