Handbook of Petroleum Refining Processes

847 Pages·2004·10.272 MB·English

by  Robert A. Meyers

Source: HANDBOOK OF PETROLEUM REFINING PROCESSES
P A R T 1
● ● ● ●
ALKYLATION AND
POLYMERIZATION
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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 fraction
4
● Steam cracker derived C fraction
4
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 CH
3 3
CH = C - CH - C - CH
2 2 3
CH
3
CH
3 2,4,4 TMP-1
2 CH = C - CH
2 3
CH CH
3 3
Isobutylene CH - C = CH - C - CH
2 2 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 and C components plus other C isomers will be formed when
7 9 8
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:
CH3 CH3 CH3 CH3
CH = C – CH – C – CH + H CH – C – CH – C – CH
2 2 3 2 2 2 3
CH3 CH3
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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NExOCTANE™ TECHNOLOGY FOR ISOOCTANE PRODUCTION
1.6 ALKYLATION AND POLYMERIZATION
C Raffinate Isooctene Hydrogen Fuel Gas
4
Isobutylene Isooctane
Product Hydrogenation
Dimerization Stabilizer
Recovery Reaction
Alcohol Recycle
DIMERIZATION HYDROGENATION
SECTION SECTION
FIGURE 1.1.1 NExOCTANE process.
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 reaction
of a small amount of water with olefin present in the feed. The alcohol content in the reactor
feed is typically kept at a sufficient level so that the isooctene product contains less than 10
percent oligomers. The dimerization product recovery step separates the isooctene product
from the unreacted fraction of the feed (C raffinate) and also produces a concentrated alco-
4
hol stream for recycle to the dimerization reaction. The C raffinate is free of oxygenates and
4
suitable for further processing in an alkylation unit or a dehydrogenation plant.
Isooctene produced in the dimerization section is further processed in a hydrogenation
unit to produce the saturated isooctane product. In addition to saturating the olefins,this
unit can be designed to reduce sulfur content in the product. The hydrogenation section
consists of trickle-bed hydrogenation reactor(s) and a product stabilizer. The purpose of
the stabilizer is to remove unreacted hydrogen and lighter components in order to yield a
product with a specified vapor pressure.
The integration of the NExOCTANE process into a refinery or butane dehydrogenation
complex is similar to that of the MTBE process. NExOCTANE selectively reacts isobuty-
lene and produces a C raffinate which is suitable for direct processing in an alkylation or
4
dehydrogenation 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. Table
1.1.1 presents the product properties of isooctene and isooctane for products produced
from FCC derived feeds as well as isooctane from a butane dehydrogenation feed.
The measured blending octane numbers for isooctene and isooctane as produced from
FCC derived feedstock are presented in Table 1.1.2. The base gasoline used in this analy-
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NExOCTANE™ TECHNOLOGY FOR ISOOCTANE PRODUCTION
NExOCTANE™TECHNOLOGY FOR ISOOCTANE PROCUCTION 1.7
C4 C4 Raffinate
DIMERIZATION ALKYLATION
FCC
Isooctene
HYDROGENATION
Hydrogen Isooctane
NExOCTANE
FIGURE 1.1.2 Typical integration in refinery.
NExOCTANE
Isooctene
iC =
4
HYDROGE-
DEHYDRO DIMERIZATION
NATION
Isooctane
HYDROGEN
DIB TREATMENT Hydrogen
Butane
RECYCLE
TREATMENT C Raffinate
4
ISOMERI-
ZATION
FIGURE 1.1.3 Integration in a typical dehydrogenation complex.
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 dehydrogenation
derived isobutylene feedstocks is shown in Table 1.1.3. In the dehydrogenation case, an
isobutylene feed content of 50 wt % has been assumed, with the remainder of the feed
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NExOCTANE™ TECHNOLOGY FOR ISOOCTANE PRODUCTION
1.8 ALKYLATION AND POLYMERIZATION
TABLE 1.1.1NExOCTANE Product Properties
FCC C Butane
4
dehydrogenation
Isooctane Isooctene Isooctane
Specific gravity 0.704 0.729 0.701
RONC 99.1 101.1 100.5
MONC 96.3 85.7 98.3
(R(cid:1)M) / 2 97.7 93.4 99.4
RVP,lb/in2absolute 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(cid:1)M) / 2 BRON BMON (R(cid:1)M) /
2
volume,%
10 124.0 99.1 111.0 99.1 96.1 97.6
20 122.0 95.1 109.0 100.1 95.1 97.6
100 101.1 85.7 93.4 99.1 96.3 97.7
TABLE 1.1.3 Sample Material Balance for NExOCTANE Unit
Material balance FCC C feed,lb/h (BPD) Butane dehydrogenation,lb/h (BPD)
4
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)
C raffinate 107,183 (12,470) 168,710 (19,510)
4
Hydrogenation section:
Isooctene feed 30,714 (2,885) 172,890 (16,375)
Hydrogen feed 581 3752
Isooctane product 30,569 (2,973) 175,550(17,146)
Fuel gas product 726 1092
mostly consisting of isobutane. For the FCC feed an isobutylene content of 22 wt % has
been used. In each case the C raffinate quality is suitable for either direct processing in a
4
refinery alkylation unit or recycle to isomerization or dehydrogenation step in the dehy-
drogenation complex. Note that the isooctene and isooctane product rates are dependent
on the content of isobutylene in the feedstock.
UTILITY REQUIREMENTS
The utilities required for the NExOCTANE process are summarized in Table 1.1.4.
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NExOCTANE™ TECHNOLOGY FOR ISOOCTANE PRODUCTION
NExOCTANE™TECHNOLOGY FOR ISOOCTANE PROCUCTION 1.9
TABLE 1.1.4 Typical Utility Requirements
Utility requirements FCC C Butane dehydrogenation
4
per BPD of product per BPD of product
Dimerization section:
Steam,1000 lb/h 13 6.4
Cooling water,gal/min 0.2 0.6
Power,kWh 0.2 0.03
Hydrogenation section:
Steam,1000 lb/h 1.5 0.6
Cooling water,gal/min 0.03 0.03
Power,kWh 0.03 0.1
NExOCTANE TECHNOLOGY ADVANTAGES
Long-Life Dimerization Catalyst
The NExOCTANE process utilizes a proprietary acidic ion-exchange resin catalyst. This
catalyst 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 at
least 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 the
recovery 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 the
dimerization reaction results in the highest product quality. Specifically,octane rating and
specific gravity are better than those in product produced with alternative catalyst systems
or competing technologies.
State-of-the-Art Hydrogenation Technology
The NExOCTANE process provides a very cost-effective hydrogenation technology. The
trickle-bed reactor design requires low capital investment, due to a compact design plus
once-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’s
largest isooctane production facility based on butane dehydrogenation. The project
includes a grassroots isooctene hydrogenation unit.
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Source: HANDBOOK OF PETROLEUM REFINING PROCESSES
CHAPTER 1.2
STRATCO EFFLUENT
REFRIGERATED H SO
2 4
ALKYLATION PROCESS
David C. Graves
STRATCO
Leawood,Kansas
INTRODUCTION
Alkylation, first commercialized in 1938, experienced tremendous growth during the
1940s as a result of the demand for high-octane aviation fuel during World War II. During
the mid-1950s,refiners’interest in alkylation shifted from the production of aviation fuel
to the use of alkylate as a blending component in automotive motor fuel. Capacity
remained relatively flat during the 1950s and 1960s due to the comparative cost of other
blending components. The U.S. Environmental Protection Agency’s lead phase-down pro-
gram in the 1970s and 1980s further increased the demand for alkylate as a blending com-
ponent for motor fuel. As additional environmental regulations are imposed on the
worldwide refining community, the importance of alkylate as a blending component for
motor fuel is once again being emphasized. Alkylation unit designs (grassroots and
revamps) are no longer driven only by volume, but rather by a combination of volume,
octane, and clean air specifications. Lower olefin, aromatic, sulfur, Reid vapor pressure
(RVP), and drivability index (DI) specifications for finished gasoline blends have also
become driving forces for increased alkylate demand in the United States and abroad.
Additionally,the probable phase-out of MTBE in the United States will further increase
the demand for alkylation capacity.
The alkylation reaction combines isobutane with light olefins in the presence of a
strong acid catalyst. The resulting highly branched,paraffinic product is a low-vapor-pres-
sure,high-octane blending component. Although alkylation can take place at high temper-
atures without catalyst,the only processes of commercial importance today operate at low
to moderate temperatures using either sulfuric or hydrofluoric acid catalysts. Several dif-
ferent companies are currently pursuing research to commercialize a solid alkylation cat-
alyst. The reactions occurring in the alkylation process are complex and produce an
alkylate product that has a wide boiling range. By optimizing operating conditions, the
1.11
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