ROBERT C. PLUMB
chemical principles exemplified
Worceller Polytechnic Institute Worrerler, Mowachusen, 01 609
Raising the Titanic by Electrolysis-Feasible? Illustrating principles at gas behavior and electrochemistry
The Titanic collided with an iceberg and sank on its maiden voyage in 1912. More than 1500 people lost their lives. Although it happened more than 60 years ago, the drama of the movie, "A Night to Remember,"' shown periodically on television, and several books on the subject have impressed the tragedy deeply in the minds of many people of all generations. The wreck lies at a depth of 2 miles about 95 miles south of the Grand Banks of Newfoundland. Salvaging it would be a formidable task, because of the great depth, but a proposal to float the ship has been made.2 The pressure at that depth is about 330 atm, too great for divers; it is not even possible to pump air a t that high a pressure with commercially available equipment. The proposal contains a clever suggestion to bypass the pressure obstacle. Instead of pumping gas down through a flexible pipe, pump electrons down through a cahle and generate the gas by electrolysis. A surface-controlled deep sea manipulator would break in some of the portholes and attach lines connected to large bags or pontoons. With 200 pontoons, each connected by ten 2-in. diameter nylon ropes. a lifting capacity of 400,000 tons could he achieved. Electricity would he generated at the recovery ship and supplied to electrodes by cahle. There would he apertures on the undersides of the pontoons, cathodes inside the pontoons, and anodes outside. Hydrogen produced a t the cathodes would collect in the pontoons; oxygen or chlorine from the anodes would he dissipated in the surrounding sea water. The question on which the technical merit of the proposal hinges is the feasibility of generating enough hydrogen by electrolysis. An unusually broad range of chemical principles is required to answer this. To estimate the minimum amount of electrical energy required for the salvage one needs to know the weight of the wreck (46,000 lightweight displacement tons, 1 ton -2240 Ih, 1 Ib -0.453 kg, hence 4.7 X 107 kg), the [CI-] and pH of sea water (0.5 M and -7). the density and temperature at that depth (1.05 g . ~ m and - ~ -2" to 4"C), and the following standard reduction potentials
The analysis is conveniently broken down into a series
of subproblems as follows, each involving a physical chemical principle. For a complete solution to each write to the author (1) Density of Hz (g) at P and T of the Titanic wreck-illustrating ideal gas laws. o m . 0 029 (2) Buoyancy of Hz (g) at stated conditions. ons. 1 . 0 2 g ~ m - ~ (3) Minimum volume of sea water to be displaced. ans. 4.7 x 1010crn3 (4) Moles of Hz ig) to be generated-illustrating ideal gas laws. o m .7.0 X 108 mol (5) Electric charge required to produce H2 (g)-illustrating Faraa m . 1.33 X 1014C day's laws of electrolysis. (6) Minimum voltage between anode and cathode-illustrating Nemst equation. The minimum voltage will be the reversible cell voltage at the pressure stated. a m . At = 1.35 for Hz(g) and 0% (g) production Ar = 1.95 for H2 (g) and Clz (g) production ans. 1.8 X lor4jaules (7) Minimum electrical energy required. (8) Generating capacity and time required. A 1 Mw ~eneratingsystem produces 3.6 x loe joules of electrical energy in 1 hr. The time to generate the minimum electrical energy for various size power plants is shown in the table below. Power Plant (Mw)
Time (hr) -
Time (wk) - - -
Accordine to those urovosine the uroiect2 a 20-Mw senerator operating for 1&k &ould"be adeqiate to generatethe necessary Hz (g). Even neglecting the internal resistance of the cahlks and-sea water,'&d tGe overvoltages of the electrode reactions, as has been done above, the calculation done here shows that it would take 15 wk, rather than 1 week. In fact, it seems unlikely that one could generate Hz (g) two miles below the sea with even 10% of the efficiency of an ideal reversible cell. At 10% efficiency a 20-Mw generator would take almost 3 yr to fill the pontoons with sufficient hydrogen. The Consolidated Edison Company of New York, with a capacity of 6000 Mw, could provide enough electrical energy in about 3% days to do the job, if it generated direct current! 'From Walter Lord. "A Night to Remember," Holt. Rinehart and Winston, New York, 1955. ZAs reported in Chem. and Eng News. Oct. 5, 1970, p. 22.
Volume 50, Number 1, January
1973
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61
