Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-09-18
2002-04-16
McKane, Joseph K. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
active
06372924
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is based on German Application DE 199 44 839.6, filed Sep. 18, 1999, which disclosure is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to a process for the preparation of epoxides by epoxidation of olefinic compounds with hydrogen peroxide in the presence of a titanium silicalite as a catalyst.
BACKGROUND OF THE INVENTION
It is known from EP-B 0 100 118 that olefins can be epoxidized with hydrogen peroxide and converted to glycol ethers in situ in the presence of alcohols if a titanium-containing zeolite, such as a titanium silicalite, is employed as a catalyst. In respect of the preparation of epoxides, the acid properties of this catalyst are a disadvantage, because some of the epoxide formed reacts further during the reaction by acid-catalyzed ring-opening to give the diol or, in the presence of an alcohol as the solvent, to give diol ethers.
It is known from EP 0 230 949 that the epoxide ring-opening reaction can be partly suppressed if the catalyst is neutralized with a neutralizing agent before and/or during the epoxidation reaction. Strong bases, such as NaOH and KOH, and weak bases, such as ammonia, alkali metal carbonates, alkali metal bicarbonates and alkali metal carboxylates, are mentioned as neutralizing agents. This document indeed imparts a doctrine for the treatment of the catalyst with a base before the epoxidation, but it gives no suggestion as to how the catalyst is to be neutralized during the epoxidation.
M. G. Clerici and P. Ingallina describe in J. Catal. 140 (1993) 71-83, a process of this type and the influence of acids, bases and salts on the catalytic activity of the titanium silicalite catalyst. According to this paper, it is known that the effect of a neutralizing agent on the catalytic properties depends greatly on the amount of neutralizing agent. While the use of a small amount of the neutralizing agent leads to an increase in the selectivity, if the amount is too large there is an inhibition of the catalytic activity for the epoxidation, up to complete blocking of the activity of the catalyst. It is furthermore known that acids present in the reaction medium can increase the rate of reaction. It is known from H. Gao, G. Lu, J. Suo, S. Li, Appl. Catal. A 138 (1996) 27-38, that this adverse effect of the neutralizing agent occurs even at low concentrations, and that concentrations of NaOH or KOH of less than 600 ppm can lead to a severe loss in catalytic activity.
The known process for the epoxidation of olefins with hydrogen peroxide and a titanium silicalite catalyst with the addition of basic substances has the disadvantage that, to date, the amount of neutralizing agent required for the desired effect of improving the selectivity and at the same time not reducing or only moderately reducing the rate of reaction, cannot be determined in advance for an individual case. For carrying out the reaction in practice, this has the disadvantage that, if a neutralizing agent is used, a small change in the quality of the starting substances and/or the properties of the catalyst can lead to a marked and unforeseeable change in the activity of the catalyst during the epoxidation. The abovementioned documents give no suggestion as to how the amount of base to be added to the system can be controlled within narrow limits.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a process for the preparation of epoxides from olefins in which the disadvantages described above for the process can be overcome. The present process allows either discontinuous or, preferably, continuous operation. The invention allows the process to be carried out such that, with the highest possible increase in selectivity, the conversion proceeds in a manner which can be determined in advance.
It has been found, surprisingly, that the object can be achieved in that the addition of the base to the epoxidation reactor is carried out with monitoring of the pH and the amount of base is chosen such that for the hydrogen peroxide employed or the mixture of hydrogen peroxide with one or more solvents employed, a constant pH can be determined beforehand by the results of one or more test experiments.
The invention thus provides a process for the preparation of an epoxide, comprising epoxidation of an olefinic compound with hydrogen peroxide in the presence of a titanium silicalite catalyst. A solution containing hydrogen peroxide and the olefinic compound are introduced as starting substances periodically or continuously into an epoxidation reactor and a base is additionally employed in the process. The base is introduced into the epoxidation reactor directly or in a mixture with one or more of the starting substances, while controlling the pH. The pH control is carried out in the reaction mixture or in the mixture(s) of the base and starting material(s). A pH in the range from 4 to 9.5 is established and kept substantially constant. Since the pH in the reaction mixture decisively influences the selectivity and the conversion, the optimum pH is determined beforehand by one or more epoxidation test experiments carried out at different pH values using the same starting substances, with subsequent determination of the selectivity and the conversion.
By choice of a suitable constant pH, the epoxide selectivity in the epoxidation of olefins with hydrogen peroxide with a titanium silicalite catalyst can be improved in a reproducible manner, while at the same time the activity of the catalyst decreases only slightly and in a reproducible manner. If a constant pH is established, variations in the quality of the starting substance or in the composition of the catalyst have less effect on the course of the reaction than if a constant amount of the neutralizing agent is added.
According to a preferred embodiment, the base is added to an aqueous or aqueous-organic hydrogen peroxide solution and the optimum pH, determined from preliminary experiments, for example a pH-dependent test series, is established and kept constant in the solution obtained in this way. In the case of an aqueous hydrogen peroxide solution, the optimum pH is in the range from 4 to 6.5, and in the case of an organic-aqueous hydrogen peroxide solution with at least 50 wt. % of an organic water-soluble solvent, the optimum pH is in the range from 5 to 9.5, the pH being based on measurement by means of a glass electrode. A combined glass electrode with integrated Ag/AgCl reference electrode is preferably used.
The process according to the invention is suitable for the epoxidation of aliphatic, cycloaliphatic and aliphatic-aromatic olefinic compounds. Olefins having 3 to 8 carbon atoms are preferably employed, particularly propene and 1-butene. The olefinic compound can contain one or more functional groups, such as e.g. hydroxyl, halogen, alkoxy or carbalkoxy. For example, allyl chloride and allyl alcohol can be readily epoxidized in the process according to the invention.
The hydrogen peroxide is employed in the process according to the invention in the form of an aqueous solution with a hydrogen peroxide content of 1 to 90 wt. %, preferably 10 to 70 wt. %, and particularly preferably 30 to 50 wt. %. The hydrogen peroxide can be employed in the form of commercially obtainable stabilized solutions. Non-stabilized aqueous hydrogen peroxide solutions, such as are obtained in the anthraquinone process for the preparation of hydrogen peroxide, are also suitable. As an alternative, hydrogen peroxide can also be used in an organic-aqueous solution or in an organic solution. Preferably, a pH-controlled aqueous or aqueous-organic hydrogen peroxide solution to which a base has been added is added to the epoxidation reactor.
Crystalline titanium-containing zeolites of the composition (TiO
2
),(SiO
2
)
1−x
, where x is from 0.001 to 0.05, and an MFI or MEL crystal structure, known as titanium silicalite-1 and titanium silicalite-2, are particularly suitable as the catalyst. The titanium silicalite catalyst can be employed as a pow
Degussa-Huls AG
McKane Joseph K.
Murray Joseph
Pillsbury & Winthrop LLP
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