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Acetic Anhydride Manufacturing process


Acetic Anhydride Manufacturing process


Reaction
 

RAW MATERIAL REQUIREMENT TO MAKE 1 METRIC TON ACETIC ANHYDRIDE
Acetaldehyde                    : 1200 kg
Catalyst                             : 1 kg
Diluent (less recovery)        : 1650 kg
Air                                     : Variable
Air is bubbled through liquid Acetaldehyde in a reactor in the presence of 2% (based on the weight of Acetaldehyde) catalyst, such as a mixture of copper and cobalt acetates or manganese acetate, which prevents the formation of explosive amounts of peracetic acid. Approximately 1.4 part of acetic acid per 1 part of acetaldehyde is present as diluent to promote acetic anhydride formation.
Methyl or ethyl acetate, triacetin, or benzene may also be used as a diluent, and the last is generally utilized in conjunction with acetic acid as a withdrawing agent in subsequent vacuum distillation to allow separation of the reaction mixture from water at lower temperatures.
The reactor is maintained at a temperature of 50 to 70 degree C, and the pressure is approximately 60 psi (410 kPa). The over heat from the acetaldehyde for recycle as the overhead and water and diluent as bottoms. The diluent is returned to the reactor after the water is separated.
The dehydrated mixture of acetic anhydride and acetic acid from the bottom of the crude vacuum column is separated by distillation. Acetic acid is removed as overhead, and the acetic anhydride is withdrawn from a bottom plate. The catalyst is taken from the bottom to be reused. The acetic anhydride may be further purified by vacuum distillation. Variations of this process involve type and amount of diluent, and several stages in the reactor (with oxygen injection into each stage) under milder reaction conditions.
Present trends are away from air and towards oxygen. In one continuous process using ethyl acetate as the diluent and a catalyst concentration of 1% (cobalt acetate and copper acetate in a weight ratio of 2:1), the reaction is carried out at 50 degree C and 45 psi (310 kPa). Oxygen is injected at various points along the path of liquid travel, with the overall oxygen supply limited to 1 to 2% excess. Under these conditions, 95% conversions of acetaldehyde are obtained. Both acetic anhydride and acetic acid are produced in a 50:50 weight ratio.
PROPERTIES
Colorless, highly refractive liquid with a storage acetic odor.
Molecular Weight            : 102.09
Specific Gravity                 : 1.083, 20 degree C/20
Weight per gallon            : 9.01 lb (29 degree C)
Melting Point                     : -73.1 degree C
Boiling Point                       : 139.9 degree C
Flash Point (open cup)   : 64 degree C
Ignition Temperature     : 390 degree C
Vapor Density (air = 1)   : 3.52
Explosive Limits % by volume in air           : Lower 2.9 and Upper 10.3
Threshold Limit value in ppm      : 5
Soluble in all proportion in ethanol and ether at room temperature. In cold water it is soluble to extant of 13.6 g/100 ml, but decomposes in hot water.
Containers & Regulations –Aluminum drum and Tank cars, tank trucks, carboys, and glass bottles. It requires a White DOT shipping label.


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