Reforming Process

Catalytic reformers are normally designed to have a series of catalyst beds (typically three beds). The first bed usually contains less catalyst than the other beds. This arrangement is important because the dehydrogenation of naphthenes to aromatics can reach equilibrium faster than the other reforming reactions. Dehydrocyclization is a slower reaction and may only reach equilibrium at the exit of the third reactor. Isomerization and hydrocracking reactions are slow. They have low equilibrium constants and may not reach equilibrium before exiting the reactor.

The second and third reactors contain more catalyst than the first one to enhance the slow reactions and allow more time in favor of a higher yield of aromatics and branched paraffins. Because the dehydrogenation of naphthenes and the dehydrocyclization of paraffins are highly endothermic, the reactor outlet temperature is lower than the inlet temperature.  The effluent from the first and second reactors are reheated to compensate for the heat loss.

Normally, catalytic reformers operate at approximately 500–525°C and 100–300 psig, and a liquid hourly space velocity range of 2–4 hr-1. Liquid hourly space velocity (LHSV) is an important operation parameter expressed as the volume of hydrocarbon feed per hour per unit volume of the catalyst. Operating at lower LHSV gives the feed more

contact with the catalyst.

Regeneration of the catalyst may be continuous for certain processes that are designed to permit the removal and replacement of the catalyst during operation. In certain other processes, an additional reactor is used (Swing reactor). When the activity of the catalyst is decreased in one of the reactors on stream, it is replaced with the stand-by (Swing) reactor.

In many processes, regeneration occurs by shutting down the unit and regenerating the catalyst (Semi-regenerative). Figure 1.1 shows a Chevron Rheiniforming semiregenerative fixed three-bed process.

Products from catalytic reformers (the reformate) is a mixture aromatics, paraffins and cycloparaffins ranging from C₆-C₈. The mixture has a high octane rating due to presence of a high percentage of aromatics and branched paraffins. Extraction of the mixture with a suitable solvent produces an aromatic-rich extract, which is further fractionated to separate the BTX components. Extraction and extractive distillation of reformate have been reviewed by Gentray and Kumar.

Figure 1.1. Flow diagram of a Chevron Rheiniforming unit: (1) sulfur sorber, (2–4) reactors, (5) separator, (6) stabilizer.