the production of highly anisotropic needle-like carbon

The production of highly anisotropic needle-like carbon from aliphatic Waxy Oil

Dr. John Clark, Sasol Synfuels Marketing

December 2011

The synthetic graphite value chain

Heavy residue

Electrodes

SecondaryGraphite

Graphitisation

Coking

Calcining

Graphitisation

PrimaryGraphite

LubricityResistivity

Electrical conductanceSoftness

Graphene slip planes

Molecular densification Sublimation

Graphene plane alignment

Pre-Mesogen formation

Cracking and poly condensation

Thermal stabilityMesophase

Micro textureVCM

combustionMolecular

densificationAsh content

Inherent aromaticity

Mineral impurityAsphaltenesNitrogen and

Sulphur content

J G Clark – December 2011Copyright 2011. Sasol Synfuels, Marketing

Waxy Oil as a anisotropic carbon pre-cursor

The Sasol Synthol reaction produces hydrocarbons from synthesis gas (hydrogen and carbon monoxide); the distillation of which produces a heavy residue product namely Waxy Oil

long normal alkanes and multi-alkylated alkanes

high catalyst concentration

low green coke yield

high oxygenate content

As Waxy Oil is devoid of stable heteroatom species, the calcined coke contains negatable nitrogen and sulphur contents


Affect of iron oxide on the characteristics of Waxy Oil cokeIron oxide increases the ash contentof Waxy Oil coke

Iron oxide increases the carbon dioxide reactivity and oxidative consumption ofWaxy Oil coke [2;3]

Iron oxide promotes multiphase graphitisation favoring iron catalysis during thermal treatment to1400 °C [4]

The effect of catalytic graphitisation is diminished in cokes thermallytreated to 2000 °C [4]

Iron oxide acts both as an physical barrier [5] occluding the development of the microstructure and asa catalyst for oxidative polymerisation [4] producing mosaic microstructures and increasing the carbonyield

Ash content: 1.84% Ash content: 11.19%Ash content: 7.47%


The effect of catalyst on structure of the Waxy Oil coke section

5 mm


20 µm

20 um

Experimental protocol

Waxy OilAsh content: 1.671%


FiltrationAsh content: 0.006%



Thermal treatment410 °C, 2 hours, 5 bar



Thermal treatment410 °C, 2 hours, 5 bar

Distillation 325 °C. N2



Distillation350 °C, -0.9 kpa


Thermo Gravimetric Analysis (TGA) of Oil [6]

-2

-1.8

-1.6

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0100 150 200 250 300 350 400 450 500 550 600

Temer ature (°C)

Molecules Unit Filtered Waxy OilAlkylated aromatics Area% 9.13Pure aromatics Area% 0.84Iso-alkanes Area% 14.10Normal alkanes Area% 38.18Oxygenates Area% 13.12Cyclo- alkanes Area% 2.021H (aliphatic/aromatic) ratio 26.5

Aromatic Index (I ar) *


Thermo Gravimetric Analysis (TGA) of distilled Waxy Oil

MoleculesUnit Distilled

to 350 °C,-0.9 kpa

Alkylated aromatics Area% 1.00Pure aromatics Area% 0.00Iso-alkanes Area% 5.33Normal alkanes Area% 46.39Oxygenates Area% 10.34Cyclo- alkanes Area% 0.001H (aliphatic/aromatic) ratio 18.62

Aromatic Index (I ar)0.0041


Thermo Gravimetric Analysis (TGA) of thermally treated Waxy Oil

-0.6

-0.5

-0.4

-0.3

-0.2

-0. 1

0100 150 200 250 300 350 400 450 500 550 600

Temeratur e ( °C )

Molecules UnitThermally treated(410 °C, 2 hrs, 5

bar)Alkylated aromatics Area% 5.42Pure aromatics Area% 0.71Iso-alkanes Area% 15.14Normal alkanes Area% 63.27Oxygenates Area% 1.57Cyclo- alkanes Area% 0.461H (aliphatic/aromatic) ratio

12.45

Aromatic Index (I ar) 0.0046


Thermo Gravimetric Analysis (TGA) of thermally treated and distilled Waxy Oil

-2

-1.8

-1.6

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0100 150 200 250 300 350 400 450 500 550 600

T em er ature (°C )

Molecules Unit Thermally treated and distilled (310 °C, 2 hrs, 5bar) and distilled

Alkylated aromatics Area% 1.89

Pure aromatics Area% 0.83Alkylated alkanes Area% 2.61Normal alkanes Area% 85.82Oxygenates Area% 1.31Cyclo- alkanes Area% 0.021H (aliphatic/aromatic) ratio

9.93

Aromatic Index (I ar)

0.0118


Static coking [1]

100 µm 100 µm

20 µm20 µm

100 µm

100 µm 20 µm

20 µm100 µm


Influence of Waxy Oil modification on coke characteristics

36.3

29.8

2222.5

19.8

0

10

20

30

40

50

60

70

80

90

100

Waxy Oil Filtered Waxy Oil Distilled Waxy Oi l Thermally treated WaxyOil

Thermally treated anddistilled Waxy Oi lWaxy Oil modification

Dom

ain

flow

and

Wax

y Oi

l fee

d to

cok

er (m

ass%

)

10

15

20

25

30

35

40

Gre

en c

oke

(mas

s%)

Domain flow (%) Waxy Oi l feed to coker (%) Green coke ye ild (%)


Producing 100% anisotropic coke

100µm

100µm

100µm

100 µm 100 µm

50 µm 50 µm

Bottom (x10 magnification)

Bottom (x20 magnification)Bottom (x20 magnification)

Top (x10 magnification)


Microstructure through the coke section [8]

100 µm100 µm

100 µm 100 µm

13% height 30% height

60% height 80% height


The mechanism of Waxy Oil carbonisation

• Waxy Oil filtration• Waxy Oil thermal treatment at 410 °C, 5 bar, 2 hours• Distillation of thermally treated residue• Carbonisation of distilled Waxy Oil residue at 450 °C for 10, 20, 40, 60 and 120 minutes


Proposed carbonisation mechanism of Waxy Oil [7]

Production of lower alkanes and hydrocarbon gasses

Slow cyclation of alkanes to form cyclo alkanes and hydro aromatics including

dimerisation thereof

Rapid Dehydrogenation to form alkylated two to five ring

aromatics

Dealkylation to form four to six ring pure aromatics

CARBONISATION TIME

Thermally treated Waxy

Oil


Composition of Waxy Oil as a function of carbonisation time

Molecules Unit (10 mins) (20 mins) (40 mins) (60 mins) (120 mins)

Normal alkanes Area% 83.84 56.89 21.96 12.14 0.00

Alkylated alkanes

Area% 2.29 3.25 1.77 2.53 0.00

Alkenes Area% 1.48 2.43 3.37 0.53 0.00

Cyclo- alkanes or hydro aromatics

Area% 0.00 3.21 6.42 0.81 0.00

Alkylated aromatics

Area% 8.72 25.87 32.68 40.21 34.68

Pure aromatics Area% 3.66 8.35 33.79 44.65 65.83


Differential Thermo Gravimetry (DTG) of carbonised Waxy Oil


Concentration of “stable alkanes” after 10 and 20 minutes

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

30 35 40 45 50 55 60 65 70 75 80

Area%

Retention time (mins)10 minutes 20 minutes

1

1413

1211

10

9

8

765

43

2

222120

19

18

17

16

15

27

26

2524

23

Hexadecane (9.94 area %)Heptadecane (4.63 area %)Octadecane (26.16 area %)Eicosane (13.74 area %)Heneicosane (13.09 area %)Octacosane (3.60 area %)


Hydro aromatics produced after 20 and 40 minutes carbonisation

Molecule Units 20 mins 40 minsCyclo-hexane orHydro-benzenes Area% 0.00 1.47

Hydro-naphthalenes Area% 1.16 2.51Hydro-chrysenes Area% 1.39 2.22Hydro-benzofluoranthenes Area% 0.00 0.54Hydro-pyrenes Area% 0.00 1.66Hydro-benzoanthracenes Area% 0.66 0.00Total Area% 3.21 6.42

The production of cyclo alkanes or hydro-aromatics provides the “backbone” for the production of aromatic molecules mostly prior to dimerisation

The production of cyclo alkanes or hydro-aromatics provides a source of hydrogen donors which are ableto cap reactive radicals formed and stabilise the carbonisation system [9]

1

4

3

2


Alkylated aromatics identified after 60 minutes [8]

Methyltriphenylene (3.95%) Methylpyrene ( 6.80%)Dimethylpyrene, ( 3.95%)

Dimethylphenanthrene (1.01%) Methylphenanthrene, (1.80%)Methylbenzoperylene (1.62%)

Trimethylphenanthrene (0.58%)


Benz[a]anthracene (4.50%)

Benzo[a]phenanthrene (13.15%)

Benzoperylene (10.95%)

Triphenylene (2.64%) Benzo[ghi]fluoranthene (5.07%)

Benzo-pyrene (5.07%)

Benzo[b]triphenylene (9.61%)

Cholanthrene (2.62%)

Benzo[k]fluoranthene (12.31%)

Pyrene (2.44%)

Fluoranthene (1.07%)

Pure aromatics identified after 120 minutes [9]


The influence of carbonisation on the Aromaticity Index (Iar)

Carbonisationduration (mins)

AromaticityIndex (I ar)

10 0.04420 0.06940 0.12660 0.189120 0.345


Waxy Oil mesophase development and coalescence

100 µm

100 µm100 µm

100 µm


Waxy Oil mesosphere coalescence with semi-coke

20 µm

Mesosphere

Carbon microstructure


Waxy Oil coke microstructure

50 µm


Conclusions

The iron oxide catalyst concentration is detrimental to the characteristics of the coke in terms of the ash content, oxidative polymerisation, catalytic graphitisation, carbon dioxide reactivity and air reactivityThe most effective manner with which to maximise anisotropicity of the coke, maximise pre carbonisation distillates and maximise green coke yield is to thermally treat Waxy Oil followed by distillation“Static” carbonisation provides a simple method to consolidate the molecular composition of modified Waxy Oils with the degree of anisotropy of the green coke from the bottom of a longitudinal coke section

The carbonisation mechanism of thermally treated Waxy Oil involves initial production of lighter hydrocarbon gasses and lower alkanes. This is followed by a slow cyclation and rapid dehydrogenation step to form alkylated aromatics (predominantly three to five ring) and pure aromatics (predominantly four to six ring)


Acknowledgements

• University of Pretoria

• Sasol Synfuels Marketing

• This work is based upon research supported by the South African Research Chairs Initiative of the Department of Science and Technology and the National Research Foundation. Any opinion, findings and conclusions or recommendations expressed in this material are those of the authors and therefore the NRF and DST do not accept any liability with regard thereto

• INSTITUTO NACIONAL DEL CARBON (INCAR)


References

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3. Walker, P; Matsumoto, S; Hanzaw a, T; Muira, T & Ismail, M 1983, ‘Catalysis of gasif ication of coal-derived cokes and chars’, Fuel, vol. 62, pp. 140-149

4. Wang, Y; Korai, Y; Mochida, I; Nagayama, K; Hatano, H & Fukuda, F 2001, ‘Modif ication of synthetic mesophase pitch w ith iron oxide, Fe2O3’, Carbon, vol. 39, pp.1627-1634

5. Obara, T; Yokono, T; Sanada, Y & Marsh, H 1985, ‘Carbonization behaviour of pitch in the presence of inert material’, Fuel, vol. 64, no. 7, pp. 995- 998

6. Perez, M; Granda, M; Garcia, R; Santamaria, R; Romero, E & Menendez, R 2002, ‘Pyrolysis behaviour of petroleum pitches prepared at different conditions’, Journal of Anal. And Appl. Pyrolysis, vol. 63, pp. 251-239

7. Domine, F; Bounaceur, R; Scacchi, G; Marquaire, PM; Dessort, D; Pradier, B & Brevart, O 2002, ‘Up to w hat temperature is petroleum stable? New insights from a 5200free radical reactions’, Organic Geochemistry, vol. 33, pp.1487-1499

8. Wang, G & Eser, S 2007, ‘Molecular composition of the high boiling components of needle coke feedstocks and mesophase development’, Energy and Fuels, vol. 21, pp. 3563-3572

9. Guillen, M; Dominguez, A; Iglesias, M; Fuente, E & Blanco, CB 1996, ‘Analysis of coal-tar pitch: relations betw een thermal behaviour and composition’, Fuel, vol. 75, no. 9, pp. 1101-1107


the production of highly anisotropic needle-like carbon

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