Acrylic Acid Production from Glycerol

The process under analysis comprises three major sections: (1) Crude Glycerol Treatment; (2) Reactions; and (3) Acrylic Acid Recovery.

Crude Glycerol Treatment. Initially, the crude glycerol stream is first mixed with a surfactant to precipitate soaps dissolved in the glycerol, then it is fed to an oil-water separator to remove free oils that might be contaminating the glycerol. The main stream is centrifuged and fed to an ion exchanger vessel, where dissolved salts precipitate. The glycerol is sent to a distillation column, where dissolved lighters and heavier contaminants are separated

Reactions. In the first reaction, glycerol is dehydrated to acrolein in the presence of a solid Bronsted acid catalyst, like tungsten oxide/zirconium oxide. Air is also added to the system to provide oxygen to the reaction medium. The presence of oxygen decreases coke formation in the catalyst and increases the reaction yield. Water and heavy by-products produced in the first reaction are removed in an absorption column to increase acrolein partial pressure in the second reaction, thus increasing its yield and selectivity for acrylic acid. In the second reaction, acrolein conversion takes place in the presence of molybdenum vanadium oxides catalysts.

Acrylic Acid Recovery. Since acrylic acid may spontaneously polymerize when subject to high temperatures, the columns of acrylic acid recovery section are fed with polymerization inhibitors and operated at or below atmospheric pressure to allow low bottom temperatures. The acrylic acid, absorbed in water, is quenched and purified by extraction with an organic solvent and distillation to remove the solvent. The crude acrylic acid stream is directed to another two columns, where first light ends are stripped off and acrylic dimers are removed. The last column overhead, consisting of high purity ester-grade acrylic acid, is condensed and stored.