SPECTRO XRF Report. SPECTRO iq II

Transcription

1 No. XRF-40 by SPECTRO 2007 SPECTRO iq II Summary The SPECTRO iq II simultaneous XRF spectrometer provides a fast, precise, accurate and economic solution for the analysis of the S content in Ethanol and Methanol blends. In addition the same analysis method can be used to monitor other important elements like Pb, P, and Cl. Analysis of Element Content in Methanol and Ethanol Blends for Use as Automotive Spark Ignition Engine Fuel SPECTRO Analytical Instruments GmbH & Co. KG, Kleve, Germany 1. Introduction One big area of biofuel development has been for road transport for both gasoline and diesel power technology. The use of sugars and other plant materials to manufacture alcohols as 100% fuels or as extenders to produce bio-gasoline has been around and actively applied in countries like Brazil and more recently Sweden for many years. In other countries regionalized programs were started to make bio-gasoline available. This has resulted in a large number of investments in bio ethanol plant production. Elemental analysis is required to show compliance with actual specifications.

2 For ethanol and methanol fuel ASTM amongst others has published specifications: ASTM D 5797, "Standard Specification for Fuel Methanol (M70-M85) for Automotive Spark Ignition Engines," ASTM International ASTM D 5798, "Standard Specification for Fuel Ethanol (Ed75-Ed85) for Automotive Spark Ignition Engines," ASTM International. ASTM D 4806, "Standard Specification for Denatured Fuel Ethanol for Blending with Gasolines for Use as Automotive Spark Ignition Engine Fuel," ASTM International. Although energy dispersive X-ray Fluoescence spectrometry (EDXRF) is currently not listed as one of the standard test methods for the elemental analysis, the technique, depending on the analyzer performance, is capable to monitor some of the elemental concentration limits in Ethanol, Methanol, and their blends when they are used as spark emission engine fuel. Test methods, which describe EDXRF and polarization EDXRF for the analysis of S content in petroleum products are: ASTM D 4294, "Standard Test Method for Sulfur in Petroleum and Petroleum Products by Energy Dispersive X-Ray Fluorescence Spetrometry," ASTM International. ASTM D 7220, "Standard Test Method for Sulfur in Automative Fuels by Polarization X- Ray Fluorescence Spetrometry," ASTM International. Besides the analysis of S content EDXRF equipment, depending on the analyzer performance, is capable of monitoring further elements like Cl, P, and Pb. For referenced ASTM standards, visit the ASTM website, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards volume information, refer to the standard's Document Summary page on the ASTM website. 2. Instrumentation SPECTRO iq II The samples were excited by a forced air cooled low power Pd end window X-ray tube combined with a doubly curved HOPG crystal for monochromatization and polarization of the primary tube spectrum. A VITUS- Silicon Drift Detector (SDD) was used to collect the fluorescence radiation from the sample. The resolution of the SDD was better than 160 ev for Mn K α. All radiation paths were flushed with Helium. The components are packaged in a compact benchtop metal cabinet with a small footprint. All measurement parameters are controlled by the system PC. 3. Calibration standards To cover the full range of various products synthetic standards for Methanol, Ethanol and mineral white oil were created to cover a full range of the pure material and their blends. Commercially available standards may be used as well. First a calibration for S in mineral white oil was created. To study matrix effects from the Oxygen content in Ethanol/Methanol calibrations for these materials were repeated with a reduced number of standard samples. Table 1: Calibration ranges and number of standards within this range Element S in mineral white oil Calibration range mg/kg Number of std s S in Ethanol S in Methanol Sample preparation 2 ml of each oil standard were poured into a 24 mm inner diameter liquid cell, assembled using a 4 µm polypropylene supporting foil. Page 2/5

3 This type of cup was equipped with a second polypropylene foil as a safety window. For blends with a higher gasoline content (>50 %) a polycarbonate film might be suitable as the gasoline will attack the Polypropylene film (see application report XRF-31) combining the newest generation of detectors with polarization technology has set new standards P, S, Cl analysis in EDXRF analysis. 5. Measurement All measurements were performed using the following conditions: Tube settings: 25 kv, 1 ma He flush 300 s measuring time K-Lines of P, S, Cl For the analysis of low levels of Pb a second measurement condition can be selected: Tube settings: 48 kv, 0.52 ma Helium flush 300 s measuring time L-Lines of Pb The following images show spectra of mineral white oil samples containing S at levels of 10, 50, and 100 mg/kg. Image 2: Spectra of samples containing 500 mg/kg P, S, and Cl. The achievable detection limits (LOD) are listed in the following table 1 (based on mineral white oil) Table 1: LODs for other important trace elements in mineral white oil Element LOD in mg/kg P 0.7 Cl 0.4 Pb Calibration Calibration was performed by measuring blank samples as well as the calibration standards. Intercept and slope of a fundamental parameter approach are determined by the least square fit. Image 1: Spectra of samples containing 10, 50, and 100 mg/kg S Especially the exact and reproducible analysis of low levels of phosphorous and chlorine in a matrix containing sulphur is a challenge for any EDXRF. As can be seen in image 2 Because of the matrix influence from the different C-H-O ratios in the samples, the measured intensities vary by matrix as can be seen from the image 3. Page 3/5

4 Intensity in cps per ma S concentration in mg/kg Image 3: Intensities vs. concentration S for mineralwhite oil (blue), Ethanol (pink) and Methanol (yellow). The effects from the different matrices can be corrected with three different approaches: Approach 1: Setting up calibration curves for each type of sample with matrix matching calibration standards. Approach 2: Calibration of one matrix with a fundamental parameters approach and adapting the matrix within the FP settings for the changing ratio of C-H-O The following correction factors for typical base material and blends were determined: Table 1: correction factors for Ethanol, Methanol and blends for the analysis of S Matrix Correction factor Mineral white oil 1.00 Ethanol (E100) 1.55 Ethanol (E85) 1.47 Ethanol (E15) 1.08 Methanol (M100) 1.79 Methanol (M85) Summary The high analytical performance of the SPECTRO iq II analyzer is demonstrated for the analysis of S content in Methanol, Ethanol and their blends, which are used as fuel for spark ignition engines. Besides the possibility to analyze the S content also lower levels of important traces like P, Cl and Pb can be monitored. Approach 3: Calibration of one matrix and correcting the analysis results with a factor depending on the Ethanol or Methanol material or blend The following image shows the correlation for S in mineral white oil as one example. S content analyzed in mg/kg S content given in mg/kg Image 4: Correlation for the calibration of S in mineral white oil (correlation coefficient: ) Page 4/5

5 Element Content in Ethanol and GERMANY SPECTRO Analytical Instruments GmbH Boschstrasse 10 D Kleve Tel: Fax: U.S.A. SPECTRO Analytical Instruments Inc. 91 McKee Drive Mahwah, NJ Tel: Fax: HONG KONG (Asia-Pacific) SPECTRO Analytical Instruments (Asia-Pacific) Ltd Sino Favour Centre 1 On Yip Street Chaiwan Tel: Fax: sales@spectro-asiapac.com.hk Subsidiaries: CHINA: Tel , Fax , specinfo@spectro.com.cn, FRANCE: Tel , Fax , info@ametek.fr, GREAT BRITAIN: Tel , Fax , sales@spectro.co.uk, IT- ALY: Tel: , Fax , info.spectro@ametek.it, SOUTH AFRICA: Tel , Fax , spectro@spectro.org.za. SPECTRO operates worldwide and is present in more than 50 countries. Please contact our headquarters for your local representative. SPECTRO 2007, Subject to modifications K-07, Photos: SPECTRO. Page 5/5