GC-101Testing of Biodiesel Using Gas Chromatography

(Image © Research Machines plc)

by Bob Armantrout

Local Biodiesel: A Biodiesel Coop ConferencePresented at:

Strategies For Community-based Biodiesel GroupsJuly 14 – July 16, 2006

Triglycerides to Methyl Ester

(Image © Research Machines plc)

www.biology.iastate.edu

Why Glycerin is Bad in BiodieselFrom: US Department of Energy Biodiesel Handling and Use Guidelines, Second Edition, March 2006

• Free and total glycerin numbers measure the amount of unconverted or partially converted fats and by-product glycerin present in the fuel.

• Incomplete conversion of the fats and oils into biodiesel can lead to high total glycerin.

• Incomplete removal of glycerin can lead to high free glycerin and total glycerin.

• If these numbers are too high, storage tank, fuel system, and engine fouling can occur.

• Fuels that exceed these limits are highly likely to cause filter plugging and other problems.

How Glycerin is Removed from Biodiesel

• Converting the triglycerides, diglycerides, and monoglycerides to methyl esters to reduce the levels of bound glycerin.

• Washing the esters to remove glycerin.

ASTM Specification for Glycerin

D6751-06e1 stipulates:

Free Glycerin 0.020% mass or less

Total Glycerin 0.240% mass or less

“The total glycerin method is used to determine the level of glycerin in the fuel and includes the free glycerin and the glycerin portion of any unreacted or partially reacted oil or fat. Low levels of total glycerin ensure that high conversion of the oil or fat into its mono-alkyl esters has taken place. High levels of mono-, di-, and triglycerides can cause injector deposits and may adversely affect cold weather operation and filter plugging.” (ASTM 6751-06e)

The Equipment

• Hewlett Packard - Model 5890A-II Gas Chromatograph

– Unit includes an autosampler, column, pc, software, and gas regulators

– AIR will provide delivery, installation, familiarization and a 6-month warranty

– AIR will provide service outside of warranty for a fee.

– Total quote price: $13,382.15 (Oct. 2005)

– Work will begin upon receipt of purchase commitment, lead-time is 1 to 2 weeks.

What the GC does

Precisely measures the percent mass of free glycerin, mono, di and triglycerides in a sample of methyl esters.

How the GC worksA Gas Chromatograph (GC) is a chemical analysis instrument for separating chemicals in a sample.

It uses a thin capillary fiber known as the column, through which different chemicals pass at different rates depending on various chemical and physical properties.

The function of the column is to separate different components, causing each one to exit the column at a different time.

As the chemicals exit the end of the column, they are detected and identified electronically. (from Wikipedia)

How the GC worksAn FID is an ion detector which uses an air-hydrogen flame to produce ions. As components elute from the GC's column they pass through the flame and are burned, producing ions. The ions produce an electric current, which is the signal output of the detector. The greater the concentration of the component, the more ions are produced, and the greater the current. (from Wikipedia)

ASTM D6584 prescribes the method for GC setup, sample prep and chromatogram analysis.

4. Summary of Test Method

4.1 The sample is analyzed by gas chromatography, after silyating with N-methyl-N-trimethylsilyltrifluoracetamide (MSTFA).

Calibration is achieved by the use of two internal standards and four reference materials. Mono-, di-, and triglycerides are determined by comparing to monoolein, diolein, and triolein standards respectively.

Average conversion factors are applied to the mono-, di-, and triglycerides to calculate the bonded glycerin content of the sample.

Copyright by ASTM Int'l

Maintenance and Repair

• Calibration – Use Standards to calibrate GC for glycerol, monolein,

diolein, butanetriol, tricaprin.

• Retention time (RT) changes indicate instrument status– Decreasing RTs are are typically caused by column aging– Increasing RTs typically caused by leaks in septa,

connections, low gas pressures.

• Repair– Septa replacement– Column replacement– Syringe replacement

Other Equipment and Supplies

• Additional Lab Ware required to use the GC:– Analytical Balance - $1500– Pipetter – 100 microliter (µL) $250– 15ml vials for sample prep– 2ml vials with septa top

• Compressed Gases– Helium, Hydrogen, Compressed Air – USP grade, tanks run

about $50 to $70 each

• Chemical Standards, Carriers– Calibration Standards – monolein, diolein, triolein– Butanetriol and Tricaprin - $150 each per 5ml– Heptane – used as a carrier for sample– Hexane for syringe cleaning

Facility Considerations

• Sturdy Desk to set GC on • Dedicated power circuit• Small refrigerator for storage of

standards• Fire Cabinet for storage of reagents• Proper storage of gas bottles

Equipment and Material Suppliers

Analytical Instrument Recycle

www.aironline.com

Telephone: 303-215-0468 Toll Free: 888-909-0468 (U.S.)

6390 Joyce Dr.Suite 200WGolden, CO 80403

Sigma-Aldrich/Supelco

www.sigmaaldrich.com

Telephone: 800-325-3010 (U.S.)

Photo Essay of GC Testing Process

Sample Preparation(logbook & glassware)

Weigh the Sample(analytical balance)

Add Internal Standards(micropipetter )- 100 microliters (µL) each of

MSTFA, and internal standards 1 & 2

Lab refrigerator

Add heptane – 8 ml

Load sample to GC vial

Place vial in GC autosampler

Load Sample Data into GC Software

Start the Run

Analysis of Chromatograms

Approximate Relative Retention Times

Calculating Glycerin Levels

Chromatograms – The Good

Chromatograms – The Good

Chromatograms – The Good

Chromatogram – The Bad

Chromatogram – The Ugly

Understanding your Processes

Conversion “recipe” development

Understanding your Processes

Tracking glycerin removal through washing

Verifying your testing process

Lab “cross checking” is a good way to assure your lab equipment and procedures are providing valid results

Verifying your testing process

Third Party GC Testing

• Magellan will test biodiesel for Free & Total Glycerin for under $100

• A 10 ml sample is required

Third Party GC Testing

• Intertek will test biodiesel for Free & Total Glycerin for $275

• A 10 ml sample is required