Sulfur thermal removal from coke

In the majority of cases, when the adsorbent bed gets exhausted, the spent activated coke loaded with sulfuric acid is thermally regenerated at 673-773 K. At this temperature range, sulfuric acid is removed from the adsorbent surface following the reaction ... 

In commercial operation, the solid catalysts usually lose their effectiveness because of (i) poisons (such as sulfur, chloride), (ii) sintering, (iii) fouling by carbon and coke, and (iv) loss of the active species via volatilization. Purthermore, the life of the catalyst depends partly on the thermal stability of the support/carrier. Poisoning is minimized by the removal of poisons from the feed stream by upstream guard units. Sintering is minimized by operating at lower temperatures. Regeneration can be used to periodically remove the coke and carbon active species may be added. 

In the present context, heavy oils and residua can also be assessed in terms of sulfur content, carbon residue, nitrogen content, and metals content. Properties such as the API gravity and viscosity also help the refinery operator to gain an understanding of the nature of the material that is to be processed. The products from high-sulfur feedstocks often require extensive treatment to remove (or change) the corrosive sulfur compounds. Nitrogen compounds and the various metals that occur in crude oils will cause serious loss of catalyst life. The carbon residue presents an indication of the amount of thermal coke that may be formed to the detriment of the liquid products. 

There are several possible flow scheme variations involved for this process. It can operate as an independent unit or be used in conjunction with a thermal conversion unit (Figure 9-25). In this configuration, hydrogen and a vacuum residuum are introduced separately to the heater, and mixed at the entrance to the reactor. T o avoid thermal reactions and premature coking of the catalyst, temperatures are carefully controlled and conversion is limited to approximately 70% of the total projected conversion. The removal of sulfur, heptane-insoluble materials, and metals is accomplished in the reactor. The effluent from the reactor is directed to the hot separator. The overhead vapor phase is cooled, condensed, and the hydrogen separated from there is recycled to the reactor. 

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