Process for producing (meth)acrylic esters

Abstract

This invention relates to a process for the continuous production of a (meth)acrylic ester by transesterification reaction between a C1-C4 light alkyl (meth)acrylate, with a heavy alcohol in the presence of a catalyst, characterised in that the flows feeding the reactor are introduced through a static mixer placed on a recirculation loop of the reactor. The use of a static mixer improves the selectivity of the reaction and consequently the overall productivity of (meth)acrylic ester synthesis process.

Claims

1. A process for continuous production of a (meth)acrylic ester, said process comprising a homogeneous transesterification reaction between a light alkyl (meth)acrylate selected from the group consisting of methyl (meth)acrylate, methyl acrylate, ethyl (meth)acrylate and ethyl acrylate, with a heavy alcohol in the presence of a homogeneous transesterification catalyst and polymermization inhibitor using a reactor comprising a static mixer, a reactor reboiler, and a recirculation loop for carrying reagents, catalyst, and recycled flows which joins an outlet of the reactor to an inlet of the reactor through the reboiler, wherein all flows feeding the reactor are introduced through the static mixer which is a pipe element with propellers or baffles or other obstacles to increase turbulence, placed on the recirculation loop, and upstream or downstream of the reactor reboiler, such that a combined flow of reagents, catalyst, and recycled flows passes through the static mixer before entering the reactor.

2. The process according to claim 1 wherein the heavy alcohol is a linear or branched, primary or secondary alcohol comprising between 4 and 12 carbon atoms, optionally comprising at least one nitrogen atom.

3. The process according to claim 1 wherein the heavy alcohol is an amino alcohol of formula (II):
HO-A-N(R.sub.2)(R.sub.3)(II) wherein A is a C.sub.1-C.sub.5 linear or branched alkylene radical R.sub.2 and R.sub.3, which are identical or different from one another, each represent a C.sub.1-C.sub.4 alkyl radical.

4. The process according to claim 1 wherein the heavy alcohol is N,N-dimethylaminoethanol (DMAE), N,N-diethylaminoethanol, or N,N-dimethylaminopropanol.

5. The process according to claim 1 wherein the heavy alcohol is a primary or secondary alcohol of formula R.sub.2OH wherein R.sub.2 represents a C.sub.4-C.sub.12 linear or branched alkyl chain.

6. The process according to claim 1 wherein the heavy alcohol is 2-ethyl hexanol, 2-octanol or 2-propyl heptanol.

7. A process for the continuous production of a (meth)acrylic ester by a homogeneous transesterification reaction between a light alkyl (meth)acrylate selected from the group consisting of methyl (meth)acrylate, methyl acrylate, ethyl (meth)acrylate, and ethyl acrylate with a heavy alcohol in the presence of a homogeneous transesterification catalyst and polymerization inhibitor, said method comprising at least the following steps: a) feeding a reactor with the light alkyl (meth) acrylate, the heavy alcohol, the transesterification catalyst, and at least one polymerization inhibitor, and subjecting the reaction mixture to transesterification conditions to form: i) a product mixture comprising the (meth) acrylic ester formed, the light alkyl (meth)acrylate and the unreacted heavy alcohol, the catalyst, the polymerization inhibitors and heavy by-products; and ii) an azeotropic mixture of the light alkyl (meth)acrylate and the light alcohol released from the light alkyl(meth)acrylate during transesterification; b) distilling, in a first distillation column, the product mixture i) of step a), and separating at the top, a stream consisting essentially of the desired (meth) acrylic ester and light products, and at the bottom, a heavy fraction comprising the catalyst, the polymerization inhibitors and heavy by-products; c) purifying said overhead stream with at least a second distillation column, to obtain a purified (meth)acrylic ester, and a light product stream which is recycled to the reaction; d) passing at least a portion of said heavy bottoms fraction to a film evaporator and separating traces of light compounds therefrom, wherein said light compounds are then recycled to the feed of the first distillation column, and the heavy residue is removed; e) optionally recycling at least a portion of said heavy bottoms fraction of the first distillation column or the heavy residue formed in step d) to the reactor; f) optionally recycling the azeotropic mixture ii) formed in step a), to a unit for producing light alkyl (meth) acrylate; g) optional thermal cracking of at least a portion of said heavy bottoms fraction of the first distillation column, or heavy residue formed in step d); wherein the reactor comprises a static mixer, a reactor reboiler, and a recirculation loop for carrying reagents, catalyst, and recycled flows which joins an outlet of the reactor to an inlet of the reactor through the reboiler, wherein all flows feeding the reactor described in steps a) and e) pass through a static mixer which is a pipe element with propellers or baffles or other obstacles to increase turbulence, placed on the recirculation loop of the reactor, such that a combined flow of reagents, catalyst, and recycled flows passes through the static mixer before feeding into the reactor.

8. The process according to claim 7, wherein the (meth) acrylic ester is N,N-dimethylaminoethyl acrylate, the light alkyl (meth)acrylate is ethyl acrylate and the heavy alcohol is N,N-dimethylaminoethanol.

Description

(1) The invention will now be more fully described in the description which follows, and with reference to the following figures:

(2) FIG. 1: illustration of a mixer usable according to the invention.

(3) FIG. 2: diagram of a reaction section including the flow introduction mode in a transesterification reactor according to the invention.

(4) FIG. 3: schematic representation of a set-up adapted to implement the process of the invention.

DETAILED PRESENTATION OF THE INVENTION

(5) In the processes of the prior art, the catalyst is introduced directly into the reactor, for example using an immersion rod, separated from the reactant flows feeding (as represented for example in patent documents WO 2013/110877; WO 2014/131970; FR 2 811986).

(6) According to the figure illustrating purification using a single distillation column, of a reaction mixture resulting from a transesterification reaction, described in document WO2014/096648, the reagents and catalyst are introduced into the reactor as a single flow formed in a recirculation loop. However, the homogenisation of the reaction medium and the uniform kinetics of the conversion of reagents are not problems in this process which mainly concerns obtaining a final high purity product. It is therefore not suggested to place a static mixer in the recirculation loop.

(7) According to the invention, the introduction of reagents and catalyst is optimised by using a static mixer in the recirculation loop of the reactor. Thus, it is ensured that the mixture of the reagents and the catalyst is properly carried out when it enters the reactor after the recirculation loop. The presence of overconcentration of the catalyst in the loop and reactor is avoided, and a better distribution of the catalyst is achieved in the reaction medium.

(8) Recommended static mixers include those marketed for example by the CTMI company at St Avoid or by the Sulzer company.

(9) FIG. 1 illustrates an example of a mixer adapted to the process according to the invention.

(10) FIG. 2 shows a reaction section comprising a transesterification reactor 1 and a static mixer 14. An alkyl (meth)acrylate flow A and a heavy alcohol flow B, as well as a catalyst flow C are grouped into a single flow which passes through a static mixer 14 which is connected at the outlet to reactor 1. The thorough mixing of catalyst C with reagents A and B is carried out inside the static mixer, before being introduced into the reactor.

(11) Static mixer 14 can be placed upstream or downstream of the reboiler in the recirculation loop of the reactor.

(12) The formation of heavy by-products being minimized because of the absence of zones with high catalyst concentrations in the reactor, the reaction conditions can be adapted in order to optimise the reaction yield, mainly by increasing the residence time in the reactor to lead to an increase in raw material conversion rates, and consequently an improvement in raw material yield.

(13) Transesterification reaction is generally carried out in reactor 1 at a pressure between 500 mm Hg (0.67105 Pa) and atmospheric pressure, preferably at a pressure of about 700 mm Hg, and temperature ranging from 70 C. to 130 C., preferably 100 C. to 120 C.

(14) The light alkyl (meth)acrylate/heavy alcohol molar ratio can range from 1 to 3, preferably, it fails between 1.3 and 1.8.

(15) The transesterification reaction is carried out in the presence of a catalyst according to methods well known to the person skilled in the art. For example, the transesterification catalyst can be a tetraalkyl titanate in solution in an alcohol such as the heavy alcohol used in the reaction, preferably tetraethyl titanate in solution in the heavy alcohol; the catalyst can also be a titanate of the heavy alcohol, for example tetra (dimethylaminoethyl) titanate, or tetra (2-ethylhexyl) titanate.

(16) The reaction is carried out in the presence of one or more polymerization inhibitors which are introduced into the reactor at a rate of 1000 to 5000 ppm relative to the crude reaction mixture. The polymerisation inhibitors that can be used include, for example, phenothiazine, hydroquinone, hydroquinone monomethyl ether, diterbutyl para-cresol (BHT), TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy), di-tert-butylcatechol, or TEMPO derivatives, such as 4-hydroxy TEMPO (4-OHTEMPO), alone or mixtures thereof in all proportions.

(17) The residence time in the reactor is generally between 5 and 8 hours.

(18) FIG. 3 illustrates a set-up adapted for the implementation of a continuous process for producing (meth) acrylic esters by transesterification from light alkyl (meth) acrylates, and heavy alcohols as defined in the invention.

(19) This set-up is described more particularly, but not limited to, the case of the production of ADAME by transesterification from EA and DMAE, which comprises steps (a) to (g) as defined in the process according to the invention.

(20) FIG. 3 shows a transesterification reactor 1, a reboiler and a static mixer 14 which can be placed upstream or downstream of the reboiler in a recirculation loop of the reactor.

(21) Reagents A and B (EA and DMAE) and a transesterification catalyst C are introduced into the recirculation loop of the reactor, to ensure they are homogeneously mixed before being introduced into reactor 1. Recycled flows from the purification section can also be introduced in the recirculation loop.

(22) According to a first step (a), the transesterification reaction between AE and DMAE is carried out in reactor 1 in the presence of catalyst C, preferably tetraethyl titanate, and polymerization inhibitors. To reactor 1 is attached a distillation column 2 which serves to remove the light alcohol formed (ethanol) as it is being formed and thus to shift the reaction equilibrium in the direction of formation of ADAME.

(23) The reaction mixture comprises the ADAME formed, unreacted EA and DMAE, catalyst C, polymerisation inhibitors, Michael adducts resulting from addition reactions on (meth) acrylic double bonds, and other heavy compounds such as oligomers or polymers.

(24) According to step (b) of the process, the reaction mixture is distilled on a distillation column (tailing column 3). At the top of column 3, a flow 7 is recovered devoid of most of the catalyst and polymerisation inhibitors and comprising the ADAME produced and light compounds such as DMAE and EA, with a minor fraction of Michael adducts and heavy products.

(25) At the bottom of column 3 a heavy fraction 4 is recovered comprising the catalyst, polymerisation inhibitors, Michael adducts and heavy compounds, with a minor fraction of ADAME and DMAE and traces of light compounds.

(26) According to step (c) of the process, flow 7 is subjected to purification which is carried out using distillation column 8, whose top flow 9 comprising the unreacted reagents is recycled to the reaction, with the bottom flow 10 directed to a distillation column 11 making it possible to obtain at the top the purified ADAME 12, and at the bottom a flow 13 rich in inhibitors which is recycled in the crude reaction mixture flow feeding the first column 3.

(27) According to step (d) of the process, the heavy fraction 4 from the bottom of column 3 which contains mainly the catalyst is partly concentrated on a film evaporator 5 which enables the separation of the traces of light compounds which are then recycled to the feeding of column 3, with the heavy residue 6 being removed or sent to a cracking unit (not shown), or optionally recycled to the reaction.

(28) The heavy fraction 4 from the bottom of column 3 can be partly recycled to the reaction (step e).

(29) This invention thus provides a simple solution to implement on existing (meth) acrylic ester synthesis plants and leading to improved productivity and selectivity. The process according to the invention also minimizes the size and energy of equipment for separation/recycling of flows generated during the purification of the reaction medium.

(30) The following examples illustrate the present invention without limiting its scope.

EXPERIMENTAL PART

Example 1

(31) On an industrial unit producing ADAME from ethyl acrylate (EA) and N,N-dimethylaminoethanol (DMAE), the catalyst (ethyl titanate solution in DMAE) is introduced to the reaction through an immersion rod, separated from the reactant flows, directly into the reactor.

(32) A static mixer was placed on the recirculation loop of the reactor as shown in FIG. 2, to replace the injection lance. The reactants and catalyst are introduced into the reactor through this mixer.

(33) The reaction conditions, temperature, residence time and flow rate were not changed.

(34) DMAE alcohol and catalyst setting, as well as the heavy quantity exiting the unit (fraction 6 in FIG. 3) for one tonne of ADAME produced, were determined over a period of 8 months before and after adding the mixer.

(35) The test results indicated that the installation of a static mixer replacing immersion rods to introduce the reagents and catalyst led to:

(36) A reduction of 3 kg/t of catalyst

(37) A reduction of 2 kg/t of DMAE

(38) The improvement of the AE yield induced by the addition of the mixer has not been quantified.

(39) In addition, the heavy quantity exiting the unit could be reduced by a mass of more than 10%.

(40) The facility productivity of the facility has globally increased.

Example 2

(41) In order to evaluate the quality of reagent mixing within a reactor, a CFD (Computational Fluid Dynamics) simulation method was applied. This method makes it possible to demonstrate low mixing zones, providing a heterogeneity of the residence times which induces a degradation of the conversion of reagents and selectivity of chemical reactions. Two approaches were used to highlight the advantages of the method according to the invention:

(42) 1) Visualization of the Flows and the Mixing of Reagents in a Reactor

(43) Particles course simulating EA and DMAE compounds from their introduction into a reactor through immersion rods was visualized. A heterogeneity of the routes followed by these reagents could be demonstrated, and the direction followed by each of the reagents was not moving towards an immediate mixing.

(44) In addition, according to the arrangement chosen in the reactor for the DMAE introduction rod, a high heterogeneity of its concentration in the reactor was observed by generating enriched zones and depleted zones of DMAE reagent. Introduction rods act as obstacles and also constitute sources of interference of reagent flows.

(45) The arrangement of the rods for introducing reagents into the reactor must be subject to optimisation studies in order to minimize these problems.

(46) According to the invention, the formation of zones with over- or under-concentration of reagents is prevented by ensuring a perfect mixture of the reagents using a static mixer upstream of the reactor, on the recirculation loop. The conversion of the reagents is then done according to uniform kinetics, and the formation of Michael-type by-products is minimized.

(47) 2) Determination of the Effective Volume in the Reactor

(48) The injection of particles of the two reagents, EA and DMAE, as well as the catalyst, was simulated in a tank, on the one hand from injection cannulas, and on the other from the free surface receiving the flow of a mixing of reagents and catalyst carried out upstream. The number of injection time steps (one step is equal to 2 ms) was varied to check the rate at which the reagents spread in the tank. At the end of the injection, the number of cells crossed by all 3 compounds was counted, in order to calculate the corresponding volume representing the effective volume of the reactor.

(49) The comparison of the 2 injection systems, expressed as the percentage of the effective volume in relation to the reactor volume, is shown in the following table.

(50) TABLE-US-00001 Method of introducing reagents and catalyst Immersion rods Upstream mixer 5000 pas time 0% 27.8% 10000 pas 0.3% 93.3% 14000 pas 50% 99%

(51) With the process according to the invention, an instantaneous and homogeneous mixture of the reagents is observed and the reagents fill up the entire reactor volume more rapidly.