Sunday, November 1, 2009

Dehydration by Molecualr Sieves (MS)

Molecular sieves are crystalline metal alumina silicates having a three dimensional interconnecting network of silica and alumina tetrahedra. Natural water of hydration is removed from this network by heating to produce uniform cavities which selectively adsorb molecules of a specific size.
A 4 to 8-mesh sieve is normally used in gas phase applications, while the 8 to 12-mesh type is common in liquid phase applications. The powder forms of the 3A, 4A, 5A and 13X sieves are suitable for specialized applications.
Long known for their drying capacity (even to 90°C), molecular sieves have recently demonstrated utility in synthetic organic procedures, frequently allowing isolation of desired products from condensation reactions that are governed by generally unfavorable equilibria. These synthetic zeolites have been shown to remove water, alcohols (including methanol and ethanol), and HCl from such systems as ketimine and enamine syntheses, ester condensations, and the conversion of unsaturated aldehydes to polyenals.
3A molecular sieve : 0.6 K2O: 0.40 Na2O : 1 Al2O3 : 2.0 ± 0.1SiO2 : x H2O
4A molecular sieve : 1 Na2O: 1 Al2O3: 2.0 ± 0.1 SiO2 : x H2O
5A molecular sieve : 0.80 CaO : 0.20 Na2O : 1 Al2O3: 2.0 ± 0.1 SiO2: x H2O
13X molecular sieve : 1 Na2O: 1 Al2O3 : 2.8 ± 0.2 SiO2 : xH2O
Regeneration (activation)
Regeneration in typical cyclic systems constitutes removal of the adsorbate from the molecular sieve bed by heating and purging with a carrier gas. Sufficient heat must be applied to raise the temperature of the adsorbate, the adsorbent and the vessel to vaporize the liquid and offset the heat of wetting the molecular-sieve surface. The bed temperature is critical in regeneration. Bed temperatures in the 175-260° range are usually employed for type 3A. This lower range minimizes polymerization of olefins on the molecular sieve surfaces when such materials are present in the gas. Slow heat up is recommended since most olefinic materials will be removed at minimum temperatures; 4A, 5A and 13X sieves require temperatures in the 200-315 °C range.
After regeneration, a cooling period is necessary to reduce the molecular sieve temperature to within 15° of the temperature of the stream to be processed. This is most conveniently done by using the same gas stream as for heating, but with no heat input. For optimum regeneration, gas flow should be countercurrent to adsorption during the heat up cycle, and concurrent (relative to the process stream) during cooling. Alternatively, small quantities of molecular sieves may be dried in the absence of a purge gas by oven heating followed by slow cooling in a closed system, such as a desiccator.

Physical Properties Of ETHANE

Physical State at 15° C and 1 atm: Gas
Molecular Weight: 30.07
Boiling Point at 1 atm: –127.5°F = –88.6°C = 264.6°K
Freezing Point: –279.9°F = –183.3°C = 89.9°K
Critical Temperature: 90.1°F = 32.3°C = 305.5°K
Critical Pressure: 708.0 psia = 48.16 atm = 4.879 MN/m2
Specific Gravity: 0.546 at -88.6°C (liquid)
Liquid Surface Tension: 16 dynes/cm = 0.016 N/m at –88°C
Liquid Water Interfacial Tension: (est.) 45 dynes/cm = 0.045 N/m at –88°C
Vapor (Gas) Specific Gravity: 1.1
Ratio of Specific Heats of Vapor (Gas): 1.191
Latent Heat of Vaporization: 211 Btu/lb = 117 cal/g = 4.90 X 105 J/kg
Heat of Combustion: –20,293 Btu/lb = –11,274 cal/g = –472.02 X 105 J/kg
Heat of Decomposition: Not pertinent
Heat of Solution: Not pertinent
Heat of Polymerization: Not pertinent
Heat of Fusion: 22.73 cal/g
Limiting Value: Currently not available
Reid Vapor Pressure: Very high

Source

Physical Properties Of METHANE

Physical State at 15° C and 1 atm: Gas
Molecular Weight: 16.04
Boiling Point at 1 atm: –258.7°F = –161.5°C = 111.7°K
Freezing Point: –296.5°F = –182.5°C = 90.7°K
Critical Temperature: –116.5°F = –82.5°C = 190.7°K
Critical Pressure: 668 psia = 45.44 atm = 4.60 MN/m2
Specific Gravity: 0.422 at –160°C (liquid)
Liquid Surface Tension: 14 dynes/cm = 0.014 N/m at –161°C
Liquid Water Interfacial Tension: (est.) 50 dynes/cm = 0.050 N/m at –161°C
Vapor (Gas) Specific Gravity: 0.55 1.0
Ratio of Specific Heats of Vapor (Gas) : 1.306
Latent Heat of Vaporization: 219.4 Btu/lb = 121.9 cal/g = 5.100 X 105 J/kg
Heat of Combustion: –21,517 Btu/lb = –11,954 cal/g = –500.2 X 105 J/kg
Heat of Decomposition: Not pertinent
Heat of Solution: Not pertinent
Heat of Polymerization: Not pertinent
Heat of Fusion: 13.96 cal/g
Limiting Value: Currently not available
Reid Vapor Pressure: Very high

Physical Properties Of OXYGEN

# Molecular Formula: O2
# Molecular Weight: 31.999
# Boiling Point @ 1 atm: -297.4°F (-183.0°C, 90oK)
# Freezing Point @ 1 atm: -361.9°F (-218.8°C, 54oK)
# Critical Temperature: -181.8°F (-118.4°C)
# Critical Pressure: 729.1 psia (49.6 atm)
# Density, Liquid @ BP, 1 atm: 71.23 lb/scf
# Density, Gas @ 68°F (20°C), 1 atm: 0.0831 lb/scf
# Specific Gravity, Gas (air=1) @ 68°F (20°C), 1 atm: 1.11
# Specific Gravity, Liquid (water=1) @ 68°F (20°C), 1 atm: 1.14
# Specific Volume @ 68°F (20°C), 1 atm: 12.08 scf/lb
# Latent Heat of Vaporization: 2934 BTU/lb mole
# Expansion Ratio, Liquid to Gas, BP to 68°F (20°C): 1 to 860
# Solubility in Water @ 77°F (25°C), 1 atm: 3.16% by volume

Physical Properties Of HYDROGEN

# Molecular Weight: 2.016
# Boiling Point @ 1 atm: -423.0°F (-252.8°C, 20oK)
# Freezing Point @ 1 atm: -434.5°F (-259.2°C, 14oK)
# Critical Temperature: -399.8°F (-239.9°C)
# Critical Pressure: 188 psia (12.9 atm)
# Density, Liquid @ B.P., 1 atm: 4.23 lb./cu.ft.
# Density, Gas @ 68°F (20°C), 1 atm: 0.005229 lb./cu.ft.
# Specific Gravity, Gas (Air = 1) @ 68°F (20°C), 1 atm: 0.0696
# Specific Gravity, Liquid @ B.P., 1 atm: 0.0710
# Specific Volume @ 68°F (20°C), 1 atm: 192 cu. ft./lb.
# Latent Heat of Vaporization: 389 Btu/lb. mole
# Flammable Limits @ 1 atm in air 4.00%: -74.2% (by Volume)
# Flammable Limits @ 1 atm in oxygen 4.65%: -93.9% (by Volume)
# Detonable Limits @ 1 atm in air 18.2%: -58.9% (by Volume)
# Detonable Limits @ 1 atm in oxygen 15%: -90% (by Volume)
# Autoignition Temperature @ 1 atm: 1060°F (571°C)
# Expansion Ratio, Liquid to Gas, B.P. to 68°F (20°C): 1 to 848

Physical Properties Of HELIUM

# Molecular Symbol: He
# Molecular Weight: 4.003
# Boiling Point @ 1 atm: -452.1°F (-268.9°C, 4oK)
# Freezing Point @ 367 psia: -459.7°F (-272.2°C, 0oK)
# Critical Temperature: -450.3°F (-268.0°C)
# Critical Pressure 33.0 psia: (2.26 atm)
# Density, Liquid @ B.P., 1 atm: 7.798 lb./cu.ft.
# Density, Gas @ 32°F (0°C), 1 atm: 0.0103 lb./cu.ft.
# Specific Gravity, Gas (Air = 1) @ 32°F (0°C), 1 atm: 0.138
# Specific c Gravity, Liquid @ B.P., 1 atm: 0.125
# Specific c Volume @ 32°F (0°C), 1 atm: 89.77 cu.ft./lb.
# Specific c Volume @ 68°F (20°C), 1 atm: 96.67 cu.ft./lb.
# Latent Heat of Vaporization: 34.9 Btu/lb. mole
# Expansion Ratio, Liquid to Gas, B.P. to 32°F (0°C): 1 to 754

Physical Properties Of NITROGEN

# Molecular Weight: 28.01
# Boiling Point @ 1 atm: -320.5°F (-195.8°C, 77oK)
# Freezing Point @ 1 atm: -346.0°F (-210.0°C, 63oK)
# Critical Temperature: -232.5°F (-146.9°C)
# Critical Pressure: 492.3 psia (33.5 atm)
# Density, Liquid @ BP, 1 atm: 50.45 lb/scf
# Density, Gas @ 68°F (20°C), 1 atm: 0.0725 lb/scf
# Specific Gravity, Gas (air=1) @ 68°F (20°C), 1 atm: 0.967
# Specific Gravity, Liquid (water=1) @ 68°F (20°C), 1 atm: 0.808
# Specific Volume @ 68°F (20°C), 1 atm: 13.80 scf/lb
# Latent Heat of Vaporization: 2399 BTU/lb mole
# Expansion Ratio, Liquid to Gas, BP to 68°F (20°C): 1 to 694

Physical Properties Of ARGON

# Molecular Weight: 39.95
# Boiling Point @ 1 atm: -302.6°F (-185.9°C, 87oK)
# Freezing Point @ 1 atm: -308.8°F (-189.4°C, 85oK )
# Critical Temperature: -188.4°F (-122.4°C)
# Critical Pressure: 705.8 psia (48.0 atm)
# Density, Liquid @ BP, 1 atm: 87.40 lb/scf
# Density, Gas @ 68°F (20°C), 1 atm: 0.1034 lb/scf
# Specific Gravity, Gas (air=1) @ 68°F (20°C), 1 atm: 1.38
# Specific Gravity, Liquid (water=1) @ 68°F (20°C), 1 atm: 1.40
# Specific Volume @ 68°F (20°C), 1 atm: 9.67 scf/lb
# Latent Heat of Vaporization: 2804 BTU/lb mole
# Expansion Ratio, Liquid to Gas, BP to 68°F (20°C): 1 to 840

Source