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Distinguishing Between Bio-ethanol and Petroleum Ethanol

By Dr. Murry Tamers, Beta Analytic Founder and Chairman
Article from Ethanol Producer Magazine Published June 1, 2006

Much of the ethanol produced in the world is actually a petroleum product. It is easily made by the hydrolysis of ethylene, a major petrochemical. Two million tons of petroleum-derived ethanol is produced annually. The principal suppliers are from South Africa and Saudi Arabia, but there are also large plants in the United States, Europe and Japan. Petroleum-derived ethanol (synthetic ethanol) is a widely used industrial solvent and has a considerable variety of other applications.

The new tax credits for ethanol in gasoline (Energy Policy Act of 2005, H.R. 6) are intended for “bio-ethanol” or “renewable ethanol,” and not petroleum-derived ethanol. The issuance of these tax credits will have to require a certification that the ethanol comes from renewable sources. The recognized scientific test is the ASTM method D6866-05. This unambiguously and quantitatively distinguishes between materials produced from fossil fuels, such as petroleum, and those produced from contemporary biomass. ASTM D6866-05 protects the interests of investors and biomass producers investing in bio-ethanol production. In fact, it is of paramount importance to the success of the domestic bio-ethanol industry.

Bio-ethanol and synthetic ethanol are chemically indistinguishable—they are both the same compound, C2H5OH. The only difference between the two is the isotopic composition of the carbon atoms. Synthetic ethanol comes from fossil raw materials, and bio-ethanol comes from contemporary materials. A common procedure for studying fossils has been applied for ASTM D6866-05; it is the technique of radiocarbon dating, known for its use in archaeology and other fossil studies. Radiocarbon dating measures the content of a naturally occurring isotope, carbon 14, in the samples studied and compares this to the content in contemporary materials.

ASTM D6866-05 uses the same techniques as radiocarbon dating. Biomass consists of contemporary materials containing carbon 14, whereas fossil materials do not have any of this isotope left. It has all decayed away over the years. Measuring the concentrations of carbon 14 in the ethanol being studied will show whether it was manufactured from renewable or from fossil materials. In some cases, there will be a mixture of bio-ethanol and synthetic ethanol. Here, ASTM D6866-05 will quantitatively determine the percentage of bio-ethanol so that the appropriate tax credit can be given. Likewise, ASTM D6866-05 would be an applicable test for bulk gasoline containing varying concentrations of bio-ethanol. The test would indicate the amount of renewable material in the total liquid. However, it must be certain that the gasoline is well-mixed so that the small sample taken is representative of the entire storage tank. This is always an important concern in bulk materials testing.

Radiocarbon dating, first developed in 1947, depends on the continuous production of a radioactive isotope, carbon 14 or radiocarbon, by cosmic rays in the upper atmosphere. The isotope combines with oxygen to form carbon dioxide, which filters down to the biosphere. It is taken up by plants, which are then eaten by animals. The carbon 14 is continuously lost by radioactive decay, but this is balanced by the continuous production by cosmic rays.

All living beings, plant and animal, will have the same concentration of carbon 14. However, when the plants or animals die, their carbon 14 is no longer replaced from the atmosphere. The content of this isotope in the dead remains or fossils gradually decreases up to the point where there is essentially none left, taking approximately 50,000 years. Radiocarbon dating procedures accurately measure the carbon 14 content in various materials, and from this, one can calculate when the plant or animal died. The dating system is an indispensable tool for archaeology, and also many studies in geology and other earth sciences.

Radiocarbon dating is a branch of nuclear chemistry and physics. Since the amounts of carbon 14 are very small, the most sensitive techniques for its measurements are required. Two procedures are currently used: radiometric and accelerator mass spectrometry. Radiometric measures the radiation produced from the disintegration of carbon 14; accelerator mass spectrometry measures the concentration of carbon 14 directly.

For both radiometric and accelerator mass spectrometry techniques, pretreatments of the samples can be important. The procedures for this vary widely, depending on the type of material being measured. The steps involve various physical and chemical operations to eliminate extraneous materials. After this, the treatments for the two techniques are different, but both involve high vacuum operations.

For radiometric measurement, the samples are combusted in a specialized vacuum system to produce carbon dioxide. This is then combined with molten lithium to produce lithium carbide. After cooling, the lithium carbide is reacted with water to produce acetylene. This gas is purified and finally converted to benzene using a silica-alumina catalyst. All of these procedures are carried out in glass vacuum systems. The benzene, which contains 92 percent carbon, is mixed with scintillator chemicals and placed in a liquid scintillation counter for radiation detection. On average, the sample will remain in a counter for two days in order to accumulate enough counts to give reasonable statistics. Both contemporary standards and background materials are also subsequently measured in the same counters.

Samples for accelerator mass spectrometry are combusted to carbon dioxide, which is then purified. The carbon dioxide is reacted with hydrogen to form graphite in a specialized glass vacuum line. The graphite, 100 percent carbon, is put into aluminum target holders and placed in the particle accelerator for measurement. The analysis here takes about 30 minutes. As with the radiometric technique, modern and background samples are subsequently measured in the same way.

In addition, all samples are analyzed for the stable isotope, carbon 13. This is essential for adjustment of the measured carbon 14 values. Carbon 13 measurement is an integral part of radiocarbon dating. It is also, in some cases, a means of verifying the source of the biomass used for the ethanol production. Carbon 13 itself is not suitable for precisely determining renewable versus fossil contents in mixtures. Although petroleum and corn, for example, have different carbon 13 concentrations, natural carbon 13 from other biomass materials has values that are quite variable. Some materials suitable for bio-ethanol production—for example, sugar beets, sweet potatoes, grapes and other fruits—have carbon 13 values that are generally indistinguishable from that of petroleum. This would result in carbon 13 analyses giving ambiguous results in the case of dilutions of bio-ethanol with 10 percent or 20 percent synthetic ethanol. On the other hand, radiocarbon dating analysis would clearly show this dilution.

The amount of chemical and electronic equipment needed for a routine radiocarbon dating laboratory is quite large. For Beta Analytic Inc., the capital equipment includes 53 liquid scintillation counters, particle accelerators with ion sources, carbon-13 mass spectrometers with elemental analyzers, 11 benzene synthesis vacuum lines, 12 graphitization vacuum lines, and extensive materials and ovens for the pretreatments and combustions.

The important tax credits for bio-ethanol in gasoline will provide a temptation for unscrupulous individuals to submit synthetic (petroleum) ethanol. It is anticipated that the most common occurrence will be the dilution of bio-ethanol with synthetic ethanol in the hope that this will not be detected. However, ASTM D6866-05 is a quantitative technique that will be able to clearly signal any significant dilution. ASTM D6866-05 will protect the biobased industry by discouraging this cheating. An ASTM D6866-05 certification should be the necessary condition for each batch of bio-ethanol that is being submitted for the tax credit.

ASTM D6866 Update

As of  May 11, 2012, ASTM D6866-12 is the current active version of the standard.

Beta Analytic no longer uses liquid scintillation counters for ASTM D6866 testing.

Page last updated – January 7, 2015