Oleum vapor pressure

There are significant differences in various data sets pubtished for oleum vapor pressure. A review of existing vapor pressure data plus additional data from 10 to 8600 kPa (1.45 to 1247 psi) over the entire concentration range of oleum is available (93), including equations for vapor pressure versus temperature. Vapor pressure curves for oleum calculated from these equations are shown in Figure 19. Additional vapor pressure data from 0.06 to 14 kPa (0.5—110 torr) is given in the titerature (92). 

Oleum Ma.nufa.cture, To produce fuming sulfuric acid (oleum), SO is absorbed in one or more special absorption towers irrigated by recirculated oleum. Because of oleum vapor pressure limitations the amount of SO absorbed from the process gas is typically limited to less than 70%. Because absorption of SO is incomplete, gas leaving the oleum tower must be processed in a nonfuming absorption tower. 

At atmospheric pressure, sulfuric acid has a maximum boiling azeotrope at approximately 98.48% (78,79). At 25°C, the minimum vapor pressure occurs at 99.4% (78). Data and a discussion on the azeotropic composition of sulfuric acid as a function of pressure can also be found in these two references. The vapor pressure exerted by sulfuric acid solutions below the azeotrope is primarily from water vapor above the azeotropic concentration S03 is the primary component of the vapor phase. The vapor of sulfuric acid solutions between 85% H2S04 and 35% free S03 is a mixture of sulfuric acid, water, and sulfur trioxide vapors. At the boiling point, sulfuric acid solutions containing <85% H2S04 evaporate water exclusively those containing >35% free S03 (oleum) evaporate exclusively sulfur trioxide. 

Lewis and Bigeleisen,71 who first determined the Hammett acidity function values for oleums, used a method to derive them from the vapor pressure measurements. Brand et al.,72 however, subsequently by the use of nitro compound indicators showed that the H0 values are not directly related to the vapor pressure. The most accurate Ho values for oleums so far have been published by Gillespie et al.7 (Table 2.4). 

The procedure for making SO -solvent complex from fuming sulfuric acid is more complicated, but less likely to arouse suspicion since fuming sulfuric acid has a lot more uses than Sulfan. It is also far more likely to be available via the five-finger discount method. Fuming sulfuric acid comes in a variety of strengths, but the ACS reagent contains 30% SO3 or oleum. Pure SO boils at 45 °C, and at room temperature has a vapor pressure of over 400 mm Hg. That is why the stuff fumes, and why the stuff can be removed from the sulfuric acid... 

Fig. 1. Flow diagram of production of sulfur dioxide from oleum 1, 30% oleum exchanger 2, SO vaporizer 3, reactor 4, coolant surge tank 5, coolant ckculatkig pump 6, coolant exchangers 7, sludge and acid pump 8, scmbber 9, SO2 cooler 10, gas cleaner 11, SO2 compressor 12, pulsation damper and 13, SO2 condenser. CM is the condensate FRC, flow recording controller PIC, pressure kidicatkig controller SM, steam TC, temperature recorder ...

Cooling water supply failure to 65% oleum cooler Possibility of high pressure in 65% oleum tower Release of SO3 vapors from vent scrubber Audio-visual tilarm to be activated... 

High pressure in SO3 condenser and chance of release of uncondensed SO3 vapors to atmosphere Possibility of high pressure in oleum boiler, which can reduce flow rate of feed oleum to oleum boiler Overheating of tubes, shell and consequent corrosion... 

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