The intension of this article is to explain the benefits of the microwave based transesterification process. The advantages of this system can be listed as rapid heating and cooling, cost saving due to energy and time saving, effective and selective heat control opportunities and short reaction times [1–5].
Transesterification (or alcoholysis), is a chemical reaction between an oil or fat with a suitable alcohol to produce esters and glycerol. This process is composed of three consecutive reversible reactions. At first step triglyceride is converted into diglyceride, then diglyceride is converted into mono glyceride and in the last step monoglyceride is converted to fatty acid alkyl ester and glycerol [6–8].
Homogenous or heterogenous catalysts are utilized in these reaction steps . In a typical homogenous catalyst supported transesterification process, the catalyst is dissolved in the medium completely and there is no phase difference between the catalyst and the reaction mixture. On the other hand, heterogenous catalysis is carried out with a catalyst that form another phase such as solid, immiscible liquid or gaseous in the transesterification medium without passing into the same phase [10, 11]. In this case heterogenous transesterification process is attributed to be a green technology issue due to the recycling facilities of heterogenous catalysts, trace amounts of water production during the process that causes the corrosion in the parts of engine during operation and the easy phase separation of biodiesel and glycerol in the end of the reaction [12, 13]. Besides, in the homogenous catalytic transesterification, required catalyst amount is vey much, since the salts are reacting with fatty acids before alcohol they yield very high saponification numbers, in the end low quality of biodiesel and glycerol, long term process and distillation are acquired for the excess reactant removal [14–17].
A large scale of heterogeneous catalysts such as alkali metal oxides and their derivatives [18–22] alkaline earth metal oxides and their derivatives [21, 23–30], transition metal oxides and their derivatives , mixed metal oxides and their derivatives , ion exchange resin using [33, 34] or sulphated oxide acidic catalysts [35, 36], carbon based catalysts , boron group based catalysts [32, 38], waste material using catalysts , enzyme based catalysts  are in the ascendant in laboratory scale biodiesel production. In a KOH or KOH-bentonite  mixture using transesterification study the author claimed that the obtained fatty acid methyl ester (FAME) content, which defines the quality of the biodiesel, increased with the increasing amounts of bentonite proportions . Since the bentonite bares some active groups (such as SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O), it chokes the water production and can trigger the presence of catalytically active methoxides during the methanolysis process by shifting the reaction direction in hydroxide/methoxide equilibrium (Eq. (1)) towards the formation of the methoxide, leading to increased amounts of FAME.
CH3OH + OH-↔CH3O- + H2O (Eq. (1)
Sepiolite is also a good candidate for this purpose by possessing very much similar active catalytic groups such as SiO2, MgO or Al2O3 and must be used in the same manner with bentonite. Menor et al. reported that MgO presence dominates the basic structure of the bentonite and glycerol production is improved by the combination with Ni impregnation onto this support . We have also enhanced the basic capability of sep. with KOH addition into this unique structure. Additionaly, there are several catalytic studies on sepiolite such as CaO loaded sepiolite used as CO2 sorbent , acid-activated sepiolite using glycerol production study  or another report claimed that using the sepiolite as additive into the slurries during catalyst preparation revealed with positive results because of enhancing adherence .
However, there is not any study about KOH impregnated sepiolite based heterogenous catalysis based on direct biodiesel production with the combination of microwave assistance. There are several methods for the biodiesel production but the crucial point is the choice of the best system avoid to time, energy, yield and quality wasting processes. It is reported that microwave assisted system using production times are lowered up to 6 folds compared to the traditional heating processes . Here we also obtained satisfactory results after 20 min. operation times compared to the previously used 3h. heating process. On the other hand, as we take a deep look into kinetics of this catalyst it can be said that according to the transesterification reaction (Eq. 2) the limiting step is methoxide formation step. In this step the excess amount of methanol addition into the medium doesn’t effect at all the order of the reaction. So the calculations can be carried out according to 1st order reaction equation. After the optimization studies reusability and waste rapeseed oil transesterification performances of the present system was tried. This study can be evaluated as a demo of the improvable performance of the presented system, the results can be improved by the incubation of final biodiesel-glycerol mixture for phase separation.