WO2011023712A1

WO2011023712A1 - Process for the production of biodiesel by transesterification of triglycerides

Info

Publication number: WO2011023712A1
Application number: PCT/EP2010/062369
Authority: WO
Inventors: Alberto Brandi; Antonella Salvini; Giacomo Cipriani; Donatella Giomi; Giovanni Bartolozzi
Original assignee: Alberto Brandi; Antonella Salvini; Giacomo Cipriani; Donatella Giomi; Giovanni Bartolozzi
Priority date: 2009-08-25
Filing date: 2010-08-25
Publication date: 2011-03-03
Also published as: ITFI20090187A1; IT1395587B1; EP2470492A1

Abstract

The present invention provides a process for the conversion of triglycerides in biodiesel by using chlorotrimethylsilane (TMSCI) as efficient catalyst, working in homogeneous phase, and not contaminating the final products. The process allows the complete conversion of triglycerides to the corresponding alkyl esters. The biodiesel and glycerol obtained are cleanly separated in two distinct phases allowing an easy separation thereof. The biodiesel obtained is pure and the process can be applied evenly to triglycerides derived from exhaust vegetable oils or animal fats or mixture thereof.

Description

Process for the production of BioDiesel by transesterification of triglycerides

TECHNICAL FIELD

The present invention regards the transesterification reaction of triglycerides for the production of alkyl esters of fatty acids, to be used as biodiesel.

BACKGROUND ART

Chemically BioDiesel (BD) is a fuel consisting of a mixture of alkyl esters of long chain fatty acids.

The production of BD from vegetable oils is a well known process largely utilized in many production sites with different sizes. The interest for BD has grown for the possibility of utilizing the product in available combustion plant without any particular variation of the combustion system. Nevertheless, processes employed up to date reveal several limitations and bothersome problems. Although the production of fuels from vegetable oils is interesting because alternative to the production from mineral oil, its intensive industrial development is nowadays criticized, particularly in underdeveloped countries and in international organizations (FAO), because it utilizes as feed stock materials that belong to the foodstuff supply. Of particular interest, therefore, becomes the production of BD from exhaust vegetable oils. Apart eliminating the ethical problem of using for the production of fuels pure vegetable oils destined for food, the recovery and use of exhaust vegetable oils, that would need an appropriate disposal, would solve in the meantime a very crucial environmental problem. These oils, in fact, deriving from a diffuse family production are inappropriately disposed of and increase the environmental risk of water contamination. In this sense, their use as energy supply represents a double additional benefit.

BD is produced mainly by transesterification reactions of lipids, particularly triglycerides, vegetable oils and/or animal fats, with low molecular weight alcohols, like methanol, ethanol, or n-butanol. The most common process employes methanol to synthesize methyl esters; ethanol can be also employed to obtain a BD composed of ethyl esters. As a byproduct of the transesterification process glycerol is obtained. The transesterification reaction requires a catalyst to occur, and alkaline catalyst, like sodium or kalium methoxide or hydroxide, have been predominantly utilized. Notwithstanding the large industrial use of base catalyst, the catalyst system brings about several problems. In fact, the total free fatty acid content in vegetable oils must be below 0.5% by weight, because of the formation of soaps (Na or K salts of fatty acids) and their emulsions with water disturb the phase of separation of pure BD, and rise the waste water disposal issue. Also the byproduct glycerol requires a further purification and separation from water before its further transformation or employment. The base catalyst BD production process suffers from higher costs for the purification issue and the need of refined vegetable oils as starting materials.

Acid catalysts (sulfuric acid, organic sulfonic acids, hydrochloric acid, phosphoric acid, boron trifluoride) have been largely studied (a) Liu, K.S. J. Am. Oil Chem. Soc. 1994, 71, 1 179-1 187. b) Fukuda, H.; Kondo, A.; Noda, H. J. Biosci. and Bioeng. 2001 , 92, 405-416) in alternative to the basic ones, but their industrial promotion has been only limited, because the conversion rate of the oil is lower than the alkaline process. However they have the clear advantage that acid catalyst can be directly used with starting materials rich of free fatty acids. Homogeneous acid catalysts studied up-to-date bring about the separation and purification problems that can lead to an increase of production costs.

Heterogeneous acid catalysts have been developed to avoid the separation of the catalyst issue, to be used in continuous flow reactors. However their efficiency is lower than the homogeneous one requiring higher reaction temperatures (200-250 °C) and pressures (50 atm) (a) E. Lotero, Y. Liu, D. E. Lopez, K. Suwannakarn, D. A. Bruce, J. G. Goodwin Ind. Eng. Chem. Res. 2005, 44, 5353-5363; b) Zaccheria F. Chim. Ind. 2009, 126-131 ).

Aim of the present invention is to provide a new process of transesterification of triglycerides which is able to convert triglycerides in BD employing an efficient catalyst that can operate in homogeneous phase, but at the same time can be easily separated from the products. Aim of the invention is also to provide a process that is efficient also with raw starting materials, like exhaust vegetable oils and animal fats, and, at the same time, is operationally uncomplicated and allows an easy separation of the BD from other byproducts of the transesterification.

DEFINITIONS AND ABBREVIATIONS BD = biodiesel

TMSCI = trimethylchlorosilane o trimethylsilylchloride

TMS₂O = hexamethyldisiloxane

FAME = fatty acid methyl esters SUMMARY OF THE INVENTION

The present invention provides a new process for the production of lower alkyl esters of fatty acids, i.e. Biodiesel (BD), by transesterification of triglycerides: said process is carried out in homogeneous phase in the presence of a lower alkyl alcohol, containing up to eight carbon atoms, and is catalyzed by Trimethylchlorosilane (TMSCI). The above said transesterification reaction can be carried out either starting from natural vegetable oils or with exhaust vegetable oils (possible cause of environmental pollution), and animal fats.

The process surprisingly secures the complete conversion of triglycerides in the corresponding fatty acid esters (preferably methyl and ethyl esters), also in the presence of free fatty acids that are eventually esterified by methanol, without producing soaps during the transformation.

The process advantageously produces, at completion of the reaction, two phases (ester phase and glyceric phase) which surprisingly are neatly and instantaneously separated and consequently easily separable, making readily accomplishable this operation, perfectly suited for a reproducibility at industrial scale. It was unexpected that, without any quenching step (e.g. adding water or other solvents), two so highly distinct phases could form, and so quickly, at the end of the reaction directly from the crude reaction mixture. On the other hand, common industrial biodiesel processes are affected by separation problems either for the formation of soaps (alkaline processes) or for the need of water to eliminate side products (acidic processes). TMSCI, during the process, evolves to a pure inert product, TMS₂O, that is conveniently separated from BD and can be chemically transformed again in TMSCI which can be used again as catalyst in the present process , or could be employed in other productive processes.

Several other advantages of the present invention will be delineated hereinafter.

DETAILED DESCRIPTION OF THE INVENTION

Here below is presented the process of the present invention describing the most preferred procedure in terms of reaction conditions and preferred alcohol reagent:

+ R¹CO₂Me + R²CO₂Me + R³CO₂Me

In which R¹, R² ed R³ are aliphatic carbon chains, containing between 5 and 28 carbon atoms, preferably between 16 and 22 carbon atoms, linear or branched saturated or partially unsaturated whose exact structure depends on the vegetable or animal species of the triglyceride starting material.

Triglyceride starting material can originate from a vegetable or animal source.

Among triglycerides of vegetable origin can be employed foodstuffs oils (e.g. sunflower, olive, soy, palm oils, and so on), non foodstuffs oils (e.g. rapeseed oil, safflower, jatropha, seaweeds oils, and so on).

Among fatty acids of animal origin can be employed: e.g. butter, fat, and so on. The process is not affected by the water content of the starting triglyceride, the only drawback being the hydrolysis of TMSCI that, in this case, should be added in higher amount to the reaction mixture.

Therefore, in the process of the present invention as starting triglycerides can be employed those deriving from industrial or home alimentary uses (like frying oils and conservation oils), or discarded animal fats, materials that otherwise should be disposed of as pollutant.

Preferably, the process of the invention requires the use of at least 1 mole equivalent, more preferably 1.3-2.0 mole equivalents, of alcohols for 1 mole of starting triglyceride. Preferably the employed amount of TMSCI is not lower than 40 mol% compared to the alcohol or, in weight, not lower than 20% respect to the weight of the starting triglyceride preferably higher than 25%. Most preferably 1.4-1.6 equivalents of alcohol compared to the starting triglycerides moles are employed and 50-60 mol% of TMSCI compared to alcohol (otherwise expressed as 27-35% by weight respect to the weight of the starting triglyceride).

It is known that TMSCI can be commonly used as a substitute for HCI, but this is not the case in the process of the present invention. A comparative test (see example 2) has been performed demonstrating that TMSCI allows a catalytic activity superior to simple HCI. The comparative transesterification reaction was carried out using a methanolic solution of HCI (3N), at the same temperature (60 °C) and time (8 h) of the present process, and resulted to give a much lower conversion of the oil (75%).

In the case of the use of exhaust triglycerides, to allow the completion of the reaction, it might be necessary to increase the above reagents' amounts; the skilled person will be able to judge case by case how to increase the reagents' amounts.

Preferably, said alcohol containing up to eight carbon atoms is chosen among MeOH, EtOH and n-BuOH.

Preferably, the reaction is carried out at 50-120 °C for 6-16 hours under vigorous stirring. In the case of vegetable oils the reaction is more preferably carried out at 50-70 °C. In the case of pure animal fat the reaction is more preferably carried out at 90-120 °C, with an higher excess (33% w/w) of reagents MeOH and TMSCI. More preferably, the animal fat is dissolved in different proportions with the vegetable oil (preferably 50% of fat for 50% of oil) by heating, in an open vessel at 120 °C for 2 hours; this dissolving pre-treatment is also useful to remove the water contained in fat. The resulting mixture is filtered to remove proteic materials and residues, then cooled. The resulting mixture of animal and vegetable fats is then subjected to the addition of the reagents, and reacted in the above described conditions for the natural vegetable oil. In this case the reaction temperature can be 50-70 °C. At the end of the reaction, once the stirring is stopped, preferably at room temperature, two neatly distinct phases quickly materialize which can be easily separated by means of techniques well known to the skilled person. The two separated phases, then, afford:

- a top phase containing BD and volatile byproducts;

- a bottom phase, or glyceric phase, containing a mixture of glycerol and 1 - chloro-2,3-propandiol.

BD can be obtained pure, devoid of volatile byproducts, simply by distilling them at low pressure, approximately 2 mmHg. The said distillation is preferably carried out at 55-75 °C, most preferably 65 °C, at a pressure about 2 mmHg.

In the case of the use of MeOH as alcohol, volatile byproducts consist of a mixture of hexamethyldisiloxane (TMS₂O), MeOH, HCI, traces of methyltrimethylsilylether (TMSOMe) and dimethylether. All the said volatile byproducts can be separated by fractional distillation, that is particularly efficient to recover TMS₂O, a product with a commercial value that can also be chemically converted into TMSCI according to the literature (B. -h. Zhang, l.-x. Shi Hebei Gongye Keji 2007, 24, 63-65; X. Cheng, Q. Zhang Huaxue Shijie 1988, 29, 65-67). The mixture of MeOH, TMSOMe, with similar boiling points, and HCI can be recycled for a further synthesis.

Preferably, the volatile compounds, including HCI, can be reacted with zinc chloride, according to the literature procedure (B. -h. Zhang, l.-x. Shi Hebei Gongye Keji 2007, 24, 63-65) to convert TMS₂O into TMSCI. The resulting mixture can be recycled for a further BD synthesis.

The glyceric phase consists of a mixture of glycerol and 1 -chloro-2,3-propandiol (α-monochlorohydrin) in various ratios according to the reaction temperatures employed, and is strongly acidic for the presence of HCI.

The lower gliceric phase after separation can be neutralised by treatment with a base, preferably inorganic (carbonates, preferably calcium carbonate). Before the basic treatment the glyceric mixture can be diluted with an organic solvent chosen among MeOH and EtOH, and usually, for convenience, with the alcohol used in the reaction for production of BD.

After removal of the base, e.g. by filtration, the glycerol and α-monochlorohydrin can be separated by fractional distillation as reported in the literature {Org. Synth., Coll. Vol. 1, 294 (1941); Vol. 2, 33 (1922)).

The process of the present invention for the production of BD shows the following features and advantages:

- fulfills the principle of "Green Chemistry" behaving as a low environmental impact process;

- provides the complete conversion of vegetable oils with a perfect separation in two distinct phases easily separable (phase 1 : Biodiesel, phase 2: glycerol and its derivative), allowing a quantitative recovery of products without additional costs;

- the BioDiesel is obtained highly pure, which allows to eliminate purification costs;

- The process occurs efficiently at not elevated temperatures (about 60 °C for oils, about 100-120 °C for animal fats);

- The process can be extended with the same efficiency to alcohols different from MeOH, in particular EtOH and n-BuOH.

- TMSCI is a low cost commercially available reagent with low toxicity and environmental impact;

- TMSCI shows a peculiar catalytic activity in the transesterification process not comparable to that of simple HCI;

- TMS₂O, conversion product of TMSCI, has a commercial value, similar to that of the starting material, but can also be converted back to TMSCI by recycling HCI produced in the process.

- Poor amounts of byproducts are formed in the process, and they can be recycled or have a low environmental impact.

- during the process the formed glycerol partially transforms in (α- monochlorohydrin. The two products can be separated by fractional distillation to yield pure products. - The process behaves as a pure conversion of oil (or fat) in BD and glycerol (and derivative) without any waste. In particular, it does not produce any fluid to be disposed of, in contrast to base catalyzed processes commonly used, which produce large volumes of waste water to be treated before immission into the environment.

- The process can be applied, with the same efficiency, to exhaust vegetable oils and waste animal fats, without any need of chemical pretreatment or washings.

The present invention can be better understood in view of the following experimental examples.

EXPERIMENTAL PART

Materials

The oil employed in this work is sunflower oil produced by "Oleificio Salvadori" - Badia a Settimo (Fl) characterized, via ¹H-NMR, to consist of linoleate 53.0%, oleate 34.0%, saturated fatty acids 13.0%. Methanol (VWR, 99.8%), chlorotrimethylsilane (Aldrich, 98%), calcium carbonate (Carlo Erba, 99.5%), deuterated chloroform (Aldrich, 99.8%), deuterated methanol (d⁴) (Merck, 99.8%), have been utilized as obtained by the dealer without further purification.

Instrumentation and analytical methods

¹H-NMR and ¹³C-NMR spectra have been recorded with a Varian VXR 200 spectrometer, operating at the 199.985 MHz frequence. All spectra are reported in ppm and referred to TMS as internal standard. Spectra elaboration has been carried out by means of iNMR 3.0.1 software.

EXAMPLE 1 - Synthesis from natural refined sunflower oil

Several syntheses have been carried out varying reaction times, reaction temperature, and TMSCI amount utilized. The syntheses have been carried out in screw-cap Sovirel^® tubes.

In a 25 ml_ screw-cap Sovirel^® tube, sunflower oil (10 g, 1 1.4 mmol [MWcalc = 878g/mol]) was added to methanol (1.64 g, 2.08 ml_, 1.5 equiv, 51.3 mmol) and chlorotrimethylsilane (TMSCI) (see Table 1 ) under nitrogen atmosphere. The resulting emulsion was allowed to react under continous stirring at 60 °C for 8 hours, then allowed to cool at room temperature. Two phases were immediately separated after ceasing the stirring. The upper phase, containing the methyl esters, was separated and heated under reduced pressure (2 mmHg) at 65 °C for 3 hours to obtain a pale yellow liquid.

The lower phase was dissolved in methanol (5 ml_) and neutralized with calcium carbonate (1.0 g). After filtration, the solution was concentrated to dryness under reduced pressure to obtain a yellow oil containing glycerol and α-monochlorydrin. Oil conversions into FAME, and composition of glyceric phase, obtained varying the quantity of TMSCI employed, are reported in Table 1.

Tabella 1. Conversion of oil and composition of glyceric phase varying the amount of TMSCI utilized (8h, 60⁰C)^*

Conversions measured via H-NMR, by comparison of the integral of the signal of methylenes -CH₂-COO- with that of CH₃O- methyl esters produced in the transesterification process (Gelbard, G.; Bres, O.; Vargas, R. M.; Vielfaure, F.; Schuchardt, U. F. J. Am. Oil Chem. Soc. 1995, 72, 1239-1341 ). In Table 2 conversions of oil varying the reaction temperature of the reaction are reported for the best conditions (entry 4, Table 1 ).

Table 2. Conversions of oil varying the reaction temperature

Conversions measured as in Table 1.

The synthesis that afforded the best results requires, then, the use of 1.5 equiv. of MeOH with respect to the vegetable oil (10 g), TMSCI (2.78 g, 25.6 mmol), 50 mol% with respect to MeOH and 27.8% by weight with respect to oil, and a temperature 60 °C for a reaction time 8 h. At the end of the reaction, after cooling at room temperature the two well distinct clear phases produced can be separated by decantation. Otherwise, the mixture is transferred to a separatory funnel and the two phases are separated. The upper phase is heated at 65 °C under vacuum (2 mmHg) to remove all volatile products that can be condensed in a cooled trap. The residue is a pale yellow liquid (10.1 g) neutral to pH analysis. Analysis by NMR spectroscopy gave a 99% conversion of the oil in FAME. ¹H-NMR and GC- MS analyses determine the following composition: methyl linoleate: 53.5%; methyl oleate: 35.2 %; methyl palmitate + methyl stearate: 1 1.3%. Other byproducts or impurities are not observed.

Volatile byproducts collected in the cool trap consist of a mixture of hexamethyldisiloxane (TMS₂O), MeOH, and traces of methyltrimethylsilylether (TMSOMe) and dimethylether.

The lower phase, or glyceric phase, is highly acidic for hydrochloric acid (HCI) adsorbed, and consists of a mixture of glycerol and 1 -chloro-2,3-propanediol (α- monochlorhydrin) in different proportions (see Table 1 ).

The lower phase can be neutralized by dissolving it in methanol (5 ml_) and treating it with calcium carbonate (1.0 g). After filtration, the solution was concentrated to dryness under reduced pressure to obtain a viscous yellow oil (0.63 g ) containing 52% glycerol and 48% α-monochlorydrin. EXAMPLE 2 (Comparative example) - Synthesis from natural refined sunflower oil and methanolic HCI

In a 25 ml_ screw-cap Sovirel^® tube, sunflower oil (3.5 g) was added to methanolic HCI (3N) (3 ml_, 9 mmol of HCI) under nitrogen atmosphere. The mixture was allowed to react under continous stirring at 60 °C for 8 hours. After cooling at room temperature, the mixture separated in two phases. The upper phase, containing the methyl esters, was heated under reduced pressure at 65 °C for 3 hours to remove all volatiles giving an oil (3.5 g). Analysis by NMR spectroscopy gave a 75% conversion of the oil in FAME.

EXAMPLE 3 - Synthesis from exhaust oil

The best conditions of example 1 have been applied to exhaust oil obtained by heating the same sunflower oil precedently used at 120 °C for 72 h under stirring in the open air.

In a 25 ml_ screw-cap Sovirel^® tube, methanol (2.08 ml_, 1.64 g, 51.25 mmol) and chlorotrimethylsilane (TMSCI) (2.78 g, 25.62 mmol) were added to exhaust sunflower oil under nitrogen atmosphere. The mixture was allowed to react under continous stirring at 60 °C for 8 hours. The oil by addition of reagents becomes light brown, and the colour darkens during the heating. After cooling at room temperature, the mixture was separated in two phases. The upper phase was heated under reduced pressure at 65 °C for 3 hours to obtain a dark brown liquid containing the FAME (10.19 g). Analysis by NMR spectroscopy gave a 93% conversion of the oil in FAME. The lower phase was dissolved in methanol (5 ml_) and pH-neutralized with calcium carbonate (1.0 g). After filtration, the solution was concentrated under reduced pressure to obtain a pink oil (0.69 g) containing glycerol (58.5%) and α-monochlorydrin (41.5%).

EXAMPLE 4 - Synthesis with EtOH

The best conditions of example 1 have been applied utilizing natural refined sunflower oil (10 g), EtOH (absolute) as alcohol (3 ml, 2.36 g) and TMSCI (3.27 ml_, 2,78 g, 25.6 mmol), 50 mol% with respect to EtOH and 27.8% by weight with respect to starting oil. The reaction was carried out at 60 °C for 8h, and after the same work up of example 1 , biodiesel (97% conversion) is obtained as a bright yellow oil (10.2 g).

The same reaction carried out for 14h gave an oil conversion >99%. The same reaction carried out for 8h using common EtOH (95%) as reagent gave a conversion of 93%.

EXAMPLE 5 - Synthesis with n-BuOH

The best conditions of example 1 have been applied utilizing natural refined sunflower oil (10 g), n-BuOH as alcohol (4.7 ml, 3.8 g) and TMSCI (3.27 ml_, 2,78 g, 25.6 mmol), 50 mol% with respect to nBuOH and 27.8% by weight with respect to starting oil. The reaction was carried out at 60 °C for 9h, and after the same work up of example 1 , biodiesel (97% conversion) is obtained as a bright yellow oil (1 1 -3 g). EXAMPLE 6 - Synthesis from pork lard

An analogous synthesis of example 1 has been carried out utilizing pork lard (5 g), MeOH (1.5 ml, 1.18 g, 37.03 mmol) and TMSCI (2.2 ml_, 1.87 g, 17.2 mmol), 30% excess with respect to the quantities used for refined oil, and a temperature of 100°C for a reaction time of 16 h. At the end of the reaction two distinct phases develop: the upper phase containing methyl esters of fatty acids (bio-diesel), besides volatile reaction byproducts, the lower phase, dark brown, containing glycerol and derivatives. Separation of the phases and work up is carried out as in example 1. A yellow oil containing the FAME (4.71 g, 94% yield) is obtained. Analysis by NMR spectroscopy gave a 98% conversion of the fat in FAME.

EXAMPLE 7- Synthesis from a 50% mixture of pure animal fat and sunflower oil

The pure animal fat is dissolved in the vegetable oil (50% of fat and 50% of oil by weight) by heating under stirring at 120 °C for 2 hours in an open vessel. A mass reduction of about 10% is observed. The oily mixture (10 g), placed in a 25 ml_ screw-cap Sovirel^® tube, was added of methanol (2.08 ml_, 1.64 g, 51.25 mmol) and chlorotrimethylsilane (TMSCI) (2.78 g, 25.62 mmol). The mixture was allowed to react under continous stirring at 60 °C for 8 hours. After cooling at room temperature, the mixture was separated in two phases. The upper phase was heated under reduced pressure at 65 °C for 3 hours to obtain a pale yellow oil containing the FAME (10 g). Analysis by NMR spectroscopy gave a 94% conversion of the oil in FAME.

Claims

1. Process for the production of lower alkyl esters of fatty acids, i.e. biodiesel, by means of transesterification of triglycerides, said process is carried out in homogenous phase in presence of a lower alkyl alcohol containing up to eight carbon atoms, and is catalysed by TMSCI.

2. Process according to claim 1 wherein at least 1 equivalent of alcohol is used, based on the moles of the starting triglycerides, and a quantity of TMSCI not lower than 20% w/w based on the starting triglycerides.

3. Process according to claim 2 wherein 1.3-2.0 equivalents of alcohol are used and TMSCI is used in quantity higher than 25% w/w based on the starting triglycerides.

4. Process according to any of claims 1 -3 wherein said lower alkyl alcohol is selected in the group consisting of MeOH, EtOH and n-BuOH.

5. Process according to any of claims 1 -4 wherein starting triglycerides are from vegetal or animal source or mixture thereof.

6. Process according to claim 5 wherein starting triglycerides are virgin or exhausted vegetal oils.

7. Process according to any of claims 1 -5 wherein the reaction is carried out at a 50-120 °C for 6-16 hours under vigorous stirring.

8. Process according to any of claims 1 -6 wherein at reaction completion the mixture is allowed to decant to obtain two clearly distinct phases which can be easily separated obtaining:

- an upper phase containing biodiesel and volatile by-products;

- a lower phase comprising a mixture of glycerol and 1 -chloro-2,3- propanediol (α-monochlorohydrin).

9. Process according to claim 7 wherein the upper phase is then distilled at reduced pressure for removing volatile by-products to obtain pure biodiesel.

10. Process according to claim 8 wherein said volatile by-products further are undergone to fractional distillation to obtain TMS₂O and a mixture of alcohol and alkyltrimethylsilylether.