Document Type


Date of Award


Degree Name

Doctor of Philosophy in Environmental Science - (Ph.D.)


Chemistry and Environmental Science

First Advisor

S. Mitra

Second Advisor

Tamara M. Gund

Third Advisor

N. M. Ravindra

Fourth Advisor

Mengyan Li

Fifth Advisor

Pradyot Patnaik


Pharmaceutical industries historically have had one of the highest amounts of solvent waste generated per unit of drug manufactured. Energy requirements and carbon footprint of current solvent recycling processes tend to be quite high, and the incineration of the solvents for waste disposal produces toxic air emissions. Also, rapidly increasing demand for energy and strict regulation on engine pollutant emissions have necessitated the use of alcohol as carbon-neutral fuels. Thermal distillation is one of the most common methods for the separation of alcohol-water mixtures. However, its application is limited due to energy requirements and high operating costs, and heating to boiling point can lead to undesirable side reactions. In this dissertation, three major challenges related to organic solvent separation are addressed. Approaches to enhance the performance of membrane distillation by modifying the commercial membranes with different carbon-based nanomaterials and alternative heating technologies to reduce energy consumption are explored. These form the basis of this dissertation.

In the first application, carbon nanotube immobilized membrane (CNIM) for enhanced separation of organic solvents from their aqueous mixtures via sweep gas membrane distillation is explored. The presence of carbon nanotubes (CNTs) on the hydrophobic membrane surface significantly alters the liquid membrane interactions to promote isopropanol (IPA) transport in IPA-water mixture by inhibiting water penetration into the membrane pores. The isopropanol flux, selectivity and mass transfer coefficient obtained with CNIM are significantly higher than the corresponding unmodified Polytetraflouroethylene (PTFE) membrane at different isopropanol concentrations and temperatures. Performance enhancement in CNIM can be mainly attributed to the preferential sorption on the CNTs followed by rapid desorption from its surface.

The second application demonstrates enhanced organic separation via microwave-induced sweep gas membrane distillation from its aqueous mixture. Microwave heated ethanol water mixtures are separated on PTFE and CNIM. The membrane performances in terms of ethanol vapor flux and separation factors are evaluated and compared between microwave-induced membrane distillation (MIMD) and membrane distillation (MD) using conventional heating. The combination of CNIM and microwave heating is most effective. Performance improvements in MIMD are due to nonthermal effects such as localized superheating and break down of hydrogen-bonded ethanol water clusters. Moreover, MIMD requires less energy to operate than conventional MD under similar conditions. The lower energy consumption along with higher flux and separation factor in MIMD represents a major advancement in the state of the art in solvent separation by MD. Furthermore, a novel approach for Acetone-Butanol-Ethanol (ABE) recovery using MIMD is investigated. CNTs and octadecyl amide (ODA) functionalized CNTs are used. The ABE flux, separation factor and mass transfer coefficient obtained with CNT and CNT-ODA immobilized membranes are remarkably higher than those of the commercial pristine membrane under various experimental conditions.

In the third major application, nanocarbon-immobilized membranes are applied for the separation and recovery of tetrahydrofuran (THF) from water via MD. Several nanocarbons, namely CNTs, graphene oxide (GO), reduced graphene oxide (rGO), and an rGO CNT hybrid is immobilized on PTFE membranes. Among the nanocarbons, rGO CNT performs the best in terms of flux and separation factor over the plain PTFE membrane. The improved membrane performances of the rGO CNT membrane is due to the preferential sorption of THF on rGO CNT, nanocapillary effect through graphene sheets, along with the activated diffusion of THF via a frictionless CNT surface.

This dissertation shows that the modification of the membranes with carbon-based materials namely CNTs, GO and their derivatives along with microwave heating as an alternative heating source are effective strategies to enhance the performance of MD. These fabricated membranes along with modification of the system configuration have great potentials for solvent removal from aqueous solution for use as biofuels and by cosmetic, paint and pharmaceutical industries using MD.



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