WO2007093326A1

WO2007093326A1 - Method for deacidifying oils and/or fats

Info

Publication number: WO2007093326A1
Application number: PCT/EP2007/001122
Authority: WO
Inventors: Maurizio Mattia Germani
Original assignee: Aser S.R.L.
Priority date: 2006-02-15
Filing date: 2007-02-09
Publication date: 2007-08-23
Also published as: ITMI20060279A1

Abstract

The present invention relates to a method for deacidifying fresh or recycled vegetable or animal oils and/or fats, which have been found suitable for human or animal nutrition, for direct use without further derivatizations as environment-friendly fuels for diesel engines, or for their subsequent transformation into methyl esters by means of a transesterification reaction with methanol so as to produce biodiesel. An apparatus for performing the method is also described.

Description

METHOD FOR DEACIDIFYING OILS AND/OR FATS Technical Field

The present invention relates to a method for deacidifying fresh or recycled vegetable or animal oils and/or fats, to an apparatus for performing said method, and to uses of oils and/or fats thus deacidified, optionally after additional chemical derivatization thereof. Background Art

It is known that (fresh or recycled) acid animal fats and vegetable oils are not suitable for use as such as fuels in diesel engines. The organic acidity that they contain (due to the free fatty acids) is in fact extremely corrosive for the materials of which the engines are made. Methods for neutralizing the acid component with soda are currently known; this method converts the acid fraction into soaps. However, this waste product suffers significant problems regarding its disposal, since the environmental toxicity of this type of surfactant is now well-known. Additional problems also arise from difficulty in reusing the soaps at the industrial level.

One alternative to saponification is distillation of the free fatty acids from the mass of triglycerides. This second method, however, is very costly in terms of energy and feasible only for low acidity contents. Conventionally, therefore, the acid component is eliminated by esterification of the acid groups with alcohols having a low molecular weight (typically methanol) and by using acid catalysts. The production of methyl or ethyl esters starting from triglycerides and fatty acids (which are present in vegetable oils and in animal fats) is currently considered a promising energy source which is an alternative to fossil fuels. In particular, the production of these esters is highly important for economically convenient production of biodiesel to be used pure or mixed in various ratios with conventional petroleum-derived fuels.

For this type of production (biodiesel), the cost of the raw material is an extremely important factor, and therefore the industry seeks to use crude raw materials of low value, such as unrefined acid vegetable oils, fats recovered from animal slaughtering, fresh or recycled vegetable oils and oleins and recovered fats, all substances which have an organic acidity due to the presence of free fatty acids known commercially as FFA. However, it is known that traditional transesterification processes cannot use oils or fats with an FFA acidity of more than 0.5% by weight (expressed as percentage of oleic acid), since such free acidity, in addition to consuming the basic catalyst (generally potassium hydrate or sodium methylate) used in the reaction, produces by reaction with the basic catalyst soaps which interfere with the production of methyl esters, causing such complications and difficulties in separating them from the methyl esters as to eliminate the potential benefits arising from the use of said less expensive raw materials.

Currently, processes are known which perform a preliminary esterification of the fatty acids with methanol and an acid heterogeneous catalyst, followed by transesterification of the unreacted triglyceride fraction, which, as mentioned above, uses a basic catalyst. By using therefore an acid initial catalyst instead of a basic one, these advanced methods avoid the problem of incompatibility between initial acidity and catalyst. However, in turn they are penalized by the fact that it is necessary to esterify only small acid fractions in the presence instead of considerable quantities of triglycerides, consequently entailing the use of large reactors with considerable equipment and running costs. Disclosure of the Invention

The aim of the present invention is therefore to provide a method for deacidifying fresh or recycled vegetable or animal oils and/or fats which overcomes the drawbacks of the cited background art.

Within this aim, an object of the invention is to provide a method for producing biodiesel starting from fresh or recycled vegetable or animal oils and/or fats which is equally effective regardless of the initial FFA value of the initial oil and/or fat. Another object is to provide a use for the oils and/or fats deacidified according to the method described above.

Still another object is to provide an apparatus for performing a method as indicated above. This aim and these and other objects are achieved by a method for deacidifying fresh or recycled vegetable or animal oils and/or fats, which comprises the step (a) of extracting free fatty acids from said oils and/or fatty acids with methanol.

The aim and objects of the invention are also achieved by an apparatus for performing the method described above.

The aim and objects of the invention are also achieved by direct use as fuel for diesel engines conventionally used to generate electric power of a composition which comprises the triglyceride fraction deriving from deacidification of fresh or recycled oils and/or fats of vegetal or animal origin, optionally combined with the fraction of fatty acids extracted from said oils and/or fats, after esterification of this second fraction with methanol. Brief Description of the Drawings

The invention is described with reference to Figures 1-4, given hereinafter merely by way of non-limiting example and wherein:

Figure 1 is a block diagram of an embodiment of the method according to the invention, in which the transesterification reaction involves the mixture in output from step (c);

Figure 2 is a block diagram of an embodiment of the method according to the invention, in which the transesterification reaction involves the deacidified triglyceride fraction in output from step (a);

Figure 3 is a view of a particular embodiment of the apparatus according to the invention.

In Figures 1, 2, 3, the circular elements represent products or mixtures of products, while the rectangular elements represent steps of the method in Figures 1 and 2 and represent elements of the apparatus in Figure 3. Ways of carrying out the Invention

It is understood that any characteristic which is mentioned regarding one of the aspects of the invention but can also be referred to other aspects must be considered equally valid regarding these aspects even if it is not repeated explicitly.

In a first aspect, the invention relates to a method for deacidifying fresh or recycled vegetable or animal oils and/or fats. By deacidification, the oils and fats are separated into their two component fractions (free fatty acids and triglycerides) by means of an extraction process which uses methanol as a solvent. The extraction process is preferably a continuous method.

The extracted acid fraction is then advantageously esterified to methyl esters and preferably combined with the fraction that contains the deacidified triglycerides, thus obtaining a mixture of deacidified oil and methyl esters which is suitable for example to be used directly as fuel in diesel engines.

In a different embodiment, the mixture of deacidified triglycerides and methyl esters can be transesterified completely to methyl esters, obtaining biodiesel.

The expression "fresh or recycled oils and/or fats" references fats and oils which are available in plants or animals, both natural and synthetic. Preferably, the initial fatty acids and/or oils to be deacidified have an initial value of FFA acidity of 1% or more. It is understood that since the oils and/or fatty acids can be recycled or natural, they can also contain traces of other substances which are typical of the field of use from which they originate or of the natural source from which they have been extracted.

The term "deacidify" references the reduction of the free organic acidity contained in the fresh or recycled oils and/or fats to an FFA value of 0.5% or less (expressed as a percentage by weight of oleic acid). Preferably, the FFA value is reduced to a value which is comparable to the value of refined oils for food use and therefore to values ranging approximately from 0.1 to 0.2% by mass, expressed as mass of oleic acid. Since the process according to the invention is based on an extraction phenomenon, which as is well known is regulated by a balance of distribution of the fatty acids between methanol phase and fatty phase, the amount of free fatty acids in the initial fatty phase might in theory be made to tend to zero, of course provided that one wishes to use an appropriate amount of methanol and time. Therefore, the preferred values indicated above of FFA acidity do not constitute an impassable chemical limit to the amount of fatty acids which can be extracted with the invention, but rather are a limit dictated by the need to use economically convenient quantities of methanol and industrially acceptable extraction times.

The expression "free fatty acids" references molecules characterized by a saturated or unsaturated linear or ramified carbon chain containing preferably 12 to 22 carbon atoms and characterized by the presence of at least one free carboxylic acid group -C(O)OH. The fatty acids are free because they are no longer bound to the skeleton of the glycerin as in the initial oils and/or fats. The term "triglycerides" here references not only triglycerides in the strict sense of the term but must also include mono- and diglycerides. Therefore, the term "triglyceride" references here a class of natural or synthetic molecules obtained by esterification of a molecule of glycerin with one, two or three identical or different fatty acids as defined above. The term "methanol" references methanol of the technical type

(usually containing no more than 0.15% by weight of water).

The expression "direct use of deacidified oils and/or fats" is understood to mean that said oils and/or fats are used without being subjected to additional chemical reactions which might modify their structure. The invention is now described with particular reference to a preferred embodiment thereof, provided here merely by way of example.

In a first aspect, the present invention provides a method which allows to separate inexpensively and selectively the two fractions which correspond to free fatty acids and triglycerides which constitute the initial oils/fats. The process by means of which the triglyceride fraction and the acid fraction are separated is an extraction process which uses as solvent methanol, which is the reagent of any subsequent steps for esterification and transesterification. The fresh or recycled oils and/or fats (raw material) are subjected to a process for extraction with methanol which is preferably performed in an extraction column, in which the two streams of fatty raw material and methanol, respectively, are fed, advantageously continuously, with a mass ratio between the methanol flow-rate and the raw material flow-rate which ranges preferably from 1.2 to 2, more preferably equal to 1.5. These values are derived from the distribution coefficient of free fatty acids in methanol and organic phases, which has a value of approximately 1 (expressed as a ratio between the concentrations by mass of free fatty acids in the two phases). The extraction device can be any of the types known in the art but preferably a continuous perforated plate or packed extraction column. It has in fact been observed that the best performance is obtained with a pulsed packed column. The column works advantageously at a temperature which is high enough to have good fluidity of the oils/fats to be treated, typically 35 to 60 ⁰C, preferably ranging from 40 to 60 ⁰C, and at atmospheric pressure. One preferred packing is structured packing. An example of commercial structured packing are packings produced by the Sulzer company, which belong to the family known commercially as Mellapack®.

The methanol phase, which has extracted the acid components, is actually not entirely inert with respect to the triglyceride component (i.e., the latter has a minimal solubility in methanol). Approximately 20% by mass of triglycerides (percentage with respect to the total mass of extracted fatty acids) in fact remains in the methanol phase.

In a preferred embodiment, the method after step (a) of extracting the free fatty acids comprises a second step (b) of esterification with methanol of the extracted fatty acids, after sending the methanol fraction which contains the extracted free acidity for example to an esterification reactor. One advantage of this embodiment is that the methanol used in this second esterification step (b) is the methanol that is already partly contained in the methanol phase used for extraction. In one embodiment, the reaction (b) for esterification of the fatty acids extracted in the methanol phase is preferably performed in a static column reactor, preferably a vertical column reactor, filled with acid catalyst, preferably a heterogeneous acid catalyst, constituted advantageously by an acid cationic ion-exchange resin. Preferred examples of this resin are the packing known commercially as Wl 5 by Rohm & Haas. Particularly preferred heterogeneous acid catalysts are strong cationic resins in granular form, known commercially as Resindion®, described in Italian patent application MI2002A00825 filed on 20 October 2002, hereby incorporated by reference, in the name of Commer S. p. A. and entitled "Ottenimento di esteή alchilici da trigliceridi di origine animale o vegetale in presenza di acidi grassi liberi" ["Production of alkyl esters from triglycerides of animal or vegetable origin in the presence of free fatty acids"]. An example of these resins is the commercial resin Resindion® Relite EXC09. The esterification reaction conditions are advantageously in the range from 60 to 110 ⁰C, under the corresponding pressure due to the vapor pressure of the methanol and to the load losses of the system. One obtains therefore from the esterification reactor a mixture of methyl esters and methanol which, in a further embodiment of the invention, can be combined advantageously with the triglyceride fraction previously separated in a third step (c) which follows said esterification. In a preferred embodiment, the mixture that leaves the esterifϊcation reactor is combined continuously with the fraction of deacidified triglycerides obtained from step (a).

During esterification, water is produced in proportion to the amount of free acidity that is present. This water, which would be present in the methanol in output from the esterification reactor, must be preferably kept at a level below 0.15% by mass, preferably below 500 ppm by mass, on the weight of methanol, so as to have good transesterification. Control of the water level can be achieved with methods which are known in the field. However, preference is given to working by drawing from the head of the esterification reactor fractions of methanol in the gaseous phase, which are sent for example to a distillation column, from the bottom of which water flows out, while anhydrous methanol is drawn from the head and is then returned in a step (bl), advantageously together with fresh methanol, in the esterification step (b).

In a preferred embodiment, after combining, preferably continuously, the deacidified triglycerides with the methyl ester fatty acids in step (c), the excess methanol that derives from esterification is eliminated and recovered with conventional techniques (preferably by distillation or another known method) in a step (d), thus obtaining a neutral mixture of methyl esters and triglycerides.

In a particularly advantageous embodiment of the invention, after step (d), the method comprises an additional step (dl) of feeding directly the mixture in output from step (d) to one or more diesel engines, mainly diesel engines of the marine type for generating electric power, advantageously diesel engines coupled to one or more electric power generators. It is possible to mix the mixture described above with additives which are known in the fuel field.

In an alternative embodiment of the method, the mixture combined in step (c) of deacidified triglycerides and methyl esters, before recovering the methanol in step (d) and optionally adding other fresh methanol, can be sent in a step (e), advantageously continuously, to transformation into biodiesel. The term "biodiesel" references the product of the transesterification of all the glyceride components of the mixture (mono-, di- and triglycerides) with the same methanol that is already present in the mixture or optionally with the addition of fresh methanol.

In a different embodiment, the transesterification reaction of step (e) involves only the fraction of deacidified triglycerides obtained in step (a) before they are combined with the fatty acids esterified with methanol in step (c). The organic phase (oils and fats) which exits from the bottom of the extraction column in fact has a residual acidity content which can be adjusted until it becomes comparable to the content of a refined oil/fat (0.1- 0.2% by mass expressed as oleic acid) and is therefore suitable to be sent to transesterification. This organic phase can of course also contain a small percentage by mass of methanol (1-2%), which in any case causes no problems in transesterification, since methanol itself is the transesterification reagent.

In every embodiment, it is preferable to perform the transesterification reaction of phase (e) (synthesis of biodiesel) in a tubular reactor which has a retention time ranging advantageously from 30 to 90 minutes with a temperature ranging advantageously from 60 to 120 ⁰C, preferably from 70 to 100 ⁰C, at a pressure which corresponds advantageously to the vapor pressure of methanol at the reaction temperature. The reaction occurs preferably in the presence of an excess of methanol with respect to the required stoichiometric quantity. Advantageously, the methanol excess ranges from 300% to 500% with respect to the required stoichiometric quantity. The preferred conditions are 80 ⁰C and 3 bars of pressure. The catalyst used in transesterification is typically a strong base, for example one or more among potassium hydrate, barium hydrate, and preferably sodium methylate, advantageously in a quantity ranging from 0.3 to 1% by mass with respect to the mass of triglycerides that is present. The methanol is advantageously present with an excess by mass of 20%-50% with respect to the mass of triglycerides that is present. In a preferred embodiment, the transesterification mixture is subsequently neutralized in a step (el) for example with carbon dioxide at moderate pressure (typically 2-5 bars), obtaining the corresponding carbonates of the base used as a catalyst.

In a preferred embodiment, after step (el) for neutralization, it is possible to proceed (step (e2)) with recovery of the methanol excess and subsequent separation (step (e3)) of the glycerin from the obtained methyl ester; these steps can be performed with methods which are known in the art.

In an advantageous embodiment, the method comprises an additional step (al), which prepares for step (a), of feeding methanol and oils and/or fats to the means for extracting the free fatty acid fraction.

In one advantageous embodiment, the method comprises all the steps from (al) to (e3) which have not been presented clearly above as being necessarily mutually exclusive and in which all the steps that are present are performed continuously.

In another aspect, the invention relates to an apparatus particularly for performing a method for deacidification of fatty acids and/or oils as defined above, wherein said apparatus necessarily comprises means 1 for performing the step (a) of extracting with methanol the fraction of free fatty acids from fresh or recycled vegetable or animal oils and/or fats. Preferred examples of these means 1 are one or more extraction columns, preferably one or more extraction columns with perforated plates and/or packed columns, more preferably a pulsed structured packed extraction column.

In another embodiment, the apparatus also comprises means 2, downstream of the means 1 and connected thereto, for esterifying the fraction of free fatty acids extracted with methanol and in output from the means 1. Preferred examples of these means 2 are one or more static column reactors, preferably a vertical column reactor, advantageously filled with acid catalyst, preferably a heterogeneous acid catalyst, constituted advantageously by a cationic ion-exchange resin in acid form.

In another embodiment, the apparatus also comprises means, downstream of the means 2 and connected thereto, for drawing a gaseous mixture of methanol and water from the means 2, anhydrifying said mixture, recovering anhydrous methanol and returning it to the means 2. Preferred examples of these means are one or more distillation columns connected to the means 2 by means of ducts and pipes.

In another embodiment, the apparatus also comprises means 3, downstream of the means 1 and 2 and connected thereto, for mixing the deacidified triglycerides obtained from step (a) with the methyl esters of the free fatty acids obtained with step (b).

In another embodiment, the apparatus also comprises means 4, downstream of the means 3 and connected thereto, for separating the mixture obtained with the means 3 into its fractions of methanol on one side and methyl esters and deacidified triglycerides on the other side. In another embodiment, the apparatus also comprises transesterification means 5 downstream of the means 3 and connected thereto or, as an alternative, downstream of the means 1 and connected thereto. A preferred example of said means 5 is one or more tubular reactors. In another embodiment, the apparatus also comprises means 6, downstream of the means 5 and connected thereto, for neutralizing the mixture in output from said means 5.

In another embodiment, the apparatus also comprises means 7, downstream of the means 6 and connected thereto, for separating the mixture in output from said means 6 into its components of methanol on one side and glycerin and methyl esters on the other.

In another embodiment, the apparatus also comprises means 8, downstream of the means 7 and connected thereto, for separating the mixture in output from said means 7 into its components of glycerin on one side and methyl esters on the other.

In another embodiment, the apparatus also comprises one or more diesel engines, downstream of the means 1 and connected thereto or, as an alternative, downstream of the means 4 and connected thereto, said engines being optionally connected to one or more electric generators, which are suitable to use as fuel the deacidified triglyceride fraction in output from said means 1 or the fraction of deacidified triglycerides and methyl esters in output from said means 4.

Although they are not described explicitly, it is understood that the apparatus according to the invention comprises means for connection between the means 1 to 8 which are suitable to convey the mixture in output from the upstream means toward the input of the downstream means. One preferred apparatus is a continuous apparatus which comprises the connection means described above and all the means 1 to 8 which have not been indicated clearly above as mutually exclusive. In another aspect, the invention relates to the direct use, as fuel for diesel engines, of a composition which comprises deacidified oils and/or fats according to the method described above.

In a preferred embodiment, the composition also comprises fatty acids esterified with methanol. In a preferred embodiment, said composition comprises the mixture of deacidified oils and/or fats which can be obtained from step (e) of the method described above.

In a preferred embodiment, said composition comprises the mixture of deacidified oils and/or fats and fatty acids esterified with methanol, which can be obtained from step (c) of the method described above. In a highly preferred embodiment, the diesel engines are coupled to one or more electric generators, so that the use of the invention allows to generate electric power.

Other characteristics and advantages of the present invention will become better apparent from the description of the following preferred embodiments, intended merely by way of non-limiting example. Example 1

10 kg of crude palm oil, having a free acidity of 5%, are extracted continuously with 14.1 kg of methanol in a glass column which is 3 m long, is filled with half-inch Raschig rings, and has a diameter of 50 mm. A methanol phase containing 97% of initial acidity and an organic phase with 0.15% residual free acidity (expressed as oleic acid) were obtained. The methanol phase was fed into a cylindrical reactor having a diameter of 50 mm, controlled by thermostat to 70° C and filled with Resindion® strong cationic resin. During this operation, approximately 70% of the methanol was drawn from the head of the reactor to be then subsequently anhydrified. The esterified methanol phase was added to the triglyceride fraction and subjected to transesterification in the presence of sodium methylate as catalyst, using a tubular reactor having a diameter of 25 mm and a length of 3 m and working at 80 ⁰C. The trend of the test is shown in the Table 1. At the end, methyl ester compliant with standards according to the EN 14214 specification as regards the content of methyl ester, monoglycerides, diglycerides and triglycerides was obtained.

TABLE l

Example 2

10 kg of crude rape oil, having a free acidity of 3%, are extracted continuously with 14.1 kg of methanol in a glass column which is 3 m long, is filled with half-inch Raschig rings, and has a diameter of 50 mm. A methanol phase containing 97% of initial acidity and an organic phase with

0.14% residual free acidity (expressed as oleic acid) were obtained. The methanol phase was fed into a cylindrical reactor having a diameter of 50 mm, controlled by thermostat to 70° C and filled with Resindion® strong cationic resin. During this operation, approximately 70% of the methanol was drawn from the head of the reactor to be then subsequently anhydrified.

The esterified methanol phase was added to the triglyceride fraction and the mixture was fed to a diesel engine which drove an electric power generator.

Although only some preferred embodiments of the invention have been described in the text, the person skilled in the art will understand immediately that it is possible to obtain other equally advantageous embodiments.

The disclosures in Italian Patent Application No. MI2006A000279 from which this application claims priority are incorporated herein by reference.

Claims

1. A method for deacidifying fresh or recycled vegetable or animal oils and/or fats, wherein said method comprises a step (a) of extracting the free fatty acids from said oils and/or fatty acids with methanol, thereby obtaining a first fraction which contains methanol and extracted free fatty acids, and a second fraction containing deacidified triglycerides.

2. The method according to claim 1, wherein said fresh or recycled oils and/or fats have an FFA acidity value of 1% or more.

3. The method according to one or more of the preceding claims, wherein step (a) lowers the free organic acidity contained in said fresh or recycled fats and/or oils down to an FFA value of 0.5% or less.

4. The method according to one or more of the preceding claims, wherein step (a) occurs in one or more pulsed packed columns, at a temperature ranging from 35 to 60 ⁰C and at atmospheric pressure.

5. The method according to claim 4, wherein column packing is a structured packing.

6. The method according to one or more of the preceding claims, further comprising, before step (a), a step (al) of feeding methanol and said oils and/or fatty acids continuously in step (a) with a mass ratio between the flow-rate of methanol and the flow-rate of fatty acids and/or oils ranging from 1.2 to 2.

7. The method according to one or more of the preceding claims, furthermore comprising, after step (a), a step (b) of esterifying with methanol the mixture of methanol and fatty acids in output from step (a), thereby obtaining a mixture of fatty acids methyl esters and methanol.

8. The method according to claim 6, wherein step (b) occurs in the presence of an acid catalyst at a temperature ranging from 60 to 1 10 ⁰C, at the corresponding pressure due to the vapor pressure of the methanol and to the load losses of the system at the reaction temperature.

9. The method according to claim 6, wherein step (b) occurs simultaneously with another step (bl) of removing percentages of gaseous methanol from step (b), and anhydrifying and then returning the anhydrified fractions into step (b), so as to maintain the percentage of water produced in step (b) at a level of less than 0.15% by mass.

10. The method according to one or more of the preceding claims, further comprising, after step (b), an additional step (c) of combining the fraction of deacidified triglycerides obtained in output from step (a) with the mixture of methanol and fatty acids methyl esters in output from step (b).

1 1. The method according to claim 9, further comprising, after step (c), an additional step (d) of separating the methanol from the mixture in output from step (c), thus obtaining a neutral mixture of methyl esters and triglycerides.

12. The method according to claim 1 1 , further comprising, after step (d), an additional step (dl) of feeding said neutral mixture of methyl esters and triglycerides to one or more diesel engines, optionally coupled to one or more current generators.

13. The method according to one or more of claims 1 to 10, further comprising, after step (c), a step (e) of transesterification with methanol of the mixture in output from step (c), obtaining a transesterified mixture of glycerin, methanol and methyl esters.

14. The method according to one or more of claims 1 to 10, further comprising, after step (a), a step (e) of transesterification with methanol of the fraction of deacidified triglycerides in output from step (a).

15. The method according to claim 13 or 14, further comprising, after step (e), a step (el) of neutralizing the transesterified mixture in output from step (e).

16. The method according to claim 15, further comprising, after step (el), a step (e2) of separating the methanol from the transesterified mixture in output from step (el).

17. The method according to claim 16, further comprising, after step (e2), a step (e3) of separating the mixture in output from step (e2) into its components of glycerin and methyl ester.

18. The method according to claim 17, comprising all steps from (al) to (e3) which are not mutually exclusive, and wherein all the steps that are present are performed continuously.

19. An apparatus particularly for performing a method as defined according to one or more of claims 1 to 18, comprising means (1) for performing said step (a) of extracting with methanol the free fatty acids from fresh or recycled vegetable or animal oils and/or fats.

20. Direct use, as fuel for diesel engines used to generate electric power, of the fraction containing deacidified triglycerides obtained as defined in claim 1.

21. Direct use, as fuel for diesel engines used to generate electric power, of a neutral mixture of methyl esters and triglycerides obtained as defined in claim 11.