Regeneration, using steam

Fig. 14.8 Schematic representation of sorption-enhanced reforming. The topmost reactor is in reforming mode, the bottom one is being regenerated using steam.

In the only study of regeneration using steam (237,270), it was found that up to 80% removal of surface sulfur from Ni steam reforming catalysts either unpromoted or promoted with Mg and Ca could be achieved at 973 K. The effluent gas analysis showed the presence of S02 and H2S, and the following reaction pattern was suggested ... 

Removal using carbon bed adsorbers is very satisfactory since toluene is stable and does not need drying when the bed is regenerated using steam, unless the recovered toluene is to be used for an unusual purpose, e.g. urethane paint. 

Example 10.4 A gas mixture with a flowrate of 0.1 m3 s-1 contains 0.203 kg m-3 of benzene. The temperature is 10°C and the pressure 1 atm (1.013 bar). Benzene needs to be separated to give a gas stream with a benzene concentration of less than 5 mg m-3. It is proposed to achieve this by adsorption using activated carbon in a fixed bed. The activated carbon is to be regenerated using superheated steam. The experimental adsorption isotherms cannot be adequately represented by Freundlich isotherms and, instead, can be correlated at 10°C by the empirical relationship ... 

SOLINOX SO,. Linde NO,] A process for removing both NOx and SOx from fluegases. The SOx is removed by scrubbing with tetra-ethylene glycol dimethyl ether, circulated in a packed tower (the Selexol process). The NOx is destroyed by Selective Catalytic Reduction ( SCR). The sorbent is regenerated with steam the SOx is recovered for conversion to sulfuric acid. Developed by Linde in 1985 and used in a lead smelter in Austria and several power stations in Germany. In 1990 it was announced that it would be used at the titanium pigment plant in The Netherlands operated by Sachtleben. 

Uses steam to regenerate the resin, minimizing disposal and material costs. 

Adsorbent can be regenerated on-site using steam stripping, thus eliminating the liability and cost of off-site regeneration or disposal. 

Fruit juices can be deacidified with a weak base anion-exchange resin. Removal of compounds which cause a bitter taste is a more popular application (26,27). It is accomplished with resins that have no ion-exchange fimctionality. In essence, they are similar to the copolymer intermediates used by resin manufacturers in the production of macroporous cation and anion exchangers. These products are called polymeric adsorbents. They are excellent for removal of limonin [1180-71-8] and naringin [1023647-2], the principal compounds responsible for bitterness in orange, lemon, and grapefruit juices. The adsorbents are regenerated with steam or alcohol. Decaffeination of coffee (qv) and tea (qv) is practiced with the same polymeric adsorbents (28). 

Steam regeneration is most commonly applied to activated carbon that has been used in the removal and/or recovery of solvents from gases. At volatile organic compound (VOC) concentration levels from 500 to 15,000 ppm, recovery of the VOC from the stream used for regeneration is economically justified. Below about 500 ppm, recovery is not economically justifiable, but environmental concerns often dictate adsorption followed by destruction. While activated carbon is also used to remove similar chemicals from water and wastewater, regeneration by steam is not usual. The reason is that the water-treatment carbon contains 1 to 5 kg of water per kg of adsorbent that must be removed by drying before regeneration or an excessive amount of superheated steam will be needed. In water treatment. 

---