Chemicals from Direct Coal Liquefaction - Chemical Reviews (ACS

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Chemicals from Direct Coal Liquefaction Isao Mochida,*,† Osamu Okuma,‡ and Seong-Ho Yoon† †

Research and Education Center of Carbon Resources, Kyushu University, 6-1 Kasuga Koen, Kasuga, Fukuoka 816-8580, Japan The New Industry Research Organization (NIRO), 1-5-2 minatojima Minamimachi, Chuo-ku, Kobe 650-0047, Japan

‡

7.5.2. Nitrogen-Containing Chemicals in Naphtha 7.5.3. Nitrogen Chemicals in Middle Distillate 7.5.4. Nitrogen Species in the Heavy Distillate 7.5.5. HDN Reactivity 7.6. Toxicology of Coal Liquefaction Products 7.7. Sulfur-Containing Chemicals in the Coal Liquefaction Products 7.7.1. Sulfur-Containing Chemicals 7.7.2. Sulfur Chemicals in Naphtha 7.7.3. Sulfur-Containing Chemicals in Middle Distillate 7.7.4. HDS Reactivity of Sulfur Species in Middle Distillate 7.8. Double-, Triple-, and Multiheteroatomic Compounds in Coal Liquefaction Products 7.8.1. Multiheteroatomic Compounds 7.8.2. Double- and Triple-Heteroatomic Aromatic Compounds in Coal Liquids and Extracts 8. Application of Chemicals from Coal Liquefaction Products 8.1. Application of Coal Chemicals 8.2. Chemicals 8.3. Jet Fuel 8.4. Sources for Carbon Materials Author Information Corresponding Author Notes Biographies Acknowledgments References

CONTENTS 1. 2. 3. 4.

Introduction: The Goal of Coal Liquefaction History of Coal Liquefaction: Coal-to-Liquid (CTL) The Coal Liquefaction Processes Chemistry, Process Scheme, and Conditions of Direct Coal Liquefaction 5. Process Yield of Coal Liquefaction 6. Chemical Composition of the Coal Liquefaction Products 7. Coal Liquefaction Chemical Products 7.1. Individual Chemical Species 7.2. Paraffins and Olefins in the Coal Liquefaction Products 7.2.1. Perspective 7.2.2. Naphtha 7.2.3. Middle Distillates 7.3. Aromatic Hydrocarbons (AHs) and Hydroaromatic Hydrocarbons in the Direct Coal Liquefaction Products 7.3.1. Aromatic Chemicals in Liquefaction Products 7.3.2. Naphtha 7.3.3. Middle Distillate and Heavy End 7.4. Oxygen-Containing Chemicals in Coal Liquefaction Products 7.4.1. Overview 7.4.2. Oxygen-Containing Chemicals in Naphtha 7.4.3. Oxygen-Containing Chemicals in Middle Distillate 7.4.4. Extraction and Liquid Chromatographic Separation of Distillate 7.4.5. Oxygen-Containing Chemicals in the Resid of Coal Liquefaction Products 7.5. Nitrogen-Containing Chemicals in Coal Liquefaction Products 7.5.1. Nitrogen-Containing Species in CoalDerived Liquid © XXXX American Chemical Society

A D E E F G K K M M M M

N N N N

X Y Y Z AB AB AB AB AB AC AC AC

AD AG AG AG AG AH AH AH AH AH AI AI

T

1. INTRODUCTION: THE GOAL OF COAL LIQUEFACTION Figure 1 illustrates a series of natural and synthetic hydrocarbon resources and fuels derived from coal, petroleum, and natural gas (CH4) according to their H/C atomic ratios. Coal has an atomic ratio of about 0.8, petroleum (crude) has one of about 1.5, while natural gas has one of about 4, because natural gas often carries a small amount of higher paraffinic gases such as ethane and propane. Coal, except for the anthracite, is usually richer in oxygen as compared to petroleum. The target of coal liquefaction is to produce substitutes for petroleum distillate fuels having an atomic ratio of 1.8−2.5, more

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Special Issue: 2014 Chemicals from Coal, Alkynes, and Biofuels

O O P Q T

Received: May 28, 2013

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dx.doi.org/10.1021/cr4002885 | Chem. Rev. XXXX, XXX, XXX−XXX

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Figure 1. A series of natural and synthetic fuels with their H/C atomic ratios.

Figure 2. History of direct coal liquefaction process development.11

Among such products, water and gaseous hydrocarbons such as methane, ethane, and propane are undesirable in direct coal liquefaction because they consume expensive hydrogen in the production of untargeted products. Hydrogen is produced from coal, petroleum, natural gas, and biomass through gasification (into H2 and CO; eq 1). Carbon dioxide is inevitably produced

particularly, replacements for gasoline and diesel fuel. To achieve this target, hydrogen is added and/or carbon and oxygen are removed. Large aromatic rings in coal are converted into smaller ones and/or liquid paraffinic hydrocarbons, as found in the petroleum products, while removing carbon and oxygen form CO, CO2, or H2O. B


distiller

middle and heavy oil

pyrite in coal

20

Bergius process trial in U.S. after the second world war

middle oil

460

reaction temp (°C) pressure (MPa) separation method solvent

30 t/d pilot plant

distiller

Fe sulfide

catalyst

100 t/day

14

slurry H2 bubbling

reactor

processing ability, stage remarks

460

light and middle distillates

product

bituminous, sub-bituminous middle and heavy oil slurry H2 bubbling none

bituminous

SRC International, U.S.

Bergius, U.S.

SRC-II

second

Bergius

first

coal

technical generation company, country

process

C

donor solvent, bottom recycle

hydrotreated middle and heavy oil 250 t/d pilot plant

distiller

14−18

425−450

light and middle distillates slurry H2 bubbling none

brown coal, bituminous

EXXON Research, U.S.

second

EDS

advanced H-oil process

200−600 t/d pilot plant

middle oil

distiller

20−21

455

Co−Mo

light and middle distillates ebullated bed

bituminous, subbituminous

HC Research, U.S.

second

H-coal

two-stage H-coal

hydrotreated middle and heavy oil 6 t/d PDU

deashing

17

light and middle distillates slurry H2 bubbling Co−Mo, Ni− Mo 450/400


Southem Co. Serv., U.S.

third

CC-ITSL (HTI)

second generation Bergius

200 t/d pilot plant

heavy oil

distiller

30−31

460−470

light and middle distillates slurry H2 bubbling Fe sulfide

Rule Cole Feba Oil, Germany brown coal, bituminous

second

new IG

Table 1. Direct Coal Liquefaction Processes Developed in the World after the Second World War11 NEDOL

donor solvent

hydrotreated middle and heavy oil 150 t/d pilot plant

distiller

17−19

460

light and middle distillates slurry H2 bubbling pyrite


NEDO/NCOL, Japan

third

BCL

hydrogenated solvent, bottom recycle, slurry dewatering, solvent deashing

50 t/d pilot plant

hydrotreated middle and heavy oil

deashing

15

450

limonite

slurry H2 bubbling


brown coal, sub-bituminous

NEDO/NBCL/KSL, Japan

third

Shenhua

commercial process, the largest capacity, donor solvent, hydrogenation by ebullated bed

6000 t/d commercialized

hydrotreated middle and heavy oil

distiller

18

450

synthetic Fe sulfide

slurry H2 bubbling


bituminous

Shenhua, China

third

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Figure 3. Chemical images of direct coal liquefaction steps.14

2. HISTORY OF COAL LIQUEFACTION: COAL-TO-LIQUID (CTL) The need for petroleum substitutes derived from coal was first recognized in Germany before the Second World War when transportation fuel for military vehicles such as airplanes, tanks, and warships became in strong demand. Coal liquefaction was developed in Germany due to the abundance of coal. There are three routes from coal to liquid hydrocarbons. The direct and indirect coal liquefaction processes were developed by Bergius (1913) and Fischer−Tropsch (1923) in the early 20th century. Pyrolysis is the third route, which converts a part of the coal into liquid hydrocarbons and other portions into gaseous hydrocarbons and coke (char) as the major products. Pyrolysis of coal has been performed since the 17th century to produce metallurgical coke;5 the liquid hydrocarbon broadly referred to as coal tar is a minor byproduct. Tar was the starting material of modern organic chemistry and many chemical industries.10 Coking produces coal tar, which can be further refined into petroleum substitutes. Figure 2 summarizes the history of coal liquefaction.11 Three routes for coal liquefaction were practiced in Germany during the Second World War: the direct, indirect, and coking processes were reported to be operated concurrently. During and after this period, the United States, the United Kingdom, and Japan as well as Germany researched and developed direct coal liquefaction process. However, great supplies of petroleum became available worldwide from the Middle East in the 1950s, and the development of coal liquefaction was nearly suspended. Gasification of coal (Lurgi process) and Fischer−Tropsch synthesis (indirect liquefaction) have been commercially

from coal to supply the energy to the endothermic gasification process. Carbon monoxide is further converted into H2 through the water−gas shift reaction (eq 2). Coal liquefaction and gasification have both been extensively studied and reviewed.1−9 A competition with petroleum exists in coal liquefaction in terms of cost, although some believe chemicals derived from coal liquefaction can compete with those from petroleum or coal tar produced in the coking industry. This section reviews principally the chemicals derived from the coal liquefaction. CnHm (coal) + pO2 → aCO + bH 2 + cCO2 + d H 2O (1)

where A + c = n, 2(b + d) = m, and (a + 2c + d)/2 = p. CO + H 2O → H 2 + CO2

(2)

The desire to liquefy coal into petroleum substitutes, particularly lighter liquid fuel, stems from the abundance of coal and increasing demand for transportation fuels that are currently produced predominantly from the crude petroleum through a series of refining processes. The upgrading of heavy crude to liquid fuels involves also hydrogenation and hydrocracking of the heavy aromatic hydrocarbons into paraffinic, small aromatic (1−3 aromatic rings), and hydroaromatic hydrocarbons. Coal and heavy crude can be converted into light liquid hydrocarbons through several routes: liquid hydrocarbons produced through pyrolysis to simultaneously produce coke of variable amount and quality, direct hydrogen addition (Bergius), and gasification of CO and H2, which are converted into liquid hydrocarbons (typically Fischer−Tropsch). D


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Figure 4. A flow diagram of direct liquefaction, two-stage coal liquefaction, clean coal technology program, and technology state report.1

acid−base, and donor−acceptor ones. Such second bonding interactions very much influence the properties and reactivities of coal. Hence, the liberation of the macromolecular interactions is a key to convert coal to be soluble in the solvent in the coal liquefaction process. During liquefaction, the weakest bonds are first broken thermally and/or hydrogenatively into smaller aromatic units, which may be inherently liquid or are dissolved in the solvent, while another part of the coal macromolecules remains solid and becomes further condensed into char (coke). The remaining portions become smaller gaseous molecules. The liquid or dissolved hydrocarbons are thermally and catalytically cracked into smaller distillate hydrocarbons [e.g., naphtha, kerosene, diesel (gas oil), and vacuum gas oil], which are similar to those found in petroleum crude oil. Uncracked and/or condensed aromatic macromolecules such as tar and pitch remain as residual products and are further hydrogenated or recovered for other purpose. Figure 3 also illustrates the basic chemistry of typical two-stage direct conversion steps of coal into the three major products. Figure 4 is a flow diagram of a typical two-stage liquefaction process,1 in which two reactors are installed to operate the liquefaction under different conditions. For example, the first stage is thermal liquefaction of the solid coal with a hydrogen donor solvent at a rather high temperature and a short contact time, while the second stage is catalytic to favor the hydrogenation of the liquid product at a relatively low temperature under higher hydrogen pressure. The liquid hydrocarbon yield is improved in this way. The single stage liquefaction process was originally developed in Germany, where the high temperature and high pressure were applied with disposal catalysts such as iron ore. A hydrogen donor solvent plays an important role, which enables the coal macromolecules to dissolve in the liquefaction solvent.8,9 The solvent provides hydrogen to the coal macromolecules to crack the weaker bonds or to capture the fragment radicals that are produced thermally from the coal macromolecules. In this way, the fragments remain as smaller molecules without recondensation. The catalyst present in the process can rehydrogenate the dehydrogenated solvent back to the hydrogen

practiced since 1950 by Sasol using coal mined in South Africa. These processes produce gasoline, diesel, and chemicals to satisfy the needs of the country because South Africa was under an embargo time on the import of petroleum from the Middle East by international agreement. Lurgi gasification produces tar in addition to syngas; tar is the aromatic hydrocarbon feedstock for the Sasol process.12 China Shenhua Energy Co. Ltd. started recently (2009) a commercial direct coal liquefaction plant in Inner Mongolia.13

3. THE COAL LIQUEFACTION PROCESSES Table 111 summarizes the direct liquefaction processes that have been developed in the United States, Germany, the United Kingdom, Japan, and China after the Second World War. Bergius was the first to apply a very high pressure (about 70 MPa) at a fairly high temperature (about 500 °C) but used an iron-based catalyst of poor activity.4 Process development after Bergius aimed to moderate the conditions and increase the liquid yield by lowering the hydrogen consumption. Solvent (aromatic and hydrogen donative), catalyst, and stepwise hydrogen addition (two or three stages in various combinations) have been explored with a plant size of a few to 200 t/d of coal. Only the Chinese one was commercialized (Shenhua, Inner Mongolia).13 That process is believed to be based on the Hydrocarbon Research, Inc. (HRI) integrated two-stage liquefaction (ITSL) and the New Energy and Industrial Technology Development Organization (NEDOL) processes.13 4. CHEMISTRY, PROCESS SCHEME, AND CONDITIONS OF DIRECT COAL LIQUEFACTION Figure 3 illustrates the chemistry of direct coal liquefaction based on Shinn.14 Polyaromatic macromolecules of coal, in which aromatic (including heteroaromatic) nuclei are bonded with C− C, C−O, and C−S units, form three-dimensional networks. The aromatic nuclei contain alkyl, carboxylic, carbonyl, phenol, thiol, thiophene, amine, indole, and pyridine groups according to the rank of the coal. Macromolecular interactions in the coal are significant to form its three-dimensional network. The interactions include aromatic stacking, hydrogen bonding, E


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in Table 1.11 The process has two stages (including the hydrotreater of products, naphtha, and diesel) and operates at a fairly high pressure of 19.0 MPa at 455 °C for both reactors and uses an iron sulfide catalyst. The primary product is hydrogenated to regenerate the circulating solvent and to refine the products.13

donor state. Hence, hydrogenation, donation, and rehydrogenation of the solvent are cycled to continue the depolymerization of the coal macromolecules. Once the coal macromolecules are liquefied or dissolved in the solvent, the solid catalyst can continue the hydrocracking process under hydrogen pressure to produce the distillate hydrocarbons. The liquefaction products include molecular interactions more or less particularly in the less soluble fraction. Such interactions influence their properties and reactivities. Thus, their liberation is useful for upgrading. The donor solvent can be also used in the second stage. Here, the liquefied coal and the solvent fraction originally derived from the coal in the primary liquefaction stage are hydrogenated together. This cohydrogenation further refines the liquefaction product and simultaneously regenerates the solvent into a hydrogen donor. Solid/liquid separation by vacuum distillation, extraction, solid precipitation, and filtration has been extensively examined. None of these approaches is ideal for the recovery of the highest-boiling liquid hydrocarbons and rejection of the solid contaminants. Scale-up to commercial operations is another issue. To date, vacuum distillation is the most mature technology in the petroleum industry.4 The temperature limitation for distillation without any coking in the vessel as well as in the preheater restricts the recovery of the vacuum distillate to below approximately 370 °C (i.e., about 570 °C at atmospheric pressure) for refining into liquid fuels. The vacuum residue can be sent to the coker to recover the more liquid hydrocarbons; the coke is sent to the gasifier. A solvent deashing (solvent extraction) is also developed for two-stage liquefaction to recover heavy organic product from vacuum residue in the primary step and to further hydrogenate it in the secondary hydrogenation step.11 The agglomeration of ash as well as extraction are intended at the same time in the solvent deashing. Ash is bound with their heavy fraction, which is insoluble in the solvent by antisolvent effects. Distillates and solvent extracts obtained through solid/liquid separation are further hydrotreated to reduce the oxygen, nitrogen, and sulfur atoms, and hydrogenated to increase the cetane number of the diesel fuel fraction through aromatic hydrogenation. In catalytic coal liquefaction, the vacuum residue can be sent back to the primary liquefaction step to reuse the catalyst and to convert the nondistillable liquid product (bottom recycle).15 The coal mineral in the residue is also sent for liquefaction to increase the mineral amount in the primary product; hence some residue must be ablated regularly. The gaseous product includes hydrogen, which is recovered and sent back to the liquefaction process after the separation. The gases are further separated into hydrocarbons, NH3, H2S, and CO2. Kobe Steel uses gas/liquid separation at the liquefaction temperature of the liquefaction reactor to recover the light hydrocarbons along with other gaseous products. These are sent to an in-line hydrotreater for further refining without losing the apparent heat of the product.15 Table 1 gives the conditions of the single- and two-stage liquefaction processes; the reaction temperature is typically 400− 460 °C at a pressure of 14−20 MPa. An iron-based catalyst is often used and may be as-mined pyrite, limonite, or finely divided synthetic FeS2. Sulfur is often added to stabilize the sulfide catalyst. Typical features of the Shenhua liquefaction process, which was the world’s first and is still the only commercial scale direct liquefaction process after the second world war, is also included

5. PROCESS YIELD OF COAL LIQUEFACTION Coal liquefaction produces C1−C3 gaseous hydrocarbons, naphtha, and middle distillates (kerosene and gas oil) as petroleum substitutes. Together, they define the total distillate. Additionally, gaseous nonhydrocarbons (such as CO, CO2, H2S, and NH3) and residual oils, including vacuum gas oil, vacuum residue or heavy tar, and solid products such as unliquefied coal and coke (char), are found in the product. The vacuum gas oil is recycled as the solvent after the hydrogenation to regenerate the hydrogen donor activity. The residual oil can be used as a coal tar substitute, which is useful as a carbon source in the coking process (blast furnace, binder and impregnation pitches, and delayed coker feed after the solid/liquid separation and pretreatment; see section 8 for details). The yields of naphtha, middle distillate, gas oil, and total distillates were approximately 20%, 22%, 5−8%, and 50%, respectively, in liquefaction during the 1980s. The yields improved in the 1990s by using two-stage liquefaction, that is, about 15−20%, 20−40%, 12−30%, and 65−73%, respectively. A major improvement was found in the increased yield of the total distillate, particularly of the middle distillate and gas oil fractions. The latter two are equivalent because gas oil is converted into middle distillates during hydrotreatment. A significant decrease in hydrocarbon gases and a decrease in naphtha yield improved the hydrogen consumption in the liquefaction process and the overall hydrogen efficiency for the distillate production. Such improvement and the slight moderation of liquefaction conditions improved the economic competiveness of coal liquids. Posthydrotreatment improves the quality of coal liquids and makes them comparable to those of petroleum products. Table 2 summarizes the product slates in the primary and secondary stages of the brown coal liquefaction (BCL) process.16 Low-rank coal produces more CO and H2O and lighter hydrocarbons. Major products are produced in the primary Table 2. Product Slate from Victorian Brown Coal (Yallourn) in the Primary and Secondary Steps of the BCL Process16

F

yield structure (wt %)

PH

SH

total

H2 sulfur CO + CO2 H2S C1−C4 C5−C6 light oil (C7-220 °C) middle oil (220−300 °C) heavy oil (300−420 °C) CLB (420 °C+) water total gas total oil total oil + CLB coal conv. (THF conv.)

−4.70 −0.95 13.19 1.20 11.05 3.34 13.04 16.82 14.85 18.35 13.81 100.00 25.43 48.06 66.41 97.95

−1.00 0.00 0.00 0.10 0.70

−5.70 −0.95 13.19 1.30 11.75

5.30 4.00 −5.10 −5.90 1.90 0.00

21.68 20.82 9.75 12.45 15.71 100.00

4.20

52.26


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give better performance in terms of a higher total distillate yield at a lower dose.19 Coal liquefaction catalysts have been studied extensively; however, poisoning by carbonaceous and mineral substance during the liquefaction, recovery, and regeneration as well as high activity and selectivity very much limit the selection of efficient catalyst.18 The bottom recycle allows the repeated use of the catalyst, the number of reuse being restricted by the amount of unreacted coal and ash in the coal. Thus, the disposal catalysts have been practically selected. Such catalytic processes have been applied for upgrading heavy crudes and residues. The catalyst for the secondary upgrading is basically developed in the petroleum refining. The catalyst is now aimed at removing nitrogen and oxygen species of significant contents, which currently increase in some crudes.

step, while the secondary step converted heavy oil (coal liquid bottom; CLB) to increase light and middle oils. The total oil yield (distillate) reduced to 52.26%.16 Table 3 compares the yield ratios of the light and middle distillates in coal liquids from several coals of different ranks Table 3. Ratio of Light and Middle Distillates in Raw Coal Liquid from Some Coals of Different Ranks in the NEDOL and BCL Processes9 light fraction n-paraffins iso-paraffins olefins cyclic olefins mononaphthenes dinaphthenes benzenes indanes phenols others unknown middle fraction saturates (SA) n-paraffins iso-paraffins monocyclicsa dicyclicsa tricyclicsa tetracyclicsa monoaromatics (MA) benzenes dicyclicsa tricyclicsb tetracyclicsb polyaromatics (PA) polars (PO) a

Tanito Harum (37.0)

Adaro (34.7)

Ikeshima (29.2)

Yallourn (42.5)

5.5 2.5 0.4 1.8 8.7 1.2 4.6 0.9 8.2 0.7 2.5 63.0 17.1 5.6 1.5 2.9 4.8 1.7 0.5 19.1

4.0 2.1 0.3 1.7 8.8 1.5 4.3 0.8 7.7 1.3 2.2 65.3 18.4 5.1 1.9 2.9 5.8 2.2 0.6 19.3

3.8 1.7 0.1 1.3 7.4 1.3 4.8 0.9 5.8 0.3 1.8 70.8 17.7

22.2

4.4 2.2 0.4 3.7 8.9 1.0 5.7 0.9 8.5 3.3 3.5 57.5 10.6 4.0 1.0 1.7 2.4 1.2 0.4 11.2

2.0 14.5 2.5 0.1 16.5

1.8 13.1 4.0 0.3 16.2

20.7

0.8 7.6 2.6 0.2 20.7

10.3

11.4

10.2

15.0

6. CHEMICAL COMPOSITION OF THE COAL LIQUEFACTION PRODUCTS Before describing the individual chemicals produced from the direct coal liquefaction process, the chemical compositions of the various liquefaction products are described below. Kobe Steel reported details of the products from Indonesian brown coal,15 Mulia, obtained through their two-stage liquefaction process. The yield of the total distillate was 63.5%, which comprised light oil (C5, bp 220 °C, 31.2%), middle oil (bp 220−300 °C, 26.2%), and heavy oil (bp 300−420 °C, 6.1%). The yield of distillation bottoms (>420 °C) was 7.3%, while the yields of H2O, CO + CO2, C1−C2, and LPG were 16.3%, 10.7%, 5.4%, and 3.9%, respectively, at the hydrogen consumption of 7.1%. Table 4 summarizes the product slate from the primary and secondary liquefaction steps of a Victorian brown coal using the BCL process.20 Ultimate analyses, 1H NMR, and the properties of the naphtha and gas oil are given. High aromatic, nitrogen, and oxygen contents are characteristic of primary coal liquid. The hydrotreatment in the second step markedly reduced the N, S, and O contents, and increased the hydrogen content. Aromatic and olefin contents are markedly reduced by increasing the amount of saturates. The H/C ratios of naphtha, kerosine, and gas oil were 2.01, 1.83, and 1.76, respectively, and suggest high degrees of saturation.20 Their nitrogen and sulfur contents were less than 10 ppm except for the naphtha, which suggests a high degree of refining. The coal-derived naphtha has high octane number, due to its aromatic content. (Octane number is a standard measure of the performance of a motor or aviation fuel. The higher is the octane number, the more compression the fuel can withstand before detonating. Fuels with a higher octane rating are used in high-compression engines that generally have higher performance.) The kerosene and gas oil contained saturates above 88.3% and 80. 0%, respectively,20 with small amounts of total aromatic hydrocarbons (11.7%) and one(17.9%), two- (1.4%), and three- (0.1%) ring aromatic hydrocarbons. Nevertheless, the cetane index of the gas oil was 38.6, which is lower than that of the petroleum derived one. (Cetane number (cetane index) is calculated on the basis of the fuel’s density and distillation range (ASTM D86).21 There are two methods used, ASTM D976 and D4737.22,23) Hence, improvement of cetane number is one of the critical issues for the coal liquefaction products. Aromatic ring-opening is required. Table 3 summarizes the chemical compounds found in the light and middle fractions of the raw coal liquid from coals of different ranks produced by the NEDOL and BCL processes.9,16−18 The yields of the light and middle fractions reflect the ranks of the coals as described in section 5. The compositions of the light fractions were rather similar, regardless of the rank,

b

Naphthenes. Naphthenobe.

using the NEDOL and BCL processes.9 Lower-ranked coal tends to give more light fractions and less middle fractions. Shenhua started the demonstration plant of 6000 t/d on September 10, 2011, which operated for 4440 h continuously.17 The plant produced 58.2 thousand tons of naphtha, 107.2 thousand tons of gas oil (20% of charged coal), and 25.8 thousand tons of gas from about 1 million tons of coal (90% of the capacity). Some of the products were sold within China. Shell gasifiers (two sets, each 2000 t/d) were also operated for hydrogen production and achieved 120 days of continuous operation. Shenhua restarted the operation again on April 3, 2012 after maintenance of the let-down valves, preheater fouling and coking, and hydrotreator leaking.13 The process is now under the commercial operation. Further improvement of the liquefaction process is still attempted. The corrosion and erosion by coal slurry must be overcome, with better anticorrosive materials to coal slurry being explored. A number of coal liquefaction catalysts have been developed in Japan. Among them, natural limonite ore, which contains γ-FeOOH, is an excellent catalyst.18 The rather high cost of the catalyst, however, may require repeated use, which is performed by the bottom recycle. The finer iron-sulfide particles G


fraction

boiling point range (°C) yield (wt %, daf) density (15 °C, g/cm3) ultimate analysis (wt %) C H N S O H/C atomic ratio 1 H NMR har. Hα Hβ Hγ fa FIA analysis A (vol %) O (vol %) S (vol %) F-1 octane number smoke point (mm) cetane index

100−200 22.8 0.852

10.5 14 51.8 23.7 0.25 20.6 14.1 65.3 81

∼100 8.7 0.7376 81.2 13.3 0.14 0.1 3.7 1.95 0.9 12.3 59.4 27.4 0.03 7.1 12.6 80.3 82

0.9252

84.5 10.6 0.47 0.085 4.6 1.56

17.3 24.4 42.9 15.4 0.38

82.5 11.6 0.13 0.16 4.7 1.68

heavy naphtha

light naphtha

total

9

22.9 29 35.9 12.2 0.44

83.4 10.2 0.27 0.05 6.3 1.46

200−240 26.2 0.9524

kerosene

primary hydrogenation

9

21.1 30.3 35.9 12.7 0.45

86.8 10.1 0.6 0.04 2.9 1.39

240−360 35.2 0.9778

light gas oil

11

28 30.8 32.8 8.4 0.6

88.4 8.3 1.1 0.07 2.7 1.12

360−420 7.1 1.0874

heavy gas oil

5.7 0.9 93.4 72

14.7 6.6 78.7 70

5.4 8.5 61.8 24.4 0.15

1.8

2.11 3 1.4 65.4 30.2 0.02

85 12.8 0.49 0.01

100−200 47.2 0.8584

heavy naphtha

secondary hydrogenation

84.6 15 0.021 0.01

∼100 5.1 0.7132

light naphtha

Table 4. Representative Properties of the Coal Liquids in the Primary and Secondary Steps of Brown Coal Liquefaction (BCL) Process20 kerosene

10.5

11.8 24.8 49.7 14.1 0.29

1.6

86.6 11.6 0.67 0.01

200−240 47.7 0.9127

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while saturates and monoaromatics from Yallourn brown coal were lower than those from the bituminous and subbituminous coals. Additionally, the polar fraction was larger for the Yallourn coal liquid. More polyaromatics were found in the liquid from bituminous Ikeshima coal than in those of the subbituminous coals in Table 3. The solvent refined coal (SRC)-I and -II processes, which were developed successively, show the higher yield of light products that are better suited as substitutes for petroleum-derived fuels by the two-stage catalytic process.24 The effect of coal rank on the product distribution was studied for the Exxon donor solvent (EDS) process recycle solvent and for H-coal heavy fuel oil (Tables 5 and 6).25 Aliphatic hydrocarbons (AlHs) were the Table 5. Chemical Class Composition of Process Materials Derived from Different Coal Ranks25 fraction weight percent sample EDS recycle solvent 5226-003 Illinois No. 6 coala 5226-107 Wyodak coalb 5226-108 Texas ligniteb H-coal heavy fuel oil 5226-118 Illinois No. 6 coalc 5226-119 Wyodak coalc

AH

PAH

NPAC

hydroxyPAH

total

46 61 61

39 22 25

7.7 3.6 3.8

12 8.7 7.0

105 95 97

38 61

42 31

7.8 5.1

12 5.8

100 103

a c

Average of four determinations. bAverage of three determinations. Average of two determinations.

Table 6. Hydroaromatic Composition of Process Materials Derived from Different Coal Ranks25 fraction weight percenta sample EDS recycle solvent 5226-003 Illinois No. 6 coalf 5226-107 Wyoming (Wyodak) coal 5226-108 Texas lignite H-coal heavy fuel oil 5226-118 Illinois No. 6 coal 5226-119 Wyodak coal

PA1b

PA2c

PA3d

PA4e

total

23 49 51

40 29 32

13 8.4 9.4

17 14 12

93 100 104

21 50

39 36

12 8.8

29 16

101 101

a

Average of two determinations, unless otherwise noted. bAH. Hydroaromatic compounds. dDihydro-PAH and Three-ringed PAH and some polar PAC. fAverage of six determinations.

Figure 5. Mass spectrograms of (a) atmospheric distillate, (b) atmospheric bottom, and (c) vacuum bottom of H-coal product, fuel mode, from Illinois No. 6 coal.26

major products in the EDS recycle solvents of three coals: 61% for subbituminous Wyodak coal and Texas lignite, and 46% for bituminous Illinois No. 6 coal. Polyaromatic hydrocarbons (PAHs) form the second major product: 39% for Illinois No. 6 coal, and 22% and 25% for Wyodak coal and Texas lignite, respectively. Nitrogen-containing polycyclic aromatic compounds (NPACs) and hydroxylated-PAHs were larger with Illinois No. 6 coal than with Wyodak coal and Texas lignite. The H-coal heavy fuel oils from Illinois No. 6 and Wyodak coals had compositions similar to those of the EDS recycle solvent. Nevertheless, slightly more PAHs were observed in the oils from both coals. The catalytic liquefaction may increase the yield of oil by making the aromatic fraction in the coal oil soluble. Thus, the rank of the coal influenced the product composition, reflecting a more aromatic structure in coals of higher rank.

The majority of the AlHs and aromatic hydrocarbons (AHs) clearly depend on the rank as shown in Table 6. Subbituminous coal and lignite produced around 50% of AlHs, while bituminous coal produced 21−23%. AHs were the major products in the bituminous coal liquid (39−40%), but were 29−36% in the subbituminous coal and lignite liquids. Low-rank coals clearly produce more AlHs. Anbar and John26 reported the molecular weight distributions of American coal liquefaction products obtained by fieldionization mass spectrometry (FI−MS). They compared the products from Illinois No. 6, West Kentucky, and Wyodak coals. The materials examined were the H-coal fuel oil fractions such as the atmospheric distillate, bottoms, and vacuum bottoms (Atlantic Richfield, formerly Illinois No. 6 coal), centrifuged synthoil from West Virginia coal (Pittsburgh Energy Research Center), SRC oil and asphaltene fractions from Illinois No. 6 Burning Star Coal, and SRC asphaltenes from West Kentucky

c

I


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Table 7. Molecular Formulas of Products in Severe Single-Stage Coal Liquefaction14 fraction

formula

molecular weight

CAR

HAR

1A 2A 3B 3C 3D 4A 4B 5B 5C 5D 5E 6B 6C 7B 8B 9B SRC residue gas H2O, H2S COx

C23H33 C22H22 C21H22O C22H23N C26H34O C25H20ON C27H20O2 C31H25OS C31H27ON C33H31O2N C35H26O3N C39H32O2N C27H22O5 C60H42O6NS C69H45O5NS C88H62O7N C579H486O37N9S3 C52H34O4N2S C18H56 H60O28S2 C3O5

309 286 290 301 362 350 376 445 429 473 508 546 426 904 999 1244 8248 782 272 572 116

6 14 16 14 14 20 24 23 25 23 30 31 22 51 61 74 448 43

3 7 6 6 5 7 9 10 13 8 13 14 10 16 20 29 176 15

OHp

1 1 1 2 1 1 2 2 4 2 4 3 24 2

CAL

HAL

17 8 5 8 12 5 3 8 6 10 5 8 5 9 8 14 131 9

30 15 15 16 28 12 9 15 13 22 11 16 8 22 21 30 283 15

functional groups

NH N OS N ON ON N O O4NHHS NOS O4N O13N9S3H3 O2(NH)2S

stage liquefaction very much simplifies many of them and hydrogenates many of the aromatic rings with smaller sizes and less heterocyclic compounds. Many alkyl groups were formed. Thus, the variety of chemical species in coal liquids results from different extents of depolymerization and/or hydrocracking of the molecular structure of the coal, which reflects its rank. Karaca et al.27 used high-temperature gas chromatography (GC) combined with mass spectroscope (HT-GC−MS) to compare a coal liquid with petroleum atmospheric residue, coal tar pitch, and low-temperature coal tar (LTT). The chemical analyses, fractional compositions, low-mass size-exclusion chromatographic peaks of the pentane- and toluene-eluting fractions, and carbon numbers of the n-alkanes are summarized in Table 9. The coal-derived liquids studied in their work were from different coals and included the following. • Coal tar pitch: Tar from the high-temperature coking of coal is distilled to leave pitch as a residue. The evaluated sample was a “soft” pitch, which contained some light ends (from anthracene oil) such as phenanthrene.28 • Coal liquefaction extract (coal digest): The coal liquefaction extract29 or coal digest was from the former British Coal Point of Ayr Coal Liquefaction Pilot Plant. It was the extracted coal by recycle solvent stream, after filtration of undissolved solids and ash. • Low-temperature tar: A low-temperature coal oil from the Coalite process30 was produced by low-temperature distillation of coal to produce a smokeless solid fuel. Their GC−MS spectra are illustrated in Figure 6.27 Coalderived liquids are very different from Petrox petroleum residue in their atomic compositions, SEC elution, and the types and carbon ranges of n-alkanes (Table 9). The petroleum residue has a high hydrogen content, larger first pentane fraction, higher molecular weight, and longer alkanes (Table 9). The coal liquids resembled LTT more so than pitch in all of these materials, reflecting their heat-treatment history, although the coal digest had more of the pyridine-soluble fraction and/or less oxygen content. This is because the coal digest is not a distillate product,

Coal (Mobil) and Wyodak coal (HRI). The molecular weights of the distillate fraction, atmospheric, and vacuum residues of the H-coal product were 100−300, 100−400, and 200−900 amu, respectively. The oil fraction (HS, vacuum distillate) ranged from 100 to 650 amu, while the asphaltene ranged from 100 to 1000 Da, as shown in Figure 5. The boiling range of a coal liquid fraction reflected its molecular weight distribution. The presence of a homologous substructure separated by 14 amu was easily detected. The asphaltene was eluted from silica gel by chloroform. Their molecular weight distributions overlapped significantly, although asphaltene had a larger median molecular weight (450 amu) than the oil. Eluting the oil and asphaltene from a silica gel column using different solvents rather than separating them by distillation may have affected the measured molecular weight distributions; Figure 5 seems to support this conclusion. Less than 50% of the more polar tetrahydrofuran(THF) and pyridine-soluble fractions of the liquefaction products could be volatilized by FI−MS. Thus, this technique could not always provide a representative molecular weight distribution of the particularly heavier fractions. Shinn14 collected molecular information on the liquefaction products from bituminous coal obtained under short contact time, severe single-stage, and two-stage conditions. His objective was to reconstruct the molecular structure of the coal using the molecular information of the products. Figure 3 and Tables 7 and 8 summarize the chemicals found under the short contact time, severe single stage, and two-stage conditions. Products obtained under single-stage short contact and severe conditions are very complex, with many heteroatomic groups and many fused aromatic rings in their structures. This complexity reflects the original coal structure. Aromatic rings basically of the peri-type along were observed with some hydrogenated rings. The short contact time in the condition broke only the weakest bonds and generated liquefied products of high molecular weight having oxygen linkages within or on the aromatic units such as furans and phenols. The severe single-stage condition caused more fragmentation and produced smaller aromatic molecules, with condensation of some units into larger aromatic units. The twoJ


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Table 8. Molecular Formulas of Products in Two-Stage Coal Liquefaction14a boiling range (°F)

original fraction

1000 C4 + oil residue gases H2O, H2S, NH3

residue

formula

molecular weight

C5H10 C6H14 C6H14 C8H18 C8H16 C9H18 C9H20 C9H20 C10H22 C10H20 C10H20 C11H22 C10H14 C11H14 C11H16 C12H24 C12H24 C13H26 C13H20 C13H16 C13H14 C13H24 C14H10 C14H24 C15H18 C15H30 C16H22 C16H26 C16H22 C16H20 C17H32 C17H34 C17H16 C18H24 C24H44 C18H18 C20H40 C20H30 C20H16 C28H30O C29H31N C572H893ON C38H26NS C42H136 H183O73N9S5

70 86 86 114 112 126 128 128 142 140 140 154 134 146 148 168 168 182 176 172 170 180 178 192 198 210 214 218 214 212 236 238 220 240 332 234 280 270 256 382 393 7787 528 640 1637

CAR

6 6 6

Table 9. Elemental Analyses and Fraction Weights by Column Chromatography of Petroleum Residue (Petrox), Pitch, Coal Digest, and Low Temperature Tar (LTT)27

HAR

Petrox

pitch

coal digest

LTT

%C 86.8 91.4 85.9 82.3 %H 13.0 4.1 6.8 7.8 %N 0.4 1.3 0.8 0.9 %S N.D. 0.8 N.D. N.D. %O N.D. 2.4b 6.6b 9.0b a fractions wt % wt % wt % wt % pentane first 50.7 3.8 12.4 10.5 pentane second 18.0 17.4 29.6 25.7 toluene 5.7 26.5 10.1 19.6 acetonitrile 1.7 5.2 3.1 13.7 pyridine 2.5 15.3 17.5 4.0 NMP 6.2 15.1 8.5 4.3 water 11.3 2.8 5.1 6.6 sum 97.0 86.1 86.4 84.4 Low-Mass SEC Peak Evaluation vs Polystyrene Calibration

4 3 5

SEC first pentane second pentane toluene

peak/upper mass

peak/upper mass

peak/upper mass

peak/upper mass

240/660 u

200/400 u

200/660 u

200/1040 u

440/3920 u

250/1010 u

200/1010 u

200/1680 u

6 6 10

4 4 7

14

10

10

6

6 6 6 10

4 4 3 4

a

14 10

7 2

7. COAL LIQUEFACTION CHEMICAL PRODUCTS

14

6

6 18 18 22 194 31

3 10 8 12 106 13

Individual chemicals in the coal liquefaction products spanned alkanes, cycloalkanes, AHs, AlHs, and oxygen-, nitrogen-, and sulfur-containing compounds of highly variable molecular sizes. Their identification and quantitation are still being analyzed. Trace or unusual chemicals have been identified using highresolution high-sensitivity mass spectroscope. The direct coal liquefaction process is basically a hydrocracking of three-dimensional macroaromatic molecules in their aggregate forms, in which the aromatic structure is hydrogenated, ring-opened, and finally cracked into smaller saturated hydrocarbons. Coals, particularly low-rank coals, also contain some paraffins and many alkyl groups. Dealkylation and cracking of alkyl chains also occur as liquefaction progresses. The oxygen, nitrogen, and sulfur heteroatoms are removed through hydroelimination reactions to leave pure hydrocarbons. Thus, the liquefaction products are upgraded to high-quality fuels similar to petroleum-derived refined fuels. In terms of chemical composition, the constituents become simpler, with some features being lost as a result of the intensive hydrotreatment and hydrocracking. The chemicals derived from the coal should reflect more or less the unique structure and function of the as-mined coal molecules. The low-temperature extract from solid coal should preserve most of the original molecular structure of the coal. However, the yield of the extract is very limited because only

700/10 800 u 300/1680 u 240/2360 u 240/2360 u Carbon Range of n-Alkanes Determined by HT-GC−MS

first pentane second pentane toluene

17−44 31−41 none

none none none

16−26 none none

16−40 none none

Material soluble in the solvents shown by sequential elution. bOxygen by difference, including sulfur if not determined separately.

coal digest, while petroleum resid and LTT consist mainly of alkanes.

7.1. Individual Chemical Species

a

Cf., 695 H atoms consumed: 136 to gas; 183 to heteroatoms; 376 to liquid.

and hydrogenation that occurs during liquefaction removes more oxygen. The coal liquid fractions were suggested by synchronous UV-fluorescence spectra to have the smaller molecular sizes because of nonaggregating forms of polar molecules. The total ion chromatograms of the first and second pentane fractions indicated discrete distributions of coal liquids except for the second pentane fraction of LTT, while both fractions for the petroleum residue had a continuous distribution. The aromatic hydrocarbons are distributed in the entire range of the pitch and K


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Figure 6. Total ion chromatograms from GC−MS of first and second pentane fractions.27 (a) First and second pentane eluted fractions of petroleum residue, C18 n-alkane, and phenanthrenes are indicated (15−18 min). (b) First and second pentane eluted fractions of pitch; molecular mass numbers (m/z) of PAH are indicated. (c) First and second pentane eluted fractions of coal digest; molecular mass numbers (m/z) of aromatics are indicated. (d) First and second pentane eluted fractions of low temperature tar; the position of C20 n-alkane is indicated.

soluble components are extracted, while most of the other components remain in a three-dimensional network of large

aromatic units. Heteroatoms often limit solubility through intermolecular bonding. L


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Figure 7. GC−AED chromatograms of alkanes in Indonesia coal liquefaction products: (a) gas oil from Tanito Harum coal, (b) hydrotreated gas oil from Tanito Harum coal, and (c) liquefied distillate from South Banko coal.33,34

carried a few methyl (mono- and disubstituted) and ethyl groups. The paraffin and olefin contents were 23−25% and 11−15% in the naphtha, respectively. Most of the paraffins were unbranched, but a few methyl branches were noted. Hydrotreated naphtha contained similar paraffins and olefins, but was much richer in saturated paraffins and cycloparaffins, which amounted to about 90%. Neither olefins nor diolefins were found in the hydrotreated products. Paraffinic chains were slightly shorter because of hydrocracking of the C−C bonds. No significant increase in branched paraffins was observed. In contrast, the naphthene content was much higher, as expected from the extensive hydrogenation of aromatic constituents in the naphtha. 7.2.3. Middle Distillates. Long-chain n-hydrocarbons and alkylnaphthalenes have been identified in coal liquefaction products. Karaca et al.27 reported C16−C26 paraffins, as described in section 6. Brodzki et al.32 reported long straightchain hydrocarbons up to C33 and alkylnaphthalenes (bearing alkyl chains up to C15) in the n-hexane-soluble fraction of the liquefaction oil derived from Freyming coal and its maceralconcentrated fractions. Sumbogo et al.33 used GC with an atomic emission detector (GC−AED) to analyze the gas oil fraction from Tanito Harum coal, which was an Indonesian subbituminous coal, before and after hydrogenative upgrading. Alkanes having 8−30 carbon atoms are clearly visible in the chromatogram (Figure 7). Hydrotreatment reserves the alkanes of this range by removing sulfur, nitrogen, and oxygen. Such alkanes are extracted as major components into the nonbasic and nonaromatic (neutral) fractions. The light distillate ( Texas lignite, as shown in Table 17 in section 7.4. The water solubility may also contribute to the toxicity of the coal liquid.

Table 26. Conversion of Nitrogen-Containing Species in South Banko Coal Liquid (50%) is pitch, which is used in the carbon industry for a variety of carbonaceous materials. Coking additives,74,75 carbon blacks, delayed coke,76−81 binder and impregnation pitches, mesophase, and isotropic pitch-based carbon fibers,82−84 activated carbon fibers,85−88 and specialty carbons89,90 are now manufactured from coal tar. Coal liquefaction can use the same sources and be performed on a large scale. Additionally, coal liquefaction processes refine the coal-derived liquid. When the heavy product is refined to make higher-quality fuels, excellent sources of carbon materials can be also supplied that are very competitive. Low heteroatom contents, no solid contaminants by an adequate separation, and a high aromatic content are its advantage as a carbon source. Three examples are cited here for the future development of the heavy end of the coal liquid. A coking additive is required to use poorly coking coals in blast furnace coke production. The additive must be able to adhere and modify noncoking coal particles during the coking process. The partially hydrogenated heavy end having high aromaticity is a candidate for such a novel coking additive.74,75 Tar-based needle coke can compete with petroleum-derived coke in its quality, except for the puffing of the formed coke, which is caused by nitrogen in the tar.73 Coal liquefaction can solve this issue. The last example is pitch-based carbon fiber. Two types of pitch-based carbon fibers exist: the general ones, which are isotropic, and the high-performance ones, which are anisotropic. The differences reflect the stacking of aromatic planes.82−84 Hydrogenated aromatics could be an excellent source for both types of fibers after controlled polycondensation. Nitrogen compounds in pitch could be special components that could provide active sites in the activated carbon fiber.85−88 Purification to a very high level would be needed to remove nonfusible particulates to less than 10 ppm. Lower contamination would provide higher-quality fibers. Zhou et al.90 described the preparation of carbon nanofibers using arc jet plasma irradiation of coal liquefaction residue. Fine fibers were produced. Pang and Wilson91 reported the production of nanofibers from coal through a similar irradiation process. The coal liquefaction residue has great potential as a raw material for high-value carbon products. The potential must be adequately utilized for value added products.

evaluated.

AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest. Biographies

Dr. Isao Mochida is a coal and petroleum scientist and a professor emeritus at Kyushu University of Japan. He earned a B.A., an M.A., and a Ph.D. in Applied Chemistry from the University of Tokyo in Japan. He has been engaged for 50 years in the following fields: carbon science (mesophase pitch, needle coke, petroleum refining, carbon fibers, carbon nanofibers, porous carbon), coal gasification and liquefaction and petroleum refining, catalysis (environmental protection), and energy storage (fuel cell, battery, capacitor, etc.). He has been awarded the ACS Storch Award, the American Carbin Sicuety Pettinos Award, and the Chemical Society Japan Technical Award. His current research interests include the high utilizations of low rank coal and heavy crude. AH


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(4) Review of Worldwide Coal to Liquids, R, D&D, Activities and the Need for Further Initiatives within Europe; RFC-2-CT-2008-00006; IEA, Clean Coal Centre, June, 2009. (5) Marano, J. Overview of Coal-to-Liquids, Presentation to NETL; April, 2006. (6) Burke, F. P.; Brandes, S. D.; McCoy, D. C.; Winschel, R. A.; Gray, D.; Tomlinson, G. Summary Report of the DOE Direct Liquefaction Process Development Campaign of the Late Twentieth Century: Topical Report, Presentation to NETL; April, 2006. (7) Mochida, I.; Sakanishi, K. Fuel 2000, 79, 221. (8) Mochida, I.; Sakanishi, K. Adv. Catal. 1994, 40, 39. (9) Mochida, I., Principal Ed. Fundamentals of Coal Liquefaction; The Japan Institute of Energy: Japan, 2004; Chemistry of Coal Utilization− Chapter 23. (10) Zander, M.; Collin, G. Fuel 1993, 72, 1281. (11) Onozaki, M.; Wakamura, O.; Mochida, I. J. Jpn. Inst. Energy 2012, 91, 508. (12) van Dyk, J. C.; Keyser, M. J.; Coertzen, M. Int. J. Coal Geol. 2006, 65, 243. (13) Lin, O. JCOAL Magazine 2010, 60, 11. (14) Shinn, J. H. Fuel 1984, 63, 1187. (15) Yasumuro, M.; Takahashi, Y.; Okui, T.; Komatsu, N.; Tamura, M. R&D Kobe Steel Eng. Rep. 2010, 60, 55. (16) Okuma, O., Sakanishi, K., Ed. CZLi. Advanced in the Science of Victorian Brown Coal; Elsevier: New York, 2004; Chapter 8, p 441. (17) Lin, O. JCOAL Magazine 2012, 98, 10. (18) Mochida, I.; Sakanishi, K.; Suzuki, N.; Sakurai, M.; Tsukui, Y.; Kaneko, T. Catal. Surv. Jpn. 1998, 2, 17. (19) Suzuki, T.; Ikenage, N. J. Jpn. Inst. Energy 1998, 77, 268. (20) Okuma, O., Sakanishi, K., Eds. CZLi. Advanced in the Science of Victorian Brown Coal; Oxford: New York, 2004; Chapter 8, p 443. (21) ASTM D86, Standard Test Method for Distillation of Petroleum Products at Atmospheric Pressure; ASTM International, 2011. (22) ASTM D976, Standard Test Method for Calculated Cetane Index of Distillate Fuels; ASTM International, 2011. (23) ASTM D4737 Standard Test Method for Calculated Cetane Index by Four Variable Equation; ASTM International, 2011. (24) Wright, C. W.; Weimer, W. C. Chromatographia 1984, 18, 603. (25) Wright, C. W.; Dauble, D. D. Effects of Coal Rank on the Chemical Composition and Toxicological Activity of Coal Liquefaction Materials; Pacific Northwest Laboratory, PNL-5805, U.S. Department of Energy: Washington, DC, 1986; available from NTIS as DE 86011015 (67 pp). (26) Anbar, M.; St. John, G. A. Fuel 1978, 57, 105. (27) Karaca, F.; Millan-Agorio, M.; Morgan, T. J.; Bull, I. D.; Herod, A. A.; Kandiyoti, R. Oil Gas Sci. Technol.-Rev. IFP 2008, 63, 129. (28) Islas, C. A.; Suelves, I.; Li, W.; Morgan, T. J.; Herod, A. A.; Kandiyoti, R. Fuel 2003, 82, 1813. (29) Herod, A. J.; Gibb, T. C.; Herod, A. A.; Shearman, J.; Dubau, C.; Zhang, S.; Kandiyoti, R. J. Planar Chromatogr. 1996, 9, 361. (30) Herod, A. A.; Millan, M.; Morgan, T.; Li, W.; Feng, J.; Kandiyoti, R. Eur. J. Mass Spectrom. 2005, 11, 429. (31) Omais, B.; Courtiade, M.; Charon, N.; Roullet, C.; Ponthus, J.; Thiebaut, D. J. Chromatogr., A 2012, 1226, 61. (32) Brodzki, D.; Abou-Akar, A.; Djega-Mariadassou, G.; Kandiyoti, R. Fuel 1995, 74, 407. (33) Sumbogo Murti, S. D.; Choi, K. H.; Sakanishi, K.; Okuma, O.; Korai, Y.; Mochida, I. Fuel 2005, 84, 135. (34) Sumbogo Murti, S. D.; Sakanishi, K.; Okuma, O.; Korai, Y.; Mochida, I. Fuel 2002, 81, 2241. (35) Wright, C. W.; Later, D. W.; Wilson, B. W. J. High Resolut. Chromatogr. 1985, 8, 283. (36) Wright, C. W.; Stewart, D. L.; Mahlum, D. D.; Chess, E. K.; Wilson, B. W. Am. Chem. Soc., Div. Fuel Chem. 1986, 31, 233. (37) Sugimoto, Y.; Miki, Y.; Oba, M.; Yamadaya, S. Bull. Chem. Soc. Jpn. 1990, 63, 1478. (38) Aczel, T.; Foster, J. Q.; Karchmer, J. H. 157th National Meeting of the American Chemical Society, Fuel Division, Minnesota, April 13−18, 1969.

Dr. Osamu Okuma is a coal scientist and a senior manager of the Research Institute of The New Industry Research Organization of Japan (NIRO). He earned a Ph.D. in the brown coal liquefaction process from Osaka University in Japan. He engaged in the research and development of brown coal liquefaction for 20 years (1976−1998) at Kobe Steel, Co. Ltd. His current research interests include the conversions of biomass and related materials.

Dr. Seong-Ho Yoon is a material scientist and a Professor at Kyushu University of Japan. He earned a B.A. and an M.A. in applied chemistry from Seoul National University at South Korea and a Ph.D. in carbon materials from Kyushu University at Japan. He had a postdoctoral fellowship at Northeastern University (U.S.). He was awarded the Pergamon award from the American Carbon Society. His current research interests include high utilization of low-rank coals and developments of high functional and performance carbon materials from coal and petroleum residues and their useful applications to energy-saving and environmental protection devices.

ACKNOWLEDGMENTS We are thankful for the financial support of the Global Center of Excellence (New Carbon Resources Science, Kyushu University) and the Research and Education Center of Carbon Resources (Kyushu University). We wish to express our gratitude to Dr. Taegon Kim who was abundantly helpful in preparing the manuscript. REFERENCES (1) Coal Liquefaction: Cleaner Coal Technology Program, Technology Status Report 010; U.K. Department of Trade and Industry: U.K., October, 1999. (2) Gasifipedia, Applications of Gasification, Coal to Liquids; U.S. Department of Energy, Office of Fossil Energy: U.S., 2010. (3) Miller, C. L. Coal Conversion−Pathway to Alternate Fuels; EIA Energy Outlook Modeling and Data Conference, 2007. AI


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Chemicals from Direct Coal Liquefaction - Chemical Reviews (ACS

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