BE1019554A3 - PROCESS FOR THE ENERGETICALLY EFFICIENT PRODUCTION OF A LACTIC ESTER FROM A FERMENTATION JUICE CONTAINING AMMONIUM LACTATE - Google Patents

Abstract

The present invention relates to an industrial process for the production of a lactic ester of more than seven carbon atoms, with a high yield and according to which it is possible to limit as much as possible the loss of lactic ester in the form of lactamide. In particular, the present invention relates to such a process, using less molar excess of alcohol for the esterification step, thus allowing a significant saving in energy during the necessary elimination of this excess.

Description

Process for the energy efficient production of a lactic acid ester from a fermentation juice containing ammonium lactate

Field of the invention

The present invention relates to an industrial process for producing a lactic ester from a fermentation juice containing ammonium lactate. In particular, the present invention relates to an industrial process for producing a lactic ester of more than seven carbon atoms, with a high yield and in which it is possible to limit as much as possible the loss of lactic acid ester in the form of lactamide . In particular, the present invention relates to such a process, using less molar excess of alcohol for the esterification step, thereby allowing a significant saving of energy when necessary to eliminate this surplus.

State of the art

The lactic acid production is very well known by the conventional fermentation process which consists of the transformation by a microorganism of a carbon substance (glucose, sucrose, starch, cellulose, fructose, etc.) in the presence of calcium carbonate. . The solution obtained is then treated with an acid in order to release lactic acid in protonated form, but this acidification step involves the production of calcium sulphate (also called gypsum). However, it is well known to those skilled in the art that the formation of gypsum implies that the precipitate must then be filtered while the lactic acid will be purified and concentrated by techniques such as ion exchange resins, carbon bleaching, nanofiltration, evaporation, distillation, liquid / liquid extraction.

It has already been proposed, as in US Pat. No. 2,565,487, to produce lactic acid esters from ammonium salts, and more particularly ammonium lactate, and alcohol. The ester product may in a second step be hydrolysed to lactic acid.

It is also known that during fermentation, the lactic acid produced by the microorganisms can be neutralized with ammonia. The ammonium lactate thus formed can be esterified with an alcohol to form the corresponding lactic ester.

However, it is also well known that the production route passing through ammonium salts also has many disadvantages, which make it particularly difficult to transpose an industrial method using this route.

Indeed, during the concentration of the fermentation juice and during the esterification step, it was observed the formation of an undesirable by-product, lactamide.

The formation of lactamide during the conversion of ammonium lactate to lactic ester decreases the selectivity of the reaction, leads to loss of yield and requires further separation and removal.

As explained in patent WO 2006/069113, to avoid the formation of lactamide, it is necessary to work with a large molar excess of alcohol of between 20 and 100 moles of alcohol per mole of ammonium lactate. The purification of the ester formed by distillation of the alcohol in large excess therefore requires a significant energy supply incompatible with a profitable industrial use of the process. This is the major disadvantage of the route from a fermentation juice of ammonium lactate, because not only, with the usual methods, still retains a significant content of lactamide, but the energy demand necessary to eliminate the amount of alcohol implemented in. the reaction remains significant for results that are not.

Moreover, when using a lactic fermentation juice in the form of unpurified ammonium lactate, the concentration and esterification steps are made difficult by the precipitation of by-products of the fermentation (residues of sugar,...). This precipitation results in a low esterification yield.

Not only does the state of the art make it possible to know well the problems relating to the presence of Lactamide, but in addition the state of the art also mentions the problem of the racemisation of esters obtained from a fermentation juice. lactic acid in the form of ammonium lactate, as described by M.ALAS in EP 517571B1, which teaches the possibility of producing lactic acid esters with a racemization rate higher than 2%, which is well known to be harmful for the ester obtained.

There is therefore a need for an industrial process for the production of lactic acid ester from a fermentation juice in the form of ammonium lactate, which makes it possible to remedy the drawbacks mentioned above, but which also requires considerable consumption. less molar excess alcohol for the esterification step, thereby limiting the energy consumption necessary for the elimination of this surplus.

One of the objects of the present invention is a method which makes it possible to use a very limited amount of excess molar alcohol during the esterification step, thus limiting the energy consumption necessary for its elimination. Indeed, the energy required to carry out the reaction is 1452 kJ for one mole of lactic acid in the process of patent WO 2006/069113 (for a molar excess of butanol of 20) against 301 kJ for a mole of lactic acid in the process of the invention (for a molar excess of butanol of 3).

Another object of the invention is a process for obtaining a lactic acid ester, with a high yield, generally greater than 95% and whose loss in the form of lactamide does not exceed 5% during the step esterification.

Yet another object of the invention is to limit the racemization to a level of less than 2% during the conversion of ammonium lactate to lactic acid ester.

Brief description of the invention

The Applicant has now unexpectedly found that a lactic ester with a carbon number greater than or equal to 7 can be produced from an ammonium lactate stream with a yield greater than 95%, by subjecting to a reactive distillation a stream of ammonium lactate, from a purified and concentrated fermentation juice, in liquid form, together with a stream of an aliphatic alcohol of 4 to 8 carbons, in vapor form, the molar ratio alcohol ammonium lactate being between 2: 1 and 5: 1 by recovering at the bottom of the column a liquid stream of the corresponding lactic ester and at the top of the column a gaseous mixture comprising the excess alcohol, the ammonia and the water.

Detailed description of the invention

The applicant company has found a process for producing a lactic ester from an ammonium lactate stream which does not involve gypsum production and which makes it possible to overcome the disadvantages mentioned above with respect to the production by way of ammonium salts.

The process of the invention comprises successively the following steps: a pre-purification of a fermentation juice in the form of ammonium lactate is first carried out; this pre-purified fermentation juice is then subjected to a concentration and then to a reactive distillation in the presence of a gas stream of an aliphatic alcohol containing 4 to 8 carbon atoms in order to carry out the esterification of the ammonium lactate; these last two operations being performed in a single apparatus consisting of 3 floors; the ester thus produced is recovered and then purified by distillation.

1. Pre-purification of the fermentation juice

The Applicant has surprisingly observed that the different stages of the pre-purification allowed no. only a decrease in the lactamide byproduct but also in the rate of racemization.

The first step of the pre-purification consists of an elimination of the biomass by any techniques known to those skilled in the art such as, in a non-limiting manner, the filtration on the pre-layer, the membrane filtration, the settling or centrifugation. This step is followed by a decationization of the fermentation juice on a. ion exchange resin previously conditioned in ammoniacal form. The fermentation juice freed from its divalent cations is then treated by nano-filtration.

2. The concentration of pre-purified fermentation juice

The fermentation juice thus purified is then concentrated until a concentration of between 50 and 80% is obtained.

A preferred version of the present invention is to exploit the thin layer evaporation techniques for this concentration step which again make it possible to limit the formation of lactamide. Under these conditions, no racemization was observed during this step. ? 3. Esterification of ammonium lactate Esterification of concentrated ammonium lactate is carried out countercurrently with an alcohol containing at least 4 carbon atoms in gaseous form in an apparatus (FIG. good liquid / gas exchange. It has been found that residence times of less than 2 hours are perfectly suitable and that excellent results can even be obtained with residence times of less than 30 minutes. The apparatus used consists of a reactive distillation column with 3 stages so that: a) The vapors leave the stage 1 (number of theoretical plates = 20) by the head of stage 1 in the foot of stage 2 and the vapors leave stage 2 (number of theoretical plates = 15) by the head of stage 2 in the foot of stage 3 (number of theoretical plates = 10) b) Liquids from floor 2 leave the foot of stage 2 in the head of stage 1 and the liquids of stage 3 leave by the foot of stage 3 in the head of stage 2.

c) Ammonium lactate with a concentration of between 10 and 80% is introduced at the top of stage 2 d) Alcohol with C ^ 4 in the form of steam coming from the top of stage 1, is introduced at the bottom of stage 2 e) The lactic ester formed is recovered at the bottom of stage 1 with a lactamide content of less than 5% f) The gas mixture alcohol (C ^ 4), water and ammonia is recovered at the top of stage 3 g) The alcohol (C ^ 4) is separated from water and ammonia by decantation and is reintroduced at the bottom of stage 2 The alcohol is heated to its temperature d boiling (the temperature and pressure being dependent on the alcohol used) and introduced into the bottom column of the stage 2 via the pipe B of Figure 1, in the form of gas. The previously pre-purified and concentrated ammonium lactate solution, in which a catalyst, preferably but not limited to para-toluenesulphonic acid (APTS), is optionally added in order to accelerate the reaction, is introduced at the top of the stage 2 via line A of Figure 1. The rising vapors of alcohol therefore cross. countercurrent the downward liquid flow of ammonium lactate. The water formed during the esterification is driven by the ascending alcohol vapors and recovered on the condenser C at the top of the stage 3 shown in FIG. 1. The ammonia released during the reaction is also removed and found in this same aqueous phase.

The excess alcohol also recovered on the condenser C is then separated from the aqueous phase containing the ammonia C by decantation, then heated and gasified in a heat exchanger E and reintroduced F at the bottom of the stage 2. The report molar alcohol / ammonium lactate is between 4: 1 and 2: 1, preferably 3: 1. In the case where the alcohol is butanol, the process may be carried out at atmospheric pressure and at a temperature of 120 ° C.

The sizing of the stages of the column can easily be carried out by those skilled in the art but, as non-limiting information, stages 1, 2 and 3 can be considered to consist of structured packing or not and contain respectively 20, 15 and 10 theoretical plates. In the context of the invention, these stages can also be constituted by trays with bells or any other column profile known to those skilled in the art to promote liquid-vapor exchanges.

This process allows the recovery via the line H at the outlet of the reboiler G of FIG. 1 of a lactic ester with a yield greater than 95%, the loss of lactamide. is less than 5% and the racemization less than 2%.

4. Purification of the Lactic Ester Produced The lactic ester thus formed may if necessary be purified by any techniques known to those skilled in the art as long as this step does not bring about a new racemisation. The distillation residue can be recovered and recycled to the esterification step.

. The purified lactic ester may optionally be hydrolyzed to lactic acid. In this case it is possible to achieve high quality grades meeting the market criteria.

Other details and particularities of the invention, given hereinafter by way of non-limiting examples, emerge from the description as some possible forms of its implementation.

Example 1: Esterification of ammonium lactate in the apparatus of the invention

The fermentation juice was filtered on a pre-layer of dicalite to remove the biomass. The filtrate was then treated with LEWATIT 2528 cationic resins preconditioned in ammonia form so as not to exceed 20 ppm divalent cations. The flow was set at 2 BV / h (a BV or "bed volume" corresponds to the volume occupied by the bed of resin in the treatment column).

This fermentation juice is then treated by nanofiltration, with a feed rate of between 500 and 600 ml / hr, on a SEPACF2 osmonics nanofiltration pilot with a GEWATER (DL) membrane.

Finally, the fermentation juice is concentrated, in a thin-film apparatus at a pressure of between 90 and 120 mbar and a temperature of between 100 and 105 ° C. with a feed rate of 6 l / h, until a concentration of 60%.

A column corresponding to the diagram of FIG. 1 is fed with butanol in the form of steam at 120 ° C. at atmospheric pressure, at the top of stage 1 (FIG. 1, position B) at the rate of 550 g / h. Stage 1 consists of structured packing and contains 20 theoretical trays. Reboiler G at the bottom of stage 1 consists of a plate heat exchanger heated to 140 ° C. The .

pre-purified ammonium lactate and concentrated to 60% is mixed with 1% APTS to be introduced at the top of stage 2 (Figure 1, position A) at a rate of 1204 g / h.

Stage 2 contains the same structured packing as stage 1 for a number of theoretical plates of 15.

The molar ratio of butanol to ammonium lactate is 3: 1. The energy required to carry out the reaction is 301 kJ. The formed water and butanol are entrained at the top of stage 3 (Figure 1, position C). Stage 3 is also composed of structured packing and contains 10 theoretical trays. The aqueous phase containing the ammonia collected on the condenser in the C position is then separated from the butanol by decantation The butanol collected after decantation is heated to boiling (Figure 1, position E) in a heat exchanger and returned to the top of the stage 1 (Figure 1, position F), to ensure equilibrium, at a feeding speed of 1500 g / h. Butyl lactate is recovered at the bottom of stage 1 (Figure 1, position H). A follow-up of the reaction as a function of time was carried out, the results are shown in Table 1.

Table 1: characteristics of butyl lactate produced as a function of time

(a) determined by gas chromatographic measurement (b) determined by Karl Fisher measurement

As shown in Table 1, the apparatus makes it possible to produce butyl lactate from ammonium lactate in a stable manner (over 12 hours) with a yield greater than 95%, a loss in the form of lactamide of less than 5% and racemization less than 2%.

EXAMPLE 2 Esterification of a Prepurified Fermentation Juice in Ammonium Lactate Form of Butyl Lactate With and Without the Use of a Column 222 g of butanol are placed in a flask and heated at 120 ° C. at atmospheric pressure, 1%. APTS (para-toluenesulfonic acid) is added. When the butanol distills, 178.3 g of a pre-purified fermentation juice in the form of 60% ammonium lactate are added dropwise into the flask. The reaction is continued until a residual acidity of zero. At the end of the synthesis, the reaction product is analyzed, the results are shown in Table 2.

Table 2: Characteristics of Butyl Lactate

(a) determined by gas chromatographic measurement (b) determined by Karl Fisher measurement

It can be noted that the conversion of ammonium lactate to butyl lactate is not very high and that against the loss of lactamide is important.

A new test is carried out by overcoming the flask of a column containing a structured packing, in order to perform the counter-current esterification of the alcohol in gaseous form.

222 g of butanol are placed in a flask surmounted by this column and heated at 120 ° C. at atmospheric pressure, 1% of APTS is added. When the butanol distils at the top of the column, 178.3 g of a pre-purified fermentation juice in the form of 60% ammonium lactate are added dropwise at the top of the column. The reaction is continued until a residual acidity of zero is obtained. At the end of the synthesis, the reaction product is analyzed, the results are shown in Table 3.

Table 3: Characteristics of Butyl Lactate

The fact of using a column makes it possible not only to increase the conversion of ammonium lactate to butyl lactate but also to reduce the loss of lactamide as well as the racemization.

The butyl lactate product is then purified by distillation, the characteristics are shown in Table 4.

Table 4: Characteristics of Distilled Butyl Lactate

Example 3 Concentration of the fermentation juice with and without pre-purification

Fermentation was performed with ammonia neutralization.

300 g of fermentation juice are directly concentrated in a balloon. The characteristics of the concentrated fermentation juice in ammonium lactate form are shown in Table 5.

Table 5: Characteristics of fermentation juice after concentration

(a) determined by titration

(b) determined by HPLC measurement

(c) determined by enzyme assay

There is a significant formation of the by-product lactamide during the concentration step.

A new fermentation was carried out with a neutralization with ammonia, this time, the fermentation juice was filtered on pre-layer of dicalite to eliminate the biomass. The filtrate was then treated with LEWATIT 2528 cationic resins pre-conditioned in ammonia form so as not to exceed 20 ppm in divalent cations. The flow rate was set at 2 BV / h (a BV corresponds to the volume occupied by the resin bed in the treatment column).

This fermentation juice is then nanofiltered, with a feed rate of between 500 and 600 ml / h, on a SEPACF2 osmonics nanofiltration pilot with a GEWATER (DL) membrane.

Finally, the fermentation juice is concentrated in a thin film apparatus, at a pressure of between 90 and 120 mbar and a temperature of between 100 and 105 ° C. with a feed rate of 6 l / h, until a concentration of 60%.

The characteristics of this fermentation juice in ammonium lactate form are shown in Table 6 /

Table 6: characteristics of pre-purified fermentation juice after concentration

It may be noted that pre-purification on resin followed by nanofiltration and concentration on a thin layer makes it possible to considerably reduce lactamide formation and racemization during the concentration.

Example 4: Esterification of 2-ethylhexyl lactate of a fermentation juice in ammonium lactate form 390 g of 2-ethylhexanol are placed in a flask surmounted by a column and heated to 130 ° C. at a pressure of 100 mbar, 0.1% APTS are added. When 2-ethylhexanol is distilled, 178.3 g of prepurified ammonium lactate and concentrated to 60% are added drop by drop at the top of the column. The reaction is continued until a residual acidity of zero. At the end of the synthesis, the reaction product is analyzed, the results are shown in Table 7.

Table 7: Characteristics of 2-ethylhexyl lactate

(a) determined by gas chromatography

The 2-ethylhexyl lactate produced is then purified by distillation, the characteristics are shown in Table 8.

Table 8: Characteristics of Distilled 2-Ethylhexyl Lactate

It can be noticed the very low concentration of lactamide and the racemization rate also low.

Example 5: Hydrolysis of the butyl lactate produced in Example 2 in lactic acid of high quality 292 g of butyl lactate, 288 g of demineralized water and 1% of APTS are placed in a flask and heated to 105 ° C. at atmospheric pressure. -The reaction is continued for 8 hours. At the end of hydrolysis, the reaction product is analyzed, the results are shown in Table 9.

Table 9: Characteristics of hydrolysed butyl lactate

99% of the butyl lactate was hydrolyzed to lactic acid without causing racemization of this lactic acid.

The lactic acid thus obtained is concentrated in order to meet the quality criterion. of the market. The results are shown in Table 10.

Table 10: Characteristics of concentrated lactic acid

Claims (7)

1. An energy efficient process for producing a lactic ester of at least 7 carbon atoms from an ammonium lactate stream with a yield greater than 95%, the lactamide loss is less than 5% and the racemization is less than 2%, characterized in that a stream of pre-purified and concentrated ammonium lactate, in liquid form, is subjected to reactive column distillation simultaneously with a stream of an aliphatic alcohol containing from 4 to 8 carbon atoms, in vapor form, the alcohol / ammonium lactate molar ratio being between 2: 1 and 5: 1, and that a liquid stream of the lactic ester is recovered at the bottom of the column; corresponding and in the lead. column a gaseous mixture comprising the aliphatic alcohol, ammonia, and water. 2. Method according to claim 1 characterized in that the prepurification of ammonium lactate is carried out preferentially by: a) elimination of the biomass; b) decationization of the fermentation juice on an ion exchange resin previously conditioned in ammoniacal form; c) nanofiltration of decationized juice. 3. Process according to claim 1, characterized in that the stream of prepurified ammonium lactate is concentrated to a concentration level of between 50 and 80%. 4. Method according to claim 2 characterized in that the concentration is carried out by evaporation thin layer. 5. Process according to claims 1 to 3, characterized in that the distillation residue of the lactic ester product can be recovered and recycled to the esterification step. 6. Process according to claims 1 to 5, characterized in that the lactic ester of at least 7 carbon atoms is hydrolyzed to lactic acid. 7. Process according to claim 6, characterized in that the alcohol resulting from the hydrolysis of the lactic ester of at least 7 carbon atoms is recycled to the reactive esterification step.