Effect of heating rate and temperature on pyrolysis of asphaltenes:

A study of char characteristics

Nirlipt Mahapatra1, Vinoj Kurian1, Ben Wang1,Frans Martens2 , Rajender Gupta1

1Department of Chemical & Materials Engineering, University of Alberta 2Nexen Energy ULC, Calgary, Canada

6th International Freiberg Conference on IGCC & XtL Technologies,

Coal Conversion and Syngas,

19-22 May 2014, Dresden/Radebeul, Germany

Outline

2

Introduction

Experimental

Results & Discussions

Conclusions

Bigger Picture on Oil sands & Bitumen

What are Asphaltenes ?

Asphaltenes Gasification

Char Preparation Characterization

Char morphology & composition

Reactivity

Objective

Importance of char

3

Introduction

4

Oil Sands in Canada

Canada

3rd Largest Oil Reserves1 5th Largest Crude Oil producer1

1.8 MMbd

5.21 MMbd

Crude Oil production from Oil sands2

2012 2030

Oil sands are primarily obtained in Alberta (Western Canada)

5

Bitumen

Bitumen (from Oil sands)6

HEAVY4,5

Higher Density, Viscosity, S, N, O,

Minerals & Carbon Residue (MCR/CCR)

15 wt.% Asphaltenes 7

Oil Sands Bitumen Crude Oil Extraction Upgrading

Asphaltenes

6

Asphaltenes

Powdered asphaltenes

Archipelago structure MW: 4133 g/mol13

Heaviest fraction of Bitumen/ petroleum

liquids 8,9,10

50% of Carbon Residue in Bitumen11,12

Highest Sulfur & Mineral Content

Complex Structure

Cause problems during

• Production

• Refining

• Transportation

7

Asphaltenes Gasification

Asphaltenes Gasification

Steam to SAGD

H2 to Hydrocracking

from de-asphalter

Asphaltenes have no use and pose disposal problems but are high

in calorific value

Gasification can provide a cleaner alternative 14,15,16

Asphaltenes as liquid streams are easier and cost effective to

handle than solid coke. 16

Schematic for Asphaltene Gasification integrated into Upgrading 16

8

Gasification

Pyrolysis

Heterogeneous Char gas reactions

Gas phase reactions

Char is important

9

Gasification

Pyrolysis

Heterogeneous Char gas reactions

Gas phase reactions

Amount and characteristics of char and volatiles17-22

Temperature Residence Time Heating Rate Feed Size

Char is important

10

Objective

Char • Structure & Composition • Morphology • Global Reactivity

Operating Temperature

Residence time at temperature

Heating rate

11

Experimental

12

Char Preparation

150-212 um solid asphaltene

feed

Mullite /Alumina tube

65 mm ID X 153 cm height

Electrical heating

Atmospheric pressure

Air and water cooled feeder

probe

N2 (entraining gas)

Entrained Flow Drop Tube Furnace

Proximate & Elemental Analysis

Scanning Electron Microscope (SEM) & Energy Dispersive X-Ray (EDX)

X-Ray Diffraction (XRD)

Fourier Transform Infrared Spectroscopy (FTIR)

Inductively Coupled Plasma Mass Spectrometry (ICP-MS)

Thermogravimetry (TGA)

13

Characterization

14

Results & Discussions

Sample Name Nominal Temperature

of DTF ( °C) Nominal Residence

Time (s)

800 °C Char 800

8.4 1000 °C Char 1000

1200 °C Char 1200

1400 °C Char 1400

11.8 s Char

1200

11.8

8.4 s Char 8.4

6.5 s Char 6.5

4.9s Char 4.9

15

Operational Parameters

Pressure: 1 atm Feed Size: 150-212 µm

16

Volatiles & Fixed Carbon

Temperature Residence Time

Temperature more pronounced effect

Temperature Residence Time => Volatiles FC

17

H/C, Sulfur & Carbon

Temperature Residence Time => H/C S C

N, O content also decreases

Rate of decrease of H/C and S Decreases at higher temperatures

Temperature Residence Time LHR

18

Re-condensed volatiles (minor)

Incomplete pyrolysis

Maximum weight loss region occurs between 350-500 ˚C with a maxima at 450˚C

Thermal Analysis

Asphaltenes Char

19

CH -, aromatic CH CH2- and CH- (wag)

C=O carbonyl

CH2-S (wag)

-OH carboxylic acid

Infrared Spectra

20

CH -, aromatic CH CH2- and CH- (wag)

Infrared Spectra

21

X-Ray Diffraction Crystalline reflection (00l) (turbostratic carbon)

2D Lattice Reflections (hk)

Turbostratic Carbon / Graphitization24

Temperature Residence time change not much effect

V, Ni most abundant in petroleum25,26

(porphyrinic and non-porphyrinic )

V, Ni accumulates in char

22

Analysis of trace metals

23

Discussions so far

Ash, V, Ni accumulates in char (0.60 wt.% asphaltenes and 2.18 wt.% ash 1400 ˚C Char)

Initally H/C ratio decreases fast due to de-alkylation and removal of H2S. At Higher Temperatures decrease is slow due to condensation & peri-condensation27

(and graphitization)

High Heating Rates Lower Char Yield

Thiophenic Sulfur remains while aliphatic Sulfur is lost as H2S. (IR Spectra and Elemental Analysis support ). Lost early as C-S < C-C 28

(Asphaltenes 40% aliphatic S; and 60% thiophenic S 23)

24

800 ˚C Char Temperature

Nominal Particle Size

Bulk Density

Fraction of fragmented particles

Morphological Study (SEM) 1000 ˚C Char

1200 ˚C Char 1400 ˚C Char

Residence Time No noticeable change in morphology

*Similar magnifications 500X

25

SEM of Char

1000X BSE SEM

1200 ˚C Char Cross-section Soot on Char Surface

25000X SE SEM

Structure of Char hollow “Cenosphere” with a vesicular porous wall White dots are minute soot deposits on char surface

26 EDX Mapping of 1200 ˚C Char (300X magnification)

V & Ni in minute quantities

aluminosilicates and iron oxides discrete particles

Sulfur evenly (more in bigger sized)

EDX Mapping of Char

27

SEM of Low Heating Rate Char

600 ˚C LHR Char

900 ˚C LHR Char

Macro-porosity increases at higher temperatures

*Similar magnifications 500X

28

Discussion on Char Morphology

Nominal particle size decreases and fragmentation increases at higher temperatures, thicker walls 29

Smooth surface of char could signify initial rapid melting of asphaltenes

Observable Porosity Higher Temperatures

Residence time (5-12s) less pronounced effect

29

Char Steam(20%) Reactivity

Temperature Residence Time

Temperature Residence Time global char steam reaction rate Less pronounced for Residence Time

30

Char CO2(100%) Reactivity Temperature Residence Time

Temperature Residence Time global char CO2

reaction rate (Boudouard Reaction)

31

Discussion on Char global reactivity

Chars obtained at higher temperature have a decreased reactivity due to ordering of carbon structure (graphitization) 30-32or thermal annealing process33. May explain increase loss due to increase in residence time as well.

800 Deg. Char significantly higher reactivity. Great difference in morphology. Decrease in micro-porosity of char at higher temperatures and an increase in observed macro-porosity. 34

32

Conclusion

Pyrolysis temperature , residence time at temperature & heating rate affect the morphology, structure and reactivity of chars. • Increase in operating temperature

– Global gasification reactivity – Nominal particle size – H/C Ratio, Number of functional groups, N, S, O, Volatile matter – Aromaticity – Graphitization – Macro-porosity

• Increase in residence time at temperature (less pronounced effect) – Global gasification reactivity – H/C Ratio, Number of functional groups, N, S, O, Volatile matter

– Change in morphology, aromaticity & graphitization not noticeable

• Very high heating rates overcome mass transfer limitations and better pyrolysis occurs

Future Work: Estimation of surface area and intrinsic char reactivity

33

Acknowledgments

34

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Thanks

Questions ?

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