/smash/get/diva2:414004/FULLTEXT01.pdf

/smash/get/diva2:414004/FULLTEXT01.pdf

Production of biodiesel from corn oil and ethanol by homogeneous alkali catalyzed transesterification

MSc. thesis

Atahualpa Moura Mendes

Department of Chemical Engineering

Royal Institute of Technology (KTH)

Stockholm, Sweden

April 2011

Production of biodiesel from corn oil and ethanol by homogeneous alkali catalyzed transesterification

MSc. thesis

Atahualpa Moura Mendes

Supervisor

Rolando Zanzi Vigouroux

Department of Chemical Engineering

Royal Institute of Technology (KTH)

Stockholm, Sweden

Examiner

Joaquín Martínez

Department of Chemical Engineering

Royal Institute of Technology (KTH)

Stockholm, Sweden

April 2011

Abstract

This report gives a general overview on biodiesel production, its motivations, characteristics and recent developments, mainly focused in the Brazilian case.

The Brazilian National Program for Production and Use of Biodiesel (PNPB) launched 2003 created a demand of biodiesel and stimulated the biodiesel production. Biodiesel is being produced from soybean oil, followed by animal fats and cottonseed oil, with palm and castor bean oil contributing in small portions. The biodiesel expansion has impacts on environmental and social issues such as deforestation from soya expansion and a decrease of employment levels due to the high degree of mechanization of the soya harvest.

Experimental work was developed, using corn oil, ethanol and NaOH as a catalyst. Experiments were made varying significant parameters to find the optimum reaction temperature, reaction time, catalyst amount and molar ratio between ethanol and corn oil. Besides that, another experiment aimed to describe the yield behavior as a function of the reaction time.

The produced biodiesel has been characterized by measurements of density, refraction index and viscosity.

The amount of 0.4 wt % NaOH, based on the weight of raw oil, was enough to catalyze the reaction of transesterification effectively. A higher amount of alcohol in excess provides a higher yield at mild temperature conditions. But the higher amount of alcohol used, the higher the amount of alcohol in excess presented in the biodiesel phase which has to be eliminated. An increase of the temperature from 40˚C to 50˚C does not increase the yield in a considerable way. Thus due to the energy saving it is not recommended to increase the temperature to 50˚C.

Regarding the evaluation of the conversion as function of time, a high conversion is obtained after 90 min. An extension of the reaction time from 90 to 150min had no significant effect i

Sammanfattning

Denna rapport ger en allmän översikt över de viktigaste aspekter vid tillverkning av biodiesel.

Produktionen av biodiesel i Brasilien redovisas i detalj. Den brasilianska

Nationellt program för produktion och användning av biodiesel (PNPB) lanserades 2003. Den skapade efterfrågan på biodiesel stimulerade produktionen av biodiesel. Biodiesel produceras i Brasilien främst från sojaolja, animaliska fetter och bomullsfröolja. Palmolja och ricinolja används i mindre utsträckning för produktion av biodiesel. Storskalig produktionen av biodiesel har påverkat miljö- och sociala aspekter. Avskogning för att ge plats till soja odlingar och en minskning av sysselsättningen på grund av den höga graden av mekanisering av soja skörd, är exempel på negativa effekter.

Experimentellt arbete omfattade tillverkning av biodiesel från majsolja och etanol genom homogen baskatalyserad transesterifiering med NaOH som katalysator. Vid tillverkning av biodiesel utvärderades effekt av temperatur, reaktionstid, mängd katalysator och molförhållande mellan etanol och majsolja, på utbyte. Dessutom studerades hur utbyte ändrades med reaktionstid.

Analysen av biodieseln gjordes genom mätning av densitet, viskositet och brytningsindex.

En katalysatormängd av 0.4 % vikt NaOH, baserat på vikten av majsoljan, var tillräcklig för att katalysera transeterifiering effektivt. En ökning av etanolmängd i överkott ger högre utbyte. Men ju högre mängd etanol som används desto större överkott på etanol i varje fas som ska avlägsnas. En ökning av temperaturen från 40 ˚ C till 50 ˚ C ökar inte utbyte på ett betydande sätt. Således med hänsyn till energiförbrukning är det inte lämplig att öka temperaturen till

50 ˚ C. Angående utvärdering av utbyte som funktion av reaktionstid, uppnås ett högt utbyte efter 90 min. En förlängning av reaktionstiden från 90 till 150min hade ingen signifikant effekt.

ii

Table of Contents

ABSTRACT

SAMMANFATTNING

TABLE OF CONTENTS

1 INTRODUCTION

1.1

1.2

1.3

M

OTIVATION

A

IM

S

TRUCTURE

2 THEORETICAL BACKGROUND

2.1

B

IODIESEL

2.2

F

EEDSTOCK

2.3

B

RAZILIAN SCENARIO

2.4

E

XTRACTION PROCESS

2.5

T

RANSESTERIFICATION

2.6

P

ROCESS VARIABLES

2.7

P

URIFICATION

3 EXPERIMENTAL METHOD

3.1

T

HE PROCEDURE

3.2

A

NALYSIS OF THE BIODIESEL

4 RESULTS

5 CONCLUSIONS

REFERENCES iii iii

1

1

3

3 i ii

22

22

23

25

4

4

5

6

12

13

18

20

35

36

1 Introduction

1.1

Motivation

The wildly spread insight that oil is a finite resource and the increasing awareness of the anthropogenic impact on climate change have made the renewable fuels important again. The “oil-feast” is soon over and the need for alternative has never been greater.

In the search of renewable substitutes for the fossil fuels, different products suit different applications. Liquid fuels are suitable for transport vehicles and a variety of different fuels has been brought in to the market: ethanol, biogas, hydrogen, methanol etc. Biodiesel is another liquid fuel made out of oil from vegetable or animal fat. Already Rudolph Diesel himself tested peanut oil in his diesel engine (Meher et al. 2006) but it is not until now, when the need of renewable fuels has exploded, that biodiesel is starting to be a product with a large scale potential.

The use of biodiesel as a fuel has achieved promising potential worldwide in a market in constant growth due to its multiple advantages, such as: i.

ii.

iii.

iv.

v.

It is a fuel produced from renewable sources: vegetable oils, waste cooking oils and animal fat. The use of waste as feedstock reduces costs with wastewater treatment and disposal (Fukuda, 2001);

It is biodegradable. The use of a mixture of 20% v/v biodiesel (B20) raises significantly the degradation of diesel in the presence of water.

Studies even observed the development of algae in biodiesel storage tanks (Graboski & McCormick, 1998);

It is a non-toxic fuel. The use of biodiesel reduces the emission of carbon monoxide and is virtually free from sulfur compounds;

It is essentially aliphatic whereas the fossil diesel contains from 20 to

40% v/v aromatic compounds, which increase the emissions of particulates and nitrogen compounds (Graboski & McCormick, 1998);

It reduces the emission of particulates in as much as 48% with B100

(Environmental Protection Agency, 2002);

1

vi.

vii.

ix.

viii.

The CO

2

emitted in its combustion is recycled. The reduced amount of

CO

2

emitted is absorbed during the growth of the oilseeds, reducing globally the presence of gases responsible for the greenhouse effect.

The replacement of diesel by biodiesel can reduce up to 41% the emissions of greenhouse gases in the atmosphere (US Department of

Energy, 2009). Besides that, biodiesel production allows a favorable position in international trading through the system of carbon credits as established by the Kyoto protocol;

It has a higher cetane number. For diesel engines, a low cetane number results in a longer delay during ignition, raising rapidly the pressure inside the combustion chamber and producing a loud and characteristic noise, not to mention the accumulation of fuel inside the chamber. Hence fuels with higher cetane number yield better ignition and efficiency. Methyl and ethyl esters have a higher cetane number than diesel. When the ester derives from saturated compounds like cooking oil and saturated fats, the cetane number is even higher

(Graboski & McCormick, 1998);

It has lubrication properties. The use of biodiesel can easily increase the lubricity of the diesel with a low sulfuric content, enhancing the operation of the moving parts of the engine and the fuel pump (US

Department of Energy, 2009);

Mainly in developing countries, it presents a number of social and economic advantages. Besides the reduction in the import of diesel, the biodiesel industry creates new opportunities in less developed regions working on an agricultural framework.

Disadvantages in the use of biodiesel are mainly the increase in the emission of

NO x

and the high costs related to feedstock and the production process.

However, extensive research is in progress to develop technology to reduce those emissions and to design more cost efficient processes.

2

1.2

Aim

The objective of this work is to describe relevant aspects of biodiesel production recollecting material published in scientific literature as well as comparing it with practical experience.

It aims at pointing out important theory regarding biodiesel properties, process characteristics and reaction mechanisms as well as its economic impact in a developing country like Brazil. The experimental work includes the production of biodiesel from corn oil and ethanol by homogenous alkali catalyzed transesterification. The influence of different process variables (molar ratio alcohol:oil, amount of catalyst, reaction time and temperature) on the yield of biodiesel is studied. The obtained data is compared with recent researches developed worldwide although focus is dispensed to the Brazilian scenario.

1.3

Structure

This report is divided into five chapters:

Chapter 1 presents the motivations for tackling the theme of biodiesel, given its characteristics and implications in the energy context;

Chapter 2 describes important theoretical aspects behind biodiesel production, making the reader familiar with terminology and relevant issues that are discussed all through the project;

Chapter 3 lists materials and procedures adopted in the experimental part of this study;

Chapter 4 presents the results of such experiments and discusses them on a broader picture, comparing the experimental conclusions with what has been observed in different studies taken as references.

Chapter 5 consists of a brief conclusion and compiles the references cited through the text.

3

2 Theoretical Background

2.1 Biodiesel

Biodiesel is a liquid mixture of free fatty acids with similar properties to diesel.

The name comes from the fact that the “diesel” is produced from renewable oils and not from fossil crude oil. The oil used to make biodiesel consists mainly of triglyceride and some free fatty acids (FFA).

The use of vegetable oils as fuel started in 1900 when Rudolph Diesel used peanut oil in some compression tests of his diesel engine (Meher et al. 2006).

During the 30s and the 40s, vegetable oils were used as fuels in emergency cases only because the properties of such oils led to poor atomization, carbon deposit, problems in lubrication, high viscosity and low volatility (Freedman, 1986).

Aiming to reduce the viscosity of vegetable oils and increase the volatility of the fuel, some alternatives were proposed, such as: dilution, microemulsions, pyrolysis and transesterification (Demirbas, 2003).

The reaction of transesterification in comparison to the direct use of vegetable oils proved to have many advantages: reduction of the viscosity in eight times and of the molecular weight in one third; increase of volatility; and minimization of carbon deposit in the injection nozzles (Fillières, 1995). Besides those features, biodiesel contains 10-11% v/v oxygen, making it easier the combustion in the engine (Barnwal and Sharma, 2005).

From 1973, as a consequence of the rise in oil prices, a new international concern about production and consumption of energy regarding non renewable fuels was set. Further in 1997, the Kyoto protocol added to the energy debate a more environmentally oriented character, establishing goals to limit the emission of greenhouse gases.

In this day and age, given the progressive exhaustion of oil sources in the world and the visible concerns with environmental pollution, biodiesel comes to the

4

scene as a promising, environmentally friendly alternative. It is the ideal fuel to replace diesel as no changes in the vehicles engines are needed (Fillières, 1995).

2.2 Feedstock

The specifications for biodiesel allow a variety of feedstocks and processes to be used in its production. Biodiesel can be produced commercially from a variety of oils and fats:

• Animal fats: edible, inedible, and all other variations of tallow, lard, choice white grease, yellow grease, poultry fats, and fish oils;

• Plant oils: soy, corn, canola, sunflower, rapeseed, cottonseed;

• Recycled greases: used cooking oils and restaurant frying oils.

Biodiesel can also be made from other oils, fats, and recycled oils such as mustard, palm, coconut, peanut, olive, sesame, and safflower oils, trap greases, and even oils produced from algae, fungi, bacteria, molds, and yeast. Some properties of finished biodiesel such as cetane number, cloud point, and stability depend heavily on the feedstock (US Department of Energy, 2009).

The words “oil” and “fats” designate substances with no solubility in water

(hydrophobic) composed mainly by products of the condensation between glycerol and fatty acids, called triglycerides (Figure 1). In general fats have a high ratio of saturated fatty acids whereas oils contain more unsaturated fatty acids.

The main distinction between them is in appearance: fats are solid whereas oils are liquid (Hartman, 1982).

5

Figure 1: Triglyceride as a product of condensation between glycerol and three fatty acids.

Besides triglycerides, oils and fats contain a small amount of other compounds, such as free fatty acids, mono and diglycerides, phosphatides, alcohols, hydrocarbons and vitamins (Sonntag, 1979).

Compared with the chemistry of diesel fuel, which contains hundreds of compounds, the chemistries of different fats and oils typically used for biodiesel are very similar. Each fat or oil molecule is made up of a glycerin backbone of three carbons, and on each carbon is attached a long-chain fatty acid that reacts with methanol to make the methyl ester, or biodiesel. The glycerin backbone is turned into glycerin and sold as a by-product of biodiesel manufacturing. The fats and oils contain 10 common types of fatty acids that have 12 to 22 carbons, more than 90% of which are 16 to 18 carbons. Some of these chains are saturated, some are monounsaturated, and others are polyunsaturated. Within the limits of the specifications, the differing levels of saturation can affect some biodiesel fuel properties (US Department of Energy, 2009).

2.3 Brazilian scenario

Brazil is a country that finds good conditions (geographic extension, tropical and subtropical climates) for obtaining a wide variety of vegetable oils for the production of biodiesel. Among the main feedstock used are cottonseed, peanut, palm (locally known as dendê

), sunflower, castor ( mamona

), jatropha ( pinhão manso

) and soybean oils.

Each oil plant – depending on the region in which it is cultivated and according to weather and soil conditions – displays specific characteristics when it comes to productivity per hectare and percentage of oil obtained. Productivity is also directly associated to harvest technologies, seed quality and processing conditions.

Table 1 illustrates the relation between the oil plants and its productivities and yield (SEBRAE, 2008).

6

Table 1. Oil plants and its properties in biodiesel production

Species

Cottonseed

Peanut

Palm

Sunflower

Castor

Jatropha

Soybean

Macaúba

Productivity (ton/ha)

0.86 - 1.4

1.5 - 2

15 - 25

1.5 - 2

0.5 - 1.5

2 - 12

2 – 3

< 30

Oil (%)

15

40 – 43

20

Lifecycle Yield (ton oil/ha)

Annual 0.1 - 0.2

Annual

Seasonal

0.6 - 0.8

3 – 6

28 – 48

43 – 45

Annual

Annual

50 – 52 Seasonal

17 Annual

0.5 - 0.9

0.5 - 0.9

1 – 6

0.2 - 0.4

22 Annual 3.8 – 6

Adapted from SEBRAE (2008)

Palm oil plant is the one that demands most man’s labor per hectare for harvesting, associated to the highest productivity. Compared to the others, the palm oil plant has occupied a prominent position worldwide, being the 2 nd in the rank of oil production. Its main producers are Malaysia, Indonesia and Nigeria and Brazil occupies the 11 th position (MAPA, 2007).

Raw sunflower oil presents a good market value, issue that could economically prevent its use as biodiesel feedstock. However, the easy extraction of this oil simplifies the productive process, lowering the investment on implementing units in remote locations as well as producing high quality ethyl esters

(Domingos et al., 2004).

The castor oil plant is easy to cultivate, resistant to drought and well adapted to high levels of insolation; has low production costs; and is easy to handle. All those features make it one of the few options for the arid underdeveloped regions of the country (Wehrmann et al., 2006).

Jatropha is a species natural from Brazil, belonging to the Euphorbiaceae family, the same as the castor oil plant. For this reason, it also adapts well to extreme climate and poor soils conditions.

Soybean oil is an alternative to the suppliers of biodiesel producers due to the organization of the soy producers in the country. When biodiesel started being

7

produced in Brazil, there was a big demand for vegetable oils available in a large scale. The most available one was the soybean oil, with an excellent infrastructure installed for the biodiesel production in the required volumes

(Domingos et al., 2004). Aiming for a more flexible biodiesel production, there was an expansion in the variety of vegetable oil sources, promoting the other applications of soybean. They include the human and animal food industries, adhesives, fertilizers, fiber production, etc (Brasil, 2009).

One vegetable oil that has been attracting the attention of the scientific community is the oil from macaúba

, a plant from the family Palmae, genus

Acrocomia

. The existing plants are natural and non fertilized, but studies show that with the right soil conditions, yield can reach 6,6 ton oil/ha, the highest amount among all Brazilian palm trees. Further advantages account for the potential applications of the oil in food, cosmetics, pharmaceutical and energy industries, with the complete use of the plant, byproducts included (Andrade et al., 2006).

Given the availability of natural resources and the relevant role it plays on

Brazilian economy, biodiesel production has gained an official character in the government’s agenda.

In 2003 the Brazilian government, by decree, launched the National Program for

Production and Use of Biodiesel (PNPB), creating a demand for biodiesel and stimulating the Brazilian production from several different oil plants. Besides boosting biodiesel production, the PNPB also aims at fostering social inclusion through the generation of income for small producers. Therefore, the government program has established incentive policies aiming at promoting the inclusion of family farming in this productive process (César and Batalha, 2010).

The PNPB program has been focusing on organizing the biodiesel productive chain by defining financial aids, structuring the technological basis, and establishing specific regulations on the new fuel. The operation of this chain has been performed by sectorial policies that have determined the development of this productive chain. The most important action taken by the PNPB program was approving the law which established an addition of 2% in the diesel oil produced in Brazil since 2008. Since then, the production of biodiesel has met

8

such demand and the sector has been developing rapidly. Nowadays, the mandatory addition content of biodiesel into diesel oil in Brazil is 4% (César and

Batalha, 2010).

The PNPB was developed to be much more than an import substitution program.

Rather than that, the program sought to rapidly expand biodiesel production and use by instituting a targeted set of fiscal incentives, financing, and blend ratio mandates. First, the PNPB mapped out a national production chain by region and cultivation to focus efforts on improving productivity and lowering costs in the long run. This variation of cropping by region was framed by soil and climate conditions, and it was driven by the economic, political and social imperatives of incorporating family farms and small producers into the production of biodiesel while also expanding cultivation of palm oil, the most efficient biomass for biodiesel production in Brazil (Langevin, 2010).

Andrade and Miccolis (2010) summarize existing research to conclude that palm oil, either for export or for use as biomass for biodiesel production and diesel substitution, makes a measurable contribution to a positive trade balance, contributes to an overall renewable energy portfolio, reduces greenhouse gas emissions, and retains capacity for carbon sequestration at over 35 tons of carbon per hectare. Indeed, the most important and driving factor is excellent yields coupled with the low production costs of palm oil as a biomass for biodiesel production, the only vegetable oil capable of competing head on with petroleum based diesel in Brazil. Recognizing palm oil’s comparative advantages, the PNPB encouraged expansion of its cultivation to improve the long term viability of Brazilian biodiesel, incorporating family farms, cooperatives, and small producers into the production chain throughout the North and Northeast regions of the country.

The PNPB established a graduated blend mandate schedule that guarantees a growing national market for production. The mandate sought to quickly incorporate biodiesel production into a two percentage- point mix with all diesel sold in Brazil, and then to gradually increase the biodiesel blend ratio. Initially the PNPB established benchmarks for production in two phases, the B2 and the

B5 phases. The B2 phase, from 2005 to 2008, would feature 16 biodiesel

9

production plants refining up to 840 million liters of biodiesel. The B5 phase, from 2008 to 2010, planned to increase the number of refineries to 43 and to produce 2.2 billion liters. During the first five years of the program, national biodiesel production has risen steadily, from approximately 70 million liters in

2005 to over 2.35 billion liters by 2010 (Langevin, 2010). Table 2 reports the production capacity and number of refineries by region and state.

Table 2. Biodiesel refineries per state and region, productivities and feedstock resources per region

Region

North

State

Pará

Rondônia

Tocantins

Northeast

SUBTOTAL

Bahia

Ceará

Maranhão

Piauí

SUBTOTAL

Goiás

Central-West

Mato Grosso

Mato Grosso do Sul

SUBTOTAL

Minas Gerais

Rio de Janeiro

Southeast

South

São Paulo

SUBTOTAL

Paraná

Rio Grande do Sul

SUBTOTAL

TOTAL

7

14

3

4

7

2

29

6

1

64

Refineries Productivity (1000 L/yr) Vegetable oils

2

2

2

23 400

22 320

139 320

Palm

Soy

1

8

4

23

6

3

3

1

185 040

358 815

217 480

129 600

97 200

803 095

583 090

1 180 425

Palm

Castor bean

Soy

Cottonseed

Castor bean

14 760

1 778 275

147 640

21 600

762 740

931 980

68 400

863 040

931 440

4 629 830

Soy

Cottonseed

Sunflower seed

Soy

Cottonseed

Sunflower seed

Adapted from Brazil Oilseeds Annual Report (2010) and Rousseff (2004)

The state of Mato Grosso, the largest producer of soy in Brazil, reports the largest production capacity with over one billion liters of potential production from 23 refineries. This state’s capacity is followed by the states of Rio Grande do Sul in the South and São Paulo in the Southeast. According to the Brazil Oilseeds

Annual Report for 2010, three quarters of all Brazilian biodiesel is produced

10

from soybean oil, followed by animal fats and cottonseed oil, with palm and castor bean oil contributing in small portions. The 2010 soybean crop in Brazil is larger than expected and capable of boosting national production levels in the coming year. Yet, the disproportionate use of soybean oil for biodiesel production, largely concentrated in the Center-west, also reveals that the planned increase in production of biodiesel from palm oil has not met PNPB objectives (Langevin, 2010).

The PNPB planned to boost biodiesel production in the North (Amazon) region, where production capacity is the lowest, to guarantee supplies and eventually lower costs of diesel and electricity to a growing regional population. The PNPB also promised greater energy security for the nation, as well as the Amazon population, in an effort to improve the country’s trade balance. The PNPB estimated that during Phase B2 the country would save some $160 million dollars by lessening diesel imports. With the B5 blend mandate enacted in 2010, it is likely that Brazil can save hundreds of millions of dollars in import costs by producing its own biodiesel and substituting an increasing share of imports.

Petrobras, Brazil's state-controlled energy company, reported that diesel imports declined by 43% between 2008 and 2009 due to increased national production of diesel, including biodiesel (Langevin, 2010).

Goes, Araújo and Marra (2010) predict that production trends will make Brazil the second largest producer of biodiesel in the world, next to Germany and superseding the United States, after the B5 blend mandate takes a measurable effect on investment and production.

Despite of the promising forecast, other studies have been pointing out the impacts biodiesel expansion have on environmental and social issues. German et al. (2010) studied how environment and society have been affected by the biofuel programmes in developing economies worldwide. In Brazil the authors analyzed especially the harvest of soya. In Mato Grosso, for example, deforestation from soya expansion related to biodiesel production is believed to represent 1.5 – 6.4 % of the total deforested area. For soya again, carbon debts range from an estimated 737 mg CO2 per ha for the Amazon biome to 85 mg for the cerrado (vegetation of the Central-West region), with payback times of 319–

11

37 years, respectively. Even for jatropha cultivated in dry forest, net negative carbon balances can be observed according to the authors.

When it comes to social and economic impacts, German et al. (2010) observe that the employment levels on soya estates are very low due to the high degree of mechanisation. A typical 5000 ha farm was found to employ as few as 10 permanent (skilled) and 15 temporary workers (1 full-time and 1.5 temporary per 500 ha).

Farmers producing feedstock for industrial-scale operations under the ‘Social

Fuel Seal’ programme are clearly benefiting from a policy which provides biodiesel producers with incentives to source their raw materials from smallholders and ‘family farms’ (defined as farms of less than 100 ha). However, the high cost of providing technical support to small farms means that settlements in which individual landholdings are much less than 100 hectares are not of interest to companies, who therefore pick and choose which land reform settlement they ´adopt´. The economies of scale associated with largescale production have also led to considerable consolidation of land holdings in these resettlement areas. In the Amazon transition zone, high transport costs and restricted access to credit (for which land titles are required) have limited the expansion of soya. In the cerrado

zone, many of the smaller landholdings distributed under the agrarian reform programme are too small to compete in the soya market, even in a protected market created by government support programmes (German et al., 2010).

What can be concluded from that scenario is that although such incentive programmes by the government have achieved the intended and desired expansion of the business, much still needs to be revised to continuously adjust environmental and social impacts.

2.4 Extraction process

Commercially there are three basic methods of oil extraction that may even be used in combination: batch hydraulic press, continuous mechanical press (also called expeller) and solvent extraction.

12

Hydraulic presses, originally widely used, have been replaced by the mechanical ones, which are more efficient, easier to operate and cheaper to acquire, being recommended for small cooperatives and organizations in developing countries

(Weiss, 1983).

The press consists of a basket made of rectangular steel bars spaced by blades, with adjustable thickness according to the seed to be pressed. The spacing of these bars is adjustable to allow the output of oil and to filter particles from the press residue (cake). In the center of the drum rotates a helical screw which moves the material forward, compressing it at the same time. The pressure is regulated through an outlet cone, driven by a crank. The drive system is done by an engine, followed by a dimmer. The crude oil typically undergoes a process of filtration or decanting to remove the particulate (Moretto and Fett, 1998).

2.5 Transesterification

As indicated before, vegetable oils need to have its viscosity reduced so they can be used in the diesel engines. This adjustment can be achieved through a variety of processes: pyrolysis, dilution, microemulsions, esterification and – the most common – transesterification (Figure 2).

Figure 2: Reaction of transesterification

Transesterification consists of a reaction between an alcohol and vegetable oil or animal fat. The alcohol must preferably have a low molecular weight (such as methanol and ethanol) so that the reaction proceeds faster. An excess of alcohol is needed to shift the reaction equilibrium in the direction of product formation.

13

The reaction occurs in three steps (Figure 3): the first one is controlled by mass transfer (slow), followed by another one kinetically controlled (fast) and a last equilibrium phase (slow). In the first step, two immiscible phases (oil and alcohol) are put together so stirring is important in order to transport the triglycerides from the vegetable oil to the interface oil/alcohol. The intermediate products (mono and diglycerides) act as emulsifying agents, making mass transfer easier and giving room for a kinetically controlled step, when the increase in temperature favors product formation and stirring no longer affects the reaction (Stamenkovic et al., 2008).

The esters produced have a long carbon tail and are badly miscible in the glycerol. Due to glycerol’s higher viscosity separation occurs and glycerol forms a brown phase at the bottom, while the biodiesel stays at the top.

Figure 3: Mechanism of transesterification

The alcoholysis, as it is also known, can occur either with or without a catalyst, homogeneous or heterogeneous. The homogeneous catalysts can be acid, basic or enzymes. Their inconvenience is the need to purify the products (esters and glycerol) in order to remove catalyst residues, making it impossible its reuse after the reaction. Heterogeneous catalysts can be recovered after the reaction and are easily removed, making purification simple.

14

Basic catalysts are the most used in large scale because they are less corrosive for industrial equipments and give a higher yield when compared to acid catalysts (Barnwal and Sharma, 2005).

Figure 4 shows the mechanism for basic transesterification. When a basic catalyst is used, first thing to be done prior to transesterification itself is the reaction between alcohol and the base, producing the anion RO . Step 1 corresponds to the nucleophilic attack of the anion RO to the carboxylic carbon of one of the three ester groups in the triglyceride, forming an intermediate compound. Then, in step 2, the intermediate compound reacts with the alcohol regenerating the catalyst and forming a new tetrahedral intermediate compound. Finally, in step 3, the intermediate compound of step 2 rearranges itself to form a molecule of diacylglycerol (R''OH) and ester (R'COOR).

Figure 4: Transesterification mechanism using basic catalyst (Meher et al., 2006)

15

Wright, 1994).

Ethanol (g)

40

40

40

40

30

40

40

40

30

30

30

30

30

30

30

40

NaOH (g)

1

0.5

0.5

0.5

0.5

1

1

1

0.5

0.5

0.5

0.5

1

1

1

1

Water (% m/m)

0.8

0.14

0.28

0.43

0.71

0.14

0.28

0.42

0.11

0.23

0.34

0.57

0.11

0.34

0.57

0.79

Yield (%)

82.8

87.9

87.3

86.4

65.8

93.5

91.7

93.5

89.4

88

79.5

61.8

96.6

90.2

90.2

90.7

16

Some authors use basic catalysts for a maximum of 0,5 % of free fatty acids

(Ertekin et al., 1996). Others defend that the catalyst consumption occurs for amounts of free fatty acids over 1 %. To prevent this reaction the free fatty acids must undergo esterification through acid catalysis and then they will be suitable for the transesterification with basic catalyst (Canakci and Gerpen, 2001).

As an example of this procedure, Berchmans and Hirata (2007) studied the production of biodiesel from

Jatropha curcas seed oil with a high content of free fatty acids. The so-called two-step acid-base catalyzed transesterification involved an acid-catalyzed esterification process followed by a base-catalyzed transesterification process. The first step was acid esterification as a pretreatment for removing FFA from the oil. It was reported that to get complete

FFA esterification in some vegetable oils, could be done in the reaction temperature 50 °C. The process was intended to convert FFA to esters using an acid catalyst (H2SO4 1% w/w) to reduce the FFA concentration of the oil below

2%. Second step was alkali base catalyzed transesterification.

The formation of ethyl esters with basic catalysts is difficult compared to the formation of methyl esters, especially because of the formation of stable emulsions during ethanolysis. In ethanolysis, these emulsions are much more stable and serious problems of separation and purification are addressed.

Emulsions are produced partly by the formation of mono and diglyceride intermediates, which have polar hydroxyl groups and nonpolar hydrocarbon chains. These intermediates are strong surface active agents and are used in the food industry as emulsifiers (Zhou et al., 2003).

Unlike the basic transesterification, the performance of acidic transesterification is not strongly influenced by the presence of free fatty acids in the raw material.

In fact, the acid catalysts can catalyze both the esterification of fatty acids

(conversion of fatty acid esters) and transesterification of triglycerides.

Figure 6 represents the mechanism for acidic transesterification. First there is the protonation of the ester’s carbonyl group to produce a compound with resonant structure. The species in resonance suffer a nucleophilic attack from the alcohol to form a tetrahedral intermediate which, in turn, rearranges to form a molecule of ester and of the catalyst (regeneration).

17

Figure 6: Transesterification mechanism using acid catalyst (Meher et al., 2006)

Enzymatic catalysis in the reaction of transesterification lead to good results even when alcohols with a long chain are used, with the advantage that it does not change the products acidity. However, it applies organic solvents which may interfere with the triglycerides solubility and the costs of the catalyst are much higher than the other alternatives (Shimada, 2002).

When a catalyst is not used, for temperatures below 300 °C the reaction rate is too slow (Khan, 2002). An option is to use the alcohol in supercritical conditions.

The process is then simplified, with no need for purification of the products and raw materials with high acidity can be used. The drawbacks are the need of high pressures and temperatures.

2.6 Process variables

The reaction of transesterification has its yield affected by some experimental conditions such as the molar ratio between alcohol and oil, the amount of catalyst, the temperature, the reaction time and the stirring speed (Meher et al.,

2006).

In general, the yield of the base catalyzed process decreases with the increasing presences of moisture and FFA. The molar ratio between alcohol and triglyceride

18

must be at least 3:1 due to the stoichiometric relation. It has been shown that a ratio of 6:1-12:1 increases the yield. This is due to the fact that the equilibrium reaction is driven to the right, towards the production of esters. Reaction temperatures used is highly dependent on the type of oil that is being used, but is in the range from 30-60C˚. The reaction time is found to be quite quick, around

15 minutes. The catalyst amount should be around 0.3-0.5 w/w% to reach maximum activity (Meher et. al. 2006).

Domingos et al. (2004) studied the influence of the molar ratio alcohol:oil (6:1 –

12:1), the amount of catalyst (0,4 – 1,2 % w/w) and the temperature (40 – 70 °C) in the yield of biodiesel from sunflower oil. As a result, they observed a tendency of increase in the yield when the molar ratio was increased; when the amount of catalyst was close to the maximum level; and for mild temperature conditions. A maximum yield of 90 % was obtained after the alcohol was evaporated from the biodiesel phase. Values of yield close to 100 % are never expected for the reaction is reversible and side reactions – such as saponification – take place whenever the acidity of the raw material is too high (over 2 mg KOH/g in this study).

Bouaid et al. (2009) studied the effects of temperature and catalyst amount in the production of biodiesel from

Brassica carinata.

The temperature presented a positive effect, indicating that heating is needed to enhance ethanol solubility in the reacting mixture, raising the rate of reaction. At low temperatures, when stirring starts, emulsions are formed. The reaction happens in the interface of the alcohol drops in the oil and as soon as ethyl ester starts being formed the alcohol dissolves gradually because esters are solvents for both alcohol and oil.

The effect of the interaction between the amount of catalyst and the temperature showed that higher levels favor saponification, reducing the yield. Due to their polarity, soaps dissolve in the glycerol phase during the separation of phases and increase the solubility of esters in glycerol. Not only is the yield reduced, but purification becomes more complicated.

Ethylic transesterification of vegetable oils was also studied by Encinar et al.

(2007). For 30 minutes of reaction, a yield of 90 % was obtained using 1 % w/w of catalyst (NaOH) and a molar ratio of 12:1 (ethanol:oil). The study concluded

19

that a high concentration of ethanol interferes in the separation of phases because it increases the solubility among the components of the mixture. This alcohol excess, according to the authors, has a tendency of favoring the conversion of diglyceride in monoglyceride and there is also a recombination of esters and glycerol into monoglyceride given the constant increase in their concentrations during the reaction.

Domingos et al. (2008) studied transesterification with ethanol through experimental planning and optimization. The molar ratio varied from 6:1 to 12:1 ethanol:oil and the amount of catalyst, 0.4 to 0.8 % w/w. In the experiments with

6:1 ethanol:oil and 0,4 % catalyst, the separation of phases was not observed.

The molar ratio had the biggest effect (positive), followed by the interaction between molar ratio vs amount of catalyst (negative). The optimum point was identified as molar ratio 11,7:1 ethanol:oil and 0.4 % w/w of catalyst.

2.7 Purification

After the reaction of transesterification, there is the separation of glycerol and ethyl or methyl esters, which are only called biodiesel after reaching the appropriate specifications, that is, after the removal of contaminants such as free glycerol, soaps, metals, excess alcohol, catalyst, and others (Cooke, 2007).

Among the most widely used treatments for the purification of biodiesel are washing it with water and acidified water. The great advantage of washing is the efficient removal of glycerol and ethanol, and residues of sodium salts and soaps, the latter dependent on the amount of free fatty acids present in the original raw material (Berrios and Skelton, 2008). Enweremadu and Mbarawa (2009) added that the washing can also remove unreacted vegetable oil (triglycerides). During washing, the use of acidified water reduces the formation of emulsions caused by the formation of soap (Wyatt et al., 2005).

The disadvantages are the possible unavailability of water; the requirement for a pre-treatment before washing; yield decrease due to biodiesel losses in the effluent; time and cost for drying the esters. High amount of soaps can cause emulsification, requiring multiple washes to fit the specifications, affecting the

20

phase separation and promoting a potential loss of the emulsified product. Thus, a long decanting time is required, as well as investments with centrifugation.

Another big investment accounts for the treatment of effluent (Cooke, 2007).

In the industry, it has been employed the so-called dry cleaning by ion exchange resins and magnesium silicate to neutralize impurities, with the advantage of not producing liquid effluents. Such practices do not have any scientifically proven results, with information only found in the brochures provided by manufacturers

(Berrios and Skelton, 2008).

TriSyl ® is a micronized silica gel of high purity, developed to remove efficiently phospholipids, soaps, metal traces, oxidized compounds and other polar contaminants present in vegetable oils, fats, tallow and oil chemicals. Its use allows, through the process of selective adsorption, to increase the efficiency of clays and/or deodorizers, stimulating the removal of pigments present in lower concentrations. It is chemically inert, acting only through physical adsorption, not interfering with the structure of fatty acids. It resembles a sponge, where contaminants in the oil are adsorbed and encapsulated (Grace Davison, 2009).

Distillation is the final step in the industrialization of biodiesel, to produce fuel within specifications. The batch distillation involves the separation of the mixture initially placed in a vessel and the cracking is done until a certain amount of desired product is distilled and reaches the desired degree of purity.

The composition of the top varies with time during operation. Some of these fractions are desired products, others are fractions out of specification that can be mixed with a new process load and then separated. The fraction of the bottom may or may not be recovered as final product (Luz Junior, 1993).

21

3 Experimental method

3.1 The procedure

Biodiesel was produced in a laboratory in Sweden using an Erlenmeyer flask as a reaction vessel. The reactants used were ethanol and corn oil, with sodium hydroxide (NaOH) as a catalyst. The vessel was kept at reaction temperature

(40˚C or 50˚C) in a water bath with good magnetic stirring during the entire reaction time (1h or 2h).

First the catalyst was pulverized, thereafter the weight was measured and the catalyst was mixed with the ethanol in the reaction vessel. The catalyst was left to dissolve in the ethanol with good stirring in the water bath at the reaction temperature, and after that poured in to another vessel containing 200 mL of corn oil. The substances where left to react. After the reaction time the content was poured into a separating funnel and left for glycerol and biodiesel to separate. The lower darker phase containing glycerol was then poured out and the remaining biodiesel was once washed with 5 % w/w water solution of phosphoric acid to remove the alkaline from the biodiesel. The water phase was poured out and the volume, viscosity, weight and the refractive index were measured.

Figure 7: Separating funnel containing the glycerol and the biodiesel phases

22

After this series of practices to evaluate the influence of the process variables in the yield of biodiesel, another single experiment was conducted to investigate the behavior of yield with time.

The same procedures were followed to start the reaction but, instead of measuring the volume at the end of the batch, small samples were taken each 10 minutes and left to separate. Twelve samples were collected and had the volumes of their phases measured.

Figure 8: Separating funnels containing samples taken each 10 minutes

3.2 Analysis of the biodiesel

Viscosity

The viscosity was measured using a viscosimeter with 20% glycerol in water as reference liquid (Vigouroux, 2010). To perform such measurements, in general, either the fluid remains stationary and an object moves through it, or the object is stationary and the fluid moves past it. The drag caused by relative motion of the fluid and a surface is a measure of the viscosity. The flow conditions must have a sufficiently small value of Reynolds number for there to be laminar flow.

23

meter, in which the fluid is stationary in a vertical glass tube. A sphere of known size and density is allowed to descend through the liquid. If correctly selected, it reaches terminal velocity, he time it takes to pass two marks on the tube.

Electronic sensing can be used for opaque fluids. Knowing the terminal velocity, the size and density of the sphere, and the density of the liquid, Stokes' law can

Time: 0.93 s

The constant k was determined to: k = 6.03

ߟ ൌ ݇ ൈ ݐ ൈ ሺߩ

௕௔௟௟

െ ߩ ሻ

(Eq. 1)

Refractive index

The refractive index is measured using a refractometer

. The refractive index is defined from Snell´s law as: n

=c/V (Eq.29) here c is the speed of light in vacuum and v the speed of biodiesel.

Figure 9: Refractometer

24

4 Results

Table 4 (in the next page) presents the variables measured and calculated in each experiment. Note that each case of failure was repeated but still no phase separation was observed.

In the first place, it is important to bear in mind when analyzing the results that the biodiesel phase consists of a mix of actual biodiesel, unreacted oil and ethanol as the main components, to a minor or major extent. Although most of the ethanol is separated along with the glycerol, some of its excess still remains in the biodiesel phase as can be shown numerically.

Table 5 presents the amount of components at the end of the reaction supposing a 100% of conversion for 125 mL of ethanol and taking biodiesel density as an average of all measurements, 0.88 g/mL.

Table 5. Output of transesterification for a conversion of 100% using 200 mL oil

Output

[mol]

[g]

Oil

0

0

Biodiesel Alcohol

0.624 1.517

191.492 69.893

Glycerol

0.208

19.146

Table 5 shows that the maximum amount of biodiesel obtained from 200 mL of corn oil is equivalent stoichiometrically to 217 mL. So a mixture of only unreacted oil and biodiesel should yield a volume between 200 mL (0% of conversion) and 217 mL (100% conversion) – changes in density are neglectable, for their values are quite close.

In many cases, though, the obtained volume is higher than 217 ml, because an excess of alcohol is still present in the biodiesel phase.

This can also be illustrated through the densities calculated for the produced biodiesel mixture: when working with 60 mL of ethanol, the values obtained remained between 0.8828 g/mL and 0.8906 g/mL, higher than the ones for 125 mL of ethanol, between 0.8672 g/mL and 0.8753 g/mL. It is clear from these numbers that a larger volume of alcohol leads to a larger excess of it in the mixture and, consequently, lower values of density.

25

Experiment

1

2

3

12

13

14

15

16

17

18

8

9

10

11

4

5

6

7

T [°C]

50

50

50

40

40

40

40

40

40

40

50

50

50

40

40

40

40

40

Table 4. Experimental data for the biodiesel production (basis: 200 mL of corn oil)

M_cat

[g NaOH]

0.8

0.8

0.8

1.5

0.8

1.5

0.8

1.5

0.8

1.5

1.5

1.5

1.5

1.5

0.8

0.8

1.5

0.8

V_EtOH

[mL]

60

90

125

125

125

125

60

90

90

60

125

90

60

90

90

60

60

125

Molar ratio

EtOH:Oil

4.9

4.9

10.2

10.2

10.2

10.2

4.9

7.4

7.4

7.4

10.2

10.2

7.4

4.9

7.4

7.4

4.9

4.9

tr [h]

1

1

1

2

2

2

1

2

2

2

1

1

1

1

1

1

1

1

η

[cP]

*

2.7650

2.9510

*

2.9231

3.1720

3.0530

3.1340

*

2.9755

3.0120

3.0030

3.2111

3.2258

*

3.2211

3.1465

3.0555

Refractive index (n)

*

1.4450

1.4450

*

1.4590

1.4520

1.4450

1.4525

*

1.4530

1.4520

1.4380

1.4430

1.4350

*

1.4415

1.4435

1.4500

Vb [mL]

*

245

265

295

295

285

*

233

240

205

*

242

210

250

255

*

190

270

ρ

bio [g/mL]

*

0.8734

0.8697

*

0.8739

0.8828

0.8784

0.8770

*

0.8884

0.8753

0.8672

0.8725

0.8742

*

0.8857

0.8778

0.8906

Observation

No separation

Little solids

No separation

Emulsion

Emulsion

Little emulsion

No separation

Little emulsion

Little foam

No separation

-

-

-

Corn oil density: 0.9155 g/mL, corn oil molar mass: 875 g/mol; ethanol density: 0.789 g/mL; ethanol molar mass : 46.07 g/mol

26

The same trend can be observed when it comes to the refractive index ( n

). The lower values were obtained for the biodiesel mixtures that used 125 mL of alcohol, only situation in which values of n < 1.44 were obtained.

Table 6 illustrates values from literature for the refractive indexes of the biodiesel produced from different types of oil. The average n measured in this study, using biodiesel from corn oil, was 1.4467, which is in accordance to the mean value found in the table. Therefore, this value can be used as a reference for the biodiesel obtained, with lower ones indicating contamination with alcohol and higher ones, unreacted oil remaining ( n corn oil

= 1.4760).

Table 6. Refractive indexes for biodiesel from different oils (Eevera, 2009)

Oil type

Pongamia

Neem

Refractive index

1.4447

1.4456

Palm

Cotton seed

Rice bran

Gingelly

Groundnut

Coconut

1.4418

1.4428

1.4487

1.4466

1.4495

1.4271

Comparisons using the viscosity were disregarded, because the viscosimeter was a major source of errors. This is due to the wide dispersion of the time measurements, regarded not only to the person who performed them but also to systematic errors, given the conditions of the equipment.

Figure 10 summarizes the results, displaying the volume of biodiesel obtained as a function of the amount of catalyst. Similar colors indicate same reacting conditions.

27

300

280

260

240

220

200

60 mL (a)

60 mL (b)

60 mL (c)

90 mL (a)

90 mL (b)

90 mL (c)

125 mL (a)

125 mL (b)

125 mL (c)

180

0,7 0,8 0,9 1,0 1,1 1,2 1,3

Amount of catalyst (g)

1,4 1,5 1,6

Figure 10: Volume of the biodiesel phase obtained as a function of the amount of catalyst in three different conditions, given the volume of ethanol: (a) 1 hour reaction at 50°C; (b) 1 hour reaction at 40°C; and (c) 2 hour reaction at 40°C.

It is easy to observe in this plot that, when using 60 mL of ethanol, the reaction does not occur under any of the conditions with only 0.8 g of catalyst. That means a larger amount of catalyst is needed to compensate the little excess of alcohol. Eevera et al. (2009), who investigated the process variables in the transesterification of a wide variety of both edible and non-edible oils with methanol and NaOH, also point out that insufficient amount of sodium hydroxide resulted in incomplete conversion of triglycerides into the esters.

Another unsuccessful separation happened with 125 mL in condition a

, indicating there must be an associated effect of the increase in acidity and high alkalinity at higher temperatures contributing to the catalyst consumption.

In general, it is possible to conclude that the increase in the amount of catalyst from 0.8 g (0.4 wt %, based on the weight of raw oil) to 1.5 g (0.8 wt%) does not change the yield significantly. The amount of 0.8 g NaOH for 200 ml corn oil is enough for catalyze the reaction of transesterification. For the experiments with

90 mL of alcohol, doubling the mass of catalyst provided no more than 7 mL difference in the final volume of biodiesel, a value that can be neglected given the errors and fluctuations in the final composition. The same applies to 125 mL of

28

ethanol at condition c

, being the difference 10 mL, insignificant given variations in the amount of alcohol in excess in the mixture. The abrupt behavior of condition b using 125 mL of ethanol should be discarded as the biodiesel obtained from experiment 12 was highly impure, being the only experiment where the formation of foam could be observed after washing it. It is common that when the solubility limit of the mixture is reached, impurities in the biodiesel form an emulsion, but not foam.

Eevera et al. (2009) observed a similar phenomenon: the formation of soap when a large amount of sodium hydroxide was used. The authors claim it happens because addition of excess alkaline catalyst caused more triglycerides’ participation in the saponification reaction with sodium hydroxide, resulting in the production of more amount of soap and reduction of the ester yield.

Regarding the overall effect of the amount of catalyst, Eevera et al. (2009) obtained the results presented on the plot below (Figure 11).

Figure 11: Effect of catalyst amount on esters’ yield. Source: Eevera et al. (2009).

29

As can be observed, the ester content reached an optimal value when the sodium hydroxide concentration reached 1.5 % w/w (based on the weight of raw oil), and further increase in catalyst concentration in all the cases caused ester production amount to decrease.

Therefore after an optimal value, increasing the concentration of catalyst leads to no gain in yield, causing it to decrease in a greater or lesser extent, according to the type of feedstock. Larger amounts of catalyst favor an increased participation of the triglycerides in the reaction of saponification rather than stimulating transesterification itself. These observations are in accordance with the experimental results obtained in this work as no raise in yield was observed with the increase of the catalyst concentration, only the formation of foam.

The influence of temperature in this case displays an interesting behavior. The higher the temperature, the more biodiesel was obtained with 60 mL of ethanol, but the opposite effect was observed with 125 mL. It works in the same direction as the previous assumption that a combination of increased acidity and high temperatures affects negatively the reaction of transesterification, favoring saponification and other side reactions. Eevera et al. (2009) realized that temperatures above an optimum value also favor side reactions along with other variables that might be taken into account. So it is not possible to define a general behavior for temperature as its influence must be analyzed in addition to the effect of other variables.

As for the effect of time, it can be said that the longer it is, the higher the yield.

For 60 mL of ethanol, it is quite clear, as it can be assumed that too little alcohol is present in the biodiesel phase. When it comes to the other volumes, though, it is more difficult to say precisely how far the conversion goes and distinguish it from the amount of alcohol in excess. In these cases it is reasonable to assume that the changes in conversion were not too pronounced, but it was the amount of alcohol in the biodiesel phase that varied. The effect of time became clearer when another experiment was done (Figure 14).

Figure 12, gathering the same results, makes it easier to visualize the effect of an increase in the excess of alcohol in the biodiesel phase volume.

30

310

290

270

250

230

210

0,8 g (a)

0,8 g (b)

0,8 g (c)

1,5 g (a)

1,5 g (b)

1,5 g (c)

190

5 7,5

Molar ratio EtOH:oil

10

Figure 12: Volume of the biodiesel phase obtained as a function of the molar ratio ethanol:oil in three different conditions, given the amount of catalyst: (a) 1 hour reaction at 50°C; (b) 1 hour reaction at 40°C; (c) 2 hour reaction at 40°C.

As stated previously, it is important to bear in mind that the final volume obtained may include excess of alcohol. Therefore, the best way to analyze this plot is comparing how much excess of alcohol was added from one experiment to the other and the gain in volume it produced.

When the volume changes from 90 mL (Molar ratio EtOH:oil = 7.5:1) to 125 mL

(Molar ratio EtOH:oil = 10:1) (35 mL difference), the gain in volume of biodiesel can be as high as 50 mL, clearly stating a raise in the conversion superior than in the interval from 60 mL (Molar ratio EtOH:oil = 5:1) to 90 mL (Molar ratio

EtOH:oil = 7.5:1). This tendency can be better visualized for 1.5 g of catalyst and does not show in most cases that use 0.8 g of catalyst (except for condition c

, which follows the same trend of an abrupt increase). It can be concluded then that a higher amount of alcohol in excess provides a higher yield at mild temperature conditions. It can be clearly observed too that the 2 hour reaction using 0.8 g of catalyst performs just as well as the reaction with 1.5 g and half of the time in conditions of high alcohol excess, proving the importance of time to

31

increase the yield over the amount of catalyst (notice, as discussed before, that for a ratio of 7.5:1, the influence of the amount of catalyst is not relevant. All volumes were obtained within a narrow interval, so differences can be neglected, given variations inherent to the measurements).

Eevera et al. (2009) provided the following plot to illustrate the influence of the amount of alcohol in the biodiesel yield (Figure 13).

Figure 13: Effect of alcohol amount on esters’ yield. Source: Eevera et al. (2009).

Figure 13 indicates that a higher amount of alcohol leads to higher yields until an optimal value, from which the latter decreases. Eevera et al. (2009) explain that for a high alcohol amount added, a longer time is required for the subsequent separation stage. In this case, separation of the ester layer from the water layer becomes more difficult due to the formation of an emulsion. This is exactly the behavior observed in the experiments carried out for this work.

In another experiment done, conversion was evaluated as a function of time.

Figure 14 shows how the percentage of glycerol (by-product) in the samples, an

32

evidence of reaction, changes with time. The biodiesel phase was not considered in this case because it is not possible to distinguish the product from unreacted oil. The percentage was preferred instead of absolute values as the samples varied in volume (although it was always around 20 mL).

14,0

12,0

10,0

8,0

6,0

4,0

2,0

0,0

0 20 40 60 80

Sampling time (min)

100 120 140

Figure 14: Percentage of glycerol (v/v) in the sample of reacting mixture as a function of time.

It is clear that a longer reaction time leads to higher yields. However, it can be concluded from the plot that after one hour the gain in yield is not as relevant as it is in the first hour. In other words, after one hour the reaction reaches a conversion similar – although inferior – to the maximum obtained. On a large scale, it is reasonable to admit that the expenses related to an extended operation time are not worth the small gain in yield. Therefore, one hour seems to be enough to convert most of the oil into biodiesel.

Eevera et al. (2009) also evaluated the influence of time on transesterification’s yield (Figure 15). The ester content increased with reaction time from 15 min onwards and reached a maximum at a reaction time of 90min at 55 °C, and then remained relatively constant with increasing further the reaction time, same trend observed in Figure 14. The authors concluded that an extension of the

33

reaction time from 90 to 150min had no significant effect on the conversion of triglycerides, conclusion similar to the one that can be drawn from Figure 14.

Eevera et al. (2009) noticed yet a reduction in the product yield from 120 min.

This happened, they claim, because longer reaction time enhanced the hydrolysis of esters (reverse reaction of transesterification), resulting in loss of esters as well as causing more fatty acids to form soap. A reduction in the yield can be seen in Figure 14 at 120 min, but as the experiment was interrupted, this point is not enough to characterize any tendency.

Figure 15: Effect of reaction time on esters’ yield. Source: Eevera et al. (2009).

34

5 Conclusions

Understanding the production of biodiesel is a quite complex task. One must bear in mind a multiplicity of factors that may influence the chemical reaction, like the presence of water or fatty acids, as well as the operating conditions, such as amount of catalyst, temperature, time of reaction and excess of alcohol.

As a general rule, one can conclude that a higher yield can be achieved by increasing the amount of catalyst, temperature, time of reaction and volume of alcohol. However, in most cases, after the variables reach an optimum, the tendency of increase of the yield ceases, becoming stable or even decreasing.

This behavior can be explained by the promotion of side reactions in extreme conditions, with saponification taking place when alkalinity (amount of catalyst) and reaction temperature are too high; hydrolysis of esters at a long reaction time; and difficulties of separation when the excess of alcohol is too large.

On the other hand, as it could be observed, many times all these elements interact in an uneven manner, being difficult to keep track of which effect is predominant for each situation. That makes each experiment unique and generalization hard to achieve.

The main contribution of this work is not to point out precisely how to obtain the highest yield in biodiesel production, but to provide means to come up with the right balance between the variables, an optimum. A best benefit-cost ratio uses enough excess of alcohol to provide a good yield, without splurging; avoids wasting catalyst, for the increase of its amount does not affect significantly the yield; and it further reduces expenses with energy and operating time as long reactions are not necessary for a good result. These operational issues compensate what originally would be a technologic improvement, a small percentage of gain in yield that would end up not being relevant in practice when other costs are considered.

This report also shows that there is more than engineering involved in biodiesel production. It is an important subject in a country’s social and economic agenda.

It impacts directly on the energy sector, closely related to a nation’s resources and productive structure. After all, energy nowadays is the fuel for development.

35

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