Patent GB-1012855-A (GB)
Title: Process for the pyrolysis of dichloroethane
IPC: C07C17/25
Filed: 1963-05-13
Abstract: Vinyl chloride made by a process for the pyrolysis of dichloroethane comprising pre-heating dichloroethane vapour to a state of incipient decomposition and subsequently pyrolysing it wherein the heat is supplied to the dichloroethane by indirect heat exchange by condensing mercury vapour, the equipment wherein the heat production occurs being separate from that in which thermal exchange occurs, and preferably one in which the mercury vapour is produced in two boilers which are at different pressures, and thus at different temperatures, the resulting lower temperature mercury vapour being employed for the pre-heating step, and the higher temperature mercury vapour being employed for the pyrolysis step. It is preferred to employ two air-cooled condensers for the fine adjustment of the temperature in the reactors, one for each boiler.  The fine adjustment of pressure in the boiler may be achieved by producing a slight excess of vapour in each of the boilers with respect to the amount required, conveying it to the respective condensers through the cooling side of which a little air is passed, the amount of air being constant in the high pressure boiler, the pressure in the high pressure boiler being adjusted by operation of the naphtha admittance valve, and the pressure of the low pressure boiler being adjusted by means of a controller operating a valve on the air pipe to the low pressure condensers.  A known amount of chlorine may be injected into the pyrolysis reactor before admission of the preheated dichloroethane vapours.  The apparatus is fabricated in stainless steel alloy containing 1.5% silicon and 5% chromium, the reactor tubes being internally coated with nickel.  The invention is described with reference to a flow diagram (not shown) and gives details of typical operating conditions which are as follows: high pressure boiler 9 to 13 ats. 520 DEG  to 550 DEG  C., low pressure boiler 2 to 5 ats. 420 DEG  to 470 DEG  C., dichloroethane vapour pressure 1 to 4 ats., inlet temperature to preheater of dichloroethane 100 DEG  to 160 DEG C., outlet dichloroethane temperature from preheater 300 DEG  to 400 DEG  C., dichloroethane pyrolysis temperature 400 DEG  to 500 DEG C.ALSO:An apparatus for pyrolysis, e.g. of dichloroethane to yield vinyl chloride, comprises a preheater for bringing dichloroethane to a state of incipient decomposition, a reactor for the subsequent pyrolysis of the dichloroethane comprising a number of reactor units connected in series with respect to the dichloroethane circuit and parallel with respect to the mercury vapour circuit and having a by-pass line, a low temperature mercury boiler for heating the preheaters by indirect heat exchange, a high temperature mercury boiler for heating the reactor by indirect heat exchange, and air cooled condensers for temperature adjustment and starting up of the boilers, the boilers being separate from the heat exchangers.  The apparatus is described with reference to a flow diagram (not shown) and includes control features such as controlling the fuel supply to the high pressure boiler governed by the pressure existing in the high pressure system, and pressurizing both the low and high temperature boiler systems via the air cooled condensers to regulate the temperature.  The preferred materials of construction of the apparatus are stainless steel containing 1,5% silica in 5% chromium, the reactor tubes being internally coated with nickel.