Cellulose carbon molecular sieves for hydrogen separation
carbon molecular sieves Hydrogen (H2) production from natural gas is considered to be one of the most potential technologies for low-carbon energy in the future and reducing greenhouse gas emissions. Compared with conventional H purification technologies, membrane-based separation technologies have received extensive attention due to their higher energy efficiency and environmental friendliness. However, currently commonly used H2 and CO2 separation membranes usually suffer from low separation performance, high cost, and low stability under high temperature and high pressure. Therefore, it is still challenging to prepare commercially viable H2 purification membranes. Carbon molecular sieve (CMS) membranes are made by controlled carbonization of polymer precursors at high temperatures and have rigid pore structures. When the CMS membrane is made into a hollow fiber suitable for a membrane module, it is expected to have the properties of high temperature and high pressure resistance. Cellulose has strong interchain and intrachain hydrogen bonds, which makes it poorly soluble in most solvents, with only a few solvents such as N-methylmorpholine-N-oxide (NMMO), ionic liquids and Inorganic salts can effectively disrupt their hydrogen bond network. However, obtaining an accurate cellulose/solvent/non-solvent ternary phase diagram is still challenging due to the huge viscosity of this system. Based on this, Xuezhong He et al. from the Norwegian University of Technology prepared carbon hollow fiber membranes (CHFMs) by adjusting the solidification temperature and final carbonization temperature of the cellulose/ionic liquid/water system and used them for H2 separation. The researchers prepared asymmetric cellulose hollow fiber precursors through a dry and wet spinning process, and then exchanged with water to remove the original solvent EmimAc and DMSO, and finally obtained the corresponding microporous structure through high-temperature carbonization. From the SEM images, it can be found that the asymmetric structures of the outer selective layer and the porous inner support layer of about 3 μm are still maintained when different carbonization temperatures are used. CHFM-550 at the lowest carbonization temperature has the lowest hardness and Young's modulus. With the increase of carbonization temperature, the hardness and Young's modulus increase gradually. The increase in hardness and modulus can be attributed to the internal structural changes caused by the increase in carbonization temperature. At the same time, with the increase of carbonization temperature, the pore peaks >5 Å weakened, while the pore peaks <5 Å increased, which indicated that the average pore size of the carbonized CHFMs decreased at high temperature. Furthermore, both the surface area and pore volume of CHFM decreased with increasing carbonization temperature, suggesting that CMS films tended to have denser packing when carbonized at higher temperatures. The membranes prepared at higher carbonization temperatures have higher H2/CO2 selectivity, but lower H2 permeability, which indicates that the gas permeability is mainly determined by the motion diameter of gas molecules, i.e. molecular sieve transport transport mechanism. When the sp3/sp2 ratio decreased from 0.73 to 0.36, the H2 permeability decreased from 466.8 GPU to 148.2 GPU, while the H2/CO2 selectivity increased from 11.1 to 83.9, which also suggested that the gas separation performance can be tuned by adjusting the carbon structure. Due to the simultaneous presence of molecular sieve and surface diffusion transport of CO2 molecules, the apparent activation energy of CO2 is relatively lower compared to H2, which indicates that temperature has a greater effect on H2 permeability, so lower CO2 adsorption at higher temperatures This leads to an increase in H2/CO2 selectivity. When the membrane was exposed to the laboratory atmosphere for 50 days, its H2 permeability and H2/CO2 selectivity decreased by about 40% and 10%, respectively, and the gas permeability and gas permeability were effectively restored after heat treatment and helium purging. Optional. CHFM exhibits excellent H2/CO2 selectivity and high H2 permeability compared to other membranes, of which CHFM-850 shows the highest overall gas separation performance with an ideal H2/CO2 selectivity of 83.9 at 130 °C, exceeding non-polymer films. At the same time, the selectivity of CHFM-850 to H2/N2 is >800 and the selectivity of H2/CH4 is >5700, which provides the possibility for H2 purification in some processes. In summary, this work produced an asymmetric cellulose hollow fiber material by spinning microcrystalline cellulose and EmimAc. The obtained cellulose hollow fibers are carbonized at high temperature to obtain asymmetric hollow fiber membranes whose microporous structure helps them to separate H2 from other gases.
4A molecular sieves, the role of 13x molecular sieves
Molecular sieves 3A molecular sieves 4A molecular sieves 5A molecular sieves 13X molecular sieves Carbon molecular sieves 3A molecular sieves is mainly used in: Desiccant for chemical, petroleum, pharmaceutical, insulating glass and other industries. It is used for industrial dehydration of unsaturated hydrocarbon materials, such as cracked gas, butadiene, propylene, acetylene, etc. It can also be used for drying of gas, polar liquid and natural gas. Due to the small pore size of 3A molecular sieves, the co-adsorption of other molecules can be effectively controlled during the adsorption process. 4A molecular sieves is mainly used in: Static dehydration in closed gas or liquid systems. As a static desiccant in household refrigeration systems, pharmaceutical packaging, automotive air conditioners, electronic components, perishable chemicals or as a dehydrating agent in coating plastic systems. It can also be used for drying of saturated hydrocarbon materials in industry, and can adsorb methanol, ethanol, hydrogen sulfide, carbon dioxide, etc. Available in R-12 and R-22 systems. It can also be used for the separation and purification of gas and liquid components, such as the purification of argon, the preparation of reagent anhydrous ethanol, etc. Molecular 4A molecular sieves that can be adsorbed by 3A molecular sieves can be adsorbed. 5A molecular sieves is mainly used in: Separation of n-isoparaffin, separation of oxygen and nitrogen, drying and refining of chemical, petroleum and natural gas, ammonia decomposition gas and other industrial gases and liquids. 13X molecular sieves is mainly used in: The pore size of 13X molecular sieve is 10A, and the adsorption of any molecule is less than 10A. It can be used for catalyst co-carrier, co-adsorption of water and carbon dioxide, co-adsorption of water and hydrogen sulfide gas. It is mainly used in the drying of medicine and air compression systems. Professional variety. Carbon molecular sieves are mainly used in: Carbon molecular sieve is the adsorbent on the PSA nitrogen generator. It adopts the principle of pressure swing adsorption (PSA) to separate nitrogen from the air.
How long does it take for 4a molecular sieves to treat acetonitrile
If the activated 4a molecular sieve becomes turbid in the process of acetonitrile dewatering, it can be washed with water first, then put into the muffle furnace for activation, and then used, so that the turbidity will not be dealt with. Water removal method for acetonitrile treated by 4a type molecular sieve 1. Add phosphorus pentoxide and reflux until phosphorus pentoxide does not turn yellow, and steam it out under nitrogen protection;. 2. Add calcium hydride and reflux for six to eight hours, and steam out under nitrogen protection; 3. Molecular sieve to remove water, dry 4A molecular sieve at about 300° for 6-8 hours, cool it to room temperature under nitrogen protection, add it to acetonitrile under nitrogen protection or let stand for more than 12 hours in a dry environment. 4. Add silica gel or 4A molecular sieve to remove the water in acetonitrile, then add calcium hydride and stir until hydrogen is no longer released, so that acetic acid can be removed, leaving only a small amount of water. Then distill at a high reflux ratio, taking care to prevent moisture from entering. For this reason, reflux on calcium hydride, or add 0.5%-1% phosphorus pentoxide to the distillation flask to remove most of the remaining water. Phosphorus pentoxide should be avoided in excess as it will form an orange polymer. 5. (1) Preliminary water removal Put the acetonitrile into the container, put it into the 4A molecular sieve (dry molecular sieve), and place it in a sealed container for 12 hours. (2) Rectification. The solution after preliminary water removal is poured into a round-bottomed flask, an appropriate amount of phosphorus pentoxide is added, and a magnetic stirring rotor is used. Distill until the phosphorus pentoxide is no longer darkened in color (usually 5 to 6 hours). The solution in the dispenser was released (used to wash the bottle containing the solution and dried with a hair dryer). After that, the bottle containing the solution was sealed and connected to the lower end of the dispenser, and the heating was continued to distill out the remaining solution, leaving about 100ml. steam out. NOTE: The solution should remain boiling throughout the process. (3) Preservation: Add the rectified solution to dry molecular sieve, and store it in a sealed place away from light. 6. Acetonitrile is infinitely miscible with water and alcohol, and can form a binary azeotrope with water. Its composition and azeotrope are as follows: azeotrope: 77 degrees Celsius (101.33kpa), acetonitrile content 77% (W) acetonitrile dehydration, due to acetonitrile and Water is infinitely miscible, and acetonitrile is difficult to dehydrate. Acetonitrile and water can form an azeotrope, but the water cannot be separated. For further purification, it can be dried with anhydrous calcium chloride, filtered and added with 0.5-1% five Phosphorus oxide (P2O5) is refluxed, and then distilled under normal pressure. Repeat this operation until the phosphorus pentoxide (P2O5) is no longer colored, and then add newly melted anhydrous potassium carbonate (K2CO3) for distillation to remove a trace amount of phosphorus pentoxide (P2O5). 7. Add phosphorus pentoxide (5-10g/V) to acetonitrile, reflux for 2-3 days, and then steam it out, which can remove most of the water. Note that a calcium chloride drying tube should be added to the condenser tube during reflux. Excessive addition of phosphorus pentoxide should be avoided as orange polymers may be formed. A small amount of potassium carbonate is added to the distilled acetonitrile for re-distillation, which can remove the trace amount of phosphorus pentoxide, and finally use a fractionation column for fractionation. It's very troublesome, but it's purer to get it out. 8. Reflux with KMnO4 and K2CO3 for 8 hours, then steam into a round-bottomed flask with P2O5. Refluxed for an additional 5 hours, then evaporated.
What is the bulk density of 4A molecular sieve?
As an adsorption desiccant, 4A molecular sieve is used more frequently. What is the bulk density of 4A molecular sieves? 4A molecular sieve spheroids and bars. 4a Molecular sieve strips have a diameter of 1.5-1.7mm, a bulk density of ≥0.66g/ml, a diameter of 3.0-3.3mm, and a bulk density of ≥0.66g/ml; 4a Molecular sieve spherical diameter 1.7-2.5mm, bulk density ≥0.7g/ml, diameter 3.0-3.3mm, bulk density ≥0.7g/ml; Parameters also include particle size qualification, wear rate, compressive strength, static water adsorption rate, formaldehyde adsorption rate, packaging water content, etc. 4a molecular sieve can adsorb water, methanol, ethanol, hydrogen sulfide, sulfur dioxide, carbon dioxide, ethylene, propylene, etc., and does not adsorb any molecules with a diameter larger than 4A (including propane), and its adsorption performance for water is better than any other molecular sieves. It is an industrial Molecular sieve varieties with a larger dosage. 110°C is ok for the evaporation of water in the atmosphere, but the water in the molecular sieve cannot be discharged. Therefore, in the laboratory, it can be activated and dehydrated by drying in a muffle furnace. The temperature is 350°C. Dry under normal pressure for 8 hours (if there is a vacuum pump, it can be dried at 150°C with air extraction). The activated molecular sieve is cooled to about 200°C in air (about 2 minutes), that is, it should be stored in a dry place immediately. If possible, use dry nitrogen to protect the device after use to prevent pollutants from reappearing in the air. The activated 4a molecular sieve should be cooled to about 200°C (about 2 minutes) in the air, that is, it should be stored immediately. . Influence of Si/Al Ratio of Molecular Sieve Below 100 is low silicon to aluminum ratio, 100-200 is medium silicon to aluminum ratio. More than 200 is high silicon. The higher the ratio of silicon to aluminum, the better the thermal stability and thermal conductivity, and the weaker the acidity. The aluminum-containing molecular sieve has surface acidity. The reason for its acidity is that Al is trivalent, while Si is tetravalent. Yes, there is a pair of charges on the three-coordinated aluminum, which is the source of the L acid of the molecular sieve. If in order to balance the charges, a hydroxyl group is attached to the aluminum, which becomes the source of the B acid. The silica-alumina ratio of molecular sieves can strongly affect its acid properties, that is, acid content and acid strength. If the ratio of silicon to aluminum is increased, there will be more silicon, the amount of acid will be reduced, and the acid strength will be increased at the same time. Molecular sieves use sodium salts in the synthesis process, so the formed molecular sieves are Na-type first, and H-type can be obtained after NH4+ ion exchange and roasting. H-type molecular sieves have a large amount of B acid. Therefore, the Si/Al ratio has a decisive influence on the acid-catalyzed reaction.
Which molecular sieve of 3A and 4A has the smallest pore size?
When purchasing molecular sieves, you do not specifically say which molecular sieve is better, only which molecular sieve is more suitable. The main function of molecular sieve is to sieve a substance molecule through the pore size of the molecular sieve's own crystal structure. When meeting the technical requirements of water removal, is it better to use 3A molecular sieve or 4A molecular sieve? First of all, this problem still needs to be specifically distinguished from the substance to be dehydrated. First, the size of the molecular diameter of the moisture (dry) needs to be removed. If the dynamic molecular diameter of the substance to be dehydrated (dry) is greater than 3nm and less than 4nm, then, If we want to get rid of water from this substance, we can only use 3A molecular sieve, because if we use 4A molecular sieve, it will not only absorb the water in the substance, but also absorb the substance that needs to be dehydrated. This is the first case, and there is another The situation is that if the dynamic diameter of the material that needs to be dehydrated (dried) is greater than 4A, then 4A molecular sieves are generally used, because 4A molecular sieves have a stronger ability to absorb moisture than 3A. If both 3A molecular sieve and 4A molecular sieve can be used to remove water, which molecular sieve should we use? In this case, we generally use 4A molecular sieve, because the water absorption of 4A molecular sieve is more than 22%, and the water absorption capacity of 3A is more than 21%. Generally speaking, the water absorption capacity of 4A molecular sieve is stronger than that of 3A molecular sieve. That is, the price of 4A molecular sieve is cheaper than that of 3A molecular sieve.
The reason why activated carbon is used as a regeneration Material
Activated carbon itself has heat resistance, acid and alkali resistance, oxidation resistance, and also has a certain strength. Therefore, in addition to ensuring the above properties of activated carbon, the regeneration treatment should also make the adsorption performance of activated carbon reach 90% of the original carbon. Above, at the same time, the mechanical abrasion and breakage of the carbon during the regeneration process are reduced as much as possible, so that the regeneration yield can reach more than 90%. In addition, the economics of the regeneration process must be considered. Taking the widely used heating regeneration method as an example, it is reported that the regeneration is only beneficial when the amount of activated carbon used per day is about 100kg or more. Therefore, the economic performance of regeneration is also an important factor for investigating activated carbon regeneration. The adsorption of activated carbon can generally be divided into reversible adsorption (also called physical adsorption) and irreversible adsorption (also called chemical adsorption) according to the adsorption mechanism. In practical applications, the two adsorptions are often mixed alternately. Generally, the reversible adsorption process occurs in gas phase solvent recovery, deodorization, air purification, etc., while the irreversible adsorption process is common in the liquid phase adsorption of wastewater treatment. The regeneration treatment method for reversible adsorption is mainly to pass heating steam above 120°C to remove the adsorbed substances and restore the adsorption performance of activated carbon. However, due to the different vapor pressures and boiling points of the adsorbed substances, their effective adsorption capacity will change, and the regeneration conditions should also change.