DE4344358A1 - Process for working up a reaction mixture by means of a column placed on the reactor - Google Patents

Description

The invention relates to a method for processing a reak tion mixture, the high boilers as undesirable by-products, easily contains boiling starting materials and in particular also catalyst residues, to one Product of high purity, its boiling point between the boiling points the heavy and low boilers lie. The product of value can be a pure substance or a mixture of isomers. After completing the reaction, it will Reaction mixture rectifi in a column placed on the reactor graces. In this context, the components of the Reaction mixture with boiling points below the boiling point of the desired ten valuable product and as low-boiling components with higher boilers to score points.

The work-up method according to the invention is not specific to reac mixed mixtures restricted. But it particularly refers to reak tion mixtures that arise in the manufacture of fragrances. These must be particularly olfactory after processing, that is, they must not show any smell as a result of by-products. Since some By-products in the ppm range are up to the task to make particularly high demands.  

In particular, the work-up method according to the invention relates to Reaction mixtures, which in the production of fragrances by Um- or Esterifications occur. Examples of this can be found in S. Arctander: "Perfume and flavor chemicals" (Aroma Chemicals) I, published 1969, Mont clair, N.J. (US) No. 218, 340, 529, 530, 1680. This is the Production of iso-amyl salicylate by esterification from salicylic acid and iso-amyl alcohol, benzyl salicylate from transesterification of benzyl alcohol with Me thyl salicylate, n-butyl salicylate by esterification of n-butanol with saline cyclic acid, iso-butyl salicylate by esterification of iso-butanol with saline cyclic acid, hexyl salicylate by esterification of n-hexanol with salicylic acid. Alternatively, these salicylates can be transesterified by methyl salicylate be prepared with the appropriate alcohol (EP 0 168 415 B1). At the alcohol, e.g. B. in the case of iso-amyl alcohol, it can be an iso act as a mixture.

The reaction is usually carried out batchwise, and at the water of reaction formed during the esterification or that during the transesterification released lower alcohol is withdrawn in gaseous form from the reaction space. The gaseous by-product and part of the starting materials are in one partial condenser or condenser and in the case of partial or complete insolubility of the substances from one another other separated and processed. The separated starting materials proceed preferably back into the reaction space. To concentrate the side pro Products in the vapors can be in front of the condenser or the partial condenser Column with internals that are arranged in an orderly packing, an orderly or disorderly fill as well as soil can.

After completion of the reaction, the crude product in the reactor washed to separate catalyst residues and by-products. Often fin detects a neutral wash, i.e. with a basic or acidic medium,  especially water instead. The remaining raw product contains a small amount Amounts (in the percentage range) of excess educts and others more easily volatile substances and less volatile by-products as well as catalyst leftovers. A discontinuous, fractio nated distillation in which the more volatile substances than Lead be deducted. The main run contains the value product.

Examples of such workup processes can be found in the German patent 406 225 from 1924 and in the already mentioned EP 0 168 415 B1 from 1987.

Another process for the production of fragrances is in the DE 39 09 128 A1 described. The reaction is carried out batchwise in one Stirred kettle with an attached rectification column performed. The Rectification column is not used to work up the reaction mixed, but to achieve a complete turnover by deduction Nene of the by-product ethanol, which from the transacetalization reaction Cyclododecanol and ethylal are obtained. That during the course of the reaction on Contains top of the rectification column distillate obtained no shares of the product of value. The value is at the end of the reaction product in the stirred kettle and is made up of the remaining ethylal and ethanol Distill cleaned. The high boilers still included not separated.

In Henkel papers 27 (1991), published by Henkel KGaA, Düsseldorf, Pages 80-84, a refurbishment process is described which in a Reactor with an attached falling film evaporator is carried out. Per Problems with the removal of the catalyst do not arise here, however a fixed bed catalyst is used. A reappraisal of the reacti onsgemisches in the reactor itself, on the rectification column is often not possible in practice, because for  Achieving a sufficiently high level of purity is often so great Number of plates, in some cases over 30 theoretical plates lies, necessary. In this case, an attached rectification co lonne lead to an uneconomically high construction of the entire plant and would not be possible in practice.

The invention has for its object an economical method to provide the type mentioned above, which is a valuable product with high Purity delivers, a wash of the raw product with the resultant eliminates the problems with the disposal of the washing liquid and shortens the processing time.

This object is achieved in that after completion the reaction in the first column placed on the reactor a mixture of the low boilers and the valuable product from the reak tion mixture separates, the high boilers and optionally the Kata lysatorreste remain in the reactor, and the separated mixture in one second Ko spatially separated from the reactor and the attached column rectified. According to the invention, the workup is in two stages performed. In the first stage, a mixture of low boilers and the product of value separated from the reaction mixture, which is then essentially lichen still contains the high boilers and catalyst residues. In the second The stage is rectified again and the product of value by the Leicht boil cleaned.

Both processing stages can be decoupled in time if you do that mixture of low boilers and the value separated from the reaction mixture product first flows into an intermediate template, from which it then flows into the second column is fed. The second processing stage leaves in this way, regardless of the first processing stage carry out. For example, you can wait until in between  present a sufficient amount of mixture of low boilers and Wertpro products has been incurred to get it in a particularly economical way the second column.

A particularly quick and economical implementation of the second order Working level can be achieved if one for the second column lower working pressure than the pressure of low boilers and recyclable material existing feeds so that at least some of the low boilers at Entry of the feed into the column evaporates spontaneously. The further concentration The valuable substance then follows in the column internals.

Only a small part of the valuable material is in the bottom of the column is evaporated, highly enriched. To improve depletion the bottom of the column can additionally contain low boilers in the product of value are heated so that the remaining low boilers evaporate.

The material is then continuously and in high purity from the sump deducted. The low boilers obtained are added to the top of the column condensed and removed.

The method is particularly suitable for working up from Ver esterification reactions or transesterification reactions obtained reaction mixture . The preferred application is the production of alkyl fatty acid Esters, especially called isopropyl myristate.

The work-up method according to the invention is also preferred for Work-up of the valuable product salicylate ester, especially benzyl salicylic lat, cyclohexyl salicylate, hexyl salicylate or iso-amyl salicylate puts. These are basic, homogeneously catalyzed transesterifications, where in the reaction mixture residues of alcohol and catalyst residues in Form of soaps that must be removed. As a cat  gates are typically sodium alcoholates, e.g. B. sodium methylate set.

In the reprocessing process according to the invention, the Rohpro is washed Products no longer required to remove unwanted components dig. There are no problems with washing liquids to be disposed of. A Another particular advantage of the method according to the invention is that shortened production time. Washing times, cooling and cooling phases as well Additional intermediate cleaning of the systems is not necessary.

An exemplary embodiment of the method according to the invention is explained in more detail below on the basis of a flow diagram ( FIG. 1).

After completion of the reaction, which has taken place in the stirred tank 1 with simultaneous circulation of the reaction mixture by the falling film evaporator 2 , the temperature is increased and / or the pressure is reduced and part of the reaction mixture is evaporated. With the attached rectification column 3 , a mixture of low boilers and the product of value is drawn off. The condensed mixture on the cooler 4 is collected in a first receiver 5 , partially recycled and partially fed directly or via a second receiver 6 and a heater 7 into a second rectification column 8 . The first template 5 is used for spatial and the second template 6 for decoupling the two workup steps. The second template preferably has a sufficiently large capacity for an entire batch cycle. In this case, the processing in the second stage can be carried out simultaneously with the next reaction cycle in the first stage.

The heated mixture is continuously pumped under pressure into the second rectification column 8 and partially evaporates as it enters the column. A first enrichment of the valuable substance is thus achieved in a simple manner. Further enrichment takes place in the internals of column 8 . The product of value can be drawn off at the bottom of the column and the low boilers can be drawn off at the top. A sump heater 9 is provided to improve the separation. The low boilers are condensed at the top of the column, passed into a third receiver 10 , partly returned as reflux and partly drawn off.

Example 1: Benzyl salicylate

After the reaction has ended, a mixture of the following composition is present in the reactor ( 1 ): 0.8% methyl salicylate, 2.1% benzyl alcohol and 96.7% benzyl salicylate. The concentrations indicated were determined by gas chromatography. At a bottom temperature of 187 ° C and a pressure of 10 mbar in the reactor ( 1 ), the mixture of starting materials and benzyl salicylate is distilled off via the first rectification column ( 3 ). At the top of the column, the temperature is 173 ° C. and the pressure is 3 mbar. From the first receiver ( 5 ), 75% of the condensate obtained after the cooler ( 4 ) is added to the second receiver ( 6 ) and the remaining 25% is returned to the first rectification column ( 3 ).

The mixture is pumped from the second receiver ( 6 ) into the heater ( 7 ). It occurs at a temperature of 120 ° C in the second rectification column ( 8 ). At a bottom temperature of 173 ° C and a pressure of 9 mbar, low boilers (in this case the benzyl alcohol and the methyl salicylate) are completely evaporated in the bottom heater ( 9 ); the sump contains olfactory pure benzyl salicylate, which has a minimum concentration of 98%.

At the top of the second rectification column ( 8 ), the distillate enriched with low boilers is obtained in the third receiver ( 10 ); the head pressure is 1 mbar and the temperature is 118 ° C. From the third receiver ( 10 ) 83% are moved back into the second column ( 8 ) and 17% are withdrawn. The stripped distillate typically has a composition comprising 12% benzyl alcohol, 5% methyl salicylate and 77% benzyl salicylate. The remaining components are volatile by-products.

Example 2: Cyclohexyl salicylate

After the reaction has ended, a mixture of the following composition is present in the reactor ( 1 ): 1.4% methyl salicylate, 4% cyclohexanol and 94.2% cyclohexyl salicylate. The concentrations indicated were determined by gas chromatography. At a bottom temperature of 166 ° C and a pressure of 12 mbar in the reactor ( 1 ), the mixture of starting materials and cyclohexylsalicylic acid is distilled off via the first rectification column ( 3 ). The temperature at the top of the column is 149 ° C. and the pressure is 3 mbar. From the first receiver ( 5 ), 75% of the condensate obtained after the cooler ( 4 ) is added to the second receiver ( 6 ) and the remaining 25% is returned to the first rectification column ( 3 ).

The mixture is pumped from the second receiver ( 6 ) into the heater ( 7 ). It occurs at a temperature of 120 ° C in the second rectification column ( 8 ). At a bottom temperature of 156 ° C. and a pressure of 8 mbar, low boilers (in this case cyclohexanol and methyl salicylate) are completely evaporated in the bottom heater ( 9 ); the sump contains olfactory pure cyclohexyl salicylate, which has a minimum concentration of 98%.

At the top of the second rectification column ( 8 ), the distillate enriched with low boilers is obtained in the third receiver ( 10 ); the head pressure is 1 mbar and the temperature is 100 ° C. From the third receiver ( 10 ) 83% are moved back into the second column ( 8 ) and 17% are withdrawn.

The distillate withdrawn typically has a composition the 24% cyclohexanol, 8% methyl salicylate and 64% cyclohexyl salicylate having. The remaining components are a total of volatile side pro products.

Reference list

1 reactor, stirred tank
2 falling film evaporators
3 (first) rectification column
4 coolers
5 first template
6 second template
7 heaters
8 second rectification column
9 sump heater
10 third template.

Claims (8)

1. Process for working up a reaction mixture which contains high boilers as undesired by-products, low-boiling starting materials and in particular also catalyst residues, to give a high-purity valuable product which consists of a pure substance or an isomer mixture and whose boiling point lies between the boiling points of the high and low boilers, wherein after the completion of the reaction, the reaction mixture is rectified in a first column placed on the reactor, characterized in that after the completion of the reaction in the first column placed on the reactor, a mixture of the low boilers and the product of value is continuously separated from the reaction mixture, where the high boilers and optionally the catalyst residues remain in the reactor, and the separated mixture is rectified in a second column spatially separated from the reactor and the attached column. 2. The method according to claim 1, characterized in that one from the Separated reaction mixture of low boilers and the value product first flows into an intermediate template, from which it then flows is fed into the second column. 3. The method according to claim 1 or 2, characterized in that one for the second column has a lower working pressure than the pressure of the feeds consisting of low boilers and recyclable material, so that to at least some of the low boilers when the feed enters the knockout lonne evaporated spontaneously. 4. The method according to any one of claims 1 to 3 for working up from Esterification reactions obtained reaction mixtures.   5. The method according to any one of claims 1 to 3 for working up from Transesterification reactions obtained reaction mixtures. 6. The method according to claim 5 for working up a product of value alkyl Reak containing fatty acid esters, especially isopropyl myristate tion mixture. 7. The method according to claim 5 for working up a product of value Sa reaction mixture containing licylate ester. 8. The method according to claim 7, characterized in that the valuable product Benzyl salicylate, cyclohexyl salicylate, hexyl salicylate or iso-amylsali is cylate.