JPH0361497B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for regenerating a supported platinum group metal catalyst used for steam reforming, hydrogenolysis, or partial combustion of hydrocarbons. The above catalysts usually contain ruthenium and oxide supports such as alumina, magnesia, zirconia, and titania.
It is constructed by supporting one or more of rhodium, palladium, osmium, iridium, and platinum as a catalyst component. In some cases, one or more compounds of chromium, molybdenum, and tungsten are also supported as catalyst components. As is well known, such catalysts (hereinafter simply referred to as platinum group metal catalysts) are very expensive, so when used on an industrial scale, it is necessary to regenerate the catalysts whose activity has decreased.
Repeated use is absolutely necessary. Conventionally, methods for regenerating platinum group metal catalysts using hydrogen, steam, oxygen, etc. are known. However, these conventional regeneration methods have a serious drawback in that, although poisonous substances adhering to the catalyst surface are relatively well removed, the catalyst activity is not sufficiently restored. As a result of extensive research into methods for regenerating platinum group metal catalysts, the present inventor discovered an aqueous solution of hydroxides, carbonates, nitrates, and sulfates (hereinafter referred to as inorganic alkalis) of alkali metals and alkaline earth metals. We have previously discovered that a two-step treatment using an aqueous solution of hydrazine, formaldehyde and sodium borohydride is extremely effective for regenerating platinum group metals (Japanese Patent Publication No. 56-25190). However, in the method of this prior invention, the damage to the catalyst during the regeneration process can reach as much as 10% by weight, and it has been found that there is room for improvement. It has also been found that the method of the prior invention cannot be applied as is in order to simultaneously regenerate catalysts of the same or different types with different reaction histories. Therefore,
As a result of further research, the present inventor discovered that the platinum group metal catalyst was housed in a mesh-structured container, and the catalyst was restrained and held so as not to flow, and the first and second stages were carried out in the same manner as in the method of the prior invention. It has been found that when regeneration treatment consisting of stage treatment is performed, not only damage to the catalyst is prevented, but also the degree of catalyst activity recovery by regeneration is significantly improved. Furthermore, catalysts of the same type or different types with different reaction histories are housed in a plurality of mesh-structured containers and regenerated, and the catalysts that have recovered a predetermined activity are sequentially recovered, and the catalysts that have recovered a predetermined activity are collected in sequence. It has been found that when the same regeneration treatment as described above is subsequently performed for catalysts that have not reached the desired level, it is possible to regenerate catalysts of the same type or different types with different reaction histories in parallel. That is, the present invention provides the following method for regenerating a catalyst: When cleaning and regenerating a supported platinum group metal catalyst for steam reforming, hydrogenolysis, or partial combustion of hydrocarbons, a cleaning liquid is used. Catalysts with different reaction histories are housed in multiple containers with a network structure that can be circulated, and each catalyst is held in a restrained state. After treatment with an aqueous solution of at least one salt and then with an aqueous solution of () hydrazine, formaldehyde or sodium borohydride, recovering the catalyst which has recovered the desired activity and which does not lead to recovery of the desired activity. A method for regenerating a catalyst, comprising further treating the catalyst by the method described above. Generally, when a platinum group metal catalyst is used for steam reforming, hydrogenolysis, or partial combustion of hydrocarbons, precipitation of carbonaceous substances, adhesion of sulfur compounds contained in the hydrocarbons, and particle coarsening due to sintering of the catalyst metal occur. (i.e., a decrease in dispersibility), the activity of the catalyst gradually decreases due to factors such as changes in the chemical properties of the catalyst metal. In particular, the latter cause, such as a change in the chemical properties of the catalytic metal, cannot be clearly detected with current analytical techniques and is not yet fully understood, but it may be the same as or more than the cause of the former cause. It is assumed that this is a factor. However, according to the method of the present invention, these factors that reduce the catalyst activity are removed, and the activity of the platinum group metal catalyst is recovered to the extent that it can be reused. The activity is restored. The processing agent used in the first stage treatment of the present invention is:
alkali metal and alkaline earth metal hydroxides,
They are carbonates, nitrates, and sulfates, and are used in the form of an aqueous solution containing at least one of these. The concentration as an aqueous solution is the amount of supported catalytic metal,
Although it may vary depending on the degree of reduction in catalyst activity (particularly the amount of attached poisonous substance and the degree of reduction in dispersibility), the temperature and pressure conditions during regeneration, etc., it is usually in the range of 0.001 to 10N, more preferably 0.001 to 5N. As stipulated.
If the concentration is too low, it will be necessary to lengthen the treatment time, make the temperature and pressure conditions significantly harsher, or perform treatment under harsher conditions with an aqueous solution such as hydrazine used in conjunction with the main treatment. On the other hand, if the concentration is too high, the support itself will begin to dissolve. Therefore, it is preferable to select at least one of the inorganic alkalis and use it within the above concentration range. In the treatment, a platinum group metal catalyst with reduced activity is placed in a container with a mesh structure that restrains and holds the catalyst so that it does not flow, but does not impede the flow of the treated aqueous solution. This is done by passing the In the present invention, it is not necessary to carry out the treatment with an inorganic alkali aqueous solution under severe conditions of high pressure and high temperature, except in cases where the degree of reduction in catalyst activity is severe. The concentration of hydrazine, formaldehyde or sodium borohydride used in the second stage treatment of the present invention as an aqueous solution depends on the amount of supported catalyst metal,
Although it may vary depending on the degree of reduction in catalyst activity, temperature during treatment, etc., it is usually sufficient if it is 0.01% by weight or more. If the concentration is too low, the final regeneration effect will not be sufficiently pronounced; on the other hand, as the concentration increases, the regeneration effect will gradually increase, but even beyond 10% by weight, the regeneration effect will become even more pronounced. Almost no improvement is observed. As in the case of the first stage treatment, this treatment is also carried out by passing an aqueous solution of hydrazine, formaldehyde, or sodium borohydride through a container with a network structure that restrains and holds the catalyst to be regenerated. Although the temperature of the aqueous solution is not particularly prerequisite, if the temperature is too high, there is a risk that hydrazine and the like will decompose. The pressure during this treatment may be atmospheric pressure, and there is no particular need to pressurize it, but there will be no disadvantages even if it is carried out under pressure. In the present invention, the catalyst after the first stage treatment is
The catalyst is subjected to the second stage treatment either as it is or after being washed and dried as necessary, and the catalyst that has completed the second stage treatment can be reused after being washed and dried. FIG. 1 shows an example of an apparatus for regenerating a catalyst according to the present invention. The catalyst to be regenerated is stored in a plurality of containers in the regeneration processing device 1, each of which has a mesh structure at least on its upper and lower surfaces; in the illustrated device, three containers 3a;
3b and 3c. Since a plurality of containers are used, catalysts of the same type or different types having different reaction histories can be housed in separate containers and processed according to the required time. The regeneration processing apparatus 1 is supplied with an inorganic alkali aqueous solution through a line 7, a pump 9, and a line 11 from a tank 5 containing an inorganic alkali aqueous solution used in the first stage treatment. The catalysts in the containers 3a, 3b, and 3c are held so that they do not flow even when the aqueous solution passes through the containers, so that the catalyst particles collide with each other due to free flow or crack due to collision with the wall surface. Such damage is substantially prevented. container 3
The inorganic alkali aqueous solution that has passed through a, 3b, 3c and the regeneration processing device 1 is transferred from the line 13 to the tank 5.
is circulated. When the aqueous solution is consumed and reduced, a predetermined amount is replenished from the hopper 15. The second stage treatment of the present invention may be carried out using other equipment similar to that used in the first stage treatment, or an aqueous solution of hydrazine or the like may be used in place of the inorganic alkali aqueous solution used in the first stage treatment. Since this may be performed using the same device as above, detailed explanation will be omitted. In the embodiment shown in FIG. 1, it is most preferable that the aqueous solution flows from the bottom to the top of the regeneration processing apparatus 1, but it is also possible to flow from the top to the bottom. Among a plurality of types of catalysts having different reaction histories stored separately in a plurality of containers, those whose catalytic activity has been recovered to a predetermined level by the treatment of the present invention are sequentially recovered from the containers. Catalysts that have not yet regained the desired activity are subsequently subjected to similar treatment. At this time, the container emptied by the recovery of the catalyst may contain a new catalyst whose activity is to be restored. According to the method of the present invention, the following remarkable effects are achieved. () Damage to the catalyst during storage and removal during regeneration treatment is prevented. () Catalytic activity is largely restored by removing poisonous substances. () Since the catalyst is not damaged by free flow, the inflow speed of the regenerated treatment liquid can be greatly increased. Therefore, the regeneration effect is further enhanced and the recovery of catalyst activity becomes even more remarkable. () With the catalyst housed in a mesh container,
Since they are handled all at once, the regeneration processing operation is extremely simplified. () When using a plurality of containers with a network structure, the same type of catalyst having different reaction histories or two or more types of different types of catalysts can be regenerated simultaneously depending on the required time. () Since there is no free flow of catalyst, uneven regeneration due to uneven flow is prevented. Reference Example 1 Catalyst (referred to as A:
Specific surface area = 43m ² /g-Ru, amount of catalyst required for reaction = 110
ml) was charged into a reactor with a diameter of 1 cm, and naphtha with a sulfur content of 2 ppm (final boiling point: 220°C) and steam were supplied, and continuous steam reforming was performed for 750 hours under the conditions shown in Table 1 below. Ta. The catalyst at this point is designated as B (specific surface area=21 m ² /g-Ru). Table 1 Reactor temperature Inlet 510℃ Outlet 518℃ Space velocity 2000/hr Steam/hydrocarbon ratio 1.9 (number of oxygen atoms per carbon atom in the feedstock) Pressure 13 atm (absolute) Reference example 2 Diameter of 4 mm Catalyst with 3.8% by weight of ruthenium supported on spherical alumina (referred to as C: specific surface area = 43
m ² /g-Ru, amount of catalyst required for reaction = 91 ml) was filled into a 1 inch diameter reactor, and continuous steam reforming was carried out for 750 hours under the same conditions as in Reference Example 1. The catalyst at this point is D (specific surface area = 20
m ² /g-Ru). Reference example 3 Catalyst in which 1.5% by weight of ruthenium and 0.1% by weight of chromium oxide are supported on spherical alumina with a diameter of 4 mm (denoted as E: specific surface area = 43 m ² /g-Ru, amount of catalyst required for reaction = 51 ml) 290 ml with a diameter of 1 An inch-inch reactor was filled, methane and air were supplied, and a continuous partial combustion reaction was carried out for 500 hours under the conditions shown in Table 2 below. The catalyst at this point is F (specific surface area = 17 m ² /
g-Ru). Table 2 Reactor temperature Inlet 310℃ Outlet 700℃ Space velocity 17500/hr Air/methane ratio 2.37 (mole ratio) Pressure 1 atm (absolute) Example 1 Catalysts B, D and F is a mesh-structured container 3 of an apparatus of the type shown in FIG.
a, 3b and 3c respectively, and the following third
After carrying out the first stage treatment and second stage treatment twice under the conditions shown in the table, containers 3a and 3b containing catalysts B and D, respectively, were removed from the apparatus, and only catalyst F contained in container 3c was removed. The sample was subjected to the first stage treatment and second stage treatment two more times. The mesh-structured container had a diameter of 5 cm, a height of 17 cm, and a mesh size of 10 meshes on the top and bottom surfaces. Table 3 1st stage treatment Regenerant 0.375N-NaOH Temperature (℃) 100 Pressure (ata) 1.0 Time (hr) 3.0 Circulation speed (cm/sec) 5.0 Post-treatment 2 hours at 100℃ After washing with water 16 hours at 100℃ Second stage drying treatment Regenerant 0.4% hydrazine Temperature (°C) 20 Pressure (ata) 1.0 Time (hr) 3.0 Circulation speed (cm/sec) 5.0 Post-treatment After washing with water at 75°C for 3 hours Drying at 100°C for 16 hours Each catalyst The results after the regeneration process are shown in Table 4.

[Table] From the results shown in Table 4, it is clear that the excellent effect of the method of the present invention in which catalysts with different reaction histories are simultaneously regenerated is treated.

[Brief explanation of drawings]

FIG. 1 shows an example of an apparatus used in the catalyst regeneration method according to the present invention. DESCRIPTION OF SYMBOLS 1... Regeneration processing device, 3a, 3b, 3c... Container with a mesh structure on the upper and lower surfaces, 5... Regeneration processing liquid tank, 9... Pump, 15... Regeneration processing liquid hopper.

Claims (1)

[Claims] 1. When cleaning and regenerating supported platinum group metal catalysts for hydrocarbon steam reforming, hydrogen cracking, or partial combustion, catalysts with different reaction histories are placed in multiple containers with a network structure that allows the cleaning liquid to flow through them. treated with an aqueous solution of at least one of alkali metal and alkaline earth metal hydroxides, carbonates, nitrates and sulfates, and then () treated with hydrazine, formaldehyde or A method for regenerating a catalyst, which comprises recovering the catalyst that has recovered a predetermined activity after being treated with an aqueous solution of sodium borohydride, and further treating the catalyst that has not recovered the predetermined activity using the above method. .