The separation of butanediol and propanediol by simulated moving bed

Abstract

This work studies the process development for the purification of PDO (1, 3-propanediol) by SMB (simulated moving bed). The propylene glycol produced by hydrogenation of glycerin generally contains BDO (1, 4-butanediol), which has a similar boiling point to PDO. In this study, Mitsubishi SP70 is used as the adsorbent for the SMB to separate BDO and PDO. Three series of experiments with 10, 100, and 200 g/L of feeding concentration, with an equal weight of BDO and PDO, were conducted to investigate the influence of feeding concentration on separation. The series of experiments was conducted at constant flow rates, and the switching time for the rotating valves was the only changed variable. Also, Langmuir adsorption isotherms, axial dispersion and mass transfer coefficients for BDO and PDO were independently evaluated through single column chromatography. From experimental results using 10 g/L of feed concentration, it is found that separation results can be well predicted by the Triangle theory as the dead volume of the SMB is assumed as 12% of the empty column. The optimized separation from this series of experiments is 100% pure BDO and 92.56% pure PDO, the productivity of the SP70 is 0.101 KKD (kg/kg/day), and the amount of water recycling is 300 L/kg. The obtained system's parameters, including the dead volume, are then used for the ASPEN simulation. It is shown that the simulated results from ASPEN can reasonably fit all experimental results. This confirms that the obtained parameters for the SMB are accurate, and the optimized operating conditions and the scale-up design can be accurately developed through simulation experiments in the future. The methods for measuring and estimating the parameters used in this study can also work as examples for the process development of SMB.