Octane boosting

Shape-selective reactions have been extensively studied since zeohtes were first used in catalytic crackers during 1967 and Mobil has introduced several octane-boosting processes since 1968. ° Gasoline composition and octane number were reviewed when the Clean Air Act was passed in 1970. This mandated the phased removal of tetraethyl lead from gasoline as catalytic converters (see Chapter 11) were introduced to treat automobile exhaust gas. Octane boosting was the first in a series of measures that led to reformulated gasoline and improved exhaust emissions standards. 

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The chemical formula for ethanol is Cl L,Cl TOIL Ethanol is less toxic and more biodegradable than gasoline. For its octane boosting capability ethanol can be use as a fuel additive when blended with gasoline. 

The concentration of the ZSM-5 additive should be greater than 1% of the catalyst inventory to see a noticeable increase in the octane. An octane boost of one research octane number (RON) will typically require a 2% to 5% ZSM-5 additive in the inventory. It should be noted that the proper way of quoting percentage should be by ZSM-5 concentration rather than the total additive because the activity and attrition rate can vary from one supplier to another. There are new generations of ZSM-5 additives that have nearly twice the activity of the earlier additives. 

These selectivities obtained with Amberlyst-15 seem to be rather optimistic in view of recent work, where only with overstoichiometric ratios high di-+tri-ether selectivity is obtained. It is also not settled why addition of tert-butanol to the reaction mixture suppresses isobutene oligomerization selectivity [34, 35], At this stage it should also be stressed that the tert-butylglycerol ethers (TBGE) mentioned are excellent substitutes for MTBE (ETBE) as gasoline octane boosting components [36]. 

Olefins, unlike paraffins, do not show significant gains in octane number with skeletal isomerization (see Table 14.2). As a result, olefin isomerization is not a useful octane boosting strategy. However, tertiary olefins (olefins with three alkyl substituents on the double bond), do react fairly readily with olefins to form ethers, which do have good octane numbers-for example, methyl tert-butyl ether (MTBE). 

Figure 1. Impact of base octane on ZSM-5 octane boost.

A model which is consistent with the chemistry described previously has been developed to predict the performance of ZSM-5 in an FGG unit. Application of this model allows the user to take full advantage of ZSM-5 s flexibility for specific applications. The model has been used in many commercial applications to determine the catalyst makeup rate required to achieve a given octane boost. It has also been used to tailor the catalyst makeup strategy to obtain a desired octane boost in a given period of time. 

The model is divided into two parts the calculation of ZSM-5 concentration required to achieve a given activity in the unit (activity maintenance) and the impact of base gasoline composition on the gasoline octane boost for ZSM-5 of a given activity. 

We now need to relate the activity of ZSM-5 to the octane boost achievable commercially. As discussed previously, the octane boost at any given ZSM-5 activity depends on the base octane, which is a characteristic of the concentration of low octane olefins and paraffins in the gasoline. Figure 1 illustrates the relationship between octane boost and activity at several different base octanes. As can be seen from the curves, as the gasoline base octane increases, more ZSM-5 activity is required to achieve a given octane increase. 

Thus, the potential octane boost which can be obtained from ZSM-5 addition is not only a function of its activity and the fraction of ZSM-5 in inventory, but it also depends on its base gasoline octane (gasoline octane without ZSM-5 addition). 

As discussed above, the potential octane boost which can be achieved from ZSM-5 addition is a function of five parameters the regenerator temperature and steam partial pressure (which determine the activity maintenance) the base and ZSM-5 catalyst makeup rates (which determine the catalyst age) and the base gasoline octane. The sensitivity of the model to these parameters is discussed below. 

The model has been verified by accurately predicting the octane boost for many different commercial applications. Figure 5 shows the model predictions versus measured data for two commercial applications. The objective of the application at Refinery A, was to increase the Research Octane by 1 number within 1 day. 

One of the main applications of the ZSM-5 performance model is to determine the optimal catalyst makeup strategy to achieve a desired octane boost in a required period of time. Since ZSM-5 is used primarily as an additive, the catalyst makeup policy can be tailored to fit the refiner s needs. 

Top, rapid octane boost and bottom, gradual octane boost. 

Gasohol is gasoline containing an alcohol additive. The alcohol provides an octane boost, allowing an engine to run more effi-ciendy with less pollution. If the alcohol is produced from biomass grown within a nation, there is the added benefit of a reduced dependence on foreign oil. 

The octane boosting processes allow us to reduce cost by increasing yield without sacrificing product quality. To reduce cost, a new catalytic dewaxing process replaces an expensive noncatalytic process. Catalytic dewaxing does not have the temperature limitation of a solvent dewaxing process. Thus, it creates a new class of super-low freeze point or pour point products for low temperature applications. The... 

Octane boosting ctane boosting 34-35) Octane boosting... 

The increase in octane number required to replace lead can be achieved in a number of ways (Ref. 16), all of which increase the manufacturing costs some require substantial additional investment. At the current state of the art and prices the average cost of an octane-ton is about 1.8. The most attractive but limited octane enhancement is obtained by the use of octane boosting catalysts in the cat cracker. 

European market such as non-dedicated tankage, or octane boosting using Pb results in Pb levels reaching the legal maximum, then as shown by the following data, there will be a high risk of contamination. 

Aluminophosphate-based catalysts are used for the catalytic cracking of heavy boiling hydrocarbons and for the selective reaction with low-octane hydrocarbons resulting in octane boost in catalytic cracking. The aluminophosphate catalyst is applied by itself or in mixture with other types of cracking catalysts. ... 

In the early 1950s, reforming processes that jdelded more octane-boosting aromatics were introduced by Standard of Indiana and Exxon. This was achieved at the expense of increased catalyst deactivation at the lower operating pressures. A regeneration cycle had to be added, which required adding one reactor to the normal set of three used in the platforming process. 

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