7 Manufacture of Higher Straight-Chain Alcohols by the Ethylene Chain Growth Process PAUL H. WASHECHECK
Conoco Chemicals, Conoco Inc., P.O. Drawer 1267, Ponca City, OK 74601
The first commercial volumes of higher molecular weight, linear alcohols were prepared from naturally occurring fats and oils. Because of this origin, these alcohols, even. the synthetic versions, are commonly called "fatty alcohols." Another common name for these products is ''detergent-range alcohols," after their highest volume use. This name helps to distinguish alcohols with eleven or more carbons from alcohols with six to ten carbons which are known as "plasticizer alcohols," after their highest volume use. For this discussion we will arbitrarily define higher molecular weight or detergent-range alcohols as those with eleven or more carbon atoms. As with many boundaries, the one between plasticizer and detergent alcohols is not distinct. Many detergent intermediates contain only ten carbon alcohols, and Shell has recently introduced a new product which contains the nine through eleven carbon homologs. On the other hand, isotridecyl alcohol, a C oxo alcohol, is commonly used as a plasticizer feedstock. Coconut oil and tallow were the principal raw material sources for early fatty alcohol manufacture. Coconut oil is a lauryl-range oil and affords primarily C and C alcohols. Tallow is a stearyl-range oil and yields primarily C and C alcohols. Both of these natural products form only even carbon-numbered alcohols. Some synthetic alcohols contain both even and odd carbon-numbered alcohols while other synthetic alcohols are like the natural products and contain only even carbon-numbered homologs. It was recognized in the late 1950's that the supply and therefore price of naturally occurring products, such as coconut oil and tallow, could fluctuate widely. Both political and climatic conditions have an influence on the supply and price of these oils, and the price of naturally-derived alcohols depends on their raw material costs. With both politics and climates to content with, natural alcohol producers often have little control over the price of their final product. 1 3
12
14
16
18
0097-6156/81/0159-0087$05.00/0 ©
1981 American Chemical Society
MONOHYDRIC ALCOHOLS
88
This s i t u a t i o n provided an i n c e n t i v e f o r development of syntheti c routes t o f a t t y a l c o h o l s . S y n t h e t i c f a t t y a l c o h o l s f a l l i n t o three broad c a t e g o r i e s and are manufactured from two b a s i c raw m a t e r i a l s — e t h y l e n e and n - p a r a f f i n s . One group i s secondary a l c o h o l s which are prepared by o x i d a t i o n of n - p a r a f f i n s i n the presence of b o r i c acid. A second group c o n s i s t s o f oxo a l c o h o l s manufactured by hydroformylation of l i n e a r o l e f i n s which are derived from e i t h e r n - p a r a f f i n s o r ethylene. Both of these a l c o h o l types are discussed i n separate chapters. The l a s t group i s Z i e g l e r a l c o h o l s which are prepared from ethylene and are the primary subject of t h i s chapter. Secondary a l c o h o l s are much d i f f e r e n t c h e m i c a l l y than primary a l c o h o l s , such as n a t u r a l a l c o h o l s . I n a d d i t i o n , comm e r c i a l secondary a l c o h o l s are prepared from both even and odd carbon-numbered n - p a r a f f i n s and thus c o n t a i n both even and odd carbon-numbered a l c o h o l s . Oxo a l c o h o l s are primary a l c o h o l s , as a r e n a t u r a l a l c o h o l s . However, oxo a l c o h o l s cont a i n from twenty t o s i x t y percent branched chain a l c o h o l s and a l s o c o n t a i n both even and odd carbon-numbered homologs. Z i e g l e r a l c o h o l s are very s i m i l a r t o n a t u r a l a l c o h o l s . They are primary a l c o h o l s and are a mixture of only even carbon-numbered homologs. The major d i f f e r e n c e s between Z i e g l e r and n a t u r a l a l c o h o l s are t r a c e i m p u r i t i e s present and the range of syntheti c products, C „ - C , a v a i l a b l e . 30
Natural Alcohols As noted e a r l i e r , n a t u r a l a l c o h o l s are produced from coconut o i l and t a l l o w as w e l l as some other f a t s and o i l s — p a l m k e r n e l o i l , palm o i l , sperm whale o i l , e t c . Most of these n a t u r a l o i l s a c t u a l l y c o n s i s t of f a t t y t r i g l y c e r i d e s , i . e . , g l y c e r o l e s t e r i f i e d by three molecules of f a t t y a c i d . There i s very l i t t l e f r e e a l c o h o l present i n these m a t e r i a l s , and the a l c o h o l s are d e r i v e d from the f a t t y a c i d moiety of the t r i g l y c e r i d e by r e d u c t i o n . Each t r i g l y c e r i d e molecule has a random d i s t r i b u t i o n of a c i d chain lengths and degrees of u n s a t u r a t i o n . However, the composition o f f a t s and o i l s from a common source i s r e l a t i v e l y uniform. While f a t t y a l c o h o l s t h e o r e t i c a l l y could be derived from any f a t o r o i l , most are prepared from coconut o i l o r t a l l o w w i t h an i n c r e a s i n g q u a n t i t y d e r i v e d from palm o i l or palm k e r n e l o i l . Approximate compositions (1) of these f o u r o i l s a r e l i s t e d i n Table I . The f i r s t commercial production of f a t t y a l c o h o l s i n the 1930's employed a sodium r e d u c t i o n process (Bouveault-Blanc) (2). However, the high usage (4 mol/mol a l c o h o l ) of expensive sodium soon l e d t o replacement of t h i s method of r e d u c t i o n by c a t a l y t i c hydrogenation.
7.
WASHECHECK
Higher Straight-Chain Alcohols
89
TABLE I F a t t y Acid Composition, Weight Percent Palm Kernel Oil
Coconut Oil
c c, c,. c c,. c,« c,.
0.8 5.4 8.4 45.4 18.0 10.9 9.9 0.4
s
12
C o 2
Palm Oil
Tallow
6.3
2.7 7.0 46.9 14.1 8.8 20.5
1.4 40.1 58.5
27-4 66.2
-
-
-
There are b a s i c a l l y two types of hydrogenation p r o c e s s e s — hydrogenation of methyl e s t e r s and hydrogenation of f a t t y a c i d s — w i t h the former predominating i n the U . S . Ashland and P r o c t e r & Gamble, the two U . S . f a t t y a l c o h o l producers, both u t i l i z e methyl e s t e r - b a s e d processes ( 3 ) . In the methyl e s t e r route (Figure 1 ) , r e f i n e d t r i g l y c e r i d e s are reacted with methanol i n the presence of a sodium methoxide c a t a l y s t to form the corresponding f a t t y a c i d methyl e s t e r s and g l y c e r i n e ( 2 ) . 0
0
II 5
II
NaO.Mp>
C,H (0CR)
3
+ 3CH3OH
'
3RCOCH3 +
C,H (0H) 5
s
T h i s i s a batch r e a c t i o n c a r r i e d out at atmospheric p r e s sure with r e f l u x i n g methanol. The crude r e a c t i o n mixture i s phase-split, and commercial g l y c e r i n e i s recovered from the lower phase by separating excess methanol. The methyl e s t e r s can be fed d i r e c t l y to a hydrogenation u n i t , or more o f t e n are d i s t i l l e d to separate unreacted t r i g l y c e r i d e s which are r e c y c l e d . The d i s t i l l e d methyl e s t e r s are hydrogenated at approximately 300°C and 3000 p s i g with a copper chromite c a t a l y s t i n s l u r r y form through t u b u l a r r e a c tors. Excess hydrogen i s used f o r r e d u c t i o n as w e l l as a g i t a t i o n of the s l u r r i e d c a t a l y s t . 0 II
RC0CH3 + 2 H
2
• RCH 0H + C H 0 H 2
3
The product mixture i s f l a s h e d to separate hydrogen and some methanol. C a t a l y s t i s then separated from crude a l c o h o l via c e n t r i f u g a t i o n and r e c y c l e d to the r e a c t o r as a s l u r r y .
90
MONOHYDRIC ALCOHOLS
The l a s t t r a c e s o f c a t a l y s t a r e removed from crude a l c o h o l by filtration. Crude a l c o h o l i s then s t r i p p e d a t atmospheric p r e s sure t o remove methanol and vacuum d i s t i l l e d t o i s o l a t e the desired alcohol f r a c t i o n s . Ziegler Alcohols In the mid 1950' s, Dr. K a r l Z i e g l e r (4) and h i s a s s o c i a t e s at the Max Planck I n s t i t u t e c a r r i e d out fundamental research which provided the b a s i s f o r schemes t o synthesize even carbonnumbered, l i n e a r a l c o h o l s s i m i l a r t o n a t u r a l a l c o h o l s . Commerc i a l p l a n t s were b u i l t by Conoco i n 1962, Condea i n 1964, and E t h y l i n 1965* The Conoco and Condea processes a r e v i r t u a l l y i d e n t i c a l and d i f f e r e n t from the E t h y l process. There a r e f o u r b a s i c p a r t s o f a Z i e g l e r a l c o h o l process. 1. P r e p a r a t i o n of t r i e t h y l a l u m i n u m . 2. Growth w i t h ethylene t o higher alkylaluminum compounds. 3- O x i d a t i o n t o aluminum a l k o x i d e s . 4. H y d r o l y s i s t o product a l c o h o l s . Both the Conoco and E t h y l processes use these f o u r b a s i c steps, and E t h y l adds a t r a n s a l k y l a t i o n step t o c o n t r o l product distribution. Synthesis o f t r i e t h y l a l u m i n u m from aluminum, hydrogen, and ethylene i s the f i r s t segment of a Z i e g l e r a l c o h o l process. I t can be c a r r i e d out i n a s i n g l e s t e p , but normally i s accomp l i s h e d on a commercial s c a l e i n two stages w i t h r e c y c l e o f two-thirds of the t r i a l k y l a l u m i n u m product. 4 A 1 ( C H ) , + 2A1 + 3H 2
5
6 A 1 ( C H ) H + 6CH =CH 2
5
2
2
2A1 + 3H + 6CH =CH 2
2
2
2
2
• 6A1(C H ) H 2
5
2
• 6A1(C H )
3
• 2A1(C H )
3
2
5
2
5
Hydroaluminum o f t r i e t h y l a l u m i n u m forms diethylaluminum h y d r i d e . A Conoco patent (5) i n d i c a t e s the hydrogenation r e a c t i o n i s c a t a l y z e d by t i t a n i u m and zirconium i n the feed aluminum and probably does not occur w i t h u l t r a p u r e aluminum. Ethylene r e a d i l y adds t o the r e s u l t i n g diethylaluminum hydride t o y i e l d triethylaluminum. In the chain growth s t e p , ethylene adds t o t r i e t h y l a l u m i n u m to form higher t r i a l k y l a l u m i n u m compounds w i t h an even number of carbon atoms. A1(C H ) 2
5
3
+ mCH =CH 2
2
• Al[(CH CH ) CH CH ] 2
2
m
2
3
3
The mole percent d i s t r i b u t i o n o f a l k y l chains f o l l o w s a Poisson curve (6,6a). The average number of ethylene u n i t s added d u r i n g t h i s growth step i s commonly r e f e r r e d t o as the "m-value" and
7.
WASHECHECK
91
Higher Straight-Chain Alcohols
i s a good d e s c r i p t i o n of the d i s t r i b u t i o n of a l k y l groups on aluminum. A d d i t i o n of ethylene to triethylaluminum i s first-order i n monomeric triethylaluminum and ethylene (7)Since t r i e t h y l aluminum i s l a r g e l y dimeric i n the l i q u i d phase, k i n e t i c s of the growth r e a c t i o n take the f o l l o w i n g form: [ A 1 ( C H ) , ] + 2A1(C H ), 2
-
5
2
d[C^U]
2
,
k [ A
C
5
» *
> 2A1R,
H
i(c H ) ]^[C H ] 2
5
3
2
%
There are three side r e a c t i o n s which occur d u r i n g the growth step ( 8 ) . At higher temperatures (>120°C), aluminum a l k y l s crack to form dialkylaluminum hydride and a - o l e f i n s (thermal displacement). (RCH CH ) A1 J (RCH CH ) A1H + RCH=CH 2
2
S
2
2
2
2
Because of the l a r g e excess of ethylene present i n the growth r e a c t o r , the reverse r e a c t i o n i s i n s i g n i f i c a n t . Ethylene reacts with d i a l k y l aluminum hydride much more r a p i d l y than does the terminal o l e f i n , and any a l k y l group thermally d i s p l a c e d i s replaced by an e t h y l group. However, terminal o l e f i n present i n the growth r e a c t o r can react with trialkylaluminum compounds. The a - o l e f i n i n s e r t s between the aluminum-carbon bond j u s t as ethylene does i n a normal growth process. R A1 + RCH=CH J R A1CH -CH-R 3
2
2
2
This side r e a c t i o n leads to the formation of branched a l c o h o l s as w e l l as branched o l e f i n s . These i m p u r i t i e s are dimeric and are about twice the average molecular weight as the product alcohols. The t h i r d side r e a c t i o n i s formation of a small amount of polyethylene during the growth s t e p . The quantity of p o l y ethylene does not represent a s i g n i f i c a n t y i e l d l o s s , but does present serious processing problems. The polymer deposits on reactor surfaces, i n h i b i t s heat t r a n s f e r , plugs v a l v e s , and must be cleaned out p e r i o d i c a l l y . A Conoco patent (9) i n d i c a t e s t h i s problem can be prevented by a d d i t i o n of small q u a n t i t i e s of carbon monoxide to the feed ethylene. The next step i n a Z i e g l e r process i s o x i d a t i o n of the trialkylaluminum growth mixture to the corresponding aluminum alkoxides. 2R A1 + 30 S
2
2(R0) A1 S
MONOHYDRIC ALCOHOLS
CRUDE TO
Figure 1.
Methyl ester hydrogenation
HYDROGEN
LA
T O
ET
2
T
S
ATE Still (I 1 0 ' C ,
30
T
PSIGJ
( I 3 5 * C , IOOOPSI6)
BY-PRODUCTS
ALCOHOLS
DISTILLATION
IROH AI(OH)
3
AIH
Hydroiiiitm noo P S I O
CRUDE
Cllcilir
ET fl
Ctitrifigi
Etkyliliu
Slirry Pnp
ALCOHOLS
DISTILLATION
(\
'
^
R O H
(R013AI
R3AJ
(0H>3 CS O
H 0—•
Flash
2
Phisi Split
H y i r 9 | y $ j J
t90*C,5PSIG)
s t r i p
AIR
Oxiiitiii Ructor
(35 ' C , 50PSIG)
Figure 2.
ALFOL alcohol process
Growth Rncter (I20'C,I600PSIG)
7.
WASHECHECK
93
Higher Straight-Chain Alcohols
This step i s c a r r i e d out very c a r e f u l l y u s i n g d r y a i r . The r e a c t i o n i s r a p i d and exothermic. By-products o f the o x i d a t i o n i n c l u d e aldehydes, e s t e r s , p a r a f f i n s , and f r e e a l c o h o l s . The f i n a l step i s h y d r o l y s i s o f aluminum a l k o x i d e s t o f r e e the product a l c o h o l s . 3R0H + A1(0H)
(R0) A1 + 3H 0 8
2
3
H y d r o l y s i s can be c a r r i e d out w i t h water, as shown above, i n which case the co-product i s aluminum hydroxide. This aluminum hydroxide i s converted t o alumina by d r y i n g and c a l c i n i n g (10). Aluminum a l k o x i d e s can a l s o be hydrolyzed w i t h d i l u t e s u l f u r i c a c i d i n which case the co-product i s aluminum s u l f a t e . 2(R0),A1 + 3H S0 2
%
6R0H +
A1 (S0J, 2
Aluminum s u l f a t e i s a s a l a b l e co-product i n c o n v e n t i o n a l mark e t s , but i t i s o f low v a l u e . Conoco ALFOL
A l c o h o l Process (11)
The ALFOL a l c o h o l process i s d e s c r i b e d i n F i g u r e 2. Conoco uses a two-step process f o r the s y n t h e s i s o f t r i e t h y l aluminum—hydrogenation f o l l o w e d by e t h y l a t i o n . Triethylaluminum i n a s o l v e n t and hydrogen a r e c i r c u l a t e d through a hydrogenation r e a c t o r . S l u r r i e d aluminum powder i s added and r e a c t s w i t h the t r i e t h y l a l u m i n u m and hydrogen t o form d i e t h y l aluminum h y d r i d e . The hydrogenation r e a c t i o n i s c a r r i e d out at 135°C and 1000 p s i g i n an a g i t a t e d v e s s e l w i t h an average residence time o f one hour. Powdered aluminum c o n t a i n i n g the patented (5) a c t i v a t o r s i s available i n railcar quantities. This powder i s s l u r r i e d with a dry solvent. Conoco uses a h i g h l y p a r a f f i n i c s o l v e n t to ensure t h a t product a l c o h o l s w i l l meet FDA standards. E f f l u e n t from the hydrogenation r e a c t o r i s depressured to about 400 p s i g . This l e v e l o f hydrogen i s r e q u i r e d t o p r e vent the reverse r e a c t i o n , diethylaluminum hydride decomposit i o n , which r e s u l t s i n p l a t i n g o f aluminum on the process equipment. Product diethylaluminum h y d r i d e , unreacted aluminum, and s o l v e n t a r e charged t o the e t h y l a t i o n r e a c t o r . Ethylene i s i n t r o d u c e d and undergoes a r a p i d , exothermic r e a c t i o n t o form t r i e t h y l a l u m i n u m . A t u b u l a r r e a c t o r w i t h h i g h heat t r a n s f e r c a p a b i l i t i e s i s r e q u i r e d t o c o n t r o l t h i s r e a c t i o n (12). The t r i e t h y l a l u m i n u m r e a c t i o n product i s d i v i d e d i n t o two streams. One stream, 70-75 percent o f /the t o t a l , i s r e c y c l e d d i r e c t l y t o the hydrogenation u n i t t o form a d d i t i o n a l d i e t h y l aluminum h y d r i d e . The other stream, 25-30 percent o f the t o t a l , i s the a c t u a l product stream. I t i s f i r s t c e n t r i f u g e d t o remove the b u l k o f unreacted aluminum which i s r e c y c l e d t o the hydrogena t i o n r e a c t o r along w i t h r e c y c l e t r i e t h y l a l u m i n u m . Product
MONOHYDRIC ALCOHOLS
94
t r i e t h y l a l u m i n u m and s o l v e n t a r e then d i s t i l l e d from unreacted aluminum f i n e s t o produce h i g h p u r i t y t r i e t h y l a l u m i n u m . The next step i n the ALFOL a l c o h o l process i s c h a i n growth. Triethylaluminum i s preheated t o 115°C i n the f i r s t tubes o f the growth r e a c t o r before ethylene i s added. Ethylene i s i n j e c t e d a t s e v e r a l p o i n t s along the l e n g t h o f the r e a c t o r to provide make-up ethylene as w e l l as t o help c o n t r o l the r e a c t i o n temperature. Temperature c o n t r o l o f t h i s h i g h l y exothermic growth r e a c t i o n i s d i f f i c u l t and a s p e c i a l r e a c t o r design has been p e r f e c t e d t o o b t a i n good heat t r a n s f e r . The growth r e a c t i o n i s c a r r i e d out below 130°C t o prevent the a l k y l decomposition o r thermal displacement (13) d e s c r i b e d earlier. Ethylene pressure i s maintained a t approximately 1600 psig. Temperature, p r e s s u r e , and residence time a r e adjusted to o b t a i n the d e s i r e d extent of c h a i n growth o r "m-value." Excess ethylene i s f l a s h e d from the t r i a l k y l a l u m i n u m product or "growth product" and r e c y c l e d . O x i d a t i o n o f the t r i a l k y l a l u m i n u m mixture i s c a r r i e d out u s i n g d r y a i r i n a g i t a t e d batch r e a c t o r s i n the ALFOL a l c o h o l process. Reactor temperature i s maintained a t approximately 35°C by c o o l i n g and the o x i d a t i o n i s operated a t about 50 p s i g . Approximately s i x hours i s r e q u i r e d f o r each batch o f growth product t o be completely o x i d i z e d . The o x i d a t i o n r e a c t o r s a r e operated i n staggered f a s h i o n t o minimize the maximum heat l o a d . The aluminum a l k o x i d e mixture o r " o x i d i z e d growth product" i s f e d t o a s e r i e s o f vacuum f l a s h evaporators t o remove s o l v e n t introduced e a r l i e r i n the t r i e t h y l a l u m i n u m p r e p a r a t i o n . This vacuum s t r i p p i n g step a l s o removes o l e f i n s formed d u r i n g the growth r e a c t i o n and the myriad of by-products formed d u r i n g o x i d a t i o n (14)• E f f i c i e n c y o f t h i s s t r i p p i n g process i s a key f a c t o r i n a l c o h o l product q u a l i t y . This i s the o p p o r t u n i t y to separate v o l a t i l e i m p u r i t i e s — o l e f i n s , e s t e r s , aldehydes, p a r a f f i n s , e t c . — f r o m product a l c o h o l s w h i l e the a l c o h o l s a r e i n a n o n v o l a t i l e form (aluminum a l k o x i d e s ) . S t r i p p e d a l k o x i d e s a r e then sent t o the h y d r o l y s i s r e a c t o r . In the c u r r e n t ALFOL a l c o h o l process, h y d r o l y s i s i s accomp l i s h e d u s i n g water i n s t e a d o f d i l u t e s u l f u r i c a c i d which r e s u l t s i n a mixture o f a l c o h o l s and alumina s l u r r y being formed i n the h y d r o l y s i s r e a c t o r . This mixture i s phase separated. A l c o h o l s a r e d r i e d and sent t o a d i s t i l l a t i o n t r a i n where they a r e separated by c o n v e n t i o n a l f r a c t i o n a l distillation. Crude a l c o h o l s a r e separated i n t o C -C , C - C , C - C C C , and C + f r a c t i o n s . High p u r i t y , i n d i v i d u a l homologs a r e prepared by r e d i s t i l l a t i o n o f the a p p r o p r i a t e mixture. The product a l c o h o l s a r e marketed as ALFOL a l c o h o l s by Conoco Chemicals. The alumina s l u r r y i s d r i e d and then c a l c i n e d t o form a very a c t i v e , high p u r i t y alumina which i s marketed by Conoco Chemicals as CATAPAL alumina. Because o f t h i s unique process of manufacturing the alumina, i t has a very low sodium content 2
1 8
20
%
6
10
1 2
U j
1 6
7.
WASHECHECK
Higher Straight-Chain Alcohols
95
and almost no other t r a c e metals a r e present. The alumina i s i n high demand as a c a t a l y s t support s i n c e i t i s n e a r l y f r e e o f contaminants which can a l t e r the performance o f a catalyst. A c a t a l y s t manufacturer can a t t a c h only the metals he wishes to a t t a c h and be assured o f t h e i r e f f e c t s . E t h y l Modified L i n e a r A l c o h o l Process
(15)
E t h y l ' s v e r s i o n o f the Z i e g l e r a l c o h o l process has been modified i n order t o c o n t r o l the product a l c o h o l d i s t r i b u t i o n . Whereas the Conoco ALFOL a l c o h o l process a f f o r d s the f u l l range o f a l c o h o l s , C -C o , i n a Poisson d i s t r i b u t i o n , E t h y l ' s product d i s t r i b u t i o n can be m o d i f i e d , f o r example, as shown i n F i g u r e 3 t o give carbon number d i s t r i b u t i o n s t o f i t the needs o f the market. 2
3
Table I I T y p i c a l Homolog D i s t r i b u t i o n s
Carbon Homolog
Conoco ALFOL Process
2
0.5
4 6 8 10 12 14 16 18 20 22
3-4 9.5 16.1 19-5 I8.4 14.1 9.1 5.1 2.5 1.1
Ethyl EPAL Process Trace 0.1 1-5 3-5 8.0 34.0 26.0 16.0 8.8 1-9 0.2
The f o l l o w i n g d i s c u s s i o n i s based on an i n t e r p r e t a t i o n of patent l i t e r a t u r e . The E t h y l process c o n s i s t s o f f i v e b a s i c steps i n s t e a d o f f o u r . 1. Preparation of triethylaluminum. 2. Growth o f ethylene t o higher alkylaluminum compounds. 3. T r a n s a l k y l a t i o n and separation o f t r i a l k y l a l u m i n u m compounds. 4O x i d a t i o n of aluminum a l k o x i d e s . 5. H y d r o l y s i s t o product a l c o h o l . Since the Conoco ALFOL a l c o h o l process has already been described i n d e t a i l , only those areas where the two processes are d i f f e r e n t w i l l be covered. Preparation of triethylaluminum appears s i m i l a r i n both processes. E t h y l ' s scheme i s b e l i e v e d to use a b a l l m i l l i n g procedure t o o b t a i n an a c t i v e aluminum
MONOHYDRIC ALCOHOLS
l
1
1
5
1
3
1
1
r
Ethyl EMl ' Alcihils (Example)
\
Figure 3.
c
4
Alcohol distribution
~ Cm
Split
1 »
AIR
Partial Oxiiitiii
«
( 5 5 * C , 5 0 PSIGI
AIR
Al2(S0 >3 4
Fiiil Oxliitlii
(65 * C , 50 PSIG)
Figure 4.
Ethyl process (based on patent literature)
WASHECHECK
7.
Higher Straight-Chain Alcohols
97
powder but the chemistry i s i d e n t i c a l . The E t h y l process, a f t e r triethylaluminum p r e p a r a t i o n , i s shown i n Figure 4E t h y l patents (16) i n d i c a t e two growth r e a c t o r s , two t r a n s a l k y l a t i o n r e a c t o r s , and two o l e f i n s t i l l s are used to accomplish the d e s i r e d a l c o h o l peaking process. In the f i r s t growth r e a c t o r , t r i e t h y l a l u m i n u m i s grown with ethylene as i n the ALFOL a l c o h o l process. However, the E t h y l growth process i s extended to a lower "m-value" (3 v s . 4) and i s c a r r i e d out at higher temperature (130° -150 C) and pressure (2000-2500 p s i g ) . Exact r e a c t i o n c o n d i t i o n s w i l l be determined by the "m-value" or a l c o h o l d i s t r i b u t i n d e s i r e d as w e l l as the r e l a t i v e q u a n t i t y of t r i a l k y l a l u m i n u m and o l e f i n s one wishes to produce (17)« The higher growth temperature used i n the E t h y l process w i l l produce a s i g n i f i c a n t q u a n t i t y of lower molecular weight a - o l e f i n s v i a thermal displacement. These o l e f i n s are used to a l t e r the product d i s t r i b u t i o n of the aluminum a l k y l s and thus the a l c o h o l s . A f t e r growth, excess ethylene i s removed i n a f l a s h drum and r e c y c l e d . The f i r s t growth product and i t s contained low molecular weight a - o l e f i n s are reacted w i t h a l a r g e excess of a - o l e f i n s (C -C 1 ) i n a t r a n s a l k y l a t i o n r e a c t o r . This r e a c t o r i s a vent u r i - t y p e r e a c t o r (18) o p e r a t i n g at 275°-300°C, 500 p s i g , and a short residence time of about 0.5 seconds. Heat i s s u p p l i e d to the r e a c t o r by super heating the l a r g e a - o l e f i n stream. Immediate quenching of t h i s product to about 120 C i s r e q u i r e d to suppress undesirable s i d e r e a c t i o n s , such as d i m e r i z a t i o n and i s o m e r i z a t i o n of the a - o l e f i n s . The t r i a l k y l a l u m i n u m compounds l e a v i n g t h i s t r a n s a l k y l a t i o n r e a c t o r now c o n t a i n p r i m a r i l y C«,-C a l k y l groups simply by the law of mass a c t i o n . The low molecular weight o l e f i n s are separated from the t r i a l k y l a l u m i n u m compounds by d i s t i l l a t i o n (19). This i s a s p e c i a l l y designed f l a s h u n i t which cont a i n s p r o v i s i o n s f o r scrubbing the overhead o l e f i n vapors w i t h p a r t i a l l y (2/3) o x i d i z e d alkylaluminum d i a l k o x i d e to remove any t r i a l k y l a l u m i n u m c a r r i e d overhead (20). o
H
0
10
RA1(0R)
2
+ R A1 S
> 2R A1(0R) 2
Scrubbing p r o v i s i o n s of t h i s u n i t are not shown i n F i g u r e 4 for s i m p l i c i t y . Low molecular weight a - o l e f i n s are sent to o l e f i n f r a c t i o n a t i o n , and the low molecular weight t r i a l k y l aluminum compounds and high molecular weight o l e f i n s are sent to a second growth r e a c t o r . Reaction c o n d i t i o n s i n the second growth r e a c t o r are s i m i l a r to those i n the f i r s t . Only a l i m i t e d arount of chain growth occurs i n t h i s r e a c t o r such t h a t the &» -C trialkylaluminum compounds are grown to about C, - C trialkylaluminum compounds. Again excess ethylene i s removed i n a f l a s h drum and r e c y c l e d . This second growth product i s fed to a second t r a n s a l k y l x
H
0
MONOHYDRIC ALCOHOLS
98
a t i o n r e a c t o r along w i t h a C -C a - o l e f i n stream. Again, an E t h y l patent (21) i n d i c a t e s t h i s i s a countercurrent r e a c t o r i n which the t r i a l k y l a l u m i n u m compounds a r e contacted w i t h vapor phase a - o l e f i n s . The countercurrent design o f t h i s r e a c tor permits the use of only a s l i g h t excess of detergent-range C -C i8 a - o l e f i n s i n s t e a d of the l a r g e excess r e q u i r e d by the c o c u r r e n t , v e n t u r i - t y p e r e a c t o r . Reaction c o n d i t i o n s are about 200 C and near atmospheric pressure ( 2 - 5 p s i g ) . Products e x i t ing t h i s r e a c t o r a r e t r i a l k y l a l u m i n u m compounds w i t h p r i m a r i l y C -C a l k y l groups and a f u l l range o f a - o l e f i n s , C,-C . A s l i p - s t r e a m (1/5 t o 1/3) of the second growth product can be sent t o the f i r s t t r a n s a l k y l a t i o n r e a c t o r r a t h e r than the second. This procedure i s r e q u i r e d i n order t o balance t h i s growth scheme. Vapor-phase o l e f i n s from the second t r a n s a l k y l a t i o n r e a c tor are scrubbed as before w i t h alkylaluminum d i a l k o x i d e t o remove any t r i a l k y l a l u m i n u m compounds and then sent t o o l e f i n distillation. Detergent-range t r i a l k y l a l u m i n u m compounds and high molecular weight o l e f i n s a r e blended w i t h s u f f i c i e n t part i a l l y (2/3) o x i d i z e d growth product t o convert the e n t i r e mixture t o a blend having a t l e a s t one a l k o x i d e group per a l u m i num atom. This r e a c t i o n i s r a p i d and does not r e q u i r e a separ a t e v e s s e l , but can take place i n the t r a n s f e r l i n e s . Convers i o n t o monoalkoxide renders the aluminum compounds l e s s v o l a tile. High molecular weight o l e f i n s a r e then separated from the p a r t i a l l y ( l / 3 ) o x i d i z e d growth product v i a a s p e c i a l f l a s h u n i t s i m i l a r t o the one d e s c r i b e d e a r l i e r (20) and sent t o olefin distillation. The p a r t i a l l y ( l / 3 ) o x i d i z e d growth product i s sent t o an o x i d a t i o n u n i t where i t i s o x i d i z e d w i t h d r y a i r t o an average of two a l k o x i d e groups per aluminum atom (2/3 o x i d i z e d ) . 1 2
1 8
1 2
1 2
1 8
30
R A1(0R) + 0 2
2
> RA1(0R)
2
This p a r t i a l o x i d a t i o n r e a c t o r i s b e l i e v e d t o operate a t about 55°C. The p a r t i a l l y (2/3) o x i d i z e d m a t e r i a l i s used as feed for the three scrubbers d e s c r i b e d above and f o r exchanging w i t h u n o x i d i z e d growth product t o form a l / 3 o x i d i z e d product. The major use f o r the 2/3 o x i d i z e d growth product i s as feed to the f i n a l o x i d a t i o n r e a c t o r . The f i n a l o x i d a t i o n i s a batch process as i n the ALFOL a l c o h o l process. A hydrocarbon s o l v e n t f o r v i s c o s i t y c o n t r o l must be added p r i o r t o o x i d a t i o n s i n c e none was introduced earlier. Based on patent l i t e r a t u r e ( 2 2 ) , o x i d a t i o n w i t h d r y a i r takes place i n an a g i t a t e d r e a c t o r a t approximately 65 C and 50 p s i g i n the presence of a t i t a n i u m promoter which improves the o x i d a t i o n s e l e c t i v i t y . The product aluminum t r i a l k o x i d e s are then s t r i p p e d i n a f l a s h evaporator t o remove s o l v e n t and o x i d a t i o n by-products described e a r l i e r . The l i g h t hydrocarbon s o l v e n t i s separated
7.
WASHECHECK
Higher Straight-Chain Alcohols
99
from these by-products v i a d i s t i l l a t i o n and r e c y c l e d t o the oxidation reactor. The aluminum t r i a l k o x i d e s are then hydrolyzed w i t h d i l u t e s u l f u r i c a c i d i n the E t h y l process (23). This forms f r e e a l c o h o l and an aqueous aluminum s u l f a t e s o l u t i o n which a r e separated by phase s p l i t . The aqueous aluminum s u l f a t e i s s o l d . Product a l c o h o l s are washed with c a u s t i c t o remove t r a c e s o f a c i d , d r i e d , and f e d t o conventional d i s t i l l a t i o n t r a i n . The product a l c o h o l s a r e s o l d by E t h y l under the trade name o f EPAL a l c o h o l s . The E t h y l EPAL process i s more complex than the Conoco ALFOL a l c o h o l process. This complexity permits the f l e x i b i l i t y o f producing both a - o l e f i n s and a l c o h o l s from the same processing u n i t as w e l l as having considerable c o n t r o l over the product homolog d i s t r i b u t i o n s . P e n a l t i e s paid f o r t h i s f l e x i b i l i t y are increased c a p i t a l cost f o r a more complex process and production of some branched a l c o h o l s .
100
MONOHYDRIC ALCOHOLS
Literature Cited 1. Weast, R. C., editor, "Handbook of Chemistry and Physics," 51st Edition, The Chemical Rubber Company, Cleveland, OH, 1970, p. D-174. 2. Peters, R. A. "Kirk-Othmer Encyclopedia of Chemical Technology," 3rd Edition, Volume 1, John Wiley & Sons, NY, 1978, p. 716. 3. Monick, J . A. J . Amer. Oil Chemists Soc., 1979, 56 (11), 853A. 4. Ziegler, K. "Organometallic Chemistry," ACS Monograph No. 147, Van Nostrand, NY, I960, p. 194. 5. Radd, F. J . and Woods, W. W. (to Conoco Inc.), U.S. 3,104,252 (1963). 6. Ziegler, K.; Gellert, H.; Zosel, K.; Holzkamp, E.; Schneider, J . ; Soli, M.; and Kroll, W. Annalen, 1960, 629, 121. 6a. Weslau, H. Ibid, 198-206. 7. Allen, P. E.; Jones, G. R.; and Robb, J . C. Trans Faraday Soc., 1963, 63, 1936. 8. Gautreaux, M. F.; Davis, W. T.; and Travis, E. D. "KirkOthmer Encyclopedia of Chemical Technology," 3rd Edition, Volume 1, John Wiley & Sons, New York, 1978, p. 740. 9. Motz, K. L. and Lundeen, A. J . (to Conoco Inc.), U.S. 3,657,301 (1972). 10. Carter, W. B. (to Conoco Inc.), U.S. 3,264,063 (1966). 11. Lundeen, A. J . and Poe, R. L. "Encyclopedia of Chemical Processing and Design," 1974. 12. Lobo, P. A. (to Conoco Inc.), U.S. 2,971,969 (1961). 13. Lobo, P. A.; Coldiron, D. C.; Vernon, L. N.; and Ashton, A. T. Chemical Engineering Progress, 1962, 58 (5), 85. 14. Foster, V. and Acciarri, J . (to Conoco Inc.), U.S. 3,104,251 (1963). 15. Davis, W. T. (to Ethyl Corp.), U.S. 3,487,097 (1969). 16. Davis, W. T. (to Ethyl Corp.), U.S. 3,384,651 (1968). 17. Davis, W. T. and Kingrea, C. L. (to Ethyl Corp.), U.S. 3,415,861 (1968). 18. Davis, W. T. (to Ethyl Corp.), U.S. 3,345,476 (1969). 19. Gautreaux, M. F. (to Ethyl Corp.), U.S. 3,412,126 (1968). 20. Presswood, J . K. and Foster, W. E. (to Ethyl Corp.), U.S. 3,400,170 (1968). 21. Kottong, G. W. and Ritter, O. A. (to Ethyl Corp.), U.S. 3,389,161 (1968). 22. Cragg, H. J . and Nolen, D. A. (to Ethyl Corp.), U.S. 30,475,476 (1969). 23. Guzick, N. D. and McCarthy, J . H. (to Ethyl Corp.), U.S. 3,475,501 (1969). RECEIVED
M a r c h 2, 1981.
