Quality of Distillates From Recycle Coking

Mohamed Shakir Japanwala Department of Chemical & Materials Eng., University of Alberta

Typical Upgrading Scheme

Hydrogen PlantHydrogen Plant

HydrocrackingHydrocracking

CokersCokers

HydrotreatersHydrotreaters

Treated Naphtha Treated Naphtha and Gas Oilsand Gas Oils

Synthetic Crude Oil Synthetic Crude Oil Storage and BlendingStorage and Blending

BitumenBitumen

Coking Process

Recycle Recycle StreamStream

FeedFeed

CokeCoke

Liquid Liquid ProductsProducts

Coking Coking ReactorReactor

Project Objectives

• How reactive are the recycled materials to further cracking and coke formation?

• What are the characteristics of the cracked products?

• How do the products affect hydrotreating catalysts?

Experimental Plan

Vac

uum

D

istil

latio

n

Vac

uum

D

istil

latio

n

Vac

uum

D

istil

latio

n

1st Stage 2nd Stage 3rd StageV

acu

um

V

acu

um

Dis

tilla

tion

Dis

tilla

tion

React

or

React

or

React

or

React

or

React

or

React

or

Vacu

um

V

acu

um

Dis

tilla

tion

Dis

tilla

tion

Vacu

um

V

acu

um

Dis

tilla

tion

Dis

tilla

tion

Residue 2Residue 2Residue 1Residue 1 Residue 3Residue 3

Distillate 1Distillate 1

CokeCoke CokeCoke CokeCoke

Distillate 2Distillate 2 Distillate 3Distillate 3

GasGas GasGasGasGas

FeedFeed

Experimental Apparatus

Nitrogen in

Acetone Dry Ice

Molten Salt Bath

Quartz Tube Reactor

U-Tube

•Reactor Temperature - 530oc

•Nitrogen Flowrate - 0.17 L/min (NTP)

•Reactor Volume - 60 mL

Cumulative Product Yields

0

5

10

15

20

25

30

35

40

45

50

Gas Naptha Distillate Coke

Cu

mu

lati

ve W

eig

ht

%

0

10

20

30

40

50

60

70

80

90

100

Cu

mu

lative Resid

ue C

on

version

Stage1

Stage2

Stage3

Cumulative ResidueConversionSeries4

Characterisation

• Analytical methods

– NMR functional group analysis– Elemental analysis (C, H, N, S)– Average molecular weight– Micro carbon residue (MCR)– Simulated distillation by gas chromatography– High performance liquid chromatography (HPLC)

Hypothetical Hydrocarbon Molecule

1 Aromatic Bridgehead C

1

2

4

3

5

6

2 Protonated Aromatic C

3 Methyl Group on Aromatic C

5 CHAIN : CH2 that are atleast from aromatic or terminal methyl or atleast to cycloparaffin or branch point

4 Naphthenic CH2

6 Terminal Chain Methyl's

Structural Changes

• Constant chain length.

• Naphthenic carbon decreases.

• Aromatic carbon increases.

Structural Parameters-Resid

0

10

20

30

40

50

60

70

80

90

100

Feed Stage1 Residue Stage2 Residue Stage3 Residue

% A

rom

ati

c C

arb

on

0

1

2

3

4

5

6

7

8

9

% P

ara

ffinic

Carb

on

Aromatic Bridgehead Carbon Total Aromatic CHAIN NAPH

Aromatic Carbon - Mass Balance

0

20

40

60

80

100

120

Stage 1 Aromatic balance Stage 2 Aromatic balance Stage 3 Aromatic balance

Wt.

% o

f ca

rbo

n i

n p

rod

uct

Residue Distillate Coke

Undesirable Constituents of Distillate

• Nitrogen compounds are known to act as catalyst poison.

• PAHs contribute to increased coke formation.

• Bitumen derived gas oil vs conventional gas oil– Higher Sulphur and Nitrogen Content– Higher Aromaticity– Higher MCR

Distillate Nitrogen Content 2D Graph 1

Cumulative Distillate Weight %

0 5 10 15 20 25 30 35 40 45 50

Wei

ght

% N

itrog

en

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Structural Parameters-Distillate

0

10

20

30

40

50

60

70

80

90

100

Stage1 Distillate Stage2 Distillate Stage3 Distillate

% A

rom

atic

Car

bo

n

0

1

2

3

4

5

6

7

8

9

% P

araffinic C

arbo

n

Aromatic Bridgehead Carbon Total Aromatic

Terminal Chain Methyl CHAIN

Naphthenic

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 5 10 15 20 25 30 35 40

Time (minutes)

Distillate 1

Distillate 2

Distillate 3

UV Absorption Spectra (282nm)

Diaromatic

Tetraaromatic

Distillate MCR2D Graph 1

Cumulative Distillate Weight %

0 5 10 15 20 25 30 35 40 45 50

Weig

ht %

MC

R

0

1

2

3

4

5

6

7

Distillate Quality

• Weight % Nitrogen increases

• MCR content increases

• Aromaticity increases

• PAHs increase

Coke Quality on Recycle

• Coke quality improves. Recycle stream excellent source to make good quality coke!

0

1

2

3

4

5

6

7

8

Stage 1 Coke Stage 2 Coke Stage 3 Coke

% W

eigh

t

Hydrogen Nitrogen Sulphur

Implications of Research - Ideal Coker

Coke

Maximize Distillate Yield

Bitumen Feed

•PAHs

•Heteroatoms

•Metals

Coking Coking ReactorReactor

Implications of Research

• The distillate quality rapidly deteriorates upon recycle coking.– A large amount of aromatic carbon is in the

form of polycyclic aromatics in the recycle stream.

– There is an increase in the weight % nitrogen.

Implications of Research

Recycle Recycle StreamStream

FeedFeed

CokeCoke

DistillateDistillate

Coking Coking ReactorReactor Coking Coking

ReactorReactor

What Next?

Is the lower quality worth the higher yield?