Sulphur trioxide absorption

Note that the sulphur trioxide is not absorbed directly by water, as the reaction is very exothermic and a corrosive mist of droplets of concentrated sulphuric acid is formed above the mixture. A double absorption sulphuric acid plant allows a 99.5% conversion of sulphur dioxide to sulphur trioxide to take place. 

After preparing the tube carry out the combustion of the substance exactly as is described in detail for the halogen determination. Since complete absorption of sulphur trioxide by the absorbent requires a long period of contact, employ a slower current of oxygen (3-4 c.c. per minute) and, correspondingly, move the Bunsen burner forward more slowly. The combustion of the substance should require about one hour. 

It attacks glass at a red heat, giving silicon tetrafluoride and sulphur trioxide. Carbon and boron are without action on the gas at a red heat, but sodium at a temperature considerably above the melting-point causes gradual decomposition with absorption. Hydrogen sulphide, aided by heat, attacks both thionyl and sulphuryl fluorides, inducing decomposition.1... 

Experimental measurements of absorption fluxes and colour development for the gas-liquid reaction between sulphur trioxide and dodecylbenzene have been carried out in a stirred cell absorber. A model with two parallel reaction paths representing sulphonation and discolouration has been applied to analyse the exothermic absorption accompanying conversions up to 70%. The results show that the two reactions have similar activation energies and that temperature increases greater than 100°C occur at the interface during absorption. The absorption enhancement factor exhibits a maximum value as liquid phase conversion proceeds. 

Even when adhering to technological parameters, certain amounts of sulphur dioxide, unreacted in the oxidation step (as much as 0.3 to 0.4% by volume in the final gases) may be released into the atmosphere. The final gases also contain sulphur trioxide and sulphuric acid aerosol, particularly in the case of inefficient operation of absorption and drying equipment. 

The solution of Eqn (25) for a highly exothermic system can be illustrated for data relevant to the absorption of sulphur trioxide in dodecylbenzene (DDB). In this case, it is impossible to measure the solubility of SO in DDB at moderate... 

Fig. 18. With reference to Fig. lH the interference of the reaction kinetic parameters is not complicated by possible multiplicity of the heat and mass transf profiles, since an activiation energy of around 25 kcal mol" can only give rise to single solutions. The exothermicity of the absorption process results in a rapid increase in the reaction speed along the jet. This is presented in terms of the half-lives of the reacting sulphur trioxide at the jet surface in Fig. 19. For the nominal 10 SO in the gas phase, the half-life has become less than 10 millrseconds at the end of the jet. The much greater surface temperature achieved in the 30% SO case means that the half-life decreases along the jet surface from around 10 milliseconds close to the jet nozzle to less than a microsecond on entry to the receiver.

Sulphur trioxide is removed from a gaseous stream of sulphur trioxide, nitrogen, oxygen and residual sulphur dioxide by absorption into 98 per cent sulphuric acid. The acid is maintained at 98 per cent (by mass) through continuous addition of water. If the flow rate of sulphur trioxide is 10 kg s and 99.8 per cent of it is absorbed, calculate the daily loss of SO3 in the gaseous effluent. 

Sulphur trioxide is absorbed in the intermediate absorber and in the final absorber. The former absorbs SO 3 from the third catalyst bed and the latter from the first bed. If water is used for absorption a fine acid mist forms which is unacceptable in practical or environmental terms. In order to prevent this the vapour pressure above the acid must be made sufficiently low. This can only be achieved if the absorption medium is greater than 97% strength sulphuric acid—in practice 98% sulphuric acid is employed. The final product is about 98.5% sulphuric acid, which is then diluted to 98% with water in the pump tanks. The heat formed in the reaction... 

The other environmental problem is due to hydrocarbon impurities and is greatest when dark sulphur is used. It is caused by the water vapour from combustion of the hydrocarbons reacting with sulphur trioxide to form a sulphuric acid mist. The amount of mist produced is lowered if bright sulphur is used and is almost eliminated by absorption of sulphur trioxide with 98% sulphuric acid instead of water. 

In order to produce gaseous as well as liquid trioxide it is essential that manufacture of oleums by absorption of sulphur trioxide from plant gases producing sulphuric... 

Oleum In addition to the equipments required for the manufacture of 23-25 % Oleum, this will need a separate absorption tower. Oleum circulation pump, cooling system etc. and facilities for generation of pure SO3 vapoms (by boiling 25 % Oleum). Certain plants produce 65 % Oleum by mixing 30 % Oleum with liquid sulphur trioxide in a controlled manner. 

A portion (a) of the residual gas, free from carbon dioxide and oxygen, is filled into a eudiometer and kept for subsequent combustion-aiialyBis, and another portion (b) filled into an absorption-tube, and the heavy hydrocarbons absorbed by sulphur trioxide, giving the Mowing results... 

In aqueous solutions of sulphuric (< 50%) and perchloric acid (< 45 %) nitrous acid is present predominantly in the molecular form, although some dehydration to dinitrogen trioxide does occur.In solutions contairdng more than 60 % and 65 % of perchloric and sulphuric acid respectively, the stoichiometric concentration of nitrous acid is present entirely as the nitrosonium ion (see the discussion of dinitrogen trioxide 4.1). Evidence for the formation of this ion comes from the occurrence of an absorption band in the Raman spectrum almost identical with the relevant absorption observed in crystalline nitrosonium perchlorate. Under conditions in which molecular nitrous... 

It is known that the conversion of sulphur dioxide to the trioxide is encouraged by high pressure. ICI have developed a process in which conversion is carried out at 5-7 atmospheres in a three-bed converter at the temperatures for the double absorption process. In this case single absorption is used (Figure 3.14) and 99% conversion is achieved. 

A concentrated nitric acid - perchloric acid - sulphuric acid digest of the polymer is analysed at 193.7 nm by atomic absorption spectrometry. The procedure is calibrated against standards of arsenic free acrylic fibre and pure arsenic trioxide. 

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