Analytical Instrumentation
33
Table 1: ASTM D6751 Specification for Biodiesel (B100)2
Glycerol esters are examined by GC using flame ionisation detector (FID). Specifications for the use of GC’s are both addressed in EN14124 and ASTM D6751. The latter references the use of ASTM D6584 for analysis whereas EN14214 uses EN 14103.
Water and Sediment content in the fuel raises several concerns that encourage manufacturers to remove this component before moving forward in the production process. If it isn’t properly addressed, water can promote microbial growth and also will lead to corrosion in tanks during storage in the presence of oxygen. Water content also causes phase separation to create emulsion as well as hydrolytic oxidation. The European standard suggests the use of titration to determine the amount of water present in a fuel sample as opposed to the centrifugal method of ASTM D2709 (referenced in D6751). Fuel oxidation can also cause an increase in the amount of sediment present in the biofuel stock.
One of the most commonly used feedstock in Europe for biodiesel production is high-oleic rapeseed oil. EN14214 restricts the presence of any methyl linolenate in its biodiesel fuel because of its tendency to oxidise. EN14103 is the test method used to determine ester and linoleic acid methyl ester content in biodiesel fuel. Oxidation Stability is one of the primary issues to be dealt with in biodiesel. EN14112 AOCS Oil Stability Index method Cd12b-92 outlines a method for testing the oxidation stability of the fuel. Oxidation stability is measured by heating the fuel sample to a specified temperature and bubbling air through it which takes up any volatile components into water. Conductivity of the water with the components in it is measured.
Injection pumps in some engines cause power loss which could adversely affect the performance of an engine. For this reason, the kinematic viscosity is measured and used to monitor the fuel during storage; the more viscous the fuel the poorer the quality. The minimum viscosity of the fuel being pumped that is required for proper operation is 1.9 mm2/s. ASTM D6751 refers to ASTM D445 and EN14214 refers to ISO3104/ISO3105 to test the viscosity of the fuel.
The Sulfated ash test (ASTM D874) is performed to measure any compounds prone to forming ash that would later contribute to fouling in the fuel system. ASTM D6751 references D874 while EN14124 refers to ISO3987; the test is designed to determine the sulphated ash from lubricating oils containing various metals. It covers Ba, Ca, Mg, Na, K and Sn. The most applicable to biodiesel is to determine the residual sodium and potassium from the catalyst.
ASTM D4951 is typically used to determine the sulphur content of a product. For biodiesel, it is determined by D5453 by analysing the sample with ultraviolet fluorescence during combustion. The presence of this element in the fuel would cause pollutant emissions in diesel engine; biodiesel typically contains less than 15 ppm. The common test used (D4951) for sulphur analysis is not used because it often results in falsely high sulphur contents due to the presence of oxygen in biodiesel. Similarly, EN14214 uses ISO20846 to determine this component via UV fluorescence.
One of the critical aspects of biodiesel production is the separation of free fatty acids. An acid number level of 0.50 has been associated with shortened lifespan of fuel pumps and filters and deposits in the fuel system over time. High levels of acid will lead to stability and compatibility issues with fuels system’s metals. This high content would fail the Copper Strip Corrosion Test. The requirements for diesel and biodiesel are the same. For pure biodiesel meeting all D6751 specification, the copper strip corrosion test is usually passed. This test is performed to predict impending difficulties with copper and bronze components of fuel systems. Prolonged
For More Info, email: Table 2: EN14214 General Requirements and Test Method
contact with copper and bronze may serve as catalyst that would degrade the biodiesel over time.
The most common number used to evaluate a diesel’s quality is its Cetane Number. A minimum cetane number is required for an engine to operate satisfactorily. Typical diesel is required to meet a cetane number of at least 40 in the United States; typically it is found to be between 40 and 52. Good low temperature start properties are associated with high cetane numbers. The minimum cetane number allowable in biodiesel by ASTM D6751 and EN14214 surpass the number tolerable for petrodiesel.
Cloud point is the most commonly used measure of low-temperature operability; fuels are generally expected to operate at temperatures as low as their cloud point. Cloud point of B100 fuel is commonly greater than that of petrodiesel. Carbon residue indicates the tendency of fuel to accumulate carbon in an engine over time. It is measured on the entire biodiesel sample rather than on 10 percent distillate that is measured on conventional diesel. Free and total glycerin values is a direct indication of the amount of left over unconverted fats and glycerin byproduct in the final product. The presence of glycerin and fats in a fuel can lead to plugging in fuel system filters. Determining this number can be very difficult because ASTM D6584 references that GC be used for this. The user may find difficulty because simply the type of column used can yield incorrect results. D6584 calls for the use of an open tubular column with a 5% phenylpolydimethylsiloxane bonded and cross linked phase internal coating.
With the use of biodiesel, catalytic converters are often susceptible to damage due to the presence of Phosphorous compounds. A maximum of 10 ppm is allowed for its content in biodiesel. The United States produces biodiesel containing a level of around 1ppm.
The test methods cited in this paper have become the back bone of the biodiesel industry for long term biodiesel storage, usage and blending. Standardisation societies are working towards making more advancement in methodology to improve the quality of biodiesel. As biodiesel continues to develop toward commercialisation as a fuel on its own and as a blend, the need for worldwide uniformity in the standards is essential.
References
1) Biodiesel Basics. Energy Efficiency & Renewable Energy. Alternative Fuels Data Center. U.S. Department of Energy, 2011. Web.
2) J. Yanowitz and R. Nelson. Biodiesel Handling and Use Guide, fourth Edition. National Renewable Energy Laboratory. 4th ed. U.S. Department of Energy. 2009. Print.
3) Colantuoni, V. and Shah, R. Challenges Faced in the Standardization and Development of Biofuels. Biodiesel Magazine. 2009. Web.
4) Bailey, Rob. The Trouble with Biofuels: Costs and Consequenques of Expanding Biofuel in the United Kingdom. Chatham House. 2013.
5) A.M. Blume and A.K. Hearn, The evolution of biodiesel, Biofuels – Plant and Technology, 20- 23, 2007. Print.
6) G. Knothe, Analyzing biodiesel: Standards and other methods, JAOCS, 83(10), 823-833, 2006. Print
7) Bradley, David. (2008, November/December). New Biodiesel Specifications Published by ASTM International. ASTM Standardization News. 56-57.
AUGUST / SEPTEMBER 2013 •
WWW.PETRO-ONLINE.COM
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52
