(Ebook) Handbook Of Petroleum Refining Processes 3 ed. by Meyers Robert A. ISBN 9780071391092, 9780071500944, 9781601198648, 0071391096, 0071500944, 1601198647 download
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During the 1990s,MTBE was the oxygenate of choice for refiners to meet increasingly stringent 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 addition,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 consumes 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 C4 fraction
● Steam cracker derived C4 fraction
The majority of the MTBE production is based on FCC and butane dehydrogenation derived feeds.
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 technology 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 conversion 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.
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
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
CH2 = C - CH2 - C - CH3
CH2= C - CH3
2,4,4 TMP-1
CH2 - C = CH2 - C - CH3 CH3 CH3
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 dimerization 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 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:
CH2 = C – CH2 – C – CH3 + H2
– C – CH2 – C – CH3
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-