Synthesis of ethylchlorosilanes by catalyzed and promoted reaction of ethyl chloride with silicon in fixed-and stirred-bed reactor.

The work described in this thesis involves the study of an important reaction of the gaseous EtCl with elemental silicon which is considered as a key step in the production of commercial silicon polymers. The above reaction involves no intermediates species; consequently it is called "Direct Synthesis". A high vacuum system was constructed from stainless steel and fitted with a number of flanges rubber O-rings which were connected by stainless steel bellows-sealed right -angle and straight-through valves. Two types of pumps were used to evacuate the system; a three-stage oil diffusion pump backed by a two-stage oil rotary pump which were capable of producing pressures as low as 106 torr (1 torr = 133.33 N.m2). Either Fixed or Stirred-Bed reactors were used to carry out the reaction. Both reactors were constructed of Pyrex glass. The reactors were connected to the apparatus through stainless steel valves. Electrothermal heating tapes, controlled by a microprocessor controller, were used to heat the reactor to the various experimental temperatures. To protect the vacuum system and reactors from the vapours of the diffusion and rotary pumps, an efficient trap used and was maintained at liquid nitrogen temperature (78 K) throughout all experiments. Quantitative and qualitative analysis were performed for the gas phase, resulting from the interaction of EtCl with Sicatalyst mixtures. These analyses were carried out using a Quadruvac-Q2oo Mass-Spectrometer partial pressure gauge. This instrument covered amass range from 1 to 200 a.m.u. The constituents of the gas mixture in the reactor were determined qualitatively (mass number) and quantitatively (partial pressure). A pressure converter was combined with Faraday cup gauge head of the mass-spectrometer, thus enabling the reduction of the total gas pressure in the gauge head to a measurable range without influencing its composition. Copper was used as catalyst in all experiments, which was mixed by chemical precipitation, through the reduction of freshly prepared copper (I) chloride with silicon powder to the extent of 5 or 10 or 15 weight percent of the total composition. Under static condition, the gas section was supplied with doses of EtCl (0.5, 1, and 2 mbar respectively), which was allowed to react with the powder mixture at three temperatures 200, 250, and 300 °C, respectively. The pressure variation was measured simultaneously during the reaction period until a relatively steady value was obtained. Under stirred condition, a similar procedure, which was adopted for the fixed-bed reactor, was applied except that the reactor was stirred by means of a magnetic stirrer. It was found that this interaction was limited at temperature = 170 °C. The adsorption was molecular at such temperatures and no products were detected in the gas phase. The adsorption of EtCl on silicon powder was found to be very slight at temperatures < 350 °C. at temperatures = 350 °C, there was some increase in the pressure of reaction products at a considerably slow rate which was accompanied by the formation of some methane, ethylene, and H2 appeared as non-silane by-products. The EtCl adsorption on copper powder didn't occur below 170 °C, but EtCl readily decomposed above this temperature. Above 350 °C, EtCl decomposed readily and the gas phase consisted of C2H6 CH4, and H2. On mixtures of Si-Cu powder, the products of the interaction were mainly ethyltrichlorosilane (ETCS), diethyldichlorosilane
(DEDCS), and ethyldichlorosilane (EDCS), at higher temperatures and with mixtures of higher copper content, a small amount of free-silicon products such as C2H6, CH4, and H2 were also observed. The gaseous products which appeared in the gas phase consisted of a mixture of (ETCS), (DEDCS), and (EDCS); (ETCS) was the major product but on increasing the temperature as well as the Cu content mixture, the percentage of (ETCS) increased while of the other two products decreased. Under stirred condition, the ethylchlorosilanes products were generally ETCS, DEDCS, and EDCS on mixtures of Si-CuCl powder. Free-silicon products were also formed such as C2H6, CH4, and H2. The production of ETCS occurred generally to a greater extent and showed higher temperature dependence, especially in the temperature range from 250 to 300 °C, as compared with the reaction in the fixed-bed reactors. A mixture 10 % Si-CuCl was selected for studying the promotion or inhibition effect of certain additives, which were mixed mechanically with silicon powder and CuCl catalyst. Either promoting or inhibiting effect were observed on the extent of adsorption or on EtCl conversion; on addition each of Al, Zn, MgO, and Sn in a Fixed-Bed reactor and of Al, CaCl Zn, ZnCl2, Zn +A1, and ZnCl2+CaCl2+Al in Stfrred-Bed reactor each by 1 % by wt. Sn acted as inhibitor while MgO had no effect on the reaction rate. The production of DEDCS increased on mixtures which were promoted with each of Zn, ZnClz, Zn +A1, and ZnCl2 + CaCl2+Al. Kinetics of the ethyl chloride interaction with Si-catalyst mixture, as well as for the formation of the main products, in both the fixed-bed and the stirred-bed reactors have been investigated over the temperature range 200 - 300 °C. these involved the determination of the pressure and the temperature dependencies of the reaction rates from which the various kinetics parameters could be elucidated such as activation energy (Ea), preexponential factor (A), and entropy of activation (S*). The rate of EtCl reaction with silicon on CuCl catalyst directly depended on its pressure giving rise to an apparent reaction order of unity with respect to EtCl reactant. Values of the activation energy and the entropy of activation in the rate equation, have been determined for the catalyzed reactions as well as for the formation of the main reaction products.