Radical reaction schemes for the cracking of ethane, propane, normal and isobutane, ethylene, and propylene were set up. The kinetic parameters of these schemes were determined by fitting experimental data obtained under nonisothermal and nonisobaric conditions In a pilot plant. The set of continuity equations for both molecular and radical species was Integrated using Gear's algorithm for stiff differential equations. The reliability of the parameters was tested by simulating the cracking of binary and ternary paraffinic mixtures. A satisfactory fit of the results of mixtures cracking was obtained with a reaction scheme derived from the superposition of the schemes for single-component cracking.

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A novel experimental setup allowed both the kinetics of the thermal cracking of ethane and of the coke formation to be studied over a temperature range extending from 750 to 870°C. The overall kinetics of ethane disappearance are in excellent agreement with previously reported pilot results. Coking rates are initially high but rapidly decrease to reach an asymptotic value. The initial product distribution also differs from the asymptotic product distribution. A kinetic model for the coking is derived from the experiments and used in conjunction with a set of conservation equations for the simulation of industrial ethane cracking. The predicted run length, thickness of the coke layer and evolution of the tubeskin temperatures are in agreement with industrial Observations. SCOPEThermal cracking of hydrocarbons around 800°C is the most important process for the production of feedstocks for the petrochemical industry. Side reactions always lead to carcycle has to be interrupted tor decoking by burning off the coke. Little is known about the rate of formation of coke. Yet, this is required for a better planning of the production and for the coking during ethane cracking in a novel experimental set up and makes use of this information to industrial operation and predict the evolution of the process parameters and the coke layer with time.bonaceous material that deposits on the wall ofthe cracking coil more optimal operation. This Paper Presents a kinetic Study of thus reducing heat transfer, requiring critical tubeskin temPeratures, increasing the Pressure drop so that after 20-60 days, depending upon the severity of operation, the production CONCLUSIONS AND SIGNIFICANCESpecially designed equipment consisting of a completely mixed reactor in which a hollow cylinder is suspended at the arm of an electrobalance allows the kinetics of the main reaction(s) and of the coking to be determined. The reactor, with a volume of some 5 mL yields kinetic parameters for the main reactions in agreement with those obtained in a pilot plant. Accurate rates of coking a r e obtained which are used in the simulation of an existing industrial cracking unit. In this way, it becomes possible to predict the evolution of conversion, product distribution, pressures, and coke layer in the cracking coil. The predicted results are in line with industrial observations.

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