Common gas separation methods and principles in industry

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Common gas separation methods and principles in industry Common industrial gases include oxygen, nitrogen, argon, carbon dioxide, liquid ammonia, liquid chlorine, acetylene, hydrogen, etc. There are various methods for producing industrial gases; here, some common production methods will be briefly introduced. I. Oxygen 　　The main methods for producing industrial oxygen include air liquefaction, separation, and distillation (referred to as the air separation process), water electrolysis, and pressure swing adsorption. The general process flow for producing oxygen by the air separation method is: air absorption → carbon dioxide absorption tower → compressor → cooler → dryer → cryogenic machine → liquefaction separator → oil separator → gas storage tank → oxygen compressor → gas filling. The basic principle is to liquefy air, and then use the different boiling points of its various components to carry out separation and distillation in a liquefaction separator in order to produce oxygen. The research, development, and deployment of large-scale oxygen production units have led to a continuous reduction in the energy consumption required for oxygen production, and they also make it possible to produce various air separation products simultaneously (such as nitrogen, argon, and other inert gases). For easy storage and transportation, the liquid oxygen separated by the liquefaction separator is pumped into low-temperature liquid storage tanks, and from there it is transported by tank trucks to various cryogenic liquefied permanent gas filling stations. Liquid nitrogen and liquid argon are also stored and transported using this method. II. Nitrogen The main methods for producing industrial nitrogen include air separation, pressure swing adsorption, membrane separation, and combustion methods. 　　Nitrogen produced by the air separation process has high purity and low energy consumption. The pressure swing adsorption nitrogen production technology utilizes 5A carbon molecular sieves to selectively adsorb the components in air, thereby separating oxygen from nitrogen to produce nitrogen gas. The nitrogen gas produced has a high pressure and low energy consumption, and its purity meets the specified standards: industrial nitrogen at ≥98.5%, and pure nitrogen at ≥99.95%. III. Argon Argon is the most abundant inert gas in the atmosphere, and its main production method is air separation. In the oxygen production process, liquid argon is obtained by separating the fraction with a boiling point of around -185.9°C from the liquefaction separator. IV. Carbon Dioxide The main methods of producing carbon dioxide include: the generation of carbon dioxide as a by-product of lime production, carbon dioxide produced during wine fermentation, carbon dioxide emitted from the combustion of heavy oil and coke, and carbon dioxide as a by-product of the ammonia synthesis industry. Currently, the raw materials used in the synthetic ammonia industry are mainly gas, refinery gas, coke oven gas, and coal. Their main components are hydrocarbons with different hydrogen-to-carbon ratios as well as elemental carbon; at high temperatures, these react with water vapor to produce syngas composed primarily of hydrogen and carbon monoxide, with the carbon monoxide being converted into carbon dioxide. The methods for purifying carbon dioxide include absorption, pressure swing adsorption, adsorption distillation, and membrane separation. V. Ammonia The main method for producing ammonia is direct synthesis. The synthetic ammonia process involves blowing air and water vapor over red-hot coke in a water-gas generator to produce a mixture of nitrogen and hydrogen gases; subsequent production steps such as washing, heat exchange, carbon dioxide condensation, and carbon dioxide absorption are then used to prepare the raw material gases. The refined mixed gas is sent to the synthesis reactor via a filter, cooler, ammonia separator, and heater, where liquid ammonia is separated out using a separator. VI. Chlorine The main method for producing chlorine used in industry is the electrolysis of saturated salt water. Chlorine of high purity is obtained when producing active metals by electrolyzing molten chlorides. Air or oxygen can be used to catalyze the oxidation of hydrogen chloride, a byproduct of the organic synthesis industry, into chlorine gas. VII. Acetylene gas The main methods for producing acetylene include the hydrolysis of calcium carbide, high-temperature combustion and cracking of methane or hydrocarbons, and plasma cracking. The calcium carbide hydrolysis process has a short production cycle and high product purity, but it requires high energy consumption. Most dissolved acetylene production uses this method. Based on the solubility properties of acetylene, acetylene gas is compressed and charged into a solvent, and stored in a steel cylinder filled with porous filler. Propane, as an excellent solvent, is adsorbed by fillers inside the cylinder to dissolve and release acetylene; its function is to increase the effective volume of the cylinder and reduce the explosiveness of acetylene gas. The overall function of the calcium silicate porous filler is to uniformly adsorb propane and prevent the spread of decompression explosions caused by acetylene. Promoting the use of dissolved acetylene cylinders not only facilitates use and improves work efficiency but also benefits the environment by reducing the consumption of calcium carbide. However, it is necessary to ensure that the porous filler inside the cylinder is not damaged or contaminated, and the amount of propylene solvent filled should be sufficient for acetylene storage, in order to ensure safety and reliability. The production and filling process for dissolved acetylene involves: the crude acetylene gas being chemically purified to remove impurities such as sulfur and phosphorus, followed by compression and drying, before it is filled into dissolved acetylene cylinders. VIII. Hydrogen The main methods for producing industrial hydrogen include: hydrogen production via the combustion of minerals, hydrogen production through water electrolysis, and hydrogen production using the semi-water gas method. The water electrolysis method for hydrogen production is reliable in terms of technology, simple to operate, easy to maintain, does not cause pollution, and produces hydrogen of high purity. However, its high electricity consumption leads to higher costs, which imposes certain restrictions on its development; it is mainly used to supply hydrogen to users with high purity requirements and relatively low consumption levels. However, with the application of new technologies, improvements have been made to water electrolysis technology, resulting in a continuous reduction in the costs associated with producing hydrogen through water electrolysis as well as lower energy consumption. This approach is expected to become the primary method for producing \"clean energy\". Currently, the hydrogen production methods under research and development include electrochemical water splitting to produce hydrogen, and photocatalytic processes to produce hydrogen. Reposted from: Chemical Engineering 707