Reactors sulphuric acid production

Main reactor with lead lining Reaction of AH with sulphuric acid Production affected severely Immediate repairs required... 

In the chemical process industry molybdenum has found use as washers and bolts to patch glass-lined vessels used in sulphuric acid and acid environments where nascent hydrogen is produced. Molybdenum thermocouples and valves have also been used in sulphuric acid applications, and molybdenum alloys have been used as reactor linings in plant used for the production of n-butyl chloride by reactions involving hydrochloric and sulphuric acids at temperatures in excess of 170°C. Miscellaneous applications where molybdenum has been used include the liquid phase Zircex hydrochlorination process, the Van Arkel Iodide process for zirconium production and the Metal Hydrides process for the production of super-pure thorium from thorium iodide. 

For processes that are well established, estimates of the reactor performance can often be obtained from the general and patent literature for example, the production of nitric and sulphuric acids. 

Waste characterized by the following elements i.e. carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur and chlorine would be oxidized in the presence of oxygen and water at temperatures above 374 °C and pressures above 221 bar in a batch-reactor to the following reaction products water, carbon dioxide, nitrogen, phosphorus acid, sulphuric acid and chlorine acid. 

The production of sulphuric acid was commercialised in the mid-18th century. In the so-called lead chamber process the oxidation of SO2 into SO3 was catalysed by NO. The acid produced is not very concentrated. The raw material used was elemental sulphur from Sicily. Later, pyrite was used because of its lower price. One of the consequences was a much higher impurity level in the feed to the reactor. As early as 1831 a process was patented in which SO2 was oxidised in the presence of finely divided platinum. The commercial application, however, was strongly delayed due to technical difficulties, the major one being catalyst poisoning. 

Although hardwoods have a lower lignin content and so give a higher yield of sugars, softwoods are preferred where ethanol is the desired end product. This is because hardwoods have more pentose sugars, which are not readily fermented by common yeasts. In a typical batch process sawdust and wood chips are loaded into the reactor vessel and treated with dilute sulphuric acid (0.5% concentration) at temperatures between 130 and 200°C for about three hours. Ideally, the sugars should be removed from the reaction zone before they, in turn, have time to break down. 

In this study protonated large pore zeolites of different structures (HY, HBeta and HMordenite) and framework Si-to-Al ratios were used in liquid phase in a batch reactor. The zeolites were calcined at 500°C and the hydrolysis was conducted at 75°C. The procedure was optimised in terms of solvent, activation, type and amount of catalyst for the hydrolysis of nitroacetanilides, currently carried out with 10 % sulphuric acid [14], and then extended to other substituted amides. The reaction, followed by GC with nitrobenzene as internal standard, was clean and no by-products or degradation were detected. 

Cyclization of 2 in concentrated sulphuric acid [14-16] predominantly leads to p-ionone (17). The reaction proceeds rapidly even below room temperature and, to avoid secondary reactions, is carried out continuously. The precooled streams of sulphuric acid and the solution of 2 in petroleum ether or liquid CO2 are mixed in a reactor and then quenched with cold water. Small amounts of a-ionone (18) can be separated off by distillation during isolation of the product. In the cyclization step large amounts of approximately 40% aqueous sulphuric acid are produced. Treatment to deal with this is expensive but is essential for environmental reasons. Organic impurities are broken down to carbon dioxide in a cracking furnace with heavy oil burners. In the course of this process, sulphuric acid is thermally converted into sulphur dioxide, which is reoxidized in the contact plant. 

Alumina hydrate (AH) (as powder or in bags) is taken up by a hoist and kept at charging floor. 98.3 % iron-free sulphuric acid is pumped to the day tank. Treated water is stored in feed tank. Measured quantities of acid and water are fed to the reactor at a controlled rate for a particular batch. There is rise of temperature due to the dilution of the acid. AH is slowly fed into the reactor. Steam is supplied (from WHRB or oil-fired boiler) to the reactor coils to complete the reaction. Samples of the product are taken and tested for purity if any unreacted AH is remaining. Steam is kept on for some more time. The hot product is drained out to mould and allowed to solidify (Table 16.2). 

Dilution of sulphuric acid and sending to feed tank for mixer (reactor) For reaction with rock phosphate If the dilution unit or transfer pump fails, the production rate is affected Keep sufficient spares ready always... 

Continuous sulphuric acid breakdown processes are possible in which the acid and ore are fed together at the top of a rotating, inclined, heated kiln. The reaction products and excess sulphuric acid can then be removed continuously from the lower end. It is necessary that the reactants and products shall not be sufficiently mobile for by-passing to take place when flowing down the reactor, otherwise residence times will vary widely about the mean value. A kiln of this type resembles that commonly used for the manufacture of hydrofluoric acid by the reaction of sulphuric acid with fluorspar (calcium fluoride). 

There are three basic stages to the process, shown in Figure 11.9, external to the electrolysis section. SO2 is absorbed and reacts with the bromine. The reactor product solution is then concentrated by evaporation using the sensible heat contained in the entering flue gas. All the HBr and the majority of the water are vaporised and an 80% to 85% sulphuric acid solution is produced. The desulphurised gas leaving the reactor is scrubbed with water to remove the HBr and the acid droplets. In the ISPRA plant the total electrode surface area is 64 m. The current density of operation is 2000 A m and at a temperature of 50°C the cell voltage is between 1.3-1.4 V and the current efficiency for bromine production is 90%. 

Moisture in the air gives rise to the formation of sulphuric acid and oleum, leading to corrosion throughout the plant and causing inferior product qu ity, in terms of colour and other undesired by-products (e.g. dioxane in alcohol ethoxy late sulphates) if condensed oleum reaches the reactor. 

A good example where process intensification has the potential to transform a complete plant operation centres on the manufacture of sulphuric add. This can be seen from a study of the SO3/H2SO4 contact process. In order to appreciate the potential impact this approach could have on a well-estabhshed process, it is worth discussing the flow sheet for the manufacture of sulphuric acid/oleum. A sulphur burner produces SO2 which is then reacted over vanadium pentoxide catalyst at 1 bar to produce gaseous SO3. This is then absorbed in recycling sulphuric acid to give product oleum. As is often the case, the reactor is the heart of the process. 

For example in Fig. 4-2 we have three splitters SI (dry air), S2 (gas products from reactor R), and S3 (sulphuric acid from absorber A2). The inlet resp. outlet streams are... 

---