Reformer octane

For commercial simulations, KINPTR s selectivity kinetics determine the reformate composition and overall yield at a target reformate octane. Reformer yield-octane behavior from pilot and commercial units are shown in Fig. 29a. The large variation in the reformate yields at a given octane, as much as 25%, results from the wide range of process conditions and naphtha feed quality used in Mobil reformers. As demonstrated in Fig. 29b, KINPTR accurately normalizes these reformate yields over a wide range of octanes, including those required for gasoline lead phaseout. 

However, at 27 days on stream, the comparison has changed dramatically. While about the same temperature was maintained, the reformer octane fell roughly 12 numbers to 83.6, but yields stayed constant. At the same octane, the model predicts a 41 K lower inlet temperature and 9 vol % higher reformate... 

In the inner loop, the composition of the hydrogen recycle gas is determined by successive substitution. If a target reformate octane is specified, an outer loop adjusts the inlet temperatures to all the reactors by equal increments until the target is reached. 

The activity of a test catalyst, either in the fresh state or after a substantial time on stream, is obtained simply by determining the space velocity required to produce the same octane number product at the standard conditions. Empirical relations between reformate octane number and naphtha space velocity as a function of temperature, hydrogen partial pressure, and other process variables for the reference catalyst make it possible to determine the activity of a test catalyst from data at a variety of conditions. For our purposes here, the absolute values shown for the activities are not important, since we will be concerned strictly with ratios of catalytic activities. 

Table II. Test Results for Steam Reforming Octane and Benzene...

In this sense, refiners have reduced the severity of the industrial reforming plants in order to decrease the amoimt of aromatics in gasoline, however it adversely affects the reformate octane [1]. 

The preceding information indicates the paths to follow in order to obtain stocks of high octane number by refining. The orientation must be towards streams rich in aromatics (reformate) and in isoparaffins (isomerization, alkylation). The olefins present essentially in cracked gasolines can be used only with moderation, considering their low MONs, even if their RONs are attractive. 

A key process in the production of gasoline, catalytic reforming is used to increase the octane number of light crude fractions having high paraffin and naphthene contents (C7-C8-C9) by converting them to aromatics. 

As a complementary process to reforming, isomerization converts normal paraffins to iso-paraffins, either to prepare streams for other conversions nCi —> /C4 destined for alkylation or to increase the motor and research octane numbers of iight components in the gasoiine pooi, i.e., the C5 or Cs-Ce fractions from primary distillation of the crude, or light gasoline from conversion processes, having low octane numbers. 

We cite isomerization of Cs-Ce paraffinic cuts, aliphatic alkylation making isoparaffinic gasoline from C3-C5 olefins and isobutane, and etherification of C4-C5 olefins with the C1-C2 alcohols. This type of refinery can need more hydrogen than is available from naphtha reforming. Flexibility is greatly improved over the simple conventional refinery. Nonetheless some products are not eliminated, for example, the heavy fuel of marginal quality, and the conversion product qualities may not be adequate, even after severe treatment, to meet certain specifications such as the gasoline octane number, diesel cetane number, and allowable levels of certain components. 

Reforming (Section 2 16) Step in oil refining in which the pro portion of aromatic and branched chain hydrocarbons in petroleum is increased so as to improve the octane rating of gasoline... 

Mixtures of CO—H2 produced from hydrocarbons, as shown in the first two of these reactions, ate called synthesis gas. Synthesis gas is a commercial intermediate from which a wide variety of chemicals are produced. A principal, and frequendy the only source of hydrogen used in refineries is a by-product of the catalytic reforming process for making octane-contributing components for gasoline (see Gasoline and OTHER MOTOR fuels), eg. 

Benzene, toluene, and xylene are made mosdy from catalytic reforming of naphthas with units similar to those already discussed. As a gross mixture, these aromatics are the backbone of gasoline blending for high octane numbers. However, there are many chemicals derived from these same aromatics thus many aromatic petrochemicals have their beginning by selective extraction from naphtha or gas—oil reformate. Benzene and cyclohexane are responsible for products such as nylon and polyester fibers, polystyrene, epoxy resins (qv), phenolic resins (qv), and polyurethanes (see Fibers Styrene plastics Urethane POLYiffiRs). 

---