Hydrogen and Oxygen Separations

We have studied the proton and oxide anion transport, conduction, and permeation in metals, dense oxide ceramics and, also briefly, in polymers (see also Chapters 2,5, and 8). This section describes the application of proton and oxide permeation in these materials in hydrogen and oxygen separations. 

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Bortolotto L., DittmeyerR. 2010. Direct hydroxylation of benzene to phenol in a novel microstructured membrane reactor with distributed dosing of hydrogen and oxygen. Separation and Purification Technology 73 51-58. 

These membranes mimic natural photosynthesis except that the electrons are directed to form hydrogen. Several sensitizers and catalysts are needed to complete the cycle, but progress is being made. Various siagle-stage schemes, ia which hydrogen and oxygen are produced separately, have been studied, and the thermodynamic feasibiHty of the chemistry has been experimentally demonstrated. 

Self-Test 4.13B Students collecting hydrogen and oxygen gases by electrolysis of water failed to separate the two gases. If the total pressure of the dry mixture is i 720. Torr, what is the partial pressure of each gas ... 

A redox equation usually can be separated by placing elements other than hydrogen and oxygen in separate half-reactions. If this does not work, use oxidation numbers to identify the oxidized and reduced species. Occasionally, an element other than O or H may be involved in both half-reactions. 

Figure 8.31. Principle of a Polymer Electrolyte Membrane (PEM) fuel cell. A Nation membrane sandwiched between electrodes separates hydrogen and oxygen. Hydrogen is oxidized into protons and electrons at the anode on the left. Electrons flow through the outer circuit, while protons diffuse through the...

A special version of the membrane reactor using Pd was made for separating hydrogen and oxygen and their controlled reaction. 

Water, however, is a wonderful solvent for ionic-bonded substances such as salt. The secret to its success lies in the electric dipoles created by the polar covalent bonds between the hydrogen and oxygen atoms. In water, the polar bonds are asymmetric. The hydrogen side is positive the oxygen side is negative. One measure of the amount of charge separation in a molecule is its dielectric constant. Water has a dielectric constant that is considerably higher than that of any other common liquid. 

Thin film-photocatalysts represent a very promising system as hydrogen and oxygen can be generated separately (Figure 4.13) [160],... 

Here, reaction 4.9, known as "Bunsen reaction," is the low-temperature exothermic reaction, where the raw material, water, reacts with iodine and gaseous sulfur dioxide producing an aqueous solution of hydriodic acid and sulfuric acid. The acids are then separated and thermally decomposed to produce hydrogen and oxygen. The total reaction scheme... 

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