Hydrogen - Overview
Hydrogen- future society From International Society of Hydrogen Energy
Hydrogen Hydrogen is not a source of energy, while solar, wind, natural gas and oil are. There are no naturally occurring sources or reservoirs of hydrogen on earth. Hydrogen can be extracted from fossil fuels, or can be produced by using the process of electrolysis to split water into hydrogen and ozxygen. Both these processes require energy. This energy can be provided by fossil fuels or renewable sources of energy like solar and wind.
Hydrogen- Usage Ammonia and methanol production as well petroleum refining require huge amounts of hydrogen In the electronic industries, hydrogen is used to produce silicon, which is needed for semiconductor processing In metallurgic industry, hydrogen is used to remove oxygen in annealing, sintering and in furnace brazing Hydrogen and oxygen are the main propellants of rocketpowered spacecraft, missiles in the aerospace industry
Hydrogen-Properties Symbol: H; gas H 2 Oxidation number +1 Density: gas 0.090 kg/m 3, (air 1.3 kg/m 3 ) liquid 70.8 kg/m 3 solid: 70.6 kg/m 3 Melting Point: -259.3 C Boiling Point: - 252.9 C
Hydrogen-Properties Molar Mass 2.106 g/mol Electron binding (ionisation) energy in 1s ground state 2.18 aj* Average distance between nucleons, H 2 0.074 nm Dissociation energy, H 2 to H at infinite separation 0.71 aj* Ionic conductance at diluted H+ ions in water at 298 K 0.035 m 2 /mol/ω Specific heat at constant pressure and 298 K 14.3 kj/kg/k Solubility in water at 1 bar, 298 K 0.019 m 2 /m 3 * aj = attojoule = 10-18 Joule
Hydrogen Hydrogen does not smell and is colorless and nontoxic. Hydrogen has a high caloric value, the lowest molecular weight, the highest thermal conductivity and the lowest density among all gases. 0.324 g of hydrogen has the same energy content as 1 kg gasoline but 1 kg gasoline corresponds to a volume of 1.3 liters while 324 g hydrogen occupies 3.932 liters.
Hydrogen 1 kg hydrogen gas contains as much energy as 2.1 kg natural gas or 2.8 kg gasoline. The fraction of hydrogen in common water is 11.2 % of weight. Approximately 500 billions m 3 hydrogen are produced, stored and transported worldwide. Mostly used in the chemical process industries.
Hydrogen Air mixtures with hydrogen are explosive in certain proportions. If the gas mixture comprises two volume parts hydrogen and one volume part oxygen the reaction is very violent. The flame temperature of hydrogen is 2600 C, almost invisible but light blue.
Hydrogen be careful
Hydrogen Production and Delivery Biological Water Splitting Fermentation Conversion of Biomass and Wastes Photoelectrochemical Water Splitting Solar Thermal Water Splitting Renewable Electrolysis, e.g., wind energy From Fossil fuels
Biological Water Splitting Certain photosynthetic microbes use light energy to produce hydrogen from water as part of their metabolic processes. Becuase oxygen is produced along with the hydrogen, photobiological hydrogen production technology must overcome the inherent oxygen sensitivty of hydrogen evolving enzyme.
Fermentation Pretreatment to convert lignocellulosic biomass into sugar-rich feedstocks that can be directly fermentated to produce hydrogen, ethanol and high value chemicals Fermentation of crystalline cellulose directly to hydrogen means lower feedstock costs
Conversion of Biomass and Wastes Hydrogen can be produced by pyrolysis or gasification of biomass resources, e.g., agricultural residues
Photoelectrochemical Water Splitting This is the cleanest way to produce hydrogen by using the sunlight to directly split water into hydrogen and oxygen
Solar Thermal Water Splitting Ultrahigh temperatures are required for thermochemical reaction cycles to produce hydrogen. High flux solar furnace reactors concentrating the solar energy generate temperatures between 1000 and 2000 C.
Renewable Electrolysis Renewable energy sources like photovoltaics, wind, biomass, hydro and geothermal can provide clean and sustainable electricity which also can be used for electrolysis splitting of water.
Illustration of Electrolysis of Water by Electricity
From fossil fuels Industrial production dominated by using methane (natural gas) Bad thing: Generation of CO 2
From fossil fuels Steam reforming is commonly used today to produce hydrogen from fuels based on hydrocarbons, like natural gas or biogas. Industrial reforming of natural gas A high temperature (700 C 1100 C) and presence of a metal based catalyst makes steam to react with methane and carbon monooxide and hydrogen are created. The reaction is endothermal and requires a lot of energy, CH 4 + H 2 O CO + 3 H 2
From fossil fuels The biproduct carbon monooxide can be used together with water to produce additional hydrogen. This process occurs at a lower temperature, The reaction is exothermal (energy is released). CO + H 2 O CO 2 + H 2
From fossil fuels Reforming of gases not being methane As oil is extracted, gases naturally present are exhausted. This may create environmental problems for workers as well as having negative effects on the climate. However, these gases can be collected and be used as fuels. Hydrocarbons not being methane are first converted to synthetic gas (H 2 + CO) and then to methane (CH 4 ), carbon dioxide (CO 2 ) and hydrogen (H 2 ). Compared to the steam reforming process, this latter reforming occurs at low temperature and less steam is needed.
Storage of Hydrogen
Storage of Hydrogen In gaseous form at high pressure (700 bar) in special high-pressure containers
Storage of Hydrogen in High Pressure Vessels Cheap and most common in steel vessels Typical pressure range: 200-700 bar Disadvantages: high weight and big volume
Storage of Hydrogen In liquid form. It needs to be chilled and compressed. Very cold, below -423.2 Fahrenheit
Storage of Hydrogen in Zeolites A zeolite is a material consisting of silicon and aluminum in crystalline and microporous form. Pore size 0.3-1 nm. At pressure 30 bar, temperature 327 C, the hydrogen molecules are forced into the material. As temperature and pressure are reduced, the hydrogen becomes bounded in the crystal. Disadvantage: low storage capacity, 0.7 % weight is hydrogen.
Storage of Hydrogen in Iron In a vessel with corroded surfaces hydrogen can be bounded in the corroded material and the material is converted to iron. To extract the hydrogen, water steam is supplied and the corrosion process restarts. Storage capacity: 4.5 % weight is hydrogen
Storage of Hydrogen in Metal Hydrides A metal hydride is an alloy of a metal and hydrogen. Magnesiumhydride has the best storage capacity, 7.6 % weight is hydrogen. The hydrogen is splitted up as it comes in contact with magnesium which is pulverized. 30-55 bar pressure during filling. Heat is released during the process and as hydrogen should be extracted heat has to be supplied.
Storage of Hydrogen in Metal Hydrides The metal hydrides are sensitive to poisoning by water and oxygen but also by sulphur oxide dihydrogensulphid, carbon monooxide and carbon dioxide.
Metal hydride storage
Storage of hydrogen in sodiumboron-hydrides - Power balls Hydrogen can be stored by using sodium-boron-hydride (NaBH 4 ) which is produced by heating sodium-hydrooxide (NaOH). As NaBH 4 reacts with water, hydrogen is created. The NaBH 4 can be formed as balls or pellets. The rest product of the reaction of NaBH 4 and H 2 O is called Borax, NaBO 2. The Borax can be exchanged and re-charged with hydrogen. Borax is available to a large extent in out-dried salty lakes. The NaBH 4 is not explosive and not risky for fires. It can be stored at atmospheric pressure. The storage capacity is estimated to be 4.3 weight % hydrogen at a density of 47 kg/m 3.
Storage in hydrogen pills In hydrogen pills, hydrogen is reacting with nitrogen to form ammonia which is stored in salt crystals of magnesium chlorine. Up to 9.1 % weight of the pills can be hydrogen. (1 litre of hydrogen pills corresponds to 1 litre of gasoline).
Properties of Some Fuels Comparison of some properties of some fuels Property Hydrogen Methanol Methane Propane Gasoline Min. Energy of Ignition, 0.02-0.29 0.25 0.24 10-3 J Flame Temperature, C 2045 1875 2200 Auto-Ignition 585 385 540 510 230-500 Temperature in Air, C Max. Flame Velocity, 3.46 0.43 0.47 m/s Range of Flammability 4-75 7-36 5-15 2.5-9.3 1.0-7.6 in Air, vol. % Range of Explosivity in 13-65 6.3-13.5 1.1-3.3 Air, vol. % Diffusion coefficient in air, 10-4 m 2 /s 0.61 0.16 0.20 0.10 0.05
Energy Density - Comparison Storage form Energy Density kj/kg Energy Density MJ/m 3 Density kg/m 3 Hydrogen, gas (100 kpa, 1 120 000 10 0.090 bar) Hydrogen, gas (200 bar) 120 000 1 900 15.9 Hydrogen, gas (300 bar) 120 000 2 700 22.5 Hydrogen, liquid 120 000 8 700 71.9 Hydrogen in metal hydrides 2 000-9 000 5 000-15 000 Hydrogen in metal hydride, 2 100 11 450 5 480 typical Methane (natural gas), (100 56 000 37.4 0.668 kpa) Methanol 21 000 17 000 0.79 Ethanol 28 000 22 000 0.79