Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2000-04-20
2003-03-04
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
C252S182320
Reexamination Certificate
active
06528674
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for preparing a contact mass. More particularly, the present invention relates to a method for preparing a contact mass for the direction reaction of powdered silicon, alkylhalide and copper catalyst.
Rochow, U.S. Pat. No. 2,380,995 discloses preparing a mixture of alkylhalosilanes by a direct reaction between powdered silicon and an alkylhalide in the presence of a copper-silicon alloy. This reaction is commonly referred to as the “direct method” or “direct process.” The reaction can be summarized as follows:
where Me is methyl.
In addition to the above methylchlorosilanes, “residue” is also formed during the production of methylchlorosilane crude. Residue means products in the methylchlorosilane crude having a boiling point greater than about 70° C., at atmospheric pressure. Residue consists of materials such as disilanes for example, symmetrical 1,1,2,2-tetrachlorodimethyldisilane; 1,1,2-trichlorotrimethydisilane; disiloxanes; disilmethylenes; and other higher boiling species for example, trisilanes; trisiloxanes; trisilmethylenes; etc.
As shown, the alkylhalosilanes formed by the direct reaction include dimethyldichlorosilane referred to as “D” or “Di” and methyltrichlorosilane, referred to as “T” or “Tri”. These are the major products of the reaction, which typically produces dimethyldichlorosilane in a range between about 80% and about 88% and methyltrichlorosilane in a range between about 5% and about 10%. Dimethyldichlorosilane has the highest commercial interest. A T/D ratio is the weight ratio of methyltrichlorosilane to dimethyldichlorosilane in the crude methylchlorosilane reaction product. An increase in the T/D ratio indicates that there is a decrease in the production of the preferred dimethyldichlorosilane. Hence, the T/D product ratio is important and is the object of numerous improvements to the direct reaction.
Gilliam, U.S. Pat. No. 2,464,033 discloses using zinc in combination with copper catalyst as a promoter to achieve a higher selectivity of dimethyldichlorosilane. Gilliam discloses that a proportion in a range between about 2% and about 50% by weight of copper in elemental form or as the halide or oxide, and preferably 5 to 20% and zinc in a range between about 0.03% and about 0.75% by weight in the form of zinc halide, zinc oxide, or zinc metal, or mixture thereof, where the weights of copper and zinc are based on the weight of silicon, can be used as a promoter for making dialkyl substituted dihalogenosilanes, such as dimethyldichlorosilane in the direct reaction between silicon powder and methyl chloride.
Radosavlyevich et al.,
Influence of Some Admixtures on the Activity of Contact Masses for Direct Synthesis of Methylchlorosilanes,
Institute of Inorganic Chemistry, Belgrade, Yugoslavia, (1965) discloses that micro quantities of silver added to contact masses resulting from the reaction of powdered silicon and methyl chloride in the presence of cuprous chloride decreases the yield of methylchlorosilanes, while tin and calcium chloride increase the rate of formation of methylchlorosilanes.
Rong et al.,
Aluminum as Promoter for the Direct Process to Methylchlorosilanes, Silicon for the Chemical Industry III,
J. Kr. Tuset Eds. 199 (Trondheim, Norway, 1996) discloses adding solid aluminum compounds to improve reactivity and selectivity of the direct process. Ward et al., U.S. Pat. No. 4,500,724 discloses that tin and zinc are important in improving the direct method and can be controlled to provide improved alkylhalosilane product selectivity.
Methods are constantly being sought for making alkylhalosilanes that will enhance the rate of dimethyldichlorosilane formation, reduce the T/D weight ratio and maintain or reduce the percent by weight of products having a boiling point greater than about 70° C.
BRIEF SUMMARY OF THE INVENTION
The present invention improves direct process dimethyldichlorosilane formation, and selectivity while maintaining or substantially reducing residuals. According to the present invention, a selective contact mass is prepared by forming a mass of silicon with a form of copper and heat treating the mass at a temperature greater than about 500° C.
In an embodiment, the present invention relates to a method for making an alkylhalosilane, comprising heat treating silicon and a form of copper at a temperature greater than about 500° C. to produce a contact mass and effecting reaction of an alkyl halide in the presence of the contact mass to produce alkylhalosilane.
In another embodiment, the present invention relates to a reactor containing a contact mass prepared by forming a mass of silicon and a form of copper and heat treating the mass at a temperature greater than about 500° C.
In yet another embodiment, the present invention relates to an alkylhalosilane reactor containing a contact mass substantially free of forms of copper other than the eta (Cu
3
Si) phase.
DETAILED DESCRIPTION OF THE INVENTION
In a typical instance, a mass for producing alkylhalosilanes is prepared by reacting silicon and cuprous chloride at a temperature in a range between about 280° C. and about 400° C. in a furnace until evolution of silicon tetrachloride (SiCl
4
) ceases. The resulting solid contains silicon and copper and is called “contact mass.” The contact mass is typically made prior to the step of contact with alkylhalide to generate alkylhalosilane. According to the present invention, silicon and a form of copper are heat treated to provide an improved contact mass.
According to the present invention, a form of copper is contacted with silicon to form a mass. The form of copper can provide a weight percent in a range between about 0.5% and about 10% relative to the entire contact mass. Preferably the amount of copper is in a range between about 1% and about 7% and more preferably in a range between about 2% and about 5%. The preparation of the contact mass proceeds according to the following equation (II):
Si+4CuCl→4Cu+SiCl
4
(II)
at a temperature less than about 500° C. to form a contact mass.
The mass is then heat treated at an elevated temperature. The heat treatment step comprises heating the mass to a temperature in a range between about 550° C. and about 1550° C. Preferably the heating is to a temperature in a range between about 850° C. and about 1250° C. and more preferably to a temperature in a range between about 975° C. and about 1125° C. The heating is conducted for a period that varies with the temperature. Typically, the heating is conducted for a period in a range between about 0.01 hour and about 8 hours, preferably in a range between about 0.05 hours and about 4 hours and more preferably in a range between about 1 hour and about 3 hours. The heating is typically conducted with a steady application of heat over the desired period. Alternatively, the heating step can be conducted by applying heat to the mass in multiple periods, in step elevations or in pulses or the like. The heating step is typically conducted under inert conditions, for example, by providing a nitrogen atmosphere or the like.
Carboxylic acid salts of copper are typically used as the copper source to make the contact mass for the process. Copper formate, copper acetate and copper oxalate are examples of suitable carboxylic acid salts. The granular material should exhibit a BET surface area in a range between about 0.5 meters
2
/gram and about 20 meters
2
/gram by the nitrogen adsorption method.
Partially oxidized copper can also be the copper source to make the contact mass. Where the copper contains a level of tin relative to copper that exceeds a required range to make a satisfactory catalyst, a copper substantially free of tin can be alternated to purge excess tin, or mixtures of tin containing copper and copper substantially free of tin can be used to maintain a desired tin concentration in the resulting catalyst. “Substantially free of tin” as used herein refers to tin being present in an amount less than about 300 ppm. An example of a partially oxidized
Bablin John Matthew
Lewis Larry Neil
Ward William Jessup
Cabou Christian G.
General Electric Company
Johnson Noreen C.
Shaver Paul F.
LandOfFree
Method for preparing a contact mass does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for preparing a contact mass, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for preparing a contact mass will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3036155