Date of Award

8-31-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemical Engineering - (Ph.D.)

Department

Chemical, Biological and Pharmaceutical Engineering

First Advisor

Sirkar, Kamalesh K.

Second Advisor

Mitra, S.

Third Advisor

Barat, Robert Benedict

Fourth Advisor

Khusid, Boris

Fifth Advisor

Wang, Xianqin

Abstract

This thesis is concerned with a cyclic pressure swing membrane absorption process (PSMAB) for separation of the feed gas mixture containing —40% CO2-He balance using pure ionic liquid, 1-butyl-3-methylimidazolium dicyanamide ([bmim][DCA]), and its solution containing poly(amidoamine) (PAMAM) dendrimer Gen 0 primarily with a dry feed gas. An advanced pressure swing membrane absorption process is developed to produce purified He as a surrogate for H2 at a high pressure from simulated low- temperature shifted syngas for different membrane modules. The PSMAB process also simultaneously produces a highly purified CO2 stream containing bulk of the CO2 in the post-shift reactor gas stream and suitable for subsequent sequestration.

The hydrophobized ceramic membrane tubule-based system produces poor quality of products. The hydrophobized poly(ether ether ketone) (PEEK) hollow fiber- based system, on the other hand, provides higher product concentrations due to a much higher contacting area per unit gas volume. Among PEEK modules, the PEEK-L III module provides the highest CO2 concentration in the CO2-rich product stream.

Measurements of the solubility and diffusivity of pure carbon dioxide, pure helium, and a feed mixture of —40% CO2-He balance are carried out in the ionic liquid, ([bmim][DCA]), and in its solution containing 20 wt% and 30 wt% PAMAM dendrimer Gen 0 with and without water. Additional solubility studies of pure CO2 and He are done in polyethylene glycol 400 (PEG 400) and 20 wt% dendrimer in PEG 400.

The solubility of CO2 decreases with an increase in temperature whereas He solubility increases with an increase in temperature. The CO2 and He solubilities increase with an increase in feed pressure. Carbon dioxide absorption increases considerably when the amine is added to the ionic liquid and then increases several-fold when moisture is added. Higher CO2/He solubility selectivity is observed as temperature decreases to as much as 55 at 50 °C. Moreover, CO2 solubilities in PEG 400 and in 20 wt% dendrimer in PEG 400 are somewhat higher than in [bmim] [DCA] and 20 wt% dendrimer in [bmim] [DCA], respectively.

A mathematical model of the three-valve PSMAB process is developed and verified so that the model may be used to carry out scale up calculations. Such a scale up model can allow determination of the cost of the process of a given CO2-containing feed gas mixture. The mathematical model is numerically solved to predict the extent of purification of the gas by pure ionic liquid [bmim][DCA] in the three-valve PSMAB device. The decreasing pressures generated by a numerical solution of the model agree well with the experimental runs for ceramic modules during the 900 second absorption step, but are significantly lower for the PEEK hollow fiber modules due to the large dead volumes present in the PEEK modules. There is a 6-10% difference in CO2 concentration in the two product streams between the predictions and the measured values. The simulation results show that purified (>90%) CO2 and He can be obtained for two PEEK- L III modules in series using [bmim] [DCA] as the absorbent.

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