Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
1999-04-06
2001-11-20
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C570S262000
Reexamination Certificate
active
06320087
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an adsorbent for separating halogenated aromatic hydrocarbons and to a method of using it for separating an isomer from a mixture of halogenated aromatic isomers.
BACKGROUND OF THE INVENTION
Halogenated aromatic compounds are of much industrial importance as intermediates for medicines, agricultural chemicals, etc. At present, these intermediates are required to have much higher purity than heretofore. Except for monohalogenated benzenes, aromatic compounds with two or more substituents each have different isomers. For separating the mixture of those isomers into individual isomers through ordinary industrial distillation, an ultra-precision distillation device is needed, since the difference in boiling points between the isomers is small. However, at present, it is still extremely difficult to obtain high-purity products of a single isomer on an industrial scale. In addition, some types of halogenated aromatic compounds could not be separated into individual isomers through distillation. Recently, for separating a mixture of isomers that have heretofore been difficult or impossible to separate into individual ones, methods using adsorption separation have been developed. For example, JP-A 57-91933 and 58-131923 disclose a method of separating a single isomer from a mixture of chlorotoluene isomers through adsorption. Japanese Patent Application No. 9-335225 discloses a method of separating a single isomer from a mixture of chloroethylbenzene isomers through adsorption. JP-A 52-62229, 53-105434, 58-131924, 58-150524, 62-175433 and 4-330025 disclose a method of separating a single isomer from a mixture of dichlorobenzene isomers. JP-A 59-199642, 60-42340, 5-70383, 58-137795 and 3-20232 disclose a method of separating a mixture of dichlorotoluene isomers. JP-B 4-46933 discloses a process comprising removing HCl and water, which are formed in isomerization of a halogenated benzene derivative, through distillation, followed by separating a specific single isomer from the mixture of the resulting isomers by the use of an adsorbing and separating zeolite.
SUMMARY OF THE INVENTION
Increasing the purity of the single isomer to be separated in those adsorption separation methods, and increasing the separation efficiency therein, is extremely important to the industrial effect. However, the methods mentioned above are not satisfactory with respect to the purity of the single isomer separated.
In using an adsorbing and separating agent that comprises zeolite for separating a single isomer from a mixture of halogenated aromatic compound isomers, the capabilities of the adsorbing and separating agent being used are lowered with the lapse of time. In the method, therefore, the adsorbing and separating agent being used must be exchanged for a fresh one or must be regenerated through firing or the like. Therefore, prolonging the life of the agent and prolonging the regeneration cycle for the agent is extremely advantageous to the industrial effect. However, the conventional techniques are unsatisfactory with respect to the prolongation of the life of the agent and to the prolongation of the regeneration cycle.
The invention is directed to solve the problems noted above, and to provide an efficient method for separating halogenated aromatic compound isomers.
In order to solve these problems, we, the present inventors have assiduously studied the capabilities of adsorbents for improving them. Adsorbents consist essentially of zeolite. Zeolite includes natural zeolite and synthetic zeolite, of which synthetic zeolite is especially preferably used. Synthetic zeolite is generally in the form of powder. For using zeolite as an industrial adsorbent, it must be shaped. Specifically, zeolite adsorbents are generally in the form of shaped articles. Having noticed the shaped articles of zeolite as adsorbents, we have investigated the factors that may govern the capabilities of zeolite to adsorb and separate halogenated aromatic compounds. As a result, we have found that the packing density of the adsorbent, the porosity of the adsorbent and the grain size of the adsorbent are important factors.
The packing density of an adsorbent depends on the porosity thereof, the shape thereof, etc. An adsorbent having a higher packing density is preferred, since its amount filled in a unit volume increases and since a larger amount of the adsorbent could be filled in an adsorbent tower. However, for an adsorbent having too high packing density, it has been found that its adsorbing and separating capabilities are lowered.
The porosity of an adsorbent is caused by the macro pores existing in the adsorbent. An adsorbent having too high porosity is unfavorable, since its packing density is lowered. Contrary to this, for an adsorbent having too low porosity, the volume of macro pores existing therein is too small. As a result, it has been found that, when a halogenated aromatic compound is applied to the adsorbent of zeolite of that type, it is prevented from being diffused in the adsorbent grains before it reaches the pores through which the compound is adsorbed by the adsorbent, zeolite, and therefore the adsorbing and separating capabilities of the adsorbent are poor.
On the other hand, it has been found that a shaped adsorbent comprising smaller grains could have higher adsorbing and separating capabilities. It is believed that, in zeolite adsorbent grains having a small grain size, the pathway through which a halogenated aromatic compound to be adsorbed by the grains are diffused into the pores of the zeolite grains will be shortened, whereby the compound could be rapidly adsorbed by the grains. It is considered that the diffusion of halogenated aromatic compounds into adsorbent grains will be much influenced by the grain size of the grains, as compared with that of halogen-free aromatic hydrocarbons. This will be probably related to the fact that halogens, for example, chlorine and bromine have a large ionic radius or a large atomic weight. However, adsorbent grains having a too small grain size are unfavorable, since they will cause increase in pressure loss.
We, the present inventors have studied production methods for aromatic compounds, and, as a result, have found that using a halogenated aromatic compound having a dissolved oxygen content of at most 15 ppm by weight prevents the deterioration of an adsorbing and separating agent and prolongs the life of the agent, and that a halogenated aromatic compound can be efficiently separated.
Specifically, the invention provides an adsorbent for separating a halogenated aromatic compound, which adsorbent is characterized by having a packing density of from 0.50 g/ml to 0.70 g/ml, a porosity of from 0.2 to 0.37 cc/cc, and a grain size of from 0.1 mm to 1.0 mm; a method of using the adsorbent for separating at least one halogenated aromatic compound isomer from a mixture of halogenated aromatic compound isomers; and a method for separating at least one halogenated aromatic compound isomer, which comprises contacting a mixture of halogenated aromatic compound isomers having a dissolved oxygen content of at most 15 ppm by weight with an adsorbent for separating halogenated aromatic compounds.
REFERENCES:
patent: 4254062 (1981-03-01), Wambach et al.
patent: 4698453 (1987-10-01), Miwa et al.
patent: 0322869 (1989-07-01), None
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patent: 4-013639 (1992-04-01), None
patent: 9-188638 (1997-11-01), None
patent: 2292736 (1987-12-01), None
Iwayama Kazuyoshi
Kato Masashi
Okino Hirohito
Yamakawa Shinobu
Schnader Harrison Segal & Lewis LLP
Siegel Alan
Toray Industries Inc.
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