Fluidized-Bed Upgrading of Wood Pyrolysis Liquids and Related

Chapter 24

Fluidized-Bed Upgrading of Wood Pyrolysis Liquids and Related Compounds

Downloaded by PURDUE UNIV on June 7, 2016 | http://pubs.acs.org Publication Date: September 30, 1988 | doi: 10.1021/bk-1988-0376.ch024

Ν. Y. Chen, D. E. Walsh, and L . R. Koenig Mobil Research and Development Corporation, Central Research Laboratory, P.O. Box 1025, Princeton, N J 08540

The effective hydrogen index (EHI) is a calculated indicator of the "net" hydrogen/ carbon ratio of a pure or mixed heteroatom -containing feed, after debiting the feed's hydrogen content for complete conversion of heteroatoms to NH , H S, and H O. Compounds with EHI's less than about 1 are difficult to upgrade to premium products over ZSM-5 catalyst due to rapid catalyst aging in continuous fixed bed processing. However, high conversions of such feeds (acetic acid, methyl acetate, and wood pyrolysis liquids) can be maintained in a fluidized bed system operating under methanol-to-gasoline conditions and employing frequent catalyst regenerations. Also, synergistic effects were observed for blends of low and high EHI model compounds, as well as for wood pyrolysis liquids coprocessed with methanol. Based on these results, a processing scheme is described in which the char from the wood pyrolysis step is gasified to make methanol which is cofed with the pyrolysis liquids over ZSM-5. 3

2

2

Z e o l i t e ZSM-5 i s p a r t i c u l a r l y e f f e c t i v e f o r the conversion of methanol t o g a s o l i n e range hydrocarbons (1). I n a d d i t i o n t o methanol, other oxygenates, i n c l u d i n g t h e i r complex mixtures, can be converted as w e l l (see, f o r example, r e f e r e n c e s 2-8). 0097-6156/88/0376-0277$06.00/0 ©1988 American Chemical Society

Soltes and Milne; Pyrolysis Oils from Biomass ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

278

PYROLYSIS OILS FROM BIOMASS

The

e f f e c t i v e hydrogen index i s d e f i n e d as: H-20-3N-2S (H/C) ££ective or EHI e

=

C

where H, C, 0, N, and S are atoms per u n i t weight of sample of hydrogen, carbon, oxygen, n i t r o g e n and sulfur, respectively. Model oxygen c o n t a i n i n g compounds, or "oxygena t e s , having EHI's 91.0 (94.9) 90.4 (89.2)

(1.8) (15.8) (42.1) (10.8) (11.4)

1.3 95

1.1 5.2 48.8 5.2 9.9

0.0 0.2 55.8 1.4 19.0

3.7 31.4 28.4 20.2 3.8

6.2 17.6 21.5 13.9 6.0

2.1 9.4 45.3 9.6 7.9

23.3

10.6

32.1

24.9 (17.0)

28.7 (19.1)

42.3

14.4

38.1

32.8 (28.4)

38.6 (33.0)

0.3

1.9

2.7

(1.2). (10.6) (46.7) ( 7.7) (13.9)

4

0.8 ( i . i )

1.1 ( 0.8)

7.6 5.4 7.2 1.5 5.6 0.6 1.6 0.1 0.7 0.4 14.2 25.9 13.8 6.7 5.2 0.5 %5.5 0.4 0.5 0.3 0.1 0.4 0.1 0.3 0.0 ic ' 1.9 5.8 1.6 15.7 1.4 nC.' 24.9 "(37.5) 44.6 14.7 23.5 (34.0) 23.3 Total C 72.3 (58.1) 54.7 74.1 (59.8) 65.0 78.7 Cg+ (gasoline) 2.8 ( 4.4) 0.7 11.7 6.6 2.4 ( 6.2) Coke 1.4*** 1.3 1.3 H/C (effective)* * 1.7 of C + * Numbers shown i n parentheses are the calculated values which would be expected i f the mixture's behavior was the arithmetic average of i t s two components. ** Small amounts of oxygen were observed i n the Cg+ l i q u i d . The use of the effective hydrogen index corrects for this. *** Approximate numbers. 2

4

4

5


284


On a weight b a s i s , a c e t i c a c i d y i e l d s only 40% as much hydrocarbon as methanol. The lower y i e l d i n ZSM-5 p r o c e s s i n g r e s u l t s p r i m a r i l y from a c e t i c a c i d ' s carbon l o s s due t o oxygen r e j e c t i o n through d e c a r b o x y l a t i o n t o

co .


2

Methylacetate has an EHI of 0.67 and thus, o r d i n a r i l y , would a l s o be considered d i f f i c u l t to process. I t s net hydrogen content, however, i s s u b s t a n t i a l l y higher than t h a t of a c e t i c a c i d . Because of i t s higher carbon content (48.6% C), and d e s p i t e d e c a r b o x y l a t i o n and coking r e a c t i o n s , the observed hydrocarbon y i e l d remains comparable t o t h a t of methanol. Moreover, hydrocarbon s e l e c t i v i t y f o r d i r e c t conversion t o C-+ g a s o l i n e i s higher than a c e t i c a c i d or methanol. Thus, the d i r e c t y i e l d of Cg+ g a s o l i n e i s 32.1% on charge vs 23.3% f o r methanol. From a hydrogen balance standpoint, both a c e t i c a c i d and methyl acetate r e j e c t l e s s HgO and more 0 0 than methanol, with r e s u l t a n t Cg+ l i q u i d s having e f f e c t i v e H/C's of approximately 1.3 vs 1.7 - 2 f o r methanol p r o c e s s i n g . χ

Mixtures of A c e t i c A c i d and Methanol. P r o c e s s i n g a 1.9/1 or a 3.8/1 molar mixture of CH^OH and a c e t i c a c i d provided o b s e r v a t i o n s s i m i l a r t o those already d i s c l o s e d by Chang e t a l (8), v i z , an enhancement i n Cg+ l i q u i d y i e l d a t the expense of C^- vs what might be expected i f the mixture behaved as the average of i t s two components, the c a l c u l a t e d values f o r which are shown i n parentheses i n Table I I . The s e l e c t i v i t i e s of the hydrocarbon products amplify the observed synergism with r e s p e c t t o Cg+ l i q u i d s . Furthermore, there i s an enhancement i n t o t a l hydrocarbon y i e l d vs l i n e a r combination expectations. As shown i n Table I I , the e f f e c t of i n c r e a s i n g mole percent methanol i n the MeOH/acetic a c i d charge i s an attendant decrease i n oxygen r e j e c t i o n as COg and an i n c r e a s e i n oxygen removal as HgO. Thus, more carbon remains a v a i l a b l e t o form hydrocarbon products, much of i t becoming Cg+ l i q u i d s . The above f i n d i n g s demonstrate t h a t a short contact time f l u i d bed r e a c t o r o p e r a t i n g i n a c y c l i c mode can be used t o process low EHI compounds to y i e l d s u b s t a n t i a l amounts of C + l i q u i d hydrocarbon products. K


CHENET AL.

Fluidized-Bed Upgrading of Wood Pyrolysis Liquids

285


By co-processing a low EHI m a t e r i a l with a high EHI compound such as methanol, a s h i f t i n oxygen r e j e c t i o n from d e c a r b o x y l a t i o n t o dehydration takes p l a c e . The s h i f t r e s u l t s i n an i n c r e a s e d y i e l d of hydrocarbons. The r e a c t i o n of a c e t i c a c i d may have p o t e n t i a l a p p l i c a t i o n i n c o n v e r t i n g fermentation products t o hydrocarbons. A c e t i c a c i d i s a major by-product i n b a c t e r i a l fermentation of biomass t o ethanol (13). Mixtures of a c e t i c a c i d and ethanol may a l s o be processed t o hydrocarbons (14). Upgrading of Wood P y r o l y s i s L i q u i d s . The products from sawdust p y r o l y s i s a t 520°C i n f l o w i n g helium a t atmospheric pressure produced the y i e l d s shown i n Table III. Table I I I .

e

Wood P y r o l y s i s a t 520 C and 1 atm.

Product CH CO C0 L i q u i d Oxygenates Char 4

2

Wt.% 1.4 7.1 8.5 55.0 28.0

Because the o b j e c t of these experiments was t o t r a c k the amount of wood carbon which could be converted t o hydrocarbons by pyrolysis/ZSM-5 upgrading schemes, the amount of water produced by p y r o l y s i s was not measured, and water i n the p y r o l y s i s l i q u i d s was f e d along with the oxygenated products i n subsequent ZSM-5 p r o c e s s i n g . Elemental analyses and the apparent EHI's ( i n c l u d i n g any water) are presented i n Table IV. I n s p e c t i o n of these data i n d i c a t e t h a t the l i q u i d products c o n t a i n about 31% o f the o r i g i n a l wood carbon. The char product accounts f o r another 49 wt% of the o r i g i n a l wood carbon, and i s a v a i l a b l e f o r i n d i r e c t l i q u e f a c t i o n v i a g a s i f i c a t i o n and methanol s y n t h e s i s . The remaining 20% of the wood carbon becomes CO, COg and methane, about h a l f of which (as C H and CO) i s a l s o p o t e n t i a l l y a v a i l a b l e f o r conversion t o methanol. When processed i n the presence of methanol, wood p y r o l y s i s l i q u i d s e x h i b i t e d synergisms and s e l e c t i v i t y s h i f t s s i m i l a r t o those d i s c u s s e d above f o r the model 4


286


Table IV.

wt%

Aqueous L i q u i d Laver (51%}

Organic L i q u i d Laver (4%)

Char

25.9 8.8 65.3

55.0 7.5 37.5

87.3 3.9 8.0

Ash

49.2 6.8 43.4 0.6

-

-

EHI

0.3

0.3

0.6

Sawdust

c H

0


Elemental A n a l y s i s ,

-

compounds. The d e t a i l s of t h i s behavior are presented below w i t h i n the context of two p o t e n t i a l p r o c e s s i n g arrangements shown i n F i g u r e s 2 and 3. A major f e a t u r e common t o both i s the use of the p y r o l y s i s char as a cheap source of methanol. F i g u r e 2 shows the products obtained i n a scheme i n which d i r e c t upgrading of the wood p y r o l y s i s l i q u i d s over ZSM-5 occurs i n p a r a l l e l with upgrading of methanol obtained from s y n t h e s i s gas d e r i v e d from g a s i f i c a t i o n of the p y r o l y s i s char. In F i g u r e 3, the methanol i s mixed with the p y r o l y s i s l i q u i d s p r i o r to co-processing over ZSM-5. Approximately 40 l b s . of methanol per 100 l b s . of dry wood feed i s p o t e n t i a l l y a v a i l a b l e from the char and p y r o l y s i s gas products. T h i s amount would provide a weight r a t i o of methanol/pyrolysis l i q u i d s of 0.73. In the p a r a l l e l p r o c e s s i n g scheme, a t o t a l of 2 0 . 6 l b s . of hydrocarbon (approximately 85% Cg+ g a s o l i n e , i n c l u d i n g a l k y l a t e ) per 95 l b s . of t o t a l feed ( p y r o l y s i s l i q u i d and methanol) i s obtained. In the co-processing mode, approximately 3 l b s . of a d d i t i o n a l hydrocarbon r e s u l t concomitant with reduced oxygenates and coke. Stated d i f f e r e n t l y , without char g a s i f i c a t i o n , o n l y about 6% of the carbon i n the wood could be upgraded t o hydrocarbon products even i f a l l the oxygenates produced by p y r o l y s i s were r e c y c l e d to e x t i n c t i o n . P a r a l l e l upgrading of methanol d e r i v e d from char g a s i f i c a t i o n can i n c r e a s e t h i s value to approximately 36%, i . e . , about 6% from the p y r o l y s i s l i q u i d s and 30% from methanol. Methanol co-processing boosts the percent of wood carbon transformed i n t o


24.

CHEN ET AL.


17 LBS. GAS ( C O . C 0 . C H ) 2

100 LBS. DRY WOOD

4

28 L B S . CHAR

PYROLYSIS

GASIFICATION AND SHIFT

OXYGEN WATER

SYNTHESIS GAS


55 LBS. PYROLYSIS I LIQUIDS

METHANOL CONVERSION

40 LBS. METHANOL

ZSM-5 PROCESSING

ZSM-5 PROCESSING

7"

J

3.2 LBS. HYDROCARBON 17.6 LBS. OXYCENATES 26.4 LBS. WATER 4.2 L B S . C 0 3.6 LBS. C O K E

17.4 LBS. HYDROCARBON 22.6 LBS. WATER

2

Figure 2 .

P a r a l l e l Processing

Scheme

17 LBS. GAS (CO, C 0 , C H ) 2

100 LBS. DRY WOOD"

PYROLYSIS

4

28 LBS. CHAR

GASIFICATION AND SHIFT

OXYGEN WATER

SYNTHESIS GAS 55 LBS. PYROLYSIS LIQUIDS

METHANOL CONVERSION 40 LBS. METHANOL

ZSM-5 PROCESSING

23.6 LBS. HYDROCARBON 10.6 LBS. O X Y C E N A T E S 59.0 LBS. WATER 1.8 LBS. C O K E

Figure

3.

C o p r o c e s s i n g Scheme


287

288


hydrocarbon products t o approximately 42%, i . e . , about 12% from the p y r o l y s i s l i q u i d s and 30% from methanol.


Conclusions Hydrocarbon y i e l d s can be increased s i g n i f i c a n t l y when wood p y r o l y s i s l i q u i d s are coprocessed with methanol over ZSM-5 c a t a l y s t vs separate p r o c e s s i n g of the two streams over the same c a t a l y s t . Thus, coprocessing p y r o l y s i s l i q u i d s with methanol produced from char g a s i f i c a t i o n i s one means of producing hydrocarbon f u e l s from wood. R e s u l t s obtained i n t h i s study provide a b a s i s f o r comparison with other p r o c e s s i n g schemes such as wood g a s i f i c a t i o n followed by e i t h e r F i s c h e r - T r o p s c h s y n t h e s i s o r methanol s y n t h e s i s plus Mobil's MTG process. Literature

Cited

1. Chang, C. D. and Lang, W. H., U. S. Patent 3 894 103, 1975 . 2. Chang, C. D. and Silvestri, A. J., J. Catal. 1977, 47, 249. 3. Kuo, J. C., Prater, C. D. and Wise, J. J., U. S. Patent 4 041 094, 1977. 4. Ireland, H. R., Peters, A. W. and Stein, T. R., U.S. Patent 4 045 505, 1977. 5. Haag, W. O., Rodewald, P. G. and Weisz, P. B., U. S. Patent 4 300 009, 1981. 6. Brennan, J. Α., Caesar, P. D., Ciric, J. and Garwood, W. E., U. S. Patent 4 304 871, 1981. 7. Weisz, P. B., Haag, W. O. and Rodewald, P. G., Science, 1979, 206, 57. 8. Chang, C. D., Chen, Ν. Υ., Koenig, L. R. and Walsh, D. E., "Synergism in Acetic Acid/Methanol Reactions Over ZSM-5 Zeolites", Am. Chem. Soc. Div. Fuel Chem. Preprints, 1983, 28 (2) 146. 9. Chang, C. D., Lang, W. H. and Silvestri, A. J., U.S. Patent 3 998 898, 1976. 10. Chantal, P., Kaliaguine, S., Grandmaison, J. L. and Mahay, Α., Appl. Catal., 1984, 10, 317. 11. Walsh, D. E., U. S. Patent 4 419 328, 1983. 12. Lee, W., Maziuk, J., Weekman, Jr., V. W. and Yurchak, S., "Mobil Methanol-to-Gasoline Process," Large Chemical Plants, Elsevier Scientific Publishing Co., Amsterdam, The Netherlands, 1979.


24. CHEN ET AL.


289

13. Cooney, C. L., Wang, D. I. C., Wang, S. D., Gordon, J. and Jiminez, Μ., Biotech. Bioeng. Symp., 1978, 8, 103. 14. Chen, N. Y., Degnan, T. F. and Koenig, L. R., Chemtech, 1986, 16, 506.


RECEIVED March 31, 1988


Fluidized-Bed Upgrading of Wood Pyrolysis Liquids and Related

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