WO2006081644A2

WO2006081644A2 - Catalytic process for the esterification of fatty acids

Info

Publication number: WO2006081644A2
Application number: PCT/BR2006/000013
Authority: WO
Inventors: Octavio Augusto Ceva Antunes
Original assignee: Universidade Federal Do Rio De Janeiro-Ufrj; Aranda, Donato, Alexandre, Gomes
Priority date: 2005-02-02
Filing date: 2006-02-02
Publication date: 2006-08-10
Also published as: BRPI0500333A; WO2006081644A3

Abstract

The present invention refers to a process of esterification of fatty acids, which can be obtained from vegetable oils or animal fats. Such a process that produces esters with high grade of purity that can be used in the production of biodiesel with high added value.

Description

CATALYTIC PROCESS FOR THE ESTERIFICATION OF FATTY ACIDS Field of the Invention

The present invention is related to the esterification process of fatty acids that were previously extracted from oils or fats, that is, generally compounded and containing more than 50% of carboxylic acids, preferentially from 12 to 20 carbon atoms derived from the process of refinement of vegetable oils and animal fats . In this invention, these fatty acids are esterified with alcohols of 1 to 4 carbon atoms by the use of homogeneous or heterogeneous acid catalysers . In this process, after the reaction and recovery of the alcohols employed excessively, the esters produced are vacuum distilled thus reaching a high level of purity. Background of the Invention

In order for the oils and fats to be used in human feeding, several properties must be achieved, thus reaching a specified product . One of the mandatory tests for this condition is the acidity rate . Oils and fats, even if they are recently extracted, present acidity rates above 0.5% , which is not advisable for human consumption . These fatty acids are removed by physical processes such as vacuum distillation or distillation by means of carrier steam or chemical processes, such as the neutralization by alkaline solutions . These physical processes generate "acid sediments", that is, mixtures of fatty acids of different molecular weight, while there may even be low concentration of glycerol , traces of monoglycerides, diglycerides, triglycerides and unsaponifiable matter. On the other hand, the chemical processes generate sediments, totally or partially neutralized with bases (also called "soapstock" ) . The addition of acids with subsequent stages of washing and filtration leads to the production of a mixture of fatty acids quite similar to those generated by the physical processes .

These acidulated sediments or "soapstocks" serve as raw material in the so-called chemical oil in the production of tensoactives, surfactants or even combustible esters and additives known as biodiesel .

Biodiesel, comprised by esters in fatty acids, is an alternative combustible obtained from renewable biological sources, such as vegetable oils and animal fats . With regard to the diesel derived from petroleum (petrol- diesel) , biodiesel is an environmentally clean combustible because it reduces the emissions of atmospheric pollutants and particulate matter, in addition to being biodegradable and non-toxic . Because it presents physical chemical properties similar to the petrol-diesel, biodiesel can be used directly in the engine with no major mechanical alterations or maintenance expenses .

Biodiesel can be produced from a number of oleaginous plants, such as soy, sunflower, canola, cole, castor oil, peanuts, dendS oil and cotton . There are four classic ways to obtain biodiesel from triglycerides (F. Ma and M.A. Hanna, Bioresource Technology 70 ( 1999 ) 1-15 ) : direct use of vegetable oils, microemulsions, thermal cracking (pirolysis ) and transesterification . The most used process for the obtention of biodiesel is the transesterification of the triglycerides with one alcohol, forming esters that constitute the fuel, and glycerol :

CH₂ -OOC-Ki R₁ - COO- R* CH₂ - OH

! I I

CH -OOC-R2 + 3 ROH 4=> R₂- COO- R" I

+ CH - OH

I I

! I

CH₂ -OOC-R₃ R₃- COO- R' CH₂ - OH

^■triglycerides alcohol esters glycerol

Scheme 1 - Reaction of Transesterification

In US patent 4 , 695, 411, Stern et al . there is a process in three stages, which allows using oils or fats with up to 50% of acidity and hydrated alcohols without compromising the output of esters . The first stage consists of a transesterification of the triglyceride with ethanol, containing between 4 and 50% of water in weight, and an acid catalyser, which can be soluble or insoluble, preferably sulphonic acid. The reaction is conducted between 80 and 130⁰C and allows conversions above 75% in ethylic esters . In the second stage, after the removal of the aqueous stage containing glycerol, the acidity in the ester phase is reduced up to 2% by esterification in the presence of a dissecting agent for alcohol, such as a molecular sieve . The last stage is the transesterification of this ester phase with basic catalysers (NaOH, KOH, comprised of lithium or ion exchange resins, at a temperature between 20 and 100⁰C. The ester thus obtained contains only traces of alkaline salts , glycerol and alcohol, with purity above 97% .

Kawahara and Ono, in US patent 4 , 164 , 506, have also highlighted the importance of a pre-esterification stage for the removal of residues of free fatty acids and impurities, such as phospholipids and polypeptides, of the oils and fats . In the proposed process, the free fatty acids are esterified with a type of alcohol , preferentially methanol, added in amounts above its solubility in oil , in the presence of an acid catalyser ( H₂SO₄ or sulphonic for toluene acid) , with a temperature between 60 and 120⁰C . The impurities are dissolved in the alcoholic layer and thus can be easily removed from the oil or fat . The oil so refined is then submitted to a conventional transesterification, with basic catalysis . The pre- esterification reduces the amount of the basic catalyser to be used and limits the saponification, increasing the yield of esters . According to Basυ et al . (US patent 5, 525, 126) , the pre-esterification stage can be eliminated, even for loads with high content of free fatty acids, using as catalyser a mixture of barium acetate and calcium acetate, which does not cause the formation of soaps . In this case, the transesterification must be conducted preferentially with anhydride methanol, at a temperature between 200 and 250⁰C for around 3 h, followed by cooling until up to around 63⁰C. The mixture of esters obtained presented acidity content below 0.8% in weight, even with loads with 50% of free fatty acids . The pre-esterification of the free fatty acids with homogeneous acid catalysis presents the disadvantage of the difficulty in removing the residue of catalyser from the pre-esterified material . The removal of the catalyser is generally made through the washing of the mixture with methanol, which is separated from the oil phase by extraction with immiscible solvent with the oil, normally glycerin. That way, part of the esterified fatty acids is lost, reducing the yield of the process . So as to bypass this problem, one may use biocatalysers (enzymes ) or solid acid catalysers . Foglia et al . (QS patent US 5, 713, 965 ) proposed the use of lipases for the esterification of the free fatty acids with regular or secondary alcohols . In this process, it becomes necessary the addition of an organic solvent, such as hexane, so as to promote an effect of interface in the mixture between the enzyme and the substrate, in addition to improving the viscosity conditions . The reaction is processed at low temperatures (between 30 and 6O⁰C) , with high yield of esters, but it becomes necessary to separate and recover the solvent . Jeromin et al . (US patent 4 , 698 , 186) proposed the use of cation exchange resins as catalysers of esterification . These resins contain sulphonic acid or carboxylic acid groups connected to a polymeric matrix, usually polystyrene . The reaction is also processed at low temperatures (55 to 65°C) , with a methanol molar ratio : fatty acids between 10 : 1 and 50 : 1 and the catalyser are easily separated from the reaction products . HOOC-R + R' OH <=> R-COO-R' + H₂O Fatty acid alcohol ester water

Scheme 2 - Reaction of Esterification

Heterogeneous acid catalysers were used by Bradin (US patent 5, 578 , 090 ) for the esterification of free fatty acids with alcohols or olefins . When the esterification is done with alcohols, water is formed as subproduct , which can dilute or destroy the acid catalyser. Making use of olefins, there is no water formation, but there must be a strict temperature control (below 70°C) in order to avoid excessive polymerization of the olefin . As catalysers, Lewis acids were used, among them, aluminum chloride and iron chloride, being the latter preferable for esterification with olefins because it minimizes the parallel reactions of dimerization and polymerization .

The effort in transforming free fatty acids is justified because their presence is usually associated with fatty raw materials of low added value, thus allowing the generation of esters of fatty acids at a cost which is competitive with petroleum diesel and other raw materials of the petrochemical industry. In addition, the use of heterogeneous catalysers minimizes the separation and purification costs, bringing an even higher attractiveness to this process .

However, as opposed to the procedures of the state of the technique, in this process, alcohols are used, specifically methanol or ethanol . Methanol is the most used one due to its low cost and high polarity. Normally, alcohol is used excessively so as to dislodge the balance to a maximum yield of ester . The reaction can be catalyzed by bases (NaOH, KOH, carbonates or alcohol oxides) , acids

(HCl, H₂SO₄ and sulphonic acids ) , or enzymes (lipases ) . The basic homogeneous catalysis is the mostly employed commercially.

After transesterification, the products are a mixture of esters, glycerol, alcohol, catalyser and tri~, di- and monoglycerides . The excess alcohol is recovered by distillation and glycerol is separated by decantation . The ester is purified by washing . The ester obtained results in a significant reduction of viscosity, fitting into the specification of the diesel oil and improving the atomatization of the fuel .

In the presence of water or free fatty acids in triglyceride, the transesterification must be performed by acid catalysis, which normally results in a reduction of the yield of the esters, which are dragged to the aqueous phase by the salts formed in the neutralization of the fatty acids . Summary of the Invention

An object of the present invention is a process for the production in high purity of ester of fatty acids, the use of catalysers, especially acids (homogeneous or heterogeneous ) and the vacuum distillation of the products obtained.

An additional object of the present invention refers to the catalytic process, presenting the reaction ranges of optimal conditions regarding temperature, pressure, spatial time and concentration of the reagents, for the efficient transformation of fatty acids, especially the ones present in the sediment of the palm, in esters, particularly the methylic or ethylic esters .

It is an additional object of the present invention a process of biodiesel production from the esters obtained with the process described herein . Description of the Drawings

Figures 1 through 4 present the conversion graphs ( % ) versus reaction time (min) for the reaction of esterification of different fatty acids .

Figure 5 presents, as an example, a chromatogram of the methylic esters of fatty acids of the palm obtained in esterification with heterogeneous catalysis (Table 1 ) .

Chromatographic Method : - Column : Carbowax

- Length : 25 m

- Internal Diameter: 0.32 mm

- Oven Temperature : 200⁰C ( isothermal )

- Temperature FID: 250⁰C - Temperature injector : 250⁰C

- Flow of the carrier gas (He) : 1.9 mL/min

- Split : 1 : 20

Detailed Description of the Invention

The objectives of the present invention include a process for the production, in high purity, of fatty acids esters, the use of acid catalysers (homogeneous or heterogeneous ) and the vacuum distillation of the products .

The examples of the achievement of the invention must not be faced so as to limit the invention, but under an illustrative point of view. Example 1

In the present invention, acid catalysers are used for the esterification of mixtures of fatty acids, defined as carboxylic acids with chains containing between 12 and 20 carbon atoms, with or without double bonds among carbons . These fatty acids may be esterified with alcohols with 1 to 4 carbon atoms . The present invention shows that the addition of alcohol in stoichiometrical excess is essential . In the present stage of international horαologation of the biodiesel, methanol and ethanol are the major alcohols employed. However, other products may be used both for the formation of biodiesel and for the formation of additives for the increase in lubricity, rate of ketene or even as tensoactives or surfactants . The esters thus formed may be also employed as solvents or intermediaries of tensoactives or detergents . In order to obtain high conversions and high selectivities for the esters, one must use molar ratios of alcohol/fatty acid between 1.5 and 15, being preferentially employed ratios between 2 and 5.

In face of these reaction environment , one needs a catalyser to promote the reaction of esterification of the fatty acids at the lowest possible temperatures , so as the reaction can be feasible economically and there is no thermal decomposition of the reagents . The process involves temperatures in the range of 60 to 200° C, being preferentially employed at the range of 120 to 170⁰C.

The high pressure favors the reaction; however, it is not indispensable . In the case of more volatile alcohols, such as methanol and ethanol, the range of reaction temperature described above makes the pressure of the process compulsorily well above the atmospheric pressure .

The reactions involve components in the liquid phase and active sites located inside the particles of solid catalysers, being, therefore, subject to limitation by mass transference . One must work with a high enough stirring so as to minimize this problem. Stirring speeds between 400 and 1500 rpm are adequate for this purpose .

Any catalysers having thermal stability and acidity of Brδnsted and/or Lewis under the reaction conditions may be employed. Preferentially, the following catalysers are employed:

Sulfated zircon ( sulfur content of 3% to 6% ) , with superficial area between 30 and 200 m²/g, pre-calcinated between 300 and 800 ⁰C;

Zircon doped with tungsten (tungsten content between 5% to 15% ) , with superficial area between 70 and 200 mVg, pre-calcinated between 300 and 800⁰C;

Zeolites having hydrogen as compensation cation, with a molar ratio silica/aluminum between 4 and 160 and superficial area between 20 and 800 m²/g;

Polynaphthalensulphonic acid, defined as product of calcinations in the range of 200 to 350⁰C, with atmosphere containing oxygen at the concentration of 0.01 to 1% and a mixture of naphthalene/concentrated sulphuric acid with a massive ratio of 0.5 to 10, respectively . The time of calcination varies from 1 to 8 hours .

Aluminum Chloride, super anhydride or chemically supported; concentrated Sulphuric Acid; Chloridric Acid, concentrated; Phosphoric Acid, concentrated; Methanosulphonic Acid, concentrated;

The esterification process of fatty acids can be operated in batches, in continuous reactor of the perfect mixture type, as well as in fixed bed reactors . In the case of the continuous system, the spatial time in relation with the fatty acid is of 10 to 90 min, being preferentially from 15 to 60 min . Both in the batch process and in the continuous process, new reaction steps may be necessary aiming at an overall higher yield. Ideally, one must remove the water produced in the first stage of the esterification, so as to favor the displacement of the chemical balance in the direct sense .

In the case of the use of heterogeneous catalysers, the catalysers are kept isolated through a fixed bed or removed after the reaction by simple filtration . In the case of the use of homogeneous catalysers, it may be necessary the neutralization of the environment after the reaction . This neutralization generates a salt that may be removed through washing .

Subsequently, one must operate the stage of recovery of the excessive alcohol, which can be done in a flash vase, or even be the reactor itself . This alcohol is evaporated together with the water, while there must be a column of distillation for the rectification of the alcohol allowing for its re-use in the process . In the case of a batch process, it is interesting that one uses at least two reactors operating intermittently. While the reaction takes place in one reaction, the other one is used as a flash vase for the elimination of the water formed and the recovery of the excessive alcohol . This way, only one battery of heat exchanger will be required for the two reactions .

After removal of the lights (alcohol + water) through the top, the fraction of esters and of the non-reacted material must be submitted to a lung vase that will be submitted to vacuum distillation . This type of distillation generates a mixture of esters of high grade of purity . Better results are obtained with absolute pressure in the lung vase from 5 to 50 Torr, preferably from 10 to 30 Torr . After distillation of traces of alcohol, water and glycerol, the set of esters leaves in the range of 180 to 260⁰C, with extremely high purity. The non-distilled residue is forwarded to the reactors to react in the next batches .

Some examples of application of the process at issue here will be shown below. Tables 1 through 4 describe the reaction conditions employed in Example 1 in detail .

Table 5 presents, as an Example, a few physical chemical properties of the methylic ester obtained in accordance with the procedure described in Table 1. The tests were performed by using ASTM standards described in the table itself.

Table 1 - Conditions of reaction employed

* Molar Ratio SiO₂/Al₂O₃.

Table 2 - Conditions of reaction employed

*Polynaphthalensulphonic Acid (calcination for 2 hours in atmosphere of N₂ at 300⁰C of Naphthalene embedded in concentrated H₂SO₄, massive ratio acid/naphthalene = 3 )

Table 3 - Conditions of reaction employed

Mass of ethanol 12 g

* Molar Ratio SiO₂/Al₂O₃.

Table 4 - Conditions of reaction employed

Table 5- Properties of Methyl±c Ester Produced in Accordance with Table 1

Claims

ClaimsCATALYTIC PROCESS FOR THE ESTERIFICATION OF FATTY ACIDS

1. Catalytic process for esterification of fatty acids in the presence of alcohol for the transformation of said fatty acids in esters , characterized by the fact of using acid catalysers in the conditions of the reaction, molar ratios alcohol/fatty acids between 1.5 and 15, temperatures between 60 and 200 ⁰C, pressure higher or equal to the atmospheric pressure, stirring speeds between 200 and 1 500 rpm.

2. Process in accordance with claimed in 1 , characterized by the fact of the acid catalyser is sulfated zircon with sulfur content of 3% to 6% , with superficial area between 30 and 200 m²/g, pre-calcinated between 300 and 800 ⁰C.

3. Process in accordance with claimed in 1 , characterized by the fact of the acid catalyser is zircon doped with tungsten with tungsten content between 5% and 15%, with superficial area between 70 and 200 m²/g, pre- calcinated between 300 and 800 ⁰C .

4. Process in accordance with claimed in 1 , characterized by the fact of the acid catalyser are zeolites having hydrogen as compensation cation, as molar ratio silicium/aluminium between 4 and 160, superficial area between 200 and 800 rrr/g .

5. Process in accordance with claimed in 1, characterized by the fact of the acid catalyser is aluminum chloride, anhydride or chemically supported.

6. Process in accordance with claimed in 1 , characterized by the fact of the acid catalyser are polynaphthalen-sulphonic acid, prepared from a calcination in the range of 200 to 350 ⁰C, with atmosphere containing oxygen at the concentration of 0.01 to 1% and a mixture of naphthalene/concentrated sulfuric acid at the massive ratio of 0.5 to 10, respectively. The time of calcinations varies from 1 to 8 hours .

7. Process in accordance with claimed in 1 , characterized by the fact of the acid catalyser is concentrated methane-sulphonic acid.

8. Process in accordance with claimed in 1 , characterized by the fact of the acid catalyser is para- toluene-sulphonic acid.

9. Process in accordance with claimed in 1 , characterised by the fact of the acid catalyser is concentrated chloridric acid.

10. Process in accordance with claimed in 1 , characterized by the fact of the acid catalyser is concentrated phosphoric acid.

11. Process in accordance with claimed in 1 , characterized by the fact that alcohol is added in stoichiometric excess .

12. Process in accordance with claimed in 1 , characterized by the fact that alcohol is methanol .

13. Process in accordance with claimed in 1, characterized by the fact that alcohol is ethanol .

14. Process in accordance with claimed in 1 , characterized by the fact that alcohol is iso- or n- propanol or iso-, sec-, or n-butanol .

15. Process in accordance with characterized 1 characterized by the fact that the free fatty acids are carboxylic acids of long chain containing from 6 to 24 carbon atoms (Ce to C2₄) such as caproic acids, caprilic acid, capric acid, lauric acid, miristic acid, palmitic acid, estearic acid, oleic acid, vacenic acid_f linoleic acid, linolenic acid, arachnidic acid, gadoleic acid, arachdonic acid, beenic acid, erucic acid, lineceric acid, ricinoleic acid and mixtures of these containing glycerol and glycerides or not .

16. Process in accordance with claimed in 1 , characterized by the fact that the molar ratio alcohol/fatty acid is preferably between 2 and 10.

17. Process in accordance with claimed in 1 , characterized by the fact that the temperature is preferably between 120 and 170 degrees .

18. Process in accordance with claimed in 1, characterized by the fact that it is operated in batch system.

19. Process in accordance with claimed in 1, characterized by the fact that it is operated in continuous system.

20. Process in accordance with claimed in 1 , characterized by the fact that it is operated in a batch system with two reactors working intermittently with reaction and flash vase .

21. Process in accordance with claimed in 19, characterized by the fact that spatial time in relation to outflow of fatty acid and volume of solid catalyser are between 30 and 160 minutes .

22. Process in accordance with claimed in 18 , characterized by the fact that the concentration of catalyser is between 0.05 and 3% .

23. Process in accordance with claimed in 20, characterized by the fact that the concentration of catalyser is between 0.05 and 3% .

24. Process in accordance with claimed in 15, characterized by the fact that the fatty acid is a mixture of carboxylic acids with chains containing preferably between 12 and 20 carbon atoms .

25. Process in accordance with claimed in 1 , characterized by the fact that the ester is a methylic ester .

26. Process in accordance with claimed in 1 , characterized by the fact that the ester is an ethylic acid .

27. Process in accordance with claimed in 1, characterized by the fact that the ester is an ester of alcohols of 3 to carbon atoms .

28. Process in accordance with claimed in 1, characterized by the fact that the esters formed are employed as fuel or additive for fuels .

29. Process in accordance with claimed in 1, characterized by the fact that the esters formed are employed as solvents, as tensoactives or intermediaries of tensoactives or as detergents .

30. Use of acid catalysers, characterized by the fact of being used for the transformation of mixtures of fatty acids, in the presence of alcohol, in esters .

31. Use of catalysers in accordance with claimed in 30, characterized by the fact that the alcohol to be added in stoichmetric excess .

32. Use of catalysers in accordance with claimed in 30, characterized by the fact that the alcohol is methanol .

33. Use of catalysers in accordance with claimed in 30, characterized by the fact that the alcohol is ethanol .

34. Use of catalysers in accordance with claimed in 30, characterized by the fact that the alcohol has 3 to 5 carbon atoms .

35. Use pf catalysers in accordance with claimed in 30, characterized by the fact that the esters formed are employed as fuel .

36. Use of catalysers in accordance with claimed in 30, characterized by the fact that the esters formed are employed as solvents, as tensoactives or intermediaries of tensoactives or as detergents .

37. Process of removal of the alcohol used in excess and the water formed in the process claimed in 1 , characterized for using the same reactor as flash vase and for submitting the reaction mixture between 120 and 170⁰C, with absolute pressure in the vase of 0.1 to 1 atm.

38. Catalytic process as claimed in 1 again applied to the residual fatty acids present in the non-evaporated product in the process claimed in 37.

39. Sequential process of flash of the alcohol used in excess and the water formed in the process claimed in 38 and, new reaction, as per claimed in 1 up to the decrease of the residual fatty acids, reading the specifications desired of the product .

40. Process of purification of the esters formed in the process claimed in 37, characterized by the vacuum distillation of these esters to work in the range of absolute pressure in the vase of distillation between 5 and 70 Torr.

41. Process in accordance with claimed in 40, characterized by the fact that the absolute pressure of the distillation vase is preferably between 10 and 50 Torr.