Formation and Recovery of Itaconic Acid from Aqueous Solutions of Citraconic Acid and Succinic Acid

The formation and recovery of itaconic acid (IA) from mixed aqueous solutions of citraconic acid (CA) and succinic acid (SA) has been developed as part of an overall process to produce itaconic acid via condensation of succinates with formaldehyde. The formation and recovery described here involves four steps: (1) removal of SA via crystallization, (2) isomerization of CA to IA at elevated temperature, (3) recovery of IA via crystallization, and (4) conversion of reaction byproducts back to CA. As part of the overall process, these steps facilitate recycling of unreacted species and reuse of byproducts, thus giving high overall yields. Itaconic and succinic acids are readily crystallized because of their low solubility relative to CA; lab-scale crystallization experiments gave high purity (99.8 wt % for SA; 99.4% for IA) crystalline solids after washing. Isomerization gave a maximum IA selectivity of 87% at 170 °C after 3 h reaction. The primary byproduct of isomerization, citramalic acid (CMA), and IA in the residual crystallization liquor are converted exclusively back to CA over γ-alumina at 270 °C.