Caustic concentration

Data, for a 32% caustic concentration at 90°C and a current efficiency of 96.0%, obtained in laboratory cells using a DSA anode and an activated cathode, where the membrane is against the anode at a 3-mm gap. 

In a caustic scmbbing system, caustic potash, KOH, is preferred to caustic soda, NaOH, because of the higher solubiUty of the resulting potassium fluoride. Adequate solution contact and residence time must be provided in the scmb tower to ensure complete neutralization of the intermediate oxygen difluoride, OF2. Gas residence times of at least one minute and caustic concentrations in excess of 5% are recommended to prevent OF2 emission from the scmb tower. 

Electrolytic Oxidation. Electrolytic oxidation of ferromanganese or manganese metal is a one-stage process that circumvents the problem of ore impurities. Moreover, this procedure can be used with low caustic concentrations at room temperature. This process is based on the following... 

In dmm boilers sodium hydroxide (caustic), sodium phosphate, or both may be added for pH and scale control. Sodium hydroxide is used more in Europe than in the United States, where sodium phosphate treatment is usually preferred. In boilers operating above 4 MPa (580 psia), caustic concentrations must be carefully controlled to prevent highly corrosive deposits from forming. In the lowest pressure boilers, phosphate treatment may be used to compensate for lower purity feedwater. As the boiler pressure increases, the allowable phosphate concentration decreases, and at 16.5 MPa (2400 psia) or above, equiUbrium phosphate treatment may be used. In this treatment, caustic is added to a low phosphate concentration in the boiler to maintain the proper pH (20). 

Caustic corrosion (gouging) occurs when caustic is concentrated and dissolves the protective magnetite (Fe O layer. Iron, in contact with the boiler water, forms magnetite and the protective layer is continuously restored. However, as long as a high caustic concentration exists, the magnetite is constantiy dissolved, causing a loss of base metal and eventual failure (Fig. 4). 

This results in the prevention of caustic buildup beneath deposits or within a crevice where leakage is occurring. Caustic corrosion (and caustic embrittlement, discussed later) does not occur, because high caustic concentrations do not develop. 

Copper alloys are attacked hy ammonium hydroxide, but corrosion rates increase only moderately with caustic concentration. 

Carbon steel Concentrated caustic Concentrated nitrate solutions Anhydrous ammonia Carbonate and bicarbonate solutions... 

For example, if tube failure occurs due to caustic gouging corrosion, the root causes are most likely related to the effects resulting from the availability offree sodium hydroxide in the BW, coupled with the development of localized caustic concentration. Control generally requires a twofold approach to remove the causes of this particular problem ... 

An operational change because caustic concentration typically results when high-firing cycle operations permit departure from nucleate boiling (DNB) to occur... 

Sodium hydroxide Caustic soda NaOH Caustic concentrates in porous deposits, resulting in caustic gouging and SCC. 

The oxidative dehydrogenation of ethanolamine to sodium glycinate in 6.2 M NaOH was investigated using unpromoted and chromia promoted skeletal copper catalysts at 433 K and 0.9 MPa. The reaction was first order in ethanolamine concentration and was independent of caustic concentration, stirrer speed and particle size. Unpromoted skeletal copper lost surface area and activity with repeated cycles but a small amount of chromia (ca. 0.4 wt%) resulted in enhanced activity and stability. 

Bansal, V.K. Chan, K.S. McCallough, R. Shah, D.O. The Effect of Caustic Concentration on Interfacial Charge, Interfacial Tension and Droplet Size A Simple Test for Optimum Caustic Concentration for Crude Oils, J. Canadian Petrol. Tech. 1978,17(1), 69. 

Caustic concentration versus voltage and current efficiency... 

The hypochlorite produced has an active chlorine concentration of 160-180 g l-1 and a free caustic concentration of 4-8 g l-1. Figure 25.1 illustrates the simplified layout of the two-step chlorine destruction unit. All measurements are carried out under steady-state conditions under different peak loads of chlorine. 

Chlorine dioxide can be formed out of the chlorite by either of the reactions described by Equation 25.3 or 25.8. Equation 25.1 describes the chlorite formation. The chlorine concentration in the liquid is normally very low as the reaction with caustic (Equation 25.4) is very fast. The concentration of chlorine and/or hypo-chlorous acid HOCl can increase on depletion of hydroxide ions in the liquid. As in step two of the hypochlorite unit, the caustic concentration is in the order of 4-10 g l-1 and it is possible to conclude that at the gas-liquid interface the concentration might be quite low owing to the fast reaction with chlorine. 

Measurements taken in the plant show that the formation of chlorine dioxide is dependent on temperature, production capacity, hypochlorite concentration, caustic concentration and residence time of the hypochlorite in the reactor at step one. 

Fig. 25.3 Emission of chlorine dioxide as a function of NaOCI concentration and free caustic concentration. 

A further experiment was performed with an extremely high caustic concentration of 38 g l-1 and an active chlorine concentration of 160 g L1. The results are shown in... 

Fig. 25.6. A free caustic concentration increased to 38 g l-1 constitutes a level that is about 32 g l-1 higher than normal and the C102 emission peak reduces by about a factor of four however, there is still a peak. In the measurements completed in the experiments described in this section no relationship was found between C102 emission and chlorate concentration in the hypochlorite solution. 

The effects of the steady-state situation and the effect of the peak load can be described using a model. When the caustic concentration is low, either through initial concentration effects or by mass transfer limitations, the reaction of chlorine with chlorite can occur and chlorine dioxide (Equations 25.3 and 25.8) is formed near the gas-liquid interface. The concentration of chlorite seems quite important and is influenced by temperature (decomposition) and the hypochlorite concentration. A higher chlorite concentration will give, according to the reactions of Equations 25.3 and 25.8, a higher chlorine dioxide content in the presence of chlorine and/or hypochlorous acid. 

The emission is very strongly dependent on the temperature. At 30°C the emission is about eight times the emission at 10°C. The reason for this strong dependency is not quite understood. The reaction of chlorine with caustic is enhanced, however, and this will result in lower caustic concentrations and also lower chlorine concentrations. The quantities of by-products formed, such as chlorite, will become higher as well as the amounts of decomposition products. Solubility in the liquid phase will decrease on increasing temperature but cannot account for the large variations in emission. 

Increasing the free caustic concentration gives higher concentrations at the gas-liquid interface and lower emissions in both the steady-state and peak-load situations. 

When the capacity is increased under the same process conditions the caustic concentration is increased on higher dosing. As the quantity of free caustic in the end-product and in the liquid flow of the jet-loop reactor is the same, the percentage of caustic reacting with chlorine increases by roughly 25-60% when the production capacity is increased. Depletion of caustic at the liquid-gas interface can then occur more easily. 

A scrubber has a closed-loop recycle of caustic. The make-up caustic solution is added continuously on an ORP (oxidation-reduction potential) controller. The caustic concentration will typically be 20 wt% and thus the blow-down stream will contain approximately 15 wt% hypochlorite. Such a system will typically be provided with a large reservoir of caustic that is released on a once-through basis for containment of emergency relief streams or operated with a permanent excess of caustic, resulting in a hypochlorite concentration in the blow-down stream in the range of 6-12 wt%. 

The test plan that was executed at Holston Army Ammunition Plant (HAAP) demonstrated that the hydrolysis process for the energetic materials of interest successfully destroyed more than 99.7 percent of the energetics treated. Over 9,500 pounds of energetic materials were destroyed while encountering only the types of problems normally expected during the implementation of a new facility and process. The suite of tests performed at Los Alamos National Laboratory (LANL) and at HAAP covered a range of reaction temperatures and caustic concentrations. Under all these conditions, the destruction of energetics was carried out safely and effectively. 

Test Run No. Energetics Feed Caustic Concentration (wt %) Agitation Speed (rpm)... 

There was also a dependence on caustic concentration in the evolution of N20 in the runs. The runs at 20 and 25 percent caustic produced higher levels of N20 during the addition phase, peaking at about 800-900 ppm, then tailing off to less than 100 ppm at the end of the run. For the run at 11.3 percent caustic, the level of N20 did not exceed 500 ppm at any time and decreased slowly after the addition phase to about 100 ppm by the end of the run. 

Area 200 control uses a batch controller. Each reactor is monitored and controlled separately. Level sensors and control valves meter the agent, energetics, or propellant along with sodium hydroxide into the empty reactor vessel. Fluid density is used to monitor and control the caustic concentration in the reactor vessel. 

Summary Validation Diagnostic Tools for ICLS, Example 2 The determination of saustic concentration in an aqueous sample containing NaOH (caustic) and salt using NIR spectroscopy is examined in this example. The goal was to cscate a model to predict caustic concentration in aqueous samples with vaniEig salt and temperature levels. The details of the data set used to construct flae calibration model are as follows ... 

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