Pressure Swing Adsorption (PSA) has proved to be an effective and economic way for hydrogen recovery.
In PSA/VPSA system, molecular sieve is the key material to adsorb nitrogen other than oxygen. After nitrogen is sieved, oxygen is concentrated. Oxygen enrichment molecular sieves used in PSA/VPSA system should have good N2/O2 selectivity, good crush strength and low loss on attrition. Cryogenic air separation and PSA/VPSA are two main methods for oxygen production. Cryogenic air separation method is energy consuming and hard to maintain, while PSA/VPSA method has such advantages. In hospitals or factories that just need oxygen of not large amount, PSA/VPSA method is cost-effective for such clients. The indicative optimal supply solutions are shown below:
The most common method for air separation is cryogenic distillation. Cryogenic air separation units (ASUs) are built to provide nitrogen or oxygen and often co-produce argon. These components of air must be removed to meet product quality specifications. In addition, they must be removed prior the air entering the distillation portion of the plant; because very low temperatures would cause the water and carbon dioxide to freeze and deposit on the surfaces within the process equipment.
Most new air separation plants employ a “molecular sieve” "pre-purification unit" (PPU) to remove carbon dioxide and water from the incoming air by adsorbing these molecules onto the surface of "molecular sieve" materials at near-ambient temperature. Molecular sieve Type 13X combined with activated alumina is designed for cryogenic air separation to remove of moisture and Co2. Activated alumina removes most of the water and 13X removes most of the Co2.
As raw nature gas normally contains saturated water, hydrogen sulphide, carbon dioxide and other impurities. These impurities should be removed as much as possible in order to meet the requirement of marketable gas.
If the temperature of pipeline walls or storage tanks decreases below the dew point of the water vapours present in the gas, the water starts to condense on those cold surfaces, and the following problems can appear:
1. Natural gas in combination with liquid water can form methane hydrate that may plug the valves, the fittings or even pipelines;
2. Natural gas dissolved in condensed water is corrosive, especially when it contains Co2 or H2S
3. Condensed water in the pipeline causes slug flow and erosion
4. Water vapour increases the volume and decreases the heating value of the gas
5. Natural gas with the presence of water vapor cannot be operated on cryogenic plants
Molecular Sieves 3A and Molecular sieve 4A with high water adsorption and Co2 capacity, excellent hydrothermal stability and good dynamic characteristic for natural gas dehydration.
H2S and CO2 are commonly found in natural gas, but unfortunately, they get highly corrosive in the presence of H2O. Natural Gas Sweetening also known as Acid Gas Removal, refers to a group of processes that remove Carbon Dioxide (Co2) and Hydrogen Sulphide (H2S) from natural gas.
Molecular Sieves 5A with high mechanical and chemical resistance, excellent adsorption capacity for removal of H2S, Co2.
molecular sieve 13X with high performance COS removal capacity and excellent crush strength.
Different types of molecular sieve specially designed for removing impurities from hydrocarbon streams in refinery factories, the following is a brief introduction of molecular sieves application in refining:
1. Dehydration of Hydrocarbon Gas or Liquid (No Olefins Present) - 4A
2. Dehydration of Hydrocarbon Gas or Liquid (With Olefins Present) - 3A
3. Isomerization Processes, Feedstock Purification - 13X
4. LPG Desulfurization - 5A / 13X
5. Butane Destenching - 13X
6. MTBE / TAME - 13X
7. Reformer Applications - 4A
Heavy vehicles such as trucks and buses use air to power their brakes. Air must be kept as dry as possible to avoid any freezing in the circuit but also any corrosion of the metallic parts.
Molecular Sieve with high crush strength, abrasion resistance is specifically designed for air actuated brake systems to dehydrate the compressed air and keep brake lines from freezing and corroding.
An insulated glass unit is composed of two glass lines at least. These are separated by a space filled with air or a special gas (argon, krypton, SF6, etc.). The lites are supported and separated by a spacer and then sealed. Water from the air and solvents from the sealant can be trapped inside the unit. Water can also penetrate through the sealant during the life of the insulated glass unit. Both phenomena lead to fogging (water or solvent condensation on glass lite).
Molecular sieve can deeply co-adsorb the resident moisture and organics in insulating glass, keep the insulating glass clear and transparent even at very low temperature.
More importantly, it can successfully avoid the tremendous air pressure un-balancely placed on the glasses, which was superposed by seasons of day-night temperature changing and ensuring air desorption and adsorption function of common insulating glass desiccant. Thus, it resolves the problems of windows distortion caused by insulating glass inflation and shrink, expanded the life span of insulating glass windows.
Refrigerant is mainly a chloride or fluoride containing hydrocarbon in refrigerating plants.
During refrigerant diffusion process, some residual moisture out of the refrigerant forms ice in the expansion valve and causes a blockage in the system, meanwhile, hydrolyzes refrigerant into some corrosive gas such as fluoride hydrogen and hydrochloride etc.
XH Refrigerant desiccants can effectively remove moisture and other contaminants from refrigerant, thus avoiding ice formation and protecting the system from blockage and corrosion. With higher crush strength and lower attrition, they are playing an important role in minimizing the refrigerant dew point and widely used in different kinds of refrigerating plants.
Using multi-pressure distillation, the ethanol and water mixtures are progressively closer to the azeotropic ratio of 95.5/4.5%. The further purification of ethanol up to 99.80% is done by dehydration using pressure swing system which includes molecular sieve 3A EDG as adsorbents.
The very precise pore size of molecular sieves enables them to select and remove molecules of particular size from a bulk mixture containing molecules with large sizes and low polarity. Molecular sieve has a porous structure containing uniform cavities of a specific size. The selection of molecular sieves depends mainly on the size of the molecules to be removed from the mixture of other molecules. The water (H2O) molecular having size 3Å is easily getting adsorbed in the cavities present in the molecular sieves, whereas the ethanol(C2H5OH) molecule being larger in size than the water molecule cannot enter the cavities present in the molecular sieves.
One of problems of Polyurethane Polymer is the moisture. If not removed, moisture will react with the isocyanate to form carbon dioxide gas and then leads to formation of bubbles in final compound:
RNCO + H2O →RNH2 + CO2
Molecular sieve powder is highly effective, non-toxic moisture scavenger for 1K- and 2K Polyurethane systems to prevent the formation of foam and bubbles by suppressing the reaction of free water with the isocyanate group. At the same time, molecular sieve powder is well compatible with commonly used polyols, polyether’s and isocyanates. They are easily dispersible and especially stabilized to ensure sufficiently long hardening times.
In certain paint and coating systems, moisture introduced into the formulation via the raw materials (solvents, pigments, extenders) causes undesirable side effects. In metallic and zinc-rich paints (such as marine paints for tank ships and yachts), water reacts with the very active metallic pigments such as zinc or aluminium, forming hydrogen. This leads to overpressure in the cans, and in extreme cases to leakage.
Zn+H2O→Zn(OH)2+H2
Al+H2O→Al(OH)3+H2
In metallic and zinc-rich paints, the adverse effect can be avoided by the use of Molecular Sieves Powder. It adsorbs the moisture rapidly, with the result that the above reactions can be suppressed, thus reducing returns and storage problems.
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