6
Biofuel Industry News
Reliable Determination of Copper, Phosphorus and Sulfur in Bioethanol Using Inductively Coupled Plasma Spectrometry
Matthew Cassap, ICP Applications Specialist, Thermo Fisher Scientific SOLAAR House, 19 Mercers Row, Cambridge CB5 8BZ, United Kingdom Tel: 01223 347 400 Email:
matthew.cassap@
thermofisher.com
The increased strain on existing fossil fuels has led to a rise in demand for alternative fuel production. Bioethanol is ethanol produced from the fermentation of sugar derived from plants such as sugar cane or beet, maize or cassava. The production of bioethanol for use as either a fuel substitute or a blending agent for gasoline has increased dramatically over the past few years. The USA produced an estimated 23.3 billion liters of bioethanol in 2007 compared with 16.2 billion liters in 2005.
Bioethanol production is not a new industry. Brazil has been producing it since the 1970s and has replaced 50% of its gasoline usage with bioethanol. In order for a car to run on pure ethanol, modification of the engine is required. In the USA and Brazil, all new cars must have converted engines, known as fuel flex engines, which can run on 100% ethanol, 100% gasoline or any combination of the two.
The use of bioethanol as a fuel substitute for gasoline offers a number of important benefits. Bioethanol can be blended with gasoline to reduce cost and increase fuel supplies while decreasing demand on fossil fuel supplies. Being an oxygenate additive, bioethanol improves the octane rating of fuels while also reducing green house gas emissions. A further benefit is that blends of 5% ethanol and 95% gasoline (E5) can be used in modern engines with no modification.
However, it has been found that organic and inorganic contaminants may be present in bio- ethanol fuels, leading to undesirable effects. Copper, phosphorus and sulfur are three contaminants that must be rigorously monitored, since they are associated with a number of problems. The analysis of sulfur in ethanol is necessary to ensure that emissions produced when the fuel is burnt comply with environmental legislation. The level of sulfur must be controlled to prevent the formation of sulfur dioxide which can lead to acid rain.
The concentration of copper and phosphorus must be also controlled as these two elements can cause adverse effects on the operation of an engine. Copper acts as a very efficient catalyst for the low temperature oxidation of hydrocarbons. Concentrations above 0.012 mg/kg rapidly increase the rate of oxidation leading to gum formation, which can deposit on engine components such as fuel injectors. Phosphorus can poison the catalyst used in the exhaust systems of engines leading to increased emissions of environmentally harmful gases as the catalyst becomes ineffective.
Global regulatory bodies have therefore introduced stringent legislation to specify the maximum allowable concentrations of various contaminants in ethanol, including copper, phosphorus and sulfur.
Regulations
The American Society for Testing and Materials (ASTM) International enforces the D4806-091
standard specific-
ation, covering nominally anhydrous denatured fuel ethanol intended for blending with unleaded or leaded gasoline at 1 to 10% volume for use as a spark-ignition automotive engine fuel. Among others, the standard mandates that denatured fuel ethanol must conform to the specified performance requirements for copper and sulfur content.
The ASTM has also published D5798-09B2 standard
specification, covering a fuel blend, nominally 75 to 85% volume denatured fuel ethanol (Ed75-Ed85) and 25 to 15% additional volume hydrocarbons for use in ground
Table 1: Calibration and check standard concentrations. The values are shown in both mg/L and mg/kg to be applicable to both the ASTM standard and the expected ISO standard.
vehicles with automotive spark-ignition engines. According to the specification, fuel ethanol must conform to the performance requirements prescribed by the D4806-09 standard.
In Europe, EN 153763,4,5 standard specifies
requirements and test methods for marketed and delivered ethanol to be used as an extender for auto- motive fuel for petrol engine vehicles. This standard specifies ethanol as a blending component at up to 5% and includes specific requirements in relation to low water content, range of non-harmful denaturants and level of impurities that will not harm exhaust gas treatment systems.
The International Organisation of Standardisation (ISO) is also expected to publish a standard for the analysis of ethanol for copper, phosphorus and sulfur in the future.
In order to comply with these regulations, the industry requires a dependable analytical method capable of providing reliable quality control of ethanol.
Analytical Technologies
Fourier transform near infrared (FT-NIR) spectroscopy can analyse key bioethanol process streams for multiple components in seconds. The use of FT-NIR simplifies the testing protocol for biofuel plants since it can replace multiple pieces of equipment, eliminate disposable laboratory supplies and significantly reduce equipment maintenance. In addition, the ability of the technique to analyse samples in-line, on-line, at-line or in the laboratory allows each biofuel production facilities to set up the ideal monitoring protocol for their process. However, FT-NIR is best suited for quantifying the level of sugars and ethanol in the bioethanol fermentation broth, rather than monitoring the presence of contaminants.
Inductively coupled plasma (ICP) spectrometry is an ideal technique for the analysis and quantification of a combination of trace contaminants in ethanol due to its multi-element capability and ability to reach the required levels of detection. ICP is a rapid method, providing time-efficient, repeatable analyses of any sample type. Further key advantages of the technology include excellent stability, flexibility, sensitivity and precision.
Experimental
A Thermo Scientific iCAP 6000 Series ICP emission spectrometer was used for this analysis, enabling full wavelength coverage from 166 nm to 847 nm with Fullframe capability offering full spectrum trend analysis and contamination identification. The dedicated radial view mode of the spectrometer was chosen for this analysis due to its freedom from interferences which are likely to be present in this matrix, such as carbon-and oxygen-based molecular emissions derived from the ethanol.
A Glass Expansion IsoMist temperature controlled spray chamber was also used for this analysis. Ethanol is much more volatile than water resulting in higher sample transport efficiency from the nebuliser to the plasma compared with an aqueous sample. The higher vapor pressure causes the plasma to move upwards into the load coil and can cause plasma instability. To overcome this problem, the sample can be cooled immediately prior to introduction to the plasma by using a temperature controlled spray chamber. The selected spray chamber temperature depends upon the vapor pressure of the sample. For a sample to be introduced into a plasma successfully, it must exhibit a vapor pressure of 30 mm Hg or less. The temperature at which the vapor pressure of ethanol falls below this value is approximately 14°C.
February/March 2010
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
