Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2000-01-28
2002-04-30
Killos, Paul J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C560S205000, C562S599000, C562S606000
Reexamination Certificate
active
06380427
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for the purification of (meth)acrylic acid, and particularly to a process for the purification of (meth)acrylic acid by crystallization with addition of a second component to a crude (meth)acrylic acid.
Hereupon, the term “(meth)acrylic acid” means acrylic acid or methacrylic acid.
BACKGROUND ART
A product obtained by subjecting isobutylene, tert-butyl alcohol, methacrolein or isobutyl aldehyde to one or two stage catalytic gas phase oxidation with molecular oxygen contains carboxylic acids such as formic acid, acetic acid, propionic acid, maleic acid, citraconic acid, benzoic acid, toluic acid and terephthalic acid or aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, methacrolein, benzaldehyde, tolualdehyde and furfural as by-products in addition to the objective methacrylic acid (boiling point 161° C./760 mmHg, melting point 15° C.). Most of these impurities can be separated by usual purification means such as extraction and distillation. However, it is very difficult to remove impurities contained in a slight amount, such as maleic acid, citraconic acid and aldehydes. Especially, aldehydes have absorption in ultraviolet region, and, therefore, methacrylic acid products in which aldehydes remain in a large amount suffer from the problem of coloration. In order to avoid the problem of coloration, residual amount of aldehydes must be reduced as much as possible. Such problems due to impurities occur not only in the production of methacrylic acid, but also in the production of acrylic acid by subjecting propylene and acrolein to gas phase oxidation.
Furthermore, in purification by distillation, since the distillation temperature is as high as about 80° C. even if it is controlled as low as possible, (meth)acrylic acid and others undergo polymerization reaction in a distillation column to often cause troubles such as clogging of the distillation column. Therefore, a distillation operation is generally carried out with addition of polymerization inhibitor, but there is the possibility of incorporation of the polymerization inhibitor into the products. For this reason, the polymerization inhibitor cannot be added in such a large amount as capable of completely avoiding the troubles caused by polymerization reaction. Thus, at present, such troubles due to the polymerization reaction cannot be avoided.
Under the circumstances, attempts have been made to remove impurities in (meth)acrylic acid by crystallization method which causes substantially no troubles due to polymerization reaction. For example, JP-A-7-163802 discloses crystallization method and apparatus; JP-B-45-32417 discloses a method for purifying methacrylic acid containing a large amount of non-polar organic solvents such as butadiene, heptane and toluene by crystallization method; JP-A-7-82210 discloses a method for adiabatic cooling by evaporating added water; and JP-A-9-157212 discloses a method for adiabatic cooling by evaporating added liquefied propylene or liquefied isobutene.
However, in the crystallization method of JP-A-7-163802, the crystallization apparatus usable therefor is restricted, and the method cannot be applied to other general crystallization apparatuses. In the method of JP-B-45-32417, a large amount such as 40-85% of non-polar organic solvent must be present as a second component in methacrylic acid, which results in decrease of methacrylic acid concentration in the treated solution. For efficient recovery of methacrylic acid from the solution, the temperature of the solution at the time of crystallization must be decreased to a very low temperature of −20° C.-−80° C. As a result, there are problems that the crystallization apparatuses must be large in scale and a great energy is required for cooling. The methods of JP-A-7-82210 and JP-A-9-157212 are limited to particular cooling methods such as adiabatic cooling, so cannot apply to general crystallization apparatus.
An object of the present invention is to provide a process for the purification of (meth)acrylic acid by crystallization method according to which impurities which are contained in (meth)acrylic acid and are difficult to diminish by distillation can be removed by an economical method which does not use a large amount of a second component and does not require very low temperatures.
Another object of the present invention is to provide an economical process for producing (meth)acrylic acid esters by using a mother liquor separated in crystallization, as it is, as a starting material for (meth)acrylic acid esters.
DISCLOSURE OF THE INVENTION
The present invention is a process for the purification of (meth)acrylic acid which comprises adding to a crude (meth)acrylic acid one or two or more polar organic substances at a concentration of 1-35% by weight as a second component, crystallizing (meth)acrylic acid from the (meth)acrylic acid solution, and separating the precipitated crystal of (meth)acrylic acid and the mother liquor from each other.
BEST MODE FOR CARRYING OUT THE INVENTION
The crude (meth)acrylic acid to be subjected to purification in the present invention means a crude methacrylic acid or a crude acrylic acid. The crude methacrylic acid can be produced by various methods such as direct oxidation method and ACH method. As the method for producing the crude methacrylic acid, there are, for example, a method which comprises subjecting a compound selected from the group consisting of isobutylene, tert-butyl alcohol, methacrolein and isobutyl aldehyde to a direct oxidation comprising catalytic gas phase oxidation in one- or two-stages with molecular oxygen to obtain a reaction gas, condensing the reaction gas to obtain a condensed liquid, or adding water to the condensed liquid of the reaction gas or absorbing the reaction gas in water to obtain an aqueous methacrylic acid solution, extracting methacrylic acid from the condensed liquid or the aqueous methacrylic acid solution using an organic solvent, and removing the organic solvent and nonvolatile matters by distillation to obtain a crude methacrylic acid and a method which comprises separating methacrylic acid by-produced in ACH method by extraction or distillation to obtain a crude methacrylic acid. Furthermore, the crude acrylic acid can be obtained in the similar manner to the production of the crude methacrylic acid by the one- or two-stage catalytic gas phase oxidation of, for example, propylene and/or acrolein with molecular oxygen.
The crude (meth)acrylic acid hereupon is (meth)acrylic acid containing the impurities to be removed by the purification process of the present invention. Even the (meth)acrylic acid purified by precision distillation or crystallization is regarded to be the crude (meth)acrylic acid to be purified in the present invention if it contains the impurities to be removed by the process of the present invention.
In the process of the present invention, first, one or two or more polar organic substances are added to the crude (meth)acrylic acid so as to give a concentration of 1-35% by weight as a second component.
The second component is not limited as far as they are polar organic substances that do not form a solid solution with (meth)acrylic acid at crystallization. As such second components, mention may be made of, for example, methanol, ethanol, propanol, butanol, diethyl ether, dioxane, tetrahydrofuran, acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, methyl methacrylate, ethyl methacrylate, methyl acrylate, and ethyl acrylate. The second component is preferably selected from the group consisting of methanol, methyl methacrylate and methyl acrylate. These substances may be used each alone or in admixture of two or more as the second component.
The second component is added in such an amount as to give a concentration of 1-35% by weight, preferably 3-30% by weight. If the concentration of the second component is less than 1% by weight, since the difference between the temperature at which crystal
Araki Mikiyoshi
Kobayashi Yoshiaki
Miyazaki Seiji
Nakashima Yasutaka
Ogawa Akira
Killos Paul J.
Mitsubishi Rayon Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Oh Taylor V.
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