Pyrolysis Oils from Biomass - American Chemical Society

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Chapter 21

Catalytic Hydrotreating of Biomass-Derived Oils Eddie G. Baker and Douglas C. Elliott 1

Pacific NorthwestLaboratory ,P.O.Box 999, Richland,WA99352 Pacific Northwest Laboratory (PNL) is investigating the catalytic upgrading of biomass-derived oils to liquid hydrocarbon fuels. Tests have been conducted in a 1 - l i t e r , continuous-feed, fixed-bed catalytic reactor at 250-450°C and 2,000 psig. Catalytic upgrading is envisioned as the second stage in a two– stage process to produce hydrocarbon fuels from biomass. Direct thermochemical liquefaction of biomass produces a phenolic oil containing very few hydrocarbons. Hydrotreating these oils can produce nearly pure hydrocarbons, primarily aromatics and naphthenes which would be useful in gasoline blending.

Two types of biomass-derived o i l s have been studied at PNL. The f i r s t type of o i l i s produced by high pressure liquefaction at r e l a t i v e l y long residence times. O i l s i d e n t i f i e d as TR7 and TR12 in Table I were produced by t h i s type of process at the Albany, Oregon Biomass Liquefaction Experimental F a c i l i t y . These highly viscous o i l s consist primarily of substituted phenols and naphthols (1-2). The other type of o i l i s produced by low-pressure, flash pyrolysis at somewhat higher temperature and very short residence times. These o i l s are highly oxygenated and contain a large fraction of dissolved water (3). Because of the soluble water, these o i l s have a much lower viscosity (4). The flash pyrolysis o i l produced at Georgia Tech is typical of this type of o i l . The fourth o i l shown in Table I was made at PNL by pretreating the Georgia Tech pyrolysis o i l to produce an o i l more similar to the high-pressure o i l s . Details of the pretreating step are given by E l l i o t t and Baker (5). operated by Battelle Memorial Institute for the U.S. Department of Energy under Contract DE-AC06-76RLO-1830.

0097-6156/88/0376-0228$06.00/0 ° 1988 American Chemical Society

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


21. BAKER & ELLIOTT

TABLE I.

Catalytic Hydrotreating ofBiomass-Derived Oils

Feedstock Oils for Hydrotreating Tests

TR7 As Fed Dry

TR12 As Fed Dry

Georgia Tech Pyrolysis Oil As Fed Dry

74.8 77.5 8.0 7.9 16.6 14.1 < 0.1 < 0.1 0.5 0.5 3.5 0.0

72.6 76.5 8.0 7.8 16.3 12.5 < 0.1 < 0.1 3.0 3.0 5.1 0.0

39.5 55.8 7.5 6.1 52.6 37.9 < 0.1 < 0.1 0.2 0.3 29.0 0.0

Treated Georgia Tech Pyrolysis Oil As Fed Dry

Elemental Analysis, wt % Carbon Hydrogen Oxygen Nitrogen Ash Moisture Density, g/ml @ 55°C Viscosity, cps, G 60°C Carboy Residue,

1.10

-

1.09

—

3,000

-

17,000

-

13.5

13.9

26.9

28.3

1.23 /_N 10

v c ;

61.6 7.6 30.8 < 0.1 0.0 14.1

71.6 7.1 21.1 < 0.1 0.0 0.0

—

1.14 (a)

-

14,200

27-31 (c)

a) at 20°C b) TGA simulated Conradson carbon c) Viscosity and carbon residue were measured for other similar pyrolysis oils


229

PYROLYSIS OILS FROM BIOMASS

230


Hydrotreating Biomass-Derived O i l s Given that biomass can be converted to a l i q u i d product that i s primarily phenolic, then oxygen removal and molecular weight reduction are necessary to produce usable hydrocarbon f u e l s . Upgrading biomass-derived o i l s d i f f e r s from processing petroleum fractions or coal l i q u i d s because of the importance of deoxygenation. This topic has received only limited attention in the l i t e r a t u r e (6-11). Single ring phenolics and c y c l i c ketones present in biomass-derived o i l s can be upgraded to gasoline b o i l i n g range hydrocarbons by deoxygenation. H y d r o g é n a t i o n of the aromatic structure i s not desirable i f high octane gasoline i s the intended product. Batch reactor tests with model compounds showed sulfided cobalt molybdenum (CoMo) catalysts to be the best choice for deoxygenation without saturating the resulting aromatics (7). Polycyclic compounds such as naphthol must be deoxygenated and cracked to make gasoline b o i l i n g range hydrocarbons. Hydrocracking of p o l y c y c l i c aromatics requires saturation of one of the rings p r i o r to cracking (12). Nickel molybdenum (NiMo) catalysts are more e f f e c t i v e f o r ring saturation than CoMo c a t a l y s t s . The heavy fraction of biomassderived o i l s i s not as well characterized and the reaction mechanism f o r upgrading i s unknown. Use of an a c i d i c support (such as a zeolite) compared with alumina may be beneficial for upgrading the high molecular weight fraction (13). Experimental The reactor system used for t h i s study i s a fixed-bed reactor operated in an upflow mode. It i s shown in Figure 1. Operation in the downflow mode (trickle-bed) plugged the outlet l i n e of the reactor with coke-like material and tests in this mode were discontinued. The o i l feedstock, preheated to 4 0 - 8 0 ° C , i s pumped by a high-pressure metering pump. Hydrogen from a high-pressure cylinder is metered through a high-pressure rotameter into the o i l feed l i n e before entering the reactor vessel. The reactor i s 7.5 cm I.D. by 25 cm and holds approximately 700 ml of c a t a l y s t . A two phase flow pattern exists in the reactor. Gas and v o l a t i l e products move through the reactor quite rapidly. Unconverted, non-volatile material does not leave the reactor until i t reaches the top of the l i q u i d level and overflows into the product line. Pressure in the system i s maintained by a Grove back-pressure regulator. Liquid product i s recovered in a condenser/separator and the o f f gas i s metered and analyzed before i t i s vented. Catalysts used in the most recent hydrotreating tests are shown in Table II. The Harshaw catalysts are conventional extruded CoMo and NiMo hydrotreating c a t a l y s t s . The Haldor Topsoe catalysts are a composite system using low a c t i v i t y rings in the bottom of the bed to prevent plugging from carbon and metals, and high a c t i v i t y extrudates in the top of the bed. The Katalco and Shell catalysts are commercially available hydrotreating c a t a l y s t s . The l a s t three catalysts are hydrocracking catalysts which incorporate the metal h y d r o g é n a t i o n component on an acidic support for cracking.


Catalytic Hydrotreating of Biomass-Derived OUs


21. BAKER & ELLIOTT

Figure 1.

Flow Schematic of 1 - l i t e r Continuous Hydrotreater


231

232



TABLE II.

Catalysts Used for Hydrotreating/Hydrocracking

Supplier

Catalyst ID

Harshaw

HT 400

Active Metals

HT 500

Hal dor Topsoe^

TK 710

Hal dor Topsoe^

TK 750

b

A1 0

NiO MoO

3.5 15.5

AI0O3

1/8-in Ε

CoO

2

AI0O3

3/16-in R

M0O3

6 2.3 10.0

A1 0

3

1/16-in Ε

3.4 14.0

A1 0

3

1/16-in Ε

3.5 14.0

AI0O3

2.67 14.48

A1 0

CoO

TK 770

CoO

M0O3 Katalco

ΚΑΤ4000

CoO

M0O3 Shell

S411

NiO

M0O3 PNL/Linde

CoMo/Y

CoO

M0O3 PNL/Grace

CoMo/SiAl

CoO

M0O3 Amoco

NiMo/Y

1/8-in Ε

3 15

M0O3 Hal dor Topsoe

Form

Support

CoO Mo0

3

Harshaw

Weight Percent

Tests

NiO

M0O3

2

2

2

2

3

3

C

1/32-in Ε 1/20-in Τ

C

3.5 13.9

AI0O3

Y-zeolite/

1/16-in Ε

3 13

13% A1 0 in S i 0

3/16-in Τ

3.5 18

Y-Zeolite/ A1 0

2

3

2

2

3

1/16-in Ε

C

a) Ε = extrudate R = ring Τ = tablet, size given is O.D. b) All three catalysts used in a layered bed. c) Includes phosphorus oxide. ;


21.

BAKER & ELLIOTT

Catalytic Hydrotreating of Biomass-Derived Otis


Results and Discussion Most of the test work has been done with two product o i l s from the Albany, Oregon Biomass Liquefaction Experimental F a c i l i t y . Both o i l s were produced in an a l k a l i - c a t a l y z e d , reducing gas environment with long residence times and high pressure (3000 p s i g ) . The TR12 represents a PERC-type recycle o i l slurry process, and TR7 represents the LBL-type aqueous slurry single pass process. Detailed process descriptions (14) can be found elsewhere. Only a limited number of tests have been conducted with pyrolysis o i l s . They behave much d i f f e r e n t l y than the high-pressure o i l s and w i l l be discussed separately. Tests with Cobalt-Molybdenum Catalysts Because of t h e i r effectiveness for hydrodeoxygenation, we have used primarily CoMo catalysts in our studies. Table III shows results obtained with the TR12 o i l and the Haldor Topsoe composite catalyst system at about 400°C, 2,000 psig and three d i f f e r e n t space v e l o c i ties. Typically, the l i q u i d product y i e l d from the TR12 o i l i s about 0.9 1/1 of o i l fed. At the low space velocity (0.11 h~ ) the o i l i s 96% deoxygenated and i s about one-third high quality aromatic gasoline (C - 2 2 5 ° C ) . At even lower space v e l o c i t i e s (~0.05 h" ) a l i q u i d product containing about 60% gasoline and almost nooxygen can be produced. At higher space v e l o c i t i e s (up to 0.44 h" ) deoxygenation i s s t i l l high, nearly 80%, but hydrogen consumption decreases 50% or more resulting in a lower H/C r a t i o , higher density, and lower gasoline y i e l d . The theoretical hydrogen requirement to deoxygenate TR12 i s about 200 1/1 of o i l . This indicates that at the low space velocity 350 1 H /l o i l i s being used for h y d r o g é n a t i o n , hydrocracking and other reactions. At the highest space velocity only about 50 1 H /l o i l i s being used by these other reactions. 5

2

2

TABLE III.

Results of Hydrotreating TR12 Oil with Haldor Topsoe Composite Catalyst HT-34

Run No.

HT-34

HT-34

Temperature, °C Pressure, psig 2,030 . Space Velocity, LHSV, h"

397 2,020

395 2,015

403

.11

.30

.44

Hydrogen Consumption, 1/1 o i l fed Product Y i e l d , 1/1 o i l fed Deoxygenation, wt%

548 .92 96

296 .88 87

212 .94 79

0.8 1.5 0.91 37

2.5 1.3 1.0 24

3.8 1.3 1.03 11

A

Product

Inspections

Oxygen, wt% H/C r a t i o , mole/mole Density, kg/1 Yield C - 225°C, LV% 5


233


234


Table IV shows results from hydrotreating TR7 with Harshaw C0M0/AI0O3 c a t a l y s t . Results obtained with the Harshaw catalyst and TR12 o i l were s i m i l a r to those obtained with the Haldor Topsoe composite c a t a l y s t . This s i m i l a r i t y indicates that the differences between Tables Ι Ι Ι - a n d IV are due primarily to the o i l . At a space velocity of 0.1 h" , the TR7 o i l i s completely deoxygenated and almost e n t i r e l y converted to gasoline b o i l i n g range hydrocarbons. At s i m i l a r processing conditions the o i l produced from TR7 i s higher quality than the o i l obtained from TR12 as shown in Figures 2 and 3. Analysis of TR7 and TR12 o i l s has shown that TR7 i s composed primarily of single ring phenolics (1) which when deoxygenated become gasoline b o i l i n g range aromatics. The TR12 o i l i s composed primarily of double ring phenolics which require additional cracking and h y d r o g é n a t i o n to produce l i g h t d i s t i l l a t e s . TABLE IV. Run.

Results of Hydrotreating TR7 Oil with Harshaw CoMo/Al 0 * 2

No.

Temperature, °C Pressure, psig Space Velocity, LHSV, h'

Ί A

Hydrogen Consumption, 1/1 o i l fed Product Y i e l d , 1/1 o i l fed Deoxygenation, wt%

3

HT-15

HT-14

HT-14

398 2,003 0.10

394 2,021 0.30

389 2,026 0.55

616 0.99 ~100

435 1.0 94

202 0.88 88

0.0 1.65 0.84 >87

1.1 1.41 0.91 60

2.6 1.32 0.96 28

Product Inspections Oxygen H/C r a t i o , mole/mole Density, kg/1 Yield C - 2 2 5 ° C , LV% 5

* adapted from reference

(U)

Results to date indicate 400°C i s about the optimum temperature for hydrotreating biomass-derived o i l s . At 350°C a much poorer quality o i l i s produced. At 450°C the product quality improves somewhat compared with 400°C but the y i e l d i s reduced due to increased gas production. Only a limited number of tests have been run at pressures other than 2000 p s i g . These results showed s i g n i f i c a n t loss of product quality at 1500 psig and no appreciable improvement at 2300 psig compared to results at 2000 p s i g . Results With Other Catalysts Our catalyst development e f f o r t i s aimed at better hydrocracking capability. Hydrodeoxygenation i s achieved readily with the C0M0 catalyst in a sulfided form. Better d i s t i l l a t e y i e l d with minimal aromatic saturation i s our current goal. To t h i s end, we have been


21.

BAKER & ELLIOTT

Catalytic Hydrotreating of Biomass-Derived Oils


5.0

Figure 3. Yield of (400°C, 2000 psig)

Gasoline Boiling Range (C

5

- 225°C)


Oil

235


236


in contact with various catalyst manufacturers to learn what suggestions for wood-oil processing might be made based on present knowledge of petroleum processing. Several hydrocracking catalyst samples have been obtained for t e s t i n g . These include the Shell S411, Katalco 4000, and Amoco NiMo/Y catalysts shown in Table II. In addition we made two hydrocracking catalysts at PNL by impregnating cobalt and molybdenum s a l t s on a Y - z e o l i t e and a s i l i c a - a l u m i n a cracking c a t a l y s t . Comparison of the results obtained to date with d i f f e r e n t hydrotreating and hydrocracking catalysts shows f a i r l y consistent results with a l l c a t a l y s t s . As seen in Figure 4 and 5, a l l the c a t a l y t i c results appear as a single set of data with l i t t l e variation among the d i f f e r e n t c a t a l y s t s . Only the zeolite-based catalysts shown in Figure 5 improved results compared with the conventional CoMo hydrotreating c a t a l y s t s . Note that the difference between Figure 4 and Figure 5 i s due to feedstock. Results with Pyrolysis O i l s When the Georgia Tech pyrolysis o i l was hydrotreated with a sulfided CoMo catalyst at conditions similar to those used with TR7 and TR12 the runs had to be terminated due to severe coking in the bed. The temperature had to be reduced to 250°-270°C to prevent coking. The properties of the o i l produced at these low temperatures are shown in Table I under the heading of treated Georgia Tech pyrolysis o i l . This o i l was further hydrotreated at 350°C and 2,000 psig with a sulfided CoMo c a t a l y s t , and the results were s i m i l a r to those obtained with TR7 and TR12. This i s the basis f o r a proposed two stage upgrading process for biomass pyrolysis o i l s (5). We are currently studying the processing of pyrolysis o i l s in a single step by varying the temperature in the catalyst bed from 270°C at the i n l e t to 400°C at the o u t l e t . Catalyst Deactivation To evaluate catalyst deactivation a 48-hour test run was completed with TR12 o i l and the Haldor Topsoe c a t a l y s t . Figure 6 shows the trend of deoxygenation and hydrogen consumption at an LHSV of 0.1 h" . Hydrogen consumption and the H/C mole r a t i o (not shown) f e l l rapidly in the early stages of the test and then leveled o f f . Deoxygenation f e l l throughout the t e s t . Two causes of deactivation have been postulated. The i n i t i a l deactivation i s l i k e l y due to coking of the catalyst which we have shown in e a r l i e r tests occurs primarily in the f i r s t ten hours (11). The longer term deactivation i s probably due to buildup of metals, primarily sodium, from the o i l . The TR12 o i l contains about 3% ash, mostly residual sodium catalyst from the liquefaction process. Conversion of the catalyst from the sulfided form to the oxide form could also cause a loss of a c t i v i t y . We have not seen any evidence that t h i s occurs in the short term. Analysis of the spent catalyst indicates i t i s s t i l l sulfided and s u l f u r has not been detected in the off-gas or the product o i l s .


21. BAKER & ELLIOTT

CatdytwHydwtreatingofBwmass-DerivedOUs


O

HT-400. CoMo (Harshaw)

•

KAT-4000. CoMo (Katalco)

Δ

C 0 M 0 / S 1 O 2 AlaOa (PNL)

•

S-411, NiMo (Shell)

Figure 4. Effect of Catalysts on Quality of Hydrotreated Oil from TR7 (400°C, 2000 psig)

O

HT-400. CoMo (Harshaw)

•

TK-710.750.770. CoMo (Haldor Topsoe)

Δ

NiMo/y (Amoco)

•

CoMo/y(PNL)

Figure 5. Effect of Catalysts on Quality of Hydrotreated Oil from TR12 ( 4 0 0 ° C 2000 psig) r


237


238


Figure 6. Catalyst Deactivation with Haldor Topsoe Catalyst and TR12 Oil (400°C, 2000 psig)


21.

BAKER & ELLIOTT

Catalytic Hydrotreating of Biomass-Derived Oils

Conclusions


A variety of biomass-derived o i l s have been upgraded by c a t a l y t i c hydrotreating in a 1 - l i t e r reactor system. S p e c i f i c conclusions from our studies are as follows: •

High y i e l d s of high-quality gasoline ( C 5 - 225°C b o i l i n g range) can be produced from biomass-derived o i l s ; however, low space v e l o c i t i e s (long residence times) are required. At high space v e l o c i t i e s a low oxygen, highly aromatic crude o i l i s produced.

•

Cracking and h y d r o g é n a t i o n of the higher molecular weight components are the rate l i m i t i n g steps in upgrading biomass-derived o i l s . Catalyst development should be directed at these reactions. Process development in biomass liquefaction should be directed at minimizing the production of multiple ring compounds.

•

The TR7 o i l i s superior to TR12 and both are much superior to pyrolysis o i l s as feedstocks for conventional c a t a l y t i c hydrotreating to produce hydrocarbon f u e l s .

•

Pyrolysis o i l s can be upgraded by c a t a l y t i c hydrotreating, however, a low-temperature c a t a l y t i c pretreatment step i s required. Studies are underway to combine the pretreating and hydrotreating in a single step.

•

Residual sodium catalyst needs to be removed from liquefaction products to prevent rapid catalyst f o u l i n g .

•

Coke formation on the catalysts i s evident in a l l cases (as expected) but appears to be more extensive with the TR12. Extended time operation may lead to higher coking l e v e l s , but t h i s may also be related to metal poisoning e f f e c t s .

Acknowledgments The authors acknowledge the dedicated e f f o r t s of W. F. Riemath and G. G. Neuenschwander of PNL who assisted in reactor operation and product analysis. The work was funded by the Biomass Thermochemical Conversion Program o f f i c e at PNL under the d i r e c t i o n of G. F. Schiefelbein, D. J . Stevens, and M. A. Gerber. We would also l i k e to acknowledge the support of S. Friedrich of the Biofuels and Municipal Waste Technology Division of the U. S. Department of Energy.

Literature Cited 1. Davis, H., G. et al. "The Products of Direct Liquefaction of Biomass," in Fundamentals of Thermochemical Biomass Conversion, R. P. Overend, T. A. Milne, and L. K. Mudge, Eds; Elsevier Applied Science Publishers, New York, 1985; p 1027. 2. Elliott, D. C. "Analysis and Comparison of Products from Wood Liquefaction," in Fundamentals of Thermochemical Biomass


239

240

3. 4. 5.


6. 7. 8.

9. 10. 11. 12. 13. 14.

PYROLYSIS OILS FROM BIOMASS Conversion, R. P. Overend, T. A. Milne, and L. K. Mudge, Eds. Elsevier Applied Science Publishers, New York, 1985; p 1003. Scott, D. S. and J. Piskorz. Can. Jour. Chem. Eng. 1984, 62, 404-412. Beckman, D. and D. C. Elliott. Can. J. Chem. Eng. 1985, 63, 99. Elliott, D. C. and E. G. Baker. "Hydrotreating Biomass Liquids to Produce Hydrocarbon Fuels," in Energy from Biomass and Wastes X, IGT, Chicago, 1987; p 765-784. Li, C. L., Z. R. Yu, and B. C. Gates. Ind. Eng. Chem. Proc. Pes. Dev. 1985, 24, 92. Elliott, D. C. Amer. Chem. Soc. Div. Petr. Chem. Prepts. 1983, 28, 3, 667. Elliott, D. C. and E. G. Baker. "Upgrading Biomass Liquefaction Products Through Hydrodeoxygenation," in Biotechnology and Bioengineering, Symposium No. 14, John Wiley and Sons, New York, 1984; p 159. Soltes, E. J. and S. C. K. Lin. "Hydroprocessing of Biomass Tars for Liquid Fuel Engines," in Progress in Biomass Conversion, Volume 5, Academic Press, New York, 1984; p 1. Furimsky, E. Catal. Rev-Sci. Eng. 1983, 25, 3, 421. Elliott, D. C. and E. G. Baker. "Hydrodeoxygenation of Wood– Derived Liquids to Produce Hydrocarbon Fuels." Presented at the 20th IECEC, Miami, Beach, 1985; SAE Paper No. 859096. Langlois, G. E. and R. F. Sullivan. Adv. Chem. Ser. 1970. No. 97, 38. Haynes, H. W., J. F. Parcher, and Ν. E. Helmer. Ind. Eng. Chem. Process Pes. Dev. 1983, 22, 401-409. Thigpen, P. L. and W. L. Berry. In Energy from Biomass and Wastes VI; Klass, D. L., Ed.; Institute of Gas Technology; Chicago, 1982; p 1057.

Received December 30, 1987


Pyrolysis Oils from Biomass - American Chemical Society

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