Purifying Hydrogen

The procedure is to pass purified hydrogen through a hot solution of the pure acid chloride in toluene or xylene in the presence of the catalyst the exit gases are bubbled through water to absorb the hydrogen chloride, and the solution is titrated with standard alkali from time to time so that the reduction may be stopped when the theoretical quantity of hydrogen chloride has been evolved. Further reduction would lead to the corresponding alcohol and hydrocarbon ... 

Pure piperitone was subjected to the action of purified hydrogen, in the presence of a nickel catalyst, for six hours, the temperature ranging between 175° to 180° C. The double bond in piperitone was readily opened out with the formation of menthone, but further action of the hydrogen under these conditions did not reduce the carbonyl group, even after continued treatment for two days. Under correct conditions, however, the reduction to menthol should take place. The ease with which menthone is formed in this way is of special interest, not only in connection with the production of this ketone, but also as a stage in the manufacture of menthol. 

Harvey (1917) noted that the fresh arm photophores of Watasenia scintillans do not show a luciferin-luciferase reaction, and Shoji (1919) using a gas chamber of purified hydrogen demonstrated that molecular oxygen is needed for the luminescence. 

Palladium Diffusion. Palladium is very permeable to hydrogen but not permeable to other gases. As a result, it is a useful hydrogen purifier. A palladium membrane, heated to 400 °C, purifies hydrogen to <10 ppb but requires a high pressure differential for net diffusion to take place at reasonable rates of hydrogen supply. 

Fig. 4. Nitrogen content of purified hydrogen vs. current density.

Modern SMR plants (Figure 2.5b) incorporate a PSA unit for purifying hydrogen from C02, CO, and CH4 impurities (moisture is preliminarily removed from the process gas). The PSA unit consists of multiple (parallel) adsorption beds, most commonly filled with molecular sieves of suitable pore size it operates at the pressure of about 20 atm. The PSA off-gas is composed of (mol%) C02—55, H2—27, CH4—14, CO—3, N2—0.4, and some water vapor [11] and is burned as a fuel in the primary reformer furnace. Generally, SMR plants with PSA need only a HT-WGS stage, which may somewhat simplify the process. 

Amine Guard A process for extracting acid gases from refinery streams by scrubbing with an alkanolamine. Many such processes have been developed, this one was developed by the Union Carbide Corp. and uses monoethanolamine. It has been used to purify hydrogen produced by steam reforming. In 1990, over 375 units were operating. 

Hydrogen Polybed PSA A version of the Polybed process, for purifying hydrogen from various industrial processes. Developed by the Union Carbide Corporation in 1975 and now licensed by UOP. More than 400 units were operating worldwide in 1992. 

HYSEC A process for purifying hydrogen from coke-oven gas by PSA, developed by Mitsubishi Kakoki Kaisha and the Kansai Coke Chemicals Company. 

At a pressure of 30 bar and with excess steam the fractional conversion of methane in the reformer is reasonably satisfactory. The high pressure of 30 bar will favour the removal of carbon dioxide, following the shift reaction CO + H2O CO2 + H2, and reduce the cost of compressing the purified hydrogen to a value, typically in the range 50-200 bar, required for ammonia synthesis. 

In some applications water-gas-shift (WGS) is coupled with other reactions. For example, the steam reforming of methane to produce hydrogen is one example where both the forward and reverse reaction may be involved. However, this reaction is accomplished at high temperatures and the reaction is usually considered to be at equilibrium at the high temperatures used. In the following these high temperature processes will not be covered only those instances where the WGS reaction is the dominant reaction that is used to produce and/or purify hydrogen is considered. 

In the US, the plan for 2010 is to develop and demonstrate technology to supply purified hydrogen for PEMFC from biomass at US 2.60/kg at the plant gate (projected to a commercial scale 75,000 kg/day). The objective is to be competitive with gasoline by 2015. There is also a Hydrogen Production from Biomass program" funded at US 1.2 million, which includes pyrolysis, gasification and fermentation. 

The annealing process was experimentally optimized using Silane in Ar [3% Silane in 97% nltra-high pnrity (UHP) Ar)]. Initial experiments were conducted with palladium-purified hydrogen as the carrier gas. Unfortunately, this method... 

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