QUARTERLY PROGRESS REPORT

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1 U.SJDOE Patet Clearace is ot required prior to publicatio of this documet. QUARTERLY PROGRESS REPORT Date: July 28,1995 Reportig Period April 1,1995 Jue 3,1995 Project Title: Silica Membraes for Hydroge Separatio from Coal Gas c Idetificatio Number: DEFG2292PC92525 Istitutio: Califoria Istitute of Techology Pricipal Ivestigator: G. R. Gavalas L Project Objectives The project objectives are (1) to explore ew silylatio reagets ad reactio coditios with the purpose of reducig the thickess ad icreasig the permeace of silica membraes, (2) to delieate mechaism ad kietics of silica depositio, (3) to measure the permeability of silica layers at differet extets of depositio ad (4) to mathematically model the relatioship of permeability ad membrae structure. I][, Work Performed Durig Reportig Period Fudametal Measuremets i TGAMS System Experimets cotiued usig the TGAMS system. I each experimet the permeace of several gases is measured through a porous Vycor tube subjected to cosecutive silylatiohydrolysis cycles which cause Si2 depositio ad arrowig of the pore size. Figures 1 ad 2 show the results of oe experimet that lasted 7 cycles. The poits are at cycles (utreated tube), 4 cycles ad 7 cycles. Figure 1 compares ormalized permeace ratios for CH4:N2 ad SF6:N2 with the Kudse value which is uity. There is a small but growig deviatio from the Kudse ratio with the selectivity chagig i favor of the gas with the smaller kietic diameter (N2). Figure 2 shows the absolute permeaces of several gases versus weight gai (or cycle umber). All gases show a gradual decrease of permeace with icreasig depositio, as expected. Computer Simulatios Cosiderable progress was achieved i the molecular dyamics simulatio of diffusio i cylidrical capillaries. I prior simulatios the capillary wall was simulated by a smooth potetial i the perpedicular directio (EverettPohl, i.e. itegrated LeardJoes) plus a periodic (siuisoidal) potetial parallel to the walls. This soft periodic potetial which has bee used previously i surface diffusio studies did ot allow adequate diffuse scatterig ad tured out to be usuitable for MD calculatios at elevated temperatures. We ow have itroduced

2 discreet spherical clusters iteractig with the gas molecules by a LeardJoes potetial. These clusters are superimposed o the cotiuous EverettPohl potetial ad provide a mechaism for diffuse scatterig. Figure 3 shows the results of oe set of simulatios. Accordig to basic diffusio theory the mea square distace a% traveled by a molecule should satisfy The figure shows that with icreasig time <r2>/2t ideed teds to a limit. This limit is compared with the Kudse diffusio coefficiet for two values of the capillary radius. The graphs for the two radii are ot directly comparable because the cluster desities used i the two cases were differet. DISCLAIMER This report was prepared as a accout of work sposored by a agecy of the Uited States Govermet. Neither the Uited States Govermet or ay agecy thereof. or ay of their employees, makes ay warraty, express or implied, or assumes ay legal liability or resposibility for the accuracy, completeess, or usefuless of ay iformatio, apparatus, product, or process disclosed, or represets that its use would ot ifrige privately owed rights. Referece herei to ay specific commercial product, process, or service by trade ame, trademark maufacturer, or otherwise does ot ecessarily costitute or imply its edorsemet, recommedatio, or favorig by the Uited States Govermet or ay agecy thereof. The Views ad opiios of authors expressed herei do ot ecessarily state or reflect those of the Uited States Govermet or ay agecy thereof. 2

3 Deviatio of Permeaces from Kudse Results oo r. i=ch, i=sf, I I I I I I I I I % Weight Gai Figure 1. Normalized permeace ratios CH4N2 ad SF6:N2 at 5 C versus weight gai durig alteratig reactats depositio of Si2. I.. I

4 Variatio of Permeace with Depositio 'E.cI 3 cd. c E?J * \ a, S cd E z, W I I I I I I I % Weight Gai Figure 2. Permeace of several gases at 5 C versus weight gai durig alteratig reactats depositio of Si2.

5 Self Diffusivity Results from MD Simulatio 1 o6 17 I I I I I 1 I 1 I t(8 kt/g2m) 2. Pore radius =24 A, Cluster desity =.1 Pore radius =I5 A, Cluster desity =.2 Figure 3. Molecular dyamics simulatio of Ar diffusio i a cylidrical capillary i the limit of low gas desity. The capillary wall is modeled as a smooth EverettPohl potetial plus a layer of discrete atoms.

Microscopic Theory of Transport (Fall 2003) Lecture 6 (9/19/03) Static and Short Time Properties of Time Correlation Functions

Microscopic Theory of Transport (Fall 2003) Lecture 6 (9/19/03) Static and Short Time Properties of Time Correlation Functions .03 Microscopic Theory of Trasport (Fall 003) Lecture 6 (9/9/03) Static ad Short Time Properties of Time Correlatio Fuctios Refereces -- Boo ad Yip, Chap There are a umber of properties of time correlatio