Concentration of Sulfuric Acid

Sulfuric acid is a very important chemical that is diluted and polluted in most of its industrial applications. The purification and reconcentration of sulfuric acid is an important task of process engineering. 

The basis of any process design is a knowledge of vapor-liquid equilibrium. It is depicted in Fig. 11,1-1 in the form of vapor pressure lines with constant H2SO4 content in the liquid. Up to liquid concentrations of 75 wt% H2SO4, the coexistent vapor consists of pure water. Therefore, the liquid can be concentrated up by single stage distillation (evaporation). The feasible acid concentration is limited by the temperature level of the steam available at the site. Typically, the acid can be heated up to approximately 170°C, that is, at a total operating pressure of 1 bar, equivalent to an acid concentration of 72 wt%. 

At higher product specifications a second evaporation step, which is operated under vacuum, has to be performed. The feasible operating pressure follows from the condition that the vapor (pure water) has to be condensed by water cooling. This constraint sets a minimum temperature of the condensate of approximately 

50°C that is equivalent to a pressure of 0.12 bar (according to the vapor pressure curve of water). Any other cooling agent would be much more expensive. At a maximum bottom temperature of 170°C (set by the available steam) the highest feasible acid concentration is approximately 86 wt%. In this concentration range the vapor contains some SO3. Therefore, the second evaporation step has to be performed in a countercurrent column. 

The process depicted in Fig. 11.1-2 clearly demonstrates that the feasible product quality is determined by the temperature levels of the heating and cooling agents. A 

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Laboratory studies indicate that the reactor yield is a maximum when the concentration of sulfuric acid is maintained at 63 percent. ... 

However, the laboratory data seem to indicate that a constant concentration in the reactor to maintain 63 percent sulfuric acid would be beneficial. Careful temperature control is also important. These two factors would suggest that a continuous well-mixed reactor is appropriate. There is a conflict. How can a well-defined residence time be maintained and simultaneously a constant concentration of sulfuric acid be maintained ... 

Using a batch reactor, a constant concentration of sulfuric acid can be maintained by adding concentrated sulfuric acid as the reaction progresses, i.e., semi-batch operation. Good temperature control of such systems can be maintained, as we shall discuss later. 

Sulfuric Acid. Sulfuric acid is a dense, colorless Hquid at room temperature, having specific gravity as shown in Figure 3 (50). Historically, the concentration of sulfuric acid has been reported as specific gravity (sp gr) in degrees Baumn. In the United States, the Baumn scale is calculated by the following formula ... 

The viscosity of sulfuric acid solutions is plotted in Figure 7 (55) other viscosity data may be found in References 54—60. Surface tension of sulfuric acid solutions is presented in Figure 8 (61). Surface tension of selected concentrations of sulfuric acid as a function of temperature up to the boiling point is given in Reference 62 other data are also available (58,59,63—65). 

Steel tank cats, often lined to minimize iron contamination, are usually employed for high concentrations of sulfuric acid. Bottom outlets or valves are not allowed, nor are internal steam coils. Tank contents must be unloaded via standpipe. Using air pressure to unload is not recommended for safety reasons, but if air pressure is used, gauge pressures should be held at <0.21 MPa (30 psi). 

Sulfates. ThaHous sulfate is a commercial product produced by reaction of the metal with sulfuric acid and concentration of the solution until crystallization begins (9). It reacts with thalHc sulfate, yielding T1 T1 (S0 2 [37475-01-7] and with SO, forming the pyrosulfate, TI2S2O2 [82391-11-5]. ThaHic sulfate is extremely unstable and therefore caimot be isolated. Reaction of thaHic oxide with dilute sulfuric acid results in HT1(S0 2 [15478-75-8] or T1(0H)S04 [37205-71 -3] depending on the concentration of sulfuric acid used. 

The temperature dependence of the open circuit voltage has been accurately determined (22) from heat capacity measurements (23). The temperature coefficients are given in Table 2. The accuracy of these temperature coefficients does not depend on the accuracy of the open circuit voltages at 25°C shown in Table 1. Using the data in Tables 1 and 2, the open circuit voltage can be calculated from 0 to 60°C at concentrations of sulfuric acid from 0.1 to 13.877 m. 

Total acidity and total chlorides can be deterrnined by conventional techniques after hydrolysing a sample. Satisfactory procedures for determining hydrogen chloride and free-sulfiir trioxide are described in the Hterature (18,41). Small amounts of both hydrogen chloride and sulfur trioxide can be found in the same sample because of the equiUbrium nature of the Hquid. Procedures for the direct deterrnination of pyrosulfuryl chloride have also been described (42,43), but are not generally required for routine analysis. Small concentrations of sulfuric acid can be deterrnined by electrical conductivity. 

Investigated is the influence of the purity degree and concentration of sulfuric acid used for samples dissolution, on the analysis precision. Chosen are optimum conditions of sample preparation for the analysis excluding loss of Ce(IV) due to its interaction with organic impurities-reducers present in sulfuric acid. The photometric technique for Ce(IV) 0.002 - 0.1 % determination in alkaline and rare-earth borates is worked out. The technique based on o-tolidine oxidation by Ce(IV). The relative standard deviation is 0.02-0.1. 

It is known that the common austenitic stainless steels have sufficient corrosion resistance in sulfuric acid of lower concentrations (<20%) and higher concentrations (>70%) below a critical temperature. If with higher concentrations of sulfuric acid (>90%) a temperature of 70°C is exceeded, depending on their composition, austenitic stainless steels can exhibit more or less pronounced corrosion phenomena in which the steels can fluctuate between the active and passive state [19]. 

This concentration of sulfuric acid is obtained by mixing concentrated sulfuric acid (sp. gr. 1.84) with water in the ratio of 5 cc. to I cc. 

Table 26 Relative humidities over various concentrations of sulfuric acid at 20°C.

Ester functions are not saponified under these ring opening conditions. However, a trans-a-acetoxy function hinders the epoxide opening reaction and a noticeable decrease in yield is observed in comparison to the cw-a-acetoxy isomer. The ring opening reaction is also dependent on the concentration of sulfuric acid. Polymer formation results when the acid concentration is too low and the reaction is markedly slower with excessive concentrations of acid. A 0.5% (vol./vol.) concentration of acid in DMSO is satisfactory. Ring opening does not occur when ethanol, acetone, or dioxane are used as solvent. 

Certain vertebrates have an astonishing ability to accumulate vanadium in their blood. For example, the ascidian seaworm Phallusia mammilata has a blood concentration of V up to 1900 ppm, which represents more than a millionfold concentration with respect to the sea-water in which it lives. The related organism Ascidia nigra has an even more spectacular accumulation with concentrations up to 1.45% V (i.e. 14 500 ppm) in its blood cells, which also contain considerable concentrations of sulfuric acid (pH 0). One possibility that has been mooted is that the ascidia accumulates vanadate and polyvanadate ions in mistake for phosphate and polyphosphates (p. 528). 

Many acids other than sulfuric acid have been used for the challenging cyclodehydration step. It is important to note that when the concentration of sulfuric acid is below 70%, hydrolysis of the imine or enamine occurs. As previously mentioned, HCl/AcOH, ZnCla, PPA, POCI3, and lactic acid have been successfully applied to promote the cyclization. Chloroacetic acid was found to perform similar to lactic acid. Concentrated HCl, p-TsOH, and have proven beneficial in generating linear... 

A lead storage battery needs sulfuric acid to function. The recommended minimum concentration of sulfuric acid for maximum effectivity is about 4.8 M. A 10.0-mL sample of battery acid requires 66.52 mL of 1.325 M KOH for its complete neutralization. Does the concentration of battery acid satisfy the minimum requirement (Note Two H+ ions are produced for every mole of H2SO4.)... 

It is recommended that the concentration of sulfuric acid in the initial solution be kept at 2-4 mol per liter for the extraction of tantalum, whereas for the extraction of niobium, the concentration of sulfuric acid must be increased to a minimum of 6 mol per liter [458,481]. In some cases, the presence, in the initial solution, of titanium in the form of fluorotitanic acid ensures the successful and selective extraction and purification of tantalum and niobium with no addition of any other mineral acid [482]. 

Influence of the Concentration of Sulfuric Acid on the Rate of Nitration in... 

Fig 7a Influence of temperature on the yield of DNT, Nitration of o- and p-nitrotoluenes in nitrating mixtures with various concentrations of sulfuric acid (Kobe, Skinner and Prindle, Ref 45)... 

SPFM experiments were performed on sulfuric acid deposited on the surface of aluminum films on silicon. A macroscopic droplet was first deposited and then rapidly dispersed using a jet of gas. This produced submicrometer-sized droplets. The initial concentration of the sulfuric acid ranged from 20 to 98 wt.%. However, the acid droplets equilibrate rapidly with the ambient water vapor. For example, at room temperature and RH = 30%, the concentration of sulfuric acid is 55 wt% at 90% RH, it is 20 wt%. The increase in droplet volume as they equilibrate with the ambient humidity is shown in Figure 35. 

The occurrence of the excess H+ ions so produced, along with the incoming SOf ions, is equivalent to an increased concentration of sulfuric acid at the anodic region. The total acidity at the anode and the cathode, taken together, remains constant. The final result namely, the evolution of 2 volumes of hydrogen at the cathode and of 1 volume of oxygen at the anode, is equivalent to the electrolysis of water. To see more clearly how the 2 1 volume... 

Nitrotoluene may be oxidized by means of strong nitric acid,2 chromic acid mixture,3 or permanganates.4 Electrolytic oxidation 5 has also been proposed. The procedure given above involves the use of chromic acid mixture, but, owing to a change in the concentration of sulfuric acid, the time of reaction is greatly shortened and the preparation is thus considerably improved. 

The Biocat II technology is an improvement of the Biocat process (U.S. Patent 5,076,927), which treats acid mine drainage and heap leach effluents. The improvements were made under a Phase I Small Business Innovation Research (SBIR) grant funded by the Defense Advanced Research Projects Agency, a component of the U.S. Department of Defense (D10362Y, p. 4). If adequate concentrations of sulfuric acid are not present, additional acid may be required to operate the process. 

Biocat is designed to operate in environments containing sulfuric acid. If adequate concentrations of sulfuric acid are not present, additional acid may be required to operate the process. 

Although infrequent, low concentrations of sulfuric acid could carry over from acid processing or alkylation. 

The concentration of sulfuric acid in SSA is typically 50-80 wt% under mid- and low-latitude stratosphere conditions. However, as the temperature drops, these particles take up increasing amounts of water, which dilutes the particles to as low as 30 wt% H2S04. Gaseous nitric acid is also absorbed by these solutions, forming ternary H2S04-H20-HN03 solutions with as much as 30 wt% in each acid. 

In the 78-92% range of concentration of sulfuric acid, the molar absorptivity of 5-(hydroxymethyl)-2-furaldehyde increases at an average rate of 4% per 1% change in the concentration of the acid the wavelength of the absorption maximum changes from 290 to 320 nm. 

Infrared spectra suggested that a sulfate ion coordinates to two titanium atoms as a bidentate in particles. The maximum particle size was found at Aerosol OT mole fraction of 0.35 in the mixtures. The particle size increased linearly with increasing the concentration of sulfuric acid at any Wo, but with increasing Wo the effect was the opposite at any sulfuric acid concentration. These effects on the particle size can be explained qualitatively in relation with the extent of number of sulfate ions per micelle droplet. These precursor particles yield amorphous and nanosized TiO particles, reduced by 15% in volume by washing of ammonia water. The Ti02 particles transformed from amorphous to anatase form at 400°C and from anatase form to rutile form about at 800°C. In Triton X-100-n-hexanol-cyclohexane systems, however, spherical and amorphous titanium hydroxide precursor were precipitated by hydrolysis of TiCl4 (30). When the precursor particles were calcinated,... 

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