APPLIED CHEMISTRY Formation and Recovery of Itaconic Acid from Aqueous Solutions of Citraconic Acid and Succinic Acid Bryan P. Hogle, ² Dushyant Shekhawat, ² Kirthivasan Nagarajan, ‡ James E. Jackson, ‡ and Dennis J. Miller* ,² Department of Chemical Engineering and Materials Science and Department of Chemistry, Michigan State University, East Lansing, Michigan 48824 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. I. Introduction Itaconic acid (2-methylenebutanedioic acid, IA) is a valuable monomer because of its unique chemical properties, which derive primarily from the conjugation of one of its two carboxylic acid groups and its methylene group. IA is thus a functionalized analogue of acrylic acid, the simplest conjugated alkenoic acid. Like acrylic acid, IA is able to take part in addition polymerization, giving polymers with many free carboxyl groups that confer advantageous properties on the polymer. Poten- tial applications of IA are numerous, but the market is currently limited by the high cost of the fungal fermen- tation-based process, which requires dilute feed solu- tions (∼10 wt % glucose) and an 8-10 days per batch cycle. 1 In this fermentation, IA yields are on the order of 50-60% of theoretical; the current price of ∼$2/lb is not expected to lead to commodity-scale production in the foreseeable future. The conversion of succinic acid (butanedioic acid, SA) to itaconic acid, through the intermediate citraconic acid (Figure 1), has potential for economic itaconic acid production. Citraconic acid (2-methyl-cis-2-butenedioic acid, CA) as citraconic anhydride (CAN) is formed via the catalytic condensation of succinic acid and its derivatives with formaldehyde. We have investigated and reported on production of CAN from succinates in earlier publications, 2,3 where our focus was to identify catalysts, feed materials, reaction conditions, and the kinetics of the conversion. Seventy percent selectivity to CAN was achieved at 50% succinate conversion; at higher succinate conversion lower selectivity was ob- served. 2 Several patents have also described CA forma- tion from succinates. 4-7 ² Department of Chemical Engineering and Materials Sci- ence. ‡ Department of Chemistry. * To whom correspondence should be addressed: phone: (517) 353-3928; Fax (517) 432-1105; e-mail millerd@egr.msu.edu. Figure 1. Reaction pathway for itaconic acid formation from succinic acid. 2069 Ind. Eng. Chem. Res. 2002, 41, 2069-2073 10.1021/ie010691n CCC: $22.00 © 2002 American Chemical Society Published on Web 04/06/2002