Get a little headspace
10 Jan 2013 by Evoluted New Media
As the demand for biofuels grows, so does the need to ensure production remains within industry standards. Here we learn that static headspace gas chromatography is ideal to monitor emissions…
The growing demand for low carbon low sulphur emissions and sustainability has placed the science of biofuels unquestionably in the mainstream. As the market demands greater and greater volumes of biodiesel, the need for a quality product, that continues to meet manufacturing standards, remains. The fuel must have little or no methanol content, no free fatty acids or glycerol and be free from particulates. Static headspace gas chromatography (SH-GC) is an analytical methodology developed to meet the challenge of ensuring toxic emissions resulting from biodiesel use remain within industry standards.
Biodiesel production is on the increase with global figures in 2009 showing production of 308.2 million barrels, of which Europe produced the ‘lion’s share’ of 172.6 million barrels and US figures for the same period were 35.2 million barrels1.
Biodiesel has been widely used in the EU for a number of years and has now become more popular in the US, following the 2005 Energy Policy Act2. Both the EU and the US manufacturing standards have been designed to assure commercial products meet emission and quality regulations and also engine specifications (ASTM D-6751, EN-14214, and EN-14110)3,4,5.
Biodiesel can be produced from a wide range of oil crops and recyclable sources including low erucic acid canola, jatropha oil, algae, microorganisms, waste vegetable oil and even used coffee grounds. Although biodiesel is inherently low in sulfur, a big issue in petrodiesel, it does not really give lower emissions of carbon dioxide. The true value of biodiesel from oil crops is sustainability, as carbon dioxide is removed from the atmosphere by the oil crop and ‘fixed’ into oils and fats, which then processed into the required fuel.
The manufacture of biodiesel is a simple process that uses oils from a variety of sources. The oil is processed by transesterification to split the long chain fatty acids, e.g., linoleic acid, which will eventually produce the biodiesel from the glycerol component of the fat or oil. As methanol is the least expensive alcohol for producing the fatty acid methyl esters (FAME) that make up biodiesel, they are produced as methyl esters. The waste product, glycerol, can be purified and used as a useful chemical feedstock and any free fatty acids can be used to produce detergents. Following the esterification reaction, glycerol, water and residual catalyst have to be removed to create a fuel of suitable quality for diesel engines. Quality problems can arise if the reaction is incomplete or if by-products are not removed effectively.
The main quality control issue with biodiesel is the quantity of unreacted methanol it contains as this can be detrimental to the engine using the fuel. Methanol can be corrosive to fuel systems and can also attack and degrade the rubber used in engine and fuel system seals.
Biodiesel is currently available as commercial mixtures with petro-diesel, which is designated by a B number to indicate the percentage of biodiesel e.g., B100 is 100% biodiesel. The most commonly sold mixtures are between B6 and B20. Both EU and US regulations have either made it compulsorily, or used tax incentive to encourage, an increase in the quantity of biodiesel used. An example is in the UK is where the Renewable Transport Fuel Obligation has required all road diesel to be B5 since 20106. This has now been taken a step further in EU states as the 2009 Renewable Energy Directive (EU Directive 2009/28) (RED) , adopted in December 2008, has introduced a 10% compulsory target for renewable energy use in transport fuels including biodiesel, which should be adopted by 20207. EU readiness for this change is variable among Member States, as are the figures for EU biodiesel production.
Many car manufacturers have now designed their cars to run on biodiesel mixtures of up to B20. Cars, buses and trains can also be modified to use B100 but this requires engine modifications, including new fuel filters and gasket seals to be fitted, which are made of a perfluoroelastomer (PFK) and provide excellent resistance to methanol. Methanol is crucial to the production of biodiesel but there should be little or no free methanol in the final product. Neither should there be particulates, free fatty acids, glycerol, water or unreacted alkali metal catalyst.
To ensure the quality of FAME-based biodiesel, standard test criteria have been produced by both the European Committee for Standardization (EN-14214) and ASTM International (ASTM D-6751). These deal with methyl esters only and state that the methanol content in the diesel must be less than 0.2% m/m. Tolerances for other impurities are also provided, as detailed in Table 15. These standards generally utilize multiple gas chromatographic (GC) analyzes, one of which uses static headspace GC for methanol analysis (EN-14110).
Methanol levels in biodiesel, as designated under EN-14110, can be monitored very accurately by the use of headspace sampling in conjunction with gas chromatography. The Bruker SHS-40 Automated Headspace Sampler, used in combination with the SCION GC-436 and the CompassCDS data system can be used for the automated processing of biodiesel samples during quality control. Since biodiesel generally does not contain volatile components other than methanol, identification and quantification is usually quite straightforward.
Methanol standards are prepared in FAME by accurate weighing at three different concentrations (0.01%, 0.1%, 0.5% (m/m)) to provide a straight line standard concentration curve (Figure 2) across the full range within the requirements of EN-14110. A number of unknown biodiesel samples were also prepared using the same protocol8.
The standard analysis method requires that 1 ml of the FAME methanol mixture is equilibrated at 80°C for 45 minutes in a 20ml vial. Then the headspace is sampled and analysed via GC on a Select Biodiesel for Methanol Fused Silica column (30 m x 0.32 mm x 3.0 ?m), using a split injection in a 50:1 ratio.
In this particular series of analyses the average concentration over 15 FAME samples from the universal sample was 0.038% methanol (standard deviation 0.0007 and relative standard deviation RSD (%) 1.96)8. Furthermore the repeatability figures indicate that the system was optimised for analysis as set out in EN-14110 as seen in Figure 3, where the analyses trend line is within the repeatability window and the addition of the average line.
There is a concerted effort across the EU and US to increase fuel sustainability and improve emissions by incorporating biodiesel into road fuel diesel mixtures. The design of automotive diesel engines cannot currently tolerate the use of 100% biodiesel and these mixtures are not widely available in any case. To maintain the fuel quality of commercially available biodiesel / petrodiesel mixtures, and prepare manufacturers for forthcoming changes in fuel composition, a series of standards have been put in place to set levels for potentially damaging components such as methanol. A gas chromatography headspace system) has been shown to be well suited for the determination of methanol content in biodiesel according to specifications outlined in EN-14110 and EN-14214.
By Ed George, Bruker Chemical and Applied Markets (CAM) division, Fremont, CA, US
References
[1] World Biodiesel Production. US Department of Energy Efficiency & Renewable Energy,
[2] Vehicle Technologies Program. Fact #662: February 14, 2011. http://www1.eere.energy.gov/vehiclesandfuels/facts/2011_fotw662.html
[3] UK Government Energy Act 2004 http://www.legislation.gov.uk/ukpga/2004/20/contents.
[4] ASTM D-6751 11b – Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels.
[5] EN-14214 Automotive fuels – Fatty Acid Methyl Esters (FAME) for diesel engines – requirements and test methods.
[6] EN-14110 Fat and oil derivatives – Fatty Acid Methyl Esters (FAME) – Determination of methanol content.
[7] UK EU Renewable Transport Fuel Obligation 2010.
[8] The 2009 Renewable Energy Directive (EU Directive 2009/28) (RED) http://www.ebb-eu.org/EBBpressreleases/EBB%20press%20release%202010%20prod%202011_capacity%20FINAL.pdf.
[9] Determination of Methanol Content in Biodiesel using Gas Chromatograph with Headspace Sampling According to EN-14110. Bruker Application Note #283027 2011.
