US2336054A - Process for dehydrogenating hydrocarbons - Google Patents

Description

Patented Dec. 7, 1943 UNITED STATES. P ATENT OFFICE 23365054 1 I I PROCESS FORDEHYD ROGENA'IING N8 HYDROOABBO Robert G. Atkinson, The Shamrock Oil rillo, Ten,

No Drawing. Continu No. 375,013, January 18,1941.

tion January 10, 1942, Serial No.

Sunray, Tex, assignor to and Gas Corporation, Amaa .corporation of Delaware ation of application Serial This applica- 426348 3-Claims. (cl. zoo-cs3) This invention relates to thermal conversion processes for hydrocarbons, and relates more particularly to a method and catalyst for dehydrogenating low molecular weight hydrocarbons. The production or olefins or unsaturated hydrocarbons from low molecular weight saturated hydrocarbons such as butane,propane, etc., is of great commercial importance. The olefinic material thus produced, which normally comprises butylenes and propylene. is directly accessible for the production of high octane gasoline or aviation fuel by either polymerization or alkylation processes. By segregation of isobutylene it is possible by processing it further by such methods as are mentioned above to produce iso-octane, which is a very valuable anti-knock motor fuel blending material. Also, the olefinic material, being relatively active from the chemical standpoint, aifords a suitable starting point for the synthesis of many chemical products, including alcohols, glycols, chlorinated material, and the like.

It is possible to subject butane to cracking temperatures and secure appreciable yields of propylene and butylene. This purely thermal type 01 process is occasionally practiced on commercial scale. However, the yield of unsaturates in the purely thermal process as it has been proposed and carried out is not as high as is desirable, and a considerable quantity of the hydro ca bons undergoing cracking is converted into sat rated, lower molecular weight hydrocarbons,

m1 as propane, ethane, or methane, which are undesirable by-products of the cracking reaction.

It is the principal object of the present invention to increase the yield of olefinic hydrocarbons, typically propylene and butylene, obtainable from a cracking of-parafiln hydrocarbons, as, ior example, butane.

Catalytic dehydrogenitic processes have been developed in which the gaseous hydrocarbons are passed over a catalytic contact mass maintained at high temperature, and by such means increased yields of unsaturates and a decreased conversion into undesired by-products may be obtained. However, the activity of such catalytic masses depends upon the condition of the surface, which in use tends to become rapidly masked or coated over or otherwise rendered inert so that the process must be repeatedly shut down for reactivation of the catalyst. Also, complex and expensive equipment is required for carrying out such cracking processes under optimum conditions.

It is an object of the present invention to provide a method and a catalyst for the dehydrogenation of hydrocarbons in which fresh catalyst is continually fed into the reaction zone, thereby maintaining a constant and undiminished catalytic activity productive of high yields of the desired olefins.

Broadly speaking, the'present invention comprises the addition of small amounts of organo-- metallic compounds, as, for example, chromium naphthenates, to the hydrocarbon material undergoing dehydrogenation. By this method I find it possible to increase the yield of unsaturates and decrease the amount of undesirable by-products which are normally formed.

hich I find to give the best results with low molecular weight hydrocarbons such as butane.

' These naphthenate catalysts may be variously in- .troduced into the reaction. zone, provided that they are introduced in a more or less continuous manner. The most convenient and preferable method is to dissolve the naphthenate in the relatively small proportion required for catalysis in v the charging stock while the latter is maintained tion into cracking tubes inthe liquid state, and then to feed this soluheated to the desired cracking temperature.

In general, I prefer to employ only moderate pressures in the cracking zone, for example, 20 pounds per square inch, and under these conditions the dehydrogenating reaction takes place largely in the vapor phase, particularly when dealing with low molecular weight hydrocarbons such as butane at cracking temperatures in excess of 1000 F., as hereinafter described.

If an organo-metallic catalyst is employed which is volatile under the conditions prevailing in the cracking zone, the catalyst will, of course, traverse the cracking zone in vapor form, along with the hydrocarbon vapors. When employing catalyst, such a catalyst may ing zone as a fog,

traverse the crackmist, or dust borne by the hydrocarbon vapors.

There may be a slow accretion of catalyst on the walls of the cracking tube, but in general I find that a very substantial proportion of the metal employed is recoverable from the hydrocarbon efliuent, as when employing tin or chromium naphthenate as the catalyst. The recovery and recirculation of the catalytic material in a.-

form which may be added to further hydrocar bon charge stock are present invention. I Among theadvantages arisingimm the pracwithin the scope oi. the

Iprefer to use tin or chromium naphthenates,

as described above" in Hydrogen Methane Ethylene Ethane Propylene Propane Mols Mols M013 M018 Mala Y Mols 14.22 43.22 25.55 44.69 49.69 6.16

lso-hutylene Normal butylene tice otthe pr nt invention are the very substantially increased yields or olc" terial, the great simplicity of the process, which neces sltates -no expensive equipment, and the peas-i=- bility of recirculating the catalytic material.

Further objects and aspects oi'the invention will become apparent from the following descrip tion and discussion or specinczexples.

s,sso,'osa-- In general, the iollowi'ng experiments were performed in an experimental cracking still in which a horizontalcraclzing tube constructed oi 234m, chromium alloy steel was employed. tube had an internal diameter of 3 inches and a length of about 72 inches and'was heated by being positioned in a gas fired furnace. The butane charging stock was pumped into a run of 1% inch pipe, approximately twice the lien oi the cracking tube, which was positioned over the cracking tube and-served as ayaporizer and preheater. The preheated stream of vapors were, then introduced downwardly end 01- the crackin tube. RUN 1.No catalytic material added The preheater tube and cracking tube situated the experimental cracking still were cleanedbe'fore starting the experiment by blowing air through them while they were 1 held at a temperature of 1000 F. The charge tank for the equipment was filled with essentially pure N-butane which was then pumped out of the tank and passed through the preheater tube and thence through the cracking tube at a rate of about 135 space velocities per hour. The cracking tube was maintained at a temperature I of 1065 F. throughout the experiment and the pressure in the reaction zone of the tube was held at 20 pounds per square inch by means of a back pressure valve on the outlet. The analysis of the eiliuent gases issuing from the tube was as follows:

Hydrogen Methane Ethylene Ethane Propylene Propane Per cent Per cent Per cent Per cent Per cent Per cent 3. 30 10. 03 5. 93 10. 37 ll. 53 l. 43

ol I lso- Uncraclred v butylene Butylem butane normal butane 5 Per cent .Per cent Per cent Per cent 0.69 .07 o 54.35

S toichiometric calculations show that the lowing products were 'iormed'per each 100 mols of butane decomposed:

Run 2.-Chromium naphthenate The charge tank of the experimental cracking still was filled with normal butane and 4.17 grams of chromium naphthenate per gallon of butane I as 101- into one end of the cracking tube proper, while the eifluent gases were removed from the opposite was dissolved the charge by adding thenaph thenate to the tank and then circulating normal through the tank until the chromium naphthenate was entirely dissolved. The normal butane butane'was cracked by pumping it throughthe experimental still in exactly the same manner as was described in tained at a temperature of'i065" F. by means of external firing throughout the experiment. The

cracked gases issuing from the cracking tube had the following analysis: I

In addition to thesecracked gases 250 cc. of aromatic liquidv polymer was produced per each thousand cubic feet of normal butane charged. Stoichiometric calculations show that, in addition to the liquid polymer, the following products were formed per each mols of butane decomposed:

Hydrogen Methane Ethylene Ethane Propylene Propane I More Mon M018 M013 M013 B1018 44.36 18.15 24.13 28.50 50.01 6.99

Iso-butylene Butylene 'Mols Mole 2.49 24.00

Run 3.--Tin naphthenate The charge tank of the experimental still was filled with N-butaneand 6.08 cc. of commercial tin naphthenate pergallon of butanewas dissolved in the charge stock by means of circulation outof the bottom and into the top of the tank. The charge stock was then pumped through the heated cracking tube where it was held at a pressure 0120 pounds per square inch and a tempera.- ture Of11Q65 F.,in,exactly the same manner as described in fRunl 1.. The analysis of the cracked gases issuing from the tube was as iollows:

Hydrogen Methane. Ethylene Ethane Propylene Propane Per cent Percent Percent. Per cent Per cent Per cent 7.40 I 2.38 4.65 7.69 1.19

lso Isa: Normal Uncracked butane-f butylene butylene normal butane Per cent .Perceni Per cent Percent 0.50 0.45 4.36 69.80

- In addition to the cracked gases. 3700 cc. of aromatic liquid polymer was formed per each thousand cubic feetv of butane vapors passed through the furnace. Calculations show that, in additionto' the liquid polymer, the following Run 1," the tube being main- 7 Hydrogen Methane Ethylene Ethane 1 Propylene Propane Per cent Percent Per and Per cent Per cent Per cent I Iso- I Uncraclred bntylcne normal butane er cent Per cent Per cent 0.37 3. 57 70. 45

products were formed per each 100 mols oi butane cracked:

It is seen from the above experiments that when no homogeneous catalyst is present in the reaction zone, as in Run 1, only 47.5% by weight of normal butane is converted into propylene and butylene; whereas Run 2 and "Run 3" show that when chromium naphthenate Or tin naphthenate are present in the reacting zone 61.8% and 66.5% by weight, respectively, ofthe normal butane is converted into propylene and butylenes. Examination of the experimental data also shows that chromium naphthenate and/or tin naphthenate greatly increase the amount oi. straight dehydrogenation which occurs in the reacting zone; i. e., when chromium naphthenate was present 26.49 mols of. butylenes were formed per each 100 mols of normal butane decomposed, and when tin naphthenate was present in the reacting zone 31.32 mols of butylenes were formed per 100 mols or normal butane decomposed, whereas "Run 1" shows that when no materials are added to the butane charge undergoing thermal decomposition only 11.89 mols of butylenes are formed per 100 mols of normal butane decomposed.

The catalytically produced oleflns may be used in the manufacture of high octane gasoline or aviation fuel by polymerization of the unsaturates in the hydrocarbons conversion mixture issuing from the reaction tubes. The reaction mixture may be cooled, condensed, then fractionated in order to remove therefrom any hydrogen, methane, ethane, or ethylene and the fractionated product subjected to conventional processes of polymerization to form high octane gasoline blending material. It is also possible to effect a removal of the butylene from the eiiluent cracked gases and subject such butylene to alkylation reactions for the purpose of producing iso-octane, which is a valuble anti-knock motor fuel blending material.

It is to be understood that the details of the above examples are illustrative rather than lim- -iting and that various modifications may be employed and practiced without departing from the essence of my invention as defined by the scope of the appended claims.

This is a continuation of my application Serial No. 375,013, filed January 18, 1941, for "Catalysts for dehydrogenating hydrocarbons.

I claim as my invention:

1. A process for dehydrogenating low molecular weight hydrocarbons, which comprises: subjecting said hydrocarbons to elevated cracking temperatures in the presence of tin naphthenate.

2. A process for increasing the yield of un- I saturated hydrocarbons obtained when hydrocarbons are thermally decomposed, which cornprises: forming a stream of said hydrocarbons substantially free from fre hydrogen: adding an organic acid derviative of tin to said stream, and subjecting said stream carrying said derivative to a temperature suflicient to cause said thermal decomposition.

3. A vprocess as in claim 2, in which the orgauic acid derivative is a tin naphthenate.

ROBERT a. ATKINSON.