Thermodynamic selection of effective additives to improve the cloud point of biodiesel fuels

doi:10.1016/j.fuel.2015.12.053

Fuel

Volume 171, 1 May 2016, Pages 94-100

https://doi.org/10.1016/j.fuel.2015.12.053 Get rights and content

Highlights

•
A thermodynamic model was used to screen CP improvement additives for FAMEs.
•
The molar mass of the additive had the most significant effect on the CP.
•
The selected additives lowered the CP of model FAME mixtures.
•
These additives also improved the CP of FAMEs derived from cooking oils.

Abstract

We assessed a simple thermodynamic model, with the aim of identifying biodiesel fuel cloud point (CP) improving additives, by predicting the CP values of fatty acid methyl esters with additives. The results showed that the molar mass of the additive has a significant effect in terms of improving the CP; the melting point and fusion enthalpy of the additive, however, produce lesser effects. On the basis of these results, we selected the additives tert-butyl alcohol, 2-butanol, cineol, 2-decanol, 2-decanone and oleyl alcohol, and examined their effects on the CP of a model biodiesel fuel (a methyl oleate and methyl palmitate mixture). The same trials were carried out using fatty acid methyl ester mixtures derived from commercial cooking oils. As predicted, the selected test additives decreased the sample CP values, with the optimum reduction obtained when using 10 wt.% of the additive. The results demonstrate that additives capable of improving the CP can be readily screened using a simple thermodynamic model.

Introduction

For some time now, fatty acid methyl esters (FAMEs) have received significant attention as alternative light oils and biomass fuels (also known as biodiesel fuels). In fact, the production and use of FAMEs are both increasing yearly. Recently, various edible vegetable oils and a number of inedible vegetable oils, waste oils, animal fats and algae oils have been used as the raw materials for the synthesis of FAMEs [1], [2], [3], [4], [5], [6], [7].

Among the disadvantages of biodiesel fuel made from FAMEs are the poor flow properties that result primarily from the presence of saturated FAMEs at lower temperatures. The flow properties of FAME mixtures may be improved through several means, including the use of a light oil blend, reduced-pressure distillation, winterization, and treatment with additives. Additives are often found in petroleum diesel fuels, where they are known as cold flow improvers, and they are a convenient and economical way to improve flow properties. As an example, additives derived from vegetable oils can noticeably decrease the pour point (PP) of biodiesel fuel [8], [9]. Polymeric improvers can also reduce the PP and the cold filter plugging point (CFPP) of biodiesel made from waste cooking oils [4], [10]. The use of additives, however, does not significantly decrease the crystallization temperature of the biodiesel fuel, known as the cloud point (CP).

In neat biodiesel, both the PP and CFPP are typically lower than the CP, and it has been reported, based on empirical studies, that the PP and CFPP are both functions of the CP [11]. Therefore, a prediction of the CP will allow for an estimate of the PP and CFPP values. Many studies have found that the CP of FAME mixtures may be theoretically estimated on the basis of several assumptions [11], [12], [13], [14]. According to these studies, the ideal solution of the Hildebrand equation readily provides an approximate prediction of the CP [14]. If the theoretical equation for the crystallization temperature of FAME mixtures is also applicable to FAME-additive mixture systems, the selection of CP-improving additives may be possible, based on specific additive properties.

The aim of the present study was to identify additives that effectively improve the CP values of FAMEs by using a thermodynamic model based on solid–liquid equilibrium, and to test the selected additives in conjunction with FAMEs derived from commercial cooking oils.

Section snippets

Preparation of biodiesel fuel

Methyl oleate (>60.0%) and methyl palmitate (>95.0%) were purchased from Wako Pure Chemical Industry, Ltd. (Osaka, Japan) and used without further purification. We blended the methyl oleate and methyl palmitate to prepare the FAME mixture we used as a pseudo-biodiesel fuel. In this process, the methyl palmitate was melted using a mantle heater set at approximately 333 K, after which the molten methyl palmitate and methyl oleate were quickly blended. The resulting FAME mixture was further

Confirmation of CP prediction

Fig. 1a presents a comparison between the theoretical crystallization temperature and the measured CP values of sample FAMEs. The measured CP of the FAME mixture varied with the mole fraction of methyl palmitate in a manner that precisely matched the theoretical crystallization temperatures calculated using Eq. (1). It was thus confirmed that the theoretical crystallization temperature can be applied to the prediction of CP for a pseudo-biodiesel fuel. From these data, it was estimated that

Conclusions

We used a thermodynamic model to predict crystallization temperature, based on the solid–liquid equilibrium, which, in turn, enabled us to effectively select additives that improve FAME mixture CP. The calculated results showed that the molar mass of the additive has a significant influence on CP improvement, while the effects of the melting point and fusion enthalpy of the additive are less important. All of the selected additives decreased the CP values of the FAME mixtures derived from

Acknowledgment

The authors wish to thank the Uchida Energy Science Promotion Foundation, Japan, for partly supporting this work (Grant Nos. 21-1-9, 23-1-32 and 26-1-21).

References (23)

A.E. Atabani et al.
A comprehensive review on biodiesel as an alternative energy resource and its characteristics
Renew Sustain Energy Rev
(2012)
Y. Zhang et al.
Biodiesel production from waste cooking oil: 1. Process design and technological assessment
Bioresour Technol
(2003)
J. Wang et al.
Effect of polymeric cold flow improvers on flow properties of biodiesel from waste cooking oil
Fuel
(2014)
L. Chen et al.
Biodiesel production from algae oil high in free fatty acids by two-step catalytic conversion
Bioresour Technol
(2012)
S.Y. Giraldo et al.
Comparison of glycerol ketals, glycerol acetates and branched alcohol-derived fatty esters as cold-flow improvers for palm biodiesel
Fuel
(2013)
T.Q. Chastek
Improving cold flow properties of canola-based biodiesel
Biomass Bioenergy
(2011)
H. Imahara et al.
Thermodynamic study on cloud point of diodiesel with its fatty acid composition
Fuel
(2006)
M.J. Ramos et al.
Influence of fatty acid composition of raw materials on biodiesel properties
Bioresour Technol
(2009)
P. Lv et al.
Improving the low temperature flow properties of palm oil biodiesel: addition of clod flow improver
Fuel Process Technol
(2013)
L. Cao et al.
Ethyl acetoacetate: a potential bio-based diluent for improving the cold flow properties of biodiesel from waste cooking oil
Appl Energy
(2014)

P.C. Smith et al.

Improving the low-temperature properties of biodiesel: methods and consequences

Renew Energy

(2010)

Cited by (27)

Effects of purified Ginkgo biloba L. leaf extract on the oxidative stability and cold flow properties of biodiesel-diesel blends
2024, Industrial Crops and Products
As an alternative energy source to petrochemical diesel, biodiesel has garnered considerable attention due to its green and renewable properties. Nevertheless, the inferior oxidative stability (OS) and unsatisfactory cold flow properties (CFPs) of biodiesel limited its commercial application. The objective of this study was to explored the potential of purified Ginkgo biloba L. leaf extract (GBLE) in improving the OS and CFPs of biodiesel-diesel blends (B20 and B30). The successful extraction of purified GBLE and its performance testing in the blends at the parts per million (ppm) level demonstrated its significant improvement effects. The results indicated that purified GBLE exhibited notable improvements in the OS and CFPs of both B20 and B30. In particular, 1250 ppm purified GBLE demonstrated the most substantial dual-functional improvement for both B20 and B30, increasing the induction period from 2.10 h to 10.93 h for B20, and from 1.02 h to 8.57 h for B30, meeting the EN 14112 standard. Additionally, it also decreased the cold filter plugging point of B20 and B30 by 10 °C and 7 °C, respectively, resulting in a 6 °C reduction for both pour point values. On the other hand, the conversion of discarded Ginkgo biloba L. leaves into valuable dual-functional additives has the potential to attract attention in the biodiesel industry. Hence, addition of purified GBLE appeared to be an effective and economically sustainable strategy to enhance OS and CFPs of the biodiesel-diesel blends (B20 and B30).
Improving the cold-flow properties of shea butter biodiesel by additive winterization
2024, Industrial Crops and Products
Poor cold flow is the main factor that affects biodiesel fuel utilization in cold regions during winter, owing to the high melting point of saturated fatty acids. In the present study, we produced fatty acid methyl esters from shea butter by transesterifying it with methanol. The esterification process was catalyzed by H₂SO₄. We obtained an optimum ester conversion of 99.54 wt% using 0.5 wt% H₂SO₄ and 1.2 wt% KOH. Subsequently, we applied additive winterization to improve the cold-flow properties of the obtained shea butter biodiesel using the nonionic surfactants sorbitan palmitate and sorbitan stearate. We selected cooling temperatures between the cloud point and the pour point of shea butter biodiesel, and achieved a 8–10 K reduction in the cloud point at 294 K using 0.5–1.0 wt% sorbitan stearate. Additive winterization significantly improved the low-temperature flow properties of shea butter biodiesel.
Effect of repeated heating of coconut, sunflower, and palm oils on their fatty acid profiles, biodiesel properties and performance, combustion, and emission, characteristics of a diesel engine fueled with their biodiesel blends
2022, Fuel
Using cooking oil multiple times is a common practice to reduce the food preparation cost, which causes many health issues, also simply throwing it away will cause environmental pollution. Hence, converting waste cooking oil into biodiesel is a solution to waste management with energy production. This study analyzed the effect of the number of heating cycles of coconut, sunflower, and palm oils on the fatty acid configuration and properties of biodiesel produced from them. A reduction in unsaturated compounds, increase in short-chain components, increase of 0.266%, 0.365%, and 0.347% in density, increase of 5.06%, 12.29%, and 8.83% in kinematic viscosity, increase of 0.266%, 0.365%, and 0.347% in calorific value are observed with five repeated heating of coconut, sunflower, and palm oils, respectively. Performance, combustion, and emission analysis of a diesel engine fueled with B20 blends of biodiesels showed a decrease of 0.27 %, 0.28 %, and 0.52 % in brake thermal efficiency, an increase of 2.44 J/deg, 3.43 J/deg, and 2.74 J/deg in peak heat release rate, an increase of 7 ppm, 65 ppm, and 60 ppm in NO_x emission, and decrease of 4.5 %, 2.8 %, and 1 % in smoke opacity with five repeated heating of coconut, sunflower, and palm oils, respectively. Even though the brake thermal efficiency and emissions (except NO_x) were found decreased for all biodiesel blends compared to diesel, coconut-based biodiesels were found to be the best alternative among all the biodiesels with reduced HC, NO_x, and smoke as compared to diesel.
Feasibility of additive winterization of biodiesel fuel derived from various eatable oils and fat
2021, Fuel
For simple removal of saturated fatty acid methyl esters (FAMEs) from a FAME mixture, our previous research described winterization using sorbitan palmitate without agitation. However, limited information exists on additive winterization of real oil biodiesels and their separation performance. We demonstrated the additive winterization of biodiesel fuel derived from commercial eatable oils and fat (palm, lard, cottonseed, rice, and soybean). Five biodiesel fuels were prepared through a transesterification reaction under alkali conditions. The biodiesel-additive mixtures were air-cooled over 48 h at a temperature equal to or several degrees lower than the cloud point (CP) of the biodiesel without agitation. The palm biodiesel showed a marked similarity to a simulated FAME mixture, and was separated into saturated FAME-rich solid fuel and unsaturated FAME-rich liquid fuel. The CP of the recovered liquid decreased by 6–10.5 °C, and the separation factors were between 2.4 and 7.7. The kinetic viscosity of the resultant liquid increased slightly because of the oleate fraction but was in the range of the biodiesel standard. These results indicate that additive winterization is useful for the separation and purification of biodiesel. Because the separation factor of the lard biodiesel winterization using sorbitan palmitate decreased (1.3–1.9), the separation improver retains scope for improvement under high stearate conditions. The relatively lower saturated FAME biodiesels (cottonseed, rice, and soybean) were predisposed to form a slurry during the winterization. However, the CP of the recovery liquid decreased 2–5 °C from the initial biodiesels. The separation factor and liquid recovery rate will increase with the use of a proper mechanical separation method such as filtration.
Optimization of sorbitan monooleate and γ-Al<inf>2</inf>O<inf>3</inf> nanoparticles as cold-flow improver in B30 biodiesel blend using response surface methodology (RSM)
2021, Journal of Industrial and Engineering Chemistry
The synergy of sorbitan monooleate (SMO) and γ-Al₂O₃ nanoparticles, which was prepared via ultrasonic sonochemistry, as cold-flow improvers (CFI) in B30 biodiesel blend is presented in this work. Response surface methodology (RSM) was employed to study the influence of both CFIs on biodiesel's cold-flow properties, i.e., cloud point (CP), cold-filter plugging point (CFPP), filter blocking tendency (FBT), and precipitate. Based on the result, the relationship between CFI and CP's concentration was best expressed with a quadratic model. Meanwhile, two-factor interaction (2FI) models were more suitable for CFPP, FBT, and precipitate. Based on the result, the most optimum concentration of SMO and γ-Al₂O₃ nanoparticles were achieved at 0.1% w/v and 50 ppm, respectively. At this condition, the predicted values of CP, CFPP, FBT, and precipitate of the sample were 8.52 °C, 6.056 °C, 7.208, and 564 mg/L, respectively. It is believed that SMO's surface-activity and the ability of γ-Al₂O₃ nanoparticles to form Pickering emulsion were responsible for the inhibition of excessive crystallization of saturated FAME but also enhancing their colloidal stability at low temperature.
Effect of additive structure on the performance of biodiesel fuel winterization
2021, Fuel
The effects of additive structure on the separation of saturated fatty acid methyl esters (FAMEs) from FAME mixtures by winterization were investigated. Six sorbitan derivatives, seven palmitate derivatives, and sorbitan monopalmitate, which is known to improve the low-temperature separation of FAME mixtures, were studied. A model FAME mixture was prepared by blending saturated FAME (methyl palmitate) and unsaturated FAME (methyl oleate). Sorbitan derivatives that had fatty-acid groups with the same carbon chain length as the main saturated FAME in the FAME mixture improved the separation significantly. Shorter chain lengths and unsaturated fatty acid groups did not promote the winterization of FAME mixtures because their interactions with the main saturated FAME were too weak. Cyclic structures and hydroxy (OH) groups in the ester groups of the palmitate derivatives were found to be essential for preventing crystal growth and liquid contamination of the recovered solid phase. Cyclic structures affected the appearance of the FAME mixture during winterization, and the presence of OH groups affected the separation factor and the cloud point (CP) of the recovered liquid FAME. Span40, which has palmitate and sorbitan groups, was found to be the most effective additive for mixtures containing approximately 50 wt% methyl palmitate. The CP of the recovered liquid decreased 4–9 K, and the separation factors were between 3.6 and 7.5. These results will be useful for the separation and purification of saturated rich-FAME mixture such as palm, lard, mahua, neem, and jatropha biodiesels.

View all citing articles on Scopus

View full text

Thermodynamic selection of effective additives to improve the cloud point of biodiesel fuels

Highlights

Abstract

Introduction

Section snippets

Preparation of biodiesel fuel

Confirmation of CP prediction

Conclusions

Acknowledgment

Renew Sustain Energy Rev

Bioresour Technol

Fuel

Bioresour Technol

Fuel

Biomass Bioenergy

Fuel

Bioresour Technol

Fuel Process Technol

Appl Energy

Renew Energy