Gasoline boiling range

Fluid Catalytic Gasoline (FCC) full boiling range gasoline has a respectible RON of about 92 and an R+M/2 of around 87. Since current no-lead grade specifications include 87 R+M/2, FCC gasoline can be utilized directly in the no-lead pool. 

Table I compares properties of Dimersol Dimate and C3 alkylate. In studying this table one sees a basic difference between dimate and C3 alkylate volatility manifested in distillation and RVP. In gasoline blending this becomes important when one is blending with reformate. To illustrate, we will show a series of bar charts giving the RON s of consecutive individual 10 volume % increments of full boiling range gasolines.

Two derivatives are used to ensure constant lead content throughout the gasoline boiling range tetraethyl- and tetramethyl lead and their mixtures in variabie proportions. 

The naphtha fraction is dorninated by saturates having lesser amounts of mono- and diaromatics (Table 2, Eig. 4). Whereas naphtha (ibp to 210°C) covers the boiling range of gasoline, most raw petroleum naphtha molecules have a low octane number and most raw naphtha is processed further, to be combined with other process naphthas and additives to formulate commercial gasoline. 

Extractive distillation, using similar solvents to those used in extraction, may be employed to recover aromatics from reformates which have been prefractionated to a narrow boiling range. Extractive distillation is also used to recover a mixed ben2ene—toluene stream from which high quaUty benzene can be produced by postfractionation in this case, the toluene product is less pure, but is stiU acceptable as a feedstock for dealkylation or gasoline blending. Extractive distillation processes for aromatics recovery include those Hsted in Table 4. 

Polymerization is a reaction in which several molecules of the same or similar material combine to form a larger molecule. We will only discuss the polymerization of C3, C4, and C5 olefins to products in the gasoline boiling range (C5 - Cl2). A typical reaction which occurs in polymerization is illustrated in Figure 24. 

To obtain light ends conversion, alkylation and polymerization are used to increase the relative amounts of liquid fuel products manufactured. Alkylation converts olefins, (propylene, butylenes, amylenes, etc.), into high octane gasoline by reacting them with isobutane. Polymerization involves reaction of propylene and/or butylenes to produce an unsamrated hydrocarbon mixture in the motor gasoline boiling range. 

This section covers the various steps used to recover and separate into useful products the desirable light ends fractions present in the large volumes of effluent gases produced by the various refinery processes. The recovery is usually accomplished by a combination of compression and absorption. The subsequent separation into useful fractions is invariably carried out by distillation, usually in combination with distillates in the gasoline boiling range which are recovered with the light ends fractions. 

Basically, a gas absorption tower is a unit in which the desirable light ends components are recovered from the gas feed by dissolving them in a liquid passing through the tower countercurrently to the gas. The liquid absorbent is called lean, oil, and it usually consists of a hydrocarbon fraction in the gasoline boiling range. After the absorption step, the liquid which now contains the desired constituents in solution is referred to as fat oil. A similarly descriptive nomenclature is applied to the gas, which is referred to as wet gas when it enters the tower and as dry gas when it leaves the absorber. 

Naphtha Any liquid hydrocarbon material boiling in the gasoline boiling range... 

Higher octane in the gasoline fraction. Isoparaffins in the ga.soline boiling range have higher octane than normal paraffins. 

The reactor yield is then determined by performing a component balance. The amount of C5+ in the gasoline boiling range is calculated by subtracting the C4 and lighter components from the total gas plant products. Example 5-4 shows the step-by-step calculation of the component yields. The summary of the results, normalized but unadjusted for the cut points is shown in Table 5-4. 

As discussed earlier in this chapter, gasoline and LCO yields are generally corrected to a constant boiling range basis. The most commonly used bases are 430°F TBP gasoline and 640°F TBP LCO end points. Since TBP distillations are not routinely performed, they are often estimated from the D-86 distillation data. The adjustments to the end points involve the following ... 

Tailpipe emissions of HC and CO are affected by the levels of heavy aromatics in gasoline. Like sulfur, the heavy aromatics are in the back end of the boiling range (Figure 10-4). As with sulfur, reduction of end point directly controls the concentration of heavy aromatics in finished gasoline. 

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