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Source: HANDBOOK OF PETROLEUM REFINING PROCESSES

●

ALKYLATION AND

POLYMERIZATION

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ALKYLATION AND POLYMERIZATION

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)

Any use is subject to the Terms of Use as given at the website.

Source: HANDBOOK OF PETROLEUM REFINING PROCESSES

CHAPTER 1.1

NExOCTANE™ TECHNOLOGY

FOR ISOOCTANE

PRODUCTION

Ronald Birkhoff

Kellogg Brown & Root, Inc. (KBR)

Matti Nurminen

Fortum Oil and Gas Oy

INTRODUCTION

Environmental issues are threatening the future use of MTBE (methyl-tert-butyl ether) in

gasoline in the United States. Since the late 1990s, concerns have arisen over ground and

drinking water contamination with MTBE due to leaking of gasoline from underground

storage tanks and the exhaust from two-cycle engines. In California a number of cases of

drinking water pollution with MTBE have occurred. As a result, the elimination of MTBE

in gasoline in California was mandated, and legislation is now set to go in effect by the end

of 2003. The U.S. Senate has similar law under preparation, which would eliminate MTBE

in the 2006 to 2010 time frame.

With an MTBE phase-out imminent, U.S. refiners are faced with the challenge of

replacing the lost volume and octane value of MTBE in the gasoline pool. In addition, uti-

lization of idled MTBE facilities and the isobutylene feedstock result in pressing problems

of unrecovered and/or underutilized capital for the MTBE producers. Isooctane has been

identified as a cost-effective alternative to MTBE. It utilizes the same isobutylene feeds

used in MTBE production and offers excellent blending value. Furthermore, isooctane pro-

duction can be achieved in a low-cost revamp of an existing MTBE plant. However, since

isooctane is not an oxygenate, it does not replace MTBE to meet the oxygen requirement

currently in effect for reformulated gasoline.

The NExOCTANE technology was developed for the production of isooctane. In the

process, isobutylene is dimerized to produce isooctene, which can subsequently be hydro-

genated to produce isooctane. Both products are excellent gasoline blend stocks with sig-

nificantly higher product value than alkylate or polymerization gasoline.

1.3

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NExOCTANE™ TECHNOLOGY FOR ISOOCTANE PRODUCTION

1.4

ALKYLATION AND POLYMERIZATION

HISTORY OF MTBE

During the 1990s, MTBE was the oxygenate of choice for refiners to meet increasingly strin-

gent gasoline specifications. In the United States and in a limited number of Asian countries,

the use of oxygenates in gasoline was mandated to promote cleaner-burning fuels. In addi-

tion, lead phase-down programs in other parts of the world have resulted in an increased

demand for high-octane blend stock. All this resulted in a strong demand for high-octane fuel

ethers, and significant MTBE production capacity has been installed since 1990.

Today, the United States is the largest consumer of MTBE. The consumption increased

dramatically with the amendment of the Clean Air Act in 1990 which incorporated the 2

percent oxygen mandate. The MTBE production capacity more than doubled in the 5-year

period from 1991 to 1995. By 1998, the MTBE demand growth had leveled off, and it has

since tracked the demand growth for reformulated gasoline (RFG). The United States con-

sumes about 300,000 BPD of MTBE, of which over 100,000 BPD is consumed in

California. The U.S. MTBE consumption is about 60 percent of the total world demand.

MTBE is produced from isobutylene and methanol. Three sources of isobutylene are

used for MTBE production:

● On-purpose butane isomerization and dehydrogenation

● Fluid catalytic cracker (FCC) derived mixed C 4 fraction

● Steam cracker derived C 4 fraction

The majority of the MTBE production is based on FCC and butane dehydrogenation

derived feeds.

NExOCTANE BACKGROUND

Fortum Oil and Gas Oy, through its subsidiary Neste Engineering, has developed the

NExOCTANE technology for the production of isooctane. NExOCTANE is an extension

of Fortum’s experience in the development and licensing of etherification technologies.

Kellogg Brown & Root, Inc. (KBR) is the exclusive licenser of NExOCTANE. The tech-

nology licensing and process design services are offered through a partnership between

Fortum and KBR.

The technology development program was initialized in 1997 in Fortum’s Research and

Development Center in Porvoo, Finland, for the purpose of producing high-purity isooctene,

for use as a chemical intermediate. With the emergence of the MTBE pollution issue and the

pending MTBE phase-out, the focus in the development was shifted in 1998 to the conver-

sion of existing MTBE units to produce isooctene and isooctane for gasoline blending.

The technology development has been based on an extensive experimental research

program in order to build a fundamental understanding of the reaction kinetics and key

product separation steps in the process. This research has resulted in an advanced kinetic

modeling capability, which is used in the design of the process for licensees. The process

has undergone extensive pilot testing, utilizing a full range of commercial feeds. The first

commercial NExOCTANE unit started operation in the third quarter of 2002.

PROCESS CHEMISTRY

The primary reaction in the NExOCTANE process is the dimerization of isobutylene over

acidic ion-exchange resin catalyst. This dimerization reaction forms two isomers of

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NExOCTANE™ TECHNOLOGY FOR ISOOCTANE PRODUCTION

NExOCTANE™ TECHNOLOGY FOR ISOOCTANE PROCUCTION

1.5

trimethylpentene (TMP), or isooctene, namely, 2,4,4-TMP-1 and 2,4,4-TMP-2, according

to the following reactions:

TMP further reacts with isobutylene to form trimers, tetramers, etc. Formation of these

oligomers is inhibited by oxygen-containing polar components in the reaction mixture. In the

CH 3

CH 2 = C - CH 2 - C - CH 3

CH 3

2,4,4 TMP-1

CH 2 = C - CH 3

CH 3

Isobutylene

CH 2 - C = CH 2 - C - CH 3

CH 3

2,4,4 TMP-2

NExOCTANE process, water and alcohol are used as inhibitors. These polar components

block acidic sites on the ion-exchange resin, thereby controlling the catalyst activity and

increasing the selectivity to the formation of dimers. The process conditions in the dimer-

ization reactions are optimized to maximize the yield of high-quality isooctene product.

A small quantity of C 7 and C 9 components plus other C 8 isomers will be formed when

other olefin components such as propylene, n -butenes, and isoamylene are present in the

reaction mixture. In the NExOCTANE process, these reactions are much slower than the

isobutylene dimerization reaction, and therefore only a small fraction of these components

is converted.

Isooctene can be hydrogenated to produce isooctane, according to the following reaction:

CH 3

CH 2 = C – CH 2 – C – CH 3 + H 2

CH 2 – C – CH 2 – C – CH 3

CH 3

Isooctene

Isooctane

NExOCTANE PROCESS DESCRIPTION

The NExOCTANE process consists of two independent sections. Isooctene is produced by

dimerization of isobutylene in the dimerization section, and subsequently, the isooctene

can be hydrogenated to produce isooctane in the hydrogenation section. Dimerization and

hydrogenation are independently operating sections. Figure 1.1.1 shows a simplified flow

diagram for the process.

The isobutylene dimerization takes place in the liquid phase in adiabatic reactors over

fixed beds of acidic ion-exchange resin catalyst. The product quality, specifically the distri-

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