Application Note · compEAct S

Determination of Total Sulfur in Light
Hydrocarbons, Spark Ignition Engine Fuel andDiesel Engine Fuel by Ultraviolet Fluorescenceaccording to ASTM D5453

Challenge
Fast, sensitive and reliable
analysis of widely varying sulfur
contents in different types ofliquid fuels, combustibles andrelated matrices.

Solution
Optimized vertical combustion
combined with HiPerSens UVfluorescence detection forconcentration-independent TS
determination.

Introduction
The determination of total sulfur (TS) by means of combustion-coupled UVfluorescence detection is an integral part of the daily routine in the process andquality control of refineries, derived fuels production, and many other labs dealing
with control and legal limit checking of fuels and related matrices. No matter ifanalyzing feeds, process streams, additives, or ultrapure end products, it is a must
to have information about the sulfur content in the shortest possible time. This
is to avoid undesirable effects such as catalyst poisoning, corrosion of installation
parts, low product quality, or exceeding legal limits. Therefore the sulfur content
of many different samples of the production process has to be determinedin close intervals. This and the fact that fewer and fewer lab technicians areanalyzing an ever-increasing number of samples, some of which are challenging,leads to an enormous pressure on performance in terms of time and reliabilityof the measurement values. Delayed or incorrect results significantly influence
performance and profitability of the laboratory. Where time is money, a techniquewhich ensures fast and reliable analyses independent of matrix effects andoperator skills is urgently needed.
The compEAct S is an analysis system which has been specifically optimized forthe fast and trouble-free determination of sulfur contents in an impressively wide2TS Determination in Light Hydrocarbons, Spark Ignition Engine Fuel, and Diesel Engine Fuel by UV Fluorescence according to ASTM D5453

concentration range. It allows the determination of sulfur at concentrations ranging from 5 µg/l up to 10,000 mg/l with one
and the same device and the same analysis method.
Materials and Methods
Samples and Reagents■■
Different fuels and related samples (diesel, gasoline, kerosene, etc.) have been analyzed■■Isooctane (C8H18), Suprasolv®, GR for gas chromatography (Merck Art.-No.: 1.15440.1000)■■
Dibenzothiophene (C12H8S), GR for synthesis (Merck Art.-No.: 8.20409.0025)■■
Standard kit for calibration and test of compEAct S (Analytik Jena, Art.-No.: 402-889.309)
Sample Preparation
The samples were analyzed directly. No sample preparation was required.
Calibration
Liquid calibration standards based on dibenzothiophene (S) in isooctane were used to calibrate the analysis system in theappropriate concentration range. Matrix-related calibration strategies were not required as the combustion is optimized andinterfering components are eliminated before detection.

Fig.1: TS calibration for ultra-trace range

Fig.2: Wide-range calibration curve of the HiPerSens UVF detector

The calibration was checked with different concentrated standards.
Instrumentation
The measurements were performed using a compEAct S, equipped with HiPerSens UV fluorescence detection for thedetermination of sulfur. Sample introduction was carried out fully automatically using the LS 2 liquids sampler to ensure ahigh sample throughput.
The analyses have been run in vertical operation mode. The samples were dosed directly into the evaporation zone of thequartz glass combustion tube. This process took place fully automatically by means of the LS 2 high-throughput autosampler.
The catalyst-free, bi-phasic combustion process is carried out at temperatures of up to 1050 °C. In the first process phase,
evaporation of volatile sample components in an inert gas stream takes place, followed by the combustion of the formed
gaseous products in an oxygen-rich atmosphere. In the second phase the heavier, nonvolatile sample components andformed pyrolysis products are quantitatively oxidized in pure oxygen. Thereby the quartz pyrolyzer ensures a uniform
evaporation, modulates the combustion process, and prevents incomplete combustion. This establishes the best conditions
for a reproducible and fast ultra-trace analysis. The implemented Auto-Protection System guarantees highest operationalsafety (particle and aerosol trap) and a complete transfer of the formed SO2 into the UVFD after a sufficient drying of thereaction gases. The compEAct S enables a detection limit of as low as 5 µg/l S.

TS Determination in Light Hydrocarbons, Spark Ignition Engine Fuel, and Diesel Engine Fuel by UV Fluorescence according to ASTM D5453

Method Parameters
The standard method ASTM D5453 from the method library of compEAct’s EAvolution software was used for allmeasurements. It is suitable for direct analysis of liquid samples with viscosities ≤ 10 cSt (syringeable liquids) and boilingpoints ≤ 400 °C. For liquids with slightly increased viscosity values, but still boiling ≤ 400 °C, a sufficient dilution (e.g., withxylene) can be applied to enable syringeability and analysis. The following table summarizes the parameter settings for thecombustion process.
Table 1: Process parameters compEAct SParameter

Specification

Furnace temperature

1050 °C

Second combustion

60 s

Ar flow (first phase)

150 ml/min

O2 main flow

200 ml/min

O2 flow (second phase)

150 ml/min

Draw up

2 µl/sInjection volume

40 µl

Injection

0.5 µl/s

Evaluation Parameters
Standard method settings were applied. The parameter settings are summarized in the following table.
Table 2: Detection parameters UVFD
Parameter

Specification

Max. integration time

300 sStart

1 cts

Stop1 cts

3

4TS Determination in Light Hydrocarbons, Spark Ignition Engine Fuel, and Diesel Engine Fuel by UV Fluorescence according to ASTM D5453Results and Discussion
The analyzed samples are a representative spectrum of crude oil-based and bio-based fuels and blends of both. The results
given in Table 3 are averages of three replicate analyses of samples and test standards. For all samples and standards aninjection volume of 40 µl was used.

Table 3: Results of the TS analysis
MeasurementTSSDRaffinate

122 ppb± 1.15 ppb

Naphtha (light)

632 ppb± 3.27 ppb

Gasoline E 1055.7 ppb± 3.95 ppb

UL Diesel (car)1.25 ppm± 0.02 ppm

Diesel+7 % FAME

9.30 ppm± 0.11 ppm

Bio-ethanol

195 ppb± 6.13 ppb

Bio-based diesel (B-t-L)

144 ppb< 0.01 ppb

Kerosene

9.90 ppm± 0.03 ppm

Jet A

14.1 ppm± 0.02 ppm

Ship diesel (yellow)

19.5 ppm± 0.23 ppm

Heating oil extra light (HEL)

107 ppm± 0.99 ppm

TS Standard (c = 145 ppm)

145 ppm± 0.48 ppm

TS Standard (c = 14.5 ppm)

14.4 ppm< 0.01 ppm

TS Standard (c = 1.45 ppm)

1.45 ppm< 0.01 ppm

TS Standard (c = 145 ppb)

144 ppb± 2.13 ppb

Figures 3–8 show typical measuring curves for selected samples resp. standards.

Fig. 3: TS analysis curve for sample “Jet A”

Fig. 4: TS analysis curve for sample “UL diesel”

TS Determination in Light Hydrocarbons, Spark Ignition Engine Fuel, and Diesel Engine Fuel by UV Fluorescence according to ASTM D5453

Fig. 5: TS analysis curve for sample “Heating oil - HEL”

Fig. 6: TS analysis curve for sample “Raffinate”

Fig. 7: TS analysis curve for TS standard “145 ppm S”

Fig. 8: TS analysis curve for TS standard “1.45 ppm S”

Due to the matrix-optimized combustion a threefold determination is generally sufficient to achieve results far below
3 % RSD. This remarkably affects the sample processing time and allows a higher sample throughput. The analysis resultsreceived and their reproducibility prove the performance of the digestion process. The overall performance of the analysis
system was validated by analyzing standard materials with known sulfur contents, the results are given in Table 3.
If desired, further time optimization can be achieved by decreasing the sample quantities for higher concentrated sample
matrices. The same process and detection parameters can be applied.
Conclusion
Together with the LS 2 liquids sampler, the compEAct S provides a fast and reliable solution for the precise determinationof widely varying sulfur contents in different fuels and related matrices from refinery applications in the daily routine. The
system can handle the samples no matter if they are crude oil-based or generated from renewable energy sources (e.g., sugar,cellulose) or mixtures of both.
Thanks to the unique HiPerSens technology, a measuring range of up to 10,000 mg/l starting at a limit of detection as
low as 5 µg/l of sulfur can be reached easily. The optimal sample digestion and the efficient Auto-Protection system,
including a high capacity membrane dryer, enable excellent reproducibility, independent of the TS concentration or digestion
characteristics and composition of the analyzed sample matrix. A high sample throughput is easily achieved by using the LS 2liquids sampler. For lower throughput demands the LS 1 liquids sampler resp. the AI autoinjector can be used. If needed, theanalysis system can be extended for the determination of TS in gaseous or liquefied pressurized fuels (e.g., CNG, LPG) by justadding the suited sampling system.
References
Groebel, A., “Productivity Boost in Sulfur (UVFD) Routine Analysis”. PIN, 08/09 2017, page 8-9
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