Poisoning catalytic reforming

TSR(l) [Trace sulphur removal] A process for removing sulfur compounds from naphtha so that they will not poison catalytic reformers. A proprietary solid absorbent is used. Developed by the Union Oil Company of California and first commercialized in 1983 at the Unocal oil refinery in San Francisco. 

Reduce harmful impurities in petroleum fractions and residues to control pollution and to avoid poisoning certain processing catalysts. For example, hydrotreatment of naphtha feeds to catalytic reformers is essential because sulfur and nitrogen impurities poison the catalyst. 

Sulfur poisons catalytic sites in the fuel cell also. The effect is aggravated when there are nickel or iron-containing components including catalysts that are sensitive to sulfur and noble metal catalysts, such as found in low temperature cell electrodes. Sulfur tolerances are described in the specific fuel cell sections of this handbook." In summary, the sulfur tolerances of the cells of interest, by percent volume in the cleaned and altered fuel reformate gas to the fuel cells from published data, are ... 

The bottom of the barrel contains heavy, smelly compounds that have polyaromatic rings and that contain up to several percent of S and N in aromatic rings and in side chains sulfides and amines. This fi action will not boil below temperatures where the molecules begin to crack, and it is called residual oil or vacuum resid if it boils at reduced pressure. This fraction also contains perhaps 0.1% of heavy metals tied up as porphyrin rings in the polyaromatics. All these species are severe poisons to either FCC or catalytic reforming... 

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. 

In selective poisoning or selective inhibition, a poison retards the rate of one catalysed reaction more than that of another or it may retard only one of the reactions. For example, there are poisons which retard the hydrogenation of olefins much more than the hydrogenation of acetylenes or dienes. Also, traces of sulphur compounds appear selectively to inhibit hydro-genolysis of hydrocarbons during catalytic reforming. 

HDS1 Catalytic reformer feedstocks Reduce catalyst poisoning... 

It follows that regeneration may consist of either (i) removal of IS sometimes poisons, most often inhibitors or fouling agents, e.g., coke (hydrogenation catalysts, e.g., selective hydrogenation of pyrolysis gasoline) or (ii) redispersion of the active species (platinum catalysts) or (iii) both (hydrodesulfurization or catalytic reforming catalysts). 

Poisoning of metal catalysts may provide a tool for improving selec> tivity by affecting the concentrations of ensembles required by different reaction paths. This is illustrated by steam reforming on sulfur passivated nickel catalysts and the results are compared with observations for sulfided platinum-rhenium catalysts for catalytic reforming and for a chlorine poisoned palladium catalyst for partial oxidation of methane. 

It should be noted that since sulfur is a poison for the platinum-based catalysts used for these changes, the feed for the catalytic reformer has to be essentially sulfur free. Sulfur is removed by passing the feedstock through a cobalt/molybdenum catalyst bed in the presence of hydrogen, Avhich can come from the catalytic reformer. Carbon-bound sulfur is converted to hydrogen sulfide (Eq. 18.30). 

Most poisons are type (1), i.e., independent compounds present tn the feed, perhaps in minute quantities, that deactivate the site with a mechanism different from the main reaction. Examples are also found of types (2) and (3), where either parallel or series reactions generate side products that poison the sites. These mechanisms may also be classified as examples of kinetic inhibition but are considered poisoning if adsorption on the site is irreversible. In situations where multiple sites are involved (for example, dual-functional catalytic reforming), poisoning patterns become more complex. 

Early workers in catalytic reforming discovered that a small amount of sulfur poisons hydrogenolysis sites and reduces coking. Studies with... 

Acidity of the support, which accelerates coke formation, is poisoned with alkali addition. The active component, promoted molybdenum sulfide, is active for dehydogenation and also has acid sites, so the general behavior discussed for catalytic reforming is the same, except for reduced activity and complications from heavier molecules. 

In the following, examples of the ensemble control by means of adsorbed poisons are discussed with the the emphasis on steam reforming of methane on sulfur passivated nickel catalysts. The conclusions for ensemble control will be compared with data for catalytic reforming on PtRe(S) catalysts and for the impact of chlorine on partial oxidation of methane on Pd-catalysts. 

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