Improved catalytic reforming
Catalyst solutions help to improve the profitability and reliability of â€¨reforming units
Anthony Poparad, Beatrix Ellis, Bryan Glover and Stephen Metro
UOP LLC, A Honeywell Company
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Modern CCR Platforming units operate with pressures as low as 35 lb/in2g, which allows for a high selectivity to desired products (C5+ reformate and hydrogen) and a minimal production of undesired products (methane, ethane and LPG). CCR reforming catalysts contain platinum, which is required to catalyse important reforming reactions. The level of platinum required on the catalyst has been considerably reduced over time as feedstock contaminant levels and regeneration quality have improved. Rhenium is not used, since CCR reforming catalysts do not need to be as stable as fixed-bed reforming catalysts. However, CCR reforming catalysts do use other metals, most notably tin, to enhance catalyst selectivity. While most CCR reforming catalysts are bi-metallic (containing platinum and tin), other proprietary promoter metals are also used in some catalysts, with their objective being catalyst selectivity enhancement. UOP offers a wide range of CCR Platforming catalysts for use in UOP-designed CCR Platforming Process units or CCR reforming units designed by other licensors. The company also offers many services that can assist reforming unit operators improve unit profitability and reliability. More than 300 CCR reforming units have been licensed throughout the world, with more than 250 of those being UOP CCR Platforming Process units. A block flow diagram of a typical UOP CCR Platforming Process unit is shown in Figure 1.
Recent shifts in the demand for reformate (used for both gasoline blending and petrochemicals production) and hydrogen have caused many reforming unit operators to have to adjust their operations considerably from their initial designs. This has caused many reforming units to be operated in a less efficient manner. Many units that were designed decades ago are also more prone to reliability issues.
Options for improving profitability
Due to shifting demands for reformate and hydrogen products, changes in feedstocks and product specifications, many reforming units are currently being operated with feed quantities, feed qualities and unit severities that are significantly different from their original design points. This can lead to inefficient operation and decrease profitability. This article will focus on several solutions involving catalysts that reforming unit operators can utilise to improve their profitability.
Evaluating current catalyst performance to determine when a changeout is warranted is a critical component to maintaining profitable operations in reforming units. Once a changeout is justified, determining which catalyst features are able to provide the most profitable operations becomes important.
Catalyst changeout criteria
The first step in evaluating how catalysts can improve the profitability of a reforming unit is to determine when a catalyst changeout will be required. In UOP CCR Platforming units, it is possible to change the catalyst “on the fly” (without needing to shut down the reactor section to unload catalyst), so a changeout can be performed at virtually any time. It is sometimes desirable to change the catalyst during a scheduled turnaround, however, since this will allow for a thorough inspection and cleaning of the reactor internals. In fixed-bed reforming units, catalyst changeouts are conducted during catalyst regeneration, although the regeneration can be abbreviated if all of the catalyst is being changed out.
Each reforming unit operator will have a different economic situation to evaluate when contemplating a catalyst changeout. However, there are several factors that all operators should consider.
Higher performance catalyst available
In some cases a changeout can be justified even if the existing catalyst is still in good condition. If the increased performance (increased yields, ability to process more feed or to run to a higher severity) results in an acceptable economic payout period, catalyst replacement can be considered at any time. Most operators typically wait until the existing catalyst performance has declined due to some factor, as described below, before changing the catalyst, however.
Low catalyst surface area
Chloride is injected into the reforming unit at prescribed rates to reach a target level of chloride on the catalyst. Controlling the chloride level on the catalyst is very important, since chloride catalyses important reforming reactions. Too much chloride on the catalyst can lead to excessive cracking, which reduces the yields of desired products. Reforming catalysts use gamma-phase alumina as their base. The gamma alumina in fresh reforming catalyst has a high surface area (in some cases, upwards of 200 m2/g), which allows the catalyst to retain chloride well. Each time the catalyst is regenerated, a small amount of surface area is lost. Since chloride retention on the catalyst is proportional to surface area, taking care to regenerate the catalyst efficiently can help to minimise the surface area loss and maintain good chloride retention of the catalyst. The higher the catalyst surface area, the easier it also is to disperse the metals on the catalyst during the regeneration procedure.
It is essential to have good metals dispersion on the catalyst to allow the metals to effectively catalyse reforming reactions. As the surface area on the catalyst slowly declines over time, it becomes increasingly difficult to keep chloride on the catalyst at the appropriate level and to keep the metals on the catalyst well dispersed. At some point in time, catalyst performance may be affected, and a catalyst changeout may become warranted. Some customers have been able to operate for extended periods with low surface area levels (near 120 m2/g); however, most customers do change their catalyst before the surface area drops this low. Some of UOP’s customers have established guidelines to automatically change a reforming catalyst when the catalyst surface area drops to a certain level.
Alumina phase damage
As mentioned above, reforming catalyst uses gamma-phase alumina as its base. Gamma alumina has a high surface area, which allows for good chloride retention and metals dispersion on the catalyst. During catalyst regeneration, excessive heat can be generated if coked catalyst is allowed to come into contact with a regeneration gas stream containing high levels of oxygen.
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