Wax crystal modification

Composition of Diesel Fuel
Chromatography analysis
of Diesel Fuel
C 18
Paraffins - important component of middle
distillate fuels (10-35%) (10 35%)
- major components of crude oils
solubility (wt%)
Wax solubility lines in decane
10
8
6
4
2
C 24
C 28 C 32 C 36
0
0 10 20 30 40 50
Temperature (°C)
Van t‘Hoff Equation: Equation
( ) /
ln
x =−∆ H +
solubility diss RT
∆S
R
diss

Crystallisation of Paraffin Waxes
I. Wax crystal in Diesel
oil plug filters
Prevent sale of certain
brands in the winter
II. Wax crystals form gels
and stop flow
Gels inhibit crude oil
recovery from deep
sea reservoirs

Polymeric Additives
Choice largely trial and error
polymers in general self assemble
interplay between polymer aggregate and wax
crystallization important
Example: poly(ethylene- poly(ethylene co- co vinylacetate), vinylacetate),
EVA
poorly characterized
not very efficient in certain oils
50% precipitation already at high T

Random Ethylene-Butene
Ethylene Butene
Copolymers
Model system for studying co-crystallization co crystallization of paraffin
and polymer additives in fuel oil at low temperatures
1,4
1,2 ( vinyl )
6444447444448 6 47448
( ) ( )
− CH − CH = CH − CD − CH − CH − −
2 2 x 2 (1 x)
2 2 2 2 2 2
CH = CH 2
− CH − CH − CH − CH .......... CH − CH −
M w ≅ 6K
CH 2
CH 2
PEB-n PEB
precursor
PEB-n PEB
n: number of
ethyl branches

Temperature Dependent
Aggregation
dΣ/dΩ(5x10 -3 Å -1 ) [cm -1 ]
50
40
30
20
10
0
dΣ/dΩ(0)=52.5cm -1
PEB-12 in d-decane, 2%
dΣ/dΩ(5x10 -3 Å -1 )=0.7cm -1
-20 0 20 40 60 80 100
Temperature [°C]
Aggregation below T = 0°C
0

Aggregation behaviour
of PEB 7.5
Large compact objects
by minority
From Porod constant
and micrograph 0.7%
polymer participation
Rod like structures at
lower temperatures
Correlation peak?
Aggregation starts around 40C

Joint Aggregation Behaviour
of Polymers and Wax
dΣ/dΩ [cm -1 ]
10 3
10 2
10 1
10 0
10 -1
10 -2
10 -3
wax visible
1% PEB-11 PEB 11 + 0.5% wax
Q -2
1% dh-PEP12 @ 0.5% wax
T ≤ -10 10°C
10 -2
Q [Å -1 ]
-22 °C
-12 °C
-10 °C
-4 °C
22 °C
10 -1
unimolecular thin plates: 30Å 30
evolving picture:
cocrystallization
Wax aggregates in thin plates; dictates the polymer structure

dΣ/dΩ [cm -1 ]
PEB-7.5 PEB 7.5 + C 36
10 5
10 4
10 3
10 2
10 1
10 0
10 -1
10 -3 10 -2
() @ 36 ( ) 74
Q -2
10 -2
polymer contrast
paraffin contrast
10°C
10 -1
Q [Å -1 ] 45Å
T = 10°C 10 C below wax solubility line
120-160Å

dΣ/dΩ [cm -1 ]
PEB-7.5 PEB 7.5 + C 36
10 5
10 4
10 3
10 2
10 1
10 0
10 -1
10 -3 10 -2
() @ 36 ( ) 74
Q -2
10 -2
Q [Å -1 ]
polymer contrast
paraffin contrast
10°C
10 -1
wax plates
thickness dwax wax < 45Å 45
single C 36 plates
polymer plates
no correlation peak
brush like form factor
wax cocrystallizes with
polymer and
suppresses
the pure PEB-7.5 PEB 7.5
aggregation features
T = 10°C 10 C below wax solubility line

Wax Modification Efficiency
Results from evaluation of structures under different contrast
Example: wax and polymer content in platelets
φwax φpol
C24 36% 64%
C36 91% 9%
3-d d structures grow from platelets
T = 0°C 0
φφ w = 2%
φφ pol = 0.6%
Take home message:
Efficiency highest if polymer and wax crystallize jointly

Conclusion
1. Crystalline – amorphous blockcopolymers
- polymers form templates
polymer templates nucleate wax crystals
commercialized as
Paraflow TM
Diesel fuel additive
Wax crystal modification by partially crystalline polymers

Conclusion
2. Random crystalline amorphous copolymers
A. Polymer aggregation commences at temperature
above wax solubility line
polymer form templates for crystallization
nucleation from the polymer structures
Limited efficiency

Conclusion
B. Wax solubility line in the order of polymer
aggregation temperature
=> cocrystallisation dominated by wax
+ PEB-11 PEB 11 + C 24
• plates instead of rods
• polymers are incorporated into plates
+ PEB-7 PEB 7 + C 36
• plates at high T, , suppression of 3-d 3 d objects
• polymer olymer incorporated in wax plates
High efficiency
nucleation is
mediated by the
joint polymer
wax structure