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ALKYLATION ANDPOLYMERIZATION

P ● A ● R ● T ● 1

Source: HANDBOOK OF PETROLEUM REFINING PROCESSES

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ALKYLATION AND POLYMERIZATION



1.3

CHAPTER 1.1NExOCTANE™ TECHNOLOGY

FOR ISOOCTANE PRODUCTION

Ronald BirkhoffKellogg Brown & Root, Inc. (KBR)

Matti NurminenFortum Oil and Gas Oy

INTRODUCTION

Environmental issues are threatening the future use of MTBE (methyl-tert-butyl ether) ingasoline in the United States. Since the late 1990s, concerns have arisen over ground anddrinking water contamination with MTBE due to leaking of gasoline from undergroundstorage tanks and the exhaust from two-cycle engines. In California a number of cases ofdrinking water pollution with MTBE have occurred. As a result, the elimination of MTBEin gasoline in California was mandated, and legislation is now set to go in effect by the endof 2003. The U.S. Senate has similar law under preparation, which would eliminate MTBEin the 2006 to 2010 time frame.

With an MTBE phase-out imminent, U.S. refiners are faced with the challenge ofreplacing 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 problemsof unrecovered and/or underutilized capital for the MTBE producers. Isooctane has beenidentified as a cost-effective alternative to MTBE. It utilizes the same isobutylene feedsused 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, sinceisooctane is not an oxygenate, it does not replace MTBE to meet the oxygen requirementcurrently in effect for reformulated gasoline.

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

Source: HANDBOOK OF PETROLEUM REFINING PROCESSES



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 increaseddemand for high-octane blend stock. All this resulted in a strong demand for high-octane fuelethers, and significant MTBE production capacity has been installed since 1990.

Today, the United States is the largest consumer of MTBE. The consumption increaseddramatically with the amendment of the Clean Air Act in 1990 which incorporated the 2percent oxygen mandate. The MTBE production capacity more than doubled in the 5-yearperiod from 1991 to 1995. By 1998, the MTBE demand growth had leveled off, and it hassince 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 inCalifornia. 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 areused for MTBE production:

● On-purpose butane isomerization and dehydrogenation● Fluid catalytic cracker (FCC) derived mixed C4 fraction● Steam cracker derived C4 fraction

The majority of the MTBE production is based on FCC and butane dehydrogenationderived feeds.

NExOCTANE BACKGROUND

Fortum Oil and Gas Oy, through its subsidiary Neste Engineering, has developed theNExOCTANE technology for the production of isooctane. NExOCTANE is an extensionof 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 betweenFortum and KBR.

The technology development program was initialized in 1997 in Fortum’s Research andDevelopment 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 thepending 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 researchprogram in order to build a fundamental understanding of the reaction kinetics and keyproduct separation steps in the process. This research has resulted in an advanced kineticmodeling capability, which is used in the design of the process for licensees. The processhas undergone extensive pilot testing, utilizing a full range of commercial feeds. The firstcommercial NExOCTANE unit started operation in the third quarter of 2002.

PROCESS CHEMISTRY

The primary reaction in the NExOCTANE process is the dimerization of isobutylene overacidic ion-exchange resin catalyst. This dimerization reaction forms two isomers of

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, accordingto the following reactions:

TMP further reacts with isobutylene to form trimers, tetramers, etc. Formation of theseoligomers is inhibited by oxygen-containing polar components in the reaction mixture. In the

Isobutylene

2

2,4,4 TMP-1

CH2= C - CH3

CH3

CH2 = C - CH2 - C - CH3

CH3 CH3

CH3

CH2 - C = CH2 - C - CH3

CH3 CH3

CH3

2,4,4 TMP-2

NExOCTANE process, water and alcohol are used as inhibitors. These polar componentsblock acidic sites on the ion-exchange resin, thereby controlling the catalyst activity andincreasing 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 C7 and C9 components plus other C8 isomers will be formed whenother olefin components such as propylene, n-butenes, and isoamylene are present in thereaction mixture. In the NExOCTANE process, these reactions are much slower than theisobutylene dimerization reaction, and therefore only a small fraction of these componentsis converted.

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

CH2 – C – CH2 – C – CH3

CH3 CH3

CH3

IsooctaneIsooctene

CH2 = C – CH2 – C – CH3 + H2

CH3 CH3

CH3

NExOCTANE PROCESS DESCRIPTION

The NExOCTANE process consists of two independent sections. Isooctene is produced bydimerization of isobutylene in the dimerization section, and subsequently, the isooctenecan be hydrogenated to produce isooctane in the hydrogenation section. Dimerization andhydrogenation are independently operating sections. Figure 1.1.1 shows a simplified flowdiagram for the process.

The isobutylene dimerization takes place in the liquid phase in adiabatic reactors overfixed beds of acidic ion-exchange resin catalyst. The product quality, specifically the distri-




bution of dimers and oligomers, is controlled by recirculating alcohol from the product recov-ery section to the reactors. Alcohol is formed in the dimerization reactors through the reactionof a small amount of water with olefin present in the feed. The alcohol content in the reactorfeed is typically kept at a sufficient level so that the isooctene product contains less than 10percent oligomers. The dimerization product recovery step separates the isooctene productfrom the unreacted fraction of the feed (C4 raffinate) and also produces a concentrated alco-hol stream for recycle to the dimerization reaction. The C4 raffinate is free of oxygenates andsuitable for further processing in an alkylation unit or a dehydrogenation plant.

Isooctene produced in the dimerization section is further processed in a hydrogenationunit to produce the saturated isooctane product. In addition to saturating the olefins, thisunit can be designed to reduce sulfur content in the product. The hydrogenation sectionconsists of trickle-bed hydrogenation reactor(s) and a product stabilizer. The purpose ofthe stabilizer is to remove unreacted hydrogen and lighter components in order to yield aproduct with a specified vapor pressure.

The integration of the NExOCTANE process into a refinery or butane dehydrogenationcomplex is similar to that of the MTBE process. NExOCTANE selectively reacts isobuty-lene and produces a C4 raffinate which is suitable for direct processing in an alkylation ordehydrogenation unit. A typical refinery integration is shown in Fig. 1.1.2, and an integra-tion into a dehydrogenation complex is shown in Fig. 1.1.3.

NExOCTANE PRODUCT PROPERTIES

The NExOCTANE process offers excellent selectivity and yield of isooctane (2,2,4-trimethylpentane). Both the isooctene and isooctane are excellent gasoline blending compo-nents. Isooctene offers substantially better octane blending value than isooctane. However,the olefin content of the resulting gasoline pool may be prohibitive for some refiners.

The characteristics of the products are dependent on the type of feedstock used. Table1.1.1 presents the product properties of isooctene and isooctane for products producedfrom FCC derived feeds as well as isooctane from a butane dehydrogenation feed.

The measured blending octane numbers for isooctene and isooctane as produced fromFCC derived feedstock are presented in Table 1.1.2. The base gasoline used in this analy-


Dimerization ProductRecovery

HydrogenationReaction

StabilizerIsobutylene

C4 Raffinate

Alcohol Recycle

Isooctane

Hydrogen Fuel GasIsooctene

DIMERIZATIONSECTION

HYDROGENATIONSECTION

FIGURE 1.1.1 NExOCTANE process.




sis is similar to nonoxygenated CARB base gasoline. Table 1.1.2 demonstrates the signif-icant blending value for the unsaturated isooctene product, compared to isooctane.

PRODUCT YIELD

An overall material balance for the process based on FCC and butane dehydrogenationderived isobutylene feedstocks is shown in Table 1.1.3. In the dehydrogenation case, anisobutylene feed content of 50 wt % has been assumed, with the remainder of the feed


FCC

ALKYLATIONDIMERIZATION

Hydrogen Isooctane

Isooctene

HYDROGENATION

C4 C4 Raffinate

NExOCTANE

FIGURE 1.1.2 Typical integration in refinery.

HYDROGE-NATION

DEHYDRO

Hydrogen

Isooctane

Isooctene

DIMERIZATION

iC4=

NExOCTANE

Butane

HYDROGENTREATMENT

RECYCLETREATMENT

ISOMERI-ZATION

DIB

C4 Raffinate

FIGURE 1.1.3 Integration in a typical dehydrogenation complex.




mostly consisting of isobutane. For the FCC feed an isobutylene content of 22 wt % hasbeen used. In each case the C4 raffinate quality is suitable for either direct processing in arefinery alkylation unit or recycle to isomerization or dehydrogenation step in the dehy-drogenation complex. Note that the isooctene and isooctane product rates are dependenton the content of isobutylene in the feedstock.

UTILITY REQUIREMENTS

The utilities required for the NExOCTANE process are summarized in Table 1.1.4.


TABLE 1.1.1 NExOCTANE Product Properties

FCC C4 Butanedehydrogenation

Isooctane Isooctene Isooctane

Specific gravity 0.704 0.729 0.701RONC 99.1 101.1 100.5MONC 96.3 85.7 98.3(R � M) / 2 97.7 93.4 99.4RVP, lb/in2 absolute 1.8 1.8 1.8

TABLE 1.1.2 Blending Octane Number in CARB Base Gasoline (FCC

Derived)

Isooctene Isooctane

Blending BRON BMON (R � M) / 2 BRON BMON (R � M) /2volume, %

10 124.0 99.1 111.0 99.1 96.1 97.620 122.0 95.1 109.0 100.1 95.1 97.6100 101.1 85.7 93.4 99.1 96.3 97.7

TABLE 1.1.3 Sample Material Balance for NExOCTANE Unit

Material balance FCC C4 feed, lb/h (BPD) Butane dehydrogenation, lb/h (BPD)

Dimerization section:Hydrocarbon feed 137,523 (16,000) 340,000 (39,315)

Isobutylene contained 30,614 (3,500) 170,000 (19,653)Isooctene product 30,714 (2,885) 172,890 (16,375)C4 raffinate 107,183 (12,470) 168,710 (19,510)

Hydrogenation section:Isooctene feed 30,714 (2,885) 172,890 (16,375)Hydrogen feed 581 3752Isooctane product 30,569 (2,973) 175,550 (17,146)Fuel gas product 726 1092




NExOCTANE TECHNOLOGY ADVANTAGES

Long-Life Dimerization Catalyst

The NExOCTANE process utilizes a proprietary acidic ion-exchange resin catalyst. Thiscatalyst is exclusively offered for the NExOCTANE technology. Based on Fortum’s exten-sive catalyst trials, the expected catalyst life of this exclusive dimerization catalyst is atleast double that of standard resin catalysts.

Low-Cost Plant Design

In the dimerization process, the reaction takes place in nonproprietary fixed-bed reactors.The existing MTBE reactors can typically be reused without modifications. Product recov-ery is achieved by utilizing standard fractionation equipment. The configuration of therecovery section is optimized to make maximum use of the existing MTBE product recov-ery equipment.

High Product Quality

The combination of a selective ion-exchange resin catalyst and optimized conditions in thedimerization reaction results in the highest product quality. Specifically, octane rating andspecific gravity are better than those in product produced with alternative catalyst systemsor competing technologies.

State-of-the-Art Hydrogenation Technology

The NExOCTANE process provides a very cost-effective hydrogenation technology. Thetrickle-bed reactor design requires low capital investment, due to a compact design plusonce-through flow of hydrogen, which avoids the need for a recirculation compressor.Commercially available hydrogenation catalysts are used.

Commercial Experience

The NExOCTANE technology is in commercial operation in North America in the world’slargest isooctane production facility based on butane dehydrogenation. The projectincludes a grassroots isooctene hydrogenation unit.


TABLE 1.1.4 Typical Utility Requirements

Utility requirements FCC C4 Butane dehydrogenationper BPD of product per BPD of product

Dimerization section:Steam, 1000 lb/h 13 6.4Cooling water, gal/min 0.2 0.6Power, kWh 0.2 0.03

Hydrogenation section:Steam, 1000 lb/h 1.5 0.6Cooling water, gal/min 0.03 0.03Power, kWh 0.03 0.1




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