DD249008A1 - PROCESS FOR THE OXICHLORATION OF DEEP 1 TO C DEEP 4 - ALKANES AND / OR THEIR PARTIALLY CHLORINATED DERIVATIVES - Google Patents

Abstract

The invention relates to a process for the preparation of lower C1- to C4-chlorohydrocarbons by oxychlorination of lower alkanes and / or their partially chlorinated derivatives. In the oxychlorination of hydrocarbons, especially alkanes, the control of the reaction temperature is of crucial importance. The temperatures should not exceed a certain value (about 300-350C) in order not to let the burnup of the hydrocarbon used become uneconomically high. This applies in particular to the reaction-oriented methane and its chlorinatable derivatives, which hitherto could not be oxoklorinated below 400-450C. The aim of the invention is a method for avoiding the high yield losses. According to the invention, the necessary lowering of the reaction temperature, in particular in the case of methane, is achieved by feeding in small amounts of azoalkanes (eg azomethane). The method can advantageously be carried out in multiple stages, in conjunction with a Deacon process. The invention can be used in existing technical systems, eg. B. in a Methanchlorierungsanlage be applied.

Description

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Field of application of the invention

The invention relates to a process for the preparation of cis to CrCh ^ hydrocarbons by oxychlorination of lower alkanes and / or their partially chlorinated derivatives.

Characteristic of the known technical solutions

Lower chlorinated hydrocarbons are in most cases relatively easily represented by gas phase chlorination. The forced attack of aqueous hydrochloric acid and the limited usability of the resulting crude acid necessarily requires their reuse for material and ecological reasons. Consequently, attempts have been made to couple the exothermic Deacon process (2HCI + 72O ₂ - ^ H ₂ O + Cl ₂ ) with the exothermic chlorination of hydrocarbons and / or incompletely chlorinated derivatives. This process known as "oxychlorination" is the subject of numerous patents and basic publications (see M. M. Mallikarjunan, 5. Zahed Husain, 7. Scient. Ind. Res. 42 [1983], 209-222) and is already technically used for vinyl chloride production or as Raschig process (oxychlorination of benzene) It is known that lower hydrocarbons, optionally proportionally, can be oxo-oxygenated, these reactions being always of a very complex nature. Reactions of chlorine, hydrogen chloride and oxygen with the hydrocarbon-containing educt conclude the presence of an oxychlorination catalyst On the other hand, the hydrogen chloride can be introduced directly, but it can also be a secondary product of the reaction of chlorine or a chlorohydrocarbon with the alkane.Also conceivable is its generation from saturated and unsaturated chlorine derivatives, which are introduced into the reaction or there by reaction By Oxidati On is formed chlorine, which reacts in the presence of Deacon catalysts to form the target products

 In the case of methane conversion to dichloromethane, the gross reaction can be represented as follows:

4 HCl + O ₂ > 2Cl ₂ + 2H,

0Η _Δ + 2 Cl ₂ > CH ₂ Cl ₂ + 2

HCl

CH ₄ + 2 HCl + O ₂ > CH ₂ Cl ₂ + 2 HgO

i.e. 1 mol of hydrogen chloride requires 0.5 mol of oxygen.

There are a number of attempts have been made, for example, chloromethane from methane, hydrogen chloride and an oxygen-containing gas, such as. B. air or pure oxygen in the presence of a metal halide catalyst at elevated temperature in the fixed and / or fluidized bed process to produce (DE-OS 1 954348 [1970], 1 996000 [1971], 2058363 [1971], DD-PS 89398 1970], SU-PS 446497 [1974], US-PS 3267161 [1966]).

The attempts to subject methane to sufficiently satisfying yield of oxychlorination are hitherto considered to be economically unsatisfactory because of the known inertness of this alkane. For the oxychlorination of methane, temperatures higher than 400 ° C are necessary. The high temperatures inevitably lead to a low yield (burnup) in the fluidized bed and to the reduction of the quality of the target products.

Another disadvantage of high reaction temperatures is the use of typical oxychlorination catalysts due to the volatility of the copper chloride. Modified catalysts, eg. B. with lanthanum and neodymium together with small amounts of praseodymium and samarium (DE-AS 1 493376 [1973]), give good results; however, their production costs are enormous

A further problem with all known oxychlorination processes is the corrosive nature of the gases and the danger of explosion due to the mixture of oxygen and hydrocarbon at elevated temperatures.

Object of the invention

The aim of the invention is a process for the preparation of chlorinated hydrocarbons, in particular of chloromethanes, hydrocarbons, hydrogen chloride and an oxygen-containing gas which largely suppresses the combustion of the hydrocarbon, preferably of methane and the corresponding chlorine derivatives at high conversion of hydrogen chloride and strong the proportion of by-products reduced.

Explanation of the essence of the invention

The object of the invention is to reduce the reaction temperatures of both oxychlorination of methane and / or other hydrocarbons in the presence of conventional catalysts to the extent that the process based on Eduktumsatz and product selectivity is economical.

According to the invention, the reaction temperature of the oxychlorination of methane and other lower hydrocarbons can be reduced by adding a free-radical initiator, preferably a lower azoalkane, to the mixture of hydrocarbons and / or their partially chlorinated derivatives, hydrogen chloride and an oxygen-containing gas in small amounts. The azoalkanes are used in concentrations of 0.01 to 1 mol%, preferably 0.02 to 0.2 mol%, based on the hydrogen chloride used.

The effect according to the invention of these azoalkanes is of particular importance in the oxychlorination of methane. In this case, the known catalysts based on copper chloride or chromium oxide can advantageously be used. Instead of 400-450 ° C, which usually have to be used for the oxichlorierenden treatment of methane - which is usually associated with a proportion of combustion of 10-30% of the methane used - can now be the oxychlorination at temperatures below 400 ° C, preferably below 330 ⁰ C, realize. The burning rate of methane is below 10%, in most cases between 2-4%.

These values are obtained when the ratio of hydrogen chloride to oxygen is adjusted to be 1.8-1.9: 1. It is recommended that such a driving regime, in which the oxygen content slightly above the o.g. Stoichiometric ratios, advantageously about 5-10%. Essential for the process is that the supply of oxygen is drastically reduced before the addition of small amounts of azoalkane takes place. A particular embodiment of the process is a multi-stage oxy-corrosion. In the process, the hydrogen chloride used is first subjected to a deacon process with traditional catalysts in a precursor with the complete application rate of oxygen. In a second stage, the chlorine obtained is reacted with the total or with a partial amount of hydrocarbons to be chlorinated or their derivatives. In a third stage, the azoalkane is metered in and the reaction is carried out in the presence of a conventional catalyst. At the same time, it is also possible to meter in a portion of the lower alkane and / or derivatives thereof in the third stage together with the application rate of azoalkane. Furthermore, according to the invention, even in the second stage, a small amount of azoalkane, preferably up to 20% of the application rate, can be added.

embodiment

The invention will be explained in more detail below with four examples.

example 1

A fluidized bed reactor is used. It consists of a 75cm long nickel tube with 5cm diameter. The reactor is equipped with an electric jacket heater. The height of the fluidized bed is 25 to 30cm. The temperature in it is measured with thermocouples. As a distributor plate is a nickel hole plate with 10 evenly distributed over the base holes of 0.8 mm diameter. The catalyst used is, for example, copper chloride with potassium and magnesium chloride on an inert support. The specific contact surface is 15m ² / g, the grain size of the catalyst is between 0.15 and 0.35 mm.

The preheated reaction mixture of the following composition is introduced into the reactor:

120 l / h of methane, 50 l / h of hydrogen chloride, 27 l / h of oxygen and 0.02 l / h of azomethane.

The reaction temperature is between 325 ⁰ C and 350 ⁰ C. The HCI conversion is 92%, the combustion of the converted methane is 3.8%.

Example 2

The reaction is carried out in several stages according to the scheme shown (FIG. 1).

A surrounding with an electric jacket heating nickel tube of 2.5 cm in diameter and 40cm length is filled with a catalyst based on copper chloride analogous to Example 1 or another Deacon catalyst. In this reactor (R 1), a preheated to about 200 ⁰ C reaction gas mixture of the following composition is passed: 161 / h of hydrogen chloride 8.41 / h of oxygen.

The reaction temperature is maintained at 450 ⁰ C. The reactor described is followed by an intermediate piece of about 50 cm in length with a cooler (K 1), which cools the reactor gas to about 150-180 ⁰ C. In the mixer (M 2) methane is admixed at a rate of 30l / h and then reacted in the reactor (R 2). R2 is constructed analogously to R1 and likewise filled with catalyst analogously to Example 1. The reaction temperature is maintained at 320 ^° C. In the following cooler (K2), the reaction gas is cooled to 120 to 150 ⁰ C. In the mixer (M3), azomethane is mixed with the reaction gas at a rate of 16 ml / h together with 10 l / h of methane. R3 is constructed and equipped analogous to R1 and R2. The reaction temperature is maintained between 315 ⁰ C and 325 ⁰ C. The hydrogen chloride conversion is 94%, the combustion of the converted methane is 3.2%.

Example 3

The Vers'jchsanordnung is analogous Example In the first stage are fed: 20l / h of hydrogen chloride 81 / h of oxygen

The reaction temperature is 450 ^° C.

In the 2nd stage are admixed and reacted at 320 ⁰ C to the reaction gas from the I.Stufe 30l / h methane. In the third stage 10 l / h of methane are fed to the reaction gas from the second stage with 8 ml / h of azomethane. The reaction temperature is 320 ⁰ C. The hydrogen chloride conversion is 78%, the combustion of the converted methane is 2.3%.

Example 4

Analog arrangement for example 2 In the 1st stage are metered:

20 l / h of hydrogen chloride and 10.5 l / h of oxygen.

The reaction temperature is kept at 45O ⁰ C. In the 2nd stage the reaction gas from the I.Stufe 35 l / h of methane, is mixed with 2 ml / h azomethane fed and reacted at 320 ⁰ C. In the third stage, 15 l / h methane with 8 ml / h azomethane are fed to the reaction gas from the 2nd stage. The reaction temperature is 320 ⁰ C. The HCI conversion is 92% and the conversion rate of the converted methane 2.5%.

Claims (3)

1. A process for the oxide chlorination of C ₁ - to C ₄ alkanes and / or their partially chlorinated derivatives by reacting the reactants to be chlorinated with hydrogen chloride or with mixtures of HCl and chlorine and an oxygen-containing gas in the gas phase in the presence of known catalysts, characterized in that a small amount of a C 1 to C ₄ azoalkane is fed into the reaction gas. 2. The method according to claim 1, characterized in that the azoalkanes are used in concentrations of 0.01 to 1 mol%, preferably 0.02 to 0.2 mol%, based on the hydrogen chloride used. 3. The method according to claim 1 and 2, characterized in that the azoalkane after a partial reaction of the alkane, optionally with a subset of alkane, is fed.