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Abstract The corrosive character of Moringa oleifera Lam biodiesel was evaluated through static immersion tests with different carbon steels (CS1015 and CS4140) in absence and presence of the antioxidant tert-butylhydroquinone (TBHQ), at room temperature in the absence of light for 84 days. Biodiesel parameters, including oxidation stability (induction period, IP), total acid number (TAN) and iron concentration released from carbon steel, were monitored. The produced biodiesel presented an IP value of 4.9 h, which was increased to 6.2 h after the addition of 500 mg kg−1 TBHQ. After 84 days of immersion, IP values decreased in the first 21 days due to the contact with the metallic coupon, while TBHQ retarded this process. TAN value increased in 20% but the values were below the recommended limits (<0.5 mg g−1 KOH according to EN14214). Iron was detected in the biodiesels exposed to CS1015 (8 μg g−1), while in the presence of TBHQ this value decreased to 5 μg g−1, indicating corrosion inhibition by TBHQ. Iron was not detected in the biodiesels exposed to CS4140, which indicated that this material was more compatible with biodiesel. Notably, the oxidation stability of Moringa biodiesel was not affected (IP > 3 h) by the high Fe content. Highlights • Static immersion corrosion test to simulate storage conditions of Moringa biodiesel. • Carbon steels of varied composition were evaluated and metal release measured. • Oxidation stability of biodiesel decreased as corrosion started. • The antioxidant TBHQ retarded the corrosion as iron release decreased. • Addition of TBHQ is required to extend storage stability of Moringa biodiesel. [ABSTRACT FROM AUTHOR]

Abstract Energy demand for modern society is ubiquitous and the liquid fuels play important role in this context. The market acceptance of liquid fuels depends on a highly rigorous quality control, which requires accurate and precise analytical methods to monitor the chemical parameters established by regulatory agencies. Fast and on-site monitoring of the quality parameters of fuels can be achieved by electrochemical techniques using disposable sensors, such as screen-printed electrodes (SPEs). This revision is devoted to recent development and application of SPEs to monitor quality parameters of liquid fuels (fossil fuels and biofuels), including the determination of organic and inorganic analytes using voltammetric or amperometric detection. Trends of SPE technology for quality control of fuels, based on the reported electrochemical methods that may be considered by regulatory agencies, are highlighted. Highlights • Screen-printed electrodes (SPE) for on-site quality control of fossil fuels and biofuels. • Voltammetric and amperometrci detection of (in) organic contaminants and additives. • Regulatory agencies define severe limits to substances that can be detected on SPE. • Substrate material and chemical modifiers selected to be compatible with liquid fuels. • Perspective on new platforms to detect adulteration and for quality control on-site. [ABSTRACT FROM AUTHOR]

This work reports the use of eucalyptus pulp as an adsorbent for metal removal from biodiesel. Fatty acid methyl esters produced from sunflower oil (SfMB) and recycled used cooking oil (RMB), which contained Fe, Mn, and Cu, were treated through filtration on a column filled with the cellulosic adsorbent, and washed with deionized water for comparison. The treatment with cellulose material resulted in the removal of 13–81%, 35–84%, and 40–74% of Fe, Mn, and Cu in biodiesels, while the water washing removed 4–40%, 10–47%, and 4–19%, respectively. In addition to the higher efficiency, the use of cellulose is a more environmentally friendly process than the purification with water, once the latter results in a considerable volume of effluent requiring treatment prior to disposal, besides the high consumption of water. Moreover, the regeneration of the cellulosic adsorbent is demonstrated. [ABSTRACT FROM AUTHOR]

This work shows that the electrochemical activity of a 3D-printed electrode fabricated using a conductive composite of polylactic acid (PLA) containing carbon black (CB) can be substantially improved through a simple and fast chemical/electrochemical pretreatment in 0.5 mol L−1 NaOH. Scanning electron microscopy and infrared spectroscopy data showed that the pretreatment process promotes the removal of the non-conductive PLA material, providing greater exposure of the conductive particles. Cyclic voltammetry of the redox probe ferricyanide/ferrocyanide indicated faster electron transfer on the treated 3D-printed surface and increase in electroactive area. Moreover, electrochemical impedance spectroscopic results also confirmed faster electron transfer after surface pretreatment. As a proof-of-concept, a low-cost and sensitive method for the determination of cadmium and lead in real urine and saliva samples by square-wave anodic stripping voltammetry was developed. The chemical/electrochemical treatment provided an impressive 30-fold current increase in the detection of both metals. Acceptable limits of detection (2.9 μg L−1 for Cd2+ and 2.6 μg L−1 for Pb2+), wide linear ranges for both metals (30 μg L−1 to 270 μg L−1; R = 0.997), high stability (RSD lower than 4.5%; n = 10), and adequate recovery values (between 93% and 112%) for the analysis of spiked samples were achieved. Additionally, interday (n = 3), intra-day (n = 3), inter-electrode (n = 2) and inter-treatment (n = 2) experiments revealed RSD values lower than 6.5%, which indicates high reproducibility of the proposed treated 3D-printed electrode. The strategy here proposed opens up new applications for 3D-printed electrode in analytical electrochemistry with improved electrochemical sensing properties in comparison to screen-printed electrodes. [ABSTRACT FROM AUTHOR]

This work investigates the oxidative stability and corrosivity of residual cooking oil (RCO) methyl biodiesel exposed to metallic coupons (copper and carbon steel) under simulated storage conditions (static immersion for 90 days within closed vessels) and the effect of antioxidants (tert-butylhydroquinone, curcumin, propylgallate, and butyl-hydroxyanisole) on biodiesel and metallic surfaces. The induction period measured during the experiment showed that all antioxidants retarded biodiesel degradation due to their antioxidant properties. Scanning-electron microscopy and X-ray diffraction of the metallic surfaces revealed the presence of oxides due to the corrosion by biodiesel in absence of antioxidants. Nevertheless, the presence of carbonaceous solids over the metallic surfaces was found which evidences the anticorrosive properties of the antioxidants, confirmed by X-Ray spectroscopy that showed increase in the content of carbon and oxygen on the surfaces. Measurements of corrosion rate also confirmed the anticorrosive action of all antioxidants. Hence, this work shows the dual properties of antioxidants acting as free radical scavengers in the RCO biodiesel as well as corrosive inhibitors, with a special performance of propylgallate, probably due to the presence of more hydroxyl groups in its structure that also may facilitate its interaction with the metallic surface. • Free radical scavenging and corrosion inhibition by antioxidants in biodiesel from residual oil. • Immersion tests using copper and carbon steel coupons prove this dual effect of antioxidants. • Higher induction period values by propyl gallate (PG) in biodiesel exposed to both metals. • PG also showed higher anti-corrosive properties in this biodiesel under simulated storage. • Protective layers of carbonaceous solids over metals were formed in biodiesel with antioxidants. [ABSTRACT FROM AUTHOR]

Highlights: [•] Biodiesels with low oxidation stability (OS) were blended with soybean biodiesel. [•] Residual cooking oil and cottonseed oil biodiesels had their OS improved. [•] Sunflower oil biodiesel had its OS improved by blending with colza oil biodiesel. [•] Binaries mixtures meet ASTM D6751 and EN 14214 requirements of OS values. [Copyright &y& Elsevier]