Environmental Engineering Reference
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injector fouling due to deposits, could be reduced. Moreover, sulfate, even in a small concentration,
accelerates corrosion of vehicle fuel system parts (IFQC 2004; WWFC 2008).
ASTM and the Agency of Petroleum, Natural Gas, and Biofuels (ANP) specifications limit the
sulfate content to 4 mg/kg maximum (ASTM D7319 and ASTM D7328 and ANP NBR 10894
methods, respectively). CEN has recently identified the problem of injector clogging due to sulfate
deposits and is currently working to determine an acceptable upper limit of sulfate in bioethanol
(White Paper 2007).
9.3.4 S ulfur c ontEnt
Sulfur reduces the efficiency of catalysts and therefore it has a significant impact on vehicle emis-
sions. Moreover, sulfur adversely affects advanced on-board diagnostic system requirements, such
as heated exhaust gas oxygen sensors. Reductions in sulfur will provide immediate reductions of
emissions from all catalyst-equipped engines (WWFC 2006).
CEN and ASTM have specifications for sulfur content. The EU specification limits the sulfur
content to 10 mg/kg for undenatured ethanol (EN 15485 or EN 15486 methods), whereas U.S. speci-
fications set the limit at 30 mg/kg for denatured ethanol (ASTM D2622 and ASTM D5453 methods),
which could be 5 mg/kg for undenatured ethanol if the hydrocarbon denaturant is neglected. Brazil
is expected to establish a sulfur specification for ethanol in the future (IFQC 2004; Gray 2005; White
Paper 2007).
However, engine manufacturers are pushing for reduction of the sulfur content limit so that
they can introduce new technologies into the market, such as lean-burn fuel-efficient technologies
or fuel-level sender units (WWFC 2006). Because of the tightening of the petrol sulfur content
specification, that of bioethanol will also likely soon decrease (Gray 2005; Costenoble 2006). Either
way, the natural concentration of sulfur in the ethanol is 1 or 2 mg/kg, much below the current limit
(White Paper 2007).
9.3.5 c oppEr c ontEnt
Copper is an active catalyst that even in very low concentration [0.012 ppm (ASTM D4806-03)]
in bioethanol can decrease fuel stability by accelerating the low-temperature oxidation of HCs
(IFQC 2004; Gray 2005; RFA 2009). The gum formed by the oxidation of hydrocarbons can
result in scale in engine pipes and injector deposits (RFA 2009). The copper and the electrical
conductivity are interrelated, and by controlling the former, the presence of the latter can be
minimized (RFA 2009). The use of metal deactivators in bioethanol can inhibit copper's catalytic
activity (Chevron 2008).
CEN and ASTM specifications currently limit the copper to 0.1 mg/kg maximum [methods EN
15488 and ASTM D1688 modified (http://goo.gl/Hkldt), respectively]. At the same time, Brazilian
specifications are slightly stricter (0.07 mg/kg for anhydrous ethanol, method ANP NBR 10893).
Although copper contamination during bioethanol production is prevented by prohibiting copper
tubes and stills, this test should remain in place to test ethanol derived from the alcoholic bever-
age industry, where copper stills are commonly used (White Paper 2007). To reduce measurement
costs, inductively coupled plasma (ICP) spectrometry could be used to measure copper (Cu), sodium
(Na), iron (Fe), and phosphorus (P) in one test (White Paper 2007).
9.3.6 E lEctrical (E lEctrolytic ) c onductivity
Electrical conductivity of bioethanol represents the concentration of metallic ions, such as chloride,
sulfate, sodium, and iron in the fuel (WWFC 2008) and is an indicator of the corrosive properties of
the fuel. Water content is another parameter that influences electrical conductivity (IFQC 2004). A
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