Manufacturers alkaline electrolysis

For several decades, commercial alkaline electrolyzers have been available in a variety of series with outputs of up to approximately 750 Nm h hydrogen. Product development for PEM electrolysis only began around 25 years ago, and thus there are fewer commercial systems (<30 Nm h ) available compared to alkaline electrolysis. However, aU major manufacturers of PEM electrolyzers are currently developing and constructing 1 MW systems (see Table 11.4). High-temperature electrolysis is currently being pursued only sporadically by industry, which means that some demonstration systems exist, but no commercial products are yet available. 

In contrast to PEM electrolysis, which has only been utilized for around 25 years, alkaline electrolysis systems of various dimensions and types with outputs of up to 750 Nm h hydrogen have been available for some decades. For alkaline electrolysis, usually a potassium hydroxide solution with a concentration of 20-40 wt% is used. This is determined by the operating temperature, which is usually at 80 °C, since the ohmic losses can be minimized by a suitable concentration of the alkaline solution and thus optimal electrical conductivity [8]. The current density ranges from 0.2 to 0.4 A cm. The state of the art of large alkaline electrolyzers has not changed much over the last 40 years [9]. This becomes apparent in the fact that since the introduction of water electrolysis more than 100 years ago, only a few thousand systems have been produced and put into operation. Some of the systems listed in Table 11.3 are no longer produced, or their manufacturers have vanished from the market. 

To use water electrolysis to produce hydrogen through surplus renewable electricity, the partial load toleration for a highly variable power output is particularly important for safe operation. PEM electrolysis has an advantage here over alkaline electrolysis due to the use of polymer membranes and the associated higher gas purity According to the manufacturer, the partial load can be adjusted down to 0 % on cell and stack level (see Table 11.4), while in industrial facilities the lower limit is estimated to be at approximately 5 % of the nominal power due to the power consumption of the peripheral components. For alkaline electrolyzers, the lower partial load range is currently specified as 20-40 % [9]. 

Table 11.3 gives an overview of the most important manufacturers/developers of alkaline electrolysis systems [9]. The costs for alkaline electrolyzers in the MW class are approximately 1000 /kW [9, 47]. These are electrolyzers operating at atmospheric pressure or pressurized electrolyzers operated at 30 bar. For the stack, lifetimes of up to 90,000 h are specified, meaning that alkaline electrolyzers usually require a complete overhaul and the electrodes and diaphragms must be exchanged every 7-12 years [9]. 

Davy s preparation of potassium and sodium became the starting point for the manufacturing techniquesalt electrolysis, which is so important at the present time. He soon used the method to obtain the alkaline earth metals magnesium, calcium and barium. 

Hydroxide. Potassium hydroxide, [CAS 1310-58-3]. caustic potash, potassium hydrate, KOH, white solid, soluble, mp 380 C, formed (1) by reaction of potassium carbonate and calcium hydroxide in H2O, and then separation of the solution and evaporation. (2) by electrolysis of potassium chloride under the proper conditions, and evaporation. Used in the preparation of potassium salts f 1) in solution, and (2) upon fusion. Also used 111 the manufacture of (3) soaps, (4) drugs. (5) dyes, (6) alkaline batteries, (7) adhesives, (8) fertilizers, (9) alkylates, (10) for purifying industrial gases, (11) for scrubbing out traces of hydrofluoric add in processing equipment, (12) as a drain-pipe cleaner, and (13) in asphalt emulsions. 

Many metals and some non-metals are made by electiolytic methods. Hydrogen and oxygen are produced by the electrolysis of water containing an electrolyte. The alkali metals, alkaline-earth metals, magnesium, aluminum, and many other metals are manufactured either entirely or for special uses by electrochemical reduction of their compounds. Some of the processes used are described below. 

The crude magnesium obtained from electrolysis or thermal reduction has to be purified (refined) before further processing. This is carried out by mixing salt melts (alkali and alkaline earth chlorides or fluorides) with the liquid metal. The purest magnesium is manufactured by distillation. 

Occurrence Formed locally in air from lightning, in stratosphere by UV radiation. Also occurs in automobile engines and by electrolysis of alkaline perchlorate solutions. Commercial mixtures containing up to 2% ozone are produced by electronic irradiation of air. It is usually manufactured on the spot because it is too expensive to ship. Tonnage quantities are used. 

Tin(IV) chloride is the main starting material for the manufacture of organotin compounds and has some applications such as flame-proofing treatment in the textile industry. Tin(lV) oxide has various uses in the glass industry. Alkaline stannates are used in tin plate electrolysis to prepare tin alloy coatings. 

About 75 percent of the caustic produced is concentrated. The remainder is used directly as alkaline cell liquor—as, for example, in the conversion of propylene to propylene oxide by the chlorhydrin process. Similarly, there is some chlorine produced by methods that do not produce caustic, as shown in Table 12.18. Fused chloride salt electrolysis produces chlorine in the manufacture of magnesium metal by the Dow process, and of sodium metal in the Downs cell. The only other process of note is the Kel-Chlor process. This process converts by-product HCl to chlorine by oxidation with NO2 through the intermediates NOCl and HNSO5. 

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