The production of carbon black by the thermal decomposition of acetylene and acetylene-hydrocarbon mixtures

Abstract

When acetylene is heated above 800° C. it decomposes into carbon black and hydrogen. The reaction proceeds quietly and the yield of carbon black is in excess of 97 per cent of theoretical with optimum operating conditions and apparatus dimensions. The acetylene throughput can be varied from 10 to 30 pounds per hour without affecting the per cent of acetylene decomposed, and throughput of 50 pounds per hour is likely to give the same high yield. The product gas from the process is essentially pure hydrogen, i. e., 99 per cent hydrogen. The reaction is highly exothermic, and some of the liberated heat can be utilized to crack other hydrocarbon gases. A gas mixture of 30 per cent natural gas, 70 per cent acetylene can be decomposed to give a yield of 90 per cent of the total carbon therein, while a 20 to 80 mixture of propane and acetylene gives a similar yield. Lesser proportions of the acetylene diluent give correspondingly higher yields of carbon black. Dilutions of less than (1) 13 per cent natural gas and (2) 9 per cent propane give yields of 99 per cent, indicating the diluent is completely decomposed. Mixtures of hydrogen and acetylene up to a mixture containing 59 per cent hydrogen produce 97 per cent of their carbon content as carbon black. The apparatus consists of a, so called, run which serves to introduce the gases into the decomposition chamber, a refractory to form a retaining wall for the reacting gases, and auxiliary equipment to remove carbon black from the product gas. The design of this run burner and the diameter of the refractory involve the items which determine both the workability of the process and the yield of carbon. The run burner is designed to keep the acetylene cool until it is released within the refractory, to deliver the acetylene at an optimum velocity, and to flush hydrogen constantly across the end or face of the burner to prevent the formation of coke upon that surface. All evidence indicates that the decomposition of acetylene proceeds by a chain mechanism which is propagated by chain carriers of atomic hydrogen and stopped by collision with the wall. It is the effect of the wall upon the chain reaction which makes the refractory diameter a critical factor in the apparatus design. Refractories larger than 9 ½ inches allow the reaction to proceed essentially to completion while smaller refractories give decreasingly smaller yields. The decomposition apparatus has been operated for periods of slightly more than one hour, but for continuous operation it needs only the addition of equipment for the continuous removal of carbon black