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www.buffalo.edu
Determining the Effect of Plasticizers on Cellulose Triacetate for CO2/CH4 SeparationMin Wei, Benjamin Lam, Haiqing LinDepartment of Chemical and Biological Engineering, University at Buffalo (SUNY), Buffalo, NY 14260, USA
Project Overview Cellulose Triacetate and Crystallinity Doping with TEC
Background on CO2 Removal from Natural Gas
Motivation A wide utilization of commercial cellulose triacetate (CTA) for natural gas sweetening has been limited by its high crystallinity, resulting in low CO2 permeability.
ObjectiveDevelop advanced cellulose triacetate membranes for CO2/CH4 separation by doping small molecular size of plasticizers
Approach Preparation of a series of CTA doped with triethyl citrate (TEC) and triethyl 2-acetylcitrate (TEAC) to reduce crystallinity and increase CO2/CH4
selectivity.
Conventional separation by amine absorption/stripping technology• Cost intensive for absorbent
replacement• Large footprint requirement• High equipment corrosion rate
Membrane technology:• Economical and reliable• Compact and easy to scale-up• Energy-efficient
Molecular Transport in Polymers Polymeric membrane
High pressure
(up-stream)
Low pressure (down- stream)
Fick’s law
P: permeabilityD: diffusion coefficientS: solubility coefficient
Wijmans and Baker, J. Membr. Sci., 107, 1 (1995)Molecular simulation performed by Dr. Xiaoyan Wang
Diffusivity selectivity Solubility selectivity
Cellulose triacetate (CTA) :• Workhorse membrane material for
industrial CO2/CH4 separation• Good chemical resistance to higher
hydrocarbons contaminants in natural gas feeds
• Semi-crystalline with crystallinity as high as 37%, which significantly reduces gas permeability
Demonstration of crystal formation in polyethylene dramatically reducing CO2 permeability
Approach: Doping with small molecular size of plasticizers
Description Mass of CTA (g)
Mass of additive (g)
Mass of CH2Cl2
(g)100:0 5.0 0.0 95.090:10 4.5 0.5 95.080:20 34.0 1.0 95.060:40 3.0 2.0 95.050:50 2.5 2.5 95.0
Doping with small molecular size of plasticizers• Reduce CTA crystallinity• Enhance gas permeability• Enhance CO2/ CH4 selectivity
Doping with TEAC
Conclusion and Future Work
FTIR-ATR Analysis
TGA Analysis XRD Analysis
FTIR-ATR Analysis
XRD AnalysisTGA Analysis
Constant Volume/Variable Pressure System
• FTIR indicated blending of plasticizers into CTA polymer.
• TGA confirmed the actual amount of plasticizers in the membrane.
• XRD indicated decrease in CTA crystallinity with increasing weight ratio of plasticizers.
• Future Work: Membrane transport properties for permeability and solubility in doped membranes.
TEC
TEAC
• Absorbance curve of polymer blends are similar to CTA
• Increasing amount of plasticizer indicated decrease in membrane crytallinity
• Absorbance curve of polymer blends are similar to CTA
• Actual ratio of polymer blend confirmed through the weight
90:10 CTA:TEAC
5 10 15 20 25 30 352-Theta (°)
Rel
ativ
e In
tens
ity
Pure CTA
50:50 CTA:TEAC
80:20 CTA:TEAC
60:40 CTA:TEAC
1000 1200 1400 1600Wavenumber (cm-1)
Abs
orba
nce
(a.u
.)
Pure TEAC
50:50 CTA:TEAC
80:20 CTA:TEAC
Pure CTA
1371 cm-1
CH3 bending
1211 cm-1 C-O stretching
Pure CTA
6040 CTA:TEC8020 CTA:TEC
9010 CTA:TEC