Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2001-01-22
2002-08-13
Geist, Gary (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S600000, C562S545000
Reexamination Certificate
active
06433222
ABSTRACT:
The present invention relates to a process for the preparation of acrylic acid.
Acrylic acid is an important key chemical. Owing to its very reactive double bond and the acid function, it is particularly suitable as a monomer for the preparation of polymers. Of the amount of acrylic acid monomers produced, the major part is esterified before the polymerization—to give, for example, adhesives, dispersions or surface coatings. Only the minor part of the acrylic acid monomers produced is polymerized directly—to give, for example, “superabsorbers”. Whereas monomers of high purity are generally required in the direct polymerization of acrylic acid, the requirements regarding the purity of acrylic acid are not so high when they are esterified before the polymerization.
It is generally known that acrylic acid can be prepared by gas-phase oxidation of propene with molecular oxygen under heterogeneous catalysis over catalysts present in the solid state at from 200 to 400° C. in one stage or two stages via acrolein (cf. for example DE-A-1 962 431, DE-A-2 943 707, DE-C-1 205 502, DE-A-195 08 558, EP-A-0 257 565, EP-A-0 253 409, DE-A-2 251 364, EP-A-0 117 146, GB-B-1 450 986 and EP-A-0 293 224). Here, oxidic multicomponent catalysts, for example based on oxides of the elements molybdenum, bismuth and iron (in the 1st stage) or molybdenum and vanadium (in the 2nd stage) are used.
DE-C-2 136 396 discloses the separation of the acrylic acid from the reaction gases obtained in the catalytic oxidation of propene or acrolein by countercurrent absorption with a mixture of about 75% by weight of diphenyl ether and about 25% by weight of biphenyl. Furthermore, DE-A-2 449 780 discloses the cooling of the hot reaction gas by partial evaporation of the solvent in a direct condenser (quench apparatus) before the countercurrent absorption. What is problematic here and in further process steps is that solids are obtained in the apparatuses, reducing the availability of the plant. According to DE-A-4 308 087, the production of these solids can be reduced by adding a polar solvent, such as dimethyl phthalate in an amount of from 0.1 to 25% by weight to the relatively nonpolar solvent mixture comprising diphenyl ether and biphenyl.
In addition to the absorption, described above, of the acrylic acid-containing reaction product into a high-boiling solvent mixture, other known processes provide total condensation of acrylic acid and of the water of reaction furthermore formed in the catalytic oxidation. This gives an aqueous acrylic acid solution which can be further worked up by distillation with an azeotropic agent (cf. DE-C-3 429 391, JP-A-1 124 766, JP-A-7 118 766, JP-A-7 118 966-R, JP-A-7 118 968-R, JP-A-7 241 885) or by an extraction method (cf. DE-A-2 164 767, JP-A-5 81 40-039 and JP-A-4 80 91 013). In EP-A-0 551 111 the mixture of acrylic acid and byproducts which is prepared by means of catalytic gas-phase oxidation is brought into contact with water in an absorption tower, and the resulting aqueous solution is distilled in the presence of a solvent which forms an azeotropic mixture with polar low boilers, such as water or acetic acid. DE-C-2 323 328 describes the separation of acrylic acid from an aqueous butanol/acrylic acid esterification waste liquor by extraction with a special mixture of organic solvents.
The disadvantage of the processes described above is that the organic solvent used for the extraction or absorption is separated off again in a further process stage, such as a rectification under high thermal stress. This gives rise to the danger of polymerization of the acrylic acid.
JP-A-07 082 210 describes a process for purifying acrylic acid which, in addition to acrylic acid contains acetic acid, propionic acid, acrolein and furfural. In this process, a crystallization is carried out under reduced pressure after the addition of water, a purity of 99.6% being achieved after isolation and washing of the acrylic acid crystals. Japanese Patent 45-32417 discloses a process in which an aqueous acrylic acid solution which additionally contains acetic acid and propionic acid is extracted with heptane or toluene, and water is then removed from the extract by distillation. In the next stage, the remaining extract is cooled to −20 to −80° C. in order to induce crystallization of acrylic acid. The crystals are isolated and the mother liquor is recycled to the extraction process. According to this patent, the use of an organic solvent or extracting agent is necessary since otherwise the solution, if it is cooled, solidifies without crystals being precipitated. The disadvantage of this process, apart from the addition of an organic solvent, is that a distillation has to be carried out to separate off water. Canadian Patent 790 625 relates to a further purification process of crude acrylic acid by fractional crystallization. There, the temperature is not reduced below the peritectic temperature of the acrylic acid/propionic acid system where propionic acid is the main impurity in the crude acrylic acid, while the temperature is not reduced below the eutectic temperature of the acrylic acid/acetic acid system where acetic acid is the main impurity. The acrylic acid used for crystallization is prepared here by conventional processes, for example by gas-phase oxidation of propene or acrolein, and then subjected to a preliminary purification by conventional known methods, e.g. extraction. According to the patent, the crystallization of the acrylic acid is preferably carried out essentially in the absence of water.
EP-A-0 616 998 describes a process for purifying acrylic acid by means of a combination of dynamic and static crystallization, the starting material used being prepurified acrylic acid, for example acrylic acid prepurified by distillation.
The common feature of the processes described in the above documents is that they require a preliminary purification of the acrylic acid before the crystallization. Since organic solvents are generally used in the preliminary purification and are subsequently separated off again under high thermal stress, the problem of undesired polymerization of the acrylic acid is always present here.
EP-A-0 002 612, which relates to a process for purifying acrylic acid present in aqueous solution by fractional crystallization, discloses the addition-of salts to the acrylic acid solution in order to break the water/acrylic acid eutectic mixture which contains 63% by volume of acrylic acid.
EP-A-0 675 100 describes a process for the preparation of &agr;,&bgr;-unsaturated C
3
-C
6
-carboxylic acids, e.g. acrylic acid, by oxidative dehydrogenation of the corresponding saturated C
3
-C
6
-carboxylic acid followed by crystallization of the melt with subsequent fractional distillation or followed by fractional distillation with subsequent crystallization of the melt. It is an object of the present invention to provide a process from which acrylic acid is obtained in high purity without expensive process stages.
We have found that this object is achieved and that, surprisingly, acrylic acid from a gaseous product mixture which is subjected to a condensation can be crystallized directly from the solution formed in the condensation. We have found in particular that no further purification stage and no addition of assistants are required for this purpose.
The present invention therefore relates to a process for the preparation of acrylic acid by:
(a) preparation of a gaseous product mixture which essentially has the composition of a reaction mixture of catalytic gas-phase oxidation of C
3
-alkanes, C
3
-alkenes, C
3
-alkanols and/or C
3
-alkanals and/or precursors thereof to acrylic acid, which comprises
(b) condensation of the gaseous product mixture,
(c) crystallization of the acrylic acid from the solution obtained in stage (b), with partial evaporation of the solution under reduced pressure,
(d) isolation of the resulting crystals from the mother liquor,
(e) recycling of at least a part of the mother liquor from stage (d) to stage (b) and
(f) recycling of at least a
Bröllos Klaus
Eck Bernd
Heilek Jörg
Machhammer Otto
Proll Theo
BASF - Aktiengesellschaft
Forohar Farhad
Geist Gary
LandOfFree
Method for producing acrylic acid 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 producing acrylic acid, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for producing acrylic acid will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2971572