Post on 18-Jan-2016
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?