. The Analysis of Biodiesel for Inorganic Contaminants, using Atomic Spectroscopy Techniques Fossil fuels (oil, natural gas and coal) contribute ~8

The Analysis of Biodiesel for Inorganic Contaminants, using Atomic Spectroscopy Techniques


Fossil fuels (oil, natural gas and coal) contribute ~80% of the total world energy supply. Depending on the production and consumption rates, the presently known reserves of fossil fuels are estimated to last anywhere from 41 to ~700 years. The limited supply of fossil fuels, concerns for energy security and the need to respond to climate change have led to growing worldwide interests in renewable energy sources such as biofuels. Many observers consider biofuels to be the only feasible option for the substitution of fossil fuels in the transport sector. Currently, the most important biofuels are biodiesel and bioethanol, commonly referred to as first-generation biofuels. Biofuels are renewable fuels derived from biological feedstocks, and include both liquid forms such as bioethanol (gasoline equivalent) and biodiesel (diesel equivalent), and gaseous forms such as biogas (e.g., methane). Biodiesel, especially those derived from vegetable oils, have been highlighted as an alternative for diesel engines due to their similar physical-chemical properties to petroleum diesel and also because they decrease pollutant emissions compared with fossil fuels. Blends with up to 20% biodiesel (B20) offer lubricity and can be used in diesel engines without modification. Blends can improve combustion processes, yielding reductions in particulate matter, oxides of nitrogen, sulfur and hydrocarbons. In its simplest analysis, biofuels are considered to be carbon neutral because all carbon dioxide released during biofuel combustion is offset by carbon fixation during plant growth. Studies over the past 15 years show that the displacement of gasoline or diesel by biofuels can result in average net reductions in green house gas emissions of 31% for bioethanol, 54% for biodiesel and 71% for cellulosic ethanol. The emissions are lower and the fuel replaces some of the lubricity lost in removing sulfur to comply with new diesel fuel regulations. Sulfur limits in conventional diesel fuel have been lowered from 500 ppm to less than 15 ppm in the U.S. and less than 10 ppm in Germany and other EU countries. Measurements of sulfur and other metals in biodiesel are important to ensure adequate performance of the fuel. The quality of biodiesel is critical in providing good combustion and in preserving engine integrity. The raw oil is generally low in inorganic contaminants, but the final material needs to be analyzed to ensure catalyst traces are low (Na and K) or that no other inorganic contaminant has been introduced during manufacturing. High Levels of Na and K can form a soap solution and are common catalysts of the biodiesel reaction. If not removed they can cause instability and filter clogging. Ca and Mg can also form soap and the creation of problems similar to those caused by Na and K. Sulfur and phosphorous are both considered “carryover elements” from vegetable oil (P from phospholipids and S from glucosinilates). Sulfur and phosphorous are both potential catalyst poisons. Presence of metals can also degrade the oxidational stability of biofuels thereby decreasing the shelf life. The U.S. and Europe have put specifications in place to define biodiesel that is of good quality and will perform well in a combustion engine. ASTM has published specification D6751-07 for FAME and B 99.9%. ASTM D975 is the specification for different diesel compositions and other blends. CEN has published specification EN 14214 for the same purpose. Testing is important for all biodiesel manufacturers to demonstrate that their product meets quality standards. Testing may be required whenever there is a change in raw material, equipment, catalyst or even material supplier. Atomic spectroscopy techniques such as atomic absorption (flame and furnace), inductively coupled plasma – optical emission (ICP-OES), and inductively coupled plasma – mass spectrometry (ICP-MS) have been used for the determination of trace elements in oils. In some cases the capabilities of the techniques overlap and several are suitable for a particular analytical scenario.