Browsing by Subject "Desorption"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Carbon dioxide absorption, desorption, and diffusion in aqueous piperazine and monoethanolamine(2009-12) Dugas, Ross Edward; Rochelle, Gary T.This work includes wetted wall column experiments that measure the CO₂ equilibrium partial pressure and liquid film mass transfer coefficient (kg') in 7, 9, 11, and 13 m MEA and 2, 5, 8, and 12 m PZ solutions. A 7 m MEA/2 m PZ blend was also examined. Absorption and desorption experiments were performed at 40, 60, 80, and 100°C over a range of CO₂ loading. Diaphragm diffusion cell experiments were performed with CO₂ loaded MEA and PZ solutions to characterize diffusion behavior. All experimental results have been compared to available literature data and match well. MEA and PZ spreadsheet models were created to explain observed rate behavior using the wetted wall column rate data and available literature data. The resulting liquid film mass transfer coefficient expressions use termolecular (base catalysis) kinetics and activity-based rate expressions. The kg' expressions accurately represent rate behavior over the very wide range of experimental conditions. The models fully explain rate effects with changes in amine concentration, temperature, and CO₂ loading. These models allow for rate behavior to be predicted at any set of conditions as long as the parameters in the kg' expressions can be accurately estimated. An Aspen Plus® RateSep™ model for MEA was created to model CO₂ flux in the wetted wall column. The model accurately calculated CO₂ flux over the wide range of experimental conditions but included a systematic error with MEA concentration. The systematic error resulted from an inability to represent the activity coefficient of MEA properly. Due to this limitation, the RateSep™ model will be most accurate when finetuned to one specific amine concentration. This Aspen Plus® RateSep™ model allows for scale up to industrial conditions to examine absorber or stripper performance.Item Simulations of removal of molecular contaminants from silicon wafer surface(2011-12) Godse, Uday B.; Sreenivasan, S. V.; Ezekoye, Ofodike A.; Stuber, John; Hidrovo, Carlos H.; Hwang, Gyeong S.With the decrease in feature size in semiconductor manufacturing, molecular contamination problems are increased significantly. In order to optimize the yields in wafer fabrication units there is a need for process modeling that addresses the details of wafer contamination. Wafer contamination and cleaning is a complex process that covers various length and time scale events and phenomena. At the largest scales, there is the availability and transport of specific species within the fabrication unit and subsequent contamination of the wafer surface either through processing steps or through simple ambient transport processes. To limit wafer contaminant levels and/or to decontaminate them, wafers in the semiconductor fabrication unit are often cleaned and transported in a closed enclosure called Front Opening Unified Pod (FOUP) and purged with an inert gas like nitrogen. For the FOUP geometry, I analyze the large scale process modeling approaches to cleaning wafers. At smaller scales, the specific molecular configuration of the contaminant species impacts the kinetic chemical-physical cleaning mechanisms. To determine, from a fundamental perspective, the mechanisms contributing to wafer cleaning requires different scale tools from transport tools aimed at characterizing equipment scale (e.g., FOUP) contamination issues. I use molecular dynamics models and optimization techniques to infer physicochemical rates for molecular desorption on wafer surfaces. This dissertation considers these problems from a common perspective. The objective of this study has been to characterize the multi-scale problem of wafer cleaning with the objective of developing appropriate tools and models at different scales to best predict the dynamics of contaminant removal from wafer surfaces. A standardized method has been presented to extract kinetic rate parameters using molecular dynamics simulation (smaller-scale) and optimization for use in a larger-scale model of wafer decontamination using computational fluid dynamics (CFD). Also, by using available experimental data and CFD analysis an optimized FOUP purging recipe for better decontamination is presented and the relative magnitude of the time scales associated with surface kinetics and FOUP purging have been estimated.