Ethene ethane ratio

Similarly, Bond et al. [4] confirmed that the microwave stimulation of methane transformation reactions in the presence of a number of rare earth basic oxides to form C2 hydrocarbons (ethene, ethane) was achieved at a lower temperature and with the increased selectivity. Microwave irradiation resulted in an increase of the ethene/ethane ratio, which was desirable. The results obtained were explained by the formation of hot spots (Sect. 10.3.3) of higher temperature than the bulk catalyst. This means that methane is activated at these hot spots. 

Pyrolysis of both kerogen and shale oil breaks larger molecules into smaller ones. For the alkene-alkane-hydrogen system to be at equilibrium, the reactions that lead to this equilibrium must be faster than those producing the smaller molecular fragments. To reach equilibrium, the ethene/ethane ratio must satisfy the condition ... 

Because the enthalpy change for the C2H4 plus H2 reaction is 34 kcal/mol (9, the ethene/ethane ratio must be a function of temperature when other conditions are constant. In addition, the ratio should be proportional to the amount of inert diluent when the system is at or near equilibrium, because the equilibrium expression has units of reciprocal pressure. 

Therefore, both the equilibrium and free-radical hypotheses predict that the ethene/ethane ratios depend on pyrolysis temperature and inert diluent. However, the predictions are quantitatively different and can be tested. 

The rates of ethene and ethane evolution, the ratio of ethene to ethane, and the partial pressure of hydrogen (relative evolution rate of hydrogen to total gas) are shown in Figure 2 for oil shale heated at 1.5°C/min under an autogenous atmosphere. The ethene/ethane ratio reaches a first minimum before the peak rate of C2 evolution. It then increases slightly before reaching a second minimum at about 540°C. A more pronounced variation in the propene/propane ratio was observed at l°C/min (Figure 3). 

If the ethene/ethane ratios are combined with the hydrogen partial pressures, we can demonstrate that the ethene-hydrogen-ethane system is far from thermal equilibrium under the conditions of the experiment shown in Figure 2. The experimental value of c2h6 Pc2h4 Ph2 s comPare< Figure 4 with the value of Keq. Only at temperatures near and above 600°C, at which the C2 evolution rate is negligible, does the ethene/ethane ratio approach equilibrium. Therefore, a nonequilibrium explanation of the observed alkene/alkane ratios is required. 

The free-radical mechanism also predicts that the ethene/ethane ratio should increase if inert diluent is added (Figure 5). The addition of an inert sweep causes both the instantaneous values above 450°C and the integral values of the ethene/ethane ratio to increase. The integral value of the ethene/ethane ratio increased from 0.21 under autogenous conditions to 0.29 in the slow-sweep experiment and to 0.33 in the fast-sweep experiment. We determined a value of 0.34 at... 

Figure 2. Product measurements for oil shale heated at 1.5°C/min under an autogenous atmosphere (a) rate of C2 evolution (b) ethene/ethane ratio (c) partial pressure of hydrogen released.

Figure 5. Effect of inert sweep gas on the time-dependent ethene/ethane ratio for oil shale heated at 1.5°C/min under autogenous conditions. The slow-sweep sample size and flow rate were 28 g and 50 cm3/min, respectively. The fast-sweep sample size and flow rate were 14 g and 100 cm3/min, respectively. Most of the ethene and ethane was evolved between 400° and 500°C.

Figure 7. Effect of cracking on the ethene/ethane ratios of the total evolved gases, shown as a function of (a) cracking losses and (b) cracking temperature. The result indicated by A is for a Fischer assay. The other points indicate cracking over burnt shale (O), retorted shale (%), and in an empty reactor ([2). The ratios correlate better with the cracking temperature than with the cracking losses.

Figure 8. Ethene/ethane ratio as a function of (a) yields as a percentage of Fischer assay (FA), (b) the logarithm of the heating rate, and (c) an Arrhenius plot using Tp.

Figure 9. Effect of temperature and inert sweep gas on the ethene/ethane ratio from retorting oil shale. Results are shown for work at LLNL and LETC. The temperature dependence of the ethene/ethane ratio can be characterized by an activation energy of about 11 kcal/mol.

When oil shale is heated at a constant rate, the alkene/alkane ratios in the evolved hydrocarbon gases change with time. In addition, the alkene/alkane ratios in both the gas and the oil are affected by an inert sweep gas. The ethene/ethane ratio is not determined by equilibrium with hydrogen, and we interpret this phenomenon in terms of a free-radical cracking mechanism. The implication is that alkene/alkane ratios, especially the ethene/ethane ratio, can be used as an indicator of retort performance only if the correct relationships are used for each set of retort conditions. 

Jacobson, I. A., Jr. Decora, A. W. Cook G. L. "Retorting Indexes for Oil Shale Pyrolysis from Ethene/Ethane Ratios of Product Gases," in Science and Technology of Oil Shale, T. F. Yen, Ed. Ann Arbor Sciences Publishers Ann Arbor, MI, 1976 p. 103. 

The effect of changing the CH4/O2 ratio (2, 4, 8) and reaction temperature (973, 1023, 1073 K) on the coupling process was determined for K2La2Ti3Oio, Rb2La2Ti30io and Na2La2Ti3Oio.The methane conversion, ethene/ethane ratio, and CO2/CO ratio decreased while the C2 selectivity and O2 conversion increased with the increase of CH4/O2 ratio. Raising the temperature resulted in higher methane and O2 conversions, ethene/ethane and CO2/CO ratios and C2 selectivity. 

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