RXN Communications FAQ - Hydrogen (H)



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Q	1. Information from the American Hydrogen Association.
A	The American Hydrogen Association is a non-profit association for the advancement of inexpensive, clean, and safe hydrogen energy systems. They provide answers to the following Frequently Asked Questions about Hydrogen: Hydrogen: Frequently Asked Questions Courtesy of: The American Hydrogen Association I. General Description II. Production Methods A. Electro-chemical B. Chemical C. Biological D. Photoconversion III. Storage A. Gas B. Liquid C. Slush D. Metal Hydrides E. Other IIIA. Purification A. Iron/Water cycle B. Etc. IV. Transportation A. Pipeline 1. Hythane B. Other V. Use A. Fuel Cells B. Internal Combustion Engines 1. Rotary-Type Engines C. Other VI. Sources For Further Information A. Professional Associations B. Periodicals and Newsletters C. Calendar of Events D. Publications Bibliography E. Vendors List F. Government Organizations G. Related Electronic Lists/Newsgroups Questions can be directed to Roy McAlister (aha@getnet.com). See also the newsgroup Sci.Energy.Hydrogen or the listserver at listerv@uriacc.uri.edu. Special thanks go to Roy McAlister, President of the American Hydrogen Association, and Daniel Morgan, Ph.D. for their help in putting together this FAQ. I. General Descriptions Hydrogen is the universes most abundant element, but most of it is bound up in chemical compounds. It must be extracted from these compounds rather than simply collected before use. Some methods of this extraction process are outlined later in this FAQ. The following chart is a summary of some of the chemical properties of hydrogen: -------------------------------------------------------------------- TABLE 1. PHYSICAL AND CHEMICAL PROPERTIES OF HYDROGEN 1. Electron Structure S1 2. Covalent Radius 0.37 A (He = 0.93 A) 3. Electronegativity (Pauling) 2.1 4. Specific Heat (Cp) 3.44 Cal/Gram deg K (Cv) 2.46 Cal/Gram deg K (Cp/Cv) 1.40 5. Gas Density (Deg. C, 1ATM) 0.0899 Gram/Liter 6. Gas Specific Gravity (Air - 1.0) 0.0695 Gram/Liter 7. Gas Self Diffusion Const. (Deg. C, 1ATM) 0.61 Cm2/Sec 8. Boiling Point -252.7 C 9. Melting Point -259.2 C -------------------------------------------------------------------- Hydrogen is extensively used in the chemical process, food,and fuels industries. Many electricity power plant generators are cooled by gaseous hydrogen because it provides the highest specific heat and best combination of dielectric strength and low viscosity. Hydrogen is used in hydride heat pumps, in Joule-Thompson cooling, and as a heat transfer medium. II. Production Methods Since hydrogen must be extracted from other sources, it can be considered an energy carrier rather than an energy source. The energy that is produced when it is used is simply the amount of energy that was stored, minus any losses. There are several different methods of extracting hydrogen from sources. They are outlined as follows: A. Electro-chemical Electrolysis is the process whereby electricity is passed through a meduim, in the case of hydrogen is usually water, and the basic elements are released. In the case of water, one mole of water yields two moles of hydrogen and one mole of oxygen. Common energy efficiencies for electrolysis are 65 percent, with 80-85 percent currently possible. Cost of production is high, so electrolysis is expected to be limited to niche markets in the near and mid term. The primary idea in lowering the cost of electrolysis is in lowering the cost of the electricity to run through the water. In the solar hydrogen scenario, solar collectors would be utilized to run electricity from the sun through water and create hydrogen. The hydrogen could then be captured and stored or used immediately. The cost of producing hydrogen in such a manner would probably drop quite a bit. B. Chemical Every elemental metal that is less noble than hydrogen will displace hydrogen from water. A well known reaction is between an active metal such as sodium or potassium and water: 2Na + 2H2O ----> H2 + 2NaOH + HEAT The "producer" reaction has been practiced since its discovery in about 1800 for producing hydrogen from a carbon donor and water: HEAT + C + H2O ----> H2 + CO Since the discovery of petrocarbons such as oil and natural gas, hydrogen has been produced in large quantities by reacting steam with petroleum hydrocarbons: HEAT + CxHy + xH2O ----> (x + 0.5y) H2 + xCO C. Biological Bacteria and other microorganisms (particularly those that live in anaerobic conditions) may release hydrogen in the process of creating heavier hydrocarbons or oxygen for assimilation. All methane that has been produced from biomass probably involved the precursor steps of hydrogen production by an anaerobic microorganism and fixing of the hydrogen with carbon from carbon dioxide as the microorganism derived the oxygen for its own use. D. Photoconversion Numerous bacteria and all green plants dissociate water into hydrogen and oxygen as the first step of photosyntheses. Hydrogen is retained to build plant tissues by reactions that combine carbon from atmospheric carbon dioxide with hydrogen. Oxygen is released to the atmosphere in the process. LIGHT + H2O -------> 2H2 + 0.5O2 LIGHT + H2 + CO2 --------> Plant Tissues III. Storage A. Gas Compressed gas storage and transportation has been widely used for more than 100 years. Common materials for storage canisters are mild steel, aluminum, and composites. Storage pressures of 3,000 to 10,000 PSI are common. B. Liquid Cooling hydrogen to below the boiling point of -252.7 C allows storage as a cryogenic liquid without the need for pressurization. Cryogenic storage of hydrogen allows regular commercial shipment by truck and rail. Many commercial processes such as glass manufacturing, brazing, heat treating, food hydrogenation, and semiconductor manufacturing are served by deliveries of liquid hydrogen. Liquid hydrogen has facilitated the U.S. space exploration program. C. Slush If liquid hydrogen is suddenly subjected to a vacuum it will evaporate with a subsequent cooling of the liquid mass to cause the temperature to fall below the freezing point of -259.2 C and solid hydrogen will be produced. This mixture of liquid and solid hydrogen is called "slush" and provides more dense storage of hydrogen than liquid hydrogen. D. Metal Hydrides Metal hydride systems store hydrogen in the interatom spaces of a granular metal. Various metals can be used. The hydrogen is released by heating. These systems are reliable and compact, but they can be heavy and expensive. E. Other IIIA. Purification A. Iron/Water cycle B. Etc. IV. Transportation A. Pipeline Hydrogen can be transported via pipelines much the same way natural gas and oil are currently transported. A1. Hythane B. Other V. Use A. Fuel Cells One type of fuel cell works because hydrogen is sent through a PEM (proton exchange membrane). The hydrogen atom is broken up so that an electron is stripped off and sent through an electrical circuit while the proton of the atom goes through the membrane. The electron travels around the circuit and rejoins the proton as it is oxidized to form water, having been harnassed for energy along the way. In this manner, we are able to get energy out of a fuel cell without any pollution. B. Internal Combustion Engines Engines can be converted from gasoline to hydrogen fairly simply. The biggest cost involvement is in purchasing the tank, although in many cities these tanks can be leased or rented. Engines can also be made to run on hydrogen initially. These would be more effective since they would be built to take advantage of the fast-burn and far-lean combustion characteristics of hydrogen. Many of the automobile companies have already designed cars and trucks that use hydrogen, most notibly BMW, Mazda, and many others have made prototype cars. Contact the professional associations listed below for more information as this is a rapidly changing field. 1. Rotary-Type Engines Mazda is currently pioneering this effort and have built several cars running this type of engine on hydrogen. There are numerous articles on this type of engine, see SAE technical paper #920302 for more information. This type of engine also has been reviewed in many popular magazines. C. Other There are many other kinds of uses for hydrogen. It is being used in stationary turbines and aircraft engines. Most notably, there were jets that were powered by hydrogen, and in 1980 a propellor plane was fitted to run on hydrogen. VI. Sources for Further Information A. Professional Associations American Hydrogen Association 216 South Clark Drive, suite 103 Tempe, AZ 85281 (602) 921-0433 National Hydrogen Association Suite 910 1101 Connecticut Avenue, S.W. Washington, DC 20036 (202) 223-5547 International Association for Hydrogen Energy PO Box 248266 Coral Gables, FL 33124 B. Periodicals and Newsletters Hydrogen Today American Hydrogen Association 216 South Clark Drive, Suite 103 Tempe, AZ 85281 (602) 921-0433 C. Calendar of Events D. Publications Bibliography E. Vendors List F. Government Organizations G. Related Electronic Lists/Newsgroups AE@SJSUVM1.SJSU.EDU -- List Manager: Clyde Visser: CVISSER@CRMATH.UCR.EDU General list for discussion of all practical aspects and applications of Alternative Energy. A message archive is maintained by the LISTSERV. To subscribe, send mail to LISTSERV@SJSUVM1.SJSU.EDU with a message consisting of: SUBSCRIBE AE your-firstname your-lastname To get a DIGEST form of the list instead of individual messages, send mail to: LISTSERV@SJSUVM1.SJSU.EDU with a message consisting of: SET AE DIGEST (These two may be combined) EV@SJSUVM1.SJSU.EDU -- List Manager: Clyde Visser: CVISSER@UCRMATH.UCR.EDU General list for discussion of all practical aspects and applications of Electric Vehicles. An anonymous FTP directory is located on: HMCVAX.CLAREMONT.EDU in the directory info-ev-archive (scans of EVs in the images subdirectory). A message archive is maintained by the LISTSERV. To subscribe, send mail to: LISTSERV@SJSUVM1.SJSU.EDU with a message consisting of: SUBSCRIBE EV your-firstname your-lastname To get a digest form of the list instead of individual messages, send mail to: LISTSERV@SJSUVM1.SJSU.EDU with a message consisting of: SET EV DIGEST (These two may be combined in one message)
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Q	2. What about water?
A	Water is made up of Hydrogen and Oxygen. The following facts about water are available: 1.0 Definitions Acidity: The quantitative capacity of aqueous media to react with hydroxyl ion. [1] Alkalinity: The quantitative capacity of aqueous media to react with hydrogen ion. [1] Brine: Water that contains dissolved matter at an approximate concentration of more than 30,000 mg/L. [1] Cell Constant: Conductivity measurements are affected by measurement cell geometry. Specific conductivity is calculated by multiplying the measured conductivity by the electrode's cell constant. For parallel plates, the cell constant is the distance of plate separation divided by the plate area. Conductivity, Electrical: The reciprocal of the resistance in ohms measured between opposite faces of a centimetre cube of aqueous solution at a specified temperature. [1] 1 Cell Area --------------- = Conductivity x ----------- Cell Resistance Cell Length Conductivity values are usually expressed in microsiemens/centimetre (uS/cm) or millisiemens/centimeter (mS/cm), where 1 siemen (S) = 1 mho. Hardness: The polyvalent-cation concentration of water, generally calcium and magnesium. [1] Ion Exchange: A reversible process by which ions are inter-changed between an insoluble material and a liquid with no substantial structural changes of the material. [1] Ion Exchange Capacity: The number of milliequivalents of exchangeable ions per millilitre of backwashed and settled bed of ion exchange material in its standard form. [1] Ion Exchange Material: An insoluble material that has the ability to exchange reversibly certain ions in its structure, or attached to its surface as functional groups, with ions in a surrounding medium. [1] Ion Exchange Resin: A synthetic, organic ion exchange material. [1] pH: The negative logarithm of the hydrogen ion activity in an aqueous solution, or, the logarithm of the reciprocal of the hydrogen ion activity. [1] Resistivity, Electrical: The resistance in ohms measured between opposite faces of a centimetre cube of an aqueous solution at a specified temperature. [3] Cell Length Cell Resistance = Resistivity x ----------- Cell Area Resistivity values are usually expressed in ohm-centimetres, or in megohm-centimetres, at a specified temperature. [3] Salinity: The saltiness of natural water. The salinity of normal seawater is 35 parts salt per 1000 parts water. [4] 2.0 Reagent Water [2] Type Type Type Type Attribute Units I II III IV Total Matter mg/L <0.1 <0.1 <1.0 <2.0 Conductivity @ 25 C umho/cm <0.06 <1.00 <1.00 <5.00 Resistivity @ 25 C Mohm-cm >16.7 >1.0 >1.0 >0.2 pH @ 25 C pH [A] [A] 6.2-7.5 5.0-8.0 KMnO4 Color Retention min >60 >60 >10 >10 Soluble Silica ug/L <1 <1 <10 any Note [A]: The measurement of pH in Type I and Type II water is not useful as the electrodes are found to contaminant the solutions. 2.1 Type I Water Type I reagent water can be used when maximum precision and accuracy are required. This water is typically prepared by distillation followed by ion exchange polishing followed by membrane filtration. This water should be protected from atmospheric contamination. 2.2 Type II Water Type II reagent water can be used for most analytical procedures and all procedures requiring water low in organics. This water is typically prepared by distillation. This water should be protected from atmospheric contamination. 2.3 Type III Water Type III reagent water can be used for general laboratory practice. This water is typically prepared by suitable distillation, ion exchange, or reverse osmosis followed by filtration. This water should be protected from atmospheric contamination. 2.4 Type IV Water Type IV reagent water can be used for high volume applications for test solutions, rinse water, and wash water. This water is typically prepared by suitable distillation, ion exchange, reverse osmosis, or electrodialysis. 2.5 Microbiological Contamination Attribute Type A Type B Type C Bacteria Count 0/ml <10/ml <100/ml 3.0 Water Measures 3.1 Electrical Resistivity Conductivity Conductivity NaCl Water (Mohm-cm) (umho/cm) (uS/cm) (ppm) 0.000004 226,000. 226,000. Saturated 0.000014 67,200. 67,200. 50,000. Sea Water 0.00002 50,000. 50,000. 25,126. 0.0001 10,000. 10,000. 5,025. 0.0002 5,000. 5,000. 2,512. 0.001 1,000. 1,000. 502.5 Tap Water 0.01 100.0 100.0 50.2 0.1 10.00 10.00 5.02 Type IV 0.2 5.000 5.000 2.51 0.4 2.500 2.500 1.26 0.8 1.250 1.250 0.63 Type II 1.0 1.000 1.000 0.50 1.6 0.625 0.625 --- 3.2 0.312 0.312 --- 6.4 0.156 0.156 --- 12.8 0.078 0.078 --- Type I 16.7 0.060 0.060 --- Ideal 18.3 0.055 0.055 --- 3.2 Total Dissolved Solids (TDS) Conductivity can be used to estimate total dissolved solids (TDS) and salinity. The general rule is that as the ion concentration increases, conductivity increases. This measurement will not differentiate between the contribution of different ions, but will give an estimate of total ion concentration. This estimate of TDS is accurate for fully ionized solids with no solution interactions (NaCl), but less accurate for solids with some ionic interactions in the solution (organics, concentrated solutions). Typical uS/cm to ppm conversion factors run from 0.48 to 0.64, depending on solution. 3.3 pH... 10.0 References [1] ASTM D1129 'Standard Definitions of Terms Relating to Water', ASTM, Philadelphia, PA, 1988. [2] ASTM D1193 'Standard Specification for Reagent Water', ASTM, Philadelphia, PA, 1988. [3] ASTM D1125 'Standard Test Methods for Electrical Conductivity and Resistivity of Water', ASTM, Philadelphia, PA, 1988. [4] R. J. Lewis, Hawley's Condensed Chemical Dictionary, 12th Ed., Van Nostrand Reinhold Company, NY, 1993.
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Q	3. Other links to Hydrogen resources?
A	A good place to look for links to Hydrogen resources might be here.
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