Wet sulfuric acid process

The main chemical reaction in the wet (sulfuric acid) process may be represented by the following equation using pure fluorapatite to represent phosphate rock ... 

Wet sulfuric acid process SO2 oxidation catalyst is similar to dry sulfuric acid catalyst (Chapter 8). However, its substrate is stronger so that it can withstand the softening effect of H20(g) (Degerman et al., 2008, Haldor Topsoe, 2008). 

This is the essence of the wet sulfuric acid process, i.e., its use of condensation to produce high-strength sulfuric acid from H20(g)-bearing, low SO2 strength acid plant feed gas. 

Sulfuric acid is produced from sulfur, oxygen and water via the conventional contact process (DCDA) or the wet sulfuric acid process (WSA). 

Wet Process Phosphoric Acid. A production process flow diagram is shown in Figure 8. Insoluble phosphate rock is changed to water-soluble phosphoric acid by solubilizing the phosphate rock with an acid, generally sulfuric or nitric. The phosphoric acid produced from the nitric acid process is blended with other ingredients to produce a fertilizer, whereas the phosphoric acid produced from the sulfuric acid process must be concentrated before further use. Minor quantities of fluorine, iron, aluminum, sUica, and uranium are usually the most serious waste effluent problems. 

Chemetics has developed a process for treating spent alkylation sulfuric acid with nitric acid to produce a sulfuric acid that can be used to acidulate phosphate rock, the major use for sulfuric acid. The organic contaminants are converted to carbon particles that are removed with the gypsum on filtration of the phosphoric acid. Special alloys are used in the fabrication of the acid reactor. Topsoe developed and, by the year 2005 had built, more than 45 Wet Sulfuric Acid (WSA) process units. This process is especially suited for... 

The SNOX process is also known as the WSA-SNOX process when both SO2 and NO are removed or, if only SO2 is removed, as the WSA process where WSA stands for Wet Sulfuric Acid. This process catalytically reduces both the SO2 and the NO in flue gases by more than 95% and, with integration of the recovered heat from the WSA condenser, is reported to have lower operating costs than conventional technologies. No chemical or additive is required other than ammonia for optional NO reduction. Sulfuric add at 93.2% concentration is produced that is said to meet or exceed U.S. Federal Specifications. The SO2 conversion catalyst can tolerate up to 50% water vapor and several hundred ppm of chlorides. CO and hydrocarbon emissions are said to be low (Collins et al., 1991). 

Table 25.1 Industries that use the WSA process (Laursen and Jensen, 2007). Most bum their sulfurous organic by-products with air to form SO2, H20(g), O2, N2, CO2 wet sulfuric acid plant feed. The exception is nonferrous metal extraction which makes SO2, H20(g), O2, N2 feed gas directly. The major sulfur-bearing components in the feed streams are H2S, CS2, and COS. ...

Other wet gas sulfuric acid processes include SULFOX and Sulfacid . SULFOX is comparable to WSA. Sulfacid only treats low, < 1 volume% SO2 gas using activated carbon. 

Figure X.l Schematic of wet gas sulfuric acid process catalyst bed.

Dry nitrocellulose, which bums rapidly and furiously, may detonate if present in large quantities or if confined. Nitrocellulose is a dangerous material to handle in the dry state because of sensitivity to friction, static electricity, impact, and heat. Nitrocellulose is always shipped wet with water or alcohol. The higher the nitrogen content the more sensitive it tends to be. Even nitrocellulose having 40% water detonates if confined and sufftcientiy activated. AH large-scale processes use nitric—sulfuric acid mixtures for nitration (127—132). 

There are numerous variations of the wet process, but all involve an initial step in which the ore is solubilized in sulfuric acid, or, in a few special instances, in some other acid. Because of this requirement for sulfuric acid, it is obvious that sulfur is a raw material of considerable importance to the fertilizer industry. The acid—rock reaction results in formation of phosphoric acid and the precipitation of calcium sulfate. The second principal step in the wet processes is filtration to separate the phosphoric acid from the precipitated calcium sulfate. Wet-process phosphoric acid (WPA) is much less pure than electric furnace acid, but for most fertilizer production the impurities, such as iron, aluminum, and magnesium, are not objectionable and actually contribute to improved physical condition of the finished fertilizer (35). Impurities also furnish some micronutrient fertilizer elements. 

The precipitated cellulose acetate is filtered from the dilute (25—36%) acetic acid. The acetic acid and salts remaining from the sulfuric acid neutrali2ation are removed by washing. The wet polymer is typically dried to a moisture content of 1—5%. The dilute acetic acid obtained from the washing and precipitation steps caimot be used in other stages of the process. Its efficient recovery and recycle are an economic necessity. 

In a typical commercial dry jet-wet spinning process, PPT polymer of inherent viscosity 6.0 dL/g is added to 99.7% sulfuric acid in a water-jacketed commercial mixer in a ratio of 46 g of polymer to 100 mL of acid. The mixture is sealed in a vacuum of 68.5—76 mL of mercury. Mixing takes place for 2 h... 

Battery breaking technologies use wet classification to separate the components of cmshed batteries. Before cmshing, the sulfuric acid is drained from the batteries. The sulfuric acid is collected and stored for use at a later stage in the process, or it may be upgraded by a solvent extraction process for reuse in battery acid. 

Separation and Recovery of Rare-Earth Elements. Because rare-earth oxalates have low solubihty in acidic solutions, oxaUc acid is used for the separation and recovery of rare-earth elements (65). For the decomposition of rare-earth phosphate ores, such as mona ite and xenotime, a wet process using sulfuric acid has been widely employed. There is also a calcination process using alkaLine-earth compounds as a decomposition aid (66). In either process, rare-earth elements are recovered by the precipitation of oxalates, which are then converted to the corresponding oxides. 

Manufacture. Phosphoric acid, H PO, is the second largest volume mineral acid produced sulfuric acid is the first. The greatest consumption of phosphoric acid is in the manufacture of phosphate salts, as opposed to direct use as acid. Markets are differentiated according to the purity of the acid. Phosphoric acid is produced commercially by either the wet process or the thermal (furnace) process. Thermal acid, manufactured from elemental... 

Wet-process acid is manufactured by the digestion of phosphate rock (calcium phosphate) with sulfuric acid. Depending on availabiHty, other acids such as hydrochloric may be used, but the sulfuric-based processes are by far the most prevalent. Phosphoric acid is separated from the resultant calcium sulfate slurry by filtration. To generate a filterable slurry and to enhance the P2O5 content of the acid, much of the acid filtrate is recycled to the reactor. 

Phosphoric acid (wet-process) 28% (20% P20 ), sulfuric acid 20—22%, duoride approx 1—1.5%, probably as hydroduosHicic acid temperature 82—110°C, average 93°C and duration of test 42 days, moderate aeration, agitation by convection only. 

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