Stripping absorption

Anodic Stripping Voltammetry Cathodic Stripping Voltammetry Absorptive Stripping Voltammetry... 

In adsorptive stripping voltammetry the deposition step occurs without electrolysis. Instead, the analyte adsorbs to the electrode s surface. During deposition the electrode is maintained at a potential that enhances adsorption. For example, adsorption of a neutral molecule on a Hg drop is enhanced if the electrode is held at -0.4 V versus the SCE, a potential at which the surface charge of mercury is approximately zero. When deposition is complete the potential is scanned in an anodic or cathodic direction depending on whether we wish to oxidize or reduce the analyte. Examples of compounds that have been analyzed by absorptive stripping voltammetry also are listed in Table 11.11. 

Natural gas contains both organic and inorganic sulfur compounds that must be removed to protect both the reforming and downstream methanol synthesis catalysts. Hydrodesulfurization across a cobalt or nickel molybdenum—zinc oxide fixed-bed sequence is the basis for an effective purification system. For high levels of sulfur, bulk removal in a Hquid absorption—stripping system followed by fixed-bed residual clean-up is more practical (see Sulfur REMOVAL AND RECOVERY). Chlorides and mercury may also be found in natural gas, particularly from offshore reservoirs. These poisons can be removed by activated alumina or carbon beds. 

Fixed-bed desulfuri2ation is impractical and uneconomical if the natural gas contains large amounts of sulfur. In this case, bulk sulfur removal and recovery (qv) in an acid gas absorption—stripping system, followed by fixed-bed residual cleanup is usually employed. 

G. Absorption, stripping, distillation, counter-current. Hi, and Hq, random packings, Cornell et al. correlation, and Belles and Fair correlation... 

Equipment Absorption, stripping, and distiUation operations are usually carried out in vertical, cylindrical columns or towers in which devices such as plates or packing elements are placed. The gas and liquid normally flow countercurrently, and the devices serve to provide the contacting and development of interfacial surface through which mass transfer takes place. Background material on this mass transfer process is given in Sec.. 5. 

For absorption, stripping, and distillation, there are three main steps involved in design ... 

Data on the gas-liquid or vapor-liquid equilibrium for the system at hand. If absorption, stripping, and distillation operations are considered equilibrium-limited processes, which is the usual approach, these data are critical for determining the maximum possible separation. In some cases, the operations are are considerea rate-based (see Sec. 13) but require knowledge of eqmlibrium at the phase interface. Other data required include physical properties such as viscosity and density and thermodynamic properties such as enthalpy. Section 2 deals with sources of such data. 

Spray chamber Cocurrent, cross-flow, countercurrent Differential Gas Absorption, stripping, humidification, dehi i midi ficati o n... 

Line mixer Cocurrent Differential Liquid or gas Absorption, stripping... 

For sieve or valve plates, h = h , outlet weir height. For bubble-cap plates, h = height of static seal. Tbe original references present vaH-dations against laboratoiy and small-commercial-column data. Modifications of tbe efficiency equation for absorption-stripping are also included. 

Introduction Packed columns for gas-liquid contacting are used extensively for absorption, stripping, and distillation operations. Usually the columns are filled with a randomly oriented packing material, but for an increasing number of applications the packing is very care-... 

Figure 8-57. Flow diagram of absorption-stripping for hydrocarbon recovery from gaseous mixture. Used by permission, Edmister, W. C., Petroleum Erjgr., Sept. (1947) to January (1948).

When choosing a separation technique (azeotropic distillation, absorption, stripping, liquid-liquid extraction, etc.), the use of extraneous mass-separating agents should be avoided for the following reasons ... 

The most widely used amine is monoethanolamine (MEA), which is considered as a benchmark solvent because of its high cyclic capacity, significant absorption-stripping kinetic rates at low C02 concentration and high solubility in water. Some other amine-based solvents such as diethanolamine (DEA), triethanolamine (TEA), diglycolamine (DGA), N-methyldiethanol-amine (MDEA), piperazine (PZ), 2-amino-2-methyl-l-propanol (AMP) and N-(2-aminoeth-yl)piperazine (AEP) have also traditionally been utilised. 

Quentel et al. [294] complexed copper with l,2-dihydroxyanthraquinone-3 sulfuric acid prior to determination by absorptive stripping voltammetry in amounts down to 0.3 nM in seawater. 

To determine down to 6 ppt of lead in seawater Wu and Batley [404] used absorptive stripping voltammetry with ligand competition using xylenol orange. 

Vega and Van den Berg [601] determined vanadium in seawater in amounts down to 70 pM by absorptive stripping voltammetry. 

Sodium citrate was recognized as a potential aqueous absorbent for absorption/stripping as early as 1934 (3, 4). It has recently reappeared in work by the U. S. Bureau of Mines (5), in process development sponsored by Peabody, Inc., and in a process offered by Flakt, Inc. (6). This paper reports on work which is part of a development program on absorption/stripping sponsored by the Electric Power Research Institute. 

In a perfectly-buffered solution the SO2 vapor pressure will be directly proportional to the total concentration of SO2 and bisulfite, giving a linear equilibrium relationship. In simple alkali sulfite solution without added buffer, the equilibrium relationship is highly nonlinear, because H-1" accumulates as SO2 is absorbed. Under these conditions is it not possible to carry out reversible SO2 absorption/stripping in a simple system, resulting in greater steam requirements than expected with a linear equilibrium relationship. Weak acid buffers such as sodium citrate have been proposed to "straighten" the equilibrium relationship and thereby reduce ultimate steam requirements (Jl, 2, 7). Citrate buffer is attractive because it is effective over a wide range, from pH 2.5 to pH 5.5 in concentrated solutions. 

Figure 7. Minimum steam requirement, simple absorption/stripping with live steam, 3000 ppm SOg in at 55°C, 90% removal, I.OM. citrate, 2.0M Na...

The steam requirement for simple absorption/stripping with 90% removal of S02 from stack gas containing 3000 ppm S02 at 55°C was estimated to be about 40 kg/kg SOj. 

These distinctions between the two operations are partly traditional. The equipment is similar, and the mathematical treatment, which consists of material and energy balances and phase equilibrium relations, also is the same for both. The fact, however, that the bulk of the liquid phase in absorption-stripping plants is nonvolatile permits some simplifications in design and operation. 

Figure 13.15. Mechanism, nomenclature, and constructions for absorption, stripping and distillation in packed towers, (a) Two-film mechanism with equilibrium at the interface, (b) Sketch and nomenclature for countercurrent absorption or stripping in a packed tower, (c) Equilibrium and material balance lines in absorption, showing how interfacial concentrations are found, (d) Equilibrium and material balance lines in stripping, showing how interfacial concentrations are found, (e) Equilibrium and material balance lines in distillation, showing how interfacial concentrations are found.

Tray column Cross-flow, countercurrent Integral Liquid and/or gas Distillation, absorption, stripping, DCHT, washing... 

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