DE19721474C1 - Batch preparation of lower alkyl ester, especially useful for making small batch - Google Patents

Abstract

Preparation of lower alkyl esters (I) by catalytic ester exchange of fats and/or oils with alcohols is carried out in batches in a reactor with recycling through a coalescence separator. Also claimed is a stirred vessel with recirculation through a coalescence separator and its use in the process. A coalescence aid, especially wire, metal, glass fibre and/or synthetic fabric, is added. More catalyst is added during ester exchange.

Description

The invention relates to a process for the preparation of lower alkyl esters Transesterification by using the process in batches in a reactor Recycling via a coalescence separator. Furthermore concerns the Invention a reactor for performing the above method, and the Use of the reactor for transesterification reactions.

State of the art

Lower alkyl esters of fatty acids are generally obtained by transesterification of Fatty acid glycerides, i.e. H. Fats and oils with a lower alcohol like for example, methanol. A basic distinction is made between two different procedures, firstly high pressure transesterification at pressures of up to 90 bar and temperatures of up to 250 ° C and secondly the Low pressure transesterification at pressures from 1 to 10 bar and temperatures below 100 ° C (Monograph "Fatty Alcohols, Raw Materials, Processes and Use", Henkel KGaA (1981)). Both processes are usually carried out continuously, however, there is also the option of batch transesterification perform. In the case of alkaline-catalyzed low-pressure transesterification Amount of catalyst to be used is a critical quantity. You just sit so much catalyst that it completely after the reaction to the  appropriate soap is implemented, the reaction is generally very slowly. If one uses the catalyst in excess, then the Reaction still free alcoholate, which in the subsequent distillative Separation of the lower alcohol catalyzes the back reaction and therefore too Loss of yield leads. The catalytic activity of the soap is compared to that of the Alcoholate significantly lower. To loss of yield through reverse reaction avoid, the free glycerol is usually by before the distillation Washing the reaction mixture with water, at the same time removed the soap. In DE-A1 30 20 612 is the possibility of Wash out the glycerin and the annoying secondary components with 50 to 150 Wt .-% water - based on the unreacted lower Alcohol - described. According to the teaching of DE-A1 31 07 318, 30 to 150 % By weight of water - based on the unreacted lower alcohol - after the Transesterification reaction added to the glycerin, the lower alcohol as well disruptive impurities that affect the color of the product, wash out. However, larger amounts fall in both processes methanol-containing waste water.

Another possibility of separating the glycerol is in DE-A1 42 09 779 described. The glycerin is first separated by gravity separated and then still in a separator of a wash with water or a buffer solution (J. Connemann, Fat. Sci. Technol. 96, 563 (1994)).

EP-A 0 706 988 describes a process for the preparation of lower alkyl esters known in which the separation of the glycerol directly after the Implementation in a stirred tank, in a separate downstream Gravity separator takes place. The procedure can be several in a row have switched stages.

WO 94/17027 describes a method in which, following the Transesterification, the separation of the glycerin takes place in that the glycerol phase  is separated after phase separation, the remaining ester phase subsequently still washed with glycerin and additionally with bleaching earth or silica is treated.

Another method of removing glycerin from a reaction mixture is disclosed in EP-A 0 708 075; in this case it is a distillation separation method.

Glycerin separation is particularly problematic in batch processes since it has been customary until now to either separate the phases by switching off the To bring agitator or by using two stirring kettles with intermediate gravity or centrifugal separators. These methods are too time-consuming or costly.

The complex object of the present invention was a method for Developing production of lower alkyl esters, which is particularly suitable for Production of small batches is suitable and in which the glycerol separation without operations are time-consuming and costly.

Description of the invention

The invention accordingly relates to a process for producing lower Alkyl ester by transesterification, which is carried out batchwise in a reactor Recycling through a coalescence separator. Another The invention relates to a reactor with recycle through a Coalescence separator and the use of the same for carrying out the catalytic transesterification.

It has now surprisingly been found that one technically very easy to install solution the glycerin continuously from the process can remove, the remaining substances being fed back to the reactor can. At the same time, this method can be used compared to the prior art Technology known batch process a much more constant product quality guarantee. In a preferred embodiment, by using the Coalescence aids effectively remove undissolved or finely emulsified glycerin  will. Furthermore, the possibility of replenishing the Catalyst the catalyst separated with the separated glycerin again replaced.

The reactor to be used according to the invention can also be used in other processes such as successfully using fat splitting.

Fatty acid glycerides

The fatty acid glycerides to be used as starting materials in the process according to the invention can be the usual natural vegetable or animal fats or oils. These include, for example, palm oil, palm kernel oil, cottonseed oil, rapeseed oil, coconut oil, peanut oil, olive oil, linseed oil, babassu oil, tea oil, olive kernel oil, meadowfoam oil, chaulmoogra oil, coriander oil, soybean oil, castor oil, lard oil, beef tallow, pork lard, and sunflower oil and rapeseed oil Fish oil is particularly preferably used according to the invention. The main components of these fats and oils are glycerides of various types of fatty acids, which contain considerable amounts of impurities such as aldehyde compounds, phospholipid compounds and free fatty acids. These materials can be used directly or after prior purification. In some cases it is particularly advisable to esterify the free fatty acids in an upstream reaction with lower alcohols. In addition to the natural fatty acid glycerides, synthetic fatty acid glycerides can also be used. B. obtained by esterification of glycerol with fatty acids. Fatty acids are to be understood as meaning aliphatic carboxylic acids of the formula (I)

R ¹ CO-OH (I)

in which R ¹ CO represents an aliphatic, linear or branched acyl radical having 6 to 22 carbon atoms and 0 and / or 1, 2 or 3 double bonds.

Typical examples are caproic acid, caprylic acid, 2-ethylhexanoic acid, Capric acid, lauric acid, isotridecanoic acid, myristic acid, palmitic acid, Palmoleic acid, stearic acid, isostearic acid, oleic acid, elaidic acid, Petroselinic acid, linoleic acid, linolenic acid, elaeostearic acid, arachic acid, Arachidonic acid, clupanodonic acid, docosahexaenoic acid, eicosapentaenoic acid Gadoleic acid, behenic acid and erucic acid and their technical mixtures, the z. B. in the pressure splitting of natural fats and oils, in the reduction of aldehydes from Roelen's oxosynthesis or the dimerization of unsaturated fatty acids.

As fatty acid glycerides for the purposes of the present invention, both Fatty acid triglycerides, as well as corresponding fatty acid partial glycerides, such as mono- and diglycerides are used.

Alcohols

Those to be used in the transesterification of the fatty acid glycerides according to the invention Alcohols are lower aliphatic alcohols, preferably with 1 to 12 carbon atoms, in particular 2 to 8 carbon atoms. Typical examples are methanol, ethanol, n- Propanol, 2-propanol, n-butanol, n-pentanol, n-hexanol, n-octanol and 2- Ethylhexanol. In addition, there are also diols such as hexanediol Suitable alcohol component.

Catalysts

The usual catalysts from the prior art for Transesterification reactions known catalysts are used. It deals are, for example, alkali and / or alkaline earth metal alcoholates or hydroxides, especially sodium methoxide and / or sodium glycerate. Farther preference is given to the use of acetates, such as zinc and / or magnesium acetate  or also titanates, for example tetrabutyl titanate and organotin compounds such as dibutyltin diacetate.

The catalysts are usually obtained in amounts of 0.2 to 2% by weight used on the triglyceride to be transesterified. The dosage is too Start of the reaction and in a particularly preferred embodiment is in In the course of the reaction, catalyst is added, in particular the Compensate for catalyst losses through continuous separation. The The catalyst can be replenished continuously, or else discontinuous.

method

The method can be known from the prior art Reaction conditions are carried out. For example, in a usual one Mixing kettle under atmospheric pressure at a temperature in the range of 60 to 220 ° C - depending on the boiling point of the alcohol to be used. This unpressurized variant is suitable for use already refined or low contaminated triglycerides, especially for refined rapeseed or Sunflower oil.

The process can also be carried out in a pressure reactor at elevated pressure Carry out 1 and 10 bar, this depends in particular on the quality of the triglycerides used. In the case of heavily contaminated goods, the Procedure under increased pressure.

reactor

According to the invention, a stirred vessel and / or is used as the reaction vessel Pressure reactor around which a loop with coalescence separator is installed. in the For the purposes of the present invention, everyone is among coalescence separators To understand the reactor, which is suitable for this, for example, through special internals is to facilitate coalescence. In this way, the Deposition of the glycerol formed by phase separation, while the rest Reactants can be returned to the boiler. According to the invention  For example, the following coalescence aids can be used: wire mesh, Plastic mesh, packing, fiberglass, metal plates, or any other common Agent that promotes coalescence. In a preferred embodiment the reaction mixture is applied to the coalescence aid via a Liquid distributor.  

Examples example 1

1200 g of refined rapeseed oil (1.83 mol) and 300 g (6.5 mol) of ethanol were mixed in one Stirred kettle with recirculation through a coalescence separator and opened Heated 60 ° C, 10 ml of 30 wt .-% aqueous were stirred Sodium ethylate solution metered in as a catalyst. The reaction mixture was further heated and at a temperature of 70 ° C Coalescence separator started up and then continued to 85 ° C heated up. The reaction proceeded with glycerol separation within the 1 hour the next hour, a further 10 ml of the catalyst solution were metered in and one the after-reaction continued for another hour.

In the course of the reaction, 149 g of a glycerol / Ethanol mixture accumulated. The residual monoglyceride content was 1.1 % By weight. The remaining ethanol was removed by vacuum distillation.

Example 2

1200 g of raw coconut oil (1.83 mol) and 500 g (6.7 mol) of n-butanol were mixed in one Stirred kettle with recirculation through a coalescence separator and heated to 60 ° C with stirring. Then 2 g of dibutyltin diacetate metered in as a catalyst. The reaction mixture was heated up to 180 ° C. with a pressure of 4 bar. Then the Coalescence separator started up and the temperature continued up to 220 ° C elevated. With simultaneous pressure increase and continuous Glycerine separation was now followed by further implementation. After 1 h, 1 g Catalyst (dibutyltin diacetate) replenished.

After the reaction had ended, 180 g of a glycerol / n-butanol Mixture separated. The residual content of monoglyceride in the reaction product was 1.7% by weight.

The pressure was then increased while the coalescence separator was operating relaxed. Another 10 g of glycerol separated out in the coalescence separator. The remaining butanol still dissolved was removed by vacuum distillation away.

Claims (6)

1. Process for the preparation of lower alkyl esters by catalytic transesterification of fats and / or oils with alcohols, characterized in that the process is carried out batchwise in a reactor with recirculation through a coalescence separator. 2. The method according to claim 1, characterized in that one Coalescence aids. 3. Process according to claims 1 and 2, characterized in that a wire, metal, fiberglass and / or plastic fabric as Coalescence aids. 4. Process according to claims 1 to 3, characterized in that catalyst added during the transesterification. 5. Stirred kettle with recirculation through a coalescence separator. 6. Use of a stirred tank according to claim 5 for the production of lower Alkyl ester by catalytic transesterification of fats and / or oils with Alcohols.