(374e) Semicontinuous Process Intensification: Combining Reactive Extraction, Reactive Distillation, And Binary Distillation For Production Of 1,3-Propanediol

Semicontinuous separation processes integrate a single column with a middle vessel to perform separations tasks that normally require multiple columns in continuous processes. For example, with semicontinuous distillation, a three species mixture can be separated into its components using only one trayed column [1]. When tightly coupled with reaction, either in the middle vessel [2], or in an auxiliary vessel [3], the semicontinuous design can have a significantly lower total cost for intermediate production rates as compared to traditional batch and continuous alternatives. In this paper, a novel semicontinuous process is proposed that combines the functionalities of liquid-liquid reactive extraction, reactive distillation, and binary distillation into a single packed column.

1,3-Propanediol (PDO) is an important chemical used in a variety of applications, such as in food, lubricants, cosmetics, medicines, and in the polymerization of polytrimethylene terephthalate [4]. Recently, several new bio-derived routes for production of PDO have been explored that can have extensive energy savings over the traditional petroleum-based methods [5]. In the bio-derived route, PDO must be recovered from a fermentation broth containing mostly water.

Ordinary distillation and evaporation procedures for removal of the water are very energy intensive due to the large amount of water to be boiled. Instead, an alternative route of separating the PDO from water has been studied [6]. The broth is combined with an aldehyde, which reacts reversibly with the PDO to form its acetal. The mixture is then sent to a liquid-liquid reactive extraction column where additional aldehyde is used both as the reactant and the extractant. The aldehyde forms an organic phase containing the acetal. The water phase leaves the bottom containing some aldehyde, and the PDO is reacted away. The water phase is then purified by ordinary distillation, with the aldehyde recycled. The organic phase is fed to the bottom of a reactive distillation column, where fresh water is fed at the top. The reaction now takes place in reverse, producing nearly pure aldehyde in the distillate and nearly pure PDO in the bottoms.

The proposed semicontinuous process combines the three separation steps of the continuous process (reactive extraction, distillation, and reactive distillation) into one multi-function packed catalytic column. The process operates in a cyclic campaign of operating modes, with each mode corresponding to one of the three separation functions. Rigorous simulations demonstrate the feasibility of the operation without flooding, and the use of only one column can lead to significant capital cost savings.

References

1. Phimister, J. R. and W. D. Seider, "Semicontinuous, middle-vessel distillation of ternary mixtures." AIChE J., 46, 8 (2000): pp. 1508-1520.

2. Adams, T. A. II and W. D. Seider, "Semicontinuous distillation with chemical reaction in a middle vessel." Ind. Eng. Chem. Res., 45, 16 (2006): pp. 5548-5560.

3. Adams, T. A. II and W. D. Seider, "Ethyl lactate production using semicontinuous distillation with reaction in an auxiliary vessel and pervaporation." AIChE Spring Meeting 2007, Houston, Texas: American Institute of Chemical Engineers (in press).

4. Cheng, K., J. Zhang , D. Liu, Y. Sun, H. Liu, M. Yang, and J. Xu, "Pilot-scale production of 1,3-propanediol using Klebsiella pneumoniae." Proc. Biochem., 42, 4 (2007): pp. 740-744.

5. Mirasol, F., "Facing Up to Corn." ICIS Chem. Bus. Amer., February 5-11, 2007: pp. 50-51.

6. Hao, J., H. Liu, and D. Liu. "Novel route of reactive extraction to recover 1,3-propanediol from a dilute aqueous solution." Ind. Eng. Chem. Res., 44, 12 (2005): pp. 4380-4385.