Date of Award

Summer 8-18-2023

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Forest Resources

Advisor

Ling Li

Second Committee Member

Jinwu Wang

Third Committee Member

Douglas Bousfield

Additional Committee Members

Douglas Gardner

Mehdi Tajvidi

Abstract

This dissertation project addressed the manufacture and evaluation of a small polydimethylsiloxane (PDMS) hollow fiber membrane system in the kiln drying of lumber in an attempt to explore air dehydration and reduced energy usage. Temperature and vacuum pressure exert the most pronounced influence on membrane efficiency. Under optimal conditions, the PDMS membrane module demonstrates a remarkable 66% efficiency in removing water vapor from a moist air stream. Based on the parameters of the lab system and its operational performance, a finite element model was developed to simulate its scaleup for a lab-scale lumber drying kiln to remove moisture from the exhaust air such that the dehydrated air can be recirculated into the kiln to dry the lumber. Traditional kiln drying methods consume substantial energy and experience heat loss through the expulsion of the high-humidity exhaust air and drawing in fresh outside dry air. To address these challenges, a closed moisture removal system was designed and simulated, where a membrane removes moisture from moist air without any phase change, enabling the recycling of warm air and retention of thermal energy, therefore, reducing the energy consumption of the kiln. The simulation has demonstrated that this novel membrane system has significant potential for energy-saving applications in wood drying and other industries with similar drying processes. By conserving heat energy within the system, it can reduce energy consumption by up to 20% depending on weather conditions and drying schedules.

Because membranes are a key component of the membrane separation technology, sustainable cellulose nanocrystals (CNCs) are incorporated into PDMS to create a composite membrane with enhanced thermal and mechanical stability, as well as water vapor permeability. The hydrophilic nature and agglomeration issues of CNCs within PDMS were addressed through silylation, resulting in a composite membrane consisting of silylated CNCs and PDMS. The silylated CNC (SCNC)/PDMS composite membrane exhibits an increase in water vapor permeability compared to pure PDMS and a significant increase in selectivity compared to both pure PDMS and unmodified CNC/PDMS membranes. Thermo-mechanical analysis indicates a decrease in the coefficient of thermal expansion (CTE) of the PDMS membrane upon the addition of both CNC and SCNC. This research highlights the challenges and potential benefits of incorporating nanocellulose in membrane materials for high-temperature applications.

Overall, this study presents a promising approach to revolutionize kiln drying processes, offering energy efficiency and sustainability through the utilization of membrane-based air dehydration with nanocellulose-modified membranes.

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