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 Outline

ƒ Why Liquefaction? Changing needs ƒ Overview of direct coal liquefaction process ♦ Types of processes ♦ Process evolution ♦ Current status ƒ Chemical Lessons ♦ Reaction pathways ♦ Coal structure: what is needed to liquefy coal ƒ Conclusions ♦ Opportunities for improvement Why Coal Liquefaction?

ƒ Alternate source for liquid fuels: national energy security ♦ Germany, Japan, South Africa ƒ Production of a clean and reactive solid fuel: SRC ♦ Liquids are a secondary product that may improve economics ƒ Oil embargos in the 1970’s reinforced need for an alternate source of transportation fuel ƒ Low oil prices in the next two decades: declining interest ƒ Now? Energy security, efficiency, climate… Liquefaction

ƒ Increasing H/C ratio is a must; Two options ♦ Reject carbon ƒ Most pyrolysis processes ♦ Add hydrogen ƒ Dry pyrolysis with hydrogen not effective ƒ Coal liquefaction; use a solvent to effect hydrogenation ƒ Products often solid at room temperature ƒ Liquefaction defined by solubility Coal Liquefaction Approaches

ƒ Pyrolysis or mild gasification ƒ Direct coal liquefaction ƒ Indirect coal liquefaction ƒ Co-processing ƒ Bioliquefaction

ƒ Substantial overlap in the chemistry of mild gasification, direct coal liquefaction, and co-processing Direct Coal Liquefaction Processes: 1970 to 1995

ƒ Single-Stage Process: SRC-II, H-Coal, EDS ƒ Two-Stage Process: NTSL, ITSL, RITSL, DITSL, CTSL, CMSL… ♦ Many variations depending on ƒ Use of catalyst in the two stages (therm-cat, cat-cat) ƒ Distillation between stages ƒ Separation of solids between two stages or after second stage ƒ Recycle of ashy bottom ƒ Operation in H-balance Single-Stage Processes

ƒ Contact coal with a solvent (2:1) with hydrogen or with hydrogenated solvent at ca. 450°C ƒ Recycle light oil fraction ƒ Yield about 3 bbl oil/ton of coal with bituminous coals ƒ Not as effective for subbituminous coals ƒ Product difficult to refine (high aromaticity, N) ƒ High yield of light hydrocarbons; efficiency of hydrogen utilization is low ƒ Demonstrated the feasibility at ca. 200 tons/day Lessons Learned

ƒ Dissolution itself is fast! ƒ Coal liquefaction is better in heavier, more aromatic solvents ƒ Longer residence time is detrimental ƒ Process economics require maximizing liquids ƒ Higher temperatures lead to more gas ♦ poorer hydrogen efficiency Two-Stage Liquefaction at Wilsonville

ITSL Initial Run

Distillate Distillate

Coal Thermal Solvent Antisolvent L-C Fining HT Solvent Slurry Liquefaction Recovery Deasher Recovery

Ash/Coke

• Short contact thermal liquefaction • Inter-stage separation • Catalytic hydrotreating of de-ashed liquid • Recycle of heavy hydrotreated solvent • Hydrogen balance from coke gasification Two-Stage Liquefaction at Wilsonville

ITSL Final Run

Distillate Distillate

Coal Catalytic L-C Fining HT Solvent Antisolvent Slurry Liquefaction Recovery Deasher

Ash/Coke

• 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 Liquefaction Product Yields, Illinois #6

100 (5.4) (5.4) (6.6) (x.x) H-consumption (4.8)

80

60 C--C3 Gases Liquids Soluble reject Char 40

20

0 EDS H-Coal ITSL-1983 ITSL-1989 Process - Schindler, 1989 Liquefaction Product Yields, Wyodak

100

(7.0) (x.x) H-consumption (4.4) (6.2) 80 (4.3)

60 C--C3 Gases Liquids Soluble reject Char 40

20

0 EDS H-Coal ITSL-1983 ITSL-1989 Process - Schindler, 1989 Liquids Yield

4.5

4

3.5

3

2.5 Illinois #6 Wyodak 2

1.5

1

0.5

0 EDS H-Coal ITSL-1983 ITSL-1989 Process - Schindler, 1989 Process Economics

80.00 O&M 60.00 Coal Capital Related 40.00

20.00

0.00 Required Selling Price

1999 $/Barrel Equiv. Crude H-Coal ITSL CMSL

Major Lesson: Liquefaction is extremely capital intensive

- Burke, Winschel, Gray, 2001 Summary

ƒ Coal liquefaction is technically feasible ƒ Process demonstrated at large scale (~200 tpd) for a variety of coals ♦ US: H-Coal, EDS ♦ Canada: Canmet Co-processing ♦ Japan: Victoria Brown Coal Liquefaction, NEDOL ♦ UK, Germany ♦ China: Shenhua project (2007) ƒ Economics not competitive, but not prohibitive either (~$20B for 50,000 bpd) Traditional View of Bond Cleavage During Liquefaction

WEAK BOND HOMOLYSIS

CH2• + •CH2 CH2 CH2

Solvent

+ CH CH3 3

Solvent merely stabilizes thermally generated radicals; not involved in inducing bond cleavage. Inadequacy of “Donor Solvent”

ƒ Liquefaction yields do not correlate with weakness of C-H bond in the donor solvent ♦ Dihydroanthracene with a much weaker C-H bond than dihydropyrene or dihydrophenanthrene consistently yields lower conversion to THF-solubles ♦ Discrepancy even more glaring under “H-shuttling” conditions ƒ Bonds too strong to cleave by simple homolysis are nonetheless broken under liquefaction conditions “Liquefaction” of a Bibenzyl Polymer FI-Mass Spectrum

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

97 kcal/mol

54 kcal/mol Emerging View of Bond Cleavage

SOLVENT MEDIATED HYDROGENOLYSIS OF STRONG BONDS

Solvent CH • 2 CH2 H

Solvent engenders bond scission

+ H •CH2

Solvent engenders bond scission Implications of Solvent-Mediated Hydrogenolysis

ƒ Draw attention to H-accepting and H-transfer properties of solvent components ƒ Rationalize otherwise inexplicable behavior ♦ Increased liquids yields from partial replacement of donor hydroaromatic with nondonor aromatic ♦ Efficacy of pyrene and related PAH ♦ Role of C-supported catalysts ƒ Design processes that maximize H-utilization efficiency of CoalandNon-Distillables Increased CoalContentAidsConversion

Aromatics incoalmobilize theHin theresidfor conversion CONVERSION (%) 70 80 80 HRI STIRRED-REACTORCOPROCESSING Coal 975 ° F + -Duddy, Panvelker, 1991 % Coal in Feed 10 40 Coal Conversion with Dispersed Catalysts

Recycled IOM is more effective than freshly activated catalyst

Yield (%maf coal)

Fresh Catalyst Recycled IOMs

THF-Solubles 86 95

Cyclohexane-Solubles 36 64

Conversion of Illinois No. 6, Burning Star coal in hydrotreated V-178 distillate Programmed heating at 8°C/min to 425°C under H2 pressure

- Bockrath, 1992 Potential Role of H-Transfer in Catalytic Systems

COAL

HH

•

H H COAL CATALYST Coal Structure

ƒ Application of polymer theory ♦ Characterization of cluster size and mean molecular weight between clusters ♦ Rank dependent trends ƒ 13C-NMR: Relatively small clusters of 8 to 18 carbons only ƒ Distribution of oxygen, sulfur, and nitrogen functionalities ƒ Role of non-covalent linkages Emerging Opportunities

ƒ Thermal efficiency of coal to oil by DCL: ~65% ♦ About 7 times worse than crude oil refining (95%) ƒ Facile dissolution of bituminous coals in certain solvents (Iino) ♦ Possible application for hyper clean coal ƒ Augmented Pyrolysis (Miura) ♦ Mild gasification of methanol soaked coals to co-produce liquids and high reactivity chars ƒ Direct carbon fuel cell: coal, biomass, petcoke… Conclusions

ƒ Coal liquefaction: technically feasible, but the process to synthetic crude is not economic ƒ Converting coal to transportation fuel for IC engines does not reduce CO2 emissions ƒ If needed for energy security, milder processes with high coal to oil yields must be demonstrated at commercially relevant scales Acknowledgments

ƒ M. Gorbaty, ExxonMobil ƒ F. Burke, D. Winschel, Consol ƒ D. Gray, Mitretek ƒ D. F. McMillen