Octane number enhancers

The importance of isobutylene in the petrochemical industry is well recognized. Isobutylene is used on a large scale for the production of (i) methacrolein by direct oxidation, (ii) polyisobutylene by polymerization, (iii) synthetic rubber (a copolymer of isobutylene and isoprene), and (iv) methyl tert-butyl ether (MTBE, a gasoline octane-number enhancer) by reaction with methanol. 

The commercial production of f-butyl methyl ether has become important in recent years. In 2002, worldwide consumption of MTBE was about 7 billion gallons. With an octane value of 110, it is used as an octane number enhancer in unleaded gasolines. It is prepared by the acid-catalyzed addition of methanol to 2-methyl-propene. The reaction is related to the hydration of alkenes (Sec. 3.7.b). The only difference is that an alcohol, methanol, is used as the nucleophile instead of water. 

TEL was not the only way to increase octane number. Those few companies who did not wish to do business with Jersey Standard, sought other means to produce a viable premium gasoline. TEL represented the most serious threat to the traditional gasoline product. It was cheap, vei y effective, and only 0.1 percent of TEL was required to increase the octane number 10 to 15 points. In contrast, between 50 to 100 times this concentration was required of alternative octane enhancers to achieve the same effect. 

Turbo-Oktan 115 A small-pack version of Feterol for increasing the octane number directly in the fuel tank. The agent eliminates detonation, enhances power and extends engine life while its excess of oxygen improves combustion and thus reduces pollution. 

OCTENAR [Octane enhancement by removing aromatics] A process for removing aromatic hydrocarbons from petroleum reformate by extractive distillation with N-formyl mor-phylane. The product can be blended with gasoline to increase its octane number — hence the name. A paraffin mixture is obtained as a side-product. Developed by Krupp Koppers from its MORPHYLANE and MORPHYLEX processes. 

World-Wide there is approximately 1000 tons of fluid cracking catalyst manufactured each day. Of this, about 35% contains some form of aluminum deficient zeolite Y, one whose SiOz/AlaOa ratio exceeds 5.5 1, and whose performance is generally characterized by enhanced olefin formation and higher gasoline research and motor octane number. The aluminum deficient... 

There are three different kinds of octane catalysts in current use. Some are based in part on an active non-zeolite matrix composed of a porous silica/alumina component. Others are based on low cell size (2.425-2.428 nm) ultra stable faujasite (USY), a catalyst composition developed in 1975 (2) for the purpose of octane enhancement. A third catalyst system makes use of a small amount (1-2%) of ZSM-5 as an additive. While the net effect in all cases is an increase in the measured octane number, each of the three catalytic systems have different characteristic effects on the composition and yield of the gasoline. The effects of the ZSM-5 component on cracking is described in other papers of this symposium and will not be discussed here. 

An arbitrary mixture of hydrocarbons is compared to a mixture of these two compounds, with its octane number that equal to the appropriate mixture of these standard compounds. Some molecules and their octane ratings are indicated in Table 2-6. Aromatics have a high octane number (toluene is 120), and some compounds such as tetraethyl lead have a strong octane enhancement when added to other mixtures (blending octane number). Oxygenates such as ethanol and ethers (MTBE) have fairly high octane numbers and supposedly produce less pollution, either alone or blended with hydrocarbons. 

The skeletal isomerization of straight-chain paraffins is important for the enhancement of the octane numbers of light petroleum fractions. The isomerization of H-butane to isobutane has attracted much attention because isobutane is a feedstock for alkylation with olefins and MTBE synthesis. It is widely believed that the low-temperature transformation of n-alkanes can be catalyzed only by superacidic sites, and this reaction has often been used to test for the presence of these sites. 

The main objective in FCC catalyst design is to prepare cracking catalyst compositions which are active and selective for the conversion of gas-oil into high octane gasoline fraction. From the point of view of the zeolitic component, most of the present advances in octane enhancement have been achieved by introducing low unit cell size ultrastable zeolites (1) and by inclusion of about 1-2 of ZSM-5 zeolite in the final catalyst formulation (2). With these formulations, it is possible to increase the Research Octane Number (RON) of the gasoline, while only a minor increase in the Motor Octane Number (MON) has been obtained. Other materials such as mixed oxides and PILCS (3,4) have been studied as possible components, but there are selectivity limitations which must be overcome. 

Methyl tertiary butyl ether (methyl-r-butyl ether, MTBE boiling point 55°C, flash point -30°C) has excited considerable interest because it is a good octane enhancer for gasoline (it blends as if it had a research octane number of 115 to 135). It also offers a method of selectively removing isobutylene from a mixed C4 stream, thus enabling the recovery of high-purity butene-1. Furthermore, methyl tertiary butyl ether can be isolated, then cracked to yield highly pure iso-butylene and methanol. 

Therefore, in the traditional complex process of gasoline fraction reforming (the process to enhance the octane number mainly due to dehydrocyclization of linear octanes), it is easy to excite driving forces at T > T to provide the direct insertion of light hydrocarbons into heavier alkanes. 

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