JP2005111366A - Catalyst for reducing polychlorinated alkane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for reducing a polychlorinated alkane decreased in the use amount of a catalytic metal while an activity as a reducing catalyst is maintained. <P>SOLUTION: The catalyst for reducing the polychlorinated alkane is a catalyst comprising at least one catalytic metal selected from group VIII, IX, and X elements and deposited on a porous carrier particle and the catalyst is obtained by forming a deposition layer of the catalytic metal on the surface layer part of the porous carrier particle. Particularly, it is preferable to use titania as the carrier and platinum as the catalytic metal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a catalyst for producing a low-order chlorinated alkane by replacing the chlorine atom of a polychlorinated alkane with a hydrogen atom.

  From the standpoint of protecting the global environment, it is desired to produce a low-order chlorinated alkane having a low chlorine content by reducing a polychlorinated alkane containing a large amount of chlorine atoms.

  For example, since carbon tetrachloride, whose production is regulated as an ozone depleting substance, is unavoidable in the production of dichloromethane and chloroform, various techniques for converting carbon tetrachloride into useful substances have been studied so far.

  As these methods, a method is known in which carbon tetrachloride is hydrogenated and reduced to chloroform using a reduction catalyst in which a catalytic metal such as platinum or palladium is supported on porous support particles such as activated carbon. (For example, patent document 1).

Japanese Patent No. 2812800

  According to the above method, it is possible to hydrogenate and reduce carbon tetrachloride to convert it into chloroform. However, in order to increase the catalytic activity, it is necessary to use a large amount of noble metal elements such as platinum used for the catalyst. Have That is, the reduction catalyst is generally produced by impregnating a porous carrier particle with a catalyst metal salt solution, and the impregnation is performed by immersing the porous carrier particle in the salt solution. After that, since it was manufactured by a method of drying and reduction treatment, the catalyst metal was present in all layers. Therefore, when the catalyst metal is supported at a concentration of 2% by weight with respect to 5 tons of the catalyst carrier, 100 kg of noble metal is required, and there is a problem that the cost for the noble metal becomes very large.

  Since only 66,000 tons of platinum group elements such as platinum and palladium, which are the catalyst metals, exist on the earth, the amount of metal used for the catalyst is reduced from the standpoint of protecting limited resources on the earth. That is important.

  Accordingly, an object of the present invention is to provide a polychlorinated alkane reduction catalyst in which the amount of catalyst metal used is reduced while maintaining the activity as a reduction catalyst.

  As a result of intensive studies to achieve the above object, the present inventors have found that the above problem can be solved by mainly supporting the catalyst metal on the surface layer portion of the porous carrier particles. Further, it has been found that the presence of the catalytic metal mainly in the surface layer portion of the porous carrier particles exhibits the surprising effect that the occurrence of side reactions in the reduction reaction can be extremely effectively reduced. It came to be completed.

  That is, according to the present invention, there is provided a catalyst in which at least one catalyst metal selected from Group 8 element, Group 9 element and Group 10 element of the periodic table is supported on porous carrier particles, Provided is a catalyst for reducing polychlorinated alkanes, wherein the catalyst metal support layer is formed on the surface layer of the support particles.

  The present invention also provides a method for producing a low-order chlorinated alkane by reducing a polychlorinated alkane using the reducing catalyst.

  That is, according to the present invention, the polychlorinated alkane and hydrogen are reacted in a liquid phase in the presence of a reducing catalyst in which the catalytic metal is mainly present in the surface layer portion of the porous carrier particles. A method for producing a low-order chlorinated alkane is provided.

  Furthermore, according to the present invention, there is also provided a method for producing a reduction catalyst that can produce a reduction catalyst in which the catalyst metal is mainly present in the surface layer portion of the porous carrier particles, by an industrially advantageous method. .

  That is, according to the present invention, a soluble salt aqueous solution of at least one metal selected from Group 8 element, Group 9 element and Group 10 element of the periodic table is sprayed on the surface of the porous carrier particles, and then dried, There is provided a method for producing a catalyst for reducing polychlorinated alkanes, characterized by performing a reduction treatment.

  According to the reduction catalyst of the present invention, when the metal catalyst is mainly present in the surface layer portion of the porous carrier particles, the polychlorinated alkane such as carbon tetrachloride is hydroreduced to the lower chlorinated alkane. In addition, it is possible to exhibit high activity without using a large amount of a metal catalyst made of a noble metal such as platinum, effectively preventing side reactions in the reduction reaction, and extremely high polychlorinated alkanes. It shows the effect that it can be converted into useful substances such as chloroform with selectivity.

  Therefore, the reduction catalyst of the present invention exhibits an excellent effect in producing a useful substance such as chloroform from an environmentally hazardous substance such as carbon tetrachloride under an economically advantageous condition on an industrial scale.

  Moreover, according to the method for producing a reducing catalyst of the present invention, the reducing catalyst can be produced by an extremely simple method, which is suitable for industrial implementation.

  In the present invention, well-known porous carrier particles constituting the reduction catalyst are used without particular limitation. In the reaction targeted by the present invention, diffusion in the pores and surface diffusion in the pores react. Therefore, porous carrier particles having an average pore diameter of about 50 to 500 μm are preferable. Specifically, particles made of a porous inorganic oxide such as alumina, silica, titania and zirconia are preferably used. In particular, it is preferable to use titania that interacts with hydrogen on the inner surface of the support pores in order to suppress side reactions and improve the selectivity of the reaction.

  In the present invention, the porous carrier particles preferably have an average diameter of 1.5 mm or more, particularly 1.5 mm to 20 mm. That is, in general, the catalyst for reducing polychlorinated alkanes is often used in a fixed bed. When a particle size smaller than the average diameter is used, the liquid resistance is remarkably increased, and it must be used industrially. It becomes difficult.

  Further, the shape of the porous carrier particles is preferably a spherical shape in order to allow the catalytic metal to be uniformly supported on the surface layer of the carrier so that the reduction reaction proceeds efficiently. A shape or an irregular shape can be used.

  In the present invention, as the catalyst metal, at least one metal selected from Group 8 elements, Group 9 elements and Group 10 elements of the periodic table such as platinum, palladium, ruthenium, rhodium, etc. can be used. It is preferable to use platinum in terms of catalyst activity and catalyst deterioration rate.

  A feature of the present invention resides in that the catalyst metal support layer is formed on the surface layer of the porous carrier particles. That is, the catalyst metal is mainly present in the surface layer portion of the porous carrier particles, and is not present inside the porous carrier particles or is extremely small even if present.

  By adopting such a configuration, the amount of catalyst metal can be reduced while maintaining the activity of the reduction catalyst high, and it becomes possible to prepare the catalyst economically, and in the reduction reaction of polychlorinated alkanes. Side reactions can be extremely effectively prevented, and the selectivity of the desired low-order chlorinated alkane can be significantly increased.

  Although the mechanism by which such an excellent effect is exhibited by the above-described configuration of the present invention is not clear, the present inventors presume as follows.

  That is, the catalytic metal present in the deep catalyst layer has a negative effect such as promoting the progress of side reactions such as the formation reaction of high-boiling compounds such as hexachloroethane by inhibiting the diffusion of hydrogen. In the reduction catalyst of the invention, since the catalyst is present only in the surface layer portion, the absence of such catalyst deep layer portion suppresses side reactions and exhibits high selectivity. Furthermore, the reaction rate and selectivity can be easily controlled by providing the inner layer portion with a portion where the catalyst metal is not supported as compared with the case where it is supported on the whole.

  In the present invention, when the thickness of the catalyst metal support layer formed on the surface layer portion of the porous carrier particles is specifically shown, when using the porous carrier particles having an average diameter of 1.5 mm or more, In order to prevent the said side reaction effectively, forming so that it may become 0.5 mm or less is preferable.

  Further, the lower limit of the thickness (t) of the support layer is preferably 0.1 d or more with respect to the average diameter (d) of the porous carrier particles in order to sufficiently exhibit the activity of the catalyst.

  Further, the supported amount of the catalyst metal can be used in the range of 0.01 to 2.0 parts by weight with respect to 100 parts by weight of the porous carrier particles. The amount is preferably 0.5 parts by weight.

  In this case, the metal concentration in the non-supported portion present inside the support layer is preferably 0.05% by weight or less of the total amount of metal supported.

  In the present invention, the method for producing the reduction catalyst described above is not particularly limited, but as a preferred production method, the catalyst metal soluble salt aqueous solution is sprayed on the surface of the porous carrier particles and then dried. Next, a reduction treatment method is exemplified.

  That is, in the production method described above, the porous carrier particles are not immersed in the soluble salt aqueous solution of the catalyst metal and impregnated deeply into the pores, but are adhered only to the surface by an operation of spraying. A catalytic metal supporting layer can be formed only on the surface layer portion of the porous carrier particles by reduction.

  The concentration of the soluble salt aqueous solution to be sprayed is not particularly limited, and the amount of liquid to be sprayed is not particularly limited, but is 50 to 100 parts by weight with respect to 100 parts by weight of the porous carrier particles in order to be supported on the surface layer part accurately. Is preferable.

  In addition, spraying is performed by spraying the soluble salt aqueous solution as a mist having a size of about 50 to 500 μm using a known spraying device, and contacting the mist while stirring or fluidizing the porous carrier particles. Is preferred. Further, at that time, it is preferable to adjust the spray amount so that the surface of the porous carrier particles is not wetted and aggregated by the sprayed soluble salt aqueous solution.

  In the above method, the porous carrier particles sprayed with a predetermined amount of the soluble salt aqueous solution are dried. The drying method is not particularly limited, but a normal method such as a drying furnace or microwave can be adopted without any problem.

  The drying time varies depending on the heating means, but is appropriately determined so that the water in the soluble salt aqueous solution can be almost removed. Generally, the drying time is 5 to 180 minutes.

  In the method for producing the reduction catalyst, it is preferable to perform a reduction treatment after the drying or simultaneously with the drying in order to obtain stable characteristics and suppress the deterioration rate. The reduction can be performed by bringing porous carrier particles, to which a known reducing agent and a soluble salt aqueous solution are attached, into contact with the reducing agent. Examples of the reducing agent include hydrogen, hydrazine, formaldehyde, sodium borohydride and the like. The contact is appropriately selected depending on the form of the reducing agent. For example, a method of reducing in a liquid phase, a method of reducing in a gas phase with hydrogen, and the like can be applied.

  The reduction treatment is preferably carried out so that most of the salt in the soluble salt aqueous solution is metallized.

  In the above-described method for producing a reduction catalyst, the thickness of the catalyst metal support layer in the obtained reduction catalyst can be controlled by adjusting the spray amount, concentration, etc. of the soluble salt aqueous solution. That is, if the spray amount is increased, the thickness of the support layer tends to increase, and if the concentration is increased, penetration can be prevented by increasing the viscosity, and the thickness of the support layer can be reduced.

  Further, the amount of all catalyst metals supported can be controlled by appropriately adjusting each variable element in adjusting the thickness of the support layer.

  The present invention also provides a method for producing a low-order chlorinated alkane using the above-described reduction catalyst.

  That is, the present invention provides a method of reacting polychlorinated alkane with hydrogen in the presence of the reducing catalyst in a liquid phase.

  By carrying out the above reaction in the liquid phase, it is possible to stably control the product selectivity and the reaction rate.

  Further, polychlorinated alkanes may be used as they are to constitute a liquid phase, or may be diluted with an appropriate solvent to constitute a liquid phase. For example, when hydrogenating and reducing carbon tetrachloride to chloroform, carbon tetrachloride can be diluted with dichloromethane, chloroform, or the like. Further, the concentration to be diluted is not particularly limited. However, since the reaction is an exothermic reaction, it is desirable to dilute it for the purpose of controlling the calorific value. It is preferable to dilute to a weight percent.

  Further, the water in the reaction solution and the diluting solvent is preferably 20 ppm by weight or less in order to be adsorbed in the catalyst carrier pores and reduce the catalyst performance.

  Furthermore, the support on which the catalyst metal is supported is preferably used as a fixed bed in the liquid phase reaction, and the product selectivity, the reaction rate, and the like can be controlled by changing the supply amount of the reaction liquid.

  On the other hand, the temperature of the reduction reaction may be appropriately determined in the range from room temperature to 200 ° C., but the side reaction is promoted in a high temperature region. Accordingly, a reaction temperature of 80 ° C. to 95 ° C. is suitable for efficiently proceeding the hydrogenation reduction.

  Further, the reaction pressure is not particularly limited at normal pressure or higher, but a pressurized system is preferable because the higher the pressure, the higher the hydrogen solubility in the liquid phase and the reaction rate increases. Specifically, a pressure of about 0.5 to 2.0 MPa is preferable.

Example 1
100 ml of gamma alumina (average diameter d = 2.0 mm) as a carrier was uniformly sprayed with 60 ml of a chloroplatinic acid aqueous solution having a platinum content of 0.25% by weight of the carrier. After drying at 110 ° C. for 60 minutes, the mixture was heated to 300 ° C. and subjected to reduction treatment using hydrogen in the gas phase for 3 hours.

  The cross section of the obtained catalyst particles was observed with an electron beam probe microanalyzer (EPMA), and the distribution of platinum was examined. Table 1 shows t and t / d.

  35 g of the reducing catalyst prepared by the above method was put into a SUS316 tube having an inner diameter of 7.26 mm to prepare a fixed bed reactor. Carbon tetrachloride was continuously supplied from the upper part of the reactor at a constant flow rate using a metering pump, then hydrogen was supplied in a gas phase, and the reaction was allowed to pass through a reduction catalyst in a fixed bed. The water content in carbon tetrachloride used for the reaction was removed to 15 ppm or less. Hydrogen was continuously supplied at a ratio of 10 mol per 1 mol of carbon tetrachloride.

  The temperature inside the reactor was kept at 90 ° C., and the pressure inside the reactor was kept at 0.5 MPa · G. As for the products, the products obtained from the outlet of the fixed bed reactor were subjected to gas-liquid separation and analyzed using gas chromatography.

  The product was confirmed to be chloroform, hexachloroethane, and methane. Table 2 shows the carbon tetrachloride conversion rate, chloroform selectivity, hexachloroethane selectivity, and methane selectivity in one pass between 1 hour and 2 hours after the start of the reaction.

Comparative Example 1
100 g of gamma alumina (average diameter d = 2.0 mm) as a carrier was added to 60 ml of a chloroplatinic acid aqueous solution containing 0.25% by weight of platinum in the amount of platinum and gently stirred to carry platinum. After drying at 110 ° C. for 60 minutes, the mixture was heated to 300 ° C. and subjected to reduction treatment using hydrogen in the gas phase for 3 hours.

  The cross section of the obtained catalyst particles was observed with an electron beam probe microanalyzer (EPMA), and the distribution of platinum was examined. Table 1 shows t and t / d.

  The reaction was performed and analyzed in the same manner as in Example 1 except that the catalyst prepared by the above method was used as the reducing catalyst. The product was confirmed to be chloroform, hexachloroethane, and methane. Table 2 shows the carbon tetrachloride conversion rate, chloroform selectivity, hexachloroethane selectivity, and methane selectivity in one pass between 1 hour and 2 hours after the start of the reaction.

Example 2
100 g of gamma alumina (average diameter d = 2.0 mm) as a carrier was uniformly sprayed with 100 ml of a chloroplatinic acid aqueous solution having a platinum content of 0.25% by weight of the carrier. After drying at 110 ° C. for 60 minutes, the mixture was heated to 300 ° C. and subjected to reduction treatment using hydrogen in the gas phase for 3 hours.
The cross section of the obtained catalyst particles was observed with an electron beam probe microanalyzer (EPMA), and the distribution of platinum was examined. Table 1 shows t and t / d.

  The reaction was performed and analyzed in the same manner as in Example 1 except that the catalyst prepared by the above method was used as the reducing catalyst. The product was confirmed to be chloroform, hexachloroethane, and methane. Table 2 shows the carbon tetrachloride conversion rate, chloroform selectivity, hexachloroethane selectivity, and methane selectivity in one pass between 1 hour and 2 hours after the start of the reaction.

Example 3
100 g of gamma alumina (average diameter d = 2.0 mm) as a carrier was uniformly sprayed with 60 ml of a chloroplatinic acid aqueous solution having a platinum content of 2.0% by weight of the carrier. After drying at 110 ° C. for 60 minutes, the mixture was heated to 300 ° C. and subjected to reduction treatment using hydrogen in the gas phase for 3 hours.
The cross section of the obtained catalyst particles was observed with an electron beam probe microanalyzer (EPMA), and the distribution of platinum was examined. Table 1 shows t and t / d.

  The reaction was performed and analyzed in the same manner as in Example 1 except that the catalyst prepared by the above method was used as the reducing catalyst. The product was confirmed to be chloroform, hexachloroethane, and methane. Table 2 shows the carbon tetrachloride conversion rate, chloroform selectivity, hexachloroethane selectivity, and methane selectivity in one pass between 1 hour and 2 hours after the start of the reaction.

Example 4
100 ml of titania (average diameter d = 2.0 mm) as a carrier was uniformly sprayed with 60 ml of an aqueous chloroplatinic acid solution having a platinum content of 0.25% by weight of the carrier. After drying at 110 ° C. for 60 minutes, the mixture was heated to 300 ° C. and subjected to reduction treatment using hydrogen in the gas phase for 3 hours.
The cross section of the obtained catalyst particles was observed with an electron beam probe microanalyzer (EPMA), and the distribution of platinum was examined. Table 1 shows t and t / d.

  The reaction was performed and analyzed in the same manner as in Example 1 except that the catalyst prepared by the above method was used as the reducing catalyst. The product was confirmed to be chloroform, hexachloroethane, and methane. Table 1 shows the carbon tetrachloride conversion rate, chloroform selectivity, hexachloroethane selectivity, and methane selectivity in one pass between 1 hour and 2 hours after the start of the reaction.

Comparative Example 2
100 g of titania (average diameter d = 2.0 mm) as a carrier was added to 60 ml of a chloroplatinic acid aqueous solution containing 0.25% by weight of the platinum, and the platinum was supported by gently stirring. After drying at 110 ° C. for 60 minutes, the mixture was heated to 300 ° C. and subjected to reduction treatment using hydrogen in the gas phase for 3 hours.

  The cross section of the obtained catalyst particles was observed with an electron beam probe microanalyzer (EPMA), and the distribution of platinum was examined. Table 1 shows t and t / d.

  The reaction was performed and analyzed in the same manner as in Example 1 except that the catalyst prepared by the above method was used as the reducing catalyst. The product was confirmed to be chloroform, hexachloroethane, and methane. Table 2 shows the carbon tetrachloride conversion rate, chloroform selectivity, hexachloroethane selectivity, and methane selectivity in one pass between 1 hour and 2 hours after the start of the reaction.

Example 5
100 ml of titania (average diameter d = 2.0 mm) as a carrier was uniformly sprayed with 100 ml of a chloroplatinic acid aqueous solution containing 0.25% by weight of the platinum. After drying at 110 ° C. for 60 minutes, the mixture was heated to 300 ° C. and subjected to reduction treatment using hydrogen in the gas phase for 3 hours.
The cross section of the obtained catalyst particles was observed with an electron beam probe microanalyzer (EPMA), and the distribution of platinum was examined. Table 1 shows t and t / d.

  The reaction was performed and analyzed in the same manner as in Example 1 except that the catalyst prepared by the above method was used as the reducing catalyst. The product was confirmed to be chloroform, hexachloroethane, and methane. Table 2 shows the carbon tetrachloride conversion rate, chloroform selectivity, hexachloroethane selectivity, and methane selectivity in one pass between 1 hour and 2 hours after the start of the reaction.

Example 6
100 ml of zirconia (average diameter d = 2.0 mm) as a carrier was uniformly sprayed with 60 ml of a chloroplatinic acid aqueous solution containing 0.25% by weight of the platinum. After drying at 110 ° C. for 60 minutes, the mixture was heated to 300 ° C. and subjected to reduction treatment using hydrogen in the gas phase for 3 hours.
The cross section of the obtained catalyst particles was observed with an electron beam probe microanalyzer (EPMA) to examine the distribution of platinum. Table 1 shows t and t / d.

  The reaction was performed and analyzed in the same manner as in Example 1 except that the catalyst prepared by the above method was used as the reducing catalyst. The product was confirmed to be chloroform, hexachloroethane, and methane. Table 2 shows the carbon tetrachloride conversion rate, chloroform selectivity, hexachloroethane selectivity, and methane selectivity in one pass between 1 hour and 2 hours after the start of the reaction.

Example 7
To 100 g of silica (average diameter d = 2.0 mm) as a carrier, 60 ml of a chloroplatinic acid aqueous solution containing 0.25% by weight of the platinum was uniformly sprayed. After drying at 110 ° C. for 60 minutes, the mixture was heated to 300 ° C. and subjected to reduction treatment using hydrogen in the gas phase for 3 hours.

  The cross section of the obtained catalyst particles was observed with an electron beam probe microanalyzer (EPMA), and the distribution of platinum was examined. Table 1 shows t and t / d.

  The reaction was performed and analyzed in the same manner as in Example 1 except that the catalyst prepared by the above method was used as the reducing catalyst. The product was confirmed to be chloroform, hexachloroethane, and methane. Table 2 shows the carbon tetrachloride conversion rate, chloroform selectivity, hexachloroethane selectivity, and methane selectivity in one pass between 1 hour and 2 hours after the start of the reaction.

Claims (8)

  A catalyst in which at least one catalyst metal selected from Group 8 element, Group 9 element and Group 10 element of the periodic table is supported on porous support particles, and the catalyst is formed on the surface layer of the porous support particles. A catalyst for reducing polychlorinated alkanes, wherein a metal support layer is formed.   The average diameter of the porous carrier particles is 1.5 mm or more, and the thickness of the support layer formed on the surface layer portion of the porous carrier particles is in the range of 0.5 mm or less. Catalyst for reduction.   The reduction catalyst according to claim 1 or 2, wherein the ratio of the catalyst metal present inside the support layer in the surface layer portion of the porous carrier particles is 0.1% by weight or less of the total amount of the catalyst metal supported.   The catalyst for reduction according to any one of claims 1 to 3, wherein the porous carrier particles are titania.   The catalyst for reduction according to any one of claims 1 to 4, wherein the amount of the catalyst metal supported is 0.01 to 2.0 parts by weight with respect to 100 parts by weight of the porous carrier.   Polychlorine characterized by spraying a soluble salt aqueous solution of at least one metal selected from Group 8, Group 9 and Group 10 elements on the surface of the porous carrier, drying, and then reducing treatment Of producing a catalyst for reducing alkane fluoride.   The method according to claim 7, wherein the amount of the metal soluble salt aqueous solution with respect to the porous carrier particles is 50 to 100 parts by weight with respect to 100 parts by weight of the carrier. A method for producing a low-order chlorinated alkane, comprising reacting a polychlorinated alkane and hydrogen in the liquid phase in the presence of the reducing catalyst according to any one of claims 1 to 8.