Biodiesel production by using heterogeneous catalyst. MSc. thesis. Samir Najem Aldeen Khurshid. Division of Chemical Technology. Department of Chemical ...
Biodiesel production by using heterogeneous catalyst MSc. thesis
Samir Najem Aldeen Khurshid
Division of Chemical Technology Department of Chemical Engineering and Technology Royal Institute of Technology (KTH) Stockholm, Sweden March 2014
Biodiesel production by using heterogeneous catalyst
MSc. thesis Samir Najem Aldeen Khurshid
Supervisor Rolando Zanzi Vigouroux Chemical Technology, Chemical Engineering and Technology Royal Institute of Technology (KTH), Stockholm, Sweden
Examiner Henrik Kusar Chemical Technology, Chemical Engineering and Technology Royal Institute of Technology (KTH), Stockholm, Sweden March 2014
ACKNOWLEDGEMENT
This work is dedicated to the soul of my big sister, the person who supported me all the time and learned me since I was child. She gave me kindness and advice and left me early. I would like to thank my supervisor PhD Rolando Vigouroux for his support, instruction and direction in my master thesis in chemical engineering for energy and environment. I thanks also the Associate Professor Yohannes Kiros for his efforts in laboratory part. Thanks and gratitude to my mother and father for they gave me discipline in life and supported me wherever I settle and I am grateful to my wife who is very a considerate person and patient in difficult times. Thanks and gratitude to my children Yousef and Amir because they brought the happiness to my heart. Thanks and gratitude to all the teachers who taught me.
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ABSTRACT Industrial development is associated with an increasing in pollution levels and rising fuel prices. Research on clean energy contributes in decreasing global warming impacts (significant environmental benefits), reducing emissions gases. The developing of renewable energies increases the energy independence and impacts on agriculture in a positive way. Transesterification reaction of triglycerides to produce fatty acid methyl ester (FAME) was investigated by using virgin rapeseed oil and doped lithium calcium oxide Li-CaO as a heterogeneous solid basic catalyst. The influence of different parameters conditions such as the catalyst weight % base oil weight, mass ratio of methanol to oil, operation time, reaction temperature and mixing intensity on the yield and properties of the produced biodiesel were studied The used catalyst and the produced biodiesel were characterized by using techniques of gas chromatography (GC), X-ray diffraction (XRD), BET surface area measurement (BET) and viscometer. The results indicate the influence of the various reaction conditions such as molar ratio of methanol to oil, mass ratio of catalyst to oil and reaction temperature on the on the yield and properties of the obtained biodiesel yield. Increasing the temperature under a range lower than methanol boiling point will increase the yield. An increase of the amount of catalyst from 2.5 wt% to 5 wt% does not increase the amount produced biodiesel. The yield of produced biodiesel increases with the alcohol to oil ratio. An amount of 2.5 wt% catalyst is enough catalyst in order to achieve high yield of biodiesel. At alcohol to oil ratio 6:1 the yield of produced biodiesel increases when the reaction time increases from 1 to 2 hours. At higher alcohol to ratio (9:1 and 12:1), an increase of reaction time from 1 to 2 hours does not increase the yield of produced biodiesel. At 60 °C, the yield of obtained biodiesel increase when the mixing rate increases from 160 to 320 rpm. 97 % yield of biodiesel has been obtained using Li-CaO catalyst using 12:1 molar ratio of methanol to oil , 60°C, 160 rpm mixing rate, catalyst loading 2,5% (base oil weight) and one hour reaction time. 3
TABLE OF CONTENTS
ABSTRACT ................................................................................................................................................................. 3 1. INTRODUCTION ................................................................................................................................................... 7 2. FEEDSTOCK AND PRODUCTS .......................................................................................................................... 8 2.1 Oil...................................................................................................................................................................... 8 2.2 Alcohol ............................................................................................................................................................. 12 2.2.1 Methanol, MeOH ....................................................................................................................................... 12 2.2.2 Ethanol ...................................................................................................................................................... 13 2.3 Biodiesel .......................................................................................................................................................... 15 2.4 Glycerol ............................................................................................................................................................ 20 2.5 Catalyst ............................................................................................................................................................. 21 2.5.1 Homogeneous Catalyst.............................................................................................................................. 21 2.5.2 Heterogeneous Catalyst ............................................................................................................................ 22 2.5.3 Enzyme Catalyst ........................................................................................................................................ 23 3 KINETIC MODEL ................................................................................................................................................. 23 3.1 Kinetic of transesterification reaction ............................................................................................................. 23 3.2 Mechanism of Reaction ................................................................................................................................... 27 4 ANALYSIS EQUIPMENTS .................................................................................................................................. 33 4.1 Gas Chromatography (GC) .............................................................................................................................. 33 4.2 Brunauer, Emmett and Teller (BET) ................................................................................................................ 34 4.3 Viscosity measurement .................................................................................................................................... 36 4.4 X-Ray diffraction ........................................................................................................................................... 38 5 - EXPERIMENTAL SETUP CONDITIONS ......................................................................................................... 42 5.1 Catalyst preparing : .......................................................................................................................................... 42 5.2 Reaction and Retention time ............................................................................................................................ 43 5.3 Calculations ...................................................................................................................................................... 45 6 - RESULTS and DISCUSION ................................................................................................................................ 46 6.1 Temperature Influence .................................................................................................................................... 46 6.2 Amount catalyst .............................................................................................................................................. 47 6.3 Mixing rate ..................................................................................................................................................... 48 6.4 Alcohol to oil ratio .......................................................................................................................................... 49 6.5 Reaction time .................................................................................................................................................. 50 6.6 Waste cooking oil ............................................................................................................................................ 51 6.7 Conversion vs. reaction time ........................................................................................................................... 52 6.8 Accuracy and Error of results........................................................................................................................... 53 4
7- CONCLUSION ...................................................................................................................................................... 54 8- REFERENCES ...................................................................................................................................................... 55
List of tables Table 1: Composition of rapeseed oil .......................................................................................................................... 8 Table 2: Oil Composition of various edible oil. .......................................................................................................... 9 Table 3: Biodiesel and feedstock generation ............................................................................................................. 10 Table 4: Biodiesel properties form different oil sources compared to petroleum derived diesel ............................ 11 Table 5: Comparison of Fuel Properties ................................................................................................................... 12 Table 6: Ethanol and petrol physical properties ........................................................................................................ 13 Table 7: Ethanol generation type .............................................................................................................................. 14 Table 8: Comparison between petrodiesel and biodiesel properties .......................................................................... 15 Table 9: Properties of the obtained biodiesel and the standards of biodiesel in the United States and Europe ......... 19 Table 10: Advantage and Disadvantage of biodiesel and fossil Diesel [65-67]....................................................... 19 Table 11. Different catalysts used in transesterification of different oils .................................................................. 23 Table 12: Stoichiometry of the transesterification reaction for biodiesel production .............................................. 24 Table 13: GC operation setup.................................................................................................................................... 34 Table 14: BET surface Area Report .......................................................................................................................... 35 Table 15: Influence of lithium amount on the CaO surface area .............................................................................. 36 Table 16: Density of different glycerol mixture and temperature [27] ..................................................................... 37 Table 17 Absolut viscosity of different glycerol mixture and temperature [28] ...................................................... 38 Table 18: Samples tested in XRD analysis: .............................................................................................................. 39 Table 19: XDR setting .............................................................................................................................................. 41 Table 20: Molecular weights for catalyst feedstock .................................................................................................. 42 Table 21: Biodiesel yield by using Li/CaO with different feedstock [90, 91 ] ......................................................... 43 Table 22: Triglycerides conversion vs. FAME yield% ............................................................................................. 53 Table 23 samples viscosities ..................................................................................................................................... 61 Table 24: Experimental Result ................................................................................................................................... 62 Table 25 Experimental Result ................................................................................................................................... 63
List of figures Figure 1: MEOH environmental production process ................................................................................................ 12 Figure 2: Ethanol production process........................................................................................................................ 14 Figure 3: EU-biodiesel production (tons) [47] .......................................................................................................... 16 Figure 4 shows the alkali-catalyzed process of biodiesel production. ....................................................................... 16 Figure 5: Process flow chart of alkali-catalyzed biodiesel production...................................................................... 17 Figure 6: Monthly Prices Received by US Farmers Since 1990 ............................................................................... 18 Figure 7: United State Annul Biodiesel production and consumption ...................................................................... 18 Figure 8: Flow chart for biodiesel and glycerol production ...................................................................................... 20 Figure 9: Flow chart for Biodiesel production .......................................................................................................... 22 Figure 10: Particle Catalyst Surface .......................................................................................................................... 25 Figure 11: LH Mechanism for transesterification of triglycerides with Alcohol [33] .............................................. 29 Figure 12: Eley-Rideal (ER) mechanism of (a) Brønsted acid and (b) Lewis solid acid catalysts ........................... 30 Figure 13: Steps in a Heterogeneous Catalyst Reaction ........................................................................................... 31 Figure 14: Reaction rate vs. the ratio of velocity to particle size ............................................................................... 32 5
Figure 15: Catalyst boundary layer ............................................................................................................................ 32 Figure 16 GC ......................................................................................................................................................... 33 Figure 17: BET ........................................................................................................................................................... 35 Figure 18 a. BET surface area , b. catalyst pore volume ........................................................................................... 35 Figure 19 Viscosimeter ............................................................................................................................................. 36 Figure 20: XRD ......................................................................................................................................................... 39 Figure 21: sample A. Li-CaO Catalyst XRD Analysis ............................................................................................. 40 Figure 22: Experimental operation system ............................................................................................................... 44 Figure 23: graduated cylinder .................................................................................................................................... 44 Figure 24: Effect of temperature on FAME yield. .................................................................................................... 46 Figure 25: Effect of temperature on FAME yield. ................................................................................................... 47 Figure 26: Effect of Catalyst % on FAME yield. ..................................................................................................... 48 Figure 27: Effect of mixing intensity on FAME yield. ............................................................................................ 48 Figure 28: External resistance to mass transfer [ 26 ] ............................................................................................... 49 Figure 29: Effect of methanol-oil mole ratio on FAME yield................................................................................... 49 Figure 30: Effect of methanol-oil mole ration on FAME yield................................................................................. 50 Figure 31: Effect of Reaction time on FAME yield .................................................................................................. 51 Figure 32: Effect of Reaction time on FAME yield .................................................................................................. 51 Figure 33: Yield of produced biodiesel vs temperature. Waste cooking oil. ............................................................. 52 Figure 34: Triglycerides conversion vs. FAME yield%............................................................................................ 53
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1. INTRODUCTION In the last decade, the world has witnessed many changes in the energy field where many companies around the world created new strategies based on reducing the environmental impact and achieving competitive prices of biofuel compared with fossil fuel. The new form of energy has several features.
It requires lower cost of infrastructure and lower
environmental impact since it will replace a big share of demand to fossil fuel. In addition it reduces effects of greenhouse gases due to less SOx, NOx and CO2 gases emissions compared with fossil fuel production. At the same time the capability to produce it from different raw agriculture material, edible and non-edible oil is increasing. However it is less than expected due to bad weather, drought affect and growth of global population which tend to increase global grain prices as occurred in 2012 that leads to raise a big question about which is more important, food or biofuel [1][2]. Today biodiesel compared with petroleum is considered an environmentally friendly fuel due to low carbon dioxide emissions, biodegradable fuel, high cetane number, high combustion efficiency, lower aromatic and sulphur content in comparison to petroleum diesel, making the biodiesel a competitive fuel in the market [3-5]. Biodiesel production aims to get good qualities and quantities by choosing suitable and cheap feedstock such as virgin vegetable oils, used cook oils and animals fats. A good raw oil for biodiesel production low least fatty acid content. In the study, rapeseed oil (a virgin oil) is used for biodiesel production. Other types of edible vegetable oil can be used for instance; soybean oil, sunflower, palm oil, canola and peanut oil or even non-edible oils such as sea mango, jatropha, rubber seed and pongamia pinnata [6]. The main structure of biodiesel consists of triglyceride molecules of three fatty acids. It has ester bonding to a single molecule of glycerol. The fatty acid has different lengths of chain depends on their number of carbon. Biodiesel is produced through esterification and transesterification reactions of vegetable oil and animal fats with an alcohol. Methanol or ethanol are usually the alcohol for biodiesel preparation. The reaction is facilitated with a suitable catalyst either homogeneous or heterogeneous. The amount of free fatty acid is import in order to select the appropriate catalyst [7] [82]. The competition of producing biodiesel related with raw materials cost is high since the production process uses edible oil. Moreover, the conflict on food prices is currently high. For these reasons, the use of cheap non-edible vegetable oils or waste cooking oils decreases the cost of the raw materials.
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Unfortunately, a significant free fatty acid content reduces catalyst activity which leads to reduce biodiesel yield. Moreover, the produced biodiesel is required to undergo an efficient purification [8] [9]. Transesterification by acid-catalysed is one of the best method dealing with free fatty acid in spite of it has a relatively slow reaction rate [10]. It can be a promising method for biodiesel production using oils with high FFA content if it is combined with an alkali-catalysed transesterification [11- 14,70-71]. Lithium a dope calcium oxide particles exhibits a high activity for TG conversion. Table 1 illustrates the composition of rapeseed oil. Oleic acid (61.5%) is the biggest component in Rapeseed Oil [41].
Table 1: Composition of rapeseed oil
Percentage % Molecular (g/mol)
Palmitic acid
Estearic acid
Oleic acid
Linolenic acid
Linoleic acid
C16H32O2
C18H36O2
C18H34O2
C18H30O2
C18H32O2
5.3
2.1
61.5
9.1
20.5
weight 256
284
282
278
280
2. FEEDSTOCK AND PRODUCTS 2.1 Oil Rapeseed oil is an extract from Brassica Napus. It is one of the cruciferous plant family (cabbage family) used as a raw material for biodiesel production. Today it is considered as one of the most important crop in Europe due to its oil content importance 40–45% [15]. Many types of edible vegetable oils like rapeseed, corn, canola and soybean are used as biofuel. They act as good diesel substitutes [16] [17]. But the high viscosity and high molecular mass of triglycerides affect directly the biofuel quality. It causes incomplete combustion, high carbon deposits and injection nozzle problems. In addition, it causes high pour point of biodiesel. Fluid dynamics are influenced by the cold weather, therefore it is necessary to improve fluid (Oil) physical properties to become similar to diesel characteristics through transesterification or pyrolysis modification [18]. For the current time, transesterification of triglycerides with alcohol is more favourable than pyrolysis method due to some unacceptable physical properties of biodiesel produced by pyrolysis, for instance high cetane number, an accepted amount of copper, sulphur and water, low viscosity product and high requirement of high temperature for operation which is approximately 500C [19][74]. 8
The waste cooking oil requires pre-treatment before transesterification reaction. Waste cooking oil contains high amounts of free fatty acids which need to be removed. Some pretreatment method for waste cooking oils are steam injection, column chromatography, neutralization, film vacuum evaporation and vacuum filtration. But these pretreatment methods make the process less efficient and more complicated. A usual method to treat the waste cooking oils is the esterification of FFA with sulphuric acid acting as catalyst. Both the homogenous and heterogeneous acid catalysts can be used in this method [20]. Table 2 shows the composition of various edible and non-edible oils [2, 9].
Table 2: Oil Composition of various edible oil. Fatty acids
Oleic
linoleic
Palmitic
Stearic
Linolenic
Palmitoleic other
Rapeseed
55.68
17.82
4.12
1.57
7.61
0.05
13.15
Palm
40
10
45
5
-
-
-
Soybean
23
51
10
4
7
-
-
Jatropha
43.1
34.3
14.2
6.9
-
-
14
Pongamia pinnata
71.3
18.3
7.9
8.9
-
-
-
Rubber Seed
24.6
39.6
10.2
8.7
16.3
-
-
Biofuel and its feedstock are classified into different generation order as shown in table 3 [21, 22].
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Table 3: Biodiesel and feedstock generation Generation
Produced material
Based on
Limitation
First
Biodiesel
Agricultural feedstock , e.g. cane, oil extracts from plants
Conflicts between fuel production, graze land for cattle and food production.
Second
Biodiesel Methanol
Chemical conversion of biomass gasification of forest residues and black liquor for the production of hydrogen, methanol /DME.
Conflicts with the forest industry. Biomass insufficient for fuel production
Third
Fully synthetic e.g. methanol
Renewable sources such as solar, hydro power, wind power
Limited efficiency
According to the table 3, biodiesel is produced from first and second generation processes while methanol is produced from second and third generations. The biggest limitations to biodiesel production are the food conflict, the vegetable oils prices and graze land for cattle while methanol production faces conflict with the forest, in addition, biomass is not enough to cover the demand for biofuel Rapeseed oil is the oil used in this study with Li-CAO acting as heterogeneous catalyst. The biodiesel produced from rapeseed oil has viscosity 4.5 cSt at 40 °C higher than petroleum diesel (2.6 cSt). The biodiesel produced from rapeseed oil has a pour point of -12 °C and it has a heating value of 170 MJ/kg as shown in table 4 where the physical and chemical properties of biodiesel from different oil sources are compared to petroleum derived diesel [64].
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Table 4: Biodiesel properties form different oil sources compared to petroleum derived diesel
Specie
Viscosity cSt, 40°C
Density g/𝑐𝑚3
Specific gravity
Pour point 𝐶0
Flash point 𝐶 0t
-
2
135
0.4
38.5
-
-
20
40.86
221
44
39.25
Jatropha curcas
4.800
0.92
Sea mango
29.57
0.92
Palanga
72
0.9
Rubber seed
5.81
Acid Heating Value value Mg KOH/g MJ/kg, LHV
Non-Edible Oil
Edible Oil
Petroleum Diesel
-
0.874
-
130
0.118
0.882
-12
170
-
-
-
Rapeseed oil
4.50
soybean
4.08
0.885
-3
69
-
Palm
4.42
0.9
15
182
0.08
sunflower
32.6
274
0.15
Petroleum Diesel
2.6
-
0.92
-
0.850
-20
68
-
39.6
-
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2.2 Alcohol
2.2.1 Methanol, MeOH MeOH is a basic alcohol used in excess in transesterification of triglycerides to produce biodiesel fuel at a present of catalyst and it is known as methyl alcohol and wood alcohol and abbreviated as MeOH. MeOH is light, volatile and colourless. MeOH is consider as a safe fuel. However, it is in fact flammable and burns with an invisible flame and it is biodegradable quickly when compared with petroleum fuels. The differences between them are shown in table 5. MeOH is a polar liquid at ambient temperature (25C), in spite of his ability of attracting water molecular in stored case, it still has bad solubility in water and petrol or organic compounds [44]. Table 5: Comparison of Fuel Properties Property
Methanol
Density at 20°C LHV (MJ/Kg)
0.79
19.7
Octane number
> 110
Fuel eqv.
GHG[ gCO2 eq/MJ ]
0.48
Waste wood methanol : 5 Farm methanol:7
Petrol
0.74
43.9
92
wood
1
Industrial Methanol is synthesized mainly from natural gas and coal as in China and South Africa. It is considered as renewable fuel when it is produced by using a conversion biomass through thermochemical or biotechnological processes. In fact it is required essential pre-treatment methods for the raw materials such as drying mechanical cutting as it is shown in Fig.1:
Figure 1: MEOH environmental production process 12
Methanol is used for synthesis of different types of industrial products e.g. formaldehyde, acetic acid, olefins and DME (an environmentally friendly alternative to diesel oil) which are used in transport segment. Methanol is used directly as a petrol by mixing it with some chemicals or using it as synthesis petrol additives like MTBE/TAME. The production MeOH in the world reached in 2007 to 40 million tons. The German company Choren Industries is producing methanol from wood since 2004 using the Carbo-V process. In Sweden about 6 tons per day of methanol have been used as an intermediate in the production of Bio DME with investment about 14 million EUR in the Chemrec AB pilot plant in Piteå [45].
2.2.2 Ethanol Ethanol is abbreviated as EtOH and it is defined as ethyl alcohol. It is a pure, grain alcohol or drinking alcohol. EtOH physical properties are light alcohol, volatile and flammable liquid. It burns with an almost invisible flame. It is colourless and biodegradable. It has characteristic odour. EtOH attracts water while storing. EtOH forms with water an azeotropic mixture [46]. Ethanol is different in physical properties than petrol as it is shown in table 6. Table 6: Ethanol and petrol physical properties Property
Ethanol
Petrol
Density (20°C)
0.79
0.74
LHV (MJ/Kg)
26.7
43.9
Octane number
> 100
92
Fuel eqv.
0.65
GHG[ g CO2 eq /MJ]
Sugar beet
ethanol : 33
Farmed wood
ethanol: 20
Wheat straw
ethanol .11
1
First generation ethanol is produced from sugar and/or starch from food crops such as wheat, corn, sugar beet and sugar cane. Cellulosic ethanol is second generation ethanol and it is produced from lignocellulosic biomass such as agricultural residues (straw, corn stover), wood chips or energy crops (miscanthus, switchgrass). The fermentation of sugar for ethanol production is represented by the reaction: C6H12O6 = 2 C2H5OH + 2 CO2 The process takes place in the presence or obscene of Oxygen. The process consumes energy through the distillation unit used to obtain high pure EtOH. It is still a complicated process due to adapted yeasts requirement, chipping, pre hydrolysis and hydrolysis requirements as it is shown in Fig.2 [47]. 13
Figure 2: Ethanol production process
It is reasonable to think that cellulosic ethanol will become increasingly important on the biofuel market as shown in table 7 [47].
Table 7: Ethanol generation type Generation type
Feedstock
First generation of EtOH
Based on agricultural feedstock e.g. Have limited Feedstock potential sugar cane oil extracts from plants and The energy efficiency is low in LCA grain. perspective. Increased conflicts between fuel production, graze land food production
Second EtOH
generation
of
a. Cellulosic ethanol b. Based on chemical conversion of biomass e.g. gasification of black liquor for the production of hydrogen or forest residues
Feature
More sustainable Biomass insufficient for fuel production Conflicts with the forest industry.
Industrial processes efficiency can reach 90 to 95 % of theoretical yields but the composition of biomass must be modified to break down the cellulose and hemicellulose at first into fermentable sugars and lignin. Currently, the conventional spark-ignition engines without technical changes can operate with low percentage ethanol to gasoline blends (E5, E10). Modern flexi-fuel vehicles can use high ethanol content blends such as 85% EtOH (E85).
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Global bioethanol production reached 84.6 Bl. in 2011. 62% was produced in the United States, 25% was produced in Brazil and 4.6% was produced in the EU. The use of methanol in biodiesel production is favourable due to the simplification of the glycerol separation from the final products. The use of ethanol in the production of biodiesel requires a low water content in both the alcohol and the oils in order to obtain efficient glycerol separation.
2.3 Biodiesel Biodiesel is a renewable fuel, non-toxic and biodegradable. It is a good alternative for conventional fossil diesel fuel since it has similar properties as shown in table 8. However, it requires the use of additives to be suitable for motor fuel in order to overcome oxidation processes limitations [48]. Currently, the main holdback for commercial biodiesel is the high cost of production, usually over US$0.5/l, compared to US$0.35/l for petroleum based diesel [84].
Table 8: Comparison between petrodiesel and biodiesel properties Density
at Viscosity at 20°C Cetane
LHV
Fuel eqv.
20°C
(m𝑚2 /s)
number
FAME
0.88
7.5
56
37.1
0.91
DIESEL
0.83
5.0
50
43.1
1
(MJ/Kg)
The essential feedstock for FAME production through transesterification process (reversible reaction) are vegetable oils and animal fats. It is also used waste cooking oils as raw materials for more environmental and economic aspects. The reaction uses to be carried out in batch reactor provided with controlled heating and mixing system. Triglycerides react with excess methanol using a strong base or strong acid as a catalyst (sodium or potassium in industrial scale) to produces FAME and glycerol:
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Because of the low established cost and running cost of biodiesel production, it is considered very promising to establish small installations of biofuel production. Biodiesel has been produced in EU since 1992, Fig 3. The EU annual production is up to 6,100,000 tones with about 120 production plants. Austria, Germany, Italy, France and Sweden are the main producers of biodiesel in EU [51]. The use of 1 kg biodiesel leads to a reduction of about 3 kg of CO2 emissions. Therefore, the use of biodiesel leads to a significant reduction in CO2 emission from 65% to 90% less compared with the use of conventional diesel.
Figure 3: EU-biodiesel production (tons) [47] Direct use of the oil causes poor fuel atomization in injection, gum formation, deposition of coke in engine, oxidation and polymerization of fatty acids due to the high viscosity of the oil. The combustion efficiency decreases because of insufficient mixing of the fuel with air leading to higher emission of hydrocarbons. By producing biodiesel the physical properties of the oils are enhanced making the biodiesel a reliable, safe fuel to use for diesel engines. The biodiesel uses to be blended with conventional diesel in different percentage. The biodiesel production requires pretreatment for feedstock oils in order to reduce the free fatty acid content under 2,5wt%. Figure 4 shows the alkali-catalysed process of biodiesel production. The alkali homogeneous catalysed process of biodiesel production is more economic today the process using heterogeneous or enzymatic catalysts [7] [43].
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Figure 5: Process flow chart of alkali-catalysed biodiesel production
The production process can occur in the following steps: 1. Mixing of alcohol and catalyst: The catalyst is normally sodium hydroxide or potassium hydroxide which dissolves in the alcohol by using a standard agitator or mixer during the reaction. The alcohol and catalyst mix then charge into a closed reaction vessel and the oil or fat is added. 2. Separation: In this section glycerine and biodiesel are separated. The reacted mixture is sometimes neutralized at this step. 3. Alcohol removal. The excess alcohol in each phase can be removed with a flash evaporation process or by distillation since the glycerine and biodiesel phases have been separated. 4. Glycerine Neutralization. The glycerine by-product contains often unused catalyst and soaps that are neutralized by adding an acid and sent lately to storage for crude glycerine. The glycerine can be used for preparation of cosmetics and medicine [43]. 5. Methyl Ester Wash. The biodiesel purifies by washing with warm water to remove residual catalyst or soaps after separating from the glycerine 6. Product Quality. The finished biodiesel must be analysed to ensure it meets any required specifications. The most important aspects of biodiesel production:
Complete Reaction
Removal of Glycerine
Removal of Catalyst 17
Removal of Alcohol
Absence of Free Fatty Acids
In the U.S. and other countries, biodiesel cost is influence by the type of used feedstock. Figure 5 shows the price of biodiesel produced from wheat, maize and soybeans [63].
Figure 6: Monthly Prices Received by US Farmers Since 1990 In fact the increase competition with food can be solved by using waste cooking oil. But the production of biodiesel using waste cooking oil is more complicated because of the high FFA content in waste cooking oils. A common process is to pretreat the waste cooking oil performing esterification with acidic catalyst (e.g. sulphuric acid). Then a base catalysts can be used for the transesterification and production of biodiesel. The United State Annul Biodiesel production and consumption is shown in Fig.6 [63] [72]. At present the amount produced biodiesel is at the same range of the consumption rate. In July 2013 the average cost of
Million Gallons
one gallon biodiesel, B20, was 3,891 $ lower than the cost of petrodiesel which was 3.91$ [65].
1200 1000 800 600 400 200 0 2000
Consumption Production 2005
2010
2015
year
Figure 7: United State Annul Biodiesel production and consumption
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Biodiesel fuel is used pure or blended with fossil diesel fuel in transport section and district heating. In table 9 the properties of biodiesel concerning ester content, free glycerol, total glycerol, density, flash point, sulphur content, kinematic viscosity, copper corrosion, cetane number, iodine value, and acid value are shown [90]. In table 10 some advantages and disadvantages of the biodiesel are listed. Table 9: Properties of the obtained biodiesel and the standards of biodiesel in the United States and Europe Property
Value
EN 14214
ASTM D-6751
Density at 15 °C, kg/m3
889
860–900
Free glycerol ,wt.%
0.008
120
>130
Sulphur content, mg/kg
2.4
10
15
Iodine number , g I2/100 g
115
< 120
Copper corrosion
1A
Class 1
NO. 3max
Cetane number
54
>51
>47
Acid value , mg KOH/g
0.10
1.9-6.0
99.5%) can be obtained. Figure 7 shows the production of biodiesel including glycerol purification [47]. A fraction of glycerol uses to be burned in order recovery energy in spite of its LHV [5]. The purification processes are expensive. The quality of the produced glycerol is variable. The selling price is low (1–8 U.S.cents / Ibm in 2011) [47, 49].
Figure 8: Flow chart for biodiesel and glycerol production
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2.5 Catalyst Currently three types of catalyst are used for biodiesel production homogenous, heterogeneous and enzymatic. Different factors interact in choosing the catalyst, for instance: catalyst thermal stability, deactivation and conversion rate [86].
2.5.1 Homogeneous Catalyst Significant amounts of work have been carried out on homogeneous acid and base catalysis transesterification of vegetable oils. Most of the biodiesel produced today is obtained with the base catalysed reaction for several reasons: It is a low temperature and low-pressure reaction. It yields high conversion (98%) with minimal side reactions and short reaction time. It is a direct conversion to biodiesel with no intermediate compounds. Biodiesel production from feed stocks with high FFA (free fatty acids) is extremely difficult using alkaline catalysed transesterification. The alkaline catalysts react with FFAs to form soap that prevents the separation of the glycerine and ester. Sulphuric acid and hydrochloric acid are normally used as acid catalysts especially when the oil contains high amount of free fatty acids and water. In the two-step method a pre-esterification operation is applied to eliminate free fatty acids (FFAs) by reacting the oil with alcohol in the presence of an acid catalyst. The purified oil was further reacted with alcohol in the presence of an alkali catalyst. Waste Cooking Oils and Jatropha oils use to have high concentration of free fatty acids. The desired products of the reaction are the methyl or ethyl esters of the fatty acids initially contained in the fat or oil. Glycerine and alkali salts (using alkaline esterification) are also obtained as by-products, which may be used as raw materials in the chemical industry. Glycerine may be used in the pharmaceutical industry. The potassium salts are used for production of potassium fertilizer. One of the major disadvantages of homogeneous catalysts is that they cannot be reused or regenerated, because the catalyst is consumed in the reaction and separation of catalyst from products is difficult and requires more equipment which could result in higher production costs.
Homogeneous acid catalyst can be used with high-FFA feedstocks. The water has to be removed during processing. Increasing water concentrations decrease the yield of obtained biodiesel. High temperatures above 100 °C at moderate pressures and with continuous flow of an inert gas such as nitrogen are used in order to remove water driving the reaction to high conversion. Homogeneous acid catalyst has lower reaction rate than homogeneous alkaline requiring higher temperatures and much excess of alcohol. Liquid acids are also associated with corrosion and environmental problems [47, 52-55]... Figure8 shows the industrial production of biodiesel. 21
Figure 9: Flow chart for Biodiesel production
2.5.2 Heterogeneous Catalyst Heterogeneous catalysts can be separated from final product by filtration and reused. This causes less consumption of both chemicals and time of course. Heterogeneous catalysts are noncorrosive. They have a high selectivity and can be easily separated from the products. Both basic solids such as metal oxides (CaO) and zeolites as well acid solid such as sulphated tin oxide are used. The use of catalyst supports such as alumina, silica, zirconia and zinc oxide in order to improve the mass transfer limitation of the three phase reaction will be included. Examples of heterogeneous catalyst are; La2O3, SrO, BaO KNO3, KF, CaO, CaCO3. Table 11 shows some heterogeneous catalysts used with different feedstock. Mass transfer limitations in heterogeneous catalyst due to two phase zone (solid – Liquid) requires well mixing efficiency in order to reduce the external limitations. It uses to be operated at high temperature and high alcohol - oil mole ratio. Overcome on diffusion limitation shifts the equilibrium towards products. Many features of acidic heterogeneous catalyst are suitable for biodiesel production, for instance insensitivity for water content and free fatty acid content. Heterogeneous catalyst can be used in batch or continues system. Acid catalysts are more expensive than alkali heterogeneous catalysts. They have also less active site, therefore, they are more affected by adsorption reactants rate, surface reaction rate, desorption product rate resulting in limiting biodiesel yield [53-58, 73, 85]. Currently, among the alkaline earth metal oxides, CaO is the most widely used for transesterification with high yield (98% during the first cycle of reaction) [83]. Modified CaO catalyst with doped lithium increases
22
biodiesel yield since the lithium improves catalyst surface basicity and enhances calcium glyceroxide formation.
Table 11. Different catalysts used in transesterification of different oils Oils
Rapeseed
Catalyst
Mg-Al HT
Soybean
Sunflower
WO3/ZrO2 CaO,SrO ETS-10 MgO, ZnO. CaO / SBA-14 Al2O3
Yield
90.5
90
95
94,6
82
95
Palm
Jatropha curcas
MgAl.CO3
CaO
86.6
93
2.5.3 Enzyme Catalyst In the last years research has been focused on use of an enzymatic catalyst for production of biodiesel. Lipases used in biotechnology are normally of microbial origin and produced by fermentation processes. The use of lipases makes the reaction less sensitive to high free fatty acid (FFA) content which is a problem with the standard biodiesel process. A number of commercial lipases are available for applied biocatalysis. Whilst some are employed as free powders the majority are used as immobilised preparations.
Enzyme catalysts have high selectivity and have approximately fixed running cost and reliable capital investment. It consumes low energy since it operates at low temperature and pressure with one or two steps of isolated enzymes and no side reactions (saponification) compared with alkali esterification. It is insensitive to water content. Enzymatic reaction has low reaction rate and the enzyme has high cost and less activity which is considered as drawback affecting the economic benefit of the process. The produced glycerol covers the enzyme and reduces its efficiency, therefore, it is required additives to observe and remove the glycerol such as silica gel [53-62].
3 KINETIC MODEL 3.1 Kinetic of transesterification reaction Biodiesel is produced by a chemical a reversible chemical reaction of three mole of alcohol methanol with one mole triglycerides (TG) to produce one mole glycerol and three moles of FAME: A (TG ) + 3B (MeOH) = C (Glycerol) + 3D (FAME)
23
The reaction as shown down is reversible, it takes place at three different steps which starts with triglycerides conversion to dig-glycerides and FAME follows by the second and third steps to produce mono glyceride and glycerol respectively and FAME [68].
Triglyceride
+ R´H3OH
Diglyceride
+ R´H3OH ↔
Monoglyceride
↔
R´H3OH
+
diglyceride
+ FAME
monoglyceride + FAME
↔
glycerol
+ FAME
The reaction runs with excess methanol to shift the equilibrium to the forward direction. Table 12 shows the stoichiometry of the transesterification reaction [26] Table 12: Stoichiometry of the transesterification reaction for biodiesel production species
Symbol
Initial mole
Change
Remaining
TG
A
NA0=1
-NA0X
NA=NA0(1-X)
MEOH
B
NB0=3NA0
-3NA0X
NB=3NA0(1-X)
Glycerol
C
NC0= 0
+NA0
NC=NA0X
FAME
D
ND0= 0
+3NA0
ND=3NA0X
The rate of the reaction is influenced by internal and external diffusion, adsorption and desorption and the surface reaction rate. The overall rate of transesterification reaction can be written if form of TG conversion. It is applied the design equation combined with the mass balance of the reactants and the products depending on a basic material (limiting material):
Design equation : dx/dt= rA .V/ NA0 Rate equation
:
rA= K1(CA.CB – CC.CD/Kc)
At equilibrium
:
Kc= CC.CD/ CA.CB
: K1=K . EXP(-E/RT) where
K= pre exponential factor,
E = Activity energy
, T= reaction temperature
24
Stoichiometry :
Combining
:
NA= NA0(1-X)
NA0 = CA0.V
NA= CA.V
dx/dt = K . EXP(-E/RT) (CA.CB – CC.CD/Kc) . V/ NA0 dx/dt = K .EXP(-E/RT) [(NA.NB – NC.ND/Kc) / NA0 ] dx/dt = K .EXP(-E/RT) [(NA0(1-X).3NA0(1-X) – 3NA0X. NA0X /Kc) / NA0] dx/dt = 3K/Kc . EXP(-E/RT) [ (1-X)2 – X2]
ʃ
dX [(1−X)^2– X^2]
= 3K/Kc . EXP(-E/RT) ʃ dt
Generally, an excess methanol is required in order to shift equilibrium for further increasing of biodiesel yield. The probable assumption for catalyst behaviour is a single site, Eley-Rideal (ER). The reaction takes place at the active site of the catalyst (fig. 10) [26]. According to this assumption, the activity of the catalyst is promoted by increasing the number of basic sites of the catalyst or enlarging the surface area of the catalysts
Figure 10: Particle Catalyst Surface
The rate of adsorption can be calculated by assuming that it has only effected of the methanol diffusion on the active sites of the catalyst:
B+S=B.S
(1)
where
B = alcohol S = catalyst site 25
B.S = adsorbed alcohol on catalyst surface.
[NB]= YB CB [N0]
(2)
Where
[NB] = alcohol concentration at the surface YB = adsorption coefficient CB = concentration of alcohol [N0] = fraction of empty catalyst sites.
The rate of reaction on catalyst surface is calculated from the adsorbed alcohol when it reacts with TG in liquid phase:
where
B.S = adsorbed alcohol at catalyst surface G = triglycerides = di glycerides =monoglycerides = Oil M = adsorbed diglycerides or monoglycerides F = produced FAME
So, the rate of surface reaction:
ra = k1 [NB] CG – k2 [NM] CF
(4)
The rate of desorption of products (di glycerides or mono glycerides) is calculated from:
MS=M + S
[NM] = YM CM [N0]
(5)
(6)
Substituting equation 6 and 2 in equation 4, it is:
26
ra = k1 YB
CB [N0].CG – k2 YM CM [N0] CF
(7)
The total number of catalyst site, Ns, is the sum of the number of empty catalyst sites [N0], the sites with alcohol at the surface [NB] and the sites with adsorbed diglycerides or mono glycerides [NM]
[NS] = [N0] + [NB] + [NM]
(8)
Substitute equation 6 and 2 in equation 8 [NS] = [N0] + YB CB[N0] + YM CM [N0]
[N0]=
NS
(9)
1+YB CB+YM CM
Substitute eq (9) in equation 7
ra = k1 YB CB 1+YB CBNS+YM CM
ra =
NS
CG – k2 YM CM .1+YB CB+YM CM CF
[ k1 YB CB CG – k2 YM CM CF ] [
NS 1+YB CB+YM CM
(10)
]
The rate of adsorption will be neglected in case it is much lower than bulk concentration. YB CB ≫ YM CM. YM CM = 0
3.2 Mechanism of Reaction
Reactions mechanism and kinetic are important to design a suitable and effective catalyst material under the biodiesel reaction conditions. Biodiesel production depends on many factors such as, vegetable oil quality, mass ratio of oil to alcohol, operating temperature and time in addition to type of the catalyst.
27
Solid acid catalysed mechanism of esterification and transesterification of FFA with MeOH is represented by two models, a single site Eley-Rideal (ER) and by dual-site mechanisms Langmuire Hinshelwood (LH) [67, 92]. LH model for heterogeneous catalyst is shown in Fig.11 for the transesterification of ethyl acetate with methanol using magnesium oxide catalyst [38]. The adsorption step (1a) and (1b) for the two reactants, methanol and ethyl acetate, takes place on the active sites of the catalyst surface. In step 2 a surface tetrahedral intermediate (unstable complex) is formed from protonized carbonyl group and alkoxid group. A fatty acid alkyl ester and diglyceride are produced in step 3 and 4 respectively [33, 38-41]. This model (dual-site) is acceptable from chemical point of view. Two reactants (Triglyceride and alcohol) are absorbed on the catalyst active site and the reaction takes places with the adsorbed species. LH model is preferred when transesterification reaction takes place in present of higher carbon alcohol while when low carbon alcohols such as methanol is used, the single site mechanisms, ER, is preferred. As it shown in Fig.12, the alcohol is adsorbed on the catalyst site in ER mechanism. Alkoxides ion on the surface attacks the positively polarized carbon of triglyceride which present in liquid phase, It is shown in Fig 12 (a) ER mechanism base on Brønsted acid site type. The (ER) mechanism by solid Lewis acid is shown in Fig 12 (b). The mechanism includes three main steps:
Physic sorption and chemisorption of triglyceride (TG) in to the catalyst site
A intermediate tetrahedral is formed when the alcohol attacks the electrophilic carbon
The final step include the cleavage of the fatty acid ester and dig glyceride from the catalyst and the desorption from the site.
28
Figure 11: LH Mechanism for transesterification of triglycerides with Alcohol [33]
29
Figure 12: Eley-Rideal (ER) mechanism of (a) Brønsted acid and (b) Lewis solid acid catalysts
30
Esterification reaction has different limitations. The heterogeneous catalyst reaction is shown in Fig. 13 [26]. External diffusion limitation are present when methanol and triglycerides moles diffuse from the bulk mixture fluid into the catalyst via a boundary layer around the catalyst particles (external mass transfer, step 1). The velocity of fluid is varied and the concentration changes from CA0 (bulk concentration) to CAs (concentration on Catalyst surface). Other limitation are represented by internal diffusion limit resistance of fluid transfer when reactants diffuse through the catalyst pores (pore diffusion, step 2). Adsorption limitation occurs when the reactants are adsorbed on the catalyst surface (step 3). The transesterification reaction takes place on the surface of the catalyst (step 4).
Figure 13: Steps in a Heterogeneous Catalyst Reaction
The products face the same limitations as in steps 1, 2 and 3 take place in steps 5, 6 and 7 respectively. At first the desorption of the products takes place (step 5). Then internal diffusion in the pores occurs when the products are diffusing through the catalyst pores (step 6). Finally external diffusion is present when the products (biodiesel and glycerol) are been transferred into the bulk mixture [26].
31
Figure 14: Reaction rate vs. the ratio of velocity to particle size
Figure 15: Catalyst boundary layer
The esterification rate limits by these previous steps can summarize by mass transfer diffusion resistance and concentration gradient across the boundary layer around the catalyst particle as shown in Fig13. Figure 14 shows the variation in reaction rate with the ratio of velocity to particle size. At low velocity the mass transfer boundary layer thickness (figure 15) is large and diffusion limits the reaction. At higher fluid velocity, increasing the mixing rate, the mass transfer boundary layer thickness decreases and no longer limits the reaction rate. At a given fluid velocity (mixing rate) reaction-limiting conditions can be achieved by using very small particles.
32
4 ANALYSIS EQUIPMENTS 4.1 Gas Chromatography (GC) Gas chromatography GC (Fig.16) is used in order to analyse the produced biodiesel. The samples of the produced biodiesel are diluted with solvent and internal standard solution before making the analysis in the GC. We use 0.5 ml of solvent (Heptane), 0.011ml Internal Standard (Propylene acetate) and 0.113ml of FAME (product) in the present work. The sample of biodiesel (FAME) is taken from the middle medium of cylindrical product container [32].
Figure 16
GC
The GC device is connected to computer program and the analysis results are obtained as graphics, GC analysis is explained in calculation part 5.3 A stream of an inert gas which commonly helium or argon acts as carrier pass. The detector gives analysis as graphics [32]. Instruction on How to Use GC for Analysis of Biodiesel Yield (Model – Agilent (GC) 6890) Equipment instruction: 1. Check the carrier gas (He and H2) tanks. They must be opened before start at least for 5 minutes. 2. Start GC using on button (power button). Wait until the machine checks each process. 3. Open the online access page on the GC computer when GC is ready 3. The GC conditions must be fulfilled as in table 13 below:
33
Table 13: GC operation setup Inlet temperature
215
Injection Volume, l
1
FID temperature
300
H2 flow, ml/min
45
Oven program , 𝐶 0
70 °C initial temp. (Hold for 0.5 min) and ramps: 10 °C / min. from 70°C 130°C. 15°C /min from 130°C -180°C, 7 °C /min from 180°C to 200°C and 30 °C min from 200°C - 235°C . The final temperature is maintained during 7 minutes.
Air flow ml/min
450
Calibration standard
Propyl acetate
Spilt ratio
80
He Make up flow, ml/min
40
Column He flow , ml/min
45
4. When checking the calibration conditions, run the blank sample to clean GC column (it can take 30 Min). 5. GC become ready for sample analysis after blank run.
4.2 Brunauer, Emmett and Teller (BET) Adsorption and desorption phenomena are the principles of BET technique Fig 17. BET is used to estimate catalyst surface area, pores volume and pore diameter. The catalyst sample is degassed overnight at 250 °C as drying temperature and 77.4 K for N2 adsorption. BET recorded adsorption and desorption curves are shown in Fig.18. A BET surface area report is shown in table 14.
34
Figure 17: BET
Table 14: BET surface Area Report BET- Surface Area
10.7225
Pore volume
0.0734
Pore diameter
254.254 𝐴0
𝑚2 /g 𝑐𝑚3 /g
Figure 18 a. BET surface area, b. catalyst pore volume Li-CaO is prepared by calcination of Ca(OH)2 with LiOH.H2O at 600°C. The exposure at high temperature during 2 hours results in expansion of the pores diameter. Calcination improves mass transfer diffusion and reduces internal diffusion resistance. The total surface area is reduced, surface basicity is increased and the catalyst activity is improved. CaO surface is reduced by Lithium ions particles that fill the micro pore of CaO [40, 81- 82]. 35
Some previous researches have studied the influence of increasing lithium amount in wt.% on CaO surface area. Increasing the amount of Li doping on CaO decreased the surface area dramatically (Table 15) [67]. In experiments performed by Watkins [36] 4 wt.% Li on CaO decreased the CaO surface area from 20 to 8 m2/g. Rane found out that 28.5% wt% Li on CaO decreased the CaO surface area from 6 to 0.3 m2/g.
Table 15: Influence of lithium amount on the CaO surface area Amount Li on CaO wt.%
Influence on surface area of CaO Reference (𝑚2 /g )
4
Decrease from 20 to 8 (𝑚2 /g )
Watkins et al [36]
28.5
Decrease from 6 to 0.2 (𝑚2 /g )
Rane et al [37]
7
Decrease from 2 to 0.076 (𝑚2 /g )
Rane et al [37]
4.3 Viscosity measurement Falling sphere viscometer DIN53015 is used in order to measure the viscosity of biodiesel (fig.19).
Figure 19 Viscosimeter
It implements Stock law to measure viscosity by calculating the falling time of the ball between lines at the two ends of the cylinder. Measuring is repeated for 9 times. Viscometer has inclination angle of 80 degree and operates in ±1-3 % error. The viscosity limits is in range 0,0006 – 250 N.S / m2 and the time is converted into viscosity value by using equation 1 [29]. 36
Table 16: Density of different glycerol mixture and temperature [27] % Glycerol
Density 15 °C
15.5 °C
20 °C
25 °C
30 °C
0.00
0.99913
0.99905
0.99823
0.99705
0.99565
1.00
1.00155
1.00145
1.00050
0.99945
0.99500
2.00
1.00395
1.00385
1.00300
1.00180
1.00035
3.00
1.00635
1.00630
1.00540
1.00415
1.00270
4.00
1.00875
1.00870
1.00780
1.00655
1.00505
5.00
1.01120
1.01110
1.01015
1.00890
1.00735
6.00
1.01360
1.01350
1.01255
1.01125
1.00970
7.00
1.01600
1.01590
1.01495
1.01360
1.01205
8.00
1.01840
1.01835
1.01730
1.01600
1.01440
9.00
1.02085
1.02075
1.01970
1.01835
1.01670
10.00
1.02325
1.02315
1.02210
1.02070
1.01905
11.00
1.02575
1.02565
1.02455
1.02315
1.02150
12.00
1.02830
1.02820
1.02705
1.02560
1.02395
13.00
1.03080
1.03070
1.02955
1.02805
1.02640
14.00
1.03330
1.03320
1.03200
1.03055
1.02885
15.00
1.03580
1.03570
1.03450
1.03300
1.03130
16.00
1.03835
1.03825
1.03695
1.03545
1.03370
17.00
1.04085
1.04075
1.03945
1.03790
1.03615
18.00
1.04335
1.04325
1.04105
1.04035
1.03860
19.00
1.04590
1.04575
1.04440
1.04280
1.04105
20.00
1.04840
1.04825
1.04690
1.04525
1.04350
At first we measure the ball density by measuring its volume and weight: Ball density = Ball weight / Ball volume = 3.78 g. / 2 ml. = 1,89 g/ml. The following equation is used in order to calculate the viscosity of the produced biodiesel: Biodiesel Viscosity = K * Full Time * (Ball Density – Biodiesel Density)
(eq.1)
The contact k is calculated using a liquid of known viscosity. A mixture of 20% glycerol in water is used. The standard density for a mixture 20% glycerol in water at 25°C is 1,045 g/ml as shown in table 16. Viscosity of a mixture 20% glycerol 80% water at 25 °C is 1.542 g/ml as it is shown in table17.
37
The constant, k, is calculated as: K= medium viscosity / [full time*(Ball Density-Biodiesel Density)] =
(eq.2)
1.542 / [ 4 (1.89 -1.045)] = 0,4663
4 s was the time of the ball between lines at the two ends of the cylinder. In appendix, table 23, the calculation of the viscosity of the biodiesel is shown. Biodiesel Viscosity = K * Full Time * ( Ball Density – Biodiesel Density ) = 0.4663. t (1.89-1.045 ) Table 17 Absolut viscosity of different glycerol mixture and temperature [28] % Glycerol by weight
Absolute Viscosity in centipoises 30 °C
25 °C
20 °C
0.00
0.800
0.893
1.005
5.00
0.900
1.010
1.143
10.00
1.024
1.153
1.311
15.00
1.174
1.331
1.517
20.00
1.360
1.542
1.769
25.00
1.590
1.810
2.095
30.00
1.876
2.157
2.501
35.00
2.249
2.600
3.040
40.00
2.731
3.181
3.750
4.4 X-Ray diffraction XRD, shown in fig.20, is used to identify crystalline phase in a material. XRD is used to estimate structure properties e.g. deflects, grain size, epitaxy and phase composition The analysis is obtain as typical XRD pattern with different coolers peaks as it is shown in Fig.21 [42, 69].
38
Figure 20: XRD
Three catalyst samples A, B, and C have been prepared and analysed (table 18).
Table 18: Samples tested in XRD analysis: Sample of
Reflection angle
catalyst
Li-CaO
Condition of preparing
amount
A
37.5
1110
Ca(OH) 2 calcinated with LiOH.H2O for 2h. at 600°C.
B
37.5
820
Ca(OH)2 calcinated for 2h at 600°C. Then mixed with half amount of LiOH.H2O and then calcinated the mixture for 2h at 600°C. Finally mixed with the rest of LiOH.H2O
C
37.5
720
Ca(OH) 2 calcinated for 2h at 600°C then mixed it with total amount of LiOH2O .
Analysis start:20.000 degree and ended at 90.000 degree with step time 0.5 s and temperature 25 °C.
39
Figure 21: sample A. Li-CaO Catalyst XRD Analysis
The calcination conditions for catalyst A give higher maximum intensity of Li-CaO with angle 37 degree. Catalyst A is selected for use in the experiments presented in this work.
40
SEMENS d 5000 OPERATING INSTRUCTION. [Ref: XRD instructions] Switch on the x-ray diffractometer 1) Put on the cooling water (as much as possible, but do not over tighten ) 2) Press the switch NETZ MAINS. 3) Check current and voltage. They should be in left bottom position (5 mA,20KV ) 4) Press the YELLOW SWITCH. 5) Press shift x ray 1 enter 6) Press the GREEN SWITCH. (x-ray tube is now in function ) 7) Turn the voltage to 40 KV stepwise according to schedule
Table 19: XDR setting Retention
time (min)
Stop (days)
20 kv
25 kv
30 kv
35 kv
40 kv
0,5 to 3
0.5
0.5
0.5
0.5
0.5
3 to 30
0.5
0.5
2
2
2
>30
0.5
0.5
2
2
2
or new tube
8) Turn the current from 5 to 30 mA
Shut off the XRD 1) Turn down the current to 5 mA. 2) Turn down the voltage to 20kv. 3) Press the RED SWITCH. 4) Press the NETZ MAINS. 5) Turn off the cooling water.
41
5 - EXPERIMENTAL SETUP CONDITIONS 5.1 Catalyst preparing: CaO is widely used as a heterogeneous catalyst in biodiesel synthesis. The condition for catalyst production such as temperature, pressure and time of sintering influence the catalyst activity and then the yield of produced biodiesel Lithium doped Calcium Oxide (Li- CaO) is prepared in order to be used as catalyst. In 6 experiments the amount of catalyst is 2.5 wt % in relation to oil, while in the other 6 experiments the amount of catalyst is increased to 5 wt % [75-81].
The catalyst consists of 99% CaO and 1% Li. For 45 grams CaO, 0.45 g Li are it are required:
At 600 °C (calcination) the reactions takes place: → CaO + H2O
Ca(OH)2
2 LiOH.H2O → Li2O +3 H2O
Table 20: Molecular weights for catalyst feedstock Specie
CaO
Ca(OH) 2
Li2O
LiOH.H2O
Mol.wt. (g/mol.)
56.08
74.1
29.9
41.96
In order to produce 45g of CaO and 0.54g of Li2O, it is required 60g of Ca(OH)2 and 1.26g of LiOH.H2O.
Ca(OH)2=
CaO weight CaO Mwt
LiOH.H2O=
* Ca(OH)2 M.wt. =
CaO weight LiO M.wt.
45 g
g 56,08 ( ). mol
*( LiOH.H2O) M.wt. =
* 74.1 (
45 g
g 29.9 ( ). mol
g
) = 60 g.
mol
* 41.96 (
g
) = 1,26 g.
mol
60g Ca(OH)2 and 1.26g. LiOH.H2O are crushed. The powder mixture is calcinated at 600 °C during two hours. 42
The prepared catalyst is kept in dry and isolated place from air contact. Li-CaO catalyst has been prepared in different conditions as it is shown in table 21. Table 21: Biodiesel yield by using Li/CaO with different feedstock [90, 91] Feedstock
Cat. weight %
Karana oil
3.4 wt.% FFA Impregnated with 1.75 T=65 °C, t=60 min, wt.% of lithium and alcohol/oil=12:1,catalyst heated at 120 °C for 24 h content=5%
>99%
Jatropha oil
8.3 wt.% FFA Impregnated with 1.75 T=65 °C, t=120 min, wt.% of lithium and alcohol/oil=12:1,catalyst heated at 120 °C for 24 h content=5%
>99%
Used 15 wt.% Impregnated with 1.5 wt.% T=65 °C, t=150 min, cottonseed oil moisture of lithium and alcohol/oil=12:1,catalyst heated at 120 °C for 24 h content=5%
>99%
Rapeseed oil 5%
Cat. Preparation
Calcination 575 °C for 4 h
Operation conditions
yield
alcohol /oil=12:1,catalyst >93% content=5%
5.2 Reaction and Retention time The operation system consists of a small glass batch reactor with three necked. It is immersed in a hot bath water controlled by electrical heater and thermometer as it is shown in Fig.22. The catalyst activity is studied changing operation conditions. The influence of the ratio alcohol to Oil, operating temperature, time of reaction, agitation rate and amount used catalyst on the yield and quality of the produced biodiesel is studied. Final sample product is kept in graduated glass cylinder as it is shown in Fig.23. After 24 h, different layers of products are formed due to the difference in density. The layers from the top cylinder to the bottom are: unreacted methanol, FAME, glycerol and catalyst. In order to analysis the biodiesel, the sample is taken from the graduate cylinders from middle. 43
Figure 22: Experimental operation system
Figure 23: graduated cylinder
Each biodiesel sample introduced to the GC consist of heptane (0.5 ml), the produced biodiesel (0.113 ml) and internal standard (IS) (0.011ml). The sample is placed in the GC injector to start the analysis. It is very important to keep the samples in an isolate place away from the sunlight to avoid decomposition. It is difficult to take the catalyst from graduated cylinder in order to reuse it. The catalyst sticks with glycerol as one phase material. It can be separated by using thermal and physical methods which increase the running cost in generally [89].
44
5.3 Calculations
Transesterification reaction is a reversible reaction: 3 alcohol (MeOH ) + 1 Oil (Triglyceride) = 3 biodiesel (FAME) + Glycerol The theoretical amount of biodiesel which can be obtained assuming 100% conversion, is calculated. Amount of oil volume = 60 mL in each experiment Oil weight = Oil Volume x Oil density = 60 mL x 0.915 g / mL = 54.9 g Oil molecular weight = 880 g / mol. Oil mole = Oil weight / Oil molecular weight =
54.9 g / 880 g / mol. = 0.0623 mol.
According to stoichiometry of the reaction, one mole of oil produces three mole of FAME. Theoretical yield of FAME = 3 x 0.0623 mol. = 0.187 mol of biodiesel. The real yield of FAME for each experimental is calculated using the results from GC analysis which appear as different peaks at different retention time depends on FAME composition. The total area of those peaks is divided by internal standard peak area, and then multiplied by the concentration of internal standard and by the inverse of response factor in order to calculate the concentration of FAME in each sample.
Concentration of FAME =
Area of FAME A rea of IS
* Concentration of IS. *
1 Response Factor
In order to calculate the response factor, two ratios (relations) are calculated:
Ratio 1 =
Ratio 2 =
Concentration of standard FAME Concentration of IS
total FAME peak area IS peak area
Response factor =
Ratio 2 Ratio 1
=
=
40864,4 1773,9
23,036 10
= = 10
= 23.036
(relation between concentrations)
(relation between areas)
= 2.3
45
In the sample introduced to the GC the biodiesel is diluted with heptane and internal standard.
Real Concentration of FAME =
Volume of sample ∗ Concentration of FAME Volume of FAME
6 - RESULTS and DISCUSION 6.1 Temperature Influence The boiling point of methanol is 64.7 °C and in order to avoid alcohol evaporation, reaction temperature has to be less than 64.7 °C. The optimal temperature runs between 50 and 60 °C. Increasing the temperature will reduce the viscosity of the oil which leads to a sufficient contact at the active site of catalyst surface between the oil and the methanol. As a result, a higher yield of biodiesel is obtained [7, 23, and 24]. The reaction temperature has a positive influence on FAME yield as it is shown in fig.24. The temperature range of 60–63 °C for 6:1 methanol to rapeseed oil mole ratio at atmospheric pressure is studied. The yield of produced biodiesel increases when both the temperature and agitation rate are increased from 60 to 63 °C and from 160 to 320 rpm respectively at constant time (1h) (figure 24).
85 84
84
Yield %
83 82 81
6:1 Mole R., 2,5% Cat., I hr. , 60-63 C,160 rpm.
80,6
80
6:1 Mole R., 2,5% Cat , I hr, 60 -63 C ,160-330 rpm.
79 78
77,8
77 59
60
61 62 Temp, °C
63
64
Figure 24: Effect of temperature on FAME yield.
Figure 24 shows the influence of the temperature and the ratio alcohol to oil on the yield of produced biodiesel. 46
At 60°C the yield of produced biodiesel is increased from 77.8% to 95% when the ratio alcohol: oil is increased from 6 to 9, and the amount of catalyst is increased from 2.5 wt% to 5wt%. At higher temperature, at 63 °C, an increase of the alcohol: oil ratio and of the amount of catalyst does not influence the yield of produced biodiesel in a positive way (figure 25). An increase of temperature from 60 to 63 °C, using an alcohol: oil ratio of 9 and 5 wt% amount catalyst, does not increase the amount of produced biodiesel. Using an alcohol: oil ratio = 6 and 2.5 wt% catalyst, an increase of temperature only produces a slight increase of the amount produced biodiesel (figure 25). At 63°C, close to methanol boiling point, the evaporation of methanol possible increases.
100
95
80
80,6 72
77,8
60
6:1 Mole Ratio, 2,5% Cat. , I hr. ,160 rpm , 60-63 C
Yield %
40 20
9:1 Mole Ratio, 5% Cat. , I hr ,160 rpm , 60-63 C.
0 59
60
61
62
63
64
Temp.C
Figure 25: Effect of temperature on FAME yield.
6.2 Amount catalyst An insufficient amount of catalysts results in an incomplete conversion of the triglycerides into the fatty acid esters [23, 25]. During experiment, the catalyst loading is varied in the range of 2.5 to 5 wt. % rapeseed oil weight as it is shown in figure 26 for three different methanol – oil mole ratios 6:1, 9:1 and 12:1 respectively. Figure 26 shows the influence of the amount of catalyst and the alcohol to oil ratio on the yield of produced biodiesel. An increase of the amount of catalyst from 2.5 wt% to 5 wt% does not increase the amount produced biodiesel. An amount of 2.5 wt% catalyst is enough catalyst in order to achieve high yield of biodiesel [34]. An increase of the alcohol ti oil ratio from 6 to 12 increases the yield of produced biodiesel, at the studied conditions (160 rpm agitation rate and 2 h reaction time). 47
120 100
Yield %
80
97 95
96
77,8
78,85 73,8
2.5-5 % Cat., 6:1 mole ratio, 1 h. ,60 °C ,160 rpm. 2.5-5 % Cat., 9:1 mole ratio, 1 h. ,60 °C ,160 rpm.
60 40
2.5-5 % Cat., 12:1 mole ratio, 1 h. ,60 °C ,160 rpm.
20 0 0
1
2
3 4 Catalyst , wt.%
5
6
Figure 26: Effect of Catalyst % on FAME yield.
6.3 Mixing rate Agitation rate influences on biodiesel yield at constant methanol-oil mole ratio (6:1), 2,5% catalyst loading and different reaction temperatures 60 and 63°C (figure 27). Increasing mixing intensity (at constant catalyst loading) from 160 to 320 rpm has affected the FAME yield. At 60 °C the yield of produced biodiesel has increased with mixing rate. At 63 °C the yield of biodiesel has decreased when mixing rate is increased from 160 to 320 rpm.
86 84
84
Yield %
82 80
80,6
78
77,8
6:1 mole ratio, 60 C, 1 hr.2,5% Cat., 160-320 rpm
76
6:1 mole ratio, 63 C, 1 hr.2,5% Cat., 160-320 rpm
76
74 0
100
200
300
400
mixing intensity , RPM
Figure 27: Effect of mixing intensity on FAME yield.
Increasing agitation rate improves mass transfer of reactants on active sites of catalyst surface due to decreasing the boundary layer between the catalyst surface and the fluid bulk as it shown in Fig.28. This leads to reduce the external diffusion resistance of reactants and products around the catalyst surface. Increasing the temperature together with agitation speed leads to increase the reaction rate due to decreasing the activation energy of the reaction [26]. 48
At 63 °C, a decrease of the yield occurs when the mixing rate is increased due the increase of the evaporation of the methanol at temperatures close to the boiling point.
Figure 28: External resistance to mass transfer [26]
6.4 Alcohol to oil ratio Effect of methanol - oil molar ratio is investigated as it is shown in Fig.29 with three different molar ratios 6, 9 and 12 respectively during one hour operation time at constant temperature 60 °C and constant rate of mixing, 160 rpm, while the catalyst amount has been changed from 2,5 % to 5% based on the weight of oil. Increasing of molar ratio achieves a proportional increasing of biodiesel yield % from 77.8 to 97 % for the first used amount of catalyst (2.5% of oil weight) and from 73.8 to 96 % for the second test with catalyst weight 5 wt% (oil weight). An excess of methanol shifts the reaction to the right and higher amount biodiesel is produced [19].
120
Yield %
100
95
80
77,8 73,8
97 96
78,85
2,5% Cat.,1hr,160 rpm, 60 C, (6-9-12)/1 mole ratio.
60 40
5% Cat.,1hr,160 rpm, 60 C, (6-9-12)/1 mole ratio
20 0 0
5
10
15
Mole Ratio
Figure 29: Effect of methanol-oil mole ratio on FAME yield 49
Figure 30 shows the influence of the alcohol to oil ration on the yield of obtained biodiesel for 2h reaction time, catalyst amount 2,5 wt% to 5 wt% at constant temperature 60 °C and constant rate of mixing 160 rpm. The yield of produced biodiesel increases with the alcohol to oil ratio. Using lower amount of catalyst (2.5 wt%) a high yield of biodiesel is obtained using an alcohol to oil ratio of 9. A further increase of alcohol to an alcohol to oil ratio of 12, increases slight the yield of biodiesel.
120
Yield %
100 80
83
60
63
94 81,7
99,7 91,8 2,5% Cat.,2hr,160 rpm, 60 C, (6-9-12)/1 mole ratio
40
5% Cat.,2 hr,160 rpm, 60 C, (6-9-12)/1 mole ratio
20 0 0
5
10
15
Mole Ratio
Figure 30: Effect of methanol-oil mole ration on FAME yield
6.5 Reaction time The effect of the reaction time on biodiesel yield in a batch reactor through is studied changing the reaction period. Generally the effect of reaction time inside a reactor can be calculated by using the residence time distribution method (RTD) to compute the expected conversion with time. There will be different reaction times due to different RTD [24-26]. In our system (batch), effect of reaction time obviously increases biodiesel yield from 77,8 to 83% at alcohol to oil ratio 6:1 when the reaction time increases from 1 to 2 h at constant temperature 60 °C, at fixed agitation rate 160 rpm and 2,5% catalyst load (base of oil weight) as it is shown in Fig.31.. At higher alcohol to ratio (9:1 and 12:1), an increase of reaction time from 1 to 2 hours does not increase the yield of produced biodiesel. At higher amount of catalyst (5 wt%) an increase of the reaction time from 1 hour to 2 hour does not increase the yield of produced biodiesel at the studied conditions.
50
120 100
99,7 94 83
97 95
80
77,8
1-2 hr, 2.5% Cat.,6:1 mole ratio , 160 rpm 60C
60
1-2 hr, 2.5% Cat.,9:1 mole ratio , 160 rpm 60C
Yield %
40
1-2 hr, 2.5% Cat.,12:1 mole ratio , 160 rpm 60C
20 0 0
0,5
1
1,5
2
2,5
Time , h.
Figure 31: Effect of Reaction time on FAME yield
120 100
96
Yield %
80
91,8 81,7
78,85 73,8
1-2 hr,5% Cat., 6:1 mole ratio , 160 rpm 60C
63
60 40
1-2 hr, 5% Cat.,9 :1 mole ratio , 160 rpm 60C
20
1-2 hr, 5% Cat.,12 :1 mole ratio , 160 rpm 60C
0 0
0,5
1
1,5
2
2,5
Time , h.
Figure 32: Effect of Reaction time on FAME yield
6.6 Waste cooking oil Some experiments have been performed with waste cooking oil. Figure 33 shows that the yield of produced biodiesel increases from 62.7 to 70.4 % when the temperature is increased from 55 °C to 60 °C and the mixing rate is increased from 160 to 320 rpm. An increase of the amount of catalyst (from 2.5 wt% to 5 wt%) does not increase the amount of produced biodiesel at 320 rpm mixing rate, 60 °C, and alcohol to oil ratio of 6:1.
51
80 70,4
70 62,7
60
160-320 rpm,55-60 C ,6:1 Mole Ratio, 1 h.,2,5% Cat.
55,6
50 40 30
320 rpm,60 C ,6:1 Mole Ratio, 1 h., 2,55% Cat.
20 10 0 54
56
58
60
62
Figure 33: Yield of produced biodiesel vs temperature. Waste cooking oil. Waste cooking oils have contain high amounts of free fatty acids. The alkaline catalysts react with FFAs to form soap that prevents the separation of the glycerol and ester. Biodiesel production from feed stocks with high FFA (free fatty acids) is extremely difficult using alkaline homogeneous catalyzed transesterification. Also heterogeneous catalyzed transterification is affected by the high amount of free fatty acids Sulphuric acid and hydrochloric acid are normally used as acid catalysts especially when the oil contains high amount of free fatty acids and water. In the two-step method a pre-esterification operation is applied to eliminate free fatty acids (FFAs) by reacting the oil with alcohol in the presence of an acid catalyst. The purified oil was further reacted with alcohol in the presence of an alkali catalyst. The purification of the oil, removing the impurities such as suspension catalyst solid particles, drops water, soap, unreacted alcohol and unfiltered catalysed is very important. Unwashed biodiesel leads to fuel degrades, reduce fuel lubricity, explosion and can corrode engine components.
6.7 Conversion vs. reaction time Experiments are carried out with 6:1 methanol-oil mole ratio, 60 °C, 2.5% catalyst loading, 160 rpm agitation speed and for 65 minutes reaction time. Seven samples of 10 ml are taken every 10 min. from the reactor as shown in table 22. In figure 34 it is observed that the yield for the first four samples, taken between 10 and 40 min, increases slowly. The amount of biodiesel contained in samples 5 and 6, taken between 50 and 60 min, increased markedly. In the sample 7 taken at 65 min a yield of biodiesel of 92% is obtained.
52
Table 22: Triglycerides conversion vs. FAME yield% 1
2
3
4
5
6
7
Time (min)
10
20
30
40
50
60
65
Yield %
11.1
12
16.27
23
32.7
55.8
91.7
Yield %
Sample
Yield vs. time
100 90 80 70 60 50 40 30 20 10 0
91,73
55,85 32,7
0
10
16,3
12
11,1 20
23
30
40
50
60
70
time , min.
Figure 34: Triglycerides conversion vs. FAME yield%
6.8 Accuracy and Error of results Any experimental work has some expectations errors occur and limit the study results due to inaccuracy readings of final results since it depends on visual reading for the intervals between the product layers in graduate cylinders e.g. the volume of the glycerol sometime can be difficult to read samples FFA volume which effect extremely on the study calculation . Catalytic activity is influenced significantly by calcination temperature where the catalyst preparation depends only on one temperature (600 C) of calcination. [87-88]. Many errors can happen in viscosity measuring. Falling time is used here. It can be errors in measuring the time of ball falling. Counting the falling time of the ball is based on the average of ten readings in order to avoid error of falling time. The most effected error comes when catalyst contacts with atmosphere air. This leads to absorb carbon dioxide by the catalyst and influence catalyst activity. This phenomena can be avoided by using a vacuum place to keep the catalyst fresh along the experiment time. 53
GC samples are prepared after some days of experiment date. This can involve some errors in measuring the yield of biodiesel through GC analysis.
7- CONCLUSION The study aims to optimize operation conditions parameters for esterification of triglycerides for producing biodiesel catalysed by Li-CaO heterogeneous catalyst. Calcium oxide impregnated with Li was shown to be effective for the complete transesterification of rapeseed oil at 60°C with an oil/methanol molar ratio of 1:12, 160 rpm agitation speed and with 2.5 wt % catalyst (based on the weight of rapeseed oil) in one hour. It demonstrates that Li-CAO catalyst particle exhibits high catalytic activity in the transesterification reaction for biodiesel production by using rapeseed oil an edible vegetable oil in reliable easy and safety way. Esterification reaction of TG with a 12:1 methanol - oil mole ratio has the highest yield (97% to 99.7 % yield of the FAME). Raising operation temperature under a temperature range lower than methanol boiling point will increase the yield. An efficient process require a good agitation rate. At 63 °C, close to the methanol boiling point, the yield of obtained biodiesel can decrease under certain conditions (high mixing velocity) because the evaporation of the methanol. An increase of the amount of catalyst from 2.5 wt% to 5 wt% does not increase the amount produced biodiesel. An amount of 2.5 wt% catalyst is enough catalyst in order to achieve high yield of biodiesel At 60 °C, the yield of obtained biodiesel increase when the mixing rate increases from 160 to 320 rpm. The yield of produced biodiesel increases with the alcohol to oil ratio. At alcohol to oil ratio 6:1 the yield of produced biodiesel increases when the reaction time increases from 1 to 2 hours. At higher alcohol to ratio (9:1 and 12:1), an increase of reaction time from 1 to 2 hours does not increase the yield of produced biodiesel. The development of the reaction has been studied showing the relation conversion vs reaction time. At 65 min a yield of 92% has been obtained with a 6:1 methanol-oil mole ratio, 60 °C, 2.5% catalyst loading, 160 rpm agitation speed. Experiments using waste cooking oil has been performed showing a lower conversion the high amount of free fatty acids in the waste cooking oil, forming soaps that prevents the separation of the glycerol and ester. It is recommended to perform further kinetic studies at long time operation condition. The reusability of catalyst as well as the use of waste cooking oil should be further studied.
54
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60
9. ANNEXES Table 23 samples viscosities
Sample
VT(ml)
V Bio
V Cat.
V Gly.
V MeOH
Fall.tim.(s)
Viscos. Cp
0
118
107
7
4
0
5
1.9
1
66
51
10
5
0
6.5
2.47
2
74
60
9
5
0
5.5
2.09
3
74
60
6
8
0
4.5
1.71
4
68
49.5
13
5
0.5
7.5
2.85
5
76
52
13.5
10
0.5
4
1.52
6
83
62.5
19
1
0.5
4.5
1.71
7
67.5
46.5
16
4
1
5.5
2.09
8
78.5
46
17.5
4.5
0.5
7.5
2.85
9
86
63
12
1
10
4
1.52
10
66
42.5
20
3
0.5
6.5
2.47
11
71
51
15
5
0
4.5
1.71
12
77
58
13
5
1
4.5
1.71
13
66
48
12
5
1
4.5
1.71
14
64
51
10
2
1
6.5
2.47
15
66
57
5
4
0
5
1.9
16
75
57
15
3
1
4.5
1.71
17
71
61
6
4
0
4.8
1.82
18
77
67
8
2
0
4.89
1.86
19
67
62
3
2
0
5.1
1.94
20
66
50
15
1
0
5
1.9
21
67
54
11
2
0
5
1.9
22
66
48
16
2
0
5
1.9
61
Table 24: Experimental Result
62
Table 25 Experimental Result
63
