Back to Table of Contents

46763-B7
New Membranes for Enhanced Purification of Natural Gas at the Wellhead

Chad J. Booth, Texas State University

            The underlying goal of this project is to develop a new series of semi-fluorinated polyimides (PIs) which exhibit enhanced selectivity without loss to permeability.  These new materials are designed to be utilized as permeable membranes for the separation and purification of natural gas.  While traditional systems rely on a combination of the inherent chemical structure along with the “tortrous path” theory for the particular permeation to occur, our use of nano-dispersed TiO₂ is designed to decrease the rate of permeation of the methane.  The decrease occurs due to the surface adsorption of the methane onto the TiO₂ nanoparticles.  The overall system, is therefore, designed to remove any “other” gases present in the mix first (their permeation rate will not be affected by the presence of the TiO₂. 

            During the first year of the project we have synthesized and characterized a novel homologous series of PIs (Figure 1) using 6-FDA and a series of a, w -alkanediamines.  The diamines include 1,2 through 1,10 as well as the 1,12.  The new materials exhibit excellent thermal stability and are capable of forming transparent sustainable films. 

Figure 1: Synthetic scheme used to achieve the polyimides (x = 2-10 and 12)

To date we have collected data pertaining to thermal stability (TGA, values recorded at 10% weight loss), crystallinity (DSC), modulus (DMA), and molecular weight (GPC, using polystyrene standards).  This data, except for the molecular weights which averaged from 70,000 to 150,000 g/mol, is summarized in table 1. 

The traditional trends expected for a homologous aliphatic series of monomers upon inclusion in a polymer system are indeed present in these materials.  Not only do they display decreasing thermal/mechanical performance as the length of the aliphatic spacer is increased, they also clearly display an “odd-even” effect, out to about seven carbons.

Table 1: Thermal/Mechanical data on the Aliphatic Series.

            We are currently working in several areas, all of which relate to directly relate to this project.  We are testing the above mentioned materials to establish their gas permeation ability.  These values will be used as comparison data (a baseline) for the materials which have TiO₂ incorporated into their matrix.  The hypothesis is that if two series of PIs are examined, differing on with respect to the inclusion of the TiO₂ nanoparticle, the nanocomposite will exhibit enhanced selectivity with minimal loss to permeability.

            In addition we have begun the synthesis of the same series of PIs discussed above.  These only differ in that they are nano-composites with utilize TiO₂ as an inorganic additive.  This nano-particle has been shown to display surface adsorption with methane.  This effect will be exploited and used to increase the selective in a homologous series of partially aromatic/partially fluorinated/partially aliphatic PIs.

Back to top