Xuefei Zhang

Date of Award

1-1-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

First Advisor

Brian M. Tande

Abstract

Although extensive research attention has been drawn to using membranes for carbon dioxide (CO2) capture from flue gas, the use of membranes for stripping CO2 solvents has rarely been studied. The technical feasibility of using polymeric membrane based separation technology to recover CO2 from CO2 saturated chemical solvents such as monoethanolamine is investigated in the present research. A membrane system was built to study the performance of several common polymeric porous membranes for the recovery of CO2 from saturated aqueous MEA solution by the thermal swing process. The stripped CO2 gas was swept by mass flow controlled N2 reference gas and was measured by a non-dispersive infrared CO2 analyzer and gas chromatography. Substantial CO2 permeation flux through the membrane together with superior selectivity suggests the promises of membrane contactors as an alternative stripping configuration for CO2 recovery.

Parametric screening design of experiments studied parameters of process temperature, retentate flow rate, and sweep gas rate. Process temperature was identified as the only significant factor, which is consistent with individual parametric study results. Heat energy efficiency characterization of this system showed that roughly half of the heat energy was used for the stripping process at 80ºC and above. The membrane material candidates screening experiment results showed that polypropylene and polytetrafluoroethylene porous membranes outperformed polyester, polyamide, polyvinylidene fluoride, polysulfone and cellulose acetate. Compositional, structural and surface morphological characterization was also utilized on the membranes before and after this process. Mass transfer mechanism study and mass transfer coefficients calculation reveals that the liquid boundary layer resistance is responsible for more than 90% of the overall mass transfer resistance, much greater than either the membrane resistance or gas layer resistance. Membrane wetting and fouling effects were found to deteriorate membrane performance. Polypropylene membranes with different pore size were studied and compared. There was no significantly change of CO2 flux for membrane pore size from 0.1micron to 2.5 micron. The membrane with pore size of 0.6 micron was found to have best selectivity. The energy utilization efficiency did not change significantly for membranes with different pore size. Membranes with pore size 2.5 micron and below were found to be not wetted during the experiments and membranes with pore size of 5 micron and 10 micron were wetted during the process.

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