Continuous method of manufacturing chlorine-free tetraalkoxysilanes

A continuous method of manufacturing chlorine-free tetraalkoxysilanes of formula (I)

• (R1O)4Si (I)
• wherein R1 is, independently in each instance, an unbranched, branched, and/or cyclic C1-6 hydrocarbon group, comprising:
• reacting metallic silicon powder with a monohydric alcohol in the presence of a basic catalyst comprising a mixture of:
• (a) at least one compound of formula (II)
• [R2O—(R3O)m]nSi(OR1)4-n (II)
• (b) at least one compound of formula (III)
• R2O—(R3O)m—M, and (III)
• (c) at least one compound of formula (IV)
• R2O—(R3O)m—H (IV)
• wherein R1 is as defined above;
• R2 represents, independently in each instance, a C1-10 hydrocarbon group, or hydrogen;
• R3 represents, independently in each instance, a C1-4 hydrocarbon group;
• M represents an alkali metal selected from the group consisting of Li, Na, and K;
• m is zero or a number in the range of 1-20;
• and
• n is zero or a number in the range of 1-4;
• further comprising:
• charging said catalyst in advance to a continuously operating reactor to which at elevated temperature is also continuously added metallic silicon powder and the alcohol;
• and then
• separating the reaction mixture in a first column, in which gaseous hydrogen is discharged from the top, high-boiling catalyst is returned to the reaction mixture in said reactor, and low-boiling components are sent to a second separation column in which the tetraalkoxysilanes of formula (I) are separated, and low-boiling alcohol(s) present is/are returned to the reactor;
• wherein the catalyst is prepared by reacting at least one tetraalkoxysilane of formula (I)
• R1O)4Si (I)
• with at least one compound of formula (IV)
• R2O—(R3O)m—H (IV)
• and at one compound of formula (V)
• R1OM (V)
• and the molar ratio of the compounds employed in preparing the catalyst is;
• 2-3 mol (IV) to 1-2 (V) to 1 mol (I).