Production process of acrylic acid

2018/8/28 19:53:24
Acetylene carbonylation process
Acrylic acid was synthesized by carbonylation (see carbonyl synthesis) of acetylene, carbon monoxide, water and solvent tetrahydrofuran with nickel halide (see complex catalyst) as catalyst and copper halide as co-catalyst at 160-200 C and 4.0-5.5 MPa. The method is being gradually replaced by propylene oxidation.
Acrylonitrile hydrolysis
In the presence of sulfuric acid, acrylonitrile can be hydrolyzed twice and then distilled under vacuum to obtain pure acrylic acid: CH2 = CHCN + H2O + H2SO4 - CH2 = CHCONH2. H2SO4
CH2 = CHCONH2. H2SO4+H2O - CH2 = CHCOOH+NH4HSO4
In recent years, the rapid development of ammoxidation of acrylic acid to acrylonitrile has provided cheap acrylonitrile for acrylic acid production.
Acrylonitrile hydrolysis
Acrylonitrile can be purified in the presence of sulfuric acid for two times and then decompressed to obtain pure acrylic acid.
CH2 = CHCN+H2O+H2SO4 - CH2 = CHCONH2. H2SO4
CH2 = CHCONH2. H2SO4+H2O - CH2 = CHCOOH+NH4HSO4
In recent years, the rapid development of ammoxidation of acrylic acid to acrylonitrile has provided cheap acrylonitrile for acrylic acid production.
Propylene oxidation
In the first step, propylene is oxidized to acrolein by molybdenum-bismuth or antimony catalysts; in the second step, acrolein is oxidized to acrylic acid by molybdenum-vanadium-tungsten catalysts (see metal oxide catalysts):
CH2 = CHCH3+O2 - CH2 = CHCHO+H2O
CH2 = CHCHO+2O2 - CH2 = CHCOOH
Propylene, steam and preheated air are mixed into the first reactor (see figure below). The reaction temperature is 320-340 C and the pressure is 270 kPa. The reaction gas is directly fed into the second reactor without separation. The reaction temperature is 280-360 C and the pressure is 200 kPa. All two reactors are molten salt as heat carrier. The gas from the second reactor was absorbed by water and 30%~40% acrylic acid aqueous solution was obtained. The total yield of pure acrylic acid was 87%. The tail gas of the absorber was partly emptied and recycled.