CRACKING OF HYDROCARBONS UNDER THE ACTION OF A HIGH-VOLTAGE ELECTRIC DISCHARGE

S. I. Smolyaninov, A. V. Kravtsov, I. I. Vishnevetskii, L. F. Kotlova

(Presented by the scientific-methodological seminar of the Department of Chemical Technology of Fuels)

As a result of the action of an electric discharge on various hydrocarbons and their mixtures, profound decomposition of the medium occurs; as a consequence, gases, condensation products (soot), and a liquid phase altered in its physicochemical properties are formed [1].

The molecules of the starting substances undergo more or less profound changes: they polymerize, dehydrogenate, crack, etc. By changing the form of the discharge or its parameters, the process can be directed toward the production of various valuable products [2]. Already at the beginning of the twentieth century, the process of voltolization of oils was carried out in a silent discharge. The use of more powerful forms of discharge (arc, pulsed, spark discharge) leads mainly to cracking of the treated feedstock, with the evolution of gaseous and solid products (soot). In this way, acetylene, hydrogen, and soot were obtained from natural gas under plant conditions [3].

A study of the electrocracking process of individual liquid organic products in a high-voltage arc showed that the yield and composition of electrocracking products depend on the nature of the feedstock being cracked [2]. The same regularity also extends to the pulsed discharge [4, 6], the use of which for electrocracking of hydrocarbon feedstock was proposed by S. Z. Roginskii and A. B. Shekhter [5]. M. D. Kushnerov and A. B. Shekhter [7] established that a pulsed discharge makes it possible to quench the decomposition products by simply changing the pulse duration, which is an advantage of this type of discharge over an arc discharge.

We carried out cracking of hydrocarbons in a condensed (pulsed) high-voltage discharge using a pulsed-voltage generator. The energy released in the discharge can be varied over a wide range. Individual hydrocarbons (n-heptane, toluene, p-xylene) were subjected to decomposition. Electrocracking of these hydrocarbons was carried out at different frequencies and pulse steepnesses.

Analysis of the cracking gas was carried out by gas-liquid chromatography. The nonhydrocarbon part of the gas and methane were separated by molecular sieves using a thermal-conductivity detector; the C₂ hydrocarbons were separated by silica gel using a flame-ionization detector.

Preliminary data obtained in the electrocracking of hydrocarbon feedstock in high-voltage pulsed discharges make it possible to assume that the general regularities of the electrocracking process

Table 1

Characteristics of gases obtained during the decomposition of individual hydrocarbons in a pulsed discharge

| Compound | Pulse repetition frequency, min\(^{-1}\) | \multicolumn{4}{c}{Component content, %} | Gas volume, ml \(\cdot 10^2\), [[unclear: unit]] | \multicolumn{4}{c}{Yields of gas components, ml \(\cdot 10^2\), [[unclear: unit]]} |
|---|---:|---:|---:|---:|---:|---:|---:|---:|---:|---:|
| | | H\(_2\) | CH\(_4\) | C\(_2\)H\(_2\) | C\(_2\)H\(_4\) | | H\(_2\) | CH\(_4\) | C\(_2\)H\(_2\) | C\(_2\)H\(_4\) |
| Toluene | 4 | 93.6 | 2.61 | 2.79 | 0.74 | 24.7 | 23.1 | 0.64 | 0.69 | 0.18 |
| Toluene | 20 | 93.6 | 2.54 | 3.31 | 0.516 | 200.0 | 187.2 | 5.08 | 6.62 | 1.03 |
| Toluene | 3 | 87.9 | 2.53 | 7.98 | 1.5 | 87.5 | 76.9 | 2.21 | 6.98 | 1.31 |
| Toluene | 8 | 89.5 | 2.38 | 6.98 | 1.043 | 217.0 | 194.0 | 5.16 | 15.15 | 2.26 |
| Toluene | 3 | 89.22 | 4.46 | 5.19 | 0.984 | 150.0 | 133.8 | 6.68 | 7.78 | 1.47 |
| Toluene | 3 | 93.2 | 2.71 | 3.08 | 0.487 | 9.25 | 8.6 | 0.25 | 0.29 | 0.04 |
| Toluene | 13 | 94.25 | 2.675 | 2.65 | 0.405 | 24.0 | 22.6 | 0.64 | 0.637 | 0.097 |
| Toluene | 20 | 90.2 | 2.91 | 5.84 | 1.002 | 200.0 | 180.4 | 5.82 | 11.68 | 2.004 |
| p-Xylene | 8.85 | 86.5 | 3.0 | 6.76 | 2.33 | 54.3 | 47.0 | 1.63 | 3.67 | 1.26 |
| p-Xylene | 3 | 71.4 | 6.98 | 9.67 | 5.07 | 200 | 142.8 | 13.96 | 19.34 | 11.94 |
| p-Xylene | 6 | 84.7 | 4.25 | 7.35 | 1.61 | 213 | 180.3 | 9.05 | 15.66 | 3.43 |
| n-Heptane | 4 | 77.9 | 2.686 | 10.53 | 8.03 | 107 | 83.2 | 2.87 | 11.29 | 8.58 |
| n-Heptane | 15 | 80.75 | 2.306 | 8.32 | 7.7 | 173 | 140.0 | 3.99 | 14.40 | 13.33 |
| n-Heptane | 3 | 86.7 | 2.09 | 5.01 | 3.98 | 70 | 60.7 | 1.46 | 3.51 | 2.79 |
| n-Heptane | 14 | 74.1 | 3.135 | 11.8 | 7.0 | 167 | 123.8 | 5.22 | 19.70 | 11.70 |

are also preserved for this type of discharge. Thus, when the energy or the pulse repetition frequency is increased, the yield of gaseous products increases, as is evident from the table. Increasing the rate of voltage rise (decreasing the duration of the pulse front) also entails an increase in the yield of gaseous products.

The possibility of varying the parameters and shape of the pulse over fairly wide limits makes it possible to determine the optimum regime for the course of the process.

Conclusions

1. Cracking of toluene, p-xylene, and n-heptane was carried out in a high-voltage pulsed discharge.

2. An attempt was made to establish a general dependence of the gas yield on the principal parameters of the pulse.

3. The yield and composition of the gas from the electrocracking of hydrocarbons were determined.

4. Increasing the energy, the pulse repetition frequency, and the rate of voltage rise leads to an increase in the gas yield.

Literature

1. N. S. Pechuro, A. N. Merkur’ev, E. Ya. Gvozdinskii, N. I. Sokolova. In: Problems of Electrical Treatment of Materials, Moscow, Publishing House of the Academy of Sciences of the USSR, 1960, pp. 14–24.

2. N. S. Pechuro, E. Ya. Grodzinskii, O. Yu. Pesin. In: Problems of Electrical Treatment of Materials, Moscow, Publishing House of the Academy of Sciences of the USSR, 1962, pp. 192–198.

3. N. S. Pechuro, E. Ya. Grodzinskii, O. Yu. Pesin. In: Problems of Electrical Treatment of Materials, Moscow, Publishing House of the Academy of Sciences of the USSR, 1962, pp. 209–213.

4. S. Z. Roginskii, A. B. Shekhter, ZhFKh, X, No. 3, 1937, pp. 473–480.

5. A. N. Merkur’ev, O. Yu. Pesin, N. S. Pechuro. In: Chemical Reactions of Organic Products in Electrical Discharges, Moscow, Nauka, 1966, pp. 173–180.

6. M. Ya. Kushnerov, A. B. Shekhter, ZhFKh, 1939, Vol. XIII, No. 2, p. 259.