The Use of a Fixed-Bed Reactor to Evaluate the Interactions of Catalysts and Promoters in the Methyl Chlorosilane Reaction and to Determine the Effect of Cu in the Form of the Eta Phase on This Reaction

Abstract

A fixed-bed reactor was employed to study the methylchlorosilane (MCS) reaction, also called the direct process. We used a copper−silicon contact mass as the main MCS catalyst. The copper−silicon contact mass was prepared by the reaction of CuCl with silicon. The effect of added zinc and phosphorus to the MCS reaction was explored, and we found that, at Cu/Zn ratios > 30, phosphorus addition resulted in an increase in selectivity for dimethyldichlorosilane (Di) at the expense of methyltrichlorosilane (Tri) and residue. Addition of tin to the MCS reaction resulted in an increased overall rate but with a decrease in Di and an increase in disilane formation. Addition of phosphorus and high tin levels resulted in a high rate but with a high selectivity for Di; phosphorus negated the selectivity penalty caused by the addition of tin alone. Phosphorus appeared to cause an increase in formation of the eta phase (Cu3Si), as determined by analysis of MCS beds formed under different conditions. Previously reported arguments show that copper diffusion is operative for Cu−Si renewal in MCS but that Cu diffusion is not the rate-limiting step in the reaction.

Effects of Multiple Promotion of the Direct Synthesis Contact Mass with P, Zn, and Sn on the Synthesis of Methylchlorosilanes

“…We do not find the reactivity of the Si-Cu toward residual oxygen surprising based on prior studies that show the Si in the Si-Cu alloy (e.g., Cu 3 Si) is more susceptible to oxidation than is pure silicon [23]. We do not suspect that this residual oxidation affects our results considering that our selectivities and relative reaction rates derived from the reactor studies agree well with prior studies [5][6][7][8][9].…”

“…We suspect that this is a result of the change in the composition of the triply promoted catalyst over time where the surface becomes more copper rich. This is an interesting point, since as mentioned above P has been shown in prior research to prevent the formation of the copper rich contact mass that is deemed detrimental to the production of DMDCS [6]. Under our experimental conditions, however, it seems as though as the DS reaction proceeds the ability to form the Cu 3 Si phase on the triply promoted contact mass becomes compromised.…”

“…It is reasonable that the presence of P increases the amount of surface CH 3 on the Zn-P-promoted contact mass and the Zn facilitates the availability of active Si for its removal as methylchlorosilane product. Prior research by Lewis and Ward [6] has also suggested that P-promotion enhanced the formation of the Cu 3 Si phase (i.e., eta-phase [25]) that is thought to be an active phase for DMDCS production. This prior research suggested that P-promotion facilitates copper diffusion away from the working surface preventing the formation of copper rich phases such as Cu 5 Si and free copper.…”

“…Because of the industrial importance of the DS for the production of silicones, there have been many prior studies that have mapped out the effects of promoters on the selectivity and reactivity of contact masses for the DS [2][3][4][5][6][7][8][9][10]. It is the general consensus from the literature that when specific combinations of promoters are added together, a synergism between the promoters is typically observed.…”

Synthesis of Novel Hollow Copper Oxide Micro-Flowers Assembled by Nanoparticles and Their Improved Catalytic Performances for the Synthesis of Organosilane

“…And the amount of CuxSi plays a key role in determining the conversion of Si and selectivity of M2 in the Rochow reaction 37 Therefore, the performances of Cu-based catalysts strongly depend on their ability to form the active species CuxSi. The above results of H 2 -TPR (Fig.…”