US2456672A - Conversion of hydrocarbons - Google Patents

Description

DSC 2 1948 H. s. BLQQH m AL l CONVERSION OF HYDROCARBONS Filed March 3l, 1945 Patented Dec. 2l, 1948 CONVERSION F HYDROCARBONS Herman S. Bloch, Chicago, and Raymond E.

Schaad, A Riverside, lll

., assignors to vUniversal Oil Products Company, Chicago, Ill., a corporation of Delaware Application March 31, 1945, Serial No. 585,997 4 Claims. (Cl. 26o-671) This application is a continuation-impart o! our co-pending application Serial No. 518,996, filed January 20, 1944, now U. S. Patent 2,389,406, which in turn is a continuation-in-part of our application Serial No. 256,760, led February 16, 1939, now U. S. Patent 2,346,657, and relates to a combination of interdependent and cooperative steps for the conversion of an isomerizable paraifinic hydrocarbon into branched-chain hydrocarbons of high anti-knock characteristics.

In a broad aspect the present invention relates to a process for converting a parainic hydrocarbon containing at least 4 carbon atoms to the molecule into a higher boiling branched chain hydrocarbon, which comprises subjecting said paraiilnlc hydrocarbon to contact with dehydrogenating and isomerizing catalysts under conditions to form branched-chain olenic hydrocarbons, and subjecting said olefinic hydrocarbons to conversion in the presence of a condensation catalyst under conditions to form said higher boiling branched-chain hydrocarbons.

One specific embodiment of the present invention relates to a process for converting normal butane, which comprises subjecting normal butane to simultaneous dehydrogenation and isomerization to form a mixture of isoand normal butylenes, polymerizing said butylenes,l separating an unconverted butane-fraction from the polymerization eluent products, and recycling the separated butane fraction to said simultaneous dehydrogenation and isomerization.

Another specic embodiment of the present invention relates to a process for converting normal butane, which comprises subjecting normal butane to simultaneous dehydrogenation and isomerization to form a mixture vof isoand normal butylenes, separating said mixture and commingling isobutane therewith, alkylating said isobutane with said butylenes, separating an unconverted normal butane fraction and an unconverted isobutane fraction from the alkylation eifluent products, recycling the normalvbutane fracy tion to said simultaneous dehydrogenation and lsomerization, and recycling the isobutane fraction to said alkylation.

In the rst step loi! the present process a parafiin containing at least 4 carbon atoms to the molecule, such as normal butane, is subjected to dehydrogenation and isomerization. The etliuent lproducts from this operation comprise a mixture 2 been found that when a mixture of isoand normal butylenes are utilized to alkylate with isobutane, a product having a higher anti-knock rating is obtained than when a fraction consisting of normal butylenes is utilized in the alkylation reaction. These advantages are further illushydrocarbons containing 4 carbon atoms and' less tothe molecule.

Buty- Buty- Isoolen Iene-l iene-2 Butylcne Isobutane to butylene ratio..- 9; 7 8. 5 8. 4

I- C Octane No. for Depentanized Alkylate with 4.6 cc. of Tetraethyl Lead 104. 7 109. 2 111 I- C Octane No. for Debutanlzed Alkylate-Cle ir 90. 2 96. l 95. 5l +4cc. of Tetracthyl lead 108. 7 l109. 7 +4.6cc. of Tetraethyl lead. 105. 5

it win be 'usted from the above table' that prodf ucts having' higher leaded .octane numbers are obtained bythe alkylationof isobutane withisobutylene as compared to alkylation with normal butylenes vand particularly butylene-l.

The eilluent products of the irst stepof the present process may'have a butylene content comprising `25l mol percent or more of isobutylene, approximately 50 mol percent of butylene-Z and the remainderl of butylene-l, and thus Will produce alkylates of higher octane number than would be obtained when utilizing the eiliuent products of conventional normal butane dehydrogenation processes when effected under substantially the same conditions.` The conventional'dehydrogenation process does lnot employ an isomerization catalyst in admixture with the dehydrogenation catalyst.

A major diiiiculty and expense in connection with the rst step of the process is the separation of the olefin products from unconverted parafnic hydrocarbons. These paraiiins and olens are of close boiling range and in many cases their boiling vpoints overlap so that separation thereof cannot be eected by purely fractional distillaf oleflns into a higher boiling product which may readily be separated by fractionation. For example, the mixture of butylenes and butanes separated in the rst step of the process may be subjected to an alkylation reaction with isobutane, in which alkylation reaction the butylenes are reacted with isobutane to form higher boiling products and the higher boiling products then may be readily separated by fractionation from the unconverted butanes. Usually an excess of isobutane is used in the alkylation reaction and the separated butanes may be further separated by fractionation into a, normalv butane fraction, which may be recycled to the first step of the process for further conversion therein, and an isobutane fraction which may be recycled to the second step of the process for further use therein.

It is thus seen that the present invention provides a unitary process for the conversion of a normal paramn into a mixture of olens particularly suitable for use in the second step of the process and that the second step of the process converts said mixture and also serves to separate the unconverted hydrocarbons for recycling to the rst step of the process. The operation of the first step of the process determines the i'inal products obtained from the second step of the process, While the second step of the process serves to segregate the products for recycling back to the first step of the process.

The paramnic hydrocarbon utilized as charging stock to the rst step of the process may comprise any suitable parafn containing at least 4 carbon atoms to the molecule, but preferably comprises normal butane, normal pentane or mixtures thereof. These paraiins may readily be converted into the desired oleinic hydrocarbons in the manner to be hereinafter set forth in detail. When charging parafiins containing 6 or more carbon atoms to the molecule, the paranic hydrocarbons may undergo some cyclization so that the eilluent products may contain aromatic hydrocarbons. However, the aromatic hydrocarbons may be alkylated in the second step of the process to produce alkyl aromatics which, if of a satisfactory boiling range, are desirable in motor fuel.

When theprocess is being operated to produce gasoline, the paralnic `hydrocarbon charging stock should not be of too high molecular weight as otherwise the nal product of the process may boil outside the range of motor fuel. In general, the parafflnic hydrocarbon should not contain more than 8 carbon atoms to the molecule when the process is operated to produce gasoline. However, with certain alkylation catalysts, decomposition of higher boiling olenlc hydrocarbons occur during the alkylation reaction. This decomposition is termed depolyalkylation and may comprise, for example, the splitting of an olenic hydrocarbon containing 8 carbon atoms to the molecule to fragments containing 4 carbon atoms to the molecule, which subsequently undergo alkylation as 4-carbon atom fragments. In such cases the use of higher boiling parafinic hydrocarbons in the first step of the process would be permissible since the nal product of the process will boil within the desired motor fuel range.

Similarly, when the second step of the process. comprises alkylation, the alkylatable hydrocarbon used therein should not be of such high boiling point that the final product of the process boils above the motor fuel range. The preferred alkylatable hydrocarbons comprise isobutane, isopentane or mixtures thereof. Isohexane, isoheptane, iso-octane, etc., may also be used within the scope of the invention, particularly when the parainic hydrocarbon charged to the first step of the process is of low molecular weight. -In some cases the alkylatable hydrocarbon utilized in the second step Vof the process may comprise an aromatic hydrocarbon and the final product of the process then will comprise alkyl aromatics which may be used for motor fuel if of satisfactory boiling range or which may be used for any other purpose desired.

In the first step of the process the parafnic hydrocarbon is subjected to conversion in the presence of mixed dehydrogenation and isomerization catalysts. The mixed catalyst may comprise separate layers of dehydrogenation and isomerization catalysts, or intimate mixtures of separately precipitated dehydrogenation and separately precipitated isomerization catalyst or coprecipitated or successively precipitated dehydrogenation and isomerization catalysts. A preferred arrangement comprises separate layers of these catalysts, the dehydrogenation catalyst being disposed above the isomerization catalyst when employing down flow of the normal parafn charge and the dehydrogenation catalyst further being considerably larger in duantity as compared to the isomerlzation catalyst.

In some cases, a relatively thin layer of isomerization catalyst may be sufficient to obtain the advantages of the present invention. Complete detaiis of suitable dehydrogenation land isomerization catalysts and of various methods of manufacturing them are given in our Patent 2,346,657, which patent' is to be considered as a part of the present specification. The preferred dehydrogenation catalyst comprises alumina composited with an oxide of a metal in the lefthand column of group VI of the periodic table, particularly chromia and molybdena, while the preferred isomerization catalyst comprises silica composited with alumina, zirconia and/or thoria.

The catalyst may be used in the shape of granules, powder or shaped particles and the process may be either of the fixed bed type, the uidized type, slurry type. or any other suitable type. Conversion may be eected at temperatures of from about 900 to about 1100 F. under subatmospheric, atmospheric, or moderate superatmospheric pressures which may range up to pounds per square inch.

In the second step of the process the olenic hydrocarbons produced in the nrst step of the process are converted tn produce higher boiling branched-chain hydrocarbons. The preferred olen conversion step comprises alkylation of an alkylatable hydrocarbon with said oleiins and this may be effected in the presence of any suitable alkylation catalyst including hydrogen fluoride, sulfuric acid, aluminum chloride and/or its organic complexes, etc. l These catalysts are usually utilized at moderate temperatures which` generally are below 200 F. and usually below a pressure of 500 pounds per square inch.

When the alkylatable hydrocarbon comprises an aromatic, phosphoric acid catalyst and particularly solid phosphoric acid catalyst as del.' scribed in Patent 2,346,657, may be used. It is understood that the present invention is Anot limited to any alkylationvcatalyst and that'any any suitable catalyst may be used. The-preferred catalyst comprises the solid phosphoric acid catalyst, and polymerization of the oleiins is preferably effected at a temperature of about 225 to about 325 F. at a pressure of about 500 to about '700 pounds per square inch. sulfuric acid is also a particularly suitable polymerization catalyst and may be employed in either of the conventional hot acid or cold acid polymerization processes.

The invention will be further illustrated in connection with the accompanying diagrammatic flow drawing which, in the interest of simplicity, will be described in connection with the conversion of normal butane. 1-

Referring to the drawing, normal butane is introduced through line I into dehydroisomerization zone 2. In zone 2 the normal butane is contacted with the dehydrogenation and isomerization catalyst in the manner hereinbefore set forth, and the effluent products are directed through line 3 to separation zone 4. Zone 4 may comprise one or a plurality of fractionating, distilling, absorbing and stripping zones, etc., in order to separate products which are higher boiling and those which are lower boiling than the desired hydrocarbons containing 4 carbon atoms per molecule. The light products, which normally will'comprise hydrogen, methane, ethane, ethylene, propane and propylene, are Withdrawn from zone 4 through line 5. Higher boiling products which may comprise pentane originally present in the charging stock or formed during the operation, as well as a minor amount of higher boiling hydrocarbons, may be withdrawn from zone 4 through line 6.

The fraction comprising 4 carbon atom hydrocarbons is withdrawn from zone 4 through line 1 and is directedio olen conversion zone 8. As heretofore set forth zone 8 preferably comprises either an alkylation or a polymerization zone and the eilluent products therefrom are directed through line 9 to separation zone I0 which may comprise one or a plurality of fractionating zones. Normally liquid products are withdrawn from zone I through line Il and may be subjected to any desired rerun fractionation in order to separate the desired fraction, or the liquid products may be subjected to any desired further treatment prior to said rerun fractionation. Thus, in the case of olein polymers, the liquid product withdrawn through line l I may be subjected to hydrogenation prior to or after rerunning.

When zone 8 comprises an alkylation process, zone I0 preferably comprises a plurality of fractionating zones so thatA the products may be separated into an isobutane fraction, a normal butane fraction, and an alkylate fraction. The isobutane fraction` may be directed through lines I2 and I3 and may be withdrawn from the process, but preferably at least a portion of the isobutane is directed through line I4 and returned through line 'I to zone 8 for further use therein. Normal butane separated in zone I0 may be removed from zone I0 and recycled 6 by way of lines I2, I2 and I to zone 2 for further conversion therein. In the polymerization operation lines I and Il may be omitted.

The following example is introduced to further illustrate the novelty and utility of the present invention but not with the intentionA of unduly limiting the same. l

When anormal butane fraction'is subjected to contact with a mixture of alumina-chromia dehydrogenation catalyst and silica-alumina isomerization catalyst at a temperature of 1000 F. and atmospheric pressure, a mixture of butylenes is formed comprising approximately 25 mol perprocess.

"a 300 F. end point fraction suitable for use as cent isobutylene, mol percent butylene-2 and 25 mol percent of butylene-l. The mixture of butylenes and unconverted butanes from the first step of the process is commingled with isobutane and the mixture subjected to alkylation at a temperature of 100 F. and a pressure of 100 pounds per square inch in the presence of a hydrogen uoride catalyst. The eilluent hydrocarbon products are separated into an isobutane fraction, normal butane fraction and an alkylate fraction. The isobutane fraction is recycled to the alkylatlon step and the normal butane fraction is recycled to the dehydrogenation-isomerization The alkylate may be rerun to separate aviation fuel which fraction is substantially saturated and of high anti-knock value.

We claim as our invention:

1. A process for converting a normal parailln having at least 4 carbon atoms to the molecule which comprises subjecting the normal paramn to simultaneous dehydrogenation and isomerization in the presence of a physical mixture of a dehydrogenating catalyst and an isomerizing catalyst to form a mixture of isoand normal olens and unconverted normal paraflln, commingling an isoparatlln with said mixture, catalytically -alkylating said isoparaflln with said oleflns in the presence of said normal parailln, separating from the elluent products of said alkylation an unconverted normal paraihn fraction and an 'unconverted isoparailln fraction, recycling the normal parafiln fraction to said simulf taneous dehydrogenaton and isomerization, and

recycling the isoparanln fraction to said alkylation.I

2. A process for converting normal butane which comprises subjecting the normal butane to simultaneous dehydrogenation land isomerization in the presence of a physical mixture of a dehydrogenating catalyst and an isomerizing catlyst to forma mixture of isoand normal butylchain hydrocarbons which comprises simultanethe process through line I5 but preferably is retion, unconverted butanes may be separated in ously dehydrogenating and isomerizing a parafiinic hydrocarbon containing at least four carbon atoms per molecule by the action of 4a dehydrogenating catalyst in physical admixture with a minor proportion of an isomerizing catalyst, reacting the resultant branched chain olenic product with an alkylatable hydrocarbon at allqrlating 7 conditions to form `a higher boiling branched chain hydrocarbon and recovering the same, and recycling unconverted parainic hydrocarbons to the dehydrogenation-isomerization step.

4. The process of claim 3 wherein said alkylatable hydrocarbon comprises an aromatic hydrocarbon.

HERMAN S. BLOCH. RAYMOND E. SCHAD.

REFERENCES CITED The following references are of record in the le of this patent:

Number 8 UNITED sTATEs PATENTS f Name Date Kemp et al Sept. 12, 1939 Deanesly et a1 Nov. 28, 1939 Schulze Dec. 19, 1939 Marschner Apr. 30, 1940 Houdry Dec. `31, 1940 Schulze July 28, 1942 Ruthrui Feb. 2, 1943?v Frey May 16, 1944i FOREIGN PATENTS Country f Datev Number Australia Mar. 15, 193sv

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