Improvements in the stability of biodiesel fuels: recent progress and challenges

Abstract

Fewer fossil fuel deposits, price volatility, and environmental concerns have intensified biofuel-based studies. Saccharification, gasification, and pyrolysis are some of the potential methods of producing carbohydrate-based fuels, while lipid extraction is the preferred method of producing biodiesel and green diesel. Over the years, multiple studies have attempted to identify an ideal catalyst as well as optimize the abovementioned methods to produce higher yields at a lower cost. Therefore, this present study comprehensively examined the factors affecting biodiesel stability. Firstly, isomerization, which is typically used to reduce unsaturated fatty acid content, was found to improve oxidative stability as well as maintain and improve cold flow properties. Meanwhile, polymers, surfactants, or small molecules with low melting points were found to improve the cold flow properties of biodiesel. Meanwhile, transesterification with an enzyme could be used to remove monoacylglycerols from oil feedstock. Furthermore, combining two natural antioxidants could potentially slow lipid oxidation if stainless steel, carbon steel, or aluminum are used as biodiesel storage materials. This present review also recommends combining green diesel and biodiesel to improve stability. Furthermore, green diesel can be co-produced at oil refineries that are more selective and have a limited supply of hydrogen. Lastly, next-generation farming should be examined to avoid competing interests in food and energy as well as to improve agricultural efficiency.

Survey on Antioxidants Used as Additives to Improve Biodiesel’s Stability to Degradation through Oxidation

“…A large part of these antioxidants can be decomposed or destroyed during transesterification or refining processes [101,102]. Considering this aspect, biodiesels obtained from unrefined vegetable oils have a higher amount of natural antioxidants in their composition and, consequently, a greater stability to degradation by oxidation, but do not meet other conditions necessary to be used as fuel [103]. Phenolic compounds extracted from plants, such as tocopherols, lycopene, carotenoids, astaxanthin, canthaxanthin, zeaxanthin, caffeic acid, gallic acid, ferulic acid, vanillin, sinapic acid, p-coumaric acid, cinnamic acid, eugenol, sesamol, vanillic acid, resveratrol, etc., have antioxidant properties, and are currently widely produced and marketed.…”

“…It was found that tocopherols show antioxidant activity only if their concentration is approximately equal to their concentration in vegetable oil, and at a higher concentration, they could act as an oxidant agent [27,105]. Further, in many studies, it has been shown that tocopherols, compared to synthetic antioxidants, have a limited antioxidant effect on biodiesel fuels, being more effective for diesel than for biodiesel produced from vegetable oils or their esters [101][102][103]. In addition, tocopherols are compounds that oxidize easily in air, and they are only stable in an inert environment (in the absence of air).…”

Advanced Method for the Detection of Saturated Monoglycerides in Biodiesel Using GC-EI-MS/MS

“…The origin of FAME can be edible feedstock (1st generation), nonedible feedstock (2nd generation), algae feedstock (3rd generation), or microbial feedstock (4th generation). The FAME feedstock used is dependent on the geographical region and mainly comprises first-generation crop oils derived from palm, rapeseed/canola, soybean, corn, and sunflower; used cooking oils (UCO); and animal fats. , The primary feedstocks in Europe are rapeseed and palm oil, UCO, and minor amounts of soybean oil, sunflower oil, and animal fats . In the US, mostly soybean, corn, and canola oils are used, as well as recycled feedstocks .…”