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One of the industrial methods for producing hydrogen: Hydrogen is an important industrial gas. In industry, hydrogen is produced using various methods, which depend on the raw materials, equipment, and costs involved, as well as the required purity of the hydrogen. ①In the electrolysis method, direct current is passed through water using platinum electrodes (or other inert materials); hydrogen gas is produced at the cathode, with a purity of 99.5–99.8%. In the chlor-alkali industry, when saturated saltwater is electrolyzed to produce chlorine and caustic soda, hydrogen gas is also generated as a by-product. ② Water-gas conversion method: Water vapor is passed through a layer of hot coke to produce water gas; this water gas is then mixed with more water vapor, and with iron oxide as a catalyst, the CO in the water gas is converted into CO2. Carbon dioxide dissolved in water can be used to produce relatively pure hydrogen gas through pressure washing. ③Hydrocarbon cracking method: Hydrocarbons are cracked at high temperatures, and the cracking gas contains large amounts of hydrogen; through a low-temperature freezing system, 90% hydrogen can be obtained. Such as methane cracking: ④ Hydrocarbon vapor conversion method – Under high temperature and in the presence of a catalyst, hydrocarbons react with water vapor to produce a mixture mainly consisting of hydrogen and carbon monoxide. For example, CO can be removed using molecular sieve adsorption or water-gas conversion methods, thereby obtaining pure hydrogen. Hydrogen can be obtained from natural gas, oil field gas, and refinery gas (by-products of oil refining plants) using hydrocarbon cracking and hydrocarbon steam reforming methods. Another industrial method for producing hydrogen: There are several ways to produce hydrogen on an industrial scale: (1) Electrolysis of water. In an electrolytic cell, a 25% NaOH solution is electrolyzed at a temperature of 80–85°C; hydrogen is produced at the cathode, while oxygen is produced at the anode. At the cathode: 4H++4e===2H2. At the anode: 4OH-====2H2O+O2+4e. Since H+ and OH- arise from the ionization of H2O, the reaction for electrolyzing H2O is as follows. The hydrogen produced in this way contains very few impurities, with a purity of 99.7%~99.8%. (2) Electrolysis of brine method: In the chlor-alkali industry, a saturated solution of salt is electrolyzed at a temperature of 70–80°C; in addition to chlorine and sodium hydroxide, hydrogen can also be produced. The main reactions are as follows: At the anode, 2Cl- ==== Cl2 + 2e; at the cathode, 2H+ + 2e ==== H2. OH- ions and Na+ ions accumulate near the cathode. (3) In the water-gas shift process, steam is first passed through hot anthracite or coke to produce water gas; then this water gas is mixed with an excess of steam, and under the action of a catalyst at temperatures between 450 and 550°C, the carbon monoxide in the water gas is converted into carbon dioxide, thereby increasing the hydrogen content in the mixture. Finally, the mixture of carbon dioxide and hydrogen is pressurized (to 12–30 atmospheres), and carbon dioxide is removed through washing with water or absorption with ammonia, thereby separating out hydrogen. (4) Obtain hydrogen from gaseous fuels such as natural gas, refinery gas (by-product gas from oil refineries), and field gas. All of these fuel gases contain large amounts of hydrocarbons. Under certain conditions, it can react with water vapor or oxygen to produce carbon monoxide and hydrogen. For example, natural gas composed mainly of methane (with a methane content of over 95%) and water vapor can be converted into carbon monoxide and hydrogen at temperatures of 800–1000°C using nickel as a catalyst. For example, refinery gas contains 9–40% hydrogen and methane, as well as 91–60% other hydrocarbons; at high temperatures, with the help of a catalyst, oxygen and the excess refinery gas undergo a partial oxidation reaction to produce carbon monoxide and hydrogen. The method for separating hydrogen from the aforementioned mixture of carbon monoxide and hydrogen is the same as that in the water-gas shift process. The third industrial method for producing hydrogen: In industrial hydrogen production, factors such as raw materials, energy sources, costs, and equipment must be taken into account. The purity and quantity of hydrogen required also determine the production method. The main methods are outlined below: 1. Hydrogen production by water electrolysis: Series electrolyzers (resembling filter presses) with iron as the cathode and nickel as the anode are commonly used to electrolyze aqueous solutions of potassium hydroxide or sodium hydroxide. Oxygen is produced at the anode, and hydrogen is produced at the cathode. This method is costly, but it yields high product purity, allowing for the production of hydrogen with a purity of over 99.7%. Hydrogen of this purity is commonly used for: ① as a reducing agent, protective gas, and for heat treatment of permalloy in the electronics, instrumentation, and meter industries; ② as a reducing agent in the powder metallurgy industry for producing tungsten, molybdenum, and cemented carbides; ③ in the production of semiconductor raw materials such as polycrystalline silicon and germanium; ④ for the hydrogenation of fats and oils; ⑤ as a cooling gas in double-hydrogen internal-cooling generators. Factories such as the Beijing Vacuum Tube Factory and the Academy of Sciences Gas Plant produce hydrogen using the water electrolysis method. II. Hydrogen production by the water-gas method: Bituminous coal or coke is used as a raw material, and it reacts with steam at high temperatures to produce water gas (C+H2O→CO+H2 – heat). After purification, it is passed together with water vapor over a catalyst to convert the CO present into CO2 (CO + H2O → CO2 + H2), resulting in a gas with a hydrogen content of over 80%. This gas is then pressed into water to dissolve out the CO2, and the remaining CO is removed using a solution containing copper formate amide (or copper acetate amide), thereby yielding relatively pure hydrogen. This method is cost-effective and allows for high production volumes; it makes use of numerous pieces of equipment, and is commonly employed in ammonia synthesis plants. Some also use CO and H2 to produce methanol, and in a few places, less pure gas containing 80% hydrogen is used to create liquid fuel. This method is widely used by places such as the Beijing Chemical Engineering Laboratory and many small nitrogen fertilizer plants across the country. III. Hydrogen production from syngas and natural gas obtained through the thermal cracking of oil. A large amount of hydrogen is produced as a by-product of oil thermal cracking, and this hydrogen is often used for the hydrogenation of gasoline, as well as to meet the hydrogen needs of petrochemical industries and fertilizer plants. This method of hydrogen production is employed in many parts of the world; in China, it is used in petrochemical complexes such as the Qinghua Fertilizer Plant and those located in the Bohai Oil Field. It is also used in some other places, such as the hydrogenation plants in Bayway and Batan Rougo in the United States. IV. Hydrogen production by cryogenic treatment of coke oven gas: The preliminarily purified coke oven gas is cooled and pressurized to liquefy other gases, leaving behind hydrogen. This method is used in a few places (such as the Ke Mepobo plant in the former Soviet Union). V. Hydrogen produced as a by-product of electrolyzing saltwater: The chlor-alkali industry generates large quantities of relatively pure hydrogen as a by-product; aside from being used for the production of hydrochloric acid, any excess can be purified to produce ordinary hydrogen or pure hydrogen. The hydrogen used in the Second Chemical Plant is a by-product of electrolyzing saltwater. VI. By-products of the brewing industry: When fermenting corn to produce propanol and butanol, more than 1/3 of the gases emitted from the fermentation tanks are hydrogen. After multiple purification steps, ordinary hydrogen (with a purity of over 97%) can be produced. By passing this ordinary hydrogen through silica gel tubes cooled to below -100°C using liquid nitrogen, impurities such as small amounts of N2 can be further removed, resulting in pure hydrogen with a purity of over 99.99%. Beijing’s brewing factories produce this by-product hydrogen, which is used for heating quartz products as well as being supplied to other organizations. VII. Hydrogen production by the reaction of iron with water vapor – the quality of the hydrogen produced is poor, and this is an outdated method that has been largely phased out. [Appendix] After pure hydrogen is supplied to the users, it still needs further purification (for example, to treat permalloy). This is achieved through the use of molecular sieves, a 105 catalyst, more molecular sieves, and finally filtration using thin tubes made of palladium-silver alloy, resulting in hydrogen with a purity of 99.99999%. This post was last edited by DAC The army rules the world on 2009-3-2 13:13]