Jones D.S.J., Pujado P.R. Handbook of Petroleum Processing

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402 CHAPTER 9

Table 9.3.1. Hydrocarbon octane values

Research octane Motor octane

by ASTM 2699 by ASTM 2700 (R + M )/2

n-Butane 93.8 89.6 91.7

i-Butane 100.4 97.6 99.0

n-Pentane 61.7 62.6 62.2

i-Pentane 92.3 90.3 91.3

n-Hexane 24.8 26.0 25.4

2-Methylpentane 73.4 73.5 73.4

3-Methylpentane 74.5 74.3 74.4

2,2-Dimethylbutane 91.8 93.4 92.6

2,3-Dimethylbutane 101.0 94.3 97.6

at two severity levels. Often, the average of these two values, or (R + M)/2, is used

to express the overall engine performance of a gasoline component or blend. Ta-

ble 3.7.1 shows that isopentane has an octane value nearly 30 numbers higher than

n-pentane (1).

Similarly, the hexane isomer, 2,2-dimethylbutane (2,2-DMB) has an octane about 67

numbers higher than n-hexane. Clearly, highly branched isoparafﬁns are the desired

isomers for motor fuel production.

Thermodynamic equilibria for the branched parafﬁn isomers are generally favored

by low temperatures. Figures 9.3.1, 9.3.2, and 9.3.3 illustrate this trend (2). The

most active catalyst, when all other variables are equal, is capable of producing the

highest-octane products.

Normal Butane

Isobutane

100

40 150 260 370 480

Temperature, °C

mole%

Figure 9.3.1. Butane equilibrium.

GASOLINE COMPONENTS 403

Normal Pentane

Isopentane

100

40 150 260 370 480

Temperature, °C

mole%

Neopentane

Figure 9.3.2. Pentane equilibrium.

Primary reaction pathways

Parafﬁn isomerization is most effectively catalyzed by a dual-function catalyst con-

taining a noble metal and an acid function. The reaction is believed to proceed through

an oleﬁn intermediate, which is formed by parafﬁn dehydrogenation on the metal site

(reaction (1)):

-CH

↔

-CH

-CH = CH

+ H

. (1)

Although the equilibrium conversion of the parafﬁn in reaction (1) is low at parafﬁn

isomerization conditions, sufﬁcient oleﬁns are present to be converted to a carbonium

ion by the strong acid site (reaction (2)):

-CH

-CH=CH

+ [H

][A

−

] → CH

-CH

-C

H-CH

+ A

−

. (2)

Temperature, °C

MCP / (MCP + CH)

100

93 149 204 260 316

mole%

2-MP + 3-MP /

∑

Paraffins

2, 2-DMB /

∑

Paraffins

n-Hexane /

∑

Paraffins

2, 3-DMB /

∑

Paraffins

Figure 9.3.3. C

fraction equilibrium.

404 CHAPTER 9

The formation of the carbonium ion removes product oleﬁns from reaction (1) and

allows the equilibrium in reaction (1) to proceed. The carbonium ion in reaction (2)

undergoes a skeletal isomerization, probably through a cycloalkyl intermediate as

shown in reaction (3):

-CH

-C

H-CH

→ CH

——

C-CH

→ CH

-C

-CH

cyclopropyl

cation

(3)

Reaction (3) proceeds with difﬁculty because it requires the formation of a primary

carbonium ion at some point in the reaction. Nevertheless, the strong acidity of iso-

merization catalysts provides enough driving force for the reaction to proceed at high

rates. The isoparafﬁnic carbonium ion is then converted to an oleﬁn through loss of

a proton to the catalyst site (reaction (4)):

-CH

+ A

−

→ CH

-C

= CH

+ [H

][A

−

]. (4)

In the last step, the isooleﬁn intermediate is hydrogenated rapidly back to the analogous

isoparafﬁn (reaction (5)):

-C

= CH

+ H

→

-CH

. (5)

In addition to these primary reaction pathways, some evidence indicates the exis-

tence of a bimolecular reaction mechanism, in which oleﬁnic intermediates dimerize,

internal carbon atoms are protonated, skeletal isomerization occurs, and the dimer

undergoes beta scission that results in the product isoparafﬁn. In addition to the C

labeling experiments that support this mechanism, a relatively small amount of hy-

drocarbons containing carbon numbers higher than the feed are always found in the

reaction products. The bimolecular mechanism has a minor impact on commercial

isomerization processing.

Isomerization catalysts

Operation at the lowest temperature results in the formation of the highest-octane

product (Table 9.3.1 and Figures 9.3.1, 9.3.2, and 9.3.3). Catalyst activity and the

lowest operating temperature are important to achieve an economic operation. In the

previous discussion of the primary reaction pathway, the primary functionality of a

parafﬁn isomerization catalyst is to protonate a secondary carbon atom. All known

parafﬁn isomerization catalysts have a combination of strong Lewis and Br¨onsted

acid sites, which result in varying levels of protonation activity.

GASOLINE COMPONENTS 405

In addition to a strong acid function, isomerization catalysts must also be capable

of hydrogenolysis, which not only assists in the protonation step, but also serves

to saturate oleﬁn intermediates and aromatic hydrocarbons and to assist in the ring

opening of cycloparafﬁns. This function also gives activity stability to isomerization

catalysts, thereby improving the process economics.

An aluminum chloride catalyst for alkane isomerization was ﬁrst developed in the

1930s (3). The original application was for the conversion of n-butane to isobutane,

which was, and still is, reacted with C

, and C

oleﬁns to produce motor fuel

alkylate. The ﬁrst application of this high-octane product was in the production of

high-octane aviation gasoline. Subsequent developments of this predominantly Lewis-

acid catalyst resulted in the current alumina-supported, bifunctional catalyst. UOP’s

I-8 catalyst is one commercial example of this catalyst system, which has seen wide

commercial application since 1981.

Chlorided alumina, the highest-activity parafﬁn isomerization catalyst available, in-

creases the octane of a typical light-naphtha stream from about 70 to as high as 85

RONC in a once-through parafﬁn isomerization unit. Higher product octanes, up to

93 RONC, can be obtained by recycling low-octane hydrocarbons. The C

yield from

chlorided alumina catalysts is the highest from any commercial catalyst because of

high catalyst selectivity and low operating temperature. Because chlorided alumina

systems are not economically regenerable, eventual reloading of the isomerization

catalyst must be considered. Nevertheless, the chlorided alumina system is often the

most-economic choice because of its inherent high activity. In addition, only chlorided

alumina catalysts have enough activity to economically isomerize butanes.

As a result of ongoing intensive research and development in parafﬁn isomeriza-

tion technology, UOP’s I-80 catalyst is one of the highest-activity chlorided alumina

catalyst currently available. The I-80 catalyst, is signiﬁcantly more active than the

I-8 catalyst, and is based on a unique formulation and manufacturing technique. By

simply reloading the I-80 catalyst in existing reactors, a gain of 0.5–1.0 RON can be

realized compared with the product RON when I-8 catalyst is used.

Zeolitic isomerization catalysts, such as UOP’s HS-10™ or I-7™ catalysts, operate at

higher temperatures than chlorided alumina catalysts. The maximum product octane

that can be achieved is limited by the unfavorable equilibrium at these conditions.

Yields are also lower as a result of the higher operating temperature and the less-

selective characteristics of zeolitic catalysts. A typical octane upgrade for a once-

through zeolitic isomerization unit is from 70 to about 79 RONC. Higher product

octanes (86–88) can be obtained in a recycle operation, such as a TIP™ unit.

The most-attractive beneﬁt of zeolitic isomerization catalysts is that they are not

permanently deactivated by water or other oxygenates and are fully regenerable.

406 CHAPTER 9

Consequently, zeolitic catalysts have often been used when revamping other process

units, such as hydrotreaters or reformers to isomerization service. Sulfur can be present

in the feedstock with catalysts such as the HS-10 catalyst, but performance is always

affected to some degree. Sulfur suppresses the platinum function as it does in any

platinum-containing catalyst. Although isomerization activity is maintained, a net C

product yield loss results. Hydrotreating is not an absolute requirement with zeolitic

catalysts, but it is necessary to get the optimum performance from the catalyst.

Sulfated metal oxide catalysts, which have been described as solid super acids, exhibit

high activity for parafﬁn isomerization reactions. These metal oxides form the basis

of the new generation of isomerization catalysts that have been actively discussed

in the scientiﬁc literature in recent years. These catalysts are most commonly tin

oxide (SnO

), zirconium oxide (ZrO

), titanium oxide (TiO

), or ferric oxide (Fe

)

that has been sulfated by reaction with sulfuric acid or ammonium sulfate. Sulfated

alumina is not an active catalyst for hydrocarbon reactions.

A typical metal oxide catalyst, UOP’s LPI-100 catalyst (4), has a considerably higher

activity than that of traditional zeolitic catalysts, and this activity advantage is equiva-

lent to about 80

◦

C lower reaction temperature. The lower reaction temperature allows

for a product with a signiﬁcantly higher product octane, about 82 RONC for a typ-

ical feed or three numbers higher than that of a zeolitic catalyst. Similar to zeolitic

catalysts, the LPI-100 catalyst is not permanently deactivated by water or oxygenates

in the feedstock. These catalysts are also fully regenerable using a simple oxidation

procedure that is comparable to the one used for zeolitic catalysts. The high activ-

ity of the LPI-100 catalyst makes it an ideal choice for revamping existing zeolitic

isomerization units for higher capacity and higher octane isomerate or for new units

where the full performance advantage of chlorided alumina catalysts is not required

or where the reﬁner is concerned about contaminants in the feedstock.

The isomerization performance of the previously discussed I-8, I-80, HS-10, and LPI-

100 catalysts is compared in Figure 9.3.4, which plots the i-C

to total C

product ratio

for all the catalysts as a function of reactor temperature. This ranking clearly illustrates

the striking activity advantage for the LPI-100 catalyst over that of the zeolitic HS-10

catalyst, an advantage that translates directly to octane improvement. Likewise, this

ranking shows the performance beneﬁt of the I-80 catalyst over the predecessor I-8

catalyst. The development and beneﬁts of the I-80 and LPI-100 catalysts, are discussed

in the following sections.

I-80 catalyst development and applications

Chlorided alumina represents the industry standard for isomerization catalysts. UOP

introduced the second-generation, high-activity I-8 chlorided alumina catalyst in

GASOLINE COMPONENTS 407

I-80

100 152

200

Relative Temperature, °C

/Total C

Ratio, wt%

I-8

LPI-100

HS-10

Figure 9.3.4. Light parafﬁn isomerization catalyst performance.

1981. The I-8 catalyst has been successfully used in more than 50 operating Bu-

tamer™ butane isomerization units and 90 operating Penex™ light-naphtha isomer-

ization units. The ﬂow schemes range from simple once-through hydrocarbon pro-

cesses to complex recycle operations to achieve high product octane that have been

described in detail elsewhere (5). In 1998, UOP introduced the I-80 catalyst, a new

generation, high-activity chlorided alumina catalyst. The I-80 catalyst has stability

and selectivity identical to that of the I-8 catalyst.

Higher catalyst activity can be used in a number of ways in existing or new isomeriza-

tion units. The best application depends on site-speciﬁc factors and whether the unit

operates in a once-through or recycle mode. Typical means to exploit higher activity

are:

Higher throughput at constant octane (Case A)

Reduced catalyst volume at constant throughput and octane (Case B)

Higher octane at the same throughput (Case C)

Longer catalyst life (Case D)

Case A operates at higher throughput but maintains a constant product octane. The per-

formance of the I-8 and I-80 catalysts is compared in Figure 9.3.5 as a plot of product

octane against relative reactor temperature. The newer I-80 catalyst has a substantial

30% activity advantage over the previous catalyst. This advantage is equivalent to

about a 12

◦

C reduction in reactor temperature. A 30% activity increase corresponds

directly to an increase in space velocity, or throughput.

If the I-80 catalyst is reloaded in place of the existing I-8 catalyst, the charge rate to

the reactor can be increased by up to 30% with no decrease in product octane. This

throughput advantage is a major beneﬁt in equipment cost savings if a higher-capacity

revamp is being considered because additional reactor volume is not required. Another

408 CHAPTER 9

Equilibrium

-20

Relative Reactor Temperature,

°C

RONC, Calculated

I-80

Catalyst

I-8

Catalyst

Figure 9.3.5. Chlorided alumina catalyst performance.

beneﬁt of a higher-activity catalyst is the increased ﬂexibility to respond to seasonal

ﬂuctuations in product demand.

The ability to operate at higher space velocities with the I-80 catalyst can be used in

existing units by reducing the volume of catalyst in the reactor of existing units by

up to 30% and using a smaller overall reactor size in new units (Case B). These cost

savings are obvious. The reﬁner also realizes a savings in platinum inventory.

As mentioned previously, isomerization reactions are equilibrium limited and the

extent of the reaction improves at lower temperatures. The 12

◦

C activity advantage

of the I-80 catalyst can be exploited by operating at a lower temperature to achieve

higher product octanes (Case C). This advantage is illustrated in Figure 9.3.6 as a

plot of product octane against C

yield. Achieving a 0.5–1.0 RON higher product

I-8 Catalyst

96 97 98 99 100

Yield, wt%

RONC

I-80 Catalyst

Figure 9.3.6. Chlorided alumina catalyst yields.

GASOLINE COMPONENTS 409

quality at similar yields is possible with the I-80 catalyst in once-through units. This

improvement in quality is equivalent to an additional revenue of about $600,000 U.S.

per year at an octane value of $0.25 per octane-barrel. Thus, the I-80 catalyst is an

obvious choice when catalyst replacement is required. The beneﬁt for recycle units is

lower because the savings are related to the cost reduction associated with maintaining

higher conversion per pass.

The higher activity of the I-80 catalyst is achieved by increasing the number of

catalytically active sites on the catalyst surface. Because the deactivation of chlorided

alumina catalysts is mostly due to ingress of moisture or oxygenates, this higher

acid-site density can translate into longer catalyst life at a constant catalyst loading

(Case D). If all other factors are equal, catalyst life may be extended by about 30%.

Increased catalyst life has the obvious beneﬁt of reducing operating costs. However,

the beneﬁt is relatively small in well-run commercial units that typically achieve a

catalyst life in excess of 5 years.

LPI-100 catalyst development and applications

The development of the LPI-100 catalyst represents the ﬁrst successful application

of sulfated metal oxide in industrial catalysis. This new catalyst is the culmination of

a joint development effort between Cosmo Research Institute (CRI) and Mitsubishi

Heavy Industries (MHI) in Japan and UOP.

The basic formulation for this sulfated metal oxide catalyst was developed by CRI

and MHI researchers in the late 1980s. Several years of intensive development were

required to translate the CRI–MHI laboratory formulation into a commercially vi-

able extruded catalyst that met all the original performance targets. The commercial

product is now the UOP LPI-100 catalyst.

The ﬁrst commercial loading of the LPI-100 catalyst was completed at the Flying J

Reﬁnery in North Salt Lake City, Utah. The catalyst was loaded in a zeolitic isomer-

ization reactor that had previously been operated with UOP’s I-7 catalyst. The loading

was completed and the reactor placed into operation in December 1996. Performance

data for the LPI-100 catalyst in the Flying J unit are compared to pilot plant predictions

in Figure 9.3.7 as a plot of the i -C

to total C

product ratio against reactor temperature.

The performance at Flying J was in line with UOP’s expectations. Since the initial op-

eration at Flying J, the LPI-100 catalyst has been used in another once-through zeolitic

isomerization unit in Canada and in other units in Canada and the Middle East.

Contaminant-sensitivity studies with the LPI-100 catalyst have shown responses

comparable to those experienced with conventional zeolitic catalysts. Water and

oxygenates at typical concentrations are not detrimental. Sulfur suppresses activity, as

410 CHAPTER 9

170 175 180 185 190

Reactor Temperature,

°C

Product Ratio, wt%

Pilot Plant Data

Commercial Data

195 200

Figure 9.3.7. LPI-100 performance at Flying J reﬁnery.

expected for any catalyst containing noble metals. The suppression effect of sulfur is

reversed by subsequent processing with clean feedstocks. The effects of other common

contaminants are similar to those experienced with conventional zeolitic catalysts.

In pilot plant evaluations, the stability of the LPI-100 catalyst is comparable that of

the HS-10 zeolitic catalyst. This stability translates to a commercial process cycle of

at least 18 months before regeneration is required. Multiple-cycle regeneration testing

was completed and showed that the catalyst was fully regenerable through more than

three regenerations. Regeneration consists of a simple carbon-burn step at conditions

comparable to those used for regenerating zeolitic catalysts.

New isomerization process technologies

The introduction of new catalyst systems, such as the LPI-100 catalyst, allows the de-

velopment of new process technologies that fully use the characteristics of the catalyst.

The process technology developed for the LPI-100 catalyst is the Par-Isom™ pro-

cess. A simpliﬁed ﬂow scheme for the Par-Isom process operating in a once-through

conﬁguration is shown in Figure 9.3.8. For simplicity, a once-through hydrocarbon

ﬂow scheme is discussed in this chapter. Recycle ﬂow schemes previously developed

for naphtha isomerization use either molecular sieve separation, such as in the TIP

process, or fractionation, such as a deisohexanizer column.

The process ﬂow scheme shown in Figure 9.3.8 is similar to that used for conventional

once-through Penex and zeolitic isomerization units. The fresh C

–C

feed is com-

bined with makeup and recycle hydrogen and directed to the charge heat exchanger,

where the reactants are heated to reaction temperature. A ﬁred heater is not required

in the Par-Isom process, because of the much lower reaction temperature needed with

GASOLINE COMPONENTS 411

Stabilizer

Bottoms

Reactor

Feed

Offgas

Reactor

Product

Separator

Makeup Gas

Figure 9.3.8. Par-Isom process ﬂow scheme.

the LPI-100 catalyst than with zeolitic catalysts. Hot oil or high-pressure steam can

be used as the heat source in this exchanger. The heated combined feed is then sent

to the isomerization reactor.

Either one or two reactors can be used in series, depending on the speciﬁc application.

Two reactors obtain the best performance from the process but at a higher capital and

additional catalyst inventory costs. In a two-reactor system, the ﬁrst reactor is operated

at higher temperature (200–220

◦

C) to improve the reaction rate, and the second reactor

is operated at a lower temperature to take advantage of the more-favorable equilibrium

distribution of higher octane isomers. One reactor is generally speciﬁed for the Par-

Isom process to reduce capital and operating cost of the unit, but a small debit in

performance can result.

The reactor efﬂuent is cooled and sent to a product separator, where the recycle hy-

drogen is separated from the other products and returned to the reactor section. The

liquid product is sent to a stabilizer column, where the light ends and dissolved hy-

drogen are removed. The stabilized isomerate product can be sent directly to gasoline

blending. In recycle ﬂow schemes, either molecular sieve or fractionation options are

used to separate the lower-octane isomers for recycle to the reactor. The selection of

the separation scheme depends on the feed composition, availability of utilities, and

the product octane desired.

The higher activity of the LPI-100 catalyst makes it an ideal candidate for revamps

of existing zeolitic isomerization units to achieve higher capacity or for revamps

of idle process units, such as reformers or hydrotreaters to isomerization service.

The integration of a Par-Isom reactor into an existing semiregeneratative reforming

unit can be a particularly attractive revamp opportunity for economically adding

isomerization capacity to a reﬁnery. A simple ﬂow scheme illustrating the integrated