Deuterium Isotope Separation via Vibrationally Enhanced Deuterium

10 Deuterium Isotope Separation via Vibrationally Enhanced Deuterium Halide—Olefin Addition Reactions J. B . M A R L I N G and J. R. S I M P S O N

Downloaded by UNIV OF SYDNEY on February 28, 2018 | https://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0068.ch010

University of California, Lawrence Livermore Laboratory, Livermore, C A M. M . M I L L E R Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, M A

Over t h e past few y e a r s , t h e r e has been much excitement i n the s c i e n t i f i c community about the prospects f o r e f f i c i e n t sep a r a t i o n o f i s o t o p e s , p a r t i c u l a r l y uranium-235 and deuterium, using l a s e r techniques. Of t h e v a r i o u s l a s e r methods which have been suggested, those which i n v o l v e t h e use o f IR photons t o enhance t h e r a t e o f i s o t o p i c a l l y s e l e c t i v e photochemical r e a c t i o n s have r e c e i v e d much a t t e n t i o n , and t h i s paper d i s c u s s e s one e x a m p l e — v i b r a t i o n a l l y enhanced gas phase deuterium h a l i d e a d d i t i o n i n t o o l e f i n s . The i n c e n t i v e f o r u s i n g IR photons i s c l e a r ; t o quote from a recent review a r t i c l e (l_) : "The a t t r a c t i v e f e a t u r e o f v i b r a t i o n a l photochemistry f o r i s o t o p e s e p a r a t i o n i s the promise o f u s i n g low energy IR photons from an e f f i c i e n t molecular l a s e r t o get a good y i e l d o f product. Since 1 mole of photons at 3000 cm" i s 1 0 kwh and some IR l a s e r s are about 10 per cent e f f i c i e n t , p r o c e s s i n g o f b u l k chemicals might even be economic." Thus, a deuterium s e p a r a t i o n process w i t h 1% quantum e f f i c i e n c y t h a t u t i l i z e d 2000 cm" photons from a 10 per cent e f f i c i e n t CO l a s e r would r e q u i r e a l a s e r process energy o f 6 . 6 kwh/mole D, e q u i v a l e n t t o a l a s e r o p e r a t i n g cost o f 13^/mole D Ξ $13/kg D 0, assuming e l e c t r i c i t y at 20 m i l l s per kwh. The s p e c i f i c l a s e r c a p i t a l investment, assuming a p r i c e o f $20 per o p t i c a l watt o f 10 per cent e f f i c i e n t l a s e r power, would be roughly $152/kg D 0/yr., e q u i v a l e n t t o approximately $30/kg D 0 at a c a p i t a l charge r a t e o f 20 per cent/year. To put these numbers i n p e r s p e c t i v e , we note t h a t t h e current Canadian p r i c e f o r heavy water made by the H S/H 0 exchange (G-S) process i s about $150/kilogram, o f which 60 per cent i s due t o c a p i t a l charges, 25 per cent due t o energy, and 15 per cent f o r operations and maintenance (2). Since heavy water i s a much cheaper commod i t y than U-235, t h i s approximate c a l c u l a t i o n i l l u s t r a t e s t h e challenge i n developing a l a s e r deuterium s e p a r a t i o n process which i s economically c o m p e t i t i v e w i t h the e x i s t i n g technology ( 3_). In t h i s paper we i l l u s t r a t e t h e problems and prospects i n v o l v e d by examining i n some d e t a i l a s p e c i f i c deuterium separation process based on deuterium h a l i d e - o l e f i n a d d i t i o n 1

- 2

1

2

2

2

2

©

2

0-8412-0420-9/78/47-068-134$05.00/0

Rae; Separation of Hydrogen Isotopes ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

10.

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r e a c t i o n s . I n S e c t i o n I I we describe t h e b a s i c r e a c t i o n mechan ism, w i t h p a r t i c u l a r a t t e n t i o n t o the problem o f e x c i t i n g t h e deuterium h a l i d e w i t h e x i s t i n g l a s e r s . S e c t i o n I I I i s devoted t o t h e c r u c i a l question o f the expected e f f e c t i v e n e s s o f v i b r a t i o n a l e x c i t a t i o n f o r t h i s c l a s s o f r e a c t i o n s . I n S e c t i o n IV, we focus on t h e "back-end" o f t h i s separation scheme i n the context of a p o s s i b l e flow-sheet f o r t h e o v e r a l l process. We conclude w i t h a summary o f our r e s u l t s and the i m p l i c a t i o n s t h e r e o f i n S e c t i o n V.


II.

Hydrogen H a l i d e - O l e f i n A d d i t i o n Reactions

An i d e a l i s o t o p i c a l l y s e l e c t i v e l a s e r photochemical process would use a s i n g l e IR photon t o e x c i t e t h e fundamental mode o f the i s o t o p i c molecule o f i n t e r e s t , f o l l o w e d by a gas phase, v i b r a t i o n a l l y - e n h a n c e d b i m o l e c u l a r r e a c t i o n , l e a d i n g t o an i s o t o p i c a l l y enriched r e a c t i o n product which could e a s i l y be separated. A primary c o n s i d e r a t i o n i n t h e choice o f r e a c t i o n i s the a c t i v a t i o n energy. I t must be high enough t o minimize t h e (thermal) r e a c t i o n r a t e i n t h e absence o f v i b r a t i o n a l e x c i t a t i o n , but low enough so that t h e r e a c t i o n r a t e o f the v i b r a t i o n a l l y e x c i t e d species exceeds t h e r a t e o f scrambling r e a c t i o n s , e.g., V-V and V-T energy t r a n s f e r s , which l e a d t o the l o s s o f i s o t o p i c s e l e c t i v i t y . I n t h i s s e c t i o n we d i s c u s s a c l a s s o f r e a c t i o n s , deuterium h a l i d e - o l e f i n a d d i t i o n s , w i t h thermal e q u i l i b r i u m a c t i v a t i o n energies i n the range 15-^0 kcal/mole. The i n i t i a l step o f t h i s process i n v o l v e s s e q u e n t i a l absorp t i o n o f s e v e r a l quanta near 5 microns from a pulsed CO l a s e r t o e x c i t e DBr o r DC1 up t h e i r v i b r a t i o n a l ladders t o t h e ν >_ 3 v i b r a t i o n a l l e v e l . A l t e r n a t e l y , a pulsed DF l a s e r near h microns can s e q u e n t i a l l y e x c i t e DF or EDO t o ν > 3. I n pure DX, c o l l i sions o f the type DX(v = l ) + DX(v = l ) •> DX(v = 2) + DX(v = 0) can a l s o e x c i t e higher v i b r a t i o n a l l e v e l s , but t h i s mechanism i s not f e a s i b l e i n n a t u r a l HX c o n t a i n i n g only 0.015% DX. The v i b r a t i o n a l l y e x c i t e d DX molecule (X = B r , C l , F, OH) then w i l l p r e f e r e n t i a l l y r e a c t w i t h unsaturated hydrocarbons ( f o r example, DBr r e a c t i n g w i t h ethylene) t o y i e l d a deuterium-tagged a d d i t i o n product, e.g., e t h y l bromide-d}. These steps may be w r i t t e n DX + nhv + DX* (v=n) η >_ 3 (pulsed CO o r DF l a s e r e x c i t a t i o n ) DX* +

(R

(1)

(2)

l5

R

2

= H, CH , CH=CH , etc.) 3

2

This type o f a d d i t i o n r e a c t i o n i n t o unsaturated hydrocarbons i n t h e gas phase occurs by a homogeneous, b i m o l e c u l a r , f o u r - o r s i x - c e n t e r process (^,5.). Both the forward r e a c t i o n (2) and t h e


SEPARATION OF HYDROGEN ISOTOPES

136

reverse r e a c t i o n (unimolecular e l i m i n a t i o n o f HX) have been very w e l l s t u d i e d i n the gas p h a s e ( 6 l ) . K i n e t i c parameters f o r the gas phase thermal a d d i t i o n r e a c t i o n are w e l l represented by the Arrhenius r a t e e x p r e s s i o n , -E /RT k(sec ) = [C]-Ae (3) 9

a


where

[c] = o l e f i n c o n c e n t r a t i o n ( m o l e s / l i t e r ) A = frequency f a c t o r ( l i t e r / m o l e - s e c ) Ε = thermal a c t i v a t i o n energy (kcal/mole) a

A r r h e n i u s parameters f o r HX a d d i t i o n i n t o simple and con jugated o l e f i n s are given i n Table I , which i l l u s t r a t e s the v a r i a t i o n o f a c t i v a t i o n energy E and frequency f a c t o r A, according t o the choice o f reagents. Examination o f Table I r e v e a l s t h a t a c t i v a t i o n energies i n the range 10-50 kcal/mole are a v a i l a b l e , depending on the choice o f reagents. Lowest a c t i v a t i o n energies occur f o r HI a d d i t i o n w i t h i n c r e a s i n g a c t i v a t i o n energy f o r l i g h t e r HX, such t h a t E ( H l ) < E ( H B r ) < E (HCl) < E (HF) < E ( H 0 ) . Table I a l s o shows t h a t a c t i v a t i o n energy decreases w i t h i n c r e a s i n g s u b s t i t u t i o n , w i t h E decreasing by about 5 kcal/mole per methyl (-CH3) group and by about 9 kcal/mole per v i n y l (-CH=CH2) group on the a- or h a l o g e n - r e c e i v i n g carbon atom. Among olefins, 2-methylpropene and 1,3-butadiene have n e a r l y i d e n t i c a l a c t i v a t i o n e n e r g i e s , but 1,3-butadiene i s a f a r s u p e r i o r reagent choice because of i t s approximately 2 0 0 - f o l d higher frequency f a c t o r (A v a l u e ) . Although HI has the lowest a c t i v a t i o n energies f o r r e a c t i o n , i t i s probably not an acceptable choice i n a l a r g e s c a l e process because of i t s tendency t o decompose. HF and H 0 are probably r e l a t i v e l y u n a t t r a c t i v e , s i n c e they have s i g n i f i c a n t l y higher a c t i v a t i o n e n e r g i e s ; t h i s l e a v e s HBr or HC1 as the most l i k e l y reagent c h o i c e . A l s o , use of HF or H 0 would r e q u i r e e x c i t a t i o n by a DF chemical l a s e r , which i s an i n h e r e n t l y more expensive and l e s s e f f i c i e n t device than the CO l a s e r , p r i m a r i l y due t o the cost of r e g e n e r a t i n g the f l u o r i n e . The CO l a s e r i s an e f f i c i e n t , well-developed device ( l l ) which i s q u i t e s u i t a b l e f o r a l a r g e - s c a l e i n d u s t r i a l process. To evaluate the s u i t a b i l i t y o f the CO l a s e r f o r e x c i t a t i o n o f DBr or DC1, a computer comparison was made o f the c a l c u l a t e d wavelengths of CO emission l i n e s and DBr or DC1 a b s o r p t i o n l i n e s . For these diatomic molecules, accurate frequencies may be gener ated from a Dunham equation f o r the energy l e v e l s : a

a

a

a

a

a

2

a

2

2

kj j+i

*™ = Z\*K)\î


(u)

10.

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Deuterium

Isotope

137

Separation

TABLE I A r r h e n i u s Parameters Olefins: Frequency Factor

Unsaturated Hydrocarbon

LogipA


propylene^

3

t

2-methylpropene Phenyl e t h y l e n e

X = I , B r , C l , F, OH A c t i v a t i o n Energy Ε (kcal/mole) a HBr HCl HF HI H 0 tot7

2

8.3°

ethylene

f o r HX A d d i t i o n t o

28.5

ko

50

57

U5

52

7.9

C

23.5

28.5

3k

6.5

C

18.5

23.5

28

20

2k

30

13

1,3-butadiene 2-methyl-l,3butadiene 1 5 3-pentadiene

3k

18.7

1

Q.k

h

7-7

I5

s

1

26

g

20

1

25

s

2k 20

f

ih.T

h

2-methyl-l,3 . pentadiene

l.k*

11

16

21

H-methyl-1,3-. pentadiene

6.3

10

15

20

J

U n i t s o f A are l i t e r s - m o l e f o r a l l HX compounds. b

Ε

a

l e

38

29

1

e

kg

sec \

L o g A i s constant ± 0 . 3 10

values from Reference 6.

c Reference k. d Computed from A o f back r e a c t i o n .

See Reference 7 ·

Reference 8. Computed from k i n e t i c data o f Reference 5 . Computed from k i n e t i c s o f back r e a c t i o n .

See Reference 9 ·

Reference 1 0 . Estimated Ε

value.

Probable accuracy:

Estimated v a l u e f o r L o g ^ A .

± 2 kcal/mole.

Probable accuracy: ± O.k.



138


For normal and i s o t o p i c y i e l d computed emission (Ref. 12) or even a few measured values f o r the

carbon monoxide, the c o e f f i c i e n t s Y frequencies accurate t o 0.001 cm" megahertz (13). For D ^ ^ c i , d i r e c t l y Υ „ were a v a i l a b l e ( l U ) . For D^Tci the £k ntr — Y were computed from D ^ C l u s i n g the Dunham i s o t o p e r e l a t i o n s (15) and the a p p r o p r i a t e atomic reduced masses ( l 6 ) . For D^^Br and D^lBr the e a r l i e r r e p o r t e d a b s o r p t i o n f r e q u e n c i e s (IT) were not s u f f i c i e n t l y accurate. T h e r e f o r e , accurate Y were generated f o r HBr u s i n g the accurate r o t a t i o n a l constants (l8) and recent higher l e v e l v i b r a t i o n a l constants (19.). The a p p r o p r i a t e reduced masses (l6) and Dunham i s o t o p e relation§^(15) then were used t o d e r i v e a l l Y except Y ^ f o r D Br and D Br. Y-|_Q was then f i x e d by r e q u i r i n g the computed 1-0 band t o be 0.25 cm" higher than i t s measured value (17) > according t o the c o r r e c t i o n suggested i n Ref. 20. The d e r i v e d Dunham c o e f f i c i e n t s f o r DC1 and DBr thus p r o v i d e d c a l c u l a t e d a b s o r p t i o n l i n e center frequencies f o r a computer search t o f i n d near-coincidences w i t h CO l a s e r emission f r e q u e n c i e s . For each near c o i n c i d e n c e , the a b s o r p t i o n co e f f i c i e n t was computed u s i n g a standard Lorentz l i n e shape f o r mula, equation (5)> which a l s o i n c l u d e d the temperature depen dence o f the r o t a t i o n a l l e v e l p o p u l a t i o n : -3m(m+l)/kT 1

Λ

1

α ( Δ ν )

= lV

(Λν/0. Ρ) 5Ύ

( 5 ) 2

In equation ( 5 ) , α(Δν) i s the a b s o r p t i o n ( i n cm" ) at a d i s t a n c e Av(cm~l) from DX l i n e center at a pressure o f Ρ atmospheres. The values f o r the pressure-broadened l i n e w i d t h γ(cm atm" ) depend on r o t a t i o n a l number m, and were taken from Ref. 21_ f o r DC1 broadening by HC1. The r o t a t i o n a l number i s m = J - l f o r R-branch and m = J f o r P-branch t r a n s i t i o n s . DBr values f o r γ were d e r i v e d from the r e p o r t e d values f o r HBr(22). The parameters Κ and 3 i n equation (5) were a d j u s t e d t o match the r e p o r t e d DC1 a b s o r p t i o n l i n e s t r e n g t h s ( 2 3 ) , and DBr values f o r Κ and 3 were d e r i v e d from the HBr values (22) by assuming K(DBr) = l/k K(HBr) and 3(DBr) Ξ 2 3(HBr), assumptions found t o be reasonable f o r the DC1/HC1 data (23). Equation (5) thus permits reasonably accurate e s t i m a t i o n of a b s o r p t i o n i n the 1-0 band o f DC1 and DBr by CO l a s e r l i n e s . A b s o r p t i o n s t r e n g t h of the higher v i b r a t i o n a l bands (2-1 through 5-U i n t h i s study) w i l l i n c r e a s e approximately p r o p o r t i o n a l t o ν (Réf. 2*0, but decrease due t o the d i s t r i b u t i o n o f p o p u l a t i o n over the s e v e r a l l e v e l s . As a f i r s t approximation, a b s o r p t i o n s t r e n g t h f o r higher v i b r a t i o n a l bands was thus taken t o be the same as the 1-0 band. Tables I I and I I I summarize the computed a b s o r p t i o n o f -^C-Ô l a s e r emission l i n e s by the v a r i o u s i s o t o p e s of DC1 and DBr. Data f o r Tables I I and I I I were computed f o r atmospheric pressure and room temperature (298°K), and i l l u s t r a t e the ease 1

-1


1

10.

MARLING ET AL.

Deuterium

Isotope

139

Separation

TABLE I I ABSORPTION OF

C O

DC1 T r a n s i t i o n * · ν ( cm" )


1

1-0 1-0 1-0 1-0 2-1 2-1 2-1 2-1 3-2 3-2 3-2 3-2 U-3 h-3 h-3 h-3 5-U

P(T) P(3)37 P(T)37 P(U) P(2) p(n) P(U) 3 5

3 5

3 5

3 5

3 7

2011.Ohl 2055-1^6 2008.282 20U6.609 2016.033 1909.678 1991.iih

R(3) 2077.3k0 P(2) 1963.IUO P(ll) 1858.853 P(6) 1918.799 P(2) 1960.51^ P ( 5 ) 5 1878.238 R(5) 1986.873 P(2) 1910.507 P(3) 1897.518 P ( 7 ) 5 I80U.358 p(i) 1868.160 3 5

3 5

3 5

3 5

3 7

3

3 5

3 5

3 7

3

5-U 5-U R ( 2 )

3 5

3 7

1903.939

LASER LINES BY D ^ C l and D^'Cl, a t P=l ATM.

1 2

l 6

c o LASER LINE 5-h P ( 7 ) 3-2 P ( 9 ) 3-2 P ( 2 0 ) 3-2 P ( l l ) 2 - 1 F(2k) 6-5 P ( 2 5 ) 5-U P ( 1 2 ) 2 - 1 P(10) 7-6 P ( 6 ) 1 0 - 9 P(13) 7-6 P ( 1 7 ) h-3 P ( 2 5 ) 10-9 P(8) 5-U P ( 1 3 ) 7-6 P ( 1 9 ) 7-6 P ( 2 2 ) 12-11 P(lU) 9-8 P ( 1 7 ) 9-8 P(8)

v

Vi- co

( c n r l )

ABSORPTION COEF. (cm" )

-0.0i+9 -0.012 -O.I38 -0.3^9 0.007 -0.001 0.090 0.201 0.058 -O.Okh -0.179 0.103 -O.OI7 -0.037 -0.02U -0.101 0.026 0.03U 0.058

* S u b s c r i p t 35 o r 37 r e f e r s t o D ^ C l o r D respectively.

1

11.8 l.U 1.1 12.6 5.1 3.0 2.9 8.7 3.6

3Λ 1.7 18.5 15.2 11.8 2.3 Ik.k 6.0 3.7

Cltransitions,



140

TABLE I I I ABSORPTION OF

1 2

C

l 6

0 LASER LINES BY D


TRANSITION*

v ( cm*" ) 1

B r and D

C C 0 LASER LINE 1 2

DBr

T 9

8 l

B r a t P=l ATM.

1 6

v

v

DBr- C0

( c m

"

1 )

ABSORPTION (cm" ) 1

1-0

R ( 2 ) 81

1863.999

9-8

P(l8)

0.011

3.2

1-0

R(3) 79

18T2.3T8

8-7

P(22)

0.0U8

2.5

1-0

P(9) 79

1757.851

lU-13 P(13)

1-0

P(3) 81

1813.573

11-10

2-1

R ( 6 ] 81

I8U7.I63

9-8

2-1

P(8] 81

1722.606

2-1

R ( 9 ! 79

1867.966

8-7

2-1

P ( 9 ! 79

1713.U97

15-lh

3-2

P(6) 81

1696.517

3-2

R ( 2 ; 81

3-2

P(l8)

2.1 0.057

1.9

P(22)

0.0U6

3.0

16-15 P(9)

0.003

3.8

-0.032

2.0

P(l8)

-0.0U6

2.0

16-15

P(l6)

0.008

h.3

1771.3h3

13-12

P(l6)

0.017

3.1

P ( 9 l 79

1669.172

18-17

P(10)

0.07^

1.3

h-3

p(u; 81

1669.H5

18-17

P(10)

0.017

3.7

h-3

R(3

79

1732.808

15-lU P(13)

0.0U3

2.7

5-U

P(T ) g

1598.386

21-20 P ( 9 )

0.016

u.o

5-U

P(T '81

1597.983

20-19

P(l6)

0.0^9

2.9

Br o r D

Br t r a n s i t i o n s ,

7

* S u b s c r i p t 79 o r 8 l r e f e r s t o D

P(23)

respectively.


10.

MARLING ET AL.

Deuterium

Isotope

141

Separation

i n a c h i e v i n g s e q u e n t i a l a b s o r p t i o n o f CO l a s e r quanta t o e x c i t e DC1 o r DBr up t h e i r v i b r a t i o n a l l a d d e r s t o ν - 5· Examination o f Table I I i n d i c a t e s t h a t the best matches o f 12^1 ο l a s e r emission w i t h D^^ci y i e l d a b s o r p t i o n c o e f f i c i e n t s of about 12 cm" a t 1 atmosphere. S i m i l a r l y , the best CO laser-DBr a b s o r p t i o n c o e f f i c i e n t s are about 3 cm" . At higher p r e s s u r e s , r a d i a t i o n from CO l a s e r l i n e s i s e a s i l y absorbed w i t h out need f o r CO l a s e r l i n e s e l e c t i o n . For example, a t 5 atmo spheres pressure any CO l a s e r l i n e i n the U.9—5·1 micron r e g i o n i s c a l c u l a t e d t o experience an average DC1 a b s o r p t i o n c o e f f i c i e n t of 2 cm" f o r the 1-0 band, which i n c r e a s e s t o about 10 cm" when a b s o r p t i o n from DC1 v i b r a t i o n a l l y e x c i t e d s t a t e s i s i n c l u d ed. Only the "best" matches were given i n Tables I I and I I I f o r each l e v e l o f v i b r a t i o n a l e x c i t a t i o n . Table I I shows t h a t most DC1 a b s o r p t i o n o f C " 0 l a s e r emission w i l l occur i n the U . 9 micron r e g i o n , and u s e f u l DBr a b s o r p t i o n w i l l occur i n the 5.^-6.2 micron r e g i o n . At n a t u r a l deuterium abundance, t h e 1/e a b s o r p t i o n depth would be about 5 meters f o r DC1 and 20 meters f o r DBr. Since a t y p i c a l r e a c t i o n mixture would a l s o c o n t a i n an o l e f i n a t near-atmospheric p r e s s u r e , i t would be important t o i n s u r e t h a t the o l e f i n i s s u f f i c i e n t l y t r a n s p a r e n t a t these wavelengths (a < 0.1 m e t e r " ) . This i s e s s e n t i a l t o a l l o w the CO l a s e r emission t o e x c i t e p r i m a r i l y DBr o r DC1, and not waste photons by o p t i c a l l y h e a t i n g the o l e f i n . Examination o f simple and conjugated o l e f i n a b s o r p t i o n bands (25) i n the 5-6 micron r e g i o n r e v e a l s q u i t e strong C = C s t r e t c h a b s o r p t i o n a t 6.0-6.2 micron. P o t e n t i a l l y troublesome combination band a b s o r p t i o n occurs a t 5·1*Μ and e s p e c i a l l y a t 5 · 6 μ i n 1,3-butadiene and i s o prene, probably the best reagent choices from Table I . Gas phase a b s o r p t i o n s p e c t r a were examined and showed an a b s o r p t i o n c o e f f i c i e n t ( t o base e) o f about 0 . 5 cm" A t m f o r both 1,3-butadiene and isoprene near 5 · 6 micron. This i s about 2-3 orders o f magnitude stronger than n a t u r a l l y o c c u r r i n g DBr a b s o r p t i o n , r e n d e r i n g photon e f f i c i e n t e x c i t a t i o n o f DBr i m p o s s i b l e . The s i t u a t i o n i s somewhat improved a t 5·1 micron, where the a b s o r p t i o n c o e f f i c i e n t s o f these two o l e f i n s are about 0.05 cm"" atm" , s t i l l about an order o f magnitude stronger than DC1 a b s o r p t i o n a t n a t u r a l abundance. T h i s suggests t h a t l i n e a r conjugated o l e f i n s w i l l be e x c e s s i v e l y absorbing, and prevent e f f i c i e n t CO-laser e x c i t a t i o n o f DC1 and e s p e c i a l l y DBr. Cyclopentadiene and 1 , 3 - c y c l o h e x a d i e n e should a l s o e x h i b i t low a c t i v a t i o n energies f o r hydrogen h a l i d e a d d i t i o n , s i m i l a r t o the l i n e a r conjugated o l e f i n s l i s t e d i n Table I , and o p t i c a l a b s o r p t i o n s p e c t r a are somewhat more promising. Cyclopentadiene (26) appears t r a n s p a r e n t i n the 5 . 0 - 5 . 3 μ r e g i o n , p o t e n t i a l l y s u i t able f o r use w i t h DC1, and 1 , 3 - c y c l o h e x a d i e n e (27) appears t r a n s p a r e n t i n the 5 · ^ - 5 · 7 5 y r e g i o n , making i t p o t e n t i a l l y s u i t a b l e f o r use w i t h DBr. E l i m i n a t i o n of o l e f i n absorption w i l l be e s s e n t i a l f o r e f f i c i e n t photon u t i l i z a t i o n a t low deuterium Ό

1

1


1

1

1 2

1

1

1

1

1


- 1


142

c o n c e n t r a t i o n s . Only ethylene (25) shows extreme t r a n s p a r e n c y , w i t h no d e t e c t a b l e a b s o r p t i o n from 1550 cm- t o 1750 cm"" , making i t o p t i c a l l y s u i t a b l e f o r use w i t h DBr. Non-reactive quenching o f v i b r a t i o n a l l y e x c i t e d deuterium h a l i d e w i l l be an important p r o c e s s , as i t competes w i t h r e a c t i v e a d d i t i o n o f t h e e x c i t e d s p e c i e s i n t o t h e o l e f i n . The r e a c t i o n e f f i c i e n c y φ w i l l be simply t h e r a t i o o f r e a c t i v e quenching t o t o t a l quenching, or 1

1

R [c] v


φ

=

( V Q ) [ c ] + Q [x] c

(6)

x

where [c] = Olefin concentration [x] = Hydrogen h a l i d e c o n c e n t r a t i o n R = Deuterium h a l i d e r e a c t i v i t y i n vibrational level ν Q = Quenching r a t e / u n i t c o n c e n t r a t i o n ° of olefin Q = Quenching r a t e / u n i t c o n c e n t r a t i o n of hydrogen h a l i d e In a d d i t i o n t o r e a c t i o n , t h e v i b r a t i o n a l l y e x c i t e d deuterium h a l i d e w i l l experience n o n - r e a c t i v e v i b r a t i o n a l quenching by both t h e o l e f i n and t h e hydrogen h a l i d e . Q denotes v i b r a t i o n a l quenching o f deuterium h a l i d e by hydrogen h a l i d e and has been measured f o r quenching o f t h e DX v = l l e v e l (28-31). For DBr, a value o f Q = 0.2 (μsec · atm)" was d e t e r mined (28) f o r quenching by HBr. For DC1 quenching by HC1, a value of Q = O.h {\isec · atm)"" may be i n f e r r e d (29). Nonr e a c t i v e v i b r a t i o n a l quenching by t h e o l e f i n may be 10-100 times f a s t e r than these r a t e s , based on t h e observed r a p i d quenching of HBr ( 3 0 ) , HC1 (31) and DC1 (31) by water and methane. Quenching r a t e s o f higher DX v i b r a t i o n a l l e v e l s w i l l be f a s t e r than f o r the v = l l e v e l , r i s i n g approximately p r o p o r t i o n a l t o ν (Ref. 2 9 ) . Thus, equation (6) reduces t o a simpler form when the o l e f i n c o n c e n t r a t i o n [θ] i s r a i s e d t o o p t i m i z e φ, x

1

x

1

x

φ ifc R /(R +Q ) i f [C] % [X] v

v

c

and Q » Q c χ

(7)

since v i b r a t i o n a l quenching by HX i s slow compared t o t h e expected o l e f i n quenching r a t e s . The upper l i m i t o f t h e DX r e a c t i o n r a t e w i t h a given o l e f i n i s simply the frequency A (Table I ) and i s expected t o be approached as t h e DX l a s e r s u p p l i e d v i b r a t i o n a l energy exceeds t h e r e a c t i o n - a c t i v a t i o n energy Ε . T h i s assumption was examined f o r other r e a c t i o n systems ( 3 2 ) , and i s d i s c u s s e d f u r t h e r i n S e c t i o n I I I . T h i s p l a c e s an upper l i m i t on t h e r e a c t i o n e f f i c i e n c y


10.

MARLING ET AL.

Deuterium

Isotope

143

Separation

(8)

max

when one assumes (32) t h a t A f o r a b i m o l e c u l a r r e a c t i o n i s i n d e pendent o f reagent v i b r a t i o n a l e x c i t a t i o n . The best value o f A from Table I occurs f o r 1 , 3 - b u t a d i e n e , A - 25 (μsec•atm) . I f o l e f i n n o n - r e a c t i v e v i b r a t i o n a l quenching i s comparable t o HX quenching r a t e s by methane ( 3 j 0 , 3 l ) , o r Q = 10-60 (μεβο •atm)*"" , then the maximum r e a c t i o n e f f i c i e n c y , from equation ( 8 ) , c o u l d l i e i n the range 0.1%-50%, w i t h the higher r e a c t i o n e f f i c i e n c i e s corresponding t o use o f o l e f i n s w i t h h i g h values o f A, such as 1,3-butadiene o r ethylene. The problem o f n o n - r e a c t i v e quenching o f v i b r a t i o n a l l y e x c i t e d DX by the o l e f i n i s r e l a t e d t o the problem o f e x c e s s i v e o p t i c a l a b s o r p t i o n by the o l e f i n , namely the presence o f o l e f i n energy resonances near DX a b s o r p t i o n f r e q u e n c i e s . DX v i b r a t i o n a l quenching by v-v energy t r a n s f e r processes becomes very r a p i d near energy resonance (30,33), but should drop t o acceptably low v a l u e s , i f the nearest resonances have an energy discrepancy o f more than about 1000 cm" . Lower n o n - r e a c t i v e quenching can be achieved by u s i n g f u l l y halogenated o l e f i n s (3*0, which may a l s o y i e l d h i g h o l e f i n transparency a t DX a b s o r p t i o n f r e q u e n c i e s . However, t y p i c a l f l u o r i n a t e d o l e f i n reagent c h o i c e s , such as h e x a f l u o r o - l , 3 - b u t a d i e n e (35.), hexafluoropropene (36), o r f l u o r i n a t e d ethylenes (36) have e x c e s s i v e o p t i c a l a b s o r p t i o n i n the 5-6 micron r e g i o n (35.,36) , and hence are not s u i t a b l e . But when i n the course o f t h i s work t e t r a c h l o r o e t h y l e n e o p t i c a l a b s o r p t i o n was examined i n the gas phase, i t was found t o be h i g h l y transparent i n the H.2-5-2 μ r e g i o n , and i s thus poten t i a l l y s u i t a b l e f o r use w i t h HC1. Experimental k i n e t i c data on a c t i v a t i o n energies are not r e p o r t e d , but c a l c u l a t e d values o f E f o r HF o r HC1 r e a c t i n g w i t h perhalogenated ethylene are 5 kcal/mole lower than w i t h normal ethylene (6). Some p e r f l u o r i n a t e d o l e f i n s are v e r y t o x i c ( 3T_), and p e r c h l o r i n a t e d o l e f i n s r e q u i r e o p e r a t i n g temperatures 100-200°C higher than normal o l e f i n s t o achieve u s e f u l vapor pressure. N e v e r t h e l e s s , t h e p o t e n t i a l f o r h i g h IR transparency and low v i b r a t i o n a l quenching makes t h i s c l a s s o f reagents (and t e t r a c h l o r o e t h y l e n e i n p a r t i c u l a r ) a t t r a c t i v e t o c o n s i d e r f o r a p r a c t i c a l process. There i s p r e s e n t l y very l i t t l e experimental data on l a s e r e x c i t e d HX a d d i t i o n i n t o o l e f i n s . However, r e a c t i o n was observed between 2-methylpropene and HCl(v=6) produced by i n t r a c a v i t y dye l a s e r e x c i t a t i o n o f the HC1 f i f t h overtone ( 3 8 ) . Quantum y i e l d s f o r r e a c t i o n were estimated (38.) t o l i e i n the range 0.01-0.1%, c o n s i s t e n t w i t h the very l o w frequency f a c t o r f o r t h i s o l e f i n (see Table I ) . Use o f 1,3-butadiene i n t h i s same experiement ( i n s t e a d o f 2-methylpropene) was not t r i e d , but should have y i e l d e d a r e a c t i o n quantum y i e l d o f 2-20%, based on i t s 2 0 0 - f o l d higher frequency f a c t o r . Economic a n a l y s i s o f l a s e r - r e l a t e d c o s t s i n heavy water p r o d u c t i o n by the D X - o l e f i n process l

1


c

1

a




144

d i s c u s s e d here i n d i c a t e t h a t r e a c t i o n e f f i c i e n c i e s must exceed 5% f o r t h i s process t o be economically v i a b l e (39)· Additional c o s t s due t o the "back-end" of t h i s process (see S e c t i o n IV) w i l l probably set a p r a c t i c a l lower l i m i t of 10% f o r an acceptable r e a c t i o n e f f i c i e n c y . In t h i s c o n t e x t , the c l a s s i c a l quantum e f f i c i e n c y i s the r e a c t i o n e f f i c i e n c y φ d i v i d e d by n, the average number of absorbed quanta per DX molecule. The assumption of η = 5 p l a c e s an approximate lower l i m i t of 2% on an economically acceptable quantum e f f i c i e n c y f o r deuterium h a l i d e a d d i t i o n i n t o o l e f i n s as a p o t e n t i a l photochemical route t o heavy water pro duction. In t h i s s e c t i o n we have shown t h a t the CO l a s e r permits s e q u e n t i a l e x c i t a t i o n of DBr or DC1 up the v i b r a t i o n a l ladder t o at l e a s t the ν = 5 v i b r a t i o n a l l e v e l . At n a t u r a l deuterium abundance, the l / e a b s o r p t i o n depth f o r s e l e c t e d CO l a s e r l i n e r a d i a t i o n i s about 5 meters f o r DC1 and about 20 meters f o r DBr, at a hydrogen h a l i d e o p e r a t i n g pressure of one atmosphere. At 5 atmospheres o p e r a t i n g p r e s s u r e , u n r e s t r i c t e d m u l t i l i n e opera t i o n of the CO l a s e r i s s u f f i c i e n t , but some l i n e t u n i n g (according t o Tables I I and I I I ) f a c i l i t a t e s DX a b s o r p t i o n at one atmosphere pressure. Troublesome o l e f i n o p t i c a l a b s o r p t i o n and v i b r a t i o n a l quenching may be reduced by u s i n g t e t r a c h l o r o e t h y l e n e . Unwanted o l e f i n o p t i c a l a b s o r p t i o n may a l s o be avoided by u s i n g e t h y l e n e , cyclopentadiene, or 1,3-cyclohexadiene. The l a r g e choice of Arrhenius parameters a v a i l a b l e f o r t y p i c a l reagent choices (Table I ) permits reagent o p t i m i z a t i o n f o r acceptable process r e a c t i o n e f f i c i e n c y . Experimental e v a l u a t i o n of the deuterium h a l i d e / o l e f i n process f o r heavy water p r o d u c t i o n i s i n progress at the Lawrence Livermore Laboratory. I I I . E f f e c t i v e n e s s of V i b r a t i o n a l E x c i t a t i o n In the preceding s e c t i o n , we have shown t h a t e x c i t a t i o n of l o w - l y i n g v i b r a t i o n a l l e v e l s of deuterated h a l i d e s should l e a d t o s i g n i f i c a n t enrichments v i a i s o t o p i c a l l y s e l e c t i v e a d d i t i o n r e a c t i o n s , I f the h a l i d e v i b r a t i o n and r e a c t i o n coordinates are e s s e n t i a l l y i d e n t i c a l . That v i b r a t i o n a l e x c i t a t i o n of hydrogen h a l i d e s l e a d s t o enhanced r a t e s f o r diatomic-atom exchange r e a c t i o n s of the type K f

A + BC

t

t

AB

+ C

(9)

have been e x p e r i m e n t a l l y confirmed; perhaps the most s t r i k i n g example i s the f a c t t h a t HC1 (v = 2) was found t o r e a c t w i t h bromine approximately 1 0 times f a s t e r than HC1 (ν = 0) (kO). The t h e o r e t i c a l e x p l a n a t i o n o f these r a t e enhancements runs as f o l l o w s : Since the forward, exoergic r e a c t i o n leaves the product AB i n a h i g h l y v i b r a t i o n a l l y e x c i t e d s t a t e (AB ), then 1 1


10.

MARLING ET AL.

Deuterium

Isotope

145

Separation

microscopic r e v e r s i b i l i t y a t the same t o t a l energy i m p l i e s t h a t the r a t e o f the r e v e r s e , endoergic r e a c t i o n - w i l l be enhanced more e f f e c t i v e l y when energy i s put i n t o AB v i b r a t i o n r a t h e r than i n t o r e l a t i v e t r a n s l a t i o n o f AB and C. I n c o n s i d e r i n g more general r e a c t i o n s i n v o l v i n g v i b r a t i o n a l l y e x c i t e d reagents, i t i s impor t a n t t o note t h a t the r e v e r s i b i l i t y argument can be a p p l i e d inde pendent o f whether the r e a c t i o n which leads t o a v i b r a t i o n a l l y e x c i t e d product i s endoergic o r exoergic. We s t r e s s t h i s because, w h i l e i t i s g e n e r a l l y b e l i e v e d t h a t t h e endoergic r e a c t i o n s u t i l i z e v i b r a t i o n a l energy more e f f e c t i v e l y than exoergic r e a c t i o n s (hi), t h e e x i s t i n g experimental evidence, as analyzed by B i r e l y and Lyman (32.) does not show any strong c o r r e l a t i o n between the e f f e c t i v e n e s s o f reagent v i b r a t i o n i n lowering the a c t i v a t i o n energy and r e a c t i o n e x o e r g i c i t y . I t f o l l o w s t h a t i n s i g h t i n t o the e f f e c t o f v i b r a t i o n a l e x c i t a t i o n o f hydrogen h a l i d e s on the r a t e o f exoergic a d d i t i o n r e a c t i o n s can best be gleaned from t h e experimental data on the energy d i s p o s a l o f the reverse r e a c t i o n s , i . e . , unimolecular hydrogen h a l i d e e l i m i n a t i o n s from, e.g., h a l o alkanes and h a l o o l e f i n s , f o l l o w i n g chemical o r photochemical a c t i v a t i o n . There i s an extensive l i t e r a t u r e i n t h i s area: The experimental evidence i s summarized by Berry (h2) who concludes t h a t , i r r e s p e c t i v e o f the a c t i v a t i o n mechanism, the t o t a l a v a i l able energy ( E ) , o r t h e molecular complexity o f the r e a c t a n t , a l l HX e l i m i n a t i o n products acquire ^ 15-h0% o f t h e p o t e n t i a l energy (E ) a v a i l a b l e t o t h e r e a c t a n t s (defined as t h e t h r e s h h o l d energy fo? HX e l i m i n a t i o n minus t h e r e a c t i o n e n d o e r g i c i t y ) as v i b r a t i o n a l energy. The remaining energy i s channeled i n t o HX r o t a t i o n , o l e f i n product r o t a t i o n and v i b r a t i o n and r e l a t i v e t r a n s l a t i o n a l energy o f t h e r e c o i l i n g products. We note t h a t a l l t h e data per t a i n s t o experiments i n which E^ >> Ε . Of g r e a t e r relevance as f a r as e f f e c t i v e n e s s o f HX v i b r a t i o n §n t h e r a t e o f t h e i n v e r s e a d d i t i o n would be data on HX e l i m i n a t i o n s f o r which E - Ε . Τ ρ Nevertheless, t h e a v a i l a b i l i t y o f many i n t e r n a l degrees o f f r e e dom o f t h e product o l e f i n makes i t improbable t h a t r a t e enhance ments f o r HX a d d i t i o n r e a c t i o n comparable t o those f o r HX-atom exchange r e a c t i o n s can be achieved. Experiments t o t e s t t h i s conjecture are i n progress a t t h e Lawrence Livermore Laboratory. IV. "Back-End" o f the Separation Cycle


5

T

m

In common w i t h most other deuterium separation schemes, t h e economic v i a b i l i t y o f an enrichment process based on l a s e r enhanced deuterium h a l i d e a d d i t i o n r e a c t i o n s n e c e s s i t a t e s p r o v i s i o n f o r r e c y c l i n g t h e working f l u i d . That i s , i t i s not f e a s i b l e t o use, e.g., h y d r o c h l o r i c a c i d , on a once-through b a s i s as feed f o r a deuterium separation p l a n t since even i f a l l t h e D i n n a t u r a l HC1 ( n a t u r a l abundance - 1 . 5 x 10" ) were removed w i t h 100% e f f i c i e n c y , t h e HC1 feed cost alone would be 4



146

$0.1

36

kgHCl

kg mole HC1 1 mole D 0

kg HC1

(1)


2 mole DC1

$2U00/kg

20 kg

2

X

^

'

to

D_0

2

kg mole D 0 2

assuming HC1 c o s t s 10φ p e r k i l o g r a m . Thus, t h e economic v i a b i l i t y o f t h i s process depends on the a b i l i t y t o redeuterate t h e HC1 which has been depleted o f D by t h e i s o t o p i c a l l y s e l e c t i v e a d d i t i o n r e a c t i o n . The "obvious" way t o accomplish t h e r e d e u t e r a t i o n i s by i s o t o p i c exchange o f HC1 w i t h n a t u r a l water (k3). For s p e c i f i c i t y , we d i s c u s s t h i s r e f l u x o p e r a t i o n i n t h e context o f the prototype system shown i n F i g u r e 1. The deuterated product of t h e a d d i t i o n r e a c t i o n (DACl) i s t h e r m a l l y d i s s o c i a t e d t o p r o duce i s o t o p i c a l l y pure DC1 (and e v e n t u a l l y D2O through exchange with n a t u r a l water), while the o l e f i n i s r e c i r c u l a t e d t o the l a s e r i r r a d i a t i o n area. The m a t e r i a l flows i n t h e r e f l u x tower assume e q u i l i b r i u m o p e r a t i o n a t 108°C (hh). At t h i s temperature the s e p a r a t i o n f a c t o r α f o r t h e exchange r e a c t i o n DC1 + H 0 $ HC1 + HDO

(2)

2

is

(U3)

(H)HÔ 2

(I)

1.9

Ή01

Besides t h e f a c t t h a t a l l t h e hydrogen h a l i d e - w a t e r exchange r e a c t i o n s are c h a r a c t e r i z e d by an unfavorable e q u i l i b r i u m as f a r as r e f l e x i s concerned, i . e . , t h e deuterium tends t o concentrate i n the water, t h e r e a r e two other p r a c t i c a l d i f f i c u l t i e s a s s o c i a t e d w i t h t h e use o f these systems: ( l ) they are h i g h l y c o r r o s i v e , n e c e s s i t a t i n g t h e use o f s p e c i a l m a t e r i a l s , e.g., Monel, and, (2) they form constant b o i l i n g ( a z e o t r o p i c ) mixtures. The s i g n i f i c a n c e o f t h e l a t t e r i s t h a t i t i s i m p o s s i b l e by s u c c e s s i v e d i s t i l l a t i o n s a t a given pressure (or a t a given temperature) t o o b t a i n both components as pure products from a hydrogen halide-water mixture. At some p o i n t i n t h e d i s t i l l a t i o n p r o c e s s , the a z e o t r o p i c c o n c e n t r a t i o n w i l l be reached (kk) ; when t h i s a z e o t r o p i c feed i s p a r t i a l l y v a p o r i z e d , t h e vapor has t h e same composition as t h e l i q u i d and no f u r t h e r s e p a r a t i o n o f com ponents i s p o s s i b l e . One convenient way t o break t h e azeotrope and separate t h e phases a f t e r t h e i s o t o p i c exchange process has been completed i s t o make use o f t h e s o - c a l l e d " s a l t e f f e c t " i n v a p o r - l i q u i d e q u i l i b r i u m . The a d d i t i o n o f a n o n - v o l a t i l e s a l t such as c a l c i u m c h l o r i d e , CaCl2, t o t h e HCl/H 0 mixture has t h e e f f e c t o f s i m u l t a n e o u s l y i n c r e a s i n g t h e vapor pressure o f t h e HC1 v i a t h e common i o n effect, and decreasing t h e vapor pressure o f the water, thus generating vapor o f higher HC1 c o n c e n t r a t i o n than t h a t c h a r a c t e r i s t i c o f t h e azeotrope. We have not been able t o 2


10.

MARLING ET AL.

Deuterium

Isotope

147

Separation

1mA

DC1 + A

1 m DAC1 DAC1


addition

dissociation

Carbon monoxide laser

13,500 m HC1 1 m DC1

1 m DC1 +

13,500

m HC1 13,501

HC1 reflux

| l m HC1

m HC1

D

2°

production

0.5m D 0 2

t

Feed: 3500 m n a t u r a l HÔ

Waste : 3500 m H 0 2

Feed: 0.5 m n a t u r a l HÔ

LEGEND : m = Mole A = Olefin DAC1 = DC1 + O l e f i n a d d i t i o n product Figure 1.

Process flow diagram for DO production by laser-augmented deuteriumchloride addition into olefins

American Chemfcaf

Society Library 1155 16th St. N. W. Rae; Separation of Hydrogen Isotopes ACS Symposium Series; American Chemical Washington, DC, 1978. 1. D. C.Society: 20038

SEPARATION O F HYDROGEN ISOTOPES

148

f i n d i n f o r m a t i o n i n the l i t e r a t u r e on t h e HCl/H O/CaCl^ system; however, from data on Isopropanol/HÔ/CaCl^ (^5.) and HCl/HÔ/H^SO^ mixtures (U6_)(HpS0^, w h i l e not a common i o n , be haves s i m i l a r l y t o a n o n - v o l a t i l e s a l t i n reducing the vapor pressure o f HÔ), we c o n j e c t u r e t h a t t h e c o n c e n t r a t i o n o f CaCl^ r e q u i r e d w i l l be approximately 2-k wt.%. A d e t a i l e d d i s c u s s i o n o f t h e design o f t h e HC1/H 0 exchange process i n c o r p o r a t i n g t h e equipment necessary t o generate r e deuterated, anhydrous HC1 f o r r e f l u x t o the l a s e r tower would c a r r y us too f a r a f i e l d (Vf) ; however, t h e b a s i c concept i s as f o l l o w s . The i s o t o p i c exchange takes p l a c e on a s e r i e s o f t r a y s w i t h the HC1 bubbling up and H 0 f l o w i n g down i n a countereurrent f a s h i o n . The l i q u i d stream from t h e exchange column, and a s a l t s o l u t i o n are f e d t o a concentrated s t r i p p e r which produces vapor of h i g h p u r i t y (> 99 mole % H C l ) ; t h i s i s r e c y c l e d t o t h e bottom o f t h e i s o t o p i c exchange column. The l i q u i d from t h e concentra ted s t r i p p e r , having a c o n c e n t r a t i o n lower than t h e azeotrope, passes t o an evaporator where t h e s a l t i s recovered f o r r e c y c l e to t h e concentrated s t r i p p e r , and vapor i s produced which i s subsequently s t r i p p e d t o produce two streams: a water stream which i s washed before d i s c h a r g e , and an a z e o t r o p i c HC1/H 0 mixture. The l a t t e r , mixed w i t h incoming f r e s h water, i s f e d t o the t o p o f t h e i s o t o p i c exchange column. Many v a r i a t i o n s o f t h e above are probably f e a s i b l e ; our main p o i n t here i s t o i n d i c a t e t h a t w h i l e t h e use o f hydrogen h a l i d e s i n t r o d u c e s c o m p l i c a t i o n s i n the design o f the "back-end" o f t h e s e p a r a t i o n scheme, these can be overcome. 2


2

2

V.

Conclusion

O p t i c a l p r o d u c t i o n o f heavy water i s beginning t o r e c e i v e s e r i o u s c o n s i d e r a t i o n . L a b o r a t o r y - s c a l e photochemical s e p a r a t i o n of deuterium v i a d i s s o c i a t i o n o f deuterated formaldehyde (HDCO)to y i e l d HD and CO has a l r e a d y been demonstrated i n t h e UV(3_) u s i n g a s i n g l e photon, and i n t h e IR at 10.6 microns u s i n g multi-photon a b s o r p t i o n (kO). To be economically v i a b l e , t h e former process awaits e f f i c i e n t low cost tunable u l t r a v i o l e t l a s e r s near 3^0 nm (39,^9) w h i l e the l a t t e r process r e q u i r e s s i g n i f i c a n t improve ment i n photon u t i l i z a t i o n (^ 1 0 photons are p r e s e n t l y r e q u i r e d per separated HD {kQ)). A l l photochemical deuterium enrichment processes w i l l probably r e q u i r e deuterium o p t i c a l i s o t o p i c s e l e c t i v i t y o f 1000-fold or b e t t e r f o r e f f i c i e n t photon u t i l i z a t i o n (3£,^9), about an order o f magnitude higher than has been demonstrated (3,^8). The deuterium s e p a r a t i o n process j u s t presented proposes t o u t i l i z e e x i s t i n g , e f f i c i e n t , h i g h average power CO l a s e r t e c h nology t o promote deuterium h a l i d e a d d i t i o n i n t o unsaturated hydrocarbons. Spectroscopic s t u d i e s o f CO l a s e r s and deuterium h a l i d e s have shown t h a t both DC1 and DBr can be s e q u e n t i a l l y e x c i t e d by t h e CO l a s e r near 5-6 microns t o a t l e a s t the ν = 5 9

6



10.

MARLING E T A L .

Deuterium

Isotope

149

Separation

l e v e l , as summarized i n Tables I I and I I I . A d d i t i o n i n t o unsaturated hydrocarbons should occur w i t h a c t i v a t i o n energies i n the range of 15-^0 kcal/mole u s i n g HC1 or HBr as the working gas, as i n d i c a t e d i n Table I . The e f f e c t i v e n e s s of hydrogen h a l i d e v i b r a t i o n a l energy toward l o w e r i n g the a d d i t i o n r e a c t i o n a c t i v a t i o n b a r r i e r is not known, but probably l i e s i n the range of 30-100%, suggesting t h a t perhaps 5-8 quanta of DX v i b r a t i o n a l e x c i t a t i o n w i l l be r e q u i r e d f o r u s e f u l l y f a s t r e a c t i o n t o occur. Two s i g n i f i c a n t problems t o be r e s o l v e d are photon l o s s by o l e f i n combination band absorption i n the 5 - 6 micron r e g i o n and p o t e n t i a l l y low r e a c t i o n quantum y i e l d s due t o non-reactive v i b r a t i o n a l quenching by the o l e f i n . These problems appear s o l v a b l e by s u i t a b l e o l e f i n s t r u c t u r a l design. The problems a t the "back-end" of t h e s e p a r a t i o n c y c l e , s p e c i f i c a l l y the breaking of the HX/H 0 azeotrope, a l s o appear s o l v a b l e . Research c u r r e n t l y underway w i l l examine the e f f e c t i v e n e s s of v i b r a t i o n a l c a t a l y s i s on the r e a c t i o n r a t e and r e a c t i o n quantum y i e l d as a f u n c t i o n of o l e f i n s t r u c t u r e . 2

Acknowledgement One of the authors (M.M.M.) would l i k e t o thank M. Benedict and J. E. V i v i a n f o r h e l p f u l d i s c u s s i o n .

Professors

Abstract The feasibility of a gas phase deuterium s e p a r a t i o n process is examined which would use IR l a s e r s t o augment a d d i t i o n re actions between HX (X = Br, Cl, F , OH) and unsaturated hydro carbons. High vibrational levels (V ≥ 4) of DF or HDO may be e x c i t e d by a p u l s e d DF laser. S i m i l a r h i g h vibrational excitation of DCl o r DBr may be achieved by a p u l s e d CO laser and s p e c t r o scopic d e t a i l s f o r excitation up t o V = 5 are examined. The thermal r e a c t i o n between HX and unsaturated hydrocarbons is c h a r a c t e r i z e d by activation exergies between 15 and 57 k c a l / m o l e , depending on olefin s t r u c t u r e and choice of HX. The e f f e c t i v e n e s s of HX/DX vibrational energy in l o w e r i n g the r e a c t i o n b a r r i e r is d i s c u s s e d . Primary emphasis is g i v e n t o an overall deuterium s e p a r a t i o n process utilizing HCl as a c l o s e d c y c l e working gas w i t h aqueous phase r e d e u t e r a t i o n . P r e f e r r e d olefin reagents are i n d i c a t e d compatible w i t h CO laser e x c i t a t i o n of DCl at a wave l e n g t h of 4.9-5.3 m i c r o n . Literature Cited 1. 2.

Letokhov, V . S . and Moore, C.B., Sov. J. Quant. E l e c t r o n (1976) 6, 129 and 259. Miller, A . I. and Rae, H.K., Chemistry in Canada (1975), 27, 25. We note t h a t ERDA's current (April, 1977) p r i c e f o r heavy water is $213/kg, a p r i c e i n c r e a s e due t o the


150

3.


4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

17. 18. 19. 20. 21. 22. 23.


diseconomy of small s c a l e p r o d u c t i o n . N e v e r t h e l e s s , a heavy water cost of approximately $200/kg f o r d e l i v e r y in 1980 is probably a conservative estimate. The possibility of deuterium separation via photopredissociation of formaldehyde has been demonstrated by J. B . M a r l i n g . See J. B . M a r l i n g , "Laser Isotope Separation of Deuterium," Chem. Phys. Lett., (1974) 34, 84, and "Isotope Separation of Oxygen-17, Oxygen-18, Carbon-13, and Deuterium by Ion Laser Induced Formaldehyde P h o t o p r e d i s s o c i a t i o n , " J. Chem. Phys. (1977) 66, 4200. Benson, S. W., and Bose, A . N., J. Chem. Phys. (1963), 39 3463. Gorton, P . J., and Walsh, R., J. Chem. Soc. Chem. Comm. (London) (1972), 782. Tschuikow-Roux, Ε., and Maltman, F . R., I n t . J. Chem. Kin. (1975), Vol. VII, 363. Benson, S. W., and O ' N e a l , Η. Ε., " K i n e t i c Data on Gas Phase Unimolecular R e a c t i o n s , " (1970), NSRDS-NBS 21. Kubota, Η . , Rev. Phys. Chem., Japan (1967) 37, 25, and (1967) 37, 32. Harding, C. J., M a c c o l l , Α., and Ross, R. Α., J. Chem. Soc. B, (1969), 634. Egger, K. W . , and Benson, S. W., J. Phys. Chem. (1967), 71, 1933. Boness, M. J. W . , and Center, R. E., J. A p p l . Phys. (1977), 48, 2705. See a l s o Sobolev, Ν. Ν., and Sokovikov, V . V., Sov. J. Quant. E l e c t r o n . (1973), 2, 305. Todd, T. R., C l a y t o n , C. Μ . , Telfair, W. Β., McCubbin, Τ. Κ . , Jr., and Pliva, J., J. M o l . Spect. (1976), 62, 201. Ross, A . H . M., Eng, R. S., and Kildal, Η . , Opt. Comm. (1974), 12, 433. Rank, D. Η . , Eastman, D. P., Rao, B . S., and Wiggins, Τ. Α., J. Opt. Soc. Am. (1962), 52, 1. Dunham, J. L., Phys. Rev. (1932), 41, 721. Townes, C. Η . , and Shawlow, A . L., "Microwave Spectroscopy," p. 644, McGraw-Hill Brook Company, Inc., New York, New York (1955). Keller, F . L., and N i e l s e n , A . H., J. Chem. Phys. (1954), 22, 294. Rank, D. Η . , F i n k , Uwe, and Wiggins, Τ. Α., J. M o l . Spect. (1965), 18, 170. Bernage, P., N i a y , P., Bockuet, Η . , and Houdart, R., Revue de Phys. A p p l . (1973), 8, 333. Mould, Η. Μ., Price, W. C., and W i l k i n s o n , G. R., S p e c t r o chimica A c t a (1960), 16, 479. James, T. C., and T h i b a u l t , R. J., J. Chem. Phys. (1964), 40, 534. Babrov, H. J., J. Chem. Phys. (1964), 40, 831. B e n e d i c t , W. S., Herman, R., and S i l v e r m a n , S., J. Chem. Phys. (1957), 26, 1671.


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Deuterium

Isotope

24. Smith, F. G., J. Quant. Spectrosc. R a d i a t . T r a n s f e r 13, 25.

151

Separation

(1973),

717.

26.

Rasmussen, R.S.,and Brattain, R. R., J. Chem. Phys. ( 1 9 4 7 ) , 120 and 131. Gallinella, Ε., F o r t u n a t o , Β., and Mirone, P., J. Mol. Spect.

27. 28.

DiLauro, C., and Neto, N., J. Mol. S t r u c t u r e ( 1 9 6 9 ) , 3, 219. Chen, M. Y.-D., and Chen, H. -L., J. Chem. Phys. ( 1 9 7 2 ) ,

29.

Weitz, Ε., and F l y n n , G., Ann. Rev. Phys. Chem. ( 1 9 7 4 ) , 25,

15,

(1967),

56,

24, 345.

3315.

275.


30. Hopkins, Β. M., and Chen, H. -L., J. Chem. Phys. ( 1 9 7 3 ) , 5 9 , 1495.

31.

Zittel,

P. F., and Moore, C. B.,J.Chem. Phys. ( 1 9 7 3 ) ,

58,

2004. 32. Birely, J. H., and Lyman, J. L., J. Photochem. ( 1 9 7 5 ) , 4, 2 6 9 . 33. Zittel, P. F., and Moore, C. B., J. Chem. Phys. ( 1 9 7 3 ) , 5 8 , 2922.

34. Moore, C. Β., private communication. 35. A l b r i g h t , J. C., and N i e l s o n , J. R., J. Chem. Phys. 36.

26,

(1957),

370.

N i e l s o n , J. R., C l a s s e n , H. H., and Smith, D. C., J. Chem. Phys. ( 1 9 5 0 ) , 1 8 , 485 and 8 1 2 ; ibid ( 1 9 5 2 ) , 2 0 , 1 9 1 6 . 37. C l a y t o n , J. W., Jr., Fluorine Chem. Rev. ( 1 9 6 7 ) , 1, 197. 38. B e r r y , M. J., paper presented a t t h e T h i r d Winter Colloquium on Laser Induced Chemistry, Park City, Utah, Feb. 14-16, 1977. 39. M a r l i n g , J. Β., Wood, L. L., and Daugherty, J. D., "The LaserR e l a t e d Costs of Some Approaches to Laser Isotope S e p a r a t i o n of Deuterium," Univ. Calif. Lawrence Livermore Laboratory I n t e r n a l Document, Feb., 1977. 40. Arnoldi, D., Kaufmann, Κ., and Wolfrum, J., Phys. Rev. L e t t . (1975),

34, 1 5 9 7 .

41. See, e.g., L e v i n e , R. D., and Manz, J., J. Chem. Phys. 63,

(1975),

4280.

42.

B e r r y , M. J., J. Chem. Phys. (1974), 61, 3114, and r e f e r e n c e s cited t h e r e i n . 43. B e n e d i c t , Μ., and Pigford, Τ. Η., "Nuclear Chemical Engineer i n g , " p. 454, Table II-9, McGraw-Hill, New York, New York (1957).

44. For HCl/H O the constant boiling mixture is 11.13 mole%HCl. It boils at 108.5°C under a pressure of one atmosphere. 45. Ohe, S., Japan Chem. Quart. ( 1 9 6 9 ) , 4, 2 0 . 46. Chu, J u Chin, e tal.,"Vapor L i q u i d E q u i l i b r i u m Data," 2nd Edition, p. 6 3 9 , Edwards, Ann Arbor ( 1 9 5 6 ) . 47. A d e t a i l e d f l o w sheet is a v a i l a b l e from one of the authors (M.M.M.). 48. Koren, G., Oppenheim,P.,Tal,D., Okon, Μ., and W e i l , R., A p p l . Phys. L e t t . ( 1 9 7 6 ) , 2 9 , 40. 49. Vanderleeden, J. C., "Laser S e p a r a t i o n of Deuterium," Laser Focus (June, 1 9 7 7 ) , 1 3 , 51. 2

RECEIVED September 12, 1977


Deuterium Isotope Separation via Vibrationally Enhanced Deuterium

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