Bioethanol from wheat straw hydrolysate solubility and stability in waste cooking oil biodiesel/diesel and gasoline fuel at different blends ratio
Biotechnology for Biofuels and Bioproducts volume 16, Article number: 15 (2023)
The work focuses on studying the solubility and stability of dissolved bioethanol as a fuel additive in different fuel blends of gasoline, diesel, 50% diesel/50% biodiesel. Dissolved ethanol fuel appears as particles with a unique size distribution inside the whole fuel blends, and its stability was measured in this work. Bioethanol dissolved fuel particles stability was improved after blending the bioethanol with 50% diesel/50% biodiesel than pure diesel or pure gasoline fuel alone. The obtained results reveal that the lowest bioethanol particles stability was obtained when commixed with gasoline and the suspended ethanol particles completely accumulated at different concentrations of bioethanol in the fuel blends of 2%, 4%, 6%, 8%, 10%, and 12% by volume after 1 h of mixing time. Furthermore, the measured data of the bioethanol particles size distribution reveals that the suspended stability in the diesel blend improve slightly for all bioethanol concentrations of 10%, 15%, 20%, 25%, and 30% by volume. While the bioethanol concentrations of 5% show acceptable particles stability and size distribution during the whole experiments time. Obtained results show that bioethanol suspended particles stability was enhanced for 50% diesel/50% biodiesel blend with different bioethanol concentrations of 5%, 10%, 15%, 20%, 25%, and 30% by volume basis. However, the size of the particles increased as the bioethanol concentration rose with the passage of time.
During the last period time, the majority of the researchers for the new resources of renewable fuels were seeking to enhance the combustion behaviors and reduce the pollutant emission by substituting lower alcohols with conventional fuels . The proposed technique of replacing the lower alcohols was considered a new solution because of the expected advantages gained, such as the economical and technological issues . The replacing the lower alcohols with diesel and diesel/biodiesel blended fuel has attracted not a few researchers to improve internal combustion engine efficiency . However, the obtained results reveal that by increasing the n-pentane as a lower alcohol additive with different volume percentages in the diesel/biodiesel fuel blends, the efficiency has improved significantly.
Air pollution and the threat of fossil fuel depletion have increased interest in seeking ecologically friendly and sustainable alternative energy sources. The production of biodiesel from an oil mixture of soybean and sunflower has been optimized and utilized as a new alternative fuel resource in the diesel engine. The results show a dramatic enhancement in engine thermal efficiency and the tailpipe exhausts. As a renewable energy source, bioethanol is one of the most widely used alternative fuels in many countries to reduce total dependency on fossil fuels . Bioethanol has a key role in reducing crude oil use. Ethanol's high oxygen content helps to improve fuel blend combustion, resulting in lower hazardous exhaust emissions compared to gasoline and diesel, supporting a cleaner environment in the future .
Also, the effect of adding 10% and 20% by volume of bioethanol as an lower alcohol additives to a mixture of WCO biodiesel/diesel#1 on internal combustion engine performance and emissions have been investigated . The obtained results elucidated that the engine NOx has reduced, while the engine brake power is dramatically increased. The authors claimed that the bioethanol additives have a pivotal role in enhancing the spray and fuel droplets distribution inside the engine combustion chamber . The main objective of adding lower alcohol such as ethanol was to enhance the phenomenon known as the “micro-explosion,” which was responsible for increasing the fuel spray behaviors during the combustion process. However, ethanol (C2H3OH) is the most famous liquid and lower alcohol fuel additives which has OH radicals and two carbon molecules with a relatively high boiling point. Methanol has been financially used to extend the combustion phasing because of its higher heating power and its capacity to combust with low smoke emissions. It has specific properties, for example, higher ignition delay and more modest cetane number, which jumbles the immediate double-dealing of methanol in CI motors . The ethanol and gasoline fuel blends with different percentages have been investigated to elucidate the phase stability . In this work, different ethanol blends of 5%, 10%, 15%, and 20% havebeen applied. The results elucidated that the phase stability of ethanol in the mixture can enhance using Cyclohexanol as a stabilizing agent.
Bioethanol is typically made by fermenting sugars derived from molasses and fruits. It is also made from starchy ingredients, including grains, corn, and wheat. Currently, lignocellulosic biomass and other sucrose-containing materials are utilized as cost-effective ethanol feedstocks . There are varieties of reasons why virtually dry ethanol must be blended into gasoline. Phase separation is one of the most important issues that might arise in the formulation of ethanol fuel, especially in cold climates with high ambient humidity. The hygroscopicity of ethanol can cause a phase separation . Because of the separated corrosive mixture of ethanol and water, this problem can result in a decline in the quality of the fuel formulation, as well as corrosion of engine parts and storage tanks . Some co-solvents and surfactants were explored for stabilizing hydrous ethanol–gasoline formulations and demonstrated a substantial efficiency in the phase stability of these blends . The stability of the emulsion is significantly influenced by the concentration of the surfactants . The amount of ethanol can also alter how stable an emulsion is. Low ethanol concentrations can improve emulsion stability by reducing oil droplet size as a result of a lower interfacial tension [14, 15]. Nevertheless, excessive ethanol content alters the solubility of surfactants and results in emulsion instability [13, 16] found that raising the emulsifier concentration to up to 10% of the total volume decreases the emulsion’s droplet size and improves the stability of the emulsified gasoline. In the literature, emulsifiers or co-solvents are necessary to have been studied to stabilize bioethanol inside fuel blends . Biodiesel (FAME) has received a lot of attention among possible co-solvents because of its full miscibility with both diesel fuel and ethanol, as well as its renewable nature .
Due to its excellent thermal efficiency and low emissions, the dual or multi-fuel components combustion mode has received a great deal of attention. Form this point; the blended fuel homogeny and its satiability have a major effect on the combustion efficiency. In conclusion, this work demonstrates that a key element in enhancing combustion qualities is the stability and solubility of bioethanol in “gasoline, diesel, 50% diesel/50% biodiesel” blends. This examination is based on optical and microscopic observation of droplet size distribution. After combining bioethanol with 50% diesel and 50% biodiesel, the fuel particles remain stable.
Novelty of the present study
The main problem of using multifuel components in an internal combustion engine is the homogeneity and stability of the blended fuel. As stated in the above introduction, biodiesel fuel has been used as a new renewable energy source instead of gasoil fuel with different portions. However, according to the author’s knowledge, there is no available data in the literature concerning the distribution of the blended fuel in the main gasoil fuel. In this context, the novelty of the present study is investigating the distribution of dissolved fuel additives such as bioethanol and their stability with time. Therefore, the stability and solubility of bioethanol inside fuel blends is an important new technology for studying the particles distribution of dissolved bioethanol also statistical analysis for these particles. This work represents a contribution to the scientific literature by improving bioethanol particles stability and their distribution through three tested blends: “gasoline, diesel, 50% diesel/50% biodiesel”. The solubility and stability of dissolved bioethanol as a fuel additive in different fuel blends of gasoline, diesel, 50% diesel/50% biodiesel will be investigated experimentally. Dissolved ethanol fuel particles size distribution inside the whole fuel blends and their stability were measured in this work using microscopic photos. Bioethanol dissolved fuel particles stability after blending the bioethanol with 50% diesel/50% biodiesel, diesel, and pure gasoline fuel alone will be studied.
Materials and methods
Bioethanol employed in this study was obtained from the fermentation of wheat straw hydrolysate using Aspergillus niger strain MZ062603 . Biodiesel was produced from restaurant waste cooking oil [6, 20, 21]. The elucidated results of the transesterification process have been optimized by investigating the effect of biodiesel production parameters such as methanol to oil ratio, NaOH concentration, reaction time, and all other parameters on biodiesel yield. In addition, the effect of using biodiesel with different blends dose with gasoil on the diesel engine performance and emissions characteristics have been applied [22, 23].
In the present study, the three fuel blends have been prepared. The gasoline fuel, diesel fuel, and 50% diesel/50% biodiesel fuel blends were added to different concentrations of produced bioethanol as follows: gasoline blend was prepared by mixing the 2%, 4%, 6%, 8%, 10%, and 12% v/v of bioethanol well with gasoline. In addition,the diesel blend was prepared by mixing well 5%, 10%, 15%, 20%, 25%, and 30% v/v of produced bioethanol with diesel. Finally, 50%diesel/50% biodiesel blend was prepared by blending well the 5%, 10%, 15%, 20%, 25%, and 30% v/v of obtained bioethanol with 50%diesel/50% biodiesel. The two-dimensional surface model has used to evaluate the blended fuel density as mentioned by Mert Gülüm and Atilla Bilgin [24, 25]. The obtained results demonstrated the values of the density of different fuel blend ratio at different temperatures rages of 278.15–368.15 K at the standards condition.
Emulsion stability evaluation
After that, bioethanol stability in three blends was checked every 10 min for 1 h. The stability percentage of bioethanol in three blends is explained in Fig. 1 and was calculated according to the following equation:
Image analysis and quantitative droplet analysis
To show fuel particles structure, all homogenized prepared samples were examined using a microscope (Leica Microsystems GmbH, Mannheim, Germany) . No. of particles, average droplet size, and their distribution were measured and calculated using ImageJ software as . First, the image can be opened using ImageJ software and analyzed by setting a scale (µm) on it. After that, the scale was cropped from the image, typed 8-bit, and adjusted by choosing Threshold. Then, particles were analyzed to determine No. of particles, average droplet size, and their distribution, Figs. (11, 12, 13, 14). Finally, droplet size distribution data was obtained from ImageJ software used for drawing histograms using Grapher software . Some physical and chemical properties of produced bioethanol, biodiesel, and commercial diesel are listed in Table 1, as stated by .
Results and discussion
Fuel blends stability
One of the main goals of applying fuel blends in engines is to keep engine modifications to a minimum, which necessitates blend stability and the formation of a single-phase liquid system . Bioethanol stability in three different blends, “gasoline, diesel, and 50% biodiesel/50% bioethanol” is illustrated in Figs. 5, 6, 7 and Figs. 2, 3, 4. The obtained results showed that 50%biodiesel/50%bioethanol blend recorded the highest stability among other blends, and the lowest stability was recorded by the gasoline blend, followed by thediesel blend. After the first 10 min of mixing, concentrations of 8%, 10%, and 12% bioethanol by volume were separated from the gasoline blend, and the separation continued until complete separation was achieved after 1 h in all concentrations, as presented in Fig. 5. The obtained results revealed that the gasoline/bioethanol blends stability was very poor, although there are studies that used bioethanol blended with gasoline at a ratio of 10% and 20% . This may have occurred under other conditions, such as adding additives to improve the blend’s stability or surfactants to lower the surface tension for ease of solubility or using an ultrasound-based mixing . In our case, the prepared blend was separated into two layers after 10 min. For this reason, commercial diesel was selected to study its stability with prepared fuel.
In the diesel blend, all bioethanol concentrations were separated, and their stability in diesel was poor except for a concentration of 5%, which remained homogeneous with diesel even after 1 h of mixing, as shown in Fig. 6. In addition, results showed that the stability of diesel/bioethanol blends was better than the previous blend. However, because bioethanol and diesel fuels are not miscible, only a tiny amount of ethanol is allowed in the blending procedure for optimal results (less than 5%) , as shown in Fig. 5.
To overcome this problem, a surfactant or emulsifier should be employed to prevent bioethanol separation from diesel fuel and to enhance its amount . Emulsifiers are materials that accumulate at the phase interface to reduce interfacial tension. Emulsifiers lower the energy needed to break dispersed phase in emulsion into droplets and stop them from collecting by creating a physical barrier or an attractive force between them . Fatty Acid Methyl Esters (FAME) could also be employed as a surface-active compound to stabilize ethanol and Diesel mixtures . Indeed, biodiesel prepared in the laboratory was blended with bioethanol and diesel, improving the stability as indicated by the previous studies. Concentrations (20%, 25%, and 30%) of bioethanol were separated from the 50%biodiesel/50%bioethanol blend, whereas the concentration of 15% showed a slight separation after 30 min, and the concentrations of 5% and 10% remained well homogenous with the blend (50% Diesel/50% biodiesel) even after 1 h, as shown in Fig. 7.
Droplet microstructure and phenomenological distribution
Droplet size distribution of three different blends, “gasoline, diesel and 50% biodiesel/50% bioethanol” is illustrated in Figs. 8, 9, and 10. The obtained result showed that there is a direct relation between Droplet size distribution and concentration of bioethanol inside the blend as time pass, this may be owing to the sudden expansion of particle size caused by the excess of bioethanol inside the blend . From the perspective of the ethanol/water ratio as a hyperparameter for emulsion stability, this parameter can have a variety of effects, including the effects on surface activity indicated above as well as potential effects on the angle of contact between the polar phase and oil . Previous studies suggested that while zein alone cannot stabilize oil-in-water emulsions, zein particles modified to be more hydrophilic do so . In the gasoline blend, the results in Fig. 8 revealed that droplet size ranged from (9.1 µm) to (46.5 µm) using 2% bioethanol after 15 min and 12% bioethanol after 60 min, respectively. While the obtained results in Fig. 9 showed that utilizing 5% bioethanol after 15 min and 30% bioethanol after 60 min resulted in droplet sizes ranging from (4.8 µm) to (82.8 µm), respectively, in the Diesel blend. In 50% Diesel/50% Biodiesel blend, droplet size was ranged from (2.5 µm) to (78.4 µm) using 5% bioethanol after 15 min and 30% bioethanol after 60 min, respectively (Fig. 10).
In this study, when blending bioethanol with gasoline and diesel blends, their distribution was not uniform throughout the blend, and the maximum value of particle size was achieved. The particle size recorded the smallest value (2.5 µm) at 5% bioethanol after 15 min, and this value increased by increasing bioethanol concentration as time passed. In contrast, when bioethanol was mixed with a blend of 50% diesel and 50% biodiesel, particle distribution became uniform. This agrees with , who showed that the amount of ethanol could also alter how stable an emulsion is. Low ethanol concentrations can make emulsions more stable by reducing the size of the oil droplets as a result of reduced interfacial tension, whereas high ethanol concentrations alter the solubility of surfactants and can make an emulsion unstable . In addition,  indicated that the region of stability of emulsions, in particular, was restricted to ethanol concentrations below 30%, where the emulsion displayed low viscosity and a monomodal droplet size distribution.
Ten % bioethanol for three different blends “Gasoline, Diesel and 50% Diesel/50% Biodiesel” after (30, 45 and 60 min) is illustrated in Figs. 11, 12, and 13 that contain pictures, no of particle, average size, and histogram for each measured sample. As time pass, the average size was increased inside each tested blend. Maximum average size was recorded using gasoline blend followed by Diesel and 50% Diesel/50% Biodiesel, as shown in Figs. 11, 12, and 13.
Results in Fig. 14 show that by increasing bioethanol concentration inside 50% Diesel/50% Biodiesel blend, the average size also increases. The average size for 10% bioethanol was 19.8 µm followed by 32 µm for 20% bioethanol and 78.4 µm for 30% bioethanol. Another study shows that the elevated ethanol dose percentage of 50–90% (based on permanent period of time) and enlarge in common droplet sizes are attend by an enlarge in the span of the droplet size distribution, where phase separation is limited . However, creating the oil in the ethanol/water emulsions favors the supplementary oil drop infringement up further and becoming dispersed in the continuous water/ethanol phase. This is seen as a depression of phase inversion for emulsions produced by the gradual addition of oil compared to other studies’ direct emulsification of two volumes of oil and water . As a result, the water/ethanol mixture will be in a continuous phase.
This study revealed that the fuel particles stability and their distribution through blend were improved after using 50% diesel/50% biodiesel blend than pure diesel and gasoline. The most significant outcome of this research is that 5% and 10% bioethanol in 50% diesel/50% biodiesel blend were acceptable to be applied inside diesel engines. The size of bioethanol particles suspended through fuel blend, depending on the type of blend, the concentration of bioethanol mixed with the blend, and the time after mixing was detected by image analysis. The highest value of particle size was achieved when ethanol was mixed with gasoline and diesel blends, and their distribution was non-uniform throughout the blend. When bioethanol was mixed with 50% diesel/50% biodiesel blend, the distribution of particles became uniform, and particle size recorded the smallest value (2.5 µm) at 5% bioethanol after 15 min and this value increased by increasing bioethanol concentration as time pass.
Availability of data and materials
All data and materials are supplied in the manuscript.
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El-Sheekh, M.M., El-Nagar, A.A., ElKelawy, M. et al. Bioethanol from wheat straw hydrolysate solubility and stability in waste cooking oil biodiesel/diesel and gasoline fuel at different blends ratio. Biotechnol Biofuels 16, 15 (2023). https://doi.org/10.1186/s13068-023-02264-9