Ind. Eng. Chem. Res. 2002, 41, 2069-2073
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APPLIED CHEMISTRY Formation and Recovery of Itaconic Acid from Aqueous Solutions of Citraconic Acid and Succinic Acid Bryan P. Hogle,† Dushyant Shekhawat,† Kirthivasan Nagarajan,‡ James E. Jackson,‡ and Dennis J. Miller*,† 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. Potential applications of IA are numerous, but the market is currently limited by the high cost of the fungal fermentation-based process, which requires dilute feed solutions (∼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 †
Department of Chemical Engineering and Materials Science. ‡ Department of Chemistry. * To whom correspondence should be addressed: phone: (517) 353-3928; Fax (517) 432-1105; e-mail
[email protected].
Figure 1. Reaction pathway for itaconic acid formation from succinic acid.
kinetics of the conversion. Seventy percent selectivity to CAN was achieved at 50% succinate conversion; at higher succinate conversion lower selectivity was observed.2 Several patents have also described CA formation from succinates.4-7
10.1021/ie010691n CCC: $22.00 © 2002 American Chemical Society Published on Web 04/06/2002
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Figure 2. Process flow diagram for producing itaconic acid from succinates and formaldehyde.
The condensation reactor and the recovery/purification steps are depicted in the process flowsheet in Figure 2. The effluent from the condensation reactor gives a product mixture containing CAN, succinic anhydride (SAN), monomethyl esters (MMC and MMS), dimethyl esters (DMC and DMS), methanol (MeOH), and unreacted formaldehyde. This mixture is first hydrolyzed along with simultaneous methanol and formaldehyde removal to give an aqueous solution containing essentially CA and SA. We report here the further processing steps for formation and recovery of IA from this CA/SA solution: (1) separation and recovery of SA from the mixture, (2) isomerization of CA to IA with byproduct formation (Figure 1), (3) separation and purification of IA from the isomerized products, and (4) reisomerization of byproducts from step 2 back to CA. An earlier study reported the isomerization of CAN to IA and byproducts;8 the work presented here gives the complete process for IA formation and recovery. II. Experimental Section Materials. Reagent grade citraconic acid (denoted CA, Aldrich Chemical Co., 98%), citraconic anhydride (CAN, Aldrich, 98%), succinic acid (SA, Aldrich, 99%), mesaconic acid (MA, 2-methyl-trans-2-butenedioic acid, Aldrich, 98%), citramalic acid (CMA, 2-methyl-2-hydroxybutanedioic acid, Aldrich, 98%), and itaconic acid (IA, Aldrich, 99+%) were used in this study in their asreceived state. Purified water (HPLC grade, J.T. Baker) was used in all experiments. The catalyst used for the reisomerization of itaconic and citramalic acids to CAN was Norpro SA3177 γ-alumina. This material has a N2 BET surface area of 100 m2/g, an acid site density of 0.34 mmol/g as measured by NH3 adsorption, and a basic site density of 0.23 mmol/g as measured by CO2 adsorption. The alumina was ground and sieved to -30+60 mesh and calcined in air for 6 h at 773 K before loading into the reactor. Methods. Isomerization of CA to IA. Isomerization reactions were conducted in a 300 mL autoclave reactor (Parr Instrument Co., model 4561) equipped with magnetic drive stirring unit and dip tube for liquid sampling. The reactor controller (Parr model 4852) provides adjustable stirring speeds and automatic temperature control via the heating mantle and air-cooling loop inside the reactor. The reactor was typically charged with 100 mL of CA (or CAN) solution in concentrations of 5-50 wt %, heated to 423-463 K under a 1 atm nitrogen blanket, and stirred for up to 3
h. Samples (1-2 mL) were taken when the autoclave reached reaction temperature and at 30 min intervals thereafter and analyzed via HPLC (described below). Gas-phase analysis was conducted once at the end of the reaction period using a Riker IR CO2 gas analyzer. Reisomerization. The conversion of byproducts of isomerization (CMA and MA) and unrecovered IA back to CA was conducted in a fixed-bed reactor described in our earlier work3 using 5.0 g of Norpro SA3177 γ-alumina as a catalyst. Feed solution concentrations and carrier gas flow rates are given for individual experiments in the Results section. Crystallization. Desired quantities of CA, SA, IA, and water were weighed out and combined in a flask to simulate solution concentrations expected in the process. A water-cooled condenser was placed on the flask, which was then heated with stirring in a constant temperature water bath to 358-368 K until all solid materials dissolved. The flask was then removed from the high-temperature bath and cooled to either 295 or 286 K (using cold tap water) in a second bath, wherein crystallization took place. After cooling for 1 h, crystals were vacuum filtered and washed with either ice water ( 4 h) because of material loss that is not accounted for in the model. The model predicts formation of mesaconic acid throughout reaction, whereas in experiments measurable quantities of MA are observed only after 4 h reaction time. The uncertainty in rate constants reported in Table 2 is based on uncertainty in species concentration of (5% based on repeated HPLC analyses. Vapor-Phase Reisomerization to CA. The byproducts (mesaconic and citramalic acids) of CA isomerization to IA remain in solution during IA crystallization, so that the recycle stream back into the process contains these byproducts, unrecovered IA, and unisomerized CA. We have found that the byproducts and residual IA can be converted back to CA via vapor-phase reaction. Citramalic acid (CMA) is the major byproduct (up to 20% yield) from isomerization of CA to IA. The conversion of CMA to CA was conducted in the fixed-bed reactor at 543 K and 0.2 MPa total pressure with a CMA feed solution (15 g/L) flow rate of 1 mL/min and with 150 mL (STP)/min helium carrier gas. Complete conversion of CMA to CA was observed with no byproduct formation. In a similar experiment, IA aqueous solution (65 g/L) was fed at 0.3 mL/min along with 55 mL (STP)/min helium at 623 K and 0.5 MPa total pressure. An IA
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Table 4. Results of Succinic Acid Crystallization
ref no.
initial concn (g/L) CA SA IA
SA-1 SA-2 SA-3 SA-4 SA-5
422 423 423 791 790
355 353 353 236 237
22 22 22 37 37
temp (K)
postcrystallization treatment
crystal composition (posttreatment) (wt %) CA SA IA
295 295 286 295 295
no wash wash with 35 g of cold water wash with 40 g of cold water no wash wash with 27 g of cold water
1.7 0.1 0.2 29.5 0.3
97.7 99.7 99.8 68.6 99.3
0.6 0.2 0.0 1.9 0.4
succinic acid recovery (%) 79.8 58.6 70.0 69.3 60.8
Table 5. Results of Itaconic Acid Crystallization
ref no. IA-1 IA-2 IA-3 IA-4 IA-5a a
initial concn (g/L) CA SA IA 336 336 342 335
