US3502569A - High octane motor fuel production by alkylation and reforming - Google Patents

Description

United States Patent HIGH 8 Claims ABSTRACT OF THE DISCLOSURE High octane number motor fuel is produced by alkylating isobutane with a C mono-olefin to produce an alkylate separable into distinct low octane and high octane fractions, reforming the low octane fraction and blending it with the high octane number alkylate fraction.

CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of my copending application Ser. No. 668,684, filed Sept. 18, 1967, now abandoned.

FIELD OF INVENTION This invention pertains to the production of high octane number motor fuel involving a combination of alkylation and reforming. In particular, this invention pertains to the alkylation of isobutane with a C. mono-olefin to form an alkylate readily separable into a high octane number and a low octane number alkylate fraction, the reforming of the low octane number fraction and the blending of the resultant reformate with the high octane number alkylate fraction.

DESCRIPTION OF PRIOR ART Production of C -C1 branched paraflins having high octane numbers and anti-knock properties suitable for use in automotive and aviation fuels is of considerable importance to the refinery industry. This is a result of the introduction of high-compression, high-performance automobile engines and the necessity for high octane motor fuels required to develop maximum power therefrom. As automotive engine manufacturers develop engines with increased performance characteristics, higher octane motor fuels are required and slight variances in octane numbers become a critical parameter in an engines performance. For example, an octane rating increase in a motor fuel of as little as 2-3 numbers can be the difference between a quiet or a knocking engine. In

addition, the demand for clear, unpolluted air has placed an emphasis on developing a motor fuel having superior anti-knock properties without the need for anti-knock additives such as tetraethyllead which pollute the air when expelled with the engine exhaust.

A common source of high octane number motor fuels .is the catalytic alkylation of low boiling isoparaflins, such as isobutane and isopentane, with mono-olefins such as propylene, the butylenes, the amylenes and mixtures thereof. The common commercial processes utilized today involve the alkylation of isobutane with butylenes and/ or. propylene. These processes typically produce a motor fuel alkylate having a research clear octane rating of 93-95.

It is well recognized in the prior art that the components present in a typical motor fuel alkylate process constitute a diverse mixture of both high octane and low octane C C isomers. The prior art further recognizes that the only portion of the alkylate product having a ice low octane number, readily separated from the total alkylate product, is the high boiling portion of the alkylate commonly referred to as alkylate bottoms. As is Well known to those trained in the art, a typical alkylate, produced by the catalytic alkylation of isobutane and/or isopentane with propylene, butylenes and amylenes, has a 50% volumetric distillation temperature of about 200- 240 F. and a temperature of about 300350 F. and often extending up to 400 F. The initial boiling point varies by the amount of butane etc., present, a determined by the particular use of the fuel and season of the year in which it is produced. The art recognizes that the very high boiling portion of the alkylate mentioned above is of a lower octane number than the rest of the alkylate produced, namely, that portion of the alkylate boiling over 270-400 F. For example, Leifer, in U.S. Patent No. 2,401,649, alkylates isobutane and butylenes in a conventional alkylation zone to produce an alkymer gasoline rich in isooctane. This is obtained by separating from the alkylate product a fraction having an end boiling point of about 350 F. and an octane number of about 92. Higher boiling constituents are removed and passed to a reforming zone for conversion to lower boiling, higher octane constituents. Deanesly, in US. Patent No. 2,684,325, separates a polymerizationalkylation reactor efiiuent to recover a fraction boiling up to 400 P. which is utilized as a goline blending component. The distillation residue boiling over 400 F., and representing about 10% by volume of the alkylation product, is recycled for upgrading to lower boiling stocks. Findlay, in US. Patent No. 2,80,995, separates a light deolefinized gasoline fraction having an end boiling point (EBP) of about F., and an octane number of about 60.4 from a conventional HF isobutane alkylation unit, reforms this light fraction and blends the resultant reformate with the higher boiling alkylate product to produce an upgraded gasoline product. Chapman, in US. Patent No. 3,211,808, separates a heavy alkylate, produced in a conventional HF alkylation unit and defined as having an initial boiling point (IBP) of 260 F. from the total alkylate product and recycles this fraction to the alkylation unit to produce a higher octane number motor fuel.

Thus, it is readily seen that the prior art recognizes that a small portion of either the light alkylate (EBP of about 200 F.) and, more particularly, a portion of the heavier alkylate (IBP of about 260-400 F.) are undesirable constituents in a motor fuel alkylate since they possess lower octane numbers than the rest of the motor fuel alkylate.

SUMMARY OF THE INVENTION It has now been discovered that a typical alkylate produced by isobutane-butylene alkylation is readily separable into not only two-i.e., heavy alkylate and light alkylate-fractions having distinct octane number differences, but into three such fractions. It has been discovered, that in addition to the recognized low-octane heavy alkylate fraction, there exists an alkylate fraction having an initial boiling point of about 200 F. to about 230 F. which has an octane number of about 10 octane numbers below the IBP to 200230 F. fraction without inclusion of the traditional heavy alkylate fraction. Inclusion of the heavy alkylate fraction increases the octane number difference to even a greater degree. This lower octane fraction is characterized in havinga substantially higher dimethylhexane content than the higher octane fraction. This fraction possesses this lower octane rating despite the presence of appreciable amounts of high octane trivmethylpentanes. This result is due to the nonlinearity 1 3 I hexane content means that the dimethylhexane content of the lower octane number fraction is at least twice the content present in the higher octane number fraction.

Accordingly, it is an object of this invention to provide a process for producing high octane number motor fuel. It is a further object to produce such fuels by a unique combination of alkydation, separation and reforming.

In an embodiment, this invention relates to a process for producing high octane number motor fuel which comprises the steps of: (a) alkylating isobutane with a C mono-olefin in contact with an aikylation catalyst at alkylation" conditions in an alkylation zone to produce an alkylate product cotaining dimethylhexanes; (b) separating said alkylate into a low-boiling, high-octane fraction and a high-boiling, low-octane fraction characterized by a dimethylhexane' content substantially higher than said low-boiling fraction and having an initial boiling point of about 200 F. to about 230 R; (c) reforming at least a portion of said lowerEbctane, high-boiling fraction, in admixture with hydrogen and in contact with a reforming catalyst at reforming conditions in a reforming zone to produce a higher octane reformate; (d) commingling at least a portion of said higher octane reformate with said high-octane, low-boiling alkylate fraction to produce a motor fuel alkylate possessing a higher octane: number thansaid alkylate product produced instep (a).

In a further more limited embodiment, the aforemen tioned high-boiling, low-octane number fraction consists of about 301 to about 60 volume percent of said alkylate product.

Alternative embodiments and a more detailed description of the alkylation and reforming zones hereinbefore mentioned will be found in the following description of the preferred embodiments:

" DESCRIPTION on THE rREEERaED EMBODIMENTS The alkylation step of the process of this invention preferably comprises alkylating isobutane and a butylene, inasmuch as the ideal alkylation product of these species is a branched C parafiin. However, it is within the scope of thisginvention to include, in addition to isobutane and butylenes, a mixed hydrocarbon feed stock containing olefinic hydrocarbons such as propylene, amylenes, etc., as Well as C to C parafiins. If such mixed streams are utilized, it ispreferred that the C mono-olefins (butylcues) and isobutane predominate in the hydrocarbon mixture. P

The alkylation step of the process of this invention comprises contacting a hydrocarbon feed stock containing isobutane and butylenes with an acid-acting alkylation catalyst in an alkylation zone. The isobutane and butylene may be introduced as separate feed streams or in admixture with one another. This contacting is preferably efiected by intimately mixing the hydrocarbons with a strong acid catalyst such as hydrofluoric acid, sulfuric acid, mixtures of sulfuric iand phosphoric acids, certain complexes of aluminum chloride and sulfuric acid, etc. Preferred alkylation catal jsts are hydrofluoric acid and sulfuric *acid, particularly hydrofluoric acid. It is also within the scope of this invention to effect the alkylation by contacting the hydrocarbon with a suitable solid alkylation catalyst.

To prevent polymerization of the olefin in the alkylation zone, the catalyst and hydrocarbons; are maintained in intimate physical admixture 'and a large mole excess of isobutane to olefin is used. This isobutane-olefin mole ratio can vary from about 2:110 about'20zl and preferably from about 6:1 to about 16:1. This excess isobutane is readily separated from the resultant alkylation product and is usually recycled to the alkylation zone. When a liquid acid such as hydrofluoric or sulfuric acidis utilized to catalyze the alkylation reaction, a catalyst to hydrocarbon volume ratio of about 0.25:1 to about 10:1 and particularly about 0.5:1 to about 5.0:1 are employed. The

reaction is effected at a temperature of about 0 F. to, 200' F., a residence time of about 20 seconds to about 1200 seconds, and preferably about 60 to about 1000 sec; onds, and a pressure of about atmospheric to about 50 atmospheres. It is particularly preferred to maintain a reaction pressure sufiicient to maintain the catalyst and reactants in the liquid phase. After the termination of the desired residence time, the resulting alkylation zone efiluent is separated into a hydrocarbon, phase and an acid phase. From the hydrocarbon phase, isobutane and other light hydrocarbons such as butane are recovered, leasing a desired amount of butane within the alkylate to control the vapor pressure of the alkylate. As used herein, alkylateirefers to the higher molecular weight reaction product from the alkylation reaction. The high molecular weight tars, etc., formed Within the reaction are also removed by appropriate distillation techniques. The resultant alkylate is then separated into a high-octane, lowboiling fraction characterized in having an EBP of about 200 F. to about 230 F. and a lower-octane, high boiling fraction, characterized in having an IBP of aboutr200 F. to about 230 F. This lower octane fraction is further characterizedin that the dimethylhexanes formed by the isobutane-butylene alkylation reaction are predominantly in this fraction; namely, the :dimethylhexane content of this fraction is at least twice that of the higher octane fraction. This lower octane fraction typically consists of about 30 to about 6;) volume percent of the total alkylate product. This exact value is a function of the amount of propylene in the alkylation zone feed stock and the C isoparafiins produced as a result. This foregoing separation is readily obtained by conventional fractional distillation techniques. i 7 I At least a portion of the high-boiling, lower-octane fraction is then passed to a reforming zone wherein the lower octane constituents in this fraction are converted to higher octane components byg the various reactions which occur in a reforming zone such as isomerization, dehydrocyclization, and cracking. As used herein, the term at least a portion refers to eithera homogenous portion of said fraction or an appropriate boiling fraction of this fraction. It is particularly preferred to operate this reforming zone in the presence of added hydrogen so that this resultant reformate will be essentially olefin-free. While the dehydrogenation of paraflins to olefins can produce a higher octane product, the olefins are an un: desired constituent in a motor fuel product because of their tendency to form gum deposits when utilized in internal combustion engines.

The conditions, catalystaand methods of reforming paraflinic hydrocarbons are well known to the art. No patentable novelty is claimed herein for the method of alkylating isobutane and butylenes and the reforming of the herein described lower octane number alkylate fraction. The inventive concept resides in the advantageous, heretofore unrecognized, method of combining these two well known refining processes to produce a high octane motor fuel as hereinbefore described.

Suitable reforming catalysts typically include the dualfunction catalysts typified in having a heavy metal component to induce a hydrogenanon-dehydrogenation function to an acid-acting cracking material of the porous, adsorptive, refractory .oxide type. While the known chromia-alumina type catalysts are applicable, it is pre ferred to utilize a reforming catalyst comprising a Group VIII metallic-L component, a halogen component, and suitable refractory inorganic oxides such as the high surface area gamma-, eta-, and theta-aluminas. Particularly preferred are the gamma-aluminas. By the term high surfce area is meant a surface area as measured by conventional surface adsorption techniques, of about 25 to about 500 or more square meters per gram, and preferably a surface area of approximately to 300 square meters per gram. In addition to the aforementioned aluminas, it is also contemplated that other refractory inorganic oxides containing at least one metal from Group VIII of the Periodic Table, such as silica, zirconia, mag nesia, thoria, etc., and combinations of the various refractory inorganic oxides containing at least one metal from Group VIII of the Periodic Table such as silica alumina, alumina-magnesia, alumina-thoria, aluminazirconia, 'etc., may also be utilized as catalysts in the reforming zone of the present invention. In addition, crystalline aluminosilicates, both synthetic and natural occurring, may also be utilized as solid supports for the reforming catalyst. It is preferable that the pore mouths of the crystalline aluminosilicates have cross-sectional diameters of from about 4 to 15 angstrom units. Among the preferred crystalline aluminosilicates are the hydrogen and/or polyvalent forms of faujasite and mordenite and particularly the hydrogen form of mordenite. The concentration of crystalline aluminosilicate may be as high as 100%, or the crystalline aluminosilicate may be held within a matrix such as silica, alumina and silica-alumina.

Typical metals from Group VIII of the Periodic Table for use in the reforming catalyst to be utilized in the reforming zone of the present invention include platinum, palladium, ruthenium, rhodium, osmium, and iridium, and mixtures thereof. Platinum and palladium are particularly preferred. In addition, the Group VIII metal may also be present with metals, such as rhenium, known p EXAMPLE The following example is presented 'to further illustrate the embodiments of the process of this invention and is not intended to be an undue limitation on the broad scope and spirit of the appended claims.

An olefin mixture containing propylene, butylenes, and amylenes, the majority of which are butylenes, was alkylated with isobutane in a conventional commercial alkylation system utilizing hydrogen fluoride as a catalyst. This system was maintained at alkylation conditions including a 12:1 isobutane to olefin mole ratio, an operating temperature of about 85 F., a residence time of about 420 seconds, a hydrogen fluoride to hydrocarbon volume ratio of about 1.5 :1 and an operating pressure of about 175 p.s.i.g. After separation of the excess isobutane, catalyst, and tars produced during the course of the reaction, a motor fuel alkylate having a 94.2 research clear octane number was recovered.

This sample was then subjected to an intensive analysis including octane number evaluation and component analysis. The sample was divided into ten equal volume portions by fractional distillation and each portion was analyzed to determine its composition and research octane number. This complete evaluation is presented in the following table.

OCTANE NUMBER EVALUATION AND COMPONENT ANALYSIS OF ALKYLATE Research Fraction No.

Octane No. 1 2 3 4 5 6 7 8 9 Botts.

Cut temp. F 164. 3 206. 6 211. 1 215. 6 219. 2 236. 3 240. 0 293 293+ Volume percent 10 10 10 10 10 10 10 10 10 Alkylate component (type) weight percent: i-Butane 102. 5

n-Butane 95.0 2 2 0.1 i-Pentane 92. 3 1. 6 0. 1 n-Pentane 61. 7 1. 5

5 a 2,3-dimethylbutane. 103. 5 28. 8 0. 7 2-methylpentane 73. 4 13. 6 0. 3 3methylpentane 74. 5 4. 2 0. 2 n-Hexane 24. 8 0.2 2,2-dimethylpenta 92. 8 0. 1 2,4-d1methylpentane 83. 1 19.8 17. 6 2,2,3-trirnethylpentane. 112. 1 1. 3 O. 4 2-methylhexane 42. 4 1. 6 1. 7 2,3-dimethy1pentane... 91. 0 22. 8 24. 5 3-methylhexane 52. 0 1.2 1.1 2,2,4-trimethylpentane 100 1. 1 3 56. 9 18. 7 2. 2,5-dimethylhexane 55. 5 14.0 14. 9 7. 8 2,4-dime thylhexane 65. 2 16. 7 18. 4 10. 6 2,2,3-tri methylpentane 109. 6 2. 2 2.8 2. 2 2,3,4-trimethylpentane 102.7 6. 2 25. 5 31. 3 2,2,3 trimethylpentane 106. 1 1. 8 13. 9 27. 9 2,3-dimethylhexane 71. 0 1. 1 5. 8 14. 6 0 70-75 2. 7

0t 100. 0 100. 0 100. 0 Research clear octane No., 10% fraction 88.9 87. 1 90. 5

to be capable of stabilizing a reforming catalyst. The Group VIII component of the catalyst will normally be utilized in an amount of from about 0.1% to about 2.0% by weight and the amount of combined halogen in the reforming catalyst can vary from about 0.01 to about 2.0% by weight based upon the solid support. Of the various halogens which may be utilized, both fluorine and chlorine, particularly chlorine, are preferred.

Within the reforming zone, the low octane number alkylate fraction, in admixture with hydrogen is contacted with the foregoing catalyst preferably maintained in a fixed bed. This reforming zone is maintained at re forming conditions which include a temperature of about 700 to about 1100 F., a pressure of about 0 to about 1,000 p.s.i.g., an LHSV (liquid hourly space velocity) of about 0.1 to about 10 hr. and a mole ratio of hydrogen to hydrocarbon of about 1:1 to about 20:1 or more.

The resulting reactor effluent is then recovered and after separation of hydrogen and light hydrocarbons is blended by meanswell known to the art with the low-boiling, high-octane alkylate fraction to produce a high octane motor fuel typically having a research octane in excess of 95.

An examination of the data presented in the foregoing table yields some rather unexpected, unanticipated results. It is readily seen that the alkylate, in addition to the lower octane alkylate bottoms (i.e., 260-300+) fraction known to the art as having a lower octane number than the rest of the alkylate, there exists a sharp difference in the octane numbers obtained for the first five 10% cuts than for the last five 10% cuts. This sharp unexpected difference of about 10 octane numbers between these segments appears to be the result of the presence of low octane number dimethylhexanes within each fraction. The presence of these compounds, despite the presence of appreciable amounts of high octane number trimethylpentanes in these cuts, yields a marked octane difference in comparison to the first five 10% cuts where these dimethylhexanes are not present. This difference is observed in other alkylates produced within both commercial and laboratory research units.

This foregoing alkylate is then fractionated to produce a high-octane, low-boiling fraction which represents 50% of the total alkylate and has an IBP -2l6 F. boiling range. The remaining alkylate (216 F.+), having a lower octane number, is then reformed in admixture with hydrogen in a conventional reforming zone containing a reforming catalyst comprising alumina combined with 0.6 wt. percent platinum and 0.8 wt. percent chloride. This reforming zone is maintained at a temperature of about 850-F., a pressure of 500 p.s.i.g., a liquid hourly space velocity of 1.0 hrr and a hydrogen tohydrocar'bon mole ratio of 10.0:1.0. Within this reforming zone portions of this alkylate are cracked, dehydrocyclized, and/or isomerized to produce a higher octane reformate. This reformate is then blended with the low-boiling, high-octane fraction to yield a final motor fuel having a research octane number of 98.5. This is a considerably higher octane number than that obtained by alkylation alone.

Thus, it has been shown that there exists a heretofore unrecognized specific fraction in an alkylate produced by isobutane-butylene alkylation which, in addition to the recognized heavy alkylate fraction, has an octane number significantly below that of the remaining alkylate. By removing and reforming this fraction, 21 motor fuel having an improved octane number is available by methods heretofore unrecognized in the art.

I claim as my invention:

1. A process for producing high octane number motor fuel which comprises the steps of (a) alkylating isobutane with a C mono-olefin in contact with an alkylation catalyst at alkylation conditions in an alkylation zone to produce an alkylate product containing dimethylhexanes;

('b) separating said alkylate into a low-boiling, highoctane fraction and a high-boiling, low-octane fraction characterized by a dimethylhexane content substantially higher than said low boiling fraction and having an initial boiling point of about 200 F. to about 230 F.;

(c) reforming at least a portion of said lower octane high-boiling fraction, in admixture with hydrogen and in contact with a reforming catalyst at reforming conditions in a reforming zone to produce a higher octane reformate; and,

(d) commingling at least a portion of said higher octane reformate with said high-octane, low-boiling alkylate fraction to produce a motor fuel alkylate possessing a higher octane number than said alkylate product produced in step (a).

2. The process of claim 1 further characterized in that said alkylation conditions include a temperature of about 0 F. to about 200 F., a contact time of about 20 seconds to about 1200 seconds, a catalyst to hydrocarbon volume ratio of about 0.5 :1 to about 5:1, a isobutane to olefin mole ratio of about 2:1 to about 20:1, and a pressure of about atmospheric to about atmospheres.

3. The process of claim 1 further characterized in that said alkylation catalyst is hydrogen fluoride.

4. The process of claim 1 further characterized in that said alkylation catalyst is sulfuric acid.

5. The process of claim 1 further characterized in that said reforming catalyst comprises a platinum component and a halogen component with a refractory inorganic oxide carrier material, and said reforming conditions include a temperature of about 700 F. to about 1100 F., a pressure of about 0 to about 1000 p.s.i.g., a liquid hourly space velocity of about 0.1 to about 10 hr. and a hydrogen to hydrocarbon mole ratio of about 1:1 to about 20:1.

6. The process of claim 5 further characterized in that said reforming catalyst comprises, on an elemental basis, about 0.01 to about 2.0 wt. percent platinum, and about 0.1 to about 2.0 wt. percent chlorine with an aluminum carrier material.

7. The process of claim 5 further characterized in that said refractory inorganic oxide comprises a crystalline aluminosilicate.

8. The process of claim 1 further characterized in that said low-octane, high-boiling fraction consists of about 30 to about volume percent of said alkylate product.

References Cited UNITED STATES PATENTS 2,401,649 6/ 1946 Lefl'er 208-70 2,684,325 7/1954 Deanesly 208-70 2,890,995 6/1959 Findlay 208 3,211,803 10/1965 Chapman 20879 HERBERT LEVINE, Primary Examiner US. Cl. X.R. 208-l7, 93, 141