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Effect of Impurities on Cellulose Acetate Membrane Performance

IP.com Disclosure Number: IPCOM000218865D
Publication Date: 2012-Jun-07

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Page 01 of 18

RECEIVED

MAR 2, ] 1986


C. A. DURR

EFFECT OF IlePlJRITITES ON CELLULOSE ACETATE I, IENBRANE PERFORNANCE

E.W. Funk, S.S. Kulkarnl, A.X. Swamikannu

SIGNAL RESEARCH CENTER INC.

50 East Algonquin Road, Box 5016

Des Plaines, Illinois 60017-6016


C. A. Durr

M. W. KELLOGG COMPANY

Three Greenway Plaza East Houston, Texas 77046

To be presented at the National Meeting of American Institute of Chemical Engineers

New Orleans, Louisiana

April 7-9, 1986


Page 02 of 18

INTROOtI~TIOM

The Slgnal Research Center is making cellulose acetate (CA) membrane spiral modules for acid gas separations. Potential applications (1,2) Include CO recycle for enhanced oil recovery, natural gas sweetening, and upgrading oI land-fill gas. The CA membranes3 have attractive performanceZcharacteristics:

CO2 permeability of ~ 7 x 10- (cm (STP)/cm .S.cmHg), [1 SCF/ft .D.psi(CO )] and CO2/CH4 selectivities of ~ 25 at 24°C.

2

Impurities present in industrial gas streams could have significant effects on the physical and chemical characteristics of membranes, Harmful effects can be avoided by specifying pre-treatment or operating conditions. (3,4) An assess- ment of the effect of various impurities is important for designing a satisfac- tory, cost-effective pre-treatment or operating procedure. This paper discusses a laboratory study of the effect of impurities such as H25, H20, and polar as well as non-polar hydrocarbons on CA membranes. CA membra6es as well as polymer resins were exposed to accelerated testing conditions. Membrane performance was examined and correlated with chemical, spectrophotometric, and microscopy studies.

It is well known in the literature (5,6) that penetrants that have strong affin- ity for the membrane are able to affect the permeation and sorption character- istics of other components in a gas mixture. As distinguished from this effect, the focus of the present paper is on whether there are any irreversible chemical or physical changes in the membrane structure as a result of exposure.

While the major focus of the paper is on the detailed chemical effect of gas impurities, we also include some major process considerations and approaches for pretreatment of the feed gas.

EFFECT OF

Experience with reverse osmosis has shown that acid hydrolysis can lead to decrease in salt rejection (7,8). Catastrophic failure can occur with cleaving of the ether link between the anhydroglucose units.


Page 03 of 18

Figure 1

  Chemical Structure of Cellulose ~cetate vith Prtmary (CG) and Secondary (C2, C3) ~cetyl Groups

It is thus important to study the effect of H2S both with and without the presence of moisture on the chemical nature of the-membrane.

Membranes exposed to 10 psi H2S for 14 days showed no evidence of deterioration (See Figure 2). Comparison of the CO?/CHaselectlvltles before and after the run showed no slgnificant difference, t-hough the permeabilities for C02 and CH4 were both 50% lower. Desorptlon of H2S under vacuum for 10 days res{ored the origin...