Page 21 - Shimadzu Journal vol.8 Issue2

Hydrocarbon Processing Industry

of 0.10% sulfur (m/m) in so-called emission control areas (ECAS). Details on the theory and fundamentals of EDXRF as an analytical
The primary stated goal of this new regulation is to improve envi- technique are provided in Grieken and Markowicz (2001) and are
10
ronmental air quality in and around port cities and areas with high presented briefly here .
shipping traffic by minimizing SOx emissions.
As a technique, EDXRF has many advantages when used for anal-
There are two ways in which fuel producers or ship owners can ysis of fuels and oils. Namely, the technique is sufficiently sensitive
comply with the new regulations. First, refiners and producers of and can be adapted for multiple element analysis. Also, EDXRF
fuel oils may process those fuels so that they are stripped of their instruments tend to be small, requiring minimal benchspace and
sulfur compounds. Alternatively, ship owners have the option to laboratory infrastructure. The analyses carried out in this study
retrofit their fleet with SOx scrubbers on their exhaust stacks to can be performed in a laboratory equipped with electricity and
minimize emissions to make them equivalent to using compliant helium gas. A brief comparison of advantages and drawbacks of
fuels. Either approach puts a significant financial burden on the common analytical techniques for sulfur in petrochemicals is pro-
responsible party, whether they be refiners or ship owners. vided in Table 1.

Due to these new regulations from the IMO, refiners and fuel produc- The EDX-7000 operates under the principles of X-ray fluorescence
ers must now assess fuel oil for its sulfur content to ensure compliance. that takes advantage of the fact that the elements that comprise
Because of its ease of use and minimal sample preparation, energy a sample each have a unique atomic structure which is conceptu-
dispersive X-ray fluorescence, (EDXRF) is a preferred method for the ally diagrammed in Figure 1. An X-ray source is used to bombard
analysis of sulfur. At concentrations of 0.50% and higher, EDXRF is a sample with X-ray radiation which excites inner-shell electrons
sufficiently sensitive for sulfur detection and avoids the challenges as- to an elevated state. Subsequently, an outer-shell electron relaxes
sociated with other analytical methods, such as atomic absorption, gas into the hole left by the ejected electron and, in that process, emits
chromatography, or combustion methods. In this paper, we describe energy in the form of an X-ray. The X-ray emission line (e.g., Kα,
the use of Shimadzu’s EDX-7000 for compliance with the new IMO Kβ, Lα) depends on the shell from which the relaxing electron
8
standards for marine fuels as well as ASTM D4294 and ISO 8754 . 9 originates and that which it ends up in. The emitted X-ray photon
energy for each element for each element are unique and can be
used to identify each element, whereas the abundance of X-rays
produced correlate to the concentration of that element. The re-
Analytical Instrumentation sulting spectra consists of the photon energy of X-rays generated
and Considerations from the sample (in kiloelectronvolts, keV) and the abundance of
those X-rays (in counts per second per microampere, cps/µA) and
The instruments used in this study were Shimadzu EDX-7000 series, is typically processed by software to interpret elemental composi-
energy-dispersive X-ray fluorescence (EDXRF) spectrometers. tion and concentration.

Table 1. General comparison table of common analytical techniques for sulfur. Note that this list is not exhaustive and other techniques are available.
Technique Advantages Drawbacks
• Easy to operate
• High detection limits (~10s of ppm)
• Minimal sample preparation
EDXRF • No speciation information
• Minimal laboratory requirements
• Solids or liquids only
• Multi-element analysis
• Quick sample throughput • No speciation information without LC or GC front end
ICP-OES • Robust for complex matrices • Low sensitivity at common sulfur emission lines
• Simultaneous multi-element analysis • Higher cost of ownership
• Quick sample throughput • No speciation information without LC or GC front end
ICP-MS • Low detection limits • Interferences on predominant sulfur isotope 32S
• Nearly simultaneous multi-element analysis • Higher cost of ownership
• Highly sensitive (ppb levels) • Non-specific to sulfur
GC-FPD
• GC separations enable speciation analysis • Matrix signal quenching
• Historically complex
• Highly sensitive (ppb levels) and specific for sulfur
GC-SCD • Only analyzes for sulfurs, other detectors required for
• GC separations enable speciation analysis
other compounds

63
Shimadzu Journal vol.8 Issue2 63