Chlorination of Methane

Abstract

0th the abundance of methane and the compara-B tive cheapness of chlorine favor the industrial utilization of chlorination for the preparation OF the chloromethanes. In most of the prior processes i t was necessary t o use some economically undesirable feature t o avoid an explosive o r burning reaction w h e n high concentrations OF chlorine w e r e employed. The present w o r k was undertaken in an effort t o apply the Hass-McBee chlorination technique t o methane. A hydrocarbon i s passed through a reactor w h i l e chlorine i s introduced through jets suitably spaced along the reactor. By this arrangement the momentary concentrations of chlorine are maintained b e l o w those w h i c h yield explosive mixtures, and the over-all mole ratio of reactants may b e any desired value-for example, 4 of chlorine t o I of methane t o produce carbon tetrachloride. Graphs of temperature gradients w e r e helpful i n selecting the most suitable bath temperature, spacings of chlorine jets, space velocity, etc. Most of the data w e r e obtained at 440" C. The ratios of the four chloromethanes in the product can b e varied from nearly 100 per cent methyl chloride t o carbon tetrachloride exclusively. HE four chloromethanes are important commercial T substances and are used in relatively large quantities.The supply of methane froni petroleum is enormous, and during peacetime chlorine is readily available a t a relatively lorn cost. These factors favor the chlorination of methane for the commercial preparation of all the chloromethanes. The large number of patents and other literature references in the field indicate extensive interest in this problem.The chlorination reaction is highly exothermic and requires careful control for successful operation. If the concentration of chlorine is within certain limits, there is danger of a violent and even explosive reaction. The approximate figures for the heats of reaction for the chlorination of methane at 400" C., calculated from the heats of combustion given by Bichomsky and Rossini, are as follows:CHh + Clz + . CHZCl + HC1 + 25 Cal. CHa + 2C12 + . CH2C12 + 2HC1 + 48 Cal. CH4 + 3 c 1 2 + . CHC13 + 3HCl + 72 Cal. CH4 + 4C12 + . CClr + 4HC1 + 96 Cal.When high reaction temperatures are attained, as by high concentration of chlorine, carbon and hydrogen chloride are 1 This paper 1s the fifteenth in a series on the subject of syntheses from natural gas hydrocarbons

Catalytic halogenation of methane: a dream reaction with practical scope?

“…In contrast to fluorination which inevitably leads to a complete hydrogen substitution, chlorination could provide a high selectivity to monohalomethanes if operated at a relatively high methane-to-chlorine ratio (typically molar CH 4 : Cl 2 ratio > 10), although CH 2 Cl 2 and CHCl 3 are formed in significant amounts at close to the stoichiometric feed composition. 12,13 In contrast, methane bromination yields a high selectivity to CH 3 Br (>90%) at smaller methane excess (CH 4 : Cl 2 > 5), while polybromination is generally limited to the formation of CH…”

A Review of Methane Activation Reactions by Halogenation: Catalysis, Mechanism, Kinetics, Modeling, and Reactors

“…This observation is different from methane chlorination where only the kinetic product distribution is observed and from methane iodation where only the thermodynamic product distribution is observed [22]. Gas phase chlorination of methane in a flow reactor equipped with jets for introducing chlorine along the reactor was investigated for industrial use in 1942 [23]. The high velocity of chlorine introduced through jets prevents burning of the mixture due to the exothermic nature of chlorination reactions.…”

“…It was assumed that oxygen terminates the chain of reaction. In 1942, McBee et al [23] published a paper on the chlorination of methane by application of the Hass-McBee chlorination technique. With this technique, a hydrocarbon flows through the reactor and jets of chlorine are positioned at suitable locations.…”

“…where X represents the halogen element. All reactions (21)- (23), except those with iodine as halogen, are exothermic [30]. Reaction (21) was studied, for example, by Lombard et al [92] in a chlorine/methane system in the temperature range between 600 and 1000 • C in an annular plug flow reactor, made of quartz, at atmospheric pressure and 10-30 ms residence time.…”

Molten Salt Technology

“…230 The yields of CH2Ch, CHCI3 , and CC4 increased with the increasing degree of conversion of methane and this was believed to be due to the slow diffusion of the products from the melt surface. However, conventional supported-solid catalysts gave yields of polychlorinated by-products intermediate between thermal chlorination and molten salt systems; possibly solid and molten catalysts gave more by-products due to higher concentrations of chlorine atoms.…”