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Direct Coal Liquefaction:Lessons Learned

Ripudaman Malhotra

SRI International

Menlo Park, CA 94025

Presented at GCEP Advanced Coal Workshop, BYU, Provo, UT; Mar 16, 2005


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Outline

Why Liquefaction? Changing needs

Overview of direct coal liquefaction process

Types of processes

Process evolution

Current status

Chemical Lessons

Reaction pathways

Coal structure: what is needed to liquefy coal

Conclusions

Opportunities for improvement


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Why Coal Liquefaction?

Alternate source for liquid fuels: national energy security Germany, Japan, South Africa

Production of a clean and reactive solid fuel: SRC

Liquids are a secondary product that may improve economics

Oil embargos in the 1970s reinforced need for analternate source of transportation fuel

Low oil prices in the next two decades: declining interest

Now? Energy security, efficiency, climate


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Liquefaction

Increasing H/C ratio is a must; Two optionsReject carbon

Most pyrolysis processes

Add hydrogen

Dry pyrolysis with hydrogen not effective

Coal liquefaction; use a solvent to effect hydrogenation

Products often solid at room temperature

Liquefaction defined by solubility


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Coal Liquefaction Approaches

Pyrolysis or mild gasification

Direct coal liquefaction

Indirect coal liquefaction

Co-processing Bioliquefaction

Substantial overlap in the chemistry of mild gasification,direct coal liquefaction, and co-processing


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Direct Coal Liquefaction

Processes: 1970 to 1995

Single-Stage Process: SRC-II, H-Coal, EDS

Two-Stage Process: NTSL, ITSL, RITSL,DITSL, CTSL, CMSLMany variations depending on

Use of catalyst in the two stages (therm-cat, cat-cat)

Distillation between stages

Separation of solids between two stages or after secondstage

Recycle of ashy bottom Operation in H-balance


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Single-Stage Processes

Contact coal with a solvent (2:1) with hydrogen or withhydrogenated solvent at ca. 450C

Recycle light oil fraction

Yield about 3 bbl oil/ton of coal with bituminous coals

Not as effective for subbituminous coals

Product difficult to refine (high aromaticity, N)

High yield of light hydrocarbons; efficiency of hydrogen

utilization is low Demonstrated the feasibility at ca. 200 tons/day


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Lessons Learned

Dissolution itself is fast!

Coal liquefaction is better in heavier, morearomatic solvents

Longer residence time is detrimental

Process economics require maximizing liquids

Higher temperatures lead to more gas poorer hydrogen efficiency


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Two-Stage Liquefaction at

Wilsonville

ThermalLiquefaction

SolventRecovery

AntisolventDeasher

Distillate

L-C Fining HT SolventRecovery

Ash/Coke

CoalSlurry

Distillate

ITSL Initial Run

Short contact thermal liquefaction

Inter-stage separation

Catalytic hydrotreating of de-ashed liquid

Recycle of heavy hydrotreated solvent

Hydrogen balance from coke gasification


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Two-Stage Liquefaction at

Wilsonville

CatalyticLiquefaction

L-C Fining HT SolventRecovery

Ash/Coke

CoalSlurry

Distillate

ITSL Final Run

Low severity catalytic liquefaction

No Inter-stage separation

Moderate severity hydrotreating and hydrocracking

Match rate of solvent hydrogenation with that of coal decomposition

Ashy bottoms recycle

Make hydrogen from steam reforming of methane

AntisolventDeasher

Distillate


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- Schindler, 1989

Liquefaction P roduct Yields, Illinois #6

0

20

40

60

80

100

EDS H-Coal ITSL-1983 ITSL-1989

Process

C--C3 Gases

Liquids

Soluble reject

Char

(4.8)

(5.4)(5.4) (6.6) (x.x) H-consumption


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- Schindler, 1989

Liquefaction P roduct Yields, Wyodak

0

20

40

60

80

100


Process

C--C3 Gases

Liquids

Soluble reject

Char

(4.4)

(7.0)

(4.3)(6.2)

(x.x) H-consumption


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- Schindler, 1989

Liquids Yield

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5


Process

Illinois #6

Wyodak


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0.00

20.00

40.00

60.00

80.00

H-Coal ITSL CMSLRequ

ire

dSe

lling

Price

1999$/Barrel

Equ

iv.

Cru

de

O&M

Coal

Capital Related

Process Economics

Major Lesson: Liquefaction is extremely capital intensive

- Burke, Winschel, Gray, 2001


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Summary

Coal liquefaction is technically feasible

Process demonstrated at large scale (~200 tpd) for avariety of coals

US: H-Coal, EDS

Canada: Canmet Co-processing Japan: Victoria Brown Coal Liquefaction, NEDOL

UK, Germany

China: Shenhua project (2007)

Economics not competitive, but not prohibitive either(~$20B for 50,000 bpd)


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Traditional View of Bond Cleavage

During Liquefaction

CH2

Solvent

CH2 CH2

+

Solvent merely stabilizes thermally generated

radicals; not involved in inducing bond cleavage.

CH2 +

CH3CH3

WEAK BOND HOMOLYSIS


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Inadequacy of Donor Solvent

Liquefaction yields do not correlate withweakness of C-H bond in the donor solventDihydroanthracene with a much weaker C-H bond

than dihydropyrene or dihydrophenanthrene

consistently yields lower conversion to THF-solublesDiscrepancy even more glaring under H-shuttling

conditions

Bonds too strong to cleave by simple homolysis

are nonetheless broken under liquefactionconditions


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Liquefaction of a Bibenzyl Polymer

FI-Mass Spectrum

Hydrogenolysis of strong Caryl-Calkyl bond comparable to thermolysis of weak Calkyl-Calkyl bond

54 kcal/mol

97 kcal/mol


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Emerging View of Bond Cleavage

olventengendersbondscission

CH2

Solvent CH2H

H CH2+

Solvent engenders bond scission

SOLVENT MEDIATED HYDROGENOLYSIS OF STRONG BONDS


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Implications of Solvent-Mediated

Hydrogenolysis

Draw attention to H-accepting and H-transferproperties of solvent components

Rationalize otherwise inexplicable behavior

Increased liquids yields from partial replacement ofdonor hydroaromatic with nondonor aromatic

Efficacy of pyrene and related PAH

Role of C-supported catalysts

Design processes that maximize H-utilizationefficiency


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CONVERSI

ON(%)

-Duddy, Panvelker, 1991

Coal 975F +

HRI STIRRED-REACTOR COPROCESSING

% Coal in Feed

1040

70

80

80

Increased Coal Content Aids Conversion

of Coal and of Non-Distillables

Aromatics in coal mobilize the H in the resid for conversion


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Coal Conversion with Dispersed

Catalysts

Recycled IOM is more effective than freshly activated catalyst

Conversion of Illinois No. 6, Burning Star coal in hydrotreated V-178 distillate

Programmed heating at 8C/min to 425C under H2 pressure

- Bockrath, 1992

Yield (%maf coal)

Fresh Catalyst Recycled IOMs

THF-Solubles 86 95

Cyclohexane-Solubles 36 64


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Potential Role of H-Transfer in

Catalytic Systems

H H

COAL

COAL

H

H

CATALYST


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Coal Structure

Application of polymer theoryCharacterization of cluster size and mean molecular

weight between clusters

Rank dependent trends

13C-NMR: Relatively small clusters of 8 to 18carbons only

Distribution of oxygen, sulfur, and nitrogenfunctionalities

Role of non-covalent linkages


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Emerging Opportunities

Thermal efficiency of coal to oil by DCL: ~65%About 7 times worse than crude oil refining (95%)

Facile dissolution of bituminous coals in certain solvents(Iino)

Possible application for hyper clean coal

Augmented Pyrolysis (Miura)

Mild gasification of methanol soaked coals to co-produce liquids

and high reactivity chars Direct carbon fuel cell: coal, biomass, petcoke


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Conclusions

Coal liquefaction: technically feasible, but theprocess to synthetic crude is not economic

Converting coal to transportation fuel for IC

engines does not reduce CO2 emissions If needed for energy security, milder processes

with high coal to oil yields must be

demonstrated at commercially relevant scales


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Acknowledgments

M. Gorbaty, ExxonMobil

F. Burke, D. Winschel, Consol

D. Gray, Mitretek

D. F. McMillen

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