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Latest Developments on Characterization of Pure Biodiesel (B100) andFinished Biodiesel Blends by Conventional GC, Ultra Fast GC and CGxCG

Daniela Cavagnino 1, Fausto Munari 1, Danilo Pierone 21. Thermo Fisher Scientific, Milan, Italy 2. Nova Analtica, So Paulo (SP), Brazil (E-mail for contact: danilo.pierone@novanalitica.com.br)

Overview

Purpose:

To describe the characterization of Biodiesel B100 in compliancewith GC-based ASTM and EN methods regulating the analysis of freeand total glycerin, residual methanol, and total FAME content.

All methods can be applied using a single assembly with two GCsautomated by a single autosampler for utmost productivity. In addition,the need to speed up the analysis time when high sample throughputis required, led to a deeper investigation into the application of anUltra Fast GC technique for the determination of Free and TotalGlycerin content. Application of GCxGC for the characterization offinished Biodiesel blends is also shown.

Results:

The reported data demonstrate the suitability of the optimizedhardware solutions for the analysis of Biodiesel in full compliance withthe official standards. In addition, the Ultra Fast GC approachgenerated promising results in terms of separation, linearity andrepeatability, offering an additional analytical tool for fast samplescreening. The advantages of GCxGC for the analysis of finishedblends are clearly stated.

IntroductionInterest in Biodiesel as a clean-burning alternative fuel produced

from renewable sources such as vegetable oils has increasedtremendously over the last few years, mainly because of its reducedenvironmental impact in comparison with conventional mineral diesel.

In order to be commercialized as pure biofuel or blending stock,biodiesel must meet a set of requirements defined in ASTM D6751 andEN 14214 standards. Gas Chromatography is commonly adopted todetermine free and total glycerin (EN 14105/ ASTM D6584), totalFAME (EN 14103) and methanol (EN 14110) in pure biodiesel.

Free and Total GlycerinEN 14105/ ASTM D6584

The analysis of glycerin, mono, di and triglycerides by GC requiresa non-discriminative injection system. The true cold On-columninjector used on the TRACE GC Ultra is a permanently cold system,able to prevent discrimination of the heavier fraction and to eliminateany risk of degradation of labile components like triglycerides.

The analytical column used is a non-polar Thermo ScientificTRACE TR-BIODIESEL(G), 10 m, 0.32 mm ID, 0.1 m f.t. Thiscolumn is designed for this high temperature GC method, featuringenhanced mechanical robustness at high oven temperature, and thusprolonged lifetime. A 1m x 0.53 mm ID pre-column is connected to thecolumn by a high temperature gas-purged metal tee. This low deadvolume leak-free metal tee has been specifically conceived for areliable connection between the guard column and the analyticalcolumn at high temperature operation, removing the need for normalglass press-fit unions. This connector remains leak-free even withextremely large and frequent oven temperature variations.

Conclusions A single dual-GC system equipped with cold On-Column and PTV-

BKF injectors is proposed, which includes the versatility of the Liquidand HS Triplus autosampler for easiest operation and maximumsample throughput. The PTV injector with backflush capabilitiesreduces the analysis time and extend the polar column lifetime. Byusing the PTV injector with backflush, it is possible to avoid the use ofthe Headspace technique for the determination of Methanol andEthanol, increasing even more the sample throughput.

In addition, an Ultra Fast method has been optimized for screeningof Glycerides content in B100 in only 5 minutes.

GCxGC has proven to be a powerful technique for thecharacterization of finished biodiesel blends, delivering added-valuedetailed information in a single analysis.

References[1] Comprehensive two-dimensional gas-chromatography applied todiesel and biodiesel analysis D. Cavagnino, A. Cadoppi, G. Zilioli, F.Pigozzo Pittcon Conference 2006.

[2] Thermo Application Notes 10212, 10215, 10216 - Determination ofTotal FAME and Linolenic Acid Methyl Ester, Free and Total Glycerin andMethanol Content in Pure Biodiesel (B100).

The system is calibrated by analyzing a 4-component calibrationmix at four different concentrations, which generates four calibrationcurves for glycerin, monoolein, diolein, triolein. The linear correlationcoefficients (R 2) exceed the specification of 0.9 as requested in EN14105 for each curve, demonstrating very good linearity of the truecold On-column injection technique.

Total FAME and Linolenic Acid Methyl Ester EN 14103

A PTV injector with Back Flush option was used, with a polarcapillary column Thermo Scientific TRACE TR-BIODIESEL(F), 30 m,0.25 mm ID, 0.25 m f.t.

When FAMEs are analyzed, the heavier fraction present in biodieselsamples (like di- and tri-glycerides) enters the column, getting stackedonto the polar phase. This means that a few nanograms of heavycompounds will accumulate inside the column, which increases the riskof compromised chromatographic performance after a number ofsequences and reduces the column lifetime.

MethanolEN 14110 requires a headspace GC method, based on either polar

or non-polar columns. In this work, the analysis was performed usingan external calibration procedure, which is preferred over internalstandard calibrations when automatic headspace equipment is used.

A Thermo Scientific TRACE GC Ultra equipped with a split/splitless

(SSL) inlet and a flame ionization detector (FID), automated by aTriPlus Autosampler configured for headspace was used. Theanalytical column is a non-polar Thermo Scientific TRACE TR-BIODIESEL(M), 30 m, 0.32 mm I.D. 3.0 m f.t. The linearity of theMethanol curve, the repeatability tested on different sample types andthe analytical parameters are reported in Figure 4.

Biodiesel Blends A very common use of biodiesel is its blending with ultra low sulfur

petrodiesel as a lubricity additive.

GCxGC has been effectively applied to get comprehensive

compositional characterization of biodiesel blends, providing tripleinformation in a single analysis: the petrodiesel composition, thepercentage of biodiesel in the blend, the FAMEs detailed composition(Figs. 6 and 7).

PTV Back flush (reverse flow device):The glycerides fraction is vented out without entering the column.

Glycerin Triolein

Add it ion al Informati onFor additional information, please browse:

www.analiticaweb.com.br/biodiesel

www.thermo.com

Instrumentation

All the methods are achieved using twoThermo Scientific TRACE GC Ultra andthe TriPlus Autosampler , able to uniquelyautomate sequences on two GCs.

The UltraFast GC technique has been accomplished with theThermo Scientific UltraFast Module , which directly heats the capillarycolumn for a faster temperature programming rate and a much shorteranalysis time.

The GCxGC analyses were performed with the Thermo ScientificTRACE GCxGC equipped with a cryogenic (CO 2 liquid) Dual Jetmodulator and a Fast FID detector.

EN 14105/ ASTM D6584 Optimized for Ultra Fast Analysis

FIGURE 2. Ultra fast separation of the calibration mix ture and typical Bio diesel samples

5 min

GlycerinR 2 = 0.9996

TrioleinR 2 = 0.9989

SampleBiodiesel #1

SampleBiodiesel #2

By incorporating the Back Flush Option into the PTV, heavy compoundsare vented out of the inlet system, preventing column contamination whilestill allowing efficient transfer of compounds of interest (Figure 3).

FIGURE 4. Analytical parameters, linearity and repeatability obtained for EN 14110

As a further possibility, methanol content can be successfullydetermined by direct liquid injection of Biodiesel diluted in n -Butanol,exploiting the PTV Backflush system to vent out the heavier fraction

without letting it enter the capillary column.This solution overcomes the time-consuming sample preparationprocedure for Headspace analysis and the possible critical availabilityof reference FAMEs mixture for calibration (Figure 5).

In addition, the same hardware configuration used for the methodEN 14103 for FAMEs analysis can be used.

FIGURE 5. Methanol determination by direct liquid injection andbackflushof heavier components

B100 in n-Butanol spi kedwith Methanol and Ethanol

BKF at 3 minutes

R2 =0.9999with external c alibrationConcentration range0.001%- 0.5%w/w

1.92074.5110133.8MeOH

%RSD%RSDSDSD Avrg AvrgNameName

Peak AreaRepeatability (10 runs)

Here below the curves obtained for glycerin and triolein are reported

For this application, an SE54 phase 0.05 m thickness on 3 m ofcapillary 0.32 mm ID has been used and integrated in an UFM.

In order to minimize the possible discrimination of heavier glyceridesduring the injection, a PTV (Programmable Temperature Vaporizing)injector was used. A deactivated glass liner with glass wool showedbetter performance with a suitable transfer of both volatile and non-volatile compounds (Figure 2).

To achieve Ultra Fast GC separation,a narrow bore column is coiled along

with a heating element and a properlyinsulated temperature sensor. It is heldin an easy to handle metal cage(UltraFast Module - UFM) installed into aTRACE GC Ultra oven.

FIGURE 3. FAMEs chromatogram of an unknown Biodiesel, along with analytical parameters.

FIGURE 6. FAMEs chraracterization in petrodiesel at 5% (v/v) (BD5 blend)

FIGURE 7. Comparison of typical comp ositional data (% m/m) in various vegetable oils