Hydrocarbon Processing - October 2022 - 45

Biofuels,
Alternative/
Renewable Fuels
L. MCHENRY, X-Ray Optical Systems,
East Greenbush, New York
ASTM D5453 vs. D7039 and the importance
of oxygen correction for B100 samples
The use of biodiesel is rapidly becoming
more popular due to growing trends
both inside and outside the petroleum
industry. The U.S. Energy Information
Administration's (EIA's) data shows that
biodiesel production in the U.S. has increased
by more than 100 MM gal/mos
since 2011, with biodiesel making up 4%
of total diesel consumption in 2016. The
EIA forecasts biofuels production to increase
between 18%-55% over the next
30 yr. Responding to the evolving industry
and social landscape, many traditional
refineries have begun to incorporate biodiesel
into their finished products.
While biofuels typically contain low
amounts of sulfur, they are still required
to adhere to fuel quality compliance
specifications either for use in vehicles or
as a blending feed for traditional refinery
fuels. As such, biorefineries must measure
the sulfur in their product to ensure that
it is below regulatory limits, typically less
than 15 parts per million (ppm). Biofuel
analysis can be challenging due to the
variety of feedstocks and to changing
sample compositions.
According to ASTM D6751-20a
[Standard Specification for Biodiesel Fuel
Blend Stock (B100) for Middle Distillate
Fuels], there are several options for testing
sulfur in biodiesel. ASTM D5453 is listed
as the referee method, but D7039 may
also be used. This article examines these
methods in more detail, using data from
the ASTM B100 Proficiency Testing Program
(PTP), and discusses renewable diesel
vs. biodiesel, as well as the importance
and methodologies for oxygen correction.
ASTM B100 PTP overview. The ASTM
B100 PTP allows biodiesel laboratories
to improve their testing performances by
comparing their biodiesel test results with
other laboratories. The statistical analysis
also provides a valuable tool to assess test
method performance on a particular matrix
type and allows comparison between
two or more test methods that measure
the same property. For the B100 PTP,
ASTM sends 1-gal
samples out three
times per year for analysis of approximately
24 biodiesel properties. This article will
focus on sulfur analyses from 2018-2021,
using ASTM D5453 and ASTM D7039.
First, understanding the test methods is
critical to interpreting the data presented.
ASTM D7039 (Monochromatic
wavelength dispersive x-ray fluorescence).
Monochromatic wavelength dispersive
x-ray fluorescence (MWDXRF) is
a subset of WDXRF that utilizes similar
principles. Rather than using filters or
traditional crystals that are flat or singly
curved, MWDXRF incorporates doubly
curved crystal (DCC) optics to provide
a focused, monochromatic excitation xray
beam to excite the sample. A second
DCC optic is used to collect the sulfur
signal and focus it onto the detector. This
Scope, ppm
1-400
D7039
400-8,000
3.2-2,822
* Where X is the average of the two results
Hydrocarbon Processing | OCTOBER 2022 45
modified methodology delivers a signalto-background
ratio that is 10 times more
precise than traditional WDXRF, which
improves method precision and limit of
detection (FIG. 1).
ASTM D5453: MWDXRF. In ultraviolet
fluorescence (UVF) technology, a hydrocarbon
sample is either directly injected
into a high-temperature (1,000°C) combustion
furnace or placed in a sample boat
that is cooled and then injected into the
combustion furnace. The sample is combusted
in the tube, and sulfur is oxidized
to sulfur dioxide (SO2
) in the oxygenrich
atmosphere. A membrane dryer removes
water produced during the sample
combustion, and the sample combustion
gases are exposed to ultraviolet (UV)
light. SO2
is excited (SO2
*), and the reFIG.
1. MWDXRF delivers a signal-tobackground
ratio that is 10 times more precise
than traditional WDXRF, which improves
method precision and limit of detection.
TABLE 1. ASTM test method scope and precision equations
Method
D5453
Repeatability, ppm*
0.1788·X0.75
0.02902·X
0.4998·X0.54
Reproducibility, ppm*
0.5797·X0.75
0.1267·X
0.7384·X0.54
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