Cold flow properties of fuel mixtures containing biodiesel derived from animal fatty waste

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Kiril Kazanceva Violeta Makarevicienea Valdas Paulauskasb Prutenis Janulisa

aLaboratory of Chemical and Biochemical Research for Environmental Technology, Institute of Environment, Lithuanian University of Agriculture, Kaunas, Lithuania bDepartment of Chemistry, Institute of Environment, Lithuanian University of Agriculture, Kaunas, Lithuania

Cold flow properties of fuel mixtures containing

biodiesel derived from animal fatty waste

The aims of the present study were to evaluate the cold temperature behavior of methyl esters of vegetable and animal origin and of their mixtures with fossil diesel fuel, as well as to investigate the effectiveness of different depressants. Various blends of rapeseed oil methyl esters, linseed oil methyl esters, pork lard methyl esters and fossil diesel fuel were prepared, and both cloud point and cold filter plugging point (CFPP) were ana-lyzed. It was found that mixtures with CFPP values of –57C and lower may contain up to 25% of pork lard methyl esters; whereas the ratio of summer fossil diesel fuel and rapeseed oil methyl esters may vary over a wide range, i.e. such mixtures can be used in a diesel engine in the summer. In the transitory periods it is possible to use up to 20% animal and vegetable ester blends (3 : 7) with winter fossil diesel, whereas only up to 5% of esters can be added to the fuel used in winter. In order to improve the cold properties of rapeseed oil, pork lard and linseed oil methyl ester mixtures, various additives were tested. Depressant Viscoplex 10–35 with an optimal dose of 5000 mg/ kg was found to be the most effective.

Keywords: Biodiesel fuel, cloud point, cold filter plugging point, depressants.

1 Introduction

Biodiesel fuel, which is being used more and more often for motor transport, decreases environmental pollution with greenhouse gas, thereby allowing renewable energy resources to be used rationally. The fatty acid methyl esters (FAME) used for diesel engines are usually pro-duced from vegetable oil (rapeseed in the European countries, and soybean in the USA) [1, 2]. However, the cost of the raw materials, as well as the biodiesel fuel made from them, is quite high, and the resources are lim-ited. Recently, interest has been drawn to using other fatty materials for the production of biodiesel fuel. In some countries, the possibility of using technical oil and oils unsuitable for food are being analyzed [3, 4]; never-theless, the perspectives of fats of animal origin (pork lard and beef tallow) or their wastes are also quite good. This results from the environmental policy executed in many countries, a policy that is related to the sound handling and utilization of waste materials. For example, the EU states are encouraged to use the waste of animal origin for technical purposes, production of energy included. This purpose may serve not just the waste from the meat

processing industry, but also the appropriately processed fatty waste of sick or dead animals. Processing methods of such wastes are provided in the following EU docu-ments: regulation 1774/2005 [5] and document SANCO/ 2153/2003 [6].

The BSE crisis has created favorable conditions for using these wastes for technical purposes, since animal fats are forbidden to be used in the production of forage; it is therefore necessary to explore the possibilities of utilizing these waste products rationally.

Scientists have researched the processing of animal fats to FAME, analyzing technologies of waste preparation, the optimal conditions for processes of esterification and transesterification [7–9], and evaluating the character-istics of esters [10]; engine emissions were also studied working with a mixture of tallow FAME with fossil diesel fuel. FAME of animal origin were determined to exhibit certain negative features that prevent their direct use in the engine. One drawback is their low oxidation stability, which, however, may be increased when methyl esters of animal origin are mixed with methyl esters of vegetable origin, the latter of which exhibit higher oxidation stability, and by certain additives, i.e. antioxidants [11].

Another negative feature of FAME of animal origin is their high crystallization temperature. This feature is due to the fact that methyl esters of animal origin contain less unsa-turated fatty acids, the methyl esters of which are char-acterized by a lower crystallization temperature than their Correspondence: Violeta Makareviciene, Laboratory of

Chemi-cal and BiochemiChemi-cal Research for Environmental Technology, Institute of Environment, Lithuanian University of Agriculture, Akademija, LT-53361, Studentu str. 11, Kaunas, Lithuania. Phone: 1370 7 52292, Fax:1370 7 52292, e-mail: agrotech@ lzuu.lt

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vegetable counterparts. In order to evaluate the cold temperature properties of fuel, several methods are applied. The two qualitative indices that are indicated in the standard for fossil diesel fuel EN 590 “Automotive fuels – Diesel – Requirements and test methods” are related to cold temperature properties: cloud point (CP) and cold filter plugging point (CFPP). The CP indicates the temperature at which small wax crystals (approx. 0.5 mm) are formed in the fossil diesel fuel. In the case of biodiesel fuel, the CP indicates the beginning of the crystallization of FAME of saturated fatty acids of high crystallization temperature. A more important index is related to the use of fuel in the engine, i.e. the CFPP – which is the temper-ature at which a fuel jams the filter due to the formation of agglomerates of crystals. In the standard of biodiesel fuel EN 14214 “Automotive fuels – Fatty acid methyl esters (FAME) for diesel engines – Requirements and test meth-ods” only the second index is indicated.

In order to decrease the CP and CFPP values of biodiesel fuel, various methods are applied: by mixing with fossil diesel fuel, by elimination of methyl esters of saturated fatty acids with high crystallization temperature through chemical combinations into stable solid compounds, or by winterization (process using solvent) or dry fractiona-tion (without solvent). However, according to some authors [12], there is no reason to eliminate saturated methyl esters from biodiesel fuel, since it possesses bet-ter properties related to ignition quality and calorific value.

In addition to the above-mentioned methods to improve the cold temperature properties of fuel, the use of certain additives, namely depressants, is recommended. Therefore, the purpose of this work was to evaluate the cold flow properties of methyl esters of vegetable and animal origin and their mixtures with fossil diesel fuel, and to analyze the effectiveness of additives in improving these properties.

2 Materials and methods

2.1 Materials

Edible-grade refined rapeseed oil and pork lard for the production of FAME were purchased from the market and stored at 47C.

Rapeseed oil methyl esters (RME), pork lard methyl esters (PME) and linseed oil methyl esters (LME) were prepared following a standard two-step transesterification proce-dure by methanol using sodium hydroxide as the catalyst [13, 14]. All the above-mentioned biodiesel samples were analyzed according to the requirements of European standard EN 14214, to check their quality.

The physical and chemical parameters of pure FAME are given in Tab. 1.

Tab. 1. Physical and chemical parameters of the investigated FAME.

RME LME PME

Ester content [wt-%] 98.5 97.7 96.9

Density at 157C [kg/m3] 870 890 877 (257C)

Viscosity at 407C [mm2/s] 3.5 3.9 4.9

Flash point [7C] 159 175 163

Sulfur content [mg/kg] 6.0 5.0 6.0

Carbon residue (on 10% distillation residue) [wt-%] 0.06 0.15 1.3

Cetane number 60 54 64

CFPP [7C] 25 27 118

Sulfated ash content [wt-%] 0.15 0.02 0.02

Water content [mg/kg] 200 300 400

Total contamination [mg/kg] 18 20 22

Oxidation stability, 1107C [h] 6.5 0.6 0.5

Acid value [mg KOH/g] 0.2 0.3 0.3

Iodine value [g I2/100 g] 118 198 56

Composition of FAME saturated FAME [wt-%] 4.7 4.4 40.7

monounsaturated FAME [wt-%] 61.2 25.1 52.0

polyunsaturated FAME [wt-%] 34.1 70.5 7.3

Methanol content [wt-%] 0.1 0.1 0.15

Free glycerol [wt-%] 0.01 0.01 0.02

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Prepared samples were stored in closed bottles, in the dark, at 18627C.

The quality of the fossil diesel fuel (D) met the require-ments of European Norm EN 590.

The following depressants were used as additives for the improvement of biofuel cold flow properties: Wintron XC-30 (Biofuel Systems, UK); Viscoplex 10–35 (ROHM GmbH, Germany); Chimec 6635 (Chimec SpA, Italy); Clarinat Sosi Flow (Clariant (Norge) AS, Norway); Infineum R-442 (Infineum, UK); Grotamar 71 (Yachticon, Germany).

2.2 Methods

Mixtures were prepared by mixing fossil diesel fuel, RME, LME and PME together in applicable amounts.

For the assessment of cold temperature properties of fuel, two parameters were chosen: CP and CFPP. CP tests were done in a PROLINE RP-845 thermostatic bath (LAUDA, Germany). CP were determined under iso-thermal conditions (the temperature was lowered in two-degree increments) according to the requirements of EN 23015 [15].

The CFPP tests were carried out in accordance with the requirements of standard EN 116 [16]. The volume of each sample was 45 mL. The temperature was lowered in one-degree increments until the liquid was unable to pass through the filter in the due time. The results obtained are presented in phase equilibrium diagrams using classical methods. The points in the phase equilibrium diagrams show the mixture composition that satisfies the required CFPP and CP values (20, 10, 5, 0 and –57C). Isotherms corresponding to the above-mentioned fixed tempera-tures were drawn by joining these points together. All experiments were carried out in two series and the arithmetic mean of the two determinations was taken as the final result. If standard repeatability requirements were not met, results were disregarded and two new determi-nations on test portions taken from the same test sample were carried out.

3 Results and discussion

Fats of animal origin are rich in saturated fatty acids, the methyl esters of which crystallize at rather high tempera-tures; their use for the production of biodiesel fuel is thus limited. However, there are several methods to decrease the crystallization temperature of FAME, including: . dry fractionation;

. winterization;

. mixing with fossil diesel fuel;

. mixing with vegetable oil methyl esters (rapeseed, lin-seed), which are characterized by low crystallization temperature;

. addition of depressants, used for FAME.

The first two approaches are the most effective, but they require much investment and high energy input. Besides, there is no market for individual saturated FAME. There-fore, the other alternatives mentioned above were exam-ined, starting with the analysis of PME mixtures with fossil diesel fuel and RME.

The EU applies two standards for diesel fuel: EN 590 for fossil diesel fuel (it allows addition of up to 5% of FAME) and EN 14214 for pure FAME. When the national standard for new FAME or their mixtures with fossil diesel fuel is prepared, these standard requirements should be met. To investigate the possible use of methyl esters of animal origin in diesel engine, we first evaluated the dependence of the CP of PME mixtures with summer fossil diesel fuel (D) and RME on the composition of the mixture. Fig. 1 shows the isotherms of the CP of the D-RME-PME sys-tem at 20, 10, 5, 0 and257C.

As previously mentioned, there is another index indicated in standard EN 590 that is related to the cold temperature properties of fuel – CFPP. The fuels used in temperate climate zones are divided into classes, the CFPP values of which vary from15 to2207C; in contrast, the CFPP values of fuel used in arctic and severe winter climate

Fig. 1. Isotherms of CP of the D-RME-PME system at 1–20, 2–10, 3–5, 4–0 and 5–(25)7C.

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zones vary from 220 to2447C. The requirements are thus variable by country, depending on climatic condi-tions. In Lithuania, in the transitory periods, the CFPP of the fuel used cannot be higher than2157C, while this value should be lower than257C in summer and2327C in winter.

The CP value indicated in EN 590 for fossil diesel fuel is different from the CFPP value by 107C. However, some authors indicate small differences between CP and CFPP values of fossil diesel fuel, e.g. 2157C and 2187C, respectively [17]. Small differences are characteristic for some FAME as well – the indicators for sunflower, soy-bean and tallow methyl esters are21 and237C, 0 and 227C,114 and1137C, respectively.

Bearing in mind that the CP method of analysis is simpler and that it could possibly be applied instead of CFPP analysis, a comparative analysis of CFPP and CP was made of the same system, D-RME-PME. The results of the CFPP analysis are presented in Fig. 2.

The larger the PME concentration in the mixtures, the higher are the CP and CFPP values (Figs. 1 and 2). The higher amount of fossil diesel fuel (D) positively affects the cold temperature properties of the mixture. When the concentration of fossil diesel is increased, it is possible to make mixtures with a higher amount of PME. The 5th iso-therm presented in Fig. 2 on the right hand cuts off the zone behind which there is an outer sphere with a larger amount of RME and corresponding to the composition of mixtures the CFPP of which is 257C or lower; i.e. the mixtures of such composition may be used in diesel

Fig. 2. Isotherms of CFPP of the D-RME-PME system at 1–20, 2–10, 3–5, 4–0 and 5–(25)7C.

engines in summer without any additives. When summer diesel (EN 590 C class) is mixed with PME and RME, a wide range of proportions of biological components may be encountered; it may reach even a 1 : 1 ratio; however, this is only possible when the total amount of FAME in fossil diesel fuel does not exceed 30%. When the amount of PME in mixtures decreases, this range gets wider; when the proportion of RME/PME becomes 7 : 3, the standard requirements for the CFPP value (257C) are not met just by such three-component mixtures that contain 10% or less of fossil diesel fuel (Fig. 2).

The area on the left of the triangle that is cut off by the isotherms is quite small as it matches the mixtures that contain more PME than RME. The area cut off by the iso-therm of the lowest temperature (257C) matches the mixtures that have up to 15% PME and up to 3% of RME. Yet the total amount of fuel of biological origin in the mix-tures that matches the above-mentioned area is quite small.

According to the results, blend ratios giving comparable CP and CFPP values are quite different from one another, especially at low temperature (257C) (Figs. 1 and 2, iso-therm 5); it is thus possible to conclude that measurement of CP is not acceptable, even for the preliminary analysis. Further experiments with winter fossil diesel mixtures were thus carried out only to address CFPP.

It is advisable to use winter fossil diesel fuel for the pro-duction of mixtures of winter biofuel. In order to assess the influence of fossil diesel fuel on CFPP of mixtures and to compare it with pure fossil diesel fuel, we chose a mixture of RME and PME in the proportion 7 : 3 (hereafter called FAME), the CFPP of which was237C. FAME was mixed with winter (CFPP 2387C) and summer (CFPP 277C) fossil diesel fuel in various proportions, and the CFPP of the mixture was then assessed.

It is evident (Tab. 2) that the CFPP of 10–60% FAME mix-tures with summer fossil diesel fuel is lower than that of pure FAME or pure fossil diesel fuel. When winter diesel was used, the CFPP depended on the amount of fossil diesel fuel. After addition of 20% or less of the investi-gated FAME, the CFPP of the mixture was less than 2237C. The temperature in Lithuania rarely falls lower. It is thus possible to add FAME up to 5% in fossil diesel fuel, as it is provided in the standard EN 590. CFPP of such mixtures with winter fossil diesel fuel reached2327C. Another way to improve the cold temperature properties of biofuel is to use special additives (depressants), fitted for FAME. Previous research evaluated the dependence of the CFPP of RME (CFPP257C) on the type and quan-tity of commercially available depressants: Wintron

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Tab. 2. CFPP of mixtures of winter and summer diesel fuel with FAME.

Mixture composition Mixture CFPP [7C] D [%] (summer or winter) FAME [%] (RME/ PME 7 : 3) Summer D Winter D 0 100 23 23 10 90 26 24 20 80 26 25 30 70 27 29 40 60 28 210 50 50 29 212 60 40 211 213 70 30 212 216 80 20 210 223 90 10 29 227 100 0 27 238

D, fossil diesel fuel.

XC-30, Viscoplex 10–35, Chimec 6635 and Clarinat Sosi Flow [18]. The optimal concentration in RME of all analyzed depressants was found to be 1000 mg/kg. Chimec 6635 was the most effective; its dose of 1000 mg/kg decreased the CFPP of RME fourfold from 257C to 2197C. Further increases in the amount of depressants in RME (over 1000 mg/kg) had no positive affect on the RME cold temperature properties. It is necessary to point out that all the analyzed depres-sants were designed for RME and that the cold tem-perature properties of animal-originating FAME should be improved by compounds specially synthesized for this purpose. In this study, we also evaluated the influence of the available depressants on the CFPP of mixtures of different methyl esters of both vegetable and animal origin. Data on the dependence of CFPP on the nature of methyl esters without depressants is presented in Tab. 1.

It is evident that vegetable oil FAME (RME and LME) are characterized by comparatively low CFPP due to the large amounts of unsaturated fatty acids, whereas the CFPP temperature of methyl esters of animal origin (TME and PME) is already positive and acceptable for the above standards. LME was characterized by the lowest CFPP value; thus, its small amount (with regard to the require-ments of EN 14214 related to the amount of iodine and linolenic acid) in the mixtures of methyl esters of animal origin with RME could have a positive effect in decreasing their CFPP. Tab. 3 presents the data on the dependence of CFPP of biological methyl ester mixtures, containing 80% RME, 16% PME and 4% LME, on the type and quantity of the depressant. According to the earlier analyses, this particular mixture is distinguished by the highest resis-tance to oxidation and it also meets the standard require-ments for the amount of iodine and linolenic acid [11]. The initial CFPP of this mixture was 237C. According to Tab. 3, it is possible to state that as an improver of cold flow properties Clarinat Sosi Flow is the most effective, but its optimal dose of 2000 mg/kg decreases the CFFP of the investigated mixture only down to277C.

The optimal concentration of all the other investigated depressants is 5000 mg/kg. The best results were received using Viscoplex 10–35, but the minimal CFPP temperature reached was2107C, i.e. lower than that of pure RME. Thus, mixing of FAME with fossil diesel fuel, especially with winter fossil diesel fuel, influences the CFPP more than the addition of depressants does. In summary, the analyzed commercially available depressants are not very effective in decreasing the CFPP of animal FAME. While it would be possible to synthesize special depressants, this task was beyond the scope of the present work. LME could slightly decrease the CFPP; however, due to the standard restrictions for iodine and linolenic acid content, it is only possible to add a small amount of LME to the mixture. Thus, the most realistic possibilities for using animal fat methyl esters are to mix them with RME and fossil diesel fuel. Winter fossil diesel

Tab. 3. Effectiveness of depressants on the CFPP of an 80% RME, 16% PME and 4% LME mixture.

Depressant Concentration [mg/kg]

1000 2000 3000 4000 5000 6000 7000 8000 9000 10,000

Chimec 6635 23 24 25 26 25 25 25 25 24 24

Clarinat Sosi Flow 23 27 27 25 24 24 24 25 25 25

Viscoplex 10–35 26 28 27 29 210 210 27 27 28 28

Grotamar 71 23 25 24 25 24 24 24 25 25 25

Wintron XC-30 24 24 24 25 25 25 25 25 25 25

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fuel is much more effective; if 20% or less of the investi-gated PME and RME mixture (FAME) is added, it is pos-sible to produce a fuel whose CFPP is lower than2237C (i.e. it meets the requirements for fuel used in the transi-tory periods – spring and autumn), while it is possible to get a fuel that meets the requirements for winter fuel if 5% of biological components are added to fossil diesel fuel. Besides, mixtures of fossil diesel fuel with 20–30% FAME have more advantages, including optimal fuel costs, minimal emissions, sufficient lubrication, etc.

4 Conclusions

(1) The use of methyl esters of animal origin is limited by high CFPP. This problem may be solved by various meth-ods: mixing with RME or LME (which have better cold properties), with fossil diesel fuel or by adding depressants. (2) LME are characterized by lower CFPP than RME, but their amount is limited when they are mixed with PME, due to the large amounts of linolenic acid methyl ester and their iodine value. The production of three-compo-nent methyl ester mixtures of animal and vegetable origin without additives (depressants), however, does not solve the problem related to using fuel in the cold season. (3) To improve the cold temperature properties of pure RME, depressant Chimec 6635 is the most appropriate; its optimal dose of 1000 mg/kg decreases the CFPP from 25 to2197C. In order to improve the properties of the RME mixture with PME and LME at a ratio of 20 : 4 : 1, depressant Viscoplex 10–35 with an optimal dose of 5000 mg/kg was found to be the most effective.

(4) The most effective way to improve the cold properties of methyl esters of animal origin is to mix them with fossil diesel fuel; in order to use more products of biological ori-gin, it is advisable to introduce a third component – RME. (5) The mixtures whose CFPP are257C and lower may contain even up to 25% PME, while the proportion of fossil diesel fuel and RME may vary over a wide range, i.e. such mixtures without additional additives may be used in diesel engines in the summer.

(6) In the transitory periods, it is possible to use up to 20% FAME mixtures with winter diesel, and the 5% FAME additive may be added to the fuel used in winter.

Acknowledgments

The research work was carried out within the framework of the EUREKA program. The authors are grateful to the Lithuanian Science and Studies Foundation for support.

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Figure

Tab. 1. Physical and chemical parameters of the investigated FAME.
Tab. 1. Physical and chemical parameters of the investigated FAME. p.2
Fig. 1. Isotherms of CP of the D-RME-PME system at 1–20, 2–10, 3–5, 4–0 and 5–(25) 7C.
Fig. 1. Isotherms of CP of the D-RME-PME system at 1–20, 2–10, 3–5, 4–0 and 5–(25) 7C. p.3
Fig. 2. Isotherms of CFPP of the D-RME-PME system at 1–20, 2–10, 3–5, 4–0 and 5–(25) 7C.
Fig. 2. Isotherms of CFPP of the D-RME-PME system at 1–20, 2–10, 3–5, 4–0 and 5–(25) 7C. p.4
Tab. 2. CFPP of mixtures of winter and summer diesel fuel with FAME.
Tab. 2. CFPP of mixtures of winter and summer diesel fuel with FAME. p.5
Tab. 3. Effectiveness of depressants on the CFPP of an 80% RME, 16% PME and 4% LME mixture.
Tab. 3. Effectiveness of depressants on the CFPP of an 80% RME, 16% PME and 4% LME mixture. p.5

References

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