Application Note · multi EA® 5000

Elemental Analysis for N/S/Cl Determination in
Biofuels and Their Precursors

Challenge
Quantitative digestion of biofuel
samples and their precursors
without soot formation in theshortest measurement time.

SolutionTime- and matrix-optimized
combustion using flame sensor
technique and optimization ofprocess parameters.

Introduction
New methods for the production of alternative fuels are a growing field ofinterest. Technologies based on fermentation of starch and sugar, and the transesterification or hydrocracking of plant and animal oil, delivering so-called first
generation biofuels, are already well established but linked to limited resources for
ethical and ecological reasons. Another promising approach consists of processes
based on the conversion of cellulose-rich biomass and waste (second generation
biofuels). With the use of biogenic materials for fuel production, the inherently
high amount of harmful nitrogen, sulfur and chlorine-containing hydrocarbons
that results has to be monitored. This is not only due to the adherence of given
regulations and legal limits (Tier 1 to 4), but also to avoid negative effects on theproduction process and environment. Therefore, a strict monitoring of the feedstocks, intermediates, and final products is crucial. The origins of such matrices
are just as different as their digestion behavior. A quantitative combustion of all
sample components is the precondition for correct elemental analysis. In the pastthis was a time-consuming challenge, requiring experience in developing specificboat programs for each sample matrix. In addition, there was frequent need formaintenance intervention and repeated measurements due to soot formationand contamination of the analyzer. The slightest changes in the process, different
matrix composition or other sample quantity affected the results‘ correctness.
To overcome this, the flame sensor technology was developed to automatically
optimize the combustion process to the specific needs of any matrix type, quantity
and composition. With the effective soot prevention, the maintenance effort isreduced to a minimum.

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Elemental Analysis for N/S/Cl Determination in Biofuels and Their Precursors

Materials and Methods
The different biofuels and precursors were analyzed for nitrogen, sulfur and chlorine contents using the multi-elemental
analyzer multi EA® 5000. Equipped with HiPerSens detection systems, it covers a wide and linear operation range fromlowest ppb to wt%.
Samples and Reagents
Six samples (feed materials, intermediates and final products) were analyzed, as well as standard materials, to check theperformance of the analyzer.
The analyzed sample matrices are a representative spectrum from the field of biofuel production. Samples 1, 2, 4 are feedstock and process materials with high viscosity and high element contents. The final products (samples 3, 5, 6) are different
biofuels. They are light volatile, have a low viscosity and contain the elements of interest just in the trace level as undesired
impurities.
Sample Preparation
Using the multi EA® 5000 in horizontal mode in combination with the flame sensor technology allows for a direct analysis of
the samples without sample preparation. The flame sensor creates ideal digestion conditions for any organic sample matrix.
Just one single method for solids or liquids is enough to analyze the full spectrum of matrices, independent of their viscosity,volatility, and combustibility.
Calibration
Liquid calibration standards based on 2,4,6-trichlorphenol (Cl), dibenzothiophene (S) and pyridine (N) in isooctane wereused to calibrate the analysis system in the appropriate concentration ranges.
Instrumentation
A multi EA® 5000 equipped with CLD, UVFD and coulometric detection for the determination of nitrogen, sulfur and chlorine
was used in horizontal operation mode. For the automated sample introduction and transfer into the analyzer the system wasequipped with an automatic boat drive with flame sensor technology and the MMS 5000 multi matrix sampler. The flamesensor ensures a trouble-free and matrix-optimized transfer and combustion of the different materials.
For the determination of chlorine sample volumes of 100 µL were used, and for nitrogen and sulfur 40 µL were used. The
sample digestion was carried out by efficient catalyst-free high temperature combustion in a quartz tube. This process iscontrolled and adapted fully automatically to the special needs of every matrix component by the flame sensor technology.
This ensures matrix-independent, optimal results in the shortest possible time. The process is split into two phases. In thefirst process phase, evaporation of volatile sample components in an inert gas stream, followed by the combustion of theformed gaseous products in an oxygen rich atmosphere, takes place. In the second phase the heavier, nonvolatile sample
components and formed pyrolysis products are quantitatively oxidized in pure oxygen. Here, the flame sensor ensures auniform evaporation of exactly the amount of sample that can be completely oxidized by the available amount of oxygen.
For this purpose the resulting combustion flame is monitored in real time. The registered flame values are used to calculate
an optimum digestion program for each matrix, including a sufficient number of waiting points, minimized waiting times,
and maximized analysis speed. This allows for a fully automated adjustment of the process to the specific requirements of
the individual components, thus optimizing the quality of analysis and its duration. The dried gaseous reaction products
were transferred into the relevant detection systems – for sulfur, UV fluorescence, and for nitrogen, chemoluminescence. The
detection of chlorine was carried out by means of microcoulometric titration.
The implemented Auto-Protection System guarantees the highest operational safety (particle and aerosol trap) and acomplete transfer (no condensation loss) of the formed HCl into the high sensitive cell. Afterwards the determination of thechlorine content is carried out by means of a microcoulometric titration. The multi EA® 5000 enables a detection limit of 50µg/L Cl. Depending on the cell type used, direct analysis of Cl contents up to 10 wt% is also possible.

Elemental Analysis for N/S/Cl Determination in Biofuels and Their Precursors

Method Parameters
Standard method settings for horizontal operation stored in the method library are applied. The parameter settings for thecombustion process are summarized in the following table.
Table 1: Process parameters
Parameter

Specification

Furnace temperature

1050 °C

Second combustion

60 s

Ar flow (first phase)

100 mL/min

O2 main flow

300 mL/min

O2 flow (second phase)

100 mL/min

Draw up

2 µL/sInjection

3 µL/s

Evaluation Parameters
Standard method settings from the method library are applied. The parameter settings for the different detection systems aresummarized in the following table.
Table 2: Detection parameters
Parameter

Specification

ParameterSpecification Cl

Max. integration time

800 s

Max. integration time

1200 sStart (N)0.2 ppb

Threshold value

300

Threshold (N)0.5 ppb

Max. drift

100

Start (S)0.1 ppb

Threshold

25

Threshold (S)0.11 ppb

Cell temperature

23 °C

Stability

7Titration delay

30 s

Results and Discussion
The examined samples are a representative spectrum from the field of biofuel production, from feed materials tointermediates to ultra-pure fuels. The results given in table 3 are averages of three replicate analyses.
Table 3: Results of the N/S/Cl determination
MeasurementTS ± RSD

TN ± RSD

TCl ± RSDBCO* (crop plants)

0.40 wt % ± 0.42 %0.41 wt % ± 0.62 %23.4 ppm ± 3.32 %Corn oil20.3 ppm ± 1.92 %54.2 ppm ± 0.18 %8.82 ppm ± 1.10 %Bio diesel (from corn oil)

0.87 ppm ± 2.83 %2.00 ppm ± 2.30 %<< 0.10 ppm %Crude tall oil

0.36 wt % ± 0.61 %99.9 ppm ± 2.89 %8.36 ppm ± 3.32 %B-t-L** (from tall oil)5.33 ppm ± 1.57 %0.38 ppm ± 2.57 %<< 0.10 ppm (< LOD)

Bio ethanol (from cellulose)

0.73 ppm ± 1.83 %0.06 ppm ± 11.2 %0.56 ppm ± 11.2 %Standard 1.44 ppm N/S/Cl

1.42 ppm ± 1.28 %1.39 ppm ± 2.21 %1.47 ppm ± 1.83 %* BCO = bio crude oil, ** B-t-L = bio mass to liquid34

Elemental Analysis for N/S/Cl Determination in Biofuels and Their Precursors

Due to the matrix-optimized combustion a threefold determination is sufficient to achieve results within 3 % RSD. This isremarkably affecting the sample processing time and thereby generating a higher sample throughput. The analysis resultsreceived and their reproducibility depict the high quality of the digestion process. The proper performance of the analysis
system was approved by analyzing standard materials for the determination of nitrogen, sulfur and chlorine (see table 3).
Typical measuring curves are depicted for the crude tall oil exemplarily in Figures 1 a–c.

Figure 1 a: TS measuring curve for crude tall oil

Figure 1 b: TN measuring curve for crude tall oil

Figure 1 c: TCl measuring curve for crude tall oil

Conclusion
The multi EA® 5000 with flame sensor technology facilitates time- and matrix-optimized decomposition, as this iscrucial for the fast and reliable analysis of challenging matrices such as pure biofuels and their precursors. Without any
effort of developing specific boat programs for each sample a maximum efficiency is ensured with the minimum need formaintenance.
Further optimization of measurement times can be done by decreasing the sample quantities for highly concentrated sample
matrices. The same process and detection parameters can be applied.
The used HiPerSens detection systems for nitrogen, sulfur, and chlorine enable the schreiben the analysis of samples in thewidest possible concentration range without additional time-consuming pretreatment. This reduces sample processing timeeffectively.

This document is true and correct at the time of publication; the information within is subject to change. Other documents may supersede this document, including technical modifications andcorrections.

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