- Email: [email protected]
CO2 scrubber design for self-contained breathing system
News and Views The optional f o u r t h d a y will cover electrodialysls, including ion-exchange membranes, equipment design, a p p l i c a t i o n s , a n d other u s e s for ion-exchange m e m b r a n e s s u c h a s a c i d a n d b a s e dialysis. The c o u r s e is i n t e n d e d for i n d u s t r i a l p r o c e s s e n g i n e e r s a n d c h e m i s t s , a s well as m a n a g e r i a l , m a r k e t i n g , a n d a c a d e m i c p e r s o n s i n t e r e s t e d in understanding modern separation techniques and their applications. Further Informatlon from: The Center f o r Professional Advancement, Oudezijds Voorburgwal 316A, 1012 GMAmsterdam, The Netherlands. Tel: +31 20 638 26 06. Fax: +31 20 620 21 36.
SuporFlow cartrldge.filters Further Information from: Gelman Sciences, 600 South Wagner Road, A n n Arbor, MI 48106, USA. Tel: +1 313 665 0651.
Membrane separations technology course A c o u r s e w h i c h p r o v i d e s a n i n t r o d u c t i o n to the t e c h n o l o g y of m e m b r a n e s e p a r a t i o n p r o c e s s e s will be held from 7 - 1 0 March 1994, in A m s t e r d a m , The Netherlands. The o p t i o n a l first d a y will cover microffltration, f e a t u r i n g d i s c u s s i o n s of m e m b r a n e types, p r e p a r a t i o n a n d p e r f o r m a n c e , m a x i m i z i n g m e m b r a n e life, p r o c e s s hardware and modules, and industrial applications. The s e c o n d d a y will look at ultraflltration, including membrane types and preparation, m e m b r a n e performance, concentration polarization a n d the gel model, effect of o p e r a t i n g p a r a m e t e r s on p e r f o r m a n c e , theoretical a n d e x p e r i m e n t a l evaluation, equipment design and applications. Reverse o s m o s i s will be covered in the t h i r d day. The t h e o r y will be d i s c u s s e d , along with m e m b r a n e types a n d p r e p a r a t i o n , p e r f o r m a n c e , e q u i p m e n t design and applications. Gas separations and p e r v a p o r a t i o n will also be considered.
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CO2 sc bber design for self-contained breathing s y s t e m R e s e a r c h e r s in S i n g a p o r e have i n v e s t i g a t e d the effectiveness of c a r b o n dioxide removal b y several hollow fibre m e m b r a n e m o d u l e s to optimize the design of self-contained b r e a t h i n g a p p a r a t u s (J. Membrane Sci., 86, p p 119-125, 1994). C a r b o n dioxide is a w a s t e p r o d u c t of n o r m a l physiological activities; its rate of p r o d u c t i o n d e p e n d e n t on the p a r t i c u l a r activity. For divers u s i n g b r e a t h i n g a p p a r a t u s , the c o n c e n t r a t i o n of CO2 m u s t be k e p t below a c e r t a i n level, so it n e e d s to be removed to stop it from b u i l d i n g u p to toxic levels. Currently, CO2 removal from m o s t closed or s e m i - c l o s e d circuit b r e a t h i n g a p p a r a t u s is carried out b y a c a n i s t e r c o n t a i n i n g a b s o r b e n t chemicals. The d i s a d v a n t a g e s of these s y s t e m s is t h a t they w a r m the air d u e to e x o t h e r m i c chemical reactions, a n d d u s t i n h a l a t i o n is m o r e p r o b a b l e . Some c a n i s t e r s have overcome these deficiencies, b u t u s i n g selective polymeric m e m b r a n e s as a n a l t e r n a t i v e h a s b e e n proposed. In t h e s e s t u d i e s , the hollow fibre m e m b r a n e module contained a microporous hydrophobic m e m b r a n e which offered no selectivity t o w a r d s gas c o m p o n e n t s in the m i x t u r e employed, b u t provided the m o d u l e with a large s u r f a c e a r e a per u n i t volume. The gas mixture, c o n t a i n i n g 4% c a r b o n dioxide, 17% oxygen a n d m o s t l y nitrogen, w a s i n t r o d u c e d into the hollow fibre l u m e n . The w a t e r u s e d a s an a b s o r b i n g m e d i u m w a s fed into the shell side. The solubility of c a r b o n dioxide in water is m u c h higher t h a n t h a t of oxygen a n d nitrogen, so the CO2 in the gas m i x t u r e m a y be preferentially removed.
M e m b r a n e T e c h n o l o g y No. 4 4
News and Views
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Figure 1: Experimental apparatus.
Polypropylene w a s u s e d for the e x p e r i m e n t s . Overall m a s s t r a n s f e r coefficients of C O 2 w e r e o b t a i n e d in t h e g a s p h a s e . A s t u d y of m a s s t r a n s f e r of CO2 s h o w e d t h a t t h e t r a n s f e r p r o c e s s is controlled solely by t h e r e s i s t a n c e in the liquid film a d j a c e n t to the m e m b r a n e p h a s e . A m e t h o d t h a t facilitates the d e s i g n of m e m b r a n e m o d u l e s for g a s a b s o r p t i o n b y providing quick e s t i m a t e s of m e m b r a n e a r e a r e q u i r e m e n t s at different r a t i o s of gas a n d liquid flows was presented.
Further information.from: W.K. Teo, Department of Chemical Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 0511, Singapore.
Helium separation using phosphazene polymers The p e r f o r m a n c e of p h o s p h a z e n e p o l y m e r s in the s e p a r a t i o n of h e l i u m from m e t h a n e h a s b e e n s t u d i e d at the I d a h o National E n g i n e e r i n g L a b o r a t o r y (INEL), a s p a r t of the I n o r g a n i c M e m b r a n e Technology R e s e a r c h P r o g r a m m e , s u p p o r t e d by the DOE's Office of I n d u s t r i a l Technology a n d the US B u r e a u of Mines. R e s u l t s from s t u d i e s on poly[bis(alkyl a n d a r y l ) p h o s p h a z e n e ] m e m b r a n e s are p r e s e n t e d in Journal of Membrane Science, 86, p p 5 7 - 6 5 , 1994.
Membrane Technology No. 44
Helium g a s c a n be recovered from n a t u r a l g a s s t r e a m s u s i n g polymeric m e m b r a n e s , a n d it is t h e n u s e d p r i m a r i l y for cryogenic a p p l i c a t i o n s , welding a n d in controUed a t m o s p h e r e s . The p r o b l e m so far h a s b e e n t h a t m a n y c o m m e r c i a l organic m e m b r a n e s y s t e m s h a v e d e g r a d e d in t h e a d v e r s e t h e r m a l a n d c h e m i c a l e n v i r o n m e n t s f r e q u e n t l y f o u n d in n a t u r a l gas wells. The p u r p o s e of the INEL p r o g r a m m e is to t e s t a variety of i n o r g a n i c p o l y m e r - b a s e d s e p a r a t i o n m e m b r a n e s s u i t a b l e for n a t u r a l g a s s t e a m conditioning. In initial s t u d i e s , p e r m e a t i o n r a t e s of h e l i u m in the p h o s p h a z e n e m a t e r i a l s were f o u n d to be sufficiently h i g h e r t h a n m e t h a n e to allow t h e s e p a r a t i o n . P h o s p h a z e n e p o l y m e r s c a n b e modified with a variety of side groups, a n d a v a r i e t y of s t r u c t u r e s provide a v a r i e t y of chemical, t h e r m a l a n d m e c h a n i c a l properties. S e p a r a t i o n p e r f o r m a n c e of the c h o s e n m e m b r a n e s w a s m e a s u r e d at 30--126"C. Two feed gas m i x t u r e s h a v i n g initial h e l i u m c o n c e n t r a t i o n s of 2 a n d 34% were u s e d . S e p a r a t i o n f a c t o r s a n d fluxes were d e t e r m i n e d . It w a s found t h a t t r a n s p o r t of the g a s e s t h r o u g h the m e m b r a n e w a s a p e r m e a b i l i t y - s i z e controlled process. It w a s c o n c l u d e d t h a t t h e s e m e m b r a n e s were s u i t a b l e for the s e p a r a t i o n of h e l i u m from m e t h a n e . They e x h i b i t e d favourable c h e m i c a l a n d p h y s i c a l c h a r a c t e r i s t i c s for a p p l i c a t i o n s over 100°C. The m e c h a n i s m w a s diffusion-limited, r e l a t e d to the m o l e c u l a r size.
Further information from: E.S. Peterson, Idaho National Engineering Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-2208, USA.
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SuporFlow cartrldge.filters Further Information from: Gelman Sciences, 600 South Wagner Road, A n n Arbor, MI 48106, USA. Tel: +1 313 665 0651.
Membrane separations technology course A c o u r s e w h i c h p r o v i d e s a n i n t r o d u c t i o n to the t e c h n o l o g y of m e m b r a n e s e p a r a t i o n p r o c e s s e s will be held from 7 - 1 0 March 1994, in A m s t e r d a m , The Netherlands. The o p t i o n a l first d a y will cover microffltration, f e a t u r i n g d i s c u s s i o n s of m e m b r a n e types, p r e p a r a t i o n a n d p e r f o r m a n c e , m a x i m i z i n g m e m b r a n e life, p r o c e s s hardware and modules, and industrial applications. The s e c o n d d a y will look at ultraflltration, including membrane types and preparation, m e m b r a n e performance, concentration polarization a n d the gel model, effect of o p e r a t i n g p a r a m e t e r s on p e r f o r m a n c e , theoretical a n d e x p e r i m e n t a l evaluation, equipment design and applications. Reverse o s m o s i s will be covered in the t h i r d day. The t h e o r y will be d i s c u s s e d , along with m e m b r a n e types a n d p r e p a r a t i o n , p e r f o r m a n c e , e q u i p m e n t design and applications. Gas separations and p e r v a p o r a t i o n will also be considered.
6
CO2 sc bber design for self-contained breathing s y s t e m R e s e a r c h e r s in S i n g a p o r e have i n v e s t i g a t e d the effectiveness of c a r b o n dioxide removal b y several hollow fibre m e m b r a n e m o d u l e s to optimize the design of self-contained b r e a t h i n g a p p a r a t u s (J. Membrane Sci., 86, p p 119-125, 1994). C a r b o n dioxide is a w a s t e p r o d u c t of n o r m a l physiological activities; its rate of p r o d u c t i o n d e p e n d e n t on the p a r t i c u l a r activity. For divers u s i n g b r e a t h i n g a p p a r a t u s , the c o n c e n t r a t i o n of CO2 m u s t be k e p t below a c e r t a i n level, so it n e e d s to be removed to stop it from b u i l d i n g u p to toxic levels. Currently, CO2 removal from m o s t closed or s e m i - c l o s e d circuit b r e a t h i n g a p p a r a t u s is carried out b y a c a n i s t e r c o n t a i n i n g a b s o r b e n t chemicals. The d i s a d v a n t a g e s of these s y s t e m s is t h a t they w a r m the air d u e to e x o t h e r m i c chemical reactions, a n d d u s t i n h a l a t i o n is m o r e p r o b a b l e . Some c a n i s t e r s have overcome these deficiencies, b u t u s i n g selective polymeric m e m b r a n e s as a n a l t e r n a t i v e h a s b e e n proposed. In t h e s e s t u d i e s , the hollow fibre m e m b r a n e module contained a microporous hydrophobic m e m b r a n e which offered no selectivity t o w a r d s gas c o m p o n e n t s in the m i x t u r e employed, b u t provided the m o d u l e with a large s u r f a c e a r e a per u n i t volume. The gas mixture, c o n t a i n i n g 4% c a r b o n dioxide, 17% oxygen a n d m o s t l y nitrogen, w a s i n t r o d u c e d into the hollow fibre l u m e n . The w a t e r u s e d a s an a b s o r b i n g m e d i u m w a s fed into the shell side. The solubility of c a r b o n dioxide in water is m u c h higher t h a n t h a t of oxygen a n d nitrogen, so the CO2 in the gas m i x t u r e m a y be preferentially removed.
M e m b r a n e T e c h n o l o g y No. 4 4
News and Views
Pr _,t,s__¢,_,reg a u g e
!
L
i
[
~ Rotm~er
I
I
zl
I
Todrain
Figure 1: Experimental apparatus.
Polypropylene w a s u s e d for the e x p e r i m e n t s . Overall m a s s t r a n s f e r coefficients of C O 2 w e r e o b t a i n e d in t h e g a s p h a s e . A s t u d y of m a s s t r a n s f e r of CO2 s h o w e d t h a t t h e t r a n s f e r p r o c e s s is controlled solely by t h e r e s i s t a n c e in the liquid film a d j a c e n t to the m e m b r a n e p h a s e . A m e t h o d t h a t facilitates the d e s i g n of m e m b r a n e m o d u l e s for g a s a b s o r p t i o n b y providing quick e s t i m a t e s of m e m b r a n e a r e a r e q u i r e m e n t s at different r a t i o s of gas a n d liquid flows was presented.
Further information.from: W.K. Teo, Department of Chemical Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 0511, Singapore.
Helium separation using phosphazene polymers The p e r f o r m a n c e of p h o s p h a z e n e p o l y m e r s in the s e p a r a t i o n of h e l i u m from m e t h a n e h a s b e e n s t u d i e d at the I d a h o National E n g i n e e r i n g L a b o r a t o r y (INEL), a s p a r t of the I n o r g a n i c M e m b r a n e Technology R e s e a r c h P r o g r a m m e , s u p p o r t e d by the DOE's Office of I n d u s t r i a l Technology a n d the US B u r e a u of Mines. R e s u l t s from s t u d i e s on poly[bis(alkyl a n d a r y l ) p h o s p h a z e n e ] m e m b r a n e s are p r e s e n t e d in Journal of Membrane Science, 86, p p 5 7 - 6 5 , 1994.
Membrane Technology No. 44
Helium g a s c a n be recovered from n a t u r a l g a s s t r e a m s u s i n g polymeric m e m b r a n e s , a n d it is t h e n u s e d p r i m a r i l y for cryogenic a p p l i c a t i o n s , welding a n d in controUed a t m o s p h e r e s . The p r o b l e m so far h a s b e e n t h a t m a n y c o m m e r c i a l organic m e m b r a n e s y s t e m s h a v e d e g r a d e d in t h e a d v e r s e t h e r m a l a n d c h e m i c a l e n v i r o n m e n t s f r e q u e n t l y f o u n d in n a t u r a l gas wells. The p u r p o s e of the INEL p r o g r a m m e is to t e s t a variety of i n o r g a n i c p o l y m e r - b a s e d s e p a r a t i o n m e m b r a n e s s u i t a b l e for n a t u r a l g a s s t e a m conditioning. In initial s t u d i e s , p e r m e a t i o n r a t e s of h e l i u m in the p h o s p h a z e n e m a t e r i a l s were f o u n d to be sufficiently h i g h e r t h a n m e t h a n e to allow t h e s e p a r a t i o n . P h o s p h a z e n e p o l y m e r s c a n b e modified with a variety of side groups, a n d a v a r i e t y of s t r u c t u r e s provide a v a r i e t y of chemical, t h e r m a l a n d m e c h a n i c a l properties. S e p a r a t i o n p e r f o r m a n c e of the c h o s e n m e m b r a n e s w a s m e a s u r e d at 30--126"C. Two feed gas m i x t u r e s h a v i n g initial h e l i u m c o n c e n t r a t i o n s of 2 a n d 34% were u s e d . S e p a r a t i o n f a c t o r s a n d fluxes were d e t e r m i n e d . It w a s found t h a t t r a n s p o r t of the g a s e s t h r o u g h the m e m b r a n e w a s a p e r m e a b i l i t y - s i z e controlled process. It w a s c o n c l u d e d t h a t t h e s e m e m b r a n e s were s u i t a b l e for the s e p a r a t i o n of h e l i u m from m e t h a n e . They e x h i b i t e d favourable c h e m i c a l a n d p h y s i c a l c h a r a c t e r i s t i c s for a p p l i c a t i o n s over 100°C. The m e c h a n i s m w a s diffusion-limited, r e l a t e d to the m o l e c u l a r size.
Further information from: E.S. Peterson, Idaho National Engineering Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-2208, USA.
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