Process for preparation of silane

In a process for the preparation of silane, and a metal halide coproduct wherein an alkali metal aluminum hydride is reacted with a silicon tetrahalide, and wherein are included the steps of:

• (I) introducing said alkali metal aluminum hydride reactant and a liquid reaction medium at a substantially constant flow rate into a primary reaction zone, and reacting said hydride in said zone with less than a stoichiometric quantity of silicon halide reactant, such that from about 90 to about 99 weight percent of the alkali metal aluminum hydride introduced is reacted in said zone;
• (II) reacting, in a second reaction zone, the unreacted alkali metal hydride component of said liquid reaction mixture above which a vapor space is provided, and wherein silicon halide is introduced at a rate that is at least substantially stoichiometric with the amount of alkali metal aluminum hydride introduced into said first reaction zone;
• (III) separating, in a separation zone, silane product and unreacted silicon halide from a slurry introduced from said secondary reaction zone comprising:
• (i) metal-aluminum-halogen containing coproduct, and (ii) said liquid reaction medium;
• (IV) recovering said silane;
• (V) introducing unreacted silicon halide from said second reaction zone into said first reaction zone for reaction with additional alkali metal aluminum hydride introduced into said zone;
• (VI) determining the difference in temperature between the temperature of the liquid reaction medium in said second reaction zone, and the temperature of reactant liquid medium from said first reaction zone substantially immediately prior to entry into said second zone;
• and
• (VII) utilizing a signal derived from said difference in temperature to regulate the flow of silicon halide to the second reaction zone to achieve substantially stoichiometric reaction of the total amounts of silicon halide and metal hydride reacted in both reaction zones, the improvement comprising
• (VIII) splitting the silicon halide reactant introduced into said second reaction zone (II) into two steams, (a) a first silicon halide stream which is introduced directly into the liquid mixture to control mass transfer between the liquid and gaseous phases, and (b) a second silicon halide stream which is introduced into the separation zone or directly into the vapor space above said liquid reaction mixture, or into both the separation zone and the vapor space to suppress the formation of combustible gaseous mixture.

In a continuous process for preparing silane and a coproduct comprising a metal and a halogen, wherein the process includes the steps of (a) reacting in a first reaction zone, an alkali metal hydride or alkali metal aluminum hydride with less than a stoichiometric quantity of silicon tetrahalide;

• (b) reacting in a second reaction zone in a liquid reaction mixture the remaining metal hydride from the first reaction zone, with a stoichiometric excess of the silicon tetrahalide reactant;
• and (c) separating in a separation zone the reactants from the second reaction zone, into a gaseous fraction comprising silane and unreacted silicon tetrahalide and a solid reaction product suspended in a diluting solution;
• the improvement which comprises splitting the silicon tetrahalide reactant introduced to the second reaction zone into two streams:
• (1) a first silicon tetrahalide stream which is introduced directly into the liquid reaction mixture to improve mass transfer between the liquid and gaseous phases, and
• (2) a second silicon tetrahalide stream which is introduced into the separation zone or directly into the vapor space above said liquid reaction mixture, or into both the separation zone and the vapor space to suppress the formation of combustible gaseous mixtures.