KR100365582B1 - Pretreatment Method of Active Carbon for Preparation of Pd/C Catalyst - Google Patents

Abstract

The present invention relates to a method for pretreating activated carbon for the production of a palladium catalyst (Pd / C) which is useful for the production of fluorohydrocarbons (HFC), which is a substitute for dechlorinating carbon fluoride (CFC) The goal is to increase the activity and selectivity of the catalyst.

Activated carbon, which is the carrier of the catalyst, is treated sequentially with HF aqueous solution and HCl aqueous solution. Impregnating the pretreated activated carbon with palladium ions at room temperature; Drying at 80 to 200 캜; And firing at 300 to 500 캜 under an air atmosphere.

Description

[0001] The present invention relates to a pretreatment method of an activated carbon for preparing a palladium catalyst,

The present invention relates to a method for pretreating activated carbon for the production of a palladium catalyst (Pd / C) useful for the production of fluorinated hydrocarbons (HFC), which is a substitute for dechlorinating carbon monoxide fluoride (CFC).

The present invention also relates to a method for preparing a catalyst by supporting palladium on activated carbon pretreated by the above method and its use.

CFC is a substance in which hydrogen atoms of saturated hydrocarbons are replaced with chlorine and fluorine. It has excellent thermal and chemical stability and has been widely used as a refrigerant, foaming agent, cleaning agent and spraying agent. However, when released into the atmosphere, the global warming index is large and photodegraded in the stratosphere As it was found to destroy the ozone layer, its production and use was regulated by the Montreal Protocol. As a result, there is a need for a method for efficiently processing the used CFC together with the development of a material capable of replacing the CFC.

In particular, the dechlorinating few digested by the catalyst _{CFC-12 (CCl 2 F 2} ) from _{HFC-32 (CH 2 F 2} ) make or _{CFC-114a (CCl 2 FCF 2} ) HFC-134a (CH 2 FCF 3) from the Which is a substitute for CFC, is considered to be an important pathway for the production of CFC or the use of CFC.

Coq et al. [B. Coq, JM Cognion and F. Figueras, J. Catal., 141 (1993) 21] describe the hydrogenation of CFC-12 on a catalyst supported with Pd using Al ₂ O ₃ , AlF ₃ , The activity and characteristics of the catalyst for the reaction were reported. They reported that the Pd / AlF ₃ catalyst did not change its characteristics during the reaction, but had very low activity, and that the activity and selectivity of Pd / graphite and Pd / Al ₂ O ₃ catalysts changed rapidly at the beginning of the reaction.

Moon et al. [Dong Ju Moon, Moon Jo Chung, Kun You Park, and Suk In Hong, Appl. Catalyzed Pd catalyst supported on activated carbon and oxides (TiO ₂ , ZrO ₂ , SiO ₂ , Al ₂ O ₃ , MgO) in the dehydrochlorination reaction of CFC-115 Respectively. In the case of the catalyst supported on the activated carbon, the change of the carrier (activated carbon) caused by the hydrofluoric acid and hydrochloric acid produced during the hydrogenation reaction of the CFC was not large, but in the case of the catalyst supported on the oxide, the structure of the carrier was destroyed, Sintering was promoted and inactivated.

Wiersma et al. Wiersma, E. J. A., A. van de Sandt, M. Makkee, H. van Bekkum, and J. A. Moulijn, Catal. Today, 27, (1996) 257], in order to improve the selectivity of catalyst activity and dechlorination reaction by hydrocracking CFC-12 to produce HFC-32, activated carbon is pretreated with NaOH and HCl to remove impurities And how to do it. However, the specific surface area of the activated carbon pretreated by this method is not so wide, and the selectivity of HFC-32 is 58% when the catalyst is prepared.

Albers et al. [P.Albers, R.Burmeister, K.Seibolt, G. Prescher, SFParker, and DKRoss, J. Catal, 181, (1999) 145] C catalyst activity and dispersion were greatly improved. However, as a result of the experiment of the present invention, the removal rate and selectivity of impurities are not sufficiently high when treated with HCl alone.

U.S. Patent No. 5,136,113 discloses a method of continuously pretreating activated carbon, which is a carrier, with two acids, HCl and HF, in the preparation of a catalyst for hydrocracking reaction of CFC-114a (CCl ₂ FCF ₃ ) (P, S, K, Na, Fe). However, it is described that the pretreatment method using HCl preferentially is excellent, and information on the degree of dispersion of the catalyst according to the pretreatment sequence and degree of washing is not provided.

However, the performance of the catalyst such as activity and selectivity varies depending on the content of impurities contained in the activated carbon, but also depends on the surface characteristics. Particularly, in the case of pretreatment with two or more acids, the surface characteristics of the activated carbon vary depending on not only the kind of acid but also the treatment order and degree of washing, and the surface characteristics are important factors determining the performance of the catalyst. However, it is difficult to predict efficient pretreatment of activated carbon by theoretical analogy or general experiment. Therefore, it is necessary to measure the performance of the catalyst by directly applying it to the reaction to be used.

It is an object of the present invention to provide a pretreatment method of activated carbon capable of producing a palladium catalyst (Pd / C) having high activity and selectivity.

Another object of the present invention is to provide a method for preparing a catalyst for dehydrochlorination reaction of CFC using pretreated activated carbon and its use.

The inventors of the present invention have conducted various pretreatment methods by selecting activated carbon as a carrier of a palladium catalyst for the dehydrochlorination reaction of CFC and have completed the present invention.

The pretreatment method for activated carbon according to the present invention is characterized in that it comprises a step of treating activated carbon with an aqueous HF solution having a concentration of 0.5 mol / l to 2 mol / l and a step of treating with an aqueous HCl solution having a concentration of 0.5 mol / l to 2 mol / do. That is, it is first treated with HF aqueous solution and later treated with aqueous HCl solution. Treatment with an aqueous alkaline solution (such as an aqueous NaOH solution) prior to the pretreatment with an aqueous acid solution (HF and HCl aqueous solution). However, as shown in the following examples, there is no particular effect. Treatment with HF aqueous solution and HCl aqueous solution is carried out by adding activated carbon to the aqueous solution and stirring for 20 hours or more.

The concentration of HF aqueous solution and HCl aqueous solution is 0.5 mol / l to 2 mol / l, and activated carbon is added to the aqueous solution and stirred for 20 hours or more.

The activated carbon is treated with an aqueous solution of HF and an aqueous solution of HCl, and then washed with distilled water until the pH value is between 3 and 6, preferably to 5 or more.

Impregnating the activated carbon pretreated by the above process with palladium; Drying at 80 to 200 캜; (Pd / C) through a step of calcining at 300 to 500 캜 under an air atmosphere. PdCl ₂ is used as a precursor of Pd.

The catalyst prepared by the above process is useful for a hydrogenation reaction of CFC, particularly, a process for hydrogenating CCl ₂ F ₂ to produce CH ₂ F ₂ .

The constitution of the present invention will become more apparent from the following examples.

In Comparative Catalyst Preparation Examples 1-3 and Catalyst Preparation Example 1-2 described below, there were prepared activated carbon (catalyst production Comparative Example 1) without pretreatment, activated carbon pretreated by a conventional method (catalyst production Comparative Example 2-3) Catalysts were prepared with the activated carbon pretreated by the method of the present invention (catalyst preparation example 1-2), and the components of impurities [Table 1] and the specific surface area and pore size [Table 2] were measured and compared. Norit RB-1 from Norit was used as the activated carbon sample. BET surface area and elemental analysis of the pretreated activated carbon were performed.

In addition, crystallinity and dispersity were measured using XRD (Shimadzu, XRD-6000, Lab-X) and TEM (CM30, Phillips, US).

≪ Catalyst Manufacturing Comparative Example 1 >

(a) Pretreatment: Not done

(b) Preparation of catalyst:

0.3366 g of PdCl ₂ was added to 43 ml of 0.087 mol HCl aqueous solution at room temperature and stirred until a clear solution was obtained to prepare an aqueous solution of H ₂ PdCl ₄ and then this solution was impregnated with 20 g of activated carbon Respectively. The first impregnated activated carbon was dried at 100 ° C. for 12 hours, then secondly impregnated again, and dried in an oven at 100 ° C. for 24 hours. Finally, calcination was carried out in an air atmosphere at 350 ° C. for 24 hours to remove Pd (Hereinafter referred to as " Pd / C ").

The contents and characteristics of the trace components of the prepared catalysts are shown in [Table 1] and [Table 2].

<Catalyst Preparation Comparative Example 2>

(a) Pretreatment:

NaOH and HCl were sequentially treated. 100 g of activated carbon was added to 2 liters of 0.5 mol of NaOH aqueous solution and stirred at room temperature for 8 hours. After washing several times with distilled water until the pH became 8 or less, the solution was added to 2 L of 0.5 mol HCl aqueous solution, stirred for 8 hours at room temperature, And washed several times until the pH reached 5 or more. Then, it was dried in an oven at 100 캜 for 24 hours to prepare NaOH-HCl-treated activated carbon (hereinafter referred to as C-NaOH-HCl).

(b) Preparation of catalyst:

Catalyst Preparation A catalyst (hereinafter referred to as Pd / C-NaOH-HCl) having 1 wt% of Pd supported on activated carbon treated with NaOH-HCl was prepared in the same manner as in Comparative Example 1.

The contents and characteristics of the trace components of the prepared catalysts are shown in [Table 1] and [Table 2].

<Catalyst Preparation Comparative Example 3>

(a) Pretreatment:

HCl and HF in that order. 100 g of activated carbon was added to 2 liters of 1 mol HCl aqueous solution, stirred at room temperature for 20 hours, washed several times with distilled water until the pH became 5 or more, and then added to 2 liters of 1 mol HF aqueous solution, stirred at room temperature for 20 hours, And washed several times until the pH reached 5 or more. Then, it was dried in an oven at 100 ° C for 24 hours to prepare HCl-HF-treated activated carbon (hereinafter referred to as C-HCl-HF).

(b) Preparation of catalyst:

Catalyst Preparation A catalyst (hereinafter referred to as Pd / C-HCl-HF) having 1 wt% of Pd supported on HCl-HF treated activated carbon was prepared in the same manner as in Comparative Example 1.

The contents and characteristics of the trace components of the prepared catalysts are shown in [Table 1] and [Table 2].

<Catalyst Preparation Example 1>

(a) Pretreatment:

Catalyst Preparation The same acid aqueous solution as in Comparative Example 2 was used in the opposite order, i.e., HF and HCl in this order. 100 g of activated carbon was added to 2 liters of 1 mol HF aqueous solution, stirred at room temperature for 20 hours, washed with distilled water until the pH became 5 or more, added to 2 L of 1 mol HCl aqueous solution, stirred at room temperature for 20 hours, 5 or more. Subsequently, the resultant was dried in an oven at 100 DEG C for 24 hours to prepare HF-HCl-treated activated carbon (hereinafter referred to as C-HF-HCl).

(b) Preparation of catalyst:

Catalyst Preparation A catalyst (hereinafter referred to as Pd / C-HF-HCl) having 1 wt% of Pd supported on activated carbon treated with HF-HCl was prepared in the same manner as in Comparative Example 1.

The contents and characteristics of the trace components of the prepared catalysts are shown in [Table 1] and [Table 2].

&Lt; Catalyst Production Example 2 &

Treated with alkali (NaOH) and two acids (HF, HCl sequence). We have tried to improve the activity and selectivity of the catalyst by changing the surface properties of activated carbon by treatment with alkali before treating the activated carbon carrier with two acids (HF, HCl order).

100 g of activated carbon was placed in 2 L of 0.5 mol of NaOH aqueous solution, stirred at room temperature for 12 hours or more, washed several times with distilled water until the pH became 8 or less, pretreated in Example 1, and treated with NaOH-HF- Hereinafter, C-NaOH-HF-HCl) was prepared.

(b) Preparation of catalyst:

Catalyst Preparation A catalyst (hereinafter referred to as Pd / C-NaOH-HF-HCl) in which 1 wt% of Pd was supported on activated carbon treated with NaOH-HF-HCl was prepared in the same manner as in Comparative Example 1.

The contents and characteristics of the trace components of the prepared catalysts are shown in [Table 1] and [Table 2].

division Analysis of trace components of activated carbon (wt%) Fe Mg Ca Si Cl- Untreated Narit RB-1 0.094 0.34 0.36 0.35 0.005 or less Catalyst Preparation Comparative Example 1 0.094 0.34 0.36 0.35 0.59 Catalyst Preparation Comparative Example 2 0.041 0.075 0.055 0.31 10.5 Catalyst Preparation Comparative Example 3 0.022 0.052 0.030 0.81 6.79 Catalyst Preparation Example 1 0.025 0.045 0.035 0.037 13.8 Catalyst Preparation Example 2 0.027 0.044 0.029 0.040 12.9

HF-HCl, and NaOH-HF-HCl in the order of pretreatment by other methods. In addition, even when treated with the same acid (HF and HCl), the extent to which impurities are removed depends on the order.

division Treatment of Activated Carbon Activated carbon / catalyst code Specific surface area (m2 / g) Average pore size (Å) alkali mountain - - - C (Norit RB-1 activated carbon) 658.8 10.37 Catalyst Preparation Comparative Example 1 - - Pd / C 767.8 9.78 Catalyst Preparation Comparative Example 2 NaOH HCl Pd / C-NaOH-HCl 774.1 10.39 Catalyst Preparation Comparative Example 3 - HCl-HF Pd / C-HCl-HF 802.4 10.25 Catalyst Preparation Example 1 - HF-HCl Pd / C-HF-HCl 883.3 10.19 Catalyst Preparation Example 2 NaOH HF-HCl Pd / C-NaOH-HF-HCl 875.6 10.30

The specific surface area of the catalyst prepared by pretreating activated carbon with an alkali and an acid or two acids was much improved in the case where the catalyst was prepared without pretreatment (Comparative Example 1). Particularly, in Examples 1 and 2 according to the present invention, the specific surface area was greatly improved, which means that the characteristics of the catalyst are changed according to the order even if the catalyst is treated with two acids.

In addition, the Pd dispersion of each catalyst was measured by using TEM. As a result, it was confirmed that the catalyst without the pretreatment had poor dispersion due to the condensation of palladium. The catalysts prepared from the pretreated activated carbon showed different dispersion results depending on the types of alkali and acid pretreated. HF-HCl, the Pd particles were the smallest and the dispersion degree was good. It is considered that the final treated HCl was the result that the surface characteristics of the activated carbon were changed so that Pd was most evenly dispersed.

In addition, the crystallinity of Pd was confirmed by using XRD. In the untreated catalyst, the Pd crystal was formed and the Pd peak was clearly observed in the XRD pattern. On the other hand, the catalyst using activated carbon which was pretreated with alkali and acid or two acids Pd peaks were not identified. Since the crystals that can be measured by XRD are larger than 50 ANGSTROM, the catalyst prepared by the method of the present invention can be considered to have a crystal size at least smaller than that. That is, it is XRD amorphous.

<Reaction Comparative Examples 1-3 and Reaction Examples 1-2>

Preparation of Catalyst Comparative Example 1-3 (Pd / C-HF-HCl, Pd / C-NaOH-HCl, Pd / C-HCl- -HF-HCl) was reacted with CFC-12 (CCl ₂ F ₂ ) at 240 ° C and atmospheric pressure.

The reaction was carried out in a typical fixed-bed reactor equipped with an Inconel-600 reactor having an outer diameter of 1/2 inch (inner diameter 10.2 mm) and a length of 30 cm. First, 0.5 g of the catalyst was charged into the reactor and hydrogen was fed at 12 cc / min The temperature was raised from room temperature to the reaction temperature (240 ° C) for 1 hour in the flowing atmosphere to reduce the catalyst.

The reactants CFC-12 and hydrogen were supplied to the reactor through a preheater at 240 ° C at a flow rate of 2 cc / min and 12 cc / min, respectively, using a flow rate controller (Matheson, Gas Products). Among the reaction products, HF and HCl were removed by passing through a water trap, and water was removed by passing through a silica gel layer. The acid and dehydrated products were analyzed by using a Poraplot Q capillary column and a gas chromatograph equipped with FID (HP-5890 Series II Plus). The products were analyzed by GC / MS (GC: HP-5890, MSDetector: 5971A ).

Reaction The conversion of the reactant (CFC-12) and the selectivity of the product (HFC-32 and the like) in Comparative Examples 1-3 and 1-2 are shown in Table 3 below.

division Used catalyst Conv. (%) Product selectivity (%) CH4 HFC-32 C2H6 HCFC-22 C3H8 Reaction Comparative Example 1 Pd / C 21.00 34.82 42.23 13.82 4.61 2.66 Reaction Comparative Example 2 Pd / C-NaOH-HCl 51.81 26.75 57.83 7.68 3.38 0.91 Reaction Comparative Example 3 Pd / C-HCl-HF 51.26 17.00 71.29 5.43 2.40 0.68 Reaction Example 1 Pd / C-HF-HCl 67.56 16.88 70.90 5.33 2.37 0.47 Reaction Example 2 Pd / C-NaOH-HF-HCl 65.45 17.95 70.48 5.38 2.25 0.59

[Table 3] shows that the conversion rate and selectivity of the reaction example 1-2 according to the present invention are greatly improved compared to the reaction example 1-2, and the selectivity is similar to that of the reaction example 3 It can be seen that the conversion rate is about 20% higher. Comparing the case of first treating with NaOH (reaction example 2) and the case of treating only with two acids (reaction example 1), it can not be said that the first treatment with NaOH is good .

As a result of XRD analysis of the catalyst after the reaction, it was confirmed that the Pd / C catalyst without the pretreatment was converted into Pd carbide (hereinafter referred to as PdC) in which Pd was bonded to the carbon of the reactant CCl ₂ F ₂ , Supported catalyst) showed no Pd or PdC peak. This is because the impurities are removed by pretreatment and the surface characteristics are changed to improve the dispersion degree of Pd, and the sintering of the catalyst and the crystal growth are suppressed during the reaction.

According to the present invention, there is provided a pretreatment method of activated carbon capable of producing a palladium catalyst (Pd / C) having high activity and selectivity.

In addition, the catalyst prepared by the present invention is particularly useful for the reaction for producing CH ₂ F ₂ by hydrogenating CCl ₂ F ₂ , which is highly durable by suppressing sintering.

Claims (7)

In the pretreatment of the activated carbon used for the production of the palladium catalyst (Pd / C) used for the dechlorination of the chlorofluorocarbons (CFC), the activated carbon is treated with an aqueous HF solution having a concentration of 0.5 mol / And a step of treating the activated carbon with an aqueous HCl solution of 0.5 mol / l to 2 mol / l. delete The pretreatment method of activated carbon according to claim 1, wherein the treatment with HF aqueous solution and HCl aqueous solution is carried out by adding activated carbon and stirring for 20 hours or more. The pretreatment method of activated carbon according to claim 1, wherein the activated carbon is washed with distilled water until the hydrogen ion concentration (pH) is between 3 and 6 after the treatment with the HF aqueous solution and the aqueous HCl solution. The pretreatment method of activated carbon according to claim 1, wherein the activated carbon is treated with HF aqueous solution and HCl aqueous solution, followed by washing with activated carbon until the hydrogen ion concentration (pH) becomes 5 or more. A process for preparing a palladium catalyst by impregnation using activated carbon pretreated according to any one of claims 1 to 5, comprising: impregnating activated carbon with palladium precursor at room temperature; Drying at 80 to 200 캜; And calcining the mixture at 300 to 500 DEG C under an air atmosphere. A catalyst for use in the process for producing CH ₂ F ₂ by hydrogenating CCl ₂ F ₂ produced by the process of claim 6.