Abstract
The direct synthesis of dimethyldichlorosilane has been studied for more than 60 years, owing to its significance in the silicones industry. The direct process is a reaction of distinct complexity because of silicon taking part in the catalytic cycle and forming Cu3Si and Cu15Si4 alloy phases, where Cu3Si is the catalytically active intermediate. In addition, the side reactions and cracking of chloromethane during the direct reaction lead to coke formation on the active surface. In spite of its importance, the role of CuCl and Zn on the coke formation, Cu3Si formation, and its transformation to Cu15Si4 phase is not entirely understood. A series of reacted contact mass samples with varying reaction time and amount of CuCl and Zn was characterized by using x-ray diffraction (XRD) to study the phase transformation. Raman spectroscopy and thermogravimetric analysis (TGA) coupled with mass spectrometry (MS) were utilized to investigate the structural order and reactivity of coke, respectively.
XRD analyses of samples with CuCl and Zn indicated that the standard amount of CuCl and Zn limited the enrichment of inactive copper and Cu15Si4 formation, while five times the amount of CuCl and Zn caused high enrichment of inactive copper. Samples without the addition of Zn exhibited a high tendency of Cu15Si4 and inactive copper formation. In addition, the investigation on the structural order of deposited coke by using Raman spectroscopy revealed that the addition of Zn changes the coke to a more ordered graphitic carbon, as the reaction proceeds. TGA analyses pointed out that coke in all the reacted contact mass samples starts to oxidize at around 200 °C. In Zn-promoted samples, the CO2 mass spectrum peak became more distinct and narrower with an increase in reaction time. While in samples without Zn, the CO2 signal was noticed to be broad with a shoulder peak at a higher temperature of 340 °C. It was found that Zn-promoted samples had slightly more reactive coke.
