Method for silicon nitride precursor solids recovery

Reference Number: N 03-03

Inventors: Crosbie, Gary M. ; Predmesky, Ronald L.; Nicholson, John M.

Owner: NISTAC

USPTO Link: 5171557

Invention Summary

In accordance with the invention, method and apparatus are provided for collecting solids, such as reaction product solids, entrained in a gas flow comprising condensable vapor. In the case of a gaseous outflow from a reaction situs during a reaction, the gaseous outflow comprises vapor condensable at a reduced temperature, that is, at a condensation temperature lower than the temperature at which it exits the reaction vessel. The gaseous outflow is passed from an outlet of the reactor vessel to a static mixer heat exchanger. The static mixer heat exchanger has a static mixer cooling chamber defining a flow path for the gaseous outflow between the inlet and an outlet. Static mixer surfaces are provided in the flow path of the static mixer cooling chamber for capturing the entrained solids in a condensate formed of the aforesaid condensable vapor. Specifically, the static mixer heat exchanger further provides cooling means for maintaining the static mixer surfaces at a temperature not greater than the aforesaid reduced temperature at which the condensable gas condenses. Entrained reaction product solids in a gaseous outflow contact, and are thereby captured in, the condensate formed on the static mixer surfaces. The condensate and the reaction product solids captured therein can be collected, for example, for return to the reactor vessel or for other processing.

The present invention provides advantages in collecting or recovering reaction product solids which may otherwise be lost or which would otherwise require different, more expensive or difficult collection methods and apparatus. Such collection of reaction product solids will in many instances increase the effective reaction product yield, thereby improving the efficiency of the production process.

In addition, in those embodiments of the invention wherein the condensate formed in the static mixer heat exchanger comprises reactant for the ongoing reaction, the return of the condensate, with the recovered reaction product solids, can further improve the efficiency of the production process. This is particularly true where the reactant in the condensate would otherwise be lost or require more expensive or difficult collection and return apparatus.

The method and apparatus of the invention are particularly advantageous in preferred embodiments of the invention, discussed further below, wherein silicon nitride precursor solids are entrained in a gaseous outflow from a reaction situs during an ongoing reaction. The static mixer heat exchanger can treat gaseous outflow from the reaction situs anaerobically, including steps of receiving the gaseous outflow, forming a condensate of a condensable vapor in the gaseous outflow to capture entrained solids, and returning the condensate, optionally through intermediate fluid communication means, to the reaction situs or other receiving point for further processing. In such preferred embodiments the invention is particularly advantageous in that the entrained solids comprise reaction product, thus directly enhancing process yield, and the condensate returned with the solids to the ongoing reaction is usable reactant.