Sulphuric acid alkali promoters

Sulphuric acid catalysts are not truly heterogeneous catalysts but so-called supported liquid phase (SLP) catalysts, where the oxidation of S02 takes place as a homogeneous reaction in a liquid film covering the internal surface of the support material [2], This was proposed already in 1940 by Frazer and Kirkpatrick [6], who found that the promoting action of the common alkali metals was due to their ability to form relatively low-melting pyrosulphates, which dissolve vanadium oxides, e.g. for potassium... 

Quadrivalent cerium salts may be volumetrically determined by arsenious acid in aqueous sulphuric acid solution using a manganese salt as catalyst, with potassium iodate present as a promoter.2 Excess of arsenious acid is used and back-titrated with permanganate. If nitric acid is present in place of sulphuric acid, an alkali chloride and a trace of iodine are used to promote the action of the manganese salt. Direct potentiometric titration with arsenious acid may also be employed. 

Sodium sulphate may be produced industrially by the reaction of magnesium sulphate with sodium chloride in solution followed by crystallization, or by the reaction of concentrated sulphuric acid with solid sodium chloride. The latter method was used in the Leblanc process for the production of alkali and has given the name salt cake to impure industrial sodium sulphate. Sodium sulphate is used in the manufacture of glass and soft glazes and in dyeing to promote an even finish. It also finds medicinal application as a purgative and in commercial aperient salts. 

Caesium-promoted catalyst for sulphuric acid plant has a lower ignition temperature and can result in higher overall conversion of SO2 SO3 but is more costly. It can reduce consumption of alkali in tail gas scrubber as compared to conventional potassium-promoted catalyst. 

Manufacture of sulphuric acid by the modified 3 + 2 DCDA process (having three catalyst passes before interpass absorption tower and two passes after it) with caesium-promoted catalyst resulted in better conversion of SO2 to SO3 and negligible escape of SO2 from exit gases. An alkali scrubber for tail gases was provided for taking care of this. 

Polyene acids undergo cyclization (without dimerization) at elevated temperatures. This reaction requires double bonds in appropriate positions and of correct configuration and reagents such as alkali (to promote double-bond migration) and sulphur or iodine (to promote stereomutation) are frequently used. Cyclization of linoleate has been... 

Effect of donor atom type on selectivity. Changing the type of donor atom at the binding site alters the nature of the ligand-cation interactions and can lead to quite subtle changes in complexation selectivity (15,26). For example, the replacement of oxygen (hard base) as the donor atom by sulphur (soft base) in 18-crown-6 enhances the complexation of transition metal ions (soft acids), for example Ag, and reduces that of alkali metals (hard acids), for example (Table 2.2) (17, 27). With nitrogen as a donor atom, however, the complexation of transition metal ions (Ag" ) is also promoted without substantially diminishing that of alkali metals (K ) (17). 

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