KR20010100302A - Pretreatment Method of Active Carbon for Preparation of Pd/C Catalyst - Google Patents

Abstract

The present invention relates to a method for pretreatment of activated carbon to prepare a palladium catalyst (Pd / C), which is useful for dechlorinating chlorofluorocarbon (CFC) to produce hydrogen fluoride (HFC), a substitute thereof. The purpose is to increase the activity and selectivity of the catalyst.

Activated carbon, which is a carrier of the catalyst, is sequentially treated with an aqueous HF solution and an aqueous HCl solution. The catalyst comprises the steps of impregnating palladium ions at room temperature with pretreated activated carbon; Drying at 80 to 200 ° C; It is prepared through a step of baking at 300 to 500 ° C. under an air atmosphere.

Description

Pretreatment Method of Active Carbon for Preparation of Pd / C Catalyst

The present invention relates to a method for pretreatment of activated carbon to prepare a palladium catalyst (Pd / C) useful for dechlorinating chlorofluorocarbons (CFCs) to produce hydrogen fluoride hydrocarbons (HFCs).

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 atom of saturated hydrocarbon is substituted with chlorine and fluorine, and has been widely used as a refrigerant, blowing agent, detergent, and propellant because of its excellent thermal and chemical stability, but when it is released into the atmosphere, it has a large global warming index and is photodecomposed in the stratosphere. As it was found to destroy the ozone layer, its production and use were regulated by the Montreal Protocol. Accordingly, there is a need for a method of efficiently treating the used CFCs along with the development of materials that can replace the CFCs.

In particular, dehydrochlorination by a catalyst produces HFC, which is an alternative to CFC, such as preparing HFC-32 (CH2F2) from CFC-12 (CCl2F2) or HFC-134a (CH2FCF3) from CFC-114a (CCl2FCF2). It has been tried by several researchers as it is recognized as an important route to deal with used CFCs.

Coq et al. [B. Coq, JM Cognion and F. Figueras, J. Catal., 141 (1993) 21 describe the hydrocracking reaction of CFC-12 on Pd-supported catalysts with Al2O3, AlF3, graphite, etc. as carriers. The activity and properties of the catalyst were reported. They report that the Pd / AlF3 catalyst did not change during the reaction but the activity was very low, and the Pd / graphite and Pd / Al2O3 catalysts showed a sharp change in activity and selectivity at the beginning of the reaction.

Moon et al., Moon Ju Moon, Moon Jo Chung, Kun You Park, and Suk In Hong, Appl. Catal., A: General, 168, (1998) 154] tested the dechlorination of CFC-115 using a Pd catalyst supported on activated carbon and oxides (TiO2, ZrO2, SiO2, Al2O3, MgO). In the case of the catalyst supported on activated carbon, the change of the carrier (activated carbon) due to hydrofluoric acid and hydrochloric acid generated during the hydrogenation of CFC was not large, but in the case of the catalyst supported on the oxide, the structure of the carrier was destroyed and the specific surface area of the catalyst was reduced. It was confirmed that sintering was promoted and deactivated.

Wiersma et al. [A. Wiersma, E. J. A. X. van de Sandt, M. Makkee, H. van Bekkum, and J. A. Moulijn, Catal. Today, 27, (1996) 257], in the preparation of HFC-32 by hydrocracking CFC-12, pretreatment of activated carbon with NaOH and HCl to remove impurities in order to improve the activity of the catalyst and the selectivity of the dechlorination reaction. It was presented how to. However, the activated carbon pretreated by this method does not have a large specific surface area, and when prepared with a catalyst, the selectivity of HFC-32 is not so high as 58.

Albers et al. [P.Albers, R.Burmeister, K. Seibolt, G.Prescher, SFParker, and DKRoss, J. Catal, 181, (1999) 145] treated activated charcoal with HCl to remove impurities. It was claimed that the activity and dispersion of the C catalyst were greatly improved. However, when the experimental results of the present invention only treated with HCl, the impurity removal rate and selectivity are not high enough.

U.S. Patent No. 5,136,113 discloses a method for the pretreatment of activated carbon as a carrier with two acids, HCl and HF, in the preparation of a hydrocracking catalyst for CFC-114a (CCl2FCF3), and the effects thereof. Information quantified in the form of S, K, Na, Fe) removal rate is disclosed. 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 or degree of washing is not provided.

However, the performance of the catalyst, such as activity and selectivity, may vary depending on the content of impurities contained in the activated carbon, but also depends on the surface properties. In particular, in the case of pretreatment with two or more acids, the surface characteristics of activated carbon vary depending on the type of acid, the order of treatment, and the degree of washing. However, the effective method of pretreatment of activated carbon is difficult to predict only by theoretical inference or general experiments. Therefore, it is difficult to determine which pretreatment method is effective only when the performance of the catalyst is measured by applying the catalyst directly to the reaction.

It is an object of the present invention to provide a method for pretreatment of activated carbon that can produce a high activity and selectivity palladium catalyst (Pd / C).

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

The inventors of the present invention have completed the present invention as a result of attempting numerous pretreatment methods by selecting activated carbon as a carrier of the palladium catalyst for dehydrochlorination of CFC.

Activated carbon pretreatment method of the present invention is characterized in that it comprises a step of sequentially treating the activated carbon with HF aqueous solution and the aqueous solution of HCl. That is, first treatment with aqueous HF solution and later treatment with aqueous HCl solution. A treatment with an aqueous alkali solution (such as an aqueous NaOH solution) may be provided prior to pretreatment with an aqueous acid solution (HF and aqueous HCl solution). However, as shown in the following embodiments, no particular effect is seen.

Concentrations of the HF aqueous solution and the HCl aqueous solution are 0.5 mol / l to 2 mol / l, and the activated carbon is added to the aqueous solution and treated by stirring for 20 hours or more.

The activated carbon is treated with an aqueous HF solution and an aqueous HCl solution, and then washed with distilled water until the hydrogen ion concentration (pH) is between 3 and 6, preferably 5 or more.

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

The catalyst prepared by the above process is useful for the hydrogenation of CFCs, in particular, a process for producing CH 2 F 2 by hydrogenating CCl 2 F 2.

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

In Comparative Examples 1-3 and Manufacture Example 1-2 described below, activated carbon (preparative Comparative Example 1) without pretreatment, activated carbon pre-treated by Comparative Example (catalyst preparation Comparative Example 2-3), and present Catalysts were prepared from activated carbon pretreated by the method of the invention (Example 1-2 of catalyst preparation), and the components of the impurities [Table 1], the specific surface area and the pore size [Table 2] were measured and compared. Activated carbon samples were Norit's Norit RB-1, and the BET surface area of pretreated activated carbon was measured and elemental analysis.

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

<Catalyst Preparation Comparative Example 1>

(a) pretreatment: not

(b) preparation of catalyst:

0.3366 g of PdCl2 was added to 43 ml of 0.087 mol HCl aqueous solution at room temperature, and stirred until it became a clear solution. Thus, an aqueous solution of H2PdCl4 was prepared, and then the solution was impregnated with 20 g of activated carbon twice. The first impregnated activated carbon was dried at 100 ° C. for 12 hours, and then again impregnated with secondary carbon for 24 hours in an oven at 100 ° C., and finally calcined for 24 hours in an air atmosphere at 350 ° C. 1 wt supported catalyst (hereinafter referred to as Pd / C) was prepared.

The content and properties of the trace components of the prepared catalyst are described in [Table 1] and [Table 2].

<Catalyst Preparation Comparative Example 2>

(a) pretreatment:

The treatment was performed in the order of NaOH and HCl. 100 g of activated carbon was added to 2 L of 0.5 mol of NaOH aqueous solution and stirred at room temperature for 8 hours, washed several times with distilled water until the pH was 8 or less. Then, it was added to 2 L of 0.5 mol of HCl aqueous solution and stirred at room temperature for 8 hours. Several times until the pH was 5 or more. Subsequently, NaOH-HCl treated activated carbon (hereinafter referred to as C-NaOH-HCl) was prepared by drying in an oven at 100 ° C. for 24 hours.

(b) preparation of catalyst:

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

The content and properties of the trace components of the prepared catalyst are described in [Table 1] and [Table 2].

<Catalyst Preparation Comparative Example 3>

(a) pretreatment:

Treatment was performed in the order of HCl and HF. 100 g of activated carbon was added to 2 L of 1 mol of HCl aqueous solution and stirred at room temperature for 20 hours, washed several times with distilled water until the pH became 5 or more. Then, it was added to 2 L of 1 mol of HF aqueous solution and stirred at room temperature for 20 hours. Several times until the pH was 5 or more. Subsequently, HCl-HF treated activated carbon (hereinafter referred to as C-HCl-HF) was prepared by drying in an oven at 100 ° C. for 24 hours.

(b) preparation of catalyst:

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

The content and properties of the trace components of the prepared catalyst are described in [Table 1] and [Table 2].

<Catalyst Preparation Example 1>

(a) pretreatment:

The same aqueous acid solution as in Preparation Example 2 was used in the reverse order, HF and HCl. 100 g of activated carbon was added to 2 L of 1 mol of HF aqueous solution, stirred at room temperature for 20 hours, washed with distilled water until the pH was 5 or more, and then added to 2 L of 1 mol of HCl aqueous solution, stirred at room temperature for 20 hours, and the pH was increased with distilled water. Wash several times until 5 or more. Subsequently, it was dried in an oven at 100 ° C. for 24 hours to prepare HF-HCl treated activated carbon (hereinafter, C-HF-HCl).

(b) preparation of catalyst:

Catalyst Preparation In the same manner as in Comparative Example 1, a catalyst (hereinafter referred to as Pd / C-HF-HCl) containing 1 wt of Pd on HF-HCl treated activated carbon was prepared.

The content and properties of the trace components of the prepared catalyst are described in [Table 1] and [Table 2].

<Catalyst Preparation Example 2>

Pretreatment with alkali (NaOH) and two acids (HF, HCl sequence). Before treating activated carbon carriers with two acids (in order of HF and HCl), an attempt was made to improve the activity and selectivity of the catalyst by changing the surface properties of the activated carbon by treating with alkali.

100 g of activated carbon was added to 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 was 8 or less, and then the pretreatment of Example 1 was performed to carry out NaOH-HF-HCl treated activated carbon ( Hereinafter, C-NaOH-HF-HCl) was prepared.

(b) preparation of catalyst:

Catalyst Preparation In the same manner as in Comparative Example 1, a catalyst (hereinafter referred to as Pd / C-NaOH-HF-HCl) containing 1 wt of Pd on NaOH-HF-HCl treated activated carbon was prepared.

The content and properties of the trace components of the prepared catalyst are described in [Table 1] and [Table 2].

division Trace component analysis result of activated carbon (wt) Fe Mg Ca Si Cl- Unpretreated Narit RB-1 0.094 0.34 0.36 0.35 Less than 0.005 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

It can be seen that the catalyst supported on the activated carbon pretreated in the order of HF-HCl, NaOH-HF-HCl was further reduced in impurities than the catalyst prepared by other methods. In addition, even when treated with the same acid (HF and HCl) it can be seen that the degree of removal of impurities in different orders.

division Treatment of Activated Carbon Activated Carbon / Catalyst Cord Specific surface area (m2 / g) Average pore size 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 alkali and acid or two acids was much improved than when the catalyst was prepared without the pretreatment (Comparative Example 1). In particular, in the case of Examples 1 and 2 according to the present invention, the specific surface area is greatly improved, which means that even if treated with two acids, the catalytic properties vary in order.

In addition, the Pd dispersion degree of each catalyst was measured using TEM, and it was confirmed that palladium condensed in the catalyst without pretreatment, resulting in poor dispersion. Catalysts prepared from pretreated activated carbon showed different degrees of dispersion depending on the type of alkali and acid pretreated. The catalyst made of activated carbon pretreated in the order of HF-HCl had the smallest Pd particles and good dispersibility, which is thought to be the result of changing the surface properties of activated carbon so that Pd is most evenly dispersed.

In addition, XRD was used to confirm the crystallinity of Pd, but the catalyst without pretreatment was able to identify a clear Pd peak in the XRD pattern due to the formation of Pd crystal, whereas the catalyst using activated carbon pretreated with alkali and acid or two acids No Pd peak was identified. Since the crystal which can be measured by XRD is 50 kPa or more, the catalyst prepared by the method of the present invention can be considered that the crystal size is at least smaller than this. That is, XRD is amorphous.

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

Catalyst Preparation Comparative Example 1-3 (Pd / C, Pd / C-NaOH-HCl, Pd / C-HCl-HF) and Catalyst Preparation Example 1-2 (Pd / C-HF-HCl, Pd / C-NaOH CFC-12 (CCl 2 F 2) and hydrogen were reacted at 240 ° C. and atmospheric pressure using a catalyst prepared in -HF-HCl).

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 of 10.2 mm) and a length of 30 cm. First, 0.5 g of catalyst was charged into the reactor, and hydrogen was 12 cc / min. The catalyst was reduced by increasing the reaction temperature (240 ° C.) at room temperature for 1 hour in a flowing atmosphere.

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

The conversion rate of the reactants (CFC-12) and the selectivity of the products (HFC-32, etc.) in Reaction Examples 1-3 and Reaction Examples 1-2 are shown in Table 3 below.

division Used catalyst Conv. () Product selectivity () CH4 HFC-32 C2H6 HCFC-22 C3H8 Comparative Example 1 Pd / C 21.00 34.82 42.23 13.82 4.61 2.66 Comparative Example 2 Pd / C-NaOH-HCl 51.81 26.75 57.83 7.68 3.38 0.91 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

According to Table 3, it can be seen that the conversion rate and selectivity are greatly improved when the reaction examples 1-2 according to the present invention are compared with the reaction comparative example 1-2, but the selectivity is similar when compared with the reaction comparative example 3. It can be seen that the conversion rate is about 20 higher. When the treatment with NaOH first and the two acids (Reaction Example 2) and the treatment with only two acids (Reaction Example 1), the treatment with NaOH first is not good. .

After the reaction, the catalyst was irradiated with XRD, and the Pd / C catalyst without pretreatment was found to be converted into Pd carbide (hereinafter referred to as PdC) bonded with carbon of CCl2F2 as a reactant. ) Did not identify Pd or PdC peaks. This is thought to be the result of removing impurities and improving the dispersity of Pd by pretreatment, thereby suppressing sintering and crystal growth of the catalyst during the reaction.

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

In addition, the catalyst prepared according to the present invention is particularly useful in the reaction for producing CH2F2 by hydrogenation of CCl2F2 by suppressing sintering phenomenon and increasing durability.

Claims (7)

In the pretreatment of activated carbon used in the preparation of the palladium catalyst (Pd / C) used for the dehydrochlorination of chlorofluorocarbons (CFC), treatment of activated carbon with an aqueous HF solution and treatment with an aqueous HCl solution are sequentially performed. Activated carbon pretreatment method comprising a. The method for pretreatment of activated carbon according to claim 1, wherein the concentration of HF aqueous solution and HCl aqueous solution to be used is 0.5 mol / L to 2 mol / L. The method for pretreatment of activated carbon according to claim 1, wherein the treatment with an aqueous solution of HF and an aqueous solution of HCl is performed by adding activated carbon and stirring for 20 hours or more, respectively. The method 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 treatment with an aqueous HF solution and an aqueous HCl solution. The method of claim 1, wherein the activated carbon is washed with distilled water until the hydrogen ion concentration (pH) is 5 or more after treatment with an aqueous HF solution and an aqueous HCl solution. A method for preparing a palladium catalyst by impregnation using activated carbon pretreated according to any one of claims 1 to 5, the method comprising: impregnating a palladium precursor into activated carbon at room temperature; Drying at 80 to 200 ° C; Method for producing a palladium catalyst (Pd / C) characterized in that the step of firing at 300 ~ 500 ℃ under an air atmosphere. Use of a catalyst prepared by the method of claim 6 for use in the process of hydrogenating CCl 2 F 2 to produce CH 2 F 2.