Process for preparing alkyl (meth)acrylates

Details Process for preparing alkyl (meth)acrylates Process for preparing alkyl (meth)acrylates

1999-10-13

2003-01-14

Killos, Paul J. (Department: 1623)

Organic compounds -- part of the class 532-570 series

Organic compounds

Carboxylic acid esters

C560S218000

Reexamination Certificate

active

06506930

ABSTRACT:

This invention relates to a process for preparing alkyl (meth)acrylates. Specifically, the process provides for the synthesis of alkyl (meth)acrylates, the hydrolysis of process impurities into starting materials, and the separation of reaction products and starting materials in one reactor.
Alkyl (meth)acrylates are important monomers in commercial polymerization processes. Conventionally, alkyl (meth)acrylates, such as butyl acrylate (“BA”), are commercially prepared by a direct esterification process. Typically, butanol (“BuOH”) and acrylic acid (“AA”) are reacted in the presence of an acid catalyst thereby yielding butyl acrylate and water. The direct esterification is generally run at elevated temperature and reduced pressure. During the reaction, impurities are formed such as dibutyl ether (“DBE”), butyl-&bgr;-butoxy propionate (“BBBP”), butyl-&bgr;-hydroxy propionate (“BBHP”), butyl-acryloxypropionate (“BAOPA”), and acryloxypropionic acid (“AOPA”). These impurities, if not converted back to starting materials, result in lower yield.
Such impurities are usually removed from the reactor and treated to produce starting materials which can be reused. As a result, these processes are less efficient and require additional capital investment costs for separate reactors. Furthermore, conventional BA preparation processes operate at reduced pressure, necessitating a need for larger sized equipment. Consequently, there is a need for a more efficient, lower cost butyl acrylate process which converts process impurities back to starting materials, does so in the same reactor in which BA is produced and which can be operated at atmospheric pressure.
The present invention discloses a process of preparing alkyl (meth)acrylates which converts process impurities back to starting materials and further reacts them in one reactor. The addition of water during the direct esterification reaction also provides an alkyl (meth)acrylate preparation process which does not require reduced pressure and facilitates the recovery of starting materials from process impurities. Furthermore, separation of the reaction product, such as BA, and the starting (meth)acrylic acid, such as AA, can also be effected in the reactor. Consequently, the present invention provides a process which is more efficient and economical than conventional alkyl (meth)acrylate preparation processes known in the art.
One aspect of the present invention provides a process which includes: (A) charging a reactor with a C
1
-C
4
alcohol, a (meth)acrylic acid, a strong acid catalyst, and at least 5% by weight water to form a reaction mixture; (B) reacting the reaction mixture to form a C
1
-C
4
alkyl (meth)acrylate and process impurities, wherein the process impurities formed are hydrolyzed in the reactor; and (C) separating the C
1
-C
4
alkyl (meth)acrylate and water formed during the reaction from the reaction mixture.
Another aspect of the present invention provides a process which includes: (A) charging a reactor with butanol, acrylic acid, a strong acid catalyst, and at least 5% by weight water to form a reaction mixture; (B) reacting the reaction mixture to form butyl acrylate and process impurities, wherein the process impurities are hydrolyzed in the reactor; and (C) separating the butyl acrylate and water formed during the reaction from the reaction mixture.
A further aspect of the present invention provides a process which includes: (A) charging a reactor with butanol, acrylic acid, 3.5 to 15% by weight sulfuric acid, 6 to 18% by weight water and at least one inhibitor to form a reaction mixture, wherein the butanol and acrylic acid are charged to the reactor in an acrylic acid to butanol molar ratio of 1:1 to 1:1.7; (B) reacting the reaction mixture to form butyl acrylate and process impurities, wherein the process impurities are hydrolyzed in the reactor; and (C) separating the butyl acrylate and water formed during the reaction from the reaction mixture by azeotropic distillation.
Another further aspect of the present invention provides a reaction mixture, including: acrylic acid, butanol, from 3.5 to 15% by weight sulfuric acid, from 6 to 18% by weight water and from 0.001 to 1.0% by weight 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy.
As used herein, the term “(meth)acrylic” acid is meant to include both acrylic acid and methacrylic acid. In a like manner, the term “(meth)acrylate” is meant to include both acrylate and methacrylate.
As used herein, BuOH refers to n-butanol, i.e., 1-butanol and the term “butanol” includes within its scope all butanol isomers as well as mixtures thereof.
The term “alkyl” is meant to include branched chain, straight chain or cyclic alkyl groups. As used herein the terminology “(C
1
-C
4
)” or “(C
1
-C
10
)” means a group having from 1 to 4 or 1 to 10 carbon atoms per group.
As used herein, the terms “AA rich” or “BA rich” are understood to mean fractions or components where AA or BA is the major (greater than 50% by weight) organic component of the composition.
Throughout this specification and claims, unless otherwise indicated, references to percentages are by weight, all temperatures by degree centigrade and all pressures are atmospheric.
FIG. 1
illustrates the equipment and the flow lines utilized in one embodiment of the process of the present invention, including the direct esterification/hydrolysis reactor
1
which is a stirred reactor having a distillation column on top of it; line
2
, which carries a vaporized distillate mixture, which includes BA, from
1
to a phase separator
3
, the phase separator
3
separates the vaporized distillate into a BA rich organic phase and an aqueous distillate phase; line
11
, which carries the BA rich organic distillate separated in
3
forward to a separation section; line
8
which carries the aqueous distillate separated in
3
to line
9
to be recycled to
1
, and to line
10
to carry it forward to be treated, generally to recover material from aqueous waste; line
4
, which carries the AA rich bottoms from
1
to bleed stripper
5
, which is the cracking reactor; line
6
, which carries the distillate, including recovered BuOH and AA from
5
to be recycled to
1
through line
22
, and to line
7
which carries the distillate from
5
forward to be treated, generally as waste; line
12
, which carries the bottoms from
5
forward to be treated, generally as waste and optionally to line
17
, which recycles bottoms from
5
to
1
; line
13
, which may feed inhibitor to the reactor; line
14
, which feeds catalyst to the reactor; line
15
, which feeds fresh AA and BuOH to the reactor; an optional plug flow reactor
16
; an optional line
18
for feeding AA, BuOH, and catalyst to
16
; an optional line
19
for taking the material from
16
to
1
; line
20
, which carries the BuOH, BA, and AA recovered in the separation section from lines
10
and
11
back to the reactor
1
; and optional line
21
which returns recovered material to an alternative feed location in reactor
1
.
As recited above, in step (A) of the present invention C
1
-C
4
alcohol, a (meth)acrylic acid, a strong acid catalyst, and water are charged to a reactor to form a reaction mixture.
Generally, the C
1
-C
4
alcohol is a branched or straight chain alkanol having 1 to 4 carbon atoms or mixture thereof. Specific examples include, but are not limited to, methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, tert-butanol or mixtures thereof. Furthermore, it is contemplated that the C
1
-C
4
alcohol may be substituted, for example, with halogen, hydroxide, alkoxide, cyano, nitro, etc. In one embodiment, the alcohol is butanol. In a preferred embodiment, the alcohol is n-butanol.
Also present in the reaction mixture is (meth)acrylic acid or substituted meth(acrylic) acid substituted with, for example, with halogen, hydroxide, alkoxide, cyano, nitro, etc. In one embodiment, acrylic acid or methacrylic acid or a mixture thereof is present. In a preferred embodiment, the unsaturated acid is acrylic acid. The (meth)acrylic acid and alcohol are presen

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