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

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392 CHAPTER 9

H¨uls AG’s Octol process for the selective dimerization of n-butenes to highly lin-

ear octenes suitable for the manufacture of isononyl alcohol plasticizers over a

solid heterogenous catalyst. The product may contain up to 20% n-octene and over

50% methyl-heptenes, with a balance of dimethylhexenes and a small amount of

trimethylpentenes, and is quite similar to that obtained with IFP’s Dimersol X pro-

cess.

Recent developments

Catalytic condensation of oleﬁns for the production of gasoline fractions and higher

oleﬁns is an old art that has recently received a boost from the planned phase-out of

MTBE in gasoline blending formulations.

MTBE (methyl-tert-butyl ether) is a high octane blending component used exten-

sively throughout the world since about 1975 and more widely since the mid-1980s.

In addition to providing a signiﬁcant increase in the octane of the gasoline relative to

that of the base stock, it also has a beneﬁcial impact in the reduction of hydrocarbon

emissions. MTBE, however, is slightly soluble in water (about 0.55 wt%) and has a

foul odor. Leakage of gasoline from underground tanks into a potable water aquifer

normally has little impact because of the lack of solubility of the hydrocarbon com-

ponents, but becomes very noticeable when MTBE is present at even a low ppb level.

This has led to the planned discontinuance in the use of MTBE in certain regions,

principally in the United States.

MTBE is made by the reaction of isobutene with methanol over a sulfonic acid resin

in the liquid phase and at temperatures in the 40–80

◦

C range in a process that was

independently pioneered by Snamprogetti SpA and by H¨uls AG. Mostly, adiabatic

plug ﬂow reactors are used, but isothermal tubular reactors have also been used; later

units use reaction combined with distillation in what is a quasi-isothermal operation.

MTBE initially was obtained by reacting the isobutene contained in the C

fraction

from an FCC unit or from a steam cracker after butadiene extraction—the other

components are not reactive under these conditions and only MTBE is formed.

However, with the advent of legislation that mandated the use of oxygenates in gaso-

line for environmental reasons, use of MTBE skyrocketed and it became necessary

to build large on-purpose isobutane dehdyrogenation units to meet the demand for

isobutene. These MTBE units often had capacities for about 600,000 to 900,000

metric tons per year, of which about 65% corresponds to the weight of the required

isobutene.

The planned phase-out of MTBE presents a costly dilemma for the existing MTBE

producers, principally for those who rely on isobutane dehydrogenation units. They

GASOLINE COMPONENTS 393

can either shut down the units or they can convert them into something else. An

obvious solution is available in two forms:

The old codimer/hydrocodimer experience can be revisited either by dimerizing

isobutene or by reacting isobutene with n-butenes over a SPA catalyst to yield the

corresponding isooctenes. However, while the older dimerization facilities operated

in the gas phase and had relatively poor selectivity to isooctenes, the newer versions

now being implemented operate in the liquid phase and have much higher isooctene

selectivity. Also, the older hydrocodimer facilities required adding a costly hydrogen

plant just to supply the hydrogen for the hydrogenation of the oleﬁns. In isobutane-

based MTBE complexes this is not necessary because hydrogen is available as a

by-product from the isobutane dehydrogenation step.

Similar experience can be derived from Bayer AG’s use of sulfonic acid resins for

the dimerization of isobutene to the corresponding isooctenes in the liquid phase

at 100

◦

C as done commercially at a plant in Dormagen operated by Erd¨olchemie.

That experience showed that sulfonic acid resins can be used in hydrocarbon envi-

ronments and can achieve over 99% isobutene conversions and about a 75 mol%

selectivity to dimers and 25 mol% selectivity to trimers. Under appropriate modi-

ﬁcations, use of sulfonic acid resins can be adapted to the selective production of

gasoline components.

Technologies for the dimerization of isobutene with isobutene, n-butenes, or other

oleﬁn components are now being offered commercially by Snamprogetti SpA, KBR

(Kellogg—Brown & Root), UOP LLC, and others. Because UOP offers both SPA

catalyst and sulfonic acid resin catalyst, the following discussion will center on UOP’s

Indirect Alkylation (InAlk) process technology. It may be further added that isobutane

dehyrogenation units operate equally well with n-butane or with mixtures of isobutane

and n-butane in the feed; the corresponding oleﬁns are obtained in these situations,

typically with a 1-butene/2-butene ratio that corresponds to the high temperature

dehydrogenation equilibrium.

Catalytic oleﬁn condensation with the InAlk process

Barring the use of MTBE and of the former hydrocodimer products, the best com-

ponents for today’s environmentally friendly gasoline formulations are high-octane

parafﬁnic components like alkylate and isomerate. From the viewpoint of octane

number and vapor pressure, alkylate is the preferred blending material.

Alkylate is made by reacting isobutane with n-butenes or other oleﬁns over con-

centrated sulfuric acid or hydroﬂuoric acid in the liquid phase, or over novel solid

heterogenous acid catalysts now being introduced.

394 CHAPTER 9

The Indirect Alkylation or InAlk process obtains a product similar to motor fuel

alkylate by reacting isobutene with isobutene, n-butenes, or other oleﬁns, and also by

dimerization reactions of n-butenes. Idealized products after hydrogenation are:

2,2,4-trimethylpentane RON = 100 MON = 100

2,2,3-trimethylpentane RON = 109.6 MON = 99.9

3,4-dimethylhexane RON = 76.3 MON = 81.7

Either SPA catalysts or sulfonic acid resin catalysts can be used for the condensation.

As usual, either noble or non-noble metal catalysts can be used for the hydrogenation.

Resin-catalyzed condensation

Sulfonic acid resin catalysts are attractive because they are the ones used for the

synthesis of MTBE. Thus, ideally, one could make isooctenes instead of MTBE with

virtually no plant modiﬁcation regardless of whether the original MTBE unit uses

a conventional adiabatic plug ﬂow (packed bed) reactor or a reactor that combines

reaction with distillation as in CD Tech’s “Catalytic Distillation” process or in the

H¨uls/UOP “Ethermax” process. In the case of the Ethermax process, it has been

established that the same process unit can be used for the production of isooctenes

without signiﬁcant modiﬁcations except perhaps for the addition of an additional

front end packed-bed reactor for added conversion and, obviously, the hydrogenation

reactor, and possibly a product stripper for the removal of light ends.

Overall isobutene conversions in excess of 95% are achievable, but the n-butene

conversion is much lower, in the order of 10%, so that an n-butene recycle should be

maintained if maximum conversion is desired. Selectivity to the desired diisobutenes

or isobutene/n-butene codimers is in the 85–90% range, while production of trimers

=) is about 10–15%, and the production of heavier compounds (tetramers, etc.)

is negligible. A typical trimethylpentane (TMP) product from an FCC C

feed at about

10% n-butene per-pass conversion can be characterized as follows:

(TMP) 88%

12%

traces

Blending characteristics

RON 97.5–98.0

MON 95.5–96.0

RV P ∼2 psi (∼14 kPa)

227/255

◦

F (108/124

◦

If not hydrogenated, the same product characteristics are obtained except that the

RON increases to about 102.0–102.5 while the MON decreases to about 85.5–86.0,

GASOLINE COMPONENTS 395

as corresponds to the higher octane sensitivity of oleﬁnic materials that was discussed

earlier.

With a high concentration isobutene feed as might be available from an isobutane

dehydrogenation unit, the product characteristics are:

(TMP) 88%

12%

traces

Blending characteristics

RON 99–101

MON 97–100

RV P ∼2 psi (∼14 kPa)

If not hydrogenated, the oleﬁnic product shows similar characteristics but with RON

in the 111–114 range and MON of about 92–95.

SPA-catalyzed condensation

Although analogous in concept to the earlier work with SPA catalysts, signiﬁcantly

enhanced results can be obtained by ﬁne tuning the operation for gasoline produc-

tion, in particular by increasing the isooctene selectivity at lower temperatures and

operation in the liquid phase. While traditional Catalytic Condensation units with

SPA catalyst had isooctene selectivity of typically about 55%, in the InAlk process,

operating in the liquid phase at lower temperatures, the selectivity can be increased to

about 90%, with the rest being C

. This material can be put directly into the gasoline

pool, usually after hydrogenation.

Again, an MTBE unit can be converted to an InAlk unit with SPA catalyst with only

minor modiﬁcations, of which the most signiﬁcant is perhaps the addition of another

front end reactor in parallel.

A typical trimethylpentane (TMP) product from an FCC C

feed at about 15%

n-butene per-pass conversion can be characterized as follows:

(TMP) 95%

Blending characteristics

RON 100.8

MON 95.7

RV P ∼2 psi (∼14 kPa)

232/275

◦

F (111/135

◦

396 CHAPTER 9

With SPA catalyst it is possible to increase the n-butene conversion to about 30%

by operating at slightly higher temperatures. Virtually the same results are obtained

except for about a one point decrease in both RON and MON.

If the feed has a high isobutene content, the product distribution after hydrogenation

is:

(TMP) 3%

87%

10%

Blending characteristics

RON 101.5

MON 97.5

RV P ∼1.4 psi (∼10 kPa)

The relative operation between the Catalytic Condensation process and the InAlk

process can be differentiated as follows:

Traditional catalytic InAlk oleﬁn

condensation condensation

Phase vapor liquid

Temperature base lower

Pressure base lower

Product recycle no yes

Space velocity base higher

= conversion base base

= conversion base lower

The effect of temperature on isooctene selectivity can be best appreciated by the

following simple comparison using traditional catalytic condensation without recycle:

190

◦

C 150

◦

average bed average bed

temperature temperature

− 8.5% 3.5%

Isooctenes 56.0% 71.1%

+ 35.5% 25.4%

Operation at the lower temperature but with added recycle improves the selectivity to

about 2.2% C

−, 84.1% isooctenes, and 13.7% C

+. Further improvements can be

achieved by operation at even lower temperatures or at other recycle rates.

GASOLINE COMPONENTS 397

100

iC4= nC4= iC5= nC5=

InAlk Feed Composition

Maximum wt% Conversion to

Alkylate

Figure 9.2.8. Comparison of InAlk conversion for C

and C

streams.

It may be further noted that by operation at these lower temperatures, the life of the

SPA catalyst can be greatly lengthened relative to that observed in traditional Catalytic

Condensation operations. The increased catalyst life is the net effect of having lower

carbon deposition on the catalyst and of requiring lower SPA hydration rates. Under

these conditions, the catalyst life is so much longer that the impact of feed impurities

may become the issue in determining the overall catalyst life.

Lastly, we can point out that, because it does not have the temperature limitations in-

herent to a sulfonic acid resin, SPA catalysts can operate over a signiﬁcantly broader

range than just propylene or butenes. Figures 9.2.8 and 9.2.9, for example, illus-

trate the comparative conversions and product RON values for isobutene, n-butenes,

isopentene, n-pentenes, and mixtures thereof.

100

105

iC4= Total C4= iC5= Total C4=,

C5=

Total C5=

InAlk Reactants

InAlk Product RONC

Figure 9.2.9. Comparison of InAlk product RON for C

and C

streams.

398 CHAPTER 9

Catalyst suppliers

The information provided herein is correct as of the time of this writing but is subject to

change without notice. The addresses provided are for the central ofﬁces; the catalysts

themselves may be sourced from other geographical locations.

Dimersol catalysts are proprietary and can be obtained through IFP

Institut Fran¸cais du P´etrole (IFP)

1 et 4, avenue de Bois-Pr´eau

92852 Rueil-Malmaison Cedex

France

IFP North America, Inc.

100 Overlook Center, Suite 400

Princeton, NJ 08540

USA

There are two recognized suppliers of SPA catalyst

UOP LLC

25 East Algonquin Road

P. O. Box 5017

Des Plaines, IL 60017-5017

USA

S¨ud-Chemie AG

Lenbachplatz 6

80333 M¨unchen

Germany

S¨ud-Chemie United Catalysts Inc.

P. O. Box 32370

Louisville, KY 40232

USA

Sulfonic acid resins come in many forms. Preferred catalysts include, but are not

limited to, highly crosslinked macroreticular resins such as those available from Rohm

and Haas (Amberlyst), Dow Chemical (Dowex), Bayer AG, Purolite, and others.

Proprietary formulations may be desirable though for speciﬁc applications in this

area, and the various suppliers should be consulted accordingly.

Conclusions

Catalytic oleﬁn condensation is one of the oldest catalytic processes used in reﬁning

and petrochemical operations and pioneered the used of acid catalysts. Many cata-

lysts have been used over the years that have been examined, albeit brieﬂy, in this

chapter. Solid phosphoric acid catalysts (SPA) were for many years the work horse

of the industry, and still command a very respectable market share. Zeolitic catalysts

are slowly making some inroads in this area, but much more slowly than originally

expected in view of their initial success in the alkylation of aromatics. More surpris-

ingly, this old technology is currently enjoying a bit of a revival by the introduction

REFERENCES 399

of highly selective, low temperature, liquid phase operations in which both sulfonic

acid resins and SPA are ﬁnding new niche opportunities. If catalysts can be found

with higher selectivity to more linear oligomers in the C

to C

range, additional

markets may develop in the production of high-quality synthetic diesels and jet fuels.

References

1. V. N. Ipatieff and R. E. Schaad, Mixed polymerization of butenes by solid phosphoric acid

catalyst. Ind. Eng. Chem. 30 (May 1938) 596–599.

2. A. Chauvel and G. Lefebvre, Petrochemical Processes. Vol. 1, Synthesis-Gas Derivatives

and Major Hydrocarbons, ed. Technip (1989) 183–187.

9.3 Isomerization technologies for the upgrading of light

naphtha and reﬁnery light ends

Peter R. Pujad´o*

Upgrading light hydrocarbon (C

–C

) streams in reﬁneries and gas processing plants

has increased in importance as new regulations affecting gasoline composition are

enacted in many regions of the world. These regulations include lead phasedown,

benzene minimization, and oxygen content requirements. Light-naphtha isomeriza-

tion plays a key role in meeting octane demands in the gasoline pool that result from

both lead phasedown and increasing market share for premium gasoline grades. By

isomerization we mean the skeletal isomerization of a parafﬁn to a more branched

parafﬁn with the same carbon number; however, because of its nature, isomerization

may also affect some of the naphthene components and will also hydrogenate aro-

matics. In fact, isomerization is the most-economic means available for reducing the

benzene content in gasoline.

Several isomerization technologies are available from various licensors. UOP’s Penex

process for the isomerization of C

–C

parafﬁns and Butamer process for the isomer-

ization of n-butane to isobutane are some of the most widely used and will form the

basis for this chapter. Developments in isomerization are usually based on the intro-

duction of new, more active or more stable catalysts, some of which will be discussed

in more detail below. Similar comments could be made for other equivalent processes

or catalysts available from other sources.

Introduction

The skeletal isomerization of alkanes is one of many important industrial applica-

tions of acid-function-promoted catalysis. Other examples of the wide commercial

application of acid-catalyzed industrial hydrocarbon reactions are the alkylation of

parafﬁns and aromatics with oleﬁns, transalkylation and disproportionation of aro-

matics, metathesis of oleﬁns, oligomerization of oleﬁns, etheriﬁcation and hydration

*UOP LLC

400

GASOLINE COMPONENTS 401

of oleﬁns, and hydrocracking. Although these various applications have some simi-

larities, they are all promoted by an acidic catalyst and often by a metal function. The

speciﬁc catalytic requirements for achieving a highly economic result have led to the

proliferation of specialized catalytic materials.

This paper focuses on light parafﬁn isomerization. The primary commercial use of the

branched isomers of C

, and C

parafﬁns is in the production of clean-burning,

high-performance transportation fuels. The elimination of tetraethyl lead over the last

30 years as a means of improving the antiknock properties of gasoline and more recent

regulations restricting motor fuel composition have led reﬁners to select alternative

means of producing high-quality gasoline. As a result of benzene concentration re-

strictions, end-point and oleﬁn content limitations, and potential limitations on total

aromatics concentration, the choices of high-quality gasoline blending components

available in the typical reﬁnery are limited. Isomerate, the gasoline blending compo-

nent from light parafﬁn isomerization, is an ideal choice. Another equally valuable

blending components is alkylate resulting primarily from the acid-catalyzed reaction

of isobutene with an aliphatic oleﬁn. Both isomerization and alkylation yield highly

branched, high-octane parafﬁnic blending components that by themselves can satisfy

the strictest environmental requirements. Often, n-butane isomerization is one of the

sources for the isobutane requirements in alkylation.

Because of the heightened demand for isomerate, reﬁners continue to look for increas-

ingly effective and economic means of producing this valuable blending component.

Over the years, UOP has developed and continues to develop new catalyst systems in

order to improve process economics and operability. This paper discusses two exam-

ples, the LPI-100 and I-80 catalysts in terms of their fundamental improvement over

existing catalysts in various processing options and, most important, the increased

value available to reﬁners who use these new high-performance isomerization cata-

lysts.

Process chemistry of parafﬁn isomerization

The octane rating of the components used in the manufacture of the various commer-

cial gasoline grades is indicative of the antiknock quality of a given fuel or compo-

nent. The inherent octane values of different hydrocarbons have led to a variety of

processing strategies to produce high-octane components for the production of high-

performance motor fuel. In the case of C

and C

parafﬁns, the most highly branched

isomers have the highest-octane values. In the case of butanes, octane is somewhat

irrelevant because the majority of isobutane is consumed in the production of motor

fuel alkylate and oxygenates. Octane values for C

and C

parafﬁn isomers are shown

in Table 9.3.1 (1). The two empirical octane measurement methods, research (ASTM

Method 2699), and motor (ASTM Method 2700), measure antiknock characteristics