In compliance with international standards

To ensure the quality of biofuels, there are numerous standards that recommend test methods and set limit values for impurities. Not only are Metrohm instruments highly suitable for carrying out the test methods and to check the limits, we are also at the forefront in compiling standards with standard-developing organizations (SDO) all over the world.

Our instruments and methods comply with the international biofuel standards.

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Ambitious biofuel perspectives

The International Energy Administration (IEA) sees second-generation biofuels as one of the key technologies to reduce CO2 emissions. By 2030, most advanced biofuels will be competitive. Instead of threatening food security and biodiversity, advanced biofuel requirements rely increasingly on microbes that ferment biomass such as grasses, algae, husks, or waste products.

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Iodine number in biodiesel

The iodine number is a measure for the number of double bonds in a sample. It is the amount of iodine (in g/100 g sample) that can be added to the sample under the given conditions.

Potentiometric titration according to EN 14111

European standard EN 14111 describes the determination of the iodine number in fatty acids or biodiesel. A sample aliquot is dissolved in a mixture of cyclohexane and glacial acetic acid and treated with Wijs reagent. After a defined time has elapsed, potassium iodide and water are added. The released elemental iodine is then titrated with sodium thiosulfate solution. EN 14111 allows both optical (with starch solution as the indicator) and potentiometric endpoint determination.


Water content using Karl Fischer titration

Biofuels are more susceptible to water contamination than fossil fuels. Water hydrolyzes the ester bonds of fatty acid methyl esters and leads to the formation of fatty acids. Consuming additional NaOH, these acids form soaps, which make the subsequent removal of glycerol more difficult. Biodiesel with a high water content has a clearly lower oxidation stability. The lower it is, the greater the probability that oxidation products will be formed during storage. These can damage the engine, in particular the fuel injection system.

Water in biodiesel according to 12937

EN 14214 limits the water content in biodiesel to 500 mg/kg. Test method EN ISO 12937 is specified in EN 14214 and describes the coulometric Karl Fischer titration.

Biodiesel additives require the use of an oven

Some biodiesel fuels contain additives that could participate in side reactions during direct coulometric Karl Fischer titration. In such cases, we recommend that the biodiesel sample is not injected directly into the reaction solution. Instead, the water contained in the biodiesel should be driven off in a Karl Fischer oven.

Water in bioethanol according to EN 15489, ASTM E 1064, or E 203

For a water content > 2%, the recommended test method is volumetric titration as per ASTM E 203. For smaller water contents, we offer methods that comply with EN 15489 and ASTM E 1064.


Oxidation stability

Crucial parameter

In contact with air, petroleum undergoes oxidizing reactions whose reaction products can cause problems in combustion engines. Polymeric, poorly soluble compounds in particular lead to deposits in and blockages of the fuel injector systems. The aging behavior, i.e., the oxidation stability, is therefore a very important property of vegetable oils and biofuels.

Rancimat method

Air is passed through the sample at an elevated temperature to bring about artificial aging. During this process, long-chain organic molecules are oxidized by oxygen, whereby highly volatile organic substances form in addition to insoluble polymer compounds. The former are driven out by the air flow, absorbed in water, and detected there by measuring conductivity. The time until these decomposition products occur is referred to as the induction time or the oil stability index (OSI) and characterizes the resistance of the sample towards oxidative aging processes, i.e., the oxidation stability.


Ion chromatography in biofuel analysis

Glycerol in biodiesel according to ASTM D 7591

The production of biodiesel from vegetable oils and animal fats leads to the formation of free and bound glycerol as by-products. Incomplete transesterification and/or separation of glycerol causes glycerol contamination in the biodiesel, which speeds up fuel aging and leads to deposits in the engine and blocked filters. To ensure engines operate properly, the American ASTM D 6751 and the European EN 14214 limit the maximum total glycerol content (i.e., free and bound glycerol) to 0.24 and 0.25% (v/v), respectively. Free and bound glycerol is determined by ion chromatography and subsequent pulsed amperometric detection in accordance with ASTM D 7591.

IC – A versatile method in biofuel analysis

With its different separation mechanisms, detection types, as well as automation and sample preparation possibilities, IC is highly versatile. IC also covers the determination of carbohydrates, organic acids, chloride and sulfate, alkali metals and alkaline earth metals as well as antioxidants.


Copper in fuel ethanol

Copper catalyzes hydrocarbon oxidation

Ethanol is used increasingly in gasoline as a blending component. Contaminants can cause problems in the engine. For example, traces of copper catalyze the oxidation of hydrocarbons. As a consequence, polymer compounds can form that can lead to deposits and blockages in the fuel system. Specifications EN 15376 and ASTM D 4806 describe the minimum requirements for ethanol that is blended with gasoline and allow a copper content of 100 μg/kg. By contrast, standard ASTM D 5798 sets the copper content in ethanol-gasoline blends E75–E85 at 70 μg/L.

Using voltammetry, copper can be measured without any sample preparation in pure ethanol or ethanol-gasoline blends (E85, 85% ethanol and 15% gasoline) in the range between 2 and 500 μg/kg.


Further applications and products

Organic acids in biofuels

Cellulosic ethanol is one of the second-generation biofuels and is produced from lignocellulose-containing waste material. For an effective fermentation, the concentration profile of low-molecular-weight organic acids has to be monitored. Ion chromatography is at the leading edge of this effort.

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pHe value and electrical conductivity

pHe value and electrical conductivity are fuel specification parameters for denatured fuel ethanol. Measurement of these electrochemical sum parameters is straightforward and allows conclusions regarding the presence of corrosive ions. Measurement of the pHe value is in line with EN 15490 and ASTM D 6423. Conductivity measurement complies with DIN 51627-4.

Stainless-steel conductivity measuring cell EtOH-Trode


Testimonial: PTT Chemical Laboratory Service Center

"We are using a total of 9 Metrohm systems to determine parameters such as water content, acid number, and many more. We have been using Metrohm instruments for 20 years. Results are very good in terms of reliability and precision. Moreover, Metrohm supports us with good after sales service."

PTT Chemical Laboratory Service Center analyzes more than 200 000 biodiesel and chemical samples per year.