Benfield-Amine process

Different variations of the hot carbonate process exist (e.g., Catacarb and Benfield) based on proprietary catalyst used to enhance the rate of reactions, for example, formaldehyde, arsenite, and hypochlorite. The activation by catalysts is apparently necessary to make the process economical compared with the amine-based processes. 

CO conversion is achieved in the HT and LT shift over standard catalyst, while C02 is removed either in the BASF-aMDEA, the UOP-Benfield or the UOP-Amine Guard process. Remaining carbonoxides are reconverted to methane in catalytic methanation to trace ppm levels. 

A minor variant to the amine scrubbing process described above is the Sulfinol process, which still uses an alkanolamine base, diisopropanolamine (35%), but in a solvent consisting of a mixture of sulfolane (40%), tetramethy-lene sulfone (CH2)4S02, a good hydrogen sulfide solvent) and water [29]. Other processes are based on hydrogen sulfide absorption in aqueous alkaline carbonate solutions, such as the Catacarb and Benfield systems (Eqs. 9.16 and 9.17). 

Hot carbonates are well suited for the removal of C02 at moderate or high levels in the presence of little or no H2S. The process acquired its name from the use of elevated temperatures in both the absorber and the regenerator (110—115°C). Hot carbonates such as the Benfield and the Koppers Vacuum Carbonate utilize K2C03 to remove H2S, COS, and C02 from gas streams [35]. Their heat requirements and high solvent circulation make hot carbonates more expensive than other acid gas removal processes. Other hot carbonate processes, including the Catacarb and the Giammarco-Vetrocoke processes, use catalysts, corrosion inhibitors, and/or activators to enhance the removal of the acid gases. Hot carbonate-promoted systems are able to decrease the C02 level from 1% to 0.1%. Promoters include DEA, amine borates, and hindered amines [36]. 

In older units, CO2 is removed with an absorber containing an amine, Sulfinol , Rectisol or by the Benfield process, which uses hot potassium carbonate. Recovered CO2 can be sold as a product. 

Figure 5-5. Flow diagram of Benfield Hi-Pure process with LoHeat system. A = cooled lean solution B = main solution stream C = rich solution D = lean amine E = rich amine 1 = feed gas 3 = acid gas. (UOP, 1993j...

The Flexsorb HP Process is a promoted hot potassium carbonate process developed and licensed by Exxon Research and Engineering Company. Four commercial plants using the process were reported to be in operation in 1992 (Exxon, 1992). The proeess is similar, with regard to flow schemes and general applications, to the activated Benfield and Cataearb proeesses. It is characterized by the use of a sterieally hindered amine as the activator. 

Several revamp options are available for modification of the carbon dioxide removal section depending on the type of carbon dioxide removal process. The processes mostly used in ammonia plants are chemical absorption processes based on either hot potassium carbonate (HPC) such as Benfield, or Vetrocoke, or amine solutions such as MEA. The chemical carbon dioxide removal processes may be improved or replaced with a physical process in which the absorbent is regenerated by simply flashing off carbon dioxide. In this way the need for regeneration heat may be reduced or eliminated. A physical carbon dioxide removal system may result in energy savings of 0.01-0.35 Gcal/MT ammonia. 

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