Biodiesel project report (meng amin) by M Mohsin Amin

The University of Western Ontario Faculty of Engineering Department of Chemical and Biochemical Engineering

Investigations of Esterification Step in Two-Step Esterification and Tranesterification Biodiesel Process M.Eng. Project report II (CBE- 9982) By Muhammad Mohsin Amin Student# 250652610 Supervisor Dr. Shahzad Barghi Co-Supervisor Dr. Anand Prakash

August 12, 2013

Abstract As a renewable liquid fuel, biodiesel is getting lot of attention worldwide. However, there is need to use low cost nonedible feedstock to avoid conflict with food supply. Nonedible oils which can be used as feedstock for biodiesel production are high in free fatty acids (FFA). High FFA feedstock can generate excessive soap formation using conventional alkaline catalyst. To avoid this problem, two step esterification and transesterification process is explored. This study investigates esterification step in more details with a view to minimize problems in the second step while keeping ensuring efficiency and cost effectiveness. Two homogeneous (H2SO4 and PTSA) and a heterogeneous (Amberlyst-15速) acid catalyst were used in esterification of high FFA containing feedstock. Semi batch or gradual feeding (G-Fed) reaction using 10 weight percent of H2SO4 was found most suitable to remove free fatty acids from nonedible oils to make them viable for the following base catalyzed transesterification reaction. Along with intrinsic catalytic performance, the process governing factors were also investigated. Without any costly post treatment to remove water from esterified oil, K2CO3 can be used as base catalyst in transesterification of feedstocks with high moisture contents. Potassium carbonate was used in transesterification reaction to determine its performance by estimating percent yields of biodiesel and glycerol. Excess amount of K2CO3 is required for transesterification process but compared to metal hydroxides and alkoxides it is more environment friendly because it is easily recoverable after the reaction as well as it neutralizes sulfuric acid to potassium sulfate that is commonly used as fertilizers.

Acknowledgement I have worked hard for this project report. However, it would not have been possible without the kind support and help of many individuals. I would like to extend my sincerest thanks to all of them.

I am highly indebted to Dr. Shahzad Barghi for his guidance and constant supervision as well as for providing necessary support in my academic progress.

I would like to extend my sincere gratitude to my professor and co-supervisor Dr. Anand Prakash for his support and intellectual guidance during the time of conducting my research. Dr. Prakashâ&#x20AC;&#x2122;s interest in renewable energy sources and environmental sustainability has allowed me to become a more conscious engineer in the field of green technology. I would also like to thank the Department of Chemical/Biochemical Engineering at Western University for supporting the growth of my career to become aware of the problems that we face today to maintain an environmental standard for energy consumption. Last but not least, I would like to thank Natalia Lesmes for introducing me to the experimental setup and helping with some of my experiments and analysis.

iii

Table of Contents

Title

Page No.

Title.............................................................................................................................................. Abstract....................................................................................................................................... Acknowledgment........................................................................................................................ Table of contents ........................................................................................................................ List of Figures............................................................................................................................. List of Tables...............................................................................................................................

i ii iii iv vi vii

1. Introduction........................................................................................................................... 1.1. Background.................................................................................................................... 1.2.Challenges in biodiesel production................................................................................. 1.3. Aims and objectives.......................................................................................................

1 1 1 3

2. Literature review.................................................................................................................... 2.1. Background and history of biodiesel.............................................................................. 2.2. Transesterification.......................................................................................................... 2.3. Esterification.................................................................................................................. 2.4. Variables affecting transesterification process............................................................... 2.4.1. Temperature and time.......................................................................................... 2.4.2. Type and amount of catalysts.............................................................................. 2.4.2.1. Base catalyst............................................................................................ 2.4.2.2. Acid catalysts.......................................................................................... 2.4.3. Alcohol/ oil ratio and type of alcohol................................................................. 2.4.4. Effect of free fatty acids and moisture contents of oil....................................... 2.4.5. Effect of cosolvent.............................................................................................. 2.4.6. Mixing speed....................................................................................................... 2.4.7. Glycerol separation.............................................................................................. 2.5. Monitoring and analysis of process................................................................................ 2.6. Novel materials and technologies for biodiesel production........................................... 2.6.1. Novel materials.................................................................................................... 2.6.2. Novel Technologies..............................................................................................

5 5 7 11 16

3. Experimental Section............................................................................................................. 3.1. Materials and Chemicals................................................................................................. 3.2. Equipment...................................................................................................................... 3.3. Experimental Procedure................................................................................................. 3.4. Esterification Process..................................................................................................... 3.5. Transesterification Process............................................................................................. 3.6. Two-Step Esterification-Transesterification Process.....................................................

29 29 29 30 32 33 35 37

16 17 17 18 19 21 22 24 24 25 27 27 28

37 38 38 39

3.7. Analysis and Characterization of Alkyl Esters............................................................... 3.7.1. Physical Characterization..................................................................................... 3.7.2. Chemical Characterization................................................................................... 3.7.2.1. Determination of Fatty Acid Content .................................................... 3.7.2.2. Determination of recovered H2SO4......................................................... 4. Results and discussion........................................................................................................... 4.1. Esterification.................................................................................................................. 4.2. Affects of catalysts and governing factors on esterification............................................ 4.2.1. Results ................................................................................................................... 4.2.2. Results of Run No. MA 1306-01........................................................................... 4.2.3. Results of Run No. MA 1306-02........................................................................... 4.2.4. Results of Run No. MA 1306-03........................................................................... 4.2.5. Results of Run No. MA 1306-04........................................................................... 4.2.6. Results of Run No.MA 1306-05............................................................................ 4.2.7. Results of Run No. MA 1306-06........................................................................... 4.2.8. Results of Run No. MA 1306-07........................................................................... 4.2.9. Results of Run No. MA 1306-08........................................................................... 4.2.10. Results of Run No. MA 1306-09........................................................................... 4.3. Estimation of H2SO4 recovery......................................................................................... 4.3.1. Results of (MA 1306-10) and ( MA 1306-11)...................................................... 4.4. Two Step Esterification and Transesterification for High FFA Feedstock..................... 4.4.1. Results for two-step transesterification.................................................................

40 40 40 42 42 43 44 47 49 50 52 54 56 58 58 62 63

5. Conclusions and Recommendations....................................................................................... 6. Nomenclature.......................................................................................................................... 7. References..............................................................................................................................

65 66 67

List of Figures

Sr No.

Title

Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9

A typical transesterification reaction.......................................................... Mechanism of base catalyzed transesterification........................................ Mechanism of acid catalyzed transesterification........................................ Mechanism of acid catalyzed esterification (Step 1- Step4)....................... Flow diagram of two step methanolysis process........................................ A summary of possible reaction routs........................................................ Experimental setup for transesterification and esterification..................... Flow diagram for esterification step........................................................... Process flow diagram for transesterification using Batch and G-fed mode.......................................................................................................... Flow diagram for a two-step esterification transesterification process...... Decrease in FFA% with time for batch reaction using 5% H2SO4 ............ Decrease in FFA% with time for batch reaction using 10% H2SO4 .......... Decrease in FFA% with time for G-Fed reaction using 5% H2SO4........... Comparison of decrease in FFA% with batch vs. G-Fed reactions using 5% H2SO4.................................................................................................. Decrease in FFA% with time with G-Fed reaction using 10% H2SO4....... Comparison of decrease in FFA% for batch vs. G-Fed reactions using 10% H2SO4................................................................................................. Decrease in FFA% with time for G-Fed reaction using 5% PTSA............ Decrease in FFA% with time for G-Fed reaction using 10% PTSA.......... Decrease in FFA% with time for G-Fed reaction using 5% Amberlyst15速 ............................................................................................................. Decrease in FFA% with time for Batch reaction using 5% Amberlyst15速.............................................................................................................. Comparison of decrease in FFA% for batch vs. G-Fed reactions using 5% Amberlyst-15速..................................................................................... Decrease in FFA% with time for batch reaction using 10% Amberlyst15速.............................................................................................................. Electrophilic addition of sulfuric acid to double bond..............................

Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure21 Figure 22 Figure 23

Page No.

8 9 10 11-12 15 22 30 33 35 37 42 43 45 46 47 48 49 51 52 55 55 57 61

List of Tables

Sr No.

Title

Page No.

Table 1

Requirements for Biodiesel (B100) Blend Stock ASTM D6751......................

Table 2

Experimental conditions for acid catalyzed esterification reactions..................

Table 3

Decrease in FFA conc. using 5 wt % H2SO4 in batch reaction..........................

Table 4

Decrease in FFA % with time with 10 wt % H2SO4 in batch reaction..............

Table 5

Decrease in FFA % using 5 wt % H2SO4 (G-Fed mode)..................................

Table 6

Decrease in FFA % using 10 wt % H2SO4 in G-Fed reaction...........................

Table 7

Decrease in FFA % using 5 wt % PTSA in G-Fed reaction..............................

Table 8

Decrease in FFA % using 10 wt % PTSA in G-Fed reaction............................

Table 9

Decrease in FFA % using 5 wt % Amberlyst-15速 in G-Fed reaction...............

Table 10

Decrease in FFA % using 5 wt % Amberlyst-15速 in batch reaction.................

Table 11

Decrease in FFA % using 10 wt % Amberlyst-15速 in batch reaction..............

Table 12

Initial and final FFA % and H2SO4 recovery % for blank run and stearic acid reactions............................................................................................................... 59

Table 13

Results of two-step transesterification reaction using 5 wt% H2SO4 and 3 wt% K2CO3........................................................................................................................................................ 64

vii

1. Introduction 1.1. Background Alternative fuels are becoming high priority of many countries and are poised to play increasingly important role in the future. Biodiesel is one of alternative fuels with high interest because it is biodegradable, environment friendly, has low emission profile and is non-toxic. It is an alternative fuel, which can be used without any modification in diesel engines. An ideal diesel fuel is composed of non-branched hydrocarbon molecules with carbon number ranging from 1218. While natural oils and fats are triglycerides (esters derived from glycerol and three fatty acids) which are several times more viscous and have very large carbon numbers. Direct combustion of triglycerides in engine is not possible because they cannot be atomized in injection system of a compression engines. Therefore, modification of triglycerides is necessary to use them in diesel engines. This can be done by hydrolysing triglycerides into free fatty acids and then reacting these fatty acids with alcohol (usually methanol) in the presence of catalyst to make fatty acid alkyl esters (or biodiesel). The method of converting fatty acids into alkyl esters (FAME) is called esterification. Transesterification refers to simultaneous hydrolysis of triglyceride and esterification of fatty acids in the presence of catalyst. This is a three step process in first step one molecule of alcohol reacts with one fatty acid group of triglyceride to give one fatty acid methyl ester, similarly second and third steps yield two more fatty acid methyl esters. Overall reaction yields three FAMEs and a glycerol molecule. 1.2. Challenges in biodiesel production Oils and fats from natural sources are various combinations of fatty acid and glycerol esters. Fatty acid components vary in length of carbon chain and number of double bonds. Generally,

fats contain saturated large chain fatty acids. While oils have highly unsaturated, small chain fatty acids. Soybean oil, sunflower oil, corn oil, canola oil, rapeseed oil, palm oil, coconut oil, castor oil, jatropha oil, and beef tallow are examples of natural oils and fats. Current technologies involved to produce biodiesel at commercial level (known as first generation biofuel technologies) depend upon these natural resources which are primary feedstocks for biodiesel production. These feedstocks are in direct competition with availability of food resources in developing countries. Using highly refined vegetable oils as raw material, results in biodiesel as an expensive energy source. Cheaper and alternative feedstocks (like: Greases, waste oil, oil from non-food crops, oil from micro algae) can accommodate challenges of availability of raw material for biodiesel production. Current technologies mostly use homogeneous catalytic transesterification of triglycerides in batch-type process. Transesterification is usually carried out in the presence of a homogeneous base catalyst (NaOH, KOH) or homogeneous acid catalyst (H2SO4, para-toluene sulfonic acid (PTSA) and H3PO4). There are few drawbacks in using these catalysts. 1) Undesirable side reaction (saponification) can take place in homogeneous base catalysed transesterification. In saponification reaction metal part of base reacts with free fatty acid to make alkaline soap of fatty acid. Saponification also involves production of water which limits the process equilibrium. This will result in low quality biodiesel and requires large amount of feed stock for production. 2) Homogeneous acid catalyst not only involves esterification of free fatty acids in feedstock but also involves transesterification of triglycerides. This process is not sensitive to the presence of free fatty acids in feedstock and gives good quality biodiesel but it is thousand times slower than base catalysed transesterification 3) Pre-treatment of feedstock with acid catalyst to convert free fatty acids into biodiesel in one reaction unit and performing transesterification of feedstock with 2

base catalyst in next reaction unit can speed up the production and hinder the saponification. This can improve the biodiesel quality but adding an extra treatment unit will increase production cost. 4) Also, transesterification reaction using homogeneous catalysts requires purification step to recover excess alcohol and catalyst. Treatment of toxic wastewater produced as result of downstream processing is another issue. Pretreatment, downstream processing and wastewater treatment are involved in energy consumption that will affect on final production cost of biodiesel. To compete with petroleum-based diesel and making biodiesel commercially available a continuous process can replace the time consuming batch process. Additionally, replacing liquid catalysts with heterogeneous catalysts can minimize separation steps. Heterogeneous acid catalysts have several advantages in biodiesel synthesis but research involved in use of acid catalysts has been limited because of unexpectedly low reaction rates. Their feasibility of using in continuous process has not been investigated. Biodiesel produced from alternative feedstocks using intensified technologies is known as second generation biodiesel. 1.3. Aims and objectives The focus of this research is biodiesel synthesis from oils with high free fatty acid contents. Two step esterification-transesterification process is required when FFA contents in feedstock are greater than 1% (Canaki and Gerpen, 2001; Jain and Sharma, 2010). Using low quality feedstock, which have higher contents of free fatty acids, transesterification process is affected by saponification. Thus, to get significant increase in yield of biodiesel, this research was focused on pre-treatment of feedstock by transforming FFAs to alkyl esters through esterification followed by transesterification. The intrinsic catalytic performance of different acid catalysts for esterification reaction, an important step for reduction of FFA contents in oils, has been studied

to compare factors that govern the process. Most relevant factors observed in this study are following: 

Ratio of alcohol to FFAs



Type of FFAs present in feedstock



Amount of catalyst



Type of catalyst



Mixing speed (RPM)



Flow rate of feedstock



Reaction temperature



Mode of reactor operation (Batch , semi-batch or continuous)

2. Literature review 2.1. Background and history of biodiesel Rudolf Diesel in 1912 proclaimed that, through vegetable oils “....Motive power can still be produced from the heat of the sun, always available, even when the natural stores of solid and liquid fuels are completely exhausted” (Pahl, 2005). Model of diesel engine at very beginning of its invention was designed to run on vegetable oil and other alternative fuels, not the low-grade petroleum distillate known today as diesel fuel. In the course of time, economics favored the use of petrodiesel (then waste by-product) over the higher cost virgin oils such as peanut and hemp (Pahl, 2005). Diesel engine’s ability to utilize vegetable oil based fuels was rediscovered during the oil embargo of 1973. G. Chavanne at the University of Brussels was the early worker who conducted experiments on the use of ethyl esters of palm oil in a diesel engine. This research resulted in Belgian patent # 422877 (Peterson, 2006). By 1974, the price for a barrel of oil had risen from $3 to $12 (Pahl, 2005). Renewable energy sources and agriculturally derived fuels were investigated. Early experiments suggested that the diesel engine had been highly optimized for the use of petrodiesel over the years and that the use of straight vegetable oil held the potential for severe engine damage (Pahl, 2005). The two viable options were either to modify the engine or to modify the fuel in order to attain compatibility (Mittelbach, 2004). It was impractical to modify diesel engine for straight use of vegetable oil. To modify the fuel was more sensible approach. Throughout 1980s a young chemist Martin Mittelbatch produced a vast body of work which resulted in the foundation of biodiesel industry. His initial process remains the primary method for biodiesel production on industrial scale. The term “biodiesel” now refers

to alkyl esters derived from vegetable oil, animal fat, waste oil and microalgal oil through the process of transesterification. In various universities of United States batch pilot plants (under 1000 gallon/batch) were designed. University of North Dakota produced sunflower methyl ester (Hasset et al., 1988); the University of Idaho produced methyl ester of rapeseed (Caringal, 1989) and Colorado school of mines produced biodiesel from waste cooking oil (Reed, 1991). Interchem Industries Inc. (Leawook, Kansas city) contracted Proctor and Gamble Co. to produce up to 15 million gallons/year of methyl ester at plants in Massachusetts and California since 1992 (Chowdhury et al. 1993; Caruana et al. 1992; Interchem, 1992). The Gratech division of Straco Inc. in Kansas city constructed plant to produce 3 to 12 million gallons/year of methyl ester (Chemical engineering, 1992a). The worldâ&#x20AC;&#x2122;s first industrial biodiesel plant with 60,000 metric ton/ year capacity at Livono, Italy started up by Milan-based Novamount in 1992; with the second biodiesel plant of increased annual capacity by 100,000 metric ton/year to 160,000 metric ton/year (Chemical Engineering 1992 b, c). Societe Annon. (1965) developed a two step process for the conversion of acidic oils to methyl ester. Fatty acids first be esterified in the absence of catalyst with added glycerol at 210 0C-230 0C at 5-10 mm of Hg and then inter esterified with methanol and alkaline catalyst to afford a yield of totally available fatty acid contents from the acidic oil of well over 90%. A German patented semi-continuous ATT process was reported in 1988 (H. Stage, 1988). Oil with 15 % FFAs was first purified by removing free fatty acids. The purified oil was then transesterified with methanol at 80 0C. Methods such as purification and recovery of by-products glycerine, FFAs and methanol were also included in the process.

2.2. Transesterification Transesterification is a reaction by which lower alcohols react with triglycerides (oil or fat) to yield a fatty acid alkyl ester. This process was described by Duffy in 1852 (Mittelbach, 2004). More broadly transesterification is also referred to as alcoholysis. For a specific alcohol the â&#x20AC;&#x201C;ysis suffix is appended to the name of reacting alcohol for example, transestrification with methanol is referred to as methanolysis (Tyson, 2002). Transesterification process is slow under normal conditions without the presence of catalyst. Reaction is catalyzed by either base or acid. Traditionally, alkaline catalyst such as sodium or potassium hydroxide is favored over acid catalyst because it gives thousand times greater reaction rate than acid catalysts under standard temperatures and pressure. Relative insolubility of alcohol in oils arises the necessity for a catalyst. Catalysts provide a phase-transfer as well as an ion exchange effect which reduces reaction times by many orders of magnitude (Mittelbach, 2004). Transesterification will occur within reasonable time without the presence of a catalyst in process called supercritcal methanolysis. Conditions are typically extreme with temperatures as high as 235 0C and pressures in the range of 62 bars (Mittelbach, 2004). Supercritical methanolysis is not practical for industrial purposes. Han (2005) investigated supercritical methanolysis using co-solvents resulting in much milder reaction conditions. A typical transesterification reaction is given in figure 1.

CH2 OCOR1 CH

CH2OH

OCOR2 +

3CH3OH

Catalyst

CH2 OCOR3 Triglyceride

CH2OH

R1COOCH3 +

R2COOCH3

CH2OH Methanol

Glycerol

R3COOCH3 Fatty acid methyl esters

Figure 1: A typical transesterification reaction Mechanism of base catalyzed transesterification involves interchange of alkoxide group between an ester and alcohol to give a new ester and a new alcohol (figure 2). While mechanism of acid catalyzed transesterification is a three step process. The first step involves protonation of carboxylic group by proton of catalyst. Second step involves nucleophilic attack of alcohol to make a tetrahedral intermediate and in third step deprotonation and breakage of tetrahedral intermediate takes places (figure 3). Overall, either by base catalyzed or by acid catalyzed transesterification reaction, each fatty acid of triglyceride molecule yields a fatty acid methyl ester (FAME). Therefore, a triglyceride molecule yields three FAME molecules and a glycerol molecule. The stoichiometry of the reaction requires molar ratio 3:1 of alcohol to triglyceride. Equilibrium constant would be close to unity because esters and alcohols appear on both sides of equation. However glycerol moiety is not such a good nucleophile as lower alcohols. As the reaction is reversible, so excess alcohol is typically used in practice to force the reaction towards ester production (Khan, 2002). Reaction formats were adapted from Mittelbach (2004).

R' OH

Alcohol

KOH

R'O K + H

CH2

Alkali O KOH

O C

CH2 O

O Ester

CH2

+ OR' Alkoxide

CH2

O Triglyceride

O O

CH2

OR' C

CH2 CH2

CH2

OH +

New Alcohol C R2

O O

CH2 CH2

C O

Diglyceride

R1COOR' New ester or Fatty acid methyl ester

Figure 2: Mechanism of base catalyzed transesterification 9

O O

CH2

H C

CH2

OH O

CH2

C R2

CH2 CH2

+ O

R'OH

CH2 CH2

CH2

OH O

CH2

C R1

CH2

C O

Diglyceride

OR '

R3 Fatty acid methyl ester

Figure 3: Mechanism of acid catalyzed transesterification

2.3.Esterification Esterification is a reaction by which free fatty acid reacts with alcohol to produce alkyl ester and water. It occurs directly between the alcohol and fatty acid molecule. Intermediate steps for cleaving of triglyceride molecule is not present this is the reason that no glycerine molecule is produced during esterification reaction. Fatty acid esterification is also known as Fischer esterification. Reaction mechanism involves following steps (Figure 4). Step 1: Protonation of fatty acid

Rearrangement:

Step 2: Reaction with Alcohol:

Step 3: Removal of water:

Step 4: Regeneration of sulfuric acid (catalyst):

Figure 4. Mechanism of acid catalyzed esterification (Step 1- Step4) Water produced as a result of esterification reaction can be removed either by distillation or by the addition of dehydrating agent such as magnesium sulfate or molecular sieves (dehydrated zeolite crystals that adsorb water). It is a commonly used method in industry (Wade, 1991). Esterification is an important step in biodiesel production from low grad feedstocks such as brown grease, thermally or chemically degraded waste oil. Degraded feedstocks contain high level of free fatty acids which can easily react with alkali in base catalyzed biodiesel production to form soap. Two problem may arise from this: 1. Catalyst is consumed in soap formation resulting in higher chemical cost or an incompllete or failed reaction.

2. Soap produced by reaction between fatty acid molecules and catalyst results in impurities in biodiesel and must be washed out (Lotero, 2005). Tyson, (2002) reported that â&#x20AC;&#x153; free fatty acids are always present in oils, however mass concentration above 4% will generate more soap than can be dealt with reasonably in a conventional base catalyzed reaction and will prevent the reaction from going to completion in almost all cases. Brown greases contain fatty acid concentrations in excess of 15% with typical values closer to 60%. It not unusual for heavily degraded brown grease to contain nearly 100% free fatty acid. Due to the greater FFA concentrations in brown grease, processing requires multiple esterification and dewatering stages as well as additional byproduct separation and purification stepsâ&#x20AC;?. Such facts result in ineffectiveness of conventional methods of biodiesel production from brown grease or other ultra high FFA oils as feedstocks. As previously discussed , the esterification reaction is important step for pre-treatment of lowgrade feedstock before going to biodiesel production because it reduces the FFA concentration from degraded oils and greases. Both esterification and transesterification reactions are employed in a two step process in industry. First to convert the FFA into alkyl esters by esterification and then to convert the remaining triglycerides into methyl esters by transesterification. Zullaikah, (2005) reported the outline of two step acid catalyzed methanolysis of rice bran oil for the complete conversion of FFA and triglycerides to fatty acid methyl esters as follows: 1. High FFA oil and methanol with molar ratio MeOH/FFA (5/1) and sulfuric acid (2 wt %) was taken in reactor at 60 0C and atmospheric pressure. Reaction was carried out for 2 hours until the FFA concentration was reduced to acceptable level for base catalyzed transesterification. 13

2. Organic phase was separated from aqueous layer and condensed (at 40 mm Hg and 100 0

C). Aqueous layer containing methanol, sulfuric acid and water was neutralized with

suitable alkali. 3. Esterified oil was then transferred to another reactor for transesterification (methanolysis) reaction. 4. Washing and post-processing steps were done to get biodiesel fuel. Glycerine byproducts were treated to remove soap and excess methanol. Samples in each step were withdrawn at regular intervals and water soluble components were removed by water washing. The organic phase after washing was characterized. The ester conversion was estimated based on change in percentage composition of triglycerides, free fatty acids, fatty acid methyl esters and partial glycerides before and after the reaction. The contents of other minor components of feedstock were neglected in the calculation of conversion. Effect of fatty acid composition of feedstock, temperature on storage of feedstock, moisture level in FFA conversion during storage, catalyst concentration and effect of rancid products on feedstock were also analyzed. Based on Zullaikaâ&#x20AC;&#x2122;s process outline a schematic flow diagram of two step methanolysis process is given in figure 5.

Separator

Oil Feed

Alcohol and catalyst for post treatment

Esterification Reactor Alcohol+Catalyst

Organic layer containing triglycerides

Step 1

Alcohol+Catalyst

Transesterification Reactor

Post treatment unit

Alkyl esters

Separator

Evaporation unit

Biodiesel

Alcohol removal Glycerol purification

Step 2

Pure glycerole

Evaporation unit

Post treatment unit

Figure 5: Flow diagram of two step methanolysis process

2.4. Variables affecting transesterification process The important variables which affect the rate of alcoholysis, yield/purity of fatty acid methyl esters include: 1) Temperature and time, 2) type and amount of catalyst, 3) alcohol/ oil ratio and type of alcohol, 4) quality of oil i.e., moisture, amount of rancid products and free fatty acid contents, 5) effect of cosolvents, 6) mixing speed, 7) and extent of glycerol separation. 2.4.1. Temperature and time Transesterification can take place at different temperatures depending on oil used. Freedman et. al. (1984) studied the transesterification of refined oil with oil/methanol ratio 6:1 and 1% NaOH at three different temperatures. After 0.1 hour yield was 94%, 87% and 64% for 60 0C, 45 0C and 32 0C, respectively. After 1.0 hour yields were identical for 60 0C and 45 0C while slightly lower for 32 0C. These results aslo indicate that conversion rate is increased with reaction time. Ma et al. (1999) studied effect of time for transesterification reaction of beef tallow with methanol. Very slow reaction was observed during first minute due to mixing and dispersion of methanol in tallow. Reaction proceeded very fast from one to five minutes and methyl ester production reached the maximum at about fifteen minutes. Acid catalyzed transesterification reactions were first conducted under high temperature and presure (Taylor and Clarke, 1927). They commonly require temperatures above 100 0C (Markey, 1961). The effect of temperature on ester formation for the reaction of 1-BuOH with SBO at molar ratio of 30: 1 catalyzed by 1 wt% H2SO4 was studied by Freedman et al., (1986). Five temperatures ranging from 77-117 0C were exmined. Results showed that ester formation is essentially complete in 3 hours at 117 0C compared to 77 0

C for 20 hours. (Freedman et al., 1984) investigated the transestrification of soybean oil with 16

methanol, ethanol and butanol using 1 wt % concentrated sulfuric acid based on 30:1 alcohol to oil molar ratios. Each alcoholysis reaction was conducted near boiling point of respective alcohol. The time needed to get conversions of 93% were 3, 22 and 69 hours for butyl, ethyl, and methyl alcohols respectively. Final conversion of 93% was similar for all three alcohols after 69 hours at 65 0C. 2.4.2. Type and amount of catalysts Generally, two types of catalysts are use for transesterification: acid catalysts and base catalysts. They are further classified as homogeneous or liquid catalysts and heterogeneous or solid catalysts. Along with acid or base catalysts several enzymes are also being explored for catalysis of transesterification reactions. 2.4.2.1. Base catalyst Base catalyzed transesterification is considerably faster than acid catalyzed reaction and can be used at ambient temperatures. Also, base catalysts are less corrosive to reactor than acid catalysts. Therefore, base catalyzed process is mostly preferred for transesterification in commercial practice. Among homogeneous alkali catalysts sodium hydroxide, sodium methoxid, potassium hydroxide and potassium methoxide are more effective Ma et al (1999). Ma et al., (1998) studied the methanolysis of beef tallow with catalysts NaOH and NaOMe. When comparing the two catalysts, NaOH was significantly better than NaOMe. Both catalysts NaOH and NaOMe reached their maximum activity at 0.3% and 0.5% w/w of the beef tallow, respectively. NaOMe causes formation of several by-products mainly sodium salts, which are to

be treated as waste Meher et al., (2006). In addition, high quality oil is required with this catalyst (Ahn, 1995). Meher et al., (2006) reported that, mostly sodium hydroxide or potassium hydroxide have been used in the process of alkaline methanolysis, both in concentration from 0.4 to 2% w/w of oil. Crude and refined oils with 1% either sodium hydroxide or potassium hydroxide catalyst resulted successful conversion. Transesterification of soybean oil with the catalyst 1% potassium hydroxide has given the best yields and viscosities of the esters Tomasevic et al., (2003). Gryglewicz (1999) reported that the alkaline-earth metal hydroxides, alkoxides and oxides catalyzed reaction proceeds slowly as the reaction mixture constitutes a three-phase system oilâ&#x20AC;&#x201C;methanol-catalyst, which for diffusion reason inhibits the reaction. 2.4.2.2. Acid catalysts Acid catalyst is preferred for transesterification reaction when oil has high free fatty acid contents and more water. Homogeneous acid catalysts could be sulfuric acid, hydrochloric acid phosphoric acid, or organic sulfonic acid. Mohamad and Ali (2002) studied acid catalyzed transesterification with waste vegetable oil. Reaction was conducted at four different catalyst molar concentrations, 0.5, 1.0, 1.5 and 2.25 HCl in presence of 100% excess alcohol and the result was compared with 2.25 molar H2SO4 and the viscosity decrease was investigate. Sulfuric acid had superior catalytic activity in the range of 1.5â&#x20AC;&#x201C;2.25 M concentration.

Although, two step transesterification process gives high ester conversion in short reaction time the reaction has several drawbacks: it is energy demanding, glycerol recovery is difficult, alkaline waste water requires treatment, acidic or base catalyst has to be removed from product, free fatty acid and water interfere the reaction.

These problems can be overcome using 18

heterogeneous catalysts Shurti et al., (2012) or enzymatic catalysts Fuduka, Kondo and Noda (2001). Limited research has been shown the ester conversion using heterogeneous catalysts so it is not yet acceptable for commercial applications. On the other hand the production cost using lipase catalyst is significantly greater than that of alkaline catalyst.

2.4.3. Alcohol/ oil ratio and type of alcohol Molar oil ratio of alcohol to triglyceride is most important variable that affects the yield of ester. Stoichiometrically transesterification requires three mole of alcohol and one mole of triglyceride to yield one mole of glycerol and three moles of fatty acid alkyl esters. While, transesterification is an equilibrium reaction and for maximum conversion to esters excess amount of alcohol is required to drive the reaction to forward direction. However, excess alcohol increase the solubility of glycerin and interfere its separation. Presence of glycerin favors the reaction to proceed backward. Base catalyzed methanolysis or ethanolysis reactions take place at the inter-phase between two phases (two slightly miscible liquids). Triglycerides are more soluble in longer chain alcohols as compared to small chain alcohols. Therefore, alcoholysis reaction rate must increase when taking place between more miscible liquids or in a solvent system where reactants are greatly soluble or in other words more in contact with each other. Branched alcohols were less reactive than the corresponding straight chain alcohols (Gauglitz and Lehman 1963). This might be due to steric hindrance. Base catalyzed formation of ethyl ester is more difficult compared to ethyl ester. This is due to formation of stable emulsion between mono- and diglyceride intermediates and ethanol during

ethanolysis. While in case methanolysis these emulsions easily and quickly break down into upper methyl ester rich layer and lower glycerol rich layer. Explanation of more stable emulsion formation in ethanolysis is: During intermediate formation glycerol backbone has a more polar hydroxyl group and one or two less polar hydrocarbon groups. On the other hand base catalyst is solubilised with polar ethanol. Mono- and diglyceride intermediates are strong surface active agents which along with base (especially NaOH or caustic) enhance reduction of surface tension of whole system. When reaction proceeds to a critcal level where mono- and diglyceride intermediates are high enough the ethoxide, (where electron pair of oxygen partly shared with two carbon atoms as compared to methoxide where electron pair is shared with one carbon) has lesser strength for nucleophillic attack to more strongly bounded second or third fatty acid group of mono or diglyceride, favors the formation of stable emulsion.

The phenomenon is different for butanolysis. When butanolysis and methanolysis take place at 6:1 molar ratio (Freedman et al., 1986). Butanolysis occurs faster than methanolysis because nbutanol provides strong solubility resulting in large mass transfer interface ( or formation of one phase). Mass transfer occurs before the formation of stable emulsion. The final acid values for the 20% FFA case were higher for ethanol than for methanol, the rate of the reaction was faster for ethanol. This may be due to the higher reaction temperature or ethanolâ&#x20AC;&#x2122;s higher solubility in oils and esters. The final acid values for ethanol reacting with the 40% FFA feedstock were lower than with methanol (Kanaki and Van, 2001). For ethanolysis these emulsions are more stable and complicate the separation and purification of esters (Mittelbatch, 2004).

Although some research has gone into the production of methanol from agriculture sources but mostly methanol is a petroleum-based product. This reason make methanol less environment friendly.

2.4.4. Effect of free fatty acids and moisture contents of oil For base catalyzed alcoholysis, the straight materials should meet certain specifications. Feedstock should have lower acid value and it should be substantially anhydrous. The addition of more sodium hydroxide catalyst compensates for higher acidity, but the resulting soap causes an increase in viscosity or formation of gels that interferes in the reaction as well as with separation of glycerol Freedman at. al.,(1984). If the reaction conditions do not meet the above requirements ester yields will be significantly reduced. In general the higher the free fatty acid contents of oil smaller is the ester conversion efficiency. Therefore, to carry out base catalyzed transesterificaion process FFA value of feedstock should be at least lesser than 3%. Both, excess as well as insufficient amount of base catalyst leads to soap formation. As shown in previous pages (in figure 2) water is formed in by equilibration of hydroxide of alkali with hydride of alcohol but it is too weak to act as nucleophile to attack the ester. However, the presence of excess water would significantly reduce the amount of alkoxide avialable for transesterification. A summary of possible reaction routes is shown in figure 6.

OH Moisture in feedstock favor hydroxide formation

Alkoxide attacks tri-, di-, monoglycerides

Alkyl ester

gr lon

OH attacks tri-, di-, monoglycerides and esters

Soap

Re-esterification is possible only at high temperature. Figure 6: A summary of possible reaction routs.

Transesterification reaction of beef tallow catalyzed by NaOH in presence of free fatty acids and water was studied by Ma et. al., (1998). In the absence of FFAs and water, apparent yield of beef tallow methyl esters (BTME) was highest. On addition of 0.6 % FFA, yield of BTME reached the lowest i.e., less than 5% while addition of any level of water resulted same. In the absence of FFAs when 0.9% of water was added the apparent yield was about 17%. The product was solid at room temperature, similar to the original beef tallow. Low quality beef tallow or vegetable oil with high FFAs should be refined by saponification to remove free fatty acids or acid catalyzed esterification can be alternative approach to refine the low quality beef tallow or oil.

2.4.5. Effect of cosolvent When two insoluble liquids are brought together into a third liquid, in which both liquids are soluble the third liquid is called cosolvent. The cosolvent is used to increase solubility and reactivity of immiscible liquids. Various co-solvents specifically for base catalyzed transesterification have been reported. Tetrahydrofuran (THF), 1,4-dioxane, diethyl ether, and 22

methyl tertiary butyl ether (MTBE) have been tested to conduct transesterification reaction in a single phase. Tetrahydrofuran is usually chosen because it boiling point is 67 0C, only two degrees higher than that of methanol, and can be co-distilled and recycles (Boocock et al., 1996). At University of Toronto (Mao, 1995) researchers reported one-phase base catalyzed methanolysis of soybean oil using tetrahydrofuran (THF) as co-solvent. Methanolysis of soybean oil at room temperature was compared with 0.5 wt %, 1.0 wt %, 2.0 wt % (NaOH), 0.5 wt %, 1.0 wt %, 1.35 wt % NaOCH, and 1wt% KOH at different methanol/ oil ratios. 98% methyl ester was resulted after only three minutes at 2.0 wt% NaOH, along with some soap. “Using tetrahydrofuran, transesterification of soybean oil was carried out with methanol at different concentrations of sodium hydroxide. The ester contents after 1 min for 1.1, 1.3, 1.4 and 2.0% sodium hydroxide were 82.5, 85, 87 and 96.2%, respectively. Results indicated that the hydroxide concentration could be increased up to 1.3 wt%, resulting in 95% methyl ester after 15 min. Similarly for transesterification of coconut oil using THF/MeOH volume ratio 0.87 with 1% NaOH catalyst, the conversion was 99% in 1 min (Boocock et al., 1998)”.

“A single-phase process for the esterification of a mixture of fatty acids and triglycerides were investigated. The process comprises forming a single-phase solution of fatty acids and triglyceride in an alcohol selected from methanol and ethanol, the ratio of said alcohol to triglyceride being 15:1–35:1. The solution further comprises a cosolvent in an amount to form the single phase. In a first step, an acid catalyst for the esterification of fatty acid is added. After a period of time, the acid catalyst is neutralized and a base catalyst for the transesterification of triglycerides is added. After a further period of time, esters are separated from the solution (Boocock et al., 2001)”.

2.4.6. Mixing speed Methanol and ethanol are immiscible with triglycerides at ambient temperature and usually reaction mixtures need mechanical stirring to enhance mass transfer. Therefore, mixing is very important for transesterification reaction. Once the two phases are mixed enough alcoholysis reaction starts and stirring is no longer required. Ma et al., (1999) studied the mixing effect on transesterification of beef tallow. There was no reaction when catalyst (NaOH) and methanol were added to melted beef tallow in without mixing. While significant mixing speed was approached reaction time was controlled to determine the yield of methyl esters. Thus, stirring speed exceed the threshold requirement of mixing. 2.4.7. Glycerol separation Glycerol is a by-product of transesterification. It has several industrial uses such as application in costmetics, soap softening, medicines, food preserving, and coolants to avoid crystallization of water. Glycerol produced by alcoholysis of refined fats is anhydrous and can directly be used in various industrial process without much refining. As shown in figure 6. If feedstock has moisture it favors formation of hydroxide ion which is a strong nucleophile and it can attack all forms of esters (tri-, di-, monoglycerides and alkyl esters to make the soap and a small amount of base. Soap formation can interfere with glycerol recovery and lower down the alkyl esters concentration by reversing esterification reaction in the presence of fatty acid soaps, glycerol and unreacted alcohol. Following the reaction, glycerol is removed from the fatty acic alkyl esters. Glycerol has low solubility in esters therefore, separation can occur quickly. Excess alcohol can solubilise the glycerol and can slow down the separation. However, this excess alcohol is usually not removed from the reaction mixture until after the glycerol and methyl esters are separated due to concern

about reversing the transesterification reaction. Usually water is added to reaction mixture after completion of transesterification, to improve the separation of glycerol ( Wimmer, 1995).

2.5.Monitoring and analysis of process Several attempts have been made to analyze individual aspects of both esterification and transesterification reactions because every researcher has focused only on specific technology, methodology, materials, parameters and interest. Considering basic process of esterification and transesterification most important aspects which should be monitored are: 

Concentration of FFA in the begining and at the end of process



Amount of mono-, di-, triglycerides and total glycerol in product



Moisture contents in feedstock.



Oxidized and rancid materials in feedstock



Impurities in final product after downstream processes

However, ASTM method (D 6751 12) specified the limits of various parameters in biodiesel Table 1 shows these limits:

Table 1. Requirements for Biodiesel (B100) Blend Stock ASTM D6751.

Requirements for Biodiesel (B100) Blend Stock ASTM D6751 Property

Test Method

Limits

Units

Calcium and magnesium combined

EN14538

5 max

ppm

Flash point

D93

93.0 min

°C

Water and sediment

D2709

0.050 max

vol %

Kinematic viscosity, 40°C

D445

1.9-6.0

mm2/s

Sulfated ash

D874

0.020 max

% mass

Sulfur

D5453

0.0015 max (S15) 0.05 max (S500)

% mass

Copper strip corrosion

D130

0.020 max

Cetane number

D613

47 min

Cloud point

D2500

Report to customer

°C

Carbon residuea

D4530

0.050 max

% mass

Acid number

D664

0.50 max

mg KOH/g

Free glycerin

D6584

0.020

% mass

Total glycerin

D6584

0.240

% mass

Phosphorus content

D4951

0.001 max

% mass

Distillation temperature, 90% recovered (T90)b

D1160

360 max

°C

Oxidation stability

EN14112

3 min

hours

Cold Soak filterability

Annex A1

360 maxc

seconds

(1) Methanol content

EN14110

0.2 max

vol %

2) Flash point

D93

130 min

°C

Alcohol control - One of the following must be met:

Carbon residue shall be run on the 100% sample.

Atmospheric equivalent temperature.

B100 intended for blending into diesel fuel that is expected to give satisfactory vehicle

performance at fuel temperatures at or below 10째F (-12째C) shall comply with a cold soak filterability limit of 200 s maximum.

2.6.Novel materials and technologies for biodiesel production: 2.6.1. Novel materials: Novel materials which are being used to produce biodiesel are: 1. lipase catalysts immobilized in membrane used in the absence of organic solvents Al-Zuhair et al., (2007), Kaieda et al., (1999) and( Shah et al., 2004). 2. Replacing methanol with diethylamine to produce N,N-diethylstearamide (amide biodiesel) (Haas, 2005). 3. Using strong oxidizing agent (H2O2) along with catalyst capable of oxidizing olefinic double bonds to vicinal diols (intermediate compounds) in first step and oxidizing vicinal diol group to carboxylic groups in second step yielding triglycerides containing more than one acid functions which are hydrolyzed to get fatty acids with more acid functions. These fatty acids can be esterified to produce molecules having more than one fatty acid methyl ester branches US Patent, 2012323028 A1 (2012). 4. Using alkaline hydrolysis of triglycerids and saponifying fatty acids to get soap stock. This soap stock can be used as feed stock in esterification process for

biodiesel production in the presence of acid catalyst and methanol Lotero et al., (2005). 5. Esterification/transesterification of low quality feed stocks in the presence of heterogeneous catalysts Liu et al., (2006). Different kinds of heterogeneous solid (both acid and base) catalysts are used.

2.6.2. Novel Technologies: Some of the novel reactor technologies explored for process intensification include: supercritical reactors, reactive distillation, two phase bubble column reactors, three phase bubble column reactors, packed bed reactors, microwave reactors, oscillatory flow reactors, ultrasonic reactors, spinning tube reactors, centrifugal contactors (Qiu et al., 2010).

3 3.1

Experimental Section Materials and Chemicals

Anhydrous grade methanol (>99.8%), anhydrous ethanol (99.5%) concentrated hydrochloric acid, anhydrous reagent grade potassium carbonate (99%), potassium hydroxide (85%), concentrated sulfuric acid (98%), and anhydrous grade sodium sulfate were supplied by Caledon Laboratories Ltd. Anhydrous grade ethyl alcohol was obtained from Commercial Alcohols. Oleic acid was obtained from Alfa Aesar and stearic acid from EMD chemicals Inc. Amberlyst15ÂŽ was obtained from Fluka Analytica and p-toluenesulfonic acid was obtained from Sigma Aldrich. Refined canola oil used in the experiments was the Messina Brands marketed by Costco grocery stores. 3.2

Equipment

All experiments were conducted in a one liter jacketed glass reactor equipped with a reflux condenser, an impeller and four baffles evenly distributed to provide a better mixing of reactants and products. A schematic of experimental set up can be seen in Figure 1. The vessel was connected to a water bath capable of maintaining a desired temperature to within Âą1oC. A thermocouple was used to monitor the reaction temperature. Three ports were accessible from the lid of the vessel, one was used to connect the condenser to the system, the other one was the inlet of the rod of the impeller, and the third was employed to feed the reactants into the reactor and to take intermittent samples for analysis. The impeller diameter was 63.5 mm and it had three pitched blades (45o) of 5mm width, placed concentrically at 36 mm from the bottom. Additionally, a drain valve was installed to empty the contents of the reactor at the end of reaction. Other equipment used during experiments included: a Brookfield viscometer, a Buchi vaporizer, a centrifuge, and separatory funnels. 29

1. 2. 3. 4. 5. 6.

Stirrer Condenser Baffle Pump Oil Tank Temperature Indicator 7. Water Jacket 8. Drain Port 9. Water Bath

3 4 7 0 9

6 8 5

Figure 7: Experimental setup for transesterification and esterification

3.3

Experimental Procedure

The reactor was operated in batch or semi-batch mode to investigate mixing effects. While most literature studies have used batch mode, a semi-batch method based on gradual feeding of oil (Gfed) into a pool of alcohol was presented by Pal and Prakash (2013). This approach allowed good dispersion of oil into alcohol phase from start of the reaction, minimizing mass transfer limitations. Initial reaction parameters including alcohol to oil molar ratio mixing speed, and temperature range were established based on literature studies. Reaction conditions selection was guided by considerations of inherent safety i.e. mild reaction temperature and pressure and low

catalyst concentration. A 6:1 alcohol to oil molar ratio has been found to be sufficient in transesterifying vegetable oil at mild temperatures and atmospheric pressure while obtaining high yields (>95%)(Agarwal et al., 2011; Dalai et al., 2012). Excess methanol is required in order to drive the reversible reaction towards the products side. Also, 600 rpm has also been proposed by scientists as an optimum value. This is an important parameter since transesterification and esterification are mass transfer limited processes; therefore, intensive mixing is needed to create a homogeneous phase at the beginning of reactions. Finally, a temperature range of 30 â&#x20AC;&#x201C; 60oC has been widely used and found to be efficient in producing high purity biodiesel (Ma and Hanna, 1999; Dalai et al., 2012; Satyanarayana and Muraleedharan, 2011). Sulfuric acid was selected as esterification catalyst. To alkaline catalysts were selected for transesterification reactions based on their environmental advantages over other type catalysts. For instance, wastewater resulted from synthesis of biodiesel using KOH and K2CO3 can be neutralized using phosphoric acid to produce potassium phosphate, which is widely used as a fertilizer. It has been documented that KOH is one of the most common catalyst used in the biodiesel industry. On the other hand, K2CO3 is not a traditional base catalyst but it is beneficial to the whole production process. For example, it produces the least amount of soaps when compared to NaOH, and KOH; this is significant especially when dealing with low quality feedstock. It has also been documented that separation of glycerol from FAAE occurs faster due to a higher molecular weight of K2CO3. Additionally, glycerol containing potassium carbonate can be an environmentally friendly deicing or anti-icing fluid (Spienza et al., 2005).

3.4

Esterification Process

All esterification reactions were conducted at 60oC at atmospheric pressure for 1 hour using a 15:1 MeOH to FFA molar ratio and 5wt.% sulfuric acid (based on weight of FFA). In batch method, the acid oil was initially fed into the vessel, preheated to the desired temperature, and agitated to a 600 rpm. In the meantime, sulfuric acid was dissolved in methanol and the resulting solution was added to the reactor. The reaction was assumed to start as soon as the catalyst and alcohol were added to the reactor and continued for 60 min. In the G-fed method, methanol and sulfuric acid were first added to the reactor, mixed for 15 minutes, and preheated to the predetermined temperature. Then, the warmed acid oil was slowly added using a pump at a constant flow rate of 18 ml/min. This allowed each oil droplet to fall into a pool of methanol increasing the molar ratio significantly at the beginning of the reaction. The impeller speed was set to 300 rpm for the first 15 minutes and then increased to 400 rpm for the remaining 45 minutes. The reaction was timed as soon as the first droplet of acid oil fell into the vessel and continued for 1 hour. Following esterification, the contents of the reactor, for both methods, were transferred into a separatory funnel and allowed to stand overnight to ensure complete separation. Two layers were identified, a methanol-rich phase at the top and a triglyceridemethyl ester phase at the bottom. Traces of water and excess methanol in the ester phase were removed in a rotary evaporator at 100oC. The pretreated oil was then conducted to another reactor to proceed with transesterification.

Oil Feed Alcohol and catalyst to treatment and recovery

Alcohol + Acid Catalyst

Reactor To Transesterification

Separator

Figure 8: Flow diagram for esterification step 3.5

Transesterification Process

Transesterification reactions were conducted at 60oC with ethanol as alcohol and KOH and K2CO3 as catalysts. In batch mode, the oil was added to the reactor and preheated to the desired temperature. Then the catalyst was dissolved in the alcohol and fed into the vessel. Reaction was carried out for 1 hour using a 6:1 alcohol to oil molar ratio and various catalyst loadings. In the G-fed method, the alcohol and the catalyst were initially poured into the reactor and preheated to the established temperature. Following this, preheated oil was slowly added to the reactor using a metering pump at a flow rate of 18ml/min (for 1hour reaction time) and 9ml/min (for 2hour reaction time). The determination of flow rate was based on the amount of feedstock used and the duration of reaction. The reaction was timed as soon as the first droplet fell into a pool of alcohol/catalyst solution and conducted for preselected duration in the range of 60 to 120 min. When half of the oil was pumped into the reactor, an agitation speed of 300 rpm was used. As the contents of the reactor increased with time, the speed of the impeller was adjusted to 400 rpm in order to avoid mass transfer limitations. G-fed was carried out in 30 min or 60 min followed 33

by a batch mode for another 30 min or 60min. At the end of the reaction, for both methods, agitation was stopped and the water bath was turned off. The contents were transferred to a separatory funnel in which the reaction mixture was allowed to stand overnight to ensure complete separation. Due to the difference in densities of alkyl esters and glycerol, two phases were observed. An alkyl ester-rich phase was obtained at the top and a viscous glycerol-rich phase at the bottom. Excess alcohol was dispersed throughout both phases as well as the catalyst. The upper phase also contained triglycerides, diglycerides and monoglycerides, depending on the conversion achieved. When high FFA feedstock was used, soaps were collected in the bottom layer as well. It is important to note that phase separation occurred more rapidly when K 2CO3 was employed. After separation was complete, alcohol was removed from both layers using a rotary evaporator for 40 min. Then the alkyl ester-rich phase was further purified using a washing process to remove impurities such as, traces of glycerol, traces of alcohol, soaps and residual catalyst. The first wash was intended to neutralize most of the remaining catalyst with 1N HCl solution. Then, two washes using distilled water were carried out to ensure proper contaminants removal. The volume of water and acidic solution was calculated based on 28% volume of the ester phase. The pH of wastewater was measured constantly obtaining a value between 7 and 8 for the final wash. Usually 3 to 5 washes were needed to completely remove impurities. The washed alkyl phase was dried using a rotary evaporator at 100oC for 40 minutes. Finally the purified product was stored in a dark place and prepared for quality analyses. The following figure shows a process flow diagram of the entire process.

1N HCl Distilled Water

S-1

Oil Inlet (for drip method)

Water

Recovered Alcohol S-10

S-6

S-13

S-8 S-3

S-2

S-4

Reaction Phase

S-12

Alkyl Esters

Alkyl esters for rota vaporizing ROTARY EVAPORATOR

Alchohol + Catalyst

ROTARY EVAPORATOR

Rota Vaporized Alkyl Esters

S-14 REACTOR

S-9

WASHER

SEPARATOR

PURE BIODIESEL

S-11

S-5

Washed Waste Water

Glycerol Purification ROTARY EVAPORATOR

PURE GLYCEROL S-7

Figure 9: Process flow diagram for transesterification using Batch and G-fed mode 3.6

Two-Step Esterification-Transesterification Process

A two-step esterification-transesterification process is required when the FFA content in the feedstock is greater than 1% (Canakci and Gerpen, 2001; Jain and Sharma, 2010). Researchers have investigated base-catalyzed processes using low quality feedstock and have found that the yield is greatly affected due to the saponification as a side reaction and purification of final product is often difficult. The acid pretreatment converts FFA to alkyl esters, followed by alkaline-catalyzed process which transforms triglycerides into alkyl esters. By using both procedures in sequence, the overall yield of final biodiesel increases significantly and the amount of soaps produced in the process is reduced. All esterification reactions were conducted at 60oC at atmospheric pressure for 1 hour using a 20:1 MeOH to FFA molar ratio and 5wt.% sulfuric acid (based on weight of FFA). In batch method, the acid oil was initially fed into the vessel, preheated to the desired temperature, and 35

agitated to a 600 rpm. In the meantime, sulfuric acid was dissolved in methanol and the resulting solution was added to the reactor. The reaction was assumed to start as soon as the catalyst and alcohol were added to the reactor and continued for 60 min. In the G-fed method, methanol and sulfuric acid were first added to the reactor, mixed for 15 minutes, and preheated to the predetermined temperature. Then, the warmed acid oil was slowly added using a pump at a constant flow rate of 18 ml/min. This allowed each oil droplet to fall into a pool of methanol increasing the molar ratio significantly at the beginning of the reaction. The impeller speed was set to 300 rpm for the first 15 minutes and then increased to 400 rpm for the remaining 45 minutes. The reaction was timed as soon as the first droplet of acid oil fell into the vessel and continued for 1 hour. Following esterification, the contents of the reactor, for both methods, were transferred into a separatory funnel and allowed to stand overnight to ensure complete separation. Two layers were identified, a methanol-rich phase at the top and a triglyceridemethyl ester phase at the bottom. Traces of water and excess methanol in the ester phase were removed in a rotary evaporator at 100oC. The pretreated oil was then conducted to another reactor to proceed with transesterification. The experimental procedure for the second stage is the same as the one described in Section 3.3. The following figure shows a process flow diagram of a two-step esterification-transesterifcation process.

Oil Inlet (for drip method)

Alcohol + Water + Sulfuric Acid

Alcohol + water

S-4

S-6

Reaction Phase

Alkyl esters + Triglycerides

Ester Phase

S-2 S-3

S-7

S-8

S-5 ROTARY EVAPORATOR

ESTERIFICTION REACTOR

TRANSESTERIFICATION REACTOR

SEPARATOR Alcohol + Catalyst

Alcohol + Sulfuric Acid

S-9 Reaction Phase

S-13

Recovered Alcohol

1N HCl Distilled Water

Alkyl esters for rota vaporizing

S-15 Water

S-10

S-14

S-19

ROTARY EVAPORATOR

Alkyl Esters

SEPARATOR

S-16

Glycerol Purification

ROTARY EVAPORATOR WASHER PURE BIODIESEL

S-20

S-11 Wastewater

S-17

ROTARY EVAPORATOR CRUDE GLYCEROL

S-12

Figure 10: Flow diagram for a two-step esterification transesterification process 3.7

Analysis and Characterization of Alkyl Esters

The quality of final biodiesel should be monitored to ensure the fuel meets ASTM or EN standards. The parameters are given in North America by ASTM D 6751: Standard Specification for Biodiesel Fuel (B100) Blend Stock for Distilled Fuels. Specific chemical properties should be met before biodiesel can be commercialized. 3.7.1 Physical Characterization Density and viscosity measurements are usually the first analyses performed in biodiesel samples as they provide a rapid method in predicting the conversion of vegetable oils to methyl esters. Determination of both parameters is ideal for process control due to its simplicity. Density and viscosity were measured after each run to ensure the values obtained were within the range given 37

by ASTM standards: 0.86-0.90 g/cc and 3.5-5 mm2/s for density and viscosity respectively. Kinematic viscosity and density are important parameters that help predict the performance of biodiesel fuel in engines. They dictate the amount of mass injected in pumps, and other equipment as well as the design of pipe and fittings in a production plant (Pratas et al., 2010). 3.7.2. Chemical Characterization Purified biodiesel were characterized by the chemical properties such as acid value and glycerol and glycerides compositions. 3.7.2.1. Determination of Fatty Acid Content The acid number is a direct measure of free fatty acid determined by the amount of potassium hydroxide in mg required to neutralize the acids in one gram of sample of oil or biodiesel. The acid values of refined oil, acid oil, esterified oil, and transesterified oil were carried out by alkalimetric titration with visual detection of the equivalence point. The method followed was in accordance with ASTM D5555. Free fatty acid content by weight was calculated using the following equation.

(1)

This method allowed monitoring the progress of the reaction at different time intervals. Conversion of FFA is defined as the change in acid value of the final product in relation to initial acid oil as can be seen in the following correlation. ( )

Where

(2)

= Conversion

So = Initial acid value (mg KOH/g) Si = Acid value at a given reaction time (mg KOH/g) All glassware was clean and oven dried prior to titrations. Oil and biodiesel samples were accurately weighted and well mixed with 2-propanol. Titration was carried out using 0.05N NaOH solution and phenolphthalein as an indicator. The endpoint was reached when a permanent pale pink color was observed and lasted for at least 30 sec. In order to better understand the progress of esterification using batch and g-fed, several samples were taken periodically and analyzed. A 5ml rector sample was withdrawn and quenched in one volume of distilled water. The samples were then cooled at 4oC and allowed to stand for 4 hours. The ester layer was then centrifuged at 4000 rpm for 15 min. The top layer was further dried using anhydrous sodium sulphate. The acid value of each sample was determined by titration. 3.7.2.2.Determination of recovered H2SO4 After esterification, ester and methanol layers were separated in a separatory funnel and weighted. Weighted amount of samples from both layers were titrated using 0.05 N NaOH solution and phenolphthalein as indicator. Weight of H2SO4 in each layer was calculated using following equation: (3) Where, N = normality of NaOH solution V = volume of NaOH used for neutralization of H2SO4 W1 = weight of sample taken for titration

W2 = total weight of either top or bottom layer Percent recovery of H2SO4 was determined by calculating the percentage of catalyst recovered to actual amount used for reaction.