Process for producing alkyl acrylate

Abstract

The invention relates to the production of alkyl acrylate according to a continuous transesterification process. In one embodiment the process of the invention uses a simple column to purify a reaction mixture of acryl acrylate in one step yielding alkyl acrylate with a purity of greater than 99.8%.

Claims

1. A process for the continuous production of alkyl acrylates, by a transesterification reaction between a light alkyl acrylate and a heavy alcohol in the presence of at least one catalyst and at least one polymerization inhibitor, said transesterification reaction represented by the reaction:
H.sub.2CCHCOOR.sub.1+R.sub.2OHH.sub.2CCHCOOR.sub.2+R.sub.1OH wherein R.sub.1 is a methyl or ethyl group, R.sub.2 is a linear or branched alkyl group having 4 to 9 carbon atoms, and optionally comprising a nitrogen atom, carrying out said reaction in a reactor coupled to a distillation column from which an azeotropic mixture comprising light alkyl acrylate and light alcohol generated by the transesterification reaction is drawn off, sending a crude reaction product comprising unreacted reactants, formed reaction products, catalyst(s) and polymerization inhibitor(s) to a single distillation column which is a simple column lacking a vertical divided wall and under reduced pressure for distillation, whereby the distillation yields: at a top portion, a stream of light products consisting essentially of residual alcohols R.sub.2OH and R.sub.1OH and unreacted reactant H.sub.2CCHCOOR.sub.1, which is recycled to the reactor, in a bottom portion, product H.sub.2CCHCOOR.sub.2 which is drawn off laterally in a gas phase, at a bottom, a stream of heavy reaction products comprising the catalyst(s), the polymerization inhibitor(s) and H.sub.2CCHCOOR.sub.2 which is recycled in part to the reactor; such that said process produces said alkyl acrylates have a purity greater than 99.8%.

2. The process as claimed in claim 1, wherein the single distillation column processing the crude reaction product is a simple column containing distillation plates with or without downcomers, or containing packing of random or structured type, optionally with recentering plates for the distribution of liquid, able to operate at pressures below atmospheric pressure.

3. The process as claimed in claim 1 wherein the alcohol R.sub.2OH is selected from the group consisting of 2-octanol, 2-ethylhexanol and N,N-dimethylaminoethanol.

4. The process as claimed in claim 3 wherein the alcohol is 2-octanol.

5. The process as claimed in claim 1 wherein the transesterification catalyst is an alkyl titanate of formula Ti(OR.sub.1).sub.4 or Ti(OR.sub.2).sub.4 in solution in the alcohol R.sub.1OH and/or R.sub.2OH.

6. The process as claimed in claim 1 wherein R.sub.1 is an ethyl group.

7. The process as claimed in claim 1 wherein the catalyst is present in an amount of 510.sup.4 to 510.sup.2 mol per mole of R.sub.2OH.

8. The process as claimed in claim 1 wherein compound H.sub.2CCHCOOR.sub.1 and the compound R.sub.2OH have a molar ratio between 1 and 3.

9. The process as claimed in claim 1 wherein the transesterification reaction is carried out at a pressure between 350 mmHg (0.4710.sup.5 Pa) and atmospheric pressure, and at a temperature between 90 C. and 150 C.

10. The process as claimed in claim 1 for the manufacture of 2-octyl acrylate, using ethyl titanate and/or 2-octyl titanate in 2-octanol as the catalyst.

Description

BRIEF DESCRIPTION OF THE FIGURE

(1) The invention is best understood from the following detailed description when read in connection with the accompanying FIGURE.

(2) The FIGURE depicts an operating example of the process according to the invention.

DETAILED DESCRIPTION

(3) In general, the light alkyl acrylate reactant is chosen from methyl acrylate or ethyl acrylate, more preferably ethyl acrylate.

(4) According to a very particularly beneficial embodiment of the process of the invention, the starting materials are of natural, renewable origin, that is to say they are bio-based. For example, the 2-octanol may be obtained by alkaline treatment of ricinoleic acid derived from castor oil.

(5) More particularly, the light alkyl acrylate may be derived from acrylic acid of renewable origin, possibly being in particular obtained from glycerol, according to a process comprising a first step of dehydrating the glycerol to give acrolein, followed by a step of gas-phase oxidation of the acrolein thus obtained; or may be obtained by dehydrating 2-hydroxypropionic acid (lactic acid) or 3-hydroxypropionic acid and their esters.

(6) The heavy alcohol reactant R.sub.2OH is a primary or secondary alcohol with a linear or branched alkyl chain comprising from 4 to 9 carbon atoms, preferably from 5 to 9 carbon atoms, and possibly comprising a nitrogen atom.

(7) In general, the reactant R.sub.2OH may be chosen, without this list being limiting, from butan-1-ol, butan-2-ol, isobutanol, penton-1-ol (amyl alcohol), 2,2-methylpropan-1-ol (isoamyl alcohol), hexan-1-ol, benzyl alcohol, 1-octanol, 2-octanol, 2-ethylhexanol, 1-nonanol, N,N-dimethylaminoethanol and N,N-diethylaminoethanol.

(8) Preferably, the alcohol is chosen from 2-octanol, 2-ethylhexanol and N,N-dimethylaminoethanol.

(9) More preferably, the reactant R.sub.2OH is 2-octanol.

(10) The catalyst is chosen from all catalysts with the capacity to catalyze the transesterification reaction between a light alkyl acrylate and a heavy alcohol, for example acids such as sulfuric acid and p-toluenesulfonic acid; basic compounds such as alkoxides, hydroxides, carbonates, phosphates, oxides or complexes of alkali metals or alkaline earth metals; metal alkoxide complexes such as aluminum alkoxide or magnesium alkoxide; titanium-based compounds such as titanium alkoxides, titanium phenoxides or alkyl titanates; compounds based on lead, zinc or tin; copper, iron or zirconium complexes.

(11) More particularly, the catalyst according to the process of the invention is chosen from an alkyl titanate of formula Ti(OR.sub.1).sub.4 or Ti(OR.sub.2).sub.4 in solution in alcohol R.sub.1OH and/or R.sub.2OH, for example a solution of 80 to 90% ethyl titanium in alcohol R.sub.2OH or ethanol, and/or the R.sub.2OH titanate in alcohol R.sub.2OH. It is understood that the alcohol used to place the catalyst in solution is the same as that used or generated in the transesterification reaction.

(12) More preferably, 2-octyl titanate in solution in 2-octanol, obtained beforehand by reacting ethyl titanate or isopropyl titanate with 2-octanol at 100 C., is used.

(13) The reaction is carried out in the presence of one or more polymerization inhibitors which are introduced into the reactor in an amount of 1000 to 5000 ppm relative to the crude reaction product mixture. As polymerization inhibitors which may be used, mention may be made for example of phenothiazine, hydroquinone, hydroquinone monomethyl ether, di-tert-butyl para-cresol (BHT), TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy), di-tert-butylcatechol, or TEMPO derivatives such as 4-hydroxy(OH)-TEMPO, on their own or mixtures thereof in any proportions. A supplementary addition of polymerization inhibitor is generally carried out during the subsequent purification processing, in particular at the distillation column.

(14) The single distillation column processing the crude reaction product according to the process of the invention is a simple distillation column, for example a column with structured packing or a plate column, generally comprising between 15 and 20 theoretical plates, for example 18 theoretical plates, the pressure of which may be adjusted to the desired level, optionally protected by thermal insulation, and optionally fitted with access devices for maintenance operations.

(15) Within the context of the present invention, the term simple distillation column is intended to mean a column containing distillation plates with or without downcomers, or containing packing of the random or structured type, optionally with recentering plates for the distribution of liquid, able to operate at pressures below atmospheric pressure. This column is fitted with a system enabling the product to be drawn off as vapor, in the lateral position of said column, and does not comprise a vertical dividing wall.

(16) An operating example of the process according to the invention is now described with reference to the appended FIGURE.

(17) The light alcohol (R.sub.1OH) formed in the reactor by the transesterification reaction between a light alkyl acrylate (3) and a heavy alcohol (1) in the presence of catalyst (2) is continuously fed (4) into a distillation column (CX1) on top of the reactor (A) in the form of an azeotropic mixture with the light alkyl acrylate (3). The azeotropic mixture may be used in a unit for synthesizing light ester (6).

(18) After reaction, according to a residence time in the reactor of generally between 3 and 6 hours, the crude reaction product mixture (5) contains the desired alkyl acrylate with as light products the heavy alcohol (R.sub.2OH) and the unreacted light alkyl acrylate, and as heavy compounds the catalyst, the polymerization inhibitor(s) and heavy by-products of the reaction.

(19) The crude reaction product mixture (5) undergoes purification processing in a single distillation column (CX2) in order to obtain on the one hand the pure desired alkyl acrylate (9) which is drawn off laterally, and on the other hand, at the top of the column, the residual alcohols (R.sub.2OH and R.sub.2OH) and the light alkyl acrylate which have not reacted (7) and are intended to be recycled (11), and at the bottom of the column, catalyst, polymerization inhibitor, heavy by-products of the reaction and the heavy ester (8) which are intended to be recycled in part (12) to the reactor (A), with the other part being sent (10): either to a film evaporator (not shown on the diagram) to recover an overhead stream containing the desired alkyl acrylate and a bottoms stream which is sent to a destruction facility, or to a destruction facility.

(20) The column (CX2) is a simple distillation column operating under reduced pressure, preferably corresponding to a column with structured packing or a plate column comprising between 15 and 20 theoretical plates, preferably 18 theoretical plates, operating under reduced pressure.

(21) Preferably, the distillation column processing the crude reaction product operates at a pressure of between 20 and 150 mmHg (or between 0.02710.sup.5 Pa and 0.210.sup.5 Pa), preferably between 20 and 75 mmHg (or between 0.02710.sup.5 Pa and 0.110.sup.5 Pa).

(22) Preferably, the desired alkyl acrylate is drawn of laterally in the gas phase in the bottom portion of the distillation column, between theoretical plates 12 and 14 for a column with 18 theoretical plates.

(23) The process according to the invention makes it possible to produce the desired product, i.e. alkyl acrylate, with a purity of greater than 99.8%.

(24) The following concrete but nonlimiting examples are given in order to illustrate and better understand the invention.

EXPERIMENTAL SECTION

(25) In the examples, the percentages are given by weight unless indicated otherwise, and the following abbreviations have been used: EA: ethyl acrylate 2OCTA: 2-octyl acrylate PTZ: phenothiazine HQME: hydroquinone methyl ester
Example

(26) Ethyl acrylate (3), 2-octanol (1) and a mixture of ethyl titanate (2) in solution in 2-octanol (90% mixture of ethyl titanate in 2-octanol) with phenothiazine inhibitor, in proportions by weight of 50.1/49.7/0.2, are fed to a perfectly stirred reactor A heated by an external exchanger and with an distillation column (CX1) on top, with 12 theoretical plates.

(27) The reactor is heated with air bubbling and as soon as the temperature reaches 125 C. under 640 millibar, the EA (3) stabilized with 2000 ppm of PTZ, the 2-octanol (1) and the ethyl titanate in solution in 2-octanol (2) are introduced continuously in proportions by weight of 50.1/49.7/0.2.

(28) At the top of the column (CX1), the EA/ethanol azeotrope (4), with a composition by weight of 40/60, is drawn off continuously. This mixture (4) is recycled to the light ester facility.

(29) The crude reaction product (5), obtained by continuous reaction, contains 2OCTA, unreacted EA, unreacted 2-octanol and a mixture comprising the catalyst with the polymerization inhibitors and heavy derivatives.

(30) The stream (5) is continuously sent to a single distillation column (CX2) with 18 theoretical plates operating under reduced pressure and heated by an external exchanger to a temperature of 140 C.

(31) At the top of the column (CX2), a mixture of 2500 ppm PTZ in EA (not shown in the FIGURE) is introduced.

(32) The column CX2 separates, at the top, a mixture (7) of EA/2-octanol/2OCTA with a composition of 52.4/34.2/4.6 which is recycled (11) to the reactor (A), and at the bottom, a mixture (8) comprising a mixture of heavy products, polymerization inhibitors and catalyst with a 2OCTA fraction with a proportion by weight of 15.9/84.1, which is recycled in part to the reaction (12), and the other part is send to the heavy processing section (10).

(33) Pure 2-octyl acrylate (9) is obtained by laterally drawing off in the gas phase in the bottom portion of the column at plate no. 13. The purity of the 2-octyl acrylate is 99.89%.