A PREVIEW OF ANODE COKE QUALITY IN 2007 

Franz Vogt, Robert Tonti, Maia Hunt, Les Edwards 

CII Carbon LLC, 1615 East Judge Perez Drive Chalmette, LA, 70044, USA 

Keywords: Calcined Coke, Green Coke, Anode, Isotropic 

Abstract 

Demand for petroleum coke for aluminum smelting anodes 

reached about 10.4 million metric tons in 2003. This created a 

coke calciner demand of 13.8 million metric tons of green coke 

suitable for making anodes. The green coke demand will increase 

to about 16.7 million metric tons by 2007. Although the oil 

refining industry will produce ample green coke to meet this 

demand, the quality will be quite different from that used in the 

past. During the last few years, the calcining industry has begun 

using green cokes of a quality that would not have been 

considered suitable for anode use ten years ago. This paper 

surveys the available quality of green cokes worldwide, and 

makes projections on the quality of anode coke by 2007. The 

calcined coke of the future will be higher in sulphur and 

vanadium, higher in porosity and more isotropic. The change in 

structure could eventually lead to higher thermal shock sensitivity 

of anodes. Smelters will need to adapt by making process changes 

and improvements. 

Introduction 

For the past five years or so, it has been apparent to the coke 

calcining industry that high quality raw materials will become 

harder to source. In a paper published in 2001 [1], it was predicted 

that the growth of green petroleum coke of the quality 

traditionally used by the aluminum industry would not keep pace

with the demand. By 2003, it was predicted that low sulphur, low 

vanadium cokes would be fully used by the industry and higher 

sulphur and vanadium cokes would be drawn into the raw material 

blend. This has happened. Cokes with vanadium levels as high as 

600 ppm are being used as blend cokes, and this trend will likely 

continue. 

The causes of the imbalance between demand and supply of good 

quality anode grade green cokes (growth of calcined coke 

demand, crude oil quality changes, refining industry changes) 

were explained in the previous paper. These factors remain 

generally the same today. 

For this paper, the authors have examined the raw materials 

available in 2003 through 2007, worldwide, to produce calcined 

coke for the aluminum industry. The regional demand and supply 

was considered, and the impact of the changing raw materials on 

key quality parameters was reviewed. 

World Anode Grade Green Coke Demand and Supply 

Figure 1 shows the demand and supply for anode grade green 

coke for the years 1995 through 2007. The demand is based on 

figures for aluminum production, past history and future 

projections, supplied by CRU [2], factored by a usage rate of 0.39 

tons calcined coke per ton of metal, and a conservative calciner 

recovery rate of 0.78 tons calcined coke per ton of dry green coke. 

Figure 1: Green Coke Demand and Availability

7500

10000

12500

15000

17500

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

Year

Green Coke (Tons)

Green Coke Demand

Traditional Green 

Coke Supply

From Figure 1, it can be seen that the green coke requirement of 

13.8 million tons in 2003 will rise to 16.7 million tons in 2007. 

This 21% increase is solely due to the demand from the aluminum 

smelting industry worldwide. Until 2002, the availability of 

traditional quality, low sulphur, low vanadium, green cokes 

exceeded demand, and an excess supply of traditional coke was 

available. This situation changed in 2003 due to the lack of 

growth in new anode grade coke sources. As a result, nontraditional cokes with higher vanadium levels and a more 

isotropic structure have been blended with traditional cokes to 

meet the shortfall. From this time, an increasing proportion of 

non-traditional cokes will meet the demand. 

Regional Supply and Demand for Green Cokes in 2007 

Figure 2 shows the global distribution of the 16.7 million tons of 

green cokes that will be used for anode grade calcined coke 

manufacture in 2007. Obviously, a number of estimates were 

made to produce such a graph. The green coke production 

distribution will not show much difference from 2003 except in 

Latin America. Brazil anticipates a doubling of the production of 

good quality green coke that may enter the anode market by 2007. 

Light Metals 2004 Edited by Alton T. Tabereaux TMS (The Minerals, Metals & Materials Society), 2004

489
Figure 2: Distribution of Green Coke in 2007

N.America

32%

W.Europe

E.Europe 11%

1%

CIS

14%

CHINA

17%

Middle East

5%

SE Asia

8%

Latin America

11%

Africa

1%

North America: North America will remain the largest producer 

of green coke for the industry. This is consistent with the fact that 

nearly 60% of the world’s green coke is produced there. 

Based on CRU projections for the period 2003 – 2007, demand 

for anode green coke created by smelters in North America is well 

below the supply. North America has a large calcining industry, 

which was developed to take advantage of the plentiful raw 

material supply of the past. This industry has for many years 

exported much of its production to other regions where coke was 

less available. These large calciners have the benefit of being able 

to source and blend a wide range of green cokes to produce 

calcined coke of suitable quality for smelters around the world. 

However, because of the large requirement of the North American 

calciners, there has been a deficit of high quality anode grade coke 

in North America for some years, and, in the future, raw material 

must be imported in ever increasing quantities. 

China: By 2007, the aluminum smelting industry in China will 

become the world’s largest, and that anode coke requirement will 

affect the supply worldwide. China will also be the second largest 

anode grade green coke producer, assuming that the crude oils 

refined there continue to support a quality that can be used by the 

industry. In spite of that, China will become a net importer of 

about one million tons (about 35%) of anode grade green coke in 

2007. 

Middle East: The Middle East will see an expansion of its 

aluminum industry. The calcining industry there will use virtually 

all of the available green coke in that region. 

Latin America: In 2007, Brazil will double their green coke 

availability, exceeding the regional demand by some 600,000 

tons. This will be a usable raw material for anode coke 

production. 

Other Regions: Other regions examined, Europe, CIS, SE Asia, 

Africa, and Australasia will increase their coke requirements, but 

the anode coke availability will not materially change, except for 

SE Asia. There, more of the cokes produced today will be drawn 

into the raw material supply for anode coke production. 

Anode Coke Quality Changes (Excluding CIS and China)

Projections of calcined coke quality between 2003 and 2007 based 

on worldwide green coke quality, excluding coke produced in the 

CIS and China, are shown below. The projections assume no net 

growth in the availability of traditional quality cokes but a steady 

increase in the use of non-traditional cokes to make up this deficit 

as depicted in Figure 3. 

Figure 3: Western World Green Coke Demand 

Compared to Supply of Traditional Cokes

5000

7500

10000

12500

2001 2002 2003 2004 2005 2006 2007

Year

Green Coke Demand

Shortfall to be Met by

Non-traditional Cokes

Coke Demand

Traditional Quality Coke

The quality projections are based on knowledge of the next 

available quality of cokes likely to be used by the calcining 

industry. There is too much uncertainty in the data for the CIS and 

China to incorporate these two regions. These projections must be 

viewed as averages for all the anode coke used in the world except 

for CIS and China. One should expect that any given smelter 

would see quality that varies above and below the average quality. 

Figure 4 shows that sulphur will increase only slightly on a 

worldwide basis. The order of magnitude will be about 0.1% 

(absolute). This may not seem like a big increase, but it comes at 

a time when pressure to reduce sulphur emissions from smelters is 

increasing. The tempering effect on sulphur increasing, especially 

in 2005, would be caused by the introduction of the new Brazilian 

coke. 

Figure 4: World Excluding CIS and China

Changing Calcined Coke Quality - Sulphur

1.80

1.84

1.88

1.92

1.96

2.00

2000 2001 2002 2003 2004 2005 2006 2007 2008

Year

Sulphur

Content (wt%)

Figure 5 shows that vanadium will increase about 20% to nearly 

270 ppm on average in 2007. This is the most dramatic change in 

quality expected. The next green cokes available are significantly 

higher in vanadium; some are above 600 ppm. 

Figure 5: World Excluding CIS and China

Changing Calcined Coke Quality- Vanadium

200

220

240

260

280

300

2000 2001 2002 2003 2004 2005 2006 2007 2008

Year

Vanadium (ppm)

490
Changes in impurity levels such as sulphur and vanadium are easy 

to measure and understand but changes in coke structure are more 

subtle. Delayed sponge coke used by the aluminum industry today 

typically has a low micro-porosity with a moderate degree of 

anisotropy with large domain sizes. Many of the non-traditional 

cokes used in the future will be more isotropic in character with 

small domain sizes and a fine-grained texture. They are also 

typically higher in micro-porosity. 

Figure 6 shows a micrograph of a traditional delayed sponge coke 

that has been used successfully by the aluminum industry for 

many years. Figure 7 shows a more isotropic sponge coke that is 

being used today in small quantities as a blend component. The 

difference in structure should be obvious. Many of the nontraditional cokes used in the future will have isotropic structures 

like those shown in Figure 7. 

Figure 6: Micrograph of a Typical Sponge Coke (100x) 

Figure 7: Micrograph of an Isotropic Sponge Coke (100x) 

Two calcined coke properties related to coke structure that can be 

expected to change in the future as more non-traditional cokes are 

used in anode manufacture are micro-porosity (as measured by 

mercury apparent density) and coefficient of thermal expansion 

(CTE). Figure 8 shows a projection for the change in mercury 

apparent density (measured via the Pechiney method). Mercury 

apparent densities are expected to drop on average by 0.01g/cm3

from the recent past. Coke bulk densities are also likely to 

decrease on average due to the higher volatile matter content of 

non-traditional green cokes. 

Figure 8: World Excluding CIS and China

Changing Coke Quality - Apparent Density

1.70

1.71

1.72

1.73

1.74

1.75

1.76

2000 2001 2002 2003 2004 2005 2006 2007 2008

Year

Apparent Density 

(g/cm3)

Figure 9 shows that the CTE of anodes made in 2007 will be 

higher than at present. The projection is based on a measurement 

of CTE’s on bench scale anodes produced with traditional cokes 

and more isotropic, non-traditional cokes. The projection is 

somewhat speculative since only limited CTE data is available. 

The trend toward a higher CTE can be expected however, since 

more isotropic cokes have a higher coefficient of thermal 

expansion. This is one of the primary reasons why the industry 

avoids using shot cokes. Although shot coke packs to a high bulk 

density, its high CTE makes it very sensitive to thermal shock 

problems when used in anodes. No use of shot coke is assumed in 

these projections. 

Figure 9: World Excluding CIS and China

Changing Coke Quality - CTE

4.00

4.05

4.10

4.15

4.20

4.25

2000 2001 2002 2003 2004 2005 2006 2007 2008

Year

CTE

One Typical New Coke 

Table 1 compares the properties of the coke shown in Figure 7 

with the average properties of a range of traditional cokes being 

used today. The properties were measured on bench scale anodes 

produced with 100% of each different coke. The non-traditional 

coke is typical of the next tier of quality available to the calcining 

industry for anode grade coke production. 

The property differences that stand out with anodes produced 

from the new, non-traditional coke are as follows: 

Baked anode density is slightly lower 

Compressive strength is significantly higher 

Modulus of elasticity is significantly higher 

CTE is significantly higher 

Air reactivity residue is lower 

Sulphur and vanadium are higher 

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Table 1: Comparison of Bench Scale Anode Properties of 

Traditional Cokes with a Non-Traditional Coke 

Property Traditional 

Cokes 

(Range) 

Traditional 

Cokes 

(Average) 

NonTraditional 

Coke 

Baked Density, g/cm3 1.48-1.53 1.51 1.46 

Specific electrical 

resistivity (m) 

67-82 75 66 

Compressive Strength, 

MPa 

21-27 23 48 

Modulus of Elasticity, 

GPa 

1.8-2.4 2.18 4.50 

CTE, 10-6/K 3.7-4.5 4.00 5.49 

Thermal Conductivity 

W/mK 

2.2-3.3 2.6 3.1 

Xylene Density (g/cm3) 2.07-2.10 2.08 2.05 

Air Permeability, nPm 2.0-2.2 2.5 2.3 

CO2 Reactivity 

Residue, % 

87-97 93.7 94.2 

Air Reactivity 

Residue, % 

60-98 79.2 54.5 

S, % 0.98-3.31 2.35 3.77 

V, ppm 44-350 167 578 

It would not be feasible for the industry to produce anodes with 

100% of a coke like this today, but it has been used successfully 

as a blend coke. The challenge that the industry faces is that a 

greater proportion of this type of coke quality will need to be used 

in the future. 

How Can the Aluminum Industry Best Adapt? 

The situation facing the aluminum industry relative to coke 

quality is somewhat analogous to the situation with coal tar pitch. 

The closing of coke ovens for economic and environmental 

reasons has left coal tar producers and users searching for 

strategies to deal with the shrinking of supply of coal tar [3]. The 

industry is adapting however, and many smelters are now using 

coal tar pitch/petroleum pitch blends with good success. 

The coke changes predicted are inevitable, and the aluminum 

industry will need to adapt to using progressively more isotropic 

cokes or other carbon based materials. Many people ask about 

coal, but high ash levels mean that expensive pre-treatments are 

required to reduce the ash to acceptable levels. A study by Goodes 

et al [4] in the mid-1980’s concluded that good results were 

possible using a flash pyrolysis process, but the economics were 

unfavorable. Research is underway again today in this area but it 

is too early to predict the technical and commercial viability. 

In the meantime, as the aluminum industry’s demand for carbon 

increases, the use of more isotropic cokes will become necessary. 

What could a smelter using a moderately anisotropic sponge coke 

with a low metals content expect today if it switched to a high 

metals, high sulfur, isotropic coke? The following negative 

consequences might be expected: 

Anode CTE would increase along with the potential for 

significant thermal shock cracking problems. 

Anode air reactivity would increase resulting in higher 

excess carbon consumption. 

Metal purity would decrease along with possible 

decreases in cell current efficiency. 

The coke may be more difficult to grind and poor pitch 

penetration of coke would reduce anode strength and 

increase permeability. 

Environmental problems associated with handling 

higher sulfur carbon materials would increase. 

It is unlikely that any smelter today or in the future could perform 

well if it switched fully to using a highly isotropic coke. Smallscale plant trials have been attempted in the past, but the results 

were disappointing, if not unexpected. Mannweiler et al. [5] 

reported on the results of a smelter trial with a highly isotropic 

Venezuelan coke containing 2280 ppm vanadium, 530 ppm nickel 

and 3.9% Sulphur. The coke had a low real density and the air 

reactivity was an order of magnitude higher than traditional 

materials. A relatively small number of anodes were produced but 

nearly all cracked when placed in the cell. The trial was aborted in 

favor of a trial with a 50/50 mixture of isotropic coke and a more 

traditional anode grade coke. More acceptable results were 

produced in this second trial and cracking in the cells was 

eliminated. 

Below are some of the adaptations or technologies the industry 

may need to explore in order to solve the type of problems 

experienced when utilizing more isotropic cokes. 

High CTE and Thermal Shock Cracking: This is a significant 

negative consequence of using isotropic cokes. Limiting the 

amount of high CTE coke in the blend is one way to control this 

along with other steps such as: 

Modifying the anode granulometry or particle size 

distribution to a recipe that offers more thermal shock 

resistance [6]. 

Limiting the physical size of anodes used in the cell 

Utilizing anode pre-heating before setting new anodes 

in a cell 

Reducing cell operating temperatures and cell process 

variations 

Eliminating the thermal shock problem completely by 

developing a modern, continuous pre-bake anode 

technology. 

Air Reactivity: The susceptibility of anodes to excess 

consumption through air oxidation or airburn is dependent on both 

the coke quality and the cell design and cover practices. Modern 

well-covered cells are not as sensitive to anode airburn problems 

as older cells, where maintaining a sufficient level of cover is 

difficult. Adaptations to limit anode airburn may include: 

Changing to deep cavity cell designs which allows good 

control of anode cover 

Adding small quantities of oxidation inhibitors to the 

carbon (This is common practice in the ceramics 

industry for materials such as silicon carbide and 

graphite.) 

Metal Purity and Loss of Current Efficiency: This is arguably the 

most difficult problem to solve when using cokes with high metals 

contents and will ultimately limit the quantity of these materials 

492
that can be used in a blend. Contaminants such as nickel, 

vanadium and silicon will report to the metal and may result in a 

loss of current efficiency as has been reported in previous studies 

[3]. Post-metal treatment (such as addition of boron) can be used 

to remove such impurities but there is a significant cost associated 

with this. 

Grinding and Pitch Penetration Problems: These problems are 

potentially the simplest to solve by changing process equipment 

or targeting particular size fractions for the isotropic coke. The 

aluminum industry has been conservative in its approach to using 

new technology in the past but this is changing. In the last 10 

years, the industry has embraced fabrication technology that has 

been in use in other industries for some time such as Eirich 

Intensive Mixer/Coolers, vacuum vibro-formers, and new 

crushing and grinding equipment. Recently, vacuum hydraulic 

presses with fully programmable pressing cycles have been 

suggested. A combination of new technology can easily overcome 

some of the processing problems that may be experienced when 

utilizing more isotropic cokes. 

Environmental: The use of higher sulphur cokes will generate 

more SO2 and it will become increasingly necessary for smelters 

to remove SO2 from the cell off gases before they are released to 

the atmosphere. Scrubbing technology is available today for this 

and the problem becomes an economic one rather than a 

technological one. 

Finally, it is worth noting that all of the above problems could be 

eliminated if the industry developed a viable inert anode. Despite 

a lot of attention in 2001, this technology still appears to a long 

way from commercial reality, and in the meantime, the industry 

will need to learn to utilize progressively more isotropic cokes. 

Conclusions 

The following conclusions can be drawn from the data presented 

in this paper. 

1. Non-traditional cokes with more isotropic structure and 

higher sulphur and vanadium levels will largely meet a 21% 

increase in anode grade green coke demand between 2003 

and 2007. 

2. The major change in calcined coke quality predicted between 

2003 and 2007 is the 20% increase in vanadium. Other 

negative changes for the aluminum industry will be higher 

coke CTE’s, increasing sulphur content and density 

decreases. 

3. Smelters must prepare for the future changes in anode quality 

by modifying their processes and developing strategies for 

removing vanadium from their product metal. 

References 

1. “Global Trends in Anode Grade Coke Availability and 

Quality for the Aluminium Industry,” F. Vogt, R. Tonti, L. 

Edwards, Proceedings of the 7th Australasian Smelting 

Technology Conference, Melbourne, Australia, November 

11-15, 2001. 

2. Aluminium Quarterly Industry and Market Outlook; CRU 

International Ltd., London, England, July 2003 

3. “Developing Coal Tar/Petroleum Residues,” R.H. Wombles 

and M.D. Kiser, Light Metals 2000, p537 

4. “Production of Anode Grade Carbon from Coal,” C.G. 

Goodes, J.A. Eady and J.C. Nixon, Light Metals 1987, p459. 

5. “High Vanadium Venezuelan Petroleum Coke, a Raw 

Material for the Aluminum Industry?,” U. Mannweiler, W. 

Schmidt-Hatting, D. Rodriguez and A. Maitland, Light 

Metals, 1989, p449. 

6. “An Approach for a Complete Evaluation of Resistance to 

Thermal Shock: Applying to the Case of Anodes and 

Cathodes,” C. Dreyer and B. Samanos, Light Metals, 1997, 

p 585. 

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