Platinum-rhenium catalysts catalytic reforming, naphthas

In the catalytic reforming of naphthas there are a number of nonhydrocarbon materials which play an important part in the performance of the catalyst. Sulfur is a poison for the reforming catalyst. There appears to be evidence developing that the platinum-rhenium catalysts may be more sensitive to sulfur than the conventional catalysts. Effective pretreatment of the feed stock to maintain sulfur at low levels is desirable. 

A typical process flow diagram of a catalytic reformer is shown in Figure 3.17. Desulfurized naphtha is heated in feed-effluent exchangers and then passed to a fired heater, where it is heated to 850 to 1,000° F (455 to 540° C) at 500 psia (3,450 kPa) in a series of reactors and fired heaters. In the reactors, the hydrocarbon and hydrogen are passed over a catalyst (often platinum/rhenium based) to produce rearranged molecules, which are primarily aromatics with some isoparaffins. The reactor effluent is cooled by exchange and then passed to a separator vessel. The gas from the separator is recycled to the reactors. The liquid is fed to a fractionator. 

Determination of Coke Location. The TPO technique allows the determination of the coke location on supported metal catalysts, such as naphtha reforming. Since the metal, typically platinum promoted with rhenium, iridium, tin, or germanium, has a catalytic effect for coke burning, the TPO profile displays two main peaks. The low temperature peak is due to the oxidation of the coke directly deposited on the metal particle, or in its vicinity . In this way, it is possible to study the effect of catalyst formulation and operational conditions on the formation of coke on the metal and on the support. 

An important commercial example of an endothermic reaction that is carried out adiabatically is the catalytic reforming of petroleum naphtha to produce high-octane gasoline. In this process, the naphtha is mixed with hydrogen and passed over a heterogeneous catalyst that contains platinum, and perhaps other metals such as rhenium or tin, on a ceramic support such as alumina. The temperature is in the region of 800-900 °F. 

Chlorinated alumina-supported metal catalysts are the typical catalysts used today for catalytic naphtha reforming, which is performed at temperatures of480-550 °C (410). Modem versions of this type of catalyst are mul-timetaUic the catalytic properties of platinum are improved by the addition of another metal, often rhenium. Further elements that may be added are tin, silicon, germanium, lead, gallium, indium, iridium, thorium, lanthanum, cerium, cobalt, and nickel. AH these components are supported on chlorinated y-alumina (with a surface area of 150—300 m g ), which provides the acid function (411). 

---