Oxidative Halogenation of C1 Hydrocarbons

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Oxidative halogenation of C1 hydrocarbons to halogenated C1 hydrocarbons.

Simon G. Podkolzin, Eric E. Stangland, Albert E. Schweizer, Mark E. Jones

Assigned to Dow Global Technologies Inc., Washington Street, 1790 Building, Midland, MI 48674 USA

World Intellectual Property Organization Publication WO/2006/118935; Publication Date: 09.11.2006              

International Application: PCT/US2006/015993; International Filing Date: 25.04.2006; IPC: C07C 17/154 (2006.01)

Link to full text on publisher's server

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Abstract

    An oxidative halogenation process involving contacting methane, a C1 halogenated hydrocarbon, or a mixture thereof with a source of halogen and a source of oxygen, at a molar ratio of reactant hydrocarbon to source of halogen in a feed to the reactor greater than 23/1, and/or at a molar ratio of reactant hydrocarbon to source of oxygen in a feed to the reactor greater than about 46/1; in the presence of a rare earth halide or rare earth oxyhalide catalyst, to produce a halogenated C1 product having at least one more halogen as compared with the C1 reactant hydrocarbon, preferably, methyl chloride. The process can be advantageously conducted to total conversion of source of halogen and source of oxygen. The process can be advantageously conducted with essentially no halogen in the feed to the reactor, by employing a separate catalyst halogenation step in a pulse, swing or circulating bed mode. The production of methyl halide can be integrated into downstream processes for manufacture of valuable commodity chemicals.

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Evolution of feed and product component traces monitored by a mass spectrometer in pulse experiments.

When a pulse of CH4+O2 is introduced over a chlorinated lanthanum catalyst, a mixture of CH3Cl and H2O is produced. These kinetic pulse experiments show that a gas-phase source of chlorine is not necessary for the reaction, and chlorine can be supplied by the catalyst surface.

Effect of removing a source of chlorine (HCl) from the feed stream for oxidative hydrochlorination of methane:

CH4 + 0.5 O2 + HCl = CH3Cl + H2O

Although the reaction rate decreases without HCl, the catalyst can sustain the chlorination reaction for a significant period of time. In addition, the selectivity in methane activation increases to practically 100% in the absence of HCl.
 
Results of reaction mechanism studies were used for optimization of reaction conditions :

     - High methane ratios improve selectivity. Practically 100% selectivity can be achieved at high methane to oxygen ratios.

     - Reaction can be conducted with 100% conversion of HCl, while maintaining high selectivity to CH3Cl. This can eliminate expensive HCl and H2O separation.

     - Methane activation can be operated in a swing, alternating feed or pulse mode: pulses of CH4+O2 can be alternated with pulses of HCl. This can simplify separations and improve selectivity.

Possible alternating feed reactor operation.

Flow scheme of an integrated process for converting natural gas into higher hydrocarbons.

Selective methane chlorination can be a part of an integrated process for conversion of natural gas to higher hydrocarbons. In the first step, methane is reacted with HCl and O2 and selectively converted into a CH3Cl intermediate over a chlorinated lanthanum catalyst. In the second step, the CH3Cl intermediate is reacted over a zeolite catalyst to produce hydrocarbons and to regenerate HCl. The recovered HCl is recycled to the first chlorination step.

In this process, three is no net consumption or production of chlorinated products. Oxidative chlorination in this flow scheme is used only as a means of selective methane activation, and the overall reaction is equivalent to that of oxidative methane coupling:

2 CH4 + O2 = C2H4 + 2 H2O

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Reaction mechanism studies of oxidative methane hydrochlorination are described in the 2007 paper by Simon Podkolzin et al. in the Journal of the American Chemical Society.

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