Characterization of Biodiesel : A Review

Characterization of Biodiesel : A Review

Sayyed Siraj R. 1 & B.M. Gitte 1, S.D. Joshi 2, H.M. Dharmadhikari. 3

1, 3 Dept. of Mechanical Engineering, Maharashtra Institute of Technology, Aurangabad,

2 Dept. of Applied Science & Humanities, Fabtech Technical Campus, Sangola, Dist. Solapur.

Abstract

It is well known for us, biodiesel is an alternative sub- stitute for fossil diesel. Biodiesel is basically Fatty Acid Methyl Ester Based Fuel, a long chain of Triglycerides and the Alcohol in the presence of Catalyst forms Ethyl Esters and the Glycerol that process is known as Transesterification, if the fatty acid content in the oil is more than 2.5% then the process by which the oil is converted to ethyl esters is known as Esterification followed by Transesterification.

This review paper mostly concentrates on the charac- terization of biodiesel; most of the Physio Chemical proper- ties like Density, Kinematic Viscosity, Flash Point, Cetane Number, and the heating value these are related to combus- tion. This paper is having the information about physio chemical properties of biodiesel and fossil diesel and the avail- ability of various feedstock for biodiesel production in the world.

Keywords: Biodiesel, Transesterification, Esterification, Char- acterization of Biodiesel.

1. Introduction

   Now a days Energy Crises is one of the important issues for us, Fossil diesel has utilized everywhere in the world for production processes of the industry, transporta- tion sectors, and also used in ships, motor Vehicle etc. But the emission produced by that fossil diesel after burning is very ineffective for our health and also for climate, it in- creases air pollution and global warming. Fossil diesel con- tributes almost 80% of the worlds energy needs [1].

   Most of the country in the world that are agricultur- al, due to fluctuating global prices of the crude oil has an adverse impact on the economy of many nations especially oil importing countries, apart from the fossil diesel is non renewable source of energy, due to the depletion of fossil diesel fuels, the prices are also increasing day by day ulti- mately it leads to the economic recession in the various de- veloping countries. If we see previous data the Diesel con- sumption of India in 2008 2009 was 51.7 million tons and

   159.7 million tons of CO2 was likely to be generated by such

   usage of fossil diesel [9].

   usage of fossil diesel [9].

   So the next alternative available for this fossil diesel is Bio diesel because it is clean and Renewable source of energy. Every country has specific variety of feedstock oil for their biodiesel production; some key countries and their feed- stock has revealed in the Table 1.

   Table 1: The Countries and Feedstock around the World: [1, 3].

   Sr. No.	Country	Raw Product or Feedstock
   1.	Mexico	Animal Fat, Waste Oil
   2.	Canada	Canola Oil, Animal Fat
   3.	USA	Soybean Oil, Waste Oil
   4.	Brazil	Soybean Oil, Palm Oil, Caster Oil, Cotton Oil
   5.	Spain	Sunflower Oil
   6.	France	Rapeseed Oil, Sunflower Oil
   7.	UK	Rapeseed Oil, Waste Oil
   8.	Sweden	Rapeseed Oil
   9.	Finland	Rapeseed Oil, Animal Fat
   10.	Germany	Rapeseed Oil
   11.	Italy	Rapeseed Oil
   12.	India	Jatropha Oil, Karanja Oil, Mahua Oil
   13.	China	Jatropha Oil, Waste Oil
   14.	Thailand	Palm Oil, Jatropha Oil, Coconut Oil
   15.	Malaysia	Palm Oil
   16.	Indonesia	Palm Oil, Jatropha Oil
   17.	Russia	Rapeseed Oil, Soybean Oil, Sunflow- er Oil
   18.	Japan	Waste Oil
   19.	Korea	Waste Oil
   20.	Philippine	Coconut Oil, Jatropha Oil
   21.	Australia	Waste Oil, Animal Fat
   22.	New Zealand	Waste Oil, Animal Fat

   As we have expected from the alternative fuel i.e. Biodiesel that must be technically feasible, economically competitive, environmentally acceptable, and easily available in the world. The current alternative fuel can be termed Biodiesel. Biodiesel can offer other benefits, including Greenhouse emissions, regional development, and social structure, espe- cially to developing countries [1, 3, 14].

   Some of the researchers like [Krawezyk et. al. 1966, Kerutzer et. al. 1984, schwab et. al. 1987, Daming Huang, 1] have put the definition for biodiesels, Biodiesel is defined as oxygenated, sulfur free, Biodegradable, Non Toxic, and ecofriendly diesel oil. [Demirbas Ayhan, 3] Biodiesel (Greek, Bio, Life + Diesel from Rudolf Diesel) refers to a diesel equiv- alent, processed fuel from biological sources. Biodiesel fuels are attracting increasing attention worldwide as blending component or direct replacement for the diesel fuel in the vehicle engine. Biodiesel comprises alkyl fatty acid (Chain length C14 C22) esters of short chain alcohols, primarily, methanol or ethanol. [Connemann and Fischer et. al. 1998, Ma and Hanna et. al. 1999, Van Gerpen et. al. 2005, Canakci et. al. 2007, Daming Huang, 1, 13] chemically, Biodiesel can be defined as a fuel composed of Mono alkyl esters of long chain fatty acids derived from renewable energy sources, such as vegetable oil, animal fat, etc. designated as B100 and it must meet to the requirements of (American Society of Testing and Materials) ASTM D 6751 standards and (European Nations) EN 14214 standards.

   Few of the Technical Properties of Biodiesels are same as that of Fossil Diesel and some properties are slight- ly higher than fossil diesel. The biodiesel is having Density is in the range of 860 900 kg/m3 as per ASTM D6751 stand- ard and Fossil Diesel is having 800 860 kg/m3 as per ASTM D 975 standard. Kinematic Viscosity of Biodiesel is in the range of 1.9 6.0 mm2/s as per ASTM D6751 standard and 3.5 5.0 mm2/s as per EN 14214 standards and for Fossil diesel the range is given 1.3 4.1 mm2/s as per ASTM D 975 standard. The Flash point of biodiesel is given 130:C mini-mum as per ASTM D 6751 standard and for Fossil diesel is 52:C as per ASTM D975 standard. The Copper Strip Corro-sion is same for both the fuels as per ASTM D 6751 and ASTM D 975 standards. The Cetane Number is slightly high-er for Biodiesel i.e. 47 minimum as per ASTM D 6751 stand-ard and for Fossil Diesel 40 minimum as per ASTM D 975 standard [15,17].

   The Biodiesel is Insoluble in water and having light to Dark Yellow, clear liquid physical appearance. The Bio- diesel is basically Light Musty or Soapy Odor and it is more biodegradable than fossil diesel. The general technical prop- erties of Biodiesel have laid downin the Table 2.

   Biodiesel is same as that of Fossil Diesel; as per the ASTM Standards comparison of Biodiesel with Fossil Diesel have laid down in the Table 3.

   The Higher Heating or Gross Heating Values of Bio- diesels are relatively high. The HHVs of Biodiesel is in the Range of 39 41 MJ/kg are slightly lower than of gasoline

   i.e. 46 MJ/kg, Petro Diesel i.e. 43 MJ/kg but higher Coal, the

   Coal is having HHVs is in the Range of 32 37 MJ/kg [3].

   Table 2: Technical Properties of Biodiesel [3].

   Common Name	Biodiesel (Bio Diesel)
   Common Chemical Name	Fatty Acid (M) ethyl Ester
   Chemical Formula Range	C14 C24 Methyl Esters or C15 25 H28 48 O2
   Kinematic Viscosity Range (mm2/s at 40:C)	1.9 6.0 as per ASTM and 3.5 5.0 as per EN
   Density Range (kg/m3 at 15:C)	860 900
   Boiling Point (:C)	>202
   Flash Point Range (:C)	147 177
   Distillation Range (:C)	197 327
   Vapour Pressure (mm of Hg at 22:C)	<5
   Solubility in Water	Insoluble in Water
   Physical Appearance	Light to Dark Yellow, Clear Liquid
   Odor	Light Musty, Soapy Odor
   Biodegradability	More Biodegradable than Fossil Diesel
   Reactivity	Stable, but avoid oxidizing agents

   Property	Test Method	ASTM D 975 (Petro- diesel)	ASTM D 6751 (Biodiesel, B100)
   Flash point (in :C)	D93	52 min	130 min
   Water & Sediments	D 2709	0.05 max % vol.	0.05 max % vol.
   Kinematic Vis- cosity @ 40:C	D 445	1.3 4.1 mm2/s	1.9 6.0 mm2/s
   Sulfated Ash	D 874	–	0.02 max %wt.
   Ash	D 482	0.01 max % wt.	–
   Sulfur	D 5453	0.05 max % wt.	–
   Sulfur	D 2622 /129	–	0.05 max %wt.
   Copper Strip Corrosion	D 130	No. 3 max	No. 3 max
   Cetane Number	D 613	40 min	47 min
   Aromaticity	D 1319	35 max % vol.	–
   Carbon Residue	D 4530	–	0.05 max % mass
   Carbon residue	D 524	0.35 max % mass	–
   Dist. Temp. (90 % vol. recycle)	D 1160	282:C min 338:C max	–

   Property	Test Method	ASTM D 975 (Petro- diesel)	ASTM D 6751 (Biodiesel, B100)
   Flash point (in :C)	D93	52 min	130 min
   Water & Sediments	D 2709	0.05 max % vol.	0.05 max % vol.
   Kinematic Vis- cosity @ 40:C	D 445	1.3 4.1 mm2/s	1.9 6.0 mm2/s
   Sulfated Ash	D 874	–	0.02 max %wt.
   Ash	D 482	0.01 max % wt.	–
   Sulfur	D 5453	0.05 max % wt.	–
   Sulfur	D 2622 /129	–	0.05 max %wt.
   Copper Strip Corrosion	D 130	No. 3 max	No. 3 max
   Cetane Number	D 613	40 min	47 min
   Aromaticity	D 1319	35 max % vol.	–
   Carbon Residue	D 4530	–	0.05 max % mass
   Carbon residue	D 524	0.35 max % mass	–
   Dist. Temp. (90 % vol. recycle)	D 1160	282:C min 338:C max	–

   Table 3: ASTM Standards of Biodiesel and Fossil Diesel [3].

   The Specifications and Test Methods of Biodiesel as Per ASTM D 6751 Standards and as per EN 14214 Standards have shown in Table 4.

   Table 4: Specification and Test Methods of Biodiesel as per ASTM D6751 & EN 14214 Standards.

   Property	Unit	Limits		Test Method
   		ASTM D 6751	EN 14214	ASTM D 6751	EN 14214
   Flash point	: C	130 min	101 min	D93	ISO CD 3679e
   Kinematic viscosity @ 40: C	mm2/s	1.9 6.0	3.5 5.0	D445	EN ISO 3104
   Cetane Number	–	47 min	51 min	D 613	EN ISO 5165
   Sulphated Ash Content	% (m/m)	0.020 max		D874	ISO 3987
   Copper Strip Corrosion	–	No. 3 max	Class 1	D 130	EN ISO 2160
   Acid Value	mg KOH/g	0.80 max	0.5 max	D 664	pr EN 14104
   Free Glycerol	% (m/m)	0.020 max		D 6584	pr EN 14105m pr EN 14106
   Total Glycerol	% (m/m)	0.240 max	0.25 max	D 6584	pr EN 141101
   Phosphorous Content
   Carbon Residue D 6751 (100% sample) EN 14214 (10% Bottoms)	% (m/m)	0.050 max –	– 0.3 max	D 4530 –	– EN ISO 10370
   Cloud point	: C	Report Customer	–	D 2500	–
   Density at 15: C	Kg/m3	–	860 900	–	EN SIO 3675 EN SIO 12185
   Distillation T90 AET	: C	360 max	–	D 1160	–
   Sulfur (S 15 grade)	ppm	0.0015 max	–	D 5453	–
   Sulfur (S 500 grade)	ppm	0.05 max	–	D 5453	–
   Sulfur content	mg/kg	–	10 max	–	–
   Water& Sediments	% vol.	0.050 max	–	D 2709	–
   Water content	mg/kg	–	500 max	–	EN ISO 12937
   Total contamination	mg/kg	–	24 max	–	EN 12662
   Oxidation stability at 110: C	h	–	6 min	–	pr EN 14112
   Iodine value	–	–	120 max	–	pr EN 14111
   Linolenic acid methyl ester	% (m/m)	–	12 max	–	pr EN 14013d
   Polyunsaturated (>= 4 double bonds) methyl esters	% (m/m)	–	1 max	–	pr EN 14103
   Ester content	% (m/m)	–	96.5 min	–	pr EN 14103d
   Methanol content	% (m/m)	–	0.2 max	–	pr EN 141101
   Monoglyceride content	% (m/m)	–	0.8 max	–	pr EN 14105m
   Diglyceride content	% (m/m)	–	0.2 max	–	pr EN 14105m
   Triglyceride content	% (m/m)	–	0.2 max	–	pr EN 14105m
   Alkaline metals (Na + K)	mg/kg	–	5 max	–	pr EN 14108 pr EN 14109

   AET: Atmospheric Equivalence Temperature.

   Biodiesel is not a simple vegetable oil and the biodiesel properties can very according to the feedstock used. All major U.S. manufacturers of diesel engine endorse the use of biodiesel.

2. Literature Survey:

   1. Density:

      The density of a material or liquid is defined as its mass per unit volume. Many researchers prefer the dimen- sionless term specific gravity, which is defined as the ratio of the density of a substance to the density of a reference substance (usually water) [20]. Density of the biodiesel, die- sel fuel and their blends can be measure by ASTM Standard D 941 or as per European Standard of EN ISO 3675 and EN ISO 12185 test methods. Most of the Researchers have used Anton Paar density meter, Pycnometer, and Hydrometer in the measurement of Density at room temperature or at stat- ed temperature i.e. 15: C [20, 22, 30]. From various re- searcher papers The (average) densities of the 25 investi- gated methyl esters, again excluding castor, range from

      870.8 to 891.5 kg/m3, with the overall average value being

      880.2 kg/m3 (i.e. almost 5% higher than the corresponding fossil diesel value). Density increases with the decrease in chain and with unsaturation [20,22]. Density can impact on fuel consumption as fuel introduced into the combustion chamber is determined by volumetrically [6]. Biodiesel fuels are, in general, characterized by higher density than conven- tional fossil diesel, which means that volumetrically- operating fuel pumps will inject greater mass of biodiesel than fossil diesel fuel [11,24]. Since the flow is controlled by volume, the expected peak power reduction for engines us- ing B100 is only 5 to 7 % less than the fossil diesel because more (g/ml) would flow and vaporize more efficiently given a set throttle (volume) [12,23]. It should be noted that bio- diesel produces more than three times the energy as the same amount of fossil fuel. Biodiesels higher Specific gravi- ty and Density relative to fossil diesel means that on road biodiesel blends are normally made by splash blending the biodiesel fuel on top of the conventional diesel fuel or fossil fuel [12]. The biodiesel has an average density i.e. Crude oil density is 12% higher than the fossil diesel [11]. Actually, it has been argued that there exists a correlation between density and NOx emissions, with lower densities favoring lower NOx, although other researchers have not confirmed such an unequivocal trend [11].

   2. Viscosity:

      Kinematic viscosity is the primary reason why bio- diesel is used as an alternative fuel instead of neat vegetable oils or animal fats [5]. Viscosity is a measure of the internal fluid friction or resistance of oil to flow, which tends to op- pose any dynamic change in the fluid motion [6,25]. Kine- matic Viscosity of the biodiesel, diesel fuel and their blends can be measure by ASTM Standard D 445 or as per Europe- an Standard of EN ISO 3104 and EN ISO 3105 test methods [31]. The Viscosity ranges have given as per the ASTM D445 standard 3.5 to 5.0 mm2/s and as per the EN ISO 3104, 05 standard 1.9 to 6.0 mm2/s [25,31]. Most of the researchers have used Redwood Viscometer, Setavis Kinematic Viscome- ter, and Canon Fenske Viscometer Tube of size No. 75, 100 used in the Viscometer Bath for Viscosity measurement [6,27]. The kinematic viscosity was determined at 40:C by multiplying the constant of viscometer tube and the meas- ured efflux time, which is the time for a known volume of liquid flowing under gravity to pass through a calibrated glass capillary viscometer tube.

      Kinematic viscosity = Calibration constant (mm2/s2) x mean time of flow (s) in mm2/s. Crude Vegetable oils have high viscosity (one order of magnitude higher than the ac- ceptable diesel fuel values), which means that they cannot be used safely as fuels in a compression ignition engine, at least not without prior heating (viscosity decreases expo- nentially with increasing temperature), and only for rela- tively small blending ratios[11]. The Crude vegetable oils have highest viscosity than biodiesel and biodiesel have higher viscosity than fossil diesel, the crude vegetable oil have viscosity 10 to 17 times higher than that of Biodiesel [18]. Several structural features influence the kinematic vis- cosities of FAME, such as chain length, degree of unsatura- tion, double bond orientation, and type of ester head group.

      Factors such as longer chain length and larger ester head group result in increases in kinematic viscosity[11]. Increas- ing the degree of unsaturation results in a decrease in kine- matic viscosity and as the temperature of oil is increased its viscosity decreases and it is therefore able to flow more readily. Double bond orientation also impacts kinematic viscosity[5,6]. Viscosity is the most important property of lubricating oil, as it affects the wear rate of engine compo- nents. Relatively higher viscosity of biodiesel helps in plug- ging the clearance between piston rings and cylinder liner effectively, thus reducing blow-by losses and fuel dilution of lubricating oil[27]. In a diesel engine, higher viscosity leads to less accurate operation of the fuel injectors, and to poorer atomization of the fuel spray, increase in the Sauter mean diameter of the fuel droplets and of the jet break -up time; these inefficiencies are exaggerated during cold starting.

      Due to the large molecular size of the triglycerides making up about 98 % of plant oils, viscosity is higher and volatility is lower than fossil diesel[5]. The Brake Power of an engine working with plant oils or blends varies in the range of

      +10% to -18% compared to engines running on fossil diesel under similar operating conditions. However, according to most reports there is power decrease around 2% to 18%.

      Possible problems are:

      • Higher viscosity interferes with the injection process and leads to poor atomization, leading in turn into inefficient mixing of air and fuel which contributes to incomplete com- bustion.

      • It also causes some lant oil to be left unburnt and pene- trate the engine crankcase which can cause loss of power [5].

   3. Flash Point:

      Biodiesel and diesel have a common boiling point, but biodiesel has higher flash point the temperature at which a fuel will catch fire because biodiesel has higher number of FAMEs which are generally not volatile [6]. Flash point varies inversely with the fuels volatility. Thus, bio- diesel is safer to handle at higher temperature than fossil diesel. Flash Point of the biodiesel, diesel fuel and their blends can be measure by ASTM Standard D 93 or as per European Standard of EN ISO 3679 and IP 523 & IP 524 test methods[31]. Most of the researchers have used Pensky Marten Closed Cup Apparatus in the measurement of Flash Point[5,6,11]. The minimum temperature ranges have given as per the ASTM D 6751 standard 130:C and 101:C as per EN 14214 standards. The Flash Point of Non Edible oils is much higher than that of fossil diesels [31].

      It also can be transported conveniently and more safely than fossil diesel, due to its high flash point which enables it to be identified as safe goods[14,15]. Flash point temperature indicates the overall flammability hazard in the presence of air, higher flash point makes for safe handling and storage. Especially Methanol which is a particular hazard to its invis- ible flame [5,17,18]. As the impurities increases in the Bio- diesel and Diesel Blends ultimately the Flash Point also in- crease [6].

   4. Cetane Number:

      One of the most influential properties of the diesel fuel is the dimensionless cetane number (CN), which repre- sents the ignitability of the fuel, particularly critical during cold starting conditions [5]. Cetane number of the fuel is defined as the percentage by volume of the normal cetane in a mixture of normal cetane and methyl naphthalene which has the same ignition characteristics (ignition delay) as the test fuel, when combustion has carried out in a stand- ard engine under specified operating conditions [6]. The cetane number of the Biodiesel and fossil diesel can be measured by D 613 as per the ASTM D6751 standard and EN ISO 5165 as per the EN 14214 standard. The limit is giv-en for Cetane Number as per the ASTM D6751 standard 47 minimum and as per EN 14214 standard 51 minimum for Biodiesel and cetane number limit is given for fossil diesel 40 minimum as per ASTM D975 standard [31]. The physical and chemical properties of the fuel play very important role in the delay period. The cetane number (CN) of the fuel is one such important parameter which is responsible for the delay period [29,30]. The ignition quality of the fuel is meas- ured by cetane number (CN) and it measures how easily ignition occurs. A fuel with good ignition quality has higher Cetane Number, where the ignition delay period between the start of the fuel injection and the onset of auto ignition is short [27]. The higher Cetane Number, Shorter the Ignition delay time and vice versa. The cetane number assists in the smooth combustion with lower knocking characteristics in the diesel engine [5]. The cetane number requirement for the engine depends on the fuel composition and influences the beginning of the process of combustion and emissions. The cetane number of methyl esters depends on fatty acids of feedstocks [11]. Cetane number decreases as the number of double bonds (or the unsaturation) increases [11]. Low cetane number lead to long ignition delay, i.e. long time be- tween fuel injection and start of combustion [12]. A fuel of higher cetane number gives lower delay period and pro- vides smoother engine operation[27]. Biodiesel has a higher cetane number because of its higher oxygen content [31].

   5. Heating Value:

      The lower (LHV) and the higher (HHV) heating val- ues are measures of a fuels heat of combustion, with the difference between them being the waters heat of vaporiza- tion [20,21]. Biodiesel contains on average 10 12% w/w oxygen, which leads to proportionally lower energy density and heating value, thus more fuel needs to be injected in order to achieve the same engine power output [30]. Some of the Researchers have measured the Heating Value of the biodiesel, and their blends can be measure by ASTM Stand- ard D 240 or as per DIN Standard of DIN 51900, DIN 51900- 1, and DIN 51900-2, DIN 51900-3 test methods [31]. Most of the researchers have used Bomb Calorimeter Apparatus in

      the measurement of Heating Value but there is no specifica- tion as regards the biodiesel heating value, neither in the EU nor in the US [5]. Previous research has shown that the en- ergy content of fatty acid methyl esters is directly propor- tional to chain length (again for pure fatty acids), whereas FAME with similar C:O but lower C:H ratios (i.e. more hydro- gen) exhibit greater LHV [11]. As a result, lower energy con- tent is obtained from progressively greater levels of unsatu- ration for methyl esters of similar chain length [26]. Increas- ing the unsaturation or the number of double bonds, results in a moderate increase in the FAME heating value [30]. The higher the oxygen content, hence the lower the heating val- ue, the higher the potential for PM reduction [27]. On the other hand, the fact that greater mass of biodiesel needs to be injected in order to achieve the same engine power as with conventional diesel fuel is responsible for an increase in NOx emissions in EGR equipped engines/vehicles; the latter engines rely on the mass flow signal in order to deter- mine the appropriate EGR valve position [27]. The low heat- ing value of Crude Vegetable oil, the maximum peak pres- sure of the cylinder reduced than fossil diesel and heat re- lease diagram reveals that the oil vaporizes and burns at a slower rate than fossil diesel. Due to higher oxygen content of the biodiesel that produces more complete combustion of the fuel and soot. B100 has lower energy content than the diesel fuel by 11% [27,31].

3. Conclusion:

   1. As the various kinds of feedstocks available in the world every country has its own biodiesel types in that every coun- try is having their own feed stocks. The biodiesel is having some properties similar to the fossil diesel but some proper- ties higher than the fossil diesel.

   2. As we see the density of biodiesel is slightly higher than the fossil diesel and less than the water. The density de- creases as the temperature increases and viceversa. It has also cleared that every feed stock having different densities.

   3. The biodiesel is having higher density thats why ASTM D6751 standard says use biodiesel for blending purpose up 20 % only because 20 % biodiesel is having kinematic vis- cosity similar to the fossil diesel. Other blends like B30 to B100 are having more kinematic viscosity than the fossil diesel.

   4. The biodiesel is having high flash point than the fossil die- sel because fossil diesel is HC based fuel and Biodiesel is FAME based. Due to high flash point it is easy in the trans- portation.

   5. Fossil diesel is having 47 dimensionless Cetane number as per the ASTM D975 standard and Biodiesel is having 51 as per the ASTM D6751 standard and 52 as per the EN 14214 standard, so higher cetane number means clean burning of the fuel with lesser time.

   6. The biodiesel is having 10 to 12 % less higher heating val- ue because of more oxygen content and the efficiency of the engine decreases 2 to 12 % because of less heating value.

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