Note: Descriptions are shown in the official language in which they were submitted.
2193~07
.` 1
sEsteriflcation of (meth)acrylic acid with an aL~canol
The invention relates to a process for the esterification of
(meth)acrylic acid with an alkanol in the p-~sence of an est~ ~ification
catalyst, in which ul~acl~d starting co,llpounds and the (meth)acrylic ester
o formed are sepal.-t~ off by ~lictill~tion and a bottom product compLisillg
oxy esters is oblaill~d. The term (meth)acrylic acid here denotes, as is
;u~tOludl~, acrylic or methacrylic acid.
The ~l~pdl~liOn of alkyl esters of (meth)acrylic acid is usually
carried out by esterification of (meth)acrylic acid with alkanols at elevated
IS lelllpclatul~ in the liquid phase in the pl~æ~ce or absellce of solvent and
in the plesen~e of acid as catalyst (DE-A 23 39 519). A disad~an~ge of
this method of pl~ar~lion is the second&~ acliol~ occulli,lg under the
ab.,~_.l,cntiol~d esterification conditions, viz. as yet unreacted starting
alcohol adds onto the double bond of alkyl (meth)acrylate already formed
20 (Michael addition) to give a coll~.Jund of the general formula I below an
as yet u,~act~d (meth)acrylic acid adds onto the double bond of the ester
formed to give a colllp~ulld of the general formula II. Multiple addition is
also pGssible. In addition, mixed types can occur. These addl-c~c (alkoxy
esters and acyloxy esters) are abbreviated as oxy esters.
2S
R'
RO--(CH2--CH--C02),~--R (I)
R' R'
3SCH2 = C--CO2 --(CH2--CH --C02)y--R (II)
2193~07
where x,y = 1-5
R = alkyl
R' = H or CH3
When R' = H, the esterification is of acrylic acid, when
R' = CH3, the esterification is of ~ lic acid.
The problem of oxy ester fo~ ation is particularly acute in the
preparation of esters of acrylic acid, with the main oxy esters formed being
alkuAy~ropionic esters and acylox~l,rol~ionic esters where x,y = 1. In the
preparation of esters of methacrylic acid, oxy ester follnalion occurs to a
o lesær extent. The formation of oxy esters is de3clil~i in DE-A 23 39 529.
This indicates that the f~J~llldlio~ of oxy esters occurs es~-n;~lly ;.~rlepe-~-dently of the specific esterification co~ ;o!~ Of very particular in~ ce,
is oxy ester formadon in the pl~alaliol of acrylates of Cl-C8-alkanols, in
particular C4-C8-alkanols, very particularly in the pl~pal~iliOII of n-butyl
acrylate and 2-ethylhe%yl acrylate.
It is a chala~tl.ist;c of the oxy esters that their boiling point is
above the boiling point of starting acid, starting alcohol, target ester formed
and any organic solvent also used.
The work-up of any such est~,ifcation reaction mi~lure is normally
20 carried out by, separadng unleact~ starting coml,uunds and the target este
- from the reaction IlliA~, by disdlladon, with the acid catalyst used for the
est~,.;fic~io.~ being able to be l~.llo~ befo.~halld, if appropriate, by
extraction with water and/or aqueous , lkali (cf. for e,~alnple, Ullmann's
Encyclopedia of In~llial Cl~.~i~,t~y, Vol. A1, 5th Ed., VCH, p. 167 ff.).
2s The bottom plul~lct re~nsini~ in such a ~ictillq~ive work-up c`ontains the
o~y esters which result in a consid~.able loss in yield.
For this reason, various further ~ have been e-~-..in~d in
order to solve the ploble~s res~ from follllalioll of the oxy esters.
Thus, JP-A-82/62229 desclibes the qllrqlinP sai~ullirlcation of the high-boiling30 esterification lesiducs. In this way, part of the alcohol used and acrylic acid
2193407
- 3 -
and ~B-hydroxypropionic acid or their salts are recovered. A simple and
econol,lical return of the products to the esterification reaction is therefore
not possible. JP-B-72/15936 describes the pl~pa,dtion of acrylic esters by
reacting ~B-alko,~,ylopionic esters with acrylic acid in the presellce of strong5 acids (transesterification). However, this forms as by-product equimolar
~ r~ i of ~B-alkuAy~lopionic acid which caMot be elu"led to the esterifi-
cation l~a~lion and ll,e.efol., r~present waste material. JP-A-93/25086 des-
cribes the dissocid~ion of the Michael addition product butyl
,B-l-lto.~yl~lopiollate (see formula I, x = 1, R = butyl) at cle~,at~d te"l~la-
o ture and in the p~c3el~ce of sulfuric acid and an excess of water. However,the yield is ody about 30%. Finally, JP-A-94/65149 desclibes the ~ oc;~
tion of the Michael addition pl~h~;ts I and II (see above, x = y - 1) in
the pl~e of lits~ .,, aiL~ ;des. In this reaction, the coll~lsio~ is
likewise low ( < 60%) and large a noun~ of titanate are luces~ y. This
15 process is thel~fol~ ullecol~o.l~ l and ell~o~e.lt~lly ullfiielldly because of
the large amounts of titanate to be dk.posed of.
GB 923 595 desclibes the .~co~ of llo~--.el~ from the residue
of the esterification of acrylic acid with alkanols in the ab~e.~ce of molecu-
lar o~ygen. It ~co..-~ c, inter alia, the removal of all volatile .llonu
20 prior to the d,issociation, tli~soc;~;on in the ple3encc of sulfuric acid and removal of the di~s~ n pr~luc~ by means of a stream of inert gas.
Accol-iing to the CA~IpleS, the dissociation is always carried out at at least
300C. Coke is formed as residue (17~0%) and this has to be dug out of
the reactor. This process is ~ fol~ neither econonlical nor can it be
25 carried out on an h~l~stlial scale. A further disadvantage is the need to
e..~lude o~ygen.
CN-A 1,063,678 dc3~,lil~s the ~k$~i~t;Q" of the aL~ ~iJnic
ester present in the est~lir.calion residue in the pl~sencc of sulfuric acid in
a cascade, with temperature and catalyst conc~,nlldtion (0.8-1.5%) being
30 ~ al in each reactor. Coupled with the dicc~;qliQn is a distillation to
2193907
separate alkanol and acrylate. The process is very cumbersome
and does not achieve high conversions.
Finally, CN-A 1,058,390 describes the dissociation
of alkoxypropionic esters in the presence of sulfuric acid,
etc., into alkanols and acrylic esters. This is carried out
stepwise. The dissociation is first carried out under reflux
and the reaction products are subsequently distilled off. The
dissociation of the acrylic acid-containing ester residues
from the preparation of ethyl/methyl acrylate (ethyl ethoxy-
lo propionate, methyl methoxypropionate) is carried out in thepresence of ethanol or methanol. Here too, the process is
complicated and does not achieve high conversions.
It is an object of the present invention to carry
out the redissociation of the oxy esters present in this
bottom product and to reuse the starting acid, starting
alcohol and target ester obtained thereby for the purposes of
the esterification without the disadvantages of the processes
of the prior art.
We have found that this object is achieved by a
20 process for esterifying (meth)acrylic acid with an alkanol in
the presence of an esterification catalyst in which unreacted
starting compounds and the (meth)acrylic ester formed are
separated off by distillation and a bottom product containing
oxy ester is obtained, wherein the bottom product is separated
off and either (a) the bottom product is admixed directly with
(meth)acrylic acid and the oxy esters present in the bottom
product are dissociated at an elevated temperature in the
presence of acid catalysts different from (meth)acrylic acid,
or (b) the oxy esters are first separated by distillation from
30 the bottom product, the distillate is admixed with
(meth)acrylic acid and is dissociated at an elevated
temperature in the presence of acid catalysts different from
(meth)acrylic acid. The alkanol is preferably n-butanol or 2-
ethylhexanol. In general, from 5 to 50% by weight, preferably
from 10 to 40% by weight, based on amount of bottom product
in (a) or distillate in (b), of (meth) acrylic acid is added.
2193~07
4a
(Meth)acrylic acid is normally added in a form known per se,
stabilized by means of polymerization inhibitors. According
to an advantageous embodiment of the invention, the process
of dissociation is carried out in the presence of molecular
oxygen.
2193407
In contrast to dissociation without the addition of (meth)acrylic
acid, the process according to the invention results in reduced formation of
by-products (dialkyl ethers, olefins).
According to an advantageous devetopment of the invention, the
5 bottom product has added to it, in addition to the acid esterification catalyst
which is di~.~lt from (meth)acrylic acid and may already be present,
further acids select~d from the group concicl;ne of mineral acids such as
sulfuric acid or phospholic acid, and alkyl- or arylsulfonic acids such as
"~ v-.lfonic acid or p-tolue!l~sulfonic acid. The total amount of acids
~o dill;~nl from (meth)acrylic acid which is then present can be from 1 to
20% by weight, p~ ,ably from 5 to 15% by weight, based on the amount
of the bottom product in (a) or destillate in (b). Co~ yonding catalytic
acid contents are a~l~anlage~ s for the l~iss~ialioll if this is pl~ceded by
sti~ ive separation of the oxy esters. It is particularly useful if a strip-
5 ping gas preferably co.-~ ;ng molecular oxygen is pæsed lhlougll the
bottom pl~lucl in (a), or tll~vugll the ~i~till~e in (b) oht~ ed ~l,el~,fio-ll, æ
an ellt~aiL~r for the dicsoci~;on pl~lU~;lS. Air or IllLl~Ui~,S of air with inert
gæ (e.g. niLI-)gel~) are advantageously used as sl,ip~ g gas.
The advantages of the process of the present hl~.dioll are, in
20 particular, that the dissociation pl~lcecds more quickly, a smaller amount ofby-plu~l~cls such as ethers or olefins is formed and a smaller ~nollnt of
acidic C~iRsoc;qt;on catalyst is co~ ...r~. Thus, among other things, smaller
losses of starting materials, particularly of alcohols, occur than in known
p~cesses. In a~dition~ high l1iC~ ion yields can be achieved. The direct
25 return of the I;cs~i~t;on llli,~l.n., does not adversely affect the purity of the
(meth)aclylic ester and leads to a low ether content. For this reason, no
coLu~licated separation of the ether from the easily polyl~ i~bl~
(meth)acrylic ester is ~esc-~y.
In the ~istill~ive sepalalion of the oxy esters from the bottom
30 p~ ct, the (1ictill~tion coL~dilions depend on the type of alcohol colll~
2193~7
~.
.- 6
used in the esterification. In general, a temperanlre of from 100 to 300C
and a pressure of from I to 50 mbar are employed. Any conventional
~i~tillq~ion appdlalus is suitable for the ~i~till~ion process. Since only a
simple 3CpalatiOII task is to be pe,~u~llled, a simple splash guard is gener-
5 ally ~ jen~, i.e. a column is not normally le~luil~d.
For the work-up accol~lh~g to the present i"~enliol~ of the oxy
esters ûbtained in the bottom pl~blcl in the esterification or of the oxy
ester ~ tillqt~ separated from the esterification bollo~lls a simple heatable
stirred reactor with jacket heating or heating coil, or else a forced-circula-
lO tion evaporator, for example a falling-film evaporator or flash e~olatol,
c~,u~ vith a ia;~1F~ e time vessel, can be used. To achieve better
separation of the ~I;R~ ';OU p.ud~ from the bottom p.û.luct or oxy ester
distillate, it may be advsn~sgeous to use a ~e~l;fi~a~ion ~ super-
posed on the diwociation apparatus, for example a packed or tray column.
15 This recdficadon attachment is generally O~l..t~ using stabUization by
polr~e.~ation inhibitu.~ (e.g. phellolhi-~, hydro~luh~ol~e mol~ol.,e~h,l
etber, etc.).
The conditiol~s for c~.yi"g out the process ûf the present invention
for dissociating oxy esters fonned in the bottom p.ol~cl in the esh,irl~lion
20 or sep~dt d f,rom the bottom p-c~-ct are as follows:
Catalyst: at least one acid selecte~ from the group consi-
sting of mineral acids, for cA~plE sulfuric acid
and phû~lJh~.ic acid, and organic acids different
from (meth)acrylic acid, for example alkyl- or
arylsulfonic acids such as ~ h~l-f;,.. ifonic or
p-toluenesulfonic acid
Amount of catalyst: 1-20% by weight, preferably 5-15% by weight,
based on the ~mo~ln~ of boKom ploducl in (a)
or on the amount of the oxy ester di~ti~ e
s~pa,~t~d from the boKom p~ . l in (b)
2193407
.
Amount of
(meth)acrylic acid: 5-50% by weight, preferably 10-40% by weight,
based on the arnount of bottom pluducl in (a)
or on the arnount of the oxy ester lictillqte
s~paldted from the bottom plOduCt in (b)
Te.n~eldt~le: 150-250C, preferably 180-230C
~I~S~ule: preferably at atlllos~he.ic ple~ ~ or under
l'educed pl~S~UI'~_ (SO that the dissociation pro-
ducts i.. ~ tely vapvli~e) (< 1 atrn)
o S~ipping gas,
if used: ~qrnolln~ 1-10" I/h
Reaction time: 1-10 hours
CGn~ ion: 2 90%
The reaction is carried out, for eAhl~le, by the bottom IJ.udu~l
15 to be dissociated being taken CV.~ U~J$IY from the distilladve work-up of
the e~t.i~cation l,~t~i~ and fed tog~ el with the dissociation catalyst to
the dissociadon reactor. However, the reaction can also be carried out
bat~h..ise. It is also possible to use a ~lllicvnlilluous lea~lion l~lvceJul~, in
which the l"vdu~:l to be dissociat~d is cG~ v!~sly fed to the ~icsoc;qt;v
20 reactor (which. cu~ i.u the ~licsoci~;on catalyst), and the bottom p.oduct isle,nv.~d batchwise frvm the dissociation reactor ody after the dissociadon
is complete. The dissociation plodu~:ts are ~palat~ off condnuously by
distillation.
The applicabiliq of the ~ksoc;~lion prvcess de~lil~ is not
25 ~tli~t~d to a sp~cific qpe of e~tlillcativl process from which the oxy
esters, i.e. the addition co~u~ds I and Il, are obt~ d as by-plvluc~.
In genetal~ the esters are plep&cd by c~-~t~""q~ i"-lh~s (see Ullmann's
E.~;)clo~ia of Industrial Ch--n;st~, Vol. Al, 5th Ed., VCH, p. 167 ff.).
2193~07
A typical example of the conditions under which the esterification
prece~ing the d6sociation of the oxy esters can take place can be briefly
~l~nt~d as follows:
Alcohol: (meth)acrylic acid 1:0.7-1.2 (molar)
Catalyst: sulfuric acid or sulfonic acids
Amount of catalyst: 0.1-10% by weight (p-~f~ bly 0.5-S%
by weight) based on starting material
Stabilization: 200-2,000 ppm of phello~ based
on the weight of the starting
o materials)
Reacdon temperature: 80-160C, preferably 90-130C
Reaction time: 1-10 hours, preferably 1-6 hours
If desired, an e~llaill~[ (e.g. cycloh~a.K or toluene) may be used
to remove the water of est~lific~tion. The e~t~lification can be carried out
~s at ato ~ .ic l,le~ , under ~u~ nû~,hr~ic ~ or subat,.~ospk--.;c
,S~, either co.~ ly or batchwise.
In the acid-catalyzed esterification of acrylic acid with aLkanols,
the bottom p~ ;l obl~d aRer sepaldting off the acid esterification
catalyst, the unreacted starting materials and the acrylic ester generally has
the following,cû~ )os;t~on:
1-20% by weight of acrylic ester
50-80% by weight of al~o~l"opio~t~s (see formula I)
5-30% by weight of acyluA~ opiollates (æe formula II)
remsi~er: mainly stabilizers (pheno~t.i~ -) and polymers
2S Further details and advantages of the pl~lcesS of the present
~ion may bc taken from the P~ p!r5 dc3elit~d bclow.
Pirstly, a result achieved using a process not acwld~g to the
prcsent in~cntion will be des~;lil,cd by means of a COnlpdl:ali~_ c~ple.
COMPARATIVE EXAMPLE
2193407
_
g
A glass circulation reactor (volume: I l) heated by means of a
heating plug was charged with 500 g of an oxy ester ~ till~te obtained
from an esterification residue from n-butyl acrylate production which has
been freed of the acid esterification catalyst, togetl,er with 40 g of p-tolue-
5 nesulfonic acid. The oxy ester distillate co"~,ised
11.0% by weight of butyl acrylate,
64.8% by weight of butoxy ester I ( R = C4H9)
20.5% by weight of acyloxy ester II ( R = C4H9).
The ~iCs~ on temperature was 195C and the ope~ling p~s~ e
was 1 atm.
During the dissociation, the esterification residue to be dissociated
was co.~ o~Qly fed to the dissociation reactor, regl~ls~.~d by the level in
the reactor.
The dissociation ploducls were taken off in vapor form and
15 CO~ ~ at the top of the column (50 cm x 2.8 cm, empty) w~yO3ed
on the dissociation reactor. Over a period of 119.5 hours, 7,401 g of
- lniAt~, (62 g/h) were fed to the ~icsoci~ion reactor and 7,080 g of
dissociation pivdu~;ls were con-1~ n5e~.
Accol~ing to analysis by gas chr~n~dtu~.alJhy, the cond~,~ate
20 C~
72.0% by weight of butyl acrylate
13.9% by weight of butanol
4.8% by weight of acrylic acid
1.4% by weight of dibutyl ether
6.6% by weight of butenes
0.2% by weight of butyl l,.~lu~ vpionate
Co.~ ;on: 96% by weight based on o~cy esters.
The dissociation bollv~s were still readily handleable (pumpable)
at 25C and co..~ rd no solids.
3~ EXAMPLE OF THE PROCESS OF THE PRESENT INVENTION
2193gO7
A glass circulation reactor (volume: I l) heated by means of a
heating plug was charged with 500 g of the oxy ester di.c~ te from the
Co",pal~tive E~ample, with addition of 40 g of p-toluenPsl~lfonic acid and
150 g of acrylic acid (stabilked with 300 ppm of phe~ h;~7i.~r,).
The dicsoci~;oll t~mpe.dtu.e was 195C and the o~.ating p.~v;,.~,~
was 1 atm.
The o~y ester distillate to be dissociated and the co.,~v~onding
addilioll of acrylic acid (30% by weight) were continuously fed to the
dissociation reactor, regl~ ~ by the level in the reactor. The ~ s~i~l;o
I,.~hl~ts were condcnsed at the top of the column (S0 cm x 2.8 cm,
empty) ;.upe.~os~ on the reactor.
Over a period of 118 hours, 12,323 g of oxy ester distillate (104
g/h) and 3,697 g of stabilked acrylic acid were fed to the dissociation
reactor and lS,S29 g of l,.odu. t ~ , were conf1e~-~d. Accolding to
5 analysis by gas chromatography, the colU~e~ COI~li~:
67.3 % by weight of butyl acrylate
S.3 % by weight of butanol
21.2% by weight of acrylic acid
0.4% by weight of dibutyl ether
2.3 % by weight of butenes
Co-~ ;on: 97 % by weight, based on o~cy esters.
It can be seen from the above e~mple of the ~.~ess of the
present il~nlion that this process is able to achieve higher co-l~e.sions and
results in srnaller losses of starting material than in known p..Jcesses.
