JP2003126692A - Method for synthesizing modified carbon-carried palladium catalyst having high activity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an improved method for synthesizing a high active carbon- carried palladium catalyst useful for dechlorination/hydrogenation to HFC-32 of CFC-12 and, to provide a method for modifying carbon by a metal oxide, preferably a metal oxide of III group such as alumina. SOLUTION: The method for synthesizing a modified carbon-carried palladium catalyst having a high activity by simultaneously impregnating palladium precursor and an aluminum precursor in an activated carbon. The carbon-carried palladium catalyst is useful for a dechlorination/hydrogenation of dichlorodifluoromethane to form difluoromethane.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for synthesizing a carbon-supported palladium catalyst having high activity. The catalyst produced by the method of the present invention is useful for dechlorinating and hydrogenating dichlorodifluoromethane to produce difluoromethane.

[0002]

BACKGROUND OF THE INVENTION Dechlorination hydrogenation is the treatment of chlorine containing compounds such as chlorofluorocarbons (CF) in the presence of hydrogen.
This is a process in which chlorine is removed from chloroorganic substances such as C). A palladium catalyst is preferred for dechlorination of CFCs in the gas phase. Difluoromethane (HFC-32), known as a refrigerant, is dichlorodifluoromethane (C) over palladium-based catalysts in the vapor phase.
It is a product of dechlorination and hydrogenation of FC-12). CFC-
The selective formation of HFC-32 by dechlorination and hydrogenation of 12 depends on the characteristics of the catalyst used, the choice of support and the method of preparation.

Many methods are known in the art for the preparation of catalysts useful in the dehydrochlorination of CFC-12. Japanese Patent Application No. 339182JP 0601731PCT
Is 80% CFC-12 conversion and 20% HFC-3.
Disclosed is a method using palladium on activated carbon as a dechlorination hydrogenation catalyst to produce HFC-32 in a yield of 2. WO9617683 discloses a method for producing HFC-32 with a selectivity of 80% or more on a palladium-platinum / carbon catalyst. Another patent application ENCS disclosing palladium supported on metal oxides or metal fluorides (Al ₂ O ₃ or AlF ₃ respectively) as a dechlorination catalyst.
See M, Montpellier (CA. No. 119: 94820t).
The major drawback of oxide supports is the HF formed during the reaction.
Lack of resistance to / HCl. HF /
In such a corrosive reaction atmosphere in which HCl is a by-product, the acidity of the catalyst changes and the oxide support becomes hydroxy /
Converts to oxide fluoride and loses activity. The fluorinated carrier catalyzes side reactions and reduces the yield of dechlorinated hydrogenation products. Also, the manufacture of fluorinated supports involves corrosive reactions due to the use of HF as a reactant. Dutch Delf
The method of patent application filed by researchers at
A high CFC-12 conversion was revealed with high selectivity to HFC-32. However, this method is reported to have been carried out under pressure of 0.3-0.5 MPa. US Patent 542652
No. 5,837,088 discloses fast deactivation of catalysts containing palladium or Group IVB metal carbides. Co-pending Indian Patent Applications No. 537 / Del / 99 and 536 / Del / 99 have 70% HFC-3
Disclosed is the use of highly active palladium on carbon-coated alumina as a catalyst for dehydrochlorination of CFC-12 at 2 selectivity and 68% conversion.
The major drawback of this method is low selectivity or conversion to HFC-32 or severe operating conditions.

Therefore, it is important to develop new or improved catalysts that overcome the above-mentioned drawbacks of the prior art.

[0005]

The main object of the present invention is to provide a process for the synthesis of an improved highly active carbon supported palladium catalyst useful in the dechlorination hydrogenation of CFC-12 to HFC-32. is there. Another object of the present invention is to provide a method for carbon modification with metal oxides, preferably Group III metal oxides such as alumina.

Still another object of the present invention is to provide a modified carbon-supported palladium catalyst having a reduced amount of metal oxide and palladium on the catalyst. A further object of the present invention is CFC-12 H which is economical and efficient.
It is to provide a catalyst for dechlorination hydrogenation to FC-32.

[0007]

An excellent Pd-based desorption by improving the activated carbon support by adding a small amount of aluminum with an organic precursor together with a palladium precursor by a co-impregnation method using a stable solvent. As a result of continuing research on the chlorine hydrogenation catalyst, an excellent dechlorination catalyst having a high conversion rate of CFC-12 and a high selectivity to HFC-32 was obtained.

The present invention provides a method for synthesizing a highly active modified carbon-supported palladium catalyst, which comprises simultaneously impregnating activated carbon with a palladium precursor and an aluminum precursor.

In one aspect of the invention, the aluminum precursor used comprises an organic precursor of aluminum. In another aspect of the invention, the organoaluminum precursor used comprises aluminum isopropoxide.

In another embodiment of the present invention, the addition rate of palladium to the carrier is 2 to 6% by weight, preferably 4% by weight, based on the carbon carrier. In another embodiment of the present invention, the addition rate of alumina to the carrier is 1 to 50% by weight, preferably 5 to 20% by weight based on the carrier.

In another embodiment of the invention, the co-impregnation of the support is carried out in the presence of an aqueous solution of tetraethylammonium hydroxide. In another embodiment of the invention, the conversion of CFC-12 is of the order of 85% and the selectivity to HFC-32 is of the order of 85% at atmospheric pressure.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION It is possible to highly disperse aluminum on carbon by selecting aluminum isopropoxide, which is an organic precursor to be attached to activated carbon. Simultaneous impregnation of activated carbon with Pd and Al precursors is performed to maintain the interaction between palladium and aluminum. This gives the combined properties of Pd / C and Pd / Al ₂ O ₃ . The use of aqueous tetraethylammonium hydroxide solution during deposition solves the solubility problem of PdCl ₂ and aluminum isopropoxide.

The catalyst obtained by the method of the present invention is produced using commercially available activated carbon as a carrier. The amount of palladium added is maintained at 2 to 6% by weight, preferably 4% by weight based on the activated carbon. The alumina content in the catalyst is maintained at 1 to 50 wt%, preferably 5 to 20 wt% with respect to the activated carbon. Prepared catalyst is reduced with H ₂ fluid before the reaction in order to obtain a palladium metal form.

The activity of the catalyst was evaluated in an online continuous flow microreactor (10 mm ID, 250 mm length) made of Pyrex® glass, coupled to a gas chromatograph equipped with TCD / FID. 1 g of catalyst,
Place between two quartz wools in the center of the reactor. The reactor is placed in an electrically heated furnace and the temperature of the catalyst is controlled / monitored by a PID temperature programmer via a thermocouple inserted in the thermowell near the catalyst bed. The catalyst in the reactor
4 ~ at a temperature of 200 ~ 500 ℃, preferably 300 ~ 400 ℃
Reduce for 6 hours in a stream of hydrogen (30-80 cc / min). Once the reaction temperature is reached, in order to maintain the required space velocity, CF
C-12 is flowed through the catalyst bed with H ₂ and an inert gas such as N ₂ . The product mixture coming out of the reactor was first blown with alkali to remove any HF or HCl formed during the reaction.
To remove. Then pass through a gas chromatograph through a 6-neck valve with a 0.5 ml loop. The HF / HCl free product mixture is analyzed by gas chromatography at regular intervals.

Prior to depositing the palladium and aluminum precursors on the activated carbon, the support was treated with hot concentrated HNO ₃ , hot deionized water, hot ammonia solution, and hot deionized water in sequence several times to remove metals and other impurities. Purify by removing. The carbon unit used here is M / s No.
Obtained from rit. The BET surface area of this carrier was 960 m ² / g. This carrier was an extrudate having a diameter of 0.5 mm.

The amounts of Pd and Al ₂ O ₃ added are low. This catalyst has CFC-12 conversion of the order of 85% and HFC
The selectivity to -32 is shown. Activated carbon can be obtained easily and cheaply, and thus the manufacturing cost can be reduced. The advantageous properties of both alumina and palladium and the properties of activated carbon which enhances alumina adhesion are advantages of the present invention.

The invention will now be described in more detail with reference to the following examples. This example does not limit the scope of the invention.

Example 1 Effect of Addition of Palladium and Aluminum Precursor In Examples 1 (a) and 1 (b), activated carbon was simultaneously and stepwise impregnated with aluminum isopropoxide and palladium chloride.

1 (a): Simultaneous impregnation of aluminum and palladium precursors 10 g of activated carbon were simultaneously impregnated with aluminum isopropoxide (4.010 g) and palladium chloride (0.68 g) in 50 ml of tetraethylammonium hydroxide. The resulting mixture was placed on a hot plate to remove excess solvent. This material was dried in a hot air oven at 120 ° C for 12 hours.
The obtained catalyst was designated as Pd / ACC-1 (a).

[0020]

[Table 1]

1 (b): Stepwise impregnation of aluminum and palladium precursors 10 g of activated carbon were impregnated with aluminum isopropoxide (4.010 g) in 40 ml of tetraethylammonium hydroxide solution, then the excess solvent was evaporated, 120 It was dried at ℃ for 12 hours. 6 g of this material was calcined in flowing N ₂ at 450 ° C. for 4 hours. This calcined material (3.8 g after calcination) was added to palladium chloride in 10 ml of tetraethylammonium hydroxide solution.
It was impregnated with (0.26 g). Excess solvent was removed by heating on a hot plate and then dried at 120 ° C. for 12 hours. The obtained catalyst was designated as Pd / ACC-1 (b).

[0022]

[Table 2]

Example 2 Effect of Aluminum Precursor To investigate the effect of aluminum precursor on activity,
Three precursors were used, namely aluminum isopropoxide, aluminum nitrate and aluminum chloride (Example 1 (a), Example 2 (a) and Example 2 (b) respectively). Pd and Al were added stepwise.

2 (a): Aluminum nitrate precursor 10 g of activated carbon was added to aluminum nitrate (7.358 g) and palladium chloride (0.6 g) in 70 ml of tetraethylammonium hydroxide.
8 g) and impregnated at the same time. The resulting mixture was placed on a hot plate to remove excess solvent. This material 120
It was dried in a hot air oven at ℃ for 12 hours. The obtained catalyst was designated as Pd / ACC-2 (a).

[0025]

[Table 3]

2 (b): Aluminum chloride precursor 7 g of activated carbon was added to aluminum chloride (1.83 g) and palladium chloride (0.47 g) in 50 ml of tetraethyl ammonium hydroxide.
8 g) and impregnated at the same time. The resulting mixture was placed on a hot plate to remove excess solvent. This material 120
It was dried in a hot air oven at ℃ for 12 hours. The obtained catalyst was designated as Pd / ACC-2 (b).

[0027]

[Table 4]

Example 3 Time analysis Pd / ACC-1 (a) catalyst was subjected to CFC at 250 ° C. in H ₂ / CFC-12 = 8 and gas hourly space velocity of 4800 / h.
Continuous tests were performed for the dechlorination and hydrogenation of -12. The table below shows the results at various times.

[0029]

[Table 5]

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Sridara Chadra Shaker             India, Andhra Pradesh, High             Delabad 500 007, Indian Lee             Institute of Chemical Tech             Noology (72) Inventor Kamaraju Shisa Ramarao             India, Andhra Pradesh, High             Delabad 500 007, Indian Lee             Institute of Chemical Tech             Noology (72) Inventor Bry David Raju             India, Andhra Pradesh, High             Delabad 500 007, Indian Lee             Institute of Chemical Tech             Noology (72) Inventor Vijaya Conda Plum Ragavan             India, Andhra Pradesh, High             Delabad 500 007, Indian Lee             Institute of Chemical Tech             Noology F-term (reference) 4G069 AA03 AA08 BA08A BA08B                       BC16A BC16B BC72A BC72B                       CB02 CB35 FB14 FB15                 4H006 AA02 AC13 BA25 BA55 BC11                       BE20                 4H039 CA11 CD20

Claims (11)

[Claims] 1. A highly active, comprising simultaneously impregnating activated carbon with a palladium precursor and an aluminum precursor,
Method for synthesizing modified carbon-supported palladium catalyst. 2. The method according to claim 1, wherein the aluminum precursor used comprises an organic precursor of aluminum. 3. The method according to claim 2, wherein the organoaluminum precursor used comprises aluminum isopropoxide. 4. The method according to claim 1, wherein the palladium precursor used comprises palladium chloride. 5. The method according to claim 1, wherein the addition rate of palladium to the carrier is 2 to 6 wt% with respect to the carbon carrier. 6. The method according to claim 5, wherein the addition rate of palladium to the carrier is 4 wt% with respect to the carbon carrier. 7. The method according to claim 1, wherein the addition rate of alumina to the carrier is 1 to 50 wt% with respect to the carrier. 8. The method according to claim 1, wherein the alumina addition rate to the carrier is 5 to 20 wt% with respect to the carrier. 9. The method according to claim 1, wherein the co-impregnation of the support is carried out in the presence of an aqueous tetraethylammonium hydroxide solution. 10. The conversion of CFC-12 at atmospheric pressure is of the order of 85%, and the selectivity to HFC-32 is 85%.
The method of claim 1, which is of the order of%. 11. Use of a carbon-supported palladium catalyst for the dechlorination hydrogenation of dichlorodifluoromethane to produce difluoromethane.