EP2205708A1

EP2205708A1 - Continuous method for the heterogenically catalyzed esterification of fatty acids

Info

Publication number: EP2205708A1
Application number: EP08844944A
Authority: EP
Inventors: Dieter Heinz; Leslaw Mleczko; Shaibal Roy; Heinrich Morhenn; Wulf Dietrich
Original assignee: Bayer Technology Services GmbH
Current assignee: Rohm and Haas Chemicals LLC
Priority date: 2007-10-30
Filing date: 2008-10-16
Publication date: 2010-07-14
Also published as: IL204938A0; NZ584970A; HN2010000893A; US20100249442A1; SV2010003551A; AU2008318001A1; PA8799301A1; CN101842471B; IL204938A; BRPI0819144A8; CO6270372A2; UY31390A1; AR071058A1; WO2009056231A1; US8299282B2; MX2010004519A; ZA201002942B; EA018797B1; CR11400A; PE20090934A1

Abstract

The invention relates to a continuous method for the esterification of free fatty acids in plant and animal fats with alcohols using a heterogenic acid catalyst.

Description

Continuous process for heterogeneously catalyzed esterification of fatty acids

The invention relates to a continuous process for the esterification of free fatty acids in vegetable and animal fats with alcohols using a heterogeneous acidic catalyst.

Vegetable and animal fat and oils often contain significant amounts of free fatty acids. Of the

Depending on the source of the fatty raw material, the content of free fatty acids can be between 0 and 100% by weight. In the case of biodiesel production processes, this proportion of free fatty acids can not be converted into the corresponding fatty acid methyl esters by transesterification of triglycerides with methanol and leads to yield losses or to the fact that raw materials with a high content of free fatty acids are not suitable for biodiesel production.

Therefore, a pretreatment of the fats is often necessary, in which the content of free fatty acids is reduced and the free fatty acids are converted by esterification with alcohol in the target product fatty acid alkyl esters.

The literature discloses deacidification processes for fats and oils, e.g. by separation of free fatty acids with the aid of steam distillation (Ulimann 's Encyclopedia of Industrial Chemistry, Electronic Edition, Topic "Fats and Fatty OiIs", p 30) By such a separation, the acid value of the fats to values below 0.2 be reduced so that the resulting fats or oils can be reacted in a transesterification process.

The acid number in this context indicates the mass of potassium hydroxide in mg, which is required to neutralize 1 g of the sample to be tested (DIN 53402, latest version DIN EN ISO 2114).

From the literature, the esterification of free fatty acids with methanol using a homogeneous acid catalyst, for example p-toluenesulfonic acid or H ₂ SO ₄ , known (Mittelbach,

Remschmidt, Biodiesel - The Comprehensive Handbook 3rd ed., 2006, p. 60). However, this process requires a relatively difficult catalyst separation by neutralization and washing with alcohol or water, the catalyst used can not be recovered and significant amounts of wastewater arise.

In EP 0192035 and DE 196 00 025 a process for the deacidification of fats or oils is described, used in the acidic solid ion exchange resins as catalysts are, and after the separation of the reaction mixture, the by-product water is separated off. Here, the esterification of the free fatty acids without prior separation of the free fatty acids in the entire fatty acid, oil mixture is performed. Since the free fatty acids account for a relatively small proportion of the total amount of fat or oil in most cases (usually 2-20 weight percent, in rare cases also over 30 wt .-%) this process leads to an unfavorable space-time yield both in the esterification as well as in a subsequent transesterification, but in particular with respect to the esterification of the free fatty acids as an additional mass flow of inert components is mitprozessiert in the reaction.

DE 196 00 025 discloses inter alia that it may be advantageous to

Pre-esterification to add additional free fatty acids. This may possibly serve to reduce the relative mass fraction of inert material in the starting material of the process. However, a fundamental solution to the technical problem of achieving higher sales and consequent increased space-time yields of a Vorveresterung is not disclosed, since in particular for increasing the proportion of free

Fatty acids used fatty acids preferably come from a later step and are thus subjected to further processing steps. This in particular, because a soap cleavage by addition of homogeneously dissolved acids is necessary here. The maximum, disclosed space-time yield in DE 196 00 025 is 34 g of fatty acid methyl ester per liter of reactor volume and hour.

For an economic processing of fat raw materials into biodiesel, wherein the fat raw materials contain a proportion of free fatty acids, it is therefore an object to develop a process which achieves esterification of the free fatty acids with high space-time yield while allowing recovery of the esterification catalyst.

It has surprisingly been found that this object is achieved by a continuous process for the esterification of free fatty acids contained in starting materials, which is characterized by at least the steps

1) separating the free fatty acids from the remaining starting material by means of a conventional deacidification method,

2) optionally reaction of the de-acidified after step 1), the remaining starting material, in the form of a transesterification, obtained fatty acid alkyl ester, 3) conversion of the free fatty acids with alcohols using at least one acidic catalyst in a fixed bed, in the form of an esterification reaction,

4) optionally separating the by-produced water formed in step 3), optionally together with at least part of the unreacted alcohol in step 3),

5) optionally further conversion of the dehydrated product obtained from step 4), optionally with the addition of further alcohol, using at least one acidic catalyst in a fixed bed, in the form of an esterification reaction,

6) mixing the reaction product obtained from step 3) and / or the reaction product optionally obtained from step 5) with the remaining starting material obtained from step 1) and / or the fatty acid alkyl esters obtained from step 2)

In the context of the present invention, starting materials are all fats and / or oils which comprise at least a proportion of free fatty acids and also a proportion of fatty acid glycerides. Preference is given to starting materials which have a share of free

Have fatty acids greater than 2 wt .-%.

Possible sources of these raw materials are oils and / or fats of plant or animal origin. Non-conclusive examples of starting materials of plant origin include rapeseed oil, palm oil, jatropha oil, coconut oil, etc. Non-exhaustive examples of raw materials of animal origin include beef tallow, fish oil, lard, etc.

Fatty acids in the context of the present invention are all aliphatic carboxylic acids of the formula (I)

R ¹ -CO-OH (I),

or mixtures of different formula (I) corresponding compounds which are already included in the starting materials as fatty acids referred to hereinafter as free fatty acids, or by hydrolytic cleavage (so-called saponification) can be obtained from the fatty acid glycerides contained in the starting materials. Thus fatty acid allyl esters describe the alkyl esters of fatty acids obtained after esterification and / or transesterification or already present in the starting material.

R ¹ in formula (I) here preferably comprises aliphatic carbon chains having 6 to 22 Carbon atoms and optionally one or more double bonds.

Fatty acid glycerides are mono-, di-, or tri-glycerides of the fatty acids described above.

Alcohols in the context of the present invention designate mono- or polyhydric C 1 - to C ₅ -carbon or mixtures thereof. Preference is given to monohydric C ₁ - to C ₃ -alcohols. Very particular preference is given to methanol. The valency of an alcohol here describes the number of covalently bonded hydroxyl groups present in the alcohol according to the invention.

Step 1) of the process according to the invention is preferably carried out by a conventional process known to the person skilled in the art under the terms distillation, rectification or extraction.

Step 1) of the process according to the invention is particularly advantageous because the reactor sizes of the esterification due to the lower mass flows to be processed can be chosen to be significantly smaller due to the previous separation of the free fatty acids from the remaining starting material and the esterification can be carried out in a single-phase system. Both facts lead to a considerably reduced risk of miscalculation in scale-up of reactors in which the method according to the invention can be carried out.

A further advantage of step 1) of the process according to the invention can be achieved in the solution of the object of reducing catalyst deactivation of the heterogeneous catalyst at conversions e.g. according to step 3) and or step 5) of the method according to the invention can be achieved. By separating the free fatty acids from the rest

Starting material are also separated from the free fatty acids and large parts of any catalyst poisons, so that they can no longer reduce the acidic catalyst in its activity.

Catalyst poisons in the context of the present invention include e.g. the ions of alkali and alkaline earth metals. As non-conclusive examples its here called the ions of sodium, potassium, calcium, strontium etc.

If a reaction in the form of a transesterification according to step 2) of the de-acidified residual starting material according to step 1) is provided, the deacidified, residual starting material preferably comprises fatty acid glycerides, or mixtures thereof. Also preferably, step 2) is carried out according to a customary method known to the person skilled in the art, that the smallest possible proportions, particularly preferably no fatty acid glycerides, are more present in the reaction product and that the greatest possible number, particularly preferably all, of the remaining glycerides have been converted into glycerol and fatty acid alkyl esters.

Step 3) of the method according to the invention is preferably carried out using at least one acid catalyst, which is characterized in that it comprises a strongly acidic ion exchange resin. Particularly preferred is the at least one acidic

Catalyst a polymeric, macroporous resin with free sulfonic acid groups. Most preferably, the at least one acidic catalyst is a catalyst derived from the

Rohm and Haas under the name Amberlyst® or a catalyst sold by the company Lanxess under the name Levatit®.

Also preferred are catalysts which have an activity of at least 0.5 kg of free fatty acid per kg of catalyst and hour. This activity is particularly advantageous because it is certainly the method of the invention with the advantageous catalyst loads according to step 3) and / or 5) feasible.

Also preferably, step 3) of the process according to the invention is carried out so that it is characterized by a catalyst loading of 0.5 to 10 kg of free fatty acid per kg of catalyst and hour. The catalyst loading is particularly preferably between 1 kg and 5. Most preferably, the catalyst loading is between 1, 5 and 4 kg - h kg kg - h

A lower catalyst loading is inefficient, since more free fatty acid could be implemented and thus would not meet the goal of a high space-time yield. A higher catalyst load leads to inadequate conversions of the free fatty acids and thus also to lower space-time yields.

The adjustment of the catalyst loading can be done by adjusting the mass flow of the free fatty acids, or adjusting the amount of catalyst.

In another preferred embodiment of the method according to the invention, step 3) is carried out such that alcohol is used in molar excess with respect to the free fatty acids contained in the starting material. More preferably, the molar excess is between 5 and 40. Most preferably, the molar excess is between 10 and 25, and more preferably between 10 and 20. According to a further preferred embodiment of the method according to the invention, step 3) is carried out at elevated temperature relative to room temperature (20 ^° C.). More preferably, the temperature is carried out at the step 3) of the process according to the invention between 70 and 120 ⁰ C. Most preferably, the temperature is between 80 and 95 ° C.

In a likewise preferred embodiment of step 3) of the process according to the invention, the conversion is carried out under ambient pressure elevated pressure (1013 hPa). Particularly preferably, the pressure of the process according to the invention after step 3) is selected such that it corresponds at least to the vapor pressure of the alcohol used under the otherwise given process conditions. The vapor pressures of the alcohols of the present invention under various environmental conditions are known to those skilled in the art, or tabulated in the VDI heat inlet or similar reference books. Very particular preference is given to pressures below 5 bar.

A last preferred embodiment of step 3) of the method according to the invention is characterized in that the empty tube velocity of the fluid phase in the

Catalyst fixed bed between 1 and 5 mm / s and the length of the fixed catalyst bed is between 1 and 10 m. As a result, a likewise preferred residence time of the free fatty acids and alcohols of less than 30 minutes is achieved, this residence time being independent of the used concentrations of the free fatty acids in the starting material.

It has been found that under the inventive and preferred conditions, a conversion based on the free fatty acids of more than 95% is achieved, resulting in a significantly increased space-time yield of the fatty acid alkyl esters starting from free fatty acids in the starting material.

According to the method of the invention, a separation of the in step 3) as

By-product formed water, take place according to step 4) of the method according to the invention. Step 4) of the process according to the invention is preferably carried out if, following step 4), a further conversion according to step 5) of the process according to the invention follows. If a further conversion according to step 5) of the process according to the invention is not provided, step 4) of the process according to the invention is preferably not carried out.

It is advantageous to couple the execution of step 4) of the method according to the invention to the execution of step 5) of the method according to the invention, since the separation of the water formed as by-product, optionally together with at least part of the unreacted in step 3) alcohol, without further conversion according to step 5) of the inventive method is energetically unfavorable, if no further conversion, for example: after step 5) of the inventive method is provided , The stream from step 4) would anyway in the product of the process according to the invention again

Step 6) of the process according to the invention with either the remaining starting material from step 1) or the residual starting material transesterified in step 2) of the process according to the invention, if no further conversion according to step 5) were provided. An improvement in terms of esterification of the free fatty acids with high space-time yield is a separation of water without further following

Sales not conducive. If, however, step 5) of the process according to the invention is carried out one or more times, prior execution of step 4) of the process according to the invention is advantageous in each case, since in this way the equilibrium position is shifted to the side of the products via the removal of the water and thus the solution to the problem the achievement of higher space-time yields under energetic and thus economically advantageous conditions succeeds.

If step 4) of the process according to the invention is carried out, the embodiment can be carried out with or without removal of at least part of the residue of alcohol which may still be present here. It is preferable to separate as small a portion of the residual amount of alcohol which may still be present. Most preferably, no alcohol is separated with. The separation is preferably carried out by membrane processes or evaporation. Particularly preferably, the separation takes place through membranes.

For energetic and / or physical reasons (e.g., formation of an azeotrope), it may be necessary to also separate parts of the alcohol. The smallest possible separation of remaining alcohol has the advantage that this u.U. following

Process stages for further reactions is available. This includes in particular the further conversion according to step 5) of the process according to the invention, as well as conceivable transesterifications of the fatty acid glycerides contained in the starting materials following the process according to the invention.

If a further conversion of the dehydrated reaction product obtained from step 4) according to step 5) of the process according to the invention is provided, this can be done with or without further addition of alcohol. Preference is given to the addition of further alcohol. The amount added is particularly preferably lower than the amount added in step 3) of the process according to the invention. Very particularly preferred is the after step 4) of the process according to the invention separated alcohol replaced. Also preferably, step 5) is carried out under the same preferred conditions with regard to temperature and / or pressure and / or catalyst loading, as step 3) of the method according to the invention. Further preferably, in step 5) the same preferred tube rate and fixed catalyst bed length is selected as in step 3).

Particularly preferably, step 5) represents a repetition of step 3) with further and / or substituted alcohol.

It was found that under these conditions, a total turnover ^'(based on the free fatty acids) is achieved in the now two reaction steps of more than 99.5%.

If it is desired to further increase the conversion, then step 5) is preferably carried out more than once. Particularly preferably, the sequence of step 4) and step 5) of the inventive method is performed more than once.

The mixing according to step 6) of the process according to the invention can be carried out using the products from step 4) and / or step 5), with the remaining starting material according to step 1) of the process according to the invention and / or optionally with that from step 2) of the process according to the invention Fatty acid alkyl esters take place. Preference is given to mixing the product from step 5) of the process according to the invention with the product from step 2) of the process according to the invention. Hereby, the desired maximum space-time yields can be achieved.

A particularly preferred embodiment of the invention comprises a continuous

A process characterized by a reaction step according to step 3) and / or one of its preferred variants, a reaction step according to step 5) and / or one of its preferred variants, and a separation according to step 4) and / or one of its preferred variants.

Compared to the prior art corresponding process for the esterification of free

Fatty acids with homogeneous catalysts allows the inventive method in addition to saving the costly catalyst removal (in the reactor of the invention, the heterogeneous catalyst is fixed in a fixed bed, so that a catalyst separation is not required) an increase in the space-time yield.

It can according to the inventive method space-time yields of

Fatty acid methyl ester of up to 380 g per liter reactor volume and hour can be achieved. For example, according to Example 1 results in a space-time yield Fatty acid methyl ester of 380 g per liter of reactor volume and hour In comparison to the prior art described in DE 19600025, this allows a dramatic reduction of the reactor size by more than one order of magnitude (in the above example, a large ratio of 1 1 1 results).

For biodiesel production process of the invention thus allows a much cheaper processing of fatty raw materials with a high proportion of free fatty acids compared to the methods of the prior art and thus opens up em larger and more cost-effective spectrum of fatty raw materials

In the following, preferred embodiments of the method according to the invention are explained in more detail with reference to drawings, without restricting them to them

1 shows a sketch of a particularly preferred embodiment. The starting material (1) is separated from the free fatty acids in apparatus (10) according to step 1) of the inventive method, whereby a stream with residual starting material (2) and a stream with free fatty acids (3 The stream with residual starting material (2) is a reaction stage (20) for transesterification (but here are also conceivable multi-stage process for

The stream of free fatty acids (3) is then a first reaction stage (30) according to step 3) of the inventive method z B consisting of a Stromungsrohrreaktor comprising a fixed bed consisting of a Schuttung the Containing catalyst particles (particle diameter 0.5 to 1 mm) with a length of 1 to 10 m, together with a stream of alcohol (4) supplied The diameter of the fixed catalyst bed is determined by the volume flow of the streams (3) and (4) such the average residence time of these two streams in the catalyst bed is 5 to 30 minutes. The linear flow rate of the liquid phase relative to the empty pipe is 1 to 5 mm / s and the friction pressure loss in the particle bed is less than

0.5 bar / m The conversion of free fatty acids at the outlet of the first reaction stage (30) is then at least 95% From the product stream (5) in a separation stage (40) according to step 4) of the inventive method, the by-product water and the excess The separation step may be, for example, a falling-film evaporator or a distillation column operated at atmospheric or reduced pressure. Stream (7) is substantially anhydrous after the separation step and becomes another with further alcohol (8) Reaction stage (50) in accordance with step 5) of the process according to the invention. This reaction stage corresponds in its structure to reaction stage (30). The conversion of free fatty acids at the outlet of second reaction stage (corresponding to stream (9)) is at least 90% based on the current from the first reaction stage (5) and at least 99.5% based on the current in the first reaction stage (3). The stream (9) of the thus converted to alkyl esters of free fatty acids in a mixer (60) according to step 6) of the process according to the invention the stream (1 1) from the reaction stage (20) for transesterification originating material, which has also been converted into alkyl esters , added so that, for example, a stream of biodiesel (12) is obtained.

The ^{^} Effindüng wifd next starting with the examples described in greater detail without, however, ^"to be limited to this.

Examples

Comparative Example:

748 g / h of a mixture of rapeseed oil, oleic acid and linoleic acid with a free fatty acid content of 10 wt .-% (corresponding to an acid number of about 20 mg KOH / g) was with 178 g / h of methanol at a temperature of 83 ⁰ C and a pressure of 4 bar with a residence time of 15 min over a fixed catalyst bed of 650 ml of acid

Ion exchange resin (corresponds to 121 g of catalyst mass (dry)) passed. The catalyst particles had a diameter of 0.8 mm and were immobilized in a fixed bed reactor with a catalyst bed length of 2.08 m. This results in a catalyst loading of 0.65 kg of free fatty acid per kg of catalyst and hour and an empty tube speed of 2.3 mm / s. In the reaction product was an acidity of

0.25 wt .-% determined.

Thus, a degree of conversion of 97.5% was achieved with a molar ratio of methanol to fatty acids of 20.8: 1. This results in a space-time yield of fatty acid methyl ester of 123.4 g per liter of reactor volume and hour.

example 1

253 g / h of a mixture of oleic acid and linoleic acid with a content of free fatty acids of 100 wt .-% was 605 g / h of methanol at a temperature of 83 ° C and a pressure of 4 bar once with a residence time of 15 over a Fixed catalyst bed from 650 ml of acidic ion exchange resin (equivalent to 121 g of catalyst mass (dry)) passed. The catalyst particles had a diameter of

0.8 mm and were in a fixed bed reactor with a catalyst bed length of 2.08 m immobilized. This results in a Katalysatorbelasrung of 2.1 kg of free fatty acid per kg of catalyst and hour and a Leerohrgeschwindigkeit of 2.3 mm / s. An acid content of 2.8% by weight was determined in the reaction product, ie a fatty acid conversion of 97.2% was achieved. This results in a space-time yield of fatty acid methyl ester of 397.1 g per liter of reactor volume and hour.

Example 2

253 g / h of a mixture of fatty acid methyl ester (97.2% by weight), oleic acid and linoleic acid with a free fatty acid content of 2.8 wt .-% was 605 g / h of methanol at a temperature of 83 ⁰ C and a pressure of 4 bar with a residence time of 15 min over a fixed catalyst bed of 650 ml of acidic ion exchange resin (corresponds

121 g of catalyst mass (dry)) passed. In the reaction product, an acid content of 0.24 wt .-% was determined. The catalyst particles had a diameter of 0.8 mm and were immobilized in a fixed bed reactor with a catalyst bed length of 2.08 m. This results in a catalyst loading of 0.06 kg of free fatty acid per kg of catalyst and hour and a Leerohrgeschwindigkeit of 2.3 mm / s. The starting mixture of this example corresponds to the reaction product of the first esterification step after removal of water, e.g. described in Example 1. Based on the starting material of the first esterification stage, a fatty acid conversion of 99.76% was achieved.

Claims

- Patent claims

1. Continuous process for the esterification of free fatty acids contained in starting materials, which is characterized by at least the steps

2) optionally reaction of the de-acidified after step 1), the remaining starting material, in the form of a transesterification, obtained fatty acid alkyl ester,

3) conversion of the free fatty acids with alcohols using at least one acidic catalyst in a fixed bed, in the form of an esterification reaction,

5) optionally further conversion of the dehydrated product obtained from step 4), optionally with the addition of further alcohol, under

Use of at least one acidic catalyst in a fixed bed, in the form of an esterification reaction,

6) mixing the reaction product obtained from step 3) and / or the reaction product optionally obtained from step 5) with the remaining starting material obtained from step 1) and / or the fatty acid alkyl esters obtained from step 2).

2. The method according to claim 1, characterized in that the at least one acid catalyst comprises a strongly acidic ion exchange resin.

3. The method according to claim 1, characterized in that the at least one acidic catalyst comprises a polymeric, macroporous resin having free sulfonic acid groups.

4. The method according to any one of the preceding claims, characterized in that the deacidified, residual starting material according to step 2) is transesterified to fatty acid alkyl ester.

5. The method according to any one of claims 1 to 4, characterized in that a separation of the water formed as by-product in step 3), optionally together with at least part of the unreacted in step 3) alcohol takes place.

6. The method according to any one of claims 1 to 5, characterized in that after the separation according to step 4) a further conversion according to step 5) is performed.

7. The method according to any one of the preceding claims, characterized in that step 5) is performed more than once, preferably the sequence of step 4) and step 5) is performed more than once.

8. The method according to any one of the preceding claims, characterized in that the alcohol in step 3) in a molar excess between 5 and 40, preferably in a molar excess between 10 and 25 and most preferably between 10 and 20 is added.

9. The method according to any one of the preceding claims, characterized in that

Sales (according to step 3)) and / or further conversion (according to step 5)) at temperatures between 70 and 120 ⁰ C, preferably between 80 and 95 ° C are performed.

10. The method according to any one of the preceding claims, characterized in that in step 3) and / or step 5) a catalyst loading of 0.5 to 10 kg of free kg

Fatty acid per kg of catalyst and hour, preferably between 1 and kg - h kg more preferably between 1, 5 and 4 prevails. kg - h

1 1. The method according to any one of the preceding claims, characterized in that the pressure in step 3) and / or step 5) is selected so that it corresponds to at least the vapor pressure of the alcohol used.

12. The method according to any one of the preceding claims, characterized in that in step 5) further alcohol is added.

13. The method according to any one of the preceding claims, characterized in that the separation according to step 4) by membrane processes or evaporation takes place.

14. The method according to any one of the preceding claims, characterized in that the empty tube velocity of the fluid phase in the fixed catalyst bed is 1 to 5 mm / s and the length of the fixed catalyst bed is 1 to 10 m, so that a residence time of less than 30 minutes results.

15. Use of the method according to any one of claims 1 to 1 1 as part of a process for the production of biodiesel.