**1. Introduction**

Fossil fuels (petrol, coal and natural gas) are nowadays the main used energy source to move most part of overland, aquatic and air means of transportation, likewise several industries and even public lighting [1]. Petrol is the most used raw material among these energetic resources, as it is a limited energetic source there is a great concern toward substituting it, petrol shows unstable price and its unbalanced distribution has even caused wars. The global petrol reserves had reached 1,668.9 billion gallons in the end of 2012, enough to guarantee 53 years of the worldwide energy production. The dada is in the annual statistic report, 2013 edition, by BP (multinational enterprise headquartered in United Kingdom, which operates in the energetic sector, mainly petrol and natural gas) thus a reference document to the sector. According to the study, throughout the last decade, global petrol reserves have increased 26%. Other Opep countries are still top ranking, controlling worldwide petrol reserves [2].

There also is the environmental concern to restraining the current climatic changing process caused mainly by CO2, methane and nitrogen oxides. The current scientific and technological development context aims to emerge new technologies and the global goal of transiting to a sustainable economy [3].

However, Brazil, as well as other countries, is facing a severe energetic crisis due to the fuel consumption increase, either for production and for fuel consumption as for petrochemical industry. Likewise the climatic changes have caused long drought periods in months that supposedly had great quantity of rain. Each of these factors contribute to focusing efforts to establish alternative sources effectively applicable in energy production.

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One way is the use of resources produced by agribusiness [3]. This transition to sustainability was mainly determining the need or strategic interest to replace oil with other materials. Vegetable oils as alternative fuels have begun being studied in the late nineteenth by Rudolph Diesel, inventor of the internal combustion engine century, and these were used in natura. But the direct use in engines came up with many problems, for example, oily material accumulation in the injection nozzles, the incomplete oil burnt, coal deposit formation in the combustion chamber, low power efficiency and, as a result of firing, the release of acrolein (propenal) which is toxic. Studies of alternatives have been considered for best performance of vegetable oils in diesel engines, for example, dilution, micro-emulsion with methanol and ethanol, catalytic cracking and trans-esterification reaction with short alcohols chains. Among these alternatives, the trans esterification reaction has been the most used, since the process is relatively simple and the product (biodiesel) has properties similar to those of petro diesel, such as viscosity and density [4].

Biodiesel can be produced from a variety of materials. These raw materials include most vegetable oils (soybean oil, cottonseed, palm, peanut, rapeseed/canola, sunflower, safflower, coconut oil) and animal fats (tallow) and discard oil (frying oils). The raw material choice for biodiesel production depends largely on geographical factors. Depending on the origin and quality of the raw material, changes in the production process may be required [5].

One of the great advantages of using biodiesel as fuel is linked to the environmental benefits; it has some features that represent advantages over petroleum-based fuels, such as absence of aromatics and sulfur; high cetane amount; average oxygen content; higher flash point; lower pollutants emission and good lubricity. Another advantage of biodiesel is the substitution of those in diesel engines without the need for any modifications to the engine [6].

The petroleum oils are stable at distillation temperature, even in the presence of excess oxygen. Unlike vegetable oils containing unsaturated compounds, the oxidation reaction can be observed up to room temperature and the temperature close to 250 °C because of the additional thermal decomposition reactions, leading to the formation of polymeric compounds by condensation reaction [7].

Toward such facts, the current context of scientific and technological development aimed at the emergence of new technologies and feasibility of application throughout the shortest time, as well as innovations that allow the search for global goal of transition to a sustainable economy. For this purpose, a possible alternative would be to replace the fossil diesel for biodiesel production or diesel/biodiesel mixture, which allows increasing the volumes of the mixtures reservations, what is highly interesting toward biodiesel production from a variety of renewable raw materials. Regarding to such purpose the use of analysis tools physico‐ chemical behavior of biodiesel or biodiesel blends containing, enabling the acquisition of information and the establishment of values that ensure the optimal operation of engines, are desirable. Therefore, the use of thermal analysis techniques, such as Thermogravimetry/ Derivative Thermogravimetry (TG/DTG) and Differential Scanning Calorimetry (DSC) has produced excellent results, contributing to a historical development of scientific applications. Thermal analysis is an important tool for the determination of thermodynamic properties, heat capacity, phase transition temperatures, among other perfectly applicable for determining the thermal characteristics of biodiesel, as decomposition temperature/combustion degree of oxidation, temperature crystallization, a polymerization potential and others.

Along the chapter, it will be discussed data about of methyl biodiesel obtainment from soybean oil at laboratory scale and its physicochemical characterization compared to two samples produced on an industrial scale: one obtained from recycled soybean oil and other from new soybean oil and diesel/biodiesel blends in varying proportions. The physical chemical parameters established by ANP were used as reference density, kinematic viscosity, acid number and iodine, flashpoint, accelerated oxidation test (RANCIMAT), cold filter plugging point, carbon residue and water content (Karl Fischer). In order to obtaining data from thermal behavior profile of the samples of biodiesel and diesel/biodiesel blends, such as thermal stability, thermal decomposition process, crystallization temperature and residue content were applied thermoanalytical TG/DTG and DSC techniques.
