Production, hydrogen

Hydrogen pipelines are used throughout the world. In the United States about 720 kilometers (450 miles) of hydrogen pipelines exist while Europe has about 1500 kilometers (950 miles). Thailand and Brazil also have hydrogen pipelines that are less than 10 miles long173. 

Hydrogen is a non-toxic, colorless, odorless and tasteless gas. It is the lightest and most abundant element (making up over 90% of the atoms in our universe), but it is present at only extremely low levels (0.1 ppm) as a pure element in the earth s atmosphere. More than 50% of the atoms in our environment (the soil beneath our feet, the atmosphere, the oceans, petroleum-based gases and liquids) are hydrogen. 

Hear I.L Aauaoiu piodnction chtancal tuctioxu tad t pj to prsdoc altejonil piodoctj. 

Some of the physical properties of hydrogen are shown in Table 5.1 

Chemical Symbol Molecular Weight h2 2.02 Metric Units English Units 

For the production of hydrogen, the steam reformer is operated at high severity to obtain maximum methane conversion and early hydrogen plants used exactly the same catalysts as ammonia plants, except for the secondary reformer. The 

Presently, the most common method for the production of molecular hydrogen on an industrial basis is steam reforming, a process in which steam is allowed to react with fossil fuels at high temperatures, according to the following reaction  

The energy required (i.e. the enthalpy change AH) for methane steam reforming, for example, is +49 kcal/mol [25]. A second well-established and widely applied method for hydrogen production, introduced during the early days of electrochemistry in the 1800s and that has recently become commercially available, concerns electrolysis of water, 

1 Hydrogen Production in Nature Fortunately, nature has found a way to produce molecular hydrogen very efficiently, by using metalloenzymes as catalysts for this reaction. The proteins that evolve hydrogen are called hydrogenases, and they catalyze both the formation and the decomposition of molecular hydrogen  

In terms of the specific components, advancement to each step of the cycle is possible because the absorption of light and the transfer of excitation energy to P680 leads to formation of an extremely strong oxidant. The preparation of an analogous durable synthetic system that can be selectively switched into a strong oxidizing form 

In conclusion, the challenge in terms of fundamental chemistry is broadly understood there are multiple potential ways to address it, but the best way is by no means 

In Table 2.1, the contributions of the different sources to the current worldwide hydrogen production are summarized, together with the available technologies used for each raw material. 

The pathways involving fossil fuels (natural gas, refinery oil and coal) that provide for almost 96% of the total production of hydrogen, release carbon dioxide in the atmosphere. 

Innovative strategies able to capture and sequestrate carbon dioxide emissions, so-called Carbon Capture and Sequestration (CCS) technologies, are the object of several analysis and heated debate. CCS technologies should be applied for an environmental-friendly diffusion of fossil fuel-based H, production methods, but they are presently in the embryonic stage of development and certainly would involve a great growth of costs. 

On the other hand, water electrolysis, which is an intrinsic carbon-free method 

the costs will certainly represent one of the most important barriers to be 

---

The hydrogen product obtained has a purity between 97 and 99.9 volume %. The balance is methane, and the by-product of the process is CO2. 

Typical COED syncmde properties are shown in Table 12. The properties of the oil products depend heavily on the severity of hydroprocessing. The degree of severity also markedly affects costs associated with hydrogen production and compression. Syncmdes derived from Western coals have much higher paraffin and lower aromatic content than those produced from Illinois coal. In general, properties of COED products have been found compatible with expected industrial requirements. 

Much more important is the hydrogenation product of butynediol, 1,4-butanediol [110-63-4]. The intermediate 2-butene-l,4-diol is also commercially available but has found few uses. 1,4-Butanediol, however, is used widely in polyurethanes and is of increasing interest for the preparation of thermoplastic polyesters, especially the terephthalate. Butanediol is also used as the starting material for a further series of chemicals including tetrahydrofuran, y-butyrolactone, 2-pyrrohdinone, A/-methylpyrrohdinone, and A/-vinylpyrrohdinone (see Acetylene-DERIVED chemicals). The 1,4-butanediol market essentially represents the only growing demand for acetylene as a feedstock. This demand is reported (34) as growing from 54,000 metric tons of acetylene in 1989 to a projected level of 88,000 metric tons in 1994. 

Fig. 1. Hydrogen production flow sheet, showing steam reforming, shift, hot potassium carbonate CO2 removal, and methanation.

Use of a low temperature shift converter in a PSA hydrogen plant is not needed it does, however, reduce the feed and fuel requirements for the same amount of hydrogen production. For large plants, the inclusion of a low temperature shift converter should be considered, as it increases the thermal efficiency by approximately 1% and reduces the unit cost of hydrogen production by approximately 0.70/1000 (20/1000 ft ) (140,141). 

Direct, One-Step Thermal Water Splitting. The water decomposition reaction has a very positive free energy change, and therefore the equihbrium for the reaction is highly unfavorable for hydrogen production. 

Table 9. Operating Conditions for Hydrogen Production Electrolyzers ...

Multistep Thermochemical Water Splitting. Multistep thermochemical hydrogen production methods are designed to avoid the problems of one-step water spHtting, ie, the high temperatures needed to achieve appreciable AG reduction, and the low efficiencies of water electrolysis. Although water electrolysis itself is quite efficient, the production of electricity is inefficient (30—40%). This results in an overall efficiency of 24—35% for water electrolysis. 

Whereas most of the technology for hydrogen production, transportation, and usage is viable as of 1994, research efforts are needed to make them more economically attractive. 

W. E. Eong and M. E. Quiatana, HyTex—v4 Novel Process for Hydrogen Production, NPRA 89th Annual Meetiag, Match 17—19,1991, San Antonio, Tex. 

Use of 1,3 cycloaHphatic diamines in polyamides may be similarly limited by internal amide dehydration of the conformationaHy labile cis isomers to form a tetrahydropyrimidine (38) rather than high molecular weight polyamide. 1,3-Cyclohexanediamine is, however, a component of Spandex polyureas Du Pont uses the hydrogenation product of y -phenylenediamine [108-45-2] (24) captively to produce Lycra (see Fibers, elastomeric). 

Shift Conversion. Carbon oxides deactivate the ammonia synthesis catalyst and must be removed prior to the synthesis loop. The exothermic water-gas shift reaction (eq. 23) provides a convenient mechanism to maximize hydrogen production while converting CO to the more easily removable CO2. A two-stage adiabatic reactor sequence is normally employed to maximize this conversion. The bulk of the CO is shifted to CO2 in a high... 

A similar but somewhat less ambitious approach is to carry out dehydrogenation of ethylbenzene and oxidation of the hydrogen product alternately in separate reactors containing different catalysts ... 

Reforming Conditions. The main process variables are pressure, 450—3550 kPa (50—500 psig), temperature (470—530°C), space velocity, and the catalyst employed. An excess of hydrogen (2—8 moles per mole of feed) is usually employed. Depending on feed and processing conditions, net hydrogen production is usually in the range of 140—210 m /m feed (800—1200 SCF/bbl). The C —products are recovered and normally used as fuels. 

The reaction is exothermic, and its equiUbrium, unaffected by pressure, favors hydrogen production as the reaction temperature is reduced (see Fuels, synthetic Hydrogen). 

---