Processing Short-Contact-Time Coal Liquefaction Products - ACS

10 Processing Short-Contact-Time Coal Liquefaction Products CONRAD J. KULIK, HOWARD E. LEBOWITZ, and WILLIAM C. ROVESTI

Downloaded by UNIV LAVAL on July 11, 2016 | http://pubs.acs.org Publication Date: October 14, 1980 | doi: 10.1021/bk-1980-0139.ch010

Electric Power Research Institute, 3412 Hillview Avenue, Palo Alto, CA 94303

A considerable effort has been expended in the past few years by many researchers in attempts to better understand the mechanism by which coal is liquefied. From this work has emerged the concept of short residence time coal liquefaction which promises potential process advantages, small reactor, minimum hydrogen flow, and the efficient utilization of hydrogen for a particular product slate. Work done for EPRI by Mobil Research (1) and Battelle (2) demonstrated that coal could be liquefied at these relatively short reaction times. This work, however, was limited, and indicated some very apparent process disadvantages: • process was out-of-solvent balance, • a viscous reactor effluent was produced resulting in poor filterability, • vacuum still bottoms had high viscosity, • the product was thermally sensitive. In order to overcome these problems, the flow schemes as shown in Figures 1 and 2 were developed. These incorporate the use of Kerr-McGee Corporation's Critical Solvent Deashing and Fractionation Process (CSD) for recovery of the SRC. The Kerr-McGee Process adds extra flexibility since this process can recover heavy solvent for recycle, which is not recoverable by vacuum distillation. EPRI contracted with Conoco Coal Development Company (CCDC) and Kerr-McGee Corporation in 1977-1978 to test these process concepts on continuous bench-scale units. A complementary effort would be made at the Wilsonville Pilot Plant under joint sponsorship by EPRI, DOE, and Kerr-McGee Corporation. This paper presents some of the initial findings. Experimental CCDC built a continuous short residence time coal liquefaction unit with throughput of about 4.5 kg/hr of coal. The SRC unit consisted of a short residence time reactor constructed from 53.3 m of high pressure tubing having an ID of 0.516 or 0-8412-0587-6/80/47-139-193$05.00/0 © 1980 American Chemical Society Whitehurst; Coal Liquefaction Fundamentals ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

Whitehurst; Coal Liquefaction Fundamentals ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

Coal preparation

Figure 1.

Solvent recovery

Ash concentrate

Light p h a s e S R C

K e r r - M c G e e solids separation and fractionation

^Distillate * storage

Fuel g a s

Coal hydroextraction with light-phase SRC recycle process

Hydroextraction coal liquefaction

Acid g a s removal

Power and steam generation

G a s and condensate separator

H recovery

Hydrogen production and pu rification 2


• SRC

>

H

w

δ

Η

η

>

r r ο c w

?

η


Coal preparation

π

H

2

recovery

Catalytic hydrogénation

Solvent recovery

L—J

Distillate storage

Gas and condensate separation

Sour fuel gas to acid gas removal

Acid gas removal

Light phase SRC

Kerr-McGee solids separation and fractionation

Ash concentrate

Hydrogen production and purification

Figure 2. Low-severity coal liquefaction with light-phase SRC recycle process

Short residence time coal liquefaction

Power and steam generation


Fuel gas

SRC


196

COAL LIQUEFACTION

FUNDAMENTALS

0*704 cm. The c o i l was heated by a r a d i a n t furnace with f o u r i n d i v i d u a l l y c o n t r o l l e d h e a t i n g zones. The furnace was cont r o l l e d to simulate a l i n e a r heat-up p r o f i l e . The bench-scale c o i l was operated i n the laminar flow r e g i o n , where c o k i n g can be a problem. On a commercial s c a l e , t h i s furnace would operate i n a h i g h l y t u r b u l e n t mode. During the e a r l y phases of work a t CCDC, work centered around o p e r a t i o n of the continuous benchs c a l e SRT u n i t w i t h d i s t i l l a b l e s o l v e n t s . P a r a l l e l i n g the work a t CCDC were the c r i t i c a l s o l v e n t deashing and f r a c t i o n a t i o n s t u d i e s done on a continuous benchs c a l e u n i t at Kerr-McGee T e c h n i c a l Center, Oklahoma C i t y , Oklahoma, F i g u r e 3. The Kerr-McGee C r i t i c a l S o l v e n t Deashing and F r a c t i o n a t i o n Process has been p r e v i o u s l y d i s c u s s e d (3)· In work p r i o r t o t h i s program, Kerr-McGee demonstrated t h a t extremely r a p i d s o l i d s s e p a r a t i o n (deashing) on the order of 30 t o 60 times f a s t e r than a c o n v e n t i o n a l d e a s p h a l t i n g u n i t and high deashing e f f i c i e n c i e s producing l e s s than 0.1 wt% ash on SRC product c o u l d be achieved. In a d d i t i o n , i t has been demons t r a t e d t h a t the SRC c o u l d be f r a c t i o n a t e d i n t o m u l t i p l e r e s i d ual f r a c t i o n s . The work i n v o l v e d the i n t e g r a t i o n of the SRC o p e r a t i o n s at Kerr-McGee w i t h those a t CCDC where the concept of r e c y c l i n g c e r t a i n r e s i d u a l f r a c t i o n s back to l i q u e f a c t i o n would be t e s t e d . T h i s program i n v o l v e d repeated product shipments between the r e s p e c t i v e l a b o r a t o r i e s . The data presented i n t h i s paper w i l l focus on the work done i n t h i s l a t t e r phase of the program. In a d d i t i o n t o continuous bench-scale work, CCDC c a r r i e d out a r a t h e r e x t e n s i v e l a b o r a t o r y program i n v o l v i n g the use o f the microautoclave r e a c t o r . The program developed t e s t s t o compare the a c t i v i t i e s of d i f f e r e n t s o l v e n t s . These t e s t s q u i c k l y evaluated a s o l v e n t so t h a t the performance under c o a l l i q u e f a c t i o n c o n d i t i o n s c o u l d be p r e d i c t e d . The t e s t s are now used at the W i l s o n v i l l e SRC P i l o t P l a n t as a means of d e t e r mining when s t a b l e o p e r a t i o n has been achieved. The microautoclave s o l v e n t a c t i v i t y t e s t s measure c o a l c o n v e r s i o n i n a small batch r e a c t o r under c a r e f u l l y c o n t r o l l e d c o n d i t i o n s . The t e s t s are d e s c r i b e d as K i n e t i c , E q u i l i b r i u m and SRT. The K i n e t i c and E q u i l i b r i u m T e s t s measure c o a l conversion t o t e t r a h y d r o f u r a n s o l u b l e s a t c o n d i t i o n s where conversion should be monotonically r e l a t e d t o hydrogen t r a n s f e r . The K i n e t i c T e s t i s performed a t 399°C f o r 10 minutes at an 8 t o 1 solvent to coal r a t i o . The combination of h i g h s o l v e n t r a t i o and low time provide a measure of performance at e s s e n t i a l l y constant s o l v e n t composition. The measured c o n v e r s i o n i s thus r e l a t e d to the r a t e of hydrogen donation from s o l v e n t of roughly a s i n g l e composition. In c o n t r a s t , the E q u i l i b r i u m T e s t i s performed a t 399°C f o r 30 minutes a t a 2 t o 1 s o l v e n t to c o a l ratio. At these c o n d i t i o n s , hydrogen donors can be substant i a l l y d e p l e t e d . Thus performance i s r e l a t e d t o hydrogen donor


10.

KULIK E T A L .

Processing

Coal Liquefaction

197

Products

Feed


Surgd tank!

Feed pump

X Mixer

X First stage settler

Second! [stage settler

Solvent tank

Third stage settler

ύ -

1

Solvent pump Solvent separator| number 1

Ash concentrate

Figure 3.

Solvent separator number 2

Deashed coal

Solvent separator number 3

Light deashed coal

Three-stage CSD pilot plant; block flow diagram—Wilsonville


program.

198

COAL LIQUEFACTION FUNDAMENTALS

concentration. The SRT Test, performed at 427°C f o r 5 minutes a t a 2 t o 1 s o l v e n t t o c o a l r a t i o , simulates performance a t s h o r t residence time c o a l l i q u e f a c t i o n c o n d i t i o n s .


D i s c u s s i o n of

Results

Autoclave R e s u l t s - Solvent A c t i v i t y T e s t . The i n i t i a l microautoclave work was done with t e t r a l i n and methylnaphthal e n e , using Indiana V bituminous c o a l (Table I ) . Base l i n e data i s shown i n Figure 4. A l l three t e s t s , K i n e t i c , SRT, and E q u i l i b r i u m , show an i n c r e a s e i n c o a l conversion with an i n c r e a s e i n the c o n c e n t r a t i o n of t e t r a l i n . The E q u i l i b r i u m T e s t shows the h i g h e s t c o a l conversion of approximately 86 wt% of the MAF c o a l (based on the s o l u b i l i t y i n the tetrahydrofuran) a t the 50% t e t r a l i n concentration. The K i n e t i c T e s t shows lower c o a l conv e r s i o n . The hydrogen t r a n s f e r r e d t o the c o a l from the t e t r a l i n i n the E q u i l i b r i u m Test a t the 50 wt% t e t r a l i n feed concentrat i o n i s approximately 0.5 wt% of the MAF c o a l . In the K i n e t i c T e s t 50 wt% t e t r a l i n feed c o n c e n t r a t i o n r e s u l t s i n a much smaller t r a n s f e r a t the s h o r t r e a c t i o n time o f 10 minutes. Microautoclave data was a l s o obtained w i t h W i l s o n v i l l e Batch I s o l v e n t u t i l i z i n g Indiana V c o a l . Batch I s o l v e n t was obtained from W i l s o n v i l l e i n mid-1977. Other batches of r e c y c l e s o l v e n t were r e c e i v e d l a t e r . Batch I s o l v e n t had i n s p e c t i o n s most l i k e the A l l i e d 24CA Creosote O i l used f o r s t a r t - u p a t the W i l s o n v i l l e P i l o t Plant. Succeeding batches of s o l v e n t r e c e i v e d by CCDC showed s u b s t a n t i a l d i f f e r e n c e s , presumably due t o e q u i l i b r a t i o n a t v a r i o u s o p e r a t i n g c o n d i t i o n s . As the W i l s o n v i l l e s o l v e n t aged and became more c o a l derived, the solvent aromat i c i t y decreased w i t h an i n c r e a s e i n such compounds as indan and r e l a t e d homologs. The decrease i n a r o m a t i c i t y has a l s o been v e r i f i e d by NMR. A l a t e r s o l v e n t (Batch I I I ) a l s o showed an i n c r e a s e i n p h e n o l i c and a decrease i n phenanthrene (anthracene) and hydrogenated phenanthrene (anthracene) type compounds. The hydrogen content of Batch I s o l v e n t was v a r i e d by c a t a l y t i c hydrogénation i n a f i x e d bed, t r i c k l e phase, a d i a b a t i c r e a c t o r at v a r i o u s s e v e r i t i e s . American Cyanamid HDS-3A, a nickel-molybdenum c a t a l y s t , was used. Reactor c o n d i t i o n s were v a r i e d from 8.4 t o 11.1 MPa and from .5 to 2 LHSV a t a r e a c t o r temperature o f 371°C and a hydrogen t o feed r a t i o of .14 m^ hydrogen per .45 kg of feed. At these hydrogénation c o n d i t i o n s , hydrogenated Batch I s o l v e n t was produced with v a r i o u s hydrogen contents. The optimum c o a l conversion under SRT Test c o n d i t i o n s was obtained w i t h Batch I s o l v e n t t o which 1 wt% hydrogen was added. With solvent hydrogen contents above 9 wt%, the c o a l conversion s l o w l y decreased, i n d i c a t i n g t h a t even though the hydrogen content of the s o l v e n t was increased, the a d d i t i o n a l chemical hydrogen was not being made a v a i l a b l e as hydrogen donors at t h i s r e a c t i o n s e v e r i t y .



INDIANA V ILLINOIS 6



2.14 1.84

0.44 0.61

2

K^Ô

69.22 70.05

4.57 4.73

Na 0

C

' H

INDIANA V. (OLD BEN) ILLINOIS 6 (BURNING STAR)

2

2

1.07 1.13

0.6 12.0

0.0 2.6

23.06 15.68

3

0.21 0.07

45.22 45.18

2

3

20.34 17.31

A1 0

4.7 23.3

32.2 15.7

WT % ON TYLER SCREEN (WET) 200 325

1.22 1.00

2

0.26 7.06

SC^

1.90 1.72

ORGANIC

47.34 47.92

0.65 0.38

ASH ANALYSIS, WT% Fe 0 Ti0 P ^ Si0

3.62 3.23

100

0.75 0.88

MgÔ

10.68 9.60

48

3.88 6.42

câô

1.36 1.39

Ν

38.22 37.87

PROXIMATE (AS RECEIVED) WT % VOLATILE MATTER FIXED **CARBON

ULTIMATE (MOISTURE FREE) WT% SULFUR FORMS Q TOTAL PYRITE SULFATE

4·35 3.61

MOISTURE

ANALYSES OF COALS

TABLE I


62.5 46.4

-325

2.48 3.95

OTHER

10.55 11.00

ASH

10.09 10.60

ASH


200


F i g u r e 5 shows t h a t the solvent hydrogen donor content p l a y s a s i g n i f i c a n t r o l e i n l i q u e f a c t i o n performance a t s h o r t r e a c t i o n times* A c o a l conversion maxima i s reached a t a p p r o x i mately 4 minutes a f t e r which measured c o a l conversion decreases due t o r e g r e s s i v e r e a c t i o n s (reconversion of the THF Solubles t o THF I n s o l u b l e s ) * Understandably, other c o a l conversion p e r formances can be expected w i t h d i f f e r e n t s o l v e n t q u a l i t i e s and o t h e r r e a c t i o n temperatures* A d d i t i o n a l work has shown t h a t not only the t o t a l hydrogen donor content of the s o l v e n t i s impor t a n t but a l s o the a c t i v i t y o f the donors p r e s e n t , i . e . , h e a v i e r molecular weight hydroaromatics such as hydrophenanthrene donate hydrogen more r a p i d l y than t e t r a l i n . The e f f e c t of solvency a l s o i s a f a c t o r and i t appears the "heavier" t h e s o l v e n t ( i . e . , h i g h e r b o i l i n g p o i n t o r molecular weight) the b e t t e r the p e r f o r mance* The i n t e r r e l a t i o n s h i p of the amount and type of hydrogen donors a l o n g w i t h the solvency e f f e c t a t a s p e c i f i c s e t o f r e a c t i o n c o n d i t i o n s appear t o be d i c t a t i n g l i q u e f a c t i o n performance p a r t i c u l a r l y a t short r e a c t i o n times* The s u p e r i o r i t y of "heavy" s o l v e n t s appears t o r e f u t e the p r o p o s i t i o n t h a t the r a t e c o n t r o l l i n g step i n c o a l conversion i s the p y r o l y s i s of the c o a l and t h a t given a s u f f i c i e n t concentra t i o n o f donors, the r a t e o f hydrogen donation would not be l i m i t i n g (j4)* Comparing the performance of n a t u r a l s o l v e n t s t o t e t r a l i n , t h e f a c t o r t h a t appears t o be l i m i t i n g conversions i s the hydrogen donation r a t e of t e t r a l i n , a t l e a s t i n the e a r l y stages o f c o a l d i s s o l u t i o n * Hydrogen donors contained by c o a l d e r i v e d s o l v e n t r e a c t e d more r a p i d l y than t e t r a l i n * Work by Whitehurst M) has a l s o shown the same phenomenon* The most dramatic discovery i n the microautoclave study was the enhancement o f c o a l conversion w i t h L i g h t SRC a d d i t i o n (see Table I I ) . Success with the high b o i l i n g d i s t i l l a b l e s o l v e n t s encouraged experimentations w i t h L i g h t SRC. L i g h t SRC i s o b t a i n e d by f r a c t i o n a t i n g SRC i n the c r i t i c a l solvent* A 50% (wt) b l e n d o f Ligfrit SRC and 256 χ 535°C Batch I I I s o l v e n t was t e s t e d on the microautoclave as shown i n Table I I * The 50% b l e n d performed w e l l i n the K i n e t i c Test and r a t h e r p o o r l y i n the E q u i l i b r i u m Test as compared t o the d i s t i l l a t e base* This presumably i s i n d i c a t i v e o f a low c o n c e n t r a t i o n o f h i g h l y a c t i v e donors* When 7 MPa c o l d gaseous hydrogen was added t o the microautoclave, and t h e K i n e t i c , E q u i l i b r i u m T e s t s reperformed, a r a t h e r remarkable phenomenon occurred* The r e s u l t s of the K i n e t i c Test remained unchanged, but i n the E q u i l i b r i u m T e s t , the a d d i t i o n of gaseous hydrogen caused a higher c o a l conver sion* I t c o u l d be surmised t h a t the gaseous hydrogen r e a c t e d w i t h the c o a l l i q u e f a c t i o n media even a t the low temperature of 399°C, where one would have expected the a d d i t i o n o f a c a t a l y s t t o be r e q u i r e d f o r aromatic hydrogénation. To f u r t h e r understand t h i s phenomenon, a base run was made w i t h Batch I I I s o l vent t o which gaseous hydrogen was added* No change was apparent i n t h e E q u i l i b r i u m Test r e s u l t . The L i g h t SRC i s thus



10.

KULIK E T A L .

Figure 4.

Processing

Coal Liquefaction

201

Products

Microautoclave tests, Indiana V coal.Tetralin-methyl naphthalene mixtures (conversion vs. percent Tetralin content)

2

4

6

8

10

Time (min.) Includes Heat Up Figure 5. Microautoclave tests, Indiana V Coal (conversion at 440°C vs. time). Batch I solvent: (O), 8.7% hydrogen solvent 3/1 S/C; (0), 8.9% hydrogen solvent 3/1 S/C; (\J), 8.0% hydrogen solvent 3/1 S/C; (A), 8.0% hydrogen solvent 2/1 S/C.


12

COAL LIQUEFACTION

202

FUNDAMENTALS

a c u r i o u s m a t e r i a l having few donors of i t s own, but promoting the r e a c t i o n o f other donors and the r e a c t i o n with gaseous hydrogen.

TABLE I I MICROAUTOCLAVE DATA-LIGHT PHASE SRC ADDITION-INDIANA V COAL


THF CONVERSION KINETIC

SRT

EQUILIBRIUM

WHOLE WILSONVILLE BATCH I I I

76.5

71.5

74.4

WHOLE WILSONVILLE BATCH I I I W/7 MPa OF COLD H

-

-

74.4

50WT% LIGHT PHASE SRC 50WT% 256 χ 535°C BATCH I I I

87.5

72.5

65.5

50WT% LIGHT PHASE SRC 50WT% 256 χ 535°C BATCH I I I W/7 MPa OF COLD H

87.5

75.7

86.6

2

9

Continuous Bench-Scale Experimentation. With encouraging r e s u l t s o b t a i n e d from microautoclave t e s t s , experimentation emphasis moved t o the bench-scale u n i t . Here the concept of adding L i g h t SRC t o the r e c y c l e s o l v e n t on a continuous b a s i s was t e s t e d . E a r l i e r work (j>) performed on s h o r t contact time c o a l l i q u e f a c t i o n showed Indiana V c o a l t o be o u t - o f - s o l v e n t balance. A l s o the o p e r a b i l i t y of the continuous bench-scale SRT u n i t was h i g h l y dependent upon the q u a l i t y o f the s o l v e n t . Short residence time vacuum bottoms were processed i n the C r i t i c a l Solvent Deashing and F r a c t i o n a t i o n U n i t t o allow recovery o f h i g h e r b o i l i n g s o l v e n t t h a t would not normally be recovered by distillation. I t was p o s t u l a t e d t h a t r e c y c l e o f t h i s m a t e r i a l back t o l i q u e f a c t i o n would help c l o s e the s o l v e n t balance and improve SRT u n i t o p e r a b i l i t y . In l i g h t o f the q u a l i t i e s o f t h e L i g h t SRC found i n microautoclave t e s t s , the i n i t i a l phase of the continuous work was expanded toward t e s t i n g the concept o f L i g h t SRC r e c y c l e i n the c o n v e n t i o n a l SRC-I mode with an I l l i n o i s No. 6 C o a l from Burning S t a r No. 2 mine. Analyses a r e given i n Table I . Burning S t a r c o a l was chosen since i t has low s o l v e n t range y i e l d s i n o r d i n a r y SRC o p e r a t i o n s .



10.

KULIK ET AL.

Processing

Coal Liquefaction

Products

203

The work was done on the continuous bench-scale hydroe x t r a c t i o n u n i t a t CCDC which was p r e v i o u s l y d e s c r i b e d (6)· The d i s t i l l a t e s o l v e n t and L i g h t SRC f o r t h i s program were obtained from the W i l s o n v i l l e P i l o t P l a n t . The p r o c e s s i n g h i s t o r y by which the r e c y c l e s o l v e n t was produced a t the W i l s o n v i l l e P i l o t P l a n t was somewhat d i f f e r e n t from the p r o c e s s i n g c o n d i t i o n s planned f o r the s o l v e n t on the bench s c a l e u n i t . I t was f e a r e d t h a t the W i l s o n v i l l e s o l v e n t may have contained r e s i d u a l hydro gen donors t h a t would not be a v a i l a b l e a t the bench u n i t opera t i n g conditions. The s o l v e n t was t h e r e f o r e r e c y c l e d f o r each s e r i e s of runs. Each s e r i e s of runs c o n s t i t u t e d ~ 60 hours of operations a f t e r which the d i s t i l l a t e s o l v e n t was recovered and r e c y c l e d t o the next s e r i e s . A base case run was made i n each s e r i e s t o i d e n t i f y changes i n the d i s t i l l a t e process s o l v e n t which c o u l d be a t t r i b u t e d t o d e p l e t i n g r e s i d u a l hydrogen donors as the s o l v e n t was b e i n g r e c y c l e d from s e r i e s t o s e r i e s . The data showed, however, no a p p r e c i a b l e change i n q u a l i t y as the s o l v e n t was r e c y c l e d . The L i g h t SRC, obtained from the Wilson v i l l e P i l o t P l a n t , was used on a once-through b a s i s except f o r Runs 4 and 5 where i n t e r n a l l y recovered L i g h t SRC was used. F i g u r e 6 shows t h a t as the c o n c e n t r a t i o n of the L i g h t SRC was i n c r e a s e d the y i e l d o f d i s t i l l a b l e r e c y c l e s o l v e n t (+206 χ 535°C) a l s o i n c r e a s e d . With 30 wt% of L i g h t SRC i n the t o t a l s o l v e n t the net y i e l d of r e c y c l e s o l v e n t was zero, e.g., the process was i n s o l v e n t balance. Without the a d d i t i o n of L i g h t SRC, i n Run 1A, there was a net r e c y c l e s o l v e n t d e f i c i t o f approximately 15% of the MAF c o a l . I t should be noted t h a t the p l o t t e d d i s t i l l a t e y i e l d s are o n l y f o r the l i q u e f a c t i o n u n i t w i t h vacuum d i s t i l l a t i o n . I f y i e l d s are obtained around the l i q u e f a c t i o n and CSD u n i t the d i s t i l l a t e y i e l d s are a p p r e c i a b l y higher due t o the recovery of heavy d i s t i l l a t e on the CSD u n i t t h a t would not normally be recovered by d i s t i l l a t i o n . These v a l u e s are footnoted i n F i g u r e 6. The L i g h t SRC a d d i t i o n had then demonstrated a very dramatic improvement i n l i q u e f a c t i o n performance even a t these m i l d o p e r a t i n g c o n d i t i o n s . From each of the runs with L i g h t SRC a d d i t i o n , Kerr-McGee recovered on the CSD Bench-Scale U n i t L i g h t SRC approximately e q u i v a l e n t t o the amount of L i g h t SRC r e q u i r e d t o s u s t a i n L i g h t SRC r e c y c l e . A second s e r i e s of runs was made t h a t i n v e s t i g a t e d the e f f e c t of l i q u e f a c t i o n temperature on y i e l d performance with 30 wt% L i g h t SRC a d d i t i o n . I n t e r e s t i n g l y , the lower temperatures r e s u l t e d i n high SRC y i e l d s with low gas and water y i e l d s and s u f f i c i e n t r e c y c l e s o l v e n t t o s u s t a i n r e c y c l e . The hydrogen consumption was low as expected i n the order of 2 wt% on MAF coal. From t h i s data i t appeared t h a t these m i l d o p e r a t i n g c o n d i t i o n s were conducive i n producing SRC with very e f f i c i e n t hydrogen u t i l i z a t i o n . Further work was done a t these condi t i o n s , as shown i n Figure 7, t o determine the e f f e c t o f r e c y c l i n g L i g h t SRC a t these m i l d o p e r a t i n g c o n d i t i o n s , 418°C and 8.3 MPa. L i g h t SRC f o r r e c y c l e was recovered by CSD f r a c t i o n a t i o n from some of the runs p r e v i o u s l y described.



204

80

MAF SRC Illinois No. 6 coal Burning Star Mine 440°C 8.3 MPa total pressure 800 kg coal/h-m 0.62 m H /kg MF coal 2/1 solvent (incl. KM)/MF coal weight ratio 3


3

2

Gases X -206°C dist.

MAF residue

Recycle solvent* +206 X 535°C

Run 1A

Weight Percent Light Phase SRC in Total Solvent

Run 1B

Run 1C

15

30

*The plotted yields are for liquefaction alone. The combined yields including CSD are as follows: Run

Yield 206 X 535°C

1B 1C

0.3 10.2

Figure 6.

Hydroextraction yields


10.

KULIK E T A L .

Processing

Coal Liquefaction

Products

70 μ -

MAF SRC


Illinois No. 6 coal Burning Star Mine 418°C 30 weight percent light phase SRC in total solvent 8.3 MPa total pressure 560 kg coal/h-m 0.62 m H /kg MF coal 2/1 solvent (incl. KM)/MF coal weight ratio 3

3

2

Gases X-206°C dist. - O MAF residue

Recycle solvent* +206 X 535°C

Hydrogen consumption

*The plotted yields are for liquefaction alone. The combined yields including CSD are as follows: Run

Yield 206 X 535°C

2B 5

18.5 8.2

Figure 7. Recycle hydroextraction yields


205


206


Data from Runs 4 and 5 (Figure 7) show that with repeated L i g h t SRC r e c y c l e the product y i e l d s remained e s s e n t i a l l y cons t a n t with the exception t h a t the hydrogen consumption increased slightly. From each of these runs Kerr-McGee recovered on the CSD Bench-Scale U n i t L i g h t SRC approximately equivalent t o the amount o f L i g h t SRC r e q u i r e d t o s u s t a i n r e c y c l e o f t h e L i g h t SRC. The composition of the recovered L i g h t SRC i n Runs 4 and 5 was n e a r l y i d e n t i c a l i n composition t o t h e L i g h t SRC i n i t i a l l y added t o Run 2B. In a d d i t i o n , v i s c o s i t y measurements made on +535°C vacuum bottoms made w i t h L i g h t SRC a d d i t i o n showed a great r e d u c t i o n i n v i s c o s i t y as opposed t o vacuum bottoms made under s i m i l a r c o n d i t i o n s without L i g h t SRC a d d i t i o n . The a d d i t i o n of L i g h t SRC should improve the o p e r a b i l i t y of the vacuum bottoms h a n d l i n g particularly w i t h s h o r t residence time products t h a t are high i n preasphaltenes. Continuous Short Residence Time Experimentation. After determining t h e e f f e c t o f L i g h t SRC a d d i t i o n t o a conventional SRC-I o p e r a t i o n , experimentation moved t o determining t h e e f f e c t of L i g h t SRC a d d i t i o n on s h o r t residence time c o a l l i q u e f a c t i o n performance. E a r l i e r short residence time work (J3) had shown the l i q u e f a c t i o n o f Indiana V c o a l t o be o u t - o f - s o l v e n t balance and t h a t the o p e r a b i l i t y of the SRT u n i t was p a r t i c u l a r l y s e n s i t i v e t o the q u a l i t y o f r e c y c l e s o l v e n t . Batch VI s o l v e n t t o be used i n t h i s t h i r d phase of the program was the l a t e s t i n the s e r i e s of s o l v e n t s r e c e i v e d by CCDC from W i l s o n v i l l e . T h i s Batch VI s o l vent was of a lower q u a l i t y than Batch I s o l v e n t which was operable on t h e SRT u n i t i n the donor mode but very s i m i l a r i n q u a l i t y t o Batch I I I . Attempts t o run Batch I I I s o l v e n t on the continuous Bench-Scale SRT u n i t were u n s u c c e s s f u l i n t h e hydrogen donor mode. Gaseous hydrogen a d d i t i o n , a t e l e v a t e d p r e s sure, was r e q u i r e d . Attempts t o improve the l a t e r s e r i e s o f s o l v e n t s by c a t a l y t i c hydrogénation proved u n s u c c e s s f u l . This l a t e r phase o f t h e program had the o b j e c t i v e o f determining whether the a d d i t i o n of L i g h t SRC would improve not only SRT u n i t o p e r a b i l i t y i n t h e hydrogen donor mode but a l s o h e l p t o c l o s e the s o l v e n t balance. Table I I I shows the r e s u l t s of o p e r a t i n g t h e SRT u n i t i n the hydrogen donor mode ( c a t a l y t i c a l l y hydrogenated s o l v e n t ) w i t h and without the a d d i t i o n of L i g h t SRC t o the d i s t i l l a t e solvent. Batch I s o l v e n t was Tised i n Run 9. A blend o f Batch VI s o l v e n t and L i g h t SRC, 70/30 weight r a t i o , were c a t a l y t i c a l l y hydrogenated as t h e feed t o Runs 1 and 3. The hydrogen donor c a p a b i l i t y of the s o l v e n t s were measured by the E q u i l i b r i u m microautoclave t e s t s . These bench-scale SRT r e s u l t s a r e r a t h e r e x t r a o r d i n a r y i n respect t o i n c r e ased d i s t i l l a t e y i e l d s and improvement i n u n i t o p e r a b i l i t y w i t h a d d i t i o n o f L i g h t SRC. In Table I I I t h e i n t e g r a t e d y i e l d s r e f e r t o the combinat i o n o f l i q u e f a c t i o n , CSD, and c a t a l y t i c hydrogénation o f the solvent.



MAX. PROCESS TEMP. °C

2

2

(

(

1

3

)

)

)

441

441

440

(1) (2) (3)

441

( 2 )

3

3.5

3.5

3.5

3.5

3.5

OPERATING PRESSURE MPa

30

30

30

30

0

% LIGHT SRC

0.55

1.54

0.55

1.54

1.20

RESIDENCE TIME ABOVE 316°C MIN.

Hydrogenated W i l s o n v i l l e Solvent Hydrogenated Blend Conversion Measured i n THF r a t h e r than CRESOL

441

( 2 )

1

I n t e g r a t e d Performance

1

(

9

Liquefaction U n i t Alone

SRT RUN NO.

( 3 )

83.4

80.6

83.6

80.6

78.4

CONVERSION (CRESOL)

( 3 )

60.0

55.2

75.1

70.0

76.4

535+°C SRC

5.5

6.8

2.0

0.8

-3.0

6

C x206°C

WT% MAF COAL

SRT LIQUEFACTION-HYDROGEN DONOR MODE WITHOUT GASEOUS HYDROGEN

TABLE I I I


7.4

10.4

-0.8

1.0

-3.6

206x535°C

208

COAL LIQUEFACTION

FUNDAMENTALS


To evaluate the e f f e c t of adding gaseous hydrogen d i r e c t l y t o t h e SPT u n i t without e x t e r n a l l y hydrogenating the s o l v e n t , one run was made with the a d d i t i o n of L i g h t SRC. Table IV shows the e f f e c t s o f L i g h t SRC a d d i t i o n and again i n c r e a s e d d i s t i l l a t e y i e l d s are noted. The i n d i c a t i o n i s t h a t the process i s i n s o l v e n t balance. F u r t h e r work i s r e q u i r e d on an i n t e g r a t e d b a s i s r e c y c l i n g both L i g h t SRC and d i s t i l l a t e s o l v e n t t o f u r t h e r s u b s t a n t i a t e these i n i t i a l f i n d i n g s . Kerr-McGee CSD Performance as R e l a t e d t o Product Q u a l i t y . As p r e v i o u s l y mentioned, t h e f i n a l phase o f the program i n v o l v e d c y c l i c shipments between CCDC t o Kerr-McGee C o r p o r a t i o n . Vacuum bottoms produced v i a c o n v e n t i o n a l SRC-I o r SRT l i q u e f a c t i o n modes were sent t o Kerr-McGee f o r c r i t i c a l s o l v e n t deashing and fractionation. I n some i n s t a n c e s the recovered L i g h t SRC was sent back t o CCDC f o r r e c y c l e . Kerr-McGee attempted t o recover an amount o f L i g h t SRC r e q u i r e d t o maintain r e c y c l e . In most i n s t a n c e s an e q u i v a l e n t amount of L i g h t SRC was recovered t o s u s t a i n r e c y c l e i n both the c o n v e n t i o n a l SRC and SRT modes. Approximately 30% o f the MAF c o a l was l o s t t o the r e j e c t e d K e r r McGee phase, ash c o n c e n t r a t e , as SRC, and i t appeared t h a t the amount of SRC l o s t t o the ash concentrate as a percent of the MAF c o a l was e s s e n t i a l l y constant and independent o f a wide range of l i q u e f a c t i o n s e v e r i t i e s . I f the CSD performance was expressed as a f r a c t i o n o f t h e SRC produced, the CSD performance was h i g h l y dependent upon the q u a l i t y o f the SRC. Higher p r e asphaltene content corresponded t o lower SRC r e c o v e r y . At t h e extreme l i m i t , low r e s i d e n c e time, no gaseous hydrogen a d d i t i o n and h i g h temperature, t h e SRC product i s o f a very podr q u a l i t y , high preasphaltene content (Table V ) . Here, c o n s i d e r a b l y more than t h e 30 wt% o f MAF c o a l was l e f t i n ash c o n c e n t r a t e . I t i s i n t e r e s t i n g t o note t h a t the comparison run, made a t h i g h e r l i q u e f a c t i o n s e v e r i t y , produced a comparable p r e a s p h a l tene content. But upon f u r t h e r examination of these products by Mobil's SESC a n a l y s e s , a n o t i c e a b l e d i f f e r e n c e between the p r o ducts was observed. The lower s e v e r i t y product showed a higher content o f t h e h i g h e r SESC f r a c t i o n s . U n f o r t u n a t e l y , the work done between CCDC and Kerr-McGee was performed i n a blocked-out f a s h i o n which n e c e s s i t a t e d t h e r e h e a t i n g o f v a r i o u s products a t e i t h e r Kerr-McGee or CCDC which can r e s u l t i n thermal degradat i o n of the products. In W i l s o n v i l l e Runs 143 and 147, thermal degradation of the c o a l - d e r i v e d products g r e a t l y a f f e c t e d t h e SRC recovery on the Kerr-McGee CSD U n i t . Both runs were made a t i d e n t i c a l l y the same o p e r a t i n g c o n d i t i o n s , except i n Run 143, where presumably c a t a l y t i c a l l y a c t i v e s o l i d s were allowed t o accumulate i n the l i q u e f a c t i o n r e a c t o r , whereas i n Run 147 the s o l i d s were removed. The product y i e l d s e x i t i n g the r e a c t o r f o r both runs were very s i m i l a r ; however, the thermal s e n s i t i v i t y o f the



MAX. PROCESS TEMP. °C

441

2

441

1

13.9

13.9

13.9

30

30

0

OPERATING* * PRESSURE % LIGHT MPA SRC

3.3

3.3

3.0

RESIDENCE TIME ABOVE 316°C MIN.

( 1 ) Hydrogen t r e a t r a t e 0.11mvkg (2) Conversion measure i n THF r a t h e r than CRESOL

2

Integrated Performance

440

22

Liquefaction U n i t Alone

SRT RUN NO

87.8

87.8

81.8

( 2 )

CONVERSION (CRESOL)

66.3

75.0

76.6

( 2 )

535+°C SRC

6

e

5.1

5.1

2.0

C x206 C

WT% MAF COAL

SRT LIQUEFACTION-DIRECT HYDROGENATION WITH GASEOUS HYDROGEN

TABLE IV


210

COAL LIQUEFACTION FUNDAMENTALS TABLE V PRODUCT RECOVERY OF SHORT CONTACT TIME FEEDS

LIQUEFACTION CONDITIONS

SRT-4

EXIT TEMPE RATURE , °C TIME ABOVE 316°C, MIN. HYDROGEN GAS, MPa

SRT-2

454 0·6 NONE

441 3.3 137

27 73

25 75

30

58


NET CSD SOLIDS FREE FEED ANALYSJg», #T% BENZENE SOLUBLE BENZENE INSOLUBLE NET RECOVERY IN CSD, WT% OF SOLIDS FREE FEED

E x c l u d i n g the amount o f L i g h t SRC r e q u i r e d t o s u s t a i n

recycle.

TABLE VI EFFECT OF PRESSURE AT WHICH SRC WAS PRODUCED ON CSD RECOVERY

WILSONVILLE COMMON OPERATING CONDITIONS KENTUCKY 6/11 COAL 800 kg/hm

3

440°C

RUN NO. SRC REACTOR PRESSURE (MPa)

150

151

11.7

14.5

CONVERSION (MAF COAL %)

94

94

SRC YIELD (MAF COAL %)

65-67

59-61

78%

85%

% SRC RECOVERY IN CSD (OPTIMIZED)


10.

KULIK E T A L .

Processing

Coal Liquefaction

Products

211

products were v a s t l y différent» Products produced from Run 147 degraded most r e a d i l y t o " p o s t - a s p h a l t e n e s . This resultant degradation lowered the CSD SRC r e c o v e r y . A d d i t i o n a l work a t W i l s o n v i l l e showed t h a t the CSD performance i s l i n k e d d i r e c t l y t o the q u a l i t y of SRC produced (Table VI)· A q u e s t i o n then a r i s e s as t o whether the CSD recovery i s being l i m i t e d by the preasphaltene content produced from d i r e c t products of c o a l l i q u e f a c t i o n o r whether by low l i q u e f a c t i o n s e v e r i t y a more thermally s e n s i t i v e product i s produced r e s u l t i n g i n r e t r o g r e s s i v e r e a c t i o n s of l i q u e f a c t i o n products t o "post-asphaltenes." There i s some i n d i c a t i o n that " v i r g i n " p r e asphaltene s, primary products o f c o a l d i s s o l u t i o n , a r e more e a s i l y recovered v i a CSD as shown i n Table V I I ; however, "postasphaltenes" made from thermal r e g r e s s i v e r e a c t i o n s are n o t . The species are inseparable by o r d i n a r y a n a l y t i c a l measures. Further work i s b e i n g done t o more c l e a r l y understand the r o l e of r e g r e s s i v e r e a c t i o n s i n low s e v e r i t y l i q u e f a c t i o n . In a d d i t i o n , r e c e n t work has r e s u l t e d i n techniques f o r o b t a i n i n g h i g h SRC r e c o v e r i e s from l e s s d e s i r a b l e feedstocks.


M

TABLE V I I CSD RECOVERY OF A SHORT CONTACT FEED

•

FEED PRODUCED AT WILSONVILLE (INDIANA V COAL)

•

CONTAINED ABOUT 1/3 DISTILLATE PRODUCTS (MOSTLY OILS)

•

CSD FEED ANALYSIS, WT% OF SOLIDS FREE FEED OIL ( i n c l u d e s D i s t i l l a t e ) ASPHALTENE PREASPHALTENE

•

30.3 35.7 33.9

CSD PRODUCT RECOVERY, WT% OF FEED COMPONENT OIL ASPHALTENE PREASPHALTENE

94.4 88.6 74.6

C o n c l u s i o n s . The q u a l i t y o f l i q u e f a c t i o n s o l v e n t i s an extremely important f a c t o r i n l i q u e f y i n g c o a l a t conventional or s h o r t r e s i d e n c e time l i q u e f a c t i o n c o n d i t i o n s . The a b i l i t y t o a l t e r the q u a l i t y of t h i s s o l v e n t by r e c y c l e of c e r t a i n SRC



212

fractions has made a marked improvement in the liquefaction performance over a wide range of liquefaction severities* The implication of these findings as to a finalized overall process scheme has yet to be determined; however, this work supports the underlying process concept of being able to efficiently u t i l i z e hydrogen to produce a particular product slate* Further work i s needed on an integrated basis to substantiate these i n i t i a l findings*


Literature Cited 1)

D. D. Whitehurst, M. Farcasiu, and T. O. Mitchell, "The Nature and Origin of Asphaltenes i n Processed Coals," EPRI Report AF480, Annual Report, RP410, July 1977.

2)

J . R. Longanbach, J. R. Droege, and S. P. Chauhan, "Short Residence Time Coal Liquefaction," EPRI Report AF780, Final Report, RP779-5, June 1978.

3)

R. M. Adams, A. H. Knebel, and D. E. Rhodes, " C r i t i c a l Solvent Deashing of Liquefied Coal," American Institute of Chemical Engineers, Miami, Florida, November 15, 1978.

4)

G. P. Curran, R. T. Struck, and E . Gorin, Ind. and Eng. Chemistry Proc. Des. and Dev. 6, No. 2, 166 (1967).

5)

J . A. Kleinpeter, F. P. Burke, P. J . Dudt, and D. C. Jones, "Process Development for Improved SRC Options: Interim Short Residence Time Studies," EPRI Report AF1158, Interim report, August 1979.

6)

E . Gorin, C. J . Kulik, and H. E. Lebowitz, "Deashing of Coal Liquefaction Products Via P a r t i a l Deasphalting. 2. Hydrogenation and Hydroextraction Effluents," INEC Process Design and Developments, V o l . 16, Jan. 1977.

RECEIVED April 30, 1980.


Processing Short-Contact-Time Coal Liquefaction Products - ACS

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