NL9401574A - Difluoromethane preparation - Google Patents

Abstract

The invention relates to a method for preparing difluoromethane, wherein dichlorodifluoromethane or monochlorodifluoromethane is brought into contact with hydrogen in the presence of palladium on activated carbon, wherein the loading of the palladium on the activated carbon is 0.1-4.0 wt.%, based on the total weight, and wherein the activated carbon used is a relatively pure activated carbon having an ash content of 0.5-6%.

Description

Title: Difluoromethane preparation

The invention relates to a process for preparing difluoromethane from dichlorodifluoromethane or monochlorodifluoromethane using a palladium-on-carbon catalyst.

Such a method is known from the article by Lacher et al. In Trans. Faraday Soc. 52, 1500-1508 (1956). This article describes the hydrogenation of carbon halides and hydrocarbon halides. In particular, a catalyst consisting of 5% palladium on activated carbon is described for the reaction of the type mentioned in the opening paragraph. Based on a number of experiments, the following conclusions are drawn: i) in a homologous series, compounds of lower molecular weight are more difficult to hydrogenate than compounds of higher molecular weight; and ii) fluorine atoms are more difficult to replace with hydrogen atoms than chlorine atoms.

European patent application 0 508 660 discloses a process for the production of difluoromethane in which mono- or dichlorodifluoromethane is reacted with hydrogen in the presence of a hydrogenation catalyst. The yield of difluoromethane was found to depend on the catalyst composition, temperature and pressure. Palladium supported on an activated carbon is preferably used as a hydrogenation catalyst. In the case where palladium on an active carbon support is used as a catalyst, this catalyst usually contains 5-20% (w / w) Pd relative to the active carbon support, preferably 8-15% (w / w). With regard to the activated carbon used as the support material, it is noted that the total yield of difluoromethane depends on the specific activated carbon used.

When starting from monochlorodifluoromethane, the process according to this patent application gives a conversion of 55-85% with a selectivity of less than 50% at a reaction temperature of above 300 ° C. In the reaction of dichlorodifluoromethane to difluoromethane, the selectivity at a conversion of 55-85% is considerably lower, i.e. around 10%.

The object of the present invention is to provide a method in which difluoromethane is obtained in a higher selectivity from dichlorodifluoromethane or optionally monochlorodifluoromethane.

This objective is achieved by using palladium as a hydrogenation catalyst at a lower degree of loading than described in EP-A-0 508 660 on a relatively pure carbon carrier.

In particular, the invention relates to a method of preparing difluoromethane, wherein dichlorodifluoromethane or monochlorodifluoromethane is contacted with hydrogen in the presence of palladium on activated carbon, wherein the loading of palladium on carbon is 0.1-4% by weight, based on the total weight, is, and wherein as active carbon an active carbon with an ash content of 0.5-6% is used.

Incidentally, international patent application 93/02029 discloses a process for the hydrogenation of fluorocarbon halides and hydrofluorocarbon halides, in which the catalyst used is Re, Co, Ni, Ru, Rh, Pd, Os, Ir and / or Pt on a very pure carbon carrier. This high-purity carbon carrier has a low ash content of less than 0.1% by weight. Such a high purity carbon support is obtained by first washing carbon with an acid which should not be hydrogen fluoride and then washing with hydrogen fluoride.

Using the process according to the invention, such a very pure carbon carrier is not necessary to obtain difluoromethane in high selectivity and yield, which is of course of practical advantage.

In addition, said international patent application is in fact directed to compounds containing 2 carbon atoms. As described in the aforementioned article by Lacher et al., Lower molecular weight compounds are more difficult to hydrogenate than higher molecular weight compounds. On the basis of this knowledge it is surprising that in the process according to the invention excellent results are obtained using an active carbon carrier which has an ash content at least five times as high.

In the process according to the invention a catalyst is preferably used in which the loading of the palladium on the activated carbon is 0.2-4% by weight. Preferably the degree of loading is 0.5-2.0 wt%, especially about 0.8-1.2 wt%.

Although it is possible to start from monochlorodifluoromethane in the method according to the invention, dichlorodifluoromethane is the preferred starting compound.

The carbon support used in the present process has an ash content of between 0.5 and 6% by weight. This ash content can be determined in all ways known to the skilled worker. In a preferred embodiment, the ash content is 0.5-4 wt%, more preferably 1-4 wt%.

If the ash content of an activated carbon exceeds 6% by weight, the selectivity of the reaction decreases. Such an insufficiently pure activated carbon must be purified, for example, by washing the activated carbon with an acid solution, such as a 0.5 M hydrochloric acid solution, followed by washing with demineralized water until no traces of salts are detected anymore.

In a preferred embodiment, the activated carbon is first washed with a basic solution, for example, a 0.5 M sodium hydroxide solution, followed by rinsing with demineralized water until all positive ions are washed away.

Palladium can be applied to the active carbon carrier using any technique known to those skilled in the art. Specifically, palladium compounds, e.g., PdBr2, PdCl2, Pdl2, Pd (CO) Cl, Pd (NO3) 2, PdO, PdS04, PdS, (nh4) 2PdCl4, and (NH4) 4PdCl6, can be impregnated onto the carbon support . Suitable impregnation methods are the "incipient wetness" method, ion exchange, precipitation and wet impregnation.

It is not necessary to activate the hydrogenation catalyst for use in the process of the invention. In situ activation takes place by introducing the catalyst into the reactor and then adjusting the reactor to the reaction temperature. It is, however, possible to pre-activate the catalyst according to known methods, for example by heating it in an atmosphere of nitrogen, air or hydrogen.

The reaction between dichlorodifluoromethane or monochlorodifluoromethane as well as mixtures thereof and hydrogen using the process of the invention is carried out at an elevated temperature, the descriptions of EP-A-0 508 660 and WO 93/02029 describe conditions which also apply to the method according to the invention applies and to which reference is made explicitly.

More specifically, the process of the invention becomes common at a temperature between 175 and 275 ° C, at a pressure of 1-10 bar, a weight hour space velocity (WHSVj of 0.5-4 kg of chlorofluorocarbon per kg of catalyst) per hour, and a hydrogen / chlorofluorocarbon ratio of 2 / 10. The reactor in which the process of the invention is used is preferably formed from a material having a high corrosion resistance to acids Suitable materials are, for example, Inconel®, Monel® and Hastelloy ® ·

The method according to the invention will now be further elaborated on the basis of the following examples.

Example 1: Catalyst preparation 50 g of an activated carbon with an ash content of 5.9% (Norit RB-1 from Norit) was placed in a glass tube with a diameter of 4 cm and a length of 50 cm. The carbon was washed with 1-10 liters of 0.5 M sodium hydroxide solution and then washed with demineralized water until the wash solution no longer contained sodium ions. Then it was washed with 1-10 liters of 0.5 M hydrochloric acid, after which it was rinsed with demineralized water until no traces of salts were detected in the effluent. In all steps of this purification step, the solutions were passed along the activated carbon at a flow rate of about 1 liter / hour.

Thus, activated carbon was obtained with ash contents between 0.5-6% by weight.

The relatively pure carbon carrier material obtained was then loaded with palladium. To this end, an acidic PdCl2 solution (PdCl2 obtained from Alfa Products) was applied to the carbon support by pore volume impregnation. The acid concentration was chosen so that a molar ratio Pd2 + / Cl "of about 12 was obtained. After impregnation, the catalyst was dried overnight at 100 ° C. Before use, the catalyst thus obtained was activated by heating it for 1 hour at 350 ° C in a nitrogen atmosphere.

Example 2 4 g of a catalyst comprising 1 wt% palladium, based on the total weight, on an activated carbon (Norit RB-1) purified according to example 1 with an ash content of 3.1 wt%, was placed in a hastelloy -C reactor tube brought.

This 1.27 cm outer diameter reactor tube was placed in an electric oven.

Hydrogen gas and dichlorodifluoromethane were passed through the reactor in a 3: 1 ratio. The flow rate of the CCI2F2 was adjusted to 1 g CCI2F2 per gram of catalyst per hour.

The catalyst was tested at 3 different temperatures (see Table 1).

The gas exiting the reactor was subjected to gas chromatography (50 m capillary GC column Pora Plot Q; Chrompack). Table 1 lists the relative amounts of the organic compounds detected in the outgoing gas.

Table 1

* Conversion of CCI2F2 * Selectivity of CCI2F2 to CH2F2 Example 3 2 g of a commercially available catalyst comprising 1 wt% palladium, based on total weight, on an activated carbon with an ash content of 2 wt% (1% Pd on Carbon Extrudates, Engelhard), was placed in a hastelloy-C reactor tube. This 1.27 cm outer diameter reactor tube was placed in an electric oven.

Hydrogen gas and dichlorodifluoromethane were passed through the reactor in a 4: 1 ratio. The flow rate of the CCI2F2 was adjusted to 1 g CCI2F2 per gram of catalyst per hour.

The catalyst was tested at 4 different temperatures (see Table 2).

The gas exiting the reactor was subjected to gas chromatography. The gas was then washed with a potassium hydroxide solution to remove acidic compounds. Table 2 lists the relative amounts of the organic compounds detected in the outgoing gas.

Table 2

* Conversion of CCI2F2 * Selectivity of CCI2F2 to CH2F2

Example 4 4 g of a commercially available catalyst comprising 0.5 wt% palladium, based on total weight, on an activated carbon with an ash content of 3.0 wt% (0.5% Pd on Carbon Extrudates; Johnson Matthey) was placed in a hastelloy-C reactor tube. This 1.27 cm outer diameter reactor tube was placed in an electric oven.

Hydrogen gas and dichlorodifluoromethane were passed through the reactor in a 3: 1 ratio. The flow rate of the CCI2F2 was adjusted to 1 g CCI2F2 per gram of catalyst per hour.

The catalyst was tested at 2 different temperatures (see Table 3).

The gas exiting the reactor was subjected to gas chromatography. The gas was then washed with a potassium hydroxide solution to remove acidic compounds. Table 3 lists the relative amounts of the organic compounds detected in the outgoing gas.

Table 3

* Conversion of CC12f2 * Selectivity of CCl2F2 to CH2F2

Example 5 4 g of a catalyst comprising 1% by weight of palladium, based on the total weight, on an activated carbon purified according to Example 1 (Norit R 0.8 extra) with an ash content of 1.9% by weight, was a hastelloy-C reactor tube. This 1.27 cm outer diameter reactor tube was placed in an electric oven.

Hydrogen gas and dichlorodifluoromethane were passed through the reactor in a 3: 1 ratio. The flow rate of the CCI2F2 was adjusted to 1 g CCI2F2 per gram of catalyst per hour.

The catalyst was tested at 2 different temperatures (see Table 4).

The gas exiting the reactor was subjected to gas chromatography. The gas was then washed with a potassium hydroxide solution to remove acidic compounds. Table 4 lists the relative amounts of the organic compounds detected in the outgoing gas.

Table 4

* Conversion of CCI2F2 * Selectivity of CCI2F2 to CH2F2

Example 6 (comparative example) 2 g of a commercially available catalyst comprising 1 wt% palladium, based on the total weight, on an activated carbon with an ash content of 7.5 wt% (2% Pd on Carbon Extrudates; Engelhard) was placed in a hastelloy-C reactor tube. This 1.27 cm outer diameter reactor tube was placed in an electric oven.

Hydrogen gas and dichlorodifluoromethane were passed through the reactor in a 4: 1 ratio. The flow rate of the CCI2F2 was adjusted to 1 g CC12F2 per gram of catalyst per hour.

The catalyst was tested at 2 different temperatures (see Table 5).

The gas exiting the reactor was subjected to gas chromatography. The gas was then washed with a potassium hydroxide solution to remove acidic compounds. Table 5 lists the relative amounts of the organic compounds detected in the outgoing gas.

Table 5

* Conversion of CC12F2 * Selectivity of CC12F2 to CH2F2

Claims (6)

A process for preparing difluoromethane, wherein dichlorodifluoromethane or monochlorodifluoromethane is contacted with hydrogen in the presence of palladium on activated carbon, wherein the loading of the palladium on the activated carbon is 0.1-4.0% by weight, based on the total weight, is, and wherein as activated carbon a relatively pure activated carbon with an ash content of 0.5-6% is used. A method according to claim 1, wherein the loading of the palladium on the activated carbon is 0.5-2 wt.%, And preferably 0.8-1.2 wt.%. Process according to claim 1 or 2, starting from dichlorodifluoromethane. A method according to any one of the preceding claims, wherein a carbon carrier with an ash content between 0.5 and 4% by weight is used. Catalyst for use in the process according to any one of the preceding claims, obtainable by washing an activated carbon with an acid solution, followed by washing with demineralized water until no traces of salts are detected anymore; and impregnating the thus purified activated carbon with palladium compounds, such that a loading of 0.1-4.0% by weight of palladium based on the catalyst is obtained. The catalyst of claim 5, wherein the activated carbon is first washed with a basic solution, followed by rinsing with demineralized water until all positive ions are washed away before rinsing with an acid solution.