Bio-Acrylic Acid Production from Glucose (Two-Step Process)

The process under analysis comprises three major sections: (1) Fermentation; (2) Separation; and (3) Purification.

Fermentation. The culture media used in the pre-fermentation and in the fed-batch fermentation are prepared by diluting the glucose syrup (carbon source) and nutrients (source of nitrogen, vitamins and minerals) in water. The main fermentation is carried out in fed-batch mode and under aerobic process conditions. The pH control is made by addition of a solution of ammonia, so as to keep the pH of the fermentation broth around 7. Due to the presence of the ammonium hydroxide, most of the 3-hydroxypropionic acid produced is neutralized to 3-hydroxypropionate, in such a way that the broth contains 3-hydroxypropionic acid mainly in its conjugate base form.

Separation. After fermentation, cell debris and other suspended solids are removed from the broth by ultrafiltration. The permeate is pumped to Evaporators, while the retentate – mostly biomass/water – is disposed. The concentrated broth is fed to an agitated vessel operating under vacuum, along with tricaprylamine (organic solvent) and dodecanol (cosolvent). The mixture is heated so that the ammonium salt of the 3-hydroxypropionic acid splits, producing ammonia and 3-HP. The liquid stream from the Salt-Splitting is then back-extracted in countercurrent contact with hot water, yielding an aqueous phase rich in 3-HP and a 3-HP-lean organic phase. The resultant aqueous solution of 3-HP is passed through a reactor column, where the 3-HP is dehydrated to acrylic acid that is fed, in turn, to an azeotropic distillation system along with toluene for water removal.

Purification. The acrylic acid solution is fed to the crude acrylic acid distillation for removal of remaining impurities, and finally submitted to a melt crystallization carried out in multitube exchangers. After operating cycles (alternating crystallizing/melting stages), glacial acrylic acid is obtained.