Date of Graduation

8-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Chemical Engineering

Advisor

Keith Roper

Committee Member

Jamie Hestekin

Second Committee Member

Tom Spicer

Third Committee Member

Darin Nutter

Fourth Committee Member

Ingrid Fritsch

Keywords

Applied sciences; Butanol; Gold nanoparticles; Nanocomposite membranes; Pervaporation; Plasmon

Abstract

Butanol derived from biological feedstocks has significant potential as a liquid fuel source, but the separation methods used in its production can be prohibitively expensive and are therefore currently the subject of extensive research. Pervaporation is a promising membrane process that is effective in butanol separations, but involves a large energy demand. This study examines the possibility of increasing flux and energy efficiency in pervaporation via plasmonic heating of gold nanoparticle-functionalized, polymer nanocomposite membranes (AuNCMs) in lieu of conventional feed heating. An economic analysis demonstrated that plasmonic pervaporation could achieve significant reductions in energy usage and utility cost in butanol production. A novel plasmonic pervaporation system was constructed to evaluate the process experimentally. The system included uniform laser excitation and infrared thermal analysis of the membrane surface, as well as automated operation. AuNCMs, fabricated by reduction of tetrachloroauric acid by the polymer crosslinker, demonstrated stable temperature increases and flux enhancements (>100%) that increased with gold content and incident laser power.

A thermal model was developed to describe heat transfer in the system and enable calculation of membrane laser absorption efficiencies and quantification of energy loss modes. An economic investigation of the system performance was conducted by coupling the thermal model with an empirical model for flux prediction. The analysis showed that the current system performance was not sufficient to reduce the energy demand/utility cost versus conventional feed heating due to: i) heat loss to the feed and ii) low laser absorption efficiencies. The latter effect was significantly more detrimental economically and, if improved, could result in a 7-fold increase in energy efficiency.

A spectroscopic analysis method was developed to approximate AuNCM physical and optical properties to provide insights into why AuNCM absorption was low. The results indicated that only a small fraction of added Au was effectively being converted to desirable, light-absorbing nanoparticles. Evidence suggested that the remaining Au formed large, light-scattering particles, reducing the absorption efficiency of the AuNCMs. The analysis demonstrated that optimization of fabrication methods could potentially improve absorption efficiencies to near 100%, making plasmonic pervaporation economically superior to conventional methods.

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