The pyrolysis of 1,2-dichloroethane

Abstract

The pyrolysis of 1.2-dichloroethane in a static system has been studied by g.1.c. analysis of the products and by pressure measurements in the temperature range 340-51 5 "C, surface :volume ratio range (1 -32-37.4) cm-l, and with initial pressures from 0.3 to 300 Torr, in reaction vessels coated with pyrolytic carbon films.The major reaction is dehydrochlorination to vinyl chloride, but ethylene is also a primary reaction product. The ethylene yield is very small (<2% of the vinyl chloride) under conditions of low surface:volume ratio. It is concluded that the ethylene is produced by a concurrent heterogeneous dechlorination of 1.2-dichloroethane.At low surface :volume ratio the vinyl chloride produced is closely paralleled by the pressure increase and the reaction is found to have a high order (2.4-2.8) and activation energy (73 k 3 kcal mol-l). The reaction is inhibited by additions of vinyl chloride, ethylene, and propene, and accelerated by added hydrogen chloride, oxygen, and chlorine. The radical-chain mechanism previously suggested by Barton and Howlett is discussed and modified to account for the experimental observations. The pressure-time curves obtained from experiments at high surface :volume ratio indicate that under these conditions the reaction is autocatalytic. The maximum rate corresponds to an order of 1.5 and an activation energy of 33.0 kcal mol-I. It is suggested that the autocatalysis is due to a heterogeneous initiation process involving adsorbed chlorine.THE pyrolysis of 1,2-dichloroethane has previously been studied under homogeneous and heterogeneous 5-7 conditions. Under static conditions it is widely accepted that the reaction is homogeneous and of the first order and shows many characteristics of a chain reaction, such as inhibition by propene, acceleration by oxygen and chlorine, and the presence of induction periods. To account for these features, Howlett suggested the mechanism of reactions ( 1)-( 4).In order to fit the(3)observed overall rate expression, i.e., equation (5), it was necessary to assume an unreasonably low pre-k1s-l = 1010.81exp (-47,00O/RT) (5) exponential factor of 1O1O s-l for reaction (3). The corollary of a long-lived C,H3C1, radical proved to be a convenient explanation for the observed induction periods, which were attributed to the slow build-up of this radical to its stationary-state concentration.Both Barton and Howlett (who used vessels with s/v 2.7 and 8.5 cm-l) and Howlett (who varied s/v from 2.2 to 22) found the rate of reaction to be little affected by packing the reaction vessel. Accordingly, Howlett suggested that steps (1) and (4) as well as ( 2) and (3) were homogeneous.Kapralova and Semenov4 have since shown, using differential calorimetry and large reaction vessels, that the reaction is isolated in a zone near the vessel walls. This implies that the reaction is initiated and in part terminated a t the vessel walls.

Decomposition of 1,2‐dichloroethane in an RF plasma environment

“…The mole fraction of HCl, however, decreased slightly from 3 to 9 Torr. Minor product species with C-Cl bonds such as CCl 4 and C 2 HCl 3 increased slightly with pressure (Fig 3(C)). Other species without a C-Cl bond, except C 2 H 6 , decreased slightly with rising pressure.…”

“…4 Dyer and Matthews 5 have used a KrF laser to induce thermal decomposition of DCE. Kang et al 6 have also used a laser to induce the chain reaction of 1,2-dichloroethane.…”

“…Thermal decomposition of DCE has been studied 3,4 and vinyl chloride and ethene were found to be the major reaction products. 4 Dyer and Matthews 5 have used a KrF laser to induce thermal decomposition of DCE.…”

Numerical simulations of the pyrolysis of 1, 2 dichloroethane

“…Many studies on the decomposition of EDC have been worked under the thermal decomposition [Barton, 1949;Barton and Howlett, 1949;Howlett, 1952;Holbrook et al, 1971, Ranzi et al, 1992Incavo, 1996], the catalysed pyrolysis by chlorine or other species [Ashmore et ai., 1982a;Ashmore et al, 1982b], and the photolysis [Yano and Tschulkow-Roux, 1980;Ma et al, 1990;Cardy et al, 1993]. The thermal decomposition is one of the most widely used methods in commercial processes for the production of vinyl chloride.…”

Continuous‐wave CO2 laser‐induced SF6‐sensitized decomposition of chloroalkanes

“…This lack of an induction period is also observed in the case of 1,2-dichloroethane which also exhibits an induction period when decomposed thermally. In the latter case, however, it has been shown that initiation probably occurs at the reaction vessel walls and the occurrence or absence of an induction period, i.e., the shape of the pressurehime curve, is markedly dependent on the extent and nature of the vessel surface [6]. The induction period may well result from the time taken for radicals produced at the walls to diffuse into the bulk of the gas.…”