WO2014006595A1

WO2014006595A1 - Process or the synthesis of esters of fatty acids

Info

Publication number: WO2014006595A1
Application number: PCT/IB2013/055509
Authority: WO
Inventors: Simona BRINI; Rinaldo Psaro; Federica Zaccheria; Maria Nicoletta Ravasio
Original assignee: Cnr - Consiglio Nazionale Delle Ricerche
Priority date: 2012-07-06
Filing date: 2013-07-05
Publication date: 2014-01-09
Also published as: ITMI20121189A1

Abstract

The present invention concerns a process for preparing fatty acid esters with the use of solid acid catalysts.

Description

PROCESS OR THE SYNTHESIS OF ESTERS OF FATTY ACIDS

" Process for the synthesis of esters of fatty acids"

[0001] Esterification of fatty acids of vegetal origin has a considerable industrial importance, since the products find a widespread application as lubricants, cooling lubricants and fluids for oleodynamic circuits. These products have important characteristics, such as a high biodegradability and a high flammability point, both due to the matrix having a natural origin.

The processes used today for the synthesis of fatty acid esters include for the use of catalysts that, however, have drawbacks (P. Bondioli, Oleochemical manufacture and applications, F.D. Gunstone, R.J. Hamilton eds . Wiley 2001, pp. 74-103):

- homogeneous acids (sulfuric acid, p-toluenesulfonic acid, methanesulfonic acid) as described, for example, in EP 712.834 requiring a successive neutralization step, and cause the corrosion of the plants;

- homogeneous ZnCl₂, which is expensive and difficult to be removed;

- organic titanates, which cannot be removed from the reaction product;

- powdery Zn, which forms soaps;

- metal oxides, such as zinc, tin (IV), iron (III) oxide, which have a low cost, but are often finely suspended in the reaction mixture and, to be removed, use has to be made of a successive step of coagulation and successive filtration;

- Sn oxalate, for example, as described in US 7.989.648 Bl, which as in the cases described in the preceding point, requires a filtration at the end of the reaction on a filtering solid, such as, for example, Celite. Furthermore, the known catalysts suffer from a reduced selectivity. This causes problems, since the presence of partial esters (mono- and diglycerides ) affects the thermal stability, and moreover^{" "}the^" hydrolytic stability; instead, the presence of residual polyols leads to the formation of insolubles, while the presence of free acid affects the flame resistance as well as the thermal and hydrolytic stability.

Both the presence of soaps and that of partial esters affects the demulsibility, i.e., the ability of an oily phase to separate from water.

On the other hand, the presence of residual catalyst causes the formation of soaps and insolubles, and affects the oxidative stability.

Therefore, there is felt the need to develop new processes and new catalysts, which may be used in preparing esters and being without the limits of the prior art. OBJECT OF THE INVENTION

[0002] Therefore, an object of the present invention is to provide a process for preparing fatty acid esters, which uses active and selective catalysts, which lead the reaction to be completed with the formation of the desired product of complete esterification of the polyol and that are easily and completely removable from the reaction medium.

The industrial application of such esters is also described .

DETAILED DESCRIPTION OF THE INVENTION

[0003] According to a first object, the process of the invention for preparing fatty acid esters comprises reacting said fatty acids with polyols in the presence of a catalyst, in which such catalyst is a solid having Lewis acid characteristics, such as, for example, a mixed oxide of silica with another oxide.

[0004] Particularly, the fatty acids that can be esterified preferably comprise C4-C24 acids.

Such acids may further comprise one or more insaturations .

Preferably, oleic acid, stearic acid, palmitoleic acid, palmitic acid, erucic acid, arachic acid, myristic acid, lauric acid, caprynic acid, pelargonic acid, caprylic acid, enantic acid, caproic acid, valeric acid, and butyrric acid are used.

[0005] As regards the polyols that are used, these comprise molecules containing from 2-4 -OH groups that preferably form esters non containing hydrogen atoms in the β (beta) position relative to the carboxylic group. In a preferred aspect, to the purposes of the present invention, tri-methylolpropane (TMP) , neo-pentylglycol (NPG) , pentaerithrytol (PE), and glycerol (GLY) are used .

Particularly, it has been , seen that the ^"reactivity^" of such polyols follows the following trend:

PE-TMP > GLY > NPG.

[0006] More in detail, the catalysts used in the present invention comprise a silica (Si0₂) solid matrix comprising a co-oxide with Lewis acid characteristics. According to a preferred aspect, such co-oxide is an aluminium (A1₂0₃) , zirconium (Zr0₂), titanium (Ti0₂) , niobium (Nb₂0₅) , lantanium (La₂03) oxide.

According to a still more preferred aspect, such co- oxide is an aluminium (A1₂0₃) , titanium (Ti0₂) , and particularly zirconium (Zr0₂) oxide.

Furthermore, the content of such co-oxide in the silica matrix preferably ranges between about 0.3-15%, about and still more preferably between 2-7%, and in a still more preferred aspect, it is about 5% by weight on the total weight of the catalyst.

In fact, it has been noticed that below 5% (by weight on the total weight of the catalyst), the reaction speed, as well as the selectivity, decrease.

[0007] The preferred catalysts according to the invention are the following ones:

wherein "% co-oxide" indicates the percentage by weight of the co-oxide (zirconium, titanium, or aluminium co- oxide) relative to the total weight of the catalyst.

[0008] In a preferred aspect of the invention, the catalysts set forth above have preset porosity characteristics.

In fact, the following Table set forth the data relative to:

- BET - PV (pore volume)

- APR (pore average radius) .

[0009] In fact, it has been noticed that the preferred catalysts have the lowest BET/PV ratio.

Particularly, such catalysts have a BET/PV ratio ranging between about 100-900, preferably between about 150-650, and still more preferably between about 170- 360.

[0010] The catalysts described in the present patent application represent a further object of the invention .

[0011] According to a further object, a process for preparing fatty acid esters is described.

Such process comprises the step of reacting the fatty acid with the polyol in the presence of one of the catalysts described above, comprising silica oxide and a co-oxide selected from Zr0₂, Ti0₂, A1₂0₃, Nb₂0₅, and La₂0₃.

[0012] As regards the stoichiometric ratios between the fatty acid and the polyol, it has been seen that an excess of acid affords a quicker and more selective reaction, the unreacted acid being able to be separated subsequently .

For example, it is possible to use up to 5% of stoichiometric excess of acid relative to the polyol.

[0013] As regards the reaction temperature, it has been noticed that the reaction may be carried out between 150-250°C, while as regards the pressure, this is preferably a reduced pressure, for example, about 400 mbar .

[0014] In a preferred aspect, the reaction is further carried out under nitrogen flow, preferably ranging between 0.3-1.5 ml/min.

[0015] Advantageously, the process of the invention does not require the use of any reaction solvents.

[0016] As regards the amount of catalyst, this preferably ranges between 1 and 15% by weight (relative to the weight of the fatty acid) , preferably between 1.5 and 10% by weight, more preferably between 2 and 7% by weight. [0017] According to a further and particularly advantageous aspect of the invention, the catalyst used in the process for the esterification of fatty acids is retrieved at the end of the reaction, and it may be used again to carry out the same reaction.

In fact, it has been noticed that the catalyst may be reused 5 times more (for 6 times in total) , preserving in an optimal manner its catalytic properties.

Particularly, to this aim, the catalyst is separated from the medium after the reaction by filtration.

Before being reused, it is washed with a polar solvent; in fact, such catalyst does not need to be calcinated at 400°C before being reused.

[0018] As stated above, a further object of the invention is represented by the use of the compounds obtained according to the process of the present invention as a lubricant, cooling lubricant, or fluid for oleodynamic circuits.

[0019] Particularly preferred examples according to the present invention are described in the following experimental section.

Example 1

In a three-neck flask provided with a condenser, a thermometer, and a vacuum/gas inlet, 70 g of technical oleic acid are added (5% excess), 10,5 g TMP and 7 g silica-zirconia at 5% by weight of zirconia (cat A) . The mixture is heated at 200 °C, and through the tap, a reduced pressure of 400 mbar is applied. Withdrawals are made after lh, 2h, 4h, and 6h. From such withdrawals, the free acidity (FFA - Free Fatty Acid) is determined through acidimetric titration (EN 14104:2003) and the composition in tri- (tri) , di- (di) , and monoesters (mono) through a GC UNI 22053:1996 method.

The results are shown in the following Table.

Conversion: 99.8%. Selectivity: 94.9%.

As it is noticed after 6 h the conversion is complete, only the excess amount of acid (5%) being left.

The selectivity to triesters is very high.

Example 2

It is proceeded as in the Example 1, but using 3.5 g of cat A.

Conversion: 99,3%. Selectivity: 98,3% t (h) PFA (%) mono di tri

0 86.9 0 0 0

1 15.1 0.1 8.1 76.7

2 9.8 0.1 0.3 92.7

4 6.5 0.2 0 96.3

⁶ 5.7 0.1 0 97.6

Example 3

It is proceeded as in the Example 1, but using 1.75 g of cat A (in which, however, the catalyst is present at 2.5% by weight, instead of 5%).

Conversion: 99%. Selectivity: 90,9%.

Example 4

Reuse of the catalyst

It is proceeded as in the Example 3. After 6 h, the reaction mixture is hot filtered, the catalyst is washed with acetone and reused further 5 times (Ex. 4(2)- Ex. 4(6)).

The results are set forth in the following table.

FFA (%) (h)

Ex. Ex. Ex. Ex. Ex. Ex.

4 4(2) 4(3) 4(4) 4(5) 4(6)

0 86.9 86.9

1 20.4 22.3 23.1 22.5 22.4 23.5

2 13.5 13.2 15.1 14.9 14.1 15.1

4 9.0 10.2 9.3 9.2 8.3 9.0

6 7.3 6.9 7.8 7.2 6.4 7.1

Example 5

It is proceeded as in the Example 3, but using 11.1 g TMP (stoichiometric ratio) .

Conversion: 99,8%. Selectivity: 83,3%

The results are set forth in the following table. Even in the presence of stoichiometric amounts of acid, the reaction conversion is complete, although in longer times .

Example 5 bis It is proceeded as in the Example 5, but using 66 g oleic acid (i.e., in defect of acid).

Conversion: 99,1%. Selectivity: 88,4%.

The results are set forth in the following table. By operating in defect of acid, the reaction times to obtain a complete conversion do not increase further compared to the Example 5.

Example 6

It is proceeded as in the Example 2, but using the catalyst B (5% excess acid, 5% by weight cat.)

Conversion: 96.8%.

The results are set forth in the following table.

Example 7

It is proceeded as in the Example 5, but using the catalyst B.

The results are set forth in the following table.

Example 8

It is proceeded as in the Example 3, but using the catalyst C .

The results are set forth in the following table.

Example 9

It is proceeded as in the Example 5, but using the catalyst C.

The results are set forth in the following table. t (h) FFA (%)

0 -

2 19, 5

4 12, 1

8 6, 4

12 5,4

Example 10

It is proceeded as in the Example 2 (5% by weight catalyst, excess of acid) , but using the catalyst D. The results are set forth in the following table.

Example 11

It is proceeded as in the Example 5, but using the catalyst E.

The results are set forth in the following table.

10 9.6

Example 12

It is proceeded as in the Example 3, but using the catalyst F.

The results are set forth in the following table.

Example 13

It is proceeded as in the Example 3, but using the catalyst G.

The results are set forth in the following table.

Example 14

It is proceeded as in the Example 3, but using the catalyst H.

The results are set forth in the following table. t (h) FFA (%)

0 -

1 27.7

2 19.7

4 14.9

6 12.3

Example 15

It is proceeded as in the Example 3, but using 7,23 g of glycerol.

The results are set forth in the following table.

Example 16

It is proceeded as in the Example 5, but using 7.88 g of glycerol.

The results are set forth in the following table.

12 4.8

Example 17

It is proceeded as in the Example 15, but using the catalyst B.

The results are set forth in the following table.

Example 18

It is proceeded as in the Example 3, but using 12.3 g of neopentyl-glycol (NPG) .

The results are set forth in the following table.

Example 19

It is proceeded as in the Example 3, but using 8.0 g pentaerithrytol .

The results are set forth in the following table. t (h) FFA (%)

0 -

1 22.7

2 13.9

4 7.5

6 6.1

Example 20

It is proceeded as in the Example 18, but with the catalyst B.

The results are set forth in the following table.

Comparative Example 1

It is proceeded as in the Example 1, but using 0.14 g Zn.

The results are set forth in the following table.

6 7.7 0.8 2.5 89.0

Comparative Example 2

It is proceeded as in the Example 1, but using 0.18 g SnO as the catalyst.

The results are set forth in the following table.

[0020] The process of the present invention has a number of advantages that those skilled in the art will be able to appreciate.

For example, the catalysts described are easily and completely removable from the reaction product, also by single technologies, such as filtration or centrifugation . Operations such as a calcination are not needed.

[0021] Furthermore, as described above, the catalysts of the invention are recyclable, i.e., they may be reused (even up to 5 times) to catalyze the same esterification reaction without decreasing the performance . Such aspect, besides being environmentally friendly, allows containing the processing costs.

[0022] Furthermore, the fact that no neutralization step is needed, and that no inorganic salts to be disposed of are produced, is positive.

In this manner, the possible further conversion steps are not compromised.

[0023] A further advantages of the process of the present invention is given by the high selectivity leading to the formation of a completely esterified polyol as the main product.

Therefore, the obtained lubricants will be characterized by a high quality.

[0024] Furthermore, the used catalysts do not give rise to the formation of soaps, and generate few partial esters, thus conferring a good demulsibility to the product .

[0025] Again, it has to be mentioned that, since they do not contain tin, with the catalysts described no toxic products are formed, which would prevent the used of the esters of the invention, for example, in cosmetics .

[0026] From the description given above of the process according to the present invention, those skilled in the art, in order to meet contingent, specific needs, will be able to make a number of modifications, additions, or replacements of elements with functionally equivalent other ones, without however departing from the scope of the appended claims.

[0027] Each of the characteristics described as belonging to a possible embodiment may be implemented independently from the other embodiments described.

_{* * * * * * *}

Claims

1. A process for preparing esters of fatty acid with polyols comprising the step of reacting the acid with the polyol in the presence of a catalyst comprising silica oxide and a co-oxide selected from Zr0₂, Ti0₂, A1₂0₃, Nb₂0₅, and La₂0₃, said catalyst having a BET/PV ratio ranging between about 1ΌΌ-9ΌΌ, preferably between about 150-650, and still more preferably between about 170-360.

2. The process according to the preceding claim, wherein said catalyst comprises a co-oxide selected from Zr0₂, Ti0₂, A1₂0₃.

3. The process according to the claim 1, wherein said fatty acids are selected from C4-C24 fatty acids.

4. The process according to the claim 1, 2 or 3, wherein said acids are selected from oleic acid, stearic acid, palmitoleic acid, palmitic acid, erucic acid, arachic acid, myristic acid, lauric acid, caprynic acid, pelargonic acid, caprylic acid, enantic acid, caproic acid, valeric acid and butyrric acid.

5. The process according to any of the preceding claims, wherein said polyol is selected from tri- methylolpropane (TMP) , neopentylglycol (NPG) , pentaerithrytol (PE) and glycerol (GLY) .

6. The process according to any of the preceding claims, wherein said acid is present in excess compared to the stoichiometric ratio up to 5%.

7. The process according to any of the preceding claims, wherein in said catalyst the co-oxide is present in a percentage by weight ranging between 0.3- 15%, preferably ranging between 1-7^"%, and still more^' preferably ranging between 2-5% (weight of co- oxide/total weight of the catalyst).

8. The process according to any of the preceding claims, wherein the amount of catalyst ranges between 1 and 15% by weight, preferably between 1.5 and 10% by weight, more preferably between 2 and 7% by weight relative to the weight of the fatty acid.

9. The process according to any of the preceding claims, wherein the reaction is carried out at a temperature of about 150-250°C.

10. The process according to any of the preceding claims, wherein no solvent is used.

11. The process according to any of the preceding claims, comprising the further step of retrieving the catalyst from the reaction medium, optionally by filtration or centrifugation .

12. The process according to the preceding claim, wherein after the recovery of the catalyst, this is subjected to a washing step with a polar solvent.

13. The process according to any of the preceding claims, wherein said catalyst is selected from the following catalysts:

14. The process according to any of the preceding claims, wherein said catalyst is selected from the catalysts having the following characteristics:

D 285 0.80 80 356

E 354 0.4 - 885

F 483 1.43 117 337

G 455 0.71 62 640

H 330 1.90 - 173

15. Esters obtainable according to the process of any one of the preceding claims.

16. A catalyst comprising silica oxide and a co-oxide selected from Zr0₂, Ti0₂, AI2O3, Nb₂0₅, and La₂0₃, said catalyst having a BET/PV ratio ranging between about 100-900, preferably between about 150-650, and still more preferably between about 170-360.

17. The catalyst according to the preceding claim, wherein said co-oxide is selected from Zr0₂, Ti0₂, AI2O3.

18. The catalyst according to the claim 16 or 17, selected from:

H Si0₂-Ti0₂ 0.3

19. The catalyst according to the claim 17 or 18 having the following characteristics:

20. A catalyst obtainable by the process according to one of the claims 11 or 12.

21. A process for preparing fatty acid esters with polyols according to any of the claims 1 to 14, wherein the catalyst according to claim 20 is used.

22. Use of the esters obtainable according to the process of any of the preceding claims as a lubricant, cooling lubricant, or fluid for oleodynamic circuits, or in cosmetics.