progress in petroleum technology - ACS Publications

Commercial Alkylation of Isobutane Α. V. MRSTIK, K. A. SMITH, and R. D. PINKERTON

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 2, 2015 | http://pubs.acs.org Publication Date: January 1, 1951 | doi: 10.1021/ba-1951-0005.ch010

Sinclair Research Laboratories, Inc., Harvey, Ill.

All phases of the process for the alkylation of isobutane with olefins as practiced in modern petroleum refining are discussed. The discussion covers the chemistry of the reaction, as well as the technological items relating to feed stock composition, catalyst types, reaction variables, and commercial adaptations. A previously unpublished correlation relating alkylate quality to operating conditions is presented. The research problems requiring solution for commercial survival of the process when jet-type aircraft utilizing low octane fuels displace the reciprocating type are outlined.

T h e use of thermal and catalytic cracking processes for the production of high-octane motor gasolines is accompanied b y the production of quantities of light hydrocarbons such as ethylene, propylene, butene, and isobutane. These materials are satisfactory gasoline components octane-wise, but their vapor pressures are so high that only a portion of butanes can actually be blended into gasoline. Alkylation is one of several processes available for the utilization of these excess hydrocarbons. I n broad terms, alkylation refers to any process, thermal or catalytic, whereby an a l k y l radical is added to a compound. I n the petroleum industry, however, the term alkylation generally refers to the catalytic process for alkylating isobutane with various light olefins to produce highly branched paraffins boiling i n the gasoline range. This specific process will be discussed i n this paper. The alkylation process had its first commercial application i n the late 1930's and has become an important commercial process for two reasons. First, the product of the reac tion is an excellent aviation gasoline blending stock, because of its high aviation octane ratings, desirable boiling range, high heat of combustion per pound, good storage stability, and low sulfur content. Secondly, i t is, i n effect, a process for the conservation of re sources, for it converts fuel gas components to gasoline components. The growth of this process has been accelerated by the increased availability of light hydrocarbons resulting from the simultaneous growth of catalytic cracking processes. M i l i t a r y demands for aviation gasoline during World W a r I I were responsible for rapid expansion of these processes b y the petroleum industry. Since aviation gasoline produc tion is limited by alkylate supply, rapid development of the alkylation process was re quired to supply the expanded requirements of aviation gasoline (5). A t the end of the war there were 59 alkylation plants i n the country with a rated capacity of 178,000 barrels per day of aviation alkylate (9).

Chemistry of the Reaction The reaction between isobutane and olefins in the presence of an alkylation catalyst results in a product that is essentially paraffinic, and consists of a mixture of isoparaffins ranging from pentanes to decanes and higher regardless of which alkylating olefin is used. 97

In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.

98

ADVANCES IN CHEMISTRY SERIES

Component analyses of a typical alkylation product are presented i n Table I . The formation of all of these compounds cannot be explained b y the simple addition of an olefin molecule to an isobutane molecule. E v e n the formation of some of the specific isomers having the expected molecular weight cannot be accounted for by simple molecular addition. The mechanism of the reaction, therefore, must be rather complex Table I.

Chemical Composition of a Typical Butene Alkylate (3)


Component Pentanes and lighter 2,3-Dimethylbutane 2-Methylpentane 3-Methylpentane 2,2-Dimethylpentane 2,4-Dimethylpentane 2,2,3-Trimethylbutane 2,3-Dimethylpentane 2-Methylhexane 3-Methylhexane 2,2,4-Trimethylpentane 2,2-Dimethylhexane 2,5-Dimethylhexane 2,4- Di methy lhexane 2,2,3-Trimethylpentane 2,3,4-Trimethylpentane 2,3,3-Trimethylpentane 2,3-Dimethylhexane 3,4-Dimethylhexane 2,2,5-Trimethylhexane 2,3,5-Trimethylhexane IsoparaflBns

B . P . at Atmospheric Pressure, ° C . 131.4

Volume % Concn. in Alkylate 8.9 4.7 1.1 0.4 0.2 3.4 0.2 2.3 Π 9 U . «5

24.3 0.2 R R Ο. Ο

1.2 13.0 12.3 3.0 0.4 4.5 0.9 12.1 100.0

Of the several theories proposed for the mechanism of the alkylation reaction 4,7), the "carbonium i o n " theory is probably the most widely accepted. Although a complete discussion of this theory is beyond the scope of this paper, an outline of the mechanisms it proposes as applied to known alkylation products is presented. A carbonium ion is defined b y this theory as a molecule containing a carbon atom which is deficient two electrons i n its outer shell, and consequently carries a positive charge. The carbonium ion is highly reactive, and can undergo several transformations and reactions, among which are the following: 1. Loss of a proton to form an olefin 2. Reaction with an olefin to form a carbonium ion of higher molecular weight 3. Proton shift from another carbon atom i n the molecule to the carbon atom de ficient in electrons to form a new carbonium ion 4. M e t h y l group shift from another carbon atom i n the molecule to the carbon atom deficient i n electrons to form a new carbonium ion having a different carbon-to-carbon skeleton 5. Cleavage of carbon-to-carbon linkage to form an olefin and another carbonium ion of lower molecular weight 6. Reaction with isobutane to form a paraffin molecule and a tertiary butyl car bonium ion The above transformations and reactions can be used to explain the formation, as an example, of different heptane isomers when alkylating isobutane with propylene. A s the first step i n the mechanism, a tertiary butyl carbonium ion derived from isobutane reacts with a propylene molecule to form a carbonium ion of seven carbon atoms as outlined i n reaction 2. This ion may then react directly with a molecule of isobutane as i n reaction 6 to form the expected heptane molecule and to convert the isobutane molecule to a tertiary butyl carbonium ion. This seven-carbon carbonium ion, however, may undergo isomerization b y the mechanism outlined in reaction 3 or 4 before reacting with isobutane to form an isomeric heptane molecule. The proposed mechanisms may also be used to explain the formation of paraffins having both lower and higher molecular weights than would be expected from simple addition of olefin molecules to isobutane molecules. A typical example is the formation of heptanes and nonanes when isobutane is alkylated with butene. The first step consists of In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.

MRSTIK, SMITH, AND PINKERTON—COMMERCIAL ALKYLATION OF ISOBUTANE

99


a reaction between a butene molecule and a tertiary butyl carbonium ion derived from isobutane to form a carbonium ion of eight carbon atoms by reaction 2. This ion may then undergo isomerization as in reactions 3 and 4, followed by carbon-to-carbon cleavage, as in reaction 5, to form an isomeric pentene molecule and an isopropyl carbonium ion. The pentene molecule then reacts with a tertiary butyl carbonium ion to form a ninecarbon carbonium ion, which in turn reacts with isobutane as in reaction 6 to form a product nonane molecule and a tertiary butyl carbonium ion. The isopropyl carbonium ion, on the other hand, may react with another butene molecule to form a seven-carbon carbonium ion, which is converted to a product heptane molecule by reaction with isobutane. REFINERY BUTANES AND BUTYLENES

CONTACTOR

CAUSTIC WASH

Figure 1.

Sulfuric Acid Alkylation Plant

It will be noted from the above examples that the tertiary butyl carbonium ions required for the reaction are constantly being replenished to establish a chain reaction. I t is assumed that the reaction is initiated b y olefin molecules accepting protons from the catalyst to form carbonium ions which react with isobutane to produce the necessary active tertiary butyl carbonium ions.

Sulfuric Acid Alkylation Commercial alkylation may be divided into three distinct types depending on whether the catalyst used is sulfuric acid, hydrofluoric acid, or aluminum chloride. These types of alkylation are similar in many respects but have some outstanding differences. I n 1946 there were 32 plants in the United States employing the sulfuric acid process, 27 using the hydrofluoric process, and one using aluminum chloride (1, 9). Since sulfuric acid alkylation is the most widely practiced of the three, it will be discussed first. Figure 1 presents a schematic flow diagram for a typical sulfuric acid plant for the alkylation of isobutane with butènes. The olefin feed stock is a depropanized refinery butane-butenes stream from catalytic and/or thermal cracking containing about 5 0 % olefins and composed essentially of isobutane, normal butane, and butènes with minor amounts of propane and isopentane. This olefin stock undergoes a caustic treatment for removal of mercaptans and hydrogen sulfide. Removal of these compounds is necessary to prevent the formation of free sulfur which would result i n a corrosive product, to reduce acid consumption, and to prevent octane degradation of the leaded product. This stock then combines with the recycle isobutane stream and goes to the reactor. The alkylation reactor or contactor serves to bring isobutane and olefin into intimate In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.


100

contact with the liquid catalyst for a sufficient length of time to obtain the desired product. Provision must also be made either i n the reactor proper or i n the reactor system to remove the heat of reaction liberated i n the process. Several types of reactors are commonly used, and a later section of this paper is devoted to that subject. REFINERY BUTANES AND BUTYLENES


^CAUSlriC WASH

cF E E D

CONTACTOR

D R Y E R

ISOBUTANE PROPANE _ SLIPSTREAM \DEPROPfVNIZER

ACID REGENERATOR]

RECYCLE

DEISOBlpTANIZER R E R U N ALKYLATE .RERUN ,HF \TOWkR eDEBUTfrNIZER

,

BAUXITE \ T O W E R

STRIPPER

BAUTXITE TOVilER

5 " Figure 2.

Hydrofluoric Acid Alkylation Plant

T h e mixture leaving the reaction zone is i n the form of a hydrocarbon-acid emulsion and passes to an acid settler for separation of acid and hydrocarbon phases. This acid settler i s usually a separate vessel from the reactor itself, although i t is an integral part of one type of system. The hydrocarbon-free acid from the acid settler recirculates to the reactor. The hydrocarbon layer, which consists of alkylate, excess isobutane, and the inert diluents introduced with the feed, receives a caustic treatment and goes to the fractionating section of the plant. Caustic treatment is necessary at this stage of the process to neutralize acidic components, such as sulfur dioxide, which are formed i n small quantities b y catalyst degeneration. T h e fractionation section of the alkylation plant consists of a deisobutanizer, a debutanizer, and a rerun tower i n series, and a depropanizer. The deisobutanizer overhead, which contains about 9 0 % isobutane, recycles to the reactor. The deisobutanizer bottoms stream passes to the debutanizer, which removes normal butane diluent as an overhead stream. T h e debutanizer bottoms or raw alkylate stream then goes to a rerun tower for removal of the high boiling alkylate bottoms or " t r i m e r s . " The rerun overhead requires no further treatment to be satisfactory as an aviation gasoline blending stock. The depropanizer removes propane diluent from a "slip-stream" portion of the recycle isobutane stream to prevent propane build-up i n the reaction system. In the alkylation of isobutane with butènes, several variables have an important bearing on the quality of the alkylate produced. The most important is the concentration of isobutane i n the reactor. Although theoretically only equimolecular ratios of isobutane and butene are required for the reaction, a large excess of isobutane i n the reaction zone has been found necessary to suppress undesirable side reactions which result in loss of yield and octane number. Over-all isobutane-olefin ratios of 5 to 1 or higher are necessary for the production of high quality aviation alkylate. Temperature is an important variable in the alkylation process. When alkylating isobutane with butènes, a reaction temperature of 40° to 50° F . produces the highest quality alkylate with the lowest catalyst consumption. Commercial operation has been In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.


101

successfully carried on at temperatures as high as 70° F . , but the alkylate produced has been of inferior quality and the catalyst consumption has been excessive.


REFRIGERANT .BAYONET TUBE C O O L I N G BUNDLE EMULSION

HYDROCARBON

ACID PUMP

Figure 3.

Impeller-Type Reactor System

The amount of acid i n the acid-hydrocarbon reaction mixture also has an important bearing on the alkylate quality. I f the reaction mixture contains less than 4 0 % acid by volume, an acid-in-hydrocarbon emulsion results. Above this 4 0 % inversion point, a hydrocarbon-in-acid emulsion is formed. The latter type produces the better product and consequently an acid volume of 60 to 7 0 % of the reaction mixture is normally maintained. The effect of reaction pressure is negligible, the pressures used being sufficient to keep the reaction mixture i n the liquid phase. The catalyst usually employed for sulfuric acid alkylation is 9 8 % sulfuric acid, a l though concentrations as high as 100% are equally satisfactory. The use of fuming acids is not desirable since the excess sulfur trioxide reacts with isobutane and does not serve as a catalyst. It is possible to use sulfuric acid of concentrations as low as 9 0 % , but the use of these weaker acids has an'adverse effect on the alkylate quality and catalyst life. TIME| T A N K PERFORATED BAFFLES

HYDROCARBON

L _ r _ S E T T L E R

EMULSION, RECYCLE

REACTOR

COOLER REFRIGERANT

Figure 4.

R E C Y C L E ACID CHILLED H Y D R O C A R B O N F B E D -CIRCULATION PUMP

Time-Tank Reactor System

A s the alkylation catalyst ages, its titratable acidity decreases because i t becomes diluted with water from the feed stock and with water and complex hydrocarbon oils produced b y side reactions. The catalyst is ordinarily discarded when its titratable acidity drops to 85 to 8 8 % . If the catalyst is used further, the quality of the alkylate deteriorates rapidly, and the hydrocarbon-acid emulsion becomes so stable that separation difficulties are encountered i n the acid settler. There are two methods ordinarily used for maintaining the acidity of the catalyst. The first of these is the continuous method where fresh acid is added to the circulating acid In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.

102


stream continuously at a rate sufficient to maintain the titratable acidity at the desired level of 88 to 9 0 % . Spent acid is constantly withdrawn to maintain the level i n the acid settler. I n this type of operation the catalyst strength is constant during processing. V A P O R S TO BUTANE

COMPRESSOR

REACTJOR D R U M E M U L S I O N LIQUID, LEVEL

HYDROCARBON

SETTLER


JETS

lEMULSION *~RECYCLE

ffif

RECYCLE ACID CHILLED HYDROCARBON FEED CIRCULATION PUMP

Figure 5.

Autorefrigerated Jet-Type Reactor System

In the second method of acid addition, the fresh acid is charged batchwise to two acid settlers which are alternately used in the reactor system. When the acid reaches the desired discard strength, the settler in use is removed from service and is replaced with a freshly charged one. The second settler is kept i n service until the acid has again become depleted, at which time it is replaced b y the original settler recharged with fresh acid. In this operation the acid strength starts at 9 8 % and gradually decreases to 8 8 % for each batch of acid used. While batchwise handling of the catalyst requires an extra acid settler, i t has two distinct advantages over the continuous method in that the average acid strength during processing is higher, resulting i n higher alkylate octanes, and the catalyst consumption is decreased because the rate of acid depletion is most rapid at low titratable acidities. RECYCLE ISOBUTANE

VAPORS TO BUTANE COMPRESSOR EMULSIFYING PUMPS7

π /

Π

XL

REACTOR SECTIONS SETTLING SECTIONJ

OLEFIN FEED

EL RECYCLE ACID

7&

HYDROCARBON

~ ACID P U M P

Figure

6.

Autorefrigerated Integral Settler System

Reactor-

The catalyst consumption for sulfuric acid alkylation is expressed in terms of pounds of fresh acid depleted per barrel of alkylate produced. When alkylating isobutane with butènes at 50° F . and maintaining an isobutane-olefin ratio of 5 to 1, the acid consumption will average 35 to 40 pounds per barrel when charging 9 8 % acid and discarding 8 8 % acid in a batchwise operation. Commercial operation of sulfuric acid alkylation plants has been relatively troublefree and shutdowns for reasons other than normal inspection and maintenance are seldom required. M a n y plants operate on a one-year regular shutdown and high on-stream efficiencies are obtained. In spite of the fact that a strong acid is used as catalyst, corroIn PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.


103

sion problems are not serious because the water content of the catalyst remains low. Consequently, unusual materials of construction are not required and ordinary carbon steel is used extensively for construction of these plants.

Hydrofluoric Acid Alkylation


Figure 2 presents a schematic flow diagram for a typical hydrofluoric acid alkylation plant. Since processing with hydrofluoric acid is very similar to processing with sulfuric acid, this discussion will point out only the significant differences i n the two processes. The feed preparation differs from that for sulfuric acid by the inclusion of a hydrocarbon feed dryer. Due to the very corrosive nature of hydrofluoric acid-water mixtures, a feed dryer is necessary to prevent water from entering the system. Activated alumina is a typical drying agent used in this service. As i n sulfuric acid alkylation, the hydrocarbon-acid emulsion passes from the contactor into an acid settler for separation of acid and hydrocarbon phases and the acid layer recirculates to the reactor. Unlike sulfuric acid, however, hydrofluoric acid is appreciably soluble i n hydrocarbons, and as much as 1% by weight may be retained i n the hydrocarbon layer. The necessity of recovering this acid from the hydrocarbon phase results i n another difference between hydrofluoric and sulfuric acid processing i n that a hydrofluoric acid stripper is required. This stripper is ordinarily packed with aluminum rings; which serve not only as tower packing but also as a catalyst for the decomposition of organic fluorides into hydrocarbons and free hydrofluoric acid.

2

Figure 7.

4

6

10 20 40 60 100 200 400 600 1000 CORRELATION FACTOR "F*

Sulfuric Acid Alkylate Octanes, ASTM Research (CRC-F-1)

The stripper overhead returns to the reactor, and the bottoms pass to a bauxite tower for removal of the remaining organic fluorides. Removal of these dissolved organie fluorides is essential because they impart corrosive properties to the resulting alkylate and lower its octane ratings. Their removal is accomplished by passing the hydrocarbon i n the liquid phase through a bauxite-packc d tower where they combine with the alumina. A low silica grade of bauxite must be used to prevent the formation of volatile silicon tetrafluoride which would migrate and cause condenser fouling i n the fractionating section. Often lime is added to these towers to neutralize traces of free hydrofluoric acid and to aid i n the control of silicon migration. The fractionation section of the plant is identical to that for sulfuric acid alkylation except that another bauxite treatment is given the total alkylate before rerunning. As i n sulfuric acid alkylation, the important reaction operating variables are isobutane concentration, catalyst purity, acid-hydrocarbon ratio, and reaction temperature. Normally these variables are maintained at the same level as i n sulfuric acid alkylation except for temperature. M o s t commercial plants operate from 75° to 100° F . This higher operating temperature often allows cooling water rather than the usual vaporizing refrigerants to be used. In contrast to the sulfuric acid process, regeneration of the catalyst in hydrofluoric acid alkylation is continuous. During processing, both hydrofluoric acid and sulfuric acid In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.


104


become diluted with tarry materials and water, but since hydrofluoric acid is rather volatile, i t is readily purified b y distillation. Consequently, a portion of the circulating catalyst stream is continuously charged to an acid regeneration tower. Hydrofluoric acid of high purity is flashed overhead and returned to the reaction zone while water and tars are drawn as bottoms. The catalyst acidity i n the reactor can be maintained at any desired strength b y regulation of the acid regeneration tower feed rate. F o r the production of aviation grade alkylate, the titratable acidity of the circulating acid is usually maintained i n the range of 85 to 9 0 % hydrofluoric acid. Fresh hydrofluoric acid used for catalyst make-up is anhydrous and of 9 9 . 5 % + p u rity. Since the acid i n the unit is continually being regenerated, the only hydrofluoric acid consumed i n the process is that which is absorbed i n the bauxite towers, lost to the acid tar, lost i n handling, or lost through venting equipment and lines for maintenance access. Typically, hydrofluoric acid consumption, including losses to all sources, will average about 0.5 to 0.8 pound per barrel of alkylate. Because of its corrosive nature and high volatility, the introduction of hydrofluoric acid as a commercial catalyst was attended by many problems i n design and operation. Among the more serious problems was the effective sealing of pumps and valves i n hydrofluoric acid service, and the prevention of valve sticking caused by iron fluoride deposits. I n such equipment as the acid regeneration tower, where a hydrofluoric acid-water mixture occurs, the corrosion problem was particularly troublesome. F r o m several years experience with the process, it has been found that ordinary carbon steel is satisfactory for hydrofluoric acid service where water concentrations are low, and where moving parts are not involved. Materials containing silica, such as cast iron, are not suitable because they are readily attacked by hydrofluoric acid. M o n e l has been found to be excellent i n hydrofluoric acid service, even where water-hydrofluoric acid mixtures are encountered, and is used extensively for valves, valve trims, pumps, and for lining the acid regeneration tower. W i t h the use of these materials i n plant construction, the service record of hydrofluoric acid alkylation plants has been satisfactory, and on-stream efficiencies of 9 6 % are not unusual (8).

Commerciol Reactor Systems Schematic sketches of four types of reactor systems commonly used for the commercial alkylation of isobutane are shown i n Figures 3, 4, 5, and 6. A typical system using an impeller type of reactor is depicted by Figure 3. I n this system mixing is accomplished by internal recirculation of the mixture, cooling by heat exchange within the reactor, and phase separation by use of an auxiliary settling vessel. The reactor consists of a vertical cone-bottomed vessel with a pump-type impeller i n the bottom and a n internal concentric baffle arranged to produce a rapid and turbulent circulation of the reaction mixture. A refrigerated tube-bundle is suspended from the top of the vessel into the central zone of the reactor to maintain the mixture at the desired temperature. Figure 4 illustrates a reaction system using a " t i m e - t a n k " reactor. T h i s system uses external recirculation to provide orifice mixing of the catalyst and reactants, and cooling is accomplished by an external heat exchanger i n the recirculation stream. A c i d separation is again carried on i n an external settling vessel. The reactor consists of a vertical vessel containing numerous multiple orifice plates through which the reaction mixture is circulated by an external pump to obtain a high degree of turbulence. A jet-type reactor system is shown i n Figure 5. Here external recirculation is used to obtain jet mixing and cooling is obtained by evaporation of a portion of the butanes i n the reactor, resulting i n an autorefrigerated system. A n auxiliary settling vessel is again employed. The reactor proper consists of a vertical vessel with jet nozzles i n the bottom through which the reaction mixture is circulated to obtain turbulent mixing. The refrigerating butane vapors from the reactor are compressed, condensed, and returned to the system. A n integral type of reactor system is presented i n Figure 6. Internal agitation is used to obtain mixing i n this system and autorefrigeration is again employed. The settling section is an integral part of the reactor vessel. The reactor is a horizontal vessel having In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.


105

several reaction sections and a settling section separated by vertical baffles which allow a cascade flow through the vessel. Special emulsifying pumps enter from the top of the reactor into each reaction zone to provide the necessary mixing. Of course, combinations and variations of these systems are in use ; however, those outlined represent some of the more common installations. A l l of these systems can be used for sulfuric acid alkylation but only the types using tube-bundle refrigeration can be used with hydrofluoric acid since its high volatility precludes the use of an autorefrigerated system.


Olefins Used for Alkylation Although the preceding discussion of the sulfuric and hydrofluoric acid processes has been confined to butene alkylation, isobutane has also been alkylated commercially with other olefins. Ethylene, propylene, pentenes, and dimers of butènes have been used for this purpose. I t is also possible to use these olefins for the alkylation of isopentane. Such an operation, however, has not achieved commercial acceptance because it produces an inferior alkylate with a high catalyst consumption, and because isopentane is a satisfactory aviation gasoline component in its own right. Because propylene is highly volatile and must be marketed as fuel gas rather than as gasoline, it is low i n cost and would appear to be a desirable alkylation feed stock. B a l anced against its low cost, however, are the increased catalyst consumption and decreased product quality encountered i n its alkylation. Consequently, its inclusion i n alkylation feed is usually limited to minor quantities b y the alkylate quality required for the maximum production of aviation gasolines. Pentene alkylation also has the disadvantages of increased catalyst consumption and decreased alkylate quality. A further disadvantage is that pentenes are a satisfactory motor gasoline blending stock and are thus a more expensive alkylation charge stock. For these reasons, commercial alkylation of pentenes is not extensively practiced. Butènes can also be alkylated in the form of various polymers, such as the by-product diisobutene polymers from butadiene plants. I n this operation, each octene molecule appears to react as two individual butene molecules, and the high alkylate quality and low catalyst consumption characteristic of butene alkylation are obtained. F o r the most part, polymers have been alkylated only as supplemental feed stocks from external sources i n periods of high aviation gasoline demand. Product inspections and yield data for typical alkylates produced from propylene, butènes, and pentenes are presented in Table I I . I n general, the optimum operating conTable II.

Properties and Yields of Typical 360° F. End Point Rerun Alkylates'

Feed, olefin

Propylene

Gravity, ° API at 60° F . 100 ce. A S T M distillation Initial b.p.,° F . 10% recovered 50% recovered 90% recovered End point

72.3

Butènes

69.0

Mixture of thermal and catalytic pentenes 66.5

108 179 196 241 360

115 197 224 261 360

124 227 247 281 360

4.0

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