ORIGIN OF ORGANIC YATTER IN EARLY SYSTEhY. I.

O R I G I N O F ORGANIC YATTER IN EARLY SOLAR SYSTEhY. I .

HYDRQCARBONS

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O R I G I N OF ORGANIC MATTER I N EARLY SOLAR SYSTEM. I HYDROCARBONS

Martin H. Studier Chemistry Division, Argonne National Laboratory,

Argonne, I l l i n o i s R y o i c h i Hayatsu and Edward Anders

Enrico Fermi I n s t i t u t e University of Chicago, Chicago, I l l i n o i s

4

Submitted to Science

December 1965

NASA Grant NsG-366 R e s e a r c h

EFINS 65-115

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ABSTRACT

1

-

.

I r o n and s t o n y m e t e o r i t e s a r e e f f e c t i v e c a t a l y s t s for a Fischer-Tropsch t y p e r e a c t i o n between carbon monoxide and hydrogen. Even i n hydrogen-rich m i x t u r e s approaching cosmic composition, a l i p h a t i c and aromatic hydrocarbons a r e produced r a p i d l y a t t e m p e r a t u r e s between 25?C and 5 8 O O C . When these h y d r o c a r b o n s a r e p a r t i a l l y e q u i l i b r a t e d by s u s t a i n e d r e h e a t i n g , they match t h e hydrocarbon d i s t r i b u t i o n i n carbonaceous chondrites i n a l l important respects.

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*

In an e a r l i e r paper ( l ) , w e reported t w o s t r i k i n g properties

of

the

trapped

volatiles

in

c

-

a

r

b

o

n

.

a_c__e-o_u>_sI-..c.--h

o

n

d

r

i

t

e

s

:

methane was

a t l e a s t 1000 t i m e s more abundant t h a n e t h a n e , and a r o m a t i c

hydrocarbons predominated o v e r a l i p h a t i c ones. The observed

distribution grossly resembled an equilibrium distribution i n a

c a r b o n - r i c h C-H-0, m i x t u r e ( 2 ) . We t h e r e f o r e p r o p o s e d t h a t t h e

o r g a n i c compounds i n meteorites formed i n t h e s o l a r nebula

u n d e r n e a r - e q u i l i b r i u m c o n d i t i o n s , d u r i n g r a p i d c o o l i n g of a

gas phase depleted i n hydrogen.

t h i s hypothesis experimentally.

,

__L_--

We

have

now a

-XI.

t

t

e

m-.p_t-

e

d

t -o

test

For our e x p e r i m e n t s w e u s e d m i x t u r e s o f CO and H2. The

choice o f CO was obvious: a t t e m p e r a t u r e s of 1000-2000?C and

m o d e r a t e p r e s s u r e s , CO is t h e dominant form o f c a r b o n i n a c o s m i c

g a s (3). The c o m p o s i t i o n o f t h e g a s m i x t u r e r a n g e d f r o m an

( a t o m i c ) C:H:O r a t i o of 1:1:1, w e l l w i t h i n t h e 7 f a s p h a l t 7rfe g i o n

o f t h e C-H-0 phase diagram ( 2 ) , t o 1:500:1, close t o t h e cosmic

value. Elemental carbon is the s t a b l e equilibrium product i n

t h e a s p h a l t region, but i f its formation is k i n e t i c a l l y i n h i b i t e d ,

l a r g e amounts of a r o m a t i c hydrocarbons c a n form i n s t e a d a s

m e t a s t a b l e p r o d u c t s ( 2 ) . Our e n t i r e h y p o t h e s i s hinged on t h e

assumption t h a t t h e formation of free carbon would be i n h i b i t e d

long enough t o allow the buildup of a metastable d i s t r i b u t i o n

r i c h i n a r o m a t i c s . Our e x p e r i m e n t s were t o t e s t t h i s a s s u m p t i o n .

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*

-4-

L

In order t o keep the system simple, w e limited our first

series of e x p e r i m e n t s t o C-H-0 m i x t u r e s , e x c l u d i n g o t h e r non-

m e t a l l i c c o n s t i t u e n t s of a cosmic gas. However, i t is known

t h a t s i l i c a t e and m e t a l p a r t i c l e s condense when a cosmic g a s

cools from high t e m p e r a t u r e s (4). Such p a r t i c l e s might c a t a l y z e

r e a c t i o n s of CO and o t h e r c a r b o n compounds. We t h e r e f o r e added

t o same o f o u r g a s m i x t u r e s 0.01-0.1 g of c o a r s e l y ground

meteorite powder, normally i r o n (Canyon Diablo) but i n one

case, s t o n e (Bruderheim). Before use, t h e meteorite powder

was baked o u t o v e r n i g h t a t 600-900?C u n t i l a l l o r g a n i c s had

been removed.

The g a s m i x t u r e , u s u a l l y a t a t o t a l p r e s s u r e of 1-2 atm a t room t e m p e r a t u r e , was p l a c e d i n a 45 c m x 1 c m I . D. q u a r t z tube sealed a t one end and j o i n e d t o a metal valve by a graded s e a l . The sealed end was i n s e r t e d t o a d e p t h of 7 c m i n a t u b u l a r furnace which was heated t o t h e desired temperature. The o t h e r end r e m a i n e d a t room t e m p e r a t u r e . I n t h i s a r r a n g e m e n t , v o l a t i l e compounds c o u l d d i s t i l l away from t h e r e a c t i o n z o n e , thus r e m a i n i n g p r o t e c t e a t o some e x t e n t f r o m f u r t h e r r e a c t i o n . The g a s p h a s e was examined p e r i o d i c a l l y on a t i m e - o f - f l i g h t mass s p e c t r o m e t e r , as described i n (1).

It s o o n became a p p a r e n t t h a t meteorite powder had a s t r o n g c a t a l y t i c e f f e c t . Without meteorite, t h e g a s m i x t u r e had t o be h e a t e d f o r a l o n g t i m e t o produce d e t e c t a b l e amounts of o r g a n i c s .

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