Hydrogen production, liquid absorption

By-product processing Hydrogen sulfide Conversion to elemental sulfur or sulfuric acid by liquid absorption, wet oxidation to elemental sulfur, combustion to SO2... 

Conventional Hydrogen Production Using Liquid Absorption Purification... 

Numerous industrial operations involve a heat transfer between a liquid phase and a gaseous phase, with an important mass transfer effect, either as desorption-evaporation or as absorption-condensation. Here are some examples reconcentration, by evaporation, of solvents, toxic industrial effluents production, by absorption, of industrial aqueous acid solutions reversible or irreversible chemical reactions (oxidation, hydrogenation, sulfonation) purification of permanent gases (air, smoke) by scrubbing of soluble vapors desorbers and absorbers for heat pumps, where these two operations occur simultaneously. 

Product purification. In a liquid absorption system, carbon dioxide is removed. The product gas undergoes a methanation step to remove the residual traces of carbon oxides. Recent SMR plants use a pressure swing absorption (PSA) unit instead, producing 99.99% pure hydrogen. 

The combined presence of H,S and C02 in a given effluent usually leads to a joint removal operation. This type of treatment stems from the fact that, among the most economical alternatives available, the liquid absorption of acid constituents is the most widespread, and also because, at the technical level, the type of product to be extracted, apart from its acidic character, has little effect on the behavior of the solvent employed. Hence, although, as a rule, hydrogen sulfide is absorbed faster than C02, the separation of the different acid gases is more or less simultaneous. For reasons of environmental protection, this scheme must also be supplemented by the direct conversion of hydrogen sulfide to sulfur,... 

Natural gas is processed mainly for the recovery of liquid hydrocarbons useful in gasoline, pure hydrocarbons as butane, propane, ethane, or mixtures of them, hydrogen sulfide (and sulfur or sulfuric acid), and carbon black but significant amounts of gas are also converted into ammonia, synthesized by the Fischer-Tropsch reaction, or oxidized into chemical products such as formaldehyde. Conventional operations, however, consist of mainly two operations, viz., recovery of liquids (absorption, etc.), and purification of the liquid. 

Equip a 1 litre bolt-head flask with dropi)ing fuuncl and a double surface reflux condenser to the top of the latter attach a device (e.g.. Fig. II, 8, 1. c) for the absorption of the hydrogen bromide evolved. Place 100 g. (108 ml.) of dry iso-valeric acid (Section 111,80) and 12 g. of pmified red phosphorus (Section 11,50,5) in the flask. Add 255 g. (82 ml.) of dry bromine (Section 11,49,5) slowly through the dropping funnel at such a rate that little or no bromine is lost with the hydrogen bromide evolved the addition occupies 2-3 hours. Warm the reaction mixture on a water bath until the evolution of hydrogen bromide is complete and the colour of the bromine has disappeared. Pour off the liquid reaction product into a Claisen flask and distil mider the reduced pressure of a water pump. Collect the a-bromo-wo-valeryl bromide at 117-122°/25-30 mm. The yield is 150 g. 

The reactor products are fed to a condenser where the chlorobenzenes and unreacted benzene are condensed. The condensate is separated from the noncondensable gases in a separator. The non-condensables, hydrogen chloride and unreacted chlorine, pass to an absorption column where the hydrogen chloride is absorbed in water. The chlorine leaving the absorber is recycled to the reactor. The liquid phase from the separator, chlorobenzenes and unreacted benzene, is fed to a distillation column, where the chlorobenzenes are separated from the unreacted benzene. The benzene is recycle to the reactor. 

Bis(trirnethylsiloxy)spiro[2.3]hex-4-ene (70 g. 0.27 mol) in anhyd cyclohexane (250 mL) was hydrogenated over a modified nickel chromite catalyst at 25 "C and under 100 atm pressure. After the absorption of hydrogen had ceased, the catalyst was filtered off and the solution was evaporated to remove cyclohexane. The residue was distilled under vacuum to give the product as a colorless liquid yield 55 g (78%) bp 92-94°C/12 Torr. 

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