US2061597A - Pyrolysis of methane - Google Patents

Description

Nov. 24, 1936. H. M. SMITH ET AL PYROLYSIS OF METHANE Filed April 26, 1934 FlGURE 1 FIGURE 2 fl m' lNVEN ORS A ORNEY t atenteei Nova 2d, lgdd sarra tried e htthtti rrnoarsre or nmrnann Harold M. Smith, Peter Grandone, and Harry 'E. Rail, hartlesvillle, (thin Application npniac, ran, seen-ac, teaser zfllaima, (crate-ice) (Granted micathe act at March a, rats, at

amended April 3%, 1928; 3% (G. W57) This invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to usv of any royalty thereon.

This invention relates to the pyrolytic synthesis oil (benzene) investigators have, been handicapped in obtaining their objective through lack of sufilcient information as to conditions necessary for the most eflicient treatment. This deficiency arises especially through lack of data concerning the decomposition rates of the hydrocarbon gases. Methane has been particularly neglected in this regard, and thermal decompositions designed to produce light oil (benzene), have been conducted largely on a trial and error basis. We, have conducted a systematic pyrolyti'c study of methane and have ascertained someIof the operating conditions necessary "when this gas is processed to produce light oil (benzene).

One object therefore pf this invention is to provide a method for the production or light-oil (benzene) from methane. I

When natural gas hydrocarbons are subjected to the action of heat the simple hydrocarbons are split and free radicals are formed. These "free radicals very quickly recombine, in numerous new and different combinations, and these new compounds are also subject to condensation and v polymerization reactions so that there finally results from the thermal decomposition a number of different products such as hydrogen, acetylene, ethylene, benzene, naphthalene, anthracene,

pyrene and increasingly heavier compounds an til the final degradation product, carbon, is obtained. Some of the products are what may be termed primary reaction products in that they are the simplest products that can be isolated in a stable condition; while other products are designated as secondary in that they may be assumed to proceed from the polymerization and condensation reactions of the primary products. Hydrogen, acetylene, and ethylene, are examples of the primary products and benzene, naphthalene, and the remainder of the heavy compounds are examples of secondary products.

Since .the object of this invention is the produc:

tion of one of the secondary products it is apparent that the time factor is of great im-, portance. In other words if a maximum production of light-oil (benzene) is to be obtained the series of reactions started by the application of heat must proceed far enough so that the pri mary products are converted to a maximum amount of light-oil (benzene), but these reac-- tions must be stopped before the production oi heavy hydrocarbons is increased at the expense of the light-oil (benzene).

We have carried out numerous experiments to determine the decomposition rates for methane at dififerent temperatures. As a result of these experiments we have found a linear relationship between the specific decomposition rate K, expressed in reciprocal seconds, and the reciprocal of the temperature in degrees Kelvin. This relationship is illustrated in Figure 1, where the logarithm of K is plotted against the reciprocal of the temperature in degrees Kelvin, and may be expressed as follows:

logmK= reacts In using this equation it is essential that I rep resent the average'temperature or the gases in the cracking zone as closely as it can be determined. v This equation is valid over the cracking rangeoi 1000 C. to 1200 0.

We have also discovered that when methane is reacting according to the above equation that the maximum yields of light-oil (benzene) at a given temperature are obtained when only sumcient time is allowed for approximately 25 percent by weight of the methane to be decomposed. In accordance with these discoveries when methane is processed to produce the maximum amount of light-oil (benzene) at a certain term perature at atmospheric pressure, the time c which a given particle of gas should remain in the reaction tube is given by the iollowing equation which results from combining these two diecoveries and expressing them in the logaritmc form:

- ia,s25 I IOQpfl- I wherein the contact time in-seconds is represented by the Greek letter theta. I

l or example, if it is desired to determine the contact time necessary to process methane tor .maximurn light-oil (benzene) yield at 115W then according to the above equation, since llb C.=l l23 K, we have then ' d= .ll-fit second Coming now to a more detaileddescription of the process, reference is made to Figure 2 which is ing chamber 3. This chamber may consist of a single tube, or of several lengths of tubing arranged in parallel or even as a coil, but regardless of its arrangement the gas must enter at 5 such a rate that it will remain in the heated In conclusion the gas containing the light-oil (benzene) vapors may now be subjected to appropriate scrubbing and recovery methods l for which the usual commercial equipment is suit- 20 able. In fact the entire process may be carried out in equipment that conforms to the usual commercial practices, the only criterion being that the cracking unit have the proper volume to provide a contact time in accord: :ice with the 26 previously cited equation.

Having described our invention, what we claim as 'new and wish to secure byLetters Patent is: 1. A process for the pyrolytic conversion of methane into benzene, consisting in limiting the methane decomposition to approximately 25 percent by weight for any temperature within the temperature range of 1000 C.1200 C. by passing the gas through a reaction tube at any temperature between 1000 C.-1200 C. at atmospheric pressure and at a time interval expressed by the formula log 0 15.0967

wherein the contact time in seconds is represented by the Greek letter theta.

HAROLD M. SMITH. PETER GRANDONE. HARRY '1. BALL.

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