Léo Ramos Chaves / Revista Pesquisa FAPESPSmall hydrogel tubes, about 5 mm long, immersed in biodiesel at the UNICAMP labLéo Ramos Chaves / Revista Pesquisa FAPESP
In the early 2010s, researchers from the School of Chemical Engineering at the University of Campinas (FEQ-UNICAMP) found that as the proportion of biodiesel mixed with fossil-originated diesel increased, technologies would be required to control the fuel’s water content, as biodiesel has a considerable affinity with water. In those days, the mix was 5% biodiesel, with a gradual increase over the following years in the plans of the Brazilian National Council for Energy Policy (CNPE). Traditional diesel is used as fuel in trucks, buses, and some cars. For the engines to function well with the diesel/biodiesel mix, the water needs to be removed from the biofuel, which is manufactured in Brazil primarily from soy or animal fat. High levels of water content, among other issues, may cause corrosion in tanks and pipes, and blocking of injection nozzles, causing problems for these vehicles.
“The first step was understanding the affinity of each biofuel with water,” recalls chemical engineer Leonardo Fregolente, a member of the team and FEQ-Unicamp professor since 2017. One of the initial studies of the group, also comprising researchers Maria Regina Wolf Maciel and Patrícia Fregolente, was published in 2012 in the Journal of Chemical and Engineering Data, and demonstrated that biodiesel is capable of carrying from 1,500 to 1,980 milligrams (mg) of water per kilogram (kg) of fuel, some 10 to 15 times more than fossil diesel, depending on temperature — the hotter it is, the more absorption. Biodiesel also has high capacity for absorbing moisture from the air: some 6.5 times more than diesel.
According to the piece in the Journal of Chemical and Engineering Data, in 10 days the fuel is saturated with water extracted from the air. However, if during or after the process the temperature drops, the capacity for retaining water will be reduced, and a part of it will separate from the fuel, accumulating in the bottom of tanks and other devices.
In early June this year professor Fregolente could not hide his satisfaction on showing Pesquisa FAPESP the result of more than a decade’s work: hollow, transparent tubelets or pellets, about 5 millimeters (mm) long, steeped in a liquid type of biodiesel. Technically known as fillers, these small hydrogel tubes can be made from synthetic polymer, known as polyacrylamide, from a group of chemical compounds that have the ability to attract water molecules.
In the laboratory, the material underwent a chemical reaction known as hydrolysis: it was treated with sodium hydroxide (NaOH) — also called caustic soda — and its water-absorbing capacity increased by almost 27 times, from 37 grams (g) of water for every gram of hydrogel to 987 g of water, as detailed in a 2023 article in Chemical Engineering Science.
The hydrogel fillers could in principle be used to reduce moisture during production, transportation, at gas stations, or directly in vehicle tanks. “Controlling the water content means you can maintain the quality of the biodiesel/diesel mix for longer,” says Fregolente, adding that the material can be used several times.
Chemical engineer Letícia Arthus, who works as a researcher, explains that the type of hydrogel used can be modulated depending on the application and dewatering requirements. “Acrylamide, the key raw material in poliacrylamide hydrogel, costs R$5 per kg, and 1 g of hydrogel absorbs up to 35 g of water,” she says. “If the hydrogel is made using sodium acrylate, which costs around R$400 per kg, its water retention capacity increases to almost 1 kg of water per gram of hydrogel.” Cost studies into the innovation, which has reached prototype stage, are ongoing, and will be important to reveal the impact of its adoption on the end cost of the fuel. The group has made five patent applications.
The national context favors innovations of this type — Brazil consumes around 700 million liters (L) of biodiesel per month. The compulsory proportion of biodiesel in diesel was set at 14% in March 2024, and may rise to 15% in 2025. The CNPE estimates that this measure will prevent the emission of 5 million tons of carbon gas (CO2) into the atmosphere, and the importation of R$7.2 billion in diesel.
Less pollution, however, means more residues in biodiesel storage tanks — being denser, the water is deposited on the bottom. In the area contiguous with the oil passage, funghi and bacteria proliferate and form a thick, dark mass, known as sludge, which can block fuel pipes, filters, and engine injection nozzles, as well as corroding the tanks. In 2021, when the minimum legal requirement was 12% biodiesel, 60% of the 710 business owners interviewed in a survey reported an increase in mechanical problems.
Biodiesel is produced from a reaction of vegetable oil with alcohol in a catalyzer, and the reaction generates glycerol, a raw material of many uses. However, the biodiesel molecules and other contaminants, such as sodium, can be combined and form a soap. The biodiesel is then washed with water and spun to remove the catalyzer, traces of alcohol, and glycerol. One of the industrial dewatering methods is to vacuum-heat the fuel through a distillation process, which is intensive in terms of energy use.
The Brazilian National Petroleum, Natural Gas, and Biofuels Agency (ANP) determines that biodiesel must leave the manufacturing plant with a maximum of 250 mg of water per 1 kg of fuel. With planned moisture absorption, the tolerance is up to 350 mg per kg in the distributor, which becomes a race against time.
“The plants produce and send the fuel out to distributors in a few days; The distributors work in the same way, and their stocks are usually sold in less than a month,” explains chemical engineer Antônio Carlos Ventilii, technical advisor to the Brazilian Association of Biofuel Producers (APROBIO). “Removing excess water from tanks at the distributors would prevent fuel not within the standard from having to undergo an industrial drying process, which is costly and involves moving biofuel around,” says Ventilii, who adds that an innovation such as hydrogel can only become a reality if its cost is lower than that of simply disposing of biodiesel outside the recommendations, and refueling trucks with diesel.
“Traditional technologies used in dewatering, which is an issue for all types of fuel, face technical and economic limitations,” observes chemist Fauze Ahmad Aouada, of São Paulo State University (UNESP), who works with hydrogels and natural hybrid nanocompounds for use in the farming and healthcare sectors. He sees one of the main advantages of the hydrogel from UNICAMP as dewatering in a relatively short time, using a low-cost, reusable material.
Projects
1. Development of hydrogel beds grafted with cellulose nanomaterials obtained by additive manufacturing for separation in biodiesel and diesel (nº 21/08438-1); Grant Mechanism Fellowship in Brazil ‒ Direct Doctorate; Supervisor Leonardo Vasconcelos Fregolente (UNICAMP); Beneficiary Letícia Arthus; Investment R$182,369.52.
2. Development of new water separation processes for biodiesel and biodiesel/diesel mixture using synthetic hydrogels grafted with cellulose nanocrystals (nº 21/03472-7); Grant Mechanism Research Grant ‒ BIOEN Program; Principal Investigator Leonardo Vasconcelos Fregolente (UNICAMP); Investment R$206,224.80.
Scientific articles
ARTHUS, L. et al. Facile tuning of hydrogel properties for efficient water removal from biodiesel: An assessment of alkaline hydrolysis and drying techniques. Chemical Engineering Science, vol. 282, 119224. dec. 5, 2023.
FREGOLENTE, P. et al. Water content in biodiesel, diesel, and biodiesel-diesel blends. Journal of Chemical and Engineering Data. vol. 57, pp. 1817–21. may 17, 2012.
