Sulfur in Ethanol: 40 CFR Part 1090 Compliance Guide

Background

The use of biofuels has been growing over the past decade as the industry adds renewable sources to the commercial product mix. This trend has seen the rise of complete fuel products such as biodiesel, as well as bioethanol blend stocks for gasoline. Most automobiles in the U.S. are able to run on gasoline with a 10% mixture of fuel ethanol (E10). Since 2014, over half of the new vehicles produced by Chrysler, Ford, and General Motors can use E85, which is a mixture of 15% gasoline and 85% fuel ethanol. According to the Title 40 Code of Federal Regulations (CFR) Part 1090 for Regulation of Fuels, Fuel Additives, and Regulated Blendstocks, specifically 40 CFR 1090.270, ethanol that is blended with gasoline must meet the 10 parts per million (ppm) maximum standard for sulfur content on a per gallon basis.

Ethanol produced through the fermentation of sugars from plants such as corn or sugar cane, sometimes referred to as bioethanol, is not a significant source of sulfur content in fuels. To restrict human consumption, ethanol is typically denatured with gasoline from various sources (including as a byproduct of natural gas production), which can potentially introduce sulfur content into the finished product. Although denaturants cannot exceed 3% by volume of the fuel ethanol, the denaturant itself may contain a maximum of 330 ppm sulfur. To ensure compliance with Title 40 CFR Part 1090 regulations, fuel ethanol is tested to confirm that the sulfur content meets the 10 ppm standard for downstream-blended oxygenate.

Challenge

Although 40 CFR Part 1090.1350 specifies ASTM D5453, sulfur by Ultraviolet Fluorescence (UVF), for measuring sulfur in neat ethanol, alternative techniques are allowed, provided the test results are correlated to D5453. This is good news for those who prefer to use X-ray Fluorescence (XRF) over UVF due to its ease of use. Measuring sulfur content in fuel ethanol by XRF shares many of the same challenges as other biofuels. The oxygen content in ethanol can create an interference that masks the presence of sulfur. This makes it more difficult to quantify for sulfur and requires specific countermeasures to ensure accurate reporting. One such countermeasure is matrix matching, another is use of correction factors, both of which are described in ASTM D2622, sulfur by Wavelength Dispersive X-ray Fluorescence (WDXRF), and ASTM D7039, sulfur by Monochromatic WDXRF (MWDXRF)

This paper will focus on matrix matching. Using a matrix matched calibration, we will demonstrate that a check sample, an ethanol Certified Reference Standard with 5 ppm sulfur, measured on Sindie +Cl using ASTM D7039 shows excellent agreement with the certified value.

Experiment

As with other samples that require oxygen correction, the first step in matrix matching is to measure calibration standards with sample matrices consistent with the samples being measured. We tested seven ethanol calibration standards with sulfur concentrations of 0, 0, 5, 15, 50, 250 and 500 ppm using Sindie +Cl in ASTM D7039 mode. The individual samples were vented and measured for 300 seconds each in low range.

Results

Figure 1 shows the calibration measurements along with the fitted calibration curve. The correlation coefficient (R2) of the calibration curve indicates an excellent fit to the measured values. The performance of the instrument was verified using 10 separate check samples with a certified sulfur concentration of 5 ppm. Each sample was vented and measured for 300s. Table 1 shows the measured concentrations of the check samples and demonstrates that there is no bias compared to the 5 ppm accepted reference value. The relative standard deviation for the 10 measurements is 8%.
 

Figure 1: Sulfur in Ethanol Calibration

Conclusion

As with gasoline, blending ethanol is subject to US EPA Title 40 Part 1090 regulations, including limits on the concentration of sulfur. While bioethanol derived from plants typically contains sulfur concentrations well below the regulatory limit, the denaturing process can potentially produce fuel ethanol which is non-compliant. By setting up a matrix matched calibration, batch testing with Sindie +Cl can provide a quick, easy-to-use method to check sulfur concentrations and ensure compliance.

Product Highlight: Sindie +Cl

Two Critical Elements with One Instrument
Sindie ^® +Cl is a two-in-one instrument enabling trace analysis of both sulfur and chlorine with one analyzer. It is the ideal solution to certify sulfur levels in finished products, assess chlorine for corrosion mitigation, and optimize process parameters.