Viscosity Analysis: A Potential Protocol to Detect Adulteration in Biodiesel

Research Article

Austin Environ Sci. 2016; 1(2): 1010.

Viscosity Analysis: A Potential Protocol to Detect Adulteration in Biodiesel

Crizel MG, Lenz V, Ritter M, Pacheco B and Pereira CMP*

Center of Chemistry, Pharmacology and Food Research, Federal University of Pelotas, Brazil

*Corresponding author: Pereira CMP, Center of Chemistry, Pharmacology and Food Research, Federal University of Pelotas, Brazil

Received: August 02, 2016; Accepted: October 04, 2016; Published: October 06, 2016


Biodiesel adulteration is normally performed seeking illicit enrichment and usually executed by adding cheaper miscible components to the fuel. In addition to harm the consumer, adulterated biodiesel not only damage car’s engine due to incomplete combustion, but also exacerbate environmental pollution by increasing pollutants emission. In concern with that, we propose an alternative protocol for monitoring bio fuel adulteration. The method hypothesized in this study aims to identify adulteration in biodiesel by detecting viscosity changes in the fuel. To understand if these changes would happen, we analyzed biodiesel viscous behaviour of four different sources, such as rice, soy, sunflower and corn oil, in four different adulterant ratios (0%, 20%, 40% and 60%). Raw soy oil was the adulterant source used in this work. We obtained an average correlation value between the proportion of adulterant and biodiesel’s viscosity of 0.9920. We concluded that the viscosity analysis has a great potential to be employed as a monitoring tool to detect adulteration in biodiesel.

Keywords: Bio combustible; Purity test; Physicochemical properties


The civilization as we know it is greatly reliant on fossil sources of energy, such as coal and petroleum. These combustible are the most used energy on earth. Energy, also, has become an important factor for continue the economic growth and maintain high standard of living especially after the industrial revolution [1]. Globally, the transportation sector is the second largest energy consuming sector after the industrial sector. The world’s road transport is currently responsible for nearly 60% of world oil demand [2].

Studies have reported biodiesel’s good impact on the environment [3,4] when the fuel is in the right conditions, however fuels are commonly adulterated. Adulteration is normally performed by adding cheaper miscible components, normally raw vegetable oil or old frying oil [5] to the fuel seeking illicit enrichment [6]. The burning of adulterated fuels cause carbon deposits, injection blocking, and incomplete combustion, due to adulterated fuel high viscosity which reduces fuel volatility and increases gum formation in engines [6].

Adulterated combustible can also result in increased fuel consumption, engine over heat, and higher pollutants emissions, such as particulate material, hydrocarbons and exhaustion gases [7]. Based on that, the Brazilian National Agency of Petroleum, Natural Gas and Bio combustibles (ANP) has developed means to improve regulations and fuel quality in Brazil. ANP has defined specific tests for fuel quality and sales standards [8]; however the tests proposed to be used routinely by the distributors are based on the samples colour and density [9].

Although the trials proposed by the regulatory agencies are based on fuel characteristics, more sophisticated techniques have been used by scientists to understand fuel properties [10]. One of them is based on elucidating the bio fuel composition. In order to comprehend biodiesel content, the fatty acid profile is an important test for biodiesel analysis. Gas Chromatography (GC) and High- Performance Liquid Chromatography (HPLC) are the most common analytical methods for elucidating fatty acids and triglycerides in samples [11,12]. Chromatographic tests are precise and well accepted; however they require specialized hand-work, sophisticated instruments and high investments.

Our group hypothesized if the viscosity analysis can be used as an analytical tool to detect adulteration in biodiesel. In this context the viscosity test would fill the gap between unreliable tests, such as colour and density, and expensive and laborious methodologies, such as GC and HPLC. In concern with that we propose an alternative protocol for bio fuel blends adulteration monitoring: a qualitative analysis based on fuel viscosity.

Materials and Methods


The heating sheets were performed under agitation by electric agitator (IKA, model C MAG-HS 7) at 75 °C, and, reflux condensers using H2O as means refrigerators utilized for sample synthesis. For the viscosity analysis was employed one viscometer (Quimis Q288SR, Brazil).

The chromatographic analysis of the profile of fatty acids of the samples were operated on gas chromatograph (GC-FID, Shimadzu QP2010, Japan) equipped with split/split less injector FID detector and capillary RTX- Wax column (30 m x 0.32 mm x 0.25 μm). The analyses were performed at the Laboratory of Chromatography and Forensic Chemistry of the Federal University of Pelotas.

Standards and chemicals

Solutions of Potassium Hydroxide 85% (KOH, Vetec, Brazil), Methanol (MeOH P.A., Vetec) and Sulfuric Acid (H2SO4, Sigma, Brazil) were the reagents and catalysers used in the transesterification. For acidity index, ether/ethanol solution (2:1 v/v), Phenolphthalein and Sodium Hydroxide (NaOH, Vetec) were employed. For saponification index Hydrochloric Acid (HCl, Proquimios, Brazil) was employed. The solution of cyclohexane (Synth, Brazil), solution of Iodine-Chlorine (Wijs, Synth), and Potassium Iodide solution (KI, Vetec) and Thiosulfate of sodium solution (Na2S2O3, Sytnh) were employed for iodine index determination.


Four samples of edible oil soy, sunflower, corn and rice from different brands were in bought in Pelotas, RS, Brazil, and employed as raw material for biodiesel obtention. The adulteration process of biodiesel was performed by adding soy edible oil in the samples.

Transesterification conditions

Biodiesel synthesis followed the chemical reaction scheme demonstrated in the Scheme 1.