US3083152A - Process for hydrocarbon conversion - Google Patents

Description

3,83,152 Patented Mar. 26, 1963 3 083 152 rnocnss non nrnizotannors coNvnnsroN Hiilis U. Foiidns, Crystal Lake, Iii assignor to The Eire iii ompany, Qhicago, lit, a corporation of No Drawing. Filed May 27, 1959, Ser. No. 816,037 '7 Claims. (ill. 2lE4--162) This invention relates to a process for conversion of hydrocarbons and is more particularly directed to a process for dehydrogenating low-molecular-weight hydrocarbons containing at least two carbon atoms to the molecule under the influence of high-energy ionizing radiations, while the hydrocarbon vapor or gas is admixed with metal vapor or highly dispersed metal particles.

It is known that high-energy radiation such as neutron, beta-, and gamma-radiation is capable of producing hydro carbon decomposition. Generally, however, the decom position reactions have been non-selective and a variety of products have been formed. Moreover, yield efliciencies have been low and large doses of radiation have been required. It has been found, also, that neutron irradiation with defined energies may be used to cause selective rupture of carbon-hydrogen bonds in hydrocarbons to produce unsaturated compounds (see McClinton et al., US. Patent No. 2,7 43,223

I have discovered that the dehydrogenation reaction can be made to proceed more readily at higher radiation eificiencies, particularly in the case of dehydrogenation of paramnic hydrocarbons, if the hydrocarbon is mixed with a small amount of metal vapor or highly dispersed metal at the time it is subjected to irradiation. Without intending to be bound by any theory of reaction, it is postulated that the irradiation increases the energy levels of the metal atoms, causing them to become an energy carrier with enough energy to promote dehydrogenation. It is further postulated that the effect of irradiation upon the hydrocarbons themselves, and equilibrium changes induced in the structure of the metal, is conducive to dehydrogenation selectivity.

It is an object of my invention to provide a process for converting hydrocarbons into less saturated hydrocarbons. It is another object of, my invention to provide a process for selectively dehydrogenating hydrocarbons. Still another object of the invention is to provide a process for dehydrogenating hydrocarbons at lower temperatures than is practical by thermal means alone. Other objects of the invention will manifest themselves from the following description.

In accordance with my invention, the hydrocarbon to be dehydrogenated is heated to a temperature of the order of 800 F. to 1200 F, depending on the nature of the charging stock and the conversion per pass desired. Where the charging stock is ethane or gas rich in ethane, temperatures approaching the upper limit are preferably used. The higher-molecular-weight hydrocarbons, such as heptane and octane, are preferably dehydrogenated at temperatures approaching the lower limit. The hydrocarbon either before or after preheating is mixed with a small amount of highly dispersed metal from the group consisting of groups IA, KB, 11113, IVE and VIlI B of. the periodic table. As specific examples of metals which can be used are lithium, sodium, potassium, cesium, zinc, cadmium, mercury, gallium, indium, tin, lead, iron, nickel, platinum and palladium. Where the metal is sufficiently volatile at the reaction temperature to be present in the reaction mixture in the desired concentration, I prefer to use metal vapors. The metal vapor may be mixed with the preheated hydrocarbon vapor in the desired proportion, or the heated hydrocarbon may be contacted with the molten metal to pick up metal vapor at the partial pressure desired. In the event the volatility of the metal is too lowto exert the desired partial pressure under reaction conditions, the metal may be suspended in the desired amount in the gas or vapor in finely dispersed form, as for example, in the form of powder, the particles of which are less than 50 microns in diameter. In general, metals of groups IA, 1113, IIIB and lVB can be used in vapor state, whereas metals of group VIIIB will be used in finely-divided suspended state. Where finely-divided metal is used, it may be charged to the stream of gas or vapor before or after heating to the desired reaction temperature. in general, where the metal is present in the vapor state, I prefer to have it present in an amount such that it will not exert a partial pressure in excess of 10% of that ofi the hydrocarbon and may be present in an amount as low as 01%. Generally, partial pressure of the order of 0.1% to around 3% is preferred. Where finely-divided metal is used, it should be present in an amount of 0.01 to 5 weight percent of the hydrocarbon.

Any suitable means may be utilized for heating the reaction mixture and maintaining it at reaction temperature during passage through the reaction zone. A convenient method for imparting heat is by means of a circulating pebble heater. Suitable means are also provided for separating dispersed metal or metal vapors from the reaction products and recycling the metal.

The process may be carried out at atmospheric or subatmospheric or at supenatmospheric pressures up to about 3 atmospheres. Space velocities are adjusted so that the contact time of the charge in the reaction zone is of the order of 0.1 to 30' seconds.

The mixture of hydrocarbon and the metal vapor, or finely-divided suspended metal, is passed through a reaction zone or tube at the desired reaction temperature while being irradiated by radiations from a high-energy, ionizing, radiation source. Such radiations may be gamma-rays, high-energy electrons, protons, neutrons or alpha-particles. Suitable sources of radiation are well known in the art. For example, gamma-rays may be obtained firom cobalt-60 or cesium-"137. Alpha-emission may be obtained from radon. Electron beams may be obtained from linear accelerators, Van de Graaif machines, and resonant transformers. Other sources of beta-, gamma-, and neutron radiation include nuclear reactors, cyclotron, betatron, uranium-235, potassium-40, strontium-9O and thorium- 233. Nuclear reactors, electron machines and cobalt-60 are convenient sources of radiation. Machines such as a linear accelerator provide an adaptable source in that high flux rates can be obtained, and the machines can be readily adapted to provide gammaor neutron-radiation. The type of radiation employed in this process is not critical, provided that the emanation is of suflicient flux and penetrating energy to be absorbed by the reaction medium. Thus, electromagnetic radiation may range from X-rays of about kev. or higher to gamma-radiation with an energy spectrum of about 0.5 to 20 mev. Generally, in the case of high-energy radiation such as gamma-rays, neutrons, or high-energy electrons, the radiation source is placed externally to the reactor and the reactants, and products pass through the reactor in the path of the radiation. The process also includes locating radiation sources, such as radioactive isotopes, within the reactor to take advantage of emanations of low penetrating power.

Radiation dosages may vary widely, dependent upon the source and operating conditions. In general, lower dosages are required when the process is carried out in the higher part of the specified temperature range. Dosages required for the process are of the order of around 5 X 10 to around 5 X10 roentgens.

vAs an example illustrating the invention, a stream of ethane is subjected to pyrolysis in an electrically-heated cent of the converted ethane reacts to form ethylene.

Vycor tube, having an internal diameter of one inch, at a temperature of 1400 F., atmospheric pressure, and a contact time of one second. A 25 percent yield of ethylene is obtained at a selectivity of 75 percent; that is, 75 per- In another run, the ethane is mixed with mercury vapor at a partial pressure of millimeters of mercury, and the mixture is passed through the tube under atmospheric pressure at a temperature of 1150 F. with the same contact time of one second. The tube is irradiated with 8 mev.

electrons from a linear accelerator at a dose rate of drocarbons to high-energy, ionizing radiations for a period of 0.1 to 30 seconds to provide a dose amount of 500 to 500,000 roentgens while in contact with at least one metal selected from the group consisting of group IA, HB, IHB,

.IVB, and VIIIB metals of the periodic table, said metal being in a highly dispersed state, said hydrocarbon being at a temperature in the range of '800-'1200 F.

2. A process according to claim 1 in which said metal is in the vapor state and present in an amount to have a partial pressure in the range of 0.01 to 10.0% of the partial pressure of the hydrocarbon.

3. A process according to claim 1 in which said metal is presented at a suspension having a particle size of not larger than 50 microns in diameter, and in an amount in the range of 0.01 to 5.0% by weight.

4. A process according to claim 2 in which the metal is selected from the group consisting of lithium, sodium,

' potassium, cesium, zinc, cadmium, mercury, gallium, in

dium, tin, lead, iron, nickel, platinum, and palladium.

-5 A process according to claim 4 in which the radiation is gamma radiation from cobalt-.

6. The method for dehydrogenating ethane to ethylene comprising subjecting a mixture of ethane-containing gas and mercury vapor at atmospheric pressure, in which the partial pressure of the mercury vapor is about 10 mm, to a temperature of about 1150" F. and to gamma-radiation for about one second to provide a dose amount of 500 to 500,000 roentgens.

7. Method in accordance with claim 6 in which the gamma'radiation is from cobalt-60.

References Cited in the file of this patent UNITED STATES PATENTS 1,961,493 Hilli-s June 5, 1934 2,655,474 Schutze et a1 Oct. 13, 1953 2,743,223 McClintonet et al Apr. 24, 1956 FOREIGN PATENTS 801,563 Great Britain Sept. 17, 1958 OTHER REFERENCES Journal of Physical and Colloid Chemistry (1948), pages 452-455.

Journal of Physical Chemistry, vol. 62 (1958),pages 33 and 34.

Bovey: Effects of Ionizing Radiation on Natural and Eynthetic High Polymers, January 1958, pages 18 and 19.