Extractive and Azeotropic Distillation - ACS Publications

7 Demulsification of Crude Oils Use of Azeotropic

Distillation

LESLIE L. BALASSA and DONALD F. OTHMER

Downloaded by UNIV OF LEEDS on May 21, 2015 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1972-0115.ch007

Slate Hill, Ν. Y. 10973 and Polytechnic Institute, Brooklyn, Ν. Y. 11201

Water and often fine sand and silt are held in various crude oils in permanent emulsions. Particularly crudes obtained by secondary methods and those from tar sands where water or steam are used contain water and mineral matter emulsified therein by the surface forces on small particles and drops. Azeotropic distillation removes the relatively small amount of water, using the solvent as an entrainer which dilutes the crude. This allows: the mineral matter to be separated easily without using centrifuges with their substantial cost and wear, free of organic material, so it may be discarded with out hazards of fire or odors; the bitumen to be recovered for such use or cracked to give volatile fractions and coked to an ash-free coke; the water to be obtained as distilled water for reuse.

" p e t r o l e u m crudes p r o d u c e d b y w a t e r

flooding,

hot water displacement,

pressure steam, or steam i n j e c t i o n u s u a l l y are e m u l s i o n s , either w a t e r i n - o i l o r o i l - i n - w a t e r , a n d are f r e q u e n t l y a c o m b i n a t i o n o f b o t h . E m u l s i o n s of these h i g h v i s c o s i t y oils often c a n n o t b e b r o k e n a n d d e h y d r a t e d b y conventional methods. A n e v e n m o r e difficult p r o c e s s i n g c o n d i t i o n arises w i t h h e a v y b i t u m i n o u s oils w h i c h a l w a y s c a r r y m u c h sand, c l a y , a n d silt of coarse a n d s m a l l p a r t i c l e sizes w h i c h s t a b i l i z e the oil—water e m u l s i o n s e v e n m o r e . T h e b i t u m i n o u s oils h a v e specific gravities of 0.9-1.4 a n d h a v e h i g h viscosi ties; thus t h e y c a n n o t b e separated f r o m the w a t e r or solids present b y s e t t l i n g or b y u s i n g the most efficient centrifuges. D i l u t i n g these e m u l s i o n s o f h e a v y oils w i t h l i g h t

solvents—e.g.,

kerosene, solvent n a p h t h a , b e n z e n e , etc.—reduces the specific g r a v i t y of the o i l phase of the e m u l s i o n s b e l o w t h a t of w a t e r a n d l o w e r s the v i s 108

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

7.

B A L A S S A

A N D

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of Crude

109

Oils

cosity so that some of the w a t e r a n d m i n e r a l matters u s u a l l y c a n b e r e m o v e d b y s e d i m e n t a t i o n , centrifuge, or h y d r o - c y c l o n e . A d d i t i o n of a l o w viscosity h y d r o c a r b o n solvent often extracts t h e o i l f r o m the w a t e r ; t h e extract l a y e r of solvent a n d solute separates f r o m the water. T h e large a m o u n t of solvent n e e d e d to separate e m u l s i o n s of w a t e r i n a viscous h e a v y o i l is u n e c o n o m i c because of t h e d i l u t e s o l u t i o n n e e d e d to o b t a i n a c o n t i n u o u s w a t e r phase. A d d i t i o n of solvent, p o s s i b l y u p to a n e q u a l a m o u n t , is reasonable a n d is d e s i r a b l e to r e d u c e t h e v i s c o s i t y suffic i e n t l y to p u m p a n d transport the h e a v y o i l . A c h e a p a l i p h a t i c s o l v e n t — e.g., k e r o s e n e — i s preferable, b u t b i t u m i n o u s o i l fractions are m u c h m o r e


s o l u b l e i n a r o m a t i c solvents, p a r t i c u l a r l y at temperatures near t h e a m bient. H o w e v e r , the w a t e r a n d s o l i d particles are not at a c c e p t a b l e l i m i t s e v e n after m u c h d i l u t i o n , e s p e c i a l l y i n the presence of fine p a r t i c l e s as i n some crudes f r o m C a l i f o r n i a a n d V e n e z u e l a a n d p a r t i c u l a r l y f r o m t a r sands as those i n A t h a b a s c a ( A l b e r t a , C a n a d a ) . P r o c e s s i n g o i l emulsions f r o m t a r sands is difficult w i t h t h e o i l a n d the aqueous phase. T h e o i l phase carries m u c h c l a y a n d silt ( s a n d ) of s m a l l p a r t i c l e size w h i c h are s u s p e n d e d a n d d o not settle o u t e v e n o n p r o l o n g e d storage.

T h e surface or m o l e c u l a r forces b e t w e e n viscous oils a n d s u c h

fine p a r t i c l e s are m o r e i m p o r t a n t i n d e t e r m i n i n g t h e latter's m o t i o n s , or l a c k of m o t i o n , t h a n t h e m e c h a n i c a l forces r e s u l t i n g f r o m differences i n specific gravity. S o m e particles i n the a q u e o u s phase are w e t b y o i l i n s t e a d of

by

water, a n d these o i l - c o a t e d p a r t i c l e s g i v e a n u n u s u a l l y stable s u s p e n s i o n for a b o u t the same reason. T h i s o i l i n t h e oil-wet m i n e r a l matter, susp e n d e d i n t h e aqueous phase, makes it u n s u i t a b l e for r e c y c l i n g i n t h e p r o c e s s i n g o p e r a t i o n or d i s c h a r g i n g b a c k i n t o surface waters.

Also, the

m i n e r a l sludge w h i c h is separated f r o m w a t e r s t i l l contains a s u b s t a n t i a l percentage of o i l ; it c a n n o t b e d i s p o s e d of e v e n b y r e t u r n i n g i t t o t h e p l a c e w h e r e it w a s m i n e d or p r o d u c e d . F i r e s h a v e o c c u r r e d f r o m s p o n taneous c o m b u s t i o n r e s u l t i n g f r o m this s l u d g e of fine p a r t i c l e s a n d o i l . P r i o r processes p r o p o s e d to d e m u l s i f y it are unsatisfactory because so m u c h o i l is a l w a y s lost i n the aqueous p h a s e o r i n t h e d e w a t e r e d sludge. A l s o , the content of w a t e r a n d m i n e r a l s i n the o i l separated b y c o n v e n t i o n a l processes is u s u a l l y a b o v e a c c e p t a b l e l i m i t s for p i p e l i n e t r a n s p o r t a t i o n or for r e f i n i n g purposes. F i n a n c i a l losses are e x p e r i e n c e d i n o i l w a s t e d , i n e q u i p m e n t a n d c a p i t a l charges of w o r n e q u i p m e n t i n plants, a n d i n l a n d v a l u e of d i s p o s a l p o n d s . T r e m e n d o u s d i s p o s a l p o n d s of d i s c a r d e d emulsions i n V e n e z u e l a a n d elsewhere

take u p available land.

I n separating emulsions from

tar sands, the extremely abrasive silt has r u i n e d expensive

centrifuges

a n d makes u s i n g t h e m i m p r a c t i c a l .


110

E X T R A C T I V E

Azeotropic

A N D A Z E O T R O P I C

DISTILLATION

Distillation

T h e w a t e r content of a n e m u l s i o n is r e m o v e d b y d i s t i l l a t i o n , h o w e v e r , d i r e c t a n d s i m p l e d i s t i l l a t i o n presents several p r a c t i c a l p r o b l e m s .

I n the

presence of a s o l v e n t - d i l u e n t after p r e l i m i n a r y s e p a r a t i o n of m u c h of the water

as a c o n t i n u o u s phase, the b a l a n c e is r e m o v e d

by

azeotropic

distillation. F o r m a n y years w a t e r has b e e n separated f r o m m a n y l i q u i d s b y a z e o t r o p i c d i s t i l l a t i o n . W a t e r is s u b s t a n t i a l l y i n s o l u b l e n o t o n l y i n the oils b u t also i n the d i l u e n t s o r solvents. T h u s , the v a p o r pressures of t h e w a t e r a n d d i l u e n t are a d d i t i v e as i n t h e f a m i l i a r steam d i s t i l l a t i o n s . A Downloaded by UNIV OF LEEDS on May 21, 2015 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1972-0115.ch007

heterogeneous

azeotrope is f o r m e d ; this a l w a y s b o i l s b e l o w t h e b o i l i n g

p o i n t of w a t e r because pressure m u s t b e r e d u c e d f o r w a t e r t o b o i l at t h e v a p o r pressure of t h e h y d r o c a r b o n . T h e p r i n c i p l e s of a z e o t r o p i c d i s t i l l a t i o n h a v e often b e e n (1,2,3,4,5,6,7),

described

a n d a p p l y i n g t h e m gives a s i m p l e m e t h o d of s e p a r a t i n g

w a t e r f r o m its o i l emulsions. T h e l o w - b o i l i n g constituents of a n o i l — o r the d i l u e n t u s e d — w o u l d b e t h e entraîner ( w i t h d r a w i n g a g e n t ) w h i c h forms t h e heterogeneous

azeotrope or steam d i s t i l l a t i o n w i t h t h e water.

B e c a u s e of n o n e q u i l i b r i u m b o i l i n g c o n d i t i o n s i n a s i m p l e d i s t i l l a t i o n , the vapors m a y n o t c o n t a i n t h e t r u e azeotrope, a n d t h e heat cost m a y b e too h i g h . T h e r e f o r e a c o l u m n is s t i l l u s e d to r e c t i f y the exact azeotrope at t h e h e a d of the c o l u m n ; h o w e v e r , o n l y a f e w trays are r e q u i r e d . T h e azeotrope contains t h e l o w e r h y d r o c a r b o n s of t h e d i l u e n t . I f a w i d e - c u t f r a c t i o n is u s e d , t h e m o r e v o l a t i l e ones c o m e to t h e t o p of t h e c o l u m n w i t h the water. A t a n y t e m p e r a t u r e t h e v a p o r pressure of w a t e r p l u s that o f t h e entraîner, o r t h e effective v a p o r pressure of the m i x t u r e of l i q u i d s o p e r a t i n g as t h e entraîner, gives t h e azeotrope's v a p o r pressure. T h e t e m p e r a t u r e w h e r e this s u m m a t i o n c u r v e crosses the a t m o s p h e r i c l i n e , o r other o p e r a t i n g pressure of t h e d i s t i l l a t i o n , is t h e a z e o t r o p i c point.

boiling

A close-cut f r a c t i o n o r a single m o r e or less p u r e c o m p o u n d as

a d i l u e n t a n d a z e o t r o p i c w i t h d r a w i n g agent is preferable, a l t h o u g h n o t necessary.

I f the m i x t u r e loses some o f its m o r e v o l a t i l e

components

at t h e h e a d of the c o l u m n o v e r a p e r i o d of t i m e , t h e a z e o t r o p i c b o i l i n g p o i n t w i l l g r a d u a l l y rise. T h e condensate has t w o l i q u i d phases. It r u n s f r o m t h e condenser to a separator o r decanter w h e r e the w a t e r layer is r e m o v e d f o r d i s c a r d a n d t h e solvent layer is r e t u r n e d , u s u a l l y as reflux to t h e c o l u m n . T h i s reflux of " a l l o r p a r t " ( t h e solvent l a y e r ) of the condensate after décantation, r a t h e r t h a n " p a r t of a l l , " w a s d e v e l o p e d i n 1927 (2)

f o r acetic a c i d d e h y -

d r a t i o n w i t h a n a d d e d solvent as entraîner a n d for b u t a n o l d e h y d r a t i o n u s i n g b u t a n o l itself as t h e entraîner.


7.

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Oils

S e p a r a t i n g w a t e r f r o m a n o i l e m u l s i o n is best d o n e b y a n entraîner a d d e d as a d i l u e n t to the o i l . F o r example, the d i l u e n t a d d e d to t h e o i l e m u l s i o n is a n a p h t h a f r a c t i o n h a v i n g a n effective v a p o r pressure e q u a l to that of octane. T h i s n a p h t h a is a d d e d to the o i l , a n d as m u c h w a t e r as possible is separated; the o i l e m u l s i o n layer w h i c h is n o t b r o k e n contains


the a d d e d n a p h t h a .

OIL, SILT β DILUENT OUT Figure 1. Flow sheet for removing emulsified water from crude oil and diluent using azeotropic distilfotion with fixed amount of entraîner

F i g u r e 1 i n d i c a t e s one o p e r a b l e

flow

sheet w h e n this o i l e m u l s i o n

c o n t a i n i n g the n a p h t h a w i l l h a v e a sufficiently l o w v i s c o s i t y to b e p u m p e d t h r o u g h a t u b u l a r condenser a n d t h e n t h r o u g h a t u b u l a r bottoms

cooler

for heat i n t e r c h a n g i n g a n d r e c o v e r y . It is t h e n p u m p e d to a n u p p e r p l a t e of a c o l u m n s t i l l . T h i s m i g h t h a v e 1 0 - 1 5 trays d e s i g n e d to a l l o w

ready

passage d o w n w a r d of a n y silt. T h e c o l u m n is thus self-cleaning as m u c h as possible, b u t p r o v i s i o n s are also m a d e for o p e n i n g to c l e a n m e c h a n i c a l l y , i f necessary. T a b l e I gives several azeotropes o f w a t e r w i t h h y d r o c a r b o n s

and

b u t a n o l , u s e d as entrainers. A s s u m i n g t h e entraîner—diluent has the p r o p -


112

e x t r a c t i v e

Table I.


a z e o t r o p i c

d i s t i l l a t i o n

Azeotropes of Water and Entrainers Composition by Weight

Temperature, °C (1 atm) Boiling Point Compound

a n d

Azeo. Temp.

Azeo. Vapors

%

Upper Layers

Lower Layers

Separated Layers

Volume,

%

Toluene Water

110.6 100

85

79.8 20.2

99.9 0.1

0.1 99.9

82 18

Up Low

m-Xylene Water

139.1 100

94.5

60 40

99.95 0.05

0.05 99.95

63.4 36.6

Up Low

n-Octane Water

125.7 100

89.6

74.5 25.5

99.98 0.02

0.02 99.98

80 20

Up Low

Butanol Water

117.7 100

93

55.5 45.5

77.5 22.5

8.0 92.0

71.5 28.5

Up Low

erties of o c t a n e , the c o l u m n has a t o p v a p o r t e m p e r a t u r e of 89.6 ° C . T h e s e v a p o r s are c o n d e n s e d i n p r e h e a t i n g the f e e d a n d i n another w a t e r c o o l e d condenser i f n e e d e d .

T h e condensate flows to a decanter w h i c h

c o n t i n u o u s l y separates 8 0 %

b y v o l u m e as the d i l u e n t - e n t r a i n e r l a y e r

a n d 2 0 % b y v o l u m e of a w a t e r layer. T h e a m o u n t of e a c h c o m p o n e n t d i s s o l v e d i n the other layer is so s m a l l that it is d i s r e g a r d e d ; t h u s the w a t e r l a y e r flows to waste. T h e entraîner l a y e r is r e t u r n e d to the t o p of t h e c o l u m n as reflux to w i t h d r a w m o r e w a t e r , a n d the d r y o i l w i t h sedim e n t passes o u t the b o t t o m a n d t h r o u g h a bottoms exchanger.

T h e silt

n o w settles a n d separates r e l a t i v e l y easily f r o m the o i l w h i c h is d e c a n t e d . T h e silt is w a s h e d w i t h t h e s o l v e n t - d i l u e n t w h i c h is t h e n r e u s e d w i t h a f o l l o w i n g o i l e m u l s i o n a n d t h e n s t e a m e d to recover the n a p h t h a . I n this flow sheet the solvent-diluent—entraîner passes t h r o u g h t h e system a n d o u t w i t h t h e o i l f o r t r a n s p o r t o r r e f i n i n g — a first step w h i c h m a y r e c o v e r n a p h t h a for reuse. H o w e v e r , i n the c y c l e at the h e a d of the a z e o t r o p i c c o l u m n w i t h t h e condenser a n d the decanter, f r a c t i o n a t i n g l i g h t - e n d s f r o m the n a p h t h a p a s s i n g t h r o u g h w i t h the o i l occurs to g i v e the a z e o t r o p e w i t h w a t e r w h i c h has a c o m p o s i t i o n d e p e n d i n g o n the effective v a p o r p r e s s u r e of the m i x t u r e of h y d r o c a r b o n s w h i c h stabilizes t h e r e as t i m e passes. T h i s m a y h a v e a c o n s i d e r a b l y l o w e r b o i l i n g p o i n t t h a n the n a p h t h a f r a c t i o n , a n d the light-ends congregate a n d b e c o m e the entraîner. S o m e of this m a y b e r e m o v e d f r o m the system b y w i t h d r a w i n g f r o m the reflux s t r e a m to the c o l u m n . If there are so m a n y l o w ends that the azeot r o p i c b o i l i n g p o i n t goes d o w n , a n a p h t h a f r a c t i o n of s o m e w h a t h i g h e r b o i l i n g r a n g e is u s e d as the d i l u e n t . A c t u a l l y this i n d i c a t e s a n o p e r a t i o n c o m p a r a b l e w i t h the d e h y d r a t i o n of m a n y other l i q u i d s w i t h a separate entraîner. T h u s , i f no d i l u e n t


7

ΒA L A S SA

A N D

O T H M E R

Demulsification

of Crude

113

Oils

is necessary to r e d u c e t h e v i s c o s i t y of t h e o i l so that i t m a y b e h a n d l e d a n d n o d i l u e n t is u s e d to g i v e a p r e v i o u s p a r t i a l d e m u l s i f i c a t i o n , e n o u g h entraîner c o u l d b e selected a n d s u p p l i e d to t h e a z e o t r o p i c system t o charge the u p p e r p a r t o f the c o l u m n , t h e condenser, decanter, a n d c o n nections. T h e a d d e d entraîner w o u l d t h e n w i t h d r a w w a t e r f r o m t h e o i l e m u l s i o n f e d i n t o a n d o u t of t h e c o l u m n , a n d t h e entraîner w o u l d t h e n act l i k e a m e c h a n i c a l p a r t of t h e system. T a b l e I shows that, as t h e b o i l i n g p o i n t of the h y d r o c a r b o n u s e d as t h e entraîner increases so does that of t h e azeotrope w i t h w a t e r a n d t h e p e r c e n t of w a t e r t h e r e i n . A h i g h percentage

of w a t e r i n t h e a z e o t r o p e


is d e s i r e d for the heat r e q u i r e d for t h e d i s t i l l a t i o n , w h i c h is m a i n l y t h a t of t h e latent heat of t h e w a t e r p l u s that of t h e entraîner. Sufficient e n t r a i n e r s h o u l d b e a v a i l a b l e i n the azeotrope f o r reflux to t h e c o l u m n a l t h o u g h this r e q u i r e m e n t is n o t large.

A l s o , the s o l u b i l i t y o r d i l u t i o n

effect is better w i t h l o w e r - b o i l i n g h y d r o c a r b o n s .

T h u s t h e r e a r e several

factors to be b a l a n c e d i n c h o o s i n g t h e azeotrope.

T h e effect of r e l a t i v e

b o i l i n g points, v a p o r pressures, a n d amounts of different

entrainers i n

t h e i r azeotropes w i t h w a t e r has b e e n d i s c u s s e d as affecting the c h o i c e o f entrainers for s e p a r a t i n g w a t e r f r o m acetic a c i d ( 5 ) .

However,

that

represents a m u c h m o r e difficult selection because there t h e q u a n t i t y of reflux is i m p o r t a n t a n d also the solvent characteristics of the entraîner for t h e acetic a c i d also c o n t r o l t h e choice. However,

t h e o p t i m u m a z e o t r o p i c entraîner for w a t e r f r o m a n o i l

e m u l s i o n is p a r t i a l l y selected a c c o r d i n g to those p r i n c i p l e s . T h e highest b o i l i n g l i q u i d s o b v i o u s l y c a r r y m o r e w a t e r for a g i v e n heat i n p u t .

A

selected a n d stable t e m p e r a t u r e at t h e t o p of t h e azeo c o l u m n is necessary f o r o p t i m u m o p e r a t i o n , a n d this m i g h t seem to b e s e c u r e d best b y a pure aromatic.

A l t e r n a t e l y , a p u r e a l i p h a t i c or a close-cut n a p h t h a

f r a c t i o n m i g h t b e o b t a i n e d a n d m a i n t a i n e d i n the a z e o t r o p i c

column.

T h e use of a p u r e c o m p o u n d is n o t advantageous i f a close-cut n a p h t h a f r a c t i o n is u s e d as a n entraîner i n this c o n t i n u o u s o p e r a t i o n because t h e losses a n d m a k e - u p of s u c h entraîner i n a c o l u m n are so s m a l l ; thus, the effective a z e o t r o p i c b o i l i n g p o i n t r e m a i n s constant. T h e entraîner s h o u l d b e a h y d r o c a r b o n w h i c h has a l o w e r b o i l i n g p o i n t t h a n t h e light-ends, w h a t e v e r the feedstock of o i l e m u l s i o n ; otherw i s e l i g h t ends c o n t i n u a l l y fractionate i n t o the azeotrope a n d h a v e to b e removed.

I n other systems i n v o l v i n g a z e o t r o p i c w i t h d r a w i n g agents w i t h

a m i x t u r e of v a r i o u s volatilities, a stable entraîner is d e v e l o p e d a n d m a i n t a i n e d at t h e d e s i r e d b o i l i n g p o i n t b y r e m o v i n g p e r i o d i c a l l y some o f t h e entraîner to k e e p its effective b o i l i n g p o i n t sufficiently h i g h .

Sometimes

s m a l l heads c o l u m n s h a v e b e e n i n c o r p o r a t e d to d o this c o n t i n u o u s l y .


114

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Laboratory

AND

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DISTILLATION

Testing

H a v i n g c o n s i d e r e d a b a s i c flow sheet a n d the e l e m e n t a r y p r i n c i p l e s of a z e o t r o p i c d i s t i l l a t i o n as t h e y m a y b e u s e d , w e c o n s i d e r e d t e s t i n g emulsions i n the l a b o r a t o r y p r i o r to process design. T h e first step i n t e s t i n g t h e m a t e r i a l f o r s u i t a b i l i t y o f t h e d e m u l s i f y i n g , d e h y d r a t i n g process is to d i l u t e t h e c r u d e o i l w i t h a solvent w h i c h is u s e d b y itself or m i x e d w i t h another i n a z e o t r o p i c d e h y d r a t i o n of the emulsion.

T h e m i n i m u m a m o u n t of solvent w h i c h is sufficient for the

first step is t h a t w h i c h cuts t h e viscosity of the c r u d e e n o u g h to a l l o w a z e o t r o p i c d i s t i l l a t i o n w i t h o u t excessive f o a m i n g . T h i s m a y r e q u i r e a b o u t Downloaded by UNIV OF LEEDS on May 21, 2015 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1972-0115.ch007

4 0 - 6 0 v o l u m e s solvent p e r 100 v o l u m e s of c r u d e , b u t this r a t i o of solvent, h o w e v e r , m a y not b e sufficient to r e d u c e the g r a v i t y of the c r u d e b e l o w that of w a t e r to a l l o w p r e l i m i n a r y décantation of some of the w a t e r . T o a c h i e v e this, a v o l u m e of solvent a b o u t e q u a l to t h a t of the c r u d e m a y h a v e to b e u s e d (sometimes a n e v e n h i g h e r r a t i o of s o l v e n t ) .

By

d i l u t i n g the c r u d e first w i t h t o l u e n e u p to a v o l u m e of 2 0 % of the c r u d e a n d c o n t i n u i n g the d i l u t i o n w i t h a l i g h t gasoline f r a c t i o n i n the r a n g e of hexane, octane, or h i g h e r , the g r a v i t y is l o w e r e d w i t h less t o t a l solvent. A l s o d i l u t i o n w i t h a n a p h t h a f r a c t i o n a l o n e m a y suffice at 80 ° C .

Each

c r u d e has to b e separately e v a l u a t e d b a s e d o n its properties a n d w a t e r content. If the w a t e r i n the p e r m a n e n t e m u l s i o n is l o w , it m a y not b e w o r t h w h i l e to a d d sufficient solvent to separate a w a t e r layer. T h e w a t e r i n the c r u d e w h i c h is not i n a p e r m a n e n t e m u l s i o n is d e t e r m i n e d b y d i l u t i n g the c r u d e w i t h a m i x t u r e of toluene a n d a n a p h t h a f r a c t i o n ; m u c h of the w a t e r together w i t h the water-set i n o r g a n i c m a t t e r t h e n settles out i n a separatory f u n n e l . If a centrifuge is u s e d , the h i g h g r a v i t y oil-wet i n o r g a n i c m a t t e r separates w i t h the w a t e r c a r r y i n g w i t h i t a s u b s t a n t i a l a m o u n t of o i l . T h u s , s i m p l e g r a v i t y s e p a r a t i o n is preferable. T h e o i l d i l u t e d w i t h the solvent only m a y b e d i s t i l l e d i n a glass flask, fitted

w i t h a r e l a t i v e l y s i m p l e l a b o r a t o r y c o l u m n . B o i l i n g i n the flask is

a c c o m p l i s h e d w i t h o u t b u m p i n g i f a n i n t e r n a l electric heater w h i c h a l l o w s l i t t l e superheat is u s e d . T h e a z e o t r o p i c d i s t i l l a t i o n b r i n g s o v e r v a p o r s w h i c h are c o n d e n s e d . C o n d e n s a t e is separated i n a c o n t i n u o u s glass dec a n t e r w h i c h returns the h y d r o c a r b o n l a y e r to the c o l u m n a n d discharges the w a t e r layer. W h e n the w a t e r content of the s o l u t i o n is r e d u c e d to b e l o w 0 . 1 - 0 . 2 % , no w a t e r is v i s i b l e i n the condensate; the t e m p e r a t u r e at the h e a d of the c o l u m n rises to the b o i l i n g p o i n t of the entraîner itself, a n d the d e h y d r a t i o n is c o m p l e t e . T h e t o t a l w a t e r separated is m e a s u r e d . T h i s v o l u m e w i t h the w a t e r w h i c h has b e e n separated b y décantation after d i l u t i o n a n d before d i s t i l l a t i o n represents the o r i g i n a l a m o u n t of w a t e r present.


7.

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A N D

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115

B a t c h a z e o t r o p i c d i s t i l l a t i o n is also a c c o m p l i s h e d i n t h e l a b o r a t o r y w i t h a s i m p l e flask, condenser, a n d r e c e i v e r w i t h o u t a c o l u m n , c o n t i n u o u s decanter, a n d c o n t i n u o u s reflux, b u t i t takes m u c h l o n g e r a n d is n o t c o m p a r a b l e to a p l a n t o p e r a t i o n , w h i c h is d e v e l o p e d f r o m s u c h l a b o r a t o r y testing. T h e oil-wet s l u d g e is r e m o v e d f r o m t h e d e h y d r a t e d o i l s o l u t i o n i n the flask b y s e t t l i n g a n d d e c a n t i n g or c e n t r i f u g i n g . solvent to free i t of o i l , d r i e d , a n d w e i g h e d .

It is w a s h e d w i t h

T h e w a s h s o l u t i o n is c o m -

b i n e d w i t h the d e h y d r a t e d o i l s o l u t i o n w h i c h contains other solvent a n d the separate entraîner, i f o n e w a s u s e d . S o l v e n t is s t r i p p e d f r o m t h e s o l u -


t i o n b y d i s t i l l a t i o n to d e t e r m i n e t h e a v a i l a b l e o i l of the c r u d e w h i c h remains. A s m a l l a m o u n t of a d d i t i o n a l i n o r g a n i c m a t t e r m a y settle o u t of c r u d e after a f e w days storage. T h i s is a n extremely s m a l l p a r t i c l e size silt w h i c h is u s u a l l y less t h a n 0 . 0 5 % of t h e o i l . It m i g h t b e r e m o v e d b y a m o r e efficient, h i g h e r speed, centrifuge t h a n u s u a l l y a v a i l a b l e . H o w e v e r , s u c h h i g h s p e e d centrifuges m i g h t b e b a d l y a b r a d e d b y t h e fine silt a n d w o u l d b e too expensive to u s e i n a c t u a l p r a c t i c e . O n e o r t w o days s e t t l i n g at 120°C for example, is a better test m e t h o d a n d is a better p r a c t i c e i n p r o d u c t i o n i f the necessary storage facilities a r e a v a i l a b l e . A d d i t i v e s t o flocculate

the fine silt m i g h t also b e u s e d .

Modified Azeotropic

Distillation

C o n t i n u o u s d i s t i l l a t i o n a l w a y s gives a better, m o r e u n i f o r m p r o d u c t at a l o w e r heat cost a n d u s u a l l y a l o w e r p l a n t cost. A c o n t i n u o u s o p e r a t i o n is essential i n a z e o t r o p i c d i s t i l l a t i o n w h e n a n entraîner is a d d e d , o r it w o u l d necessarily h a v e to b e f r a c t i o n a t e d off to reuse i t after e a c h b a t c h . S e v e r a l v a r i a t i o n s of t h e flow sheet for a z e o t r o p i c d i s t i l l a t i o n are possible, e a c h h a v i n g a c o n t i n u o u s d e c a n t e r w h i c h discharges p u r e w a t e r (less t h a n 0 . 1 % d i s s o l v e d h y d r o c a r b o n o r a r o m a t i c s a n d less t h a n 0 . 0 1 % for a l i p h a t i c s ). F i g u r e 1 is the s i m p l e s t flow sheet. T h e entraîner selected is c h a r g e d to t h e a z e o t r o p i c c o l u m n a n d r e m a i n s s u b s t a n t i a l l y there, rem o v i n g w a t e r c o n t i n u o u s l y b u t b e i n g a l m o s t u n c h a n g e d i f i t has a l o w e r b o i l i n g p o i n t t h a n t h e l i g h t ends of t h e feedstock.

T h e reboiler m a y be

h e a t e d b y other w a y s t h a n b y t h e steam s h o w n i n F i g u r e 1. F i g u r e 2 shows a c o n t i n u o u s a z e o t r o p i c c o l u m n u s i n g a fixed a m o u n t of entraîner w h i c h r e m a i n s i n t h e u n i t . S i n c e reflux is l a r g e l y s u p p l i e d b y f e e d of the e m u l s i o n near the t o p of t h e c o l u m n , t h e entraîner f r o m the d e c a n t e r passes to a r e b o i l e r a n d is f e d b a c k to t h e t o w e r as vapors. T h i s gives a m o r e n e a r l y c o u n t e r - c u r r e n t a c t i o n of the a z e o t r o p i c d i s t i l l i n g o p e r a t i o n , a n d a lesser heat i n p u t r e q u i r e d i n t o t h e viscous o i l at the base of the c o l u m n , u s u a l l y w i t h m o r e or less silt i n suspension w h i l e


116

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AND

AZEOTROPIC

DISTILLATION


CONDENSER >

Figure 2. Flow sheet for removing emulsified water by azeotropic distillation using a vapor feed of the reflux of a fixed amount of entraîner the b a l a n c e of the heat r e q u i r e m e n t s for the a z e o t r o p i c d i s t i l l a t i o n w o u l d b e s u p p l i e d to the t h i n , p u r e , entraîner i n a separate reboiler. F i g u r e 3 u t i l i z e s the d i l u t i n g of the o i l e m u l s i o n w i t h the entraîner c o m i n g f r o m the decanter.

T h i s occurs at or near t h e a z e o t r o p i c b o i l i n g

p o i n t . T h i s m i x e r dissolves t h e o i l i n the e m u l s i o n a n d p a r t i a l l y breaks i t w i t h some of the w a t e r a n d silt b e i n g d e c a n t e d off of the f e e d stream of p e r m a n e n t column.

e m u l s i o n a n d entrainer-solvent

g o i n g to the t o p of

the

M o r e entraîner m u s t b e u s e d i n this system to s u p p l y t h a t i n

the m i x e r a n d the decanter; h o w e v e r , it is m i x e d w i t h the o i l p a s s i n g through continuously. F i g u r e 4 is a m o d i f i c a t i o n o f F i g u r e 3 w h e r e the f u n c t i o n of the m i x e r i n d i s s o l v i n g the entraîner a n d the f e e d of o i l e m u l s i o n a n d t h e f u n c t i o n of t h e decanter i n s e p a r a t i n g t h e w a t e r layer f o r m e d is t a k e n o v e r b y a n extractor. I t is one o f the several m e c h a n i c a l l y a g i t a t e d types w h i c h washes o r extracts the o i l out of t h e e m u l s i o n a n d precipitates or discharges as a raffinate l a y e r the w a t e r a l o n g w i t h most of the silt. T h e r e m a i n i n g perm a n e n t e m u l s i o n o i l l a y e r c a r r i e d b y the d i s s o l v i n g entraîner solvent goes to t h e top of the c o l u m n .


7.

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O T H M E R

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117

T h e b o t t o m of F i g u r e 4 i n d i c a t e s one system for the h a n d l i n g of t h e c r u d e w i t h silt f r o m the b o t t o m of t h e c o l u m n before, after, or w i t h o u t a heat exchanger to r e c o v e r the sensible heat of the bottoms f r o m this still. A c o n t i n u o u s t h i c k e n e r , of t h e u s u a l r o t a t i n g t y p e w i t h hoes, t h i c k e n s the s u s p e n d e d silt i n t o a n o i l - m u d w h i c h is r e m o v e d , w a s h e d , a n d steamed b e f o r e d i s c a r d . T h e solvent r e c o v e r e d f r o m this w a s h i n g of m u d goes b a c k to t h e f e e d d i s s o l u t i o n . T h e c l e a r c r u d e kerosene s o l u t i o n , n o w free of w a t e r a n d silt, has kerosene r e m o v e d b y d i s t i l l a t i o n , o r i t is p u m p e d t o the refinery. O f t e n w h e r e the c r u d e does not c o n t a i n too m u c h w a t e r i n a p e r m a n e n t e m u l s i o n o r is not too difficult to p u m p , i t w o u l d n o t r e q u i r e


the i n i t i a l d i l u t i o n . O t h e r v a r i a t i o n s of flows are p o s s i b l e ; i n e a c h case i f m o r e solvente n t r a i n e r is a d d e d to the e m u l s i o n i n a d v a n c e , it is r e c o v e r e d b y d r a w i n g off a c o r r e s p o n d i n g percentage

of the entraîner layer w h i c h discharges

f r o m the decanter a n d r e c y c l i n g i t b a c k to s o l u t i o n t a n k w h e r e i t is a d d e d to the o p t i m u m p r o p o r t i o n a l a m o u n t of f e e d e m u l s i o n . T h u s , i f kerosene a n d a n a r o m a t i c solvent—e.g., t o l u e n e or x y l e n e — a r e u s e d i n d i s s o l u t i o n of t h e e m u l s i o n , t h e a r o m a t i c c h o s e n as the entraîner is c o n t i n u o u s l y

Figure 3. Flow sheet using entraîner as diluent with premixer and predecanter for separating some of the silt and water



118

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

Figure 4. Flow sheet using entraîner as diluent solvent in an extractor used to extract oil from an emulsion with water and to remove a raffinate layer of silt and water (with removal of final silt from the bottoms stream by a thickener, either before or after a heat exchanger) s e p a r a t e d i n the a m o u n t of its a r r i v a l i n the c o l u m n a n d r e c y c l e d b a c k for c o n t i n u o u s d i s s o l u t i o n i n t h e m i x e r . T h i s is c o n t r o l l e d b y o b s e r v i n g the temperatures at several m i d s e c t i o n plates, t h e same as t h e a m o u n t of b u t y l acetate i n the c o l u m n is c o n t r o l l e d i n acetic a c i d d e h y d r a t i o n

(5).

T h e h i g h e r b o i l i n g kerosene is d i s t i l l e d a w a y f r o m t h e c r u d e i n a separate c o l u m n , or it m a y r e m a i n to t h i n the c r u d e i n its t r a n s p o r t to the refinery. Comparison of Azeotropic

Demulsification

with GCOS Process

T o e x e m p l i f y the p r o b l e m s of d e m u l s i f i c a t i o n of o i l , some steps i n the r e c o v e r y of b i t u m i n o u s o i l f r o m t a r sands are c o n s i d e r e d . T h e G r e a t C a n a d i a n O i l Sands, L t d . ( G C O S ) Process has b e e n d e s c r i b e d i n v a r i o u s


7.

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O T H M E R

p u b l i c a t i o n s (e.g., 8),

of Crude

119

Oils

a n d because of the major p r o b l e m s of s e p a r a t i n g

w a t e r a n d a b r a s i v e m i n e r a l s f r o m the c r u d e , o p e r a t i o n a l losses of m a n y m i l l i o n s of dollars h a v e r e s u l t e d . Mining—overburden,

r e m o v a l , a n d m i n i n g of tar sands

T r a n s p o r t — t a r sands c o n v e y e d , stored, a n d l o a d e d i n extractors Primary Extraction. T h i s is a c c o m p l i s h e d w i t h steam a n d hot w a t e r i n r o t a t i n g c o n d i t i o n i n g d r u m s at a b o u t 190 °F.

T h e t o t a l mass is p i p e d

i n t o a v e r t i c a l s e p a r a t i o n c e l l w h e r e — ( a ) t h e c r u d e b i t u m e n , as a f r o t h , rises to the surface a n d is r e m o v e d ; ( b )

a b o t t o m layer c o n t a i n i n g m a i n l y

sand, c l a y , a n d w a t e r w i t h n o t m o r e t h a n a b o u t 2 % b i t u m e n is p i p e d to


the t a i l i n g p o n d ; ( c )

a " m i d d l i n g s " layer w i t h o u t s h a r p d i v i d i n g lines

b e t w e e n the f r o t h a b o v e or the s a n d a n d w a t e r b e l o w . T h i s is a tenacious e m u l s i o n of b i t u m e n i n w a t e r , s t a b i l i z e d b y a s u b s t a n t i a l a m o u n t of s a n d a n d c l a y — m o s t l y oil-wet.

M o s t of the b i t u m e n is r e m o v e d i n

cells b y a i r - f r o t h i n g . T h e s a n d , clay, a n d w a t e r a n d some b i t u m e n is p u m p e d to t h e t a i l i n g s p o n d .

scavenger

unrecoverable

B i t u m e n r e c o v e r y is n o t m o r e

t h a n 9 0 % , thus the tailings c a r r y off at least 1 0 % of that o r i g i n a l l y present. Final Extraction. T h e b i t u m e n f r o m the f r o t h , c o n t a i n i n g s u b s t a n t i a l q u a n t i t i e s of s a n d , clay, a n d w a t e r , is d i l u t e d w i t h n a p h t h a to r e d u c e its v i s c o s i t y so i t c a n b e p u m p e d r e a d i l y .

It is first p u m p e d to 14 s c r o l l -

t y p e centrifuges to r e m o v e l a r g e m i n e r a l particles a n d t h e n to 26 n o z z l e t y p e centrifuges A b r a s i o n i n the charge.

to r e m o v e m o s t of t h e r e m a i n i n g m i n e r a l s a n d expensive

centrifuges

has b e e n

a major

water.

operational

T h e d i l u t e d b i t u m e n s t i l l contains significant q u a n t i t i e s of w a t e r

a n d h y d r o p h i l i c s a n d a n d clay. Cracking and Coking.

T h e d i l u t e b i t u m e n is p u m p e d i n t o

d r u m s , w h e r e i t is c r a c k e d to y i e l d gas a n d c r u d e o i l o v e r h e a d , goes to the refinery.

coker which

R e s i d u a l c o k e contains a l l of the r e s i d u a l s a n d a n d

c l a y w h i c h c o u l d not b e r e m o v e d i n the final extraction, a n d therefore i t is u s e d o n l y as a f u e l for t h e boilers. I n the a z e o t r o p i c system ( J ) , the m i n i n g a n d transport steps are the same, also the c r a c k i n g a n d c o k i n g step, except t h a t i t gives a m u c h i m p r o v e d coke w h i c h is u s e d for m o r e v a l u a b l e p r o d u c t s t h a n as a h i g h ash f u e l . I n the p r i m a r y extraction, h o w e v e r , a h y d r o c a r b o n solvent is a d d e d . This allows a relatively sharp separation between the " m i d d l i n g s " a n d the aqueous b o t t o m layer.

A f r a c t i o n w i t h b o i l i n g r a n g e of octane

suitable, since i t t h e n becomes the a z e o t r o p i c

entraîner for the

A n a r o m a t i c solvent—e.g., t o l u e n e — m i g h t b e better, b u t i t m a y

is

water. require

another s e p a r a t i o n later. I n the final e x t r a c t i o n because of solvent a d d i t i o n i n t h e p r i m a r y extraction, the m i n e r a l matter r e a d i l y separates f r o m the b o t t o m


aqueous

120

EXTRACTIVE

AND

AZEOTROPIC

DISTILLATION

l a y e r i n s t e a d of r e q u i r i n g batteries of expensive centrifuges w i t h c o n s i d e r a b l e d a m a g e r e s u l t i n g f r o m a b r a s i o n of the fine s a n d . A

suitable

s e t t l i n g a i d assists this, a n d the w e t sediment, a l m o s t free of b i t u m e n , is u s e d as fill. T h e w a t e r contains o n l y a s m a l l a m o u n t of d i s s o l v e d solvent w h i c h is r e c o v e r e d b y s t r i p p i n g , o r w a s t e d , a n d the w a t e r itself is r e u s e d or d i s c a r d e d to surface waters as it is e n v i r o n m e n t a l l y

acceptable.

T h e t o p b i t u m e n l a y e r a n d t h e " m i d d l i n g s " l a y e r are c o m b i n e d a n d are p u m p e d to a n a z e o t r o p i c d i s t i l l a t i o n system, as d i a g r a m m e d i n F i g ures 1, 2, 3, a n d 4. T h e c h o i c e of

flow

sheet d e p e n d s o n the

relative

a m o u n t s of w a t e r r e m a i n i n g a n d the a m o u n t s a n d characteristics of the


m i n e r a l matter. T h e systems of F i g u r e s 3 a n d 4 r e m o v e m o r e w a t e r a n d silt b e f o r e the a z e o t r o p i c d i s t i l l a t i o n , thus s a v i n g heat. U s i n g t h e system of F i g u r e 4 i n s t e a d of the t h i c k e n e r , a s i m p l e storage t a n k a l l o w i n g t w o days residence for settling o u t a l l silt, i n c l u d i n g c o l l o i d a l c l a y w h i c h passes t h r o u g h the c o l u m n , m a y b e u s e d after the heat exchanger. If a n a p h t h a f r a c t i o n has b e e n u s e d i n the d i l u t i o n a n d as the entrainer, it is left i n as a d i l u e n t for r e d u c i n g the v i s c o s i t y i n p u m p i n g the o i l to t h e refinery.

A l t e r n a t i v e l y , some o r a l l is r e m o v e d as a s l i p stream

f r o m t h e reflux g o i n g to the t o p of the a z e o t r o p i c c o l u m n . If toluene or other a r o m a t i c solvent is u s e d , i t w o u l d b e so r e m o v e d or r e m o v e d i n a separate d i s t i l l a t i o n for recycle. O i l - w e t materials, s a n d , a n d clay, s e p a r a t e d f r o m either o i l or w a t e r layers, are w a s h e d w i t h the solvent o r d i l u e n t u n t i l t h e y are free of b i t u m e n a n d the r e s i d u a l solvent is s t r i p p e d f r o m the m i n e r a l m a t t e r w i t h steam. T h e m i n e r a l m a t t e r is c l e a n a n d is sent to waste or u s e d as

fill

w i t h o u t d a n g e r of spontaneous c o m b u s t i o n , or i t is u s e d i n cement m a n u facture.

T h e aqueous phases c o n d e n s e d f r o m s u c h s t r i p p i n g a n d f r o m

the d e c a n t e r of the a z e o t r o p i c system has so l i t t l e solvent, i n h u n d r e d t h s of a percent, that i t is neglected.

It evaporates r e a d i l y i n o p e n storage.

T h i s d i s t i l l e d w a t e r is u s e d for a n y s u i t a b l e p u r p o s e . R e c o v e r y of the b i t u m e n b y this system has b e e n almost 9 8 % c o m p a r e d w i t h the losses i n the G C O S system, a n d the solvent losses are l o w . T h e major a d v a n t a g e of this system is e l i m i n a t i o n of the 14-scroll t y p e centrifuges a n d 26-nozzle t y p e m a c h i n e s u s e d i n the G C O S p l a n t w h i c h h a v e h a d excessive r e p l a c e m e n t , m a i n t e n a n c e , a n d r e p a i r costs because o f the a b r a s i v e a c t i o n of the fine solids o n these h i g h speed, p r e c i s i o n machines. T h e b i t u m e n o b t a i n e d is the u n m o d i f i e d n a t i v e b i t u m e n w i t h a s u b s t a n t i a l percentage of h i g h m e l t i n g , a l i p h a t i c s o l u b l e c o m p o n e n t s .

These

are separated f r o m t h e l o w m e l t i n g c o m p o n e n t s b y solvent e x t r a c t i o n or solvent p r e c i p i t a t i o n . T h e h i g h m e l t i n g c o m p o n e n t s are u t i l i z e d i n p r o tective coatings for metals o r i n heat resistant r o a d surface compositions. If coke is o b t a i n e d f r o m this process, it is free of m i n e r a l m a t t e r a n d


7.

BALASSA AND OTHMER

Demulsification of Crude Oils

121


is used for the same uses as other high grade petroleum cokes—e.g., in electrodes or activated carbon, as well as in metallurgical uses where the high ash content resulting from the residual minerals would prevent that from the GCOS system being used. Another advantage is that little water is required in the azeotropic process since most of the water is recycled and that which is not recycled is immediately passed to surface waters without environmental damage. Also, removing all organics from the mineral matters means that these can be used as fill or otherwise without fire hazard, odors, or other environmental problems caused by microbiological attacks on any residual bitumen left on the minerals as in the GCOS process. Literature Cited 1. Balassa, L. L., U.S. Patent 3,468,789 (Sept. 23, 1969). 2. Clarke, H. T., Othmer, D. F., U.S. Patent 1,804,745 (May 12, 1931). 3. Othmer, D. F., "Encyclopedia of Chemical Technology," 2nd ed., Vol. 2, p. 839, 1963. 4. Othmer, D. F., U.S. Patent 1,917,391 (July 11, 1933). 5. Othmer, D. F., Chem.&Met. Eng. (1941) 48, 91. 6. Othmer, D. F., Chem. Eng. Progr. (1963) 59, 6, 67. 7. Othmer, D. F., TenEyck, Ε. H., Ind. Eng. Chem. (1949) 41, 2897. 8. "Our Sun," Sun Oil Co., House Publication (Autumn, 1967). RECEIVED November 24, 1970.


Extractive and Azeotropic Distillation - ACS Publications

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