Hydrogen Production

1. Hydrogen Production Hocking College Nelsonville, Ohio

2. One Advantage of using hydrogen • One advantage is that it stores approximately 2.6 times the energy per unit mass as gasoline, and the disadvantage is that it needs about 4 times the volume for a given amount of energy. A 15 gallon automobile gasoline tank contains 90 pounds of gasoline. The corresponding hydrogen tank would be 60 gallons, but the hydrogen would weigh only 34 pounds.

3. Current global hydrogen production • 48% from natural gas • 30% from oil • 18% from coal • 4% from electrolysis of water

4. Primary Uses for Hydrogen Today • 1. About half is used to produce ammonia (NH3) fertilizer. • 2. The other half of current hydrogen production is used to convert heavy petroleum sources into lighter fractions suitable for use as fuels.

5. Hydrogen Production Processes • Steam Methane Reforming • Coal Gasification • Partial Oxidation of Hydrocarbons • Biomass Gasification • Biomass Pyrolysis • Electrolysis • Thermochemical • Photochemical • Photobiological

6. Steam Methane Reforming • most common method of producing commercial bulk hydrogen. • Most common method of producing hydrogen used in the industrial synthesis of ammonia. • It is the least expensive method. • High temperature process (700 – 1100 °C. • Nickel based catalyst (Ni)

7. The Steam Methane Reforming Process • At 700 – 1100 °C and in the presence of a nickel based catalyst (Ni), steam reacts with methane to yield carbon monoxide and hydrogen. • CH4 + H2O → CO + 3 H2 • Additional hydrogen can be recovered by a lower-temperature gas-shift reaction with the carbon monoxide produced. The reaction is summarized by: • CO + H2O → CO2 + H2

8. Purification of Hydrogen • Carbon dioxide and other impurities are removed from the gas stream, leaving essentially pure hydrogen. • Endothermic reaction (Heat must be added to the reactants for the reaction to occur.)

9. H2O Water Methane Gasoline Ethanol Methanol <100ppm CO 2,000ppm CO 10% CO REFOR MER H2 O2 WATER GAS SHIFT REACTOR REMOVAL OF CO AND CO2 FUEL CELL STACK Schematic of the SMR Process

10. Coal Gasification • well-established commercial technology • competitive with SMR only where oil and/or natural gas are expensive. • coal could replace natural gas and oil as the primary feedstock for hydrogen production, since it is so plentiful in the world.

11. Partial Oxidation Hydrocarbons • process can be used to produce hydrogen from heavy hydrocarbons such as diesel fuel and residual oil. • Any hydrocarbon feedstock that can be compressed or pumped may be used in this technology.

12. Partial Oxidation • methane and other hydrocarbons in natural gas are reacted with a limited amount of oxygen (typically, from air) that is not enough to completely oxidize the hydrocarbons to carbon dioxide and water. • CH4 + ½O2 → CO + 2H2 (+heat) • Exothermic reaction (heat is evolved)

13. Schematic of Partial Oxidation Partial Oxidation Plant Diagram

14. Thermochemical Production of Hydrogen • When water is heated to above 2500 oC, it separates into oxygen and hydrogen in a process known as thermolysis. • However, at such high temperatures, it is difficult to prevent the oxygen and hydrogen from recombining to form water.

15. Thermochemical Production of Hydrogen • Thermochemical water-splitting cycles can lower the temperature and help separate oxygen and hydrogen products to produce pure hydrogen gas. • These cycles can improve the efficiency of hydrogen production from 30% for conventional electrolysis to around 50% efficiency • One of the most promising cycles so far is the sulfur-iodine (S-I) cycle.

16. Sulfur dioxide (SO2 ) and iodine (I2) are fed into the cycle as chemical catalysts.. • A catalyst lowers the activation energy of a reaction without being used up by the reaction.

17. Sulfur-Iodine Thermochemical Cycle • In this cycle, sulfur dioxide (SO2) and iodine (I2) are feed into the cycle as a chemical catalyst. • A catalyst lowers the temperature at which the reaction will occur without being used up by the reaction.

18. There are three steps in the S-I cycle • Step 1: • I2 + SO2 + 2H2O 2HI + H2SO4 • The reaction is run at 120 degrees C. • The hydrogen iodide and sulfuric acid are separated, usually by distillation.

19. Step 2: • Generation of oxygen and regeneration of SO2. • H2SO4 H2O + SO2 + 1/2 O2 • This reaction is run at 850 degrees C.

20. Step 3: Generation of hydrogen and regeneration of I • 2HI H2 + I2 • This reaction is run at 450 degrees C.

21. Sulfur—Iodine Cycle • These reactions can reduce the high temperature demands of the thermolysis of water for the production of hydrogen gas and can provide a mechanism for the separation of oxygen and hydrogen products to prevent recombination. Source: Office of Nuclear Energy, Science and Technology

22. Biomass Production of Hydrogen • Hydrogen can be produced numerous ways from biomass. • Biomass is defined as a renewable resource made from renewable materials. Examples of biomass sources include: >switchgrass >plant scraps >garbage >human wastes • Gasification of biomass could be a way of extracting hydrogen from these organic sources.

23. Biomass Production of Hydrogen • The biomass is first converted into a gas through high-temperature gasifying. • The hydrogen rich vapor is condensed in pyrolysis oils. • These oils can be steam reformed to generate hydrogen. • This process has resulted in hydrogen yields of 12% - 17% hydrogen by weight of the dry biomass. • When biological waste material is used as a feedstock, this process becomes a completely renewable, sustainable method of hydrogen generation.

24. Electrolysis • Electrolysis is the technical name for using electricity to split water into its constituent elements, hydrogen and oxygen. • The splitting of water is accomplished by passing a DC electric current through water. • The electricity enters the water at the cathode, a negatively charged terminal, passes through the water and exists via the anode, the positively charged terminal. • The hydrogen is collected at the cathode and the oxygen is collected at the anode. Electrolysis produces very pure hydrogen for use in the electronics, pharmaceutical and food industries

25. Electrolysis • The hydrogen is collected at the cathode and the oxygen is collected at the anode. • Electrolysis produces very pure hydrogen for use in the electronics, pharmaceutical and food industries.

26. Photobiological • This method involves using sunlight, a biological component, catalysts and an engineered system. • Specific organisms, algae and bacteria, produce hydrogen as a byproduct of their metabolic processes. • These organisms generally live in water and therefore are biologically splitting the water into its component elements. • Currently, this technology is still in the research and development stage and the theoretical sunlight conversion efficiencies have been estimated up to 24%.