Electrolysis System

The system used to produce hydrogen via electrolysis consists of more than just an electrolyzer stack. A typical electrolysis process diagram is shown in Fig. 6.45 The primary feedstock for electrolysis is water. Water provided to the system may be stored before or after the water purification unit to ensure that the process has adequate feedstock in storage in case the water system is interrupted. 

A second feedstock needed for electrolysis is electricity. Typically electricity is not considered a feedstock but a utility however it is a critical component in the splitting of the water molecule into hydrogen and oxygen. An electrolyzer typically will convert supplied AC to DC, as the stack requires DC to split water. 

Typical utilities that the electrolysis systems need include electricity for other peripheral equipment cooling water for the hydrogen generation unit prepressurization gas and instrumentation gas (Fig. 6). 

Manufacturer Technology Lower capacity (kg day4) Upper capacity (kg day4) Pressure Location Ref. 

Industrie Haute Techno-logie SA Alkaline 1639.4 1639.4 up to 32 barg Monthey, Switzerland 34 

Peak Scientific Ion exchange membrane 0.01 0.01 0-100 psig Scotland 30 

Schmidlin-DBS AG Membrane 0.005 0.026 1-155 psig Neuheim, Switzerland and Padova, Italy 37 

Siam Water Flame Co. Alkaline 0.647 0.647 unknown Bangkok, Thailand 38 

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Eig. 6. Comparison of current density and cell voltage characteristics of the electrolysis systems where lines A and B represent steam electrolysis and the use of SPE, respectively, the conventional KOH water electrolysis, and, 2ero-gap cell geometry employing 40% KOH, at 120—140°C. 

Heavy water [11105-15-0] 1 2 produced by a combination of electrolysis and catalytic exchange reactions. Some nuclear reactors (qv) require heavy water as a moderator of neutrons. Plants for the production of heavy water were built by the U.S. government during World War II. These plants, located at Trad, British Columbia, Morgantown, West Virginia, and Savaimah River, South Carolina, have been shut down except for a portion of the Savaimah River plant, which produces heavy water by a three-stage process (see Deuterium and tritium) an H2S/H2O exchange process produces 15% D2O a vacuum distillation increases the concentration to 90% D2O an electrolysis system produces 99.75% D2O (58). 

There have been a number of cell designs tested for this reaction. Undivided cells using sodium bromide electrolyte have been tried (see, for example. Ref. 29). These have had electrode shapes for in-ceU propylene absorption into the electrolyte. The chief advantages of the electrochemical route to propylene oxide are elimination of the need for chlorine and lime, as well as avoidance of calcium chloride disposal (see Calcium compounds, calcium CHLORIDE Lime and limestone). An indirect electrochemical approach meeting these same objectives employs the chlorine produced at the anode of a membrane cell for preparing the propylene chlorohydrin external to the electrolysis system. The caustic made at the cathode is used to convert the chlorohydrin to propylene oxide, reforming a NaCl solution which is recycled. Attractive economics are claimed for this combined chlor-alkali electrolysis and propylene oxide manufacture (135). 

A classic reaction involving electron transfer and decarboxylation of acyloxy radicals is the Kolbe electrolysis, in which an electron is abstracted from a carboxylate ion at the anode of an electrolysis system. This reaction gives products derived from coupling of the decarboxylated radicals. 

The standard emf series based on hydrogen is obviously not applicable to molten salt electrolysis systems. No emf series similar to that for aqueous systems has been established for molten electrolytes this is due to the nonavailability of accepted standard electrodes and the use of numerous molten electrolytes involving widely differing tamperers, consequent to the widely varying melting temperatures of the salts used. In spite of these, many emf series have been compiled, using a variety of molten salts with different stand-... 

The special requirements of the indigo dyeing of cotton warp yarns for denim are capable of being met by indirect electrolysis systems [241]. Examples of four suitable redox systems are shown in Table 12.37. Uniform build-up of depth was observed with each successive step, the results being at least equal to those from the conventional dithionite-based process. Apparendy these processes are amenable to scaling up to bulk production levels [241]. 

Schucan T., Hydrogen generation from stand-alone wind-powered electrolysis systems, in Case Studies of Integrated Hydrogen Energy Systems, Final Report of the IEA Task 11 Integrated Systems, 129-145, Switzerland, 1998, Chapter 9. 

Khaselev, O., Bansal, A., and Turner, J.A., High-efficiency integrated multijunction photovoltaic/ electrolysis systems for hydrogen production, Int.. Hydrogen Energ., 26,127,2001. 

Aqueous alkaline electrolysis, 13 784 Aqueous alkaline electrolysis system,... 

In the brine electrolysis system, silica is also contained in raw salt. Silica will precipitate on to membranes in the presence of calcium, strontium, aluminium and iodine resulting in the loss of current efficiency [8-10]. Silica can also be removed in a column filled with ion-exchange resin containing zirconium hydroxide, just like the iodide ion. 

Ring construction of pyrrolidinoenami-nes (52) of alicyclic ketones, giving the bicyclo compound (53), has been attained by using the iodide ion as a mediator in an MeOH-NaCN-(Pt) electrolysis system [70] (Scheme 19). 

An electroreductive Barbier-type allyla-tion of imines (434) with allyl bromide (429) also occurs inaTHF-PbBr2/Bu4NBr-(Al/Pt) system to give homoallyl amine (436) (Scheme 151) [533]. The combination of Pb(II)/Pb(0) redox and a sacrificial metal anode in the electrolysis system plays a role as a mediator for both cathodic and anodic electron-transfer processes. The metals used in the anode must have a less positive anodic dissolution potential than the oxidation potentials of the organic materials in order to be present or to be formed in situ. In addition, the metal ion plays the role of a Lewis acid to form the iminium ion (437) by associating with imine (435) (Scheme 151). 

A new electrolysis system comprising two metal redox couples, Bi(0)/Bi(III) and A1(0)/A1(III), has been shown to be effective for electroreductive Barbier-type allylation of imines [533]. The electrode surface structure has been correlated with the activity towards the electroreduction of hydrogen peroxide for Bi monolayers on Au(III) [578], Electroreductive cycliza-tion of the 4-(phenylsulfonylthio)azetidin-2-one derivative (502) as well as the allenecarboxylate (505) leading to the corresponding cycKzed compounds (504) and (506) has been achieved with the aid of bimetallic metal salt/metal redox systems, for example, BiCh/Sn and BiCh /Zn (Scheme 175) [579]. The electrolysis of (502) is carried out in a DMF-BiCh/Py-(Sn/Sn) system in an undivided cell by changing the current direction every 30 s, giving the product (504)in 67% yield. 

Fischer M (1986) Review of hydrogen production with photovoltaic electrolysis system. Int J Hydrogen Energy 11 495-501... 

Fig. 8.9 Schematic diagram of PV-electrolysis systems proposed for solar water splitting (a) Electricity generated from photovoltaic cell driving water electrolysis (b) PV assisted cell with immersed semiconductor p/n junction as one electrode.

Fig. 8.10 Schematic diagram of PV-electrolysis system pilot plant [88-90],...

Esteve D, Ganibal C, Steinmetz D, Vialason A (1980) Performance of a photovoltaic electrolysis system. Proc 3 word Hydrogen Energy Conference, Tokyo. V. 3, pp.l583-1603... 

Delahoy AE, Gao SC, Murphy OJ, Kapur M, Bockris JOM (1985) A one-unit photovoltaic electrolysis system based on a triple stack of amorphous silicon (pin) cells. Int J Hydrogen Energy 10 113-116... 

Fig 1 Water Electrolysis System Propulsion Concept (from Ref 2)... 

For the mission/system analysis and flight-weight system design studies conducted, the water electrolysis system was 27% lighter than the monopropellant system and 6% lighter than the earth storable bipropellant system... ]... 

Aqueous electrolysis has been used by Margerum and co-workers to oxidize oligopeptide complexes of nickel(II).3047,3057-3059 They used a flow electrolysis system with a graphite powdered electrode packed in a porous glass column externally wrapped with a platinum wire electrode. 

Figure 22.15 Schematic diagram of a flow-through electrolysis system (1 = heat exchanger 2 = containers 3 = pumps 4 = Teflon body 5 = diaphragm or ion exchange membrane W = working electrode AUX = auxiliary electrode R = reference electrode).

Practical utilization of photo-assisted electrolysis systems is hampered by poor overall conversion efficiencies. Essentially, this problem results from poor quantum efficiencies at low bias. 

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