『Original by HaiChuan Translation Team』Applications of Zeolite Molecular Sieve Adsorbents in the Chemical Processing Industry (Part 2)

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English title: Zeolite-Based Molecular Sieve Adsorbents In The Chemical Process Industry. Original article link: Click here. Original author: ankur2061. Translator ID: @YuHuan. Proofreader ID: @MyChemicalRomance. Those who wish to subscribe to the articles published by the “Haichuan Translation Team” are invited to leave a message below saying “I want to subscribe” or send me a message; we will notify everyone as soon as new articles are available. Applications of adsorbents: Drying – The main purpose of using TSA in most single-component gas-phase applications is for drying. The natural gas industry, the chemical industry, and the cryogenic industry all use zeolites, silica gel, and activated alumina to dry streams. Traces of adsorbents can even be found in mufflers. Zeolites, activated alumina, and silica gel are all used for the drying of pipeline natural gas. The advantages of alumina and silica are that they have high equilibrium capacity, and they are easier to regenerate when using waste heat for regeneration. However, since zeolites have a much lower dew point and those of type 4A have a longer lifespan, zeolites have become the mainstream adsorbents. In natural gas containing large amounts of acidic gases (such as H2S and CO2), specialized acid-resistant zeolites are used. To prevent the dried raw material from freezing at the process temperature when entering the cryogenic process, it is particularly important to have a low dew point that zeolites can achieve. During peak gas usage and under normal load conditions, natural gas is dried before being liquefied into liquefied natural gas (LNG). In the cryogenic expansion ethane recovery process and the helium recovery process, zeolites, which are used as desiccants, have been largely replaced by silica gel and activated alumina. Air used for cryogenic separation to produce nitrogen, oxygen, and argon must have its moisture and carbon dioxide removed, a process achieved through 13X zeolite. 4A zeolite, silica gel, and activated alumina are used in the drying of syngas, inert gases, cracking gas, noble gases, and recycled hydrogen. Before low-temperature distillation to produce olefins, the cracking gas is an active gas; 3A zeolite or closed-pore 4A zeolite selectively adsorbs water but not hydrocarbons, thereby preventing coking. At the same time, this also prevents the hydrocarbons from being lost along with the moisture during the separation process, after they have been adsorbed together. When extracting ethylene, propylene, and acetylene from storage tanks, these gases should also be dried using microporous zeolites. Acid-resistant zeolites are used when drying industrial gases containing chlorine, sulfur dioxide, and hydrogen sulfide. A new application of zeolites is to prevent corrosion in automatic silencers. Desulfurization: Another typical purification application in the field of adsorption is desulfurization. Hydrogen sulfide, thiols, organic sulfur and disulfides, as well as thiocarbonyls, need to be removed to prevent corrosion and catalyst poisoning. Such substances can be found in hydrogen, natural gas, the overhead gas from deethanization towers, and biogas. Generally, adsorption is more attractive because it dries the stream simultaneously during the desulfurization process. In the natural gas desulfurization process at the wellhead to prevent pipeline corrosion, 4A zeolite can be used to remove only the sulfur components without removing the carbon dioxide components (thereby reducing shrinkage), or it can remove both components to improve the calorific value of gases with low calorific values. If it is necessary to reduce the COS content during direct desulfurization, calcium-exchanged zeolites are typically used, as they have lower catalytic activity for the reaction between CO2 and H2S that produces COS and H2O. In the steam-methane ammonia synthesis process, natural gas must be desulfurized to avoid catalysts that are sensitive to sulfur and have low conversion temperatures. Zeolites are better than activated carbon because thiols, COS, and organic sulfur can be removed simultaneously. Many refineries require hydrogen to be purified using 4A and 5A zeolites to remove hydrogen sulfide and water, in order to prevent catalyst poisoning during regeneration. Other separations: Other temperature-dependent adsorption separations include the removal from sulfur dioxide towers to carbohydrate separation, as well as the removal of air pollutants and odors, as well as the purification of materials containing HCl and boron. Due to their high sensitivity to carbon dioxide and their compatibility with dry materials, 4A, 5A, and 13A zeolites are the mainstream adsorbents for CO2 removal in temperature-swapped adsorption processes. The air feed to the air separation unit must have its moisture and carbon dioxide removed to prevent corrosion of the heat exchangers under cryogenic conditions ； 13X is designed for use in such situations. Another use of 4A zeolite is the removal of carbon dioxide during normal operation and peak-shaving in natural gas liquefaction plants. Highly acid-resistant zeolites, such as mordenite and offretite, can effectively remove sulfur dioxide from sulfuric acid exhaust gases. Zeolite adsorbents specific to this application have been incorporated into the UOP PURASIV S process. The UOP PURASIV S process shows that nitrogen oxides (NOx) in wet nitric acid can also be removed using zeolites. Mordenite and offretite are used to remove Cl2, chlorinated hydrocarbons, and HCl from the regenerated gas. Additionally: Refer to the table below for an overview of zeolite molecular sieves in the chemical industry. Properties of typical zeolite molecular sieves: Model, Ionic characteristics, Typical unit cell, Molecular formula, Lattice dimensions (in nm), Nominal diameter, Density (kg/m3), Maximum adsorption heat (KJ/kg H2O), Average water capacity (Eq H2O capacity, wt%), Applications. 3A: K+K12(AlO2)12(SiO2)12; Structure: Obstructed; 8-ring structure; Particle size: 0.3; Form: Powder or spherical; Dimensions: 1.6 mm × 3.2 mm; Bead shape: 8X12/4X8; Parameters: 560, 640, 640, 710, 710, 418, 726; Density: 2121 kg/m3; Suitable for commercial use in molecular sieve adsorption dehydration of HC streams (pyrolysis gases, propylene, butadiene, acetylene); can also be used for drying methanol and ethanol. 4A: Na+Na12(AlO2)12(SiO2)12; Structure: Obstructed; 8-ring structure; Particle size: 0.4; Form: Powder or spherical; Dimensions: 1.6 mm × 3.2 mm; Bead shape: 8X12/4X8; Structure type: Networked; Dimensions: 14X30; Parameters: 510, 710, 710, 710, 418, 727; Density: 2222 kg/m3; Suitable for molecular sieve adsorption static dehydration in closed gas or liquid systems; commercially used for drying saturated HC gases. 5A: Ca2+ + Ca2Na2(AlO2)12(SiO2)12; Structure: Free 8-ring structure; Particle size: 0.5; Form: Powder or spherical; Dimensions: 1.6 mm × 3.2 mm; Parameters: 510, 710, 710, 418, 726; Density: 21.5 kg/m3; Used for selective adsorption to separate n-paraffins from branched alkanes and cycloalkanes. 10X: Ca2+ + Ca43(2)86(SiO2)106; Structure: 12-ring structure; Obstructed; Particle size: 0.8; Form: Powder or spherical; Dimensions: 1.6 mm × 3.2 mm; Parameters: 480, 580, 580, 418, 736; Density: 2828 kg/m3; Used for aromatic separation. 13X: Na+Na86(2)86(SiO2)106; Structure: 12-ring structure; Free; Particle size: 0.5; Form: Powder or spherical; Dimensions: 1.6 mm × 3.2 mm; Bead shape: 8X12/4X8; Parameters: 480, 640, 640, 640; Density: 418, 730; Used for general gas separation, purification of air separation feed (simultaneous removal of H2O and CO2), and desulfurization of liquid hydrocarbons and natural gas (removal of hydrogen sulfide and mercaptans)