Electrolysis aqueous hydrochloric acid

Ziegelbauer JM, Guild AF, O Laoire C, Urgeghe C, Allen RJ, Mukerjee S (2007) Chalcogenide electrocatalysts for oxygen-depolarized aqueous hydrochloric acid electrolysis. Electrochim Acta 52 6282-6294... 

Oxygen-depolarised cathode for aqueous hydrochloric acid electrolysis... 

Aqueous Hydrochloric Acid. Muriatic acid consumption in 1993 was about 1.57 million metric tons (100% basis). The largest captive use of aqueous HCl is for brine acidification prior to electrolysis in chlorine/caustic cells and the largest merchant markets for HCl are steel pickling and oil-well acidizing, which accounted for 25 and 16% of merchant production, respectively, during 1989. 

In conventional hydrochloric acid electrolysis [1], aqueous hydrochloric acid (HClaq) is electrolysed in a cell, constructed basically from graphite, which is divided by a porous diaphragm or a membrane. The overall reaction is... 

Reduction of lactams to amines resembles closely the reduction of amides except that catalytic hydrogenation is much easier and was accomplished even under mild conditions. a-Norlupinone (l-azabicyclo[4.4.0]-2-oxodecane) was converted quantitatively to norlupinane (l-azabicyclo[4.4.0]decane) over platinum oxide in 1.25% aqueous hydrochloric acid at room temperature and atmospheric pressure after 16 hours [1122]. Reduction of the same compound by electrolysis in 50% sulfuric acid over lead cathode gave 70% yield [1122]. 

The preparation of organic chloro-compounds usually involves chlorination according to RH + CI2 — RC1 + HC1. Then half of the chlorine necessary for the reaction ends up as either HC1 gas or aqueous hydrochloric acid. One possibility for the recycling of HC1 is the hydrochloric acid electrolysis to give CI2 and H2 again. 

Recently, rhodium and ruthenium-based carbon-supported sulfide electrocatalysts were synthesized by different established methods and evaluated as ODP cathodic catalysts in a chlorine-saturated hydrochloric acid environment with respect to both economic and industrial considerations [46]. In particular, patented E-TEK methods as well as a non-aqueous method were used to produce binary RhjcSy and Ru Sy in addition, some of the more popular Mo, Co, Rh, and Redoped RuxSy catalysts for acid electrolyte fuel cell ORR applications were also prepared. The roles of both crystallinity and morphology of the electrocatalysts were investigated. Their activity for ORR was compared to state-of-the-art Pt/C and Rh/C systems. The Rh Sy/C, CojcRuyS /C, and Ru Sy/C materials synthesized by the E-TEK methods exhibited appreciable stability and activity for ORR under these conditions. The Ru-based materials showed good depolarizing behavior. Considering that ruthenium is about seven times less expensive than rhodium, these Ru-based electrocatalysts may prove to be a viable low-cost alternative to Rh Sy systems for the ODC HCl electrolysis industry. 

When cold aqueous sulphuric acid of suitable concentration is electrolysed in a divided cell, a solution of perdisulphuric acid is obtained at the anode.1 The most favourable concentration of sulphuric acid is 45 to 60 per cent., but even with this the yield is far from quantitative, and, indeed, after a time further electrolysis actually effects a decrease in the quantity of perdisulphuric acid. If the sulphuric acid is too weak the anodic product may be only oxygen, whilst with too concentrated an acid the perdisulphuric acid will undergo conversion into permonosulphuric acid, which decomposes readily. The addition to the electrolyte of a few drops of hydrochloric acid,2 or of a solution of perchloric acid, or of an alkali perchlorate,8 has been found to favour the formation of the perdisulphuric acid it is also advisable that the platinum anode should be smooth or polished and not rough or platinised. 

On reduction, selenious acid readily gives selenium electrolysis of the aqueous solution therefore yields selenium at the cathode and selenic acid at the anode. With nascent hydrogen an aqueous solution of selenious acid will yield hydrogen selenide.3 Sulphurous acid, preferably in the presence of hydrochloric acid, also reduces selenious acid to selenium, which separates as a red precipitate 4... 

The phenomena of electrolysis are not always as simple as discussed in connection with hydrochloric acid, but it is always true that electrons are taken up by ions on the cathode and electrons are released by ions on the anode. It is not necessarily the cation or anion of the dissolved substance, which reacts on the electrodes, even though these ions carry the electrical current by migration. In aqueous solutions very small amounts of hydrogen and hydroxyl ions are always present due to the slight dissociation of water (cf. Sections 1.18 and 1.24) ... 

Uranium Difluoride, UFg.—The solution obtained after electrolysis of an aqueous solution of uranyl chloride acidified with hydrochloric acid yields, on addition of excess of hydrofluoric acid, a green precipitate of composition UF2.2H,0. ... 

All the arsinic acids dealt with in the following pages arc crystalline solids. Some of tlie primary acids, when heated above their melting-points, eliminate water and form anliydrides. The acids are very stable but may be reduced by amalgamated zinc dust and hydrochloric acid, or by electrolysis in aqueous alcoholic hydrochloric acid, to arylarsines, RAsIIs- An exception to tlie above-mentioned stability is the case of benzylarsinic acid, which is decomposed by mineral adds, and differs from all other members of this series in its reactions. The salts formed with alkali and alkaline earth metals show that the acids are dibasic. Esters may be formed by heating the silver salts of tlie acids in ethereal solution under reflux with the calculated amount of alkyl iodide, but excess of the latter must be avoided or alkyi-arylarsenites are formed ... 

Often, from the point of view of electrolysis, the choice of electrolyte or solvent is free within certain limits, and the workup may then be facilitated considerably by a suitable selection of experimental conditions. For example, the reduction of a nitroalkane [50] to a hydroxylamine requires an aqueous acid medium sulfuric acid is just as good as hydrochloride acid for the electrolysis, but whereas hydrochloric acid may be removed in vacuo at a low temperature, leaving an alkylhydroxylamine hydrochloride, the sulfuric acid must be neutralized and the free, less stable base extracted. 

Hydrochloric acid is an aqueous solution of hydrogen chloride gas produced by a number of methods including the reaction of sodium chloride and sulfuric acid the constituent elements as a by-product from the electrolysis of sodium hydroxide and as a by-product during the chlorination of hydrocarbons. 

Almost the whole production of chlorine is produced by the electrolysis of aqueous sodium chloride solutions. Only a small part is obtained by the electrolysis (or oxidation) of hydrochloric acid (or hydrogen chloride) (see Section 1.7.3). Small quantities of chlorine are also produced in the electrochemical manufacture of metals such as sodium. 

Derivation From tantalum potassium fluoride by heating in an electric furnace, by sodium reduction, or by fused salt electrolysis. The powdered metal is converted to a massive metal by sintering in a vacuum. Foot-long crystals can be grown by arc fusion. Corrosion resistance 99.5% pure tantalum is resistant to all concentrations of hot and cold sulfuric acid (except concentrated boding), hydrochloric acid, nitric and acetic acids, hot and cold dilute sodium hydroxide, all dilutions of hot and cold ammonium hydroxide, mine and seawaters, moist sul-furous atmospheres, aqueous solutions of chlorine. 

Finally, thiocyanogen may be prepared in the presence of the substance that is to react with it by electrolysis of a solution of an alkali or ammonium thiocyanate in aqueous-ethanolic hydrochloric acid,763 but this process has no preparative advantage over those described above. 

The Group VIIA elements, or halogens, are reactive. Chlorine (CI2), a pale greenish-yeUow gas, is prepared commercially hy the electrolysis of aqueous sodium chloride. Its principal uses are in the preparation of chlorinated hydrocarbons and as a bleaching agent and disinfectant. Hydrogen chloride, HCl, is one of the most important compounds of chlorine aqueous solutions of HCl are known as hydrochloric acid. 

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