Oxidative Chlorination Of Methane Research Articles

Oxidative chlorination of hydrocarbons. Part 1. The Deacon reaction. Oxidative chlorination of saturated hydrocarbons C1 and C2

The review paper considers main regularities of the hydrogen chloride oxidation (the Deacon reaction) and oxidative chlorination of methane and ethane. The most efficient catalysts for these processes were shown to be the copper chloride systems on various supports, which contain also chlorides of alkaline and rare-earth metals that decrease the carry-over of the active phase from the catalyst surface and increase the activity. The main kinetic and technological regularities of the oxychlorination processes were considered. The conditions that promote an increase in the yield of target products – lower chloromethanes at oxychlorination of methane and vinyl chloride at oxychlorination of ethane – were revealed. Variants of technological schemes for the oxychlorination processes were proposed.

KINETICS OF OXIDATIVE CHLORINATION OF METHANE

Heterogeneous oxidative chlorination of methane was investigated. The target product is methyl chloride. The investigated terms and conditions of oxychlorination of methane: process temperature 400°C, pressure 0.1-0.9 MPa, catalyst (% weight.): copper chloride (II) 1-8%; potassium chloride 2.5%; lanthanum chloride 1%; carrier - aluminosilicate. Powder X-ray diffractometry and electron microscopy showed that the active catalyst components (CuCl2, KCl, LaCl3) are unevenly distributed on the support surface (α-Al2O3·SiO2) and form agglomerates with a high salt content, including binary chlorides such as KCuCl3, K2CuCl3 or K2CuCl4, hydrates K2CuCl4·2H2O and CuCl2·2H2O and hydroxychlorides Cu3Cl4(OH)2 and Cu2Cl(OH)3. The kinetics of methane oxychlorination was studied in a gradientless reactor at 400°C and pressure 0.1 - 0.9 MPa by varying the partial pressures of the reactants. Analysis of the products was carried out by GC. An equation of the reaction rate including partial pressures of methane, hydrogen chloride and water to the 0.77, 0.01 and 0.64 power, respectively, but of zero order by oxygen and chlorine provides an adequate description of methyl chloride formation rate. Significant influence of water partial pressure is proved for the reaction under consideration.

Technologies for the synthesis of ethylene and propylene from natural gas

Different technologies for the synthesis of ethylene and propylene from natural gas are considered. The simplest ethylene synthesis method is the oxidative condensation (or dimerization) of methane (OCM process), but the implementation of this method is discouraged by a low ethylene yield. Among the relatively simple methods for the synthesis of ethylene (together with acetylene) immediately from methane are thermooxidative pyrolysis (TOP process) and pyrolysis in the presence of chlorine (Benson process), whose disadvantages are a high temperature and a great number of by-products. A wide range of processes for the synthesis of ethylene and propylene with a small amount of butylenes are based on the intermediate synthesis of syngas from methane and its further use for the direct synthesis of lower olefins or products for subsequent catalytic pyrolysis to lower olefins, such as methanol (methanol-to-olefins (MTO) and methanol-to-propylene (MTP) processes), dimethyl ether, and liquid fuel (Fischer–Tropsch method). The methyl chloride-to-olefins (MCTO) process consisting of the synthesis of methyl chloride via the oxidative chlorination of methane and the catalytic pyrolysis of methyl chloride differ from these three-stage processes in the absence of the syngas production stage. The direct oxidation of methane to methanol and the homologyzation of methanol to ethanol with further dehydration of ethanol to ethylene are also considered.

Studies of the Stability of Catalysts for Oxidative Chlorination of Methane

The studies were focused on the influence of various factors on the stability of catalysts for oxidative chlorination of methane due to evolution of the active catalyst components (copper chlorides). The volatility of copper chlorides was shown to depend mainly on the catalyst composition and temperature. When the average temperature in the reactor was 350 °C, 0,45 % and 0,72 % of copper chlorides escaped, respectively, the catalyst containing copper and nickel oxides and the catalyst containing lanthanum chloride as the activating impurity after 5 hours. Another way to improve the catalyst stability, apart from diminishing the copper chloride volatility, is to feed hydrogen chloride bearing copper chloride solutes isolated from the outlet reaction gas in order to abstract the reaction heat and to feed back the unreacted hydrogen chloride.

Mechanism of the formation of carbon oxides under conditions of the oxidative chlorination of methane: III. Kinetics of the reaction of CCl4 with oxygen on copper-containing salt catalysts

The kinetics of the oxidative dechlorination of CCl4 on two supported catalysts for methane oxychlorination (CuCl2-KCl and CuCl2-KCl-LaCl3) at 350–425°C was studied using a gradientless method. Although these catalysts exhibited different activities, the rate of reaction on them was described by one exponential equation at the same activation energy of E ≈ 26.3 kcal/mol. A two-path reaction mechanism was proposed, which involved the dissociative adsorption of initial reactants and chlorine with the formation of phosgene and the oxidation of phosgene to CO2. The occurrence of two types of active sites on the catalyst surface was assumed.

Low-temperature oxidative chlorination of methane over supported platinum chloride catalyst

The PtII (catalyst)+PtIV (oxidant) system with a deficiency of Cl ligands is active in the oxidative chlorination of alkanes not only in aqueous solutions but also in the SiO2-supported state. In heterogeneous as well as in homogeneous conditions, the reaction proceeds at 100°C through platinum-alkyl intermediates.