US3209052A

US3209052A - Integrated hydration-isomerization process

Info

Publication number: US3209052A
Application number: US252180A
Authority: US
Inventors: Lawrence B Scott; Richard D Mullineaux
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1963-01-17
Filing date: 1963-01-17
Publication date: 1965-09-28
Anticipated expiration: 1982-09-28

Description

United States Patent 3,209,052 INTEGRATED HY DRATION-TSOMERIZATION PRQCE'SS Lawrence B. Scott, East Alton, Ill., and Richard D. Mullineaux, Oakland, Calif., assignors to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed Jan. 17, 1963, Ser. No. 252,180

7 Claims. (Cl. 260683.65)

This invention relates to a process for converting normal and iso-olefin into high octane gasoline components.

Although of recent times, catalytic reforming of various gasoline boiling hydrocarbon fractions has come into relatively wide use, a main source of premium grade motor gasoline has been from catalytic cracking higher boiling oils. The octane number of premium gasoline has steadily increased and this has required the use of more and more catalytically cracked gasoline to meet octane requirements. Furthermore, severity of catalytic cracking has been increased to produce catalytically cracked gasolines having the highest possible octane number consistent with permissible losses.

In the practice in the past, higher boiling hydrocarbon oils have been catalytically cracked to produce gasoline along with gaseous products including propylene and butylene. The common practice was to polymerize a propane-propylene fraction from a catalytic cracking unit and blend the resulting polymer in gasoline. Furthermore, it has been the practice to alkylate a butylene fraction with isobutanes to produce alkylate which is also blended with catalytically cracked gasoline. These operations have not been entirely satisfactory for several reasons. In the first place, when effecting the catalytic cracking under Severe conditions to produce a gasoline having a high octane number, it has been found that the gasoline so produced has a sensitivity higher than desired. (Sensitivity is an inverse function of the gasolines ability to maintain its resistance to detonation as engine operating conditions become more severe, e.g., on the road, from city-type driving to high-speed, freeway-type driving. The sensitivity of a fuel is defined quantitatively as the difference between research and motor octane numbers.) This condition has been further aggravated by the polymer produced and blended in the gasoline. The increased sensitivity of these more severely cracked hydrocarbons has been attributed, to a large extent, to the greater amount of olefins produced. In addition, anti-smog legislation has been proposed in certain areas, to reduce the amount of olefins in gasoline.

It has been suggested that the higher molecular weight olefins in the catalytically cracked gasoline such as C and heavier olefins be alkylated in the presence of conventional mineral acid catalysts. However, alkylation has not been the best solution since mineral acid alkylation of a catalytically cracked C /C fraction, which contains a large amount of diolefin, results in uneconomically high acid consumption.

Another process which has been practiced in the hydrogenation of catalytically cracked gasoline. Hydrogenation of the gasoline has been unsatisfactory because, while there has been a gain in sensitivity control as a result of saturation of the olefins to paraflins, there has been a substantial loss in research octane number. Therefore, it has been a practice to hydrogenate this stream only partially (4060% conversion) which has resulted in some improvement in sensitivity with only small loss, when compared to total hydrogenation, in research octane number.

These disadvantages are largely overcome by the combination process of the present invention, which provides a blended gasoline having a high octane number and low sensitivity. According to the invention, a mixture of normal and iso-olefins having from 5 to 7 carbon atoms, such as a light, catalytically cracked fraction is selectively hydrated under acid conditions to produce a mixture of predominantly tertiary alcohols. The unreacted hydrocarbon fraction containing normal olefins is recovered from the hydration unit and is subsequently hydro isomerized to produce a fraction rich in isoparaffin. In a preferred embodiment of the invention, a portion of the alcohol is esterified to produce monoacetates. These and additional advantages of this process will be apparent as the invention is described with reference to the drawing consisting of two figures, each of which illustrates several preferred embodiments of the invention.

The invention is broadly applicable to a mixture of normal and iso-olefins having from 5 to 7 carbon atoms. It is particularly applicable to gasoline fractions containing C to C normal and iso-olefins obtained from the cracking of hydrocarbon oils.

In order to set forth more fully the nature of the invention, without however intending to limit the scope of the invention, it will be described in detail as applied to the selective hydration, under sulfuric acid conditions, of a C to C catalytic-cracked fraction and the subsequent hydroisomerization to isoparaffins of the normal olefins in the unreacted hydrocarbon fraction.

Referring now to FIGURE 1: a catalytically cracked gasoline is introduced into fractionation tower 2 through line 4. Auxiliary equipment such as pumps, heat exchangers, valves, control mechanisms, etc., which are obvious to those skilled in the art are not shown. This tower is operated to produce (1) a C to C fraction containing normal and iso-olefins and (2) a C and heavier fraction. The C and heavier fraction is withdrawn from fractionation tower 2 through line 6. The C through 0; fraction is withdrawn from fractionation tower 2 through line 8 and is preferably purified to remove sulfur compounds, notably hydrogen sulfide, by Washing for example in treater 10 with diethanolamine or a similar organic or inorganic base. Alkaline compounds can also desirably be removed from the feed in any known matter and such purification steps as such do not form a part of this invention.

The C to C fraction enters reactor 12 via line 14- whrein it is contacted with sulfuric acid added through line 16. The hydrocarbon can be contacted with acid in a single reactor. However, it is preferred to employ a plurality of reactors in order to appoach equilibrium conditions. For example, when employing two reactors, effluent from reactor 12 enters reactor 18 via line 20. The reactors can be of suitable design such as stirred reactors or can be of the tower reactor design with or without contacting means such as perforated trays. Isoolefins are selectively hydrated with sulfuric acid of from about 40% to about concentration, preferably from about 50% to about 70% concentration. The hydration temperature can be in the range of from about 0 C. to about 30 C., preferably from about 0 to about 20 C. The ratio of acid to hydrocarbon is from about 1:3 to about 3:1, preferably about 1:1.

A hydrocarbon-acid mixture is withdrawn from reactor 18 and enters settler 22 through line 24. Settled acid is withdrawn and recycled via line 16. A hydrocarbon phase containing alcohol and entrained acid is withdrawn from the settler and introduced into waterwash settler 26 through line 28. At the low hydration temperatures, the tertiary C and heavier alcohols are soluble in the hydrocarbon phase while the majority of the tertiary C alcohols initially produced remain in the acid phase and are recycled with the acid. As the amount of tertiary C alcohols builds up in the acid phase, more of the tertiary C alcohols produced by isoolefin hydration will be withdrawn in the hydrocarbon phase with, of course, the tertiary C and heavier alcohols until equilibrium is obtained, when substantially all of the tertiary C alcohols thereafter produced will be withdrawn in the hydrocarbon phase. Water is introduced into the water-wash settle through line 30. While it is not necessary in the practice of the invention, it is preferred to use only minimum amount of water, usually the stoichiometric amount necessary to convert the olefin to alcohols, in order to minimize water handling and concomitant corrosion problems. It is desirable, when using this small amount of water, to use multiple contacting stages for greater washing efficiency. When using only the stoichiometric amount of Water for Washing, the water, containing acid, is withdrawn via line 30, combined with the acid from settler 22, and recycled to the reaction zone. Sulfuric acid can be added to the system as necessary.

Hydrocarbon is withdrawn from water-wash settler 26 via line 32 given a caustic wash in vessel 34 to neutralize any entrained acid and introduced into fractionation tower 36 through line 38 wherein alcohol is separated from unreacted hydrocarbon. An alcohol fraction is withdrawn as a bottom product and is routed to alcohol storage vessel 40 through line 42. A fraction containing normal olefin is recovered as an overhead product via line 44.

The synthesis of alcohols by the hydration of olefins can be carried out by other processes such as by contacting the olefin with water in the presence of an organic ion exchange material (of the sulfonated resin type), a catalytic system comprising hydrogen fluoride and boron trichloride, a supported phosphoric acid catalyst, oxides or sulfides of tungsten on a carrier, etc.

The fraction containing normal olefin from the hydration process is routed to a hydroisomerization unit through line 44. The hydrocarbon fraction is heated to reaction temperature in furnace 52, and passed together with hydrogen from line 54 through line 56 into reaction zone 58 which contains a hydroisomerization catalyst comprising a hydrogenation function deposited on an acid-acting support, such as nickel sulfide on an acid-acting refractory oxide support, e.g., silica-alumina.

The conversion in reaction zone 58 is carried out at a temperature in the range of about 400 F. to about 900 F., preferably from about 500 F. to about 750 F., and at a pressure in the range of from about atmospheres to about 100 atmospheres, preferably from about atmospheres to about 80 atmospheres. At the lower pressures, isomerization activity of the catalyst has a shorter life where at pressures exceeding 100 atmospheres the yield of branched hydrocarbons is lower. The hydrogen partial pressure can vary within wide limits and is preferably from about 50% to about 90% of the total pressure. Pure hydrogen is not necessarily used since hydrogen-containing gas, such as hydrogen-rich gas from a reforming process is highly suitable. Hydrogen to oil molar ratios for the conversion reaction can vary from about 1:1 to about 20:1, preferably from about 2:1 to about 10:1. Liquid hourly space velocities (volume of hydrocarbon feed per volume of catalyst per hour) of from about 0.5 to about 10 are used, and preferably from about 1 to about 5. Particularly suitable reaction conditions for the conversion reaction are 675 F. temperature and 55 atmospheres pressure, 2.0 liquid hourly space velocity and 4.0 hydrogen to oil molar ratio. Other suitable catalysts are for example the sulfides of chromium, aluminum, tungsten, iron, cobalt or mixtures thereof.

Reaction zone efiiuent containing hydroisomerizate is partially condensed and passed into separator 60 through line 62. Hydrogen is withdrawn from the separator and is recycled to reaction zone 58 through line 54. Hydrogen is introduced as necessary to make up for that consumed in the reaction and that lost in processing.

Liquid efiiuent from separator 60 is introduced into fractionation tower 64 through line 66 to stabilize the hydroisomerizate. Light hydrocarbons are taken overhead, cooled and are routed to, for example, refinery fuel or other process through line 68. The hydroisomerizate substantially free of olefin and having an increased isoparaifin content is withdrawn from the bottom of the fractionation zone through line 70.

The conversion in reaction zone 58 is exothermic reaction. It is often desirable to recycle a portion of the hydroisomerizate to the reaction zone as a diluent through line 72 to avoid an excessive temperature rise in the reaction zone and for added conversion.

A particular advantage of the combination process is that diolefins are removed from the C to C fraction during the hydration of olefins to produce alcohols. The diolefins polymerize at the high reaction temperature and pressure in the hydroisomerization plant to form polymers. These polymers plate out on heat exchange surface to reduce the efficiency of the heat exchangers and furnaces; result in increased utilities and maintenance cost and further create a safety hazard.

In a preferred embodiment, all or a part of the C and heavier fraction can be mixed via line 14 with the unreacted hydrocarbon fraction from the hydration process prior to the hydroisomerization reactor. In this manner sulfur is added, by means of the C and heavier fraction, to condition a sulfided hydroisomerization catalyst and it is not generally necessary to add extraneous sulfur for catalyst conditioning.

Hydroisomerizate is routed through line 70 into gasoline blending tank 76. A portion of the C and heavier gasoline fraction which has not been hydroisomerized can be routed to gasoline blending tank 76 or preferably routed for further processing such as air-inhibitor sweetening solutizer treating, etc. Alcohol is withdrawn from storage vessel 40 and is routed into gasoline blending tank 76 through line 78.

In one particularly attractive embodiment of the invention, as shown in FIGURE 2, it is desirable to further react a portion of the alcohols to form monoacetates. A portion of the alcohol is routed into esterification zone 80 through line 82. The monoacetates can be produced by the reaction of alcohol with for example acetic acid, ketene, or acetic anhydride in the presence of suitable catalyst. A preferred method of making this monoacetate is reacting alcohol with ketene in the presence of a small amount of sulfuric or p-tolene sulfonic acid catalyst, e.g., from about 0.05% to about 10% sulfuric acid, preferably from about 0.1 to about 5% sulfuric acid, and at ambient temperatures. In certain situations, it is desirable to react a C to C catalytically cracked olefin fraction in the pres ence of esterification catalyst such as sulfuric or phosphoric acid or acidic solids such as phosphoric acid on a solid catalyst, acid ion exchange resins, etc., in order to directly produce the monoacetates. The monoacetates are a particularly desirable blending component as they are lead octane appreciators.

T he monoacetates are routed into gasoline blending tank 72 through line 84.

A portion of the alcohol can be purified and routed to other storage for sales as chemicals, etc. The monoacetates can also be purified and routed to storage for sales, etc.

The following examples are illustrative of some of the advantages derived from the invention, but are not to be considered to limit the scope of the invention.

EXAMPLE I The benefits derived from selectively hydrating a catalytically-cracked fraction containing C through C, normal and iso-olefins under acid conditions to produce a mixture of predominantly tertiary alcohols is seen from a comparison of the component blending octane numbers of tertiary amylenes and tertiary amyl alcohol given below in Table I.

Table I COMPONENT BLENDING OCTANE NUMBER Clear 8 cc. TEL/gal.

Component Re- Motor Sensi- Re- Motor Sensisearch tivity search tivity Tertiary amylene... 112 87 25 106 80 26 Tertiary alcohol. 105 91 14 109 101 8 The sensitivity of the alcohol relative to the corresponding olefin is considerably lower. The sensitivity of the alcohol is reduced markedly by the addition of 3 cc.s tetraethyl lead per gallon of fuel. However, the sensitivity of the olefin is unaffected by addition of lead. It is a particularly attractive expedient to adjust hydration conditions to selectively hydrate the isoolefins to tertiary alcohols because the secondary and primary alcohols have sensitivities not substantially different from their olefinic counterparts.

EXAMPLE 11 Some of the advantages of hydroisomerizing a catalytically cracked fraction containing normal olefins [rather than catalytically reforming this fraction can be seen by an examination of the relative octane numbers of the olefin (hexene-l), the hydroisomerization products of this olefin (2- and 3-methylpentanes) and the catalytically reformed product of this olefin (n-hexane). The octane numbers are given below in Table II.

Table II Octane Number, 3 cc. TEL/gal. Component Research Motor Sensitivity The olefin (hexene-l) possesses a high research octane EXAMPLE III Catalytically cracked gasoline fractions although of high research octane number, have an extremely high sensitivity because of their large olefin content. In the past, refineries have been forced to hydrogenate such gasoline fractions in order to saturate the olefins and thereby reduce their sensitivity. Such hydrogenation processes use conventional catalysts such as cobalt-molybdenum on alumina. The improvement in sensitivity results partly from a decline in research octane number, which is quite severe on complete hydrogenation and involves a costly loss of value of blended gasoline containing such hydrogenated fractions. It is far more advantageous to hydroisomerize this fraction since many of the normal olefins contained therein, which would have extremely low octane numbers when hydrogenated to the corresponding normal paraffins, are converted to the corresponding isoparafiins in the hydroisomerization process. Thus, sensitivity is greatly reduced with less loss in research octane number as compared to conventional hydrogenation. The hydroisomerized gasoline, which is completely or substantially completely saturated, will usually have a sensitivity less than about 3. The yield of branched chain hydrocarbons from hydroisomerization with 'nickel sulfide on silica alumina cracking catalyst compared to the yield from conventional hydrogenation with cobalt-molybdenum on alumina catalyst is given in Table III.

Table III HYDROPROCESSING OF CATALYTIOALLY CRACKED GASOLINE FRACTION TO 200 F. FRACTION) Composition, percent by Hydrogenation Hydroisomerization weight Total O s Trace Total 01s 2. 1 Isopentane 3. 8 9. 4 Normal pentane 1. 6 2,2-dimethyl butane and bu- 0. 6

tone 9. 4 2,3-dimethyl butane and butene 4. 0 5. 0 2-methylpentane 14. 3 21. 0 3-methylpentane 9. 9 13 8 Oyol0pentane 3. 5 Normal hexane. 8. 6 2. 1

EXAMPLE IV Experiments were conducted on the hydroisomerization of pentene-l in the presence of nickel sulfide on silica-alumina cracking catalyst. Conditions and results are given in Table IV. The octane rating of the product is considerably improved compared to a research octane number (clear) of 62 for normal pentane which would be obtained by hydrogenation of the pentene-l.

Table IV Conditions:

Temperature, C. 300 Pressure, kg./cm. 20 Molar ratio, H /oil 4/1 LHSV, l./h.l 2.0

Composition of product, percent by weight:

C -C 2 Isobutane 13 Normal butene 2 Isopentane 61 Normal pentane 6 Total C 16 Research octane number (clear):

EXAMPLE V Hexene-l was hydroisomerized in the presence of a nickel sulfide on silica-alumina cracking catalyst. Conditions and results are given in Table V.

T able V \HYDROUESOMERHZINIG HEXENE 1 OV ER SU DFIDED MCKEL (4.8%) ON SIIIECA-WLU'MIIMA 'C-RAICKING KEATAIJY'IST Conditions:

Temperature, C. 3 20 Pressure, kg./cm. 29 Molar ratio, H /oil 4/1 LHSV, l./h.l 2.0

The octane rating of the product is considerably improved when compared to a research octane number (clear) of 25-30 for normal hexane which would be obtained by saturation of the hexene-l.

EXAMPLE VI A catalytically cracked gasoline boiling from about 95 F. to about 212 F. was hydroisomerized over a sulfided nickel (4.8% w.) on silica alumina cracking catalyst. Table VI shows the properties of the starting material, the reaction conditions and the properties of the product obtained in the present experiment.

Table VI HYDROISOMERIZATION OF CATALYTICALLY CRACKED GASOLINE OVER SULFIDED NICKEL (5% W.) ON SILICA- ALUMINA CRACKING CATALYST Conditions Temperature, 0.. Pressure, kg./cm.

Molar ratio, 11 /01 LHSV, l./l1.l

Properties of feed and reaction of products Product Yield by weight based on feed 9 Research octane number, 1% cc. TEL/gal. 91. Motor octane number, 1% cc. TEL/gal 98.

Sensitivity It is evident that a substantial gain in sensitivity control is realized by hydroisomerizing the catalytically cracked gasoline. However, there is also experienced an overall loss in research octane number from 98.0 to 91.5 and further there is experienced a yield loss. In accordance with the present invention, when the isoolefins are hydrated to form the tertiary alcohols and the unreacted hydrocarbons containing normal olefins are subsequently converted to isoparaffins, the overall octane number of the blended gasoline is increased with a concomitant decrease in sensitivity and minimum loss of hydrocarbon during the hydroisomerization process. Improved motor gasoline blends result from the combination of (1) replacing the isoolefins with alcohols which have superior sensitivities and comparable octane numbers, (2) providing a superior feed to the hydroisomerization process and (3) blending isoparaffins produced from the hydroisomerization process rather than saturated normal parafiins obtained from a catalytic reforming process.

We claim as our invention:

1. A process for the conversion of a mixture of normal and isoolefins having from 5 to 7 carbon atoms which comprises in combination:

passing the mixture into a hydration zone containing a hydration catalyst under conditions conducive to the selective hydration of isoolefin to tertiary alcohols;

recovering tertiary alcohol and a fraction containing normal olefin; passing the fraction containing normal olefin, together with a hydrogen-containing gas, over a hydroisomerization catalyst at hydroisomerization conditions;

and recovering a hydroisomerization product substantially free of olefin and having an increased isoparaffin content.

2. A process for the conversion of a mixture of normal and isoolefin in a catalytically cracked gasoline which comprises in combination:

separating the gasoline into a C to C fraction containing normal and isoolefin and a C and heavier fraction;

passing the C to 0; fraction into a hydration zone containing a hydration catalyst under conditions conducive to the selective hydration of isoolefin to tertiary alcohols;

recovering tertiary alcohol and a fraction containing normal olefin;

passing the fraction containing normal olefin, together with hydrogen and at least a portion of the C and heavier fraction, over a hydroisomerization catalyst at hydroisomerization conditions;

and recovering a hydroisomerization product substantially free of olefin and having an increased isoparafiin content.

3. The process according to claim 1 wherein the hydration catalyst is sulfuric acid having a concentration of from about 40% to about and the hydration conditions comprise a temperature range of from about 0 C. to about 30 C.

4. The process according to claim 1 wherein the hydration catalyst is sulfuric acid having a concentration of from about 50% to about 70% and the hydration conditions comprise a temperature range of from about 0 C. to about 20 C.

5. The process according to claim 1 wherein the hydroisomerization catalyst comprises a hydrogenation function deposited on an acid-acting support and the hydroisomerization conditions comprise a temperature in the range of from about 400 F. to about 900 F., a pressure in the range of from about 10 to about atmospheres, and a hydrogen to oil ratio of from about 1:1 to about 20:1.

6. The process according to claim 1 wherein the hydroisomerization catalyst comprises nickel sulfide on silicaalumina cracking catalyst and the hydroisomerization conditions comprise a temperature in the range of from about 500 F. to about 750 F., a pressure in the range of from about 20 to about 80 atmospheres, and a hydrogen to oil ratio of from about 2:1 to about 10:1.

7. A process for the conversion of a mixture of normal and isoolefins having from 5 to 7 carbon atoms which comprises:

contacting the mixture with sulfuric acid having a concentration from about 40% to 80% in a hydration zone at a temperature from about 0 C. to about 30 C., thereby selectively hydrating isoolefins to tertiary alcohols;

recovering tertiary alcohol and a fraction containing a substantial amount of normal olefin;

passing the fraction containing normal olefin, together with a hydrogen-containing gas, over a hydroisomerization catalyst which comprises a hydrogenation function deposited on an acidic support at a temperature of about 400 to about 900 F. and a pressure of from about 10 to about 100 atmospheres,

and a hydrogen-to-oil ratio of about 1:1 to about parafiin content.

References Cited by the Examiner UNITED STATES PATENTS Thomas 260683.65 X Voorhies 260683.9 Barry 260683.9 X

Bloecher 260641 10 OTHER REFERENCES Groggins: Unit Processes in Organic Syntheses, 5th Ed. (1958), pp. 78586.

Van Winkle: Aviation Gasoline Manufacture, pp. 5 222'23 (1944).

Wagner: Synthetic Organic Chemistry, pp. 174 and 480-81 (1953).

DELBERT E. GANTZ, Primary Examiner. LEON ZI'TVER, Examiner.

Claims

1. A PROCESS FOR THE CONVERSION OF A MIXTURE OF NORMAL AND ISOOLEFINS HAVING FROM 5 TO 7 CARBON ATOMS WHICH COMPRISES IN COMBINATION: PASSING THE MIXTURE INTO A HYDRATION ZONE CONTAINING A HYDRATION CATALYST UNDER CONDITIONS CONDUCIVE TO THE SELECTIVE HYDRATION OF ISOOLEFIN TO TERTIARY ALCOHOLS; RECOVERING TERTIARY ALCOHOL AND A FRACTION CONTAINING NORMAL OLEFIN; PASSING THE FRACTION CONTAINING NORMAL OLEFIN, TOGETHER WITH A HYDROGEN-CONTAINING GAS, OVER A HYDROISOMERIZATION CATALYST AT HYDROISOMERIZATION CONDITIONS; AND RECOVERING A HYDROISOMERIZATION PRODUCT SUBSTANTIALLY FREE OF OLEFIN AND HAVING AN INCREASED ISOPARAFFIN CONTENT.