IMPROVED METIIOD FOR I'RODIJCING ALICYL (METI1)ACRYLATES
FIELD OF TECHNOLOGY
The present invention rclates to the production of alkyl (meth)acrylates by direct
5 esterification of (meth)acrylic acid by the corresponding alcohol, said reaction being
catalyzed by a cationic resin.
It relates more particularly to an improved method for producing Cs-Clo alkyl
(meth)acrylates, in particular 2-ethylhexyl acrylate, employing novel reaction
conditions leading to simplification of the method and an increased rate of production of
10 a product complying with the standards with respect to purity.
PRIOR ART AND THE TECHNICAL PROBLEM
The problems that arise during production of C.+-CIa~lk yl (meth)acrylates by
direct esterification of (meth)acrylic acid in the presence of a cationic resin as catalyst
15 are most often linked to the complexity of the purification steps required after the
reaction step to obtain a product of high purity, generally to the detriment of process
productivity.
In order to simplify the downstream purification operations, it was proposed in
the method for producing unsaturated carboxylate described in document EP 1219587
20 in the applicant's name, to carry out the esterification reaction by ascending passage of
the mixture of the reactants through a bed of a cationic resin, in a recirculating loop that
is connected to a stirred tank in which the reactants are mixed together and from which
the water of reaction is removed in the form of an azeotrope with the esterifying
alcohol. The esterification reaction is carried out in the presence of a slight excess of
25 alcohol, in particular with an overall acid/alcohol molar ratio between 0.6 and 1.
According to one embodiment, a partial reaction upstream of the stirred tank is carried
out by directing the mixture of reactants in ascending mode through a second bed of the
cationic resin as catalyst.
Although this method leads to high degrees of conversion and to high
30 selectivities, it seemed to the applicant that the complexity of the reaction zone and of
its operation made the method difficult to implement and did not allow the desired
purity to be obtained for the finished product.
111 the method for producing methacrylic esters by direct esterification catalyzed
by sulfuric acid, described in document US 4,748,268, the reaction mixture at reactor
outlet is fractionated co~~tinuousliyn a distillation col~unn,i nto tops rich in the ester
produced, and a bottoms stream containing the unreacted reactants, water, nonvolatile
5 byproducts, the catalyst and a small amount of ester. This bottoms stream is partly
returned to the reactor, thus constituting a recirculating loop in the installation.
After much research, the applicant found that it is possible to produce
(meth)acrylic esters or high purity by direct esterification in a simplified reaction zone,
using an excess of alcohol for the esterification reaction and recycling a high proportion
10 of the reaction mixture in a recirculating loop only comprising the esterification reactor
and a distillation column that removes the water produced in the form of an azeotrope
with the esterifying alcohol. Surprisingly, these operating conditions make it possible to
optimize the yield of the reaction, with efficient removal of the water produced by the
reaction, thus minimizing the secondary reactions responsible for the formation of
15 impurities and heavy byproducts, and therefore for a drop in process productivity.
The present invention therdore relates to an improved method for producing
alkyl (meth)acrylates that is simple to implement, with a high yield and little generation
of heavy byproducts, which simplifies the domstream purification operations.
Moreover, the purified product only contains slight traces of impurities associated with
20 the acid and the alcohol employed.
SUMMARY OF TIE INVENTION
The present invention relates to a method for producing a C ~ - CaIl~ky l
(meth)acrylate by direct esterification of (meth)aerylic acid by the corresponding
25 alcohol, the water of reaction being removed in the form of an azeotrope with the
esterifying alcohol from a distillation column positioned above the esterification reactor
comprising a cationic resin as catalyst, characterized in that the alcoholiacid molar ratio
at reactor inlet is between 1.4 and 3, and in that the crude reaction mixture circulates in
a recirculating loop linking together the reactor and the column for removing the water,
30 at a recirculation rate ranging from 6 to 25, expressed as the weight ratio of the stream
directed into the loop to the stream sent to a purification treatment.
PC' 1 It 1120 15105 1648
The method of the invention S~lrther comprises a pul.ification treatment of thc
crude reaction mixture leaving thc recirculating loop colnprising at least the steps:
(i) submitting the crude reactionmixture .to distillati011 in a topping column
to oblain:
5 o at the top, a stream consisting essentially of the unreacted reactants;
o at the bottom, a stream comprising the required ester, impurities
associated with the acid and the alcohol, and heavy byproducts;
(ii) directing the bottom stream from the topping coluinn to a rectification
column [or separating:
o at the top, the purified ester that is required;
o at the bottom, a stream containing impurities associated with the
acid and the alcohol and heavy byproducts, which is concentrated
on a film evaporator or distilled in a tailing coluinn in order to
recycle the light compounds present to the rectification column,
and remove the final residue of heavy byproducts.
According to one embodiment of the invention, the operating conditions of the
topping column are adjusted to entrain, at least partly, the light impurities associated
with the acid or with the alcohol.
20 According to one embodiment of the invention, the bottom stream from the
topping column is submitted to washing with an aqueous stream before it is sent to the
rectification column in step (ii).
According to onc embodiment of the invention, the topping step (i) is preceded
by a step of distillation of the crude reaction mixture in a tailing column for separating
25 part of the heavy byproducts.
BMEF DESCRIPTION OF THE FIGURES
- Fig. 1 is a schematic representation of the reaction section for carrying out the method
according to the invention.
30 - Fig. 2 is a schematic representation of the purification section of the method according
to the invention.
- Fig. 3 illustrates one embodiment of the purification section of the method according
to the invention, including a step of washing the topped stream.
- Fig. 4 illustrates oilc e~nbodiment of the put.ilication section of the method according
to the invention, including a prelinlinary step of tailing the crude reaction mixture.
DETAILED ACCOUNT OF THE INVENTION
The invention will now be described in more detail in the following ~lonlimiting
description.
In the present description, the terms "between" or "ranging from" denote the
inclusive range.
Referring to Fig. 1, generally the esterification reaction is carried out in a reactor
(1 07) surmounted by a distillation column (105) for extracting the water generated by
the reaction. The water of reaction is removed as it is formed in the form of an
azeotrope with the esterifying.al.coho1 in stream (104), in order to shift the esterification
equilibrium.
The reactor may be a fixed-bed reactor or a suspended-bed reactor.
The assembly shown in Fig. 1 forms a recirculating loop in which the crude
reaction mixture makes a certain number of passages through the reactor before being
sent to a purification section. The assembly thus constitutes a stirred loop reactor with
water removal. It is not necessary to include a stirred tank to ensure mixing of the
reactants, said mixing being carried out directly in line owing to the presence of the
recirculating loop.
The reactor may have descending or ascending feed, preferably descending. The
(meth)acrylic acid may be fed to the inlet of the column (stream 101) or to the bottom of
the column (stream 101 bis). The alcohol (103) is fed directly to the distillation column.
A recycling stream (102) containing uxeacted alcohol and acid from the purification
section may also be introduced into the recirculating loop, notably at the inlet of the
distillation column.
The distillation column, generally packed, is equipped with a top condenser, a
decanter, receiver and trap (not shown in the figure), for decanting the vapors
condensed at the top and separating an organic phase comprising alcohol and traces of
ester, which is recycled to the column, and an aqueous phase, which is removed. The
column generally operates at a pressure in the range from 50 to 70 rnmHg.
According th the invention, the esterification reaction is carried out in conditions
with excess of alcohol; in particular, the alcohollacid molar ratio at reactor inlet is
between 1.4 and 3, preferably between 1.8 and 2.3. The alcohollacid molar ratio refers
to the contents of alcohol and acid in the various streams feeding the esterification
reactor (stream of pure reactants, rccycled strean1 and recirculatecl stream). In--line
analysis of stream (106) afier removal of the water of reaction entering the reactor
malies it possible to adjust the feed streams of pure reactants to obtain the desired ratio.
The reactor comprises a cationic resin as csterification catalyst, prcfcrably a
5 strong cationic resin, for example a strong sulfonated cationic resin of the
styreneidivinyl benzene type with sulfonic groups. As examples of resins, we may
mention those marketed under the names DIAION" PK208 or PK216 by the company
Mitsubishi, or those marketed under the name LEWATIT" K2620 or IC2621 by the
company Lanxess, or those marketed under the name AMBERLYST" A15, A16 or A46
10 by the company Rohrn & I-Iaas.
The reaction temperature is generally between 70" and 10O0C, preferably
between 75°C and 95°C. The presence of the recirculating loop makes it possible to use
. , a lower temperature with a constant. production rate. ... , ,.
The reaction is generally carried out in the presence of at least one
15 polymerization inhibitor selected from phenothiazine, hydroquinone (HQ), and
derivatives thereof such as bydroquinonc methyl ether (I-IQME), 2,6-di-tea.-butyl-4-
methylphenol (BHT), 2,4-dimethyl-6-tea.-butylphenol (Topanol A), salts of
thiocarhamic or dithiocarbamic acid, N-oxyl compounds, such as 4-hydroxy-2,2,6,6-
tetramethyl piperidinoxyl (4-OH Tempo), compounds with nitroso groups, such as N-
20 nitrosophenyl hydroxylamine and ammonium salts thereof, quinones such as
benzoquinone, and amino compounds such as derivatives of paraphenylenediamine, at
contents in the reaction mixture that may be between 50 ppm and 5000 ppm, optionally
in the presence of depleted air, but generally at contents between 150 ppm and 1000
ppm. The polymerization inhibitors may be added in various places, with the
25 introduction of the reactants or at the top of the distillation column.
According to the invention, the crude reaction mixture from the reaction is sent
to the recirculating loop, at a recirculation rate ranging from 6 to 25, this rate being
expressed by the weight ratio of the stream directed into the loop to the stream sent to
the purification treatment, in particular by the weight ratio betweell the flow rate of
30 recirculating crude reaction mixture (108) and the flow rate of crude reaction mixture
leaving the loop (109). Preferably, the recirculation rate is between 10 and 20, more
preferably between 10 and 15. In these conditions, the total residence time of the crude
reaction mixture in contact with the catalytic resin, expressed by the ratio of the volume
of resin to the total volume flow ratc of reactant fced is betwcen 2 hours and 6 hours,
advailtageously between 2.5 hours and 5 hours.
The method according to the invention applies to the synthesis of C,,-Clo alkyl
(mcth)acrylatcs, the esterifying alcohol being a primary or secondary aliphatic alcohol,
5 comprising a linear or branched alkyl chain having from 4 to 10 carbon atoms. As
examples of alcohols, we may mention butanol, 2-ethylhexanol, n-octanol, 2-octanol, 11-
decanol and 2-propylheptanol.
Preferably, the alcohol is 2-ethylhexan01 or 2-octanol.
Preferably, acrylic acid is used.
10 The method according to the invention makes it possible to optimize reilloval of
the water of reaction from the stream entering the reactor, which advantageously has the
effect of limiting tlie formation of acidic impurities associated with' the p r e h c e of
(meth)acrylic acid.
In fact the problem that arises when using acrylic acid is formation of P-
15 hydroxypropionic acid (called "HPA" hereinafter), and of P-aeryloxypropionic acid
(called AA "dimer" hereinafter).
HPA probably forms from the AA dimer in the presence of water and in contact
with the resin. Its formation depends on the reactionoperating conditions, the nature of
the cationic resin used, and the amount of water present.
20 Regarding the AA dimers, their formation is detrimental to the amount of heavy
byproducts to be incinerated, and consequently to the productivity.
The same types of impurities may also form in the case of methacrylic acid, in
particular P-hydroxymethylpropionic acid and P-methacryloxypropionic acid.
The operating conditions of the invention minimize the formation of these
25 impurities and make it possible to obtain, after the purification section, the'required
ester free from impurities associated with the acid, and complying with the standards
with respect to purity for preparing polymers in most fields of application, notably
pressure-sensitive adhesives (PSA).
Owing to the other secondary reactions that may lead to the formation of heavy
30 byproducts, the esterifying alcohol and the (meth)acrylic acid that have net yet reacted
add on to the double bond of the ester already formed (Michael addition) to form
(nlethyl)propionic and (meth)acryloxypropionic derivatives whose boiling point is
above the boiling points of (mcth)acrylic acid, the esterify~~iaglc ohol and the cstcr
formed.
Thcse heavy byproducts pose a problem of loss of raw materials and a problem
of separation and treatment for final removal.
5 It was observed, surprisingly, that the operating conditions of the method
according to the invention lead to less formation of heavy byproducts, resulting in
simplification of the purification section and improvement of the materials balance.
After the reaction zone, the reaction mixture leaving the recirculating loop is
10 submitted to a purification treatment, shown for cxample in Fig. 2, in which the
recirculating loop is shown schematically at (1).
The crude reaction mixture (2) leaving the recirculating loop is sent to a topping
column (3) which separates, at the top, a stream (4) essentially comprising the unreacted
reactants, and at the bottom, a stream (5) mainly comprising the required ester with
15 impurities associated with the acid and the alcohol and heavy byproducts. Column (3) is
for example a plate column, of the perforated plate type, or a packed column. Stream (5)
is sent to a rectification column (6) leading at the top to a stream (7) of purified ester,
and at the bottom to a stream (8), which is concentrated in a film evaporator (9) or
distilled in a topping column (not shown) in order to recycle the light compounds (10)
20 present to the start of the purification section, such as traces of unreacted reactants, and
remove the final residue (1 1) of heavy products.
Stream (4) essentially comprises the un~cacted reactants, (meth)acrylic acid and
esterifying alcohol, which are separated from the required ester on account of their
lower boiling point. This stream (4), which can be utilized, is recycled to the reaction. In
25 the case when impurities associated with the acid are formed in the reaction zone, it is
possible to adapt the operating conditions of the topping column so as to entrain the
HPA formed (in the case of acrylic acid) in the overhead stream rccycled to the reaction.
The HPA recycled to the reaction may react with the esterifying alcohol to give alkyl
hydroxypropionate, which is easily removed with the fraction of heavy byproducts at
30 the bottom of the rectification column. This embodiment of the invention also
colltributes to the production of a final product free from residual acidity.
According to onc embodiment of the invention, the reaction mixture is washed
with water afler topping, belbre separating the impurities and the heavy byproducts in
the rectification column.
According to this embodiment, illustrated in Fig. 3, the purification treatment of
5 the reaction mixture leaving the recirculating loop comprises at least the steps:
(i) submitting the crude reaction mixture to distillation in a topping column
to obtain:
o at the top, a stream consisting essentially of the unreacted reactants;
o at the bottom, a stream comprising the required ester, impurities
associated with the acid and the alcohol, aid heavy byproducts;
(i)a submitting the bottoms stream from the topping column to washing with
... an aqueous stream to obtain, aler decanting, . .
o an aqueous phase comprising all of the impurities associated with the
(meth)acrylic acid, and
o an organic phase comprising the required ester, heavy byproducts and
traces of water and of (meth)acrylic acid;
(ii) submitting said organic phase, after removal of the water, to a
rectification column for separating:
o at the top, the purified required ester
o at the bottom, a stream containing heavy byproducts, which is
concentrated on a film evaporator or distilled in a tailing column in
orcler to recycle the light compounds present to the rectification
column, and remove the final residue of heavy byproducts.
25 Referring to Fig. 3, the bottoms stream (5) from the topping column (3)
generally contains more than 90 wt% of ester, or even more than 94 wl% of ester,
impurities associated with the acid and the alcohol, and heavy byproducts, as well as the
polymerization inhibitors.
According to the invention, the watel extraction step is cairicd out with an
30 aqueous stream (20), which comprises pure water, or water from the reaction step, or a
mixture of the two in all proportions.
The washing tetnperatnre is not critical; it is generally between 25°C and 10O0C,
preferably between 50°C and 70°C.
Or the order oT 5g to 10g of water is uscd pcr l00g of stream (5); in order to
remove all the impurities associated with the acid, which wot~ld pose a risk of
catalyzing the decomposition of the heavy compounds subsequently in the purification
process. It is not necessary to use more water to remove all the acidic impurities.
5 Washing with 10% of water makes it possible, for example, to lower a content of
HPA of the order of 120 ppln to less than 1 ppm and reduce the content of AA dimer by
15 to 20%.
The amount of washing water is preferably optimized in relation to the content
of AA di~nepr resent in stream (5).
10 The aqueous phase (22) contains the bulk of the inlpurities associated with the
acid, and a small amount of acid.
The organic phase (13)- decanted in the decanter (12) contains the ester aud a
minor fraction of heavy compounds and light con~pounds with residual water, of the
order of 3500 ppm to 5000 ppm of water, which it is preferable to remove before
15 submitting said phase to the final distillation.
The organic phase obtained after washing with wxteter is therefore submitted to a
step of removal of water, and the water recovered can be recycled to the washing step.
The water present in said organic phase (13) may be removed by distillation
using a distillation column or using a thin film evaporator (15). In a preferred
20 embodiment of the invention, a thin film evaporator of the Luwa type is used. The
operating conditions, given only as a guide, arc in this case a pressulc of 150 mbar, a
temperature at the top of the evaporator of 24"C, an oil temperature of 130°C, an
evaporator toplbottom mass distribution of 10190.
Passage through the evaporator (or distillation column) males it possible to
25 reduce the water content to more than 95% in stream (14) and generate an aqueous
distillate (21), which may contain a small amount of ester, which is recycled, hlly or
partly, to the washing step.
The aqueous stream (20) used for washing is thus preferably a mixture of the
aqueous stream (21) fro111 the process, topped up with fresh water.
30 The water-free stream (14) is then sent to the last rectification column (6) of the
pure ester. Column (6) is for example a plate column, of the perforated plate type, or a
packed column. Because the bulk of the acid dimcr was removed in thc water washing
step, the opcratiilg conditions of colu~nn (6) arc facilitated and decomposition of the
heavy compo~indsis minimized.
The product distilled at the top of 'column (6) is a purified ester no longer
contai~ling impurities such as HPA, and having a content of esterifying alcohol
5 generally below 500 ppm and a content of acid di~nerg enerally below 100 ppnl.
Stream (16) at the bottom of column (6), rich in heavy compounds and possibly
containing traces of ester, may be partially recycled or removed.
According to anothcr embodiment of the invention illustrated in Fig. 4, the
10 topping step (i) is preceded by a step of distillation of the reaction mixture in a tailing
column for separating, at the bottom, a stream comprising the bulk of the acid dimer and
heavy compounds, with traces of ester, and at the top, a stream comprising the ester, the
unreacted reactants and impurities associated with the acid and traces of heavy
compounds, said overhead stream then being submitted to the topping step (i).
15 According to this embodiment of the invention, the bottoms stream from the
topping column in step (i), as well as the organic phase washed in step (i)a, contain
impurities associated with the acid and heavy compounds in reduced amount, which
makes it possible to reduce ihe amount of bottoms stream from the final distillation
column and obtain a pure product without residual acidity and free from residual
20 alcohol.
Referring to Fig. 4, the topping column (3) is preceded by a tailing column (30),
ofthe plate column or packed column type.
The reaction mixture (1) is sent to a first distillation column (30) in ordcr to
separate the bulk of the acid dimer and heavy compounds (tailing) and submit a stream
25 depleted of acid dimer and heavy compounds to the topping step.
The bottoms stream (31) from column (30) contains, besides the acid dimer and
heavy compounds, traces of light compounds and ester.
This stream (31) is advantageously concentrated, for example on a film
evaporator (35) allowing the light compounds with the ester to be recycled to the feed of
30 column (30), and remove the heavy residues (34), for example by incincration.
The overhead stream (32) from column (30), from which the majority of the
heavy compounds and almost all the acid dimers have been removed, is then sent to the
topping column (3), giving an overhead stream (4) containing the light products with
traces of ester. The bottoms strcam (33) froi~?th e topping colunln (3) conq?rises more
than 90 wt%, or even more than 94 wt% of ester, iinpurities associated with the acid and
heavy compounds not separated in the tailing step, and traces of light compounds.
As in the cmbodimerlt describcd above, this stream (33) is treated with an
5 aqueous stream (20) so as to remove impurities associated with the acid.
An amount of water of the order of 10% relative to the stream to be treated
generally malces it possible to remove all of the impurities associated with the acid in
the aqueous phase, and part of the acid dimer, the content of which is already reduced
owing to the prior tailing step.
10 The decanted aqueous phase (22) containing the impurities associated with the
acid is removed or recycled. The organic phase (13) is sent to the dryer (15), which may
consist of a colunni or preferably a film evaporator. . ., ..
The stream (21) containing water and ester is recycled, wholly or partly, for
washing the stream (33), thus minimizing the content of fresh water (20) to be
15 introduced into the washing circuit.
The dried stream (23) is sent to a final rectification column (6), fiom which the
purified ester (18) leaves at the top. At the bottom, stream (24) containing ester and
traces of alcohol is advantageously recycled to the feed of column (30).
According to this embodiment of the invention, an ester is obtained that is free
20 from residual acidity and has an alcohol content generally below 200 ppm and a content
of acid dimer generally below 5 ppm.
By employing a step of separation of the heavy compounds in thc tailing column
(30) upstream of separation of the light compounds in the topping colunm (3), a stream
that is almost free from acid dimer and heavy compounds can be transported to the rest
25 of the distillation train.
Absence of these impurities in the stream (23) feeding the rectification column
(6) of the pure product can facilitate the operation of this distillation column, reduce the
reflux ratio and the heating power on the column, which leads to better productivity of
the plant, reduced production of bottoms stream (24), and virtual absence of acid dimer
30 in the pure ester. The content of residual alcohol in the pure ester is also reduced, owing
to the virtual absence of heavy compounds and impurities associated with the acid in the
feed of the final distillation column.
The following examples illustrate the present illvention but without limiting its
scope.
EXPERIMENTAL, SECTION
In the examples, percentages are indicated by we~ght unless stated othcrwisc and the
5 following abbreviations have been used:
AA: acrylic acid
A2EH: 2-ethylhexyl acrylatc
2EH: 2-ethylhexanol
HPA: P-hydroxypropionic acid
10 Di-Ah: AA dimers
PTZ: phenothiazine
: influence of the alcohol/acid molar ratio (MR)
The equipment used for synthesis of 2-ethylhexyl acrylate is a small synthesis pilot
15 plant reproducing the operation of a stirred loop reactor with water removal, as shown
in Fig. 1.
The reactor contains 340 ml (initial apparent volume) of cationic resin K2620 from
Lanxess.
The reactor is fed with pure acrylic acid and 2-ethylhexanol. No recycled stream is
20 introduced.
For each passage, the residence time of the reaction mixture on the resin, represented by
the ratio of the volunle of resin to the volume flow rate of the stream recirculated to the
loop, is equal to 18 min. The total residence time, represented by the ratio of the volume
of resin to the volume flow rate of the feed stream, is equal to 2.9 hours.
25 The distillation column is a laboratory column of the Vigreux type corresponding to
about 6 theoretical stages, operating at a pressure of 80 mmHg, with a head temperature
of 35°C. The water of reaction is removed in the form of an azeotrope with 2-
ethylhexanol.
Two test series were carried out, the first series at a temperature of the bed of resin of
30 87"C, the second series at a temperature of 95°C.
The recirculation rate in the recirculating loop is equal to 7.9 or 8.
For each series, the feed rate of alcohol and acid was adjusted so that the molar ratio at
rcactor inlet was equal to 1.1 (or 1.2) and 2 (2.2).
For each test condition, 2 to 3 samples of ~zaction mixture wele taken after at least 48 11
of operation. The samples takcn were analyzed by gas or liquid chromatography, to
determine their composition by weight, and calculate the degrees of conversion and
sclcctivities according to thc following formulas:
5 Degree of conversion to acid, % = moles of acid conveiled / moles of acid in the
feed x 100
Selectivity of the ester relative to the acid, % = moles of ester forrnedimoles of
acid converted x 100
Selectivity orthe ester relative to the alcohol, % = moles of ester formedimoles
10 of alcohol converted x 100
With the number of moles of acid converted calculated from thc
difference between'the number of moles of acid in the Seed and the number of
moles of acid leaving the recirculating loop (in the aqueous phase at column top
and in the outgoing crude reaction mixture);
15 With the number of moles of alcohol converted calculated from the
difference between the number of moles of alcohol in the Seed and the number of
moles of alcohol leaving the recirculating loop (in the outgoing crude reaction
mixture)
20 A balance is performed at the ends of the compleie loop, quantifying the main
byproducts.
The results are presented in Table 1.
Table 1
TemperaturePC
Molar ratio
2EHiAA reactor
inlet
Recirculation rate
Conversion AA, %
Test 2
87
2
7.9
71.5
Tesi 1
comparative
87
1.1
7.9
66.0
Test 3
comparative
95
1.2
8
73.8
Test 4
95
2.2
8
- 79.3
/ Test 1 1 Test 2
comparative
Selectivity ester /
AA converted, % 1 1
2EH converted, %
Balance, heavy 43.1 34.3
byproducts / ester I formed, gkg
Di-AA 1 ester 1.3 0.6
formed, gkg
-31 HPA / ester 0.19
formed, glkg
Test 3
comparative
97.5
'Test 4
71
These tests show that increasing the alcohollacid molar ratio at reactor inlet makes it
possible to improve the conversion of the acid (the concentration of AA at inlet being
5 lower), but also the selectivity of the ester relative to the acid converted, for a selectivity
of the ester relative to the alcohol that is roughly constant.
The alcohollacid molar ratio at reactor inlet has an effect on the production of heavy
byproducts, according to the invention, the amount of byproducts generated during the
reaction decreases by more than 20%, which has a beneficial effect on purification of
10 the ester and on the amount of materials removed. This effect is accentuated at the
higher temperature.
The impurities associated with the acid are generated in a reduced amount in the
conditions of the invention.
15 Examvle 2: influence of the alcohol/acid molar ratio (MR)
Thls example illustrates the effect of the MR on an industrial productio~l unit for 2-
ethylhexyl acrylate at a scale of 90 tonnesiday.
The unit was operated with an alcohol/acid molar ratio at inlet of a catalyst bed ranging
from 1.25 to 1.9 (3 prodnctions PI, P2 and P3). 'The temperature was kept constant at
20 85"C, and the recirculation rate remained roughly identical.
The reactor is a fixed bed of 40 n1' of a strong cationic resin oS the rnacroporous type. 1t
is fed in descending mode.
The results are presented in 'Table 2.
Table 2
7 ~ 2 1
Recirculation rate 1 10.5 1 11 1 12
Temperature,"C
MR
Industrial production carried out in the MR conditions according to the invention gave a
substantial improvement in selectivity of the ester relative to the acid and the alcohol
and a crude product of 2-ethylhexyl acrylate containing only traces of impurities
associated with the acid. Moreover, the method generated a smaller amount of heavy
byproducts.
comparative
85
1.25
Overall degree of
conversion of AA %
Selectivity ester / AA
converted, %
Selectivity ester / 2EH
converted, %
Di-M in the crude
product, ppm
HPA in the crude product,
PPm
Heavy byproducts in the
crude product, ppm
: Effect of water on the formation of impurities associated with the acid and
heavy byproducts
This example has the aim of demonstrating the harmful effect of the presence or water
in the reactor on the formation of HPA and of AA dimer, and on the total amount of
heavy byproducts.
The equipment used is as in example 1 with the following operating conditions:
85
1.6
69.1
89.1
91.1
325
75
17900
85
1.9
69.4
93.5
94.5
240
75
12800
71.3
95.8
95.9
149
6 1 -
11600
Rcsin A16 from DOW.
llcaction tcmpcraturc: 88'C
Feed rate of fresh AA: 39 g/h
Flow rate of the stream recirculating in the loop: 950 g/h
5 Recirculation rate: 8
Alcohol/acid molar ratio in the feed: 1.1
Alcohol/acid molar ratio entering thc reactor: 1.2-1.3
Residence time in the reactor for one passage: 20.6 mill
Total residence time in the reactor: 3.6 hours
10 Test A was carried out using pure AA, and tcst B with a stream of AA with 1 wt% of
water added.
The results in Table 3 show that the amount of impurities associated with the acid and
heavy byproducts is greater in test B compared to tcst A.
15 Table 3
: influence of the recirculation rate
Test B
AA + 1 % watcr
7.6
62.5
42.4
Test B
74.3
54.5
Acid feed
Conversion AA, % in one
pass
Overall conversion of AA,
%
Selectivity ester / AA
converted, %
Selectivity ester / 2EH
converted, %
Balance of heavy
byproducts / ester
formed, gkg
Di-AAIester formed, glkg
HPA / ester formed, gkg
Test A
Pure AA
15.8
68.1
40.2
Test A
72.4
41.9
1.2
0.34
2.3
0.79
. > lwo scrics of tests were carried out on an industrial ~uuit,v arying the recirculation ratc
in thc recirculating loop.
In the same way, the conversion to acid, the selectivities for ester and the ainouut of
heavy byproducts were deterinined from samples taken after at least 48 h of operation.
5 The results are presented in Table 4.
Table 4
Test (a) Test (b)
Tempcrature,"C
Molx ratio 2EHIAA
reactor inlet
Recirculation rate
I byproducts 1 ester formed, / I I
79
2.3
Conversion AA, %
Balance of heavy
2.3
24
The degree of conversion of the acrylic acid increases when the recirculation rate
10 increases. The amount of heavy byproducts relative to the production of cster decreases
when the recirculation rate increases.
15
7
75-80
22
kglt
Di-AA / ester formed, kglt
HPA I ester formed, kglt
The crude reaction mixture obtained in test (a) was submitted to a purification section as
shown in Fig. 2. In particular, the topping column was controlled so as to separate most
15 of the HPA column top and obtain an ester virtually frce fiom impurities associated
with the acid.
Table 5 presents the composition in wt% of the various streams: stream (2) at outlet of
the reaction loop, stream (5) at the bottom of the topping column, stream (4) at the top
of the topping column, and the stream of purified ester (7).
20
68-72
26
0.001~
0.02
0.001
0.1 1 .
Example 5 (referring to Fig. 3)
5 A crude reaction mixture (I) obtained by the method of the invention has the following
composition by weight:
- A2EN: 67.8%
- 2EH: 19.4%
- AA: 7.7%
10 -HPA:119ppm
- AA dimer: 780 ppm
- Heavy compounds: q.s. 100%
The crude reaction inixture is sent to a topping column (3) which separales, at the top, a
stream (4) essentially comprising light compounds, notably the residual reactants AA
15 and 2EH, water, octenes, a small amount of 2-ethylhexyl acetate and traces of A2EH,
and, at the bottom, a stream (5) mainly comprising the required A2EH with impurities,
including heavy hyproducts.
Stream (4) is recycled to the reaction.
Stream (5) at the bottom of the topping column (3) has the following composition:
20 - A2EH: 94.35%
- 2EH: 0.041%
- M: 17 ppm
- HPA: 32 ppm
- AA dimer: 1340 ppm
wt%
A2EH
A A
di-AA
HPA
Heavy
products
Light
compounds
Stream (5)
- 97.4
< 0.001
0.032
0.0017
2.6
Stream (2)
61.2
5.8
0.0068
0.0029
4.9
Stream (4)
26.1
11.9
0.0042
7.4
- Stream (7)
99.79
0.0007
0.0002
0.0023
-
Stream (5) is washed Sor 10 inin at 70°C with pure water (20), at a ratc of 10g of water
pcr l0Og of streani (S), in a stirred vessel heated by circulation oS oil in a double jacket
(not shown), then the washcd streani is dccanted for 30 min at 70°C in tllc decanter
5 (12).
The decanted organic phase (13) has the following con~positionb y weight:
- A2EH: 94.22%
- 2EH: 580 ppm
- water: 3800 ppm
10 -AA:lSppm
- AA dimer: 1070 ppm
- HPA. none
-heavy compounds: q.s. 100%
It is observed that:
15 19% of the AA dimer passed into the decanted aqueous phase (22);
100% of the HPA is extracted in the aqueous phase;
10% of the total acidity (HPA + AA+ AA dimer) passcd into the aqueous phase.
The organic phase (13) is sent to a Luwa thin film evaporator (1 5), to remove the water
from it, under the following conditions: To oil 130°C - P: 150 mbar.
20 The residual water content in the dried organic phase (14) is 100 ppm.
The composition by weight of stream (14) is as follows:
- A2EH: 94.32%
- 2EH: 400 ppm
- AA: 16 ppin
25 - NPA: none
- AA dimer: 11 05 ppm
- water: 100 ppm
This stream (14) is distilled continuously on a packed column (6) having an efficiency
of about 6 theoretical plates, with the conditions:
30 Top pressure: 39 mbar - To top of column: 107°C - To bottom: 120°C
Stream (7) of purified A2EW, distilled at the top of the column, has the following
conlposition:
- A2EH: 99.64%
- 2EH: 474 ppm
- AA: 1 8 pprn
- IIPA: none
5 - AA dimer: 60 ppm
We obtain 2-ethylhexyl acrylate, free from HPA and depleted of residual 2-
ethylhexanol.
Example 6
10 Example 5 is repeated, reusing the aqueous phase (22) 3 times in succession for
washing the stream (5) (not shown in the figure).
Stream (5) is washed in the conditions of example 2 and then the decanted aqueous
phase ($A,) is reused for washing the stream (5).
The decanted aqueous phase ($&) is used for washing the stream (5) a third time. The
15 decanted aqueous phase is designated ($A3)
This example shows that the washing water may be reused several times without loss of
efficiency in removal of HPA, and thus reduce the consumption of clean water in the
20 washing step.
HPA,ppm
AA dimer,
PPm
PPm
Example 7 (referring to Fig. 4)
A crude reaction product (1) has the following composition by weight:
- A2EH: 66.26%
25 - 2EH: 20.64%
- AA: 8.56%
- HPA: 130 ppm
- AA dimer: 684 ppm
(22)
30
1332
142
$A1
287
2003
28
$0 1
none
1068
30
$A2
563
2357
32
$ 0 2
none
11 10
33
$A3
832
2386
37
$03
none
1200
34
- Hcavy conlpounds: q.s. 100%
The main hcavy byproducts prcscnt in the crude (1) are:
- 2-ethylhexyl hydroxypropionate: 0.54% - 2-ethylhexyl acryloxypropionate: 0.87% - 2-
ethylhexyl oxypropionate: 0.42%.
5 The total of the heavy byproducts prcsent in the crude reaction product (1) represents
67.5gh.
The crude reaction product ( I ) is sent continuously to a Vigreux column (30) having a
theoretical efficiency of about 5 theoretical plates at a flow rate of 3245gh for
separating the bulk of the heavy byproducts (tailing). The conditions are as follows:
10 Column top pressure: 47 mbar;
Column top temperature: 100-108°C;
Column bottom temperature: 1 15-120°C.
Flow rate of the overhead stream (32): 2953gih
Flow rate of the hotton~ss tream (31): 291.8gh
15 The composition by weight of the overhead stream (32) of the tailing column (30) is:
- A2EH: 65.46%
- 2EH: 22.92%
- AA: 9.66%
- HPA: 135 ppm
20 - AA dimer: 14 ppm
-heavy compounds: none
The composition by weight of the botton~ss tream (3 1) of the tailing colurnn (30) is:
- A2EH: 60.43%
- 2EH: 0.053%
25 - AA: llppm
- AA dimer: 6340 ppm
- Heavy compounds: 17.5% (i.e. 51.2glh)
Almost all the heavy compounds, as well as 97% of the AA dimer, are separated from
the crude reaction product (1) and remain at the bottoln of the tailing column (30).
30 The overhead streain (32) is free from heavy compounds and AA dimer, but contains
nearly all the HPA.
The bottoms streain (3 1) is trcated on a Luwa thin fihn evaporator (35), in the following
condit~oiis:
Tooil: 162°C - pressure: 65 mbar - fccd rate: 270 g!h
86% of the heavy compounds rcinain at the bottom of the evaporator (35) and are
removed in stream (34).
At the top oS the cvaporator (39, the outgoing stream (36) contains 70% of the A2EI1,
5 86% of the 2EH and 39% of the AA dimer contained in stream (3 1); stream (36) is
recycled to the tailing column (30).
The overhead stream (32) of the tailing column (30) is sent to the topping column (3).
The topping column (3) is of the same type as in the installations in Figs. 2 and 3.
10 The operating conditions of column (3) are as follows:
Top pressure: 47 mbar
Top temperature: 105°C - bottom temperature: 143-148°C.
Feed rate of stream (32): 2234gih
Flow rate of the overhead stream (4): 1203 g!h
15 Flow rate of the bottoms stream (33): 1030.9 gih
The composition by weight of the overhead stream (4) of the topping column (3) is:
- A2EH: 40.44%
- 2EH: 40.06%
- AA: 17.01%
20 - HPA: 174 pprn
- AA dimer: 26 pprn
- Heavy compounds: none
The overhead stream (4) from the topping column (3) is returned to the reaction.
The composition by weight of the bottoms stream (33) of the topping column (3) is:
25 - A2EI-I: 99.49%
- 2EH: 0.03%
- AA: <1 ppm
- HPA: 24 ppm
- AA dimer: 90 ppm
30 - Heavy compounds: 0.03%
The bott0117s stream (33) of the topping column (3) is washed with a stream of water
(20) at 70°C ibr 10 min (92.28 of water ibr 922.28 of stream (33)), then decanted at
70°C for 30 inin in the decanter (1 2).
915.7g of dccanted organic phase (13) and 94.7g of aqueous phase (22) are recovered.
5 The organic phase (13) is dried on a Luwa thin film evaporator (IS), to remove the
water from it, operating in the following conditions: To oil: 100°C -pressure: 38 mbar.
The con~positionb y weight of the dried stream (23) is:
- A2EH: 99.45%
- 2EH: 0.03%
10 -AA<,Ippm
- HPA: none
- AA dimer: 7'7 ppm
- water < 100 ppm
- Heavy compounds: 0.03%
15
Stream (23) is sent to the final distillation column (6), identical to that in examples 1
and 2, separating a stream (1 8) of pure A2EH at the top.
The operating conditions of column (6) are:
Top pressure: 39 mbar - To top of column: 107°C - To bottom: 120°C
20 The overhead stream (18) has the following composition:
- A2EH: 99.72%
- 2EH: 195 ppm
- AA: 8 ppm
- HPA: none
25 - AA dimer: <1 ppm
- Heavy compounds: none
We obtain a 2-ethylhexyl acrylate free from I4PA and having a very low residual
content of 2-ethylhexanol.
Stream (24) at the bottom of the distillation column of the pure product is rctumed to
30 , the feed of the tailing column (30).
1. A method for producing a C4-Cj0 alkyl (meth)acrylate, by direct esterification of
(rneth)acrylic acid by the corresponding alcohol, the water of'reaction being removed in
5 the form of an azeotrope with the esterifying alcohol [rom a distillation colu~nn
positioned above the esterification reactor comprising a cationic resin as catalyst,
characterized in that the alcohollacid molar ratio at reactor inlet is between 1.4 and 3,
and in that the crude reaction mixture circulates in a recirculating loop linking together
the reactor and the column for removing the water, at a recirculation rate ranging from 6
10 to 25, expressed by the weight ratio of the strea1-11 directcd into the loop to the stream
sent to a purification treatment.
2. The method as claimed in claim 1, characterized in that the alcohollacid molar
ratio at reactor inlet is between 1.8 and 2.3.
15
3. The method as claimed in claim 1 or 2, characterized in that the recirculation
rate is between 10 and 20, preferably between 10 and 15, expressed by the weight ratio
of the stream directed into the loop to the stream sent to a purification treatment.
20 4. The method as claimed in any one of the preceding claims, characterized in that
the acid is acrylic acid.
5. The method as claimed in any one of the preceding claims, characterized in that
the alcohol is butanol, 2-ethylhexanol, n-octanol, 2-octanol, n-decanol and 2-
25 propylheptanol, preferably 2-ethylhexanol or 2-octanol.
6. The method as claimed in any one of the preceding claims, characterized in that
the total residence time of the crude reaction mixture in contact with the catalytic resin,
expressed by the ratio of the volume of resin to the total volume flow rate of reactant
30 feed, is between 2 hours and 6 hours, preferably between 2.5 hours and 5 hours.
4. Thc method as claimcd in any one of the preceding claims, characterized in that
it further comprises a purification treatment of the crude reaction mixture leaving the
recirculating loop, comprising at least the steps:
(i) submitting the crudc reaction rnixturc to distillation in a topping columi~
5 to obtain:
o at the top, a streain consisting essentially of the unreacted reactants;
o at the bottom, a stream comprising the required ester, impurities
associated with the acid and the alcohol, and hcavy byproducts;
(ii) directing the bottom stream from the topping column to a rectification
10 column for separating:
o at the top, the purified ester that is required;
o at the bottom, a streain containing impurities associated with the
acid and the alcohol and heavy byproducts, which is concentrated
on a film evaporator or distilled in a tailing column in order to
recycle the light compounds present to the rectification column,
and remove the final residue of hcavy byproducts.
8. The method as claimed in claim 7, characterized in that the operating conditions
of the topping column are adjusted to entrain, at least pai-tly, the impurities associated
20 with the acid.
9. The method as claimed in claim 7 or 8, characterized in that the bottoms stream
from the topping column is submitted to a washing step (i)a with an aqueous stream
before it is sent to the rectification column in step (ii).
25
10. The method as claimed in claim 9, characterized in that the washing step (i)a
makes it possible to obtain, after decanting,
o an aqueous phase comprising all of the impurities associated with the
(meth)acrylic acid, and
30 o an organic phase comprising the required ester, heavy byproducts and
traces of water and (meth)acrylic acid;
said organic phase, after removal of the water, being submitted to step (ii).
11. The niethod as claimed in any one of the preceding claims, characterized in that
the topping step (i) is preceded by a step of distillation of the crude reaction mixture in a
tailing coluinn for separating part of the heavy byproducts.