EP3266857B1 - Method for the production of fatty acids by hydrolytic ester cleavage with high temperature water - Google Patents

Description

Field of the Invention

The invention relates to a process for the production of fatty acids by hydrolytic cleavage of fatty acid alkyl esters, in particular fatty acid methyl esters (FAME), or alternatively of fatty acid triglycerides contained in oils and fats of vegetable and animal origin, at high temperature and high pressure in the liquid phase without the addition of external, foreign substances as homogeneous or heterogeneous catalysts, and the processing of the cleavage product obtained to free fatty acids. The invention further relates to a plant for performing the method.

State of the art

The reverse reaction of the esterification is the so-called ester cleavage or ester hydrolysis. In this hydrolytic cleavage, one mole of water is consumed per mole of ester bond, one mole of free acid and alcohol being formed in each case. As a back reaction of the esterification, the hydrolysis is also an equilibrium reaction.

In oleotechnology, the hydrolytic cleavage of triglycerides, ie the hydrolytic cleavage of oils and fats of vegetable and animal origin, is one of them Procedure well known to those skilled in the art to produce free fatty acids. Triglycerides are hydrolytically split into glycerin and free fatty acids (FFA) with the addition and consumption of water at temperatures of 200 ° C and higher and corresponding water vapor pressure in the liquid phase. A technical embodiment of this process is, for example, the Lurgi split tower process. This type of reaction for ester cleavage is technically established and takes place with high efficiency, since the glycerin formed separates out of the reaction mixture as a separate phase during the reaction and thus promotes a shift in the reaction equilibrium in the direction of the target reaction product FFA. Further details on the known methods of hydrolytic cleavage of triglycerides can be found, for example, in Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, 1998 Electronic Release, keyword "Fatty Acids", chapter 3.2 "Fat splitting".

For the production of fatty acids by hydrolytic cleavage of fatty acid alkyl esters, in particular of fatty acid methyl esters (FAME), processes are described in the literature which counteract the establishment of an equilibrium by the evaporation of formed methanol from the reaction mixture. These methods work at low pressure, for example ambient pressure, in a temperature range of e.g. B. 70 to 150 ° C. Due to these low reaction temperatures, it is necessary to accelerate the reaction catalytically in order to achieve the desired high conversions based on the reaction times and residence times customary in industry.

For example, the patent publication describes DE 69321607 T2 a cleavage of a FAME mixture of methyl caprylate and methyl capronate in the range from 70 to 110 ° C., operated at ambient pressure, an acidic, homogeneously dissolved catalyst comprising alkylbenzenesulfonic acids being used. As with many homogeneously catalyzed processes, there is also the disadvantage of separating and working up to reuse the catalyst from the reaction mixture. A distillative workup of the reaction mixture under reduced pressure is also described here, with methanol, water and unreacted in a first stage Fatty acid methyl ester is removed. In a second stage, the FFA product is then separated from the catalyst and this is returned to the reaction system.

The patent publication GB 594 141 A describes a process for the production of free fatty acids. First, a triglyceride for hydrolysis is made. The hydrolysis is then carried out at a temperature of 240 to 250 ° C using liquid water.

Also in the publication " Hydrolysis of Vegetable Oils in Sub- and Supercritical Water ", Russel L. Holliday et al., Ind. Eng. Chem. Res. 1997, 36, 932-935 describes the use of water as a solvent and as a reactant for the hydrolysis of triglycerides.

C. da Silva and JV Oliveira describe in the Brazilian Journal of Chemical Engineering, Vol. 31, No. 02, 271-285 (2014 ), biodiesel production through non-catalytic, supercritical transesterification. of triglycerides with supercritical alcohols.

The patent publication WO 2009/075762 A1 describes a process for the production of biodiesel and fatty acid esters, the fatty acid source and the reagent used being soluble in one another to a limited extent.

The patent publication US 2002/0197687 A1 describes a process for the enzymatic cleavage of oils and fats in order to obtain fatty acids and glycerol.

The patent publication WO 2009/075762 A1 describes a process for the extraction of fatty acids from algae biomass by acid hydrolysis and extraction with an organic solvent.

The internet reference " Fat Splitting: For Production of Fatty Acids and Crude Glycerine ", 2008, http://www.lipico.com/processes_fat-splitting.html (found on September 10, 2018 ) describes oil splitting using high pressure steam at temperatures between 245 - 255 ° C and pressures between 55 - 60 bar.

In the U.S. patent US 4185027 is an acid-catalyzed process using sulfuric acid, toluene-p-sulfonic acid or acidic ion exchanger in a similar temperature range as in the DE 69321607 T2 described, with additional propionic acid being added as a short-chain carboxylic acid. This reacts with release of the fatty acid to methyl propionate. Here, too, the added short-chain carboxylic acid must be separated from the reaction mixture in addition to the catalyst. If ion exchangers are used as catalysts, the catalyst separation is simplified, but the conversions described are significantly lower compared to the conversions achieved with homogeneous catalysis (sulfuric acid, toluene-p-sulfonic acid) or high concentrations of, for example, 12 to 27 g ion exchanger per 100 g FAME required to achieve high sales in a reasonable time. In addition, the added propionic acid must also be finally removed from the reaction mixture in this variant.

Description of the invention

The present invention is therefore based on the object of specifying the simplest possible process for the production of fatty acids by hydrolytic cleavage of fatty acid alkyl esters at high temperature and high pressure in the liquid phase without the addition of external, foreign substances as homogeneous or heterogeneous catalysts, in which the disadvantages mentioned above do not occur or only to a minor extent.

This object is achieved by a method with the features of claim 1. Further refinements of the invention result from the respective subclaims.

1. a) Mittel zum Bereitstellen der Fettsäurealkylester oder der Fettsäuretriglyceride,
2. b) mindestens einen Hydrolysereaktor zum Umsetzen der Fettsäurealkylester oder der Fettsäuretriglyceride mit Wasser unter Hydrolysebedingungen bei Temperaturen von mindestens 200 °C, geeignet zum Einstellen eines Druckes, bei dem das Wasser bei der Reaktionstemperatur in flüssiger Phase vorliegt,
3. c) Mittel zum Ausleiten eines Spaltproduktes, umfassend freie Fettsäuren (FFA), Wasser, nicht umgesetzte Fettsäurealkylester und das entsprechende Alkanol, insbesondere Methanol, oder nicht umgesetzte Fettsäuretriglyceride und Glycerin,
4. d) eine Phasentrennvorrichtung, geeignet zum Auftrennen des Spaltproduktes unter Phasentrennungsbedingungen in eine freie Fettsäuren und nicht umgesetzte Fettsäurealkylester oder nicht umgesetzte Fettsäuretriglyceride umfassende leichte Phase und eine Wasser und Methanol oder Glycerin umfassende schwere Phase, Mittel zum Zuführen des Spaltproduktes zu der Phasentrennvorrichtung, Mittel zum Ausleiten der leichten Phase, Mittel zum Äusleiten der schweren Phase,
5. e) eine nach einem thermischen Trennverfahren arbeitende, erste Trennvorrichtung, geeignet zum Auftrennen der leichten Phase in ein an freien Fettsäuren angereichertes, erstes Trennprodukt und in ein an nicht umgesetzten Fettsäurealkylestern oder an nicht umgesetzten Fettsäuretriglyceriden angereichertes, zweites Trennprodukt, wobei das zweite Trennprodukt ferner einen Anteil an freien Fettsäuren enthält, Mittel zum Zuführen der leichten Phase in die erste Trennvorrichtung, Mittel zum Ausleiten eines ersten Trennprodukts aus der ersten Trennvorrichtung, Mittel zum Ausleiten eines zweiten Trennprodukts aus der ersten Trennvorrichtung,
6. f) Mittel zum Ausleiten des ersten Trennprodukts als FFA-Produkt,
7. g) Mittel zum Rückführen mindestens eines Teils des zweiten Trennprodukts zum mindestens einen Hydrolysereaktor.

The scope of the present invention is limited only by the claims.

1. a) means for providing the fatty acid alkyl esters or the fatty acid triglycerides,
2. b) at least one hydrolysis reactor for reacting the fatty acid alkyl esters or the fatty acid triglycerides with water under hydrolysis conditions at temperatures of at least 200 ° C., suitable for setting a pressure at which the water is in the liquid phase at the reaction temperature,
3. c) agents for discharging a cleavage product, comprising free fatty acids (FFA), water, unreacted fatty acid alkyl esters and the corresponding alkanol, in particular methanol, or unreacted fatty acid triglycerides and glycerol,
4. d) a phase separation device suitable for separating the cleavage product under phase separation conditions into a light phase comprising unconverted fatty acid alkyl esters or unconverted fatty acid triglycerides and a heavy phase comprising water and methanol or glycerol, means for feeding the cleavage product to the phase separation device, means for discharging the light phase, means for discharging the heavy phase,
5. e) a first separation device working according to a thermal separation process, suitable for separating the light phase into a first separation product enriched in free fatty acids and in a second separation product enriched in unreacted fatty acid alkyl esters or in unreacted fatty acid triglycerides, the second separation product further comprising Contains free fatty acids, means for feeding the light phase into the first separation device, means for discharging a first separation product from the first separation device, means for discharging a second separation product from the first separation device,
6. f) means for discharging the first separation product as an FFA product,
7. g) means for recycling at least a part of the second separation product to the at least one hydrolysis reactor.

Hydrolysis conditions are understood to mean those reaction conditions which bring about at least a partial conversion, preferably a technically or economically relevant conversion of the fatty acid alkyl esters or the fatty acid triglycerides to free fatty acids. The person skilled in the art will be familiar with hydrolysis conditions known from the prior art select and, if necessary, modify them on the basis of routine tests in order to adapt them to other boundary conditions of the process implementation.

External substances which are foreign to the process are understood to be those substances which do not participate as reaction partners in the hydrolysis reaction or - in their reversal - in the esterification reaction and therefore do not appear in the corresponding reaction equations.

The terms "light phase" and "heavy phase" refer to the respective density (the "specific weight") of the two liquid phases obtained from the cleavage product under phase separation conditions.

Phase separation conditions are understood to mean all physico-chemical parameters which enable, favor or accelerate the formation of the two liquid phases obtained from the fission product. Important parameters in this context are the temperature and the strength of the gravitational field (e.g. earth's gravity or higher gravitational effect, for example during centrifugation).

Thermal separation processes are understood to mean all separation processes which are based on the establishment of a thermodynamic phase equilibrium. In particular, in the context of the present invention, this is distillation or rectification, which make use of the evaporation equilibrium of the substances involved.

If it is required that the separation be carried out in such a way that the second separation product also contains a proportion of free fatty acids, the person skilled in the art will be able to design the underlying thermal separation process in such a way that this objective is achieved. Thus, when using the distillation, he will select the temperature profiles in the distillation apparatus, the reflux ratio and the mass flows of the top product and the bottom product accordingly.

Means for introducing, discharging, feeding, returning etc. are understood to mean all means which serve this purpose, that is to say in particular, but not exclusively, pipelines, pumps, compressors and intermediate containers.

In particular when the reaction is carried out continuously, all parts of the system are in fluid communication with one another. A fluid connection between two system parts is understood to mean any type of connection that enables a fluid, for example the reaction mixture, the cleavage product or the individual separation products, from which one to the other of the two system parts can flow, irrespective of any intermediate areas or components ,

The person skilled in the art will select a suitable reaction apparatus as the hydrolysis reactor. In particular, these are reaction apparatuses with high mixing or backmixing. Therefore, in the case of batchwise reaction control, in particular stirred reactors, in the case of continuous stirred reactors, for example, continuous stirred tank reactors, stirred tank cascades or tower reactors with segmental mixing (split tower) are suitable. These are to be designed in such a way that they are suitable for setting the required pressure, which is achieved, among other things, by selecting appropriate wall thicknesses and providing suitable pressure-maintaining members.

The invention is based on the finding that the hydrolytic cleavage of fatty acid alkyl esters and fatty acid triglycerides can be accelerated autocatalytically. As soon as the first, minor conversion to the reaction products takes place (initiation phase), the free fatty acid formed acts as a catalyst for the hydrolysis reaction due to its acidity, which subsequently accelerates the ester cleavage. In terms of time, there is a typical S-shaped course of the sales curve.

By carrying out the separation of the light phase of the cleavage product in such a way that a certain proportion of free fatty acid is still present in the fraction which also contains the unconverted fatty acid alkyl esters and fatty acid triglycerides, and the subsequent recycling of at least part of this fraction into the Hydrolysis reaction, a portion of free fatty acid enters the hydrolysis reactor and can accelerate the reaction rate of the hydrolysis there.

It should be noted that the equilibrium position of the hydrolysis reaction is shifted to the starting materials by adding free fatty acid as the reaction product. In view of the small amounts of free fatty acid required for the catalytic effect, this effect can only be assessed as minor. Overall, the higher reaction speed results in economic advantages. These are particularly noticeable when the reaction is carried out continuously, for example in a continuous stirred tank reactor, a stirred tank cascade or another continuous reaction apparatus with high backmixing: in the steady state, the fresh, ie. H. unreacted starting materials to a non-zero concentration of free fatty acid as a catalyst in the hydrolysis reactor. As a result, the initiation phase is skipped and the sales curve over time rises steeply. The reactor size required is therefore reduced in order to achieve a defined final conversion.

If the reaction is carried out in batches, the invention can be applied, for example, in such a way that a part of the free fatty acids obtained is retained from a previous reaction batch and then added to a subsequent reaction batch as a catalyst.

Preferred embodiments of the invention

A preferred embodiment of the method according to the invention provides that the separation of the light phase (step e)) and / or the recycling of at least part of the second separation product to the reaction step b) (step g)) take place in such a way that during the reaction step b) The proportion of free fatty acids, based on the proportion of fatty acid alkyl esters or fatty acid triglycerides, is> 0 to 10% by weight, preferably 0.1 to 8% by weight, most preferably 0.5 to 5% by weight. It has been shown that in these free fatty acid concentration ranges there is a favorable compromise between the catalytic acceleration of the reaction on the one hand and the negative influence on the equilibrium position on the other hand is obtained.

In a further preferred embodiment of the process according to the invention, reaction step b) is carried out at a temperature of at least 220 ° C., preferably at least 240 ° C., most preferably at least 260 ° C. These reaction temperatures represent favorable compromises between high reaction rates, incipient side reactions due to thermal decomposition of the substances involved and technical expenditure for maintaining pressure in order to keep water in the liquid phase.

In a preferred embodiment of a process for the production of fatty acids by hydrolytic cleavage of fatty acid methyl esters (FAME), the heavy phase comprising methanol obtained in step d) is fed to a second separation device which operates according to a thermal separation process and into a third separation product enriched in methanol and separated into a fourth separation product enriched in water, the third separation product being discharged from the process as a methanol product and the fourth separation product being at least partially returned to the reaction step b). In this way, the use of fresh water as a starting material is reduced and, if necessary after further processing, it contains a marketable methanol product as a by-product. Alternatively or additionally, methanol can already be discharged from the reaction apparatus as a top product. As a result, the reaction equilibrium is shifted towards the cleavage products and thus the hydrolysis reaction is promoted.

In a further aspect of the invention, in a process for the production of fatty acids by hydrolytic cleavage of fatty acid methyl esters (FAME), the cleavage product obtained in reaction step b) is first fed to the second separation device in which a top product enriched in methanol is selectively separated from the cleavage product and as methanol -Product is derived from the process. This will also contain a marketable methanol product as a by-product, if necessary after further processing. Alternatively or additionally, methanol can already be discharged as a top product from the reaction apparatus. As a result, the reaction equilibrium is shifted towards the cleavage products and thus the hydrolysis reaction is promoted. Furthermore, the quantity or the quantity flow of the fission product is reduced, so that the subsequent phase separation device can be made smaller. If the fission product freed from part of the methanol is to be cooled before being introduced into the phase separation device in order to promote phase separation, the quantity of cooling energy additionally reduced by the quantity reduction.

It is particularly preferred that the second separation device is designed as a relaxation stage (flash), which is preferably designed and operated adiabatically. As a result, the fission product freed from part of the methanol is already precooled before being introduced into the phase separation device, so that the required amount of cooling energy is reduced. In particularly favorable cases, in which the adiabatic relaxation already provides a sufficient cooling effect, a cooling device upstream of the phase separation device can thereby be completely dispensed with. However, it is generally preferred that a cooling device upstream of the phase separation device is also present, since this results in greater degrees of freedom with regard to the setting of the temperature in the phase separation device.

In a further development of the two preferred embodiments discussed above, the cleavage product depleted in methanol is fed to the phase separation device and there separated under phase separation conditions into a light phase comprising free fatty acids and unreacted fatty acid alkyl esters and a heavy phase comprising water and methanol, the heavy phase being at least partially Implementation step b) returned and the light phase is fed to the first separation device. The previous removal of part of the methanol from the cleavage product improves and facilitates phase separation in the phase separation device, since methanol acts as a solubilizer between the light, organic or non-polar and the heavy, aqueous or polar phase and thus impedes phase separation.

The phase separation conditions preferably comprise cooling the cleavage product or the cleavage product depleted in methanol to a temperature of 220 220 ° C., preferably 200 200 ° C., most preferably 180 180 ° C. As a result, the phase separation in the phase separation device is further improved and facilitated. The improvement and simplification of the phase separation is understood to mean the formation of a sharp, well-defined phase boundary in the shortest possible time.

With regard to the aforementioned aspect of the invention, the cooling is effected by a cooling device upstream of the phase separation device and / or by the fact that the removal of the methanol-enriched top product from the cleavage product is carried out adiabatically. As a result of the adiabatic cooling, the fission product freed from part of the methanol is already pre-cooled before being introduced into the phase separation device, so that the required amount of cooling energy is reduced. In particularly favorable cases, in which the adiabatic relaxation already provides a sufficient cooling effect, a cooling device upstream of the phase separation device can be completely dispensed with. In other cases, the remaining cooling is carried out by a cooling device connected upstream of the phase separation device, which, however, can be made smaller due to the adiabatic pre-cooling.

In a preferred embodiment of the process according to the invention, when the fatty acid methyl ester is reacted with water in step b), the ratio of water to fatty acid methyl ester is at least 2 mol / mol, preferably at least 10 mol / mol, most preferably at least 20 mol / mol. It has been shown that a favorable compromise between the desired high degrees of conversion and the required reactor volume is achieved in this way.

In a special embodiment of the plant for the production of fatty acids by hydrolytic cleavage of fatty acid methyl esters (FAME), this includes a second separation device suitable for separating the heavy phase into a third separation product enriched with methanol and into a fourth separation product enriched with water, means for feeding the heavy phase into the second separation device, means for discharging the third separation product from the second separation device and for discharging from the plant as a methanol product, means for discharging the fourth separation product from the second separation device, means for returning at least a part of the fourth separation product to the at least one hydrolysis reactor. In this way, the use of fresh water as a starting material is reduced and, if necessary after further processing, it contains a marketable methanol product as a by-product.

Preferably, the plant for the production of fatty acids by hydrolytic cleavage of fatty acid methyl esters (FAME) further comprises means for feeding the cleavage product obtained in the at least one hydrolysis reactor to the second separation device, means for selectively separating an overhead product enriched in methanol from the cleavage product, means for discharging the Methanol-enriched top product from the plant as a methanol product. This will also contain a marketable methanol product as a by-product, if necessary after further processing. Furthermore, the quantity or the quantity flow of the fission product is reduced, so that the subsequent phase separation device can be made smaller. If the fission product freed from part of the methanol is to be cooled before being introduced into the phase separation device in order to promote phase separation, the quantity of cooling energy additionally reduced by the quantity reduction.

With regard to the configuration of the system discussed last, it is particularly preferred if the second separation device is designed as a relaxation stage (flash), preferably as an adiabatic relaxation stage. As a result, the fission product freed from part of the methanol is already precooled before being introduced into the phase separation device, so that the required amount of cooling energy is reduced. In particularly favorable cases, in which the adiabatic relaxation already provides a sufficient cooling effect, one of the Phase separation device upstream cooling device completely eliminated. However, it is generally preferred that a cooling device upstream of the phase separation device is also present, since this results in greater degrees of freedom with regard to the setting of the temperature in the phase separation device.

In a further aspect of the plant for the production of fatty acids by hydrolytic cleavage of fatty acid methyl esters (FAME), this further comprises means for feeding the cleavage product depleted in methanol to the phase separation device, means for returning at least part of the heavy phase to the at least one hydrolysis reactor, means for feeding the easy phase to the first separator. The removal of some of the methanol from the cleavage product improves and facilitates phase separation in the phase separation device, since methanol acts as a solubilizer between the light, organic or non-polar and the heavy, aqueous or polar phase.

The system preferably further comprises a cooling device upstream of the phase separation device. This can be used advantageously if the cooling effect of the adiabatic relaxation stage for the partial separation of methanol alone is not sufficient to achieve good and rapid phase separation in the phase separation device.

Execution and numerical examples

Further developments, advantages and possible uses of the invention also result from the following description of exemplary embodiments and numerical examples and the drawings.

Fig. 1

die schematische Darstellung des erfindungsgemäßen Verfahrens bzw. der Anlage nach einer ersten Ausgestaltung,

Fig. 2

die schematische Darstellung des erfindungsgemäßen Verfahrens bzw. der Anlage nach einer zweiten Ausgestaltung.

Show it:

Fig. 1

the schematic representation of the method according to the invention or the system according to a first embodiment,

Fig. 2

the schematic representation of the method according to the invention or the system according to a second embodiment.

In the in Fig. 1 The schematic flow diagram shown in a first embodiment of the process or plant according to the invention, the fatty acid methyl ester (FAME) and water (H ₂ O) are fed via lines 1 and 2 to the hydrolysis reactor 3. The hydrolysis reactor, which is only indicated schematically, operates continuously with vigorous backmixing and is designed, for example, as a continuous stirred tank reactor. Part of the water required for the ester hydrolysis can also be introduced as steam into the hydrolysis reactor. This is preferably done in a way that additionally contributes to the mixing of the liquid reaction mixture, for example by blowing into the liquid mixture. If necessary, the steam also serves as a heat carrier for heating the reactor contents.

The reactor pressure is selected so that the reaction mixture remains in the liquid phase at the reaction temperature set by a heating device (not shown). The pressure is adjusted in a known manner via the vapor pressure of the components involved and, if appropriate, additionally by adding an inert gas.

After reaching a certain final conversion, the cleavage product leaves the hydrolysis reactor via line 4, is cooled in the cooling device 5 and then fed to the phase separation device 7 via line 6. In the example shown, the phase separation device is a simple container with overflows and drains for a heavy and a light liquid phase, in which the phase separation is gravitationally driven due to the different density of the two liquid phases.

The light, non-polar phase, which contains the free fatty acid product (FFA) and unreacted fatty acid methyl ester, is removed from the phase separation device via line 8 and introduced into the first separation device, which in the example shown is designed as a distillation. When the light phase is separated by distillation, a fraction enriched in free fatty acids is obtained (first separation product) and is discharged from the process as an FFA product via line 10. The remaining fraction (second separation product), which is returned via lines 11 and 1 to the hydrolysis reactor 3, contains not only unreacted fatty acid methyl ester but also traces of methanol and significant proportions of free fatty acid. After the latter has been returned to the hydrolysis reactor, it acts as a catalyst for the conversion of further fatty acid methyl esters to free fatty acid.

The heavy, polar phase, which contains unreacted water and methanol as a by-product of the ester hydrolysis, is removed via line 12 from the phase separation device 7 and introduced into the second separation device 13, which in the example shown is also equipped as a distillation. When the heavy phase is separated by distillation, a methanol product (MeOH) (third separation product) is obtained as the top product of the distillation, which is discharged from the process via line 14 and, if appropriate, fed to further processing. A water-enriched fraction is obtained as the bottom product (fourth separation product), which is returned via lines 15 and 2 to the hydrolysis reactor 3.

In the in Fig. 2 shown, schematic representation of a second embodiment of the method according to the invention or the system corresponds to the process sequence up to reference number 3 that in Fig. 1 , After reaching a certain final conversion, the cleavage product leaves the hydrolysis reactor via line 4, but is now adiabatically expanded (flash) by means of expansion valve 16 and introduced into the second separation device 13a via line 17, which in this case acts as a simple phase separation device for separating a gaseous phase enriched in methanol (third separation product) is designed from a liquid phase depleted in methanol (fourth separation product). As the top product of the phase separation device 13a receive a methanol product (MeOH) (third separation product) which is discharged from the process via line 14 and, if appropriate, fed to further processing.

Because of the adiabatic expansion, the temperature of the fourth separation product is lower than that of the cleavage product leaving the hydrolysis reactor 3. As a result, the cooling device 5, to which the liquid phase depleted in methanol is fed via line 18, can be designed to be smaller in terms of the cooling power required to set a defined temperature in the phase separation device 7.

The liquid phase depleted in methanol of the phase separation device 7 is fed in via line 6, the properties and mode of operation of which largely correspond to those described in Fig. 1 was explained. However, the phase separation is compared to that in FIG Fig. 1 Design shown easier or faster because methanol was previously removed from the liquid phase, which acts as a solubilizer between the polar and the non-polar phase and thus complicates the phase separation. Due to the faster phase separation, the phase separation device 7 can thus Fig. 2 shown configuration can be designed smaller.

In the separation by distillation in the first separation device 9, to which the light phase is fed via line 8, a fraction enriched in free fatty acids is obtained (first separation product), which is discharged from the process as a FFA product via line 10. The remaining fraction (second separation product), which is returned via lines 11 and 1 to the hydrolysis reactor 3, contains not only unreacted fatty acid methyl ester but also traces of methanol and significant proportions of free fatty acid. After the latter has been returned to the hydrolysis reactor, it acts as a catalyst for the conversion of further fatty acid methyl esters to free fatty acid.

The heavy, polar phase discharged from the phase separation device 7 via line 12, which contains unreacted water and methanol as a by-product of the ester hydrolysis, is returned via line 12 and line 2 to the hydrolysis reactor 3.

Of all recycle streams in the Fig. 1 and Fig. 2 The exemplary embodiments shown can be discharged and discarded (purge) in order to prevent the accumulation of impurities and other undesirable components.

In both of the exemplary embodiments discussed, it is possible to discharge a methanol-rich stream as top product from the reaction apparatus via a line (not shown). As a result, the reaction equilibrium is shifted towards the cleavage products and thus the hydrolysis reaction is promoted.

Numerical examples reaction parameters

To demonstrate the hydrolysis reaction, tests were carried out in an autoclave with different test parameters and FAME chain lengths. The reaction mixture was stirred at a stirrer rotation speed of 500 min ^-1 . The test results obtained are summarized in Table 1.

Within the test series 1, a clear acceleration in the course of sales with increasing temperature can be seen. At 240 and 260 ° C an identical final state is reached, while at 220 ° C the observation time was not sufficient to achieve this.

The effect of discharging methanol using flash evaporation during the reaction is shown by the comparison between Examples 1c and 2a. The conversion achieved is about 5% higher at the end state of the reaction mixture when methanol has been removed from the equilibrium. <b> Table 1: </b> FAME turnover depending on the reaction time, temperature and water FAME ratio Attempt. No. 1a 1b 1c 2a 2 B 2c 3a 3b 3c 4a 4b FAME chain length C8 C8 C8 C8 C8 C8 C8 C8 C8 C10 C10 Water / FAME * 16 16 16 16 8th 2 24 16 8th 16 8th T / ° C 220 240 260 260 260 260 240 240 240 260 260 MeOH-discharge ** Yes Yes Yes No No No No No No No No Response time / h FAME sales 0.5 h 2% 5% 24% 21% 12% 5% 7% 10% 3% 12% 10% 1.0 h 7% 23% 60% 63% 43% 32% 26% 33% 13% 44% 41% 1.5 h 19% 61% 74% 73% 61% 44% 52% 58% 37% 68% 58% 2.0 h 35% 76% 78% 75% 63% 45% 72% 72% 52% 71% 62% 3.0 h 58% 80% 80% 75% 63% 45% 77% 75% 62% 72% 63% 4.0 h 67% 80% 80% 75% 63% 45% 79% 75% 62% 72% 63% * Water / FAME ratio [mol water per mol FAME]
** During the reaction, methanol was evaporated from the reaction mixture by reducing the pressure (flash)

Test series 2 and 3 show the effect of the water / FAME ratio. The amount of conversion achieved in the final state is increasingly associated with an increased amount of water. With identical water / FAME ratios, an increase in temperature shortens the reaction time required to reach this final state.

The effect of the FAME chain length becomes clear when comparing experiments 2a and 2b with experiments 4a and 4b. Under otherwise identical conditions, sales are achieved at a comparable level after an identical response time.

The experiments were repeated at different stirrer rotation speeds. Within the first two hours of testing, faster increases in the turnover curve over time occurred at higher stirrer rotation speeds. Each after 2 h, however, an identical final state of the conversion was achieved in all experiments.

Catalytic influence of free fatty acids (FFA)

To demonstrate the catalytic influence of free fatty acids on the hydrolysis reaction, further tests were carried out in an autoclave at different temperatures under otherwise identical conditions both with and without the addition of FFA. The amount of FFA added was 5.28% g / g, based on the amount of C ₁₀ -FAME used, which corresponds to an FFA concentration of 5% by weight in FAME, or approximately 3% by weight the entire reaction mixture corresponded. The reaction mixture was stirred at 500 min ^-1 . The results obtained are summarized in Table 2 below.

Test series 6 served as a reference since an FFA addition was not used here. A significant delay in the course of sales with decreasing temperature was evident within test series 6. In contrast to the results with C ₈ -FAME (cf. Table 1, experimental areas 1a to 1b), an identical final state was not achieved at the varying temperature from 240 to 260 ° C.

A comparison with test series 7 (with FFA addition) reveals the catalytic effect of the free fatty acid at the start of the reaction. Here a constant final state was reached after only 2 h, whereas in test series 6 this was only reached after 3 h (test 6b + 6c).

The level of the FAME turnover at the end state in the experiments with the addition of FFA decreases proportionally to the concentration of the added FFA in the FAME, since the FFA concentration at the end state of the reaction occurs due to equilibrium and thus leads to a limitation of the maximum FAME turnover , <b> Table 2: </b> FAME conversion depending on the reaction time and temperature with and without FFA as a catalyst Attempt. No. 6a 6b 6c 7a 7b 7c FAME chain length C10 C10 C10 C10 C10 C10 Water / FAME * 9.5 9.5 9.5 9.5 9.5 9.5 T / ° C 260 250 240 260 250 240 MeOH-discharge ** No No No No No No FFA Booster No No No Yes Yes Yes Response time / h FAME sales 0.5 h 7% 4% 1 % 45.1% 30% 23% 1.0 h 41% 23% 8th % 62.0% 53% 46% 1.5 h 64% 52% 27% 64.1% 58% 54% 2.0 h 68% 61% 48% 64.4% 60% 57% 3.0 h 68% 64% 60% 64.4% 60 57% 4.0 h 68% 64% 60% 64.4% 60% 57% * Water / FAME ratio [mol water per mol FAME]
** During the reaction, methanol was evaporated from the reaction mixture by reducing the pressure (flash)

Phase separation of the reaction mixture at the final state from experimental example 2a

The reaction mixture from experimental example 2a (see Table 1) with a water / FAME ratio of 16 mol / mol was generated in an autoclave equipped with a sight glass. This enabled the observation of phase quantities and the targeted sampling of the individual phases. Due to the good solubility ratios of the relatively short-chain reactants and products to one another (in this case C ₈ -FAME as starting material), a homogeneous reaction mixture formed at the end state of the reaction. When this homogeneous reaction mixture cooled, a beginning phase formation was observed from 224 ° C (cloud point). The cooling was continued successively and the phases that formed were each determined and analyzed volumetrically (see Table 3). <b> Table 3: </b> phase formation and phase composition; Reaction mixture from experimental example 2a Example No. 2a / 1 2a / 2 2a / 3 Phase portion above 50% vol 46% vol 43% vol FFA + FAME-rich easy phase % w / w % w / w % w / w water 33.8 26.2 18.6 methanol 4.3 4.3 3.8 FAME 18.2 20.9 23.2 FFA 43.7 48.6 54.4 Reaction mixture at the final stage of the cleavage reaction Cooling down to 217 ° C Cooling down to 199 ° C Cooling down to 177 ° C % w / w water 64.2 methanol 5.3 FAME 8.3 FFA 22.2 Phase portion below 50% vol 54% vol 57% vol heavy phase rich in water + methanol % w / w % w / w % w / w water 89.1 92.1 93.2 methanol 5.9 5.7 5.9 FAME 1.1 0.4 0.2 FFA 3.9 1.8 0.7

The formation of an FFA- and FAME-rich light phase as well as a water- and methanol-rich heavy phase was observed. With decreasing phase separation temperature (2a / 1> 2a / 2> 2a / 3) the separation was completed in such a way that further enrichment of FFA and FAME occurred in the light phase and further enrichment of water and methanol in the heavy phase.

Phase separation of the reaction mixture at the final state from experimental example 2b

The reaction mixture from experimental example 2b (preparation see Table 1) with a water / FAME ratio of 8 mol / mol was generated in an autoclave equipped with a sight glass. This enabled the observation of phase quantities and the targeted sampling of the individual phases. Due to the good solubility ratios of the relatively short-chain reactants and products to one another (in this case C ₈ -FAME as starting material), a homogeneous mixture was also formed here at the end state of the reaction Reaction mixture. When this homogeneous reaction mixture cooled, a beginning phase formation was observed from 227 ° C (cloud point). The cooling was continued successively and the phases that formed were each determined and analyzed volumetrically (see Table 4).

Again, the formation of an FFA- and FAME-rich light phase and a water- and methanol-rich heavy phase was observed. Here, too, the separation was completed with decreasing phase separation temperature (2b / 1> 2b / 2> 2b / 3) so that there was further enrichment of FFA and FAME in the light phase and further enrichment of water and methanol in the heavy phase came. An exception here is the heavy and water-rich heavy phase in Example 2b / 3. When cooling to 180 ° C, a turbidity (emulsion) was observed, which explains the difference in its composition. <b> Table 4: </b> phase training and its phase composition; Reaction mixture from experimental example 2b Example No. 2b / 1 2b / 2 2b / 3 Phase share above not determined 52% vol 61% vol FFA + FAME-rich easy phase % w / w % w / w % w / w water 30.5 22.6 17.5 methanol 6.3 5.7 5.4 FAME 28.8 29.3 33.5 FFA 34.3 42.5 43.5 Reaction mixture at the final stage of the cleavage reaction Cooling down to 215 ° C Cooling down to 197 ° C Cooling down to 180 ° C % w / w water 43.1 methanol 6.8 FAME 19.9 FFA 30.1 Phase portion below not determined 48% vol 39% vol heavy phase rich in water + methanol % w / w % w / w % w / w water 86.9 89.5 84.6 methanol 8.1 8.1 8.3 FAME 1.8 0.7 3.7 FFA 3.2 1.7 3.4

Commercial applicability

The invention provides a method with which free fatty acids can be obtained in a simple manner by hydrolytic cleavage of fatty acid alkyl esters, in particular fatty acid methyl esters (FAME), or alternatively of fatty acid triglycerides contained in oils and fats of vegetable and animal origin. Since the process does not require the use of external, non-process substances as homogeneous or heterogeneous catalysts, special economic and ecological advantages are obtained since no catalysts have to be recovered from the cleavage product and subsequently have to be regenerated or disposed of in a complex manner. The autocatalytic effect of the free fatty acids added to the reaction mixture allows a reduction in the size of the reaction apparatus used in order to achieve a fixed production rate.

LIST OF REFERENCE NUMBERS

[1]

management

[2]

management

[3]

hydrolysis reactor

[4]

management

[5]

cooler

[6]

management

[7]

Phase separator

[8th]

management

[9]

first separation device (distillation)

[10]

management

[11]

management

[12]

management

[13]

second separation device (distillation)

[13a]

second separation device (phase separation device, flash)

[14]

management

[15]

management

[16]

expansion valve

[17]

management

[18]

management

Claims (10)

1. Method for the fabrication of fatty acids by hydrolytic cleavage of fatty acid alkyl esters, more particularly fatty acid methyl esters (FAME), comprising the following steps:

   a) providing the fatty acid alkyl esters,

   b) reacting the fatty acid alkyl esters with water under hydrolysis conditions at temperatures of at least 200°C, wherein the pressure is chosen such that the water is present in liquid phase and wherein no external substance extraneous to the method is added as homogeneous or heterogeneous catalyst,

   c) discharging a cleavage product, comprising free fatty acids (FFA), water, unconverted fatty acid alkyl esters and the corresponding alkanol, in particular methanol,

   d) feeding the cleavage product to a phase separation device and separating the cleavage product under phase separation conditions into a light phase comprising free fatty acids and unconverted fatty acid alkyl esters and a heavy phase comprising water and methanol,

   e) feeding the light phase into a first separation device that works by a thermal separation method and separating the light phase into a first separation product enriched in free fatty acids and into a second separation product enriched in unconverted fatty acid alkyl esters, wherein the separation is conducted in such a way that the second separation product further contains a proportion of free fatty acids,

   f) discharging the first separation product as FFA product,

   g) returning at least a portion of the second separation product to reaction step b).
2. Method according to claim 1, characterised in that the separation of the light phase (step e)) and/or the return of at least a portion of the second separation product to reaction step b) (step g)) are effected in such a way that, during reaction step b), the proportion of free fatty acids, based on the proportion of fatty acid alkyl ester, is > 0 to 10 wt.%, preferably 0.1 to 8 wt.%, most preferably 0.5 to 5 wt.%.
3. Method according to claim 1 or 2, characterised in that the reaction step b) is conducted at a temperature of at least 220°C, preferably at least 240°C, most preferably at least 260°C.
4. Method according to any of claims 1 to 3 for the fabrication of fatty acids by hydrolytic cleavage of fatty acid methyl esters (FAME), characterised in that the methanol-comprising heavy phase obtained in step d) is fed to a second separation device that works by a thermal separation method and is separated into a methanol-enriched third separation product and into a water-enriched fourth separation product, the third separation product being discharged from the method as methanol product and the fourth separation product being at least partly returned to the reaction step b).
5. Method according to any of claims 1 to 3 for the fabrication of fatty acids by hydrolytic cleavage of fatty acid methyl esters (FAME), characterised in that the cleavage product obtained in step b) is first fed to the second separation device in which a methanol-enriched top product is selectively separated from the cleavage product and discharged from the method as methanol product.
6. Method according to claim 5, characterised in that the second separation device is configured as an expansion stage (flash) which is preferably configured and operated in an adiabatic manner.
7. Method according to claim 5 or 6, characterised in that the methanol-depleted cleavage product is fed to the phase separation device and separated there under phase separation conditions into a light phase comprising free fatty acids and unconverted fatty acid alkyl esters and a heavy phase comprising water and methanol, the heavy phase being at least partly returned to the reaction step b) and the light phase being fed to the first separation device.
8. Method according to any of the preceding claims, characterised in that the phase separation conditions comprise cooling the cleavage product or the methanol-depleted cleavage product to a temperature of ≤ 220°C, preferably ≤ 200°C, most preferably ≤ 180°C.
9. Method according to claim 8, characterised in that the cooling is brought about by means of a cooling device upstream of the phase separation device and/or by virtue of the separation of the methanol-enriched top product from the cleavage product being conducted adiabatically.
10. Method according to any of the preceding claims, characterised in that the ratio of water to fatty acid methyl ester in the reaction of the fatty acid methyl ester with water in step b) is at least 2 mol/mol, preferably at least 10 mol/mol, most preferably at least 20 mol/mol.

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