201). Likewise, the produced gases should be monitored to detect inadvertent mixing. (This can occur, for example, if the polarity is reversed-Ellis 585, or by injury to the diaphragm, blockage in the system, or too great current density-Greenwood 202.) . This can be done by sampling the gas and igniting the sample under controlled conditions; they should burn not detonate. (Taylor 73).
From a portability standard, decomposing water with electricity has the advantage that you don't need to transport reactants. As to the weight of the apparatus itself, a Schukert 600 amp electrolyzer holding 50 liters solution and producing 5 m3/24h weighed 220 kg (Englehardt 86). A 110V, 150 amp, 16.5 kw Schmidt system producing 66 m3/24 h weighed 14,000 kg, while a 1.65 kw plant producing one-tenth that weighed 700 kg. (33). Unfortunately, because access to electricity is required, this is not really a method suitable for launch site production. (Batteries are heavy.)
I have gotten mixed signals on the issue of the space requirements for electrolysis. Ells first says that it requires a 'relatively large floor space.' (570) and then that 'for small plants electrolysis has much in its favor.' (595; cp. Teel 132). It may depend on the design; Schuckert demands relatively more room (Greenwood 198) while Schmidt is compact (199). Still, there was a
The only apparatus for which I have specifics is the Levin generator; 100 will occupy 31 feet by 4.5 feet, and produce 320 cubic feet/hour at 200 amperes. (580). With normal room height, they can be installed in two tiers.
But an electrolytic cell can be very small. With 12.2 watts of solar-based electricity, a modern homemade cell in a 3.5'x5.5'x1.5' plastic container produced 0.399 milliliters/second hydrogen. (Businelli). So the real question is, what is the required cell volume to achieve the desired production rate?
One nice thing about electrochemistry is that you can predict performance. A chemist would expect that 96,500 coulombs (ampere-seconds) of electricity would liberate 1 gram of hydrogen and 8 grams of oxygen, those being the 'equivalent weights' (ionic weight/ionic charge). So one ampere-hour produces 0.03731 gram- equivalents, which works out as 0.01482 cubic feet of hydrogen at STP (0oC, 760 mm Hg), 0.00741 cubic feet oxygen. At 20oC we do better; 0.01585 of hydrogen and 0.00792 of oxygen. (Taylor 103). The current supplied is typically 200-600 amperes. So, if the current were 400 amps, production would be 5.93 cubic feet hydrogen and 2.96 cubic feet oxygen per hour. (Ellis 536).
Teed (39) considered electrolysis to be suitable only for production of up to 1000 cubic feet hydrogen/hour.
In theory, the required voltage is 1.23, but because of secondary effects (overvoltage) it will probably be found that 1.7 volts are needed for continuous decomposition of water. (Taylor 104; Ellis 536). However, the diaphragm will tend to increase the resistance of the cell, necessitating a voltage of 2-4 volts. (106). As a result, energy efficiencies are in the 50-60% range. (Engelhardt 18, 20, 31).
The first electrolytic oxygen generator constructed for laboratory purposes was that of D'Arsonval (1885), and the first large scale apparatus was that of Latchinoff (1888). (Taylor 108). The first with significant industrial adoption was probably Schmidt's (1899), which produced 99% pure hydrogen and 97% pure oxygen. (Engelhardt 31).
2002McGHEST says that 'although comparatively expensive, the process generates hydrogen of very high purity (over 99.9%). However, I think it's a mistake to count out the electrolytic process. Water, of course, is cheap, so the main expenses are those of providing electricity, and separating out the oxygen.
1890-1910 prices for electricity ran around 0.25 cents/kwh for hydroelectric and 1.25 for coal-fired steam plants. (Engelhardt 17). (Ellis 538 assumes 1 cent/kwh, and 569 quotes prices of 3-4 cents in New York City and 0.5 cents in South Chicago.)
Chances are that the recovered oxygen can be sold, thus defraying at least some of the production costs. In fact, the zeppelin hydrogen produced in 1934-38 was a byproduct of the electrolytic production of oxygen. (Dick 193). in 1904, oxygen sold for $1/m3 and hydrogen for $0.3125. (Engelhardt 40).
Bear in mind that 'a normal military balloon requires, in order to be filled in twenty-four hours, a plant of about 200 kilowatts.' An airship requires a lot more hydrogen than that.
Still, in 1904, the Italian, French and Swiss armies all relied on electrolytic hydrogen. (123).
In 2004, the average cost of electricity in America was 5 cents/kwh and at that price, with 80% electrolysis efficiency and 90% compression efficiency, the power cost for compressed electrolytic hydrogen was $2.70/kg. (Doty).
The higher the temperature, the less electrical energy is needed. If heat is cheaper than electricity, then higher operating temperatures are desirable. (Kirk-Othmer 13:868).
2Na+ + 2Cl- + 2H2O -› 2NaOH + H2 + Cl2
With 100% current efficiency, each ampere-hour would produce 1.322 grams of chlorine, 1.491 grams of sodium hydroxide and 0.0373 grams of hydrogen.' (Actual current efficiencies were 90-98%.) The caustic soda may be used to make soap, and the chlorine bleach, and of course there are other uses, too. (Taylor 120). At 15oC, each ton of salt electrolyzed produces 72320 cubic feet hydrogen. Hydrogen purity is 90-97%. (Greenwood 203). Naturally, you want to prevent intermixing of hydrogen and chlorine after production.
In 1904, this was the method used to produce hydrogen for German army balloons. (Englehardt 123).
The Rincker-Wolter system is of some interest because they started with oils and tars, and the demand for tar in163x is limited. The required temperature was 1200oC for the hydrogen to be of acceptable purity. In 1912, a plant producing 3500 cubic feet/hour would cost $2575 plus 'erecting expenses,' and with the oil at 4 cents/gallon, the hydrogen cost would be $1.75/1000 cubic feet. (Ellis 473ff). A semiportable plant with such capacity has been successfully mounted on two railway trucks. Greenwood 193 reports a cost of 550 pounds sterling for the plant and 2s/6p to 4s/0p per 1000 cubic feet.
A variation on this is the Carbonium process; acetylene gas is compressed to two atmospheres and exploded by an electric spark, yielding carbon (deposited as lamp-black) and high purity hydrogen. You need an explosion chamber, and the lamp black is scraped off the walls. If there's a market for the lamp black (one kg per cubic meter of hydrogen), this method can be advantageous. (Ellis 473). The good news about the process is that it was used to supply hydrogen for the zeppelins at Friedrichshafen. The bad news is that the factory was destroyed by an explosion in 1910! Before this slight mishap, the cost of production was 4 shillings per 1000 cubic feet. (Greenwood 192).
CH4+H2O-›CO+3H2.
The encyclopedia notes that carbon dioxide may be removed by scrubbing with aqueous monoethylamine. However, there's a much easier method; pass the gas mixture through water under high pressure; the carbon dioxide reacts with water to form carbonic acid and dissolves; the hydrogen doesn't dissolve and bubbles to the surface.
Even with these hints, the method may take a while to get working. In the old time line, experiments began
