Molecular separator apparatus

Details Molecular separator apparatus Molecular separator apparatus

2001-06-29

2004-03-16

Reifsnder, David A. (Department: 1723)

Gas separation: apparatus

Solid sorbent apparatus

Dispersed or impregnated solid sorbent bed

C062S101000, C062S106000, C062S480000, C095S090000, C095S117000, C096S108000, C096S121000, C096S126000, C096S131000, C096S133000, C204S660000, C210S651000

Reexamination Certificate

active

06706097

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a magnetic/adsorbent material composition, and more specifically to a magnetic/adsorbent material composition that uses different types of adsorbent material bonded to magnetic materials to adsorb and then remove the molecules adsorbed from a fluid or gas.
BACKGROUND OF THE INVENTION
Molecular sieves are porous, synthetic, crystalline alumino-silicates that function to adsorb some molecules and reject others. The adsorption and desorption are completely reversible. These molecular sieves are adsorbents and referred to in the industry as zeolites. Other adsorbents exist, such as carbon fiber, carbon foam, silica gel, and activated alumina, and each has a unique application. Zeolite molecular sieves have a high kinetic rate of adsorption and have over 50 species that perform differently. The wide range of molecular sieve custom choices make zeolites a desirable material for many applications. Zeolite properties of ion exchange, reversible loss and gain of water, and the adsorption of other gases and vapor make zeolites useful adsorbents.
The molecular sieve crystal structure is a tetrahedron of four oxygen anions surrounding smaller silicon or aluminum cations. Sodium ions, calcium ions, or other exchangeable cations make up the positive-charge deficit in the alumina tetrahedral. Each oxygen anion is also shared with another silica or aluminum tetrahedron, extending the crystal lattice in three dimensions.
The crystal structure is honeycombed with relatively large cavities that are interconnected by apertures or pores. The entire volume of these cavities is available for adsorption. For example, the free aperture size of the sodium-bearing Type 4A molecular sieve (manufactured by UOP Inc. of Des Plaines Ill.) is 3.5 angstroms in diameter, which allows the passage of molecules with an effective diameter as large as 4 angstroms. Altering the size and position of the exchangeable cations can change the size. By replacing the sodium ions with calcium ions, for example, the effective aperture size can be increased to 4.2 angstroms. Using different or modified crystal structures can also change the aperture size.
Adsorbents are a versatile process tool in adsorption systems. They are usually used in multiple-bed molecular sieve systems common to large scale, commercial fluid purification units. These separate beds can be plumbed together. A common approach involves one onstream bed that is drying and/or purifying the fluid, and another that is regenerated by hot purge gas and then cooled. In regenerated beds, the beds are heated by convection or conduction. In carbon fiber monolith beds, electrical current can be applied across the fibers. As the adsorbent bed cools, the bed begins the process of adsorbing gas from the working fluid and starts the cycle over again. When an adsorbent bed is saturated with working gas fluid, the cycle is complete. The adsorbent vessel beds are then reheated and cooled to repeat the previous cycle.
In situations where an interrupted flow is acceptable, a single adsorption bed can be used. Then when the adsorption capacity of the bed is reached, the bed is taken off-line and regenerated for subsequent use. Molecular sieves are particularly useful in situations that require gas streams that are extremely dry. Molecular sieves can obtain water concentrations below 0.1 ppmw in a dynamic drying service over a wide range of operation conditions.
When co-adsorption of carrier stream molecules is a serious problem (e.g., in olefinic process streams) co-adsorption can be prevented by selecting a molecular sieve with a critical pore diameter small enough to prevent other stream components from being admitted to the active inner surface of the adsorption cavities. Molecular sieves can also be used for one-step drying and purification by selecting the proper molecular sieve and providing sufficient bed to retain the other impurities along with water.
Since molecular sieves adsorb materials through physical forces rather than through chemical reaction, they retain their original chemical state when the adsorbed molecular is desorbed. There are five types of adsorption/desorption cycles:
1. Thermal swing cycles involving rising desorption temperatures;
2. Pressure or vacuums swing cycles involving decreased desorption pressures;
3. Purge-gas stripping cycles using a non-adsorbed purge gas;
4. Displacement cycles using an adsorbable purge to displace the adsorbed material; and
5. Absorptive heat recovery, using the retained heat of adsorption to desorb certain molecules (e.g., water).
Molecular sieves are available in a variety of shapes and sizes. The most common are: {fraction (1/16)} and ⅛ inch pellets; beads, 8 by 12 and 4 by 12 mesh; three pellets bonded into a triangular type extrusion, granulated particles in sizes from 6 to 60 mesh; and powders. Zeolites in prior art are typically beads, cylindrical pellets, or solid molded shapes to prevent raw zeolite crystal powder from going into an airborne state when hot air is used for cooling. The raw zeolite crystal powder is approximately 3 to 5 microns in size and very difficult to handle. These pure crystals are mixed with a clay and binder like polyphenylene sulfide (PPS) or aluminum phosphate, to form the zeolite beads, pellets, and molds. Beads and pellets have an attrition rate that is predictable based on the type of liquid, gas, or vapor adsorbed, vibration, heating cycles, and hot air-drying velocity. Screen meshes are used to contain the beads and pellets and allow cleaning.
Zeolite has a large internal surface area (of up to 100 m
2
/g), and a crystal lattice with strong electrostatic fields. Adsorbates are the gases or fluids that zeolite adsorbents adsorb. Zeolite retains adsorbates by strong physical forces rather than by chemical adsorption. Thus, when the adsorbed molecule is desorbed by the application of heat or by displacement with another material, it leaves the crystal in the same chemical state as when it entered. The very strong adsorptive forces in zeolite are due primarily to the cations, which are exposed in the crystal lattice. These cations act as sites of strong localized positive charge, which electrostatically attract the negative end of polar molecules. The greater the dipole moment of the molecule, the more strongly it will be attracted and adsorbed. Polar molecules are generally those, which contain O, S, Cl, or N atoms and are asymmetrical. Water is one such molecule. Other molecules that adsorb include, but are not limited to Ar, Kr, Xe, O
2
, N
2
, n-pentane, neopentane, Benzene, Cyclohexane, and (C
4
H
9
)
2
N. Under the influence of the localized, strong positive charge on the cations, molecules can have dipoles induced in them. The polarized molecules are then adsorbed strongly due to the electrostatic attraction of the cations. The more unsaturated the molecule, the more polarizable it is and the more strongly it is adsorbed.
Carbon fiber and carbon foam monoliths (developed by Oak Ridge National Lab Tennessee, U.S.A.) reduce attrition and increase thermal efficiency, however these monoliths are still batch adsorptions like the pellets. These carbon fiber monoliths are more efficient to heat and do not require screens to contain the adsorption materials. Activated carbon fiber has a strong attraction to carbon dioxide and a surface area greater than 1000 m
2
/g. Carbon fibers can be activated for a wide range of molecules. Carbon foam has the highest thermal transfer rate, and gas or fluid can pass through it. Carbon foam can have additives applied, to make it an adsorbent and it can be atomized into smaller pieces.
A further drawback of current adsorbent batch systems is that the capacity of the adsorbent bed has to be matched to the volume of working substance. If the adsorbent capacity is too low, the adsorbent bed size has to be increased, or increased capacity can be gained by adding more beds. Further, adsorbents can become saturated while there is still working substance in presence of the bed, preventing th

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