Chemistry of inorganic compounds – Zeolite – Organic compound used to form zeolite
Reexamination Certificate
2000-06-28
2001-10-16
Sample, David R (Department: 1755)
Chemistry of inorganic compounds
Zeolite
Organic compound used to form zeolite
C423S707000, C423SDIG002, C423SDIG002, C423SDIG003, C502S077000, C502S086000
Reexamination Certificate
active
06303099
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing pentacyl-type crystalline zeolites and a process for producing &egr;-caprolactam by use of the same.
2. Description of the Related Art
&egr;-Caprolactam is an important and fundamental chemical material used as a starting material for producing nylon etc., and one of proposed processes for producing &egr;-caprolactam is Beckmann rearrangement (gaseous-phase Beckmann rearrangement) of cyclohexanone oxime under gaseous-phase reaction conditions in the presence of a pentacyl-type crystalline zeolite catalyst (e.g., JP-A 2-275850 and JP-A 2-250866).
Pentacyl-type crystalline zeolites are produced by hydrothermal synthesis reaction of a silicon compound such as tetraalkyl orthosilicate by using a compound such as tetrapropyl ammonium hydroxide as the so-called template agent. Such a process has problems such that a pentacyl-type crystalline zeolite having high activity cannot always be obtained. Further, in such a process, the unreacted silicon compound and the unreacted tetrapropyl ammonium hydroxide remain in the residual solution obtained after the product zeolites were recovered, and thus their recycling for use is considered appropriate, but there is a problem in that even if such unreacted materials are recycled and used as the starting materials in the hydrothermal synthetic reaction, a pentacyl-type zeolite having high catalytic activity is hardly obtained with good reproducibility.
SUMMARY AND OBJECTS OF THE INVENTION
Under such circumstances, the present inventors made extensive study with the aim of finding a process wherein a pentacyl-type crystalline zeolite catalyst having high activity can be produced with good reproducibility, while the unreacted silicon compound and tetrapropyl ammonium hydroxide can be effectively utilized through recycling. As a result, the present inventors have found that the amounts of specific components contained in the starting materials are regulated in production of a pentacyl-type crystalline zeolite catalyst, whereby a zeolite catalyst having superior performance can be produced with good reproducibility while the unreacted starting materials can be effectively utilized through recycling, thus completing the present invention.
That is, the present invention provides a process for producing a pentacyl-type crystalline zeolite which comprises the steps of (i) preparing a mixture of a silicon compound, water and tetrapropyl ammonium hydroxide, (ii) conducting a hydrothermal reaction of the mixture to obtain a reaction mixture containing zeolite crystals, (iii) separating zeolite crystals from the reaction mixture to collect a remaining solution, (iv) calcinating the resulting zeolite crystals, (v) treating the calcinated zeolite crystals with an aqueous solution containing a compound selected from ammonia and ammonium salts to obtain a pentacyl-type crystalline zeolite and (vi) recycling the solution collected in step (iii) to the mixture-preparing step (i), wherein a molar-ratio composition of the mixture prepared in step (i) is adjusted so that a molar ratio of hydroxide ion to silicon falls within a range of from about 0.1 to about 0.4 and that a molar ratio of potassium to silicon is about 0.1 or less.
Further, the present invention provides a process for producing &egr;-caprolactam which comprises subjecting cyclohexanone oxime to a gaseous phase catalytic rearrangement reaction using a pentacyl-type crystalline zeolite obtained by the process described above.
DETAILED DESCRIPTION OF THE INVENTION
A pentacyl-type crystalline zeolite in the present invention is produced by:
(i) preparing a mixture of a silicon compound, water and tetrapropyl ammonium hydroxide,
(ii) conducting a hydrothermal reaction of the mixture to obtain a reaction mixture containing zeolite crystals,
(iii) separating zeolite crystals from the reaction mixture to collect a remaining solution,
(iv) calcinating the resulting zeolite crystals,
(v) treating the calcinated zeolite crystals with an aqueous solution containing a compound selected from ammonia and ammonium salts to obtain a pentacyl-type crystalline zeolite and
(vi) recycling the solution collected in step (iii) to the mixture-preparing step (i).
In the process, the mixture in step (i) is prepared so as to have such a molar-ratio composition that a molar ratio of hydroxide ion to silicon falls within a range of from about 0.1 to about 0.4 and that a molar ratio of potassium to silicon is about 0.1 or less. When a pentacyl-type crystalline zeolite catalyst is produced by the process of the present invention described above, a zeolite catalyst having superior performance can be produced with good reproducibility, while the unreacted starting materials can be used effectively through recycling thereof.
The silicon compound used in step (i) includes e.g. tetraalkyl orthosilicates. Examples of such tetraalkyl orthosilicates include tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate and tetrabutyl orthosilicate. One or more compounds selected from these orthosilicates are preferably used, among which tetraethyl orthosilicate is preferably used.
In the mixture prepared in the step (i), a molar ratio of each component to silicon is controlled as follows: a molar ratio of water to silicon is preferably about 5 to about 100, more preferably about 10 to about 60, a molar ratio of tetrapropyl ammonium hydroxide to silicon is preferably about 0.1 to about 0.3, more preferably 0.15 to about 0.3, a molar ratio of carbonate ion to silicon is preferably about 0.06 or less, more preferably about 0.04 or less (smaller ratio than that is much better), and a molar ratio of potassium is preferably about 0.1 or less, more preferably about 0.04 to about 0.1.
In the mixture prepared in the step (i), a molar ratio of hydroxide ion to silicon falls within a range of from about 0.1 to about 0.4. When a molar ratio of carbonate ion to silicon in the mixture falls within a range of from about 0.06 to about 0.12, it is preferred that the molar ratio of hydroxide ion to silicon falls within a range of from about 0.2 to about 0.4. When a molar ratio of carbonate ion to silicon in the mixture is about 0.06 or less, the molar ratio of hydroxide ion to silicon may fall within a range of from about 0.1 to about 0.3.
It is preferred that the mixture in step (i) is prepared using tetrapropyl ammonium hydroxide in an amount of from about 0.2 to about 1 molar time as large as the total amount of the anions therein (excluding hydroxide ion and bromide ion) which exceeds an amount equivalent to the molar ratio of about 0.03 of said anion to silicon, in addition to the amount used for conducting the hydrothermal reaction of said mixture.
In the composition of the mixture, when the molar ratio of tetrapropyl ammonium hydroxide to silicon is less than about 0.1, or the molar ratio of hydroxide ion to silicon is less than about 0.1, then the size of the resulting zeolite crystals is enlarged, and as a result, their total area of outer surface of the crystals is decreased so that zeolites obtained after calcination may not achieve sufficient conversion of starting material(s) in various reactions such as in production of &egr;-caprolactam. On the other hand, when the molar ratio of tetrapropyl ammonium hydroxide to silicon is more than about 0.3, or the molar ratio of hydroxide ion to silicon is more than about 0.4, then the resulting zeolite crystals are small and not preferred since their filtration in step (iii) tends to be difficult. When the molar ratio of carbonate ion to silicon is more than about 0.06 and the molar ratio of hydroxide ion to silicon is less than about 0.2, or when the molar ratio of potassium to silicon is more than about 0.1, then the resulting zeolite may not achieve a sufficient conversion of cyclohexanone oxime in the production of &egr;-caprolactam from cyclohexanone oxime, and the selectivity for &egr;-caprolactam tends to be decreased.
Even if potassium is not contained in the mixture,
Ichihashi Hiroshi
Sugita Keisuke
Yako Makoto
Birch & Stewart Kolasch & Birch, LLP
Sample David R
Sumitomo Chemical Company Limited
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