Regeneration replacement

Steam strip spent doctor solution to hydrocarbon recovery before air regeneration replace treating unit with other, less objectionable units (Merox) Use sour water oxidizers and gas incineration ... 

The net result of any or all of these factors is that the catalyst may lose activity and/or selectivity and the catalyst will have to be regenerated/replaced after a period of time. 

Advantages of In-situ Catalyst Regeneration. Replacement of hydrotreating catalysts is an expensive operation in refineries. 

Examples of enzymatic and electrochemical cofactor regeneration as well as chemical and electrochemical cofactor-substitution systems are depicted in Fig. 1. Cofactor regeneration replaces the metabolic cofactor regeneration fotmd in vivo, while cofactor substitution shortcuts the natural system and transfers electrons via the mediator directly to the oxidoreductase or possibly another protein in the electron-transfer chain. The natural monooxygenase system depicted here consists of three proteins, typical for several bacterial P450s, but systems with two or only one component also exist and the principles for the cofactor regeneration and substitution are the same. 

The rate at which the catalyst is lost or degrades has a major influence on the design. If degradation is rapid, the catalyst needs to be regenerated or replaced on a continuous basis. In addition to the cost implications, there are also environmental implications, since the lost or degraded catalyst represents waste. While it is often possible to recover useful materials from degraded catalyst and to recycle those materials in the manufacture of new catalyst, this still inevitably creates waste, since the recovery of material can never be complete. 

Rotary kilns and, to a lesser extent, Fluo-SoHds kilns are used to calcine a wet precipitated calcium carbonate filter cake in the kraft or sulfate paper-pulp process (15). Lime is regenerated for use as a causticization reagent in recovering caustic soda for pulp digestion. Losses in lime recovery are replaced by purchased lime (see Paper Pulp). 

The Lo-Cat process, Hcensed by US Filter Company, and Dow/Shell s SulFerox process are additional Hquid redox processes. These processes have replaced the vanadium oxidizing agents used in the Stretford process with iron. Organic chelating compounds are used to provide water-soluble organometaHic complexes in the solution. As in the case of Stretford units, the solution is regenerated by contact with air. 

Reactions tend to deposit carbon on the catalyst, which ultimately leads to loss of activity. At this stage reactions are stopped, the catalyst purged and regenerated by a controlled oxygenating vapor. AH the vapors from the regeneration process are also passed to the incinerator. A catalyst can undergo many regenerations before replacement becomes necessary. 

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