GB741067A - Process for the production of organic silicon compounds - Google Patents

Abstract

Polymeric and monomeric organo-substituted silanes are prepared by reacting elemental silicon with hydrocarbon-containing gases by passing said gases through an electric arc formed between hot or cold electrodes and allowing said gases to react with silicon of small particle size either while passing through the arc or shortly thereafter, or by heating the hydrocarbon containing gases and silicon of small particle size to a temperature at which silicon vaporizes or the <PICT:0741067/IV(a)/1> <PICT:0741067/IV(a)/2> <PICT:0741067/IV(a)/3> hydrocarbons dissociate, or by passing hydrocarbon containing gases through a silicon containing melt, and rapidly cooling the reaction products after their formation. The cooling of the reaction products may be effected by rapid removal from the source of heat and/or by injection of water or other inert liquid substances having a relatively high heat of evaporation and/or by passing said reaction products through a fluidized bed of an inert solid substance of small particle size. The silicon used may be amorphous silicon or an alloy of silicon in powdered form. Copper and silver are given as examples of metal catalysts that may be used in the reaction. Elevated reaction pressures may also be used. The hydrocarbon containing gases may be admixed with hydrogen, oxygen, nitrogen or small quantities of carbon monoxide, and when oxygen is present, oxygen containing silicon products are formed. The products of the process may contain silicon-hydrogen and/or silicon-silicon linkages which are suitable for hydrolysis to form condensation products. The electric arc method may be carried out by recycling a mixture of one or more hydrocarbons and silicon dust, and separating the reaction products, e.g. by dissolving the reaction products in a mixture of methanol and aqueous concentrated ammonia and then distilling off the methanol, water and ammonia to leave an oily hardenable resin. Three methods for the preparation of the desired silicon compounds are detailed as follows: (a) a hydrocarbon, e.g. propane, is recycled through a melt of silicon, aluminium and tin at a temperature of about 400 DEG C. to form oily polymeric alkyl silanes which can be extracted with caustic potash solution and precipitated with acid; (b) a mixture of ethylene and hydrogen are passed through amorphous silicon in the presence of magnesium iodide under a pressure of 400 atmospheres and at a temperature of 400 DEG C. to form alkyl silanes; (c) a ferro-silicon rod, heated electrically, is arranged axially in a water-cooled metal tube, and a mixture of hydrogen and methane is passed under pressure through the tube to form volatile, oily and solid hydrocarbon-substituted silicon compounds. In Fig. 1, a blower 1 circulates a mixture of hydrogen and silicon dust through tube 2, and an electric arc 3 is provided between carbon electrodes 4 and 5. Hydrogen is introduced through inlet 6 and gaseous products are withdrawn from the cycle through dust separator 7. The temperature of the gases may be controlled by means of water trough 8. The gaseous products are extracted with methanolic ammonia, the resulting solution is evaporated to dryness, and the desired silicon containing oil is extracted with cyclohexanone to remove silica. In Fig. 2, the hydrocarbon gases to be reacted are introduced at 11, the silicon in the form of ferrosilicon dust trickles down the conically-shaped vessel 12, and the reaction takes place in an arc between a water-cooled copper cathode 9 and a water-cooled iron anode 10. Aryl and alkyl silanes are the main products when natural gas is employed in this apparatus. In Fig. 3, ground iron containing silicon together with coke oven gas free from carbon monoxide are recycled with the aid of blower 1. Portion 16 of the apparatus operates as a centrifugal separator so that the quantity of silicon dust reaching the electrodes 4 and 5 can be regulated. The inlet for the gas to be reacted is at 18. Condensable reaction products-mainly liquid alkyl silanes are separated in cooler 17.ALSO:<PICT:0741067/IV(a)/1> <PICT:0741067/IV(a)/2> <PICT:0741067/IV(a)/3> Organic compounds containing silicon, e.g. partially alkyl and/or aryl substituted silanes, are prepared by reacting elemental silicon with hydrocarbon-containing gases by passing said gases through an electric arc formed between hot or cold electrodes and allowing said gases to react with silicon of small particle size either while passing through the arc or shortly thereafter, or by heating the hydrocarbon containing gases and silicon of small particle size to a temperature at which silicon vaporizes or the hydrocarbons dissociate, or by passing hydrocarbon containing gases through a silicon containing melt, and rapidly cooling the reaction products after their formation. The cooling of the reaction products may be effected by rapid removal from the source of heat and/or injection of water or other inert liquid substances having a relatively high heat of evaporation and/or by passing said reaction products through a fluidized bed of an inert solid substance of small particle size. The silicon used in the above reaction may be amorphous silicon or in the form of an alloy in powdered form. Copper and silver are given as examples of metal catalysts suitable for use in the reaction. Elevated reaction pressures may also be used. The electric arc method is advantageously carried out in a fluidized bed of the silicon maintained by an upwardly directed stream of the gaseous reaction components. The electric arc method may be modified in that the hydrocarbon-containing gases are wholly or partly formed by passing a mixture of silicon of small particle size and hydrogen through an arc formed between carbon electrodes, or by passing a mixture of methane, hydrogen and silicon of small particle size through an arc so that the carbon formed by cracking the methane reacts with the hydrogen to form the hydrocarbon containing gases. The products of the processes may contain silicon-hydrogen and/or silicon-silicon linkages, the preferred products being alkyl and aryl silanes of the general formula RnSiH4-n, wherein R represents an alkyl or aryl group and n is an integer of 1 to 4, e.g. dimethylsilane. The hydrocarbon containing gases can be admixed with hydrogen, oxygen, nitrogen or small quantities of carbon monoxide, and when oxygen is present, oxygen containing organic silicon compounds are formed. The electric arc method may be carried out by recycling a mixture of one or more hydrocarbons and silicon dust, and the reaction products are then separated, e.g. by dissolving the reaction products in a mixture of methanol and aqueous concentrated ammonia, and then distilling off the methanol, water and ammonia to leave an oily hardenable residue. The hydrocarbon containing gases can be directed upwardly into the electric arc (preferably formed between a water cooled copper electrode and a water cooled iron electrode) to maintain a fluidized bed of silicon. Three methods for the preparation of the desired silicon compounds are detailed as follows: (a) a hydrocarbon, e.g. propane, is recycled through a melt of silicon, aluminium and tin at a temperature of about 400 DEG C. to form oily polymeric alkyl silanes which can be extracted with caustic potash solution and precipitated with acid; (b) a mixture of ethylene and hydrogen are passed through amorphous silicon in the presence of magnesium iodide under a pressure of 400 atmospheres and at a temperature of 400 DEG C. to form alkyl silanes; (c) a ferro-silicon rod, heated electrically, is arranged axially in a water-cooled metal tube and a mixture of hydrogen and methane is passed under pressure through the tube to form volatile, oily and solid hydrocarbon substituted silicon compounds. Apparatus suitable for carrying out the electric are method are shown in the Figures. In Fig. 1, a blower 1 circulates a mixture of hydrogen and silicon dust through tube 2, and an electric arc 3 is provided between carbon electrodes 4 and 5. Hydrogen is introduced through inlet 6 and gaseous products are withdrawn from the cycle through dust separator 7. The temperature of the gases may be controlled by means of the water trough 8. The gaseous products may be extracted with methanolic ammonia, the resulting solution is evaporated to dryness, and the desired silicon containing oil is extracted with cyclohexanone to remove silica. In Fig. 2, the hydrocarbon gases to be reacted are introduced at 11, the silicon in the form of ferrosilicon dust trickles down the conically-shaped vessel 12, and the reaction takes place in an arc between a water-cooled copper cathode 9 and a water-cooled iron anode 10. Aryl and alkyl silanes, particularly dimethyl silane are the main products when natural gas is employed in this apparatus. In Fig. 3, ground iron containing silicon together with coke oven gas free from carbon monoxide are recycled with the aid of blower 1. Portion 16 of the apparatus operates as a centrifugal separator so that the quantity of silicon dust reaching the electrodes 4 and 5 can be regulated. The inlet for the gas to be reacted is at 18. Condensable reaction products-mainly liquid alkyl silanes, including dimethyl silane, are separated in cooler 17.