Date of Award

12-31-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry - (Ph.D.)

Department

Chemistry and Environmental Science

First Advisor

S. Mitra

Second Advisor

Tamara M. Gund

Third Advisor

Yong Ick Kim

Fourth Advisor

Pradyot Patnaik

Fifth Advisor

N. M. Ravindra

Abstract

As water scarcity increases globally under the stresses of increasing demand, aquifer depletion, and climate change, the market for efficient desalination technologies has grown rapidly to fill the void. One such developing technology, membrane distillation (MD), has found much interest in the scientific community. MD has also been powered by solar energy and waste heat resources because it can be operated at relatively low temperatures. Recent studies indicate that MD could potentially achieve the efficiencies of state-of-the-art mature thermal desalination technologies, although additional engineering and scientific challenges must first be overcome.

MD can be used to treat high salinity water where the salt concentration is high. The aim of this research is to better understand and provide solutions for one of the major challenges being faced by high concertation applications of MD, more specifically membrane fouling. Through experiments, this thesis compares different heating systems in MD, namely conventional and microwave heating, and their effect on fouling. It also looks at carbon nanotube immobilized membrane, and studies the effect of carbon nanotubes on fouling. In this research MD is carried out using highly concentrated aqueous calcium carbonate, calcium sulfate and barium sulfate solutions, and it is observed that the decline in flux over time is significantly less in microwave induced membrane distillation (MIMD).

As compared to conventional heating, the salt deposition on the membrane is 50-79 % less during microwave heating.

The second and third part of this research shows the effects of adding different antiscalant materials to the feed side of the experiment to investigate the fouling behavior under fixed operating parameters such as feed concentration, temperature, and feed flowrate. The results show a strong influence of using antiscalant materials on the highly concentrated salt solutions and on produced water from hydraulic fracturing as well. It is observed that using carbon nanotube based membranes and antiscalants, the fouling behavior could be reduced and water vapor flux in MD can be enhanced. Results also show that the presence of CNTs facilitates the removal of deposited salts by washing and the CNIM regains 97% of its initial water flux, whereas the unmodified polypropylene only regains 85% of the original value.

Share

COinS