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Gasoline Blending - NMR Application Overview This application marketed by NMR
Process Systems LLC - Paper Presented at
Experimental NMR Conference - 1996
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Much has been written
on the subject of NIR and Mid-IR spectroscopy applied to gasoline
blending. Over the past 15 years repeated attempts have been made to
validate these on-line systems. Bottom line is the systems validate when
close attention is paid to the modeling effort. The modeling effort very
quickly becomes cumbersome owing to the large number of models that must
be maintained. As an example - for octane, separate models must be
developed for high and low octane, for mid octane, for CARB fuel, for
oxygenated fuel (EtOH, MTBE, TAME), for finished blends, for each blend
component, for European fuels, etc. Dozens of models are required just for
RON. Continuous model updates are required after each crude slate change
(the analyzer is not available until the new gasolines have been produced
and placed in the model. Bluntly, if onsite expertise is not continuously
available the project will fail and the analyzer will never be
validated.
NMR is quite
different on the modeling side of the gasoline blending project. Being a
relatively insensitive technique (by insensitive we mean that no small
component change can have a dramatic effect on the spectrum) the NMR does
not have the continual model maintenance issue of spectral changes caused
by crude slate changes. The NMR is also an inherently linear spectroscopy
across all hydrocarbon types and compositions (this is not the case with
IR or NIR). This inherent linearity means that one can build a single RON
model for example that span 70 octane to 110 octane and have an SECV of
0.9 octane numbers (mainly caused by the repeatability/reproducibility of
the engine test at the high and low ends of the model range). Narrowing the range will yield more accurate
models with SEP's of 0.2 to 0.5 octane numbers.
Another advantage of
NMR over other spectroscopies is the orthogonality of the chemical types
within the NMR spectrum itself. Polynuclear aromatics (di, and tri),
mono-aromatics, internal olefins, terminal olefins, oxygenates, xylenic,
toluenic, substituted aromatics, CH, naphthenes, CH2 and
CH3 all fall into their own distinct chemical shift regions
allowing easy modeling of all chemical based parameters (PIONA,
Polynuclear aromatics, benzene, xylenes, toluene, FIA, total aromatics,
oxygenates, etc.).
Distillation and
density are readily modeled. More difficult is RVP which does need several
models to be able to accurately predict RVP of different gasoline types.
Below are a few figures
that show the data rich nature of the NMR spectrum. With a little know-how
it is possible to be able to look at an NMR spectrum and estimate the RON,
aromatic content or any other parameter. The spectral differences are
huge.
Below is a listing of
ASTM repeatabilities and reproducibilities. If the NMR system is validated
following the procedures set out in ASTM D3764 (or D6122) the the expected
agreement between the NMR predicted number and the average value from
multiple lab tests on the same sample will approach the ASTM repeatability
for the various tests. If the NMR is validated against single point lab
data (one sample, one test) then the expected agreement between lab and
NMR will be closer to the ASTM reproducibility for the various test
methods.
ASTM Precision
(Gasoline Testing)
1.API – ASTM D4052
|
SG |
Repeatability |
Reproducibility |
|
0.68 – 0.97 |
0.0001 |
0.0005 |
NMR Correlation cannot
attain reproducibility level of density test.
NMR Reproducibility will be within 0.0025
g/litre
2. RVP – ASTM
D5191
|
Parameter |
Repeatability |
Reproducibility |
|
Dry Vapor
Pressure Equivalent (DVPE) |
0.00807
(DVPE+B) |
0.0161 (DVPE
+B) |
B=124 kPa or 18.0 psi
depending on the units of DVPE
3. FIA – ASTM D1319
|
FIA Precision, Oxygenate Free
Sample |
|
Level, Volume
% |
Repeatability |
Reproducibility |
|
Aromatic |
Olefin |
Saturate |
Aromatic |
Olefin |
Saturate |
|
1 |
|
0.4 |
0.3 |
|
1.7 |
1.1 |
|
5 |
0.7 |
0.9 |
0.8 |
1.5 |
3.7 |
2.4 |
|
15 |
1.2 |
1.5 |
1.2 |
2.5 |
6.1 |
4.0 |
|
25 |
1.4 |
1.8 |
1.5 |
3.0 |
7.4 |
4.8 |
|
35 |
1.5 |
2.0 |
1.7 |
3.3 |
8.2 |
5.3 |
|
45 |
1.6 |
2.0 |
1.7 |
3.5 |
8.5 |
5.6 |
|
55 |
1.6 |
2.0 |
1.7 |
3.5 |
8.5 |
5.6 |
|
FIA Precision, Oxygenate Containing
Sample |
|
|
Range |
Repeatability |
Reproducibility |
|
Aromatic |
13 -
40 |
1.3 |
3.7 |
|
Olefin |
4 –
83 |
0.2578X0.6
|
0.8185X0.6
|
|
Saturate |
45 -
68 |
1.5 |
4.2 |
X = the volume percent of olefins
4.
Distillation – ASTM D86 (Group 1)
|
Evaporated
Point |
Manual |
Automated |
|
|
Repeatability |
Reproducibility |
Repeatability |
Reproducibility |
|
IBP |
6 |
10 |
7 |
13 |
|
5% |
r1 +
1.2 |
R1 +
2.0 |
r2 +
1.8 |
R2 +
3.2 |
|
10% |
r1 |
R1 |
r2 +
1.8 |
R2 +
1.3 |
|
20% |
r1 |
R1 |
r2 |
R2 +
1.3 |
|
30 –
70% |
r1 |
R1 |
r2 |
R2 |
|
80% |
r1 |
R1 |
r2 |
R2 –
1.7 |
|
90% |
r1 |
R1 –
2.2 |
r2 |
R2 –
3.5 |
|
95% |
r1 |
R1 –
1.7 |
r2 +
1.8 |
R2 |
|
FBP |
7 |
13 |
8 |
16 |
r1 = 0.864 (DF/DV%)
+ 2.186 R1 = 1.736 (DF/DV%)
+ 3.589 r2 = 0.673 (DF/DV%)
+ 2.036 R2 = 1.998 (DF/DV%)
+ 4.711
DF/DV%
= slope at evaporated point, °F/Volume%
5.
Benzene – ASTM D3606
|
Component |
Range, Volume
% |
Repeatability |
Reproducibility |
|
Benzene |
0.1 –
1.5 |
0.03X +
0.01 |
0.13X +
0.5 |
|
Benzene |
>1.5 |
0.03 |
0.28X |
X = the mean volume % of the component
6.
Oxygenates – ASTM D5599
Repeatability and Reproducibility Vary Depending on Oxygenate
Component
|
Component |
Repeatability |
Reproducibility |
|
Ethanol |
0.03
(X0.49) |
0.27
(X0.80) |
|
MTBE |
0.05
(X0.58) |
0.10
(X0.95) |
|
ETBE |
0.04
(X0.86) |
0.25
(X0.79) |
|
TAME |
0.04
(X0.58) |
0.24
(X0.69) |
X= Mean Vol% of
Component
7.
Aromatics – ASTM D5769
|
Component |
Repeatability |
Reproducibility |
|
Total
Aromatics |
0.027(X+4.4) |
0.10(X+4.4) |
X= Mean Vol% of Component
8. RON – ASTM D2699
|
Range |
Repeatability |
Reproducibility |
|
80 |
Unknown |
1.2 |
|
85 |
Unknown |
0.9 |
|
90 |
0.2 |
0.7 |
|
95 |
0.2 |
0.6 |
|
100 |
Unknown |
0.7 |
|
105 |
Unknown |
1.1 |
|
110 |
Unknown |
2.3 |
9.
MON – ASTM D2700
|
Range |
Repeatability |
Reproducibility |
|
80 |
Unknown |
1.2 |
|
85 |
0.3 |
0.9 |
|
90 |
0.3 |
1.1 |
|
95 |
Unknown |
1.1 |
|
99 |
Unknown |
1.5 |
|
100 |
Unknown |
1.1 |
|
105 |
Unknown |
1.8 |
For more information on this topic please contact:
John Edwards
Manager, Process and Analytical NMR Services
Process NMR Associates LLC,
87A Sand Pit Rd
Danbury, CT 06810, USA
Tel:(203)744-5905
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