Epoxidation catalyst and process

A titanium/silica epoxidation catalyst is prepared from silica which has been treated with strong aqueous acid solution, the catalyst is especially useful for propylene oxide production.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the preparation of a titanium on silica 
catalyst and to the use of the catalyst for the epoxidation of olefins to 
produce products such as propylene oxide. 
2. Description of the Prior Art 
A process for the epoxidation for olefins such as propylene to produce the 
oxirane product such as propylene oxide involves the reaction of the 
olefin with an organic hydroperoxide in the presence of various catalyst 
materials. The basic patent which describes this process is U.S. Pat. No. 
3,351,635. 
A particular embodiment of this technology which has been commercially 
practiced involves the use of a solid epoxidation catalyst comprised of 
titanium on silica. There are a number of patents which describe this 
embodiment of the technology including U.S. Pat. Nos. 3,829,392, 
3,923,843, 4,021,454, 4,367,342, and British Patent 1,249,079. 
Although good results have been achieved with the titanium on silica 
catalyzed epoxidation of olefins, there remains room for further 
improvement. It is an objective of the present invention to provide an 
improved epoxidation catalyst of the titania on silica type and to provide 
a process for the epoxidation of olefins using this catalyst. 
In the technology associated with catalytic reduction of nitric oxide with 
ammonia the preparation of titania on silica catalysts has been described 
where the silica has been pretreated by refluxing in hydrochloric acid. 
See Applied Catalysis 69, p. 149-167 (1991), "Influence of the preparation 
method on the V.sub.2 O.sub.5 /TiO.sub.2 /SiO.sub.2 catalysts in selective 
reduction of nitric oxide with ammonia", Wauthog et al.

EXAMPLES 
Acid Washing of Silica Support 
Silica (Grace V432, 30 g) is washed with HCl (0.4 M, 2500 cc) in a fixed 
bed reactor at 70.degree. C. and 150 psi, the acid flow rate being 8.33 
cc/min. The silica is then washed with deionized water (750 cc) to remove 
any residual chloride followed by an IPA (750 cc)wash. Catalyst is removed 
from the reactor and dried at 400.degree. C. in a muffle furnace. The 
silica was tested before and after washing for metal impurities, and the 
results are shown in Table 1. The amount of each impurity, with the 
exception of Fe (possibly from stainless steel), is reduced. 
TABLE 1 
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Impurity profile of washed and non-washed silica 
Amount before wash 
Amount after wash 
(ppm by weight of 
(ppm by weight of 
Silica Impurity 
silica) silica) 
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Na 800 100 
Al 250 100 
Ca 120 42 
K 50 &lt;20 
Mg 20 12 
Fe 40 87 
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Catalyst Preparation 
The epoxidation catalyst is produced by the incipient wetness method. The 
acid washed silica (14.5 g) is weighed into a 250 cc round-bottomed flask. 
A mixture Ti(acac).sub.2 (.sup.i OPr).sub.2 (1.5 g) in anhydrous IPA (14.5 
g) is added to the silica. The reaction mixture is thoroughly mixed for 
0.5 hours then residual solvent is removed on a rotary evaporator. The 
catalyst is then calcined in a muffle furnace at 800.degree. C. and then 
silylated at 200.degree. C. with hexamethyldisilazane (2.5 cc) for 3 hours 
in a quartz tube heated in a 3-zone furnace. 
A similar catalyst was prepared by the same method using non-acid washed 
silica as a comparative example. 
Batch Epoxidation of 1-Octene with EBHP Oxidate 
Catalyst (0.5 g) was added to a 4-neck round-bottomed flask charged with a 
condenser, a thermocouple, a stir bar and a sampling port. A mixture 
containing 17.0 g 1-octene, 10 g EBHP oxidate and 1 g nonane (internal 
standard) was added to the flask. A sample was taken after the reaction 
mixture was stirred thoroughly under inert atmosphere. The mixture was 
heated to 90.degree. C. and the reaction lasted for 1 hour at 90.degree. 
C. 
The batch epoxidation results obtained for the catalysts are shown in Table 
2. The catalyst prepared using acid washed silica in accordance with the 
invention was more active by 11% conversion points than that prepared 
using non-acid washed silica. 
TABLE 2 
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Batch Epoxidation Results of 1-Octene with EBHP Oxidate 
Conversion 
Selectivity 
Catalyst from % Ti % C (%) (%) 
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Acid washed silica 
.89 2.3 80 82 
Non-washed comparison 
.94 1.81 69 89 
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