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Zinc–zinc Oxide Cycle
For chemical reactions, the zinc–zinc oxide cycle or Zn–ZnO cycle is a two step thermochemical cycle based on zinc and zinc oxide for hydrogen production with a typical efficiency around 40%. Process description The thermochemical two-step water splitting process uses redox systems: *Dissociation: ZnO → Zn + 1/2 O2 *Hydrolysis: Zn + H2O → ZnO + H2 For the first endothermic step concentrating solar power is used in which zinc oxide is thermally dissociated at into zinc and oxygen. In the second non-solar exothermic step zinc reacts at with water and produces hydrogen and zinc oxide. The temperature level is realized by using a solar power tower and a set of heliostats to collect the solar thermal energy. See also * Cerium(IV) oxide–cerium(III) oxide cycle * Copper–chlorine cycle * Hydrosol-2 * Hybrid sulfur cycle * Iron oxide cycle * Sulfur–iodine cycle The sulfur–iodine cycle (S–I cycle) is a three-step thermochemical cycle used to produce hydrogen. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zinc Zinc-oxide Thermochemical Cycle
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic table. In some respects, zinc is chemically similar to magnesium: both elements exhibit only one normal oxidation state (+2), and the Zn2+ and Mg2+ ions are of similar size.The elements are from different metal groups. See periodic table. Zinc is the 24th most abundant element in Earth's crust and has five stable isotopes. The most common zinc ore is sphalerite (zinc blende), a zinc sulfide mineral. The largest workable lodes are in Australia, Asia, and the United States. Zinc is refined by froth flotation of the ore, roasting, and final extraction using electricity (electrowinning). Zinc is an essential trace element for humans, animals, plants and for microorganisms and is necessary for prenatal and postnatal development. It is the second ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermal Decomposition
Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is required to break chemical bonds in the compound undergoing decomposition. If decomposition is sufficiently exothermic, a positive feedback loop is created producing thermal runaway and possibly an explosion or other chemical reaction. Decomposition temperature definition A simple substance (like water) may exist in equilibrium with its thermal decomposition products, effectively halting the decomposition. The equilibrium fraction of decomposed molecules increases with the temperature. Examples * Calcium carbonate (limestone or chalk) decomposes into calcium oxide and carbon dioxide when heated. The chemical reaction is as follows: ::CaCO3 → CaO + CO2 :The reaction is used to make Calcium oxide, quick lime, which is an industrially impor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemical Reactions
A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei (no change to the elements present), and can often be described by a chemical equation. Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes can occur. The substance (or substances) initially involved in a chemical reaction are called reactants or reagents. Chemical reactions are usually characterized by a chemical change, and they yield one or more products, which usually have properties different from the reactants. Reactions often consist of a sequence of individual sub-steps, the so-called elementary reactions, and the information on the precise course of acti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sulfur–iodine Cycle
The sulfur–iodine cycle (S–I cycle) is a three-step thermochemical cycle used to produce hydrogen. The S–I cycle consists of three chemical reactions whose net reactant is water and whose net products are hydrogen and oxygen. All other chemicals are recycled. The S–I process requires an efficient source of heat. Process description The three reactions that produce hydrogen are as follows: # I2 + SO2 + 2 H2O 2 HI + H2SO4 (); Bunsen reaction #*The HI is then separated by distillation or liquid/liquid gravitic separation. #2 H2SO4 2 SO2 + 2 H2O + O2 () #*The water, SO2 and residual H2SO4 must be separated from the oxygen byproduct by condensation. #2 HI I2 + H2 () #*Iodine and any accompanying water or SO2 are separated by condensation, and the hydrogen product remains as a gas. : : Net reaction: 2 H2O → 2 H2 + O2 The sulfur and iodine compounds are recovered and reused, hence the consideration of the process as a cycle. This S–I process is a chemical heat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Iron Oxide Cycle
For chemical reactions, the iron oxide cycle (Fe3O4/FeO) is the original two-step thermochemical cycle proposed for use for hydrogen production. It is based on the reduction and subsequent oxidation of iron ions, particularly the reduction and oxidation between Fe3+ and Fe2+. The ferrites, or iron oxide, begins in the form of a spinel and depending on the reaction conditions, dopant metals and support material forms either Wüstites or different spinels. Process description The thermochemical two-step water splitting process uses two redox steps. The steps of solar hydrogen production by iron based two-step cycle are: : \begin \ce &\ce \\ \ce & \ce \end Where M can by any number of metals, often Fe itself, Co, Ni, Mn, Zn or mixtures thereof. The endothermic reduction step (1) is carried out at high temperatures greater than , though the "Hercynite cycle" is capable of temperatures as low as . The oxidative water splitting step (2) occurs at a lower ~ temperature which prod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hybrid Sulfur Cycle
The hybrid sulfur cycle (HyS) is a two-step water-splitting process intended to be used for hydrogen production. Based on sulfur oxidation and reduction, it is classified as a hybrid thermochemical cycle because it uses an electrochemical Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an outco ... (instead of a thermochemical) reaction for one of the two steps. The remaining thermochemical step is shared with the sulfur-iodine cycle. The Hybrid sulphur cycle (HyS)was initially proposed and developed by Westinghouse Electric Corp. in the 1970s, so it is also known as the "Westinghouse" cycle. Current development efforts in the United States are being led by the Savannah River National Laboratory. Process description The two reactions in the HyS cycle are as follows: # H2SO4 → H2O + SO ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Copper–chlorine Cycle
The copper–chlorine cycle (Cu–Cl cycle) is a four-step thermochemical cycle for the production of hydrogen. The Cu–Cl cycle is a hybrid process that employs both Thermochemistry, thermochemical and electrolysis steps. It has a maximum temperature requirement of about 530 degrees Celsius. The Cu–Cl cycle involves four chemical reactions for water splitting, whose net reaction decomposes water into hydrogen and oxygen. All other chemicals are recycled. The Cu–Cl process can be linked with nuclear plants or other heat sources such as solar and industrial waste heat to potentially achieve higher efficiencies, lower environmental impact and lower costs of hydrogen production than any other conventional technology. The Cu–Cl cycle is one of the prominent thermochemical cycles under development within the Generation IV reactor, Generation IV International Forum (GIF). Through GIF, over a dozen countries around the world are developing the next generation of nuclear reactor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cerium(IV) Oxide–cerium(III) Oxide Cycle
The cerium(IV) oxide–cerium(III) oxide cycle or CeO2/Ce2O3 cycle is a two-step thermochemical process that employs cerium(IV) oxide and cerium(III) oxide for hydrogen production. The cerium-based cycle allows the separation of H2 and O2 in two steps, making high-temperature gas separation redundant. Process description The thermochemical two-step water splitting process (thermochemical cycle) uses redox systems: *Dissociation: 2 CeO2 → Ce2O3 + 0.5 O2 *Hydrolysis: Ce2O3 + H2O → 2 CeO2 + H2 For the first endothermic step, cerium(IV) oxide is thermally dissociated in an inert gas atmosphere at and 100-200 mbar into cerium(III) oxide and oxygen. In the second exothermic step cerium(III) oxide reacts at – in a fixed bed reactor with water and produces hydrogen and cerium(IV) oxide. See also * Copper–chlorine cycle * Heliostat * Hybrid sulfur cycle * HYDROSOL * Iron oxide cycle * Solar thermal energy * Sulfur–iodine cycle * Zinc–zinc oxide cycle For chemical react ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
