Hydrogenation, exhaustive

The question of why stars become red giants after core hydrogen exhaustion has been discussed and argued about in many papers. Notable among these are the numerical experiments of Iben (1993) and an analytical discussion by Faulkner (2005). 

When He fuses in the hydrogen-exhausted core at the center of a star, itliberates more nuclear power by making l60 than by making 12C, as the smaller atomic mass excess for l60 reveals. The relative amounts of 12C and l60 made during He burning depend on the rate ofthe nuclear reaction12 C + 4He l60. The quantum probability for this reaction to occur has been very hard to pin down. Its precise value is very... 

Fig. 8. The composition profile for the C, N, and O isotopes as a function of the interior mass for the 1M and 3M Z = 0.02 models. The unit on the y-axis is the logarithm of the number fraction, Y, where the mass fraction is given by X = YA, and A is the atomic mass. The composition profile is a snap-shot of the interior composition of the star at an instant in time, in this case at the end of core hydrogen exhaustion...

Fig. 13. The mass of the hydrogen-exhausted core (solid line) and helium-exhausted core (dashed line) as a function of time for the 3M , Z = 0.02 model (top) and 5M , Z = 0.02 model (lower)...

The water content in hydrogen exhaust is equal to water brought into the cell with hydrogen inlet minus the net water transport across the membrane. As discussed in Chapter 3, water gets "pumped" from anode to cathode because of electroosmotic drag. At the same time, some water diffuses back because of water concentration gradient and because of pressure differential. The net water transport is then the difference between these two fluxes. 

Depending on the hydrogen flow rate, that is, stoichiometry, and conditions at the outlet (temperature and pressure), water at hydrogen exhaust may be present as vapor only, or liquid water may be present after the gas is saturated with water vapor. The water vapor content/flux at anode outlet is the smaller of total water flux at anode outlet and the maximum amotmt the exhaust gas can carry (saturation) ... 

FIGURE 9-17. Use of hydrogen exhaust in a burner to enhance operation of the expander/ turbine. 

It should be noted that hydrogen does not carry much water out of the system. The dashed lines in Figure 9-21 take into account water taken away from the system by hydrogen exhaust assuming hydrogen stoichiometry of 1.2. 

It is a typically aromatic compound and gives addition and substitution reactions more readily than benzene. Can be reduced to a series of compounds containing 2-10 additional hydrogen atoms (e.g. tetralin, decalin), which are liquids of value as solvents. Exhaustive chlorination gives rise to wax-like compounds. It gives rise to two series of monosubstitution products depending upon... 

Trichloroacetic acid is manufactured in the United States by the exhaustive chlorination of acetic acid (38). The patent Hterature suggests two alternative methods of synthesis hydrogen peroxide oxidation of chloral (39) and hydrolytic oxidation of tetrachloroethene (40). 

Final purification of argon is readily accompHshed by several methods. Purification by passage over heated active metals or by selective adsorption (76) is practiced. More commonly argon is purified by the addition of a small excess of hydrogen, catalytic combustion to water, and finally redistiHation to remove both the excess hydrogen and any traces of nitrogen (see Fig. 5) (see Exhaust control, industrial). With careful control, argon purities exceed 99.999%. 

Some time earlier, Eastman-Kodak has been working on a novel polyester as an entry into the important polyester fiber market and had devised a new ahcychc diol, 1,4-cydohexanedimethanol [105-08-5] effectively made by exhaustive hydrogenation of dimethyl terephthalate. Reaction of the new diol with dimethyl terephthalate gave a crystalline polyester with a higher melting point than PET and it was introduced in the United States in 1954 as a new polyester fiber under the trade name Kodel (5). Much later the same polyester, now called PCT, and a cyclohexanedimethanol—terephthalate/isophthalate copolymer were introduced as mol ding resins and thermoforming materials (6). More recentiy stiU, copolymers of PET with CHDM units have been introduced for blow molded bottie resins (7). 

Di(aininomethyl)cyclohexanes aie potentially available from large volume starting materials. The 1,3-isomer (29) may be produced by reduction of yW-xylylenediamine (28) [1477-55-OJ or directiy upon exhaustive hydrogenation of isophthalonitrile (27) [626-17-5J. 

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