| Byproducts including 5-15wt%methyltrichlorosilane (M1), 1wt%trimethylchlorosilane (M3) and methylhydrodichlorosilane (MH), 1-2wt% low-boiling residues (LBR) and 6-8wt%high-boiling residues (HBR) were produced from the direct process of synthesizing dimethyldichlorosilane (M2) because of some unavoidable side reactions. At present, how to utilize the above byproducts plenty and reduce their harm to environment had been a much serious problem for methylorosilane industry in china. In this dissertation, methyl choride and hydrogen choride were used as existing resources for the research on how to select an economical and feasible method to realize the above byproducts comprehensive utilized. The researches consisted of the following three parts:A. Conversion of HBR to valuable monosilanes through cleavage reaction with HClThe HBR could be converted into monosilanes by cleaving Si-Si bonds in methylchlorodisilanes in the presence of hydrogen chloride. On the base of technology rotue and device were determined, the results showed that N,N-dimethylaniline was the best catalyst. The dissolvable components of HBR must be removed by distillation. The other optimum reaction conditions were obtained as stirred rate = 300r/min, reaction temperature = 135-140℃, fulx of HC1 = 5.0-6.0 L/h , catalyst component = 0.75 -1.0wt% and catalyst perfected good reused catalytic. Generally, under the optimum reaction condition, the best cleavage ratio of HBR and the monosilane yield could reach to 85% and 78% respectively.In order to comprehend the cleavage process and mechanism of the HBR reacting with HCl, the composition of HBR was first determined by GC-MS. The results showed that 140-170℃fraction of HBR were mainly composed with 56.61 wt % of CH3Cl2SiSiCl(CH3)2, 27.57wt% of CH3Cl2SiSiCl2CH3, and 6.18% of (CH3)2ClSiSi. Cl(CH3)2. Under this analysis results and the GC analysis for the cleavage products, the reaction mechanism was educed and validated. Based on the mechanism, the double-film theory and the low rate hypothesis for the gas-liquid reaction system, a macrokinetic model was developed as follows, B. Conversion of M1 in stirred bed reactor by methylaluminum chloride methodAs one of the main byproduct in the direct synthesis of M2, we focused on the reaction technique of converting M1 to more valuable methylchlorosilanes by utilizing methl chloride reource. The conversion reaction of M1 in a continuous stirred tank bed reactor by methylaluminum chloride method with aluminum powder and methyl chloride as raw materials was systematically investigated. It was found that after an introductive stage of about 100 minutes, the reaction reached a steady state with good activity in the absence of catalysts by the aid of mechanical stirring in the reactor which promoted the elimination of oxidized layer on the surface of the aluminum powder and speeded up the surface renewal process. Increasing the stirring speed and reaction temperature to the optimum levels were propitious to the conversion reaction. The molar proportion of methyl chloride to M1 (m) in feeding had great effects on reaction conversion and the product composition, in that the concentrations of M2 and M3 in the products were relatively higher while the reaction conversion of M1 was lower when m<2.0, and the M3 was the main converted product when m=2.0, and the tetramethylsilane (M4) became the main product while higher reaction conversion of M1 was obtained when m>2.0. Based on the SEM observation of the aluminum powder surface before and after reaction, the reaction mechanism was discussed.C. Redistributed reactions between M1 and M3 (or LBR) by using supported solid acid catalystWith a redistribution reaction, the byproducts including M1, M3 and LBR could be converted into more valuable M2. In the literatures, with AlCl3 as most effectively catalyst, the redistribution was conducted in a batch tank reactor on temperature 473-673 K and high pressure. Because AlCl3 behaved a homogeneous catalyst in this reaction system, it would become difficult to separate from the products as well as to reuse as recyling. Also the drawback of high pressure in the process restricted large scale disposing the above by-products. In this work, several AlCl3 supported catalysts were prepared by the impregnation-evaporation-calcination method, and the model redistribution reaction of M1 and M3 investigated in theΦ20×800 mm fixed bed reactor. The results showed that AlCl3 supported on 40-60 mesh coconut shell actived carbon catalyst behaved the best activity.As an attempt to optimize the supported solid acid, effects of acid-treated conditions, AlCl3 loading, activated temperature and activated time on the catalytic activity were examined for the model redistribution reaction under conditions of 310℃, n(M1/M3)=1.0 and LHSV=1.5h-1. The results revealed that it would be better if the activated carbon were treated by hydrochloric acid of 2.0 mol·L-1 for 6.0 h. And suitable conditions for AlCl3 loading, calcination temperature and activated time were 1.87mmol/g, 450-500℃and 6h respectively. And also, the optimum conditions of the redistribution reaction were determined as that n(M1/M3) was 1.0, LHSV was 1.0-1.5h-1, reaction temperature was 320℃. At this condition, we can get the same yeild of M2 as the reference literature. The catalyst took on good catalytic stability in the reaction within 100h.The structure and surface properties of supported solid acid catalysts were characterized by BET, XRD, TG-DSC and pyridine adsorbed Raman spectroscopy. The stability of the activated carbon supported AlCl3 catalyst is good at least 100h. The XRD and TG -DSC results indicated that AlCl3 would not longer exist in the form of AlCl3 crystal after supported on activated carbon. The TG-DSC analysis showed that heating of the catalyst at 485-600℃resulted in decomposition and removal of active component from the catalyst surface. The pyridine-adsorbed Raman spectroscopy revealed that the active component of the catalyst behaved as Lewis acid. According to these characterized results, the mechanism of model reaction was educed.The recovering technology is very important in the catalyst developed. We investigated the deactivation behavior of the AlCl3/AC catalyst firstly. It was found that there were such methchlorodisilanes and polymutilsilanes accumulated on the catalyst surface that covered the acidic sites on the catalyst. To recover the catalyst, both methods by the high temperature calcination and the solvent washing were investigated. The results showed that the solvents washing method was very effective for regenerating the deactivited catalyst.On the basis of the catalyst development, the gas-solid heterogenous macrokinetic study of M1 and M3redistribution reaction was done. A kinetic model was developed as follows, The simulated results were good agreement with those of our plant runnings.As a clean and contiuous rotue to solve the LBR, M1 was used to redistribute with it catalytized by the solid acid in the fixed bed reactor. Through systematically investigating, the optimum reaction conditions for the redistribution reaction were determined as follows: the mass ratio of methyltrichlorosilane to low-boiling residues was 2.0-3.0, the reaction temperature was 310℃and LHSV was 1.5h-1. The AC supported AlCl3 catalyst required only a mild reaction conditions and it shows a good catalytic stability in the redistribution reaction within 120h.
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