EP2591079A1

EP2591079A1 - Method for purifying a fatty-acid alkyl ester by liquid/liquid extraction

Info

Publication number: EP2591079A1
Application number: EP11738018.8A
Authority: EP
Inventors: Jean-Luc Dubois; Antoine Piccirilli; Julien Magne
Original assignee: Arkema France SA
Current assignee: Arkema France SA
Priority date: 2010-07-08
Filing date: 2011-06-24
Publication date: 2013-05-15
Also published as: MY183587A; AR082124A1; CA2804620A1; US8816108B2; WO2012004489A1; US20130211115A1; FR2962434B1; FR2962434A1; JP2013532165A; CN103080282A; KR20130091311A; BR112013000398A2

Abstract

The present invention relates to a method for selectively extracting monoglycerides present in a blend of fatty acid alkyl esters (FAAEs), which includes at least one liquid-liquid extraction step using a polar solvent (PS), comprising a light alcohol, and optionally an apolar solvent (AS), comprising a solvent immiscible with the light alcohol. The present invention relates in particular to a blend of fatty acid alkyl esters (FAAEs) of plant or animal origin, especially one used in biodiesel, which can be obtained according to the method of the invention, so that its monoglyceride content is less than 0.6%.

Description

PROCESS FOR THE PURIFICATION OF AN ALKYL ESTER OF FATTY ACID BY LIQUID / LIQUID EXTRACTION

Description

The present invention relates to a process for extracting residual monoglycerides in a cross section of fatty acid alkyl esters derived from transesterification, used in particular to manufacture biodiesel.

For the purposes of the invention, the term "alkyl esters of fatty acids" (abbreviated EAAG) is understood to mean, preferably, the esters resulting from the transesterification of C1 to C8 alcohols with C8 to C36 fatty acids. These EAAGs therefore correspond to the formula: R ¹ CO-OR ² , where R ¹ CO is an aliphatic acyl group containing from 8 to 36 carbon atoms and R ² is a linear or branched alkyl group containing from 1 to 8 carbon atoms .

Thus, the fatty acid methyl esters (abbreviated EMAG) are obtained by transesterification of fatty acids of vegetable or animal origin with methanol, generally in the presence of a basic catalyst, such as NaOH. The fatty acids come mainly from vegetable oil, such as rapeseed, sunflower, soy, peanut, olive, sesame, safflower, coconut, palm, castor oil, jatropha, microalgae, etc. Fatty acids can also come from animal sources, such as residues from the agri-food industry such as slaughterhouse residues, animal fats such as chicken fat, beef, pork, fish, or used cooking oils.

Methyl esters of fatty acids (abbreviated EMAG) are the major constituents of biodiesel produced today. Therefore, the present invention is generally described in the following text and examples with reference to the purification of a section of fatty acid methyl esters. Nevertheless, the process of the invention is obviously not limited to the purification of fatty acid methyl ester cuts, but applies to any section of alkyl esters of fatty acids as defined above, such as for example, ethyl esters of fatty acids or esters derived from transesterification of fatty acids with 2-ethylhexanol. The EN 14214 standard (or ASTM D6751) describes the requirements for EAAGs (EMAGs) used as biodiesel. One of the criteria is the filterability limit temperature (TLF) according to EN 1 16 in Europe (or ASTM method D 2500 in the USA). This TLF criterion corresponds to the blocking temperature of a cold filter in the presence of EAAG. This temperature depends in part on the residual saturated monoglyceride content of the EAAGs resulting from transesterification. In particular, the residual monoglyceride content of the EAAGs must be less than or equal to 0.8% by weight relative to the weight of the EAAGs according to the EN 14214 standard. This residual monoglyceride content is measured according to the EN 14105 standard in biodiesels.

US2007 / 0151 146 discloses a method of separation and filtration, using adsorbent compounds (such as granular glucose, boric acid, or diatomaceous earth), steryl glycosides biodiesel. This process can sometimes result in a small amount of residual monoglycerides simultaneously with the steryl glycosides. On the other hand, the method described in this document does not make it possible to selectively, efficiently and simply extract almost all residual monoglycerides from EAAGs, in particular EAAGs highly loaded with monoglycerides, that is to say containing more of 2% by weight of monoglycerides.

The object of the present invention is therefore to provide a simple method for the selective extraction of residual monoglycerides from EAAGs, in order to improve the cold resistance of EAAGs, and to make them usable as biodiesels, (in accordance with the EN 14214 standard).

The subject of the present invention is therefore a process for the selective extraction of monoglycerides present in a section of fatty acid alkyl esters (EAAG), comprising at least one liquid-liquid extraction step by means of: a solvent polar (SP) composition comprising a light alcohol, i.e. a lower aliphatic alcohol whose carbon number is in the range of 1 to 8, preferably 1 to 5, or even more preferably 1 to 4; and optionally an apolar solvent (SA) comprising a solvent immiscible with the light alcohol.

By liquid-liquid extraction within the meaning of the invention means an extraction in which the solvent (s) used are liquid at the extraction temperature.

Advantageously, the light alcohol is chosen from methanol, ethanol, isopropanol, n-propanol, butanol, isobutanol, 2-ethylhexanol, and mixtures thereof. According to a preferred embodiment of the invention, the light alcohol is methanol, which has the advantage of being already used during the transesterification of the EMAGs. Advantageously, the selective extraction process of the monoglycerides according to the invention does not require the use of a special adsorbent product, nor does it require a subsequent filtration step.

Said polar solvent preferably comprises 99.9 to 70% light alcohol and 0.1 to 30% water, preferably 80 to 99% light alcohol and 1 to 20% alcohol. water, preferably 85 to 95% light alcohol and 5 to 15% water. Indeed, the amount of monoglycerides extracted according to the process of the invention increases when the degree of hydration of the light alcohol increases (see the examples below).

Advantageously, said apolar solvent is chosen from hexane, heptane, benzene, bicyclohexyl, cyclohexane, decalin, decane, hexane (Texsolve C), kerosene, methylcyclohexane, Texsolve S or S-66, Naphtha (Texsolve V), Skellite, Tetradecane, Texsolve (B, C, H, S, S-2, S-66, S-LO, V), supercritical CO2, propane or butane pressurized, solvents natural, such as terpenes (limonene, alpha and beta pinene, etc.), and mixtures thereof; and preferably is hexane. The use of an immiscible solvent with the light alcohol makes it easier to separate the phase containing the purified EAAGs from the phase containing the extracted monoglycerides with the light alcohol.

By "cutting fatty acid alkyl esters (EAAG)" within the meaning of the invention is meant the group formed by the alkyl esters of fatty acids from transesterification and impurities which contain in particular monoglycerides (also called monoacylglycerols).

Preferably, the EAAG cut comprises at least 90% by weight of fatty acid methyl esters (FAMEs), relative to the weight of said cut.

The alkyl esters of fatty acids used as raw material in the process of the invention comprise at least one ester chosen, for example, from the methyl esters of rapeseed oil, safflower oil, sunflower oil, nasturtium oil, mustard seed oil, olive, walnut, hazelnut, avocado, grape, sesame, soya, maize, peanut, cottonseed, rice, babassu, castor oil, palm, palm kernel, rapeseed, lupine, jatropha, coconut, linseed, evening primrose, jojoba, camelina, seaweed, tallow, such as beef or pork tallow, fish, chicken fat , lard, milk fat, shea butter, biodiesel, used cooking oil, used cooking oil, miscella, derivatives of these oils, in particular hydrogenated derivatives, conjugated derivatives, slices of these oils, and mixtures thereof.

A section of fatty acid alkyl esters derived from transesterification generally comprises from 0.5 to 5%, more usually from 0.8 to 3%, by weight of monoglycerides relative to the total weight of said cut, before liquid-liquid extraction step of the process of the invention.

According to the process of the invention, the monoglycerides are extracted in the phase containing the light alcohol (phase of the polar solvent).

According to a preferred embodiment of the method of the invention, the polar solvent (SP) is introduced against the current of the EAAG cut, leading to the production of a heavy phase comprising the purified EAAGs, and a light phase enriched with monoglycerides.

In fact, when no apolar solvent, such as hexane, is used, it is the phase containing the light alcohol having extracted the monoglycerides which is lighter than the phase comprising the purified EAAGs.

This embodiment, which uses only the polar solvent for extraction (without apolar solvent) and which already has excellent results, is preferred. extraction performance as demonstrated in the examples below. In addition, light alcohol, usually methanol, is already available on site for transesterification. We will not try to introduce in addition and especially a hydrocarbon that is not used until then.

According to a second embodiment, the method of the invention comprises the following steps:

1 - Mix the EAAGs with the SA and the SP, shake the mixture obtained, then decant it until obtaining a heavy phase 1 (PL1) enriched in monoglycerides, and a light phase 1 (pl 1) comprising the purified EAAGs.

In this second embodiment of the process of the invention, the apolar solvent is lighter than the polar solvent, and it is the apolar solvent which contains the purified ester.

According to a variant of this second embodiment, step 1 is followed by the following steps in the method of the invention:

2- Mix, shake, then decant pl1 + SP -> PL2 + pl2

3- Mix, shake, then decant PL1 + PL2 + SA - »PL3 + pl3

4- Mix, stir and then decant PL3 + SA -> PL4 + pl4, in which:

PL4 is the heavy phase enriched in monoglycerides, and

the sum of the light phases p12 + p13 + p14 comprises the purified EAAGs, which preferably have a monoglyceride content of less than or equal to 0.8% by weight relative to the weight of purified EAAGs.

The process according to the invention can easily be carried out on an industrial scale, batchwise or continuously, using one or more devices chosen from mixer-settlers, stirring mixers, static mixers, gravity settlers, centrifugal decanters, coalescers, centrifugal liquid-liquid extractors, liquid-liquid hydrocyclones, individual-stage extractors, non-individualized stage extractors (differential extractors), countercurrent columns, on one or more consecutive stages, in particular gravity columns , spray columns, packed columns, perforated tray columns, columns agitated, pulsed columns, rotating disk columns, contactors, and any other device used for liquid extraction. These liquid-liquid extraction devices are described in the booklets J 2764, J 2765 and J 2766 of the Techniques de l'Ingénieur.

Advantageously, the method of the invention, whatever the embodiment described above, comprises at least two extraction stages. Advantageously, said method comprises at least five extraction stages.

Preferably, the ratio by weight polar solvent / EAAG is in the range of 1/5 to 5/1, preferably 1/4 to 4/1, preferably 1/4 to 1/1.

The present invention also relates to a section of fatty acid alkyl esters (EAAG) of plant or animal origin, obtainable according to the process of the invention, characterized in that its monoglyceride content is lower than at 0.6%, preferably less than 0.5%, preferably less than 0.4%, preferably less than 0.3%, preferably less than 0.25% by weight, on the weight of the cup of EAAG.

The subject of the present invention is also a biodiesel comprising a purified EAAG cut whose monoglyceride content is less than 0.6%, preferably less than 0.5%, preferably less than 0.4%, and preferably less than 0.4%. 0.3%, preferably less than 0.25% by weight, based on the weight of the EAAG cut; said section being obtained according to the method of the invention.

The invention and its advantages will be better understood on reading the examples hereinafter given purely by way of illustration and not limitation.

Examples

Unless otherwise indicated, all percentages are by weight.

The term "Φ" means "phase".

The following examples illustrate the liquid / liquid extraction processes according to the invention, for the extraction of the monoglycerides (MG) present in a fraction of fatty acid methyl esters (EMAG) which do not comply with the EN 14214 standard. as regards its residual monoglyceride content (monoglycerides> 0.8%). For this purpose, it was deliberately doped with monoglycerides a conforming rapeseed methyl ester (EMCC) titrant before doping 0.4% of monoglycerides. Several levels of doping were retained, in particular 1; 1, 3 and 2.4%.

In Examples 1 to 3, liquid-liquid extraction tests were carried out in the presence of a mixture of polar (SP) and apolar (SA) solvents, namely hydrated methanol and hexane, in the Examples 1 and 2, according to the following procedure:

1. 5g EMCC doped MG + 30ml_ SA + 15ml_ SP - »Φ heavy 1 + Φ light 1

2. Φ light 1 + 15ml_ SP -> Φ heavy 2 + Φ light 2

3. Φ heavy 1 + Φ heavy 2 + 30ml_ sa - Φ heavy 3 + Φ light 3

4. Φ heavy 3 + 30ml_ SA -> Φ heavy 4 + Φ light 4

SA: apolar solvent (hexane)

SP: polar solvent (Methanol / water with different water contents)

Concentration:

1. Φ heavy 4 -> polar fraction

2. Φ mild 2 + Φ mild 3 + Φ mild 4 -> apolar fraction

In Examples 1 to 4, the solvent is removed from each fraction or final phase by distillation under vacuum on a rotary evaporator, at 90 ° C. and under a vacuum of 20 mbar. Thus, in the following Tables 1 to 9, the "mass distributions" are given in%, after evaporation of the solvent. Likewise, the monoglyceride contents (%) are measured with respect to the "dry mass" (once the solvent has evaporated) of the phase which contains the purified EMAG.

Example 1

The analytical balance of the esters purified from a section of methyl esters heavily loaded with monoglycerides (2.4%) is detailed in Table 1 below. Table 1

Comments:

The amount of material extracted in the light phase decreases as the degree of hydration of methanol tends to decrease.

However, the selectivity of extraction of monoglycerides passes through a maximum depending on the water content in the polar solvent, for a weight ratio methanol / water in the range of 80/20 to 99/1.

The process according to the invention makes it possible to reduce the monoglyceride content of a fraction of initially heavily loaded methyl esters by a factor of 2.5.

Example 2

The analytical balance of the esters purified from a section of moderately charged methyl esters (1, 3%) to monoglycerides is detailed in Table 2 below. Table 2

Comments:

However, the selectivity of extraction of monoglycerides passes through a maximum depending on the water content in the polar solvent, for a methanol / water ratio in the range of 80/20 to 99/1.

The process according to the invention makes it possible to reduce by a factor of 2 the monoglyceride content of a highly charged methyl ester. Thus, a methyl ester which does not comply with the European standard for biodiesel (monoglyceride> 0.8%) can be purified by liquid-liquid extraction.

Example 3

The analytical balance of the esters purified from a fraction of EMAG moderately charged with monoglycerides (1.03%) is described in Table 3 below. Table 3

Comments:

the selectivity of the process is confirmed since a yield of monoglyceride extraction of 66% is obtained from a batch of ester moderately charged with monoglycerides. The EMAG resulting from the light phase is then in compliance with the European standard for biodiesel (monoglyceride content <0.8%).

Example 4: Countercurrent column purification tests

a) Extraction of the MG from a moderately charged fraction of EMAG by a polar solvent according to a single-stage extraction:

Operating mode: 20g EMCC doped MG + 20g SP -> Φ heavy 1 + Φ light 1

Table 4 below gives the analytical balance of purified esters from a fraction of EMAG moderately loaded in MG (1.03%): Table 4

Comments:

In the absence of hexane, the monoglycerides are methanol-entrained. Methanol becomes the light phase.

In a single extraction and in the presence only of hydrated methanol (90/10), the MG are extracted with a yield of 40%, making it possible to reduce the MG content to compliant levels (biodiesel) and this with a high yield of EMAG. purified (96%). This test demonstrates the feasibility of the process with an industrially realistic solvent / ester ratio.

The methanol-rich phase, containing the monoglycerides, but also the methyl esters can be easily recycled upstream of the extraction process in the transesterification unit, where the conversion process of the monoglycerides will be repeated until complete conversion, so that there is no loss of material.

b) Single-stage extraction of MG from an ester fraction weakly loaded with a polar solvent:

Procedure: 20g EMCC + 20g SP - »Φ heavy 1 + Φ light 1

The analytical balance of the esters purified from a batch of weakly charged esters (0.67% of MG) is given in Table 5 below. Table 5

Comments:

The MGs are extracted with a yield of the order of 50%, making it possible to reduce the MG content to very low levels (<0.4%) and this with a high yield of purified ester (96%). This test demonstrates the feasibility of the process with an industrially realistic solvent / ester ratio,

c) Two-stage extraction of MG by a polar solvent

Operating mode:

20 g EMCC currently compliant + 20g SP -> Φ heavy 1 + Φ mild 1 Φ heavy 1 + 20g SP - »Φ heavy 2 + Φ mild 2

The analytical balance of the esters purified from a batch of weakly charged esters (0.67% MG) by two-stage countercurrent extraction is shown in Table 6. Table 6

Comments:

Starting from a weakly loaded ester of MG, the extraction of the glycerides is carried out in an efficient manner, countercurrently on two stages: extraction yield of the MG> 71% and MG content of the purified esters of 0.2 % about. The yield of the purified ester process is greater than 90%, the fraction enriched in MG can be recycled in transesterification. This test confirms the industrial relevance of the process according to the invention. d) Single-stage extraction of MG by a polar solvent - Influence of the polar solvent / EMAG ratio:

The objective is to evaluate the influence of the polar solvent / ester ratio in order to reduce the quantities of solvent involved. A solvent / ester ratio of 1/2 was tested.

Procedure: 20g EMCC + 10g SP - »Φ heavy 1 + Φ light 1

Table 7 below shows the analytical balance of the purified esters from a batch of weakly charged esters (0.67% of MG) by counter-current single-stage extraction with a solvent / ester ratio of 1/2. . Table 7

Comments:

In comparison with the test 9, a reduction of the amount of solvent employed by half makes it possible to maintain a high extraction yield of the MGs of 40% and to reach a residual MG content in the purified esters of 0.4%. approximately, very slightly above test 9 (0.34%) but far below current biodiesel specifications. The overall yield of purified ester is logically improved: 97.6% vs 96.0 in test 9. e) Two-stage extraction of MG by a polar solvent on a two-stage column - Influence of the solvent / ester ratio

Operating mode:

20g EMCC currently compliant ^ 10g SP -> Φ heavy 1 + Φ mild 1 Φ heavy 1 + 10g SP -> Φ heavy 2 + Φ mild 2

Table 8 shows the analytical balance of the purified esters from a batch of weakly charged esters (0.67% of MG) - two-stage extraction against the current with a solvent / ester ratio of 1/2. Table 8

Comments:

In comparison with the test 10, a reduction of the amount of solvent employed by half makes it possible to maintain a high extraction yield of 54% and to reach a residual monoglyceride content in the purified esters of

0.3. approximately, slightly above test 10 (0.2%) but far below current biodiesel specifications. The overall yield of purified ester is logically improved: 96.0% vs 91.7 in the test 10. EXAMPLE 5 Multi-stage counter-current extraction (5 stages) of the monoglycerides of a methyl ester by a polar solvent .

Simulation procedure of a column extraction against the current (5 stages):

40g EMCC currently compliant (0.67%) + 10g SP - ^ Φ heavy 1 + Φ light 1 The mass ratio polar solvent / EMAG is equal to 1/4

Install 5 decantation bulbs and name them A1, A2, A3, A4 and A5

1. Load the 5 ampoules with 40g of ester and 10g of 90/10 hydrated methanol, shake well and allow to settle. Let H1 be the upper phase of bulb n ° 1 and B1 the lower phase of bulb n ° 1 and so on for the other bulbs.

2. Lift B1 into a flask and concentrate it, put H1 in a beaker, put 10g of methanol in blister n ° 1 3. Put B2 in ampoule # 1, put H2 in a beaker and put H1 in ampoule # 2.

4. Put B3 in ampoule # 2, put H3 in a beaker and put H2 in ampoule # 3.

5. Put B4 in ampoule # 3, put H4 in a beaker and put H3 in ampoule # 4.

6. Put B5 in ampoule # 4, put H5 in a flask and concentrate, place H4 and 40 g of methyl ester in ampoule # 5. All bulbs are then shaken and allow to settle.

Steps 2 to 6 form a first sequence representing the 1st extraction stage. Phases B1 and H5 are then weighed and analyzed (see Table 9, end sequence 1). The continuation of the test consists of starting the second sequence in the presence of the contents of the ampoules resulting from the preceding sequence and re-injecting fresh methanol and the raw material ester respectively into ampoules 1 and 5. And so on, until you realize 5 complete sequences. In fact, the sequences simulate the setting in regime of the column with 5 stages. The mass and analytical balances made on the outgoing phases at the end of each sequence are presented in Table 9. FIG. 1 schematizes the column extraction against the current (5 stages). Table 9 shows the mass and analytical balance of the 5-stage countercurrent extraction (MS percentages are given for the dry mass).

Table 9

Comments:

- after 1 ^st extraction stage, the MG content decreases rapidly (below 0.5%);

- The MG content quickly reaches a 0.45% level in the second sequence since it hardly evolves during extraction;

- The overall yield of esters following the 5 extraction stages is 97.2% and the overall yield of extraction of MG is 34.6%.

The results of the tests of Examples 1 to 5 according to the invention demonstrate the effectiveness of the liquid-liquid extraction process in the presence of hydrated methanol as extraction solvent.

Claims

1. A process for the selective extraction of monoglycerides present in a fatty acid alkyl ester (EAAG) cut comprising at least one liquid-liquid extraction step by means of:

a polar solvent (SP) comprising a light alcohol,

and optionally an apolar solvent (SA) comprising a solvent immiscible with the light alcohol.

2. The method of claim 1, wherein the light alcohol is selected from: methanol, ethanol, isopropanol, n-propanol, butanol, isobutanol, 2-ethylhexanol, and mixtures thereof.

The method of claim 1 or 2, wherein said polar solvent comprises 99.9 to 70% light alcohol and 0.1 to 30% water.

4. Method according to any one of claims 1 to 3, wherein the apolar solvent is selected from hexane, heptane, benzene, bicyclohexyl, cyclohexane, decalin, decane, hexane, kerosene, methylcyclohexane, Texsolve S or S-66, Naphtha, Skellite, tetradecane, Texsolve, supercritical CO2, propane or butane pressurized, natural solvents, and mixtures thereof.

5. Process according to any one of claims 1 to 4, in which the EAAGs comprise at least one ester chosen from the esters of rapeseed, safflower, sunflower, nasturtium, mustard seed and olive oil. , sesame, soya, maize, peanut, walnut, hazelnut, avocado, grape, cottonseed, rice, babassu, castor oil, palm, palm kernel, rapeseed, lupine, jatropha, coconut, linseed, evening primrose, jojoba, camelina, seaweed, tallow, such as beef or pork tallow, chicken fat, bacon, fish , milk fat, shea butter, biodiesel, used cooking oil, used cooking oil, miscella, derivatives of these oils, in particular hydrogenated derivatives, conjugated derivatives, cuts of these oils, and mixtures thereof.

The process according to any one of claims 1 to 5, wherein the EAAG cut comprises from 0.5 to 5% by weight of monoglycerides to the total weight of the ester cut prior to the extraction step. liquid-liquid.

The process according to any one of claims 1 to 6, wherein the EAAG cut comprises at least 90% by weight of fatty acid methyl esters (FAMEs), based on the weight of the cut.

The process of any one of claims 1 to 7, wherein the light alcohol is methanol.

The process of any one of claims 1 to 8, wherein the apolar solvent is hexane.

10. Process according to any one of claims 1 to 8, wherein the polar solvent (SP) is introduced against the current of the EAAG cut, leading to the production of a heavy phase comprising the purified EAAGs, and a light phase enriched with monoglycerides.

1 1. Process according to any one of Claims 1 to 9, comprising the following steps: mixing the EAAGS with the SA and the SP, shaking the mixture obtained and then decanting it until an enriched heavy phase (PL1) is obtained monoglycerides, and a light phase (pl 1) comprising the purified EAAGs.

12. Method according to any one of claims 1 to 1 1, comprising at least two extraction stages.

13. The method of claim 12, comprising at least five extraction stages.

The process according to any one of claims 1 to 13, wherein the polar solvent / EAAG weight ratio is in the range of 1/5 to 5/1, preferably 1/4 to 4/1, of preferably 1/4 to 1/1.

15. Section of fatty acid methyl esters (EAAG) of vegetable or animal origin, obtainable according to the method of any one of claims 1 to 14, characterized in that its monoglyceride content is lower than at 0.6%, preferably less than 0.5%, preferably less than 0.4%, preferably less than 0.3%, preferably less than 0.25% by weight, on the weight of the cup of EAAG.

16. Biodiesel comprising a purified EAAG cut whose monoglyceride content is less than 0.6%, said cut being obtained according to the method of any one of claims 1 to 14.