Purification of Biodiesel Produced by Lipase Catalysed Transesterification by Two-Phase Systems Based on Deep Eutectic Solvents in a Microextractor: Selection of Solvents and Process Optimization

The most important and the most used process of biodiesel synthesis is transesterification. The main byproduct formed in the biodiesel synthesis by transesterification is glycerol. Biodiesel produced by transesterification is not suitable for application in engines since it contains soap (if biodiesel is produced by chemical catalysis), traces of the catalyst, methanol, metals, water, oil, and glycerides. All those impurities must be removed in order to reach the standards (ASTM D6751 and EN 14214). The most dominant industrial method for biodiesel purification is wet washing, which generates up to 10 L of wastewater per 1 L of purified biodiesel. Therefore, cheaper and more efficient solutions for biodiesel purification should be found. Deep eutectic solvents (DESs) have been already demonstrated as viable options in biodiesel purification. DESs, a mixture of two or more components with a lower melting point than each individual component, are considered less toxic to the environment, non-volatile, biodegradable, and more stable; in other words, they are economically and environmentally friendly in comparison with organic solvents. In this study, purification of biodiesel produced by lipase catalysed transesterification by DESs was performed by two-phase liquid extraction in a microextractor. A total of 13 different DESs were synthesized and used for biodiesel purification in order to find the one that provides the best glycerol extraction efficiency. After initial screening, three DESs were selected and used for the optimization of process conditions for extraction performed in a microsystem. A three-level-four-factor Box–Behnken experimental design was employed to define the optimal process conditions (biodiesel–DES mass ratio, temperature, residence time). At optimal process conditions, the glycerol content in biodiesel was reduced below 0.02% (w/w), which is the value specified by standards (ASTM D6751 and EN 14214).

Biodiesel Purification via Ultrasonic-Assisted Solvent-Aided Crystallization

Wet washing is a widely used method for biodiesel purification. However, this technique generates a large amount of wastewater that needs to be treated afterward, which is costly and time-consuming. Thus, solvent-aided crystallization (SAC) with ultrasonic irradiation as solution movement assistance was introduced. This technique is based on the addition of 1-butanol to biodiesel to enhance purification via crystallization. During crystallization, two phases are formed, where glycerol solidifies (solid phase) and pure biodiesel remains (liquid phase). Technically, the implementation of ultrasonic technology can optimize laboratory work by saving time, as no cleaning or washing of the propeller is needed. Biodiesel purity was analyzed using gas chromatography-mass spectroscopy (GC-MS), where a purity of 99% was achieved. The optimum parameters in achieving higher purity fatty acid methyl ester (FAME) were a 1-butanol concentration of 1 wt.%, a coolant temperature of 9 °C, and a crystallization time of 40 min.

Adsorption Characteristics and Potential of Olive Cake Alkali Residues for Biodiesel Purification

Mediterranean countries produce up to 97% of the total global olive production. Besides being a serious environmental burden, olive mill waste represents a potential resource of useful materials for recovery and valorization. In this work, the adsorption characteristics and potential of bioadsorbent material manufactured by alkali treatment of olive cake was evaluated. The resultant bioadsorbent was able to purify biodiesel to meets both ASTM D6751 and EN 14214 standards. Further, the sorption equilibrium was investigated at 25 °C. Langmuir, Freundlich, and Temkin isotherms fit to the experimental data were evaluated by applying the non-linear Chi-square test. Freundlich and Temkin isotherms were shown to adequately described the adsorption isotherms of the produced bioadsorbent.

Homogenous Acidic and Basic Catalysts in Biodiesel Synthesis: A Review

Several techniques, in which different homogenous catalysts and procedures, that are in use for transesterification of a vegetable oil or an animal fat have been successful in synthesizing biodiesel, although with some certain limitations. For such a purpose, among the catalysts employed are acidic as well as basic catalysts. It has been found that acidic catalysts can be tolerant with a high content of free fatty acids found in those low value feedstock oils/fats to be transesterified, although some sort of pretreatment by means of esterification might be required in order to synthesize biodiesel. Moreover, with employing homogenous acidic catalysts, it seems that biodiesel purification procedures are simplified; thus, reducing synthesis cost. In fact, these features of homogenous acidic catalysts render them advantageous over basic ones. With basic homogenous catalysts this; however, has not been possible due to the development of saponification reaction. To effectively perform, such catalysts require that the content of free fatty acids in the feedstock oil/fat is minimal. This requirement is also applicable to the moisture level in the feedstock. In terms of corrosive effects; nevertheless, acidic catalysts are disadvantageous compared to basic ones.

MODIFICATION OF NANO HYBRID PES-ZNO MEMBRANE USING UV IRRADIATION FOR BIODIESEL PURIFICATION

The purification of biodiesel is one of the crucial processes involved in biodiesel production. This study aims to examine the effect of the polymer composition, nano-ZnO loading, and UV irradiation on the performance of membranes for biodiesel purification. The membranes were fabricated with the polyethersulfone composition of 17, 18, and 20 wt%. The compositions of nano ZnO were varied at 1.5, 2, and 2.5 wt%, while the duration of UV irradiation was varied for 0.5, 1, and 1.5 minutes. The results indicate that the compositions of PES, nano ZnO, and UV irradiation affected the performance of the membrane. The best membrane performance was achieved when the membrane was produced using PES 17 wt%, nano ZnO 1.5 wt% involving irradiation UV light for 1 minute. The fabricated membrane exhibits 3 hours flux profile stability and 61.5% glycerol rejection.