Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
1999-05-25
2001-01-23
Geist, Gary (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C560S218000
Reexamination Certificate
active
06177590
ABSTRACT:
The invention relates to a process for preparing esters of acrylic acid or methacrylic acid [(meth)acrylic acid].
(Meth)acrylic esters are generally prepared industrially by esterifying (meth)acrylic acid with alkanols in the presence of strong acids as esterification catalysts (eg. a mineral acid, such as sulfuric acid or phosphoric acid, alkanesulfonic acids or arylsulfonic acids). Processes of this type are disclosed, for example, by Kirk Othmer, “Encyclopedia of Chemical Technology”, Vol. 1, pp. 347-348. The content of catalysts in the esterification mixture can vary in an order of magnitude from a tenth of a percent to several percent. When polybasic mineral acids are used as catalyst, the mineral acid is readily esterified by the alkanol present, forming the monoester, which is the actual esterification catalyst. The reaction mixture contains a relatively large amount of this monoester when the esterification is completed.
The acids used as catalysts and their esters which may be formed must be eliminated from the reaction mixture prior to further processing. Generally, this is achieved by extracting and neutralizing the reaction mixture with alkali metal hydroxide solution and alkaline earth metal hydroxide solution or carbonate solutions. This operation produces wastewaters whose disposal is complex and environmentally polluting. If sulfuric acid is used as catalyst, as mentioned, the monoester of sulfuric acid with the alkanol in question is primarily formed. The salts of the sulfuric monoesters, in particular of the esters with higher alkanols, are surface-active and on their disposal they would considerably impair the quality of the wastewaters from the process and would cause a not insignificant loss of product of value. For economic and ecological reasons, recovery and recycling of the catalyst is thus desirable.
The prior art includes a plurality of processes, all of which are burdened with considerable disadvantages, however.
EP-A-0 609 127 describes a process for preparing (meth)acrylic esters, in which the alcohol component is recovered by acid hydrolysis from the corresponding sulfuric monoester which is formed from sulfuric acid and the alcohol during the esterification. This process is complex, environmentally polluting and uneconomic.
CZ-B-179 808 describes a process for recovering mineral acids from esterification mixtures by extracting the esterification mixture with water, concentrating the aqueous phase by distillation and recycling the concentrated aqueous catalyst solution thus obtained to the esterification reaction. This process is energy-consuming.
EP-A-0 618 187 ({circumflex over (=)} U.S. Pat. No. 5,386,052) describes a process for preparing (meth)acrylic esters, in which the catalyst is extracted with water and the extract, with or without concentration by distillation, is recycled to the esterification reaction. However, it is particularly emphasized here that sulfuric acid, owing to the poor extractability of the monoalkyl sulfate, is unsuitable as a catalyst, because the large amount of water which would be necessary for adequate extraction of the monoalkyl sulfate would adversely affect the esterification reaction. As catalyst, therefore, use is made of alkylsulfonic or arylsulfonic acids (column 2, lines 55ff), which are considerably more expensive than sulfuric acid, however.
It is an object of the present invention to develop a technically simple and economic process for preparing (meth)acrylic esters which successfully uses sulfuric acid as esterification catalyst and which permits the esterification catalyst (sulfuric acid or monoalkyl sulfate) to be separated off very simply and substantially completely from the resulting reaction mixture. In addition, the catalyst shall be recyclable back to the esterification directly, ie. without additional concentration by distillation, without affecting the esterification.
It has surprisingly been found that the catalyst can be extracted from the reaction mixture (esterification mixture) if the content of alkanol in said mixture is not more than 5% by weight.
We have found that this object is achieved by a process for preparing (meth)acrylic esters by reacting (meth)acrylic acid with C
4
-C
12
-alkanols, preferably C
4
-C
10
-alkanols, particularly preferably C
4
-C
8
-alkanols, in the presence of sulfuric acid or a mono-C
4
-C
12
-alkyl sulfate as catalyst, which comprises regenerating the catalyst by extraction with water from the reaction mixture and recycling the aqueous catalyst solution back to the esterification, the concentration of unreacted alkanol in the reaction mixture to be extracted being not more than 5% by weight, based on the reaction mixture to be extracted.
It has surprisingly been found that the alkanol content has a great influence on the extractability of the monoalkyl sulfate, which is formed from sulfuric acid and alkanol and which acts as the actual esterification catalyst; surprisingly the catalyst can be extracted from the reaction mixture (esterification mixture) if the alkanol content in the mixture is not more than 5% by weight (see Table 1). As a result, the catalyst can be extracted with small amounts of water, so that the extract can be directly recycled back to the esterification. Preferably, a reaction mixture whose alkanol content is ≦3% by weight, and in particular ≦1% by weight, is extracted.
In order to achieve an alkanol content of not more than 5% by weight, preferably, a high degree of esterification is brought about, eg. by distilling off the reaction water; and/or a suitable ratio of starting materials is selected. If the residual alkanol content is then still more than 5% by weight, the alkanol is distilled off in a conventional distillation apparatus (eg. column equipped with sieve trays, Raschig rings, ordered packings etc.). Surprisingly, despite the presence of the strongly acid esterification catalyst, no acid-catalyzed side reactions, such as ether or olefin formation or addition of the alkanol to the double bond of the (meth)acrylate (Michael addition), may be observed here to any significant extent.
The distillation is carried out in a customary manner; the distillation conditions depend on the type of alkanol used.
The alkanol is preferably distilled off down to a residual alkanol content in the reaction mixture which enables the catalyst (sulfuric acid) to be extracted with water without problems. In particular, the residual alkanol content is ≦5% by weight, preferably ≦3% by weight, particularly preferably ≦1% by weight, based on the reaction mixture.
Preferably, the conditions for extracting the catalyst from the esterification mixture are selected in such a manner that the catalyst concentration (sulfuric acid and monoalkyl sulfate) in the aqueous phase is at least 20% by weight, in particular at least 25% by weight, based on the aqueous extract, and the degree of extraction is at least 70% by weight, in particular at least 80% by weight, based on the amount of catalyst in the reaction mixture. To achieve this, from about 5 to 20% by weight of water, in particular from about 8 to 15% by weight of water, based on the total weight of the esterification mixture, is used for the extraction. The resulting extract can be recycled, without concentrating it, back to the esterification.
The extraction can be carried out in a manner known per se. Preferably, extraction is performed in counter-current, eg. in columns having no energy input, pulsed columns, columns equipped with internals, mixer-settler apparatuses or in static mixers.
The extraction can be carried out at ambient temperature or above, but expediently in the range from about 15 to 40° C.
The esterification is essentially carried out in a conventional manner, ie. by reacting (meth)acrylic acid with a C
4
-C
12
-alkanol in the presence of a catalyst and at elevated temperature. The molar ratio of alkanol:acrylic acid or methacrylic acid is generally 1:0.8-1.2. C
4
-C
12
-Alkanols are, for example, pentanol, hexanol, heptanol, octanol, 2-ethylhexanol, non
Aichinger Heinrich
Dams Albrecht
Fried Michael
Nestler Gerhard
BASF - Aktiengesellschaft
Geist Gary
Maier Leigh C.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Method for the production of (meth)acrylic acid esters does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for the production of (meth)acrylic acid esters, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for the production of (meth)acrylic acid esters will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2520877