CO2 scrubbing

An ultasensitive simultaneous multi-element method of determination for As, Se, Sb and Sn in aqueous solution, consists of hydride generation, collection in a cryogenic trap and end analysis by GC-PID (photoionization detector) LOD ca 1 ng Sn/L for a 28 mL sample. No drying or CO2 scrubbing is necessary before the cold trap35. 

The gas composition is optimized with DOFs outside the CO2 scrubbing system with regard to inert composition (methane and argon) and hydrogen to nitrogen ratio since the levels of these components affect downstream (ammonia synthesis) reaction kinetics. Improved kinetics at lower inert levels are achieved at the expense of using more fuel or feedstock, since lower inerts can be achieved by firing the primary... 

In the process depicted in figure 1.2, coffee beans charged to the extractor, 10, via line (18) are decaffeinated with supercritical carbon dioxide. The caffeine-laden CO2 stream leaving the extractor is passed into the bottom of a water-wash column where the caffeine is removed from the CO2. (Chapter 8 describes the thermodynamic equilibrium situation for the water-wash column.) The caffeine-free CO2 is recycled to the coffee bean column, and decaffeinated coffee beans leave the extractor via line 20. Let s now follow the water stream leaving the bottom of the CO2 scrubbing tower. The caffeine-... 

These results demonstrate the appreciable electrostatic effects - as well as extremely high enhancement factors - in CO2 transport in highly alkaline solutions. It is interesting to note that the importance of the same phenomenon in CO2 scrubbing with caustic solutions was recognized long ago by several investigators (14,15,16). 

If CO2 sources with low partial pressure (< 1 bar) are utilised an additional process step for the extraction or enrichment of the CO2 has to be applied upstream of the liquefaction unit. Most commonly an absorption process (CO2 scrubbing) is used but a pressure swing adsorption (PSA) process (cf Section 5.2.3.4) or a combination of partial condensation and wash unit can also be applied. 

Do some reading and discuss the major approaches available for CO2 scrubbing from atmospheric air. Is the major impediment to application of this to AFCs efficiency of conversion, cost of the approach, bulk, or something else ... 

These reactions are used industrially for scrubbing operations and for selective removal of H2S from natural gas containing CO2. 

The solubilities of the various gases in [BMIM][PFg] suggests that this IL should be an excellent candidate for a wide variety of industrially important gas separations. There is also the possibility of performing higher-temperature gas separations, thanks to the high thermal stability of the ILs. For supported liquid membranes this would require the use of ceramic or metallic membranes rather than polymeric ones. Both water vapor and CO2 should be removed easily from natural gas since the ratios of Henry s law constants at 25 °C are -9950 and 32, respectively. It should be possible to scrub CO2 from stack gases composed of N2 and O2. Since we know of no measurements of H2S, SO, or NO solubility in [BMIM][PFg], we do not loiow if it would be possible to remove these contaminants as well. Nonetheless, there appears to be ample opportunity for use of ILs for gas separations on the basis of the widely varying gas solubilities measured thus far. 

A process stream containing mostly nitrogen and carbon dioxide is to be scrubbed with 10% (wt) NaOH for CO2 removal, but not recovery. The requirements are ... 

The quenched gas passes to an H2S removal stage where it may be assumed that H2S is selectively scrubbed down to 15 parts per million with substantially nil removal of CO2. Solution regeneration in this process is undertaken using the waste low-pressure steam from another process. The scrubbed gas, at 35°C and saturated, has then to undergo CO conversion, final H2S removal, and CO2 removal to allow it to meet the product specification. 

Figure 1 shows how acid-gas-bearing process gases can be generally treated in industrial processes. The sulfur compounds and CO2 may be absorbed in a liquid medium, such as amines, alkali salts (NaOH, K2CO3), physical solvents (methanol, propylene carbonate), or water (3). The absorbed acid gases are released by reduction of pressure and/or by application of heat. Alternatively, the H2S and CO2 may chemically combine with the absorbent (as in NaOH scrubbing) to form salts which are removed in a liquid treatment unit. This requires continual and expensive makeup of sodium to the system. 

The raw gas is purified in the Lurgi Rectisol process (cold methanol scrubbing) where various by-products (eg tar naphthas) and impurities (eg CO2 and H2S) are removed. 

In the gasifiers the sulphur present in the coal is converted to H S which is scrubbed out, together with the C0 in the downstre Rectisol unit. The effluent stream from this unit (typically 1.5 % HpS in CO2) is treated in a homogeneous catalytic process in which tne H S is converted to high grade elemental sulphur. The catalytic liquor consists essentially of an alkaline vanadium solution. In the... 

In the coal gasification, as well as in the FT process massive amounts of CO are inevitably produced. CO is the main component of the off-gas in the Sulphur recovery plarft (see above) and in the Benfield plant (which scrubs CO2 from the Synthol tailgas). The latter source is the purer of the two. CO is used in fire extinguishers and the production of "dry ice". 

The exothermicity of reaction 9.7 dictates a low temperature (450 °C or less) and use of a catalyst (Fe203/Al203, usually) if good yields are to be obtained in a reasonable time. Usually, the reaction is carried out in two steps. First temperatures of 450 to 500 °C are used and a substantial degree of conversion quickly results. Then the temperature is dropped to about 200 °C to optimize the yield. The C02 is removed by scrubbing the gas with water, in which CO2 is much more soluble than H2. 

There are many factors that affect the recirculating water actual or measured pH (pHactuai) in recirculating cooling systems. The major factors are usually considered to be the source and quality of the makeup water, the operating conditions of the cooling system, and the partial pressure of the CO2 in the air. (As the air is continually scrubbed by the cooling water, this in effect means the carbonate-bicarbonate/C02 equilibrium). 

The example CO2 capture process, shown in Figure 8 as an Aspen Plus EO model representation, is part of an ammonia plant. Designed to scrub CO2 from ammonia synthesis gas, it includes an absorber and two solution regeneration columns, one stripping the rich, C02 laden solution leaving the absorber to semilean concentration of absorbed CO2, and the other cleaning the solution even further to lean solution... 

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