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Wed, Mar 2nd 2011, 09:20 by Indresh Mathur

Differences Between Corn and Sugar Cane Derived Ethanol for Fuels

Corn and sugar cane are the two primary source of feedstock from which ethanol is derived for use in automobile fuels. Our customers have frequently asked, “Are there differences in the corn ethanol sold in the USA and the sugar cane ethanol sold in Brazil?” The answer is not so clear-cut. Our analysis would suggest that further studies are warranted.

In an attempt to provide an answer the above question, Haltermann Solutions procured anhydrous ethanol from two major US ethanol producers of corn ethanol along with hydrous and anhydrous ethanol produced in Brazil from sugar cane, and compared them.

The impurities in ethanol can adversely impact the properties and performance of Ethanol Fuel as an automotive spark-ignition engine fuel. The quantities of impurities like water, acidity, pHe, chloride, sulfate, sodium, potassium, phosphorus, copper, sulfur, silicon, calcium, magnesium etc. in Fuel-Grade Ethanol is controlled within specified limits. The following summarizes the reasons for limiting various impurities:

Water reduces the energy content of the fuel and therefore adversely affects fuel economy and power. Also, water can cause phase separation problems in some ethanol-gasoline blends. Water is soluble in ethanol but ethanol is soluble in gasoline. When there is excess water in a fuel that is comprised of a preponderance of gasoline (i.e. E5-E25), there is phase separation. Water, in anhydrous ethanol, is generally limited to 0.3%, whereas water content of hydrous ethanol is typically in the range of 5-6%.

Acidity and pHe. Aqueous organic acids in very small presence, such as acetic acid, can be highly corrosive to a wide range of metals and alloys. When the pHe of the fuel is below 6.5, excessive corrosion can occur which may result in fuel injector failure and cylinder wear. Acidity (as acetic acid) is limited to 0.007 %m/m.

Inorganic (ionic) chloride compounds can be corrosive and can damage fuel system components.    Inorganic chloride compounds are generally limited to a concentration of

Sulfate levels are generally limited to <4mg/kg.

Phosphorus, like lead, deactivates exhaust catalysts if present in more than trace quantities.

Copper is a very active catalyst and can promote gum formation in gasoline. Copper is usually limited to <0.100mg/kg.

Sulfur is limited in order to protect against engine wear, deterioration of engine oil, corrosion of exhaust systems, and to prevent catalytic muffler deactivation. Sulfur levels are usually limited to <10mg/kg. Generally, sulfur in non-denatured ethanol is lower than sulfur in denatured ethanol because of the sulfur impurity in the natural gasoline typically used to denature the ethanol.

Silicon in ethanol is unacceptable.  Combustion of a fuel that contains silicon results in the formation of silica deposits on the oxygen sensor in the engine exhaust.

Methanol content in ethanol is limited to 0.5 % m/m. This is important to in order to protect against engine and fuel system wear, corrosion, and deterioration.

C3-C5 saturated alcohols usually enter fuel ethanol as by-products of the manufacturing process, and are limited by the producer as a way to control the purity of the ethanol.

The results of the detailed analytical work carried out on the various types of ethanol are given in the attached table. At first glance, there appears to be little difference between corn and sugar cane ethanol. The ethanol content is consistent with whether the particular ethanol being analyzed was anhydrous non-denatured, anhydrous denatured, or hydrous non-denatured.  The heat of combustion is consistent with the water content of the ethanol.

A closer look at the analytical data shows that hydrous Brazilian ethanol derived from sugar cane consistently has higher levels of inorganic impurities as evidenced by the higher levels of sulfate, sodium, potassium, calcium, magnesium and sulfur. While natural gasoline as a denaturant in ethanol generally contributes to higher sulfur levels, it is worth noting that the sulfur level found in the hydrous Brazilian ethanol was higher than the sulfur level found in the natural gasoline-denatured ethanol. It appears sodium sulfate is the major impurity in the hydrous Brazilian cane ethanol. It is reasonable to assume that higher inorganic impurities in the hydrous Brazilian cane ethanol are a result of dissolved salts in the higher water content of this ethanol.

The relatively higher inorganic content of the Brazilian hydrous cane ethanol may not, at first glance, seem like a problem until one considers how hydrous cane ethanol is used in Brazil. Brazil has aggressively developed cars that can operate on either 100 percent ethanol, E85, or E25. In Brazil, both ethanol-only fuel and E85 fuel utilize hydrous ethanol. Anhydrous ethanol is used in E25 gasoline blends because water causes phase separation in these lower ethanol-content blends.

The impact of higher inorganic impurities in hydrous cane ethanol is amplified 3-4 times when ethanol is used neat or as an E85. This is an important consideration for the OEMs developing flex fuel cars.

Haltermann Solutions is an importer of Brazilian ethanol and is ready to assist its customers as they develop vehicles that will operate on hydrous cane ethanol.

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