Securing the Energy Future: Work Flow Solutions for Biodiesel Quality Control

The global energy crisis is starting to have a significant impact on the world economic climate. Record-breaking prices of crude oil have already been reached in 2011, with costs expected to soar again due to demand in the summer months. The impact of high oil prices on the general public and commercial trade could suppress the economic recovery following the global financial crisis. Nuclear power can offer some respite from the rising energy demands and rapidly diminishing fossil fuel reserves. However, nuclear power will never be able to overcome the societal stigma surrounding the safety of nuclear fission; the recent incident in Japan is testimony to this. Never before has the pressure to resource and develop sources of sustainable energy and fuel been so high.

Technological advances in the production of renewable energies mean that they are increasingly cost-effective and efficient, but will do little to alleviate our immediate fuel and energy concerns. Alternative fuels, such as biodiesel, are a sustainable and environmentally conscious solution to supplement fossil fuel reserves and ease the upcoming transition between fossil and renewable energy sources.

Biodiesel is a vehicle and heating fuel generated from vegetable and animal fats. The industrial process for producing this has been optimized to produce viable fuel; however, the raw product contains a number of contaminants that need to be removed. Therefore, once processed, the fuel is required to undergo extensive chromatographic-quality testing to detect the levels of contaminants and determine the fuel quality. Worldwide public and environmental safety agencies have produced a number of regulatory guidelines to control the levels of potentially harmful contaminants and ensure that the fuel can satisfy engine performance requirements. This article discusses the methods for assessing the quality of biodiesel products, and examines the possible work flow solutions to make these analyses more efficient and cost-effective.

Figure 1 - Work flow diagram for the production of biodiesel.

Producing the fuel for the future

Biodiesel can be produced from a number of virgin fatty acid sources, including soybean, canola, olive, and other plant oils. It may also be derived from recycled animal and vegetable fats, and there is increasing interest in using farmed algal species, with inherent oil content of over 50%, as the biodiesel oil source. The production of biodiesel can be complicated by the presence of impurities within the source materials (see Figure 1). Charred foodstuffs and solid particulates are filtered out and water is removed by evaporation. Water in the reaction mixture can lead to soap formation (saponification). To maintain a cost-effective yield, it is vital that excess water be removed prior to the esterification of fatty acids for the production of biodiesel.

Figure 2 - Analysis of a biodiesel sample highlighting fatty acid contamination.

Feedstock samples are titrated with an alkali, typically sodium hydroxide (NaOH), to calculate the concentration of fatty acids (carboxylic acids) within the source oil. The calculated fatty acid concentration is used as a basis for the addition of a sixfold excess of alkalinated alcohol, typically ethanol or methanol, to the oil feedstock to drive the esterification of the fatty acids to completion (Figure 2).

The esterification reaction is naturally slow, and the addition of heat or an alkali catalyst can increase the rate of reaction to commercially viable levels. Extensive heating of the reaction is heavily energy dependent and leads to an increase in the cost of the end product. The base catalyzed product is therefore most frequently used since the addition of the NaOH catalyst causes deprotonation of the alcohol, increasing its nucleophilic activity. Excess alcohol is used to drive the reaction to completion, and because of this alcohol is one of the most significant contaminants in the end product.

Contaminant quantification

The presence of excess alcohol can cause the fuel to burn inefficiently and make it considerably more volatile, reducing the flashpoint to dangerous levels. For this reason, regulatory protocols are in place to assess the level of alcohol contamination, e.g., the European Method EN14110 for methanol assessment. Headspace gas chromatography is required to accurately assess the methanol contamination and can be coupled with polar and nonpolar stationary phase chromatography, typically a 100% dimethyl polysiloxane phase such as the Thermo Scientific TRACE TR-BioDiesel (M) (Thermo Fisher Scientific, Runcorn, U.K.). When coupled with a flame ionization detector, the system is capable of measuring the level of methanol contamination between 0.001 and 0.5% m/m, which satisfies the regulatory limits set out in EN14214:2003.

Figure 3 - Analysis of biodiesel for mono-, di-, and triglyceride content, in line with EN14105.

Fats and oils consist of high concentrations of triacyl glycerides (TAGs) (Figure 2), which are based on a tri-ol (glycerine) backbone with three fatty acid side chains. Addition of the NaOH causes hydrolysis of the ester bonds between the glycerol and the fatty acid chains. Glycerine is therefore the major by-product of the reaction. Fortunately, the glycerine component is significantly denser than the fatty acid esters and can be separated by gravity. Low concentrations of glycerine are required to ensure good cold weather performance and prevent injector port deposits from reducing engine efficiency. The levels of glycerine in the biofuel are carefully regulated for in European Method EN14105 (Figure 3) and American Society for Testing and Materials (ASTM) Method D6751.

GC analysis for the concentration of total glycerine requires a nondiscriminative cold injection system that can transfer volatile and heavy sample components to the column. A 5% phenyl polysilphenylene-siloxane stationary phase such as the Thermo Scientific TRACE TR-BioDiesel (G) is coupled with a flame ionization detector for the accurate quantitation of the glycerine and glycerides contained in the sample. A total glycerine level of 0.25% m/m is permitted under EN14214:2003 (Figure 3), and the analysis must be capable of detecting levels of total glycerine between 0.05 and 0.5% m/m.

Assessing fuel quality

The cetane number of a diesel fuel is a measure of its ability to perform under compression ignition. Cetane number is assessed by comparing the ignition delay of a diesel fuel with that of mixtures of cetane (hexadecane [C16H34]) and isocetane (2,2,4,4,6,8,8-heptamethylnonane [C16H34]). Regulatory requirements for the cetane number of a diesel fuel are legislated for by European EN590 and U.S. ASTM D975.

Biodiesel may be used as a blending stock for addition to petroleum-derived diesel fuel, or as a pure biofuel known as B100. The cetane number of B100 is dependent on the distribution and availability of fatty acids within the oils used in the initial esterification reaction. Measuring the quantity of the fatty acid methyl esters (FAMEs) and linolenic methyl esters within B100 allows for an accurate calculation of the cetane number of the biofuel.

Measurement of FAME concentration is prescribed for by GC method EN14103 and requires a split/splitless (SSL), or programmable temperature vaporizing (PTV) injector, to introduce fuel samples onto the column. Accurate, sensitive detection and quantitation of the FAME concentration is best achieved on a polar GC column capable of separating the esterified fatty acids and linolenic methyl esters. GC analysis of a biodiesel sample should provide verification that levels of FAME within the sample exceed 96.5% m/m, with the level of linolenic methyl esters being <12% m/m. This GC method is suitable for the separation of samples of B100 containing FAMEs of chain length from C14 to C24.

Chromatography work flow

Sample testing such as that described above is often an outsourced quality control measure, with external companies providing the chromatographic expertise. The outsourcing analysis industry is a growing market, with new methods and sample types being added frequently. Establishing new chromatographic techniques in a laboratory is expensive in terms of the downtime and consumables required for method validation (Figure 1). New techniques that conform to regulatory standards can take as long as a month to validate, during which time the instrument and technicians are out of general service. In-house analyses, performed by manufacturing industries, are equally affected by the time taken to develop new methods. A second consideration is the consistency of measurement between samples and column changes.

Biodiesel quality control analyses must assess the levels of contaminating methanol (EN14110; EN14214:2003) and glycerine (EN14105), and meet the cetane number requirements of ASTM directive D6751. Although conformance to these regulations is vital for public and environmental safety, the expense of establishing and validating these techniques adds to the production costs of the fuel. In the interest of maintaining an acceptable at-the-pump price and reducing the impact of the energy crisis, it is essential to keep production costs as low as possible. To achieve this, work flow solutions that fast-track sample analysis while maintaining the quality of the data are needed.

One potential work flow solution is a series of applications kits that provide all of the columns, calibration solutions, derivatization reagents, standards, syringes, and vials required for the method. The Thermo Scientific ENBioDiesel GC productivity solution and Thermo Scientific ASTM GC productivity solution are work flow adaptations for compliance of biodiesel products with the European and American regulatory guidelines. These European and American productivity solutions were responsible for generating the high-quality data shown in Figures 2 and 3. The ability to resource the method in this way, with all the necessary consumables for validation of the method and results, would allow the scientist to provide data that satisfy all of the regulatory standards in an efficient and cost-effective manner. Biofuels will become an important cornerstone of the energy economy of the future. Use of work flow-enhancing products to improve the accuracy and speed of the quality control process will greatly assist in reducing costs and ensure a secure energy future.

Mr. Wheeler is GC Applications Specialist, Thermo Fisher Scientific, Chromatography Consumables Division, Tudor Rd., Manor Park, Runcorn WA7 1TA, U.K.; e-mail: paul.wheeler@thermofisher.com.

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