p. 1 of 3 

From: Curt Wells [mailto:cwells@aluminum.org] 

Sent: Friday, May 30, 2014 11:29 AM 

To: Charles D. Johnson; Putney, David 

Cc: Michael A. Palazzolo 

Subject: RE: Anode coke questions 

David – 

We have researched the questions that you asked below and have the following answers regarding 

them – 

Anode coke specifications – Smelters set specifications for the upper amount of certain metals that 

may affect aluminum quality or the smelting process. Coke suppliers provide a metals analysis for 

those specific metals, which typically include As, Be, Cd, Cr, and Pb. V is also an important metal of 

concern in anode performance so it’s presence is monitored as well. 

Using coke produced from coal in anode production - Coke produced from coal, including 

metallurgical coke, has been evaluated in the past as an alternate for the petroleum-based coke used to 

produce aluminum today. However, unprocessed coke produced from coal does not have properties 

suitable for the production of carbon anodes. Coal-based coke has a high ash content (high level of 

impurities) and this leads to unacceptable properties, including poor electrical conductivity, high 

carbon consumption and unacceptable aluminum purity. 

Coal or coal-based coke could be processed (for example by solvent extraction) to remove the 

impurities at a considerable cost. However, anodes produced with 100% processed coal-based coke 

have similar drawbacks, such as brittleness and high carbon consumption. (See attached 2010 

article). While it may be technically feasible to produce acceptable anodes by blending petroleumbased coke and processed coal-based coke, the need to blend with petroleum coke to produce usable or 

acceptable anodes defeats the initial benefits of removing the impurities. Suitable processed coal-based 

coke is not commercially available today in any case. 

Please let me know if you have any questions regarding this information and/or would like to discuss it 

further. 

Thanks. 

Curt Wells 

Manager, Regulatory Affairs 

The Aluminum Association 

(703) 358-2976 (w) 

(804) 385-6351 (c) 

cwells@aluminum.org
p. 2 of 3 

From: Charles D. Johnson 

Sent: Monday, May 19, 2014 10:13 AM 

To: Putney, David 

Cc: Charles D. Johnson; Michael A. Palazzolo; Curt Wells 

Subject: Re: Anode coke questions 

David, 

We're looking in to this and we will get back to you as 

soon as possible. 

Regards, 

Chuck 

Sent from my iPhone 

On May 17, 2014, at 4:24 AM, "Putney, David" 

<putney.david@epa.gov> wrote: 

Chuck/Mike, 

 

Once again, I’m reaching out to The Aluminum Association 

and the technical subcommittee for assistance/information. 

Specifically, I’m wondering if the primary aluminum

facilities generally get information on the metal HAP 

content of the petroleum coke that they purchase for use in 

manufacture of anodes. That is, do the facilities get 

specifications from the petroleum coke providers on how 

much nickel, arsenic, cadmium, etc. is in the petroleum 

coke that you buy from them? 

 

Also, is there any technical reason why metallurgical coke 

(as opposed to petroleum coke) could not be used in anode 

production? That is, is there any reason other than cost 

that drives primary aluminum reduction facilities to use 

petroleum coke instead of metallurgical coke in their anode 

production operations? 
p. 3 of 3 

 

Thanks, 

 

David Putney, Environmental Engineer 

U.S. Environmental Protection Agency 

Office of Air Quality Planning and Standards 

Sector Policies and Programs Division 

109 T.W. Alexander Drive, RTP, NC 27711 

Mail Drop D243-02 

Ph: (919) 541-2016 Fax: (919) 541-3207 

Email: putney.david@epa.gov

 

 
PREBAKED ANODE FROM COAL - UTILIZATION OF COAL EXTRACT AS A COKE 

FEEDSTOCK1Maki Hamaguchi, 1Noriyuki Okuyama, 1Nobuyuki Komatsu, 2

Jiro Koide, and 2Keisuke Kano 

1Kobe Steel, Ltd. ; Takasago, Hyogo 676-8670, Japan. 

2

Sumitomo Corporation, Harumi, Chuo-ku, Tokyo 104-8610, Japan 

Keywords: Coal, Solvent Extraction, Coke, Anode. 

Abstract 

Preparation of prebaked anode utilizing coal solvent extraction 

technology has been reported for the first time. A steaming coal 

was extracted with methylnaphthalenes under nitrogen 

atmosphere at 653K, and ash-free coal extract (Hypercoal, HPC) 

was obtained at ca. 60wt% yield. The HPC was further heattreated at 1273K to convert HPC to HPC coke (HPCC). Prebaked 

anode test specimen were fabricated from HPCC according to the 

conventional procedures, and were evaluated in terms of the 

standard prebaked anode test methods. It was demonstrated that 

prebaked anodes prepared from HPCC have various advantages 

such as extremely low impurities such as Sulfur, Vanadium and 

Nickel, high apparent density, and low air- and CO2

-reactivity 

compared to those from anode grade calcined petroleum coke. 

Introduction 

In the prebaked anode industry, it is recognized that the quality of 

anode coke has continuously declined, namely, higher sulfur and 

impurities, higher volatile matter content, and lower density, 

mostly due to the deterioration of crude oil quality. Thus, 

technologies for alternative sources for anode coke are of great 

interest. 

We at Kobe Steel, Ltd., have been developing a new nonhydrogenative solvent extraction process for coal with the aim of 

applying the coal-extract as a binder for the metallurgical coke 

making. We named this process and the product (the ash-free 

coal-extract), a Hypercoal (HPC) [1-3]. 

Since the content of ash in HPC is usually extremely low, HPC is 

considered to be a promised candidate for alternative feedstock of 

anode cokes. 

In this paper, we will describe fabrication of prebaked anode test 

specimen using HPC as a feedstock of coke. It was demonstrated 

that prebaked anodes prepared from HPC coke have various 

advantages such as extremely low impurities such as Sulfur, 

Vanadium and Nickel, high apparent density, and low air- and 

CO2

-reactivity compared to those from anode grade calcined 

petroleum cokes. 

Experimental section 

Materials 

A steaming coal from Australia was used as the starting material. 

Proximate and ultimate analyses of the coal are shown in Table 1. 

Solvent extraction of the coal was carried out under the following 

conditions: solvent, a mixture of 1-methyl and 2-methylnaphthalenes; solvent/ coal ratio (v/v), 4; temperature, 653K; 

initial nitrogen pressure, 2MPa; duration, 20min. A continuous 

bench scale extraction apparatus was employed. The coal extract 

(HPC) was recovered from the extraction slurry by filtering at 

high temperature and evaporating the solvent. In Figure 1 was 

shown a schematic diagram of the HPC process. Since the asprepared HPC possesses extremely high dilatation during 

carbonization, the HPC was subjected to post heat treatment to 

suppress dilatation rate. The reaction conditions of the heattreatment were as follows: temperature, 693K; initial nitrogen 

pressure, 2MPa; duration, 60 min. Proximate and ultimate 

analyses of the HPC and the post treated HPC are also listed in 

Table I. 

A commercially available coal tar pitch was used as the binder to 

fabricate the prebaked anodes. The properties of the pitch are 

listed in Table II. 

Figure 1. Schematic for the HPC process diagram 

TABLE I. Proximate and ultimate analyses for the coal and HPCs

Product Moisture Ash VM C H N S Odiff.

[wt%] [wt%]db [wt% daf]

Raw coal 2.9 12.2 41.3 82.5 5.5 2.0 0.6 9.5

HPC 0.3 0.12 41.2 86.6 5.4 1.9 0.6 5.5

HPCa) 0.1 0.10 26.2 88.6 4.4 1.9 0.7 4.4

a) After post heat-treatment

Coking of HPC and preparation of prebaked anodes 

The post treated HPC was carbonized according to the 

conventional metallurgical coke making procedures. Namely, the 

HPC crushed under 3mm was poured into an iron-made container 

of 0.02m3, and was heated to 1273K at a rate of 3 K/min under 

inert atmosphere. Duration was 30 min. 

Prebaked anode specimen of cylindrical shape of 50mm in 

diameter and 100mm length were fabricated according to the 

conventional methods. The crushed HPCC was mixed with the 

C oal feeder

Preheater E xtr actor

Filter

S pray dryer

Spray dryer

Slurry m aker

Settler

HPC

Coal

Recycle solvent

Residue

coal

C oal feeder

Preheater E xtr actor

Filter

S pray dryer

Spray dryer

Slurry m aker

Settler

HPC

Coal

Recycle solvent

Residue

coal

923

Attachment 1, 6 pages
binder pitch of various amounts (13-17wt% in the paste), and was 

hot-pressed at a pressure of 400 bar at 393K. The pressed green 

molds were carbonized at 1373K for 20 hours. Prebaked anodes 

utilizing blends of HPCC and a high-sulfur petroleum coke (HS 

coke) were also prepared. HPCC and prebaked anodes were 

evaluated in terms of the ISO standard test methods for anode 

cokes and prebaked anodes. The scheme of the prebaked anodes 

from HPCC and PC cokes is shown in Figure 2. 

Table II. Properties of the binder pitch used 

Figure 2. Schematic of prebaked anode preparation from coal. 

Results and Discussion 

Characteristics of HPC Cokes 

Properties of HPCC were listed in Table III in comparison with 

the ranges of typical petroleum coke and a high sulfur PC coke 

(HS coke). Polarized light microphotographs of HPCC and PC are 

shown in Figure 3. 

It was noted that HPCC possessed lower real density in xylene, 

larger electrical resistance, and smaller crystalline size than pet 

cokes, which can be attributed partly to the lower calcination 

temperature employed for the HPCC (1273K) than that for 

petroleum cokes (1473K). The solid-state carbonization nature 

observed in this HPC may also be a cause for the slightly poor 

graphtizability of this HPC. The fact that the Hg apparent density 

of HPCC was larger than that of PC irrespective of its smaller real 

density suggests the existence of closed micropores in HPCC. 

From the detailed analyses of the coke and ash, it was revealed 

that the HPC gives highly purity coke in particular in sulfur, 

sodium, nickel and vanadium contents compared to petroleumderived coke. 

Table III. Properties of HPC coke compared to the typical range 

of petroleum calcined cokes 

Properties Unit Range for PC HPCC HS Coke

Sieving analysis +4mm % 30-45 45 31

-1mm % 25 27 33

Tapped bulk density 8-4mm kg/dm3 0.64-0.70 0.735 0.68

2-1mm kg/dm3 0.80-0.86 0.813 0.80

0.5-0.25mm kg/dm3 0.88-0.93 0.87 0.87

Hg apparent density kg/dm3 1.72-1.80 1.85 1.73

Grain stability % 75-90 93 82

Pulverizing factor - 0.80-1.20 0.43 1.12

Real density in xylene kg/dm3 2.05-2.10 1.89 2.067

Crystalline size Å 25-32 16.9 27.0

Sp. el. resistance μΩm 460-540 933 489

Air reactivity (798K) %/min 0.05-0.30 0.03 0.28

CO2

 reactivity % 3-15 4.1 6.8

S % 0.5-3.5 0.56 2.71

V ppm 60-350 5 243

Ni ppm 100-250 14 163

Si ppm 50-250 241 99

Fe ppm 50-400 125 112

Ti ppm 0-5 60 1

Na ppm 30-120 1 60

Ca ppm 20-100 77 51

 100μm 

Figure 3. Polarized light microphotographs of HPCC (upper) 

and PC (bottom) 

Characteristics of prebaked anode from HPCC 

Figure 4 shows the properties of prebaked anodes prepared from 

the HPCC and the binder pitch as functions of the pitch contents 

in the coking blends. 

Raw coal

Solvent

Extraction

HPC

Post

treatment Coking

HPCC Prebaked anode

Molding

& Baking

Binder pitch

PC coke (option)

Properties Method Value Unit

Softening Point MettlerISO 5940 386 K

Insoluble in Quinoline ISO 6731 8.4 %

Insoluble in Toluene ISO 6376 27.7 %

Viscosity 433K ISO 8003 1555 mPas

Density in Water ISO 6999 1.312 kg/dm3

Ash content ISO 8006 0.25 %

S ISO 12980 0.47 %

Na " 202 ppm

Ca " 59 ppm

Si " 106 ppm

Fe " 277 ppm

Zn " 311 ppm

Pb " 232 ppm

924
Whereas the green apparent density of HPCC anode was 

comparable to the typical range of conventional PC coke anodes, 

the apparent density of the baked HPCC anodes was noticeably 

smaller than that of PC anodes. This is consistent with the 

existence of closed pores in HPCC as suggested by the relatively 

small real density of HPCC. The elasticity modulus and 

compressive strength of HPCC anode were superior to those of 

PC anode, which may by attributable to the hardness of the HPCC 

particle. The electrical resistance of HPCC anodes was slightly 

lower than PC anode. 

The HPCC anodes exhibited substantially larger CTE than those 

of PC anodes, which may be of concern for the formation of 

cracks or deformation during the course of industrial scale anode 

baking process. 

The CO2

 reactivities are poorer than usual even though the HPCC 

itself showed a good resistance to the CO2 attack. This is related 

to the addition of pitch that are always contaminated with Na and 

Ca (200 and 60ppm resp. in the standard pitch used). Both 

catalysts are quite efficient on the HPCC as it contains low Sulfur 

level. Sulfur is known to be a strong inhibitor of the CO2 burn and 

is normally present at a concentration 3 to 4 times higher in 

petroleum cokes than in the HPC coke. 

The air reactivities are excellent as the HPCC does not have any 

Vanadium contamination. V is known to be a strong catalyst of 

the air burn. 

Green apparent density (kg/dm3)

1.54

1.56

1.58

1.60

1.62

1.64

1.66

1.68

1.70

13 14 15 16 17

% Pitch

Baked apparent density (kg/dm3)

1.46

1.48

1.50

1.52

1.54

1.56

1.58

1.60

1.62

13 14 15 16 17

% Pitch

Compr. Strength (MPa)

20

30

40

50

60

70

80

90

100

13 14 15 16 17

% Pitch

Spec. El. Resistance (μΩm)

40

45

50

55

60

65

70

75

80

13 14 15 16 17

% Pitch

Elasticity modulus (GPa)

3.50

4.00

4.50

5.00

5.50

6.00

6.50

7.00

7.50

13 14 15 16 17

% Pitch

Thermal expansion (10-6/K)

2.50

3.00

3.50

4.00

4.50

5.00

5.50

6.00

6.50

13 14 15 16 17

% Pitch

CO2 reactivity residue (%)

82

84

86

88

90

92

94

96

98

13 14 15 16 17

% Pitch

Air reactivity residue (%)

80

85

90

95

100

13 14 15 16 17

% Pitch

Figure 4. Properties of prebaked anodes prepared from HPCC and 

binder pitch as functions of the binder pitch 

Blue hatched area shows the range of PC anodes.

925
Characteristics of prebaked anodes from HPCC and PC blends 

As described in the previous section, it was demonstrated that the 

HPC coke can be used as an alternative feedstock for prebaked 

anodes. At the same time, it is also clear that the HPCC prebaked 

anode has both several advantages and drawbacks compared to 

conventional petroleum coke based anodes. Thus, we have 

investigated the possibility of blending technology for HPCC and 

PC coke. In particular, we focused the utilization of a high-sulfur 

and low density PC by blending with HPCC. 

Table IV and Figure 5 summarize the results of evaluation for 

prebaked anodes prepared from the HPCC, the HS-coke, and the 

blends of the HPCC and HS-coke. In this experiment, we have 

examined the blending effects of HPCC grains and HPCC fines, 

separately on the properties of the prebaked anodes. 

The prebaked anodes from HS coke are characterized by their 

relatively low apparent density, large air reactivity, and high 

sulfur level. 

When the HPCC grains were substituted to half of the HS coke 

grains (35wt% in total), and the binder pitch was adjusted at 

15wt%, the most appropriate properties has been achieved. That is, 

the anode from the blend of the HPCC and the HS coke exhibited 

a apparent density almost the same as those of PC coke anodes, 

and superior reactivities to air and CO2

, and lower impurities such 

as sulfur, vanadium, and nickel, etc. 

On the contrary, when the HPCC fines were used in place of HS 

coke fines, the properties of the anodes were not satisfactory. This 

suggests that some inhomogeneity may exist in the HPCC. 

Table IV. Properties of prebaked anodes prepared from the HPCC, the HS-coke, and 

the blends of the HPCC and HS-coke. 

Properties

Pitch (%) 15% 16% 14% 16% 14% 15% 16% 15%

Apparent density green kg/dm3

1.600 1.619 1.563 1.608 1.615 1.633 1.654 1.630

Apparent density baked kg/dm3

1.526 1.534 1.499 1.513 1.550 1.558 1.531 1.560

Baking loss % 5.20 5.62 5.05 5.94 5.19 5.55 6.27 5.20

Shrinkage % 0.58 0.37 1.06 0.04 1.28 1.06 -1.30 0.80

Sp. el. resistance μΩm 64 60 71 62 68 64 64 60

Compr. Strength MPa 35 40 32 45 37 42 43 42

Elasticity Modulus GPa 3.5 4.1 2.8 4.7 3.4 3.7 3.8 4.2

Thermal expansion 10-6/K 3.80 3.81 4.22 4.23 4.44 4.55 4.44 3.6-4.4

Themal conductivity W/mK 3.40 3.53 3.210 3.44 3.42 3.55 3.55 3.50

Density in xylene kg/dm3

2.070 2.071 2.051 2.042 2.029 2.034 2.031 2.07

Air permeability nPm 1.40 1.30 2.03 1.58 1.42 1.69 5.91 1.20

CO2 reactivity residue % 94.2 94.7 92.2 90.3 94.8 95.3 93.1 93.0

dust % 0.4 0.2 0.6 1.5 0.3 0.2 0.9 2.0

loss % 5.4 5.1 7.2 7.7 5.0 4.6 5.9 5.0

Air reactivity residue % 79.2 80.1 87.1 90.4 86.5 89.3 89.6 80.0

dust % 4.1 3.4 0.6 0.1 2.4 1.1 0.3 3.0

loss % 16.7 16.5 12.3 9.5 11.1 9.6 9.5 17.0

S % 2.38 2.37 2.17 2.16 1.85 1.73 1.79 2.00

V ppm 216 214 183 173 146 149 140 200

Ni ppm 156 154 132 132 116 113 114 160

Si ppm 132 133 120 137 140 152 150 180

Fe ppm 188 192 137 140 139 141 142 250

Al ppm 79 76 78 83 90 101 97 80

Na ppm 80 81 69 69 67 57 67 80

Ca ppm 64 65 53 65 68 65 69 70

Typical

Unit Pet. Coke HS coke

15% in fines 35% in grains

Blends of HPCC (%) in HS coke

926
As to the reactivity of the prebaked anodes, the CO2

 reactivity 

figures are not deteriorated by the addition of HPCC. This is 

probably due to firstly the fact that the binder matrix contains no 

HPCC, and secondly there is enough Sulfur content in these 

anodes to inhibit the catalytic effect of Ca and Na species on the 

low Sulfur HPC cokes. 

Interestingly there is a dramatic improvement of the air reactivity 

figures thanks the massive reduction of the V content, which is a 

powerful catalyst of the air oxidation. 

Conclusions 

Results of this study can be summarized as follows: 

1. The Hypercoal coke (HPCC) derived from the ash-free coal 

extract (Hypercoal, HPC) showed significant advantages 

such as lower impurities like S, Ni, Fe, V, Na and Ca, and 

consequently the excellent Air and CO2

 reactivity resistances. The 

HPCC is regarded as a promising candidate for alternative of 

deteriorating current calcined petroleum anode grade cokes. 

2. The prebaked anode specimen of pure HPCC (without 

blending) showed the excellent air reactivity resistance as 

expected, however some drawbacks were observed such as the 

higher CTE, the brittleness, and the poor CO2

 reactivity resistance 

contrary to the expectation from lower impurity of coke itself. 

3. The blending of HPCC in grains to the current HS petroleum 

coke maintained the inherent excellent air reactivity resistance and 

improved significantly the drawbacks observed with the pure 

HPCC specimen such as the higher CTE, the brittleness and the 

poor CO2

 reactivity resistance. 

4. It is concluded that the blending of the HPCC in grains to the 

current HS petroleum coke is the best practical way to apply the 

superiority of the HPCC in purity and to avoid some nonessential 

drawbacks of the HPCC. 

Figure 5. Properties prebaked anodes prepared from the HPCC, the 

HS-coke, and the HPCC-HS-coke blends 

Blue hatched area shows the range of PC anodes. 

Green apparent density (kg/dm3)

1.54

1.56

1.58

1.60

1.62

1.64

1.66

1.68

1.70

13 14 15 16 17

% Pitch

Baked apparent density (kg/dm3)

1.46

1.48

1.50

1.52

1.54

1.56

1.58

1.60

1.62

13 14 15 16 17

% Pitch

Compr. Strength (MPa)

20

30

40

50

60

70

80

90

100

13 14 15 16 17

% Pitch

Spec. El. Resistance (μΩm)

40

45

50

55

60

65

70

75

80

13 14 15 16 17

% Pitch

Elasticity modulus (GPa)

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

13 14 15 16 17

% Pitch

Thermal expansion (10-6/K)

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

13 14 15 16 17 % Pitch

CO2 reactivity residue (%)

82

84

86

88

90

92

94

96

98

13 14 15 16 17

% Pitch

Air reactivity residue (%)

75

80

85

90

95

100

13 14 15 16 17

% Pitch

○: HS coke

△: 15% HPCC in fines

■: 35% HPCC in grains

927
Furthermore, these results indicate that the HPCC become the 

beneficial sweetener to the high S and/or high metals offspecification petroleum cokes increasing in the future. 

Acknowledgement 

Preparation and evaluation of anode was carried out at R&D 

Carbon Ltd., Sierre, Switzerland. 

References 

[1] Okuyama, N., Komatsu, N., Kaneko, T., Shigehisa, T. and 

Tsuruya, S. (2004) Fuel Processing Technology, 85 947. 

[2] Okuyama, N., Furuya, A., Komatsu, N. and Shigehisa, T. 

(2005) International Conference of Coal Science and Technology 

Proceedings. 

[3] Komatsu, N., Okuyama, N., Furuya, A. and Shigehisa, T. 

(2006) International Pittsburgh Coal Conference. 

928