BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS FACULTY OF CHEMICAL AND BIOENGINEERING
DEPARTMENT OF CHEMICAL AND ENVIRONMENTAL PROCESS ENGINEERING
BIODIESEL TECHNOLOGY WITH PHASE TRANSFER AVOIDED MASS TRANSFER
A thesis submitted in partial fulfillment for the degree of Doctor of Philosophy
AUTHOR: dr. techn. KOVÁCS, ANDRÁS SUPERVISOR: PROF. FEKETE, JENŐ
December, 2012
ACKNOWLEDGEMENT
This is to express my gratitude to everybody who stood by my side and motivated me in compiling this thesis.
To my family for their love and for supporting and encouraging my strives to conduct research and development works in my own private research company even when economic circumstances were far not favorable for such. My wife Johanna and son Daniel David have had to endure those difficult days and have never asked me to give up for a better income job. My mother motivated me for regular use of both technical and general culture library, my passed away father did ask for modesty, my brother for responsibility to take care of those weaker than me, my passed away parents in law for their love.
To Prof. Jenő Fekete for continuous support and encouragement to conclude the lessons learned in more than 10 years active research in practice and science of technology and use of biodiesel in script, for pushing me to structure these into a thesis that provides me an academic qualification, even though my earned doctorate have been accepted by respected foreign academic institutions (MIT, The Hebrew University).
To Prof. Tungler for recommendations, advices for reshaping the thesis for presenting the document more comprehensive in content and format and for struggling to conclude to concise theses phrases.
To late Dr. Endre Vámos for providing an example for sound scientific basis and rational technical solutions in every aspects of fuels, lubricants and related products.
To my friends, with special thank to Dr. János Pintér for discussions about phenomena and processes in colloid chemistry.
I apologize for not detailing the roles of my friends in progressing my knowledge in the technology and use of biodiesel, Dr. Sándor Vida, Prof. János Schmidt, Prof. Péter Mizsey, Prof. László Tolner, Prof. Imre Czinkota, Prof. Botond Sinoros Szabó, Lóránt Haas and János Tóth.
CONTENT
section Title page No.
Acknowledgement II
Content III
List of figures V
List of tables VII
Abbreviations VIII
Executive summary IX
1. LITERATURE SURVEY, STATE OF THE ART 1
1.1 Fundamental, what is Biodiesel? 1
1.2 History of biodiesel 2
1.3 Leitmotives of global biodiesel development efforts 3
1.4 FEEDSTOCK VARIETIES FOR BIODIESEL SYNTHESIS 4
1.5 AGRO-INDUSTRIAL ECOLOGY PERSPECTIVES 5
1.6 State of the art of biodiesel processing 10
1.6.1 UNIT OPERATIONS INVOLVED 10
1.6.2 COLLOID CHEMICAL ASPECTS 25
1.6.3 CATALYSIS ASPECTS 28
1.6.4 Technologies 31
1.6.5 Glycerol byproduct related matters 36
2 EXPERIMENTAL 39
2.1 Frame of the test methods 39
2.1.1 Free fatty acids (FFA) (ISO 6619) 41
2.1.2 Water content (ISO 12937) 43
2.1.3 Peroxide number (ISO 27107) 43
2.1.4 Iodine number (IN) EN 14111) 43
2.1.5 Conversion 44
2.1.6 Theoretical loss on refining (AL 121) 47
2.1.7 Phosphorous content (EN 14107) 47
2.1.8 Viscosity (EN 3105) 47
2.1.9. Specific gravity 48
2.1.10. Ash content (EN ISO 3987) 49
2.1.11. Methanol content, flash point (EN ISO 14110, 3679) 49
2.1.12. Free and total glycerol and glycerides (EN ISO 14105) 49
2.1.13. Cold temperature behavior (EN ISO 14105) 49
2.2 Techniques and apparatus 50
2.2.1 Seed preparation 50
2.2.2 Oil extraction 50
2.2.3 Feedstock (oil) refining 51
2.2.4 Esterification/trans-esterification 53
2.2.5 Product refining 58
3 RESULTS AND DISCUSSIONS 60
3.1 Feedstocks of experiments 60
3.1.1. Sunflower 60
3.1.2. (Distillers) corn oil 63
3.1.3 Yellow grease 63
3.1.4 Algae oil 65
3.2. Phase behavior tests 67
3.3. Esterification 74
3.4 Neutralization 88
3.5 Trans-esterification 89
3.6 Byproduct G-phase refining 91
3.7 The proposed technology variants 98
3.8 Industrial ecology principles to potentials of small and medium size companies
101
4. CONCLUSIONS, THESES, RECOMMENDA- TIONS FOR FUTURE WORKS
109
Articles and communications related to the subject of the thesis 112
Literature cited 115
LIST OF FIGURES
SECTION TITLE PAGE NO.
1.1 Basic chemical reactions involved in synthesis of biodiesel 1 1.2 More plants have been built than operated in the world 10 1.3 Sequence of operations in biodiesel production – series of losses 11 1.4 Consecutive extraction of oil from pressed sunflower cake,
comparison of oil yields in function of seed-‐cake preparation 13
1.5 Structure of glycerides 15
1.6 Biodiesel technology scheme of Agrar Technik with solvent
extraction deacidifying vegetable oil feedstocks 19
1.7 Duo-‐sol refining of partially refined sunflower oil 19 1.8 Kinetics of sunflower trans.esterification at MeOH:Oil=12:1, with
different catalysts
27
1.9 Esterfip technology of IFP 31
1.10 Lurgi biodiesel technology with two special trans-‐esterification
reactors including a mixer and a coalescer in downstream 32
1.11 Esterfip-‐H technology of IFP 33
1.12 Operational units of Biox technology 36
1.13 Standard industrial glycerine production by the use of high vacuum
distillation 37
2.1 Calibration curves for ester contents of biodiesel samples 46
2.2 Mixer-‐settler 51
2.3 Counter current reaction-‐extraction apparatus 52
2.4 Four neck reaction/distillation gear 53
2.5 50 ml apparatus 54
2.6 Loop reactor apparatus 55
2.7 Continuous counter current system made of glass 57
2.8 Stainless steel continuous counter current reactor 58
3.1 Husk:kernel rate of a number of sunflower species 61
3.2 Oil content of seeds, husk and kernel of selected species, significance
of dehulling 61
3.3 Oil content of seeds as a function of seed weight 62
3.4 Overall oil content of seeds 62
3.5 Gas chromatogram of the algae oil feedstock 65
3.6 Higher hexane:methanol rates are showing evidence of refining 71
3.7 Hexane brings methanol into vegetable oil phase 71
3.8 There is an optimal rate of hexane usage 72
3.9 25-‐30% of the methanol can easily be wasted 72
3.10 Hexane brings methanol into reaction phase 73 3.11 Esterification kinetic of sunflower oil doped with oleic acid 76 3.12 Figure 3.12 Mono-‐gliceride pattern, trans-‐esterification kinetics of
algae oil
76 3.13 Figure 3.12 Di-‐gliceride pattern, trans-‐esterification kinetics of
algae oil
77 3.14 Figure 3.12 Tri-‐gliceride pattern, trans-‐esterification kinetics of
algae oil
77 3.15 Esterification kinetic of distillers corn oil as a function of addition of
apolar solvent 79
3.16 Esterification kinetic of yellow grease as a function of addition of
apolar solvent 79
3.17 Esterification kinetic of yellow grease as a function of addition of
asorbent and apolar solvent 80
3.18 Esterification profile along the column height 82
3.19 Esterification profile along the column height-‐ sunflower oil doped
with oleic acid distillers corn oil, counter-‐current 82 3.20 Esterification profile along the column height-‐ distillers corn oil,
counter-‐current
83 3.21 Esterification profile along the column height-‐ yellow grease,
counter-‐current 84
3.22 Addition of more reagent presents solvent extraction profile 87 3.23 Batch transesterification of sunflower oil in presence and in absence
of an apolar solvent 90
3.24 Titration curve of crude G-‐phase with concentrated sulfuric acid 93
3.25 Viscosity of industrial G-‐phase sample 94
3.26 Viscosity of partially refined glycerine 95
3.27 Viscosity of partially refined glycerine 95
3.28 Proposed Pickering emulsion structure of G-‐phase 96
3.29 Adsorption treatment of refined (“control”) glycerine 97 3.30 Process flow scheme of the truly continuous counter current
biodiesel pilot plant 98
3.31 Process flow scheme, retrofitted biodiesel demonstration plant 100
3.32 Time flow comparison 102
3.33 Principles of agro-‐industrial ecology in biodiesel production 103 3.34 Potential for improving revenue generation through feedstock
processing 104
3.35 Sketch for comparing capacity efficiencies in conventional and revamped schemes
108
LIST OF TABLES
SECTION TITLE PAGE NO.
1.1 Most important industrial ecology principles to biodiesel systems
7
1.2 An overview of biodiesel technology market 35
2.1 EN 14214 specifications for B100 biodiesel 39
2.2 ASTM D 6751-‐09 specification for B100 biodiesel
40
2.3 Comparison of test methods employed in feedstock and product
analysis
41
2.4 Influence of seed preparation in Soxhlet oil extraction 51 2.5 Comparison of the glass and stainless steel systems 56 3.1 Fatty acid distribution and characteristics of corn oils 63
3.2 Properties of yellow grease feedstocks 64
3.3 Properties of the algae oil feedstock 64
3.4 Mass balance of liquid-‐liquid equilibria in phase transfer
experiments 66
3.5 Raffinate characteristics in phase transfer experiments
69 3.6 Extract characteristics in phase transfer experiments 70 3.7 Degumming in esterification of sunflower oil doped with oleic
acid 75
3.8 FFA reduction along the column height in counter current
esterification of sunflower oil doped with oleic acid 82 3.9 Counter current esterification of sunflower oil of 12.5% FFA 83 3.10 Esterification, 2.5 m GLASS counter current reactor extractor 85 3.11 Esterification, 3 m stainless counter current reactor extractor 86 3.12 Esterification of YG , atmospheric conditions and total reflux 86 3.13 Trans-‐esterification of sunflower oil with an FFA content of
0.95% and esterified corn oils of similar FFA level 88 3.14 Solvent extraction by adding glycerol to neutralization reagent 90 3.15 Trans-‐esterification of sunflower oil with an FFA content of 0.95%
and esterified corn oils of similar FFA level 91
3.16 Characteristics of the G-‐phase 93
ABBREVIATIONS
ABBREVIATION DESCRIPTION
AL Alfa Laval test method
AMEI Ásványolaj Minősítő Intézet (Hydrocarbon Testing Institute)
AN Acid number
ASTM ASTM International, formerly known as the American Society for Testing and Materials
C6 Hexane solvent
DG Di-glyceride
E-i/T-i Esterification/Trans-esterification reactor –designation EN European Norm (standard test methods in EU)
F Feedstock
FAME Fatty acid methyl ester FFA Free fatty acid
FID Flame ionization detector
G Glycerol (glycerine)
IFP Actual name: IFP Energies Nouvelles, former Institute Francais du Petrol
IN Iodine number
ISO International Standards Organisation
MG Mono-glyceride
MSTFA N-‐Methyl-‐N-‐(trimethylsilyl)trifluoroacetamide Refractive index @20°C
PN Peroxide number
R Reagent
R-i Reactor-designation
S Solvent
S-i Settler-designation S:F Solvent to feed ratio SE Solvent in extract phase
SMEU Small and medium size production unit SR Solvent in raffinate phase
SVO Straight vegetable oil
TG Tri-glyceride
YG Yellow grease
η Rate of improvement (industrial ecology)
€
n20D
(EXECUTIVE) SUMMARY
Biodiesel has been the most matured clean burning renewable energy based alternative automotive fuel. By definition biodiesel consists of a mixture of alkyl esters of C14 -‐ C24 fatty acids. Since most generally the alcohol constituent is methanol, biodiesel ids generally referred as FAME, fatty acid methyl ester. It’s short history of production technologies has been broadened from the basic trans-esterification of refined food grade oils to conversion of various refuse oil bearing wastes. The chemistry of production is being based on the following sequence of chemical reactions:
Methanolysis of triglycerides Methanolysis of diglycerides Methanolysis of monoglycerides Esterification of fatty acids
The so called hydrodiesel, that is produced by complete hydrogenation of unsaturated and heteroatomic links and isomerization of the alkane products, has not been the scope of the present work. In this thesis I have addressed specific aspects of producing standard quality biodiesel by the use of an apolar solvent. This technique makes the production technology more efficient, improves the reliability of product quality, reduces the carbon footprint by cutting the specific consumption of energy and auxiliaries.
An industrial system is ecological if the resources and assets of the system are not misused hence the trend in biodiesel technology development shows that first generation plants (in which the feedstock is food quality oil) has been upgraded to second and higher generation plants in which high fatty acid content refuse stocks, such as used cooking oil and grease, yellow and brown grease constitute the feedstock to convert into standard quality fuel. It has been an objective of the present work to recommend techniques for retrofitting first generation plants to higher rank plants. A concise analysis of ecological principles related to biodiesel processing is being presented in the theoretical section.
In assessing the supporting scientific knowledge the following aspects have been revisited for the sake of a complete picture of the state of the art of biodiesel technology:
feedstock pool varieties, agro-industrial perspectives, unit operations involved, colloid chemistry, catalysis, commercial technologies and state of the byproducts. Unit operations have been analyzed as potential sources for losses in production. This “detective” approach collects ideas and concepts for development objectives that lead to improving the overall yield and quality of the products.
Description of standards, specifications, test methods and experimental techniques is compiled to include specific procedures and routines employed.
Feedstock matters: it has been acknowledged that the most valuable asset of biodiesel processing is the feedstock, therefore extremely important operations of seed preparation and oil extraction are revisited. Seeds are biological colloid systems. The selected process technology must respond to specific needs as determined by the species and conditions of cultivation.
• Sunflower species have been the predominantly cultivated oilseed in Hungary, husk- kernel ratio, oil contents distribution between husk and kernel are those features that must he considered for optimal oil extraction conditions.
• Distillers corn oil is a byproduct of automotive ethanol production. This is a high FFA, high wax content feedstock. It has been studied because of ample interest in USA.
• Yellow grease has saved the biodiesel industry in EU. Colloid chemical structure of these feedstocks becomes more complex in the order of the above presentation.
• Algae oil. It is to anticipate that I see weak chances for algae oil to become a biodiesel feedstock commodity. High content of omega 3 constituents has much higher value potential than combustion. A perspective area of research will be the separation of omega 3 essential fatty acids and converting the rest of the processing into biodiesel.
The core mechanism of the biodiesel technology developed consists in altering the phase behavior of components in the sequential system of the chemical reactions. It has been known that vegetable oil, the substrate of biodiesel synthesis, does not dissolve in the reagent methanol. Neither methanol is dissolved in refined vegetable oil. Since the reagent and the substrate form two distinct immiscible phases intensive mixing is needed to bring reaction partners, including the catalyst methoxy into intimate contact.
It has therefore been the general practice to use intensive mixing and high excess of reagent. These promote trans-‐esterification conversion to equilibrium within a period of about 30 minutes, at 55°C and K-‐methoxy catalyst. The intensive mixing does not only promote the forward (methanolysis), but the reverse (hydrolysis) reactions alike.
I proposed the use of an apolar solvent to avoid phase transfer related transport and phase separation difficulties in synthesis and refining steps in biodiesel processing. The idea was born in technique of acid number test of lubricating oils. A related recommendation was invented by Boobcock by the use a polar solvent for the same sake, to eliminate the mass transfer resistance. I opted for the use of an apolar solvent. By considering reasons considering basic chemical engineering principles:
• The feedstock and the biodiesel are predominantly apolar. Less apolar solvent dissolves more feedstock than do a polar solvent.
• The use of a polar solvent incurs the use of high excess of reagent. The rate of methanol used in polar solvent system exceeds the extent of 16 times to stochiometry,
• The polar solvent dissolves the byproduct glycerol and maintains the conversion in both directions. The difference between polar solvent and no solvent systems consists in faster kinetics to equilibrium.
• The apolar solvent rejects the byproduct glycerol, full conversion can theoretically can be achieved in a single reaction step.
• To separate the byproduct to promote the reaction from partial to full conversion the polar solvent must be separated between two reaction sequences. Separation of the solvent by distillation is highly energy demanding operation.
My goal was to perform trans-‐esterification to full conversion in a single operational contact. Phase behavior experience affirmed that the apolar solvent brings the substrate and reagent into a single phase and rejects the glycerol into a distinct phase as the reaction progresses. Expelling water into the glycerol phase protects the catalyst.
Findings of phase behavior tests:
1. Without addition of apolar solvent the system forms a homogeneous liquid phase, the possibility of intimate contact of reaction partners allow fast and efficient reaction. Lack of the solvent prevents the intimate contact.
2. Addition (formation) of glycerol turns the system into a duo-sol solvent extraction refining system. In such the apolar solvent (hexane) dissolves the biodiesel feedstock components and rejects the polar ones into the selective polar solvent (glycerol) phase.
3. This duo-sol type feedstock refining lowers the gum and other components that if present make biodiesel processing difficult to perform.
4. Colloid chemistry principles control the phase behavior. Salting effect cannot be disclosed if the catalyst is acidic. Hexane as a solvent had clean effect of avoiding emulsion formation and contributes to breaking temporary emulsion structures.
5. Hexane is necessary to bring vegetable oil and methanol into a single phase.
Despite earlier myths vegetable oil does not dissolve methanol. Intensive mixing can solubilize some methanol in oil. This solubilized (encapsulated) form of the methanol can initiate trans-‐esterification reactions under optimal conditions. Even in this case phase transfer cannot be avoided. The catalyst is preferably staying dissolved in the polar phase. For catalytic activity at least 0.5% catalyst must be present in the “reaction phase” and this is only possible to meet in dispersions in two phase systems.
Esterification proved to be a cornerstone operation in biodiesel processing of higher ranked generation process technologies. More than 370 individual esterification reactions have been performed in batch and continuous setups. Modes of operations included esterification under atmospheric and pressure conditions, with partial or total reflux, in loop reactor and in co- and counter current mode of contact. It revealed from the experiments that the proposed phase transfer avoidance in trans-esterification was a relatively easy task compared to stubborn pattern of colloid chemically controlled esterification. In esterification with sulfuric acid the catalyst forms a distinct disperse phase with part of the reagent.
Properties of the disperse phase are altered by polar components. The more I progressed with research of the technology the more questions raised, mainly because of the use of difficult to process feedstocks. Some of these questions have not been addressed before and some have been simply ignored. While esterification of oleic acid was an easy to execute exercise, yellow grease and distillers corn oil presented unexpected difficulties and outcomes. In this series I had to answer some never asked before questions:
• Is degumming a necessary upstream operation to esterification?
• Can the reaction be influenced by the use of a promoter?
• Can the high reagent excess of 60-120 to stochiometry reduced to much lower level?
In conventional biodiesel units, the scope of chemical conversion is limited to trans- esterification of triglycerides. Majority of technology vendors specifies low FFA and P-‐
content. Accordingly degumming is necessary to promote this core reaction. Similar to industrial refining for food grade edible oil, super degumming technique (neutralization to separate acids and hydrolysis with phosphorous acid to convert phosphatides into water soluble molecules) results in 5% loss in final yield for every % of FFA separated. In the case of processing high FFA feedstocks with esterification as a first conversion step it appears to common chemical engineering sense to perform a degumming. The high dosage of reagent seems to be reasoned to weaken the colloid chemical interferences, influences.
It has been shown that:
• Esterification with sulfuric acid catalyst does also degum the esterified stream.
Sulfuric acid has been proved to be equally efficient to phosphoric acid in degumming. Ion exchange resins are more favorable, although operational costs are higher.
• Conversion and kinetics can be promoted by means of adding adsorbent. Fuller earth type adsorbents and 3A molecular sieves have been found to be equally beneficial.
• The excess of reagent to stochiometry can be reduced by 5-10 times with reference to industrial practice. For such reduction the esterification must be carried out at higher pressure. This allows the raise of temperature above 100 °C and makes possible the intimate contact of reaction partners in counter current mode of operation. Significant reduction in excess of methanol contributes to reduction of distillation duty for reagent recycle.
Contrary to phase transfer avoidance in trans-esterification the mechanism in esterification reaction follows an interfacial pattern in presence of sulfuric acid catalyst. For progress in esterification conversion there is no need to bring either of the reaction partner into the phase of the other partner via phase transfer mechanism. The reaction takes place at the interface, for such there must be an easy renewal of interface, for the reactions at the interface. I had to yield in concluding that esterification of FFA with sulfuric acid catalyst could not have been performed in phase transfer avoided mode of operation. The case was different with ion exchange resin catalyst. In such system the phase transfer avoidance could have been profited. The reagent and substrate formed a single phase, diffused onto the active site of the resin and the reaction took place at the active site, such as is the case of heterogeneous catalysis. By the reduced viscosity both the starting materials and the reaction products could more easily diffuse to and from the surface from and into the bulk than in the case of absence of the suitable solvent. By intensive mixing the number of intimate contact events can be increased at enlarged surface area and under intensified product transport from the interface toward to bulk. Dilution of the apolar phase is beneficial for renewal of the interface from the apolar side, while high excess of reagent promotes the same mass transfer in the polar phase. According to this observation the rate limiting factor in esterification is a function of the rate of renewal of the interface for intimate contact of the reagent, catalyst and substrate.
Neutralization of the esterified stream is a unit operation with decisive influence on the downstream operations. If the esterification conversion is not adequate the remaining free fatty acids convert into soap and soap initiates emulsification and the emulsion can foul the column of neutralization and the column of trans-esterification.
Trans-esterification in phase transfer avoided conditions can be conducted to close to full conversion within minutes either in batch or in counter current operation. The specific benefit of performing the trans-esterification under such conditions is the better yield of the better quality biodiesel due to less dissolution of the biodiesel in the polar G-phase. The higher kinetic rates are observed both in reaction kinetic and in phase settling rates. The success of shifting the reaction of trans-‐esterification toward completion is supported by the very fast separation of the byproduct. This separation is in fact a rejection from the reaction-‐main product phase into the byproduct phase. This rejection has been visualized in an all-‐glass made loop reactor experimental apparatus, in which the drop of glycerol were dropping down in the loop and collected at the bottom of that. This visualized and practically counter-‐current settling made me to think about designing the counter-‐current apparatus and to work techniques that makes possible retrofitting conventional, low in efficiency biodiesel production systems.
Recommended technology variants are presented for fully continuous, counter current technique and for retrofitting conventional, first generation plants into second generation according to research recommendations of the present thesis.
G-phase related works revealed that low in efficiency biodiesel production systems dissolve significant amount of main product and this content turns the G-phase system into a
Pickering emulsion system, in which an ionic core is surrounded by a multiple emulsion structure. The encapsulated oil content constitute a major difficulty in producing higher grade glycerol. After this emulsion being broken the technology of producing higher grade glycerol follows the sequence of conversion of not reacted glycerides and FFA in a sulphuric acid catalyzed (trans-)esterification, separation of the solid components by centrifuge and decanting the apolar (oil) phase above the polar (glycerol) phase. The salt can refined by washing with MeOH and dried. The glycerol can be treated with selective adsorbent and the such refined product’s quality is good for animal forage.
By revisiting principles and applying the recommendations of the thesis conventional biodiesel production units can be converted to “second generation” technologies by revisiting the scientific basis of esterification and trans-‐esterification and redesigning the unit to optimize these reactions. Existing assets can be reused to improve capacity and efficiency of the unit, thus lowering costs of conversion and increasing the profit generation potential of the assets, especially if operated in symbiotically connected industrial units.
The most important findings of the research: The feedstock of biodiesel processing can be as different as many production variables can pertain. Based on the findings that the most valuable asset of any FAME production consists in the feedstock special attention must be paid to selection of the kind of the seed and to strictly adhering to recommended technology conditions. Production of biodiesel at small and medium scale units are at best incorporated into an (agro)-industrial ecological system. Algae feedstocks do not seem to be explored in the near future, mainly because of cost and properties. The most beneficial feature of algae oil can be explored in the field of healthy food, because of high content in polyunsaturated fatty acids and phosphorous.
BY THE USE OF SUITABLE APOLAR SOLVENT PHASE TRANSFER RESISTANCE IN TRANS-ESTERIFICATION CAN BE AVOIDED
The aim of my research when conceived was to find a technique by which the rate of reaction of trans-esterification can be increased. My results showed that by avoiding interfacial resistance to mass transfer this can be achieved.
I have demonstrated through liquid-liquid equilibrium tests that there is a beneficial range of addition of apolar solvent to form a single liquid phase by reaction partners. By such removal of the interfacial resistance the rate of trans-esterification reaction could have been significantly improved. The outcome of avoiding phase transfer resistance complete conversion was achieved in 5 minutes, in comparison to 30-60 minutes times on stream for reaching the equilibrium conversion if the solvent was not present. Avoidance of phase transfer resistance can be done with polar solvents too.
BY THE USE OF SUITABLE APOLAR SOLVENT THE REVERSIBLE TRANS-
ESTERIFICATION REACTION CAN BE SHIFTED TOWARD COMPLETE CONVERSION: Another aim of the research was to shoft the reversible trans-esterification toward methanolysis on the expense of the reverse glycerolysis reaction. In practice of bioiesel production complete conversion can only be approached if the byproduct is separated after the reaction reached the equilibrium condition. By the use of polar solvents the duty of separation is extended to recycle of the solvent too. In operational practice this equilibrium condition is at about 80% conversion, while the standard requires a conversion of at least 96.5%. A common weak point is the either lengthy or high energy demand byproduct separation for preparing the reaction mixture for a second step of trans-esterification conversion.
I have demonstrated, that by rejecting the byproduct from the reaction mixture the conversion can be shifted toward completion in a single contact event without intermittent
separations of the byproduct and the solvent. The techniques were demonstrated both in batch and continuous counter current setups.
The mechanism is based on the engineered condition by the addition of the selected apolar solvent to reinstall an interfacial barrier against the return of the byproduct into the reaction phase. The reinstalled interfacial resistance efficiently bars the reverse glycerolysis reaction of FAME. By such mechanism becomes possible to shift the reversible reaction toward the desired direction. This shift cannot be done by lack of solvent or by the use of a polar solvent. With lack of solvent a desperse condition must be maintained by high input of energy, with the polar the byproduct stays dissolved in the homogeneous reaction mixture.
BY THE USE OF APOLAR SOLVENT THE RATE AND SELECTIVITY OF SEPARATION OF MAIN AND BYPRODUCTS CAN BE IMPROVED:
Most common drawback of operational production systems is associated with either lengthy or energy consuming separation of the main and byproducts after reaction steps of transesterification. It has also been subject of concern that the byproduct phase dissolves relatively high amount (10-20%) of main product. My aim was to search for technique to shorten the time and specific energy consumption of this operation with significant improvement of separation selectivity between the by and main products.
I have demonstrated that if the suitable apolar solvent was added at proper rate the rejection of the glycerol has been almost instantaneous and complete. This finding made possible to execute the reaction contact and the phase separation in a single contact device.
This contact device is preferably a counter current reactor-extractor. For existing systems modification of reactors to a loop reactor configuration can be a practice for performing the
same operations.
In addition to faster splitting of the fuel and glycerol phases the selectivity of selectivity of this operation can be significantly increased to reduce the loss of product into the polar byproduct. The amount main product in the G phase could have been reduced to 0.5-1%.
ESTERIFICATION AND TRANS-ESTERIFICATION PROVIDES SOLVENT REFINING FEATURES
In carrying out the experiments of esterification and trans-esterification in solvent assisted mode the solvent refining feature explained to me that mainly because of the selectivity of phase separation the process is a chemical reaction associated solvent refining process. To prove this I demonstrated by addition of glycerol that it forms a polar extractant to selectively extract gum and phosphorous components into the polar phase.
Because of kinetic characteristics this can be accomplished in counter current mode of operation too.
Because of the selective refining action of the newly formed polar phase pretreatment of the feedstock must not be as strict as the requirement for first generation biodiesel plants to remove gum components. In those systems these polar compounds, if not separated selectively and efficiently can initiate the formation of dispersed liquid system, that is a major reason for slow and difficult separation of main and byproduct phases. The industrial relevance and significance of this is to reduce the loss of valuable feedstock in conventional degumming operation. This efficient degumming along with esterification can save significant amount of triglycerides for the synthesis. It has been reported that every percent of polar constituent to be removed can contribute to a loss of up to 5% of the feedstock. The developed technology makes possible to improve the use of resources.
ESTERIFICATION OF FREE FATTY ACID CONSTITUENT FOLLOWS AN INTERFACIAL REACTION PATTERN
There is no unique description of the mechanism of ester formation in biodiesel processing technologies. Some state that the reaction takes place in a reaction phase into
which the reagent is dissolved, some are claiming that the reaction takes place at the interface of the dispersed globules.
While in trans-esterification the reaction mechanism in solvent media follows a homogeneous pattern in esterification with sulphuric acid catalyst, the reagent distributes between the continuous fuel-reagent and disperse sulfuric acid-reagent liquid phases. The reactive contact occurs at the interface. The mechanism of esterification is of interfacial reaction type. The rate limiting is being dependent on interface renewal. At the interface the polar head of the free fatty acids orients toward the polar phase, while the hydrocarbon chain stays in the apolar oil phase. As the FAME leaves the interface a next FFA can substitute the gap at the interface. High reagent:substrate rates and high solvent:reagent rates are beneficial because of contributing to promotion of diffusion and by such the renewal of the interface.
Interface renewal is similarly important in trans-esterification for efficient extraction of polar constituents into the reaction generated polar phase.
By the use of ion exchange resin the reaction is interfacial similar to heterogeneous catalytic chemistry.
COLLOID CHEMISTRY AS IMPORTANT CONTROL MECHANISM IN TECHNOLOGIES BIODIESEL PROCESSING
The process of main and byproducts separation has shown clearly features of colloid chemical principles basis. Beside of this evident colloid chemistry feature of interface renewal there were other findings in my the research related to colloid chemistry
• The more complex the colloid structure of the feedstock was the more difficult and more severe treatment conditions had to be employed. Processing of food grade oils proved to be a simple task, especially if the selected apolar solvent was exploited. With difficult feedstocks, such as distillers grain with dissolved solids and yellow grease the limiting factor was the complex dispersion of the feedstock with encapsulated oily compounds.
• Refining the byproduct G-phase made possible to demonstrate that the main limiting action is based on colloid chemical principles. According to the model proposed there is a multiple, solid particles stabilized emulsion structure (so called Pickering type emulsions) that encapsulates solid and oil components. This structure acted against complete conversion into biodiesel, leaving the oily components encapsulated. Release of the encapsulated compounds must have been done by taking into considerations colloid chemical limitations. Small and medium size companies can profit of these findings by processing G-phase of conventional technology employing units.
DEVELOPMENTS WITH RELEVANCE TO INDUSTRIAL REALIZATIONS:
BY THE USE OF APOLAR SOLVENT THE OVERALL SPECIFIC ENERGY DEMAND CAN BE REDUCED
I have been looking for a technique to reduce the overall specific energy demand of biodiesel processing.
The most important contribution to reduction of specific energy demand is associated with less energy consumed for intensive mixing and some for pumping. It has been proved that the specific energy demand of maintaining the disperse state for the promotion of contact of reaction mixture components surpasses the energy needed for pumping. I calculated that the additional amount of energy needed for solvent and reagent recycle is significantly lower (by 20-40%) than the specific energy consumption in cases of reference.
TECHNOLOGY DEVELOPED
These findings made possible to develop two variants of the apolar solvent assisted biodiesel processing.
A truly continuous operation realized with counter current reaction extraction and distillation columns as the main contact devices. The truly continuous operation makes possible to profit of heat exchangers for rational energy management. Footprint of the operational units and amount of inventory under operational conditions can be reduced accordingly. These features make the system more environmentally respectful, more safe than those mixer-settler based technologies in which the time on stream to product is more than 3 times longer than in the proposed system.
I have recommended a system for retrofit of conventional unites to more efficient, more ecological systems. This can be done switching from mixer-settler operation to loop reactor system by the use of suitable apolar solvent.
Future works are planned in the pilot plant of the truly continuous biodiesel processing and in industrial scale demonstration of retrofitting.
Future works are ongoing to explore other type of feedstocks that are high in essential fatty acids, such as algae and fish oil.
I. LITERATURE SURVEY, STATE OF THE ART
1.1. FUNDAMENTAL, WHAT IS BIODIESEL?
By general apprehension biodiesel is mostly referred as being a clean burning renewable energy based alternative automotive fuel.
By chemistry, it is a mixture of alkyl - methyl - esters of C14 -‐ C24 fatty acids. It has been referenced by chemical abstract under CAS registry No of 67784-80-9.
Biodiesel regularly constitutes an extension component to different grades of fossil gas oils in the pool to blend standard diesel fuel. Biodiesel is associated with a series of beneficial features if used in combustion engines. It contributes to curbing tailpipe and life cycle emissions, reducing carbon dioxide emissions and promoting generation of income to people active in rural society. Even if spilled does not directly harm the environment, being benign and easy to degrade under natural aerobic conditions.
Chemistry basis of production stretches beyond the border of applying simple trans-‐
esterification {∑r-‐1i} and esterification {r-‐2} synthesis to fatty acid methyl ester (FAME). Even though the common process of biodiesel synthesis and refining involves a series of mass transfer process steps and chemical reactions of components often separated in distinct liquid phases, little attention has been paid to colloid chemistry related special aspects, special questions of mass transfer and chemical engineering in production technologies of this renewable energy based automotive fuel substitute.
This thesis is intended to explore chemical engineering, mainly colloid chemistry principles to improve existing and to develop and recommend new biodiesel production technologies.
{r-‐11} {r-‐12} {r-‐13}
€
TG+3CH3OH methanolysis
⎯ ⎯ ⎯ ⎯ → hydrolysis/
glycerolysis
← ⎯ ⎯ ⎯ ⎯ 3FAME+G {Σr-‐1i} {r-‐2}
FIGURE 1.1 BASIC CHEMICAL REACTIONS INVOLVED IN SYNTHESIS OF BIODIESEL
TG: tri-acyl-glyceride; DG: di-acyl-glyceride; MG: mono-acyl-glyceride; G: glycerol; FFA: free fatty acid;
FAME: fatty acid-methyl ester
There is ample discussion on how to classify a biodiesel and its production technology and especially on what basis? What is clear, straight, not refined vegetable
€
TG+CH3OH methanolysis
" " " " → ← " hydrolysis" " " FAME+DG
€
DG+CH3OH methanolysis
" " " " → ← " hydrolysis" " " FAME+MG
€
MG+CH3OH methanolysis
→ ← hydrolysis FAME+G
€
FFA+CH3OH esterification
" " " " → ← " hydrolysis" " " FAME+H2O
oils (SVO) must be disclosed from the class of biodiesel fuels because of a number of possible harms it can cause.
There are publications with terms related to ranks in generations of biodiesel production units without any reference to define the basis of classification. It has not been clearly defined how to declare a production system first, second or more advanced generation? Biodiesel experts generally accept that first generation technologies convert refined vegetable oils into standard biodiesel. Fuels produced in such processing technologies are also referred as first generation fuels. Higher ranked -‐
second, third and subsequent – generations must respect criteria on ecologic basis. If secondary, refuse feedstocks are converted to biodiesel, the rank is usually of second, if similar resources are converted into very clean burning hydrocarbons by hydrotreatment the rank of 3rd level is usually accepted..
The severely hydrotreated biodiesel is also called hydrodiesel. This product can excellently be used as cetane improver component added to conventional fossil diesel fuels. I lean to clearly discern biodiesel from hydrodiesel. I would refer to biodiesel if it is mainly consists of FAME. Hydrotreatment has been the most accepted refinery practice in a petroleum refinery -‐ right as a workhorse -‐ to remove most hetero-‐atomic constituents from fuels and lubricants. Even this most advanced high temperature, high pressure catalytic hydrogenation route of vegetable oils has a long history. A.
Mailhe converted vegetable oils into hydrocarbons using metallic salts such as MgCl2, ZnCl2 in the early twenties of the 20th century [1].
1.2. HISTORY OF BIODIESEL
Production and use of straight vegetable oil based automotive fuels has been started in the 19th century. The very first patent for this kind of application was issued to Rudolf Diesel for the machine with compression ignition engine in 1893. The first public demonstration of the use of biodiesel was commissioned by the French government at the turn of that century. Diesel built a demonstration engine for the World Trade Fair and selected peanut oil for fuel. He stressed that this is only a selected commodity fuel among other possible and available plant derived combustibles. Even today there are partisans for the use of SVO. But taking into account difficulties experienced and the firm view of automotive manufacturers – and most importantly safety in manufacture, use and distribution – SVO cannot be accepted as a scientifically sound bio-‐fuel variety. It is to stress that any fuel must confirm strict regulations and any product that does not meet specifications risks the safety and life of drivers and participants in traffic. Fuels used in compression engines must meet specifications of EN 590 in vigor. This is why SVO is not part of my discussion1.
Trans-‐esterification reaction has been proven to be the right tool of chemistry to convert triglyceride content of straight vegetable oils and animal greases into clean burning fuels. In trans-‐esterification triglyceride reacts with alcohol in the presence of a catalyst (either strong acid or base) to produce a mixture of fatty acid alkyl esters and glycerol [2] (figure 1.1). The history of trans-‐esterification is older than the engine
1 I am not blindly opposed to the use of SVO. I would accept and recommend the use in off road vehicles, with a condition of starting and stopping the engine with advanced automotive fuel with adequate content of detergent and dispersant additives.
system of Rudolf Diesel. Dufy and Patrick studied and recommended the trans-‐
esterication reaction to produce glycerol at competitive cost level, in the mid of 19th century. The said reaction was first explored by du Pont and Colgate in industrial practice in the middle of the 20th century [3]. The definite aim of this early development, to produce glycerol, could sound ironic today. The relative abundance of glycerol output by the maturing biodiesel industry made that almost all synthetic glycerol production units have been temporarily closed in the World. The exception is being the production unit of Dow in Europe for the delicate pharmaceutical grade product. Biodiesel scientists around the Globe have been engaged to look for new, rational use of the plentifully available biodiesel byproduct glycerol.
Today glycerol constitutes a natural resource commodity based mostly on biodiesel production. Demand and supply irregularities have remarkably shocked the market.
These irregularities are in strong relationship to governmental supports to biodiesel industry and to prices of products that can be replaced by glycerol based products.
Volatile market price dropped dramatically along with the extension of the biodiesel industry. Temporarily stopped synthetic glycerol production route had positive effect on emissions (carbon footprint) since synthetic route consumes 18 times of own energy of glycerol. The price of glycerol is vulnerable, as dramatic was the drop of market price of biodiesel in the first half of this decade the same surprise was created by peculiar kick jump of price of crude glycerol from around 20 €/t to even above 200
€/t this year. Market circumstances predict that abundance of secondary glycerol resources will spur the business based on byproduct glycerol and will create additional demands. We have concluded that the price of glycerol is commensurable to price of corn for animal forage [4].
1.3. LEITMOTIVES OF GLOBAL BIODIESEL DEVELOPMENT EFFORTS
Environmentalists and politicians acknowledged the positive impact of this renew-‐
able energy alternative automotive fuel for curbing greenhouse gas emissions and mitigation consequences of emissions and for promoting economic activities.
Legislators around the World have translated support ideas into directives, re-‐
commendations and legal requirements that made to mandate inclusion of standard quality bio-‐fuels (bioethanol and biodiesel) into the pools of automotive fuels. The European Parliament, the Council and the Commission, decided to establish manda-‐
tory national targets consistent with a 20 % share of energy from renewable sources and a 10 % share of energy from renewable sources in transport in Community energy consumption by 2020 [5]. Sweden set more aspiring goals for making the car fleet independent of fossil fuels by 2030 [6]. This has not been a political slogan without concrete activities. In 2009, bio-‐energy represented 31.7% of the final energy use (without the contribution of hydro-‐power), surpassing the role of fossil fuels, that has been shrunken to 30.8%, according to Swedish Energy Agency statistics.
The EU directive, along with similar regulations in other developed economies issued ecological criteria for the term of “ecology footprint”. The first nation to issue a law with reference to ecologically acceptable production was Germany. Accordingly bioethanol is considered a renewable fuel constituents, biodiesel is accepted for whole fuel being constructed only by renewable building blocks.
Concawe studies [7] concluded that sunflower is more favorable than rape on the
basis of environmental impacts. The study also concluded to a nonexpected result that the use of glycerol has a relatively small impact. Stress is to be set on N2O emissions, since these play a major contribution to green house gas (GHG) balance. N2O emissions are responsible for large contribution and uncertainty too in estimating the real impacts. 1 mol N2O emission is equivalent to 296 CO2eq/km, hence any progress in reducing this emission in agriculture has multiple beneficial effect on positive impact of biodiesel. As a conclusion of the joint study biodiesel saves significant amount fossil energy and curbs definitely GHG. If compared to conventional diesel it emits 49 CO2eq/km versus 130 in CO2eq/km. In ongoing Tech09 research project we demon- strated that the use glycerol byproduct streams is beneficial in soil chemistry [8].
My technical motive in engaging to biodiesel research and development are related to the idea of connecting petroleum refinery technology unit operations to practice of biodiesel synthesis. My environmental conscious motives have been backed by a desire to explore externalities of this field. A direct externality of restituting dignity to rural people who had to give up working as before in conventional agriculture because of instituted limits in output of products. If these people get a chance to cultivate oil plants on set aside fields and earn a living than they will, most probably, not sitting in the waiting room of neurology because of becoming upset in waiting the postman for the unemployment compensation payment. This social – macro economic -‐ motive can overweight many technical excellence of biodiesel, indifferent of the technology of conversion into automotive fuel.
1.4. FEEDSTOCK VARIETIES FOR BIODIESEL SYNTHESIS
Pioneers of biodiesel technology in EU have been backed by strong agricultural support to cultivate set aside land and to respect the Blair House agreement to limit production of oil bearing plants in Europe and to provide active jobs in the field. This made that the dominant vegetable oil turned to be rapeseed. This was reflected in first biodiesel product standards, by setting the iodine number to a level that is specific to rapeseed oil. Sunflower and soy have higher iodine number, even though studies demonstrated that speculations on lower stability associated with more unsaturated links in the hydrocarbon chain have not lead to engine failure, even up to a iodine number of 160, that is significantly higher (≈30%) than the EU standard [9]. Climatic conditions are less favorable to rapeseed than to sunflower cultivation In Hungary. The accent is on producing soy in the US and South America. When I compiled my book titled Biodiesel Technology, in 2000, I found indications that almost 200 vegetable oil plants qualify for considering feedstock in biodiesel processing. Mittelbach [10] and more recently Sanford et al [11] and Razon [12] comprehensively evaluated a series of plant oils and animal fats for biodiesel feedstock suitability. Here are the samples of the latest of such: algae, babassu, beef tallow, borage, camelina, canola, castor, choice white grease, coconut, coffee, distiller's corn, cuphea viscosissima, evening primrose, fish, hemp, high and low iodine value hepar, jatropha, jojoba, karanja, Lesquerella fendleri, linseed, moringa oleifera, mustard, neem, palm, perilla seed, poultry fat, rice bran, soybean, stillingia, sun-‐flower, tung, used cooking oil and yellow grease. Although the literature sources are enthusiastic about inexpensive and abundant secondary feedstock kinds, such as algae and waste water sludge, the real industrial breakthrough is not expected to happen within a decade. Feasibility criteria, especially demands to
