US3106590A - Iodinative hydrocarbon conversion process - Google Patents

Description

United States Patent Ofiiice 3,106,590 Patented Oct. 8, 1963 3,1065% IODINATIVE HYDROCARBON CONVERSION PRQCESS Clarence W. Bittner, Orinda, Califi, assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware No Drawing. Filed June 26, 1961, Ser. No. 119,334 9 Claims. (Cl. 260-6735) This invention relates to an improved process for converting organic compounds containing aliphatic carbon atoms to form new carbon-to-carbon structures from aliphatic carbon atoms initially present therein. More particularly, it relates to the iodinative dehydrogenation of aliphatic hydrocarbons to form a different carbon-tocarbon linkage.

It is a principal object of the invention to provide an improved process for the iodinative conversion of hydrocarbons containing aliphatic carbon atoms to different hydrocarbons having a different carbon-to-carbon linkage between aliphatic carbon atoms of the original hydrocarbon. Another object is to provide an improved process for the formation of a different carbon-to-carbon linkage between aliphatic carbon atoms in a given hydrocarbon to produce an olefinic or an acetylenic hydrocarbon. A particular object is to provide an improved process for iodinatively dehydrogenating a saturated aliphatic hydrocarbon, an alkane, to an olefinic aliphatic hydrocarbon, an alkene, which may be a monoor polyene. Other objects and features of advantage will be apparent and more fully understood from a consideration of the following description of the invention.

The art teaches that new carbon-to-carbon linkages between initially aliphatic, i.e., non-aromatic, carbon atoms of a hydrocarbon can be produced by subjecting a vaporous mixture of hydrocarbons containing such carbon atoms with a reactive proportion of free iodine to an elevated temperature suflicient to effect a C-to-H bond cleavage in the molecule in the presence of free iodine. The art further teaches that the iodine can be supplied to the reaction zone as free iodine or as an iodine compound which yields free iodine. This type of conversion will be referred to herein as iodinative conversion or more specifically as iodinative dehydrogenation. Certain inherent disadvantages exhibit themselves in iodinative dehydrogenations heretofore proposed.

The present invention provides an improved iodinative conversion process in which the reaction of an organic compound, containing aliphatic carbon, and iodine is effected in the presence of a particulate solid material, preferably in a fluidized or dispersed state, having a metal iodide deposited thereupon or impregnated therein. The metal iodide may advantageously be molten at the reaction temperature, and must be sufficiently adherent to the particulate solid at reaction temperature to provide and maintain metal iodide on the surface of the solid particles while leaving them fluidizable, and reactive with free oxygen at the reaction temperature to liberate free iodine and form a corresponding metal oxide which remains with the particulate supporting solid and which is reactable with hydrogen iodide to reform the metal iodide. The advantages attendant the practice of the present invention whereupon the iodinative conversion effected in the presence of particles in the solid state having incorporated therewith the reactive iodine material, and in particular the use of fluidized solid-reactant particulate material, will best be understood and appreciated by those familiar with the movement of solid particles in a reaction zone. The principles, features, and requisites of fluidization of finely divided solids are well known and have been applied in other processing fields. It has now been found that they can be adapted to the iodinative conversion process.

With regard to the application of a fluidized system incorporating the process of the present invention and constituting a preferred embodiment thereof, the reaction zone will comprise as continuous phase the reaction gases in which the magnesia support means impregnated with metal iodide, in certain instances in a liquid state under the conditions of reaction, constitutes the dispersed phase in the continuum. In other words, the particulate solid magnesia support along with the metal iodide is dispersed within the gaseous materials, including iodine and oxygen, present in considerable quantities in the reaction zone. Accordingly, the reactants are supplied to the reaction zone at a sufiicient rate that the resulting space velocity of the gases in the reaction zone relative to the condensed materials is such that the gaseous materials are in a continuous phase and the condensed materials are dispersed therein in a fluidized state.

The iodinative dehydrogenation aspect of the invention involves subjecting a mixture containing at least one suitable feed hydrocarbon, such as an alkane having at least two carbon atoms per molecule, an alkene having at least two carbon atoms per molecule, or a cyclic hydrocarbon having at least one non-aromatic saturated carbon-tocarbon bond per molecule, and at least 0.05 mole of available iodine per mole of reactive hydrocarbon, to a temperature of at least 300 C. to dehydrogenate at least a substantial portion of the hydrocarbon whereby a product having the same carbon skeleton as the feed hydrocarbon but having a higher carbon-to-hydrogen ratio is recovered from the reaction mixture.

More particularly, in accordance with the invention, the hydrocarbon feed is intimately contacted with free iodine derived from a suitable metal iodide incorporated into a magnesia support and at a temperature sutficient to promote the release of free iodine from the metal iodide through the action of free oxygen. The amount of the available free oxygen is selected so as to liberate an amount of iodine from the metal iodide to effect the desired extent of dehydrogenation of the hydrocarbon feed. Metal oxide is also incorporated into the magnesia support in an amount sufiicient to maintain the hydrogen iodide content of the system :at an extremely low level (i.e., by reaction of the formed HI with the corresponding metal oxide). By this is meant a system in which the hydrogen iodide concentration is below a point at which it adversely affects the desirable reaction products. Usually, the system is such that hydrogen iodide exists only momentarily, being converted almost immediately to metal iodide. For the most part the metal oxides :are solids and hence will exist as suspensions in the magnesia-supported metal iodide environment when the process is operated at sufiicient temperatures in excess of the melting point of the metal iodide, in the case of lithium iodide, for example, in excess of 440 C. It is preferred that the effective equivalent mole proportion of metallic iodide to magnesia be main tained between about 0.01:1 and about 0.5 :1 so as to insure substantially immediate conversion of hydrogen iodide (formed in the dehydrogenation reaction) to metallic iodide while still maintaining an essentially fluidized system of iodide supported on finely divided solid magnesia particles.

The proportion of oxygen injected into the system to form the optimum amount of metallic oxide may vary [from about 0.025 mole of oxygen per mole of dehydrogenatable feed to even as much as 10 moles of oxygen per mole of dehydrogenatable feed. The proportion of oxygen employed is determined at least in part by the results desired. For example, if the feed is a gasoline and it is desired to convert only a limited proportion thereof to aromatics, then the oxygen input is correspondingly restricted. Hence, the term free iodine as used herein connotes the iodine liberated as a reactant from the metal iodide by the free oxygen supplied to the reaction zone. The term free oxygen as used herein is intended to signify oxygen in a form more or less conventional which is sufficiently reactive to liberate the free iodine from the metal iodide. While such free oxygen may be supplied in the form of relatively pure gas, it will, of course, be found economically advantageous as well as very convenient to use air as an oxygen-containing gas in the reaction zone. As an alternate embodiment of the invention, certain carbonate-iodide salt systems may be employed. These may include, in particular, barium or sodium and their corresponding iodides. The formation or additional injection of water makes possible the use of certain regenerable hydroxides such as, for example, lithium hydroxide. Accordingly, whenever reference is made herein to the term oxide, it will be understood that carbonates and hydroxides are included, so long as they meet the aforesaid criteria of ready regeneration under the conditions of dehydrogenation.

The metal iodide may be a single salt or a mixture of two or more metal iodides although it has been found that a preferred material for use as a supplier of free iodine in the present process is lithium iodide. Other iodides such as, for example, manganese iodide, may also be used to advantage. Iodides and corresponding oxides useful in the process of the present invention are particularly those which meet two criteria: (1) I- dides which are chemically and thermally stable but also convertible at the dehydrogenation temperature (especially 300 to 1000 C.) to the corresponding oxide by reaction with oxygen, and (2) corresponding oxides which form iodides by reaction with hydrogen iodide at the dehydrogenation tempcrature. While various metal iodides may be satisfactory in the process of the present invention, it is of paramount importance that the support medium be magnesia, represented generally by the chemical formula MgO. For example, a preferred magnesia may have a surface area of from about 1-300 ru /gm. and a pore volume of from about 0.05-0.5 cc./gm. Moreover, in the iodinative conversion process, it has been found that materials exhibiting catalytic functions other than that directly concerned with the iodinative process are to be avoided. For example, materials such as silica-alumina cracking catalysts exhibit acidic properties and such acidity is highly undesirable in the iodinative reaction.

Iodides are preferably present in substantial excess, i.c., sufficient to provide a solid phase consisting essentially of magnesia support throughout which metal iodide is present as an impregnant thereof and sufiicient that dehydrogenation may occur while at the same time provid ing a portion of impregnant to be converted by oxidation to the corresponding metallic oxide. It is preferred that the mole proportion of the metal iodide to hydrocarbon in the reactor at any given time is maintained between 2:1 and 100:1.

The process of the present invention has wide application for the conversion of various types of hydrocarbons containing aliphatic carbon atoms to related hydrocarbons having at least one different carbon-to-carbon linkage between initially aliphatic carbon atoms. Thus, alkanes of at least two carbon atoms can be dehydrogenated to alkenes. For example, ethane can be dehydrogenated to ethene; propane to propene; isobutane to isobutene; and so forth. Alkanes and alkenes having a chain of at least four carbon atoms can be dehydrogenated to alkadienes. For instance, n-butane can be dehydrogenatcd to butadiene-1,3 and n-pentane and isopentane to corresponding pentadienes. Various hydrocarbons may be coupled through aliphatic carbon atoms. For instance, propylene can be dehydrocoupled to give diallyl, dehydrocoupled and dehydrocyclized to benzene, and also coupled without net change in C/H ratio to a hexene; isobutylene dehydrocoupled to give dimethallyl, dehydrocoupled and dehydrocyclized to p-xylene, and coupled without net change in C/ H ratio to an octene. Aliphatic hydrocarbons containing at least six non-quaternary carbon atoms, whether saturated or unsaturated, can be cyclized, often with aromatization. For example, n-hexane may be dehydroaromatized to benzene; nheptane to toluene; n-octane to o-xylene and ethylbenzene; 2,5-dimethylhexane to p-xylcne; hexadiene-1,3 to benzene; and the like.

Aliphatic hydrocarbons containing at least six carbon atoms, one of which is a quaternary carbon atom, can be structurally iscmerized and/ or dealkylatcd to change the quaternary C-atorn to a non-quaternary C- atom. For example, 2,2,5-trimethylhexane can be de methylated and dehydroaromatized to give p-xylene and also dchydroisomerizcd with demethylation and aromati zation to give m-xylene. Instead of all the carbon atoms being aliphatic, as in the preceding illustrative examples, the aliphatic carbon atoms which are involved in the conversion and the formation of a new carbon-to-carbon bond, as already indicated, can be in one or more ali' phatic hydrocarbon radicals attached to a cyciic nucleus, such as in aromatic nucleus. In that case, one or more of the aliphatic carbon atoms may be involved in the conversion when it involves the formation of a new ring, such as an aromatic ring. For example, ethylbenzcnc can be dehydrogenated to styrene; toluene dehydrocoupled to dibenzyl and stilbene; o-diethylbenzene dehydroa-romatized to naphthalene; o-methylpropylbenzene dchydroaromatized to naphthaline; o-methylethylbenzenc dehydrogenated to o-methylstyrene; n-butylbcnzene dehydrogenated to 4-phenylbutadiene-l,3 and dehydroaromatized to naphthalene; 2,3-diethylnaphthalene to anthracene; butylcyclohexane to naphthalene; and butylcyclopentadiene to indene.

Alicyclic (cycloaliphatic) hydrocarbons are similarly dehydrogenated. For example, cyclohexane may be io dinatively dehydrogenated to benzene, methylcyclohexane to toluene, cyclopentane to cyclopentene and cyclopentadiene, decalin to tetraline and naphthalene, bicyclo- (2,2,1)heptene-2 to bicyclo(2,2,1)heptadicne-2,5 and ey clobutane to cyclobutene.

The conditions for carrying out the process of the present invention depend to a degree upon the particular com pound to be converted, as well as upon the hydrocarbon desired as principal product. Thus, for the dehydrocycli zation of hydrocarbons the temperature required is at least about 300 C., generally being at least about 350 C. and usually preferably in the order of about 425 to 525 C., although higher temperatures may be utilized up to about 600 C. but preferably not above about 575 C. Higher temperatures are not objectionable so long as other undesirable changes are not brought about. However, excessively high temperatures are not required in order to effect suitable dehydrocyclization in the presence of substantial amounts of iodine reactant. In the case of less thermally stable substances, the temperature is more suitably adjusted within the lower range of values, such as about 400 to 450 C., and in some cases it may be as low as about 300 to 350 C. Conversely, in the case of more thermally stable substances, such as the lower molecular Weight hydrocarbons, e.g., ethane and propane, the temperature is more suitably adjusted at the higher range of values, such as about 550600 C., and it can even be 600800 C.

In accordance with the invention, a dehydrogenatable feed is passed into a dehydrogenation zone which is at least partially filled with a mass or fluidized bed of metallic iodide supported on magnesia. Oxygen, generally in the form of air containing the same, is injected into the zone containing the metal iodide to convert at least a substantial portion of the metallic iodide impregnant, at a temperature of from about C. to 800 C., in some cases, into metallic oxide in suspension therewith. If desired, oxygen can be admixed with the feed or injected separately into the zone containing the metal iodide. The temperature of the dehydrogenation zone is at least 300 C. so as to enable dehydrogenation to occur by reaction of the feed with iodine'which is released upon conversion of the metallic iodide into the corresponding metallic oxide. To compensate for any iodine losses, minor though they may be, supplementary amounts of magnesia-supported metallic iodide may be injected into the dehydrogenation zone in order to maintain the iodine content therein at the appropriate level. The effluent removed from the dehydrogenation zone comprises the product consisting essentially of a dehydrogenated feed, and water, with substantially no effective amount of iodine. In accordance with a preferred embodiment of the invention, the efiiuent from the dehydrogenation zone is cooled and transferred to a separation zone wherein dehydrogenated product is separated and recovered. The remaining aqueous phase comprises principally water and any small amount of iodine species which may have evaded entrapment by the metallic oxide in the dehydrogenation Zone. This mixture may be fed to an iodine scavenging zone wherein an iodine scavenger removes substantially all of the iodine species from the system, leaving behind the separated water. The iodine scavenger may be such a material as a metallic oxide which performs the same [function that it does in the dehydrogenation zone or it may be a reactive metal such as copper, which immediately reacts with iodine species to form various copper iodides. These iodine species are then removed to an iodine regenerator wherein elemental iodine is regenerated and recycled to the dehydrogenation zone. The term iodine species is intended .to comprise in the reaction mixture iodine, hydrogen iodide, and compounds which liberate either iodine or hydrogen iodide at reaction temperature.

The invention is further illustrated by means of the following examples and table appended herewith.

at a mole ratio of oxygen to n-butene of 0.76 was passed with helium into a single-stage fluidized-fixed bed of material containing 10% wt. lithium iodide plus 2.5%

lithium hydroxide supported on magnesia at 1 atmosphere pressure and 500 C. and at a nominal residence time of 5.1 seconds (based on total input flow rate at reaction temperature), analysis of the total product stream indicated a reaction of 58% of the n-butane and 100% of the oxygen. On the basis of 1100 moles of n-butane reacted, the product contained moles of butadiene and 6 moles of n-butylenes. The loss of iodine of all species from the solid which might necessitate iodine scavenging outside the reactor was only 0.10 pound per 100 pounds of unsatunate (butadiene plus butylenes) produced.

EXAMPLE II When a vaporous feed mixture of n-heptane and oxygen at a mole ratio of oxygen to n-heptane of 0.76 was passed IWlth helium into a single stage fluidized-fixed bed containing 15% lithium iodide plus 6% wt. lithium hydroxide supported on magnesia at 1 atmosphere pressure and 525 C. at a nominal residence time of 5.4 seconds, 42% of the n-heptane and 100% of the oxygen reacted. For each 100 moles of n-heptane reacted, there were formed 8 moles of benzene, 66 moles of toluene and 1 mole of C aromatics.

EXAMPLE III 1 A circulating solids system has been employed in which the oxygen and hydrocarbon have been injected in this order in two separate stages. When oxygen and ethane at a mole ratio of 0.41 were injected in separate stages into a solid consisting of 17% manganous iodide (Mnl and 3.5% manganous oxide (MnO) supported on magnesia at 1 atmosphere pressure and at 610 C. and a nominal residence time of 2.4 seconds and at 565 C. and a nominal residence time of 4.0 seconds in the hydrocarbon injection stage and in the oxygen injection stage, lespectively, it was observed that 70% of the ethane and 100% of the oxygen had reacted. On the basis of 100 moles of ethane reacted, moles of ethylene and 1 mole of butadiene were formed. The loss of iodine of all species which might be recovered by a scavenger outside the reactor was only 0.5 pound per pounds of ethylene produced.

Table I Oxidative Dchydrogenation with LiI=LiOH on MgO [MgO supp0rt= 60 mesh, 120 mfl/g. surface area, 0.3 ccJgram pore volume] 2-Stagc Cocurrent l-Stage Fluidized- Apparatus Circulating Solids Fixed Bed Catalyst:

Percent wt. LiI 18 14 10 10 Percent wt. LiOH 0.9 1. 6 2. 5 2. 5 Gas Rates, cc./min. (STP Hydrocarbon (alkanc) 154 O; 228 C3 173 n-C4 166 i-C5 Oxygen 100 132 132 Inert to regenerator 400 Inert to transfer line. 250 137 724 770 Inert to reservoir 200 225 Oz/Hydmcarbon Mole Ratio 0. 60 0. 44 0.76 0.80 Hydrocarbon Gas Hourly Space Velocity (cc. hydrocarbon gas at SIP per cc. catalyst in reactor per hour) 142 210 42 40 Temperatures, 0.:

Reactor 625 540 Regenerator 550 475 500 500 Reservoir 480 440 Nominal Residence Time, sec.:

Reactor 2. 9 3. 3 5 1 Regenerator 3. 5 6. 4 0 Hydrocarbon Conversion, percent Wt. 96 33 68 31 Selectivity, Equivalents per 100 Moles 1Hyidocarbon Converted (no-loss as s 1 2+C 4 2 O H 11. 2 2 a 2 O2 i 93 0,114 l O1 56 0311s 2 1 CA 3 85 04H!) 5 6 C4HB CnHn 13 f Other 2 OuCw Oxidation to C0+OO +H20 4 18 6 32 Iodine Loss, 1bs./100 lbs. Unsaturate Produced 0. 27 0. 10 o, 50

I claim as my invention:

1. In a process for the conversion of a first hydrocarbon compound containing aliphatic carbon to a second hydrocarbon compound having a higher carbon-tohydrogen ratio wherein the first compound and a reactive iodine species are reacted at a temperature in excess of 300 C. whereby the second compound and hydrogen iodide are produced, the improvement comprising conducting the reaction in a fluidized environment comprising a metal iodide from the group consisting of lithium iodide and manganese iodide supported on particulate magnesia as the dispersed phase in said fluidized environment, and injecting oxygen in an amount at least suflicient to liberate an amount of iodine from the metal iodide to elfect dehydrogenation of the first organic compound and wherein the gaseous reactants provide a continuous gaseous phase in said fluidized environment.

2. Process for converting a first hydrocarbon into a second hydrocarbon having a higher carbon-to-hydrogen ratio which comprises contacting in a dehydrogenation zone a mixture comprising the first hydrocarbon with a reactant iodine species in suflicient amount to furnish at least 0.05 mole of iodine per mole of first hydrocarbon at a temperature of at least 300 C. to effect a carbonto-hydrogen bond cleavage in the first hydrocarbon, contact of the reactant iodine species and the first hydrocarbon being with a metal iodide from the group consisting of lithium iodide and manganese iodide supported on particulate magnesia and constituting a dispersed phase in said dehydrogenation zone, and introducing oxygen into said dehydrogenation zone in an amount at least sufficient to liberate an amount of iodine from the metal iodide to effect the desired cleavage and wherein the 8.. gaseous reactants provide a continuous gaseous phase in said dehydrogenation zone, and recovering the second hydrocarbon produced therein.

3. Process for converting a first hydrocarbon into a second hydrocarbon having a higher carbon-to-hydrogen ratio which comprises contacting in a fluidized environment a metal iodide from the group consisting of lithium iodide and manganese iodide supported on particulate magnesia with oxygen under conditions sufl'icient to libcrate iodine from said metallic iodide and to form metallic oxide therefrom, contacting said iodine and said metallic iodide in a fluidized state with said first hydrocarbon under conditions suflicient to form said second hydrocarbon therefrom.

4. A process according to claim 1 wherein the metal iodide is lithium iodide.

5. A process according to claim 1 wherein the metal iodide is manganese iodide.

6. A process according to claim 1 wherein the first compound is ethane.

7. A process according to claim 1 wherein the first compound is heptane.

8. A process according to claim 1 wherein the first compound is a hydrocarbon in the gasoline boiling range.

9. A process according to claim 1 wherein the first compound is butane.

References Cited in the file of this patent UNITED STATES PATENTS 11,925,421 Van Peski Sept. 5, 1933 2,719,171 Kalb Sept. 27, 1955 2,921,101 Magovern Jan. 12, 1960

Claims (1)

1. IN A PROCESS FOR THE CONVERSION OF A FIRST HYDROCARBON COMPOUND CONTAINING ALIPHATIC CARBON TO A SECOND HYDROCARBON COMPOUND HAVING A HIGHER CARBON-TOHYDROGEN RATIO WHEREIN THE FIRST COMPOUND AND A REACTIVE IODINE SPECIES ARE REACTED AT A TEMPERATURE IN EXCESS OF 300*C. WHEREBY THE SECOND COMPOUND AND HYDROGEN IODIDE ARE PRODUCED, THE IMPROVEMENT COMPRISING CONDUCTING THE REACTION IN A FLUIDIZED ENVIRONMENT COMPRISING A METAL IODIDE FROM THE GROUP CONSISTING OF LIGHIUM IODIDE AND MANGANESE IODIDE SUPPORTED ON PARTICULATE MANGNESIA AS THE DISPERSED PHASE INSAID FLUIDIZED ENVIRONMENT, AND INJECTING OXYGEN IN AN AMOUNT AT LEAST SUFFICIENT TO LIBERATE AN AMOUNT OF IODINE FROM THE METAL IODIDE TO EFFECT DEHYDROGENATION OF THE FIRST ORGANIC COMPOUND AND WHEREIN THE GASEOUS REACTANS PROVIDE A CONTINUOUS GASEOUS PHASE IN SAID FLUIDIZED ENVIRONMENT.