CA1301965C - Method for treatment of waste water - Google Patents
Method for treatment of waste waterInfo
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- CA1301965C CA1301965C CA000544862A CA544862A CA1301965C CA 1301965 C CA1301965 C CA 1301965C CA 000544862 A CA000544862 A CA 000544862A CA 544862 A CA544862 A CA 544862A CA 1301965 C CA1301965 C CA 1301965C
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Abstract
ABSTRACT OF THE DISCLOSURE
Efficient treatment of waste water is accomplished by subjecting the waste water to wet oxidation under continued supply of an oxygen containing gas at a temperature of not more than 370°C under pressure enough for the waste water to retain the liquid phase thereof intact, in the presence of a catalyst (excluding a molded monolithic catalyst having plural through holes) containing a composite oxide of at least two metals selected from the group consisting of Ti, Si, and Zr and at least one metal selected from the group consisting of Mn, Fe, Co, Ni, W, Cu, Ce, Ag, Pt, Pd, Rh, Ru, and Ir or a compound of the one metal mentioned above.
Efficient treatment of waste water is accomplished by subjecting the waste water to wet oxidation under continued supply of an oxygen containing gas at a temperature of not more than 370°C under pressure enough for the waste water to retain the liquid phase thereof intact, in the presence of a catalyst (excluding a molded monolithic catalyst having plural through holes) containing a composite oxide of at least two metals selected from the group consisting of Ti, Si, and Zr and at least one metal selected from the group consisting of Mn, Fe, Co, Ni, W, Cu, Ce, Ag, Pt, Pd, Rh, Ru, and Ir or a compound of the one metal mentioned above.
Description
MET~OD FOR TREATMENT OF WASTE WATER
BACKGROUND OF THE INVENTION
Field of the Invention:
This invention relates to a method for the treatment of waste water. Particularly, it relates to a method for effecting wet oxidation of waste water containing a substance of chemical oxygen demand (hereinafter referred to as "COD component") in the presence of a catalyst. More particularly, it relates to a method for effectively detoxifying waste water containing a COD component, i.e. a harm~ul oxidizable organic or inorganic substance, by subjecting the waste water to catalytically wet oxidation in the presence of molecular ox~gen theraby converting the harm~ul substance into such harmless compounds as carbon dioxide, water, and nitrogen.
Description of the Prior Art:
Among the conventional means available for the treatment of waste water, there are counted a biochemical method called an activated sludge method and a wet oxidatio~ method called a Zimmerman method.
As widely lcnown, the activated sludge method consumes much time in the decomposition of organic matter and, moreover, requires the waste water to be diluted to a concentration suitable ~or the of algae and bacteria and, there~ore, has a disadvantage that the ground area for installation of facilities for the activated sludge treatment is very large. Further in r~cent years, particularly in the urban districts, the disposal of grown excess sludge has been entailing a huge expense. The Zimmerman method consists in effecting oxidative decomposition of organic matter contained in a high concentration in an aqueous solution by introducing air under a pressure in the range of 16 to 200 atmospheres at a temperature in the range of 200 to 370C into the `~
~30~6S
aqueous solution. This method requires the use of a large reactor because the reaction proceeds slowly and the decomposition consumes much time. Further, the reactor itself requires the material thereof to possess high durability. Thus, this method is not economically advantageous because of high cost of equipment and high cost of operation. In connection with this method, it has been proposed to use various o~idative catalysts aimed at accelerating the reaction velocity.
Among the catalysts heretofore used popularly in the catalytically wet oxidation method, there are counted compounds of such noble metals as palladium and platinum (Japanese Patent Laid-Open SHO 49(1974)-44,556) and compounds of such heavy metals as cobalt and iron (Japanese Patent Laid-Open SHO 49(1974)-94,157). They are catalysts which have the compounds deposited on spherical or cylindrical carriers of alumina, silica-alumina, silica gel, and activated carbon. More often than not, in the catalytically wet oxidation of waste water, these catalysts are put to use in the reaction at a pH value of not less than 9. In our experiment, the catalysts, in the course of their protracted use, have been found to suffer from loss of s~rength and disinte~ration of individual particles and, in an extreme case, entail dissolution of their carrier.
In an effort to solve this problem, there have been recently proposed methods for reinforcing the catalysts by using titania or zirconia as a carrier therefor (Japanese Patent Laid-Open SHO 58~1983)-64,188 and SHO 59(1984)-19757). To be specific, these inventions disclose catalysts which have compounds of such noble metals as palladium and platinum or compounds of such heavy metals as iron and cobalt deposited on spherical or cylindrical carrier particles of titania or zirconia. By experiment, the carriers are certainly found to possess greater strength than the conventional carriers. These catalysts, however, are invariably in a particulate form.
~3~)19~
Moreover, they are not fully satisfactory in terms of catalytlc acti~ity and durability.
Incidentally, when the waste water is subjected to wet oxidation, there inevitably arises the necessity of disposing of a large volume of water. As regards the manner of reaction, therefore, the method of using a fixed bed in a system designed for flow of waste water is frequently adopted. Mor~over, numerous samples of waste water contain solid substances. If, in any of these cases, a given catalyst is in a particulate form, since the flow of the waste water induces heavy loss of pressure, the waste water cannot be treated at a high linear velocity and the current of this waste water must be given a large cross section. In the treatment of waste water entraining a solid substance, since the solid substance clogs the fixed bed of catalyst even to an extent of increasing the resistance which the fixed bed of catalyst offers against the flow of waste water, this treatment entails a disadvantage that the running cost is increased and the apparatus for treatment cannot be operated continuously for a long time. In the treatment of waste water by the catalytically wet oxidation method using such particulate shaped catalyst, since the reaction is carried out at an e.levated temperature under a high pressure and the ground area occupied by the reactor must be proportionately large, the cost of equipment is huge. The high cost of equipment constitutes a critical problem.
As regards the life of the catalyst, the particulate catalyst has a disadvantage that by mutual contact of the particles, the catalyst is comminuted by friction and disintegration. For the purpose of diminishing the loss of pressure due to the catalyst bed, there has been proposed a fluidized-bed method which comprises fluidizing a catalyst in a powdery form in a current of waste water. This method, however, has not yet been adopted for actual use because the catalyst by nature is diluted and the reactor used for the treatment, ~.~
13C~6~ii therefore, must possess a huge capacity and the separation of the catalyst from the treated waste water is very difficult.
There are also methods which effect oxidative decomposition of organic matter in waste water at normal room temperature under normal atmospheric pressure by using ozone or hydrogen peroxide as an oxidizing agent.
Japanese Patent Laid-Open SHO 58(1983)-55,088, for example, discloses a method which effects oxidative decomposition of such organic substances as fumic acid contained in waste water by treating this waste 2water with ozone and hydrogen peroxide at 20C under normal atmospheric pressure in the absence of a catalyst. Japanese Patent Publication SHO
58(1983)-37,039 discloses a method which effects oxidative decomposition of an aromatic ring-containing organic compound contained in waste water by adding a surfactant to the waste water, further adding thereto at least one member selected from the group consisting of transient metal compounds and alkaline earth metal compounds, and then exposing the resultant mixture to ozone at normal room temperature under normal atmospheric pressure. Since the former method efEects the treatment in the absence of a catalyst, it is incapable of effectively treating sparingly oxidizable substances suspended in waste water. Since the latter method uses the metal ion such as that of a transient metal or alkaline earth metal as a catalyst, it is required to recover the metal ion contained in the treated waste water before this treated waste water is released into a nearby body of running water. It has a disadvantage that it inevitably requires an extra step of aftertreatment. Further, since both these methods require the treatments for waste water to be carried out at normal room temperature under normal atmospheric pressure, the~
have a disadvantage that they call for supply of a large volume of expensive ozone, their reactions proceed at a low rate, their ratios of decomposition of organic matter are li..~,~l) 13~
low, and the treated waste water require a treatment for detoxification because the unaltered ozone leaks in the treated water.
An object of an aspect of the present invention, therefore, is to provide a method for efficient and long continuous treatment of waste water.
An object of an aspect of this invention is to provide a method for enabling the treatment of waste water to be carried out efficiently in a high linear velocity.
~n object of an aspect of this invention is to provide a method for enabling waste water containing solid substances to be treated stably at a high linear velocity continuously for a long time.
SUMMARY OF THE INVENTION
The objects described above are accomplished by a method for the treatment of waste water, which method is characterized by subjecting the waste water to wet oxidation at a temperature of not more than 370C under a pressure enough for the waste water to retain the li~uid phase thereof intact under continued supply of a gas containing oxygen in an amount of @.0 to 1.5 times the theoretical amount necessary for enabling the organic and inorganic substances contained in the waste water to be decomposed thoroughly into nitrogen, carbon dioxide, and water, in the presence of a catalyst composed of catalyst component A comprising a composite oxide of at least two metals selected from the group consisting of titanium, silicon, and zirconium and catalyst component B comprising at least one metal selected from the group consisting of manganese, iron, cobalt, nic~el, tungsten, copper, cerium, silver, platinum, palladium, rhodium, ruthenium, and iridium or a water-insoluble or sparingly water-soluble compound of the metal.
This invention also concerns a method for the treatment of waste water wherein the catalyst has monolithic structure. This invention further pertains to ,, " j ..."i ~30~6S
a method for the treatment of waste water wherein the catalyst is a honeycomb type having through holes of a equivalent diameter in the range of 2 to 20 mm, a cell wall thickness in the range of 0.5 to 3 mm, and an opening ratio in the range of 50 to 30%. This invention also relates to a method for the treatment of waste water, which method effects the passage through the catalyst of the waste water in combination with an oxygen-containing gas in the presence of ozone and/or hydrogen peroxide.
D~SCRIPTION OF THE PREFER~ED EMBODIMENT
The catalyst to be used in the present invention is a catalyst which is composed of catalyst component A
comprising a composi.te oxide of at least two metals selected from the group consisting of titanium, silicon, and zirconium and catalyst component B comprising at least one metal selected from the group consisting of manganese, iron, cobalt, nickel, tungsten, copper, cerium, silver, platinum, palladium, rhodium, ruthenium, and iridium or a water-insoluble or sparingly water-soluble compound of the metal.
The catalyst contemplated by the present invention is characterized by using as a catalytic component thereof a binary composite oxide comprising titanium and silicon (hereinafter referred to as "TiO2-ZrO2l'), a binary composite oxide comprising titanium and zirconium (hereinafter referred to as 'ITiO2-ZrO2"), a binar~ composite oxide comprising z.irconium and silicon (hereinafter referred to as "ZrO2-SiO2"), or a ternary composite oxide comprising ti~anium, silicon, and zirconium (hereina~ter referred to as "Tio2 SiO2-ZrO2").
Generally, the binary composite oxide comprising titanium, and silicon, from the report of Kozo Tanabe "Catalyst,~' Vol.17, No.3, page 72(1975), has been widely known as a solid acid. It exhibits conspicuous acidity not found in either of the component oxides thereof and possesses a large surface area.
~301965 The Tio2-sio2 is not a mere mixture of titanium dioxide with silicon dioxide but is a product which is inferred to manifest the peculiar physical attributes mentioned above because titanium, and silicon are combined to form the so-called binary type oxide. Further, the binary composite oxide containing titanium and zirconium, the binary composite oxide containing zirconium and silicon, and the ternary composite oxide containin~
titanium, zirconium and silicon are characterized as composite oxides possessing the same qualities as Tio2-Sio2~
The composite oxides, on analysis by the X-ray diffraction, are found to possess an amorphous or substantially amorphous microstructure.
We have learned that when the catalyst composition using a composite oxide of the foregoing description as catalyst component A is molded in the form of pellets, beads or honeycombs, since this catalyst component A eminently excels in moldability, the produced catalyst is enabled to retain its form intact for a long time in a continuous use even in a treatment of waste water demanding harsh conditions such as a high temperature, a high pressure, and a hiyh pH value. Moreover, we have learned that the catalyst excels in the efficiency with which the treatment of waste water is carried out.
By our experiment, it has been found that no satis~actory moldability is acquired by any of the several oxides of titanium, silicon, and zirconium or by a mere mixture of these elements, that if the oxide or the mixture is molded at all in the form of honeycombs, for example, the produced honeycombs cannot endure any protracted use, but '~ :
~3 [)196~;
that when these elements are converted into a composite o~ide, the produced oxide manifests outstanding moldability and possesses highly satisfactory durability The catalyst component A of the catalyst used in S this invention, i.e. one member selected from the group consisting of TiO2-Sio2, TiO2-ZrO , ZrO2-SiO2, and TiO2-SiO2-ZrO2, is desired to have a surface area not less than 30 m /g, preferably falling in the range of 50 to 300 m /g.
As regards the composition of the catalyst component A, the TiO2-SiO2 composite is desired to contain TiO2 in the range of 20 to 95 mol%, preferably 50 to 95 mol~, and SiO2 in the range of 5 to 80 mol~, preferably 5 to 50 mol~, the TiO2-ZrO2 composite is desired to contain TiO2 in 15 the range of 20 to gO mol~, preferably 30 to 90 mol%, more preferably 30 to 80 mol%, and ZrO2 in the range of 10 to 80 mol~, preferably 10 to 70 mol% , more preferahly 20 to 70 mol~, the ZrO2-SiO2 composite is desired to contain ZrO2 in the range of 20 to 90 mol~, preferably 40 to 90 mol%, and 20 SiO2 in the range o~ lO to 80 mol~, preferably lO to 60 mol~, and the TiO2-SiO2-ZrO2 composite is desired to contain TiO2 in the range o~ 20 to 95mol~, preferably 30 to 95 mol~, and the sum o~ SiO2 and ZrO2 in the range of 5 to 80 mol~, preferably 5 to 70 mol~ tinvariahly based on the total of 25 TiO2, ZrO2, and SiO2 taken as 100 mol%), calculated as an oxide. The ranges specified above are desirable for the purpose of enabling the produced catalyst to retain durability and catalytic activity long. Among other composite oxides mentioned above, the binary composite oxide 30 of TiO2-ZrO2 proves to be particularly excellent in durability.
The ratio of the catalyst components making up the catalyst to be used in this invention is desirably such that the proportion o the catalyst component A falls in the range 35 of 75 to 99.95~ by weight as oxide and the catalyst component A falls in the range of 0.05 to 25~ by weight as metal or ~3~L965 compound. Desirably, of the elements which make up the catalyst component B, the amount of manganese, iron, cobalt, nickel, tungsten, copper, cerium, or silver to be used is in the range of 0 to 25~ by weight as compound and the amount 5 of platinum, palladium, rhodium, ruthenium, or iridium to be used is in the range of 0 to 10~ by weight as metal (providing that the total amount of the two metals falls in the range of 0.05 to 25% by weight). More desirably, the catalyst component A accounts for a proportion in the range 10 of 85 to 99.9% by weight as oxide and the catalyst component B for a proportion in the range of 0.1 to 15~ by weight as metal or compound. Desirably, in the metals making up the catalyst component B, the amount of manganese, iron, cobalt, nickel, tungsten, copper~ cerium, or silver to be used falls 15 in the range of 0 to 15~ by wight as compound and the amount of platinum, palladium, rhodium, ruthenium, or iridium to be used falls in the range o 0 to 5~ by weight as metal, providing that the total amount of the two metals is in the range of 0.1 to 15~ by weight. O course, the total of the 20 catalyst component A and the catalyst component B accounts for 100~ by weight.
If the catalyst component B falls outside the aforementioned range, then the produced catalyst is deficient in oxidative activity. If any of the noble metals such as 25 platinum, palladium, and rhodium is used in an unduly large amount, the cost of raw materlal is high and the effect to be manifested is not proportionately increased.
The catalyst to be used in this invention is desired to have a specific composition described above. As 30 to the shape of the catalyst, the catalyst can be used in any of various shapes of monolithic structure such as, for example, pellets, beads, rings, saddles, granules, crushed particles, and honeycombs. The catal~st contemplated by this invention can be used in the form of a fixed bed or a 35 fluidized bed. Our study performed as to the shape of the , ~3~9~5 catalyst to be used in the treatment of waste water has led to a knowledge that the catalyst in the shape of honeycombs is most effecti~e and that the honeycombs of catalyst produce an outstanding effect when they have through holes of a 5 equivalent diameter in the range of 2 to 20 mm, a cell wall thickness in the range of 0.5 to 3 mm, and an opening ratio in the range of 50 to 80%. When the honeycombs of catalyst are given a large hole diameter (equivalent diameter of through holes), the resistance offered to the flow of waste 10 water is proportionately small and the otherwise possible clogging of the holes with solid particles can be precluded and, at the same _ime, the geometric surface area of the catalyst is proportionately small. For the catalyst to manifest a stated efficiency of treatment, therefore, the 15 amount of the catalyst must be increased in proportion as the hole diameter is increased. This hole diameter is accordingly restricted by the relation between the efficiency of treatment and the catalytic performance.
In the honeycomh-shaped catalyst, the equivalent 20 diameter of the through holes is desired to fall in the range of 2 to 20 mm, preferably 4 to 12 mm. If this equivalent diameter is less than 2 mm, the catalyst cannot be easily used long in a continued treatment particularly when the waste water under treatment contains solid particles because 25 the pressure loss is unduly heavy and the holes tend to be clogged. I the equivalent diameter exceeds 20 mm, the catalyst is de~icient in cataly~ic activity, though the pressure loss i9 small and the possibility of clogging of the holes is low.
The cell wall thickness is in the range of 0.5 to 3 mm, preferably 0.5 to 2 mm. If the cell wall thickness is less than 0.5 mm, though there ensues an advantage that the pressure loss is small and the weight of the catalyst is small as well, the catalyst suffers from deficiency in 6~
mechanical strength. If the cell wall thickness exceeds 3 mm, though the mechanical strength is sufficient, the catalyst suffers from heavy pressure loss.
For the same reason as given above, the opening ratio of the catalyst is desired to be in the range of 50 to 80~, preferably 60 to 75%.
In due consideration of the various factors dealt with above, the honeycomb-shaped catalyst desirably used in the present invention is required to be such that the e~uivalent diameter of through holes is in the range of 2 to 20 mm, the cell wall thickness in the range of 0.5 to 3 mm, and the opening ratio in the range of 50 to 80%. The honeycomb-shaped catalyst which fulfils all these conditions possesses sufficient mechanical strength even under such harsh reaction conditions as a high reaction temperature falling not more than 370OC, preferably 100 to 370C and a high enough pressure for waste waster to retain the liquid phase thereof intact. Moreover, the catalyst possesses a sufficiently large geometric surface area and, therefore, excels in durability. Thus, it can treat waste wate.r at a high linear velocity with low pressure loss.
Even when the waste water under treatment happens to contain solid particles, the catalyst can retain high activity for a long time without suffering from clogging.
The through holes in the honeycomb-shaped catalyst can have any of popular cross-sectional shapes such as s~uare, hexagon, and undulating circle. Any desired cross-sectional shape can be adopted so long as the equivalent diameter falls in the aforementioned range.
Our study of the oxidizing agent to be used in the treatment of waste water has led to a knowledge that when molecular oxygen and ozone and/or hydrogen peroxide are used collectively as an oxidizing agent, even organic substances such as acetic acid which are widely held to be rather poorly oxidizable can be decomposed with high "'''`) ~3~96~
efficiency and the reaction is enabled to proceed at relatively low temperature and low pressure. In any of the various applied treatments of the Zimmerman method which uses molecular oxygen as an oxidizing agent under conditions of 5 high temperature and high pressure, combined use of molecular oxygen with ozone and/or hydrogen peroxide has never been reported in art. Further, since the catalyst used in this invention possesses an ability to decompose ozone thoroughly to oxygen, it enjoys a characteristic advantage that it will 10 effect substantial decomposition of used ozone and prevent leakage of the used ozone from the system.
Sufficiently, the amount of ozone to be used is in the range of 0.001 to 0.6 mol, preferably 0.003 to 0.2 mol, per mol of the theoretical amount of ozone necessary for the 15 organic and inorganic substances in the waste gas to be thoxoughly decomposed into nitrogen, carbon dioxide gas, and water. It is sufficient to use hydroge~ peroxide in an amount falling in the range of 0.001 to 1.8 moles, preferably 0.003 to 0.2 mol, per mol of the aforementioned theoretical 20 amount. By using 020ne and/or hydrogen peroxide in combination with molecular oxygen, the reaction temperature, though variable with the attributes of waste water under treatment, the amount of the oxidizing agent to be used, and other sin~ilar factors, is lower than when molecular oxygen is 25 used alone. Where the reaction t~mperature is in the range of 200 to 300C in the reaction using molecular oxygen alone, for example, the temperature falls in the range of 100 to 250C in the same reaction using molecular oxygen in combination with oxidizing agent.
In the preparation of the TiO2-SiO2 for use in the present invention as catalyst component A, for example, the titanium source may be selected from among inorganic titanium compounds such as titanium chloride and titanium sulfate and organic titanium compounds such as titanium oxalate and 35 tetraisopropyl titanate and the silicon source from among 13~9~;5 inorganic silicon compounds such as colloidal silica, water glass, and silicon tetrachloride and organic silicon compounds such as tetraethyl silicate. Some of the raw materials enumerated above contain a minute amount of extraneous substance. The inclusion of the extraneous substance does not matter very much so long as it has no appreciable effect upon the qualities of the Tio2-Sio2.
Preferably, the preparation of the Tio2-Sio2 is attained by any of the following methods:
1 A method which comprises mixing titanium tetrachloride with silica sol, adding ammonia to the resulting mixture thereby inducing precipitation, separating and washing the resulting precipitate, drying the washed precipitate, and calcining the dry precipitate at a temperature in the range of 300 to 650C, preferably 350 to 600C;
BACKGROUND OF THE INVENTION
Field of the Invention:
This invention relates to a method for the treatment of waste water. Particularly, it relates to a method for effecting wet oxidation of waste water containing a substance of chemical oxygen demand (hereinafter referred to as "COD component") in the presence of a catalyst. More particularly, it relates to a method for effectively detoxifying waste water containing a COD component, i.e. a harm~ul oxidizable organic or inorganic substance, by subjecting the waste water to catalytically wet oxidation in the presence of molecular ox~gen theraby converting the harm~ul substance into such harmless compounds as carbon dioxide, water, and nitrogen.
Description of the Prior Art:
Among the conventional means available for the treatment of waste water, there are counted a biochemical method called an activated sludge method and a wet oxidatio~ method called a Zimmerman method.
As widely lcnown, the activated sludge method consumes much time in the decomposition of organic matter and, moreover, requires the waste water to be diluted to a concentration suitable ~or the of algae and bacteria and, there~ore, has a disadvantage that the ground area for installation of facilities for the activated sludge treatment is very large. Further in r~cent years, particularly in the urban districts, the disposal of grown excess sludge has been entailing a huge expense. The Zimmerman method consists in effecting oxidative decomposition of organic matter contained in a high concentration in an aqueous solution by introducing air under a pressure in the range of 16 to 200 atmospheres at a temperature in the range of 200 to 370C into the `~
~30~6S
aqueous solution. This method requires the use of a large reactor because the reaction proceeds slowly and the decomposition consumes much time. Further, the reactor itself requires the material thereof to possess high durability. Thus, this method is not economically advantageous because of high cost of equipment and high cost of operation. In connection with this method, it has been proposed to use various o~idative catalysts aimed at accelerating the reaction velocity.
Among the catalysts heretofore used popularly in the catalytically wet oxidation method, there are counted compounds of such noble metals as palladium and platinum (Japanese Patent Laid-Open SHO 49(1974)-44,556) and compounds of such heavy metals as cobalt and iron (Japanese Patent Laid-Open SHO 49(1974)-94,157). They are catalysts which have the compounds deposited on spherical or cylindrical carriers of alumina, silica-alumina, silica gel, and activated carbon. More often than not, in the catalytically wet oxidation of waste water, these catalysts are put to use in the reaction at a pH value of not less than 9. In our experiment, the catalysts, in the course of their protracted use, have been found to suffer from loss of s~rength and disinte~ration of individual particles and, in an extreme case, entail dissolution of their carrier.
In an effort to solve this problem, there have been recently proposed methods for reinforcing the catalysts by using titania or zirconia as a carrier therefor (Japanese Patent Laid-Open SHO 58~1983)-64,188 and SHO 59(1984)-19757). To be specific, these inventions disclose catalysts which have compounds of such noble metals as palladium and platinum or compounds of such heavy metals as iron and cobalt deposited on spherical or cylindrical carrier particles of titania or zirconia. By experiment, the carriers are certainly found to possess greater strength than the conventional carriers. These catalysts, however, are invariably in a particulate form.
~3~)19~
Moreover, they are not fully satisfactory in terms of catalytlc acti~ity and durability.
Incidentally, when the waste water is subjected to wet oxidation, there inevitably arises the necessity of disposing of a large volume of water. As regards the manner of reaction, therefore, the method of using a fixed bed in a system designed for flow of waste water is frequently adopted. Mor~over, numerous samples of waste water contain solid substances. If, in any of these cases, a given catalyst is in a particulate form, since the flow of the waste water induces heavy loss of pressure, the waste water cannot be treated at a high linear velocity and the current of this waste water must be given a large cross section. In the treatment of waste water entraining a solid substance, since the solid substance clogs the fixed bed of catalyst even to an extent of increasing the resistance which the fixed bed of catalyst offers against the flow of waste water, this treatment entails a disadvantage that the running cost is increased and the apparatus for treatment cannot be operated continuously for a long time. In the treatment of waste water by the catalytically wet oxidation method using such particulate shaped catalyst, since the reaction is carried out at an e.levated temperature under a high pressure and the ground area occupied by the reactor must be proportionately large, the cost of equipment is huge. The high cost of equipment constitutes a critical problem.
As regards the life of the catalyst, the particulate catalyst has a disadvantage that by mutual contact of the particles, the catalyst is comminuted by friction and disintegration. For the purpose of diminishing the loss of pressure due to the catalyst bed, there has been proposed a fluidized-bed method which comprises fluidizing a catalyst in a powdery form in a current of waste water. This method, however, has not yet been adopted for actual use because the catalyst by nature is diluted and the reactor used for the treatment, ~.~
13C~6~ii therefore, must possess a huge capacity and the separation of the catalyst from the treated waste water is very difficult.
There are also methods which effect oxidative decomposition of organic matter in waste water at normal room temperature under normal atmospheric pressure by using ozone or hydrogen peroxide as an oxidizing agent.
Japanese Patent Laid-Open SHO 58(1983)-55,088, for example, discloses a method which effects oxidative decomposition of such organic substances as fumic acid contained in waste water by treating this waste 2water with ozone and hydrogen peroxide at 20C under normal atmospheric pressure in the absence of a catalyst. Japanese Patent Publication SHO
58(1983)-37,039 discloses a method which effects oxidative decomposition of an aromatic ring-containing organic compound contained in waste water by adding a surfactant to the waste water, further adding thereto at least one member selected from the group consisting of transient metal compounds and alkaline earth metal compounds, and then exposing the resultant mixture to ozone at normal room temperature under normal atmospheric pressure. Since the former method efEects the treatment in the absence of a catalyst, it is incapable of effectively treating sparingly oxidizable substances suspended in waste water. Since the latter method uses the metal ion such as that of a transient metal or alkaline earth metal as a catalyst, it is required to recover the metal ion contained in the treated waste water before this treated waste water is released into a nearby body of running water. It has a disadvantage that it inevitably requires an extra step of aftertreatment. Further, since both these methods require the treatments for waste water to be carried out at normal room temperature under normal atmospheric pressure, the~
have a disadvantage that they call for supply of a large volume of expensive ozone, their reactions proceed at a low rate, their ratios of decomposition of organic matter are li..~,~l) 13~
low, and the treated waste water require a treatment for detoxification because the unaltered ozone leaks in the treated water.
An object of an aspect of the present invention, therefore, is to provide a method for efficient and long continuous treatment of waste water.
An object of an aspect of this invention is to provide a method for enabling the treatment of waste water to be carried out efficiently in a high linear velocity.
~n object of an aspect of this invention is to provide a method for enabling waste water containing solid substances to be treated stably at a high linear velocity continuously for a long time.
SUMMARY OF THE INVENTION
The objects described above are accomplished by a method for the treatment of waste water, which method is characterized by subjecting the waste water to wet oxidation at a temperature of not more than 370C under a pressure enough for the waste water to retain the li~uid phase thereof intact under continued supply of a gas containing oxygen in an amount of @.0 to 1.5 times the theoretical amount necessary for enabling the organic and inorganic substances contained in the waste water to be decomposed thoroughly into nitrogen, carbon dioxide, and water, in the presence of a catalyst composed of catalyst component A comprising a composite oxide of at least two metals selected from the group consisting of titanium, silicon, and zirconium and catalyst component B comprising at least one metal selected from the group consisting of manganese, iron, cobalt, nic~el, tungsten, copper, cerium, silver, platinum, palladium, rhodium, ruthenium, and iridium or a water-insoluble or sparingly water-soluble compound of the metal.
This invention also concerns a method for the treatment of waste water wherein the catalyst has monolithic structure. This invention further pertains to ,, " j ..."i ~30~6S
a method for the treatment of waste water wherein the catalyst is a honeycomb type having through holes of a equivalent diameter in the range of 2 to 20 mm, a cell wall thickness in the range of 0.5 to 3 mm, and an opening ratio in the range of 50 to 30%. This invention also relates to a method for the treatment of waste water, which method effects the passage through the catalyst of the waste water in combination with an oxygen-containing gas in the presence of ozone and/or hydrogen peroxide.
D~SCRIPTION OF THE PREFER~ED EMBODIMENT
The catalyst to be used in the present invention is a catalyst which is composed of catalyst component A
comprising a composi.te oxide of at least two metals selected from the group consisting of titanium, silicon, and zirconium and catalyst component B comprising at least one metal selected from the group consisting of manganese, iron, cobalt, nickel, tungsten, copper, cerium, silver, platinum, palladium, rhodium, ruthenium, and iridium or a water-insoluble or sparingly water-soluble compound of the metal.
The catalyst contemplated by the present invention is characterized by using as a catalytic component thereof a binary composite oxide comprising titanium and silicon (hereinafter referred to as "TiO2-ZrO2l'), a binary composite oxide comprising titanium and zirconium (hereinafter referred to as 'ITiO2-ZrO2"), a binar~ composite oxide comprising z.irconium and silicon (hereinafter referred to as "ZrO2-SiO2"), or a ternary composite oxide comprising ti~anium, silicon, and zirconium (hereina~ter referred to as "Tio2 SiO2-ZrO2").
Generally, the binary composite oxide comprising titanium, and silicon, from the report of Kozo Tanabe "Catalyst,~' Vol.17, No.3, page 72(1975), has been widely known as a solid acid. It exhibits conspicuous acidity not found in either of the component oxides thereof and possesses a large surface area.
~301965 The Tio2-sio2 is not a mere mixture of titanium dioxide with silicon dioxide but is a product which is inferred to manifest the peculiar physical attributes mentioned above because titanium, and silicon are combined to form the so-called binary type oxide. Further, the binary composite oxide containing titanium and zirconium, the binary composite oxide containing zirconium and silicon, and the ternary composite oxide containin~
titanium, zirconium and silicon are characterized as composite oxides possessing the same qualities as Tio2-Sio2~
The composite oxides, on analysis by the X-ray diffraction, are found to possess an amorphous or substantially amorphous microstructure.
We have learned that when the catalyst composition using a composite oxide of the foregoing description as catalyst component A is molded in the form of pellets, beads or honeycombs, since this catalyst component A eminently excels in moldability, the produced catalyst is enabled to retain its form intact for a long time in a continuous use even in a treatment of waste water demanding harsh conditions such as a high temperature, a high pressure, and a hiyh pH value. Moreover, we have learned that the catalyst excels in the efficiency with which the treatment of waste water is carried out.
By our experiment, it has been found that no satis~actory moldability is acquired by any of the several oxides of titanium, silicon, and zirconium or by a mere mixture of these elements, that if the oxide or the mixture is molded at all in the form of honeycombs, for example, the produced honeycombs cannot endure any protracted use, but '~ :
~3 [)196~;
that when these elements are converted into a composite o~ide, the produced oxide manifests outstanding moldability and possesses highly satisfactory durability The catalyst component A of the catalyst used in S this invention, i.e. one member selected from the group consisting of TiO2-Sio2, TiO2-ZrO , ZrO2-SiO2, and TiO2-SiO2-ZrO2, is desired to have a surface area not less than 30 m /g, preferably falling in the range of 50 to 300 m /g.
As regards the composition of the catalyst component A, the TiO2-SiO2 composite is desired to contain TiO2 in the range of 20 to 95 mol%, preferably 50 to 95 mol~, and SiO2 in the range of 5 to 80 mol~, preferably 5 to 50 mol~, the TiO2-ZrO2 composite is desired to contain TiO2 in 15 the range of 20 to gO mol~, preferably 30 to 90 mol%, more preferably 30 to 80 mol%, and ZrO2 in the range of 10 to 80 mol~, preferably 10 to 70 mol% , more preferahly 20 to 70 mol~, the ZrO2-SiO2 composite is desired to contain ZrO2 in the range of 20 to 90 mol~, preferably 40 to 90 mol%, and 20 SiO2 in the range o~ lO to 80 mol~, preferably lO to 60 mol~, and the TiO2-SiO2-ZrO2 composite is desired to contain TiO2 in the range o~ 20 to 95mol~, preferably 30 to 95 mol~, and the sum o~ SiO2 and ZrO2 in the range of 5 to 80 mol~, preferably 5 to 70 mol~ tinvariahly based on the total of 25 TiO2, ZrO2, and SiO2 taken as 100 mol%), calculated as an oxide. The ranges specified above are desirable for the purpose of enabling the produced catalyst to retain durability and catalytic activity long. Among other composite oxides mentioned above, the binary composite oxide 30 of TiO2-ZrO2 proves to be particularly excellent in durability.
The ratio of the catalyst components making up the catalyst to be used in this invention is desirably such that the proportion o the catalyst component A falls in the range 35 of 75 to 99.95~ by weight as oxide and the catalyst component A falls in the range of 0.05 to 25~ by weight as metal or ~3~L965 compound. Desirably, of the elements which make up the catalyst component B, the amount of manganese, iron, cobalt, nickel, tungsten, copper, cerium, or silver to be used is in the range of 0 to 25~ by weight as compound and the amount 5 of platinum, palladium, rhodium, ruthenium, or iridium to be used is in the range of 0 to 10~ by weight as metal (providing that the total amount of the two metals falls in the range of 0.05 to 25% by weight). More desirably, the catalyst component A accounts for a proportion in the range 10 of 85 to 99.9% by weight as oxide and the catalyst component B for a proportion in the range of 0.1 to 15~ by weight as metal or compound. Desirably, in the metals making up the catalyst component B, the amount of manganese, iron, cobalt, nickel, tungsten, copper~ cerium, or silver to be used falls 15 in the range of 0 to 15~ by wight as compound and the amount of platinum, palladium, rhodium, ruthenium, or iridium to be used falls in the range o 0 to 5~ by weight as metal, providing that the total amount of the two metals is in the range of 0.1 to 15~ by weight. O course, the total of the 20 catalyst component A and the catalyst component B accounts for 100~ by weight.
If the catalyst component B falls outside the aforementioned range, then the produced catalyst is deficient in oxidative activity. If any of the noble metals such as 25 platinum, palladium, and rhodium is used in an unduly large amount, the cost of raw materlal is high and the effect to be manifested is not proportionately increased.
The catalyst to be used in this invention is desired to have a specific composition described above. As 30 to the shape of the catalyst, the catalyst can be used in any of various shapes of monolithic structure such as, for example, pellets, beads, rings, saddles, granules, crushed particles, and honeycombs. The catal~st contemplated by this invention can be used in the form of a fixed bed or a 35 fluidized bed. Our study performed as to the shape of the , ~3~9~5 catalyst to be used in the treatment of waste water has led to a knowledge that the catalyst in the shape of honeycombs is most effecti~e and that the honeycombs of catalyst produce an outstanding effect when they have through holes of a 5 equivalent diameter in the range of 2 to 20 mm, a cell wall thickness in the range of 0.5 to 3 mm, and an opening ratio in the range of 50 to 80%. When the honeycombs of catalyst are given a large hole diameter (equivalent diameter of through holes), the resistance offered to the flow of waste 10 water is proportionately small and the otherwise possible clogging of the holes with solid particles can be precluded and, at the same _ime, the geometric surface area of the catalyst is proportionately small. For the catalyst to manifest a stated efficiency of treatment, therefore, the 15 amount of the catalyst must be increased in proportion as the hole diameter is increased. This hole diameter is accordingly restricted by the relation between the efficiency of treatment and the catalytic performance.
In the honeycomh-shaped catalyst, the equivalent 20 diameter of the through holes is desired to fall in the range of 2 to 20 mm, preferably 4 to 12 mm. If this equivalent diameter is less than 2 mm, the catalyst cannot be easily used long in a continued treatment particularly when the waste water under treatment contains solid particles because 25 the pressure loss is unduly heavy and the holes tend to be clogged. I the equivalent diameter exceeds 20 mm, the catalyst is de~icient in cataly~ic activity, though the pressure loss i9 small and the possibility of clogging of the holes is low.
The cell wall thickness is in the range of 0.5 to 3 mm, preferably 0.5 to 2 mm. If the cell wall thickness is less than 0.5 mm, though there ensues an advantage that the pressure loss is small and the weight of the catalyst is small as well, the catalyst suffers from deficiency in 6~
mechanical strength. If the cell wall thickness exceeds 3 mm, though the mechanical strength is sufficient, the catalyst suffers from heavy pressure loss.
For the same reason as given above, the opening ratio of the catalyst is desired to be in the range of 50 to 80~, preferably 60 to 75%.
In due consideration of the various factors dealt with above, the honeycomb-shaped catalyst desirably used in the present invention is required to be such that the e~uivalent diameter of through holes is in the range of 2 to 20 mm, the cell wall thickness in the range of 0.5 to 3 mm, and the opening ratio in the range of 50 to 80%. The honeycomb-shaped catalyst which fulfils all these conditions possesses sufficient mechanical strength even under such harsh reaction conditions as a high reaction temperature falling not more than 370OC, preferably 100 to 370C and a high enough pressure for waste waster to retain the liquid phase thereof intact. Moreover, the catalyst possesses a sufficiently large geometric surface area and, therefore, excels in durability. Thus, it can treat waste wate.r at a high linear velocity with low pressure loss.
Even when the waste water under treatment happens to contain solid particles, the catalyst can retain high activity for a long time without suffering from clogging.
The through holes in the honeycomb-shaped catalyst can have any of popular cross-sectional shapes such as s~uare, hexagon, and undulating circle. Any desired cross-sectional shape can be adopted so long as the equivalent diameter falls in the aforementioned range.
Our study of the oxidizing agent to be used in the treatment of waste water has led to a knowledge that when molecular oxygen and ozone and/or hydrogen peroxide are used collectively as an oxidizing agent, even organic substances such as acetic acid which are widely held to be rather poorly oxidizable can be decomposed with high "'''`) ~3~96~
efficiency and the reaction is enabled to proceed at relatively low temperature and low pressure. In any of the various applied treatments of the Zimmerman method which uses molecular oxygen as an oxidizing agent under conditions of 5 high temperature and high pressure, combined use of molecular oxygen with ozone and/or hydrogen peroxide has never been reported in art. Further, since the catalyst used in this invention possesses an ability to decompose ozone thoroughly to oxygen, it enjoys a characteristic advantage that it will 10 effect substantial decomposition of used ozone and prevent leakage of the used ozone from the system.
Sufficiently, the amount of ozone to be used is in the range of 0.001 to 0.6 mol, preferably 0.003 to 0.2 mol, per mol of the theoretical amount of ozone necessary for the 15 organic and inorganic substances in the waste gas to be thoxoughly decomposed into nitrogen, carbon dioxide gas, and water. It is sufficient to use hydroge~ peroxide in an amount falling in the range of 0.001 to 1.8 moles, preferably 0.003 to 0.2 mol, per mol of the aforementioned theoretical 20 amount. By using 020ne and/or hydrogen peroxide in combination with molecular oxygen, the reaction temperature, though variable with the attributes of waste water under treatment, the amount of the oxidizing agent to be used, and other sin~ilar factors, is lower than when molecular oxygen is 25 used alone. Where the reaction t~mperature is in the range of 200 to 300C in the reaction using molecular oxygen alone, for example, the temperature falls in the range of 100 to 250C in the same reaction using molecular oxygen in combination with oxidizing agent.
In the preparation of the TiO2-SiO2 for use in the present invention as catalyst component A, for example, the titanium source may be selected from among inorganic titanium compounds such as titanium chloride and titanium sulfate and organic titanium compounds such as titanium oxalate and 35 tetraisopropyl titanate and the silicon source from among 13~9~;5 inorganic silicon compounds such as colloidal silica, water glass, and silicon tetrachloride and organic silicon compounds such as tetraethyl silicate. Some of the raw materials enumerated above contain a minute amount of extraneous substance. The inclusion of the extraneous substance does not matter very much so long as it has no appreciable effect upon the qualities of the Tio2-Sio2.
Preferably, the preparation of the Tio2-Sio2 is attained by any of the following methods:
1 A method which comprises mixing titanium tetrachloride with silica sol, adding ammonia to the resulting mixture thereby inducing precipitation, separating and washing the resulting precipitate, drying the washed precipitate, and calcining the dry precipitate at a temperature in the range of 300 to 650C, preferably 350 to 600C;
2 A method which comprises adding as aqueous sodium silicate solution to titanium tetrachloride, causing them to react with each other and give rise to a precipitate separating and washing the precipitate, drying the washed precipitate, and calcining the dry precipitate at a temperature in the range of 300 to 650C, pre~erabl~ 350 to 600C;
3 ~ method which comprises adding ethyl silicate [(C2Hso)4Si] to a water-a].cohol solution of titanium tetrachloride thereby causiny hydrolysis and consequent precipitation, separating and washing the resulting precipitate, drying the washed precipitate, and calcining the dry precipitate at a temperature in the range of 300 to 650C, preferably 350 to 600; and 4 A method which comprises adding ammonia to a water-alcohol solution of titanium oxygen chloride (TiOC1~) and ethyl silicate thereby giving rise to a precipitate, separating and washing the precipitate, drying the washed precipitate, and calcining the dry precipitate at a temperature in the range of 300 to 650C, preferably 350 to 600C.
;
~30~9~;S
Among in the preferred methods cited above, the method of tl) proves to be particularly desirable.
Specifically, this method is carried out as follows:
Compounds selected severally from the group of typical examples of the titanium source and the silicon source are weighed out in amount to form a composite oxide consisting of Tio2 and sio2 in a prescribed ratio, mixed in the form of an acidic aqueous solution or as a sol containing titanium and silicon in a concentration in the range of 1 to 100 g/liter, preferably 10 to 80g/liter as oxide, and then held at a temperature in the ranye of 10 to 100C. The solution or sol is kept stirred, with aqueous ammonia added dropwise thereto meanwhile as a neutralizing agent, for a period of 10 minutes to three hours until a coprecipitate composed of titanium and silicon is formed at a pH in the range of 2 to 10. This coprecipitate is separated by filtratlon, thoroughly washed, then dried at a temperature in the range of 80 to 140C for a period of 1 to 10 hours, and calcined at a temperature in the range of 300 to 650C, preferably 350 to 600C for a period of one to 10 hours, preferably 2 to 8 hours, to give birth to Tio2-Sio2.
The TiO2-ZrO2-SiO2 is prepared by the same method as used for the preparation of the Tio2-Sio2. In this case, the zirconium source may be selected from among inorganic zirconium compounds such as zirconillm chloride and zirconium sulfate and organic zirconium compounds such as zirconium oxalate. Specifically, by handling a zirconium compound and a titanium compound suitably selected ~y the same method as described above, there can be easily prepared the TiO2-ZrO2-SiO2. The amount of zirconium to be present in this ternary composite oxide is desired to be not more than 30% by weight as ZrO2, based on the total amount of the TiO2+ZrO2+SiO2. The preparation of the TiO2-ZrO2 can be carried out in the same manner as described above.
Desirably, the TiO2-ZrO2 composite can be prepared by either of the following methods:
~3~ 9~S
1. A method which comprises mixing titanium chloride with zirconium oxychloride, adding ammonia to the resultant mixture thereby inducing precipitation in the mixed system, washing and drying the precipitate, and calcining the clean dry precipitate at a temperature in the range of 300O to 6500C, preferably 350 to 600C;
2. A method which comprises adding zirconyl nitrate to titanium tetrachloride, subjecting the resultant mixture to thermal hydrolysis thereby inducing precipitation in the mixed system, washing and drying the precipitate, and then calcining the clean dry precipitate at a temperature in the range of 300 to 650C, preferably 350O to 600OC; and From the Tio2-sio2~ TiO2-ZrO2, ZrO2 SiO2, or TiO2-SiO2-ZrO2 composite prPpared by either of the foregoing methods, a complete catalyst is obtained by a suitable method. A typical method comprises mixing the Tio2-sio2 composite in a powdery form with a molding auxiliary, kneading the resultant mixture under addition of a suitable amount of water, and molding the resultant blend in the shape of beads, pellets, sheets, or honeycombs by the use of an extrusion molder.
By drying the molded composite at a temperature in the ran~e of 50 to 120C and then calcining the dried molded composite as swept with air at a temperature in the range of 300 to 800C, preferably 350 to 600C, for a period in the range of 1 to 10 hours, preferably 2 to 6 hours, there is obtained a catalyst.
Production of a catalyst by the addition of metals selected from the group consisting of manganese, iron, nickel, cobalt, tungsten, copper, cerium, silver, platinum, palladium, rhodium, ruthenium, and iridium to the TiO2-ZrO2 composite can be accomplished by causing an aqueous solution of the metal salts to impregnate the molded TiO2-ZrO2 composite thereby effecting deposition of the metal salts on the composite and drying and calcining the resultant impregnated composite.
-- .
~L30~965 Alternatively, the production may be attained by adding the aqueous solution of the metal salt in combination with a molding auxiliary to the TiO2-ZrO2 composite in powdery form, blending them, and molding the resultant blend.
Examples of the starting materials for the catalyst component B to be used in combination with the catalyst component A in the preparation of the catalyst of this invention include oxides, hydroxides, inorganic acid salts, and organic acid salts. More specifically, the starting materials may be suitably selected from among ammonium salts, oxalates, nitrates, sulfates, and halides.
In accordance with the present invention, wet oxidation can be effectively carried out on various forms of waste water containing oxidizable organic or inorganic substances, such as supernatant and sedimented activated sludge occurring in the activated sludge treatment, waste water from fermentation, effluent from the process for polymerization of an organic compound, cyan-containing plant effluent, phenol-containing plant effluant, oil-containing waste water, effluent from a chemical plant, general industrial waste water from a food processing plant, etc., raw sewage, sewage, and sewage sludge. When the present invention is worked out by the use of the catalyst in the shape of honeycombs, even waste water containing solid particles in a concentration of more than O.lg/liter can be treated stably for a long time.
As to the reaction conditions befitting the purpose of this invention, the reaction temperature is below 370C, generally in the range of 100 to 370C, preferably 200 to 300C. The pressure inside the reaction system is required to be enough for the waste water under treatment to retain the liquid phase thereof intact, specifically falling in the range of 0 to about 200 kg/cm2, preferably 0 to 150 kg/cm2. The molecular oxygen-containing gas to be fed into the reaction system is used in an amount of 1 to 1.5 times, preferably 1.2 to 1.5 times, the B
~3(~ 65 theoretical amount necessary for the oxidative decomposition aimed at. The amount of the catalyst to be packed in the reaction column is approximately 5 to 99%, preferably 20 to 99%, of the spacial capacity of the reaction column. The waste water, to be effectively oxidized, is fed in combination with the molecular oxygen-containing gas to the catalyst bed kept at a prescribed temperature at a flow rate such that the retention time thereof will be in the range of 6 to 120 minutes, preferably in the range of 12 to 60 minutes.
Examples of the molecular oxygen-containing gas used effectively herein include air, mixed gas of oxygen with air, and a gas generally called an oxygen-enriched air. This gas is desired to have an oxygen content of not less than 25~. Thouyh the pH value of the reaction system may be on the acid or on the alkali side, it is desired to fall in the range of 9 to 11.
As to the reaction conditions in the treatment using ozone and/or hydrogen peroxide as an oxidizing agent in combination with the molecular oxygen, the reaction temperature generally falls in the range of 100 to 250C, the r~action pressure .is such as to enable the waste water to retain the li~uid phase thereof intact inside the reaction column, speciEically falling in the range of 0 to 200 kg/cm2, preferably 0 to 150 kg/cm2, and the retention time falls in the range of 3 to 120 minutes, preferably 5 to 60 minutes. The amount of ozone to be used is in the range of 0.001 to 0.6 mol, preferably 0.003 to 0.2 mol, per mol of theoretical amount of oxygen. The amount of hydrogen peroxide to be used falls in the range of 0.001 to 1.8 mols, preferably 0.003 to 0.2 mol, per mol of the theoretical amount of oxygen.
Now, the present invention will be described more specifically below with reference to working examples. It should be noted, however, that this invention is not limited to these examples.
~3~)~9~;5 Example 1 A composite oxide comprising titanium and silicon was prepared as follows. An aqueous sulfuric acid solution of titanyl sulfate having the following composition was used as a titanium source.
Tioso4 (as Tio2) 250 g/liter Total l~2SO4 1,100 g/liter Separately, 28 liters of aqueous ammonia (NH3, 25~) was added to 40 liters of water and 2.4 kg of Snowtex-NCS-30TM (silica sol containing about 30% by weight of silica as SiO2; product of Nissan Chemicals Industries Ltd.) was added further added theretoO To the resulting solution, a titanium-containing aqueous sulfuric acid solution prepared by diluting 15.3 liters of the aqueous sulfuric acid solution of titanyl sulfate with 30 liters of water was gradually added dropwise while under agitation to give rise to a coprecipitate gel. The resulting reaction mixture was left standing at rest for 15 hours. The Tio2-Sio2 gel thus obtained was separated by filtration washed with water, and then dried at 200C to for 10 hours.
The dry Tio~-Sio2 gel was calcined under an atmosphere of air at 550C for six hours. The powder thus obtained had a composition of TiO2:SiO2=4:1 (molar ratio) and a BET surface area of 185 m2/g. The powder which will be referred to hereinafter as TS-1 was used to prepare an ozone decomposition catalyst as follows.
In a kneader, 900 ml of water, 1,500 g of the powder, and 75 g of starch were thoroughly kneaded. The resultant blend was further kneaded with a suitable amount of water. The blend consequently obtained was extrusion molded in the shape of honeycombs having a hole diameter ~equi~alent diameter of through holes) of 3 mm and an opening ratio of 64%, dried at 120C for 5iX hours, and thereafter calcined at 450C for 5iX hours in an atmosphere having an oxygen concentration adjusted to below 15%.
~3 ID191E~
The molded composite so obtained was immersed in an aqueous palladium nitrate solution until sufficient impregnation, then dried at 120C for six hours, and calcined at 450C for six hours in an atmosphere of air.
The complete catalyst thus obtained had a percentage composition of TS-l : Pd = 97 : 3.
Example 2 TiO2-ZrO2 was prepared as follows.
In 100 liters of cold water, 1.93 kg of zirconium oxychloride (ZrOCl2 8H2O) was dissolved. In the resulting solution 7.7 liters of an aqueous sulfuric aci~ solution of titanyl sulfate having the same composition as used in Example 1 was added and thoroughly mixed. The mixture thus formed was kept amply stirred at a ~emperature of about 30C and aqueous ammonia was gradually added thereto until the pH reached 7. The resulting reaction mixture was left standing at rest for 15 hours.
The TiO2-ZrO2 gel thus obtained was separated by filtration, washed with cold water, and then dried at 200C
for 10 hours. Then, the dry gel was calcined undsr an atmosphere o air at 550C for six hours. The powder conse~uently obtained had a composition of TiO2:ZrO2 = 4 :
1 (molar rativ) and a BET surface area of 140 m2/g. The : powder thus obtained will be referred to hereinafter as TZ~l.
t.~
"~"`'~
~3~L9~5 By using this TZ-l and following the procedure of Example 1, there was obtained a honeycomb shaped article.
Then by using an aqueous chloroplatinic acld solution instead of the aqueous palladium nitrate and following the procedure 5 o~ Example 1, there was obtained a catalyst having weight ratio of TZ-l:Pt = 99 : 1.
Example 3 TiO2-SiO2-ZrO2 was prepared by following the procedures of Examples 1 and 2. The powder conse~uently 10 obtained had a composition of TiO2 : SiO2 : ZrO2 - 80 : 16 :
4 (molar ratio) and a BET surface area of 180 m /g. The powder thus obtained will be referred to hereinafter as TSZ-l.
By using this TSZ-l instead of TS-l and following 15 the procedure of Example 1, ther~ was obtained a honeycomb shaped catalyst having weight ratio of TSZ-l : Pd = 97 : 3.
Example 4 Catalyst having weight ratio of TZ-l : Ru = 98 : 2 was ~repared by using an aqueous solution of ruthenium 20 chloride solution instead of the aqueous chloroplatinic acid solution and following the procedure o Example 2.
Examples 5 ~ 6 Ca~alysts were prepared by following the procedure of Example 4, .except that TiO2-ZrO2 composite oxide powder 25 was used with different TiO2/ZrO2 molar ratios.
Tio2 : ZrO2 (molar ratio) Example 5 60 : ~0 Example 6 40 : 60 Example 7 A honeycomb-shaped molded composite having through holes of a equivalent diameter of 4 mm, a cell wall thickness of 0.8 mm, and an opening ratio of 69~ was obtained from the TZ-l powder produced in Example 2. Then, the molded composite was immersed in an aqueous chloroplatinic acid 35 solution, dried at 120C, and thereafter calcined at 450C in ~3~)~9~iS
an atmosphere of air, to produce a complete catalyst. The complete catalyst thus obtained had a weight ratio of TZ-1 : Pt = 99 : 1.
Example 8 ~ complete catalyst was produced by following the procedure of Example 7, except that honeycomb-shaped molded composite having through holes of equivalent diameter of 8 mm, a cell wall thickness of 2 mm, and an opening ratio of 64% was used instead. The complete catalyst had a weight ratio of TZ-1 : Pt = 99 : 1.
Control 1 By following the procedure of Example 1, palladium was deposited on commercially available carrier beads of titanium dioxide 5 mm in diameter. The complete catalyst consequently obtained had a weight ratio of Tio2 :
Pd = 97 : 3.
Example 9 Treatment of waste water by wet oxidation was carried out by the following method, using each of the catalysts obtained in Example 1-3 and Control 1. A
reaction column of stainless steel was packed with the catalyst. The waste water heated and mixed in advance and a gas containing oxygen in a concentration of 30% were fed into the reaction column via an inlet at the base. After 500 hours' treatment continued in this manner, the treated waste water was analyzed to determine the ratio of removal of foulin~ matter. The waste water used in the treatment had a COD tCr) content of ~0 y/liter, a total nitrogen content of 2.5 g/liter (inclusive of an ammoniac nitrogen content of 300 mg/liter), and a total solids content of 10 g/liter~ This waste water admixed with caustic soda was continuously introduced into the reaction column. Samples of the waste water taken at the inlet and the outlet of the reaction column were analyzed for COD lCr) content, total nitrogen content, and ammoniac nitrogen content, to determine the ratio of removal of fouling matter. Prior to the delivery to the reaction column, this waste water had `'~
~30~
the pH value thereof adjusted to 10 by addition of caustic soda. As to the reaction condition, the reaction temperature was 260C, the reaction pressure was 75 kg/cm2, the special velocity of waste water was 1.3hr~ (based on empty column), and the linear ~elocity of waste water was 10 m/hr. The oxygen containing gas was introduced at a space velocity of 190 hr~~ based on empty column under standard condition) into the reaction column.
~he results obtained of the catalysts of Examples 1, 2, and 3 indicate that the ratios of COD removal were respectively 99.9%, 99.9~, and 99.9%, the ratios of removal of total nitrogen were respectively 99.2%, 99.1%, and 99.3%, and the ratios of removal of ammoniac nitrogen were 99.9% 99.8%, and 99.9%.
In the treatment using the catalyst of Control 1, the catalyst bed was clogged after 70 hours following the start of the reaction so that the flow of the waste water was impeded and the treatment could not be thoroughly carried out.
Example 10 Treatment of waste water was carried out by the following method using each of the catalysts obtained in Examples ~-6. A reaction column of stainless steel was packed with the catalyst. The waste water he~ted and mixed in advance and a gas containing oxygen in a concentration of 30% were continuously fed into the reaction column via an inlet at the base for 800 hours. Samples of waste water taken at the inlet and the outlet of the reaction column were analyzed for COD (Cr) content, total nitrogen content, and ammoniac nitrogen content to determine the ratios of removal. The waste water used in the treatment had a COD
~Cr) content of 30 g/liter and a total nitrogen content of l.9g/liter (including an ammoniac nitrogen content of 900 mg/liter). This waste water was adjusted to pH 10 by addition of caustic soda. As to the reaction conditions, the reaction temperature was 260C, the reaction pressure was 75 kg/cm2, and the space velocity of waste water was 1.5 ~3(~,~965 hr~' (based on empty column). The oxygen-containing gas was fed into the reaction column at a space velocity of 150hr~l based on empty column under standard conditions). The results were as shown in Table l.
Table 1 Ratio of Ratio of Ratio of removal of COD removal of removal of (%) totalammoniac nitrogennitroger.
Example 4 99.9 99.499.8 Example 5 99.9 99.199.6 Example 6 99.9 99.399.6 Example 11 Treatment of waste water by wet oxidation was carried out by the following method, using each of the catalysts obtained in Examples 7 and 8. A reaction column of stainless steel was packed with the catalyst. The waste water heated and mixed in advance and a gas containing oxygen in a concentration oE 40% were continuously introduced into the reaction column via an inlet at the base for 500 hours. Samples of waste water taken at the inlet and the output of the reaction column were analyzed for COD (Cr) content, total nitrogen content, and ammoniac nitrogen content. The waste water had the pH value thereof adjusted to 10 by addition of caustic soda. As to the reaction conditions, the reaction temperature was 240C, the reaction pressure was 50 kg/cm2, the space velocity of waste water was 1 hr~ (based on empty column), and the linear velocity of waste water was 10 m/hr~ The oxygen-containing gas was introduced into the reaction column as a space velocity of 100 hr~l (based on empty column under standard conditions). The results consequently ':
~ - 23 -:
': ~
`' ' '` '' ` ' ' ' ' ' ~ , 1301~;5 obtained in the treatments using the catalysts of Example 7 and Example 8 indicate that the ratios o removal of COD were respectively 99.9% and 98.9%, the ratios of removal of total nitrogen were respectively 98.4~ and 93.5~, and the ratios of 5 removal of ammoniac nitrogen were respectively 99.6% and 97.5~.
Example 12 Treatment of waste water by wet oxidation was carried out by the following method using the catalyst 10 obtained in Example 2. A reaction column of stainless steel was packed with the catalyst. The waste water heated and mixed in advance and a gas containing oxygen in a concentration of 30~ and 020ne in a concentration of 1% were continuously introduced into the reaction column via an inlet 15 at the base. Samples of waste water taken at the inlet and outlet of the reaction column were analyzed for COD (Cr) content to determine the ratio of removal. The waste water used in the treatment had a COD (Cr) content of 10 g/liter.
It was adjusted to pH 10 by addition of caustic soda. As to 20 the reaction conditions, the reaction temperature was 190C, the raaction pressure was ~0 kg/cm2, and the space velocity of waste water was 2 hr 1 (based on empty column). The gas containing oxygen and ozone was introduced into the reaction column at a space velocity of 60 hr 1 (based on empty column 25 under standard conditions). The results indicate that the ratio of removal of COD was 92~.
E~ample 13 Treatment of waste water was carried out by following the procedure of Example 12, except that a mixed 30 gas containing oxygen in a concentration of 30~ and ozone in a concentration of 1% was introduced at a space velocity of ~0 hr 1 (based on empty column under standard conditions) and, at the same time, an aqueous 3~ hydrogen peroxide solution was introduced at a space velocity of 0.004 hr 1 -.
, i5 (based on empty column under standard conditions) into the reaction column. The results indicate that the ratio of removal of COD was 93%.
;
~30~9~;S
Among in the preferred methods cited above, the method of tl) proves to be particularly desirable.
Specifically, this method is carried out as follows:
Compounds selected severally from the group of typical examples of the titanium source and the silicon source are weighed out in amount to form a composite oxide consisting of Tio2 and sio2 in a prescribed ratio, mixed in the form of an acidic aqueous solution or as a sol containing titanium and silicon in a concentration in the range of 1 to 100 g/liter, preferably 10 to 80g/liter as oxide, and then held at a temperature in the ranye of 10 to 100C. The solution or sol is kept stirred, with aqueous ammonia added dropwise thereto meanwhile as a neutralizing agent, for a period of 10 minutes to three hours until a coprecipitate composed of titanium and silicon is formed at a pH in the range of 2 to 10. This coprecipitate is separated by filtratlon, thoroughly washed, then dried at a temperature in the range of 80 to 140C for a period of 1 to 10 hours, and calcined at a temperature in the range of 300 to 650C, preferably 350 to 600C for a period of one to 10 hours, preferably 2 to 8 hours, to give birth to Tio2-Sio2.
The TiO2-ZrO2-SiO2 is prepared by the same method as used for the preparation of the Tio2-Sio2. In this case, the zirconium source may be selected from among inorganic zirconium compounds such as zirconillm chloride and zirconium sulfate and organic zirconium compounds such as zirconium oxalate. Specifically, by handling a zirconium compound and a titanium compound suitably selected ~y the same method as described above, there can be easily prepared the TiO2-ZrO2-SiO2. The amount of zirconium to be present in this ternary composite oxide is desired to be not more than 30% by weight as ZrO2, based on the total amount of the TiO2+ZrO2+SiO2. The preparation of the TiO2-ZrO2 can be carried out in the same manner as described above.
Desirably, the TiO2-ZrO2 composite can be prepared by either of the following methods:
~3~ 9~S
1. A method which comprises mixing titanium chloride with zirconium oxychloride, adding ammonia to the resultant mixture thereby inducing precipitation in the mixed system, washing and drying the precipitate, and calcining the clean dry precipitate at a temperature in the range of 300O to 6500C, preferably 350 to 600C;
2. A method which comprises adding zirconyl nitrate to titanium tetrachloride, subjecting the resultant mixture to thermal hydrolysis thereby inducing precipitation in the mixed system, washing and drying the precipitate, and then calcining the clean dry precipitate at a temperature in the range of 300 to 650C, preferably 350O to 600OC; and From the Tio2-sio2~ TiO2-ZrO2, ZrO2 SiO2, or TiO2-SiO2-ZrO2 composite prPpared by either of the foregoing methods, a complete catalyst is obtained by a suitable method. A typical method comprises mixing the Tio2-sio2 composite in a powdery form with a molding auxiliary, kneading the resultant mixture under addition of a suitable amount of water, and molding the resultant blend in the shape of beads, pellets, sheets, or honeycombs by the use of an extrusion molder.
By drying the molded composite at a temperature in the ran~e of 50 to 120C and then calcining the dried molded composite as swept with air at a temperature in the range of 300 to 800C, preferably 350 to 600C, for a period in the range of 1 to 10 hours, preferably 2 to 6 hours, there is obtained a catalyst.
Production of a catalyst by the addition of metals selected from the group consisting of manganese, iron, nickel, cobalt, tungsten, copper, cerium, silver, platinum, palladium, rhodium, ruthenium, and iridium to the TiO2-ZrO2 composite can be accomplished by causing an aqueous solution of the metal salts to impregnate the molded TiO2-ZrO2 composite thereby effecting deposition of the metal salts on the composite and drying and calcining the resultant impregnated composite.
-- .
~L30~965 Alternatively, the production may be attained by adding the aqueous solution of the metal salt in combination with a molding auxiliary to the TiO2-ZrO2 composite in powdery form, blending them, and molding the resultant blend.
Examples of the starting materials for the catalyst component B to be used in combination with the catalyst component A in the preparation of the catalyst of this invention include oxides, hydroxides, inorganic acid salts, and organic acid salts. More specifically, the starting materials may be suitably selected from among ammonium salts, oxalates, nitrates, sulfates, and halides.
In accordance with the present invention, wet oxidation can be effectively carried out on various forms of waste water containing oxidizable organic or inorganic substances, such as supernatant and sedimented activated sludge occurring in the activated sludge treatment, waste water from fermentation, effluent from the process for polymerization of an organic compound, cyan-containing plant effluent, phenol-containing plant effluant, oil-containing waste water, effluent from a chemical plant, general industrial waste water from a food processing plant, etc., raw sewage, sewage, and sewage sludge. When the present invention is worked out by the use of the catalyst in the shape of honeycombs, even waste water containing solid particles in a concentration of more than O.lg/liter can be treated stably for a long time.
As to the reaction conditions befitting the purpose of this invention, the reaction temperature is below 370C, generally in the range of 100 to 370C, preferably 200 to 300C. The pressure inside the reaction system is required to be enough for the waste water under treatment to retain the liquid phase thereof intact, specifically falling in the range of 0 to about 200 kg/cm2, preferably 0 to 150 kg/cm2. The molecular oxygen-containing gas to be fed into the reaction system is used in an amount of 1 to 1.5 times, preferably 1.2 to 1.5 times, the B
~3(~ 65 theoretical amount necessary for the oxidative decomposition aimed at. The amount of the catalyst to be packed in the reaction column is approximately 5 to 99%, preferably 20 to 99%, of the spacial capacity of the reaction column. The waste water, to be effectively oxidized, is fed in combination with the molecular oxygen-containing gas to the catalyst bed kept at a prescribed temperature at a flow rate such that the retention time thereof will be in the range of 6 to 120 minutes, preferably in the range of 12 to 60 minutes.
Examples of the molecular oxygen-containing gas used effectively herein include air, mixed gas of oxygen with air, and a gas generally called an oxygen-enriched air. This gas is desired to have an oxygen content of not less than 25~. Thouyh the pH value of the reaction system may be on the acid or on the alkali side, it is desired to fall in the range of 9 to 11.
As to the reaction conditions in the treatment using ozone and/or hydrogen peroxide as an oxidizing agent in combination with the molecular oxygen, the reaction temperature generally falls in the range of 100 to 250C, the r~action pressure .is such as to enable the waste water to retain the li~uid phase thereof intact inside the reaction column, speciEically falling in the range of 0 to 200 kg/cm2, preferably 0 to 150 kg/cm2, and the retention time falls in the range of 3 to 120 minutes, preferably 5 to 60 minutes. The amount of ozone to be used is in the range of 0.001 to 0.6 mol, preferably 0.003 to 0.2 mol, per mol of theoretical amount of oxygen. The amount of hydrogen peroxide to be used falls in the range of 0.001 to 1.8 mols, preferably 0.003 to 0.2 mol, per mol of the theoretical amount of oxygen.
Now, the present invention will be described more specifically below with reference to working examples. It should be noted, however, that this invention is not limited to these examples.
~3~)~9~;5 Example 1 A composite oxide comprising titanium and silicon was prepared as follows. An aqueous sulfuric acid solution of titanyl sulfate having the following composition was used as a titanium source.
Tioso4 (as Tio2) 250 g/liter Total l~2SO4 1,100 g/liter Separately, 28 liters of aqueous ammonia (NH3, 25~) was added to 40 liters of water and 2.4 kg of Snowtex-NCS-30TM (silica sol containing about 30% by weight of silica as SiO2; product of Nissan Chemicals Industries Ltd.) was added further added theretoO To the resulting solution, a titanium-containing aqueous sulfuric acid solution prepared by diluting 15.3 liters of the aqueous sulfuric acid solution of titanyl sulfate with 30 liters of water was gradually added dropwise while under agitation to give rise to a coprecipitate gel. The resulting reaction mixture was left standing at rest for 15 hours. The Tio2-Sio2 gel thus obtained was separated by filtration washed with water, and then dried at 200C to for 10 hours.
The dry Tio~-Sio2 gel was calcined under an atmosphere of air at 550C for six hours. The powder thus obtained had a composition of TiO2:SiO2=4:1 (molar ratio) and a BET surface area of 185 m2/g. The powder which will be referred to hereinafter as TS-1 was used to prepare an ozone decomposition catalyst as follows.
In a kneader, 900 ml of water, 1,500 g of the powder, and 75 g of starch were thoroughly kneaded. The resultant blend was further kneaded with a suitable amount of water. The blend consequently obtained was extrusion molded in the shape of honeycombs having a hole diameter ~equi~alent diameter of through holes) of 3 mm and an opening ratio of 64%, dried at 120C for 5iX hours, and thereafter calcined at 450C for 5iX hours in an atmosphere having an oxygen concentration adjusted to below 15%.
~3 ID191E~
The molded composite so obtained was immersed in an aqueous palladium nitrate solution until sufficient impregnation, then dried at 120C for six hours, and calcined at 450C for six hours in an atmosphere of air.
The complete catalyst thus obtained had a percentage composition of TS-l : Pd = 97 : 3.
Example 2 TiO2-ZrO2 was prepared as follows.
In 100 liters of cold water, 1.93 kg of zirconium oxychloride (ZrOCl2 8H2O) was dissolved. In the resulting solution 7.7 liters of an aqueous sulfuric aci~ solution of titanyl sulfate having the same composition as used in Example 1 was added and thoroughly mixed. The mixture thus formed was kept amply stirred at a ~emperature of about 30C and aqueous ammonia was gradually added thereto until the pH reached 7. The resulting reaction mixture was left standing at rest for 15 hours.
The TiO2-ZrO2 gel thus obtained was separated by filtration, washed with cold water, and then dried at 200C
for 10 hours. Then, the dry gel was calcined undsr an atmosphere o air at 550C for six hours. The powder conse~uently obtained had a composition of TiO2:ZrO2 = 4 :
1 (molar rativ) and a BET surface area of 140 m2/g. The : powder thus obtained will be referred to hereinafter as TZ~l.
t.~
"~"`'~
~3~L9~5 By using this TZ-l and following the procedure of Example 1, there was obtained a honeycomb shaped article.
Then by using an aqueous chloroplatinic acld solution instead of the aqueous palladium nitrate and following the procedure 5 o~ Example 1, there was obtained a catalyst having weight ratio of TZ-l:Pt = 99 : 1.
Example 3 TiO2-SiO2-ZrO2 was prepared by following the procedures of Examples 1 and 2. The powder conse~uently 10 obtained had a composition of TiO2 : SiO2 : ZrO2 - 80 : 16 :
4 (molar ratio) and a BET surface area of 180 m /g. The powder thus obtained will be referred to hereinafter as TSZ-l.
By using this TSZ-l instead of TS-l and following 15 the procedure of Example 1, ther~ was obtained a honeycomb shaped catalyst having weight ratio of TSZ-l : Pd = 97 : 3.
Example 4 Catalyst having weight ratio of TZ-l : Ru = 98 : 2 was ~repared by using an aqueous solution of ruthenium 20 chloride solution instead of the aqueous chloroplatinic acid solution and following the procedure o Example 2.
Examples 5 ~ 6 Ca~alysts were prepared by following the procedure of Example 4, .except that TiO2-ZrO2 composite oxide powder 25 was used with different TiO2/ZrO2 molar ratios.
Tio2 : ZrO2 (molar ratio) Example 5 60 : ~0 Example 6 40 : 60 Example 7 A honeycomb-shaped molded composite having through holes of a equivalent diameter of 4 mm, a cell wall thickness of 0.8 mm, and an opening ratio of 69~ was obtained from the TZ-l powder produced in Example 2. Then, the molded composite was immersed in an aqueous chloroplatinic acid 35 solution, dried at 120C, and thereafter calcined at 450C in ~3~)~9~iS
an atmosphere of air, to produce a complete catalyst. The complete catalyst thus obtained had a weight ratio of TZ-1 : Pt = 99 : 1.
Example 8 ~ complete catalyst was produced by following the procedure of Example 7, except that honeycomb-shaped molded composite having through holes of equivalent diameter of 8 mm, a cell wall thickness of 2 mm, and an opening ratio of 64% was used instead. The complete catalyst had a weight ratio of TZ-1 : Pt = 99 : 1.
Control 1 By following the procedure of Example 1, palladium was deposited on commercially available carrier beads of titanium dioxide 5 mm in diameter. The complete catalyst consequently obtained had a weight ratio of Tio2 :
Pd = 97 : 3.
Example 9 Treatment of waste water by wet oxidation was carried out by the following method, using each of the catalysts obtained in Example 1-3 and Control 1. A
reaction column of stainless steel was packed with the catalyst. The waste water heated and mixed in advance and a gas containing oxygen in a concentration of 30% were fed into the reaction column via an inlet at the base. After 500 hours' treatment continued in this manner, the treated waste water was analyzed to determine the ratio of removal of foulin~ matter. The waste water used in the treatment had a COD tCr) content of ~0 y/liter, a total nitrogen content of 2.5 g/liter (inclusive of an ammoniac nitrogen content of 300 mg/liter), and a total solids content of 10 g/liter~ This waste water admixed with caustic soda was continuously introduced into the reaction column. Samples of the waste water taken at the inlet and the outlet of the reaction column were analyzed for COD lCr) content, total nitrogen content, and ammoniac nitrogen content, to determine the ratio of removal of fouling matter. Prior to the delivery to the reaction column, this waste water had `'~
~30~
the pH value thereof adjusted to 10 by addition of caustic soda. As to the reaction condition, the reaction temperature was 260C, the reaction pressure was 75 kg/cm2, the special velocity of waste water was 1.3hr~ (based on empty column), and the linear ~elocity of waste water was 10 m/hr. The oxygen containing gas was introduced at a space velocity of 190 hr~~ based on empty column under standard condition) into the reaction column.
~he results obtained of the catalysts of Examples 1, 2, and 3 indicate that the ratios of COD removal were respectively 99.9%, 99.9~, and 99.9%, the ratios of removal of total nitrogen were respectively 99.2%, 99.1%, and 99.3%, and the ratios of removal of ammoniac nitrogen were 99.9% 99.8%, and 99.9%.
In the treatment using the catalyst of Control 1, the catalyst bed was clogged after 70 hours following the start of the reaction so that the flow of the waste water was impeded and the treatment could not be thoroughly carried out.
Example 10 Treatment of waste water was carried out by the following method using each of the catalysts obtained in Examples ~-6. A reaction column of stainless steel was packed with the catalyst. The waste water he~ted and mixed in advance and a gas containing oxygen in a concentration of 30% were continuously fed into the reaction column via an inlet at the base for 800 hours. Samples of waste water taken at the inlet and the outlet of the reaction column were analyzed for COD (Cr) content, total nitrogen content, and ammoniac nitrogen content to determine the ratios of removal. The waste water used in the treatment had a COD
~Cr) content of 30 g/liter and a total nitrogen content of l.9g/liter (including an ammoniac nitrogen content of 900 mg/liter). This waste water was adjusted to pH 10 by addition of caustic soda. As to the reaction conditions, the reaction temperature was 260C, the reaction pressure was 75 kg/cm2, and the space velocity of waste water was 1.5 ~3(~,~965 hr~' (based on empty column). The oxygen-containing gas was fed into the reaction column at a space velocity of 150hr~l based on empty column under standard conditions). The results were as shown in Table l.
Table 1 Ratio of Ratio of Ratio of removal of COD removal of removal of (%) totalammoniac nitrogennitroger.
Example 4 99.9 99.499.8 Example 5 99.9 99.199.6 Example 6 99.9 99.399.6 Example 11 Treatment of waste water by wet oxidation was carried out by the following method, using each of the catalysts obtained in Examples 7 and 8. A reaction column of stainless steel was packed with the catalyst. The waste water heated and mixed in advance and a gas containing oxygen in a concentration oE 40% were continuously introduced into the reaction column via an inlet at the base for 500 hours. Samples of waste water taken at the inlet and the output of the reaction column were analyzed for COD (Cr) content, total nitrogen content, and ammoniac nitrogen content. The waste water had the pH value thereof adjusted to 10 by addition of caustic soda. As to the reaction conditions, the reaction temperature was 240C, the reaction pressure was 50 kg/cm2, the space velocity of waste water was 1 hr~ (based on empty column), and the linear velocity of waste water was 10 m/hr~ The oxygen-containing gas was introduced into the reaction column as a space velocity of 100 hr~l (based on empty column under standard conditions). The results consequently ':
~ - 23 -:
': ~
`' ' '` '' ` ' ' ' ' ' ~ , 1301~;5 obtained in the treatments using the catalysts of Example 7 and Example 8 indicate that the ratios o removal of COD were respectively 99.9% and 98.9%, the ratios of removal of total nitrogen were respectively 98.4~ and 93.5~, and the ratios of 5 removal of ammoniac nitrogen were respectively 99.6% and 97.5~.
Example 12 Treatment of waste water by wet oxidation was carried out by the following method using the catalyst 10 obtained in Example 2. A reaction column of stainless steel was packed with the catalyst. The waste water heated and mixed in advance and a gas containing oxygen in a concentration of 30~ and 020ne in a concentration of 1% were continuously introduced into the reaction column via an inlet 15 at the base. Samples of waste water taken at the inlet and outlet of the reaction column were analyzed for COD (Cr) content to determine the ratio of removal. The waste water used in the treatment had a COD (Cr) content of 10 g/liter.
It was adjusted to pH 10 by addition of caustic soda. As to 20 the reaction conditions, the reaction temperature was 190C, the raaction pressure was ~0 kg/cm2, and the space velocity of waste water was 2 hr 1 (based on empty column). The gas containing oxygen and ozone was introduced into the reaction column at a space velocity of 60 hr 1 (based on empty column 25 under standard conditions). The results indicate that the ratio of removal of COD was 92~.
E~ample 13 Treatment of waste water was carried out by following the procedure of Example 12, except that a mixed 30 gas containing oxygen in a concentration of 30~ and ozone in a concentration of 1% was introduced at a space velocity of ~0 hr 1 (based on empty column under standard conditions) and, at the same time, an aqueous 3~ hydrogen peroxide solution was introduced at a space velocity of 0.004 hr 1 -.
, i5 (based on empty column under standard conditions) into the reaction column. The results indicate that the ratio of removal of COD was 93%.
Claims (15)
1. A method for the treatment of waste water which comprises subjecting said waste water to wet oxidation at a temperature of not more than 370°C under pressure enough for said waste water to retain the liquid phase thereof intact under continued supply of a gas containing oxygen in an amount of 1.0 to 1.5 times the theoretical amount necessary for enabling organic and inorganic substances contained in said waste water to be decomposed thoroughly into nitrogen, carbon dioxide, and water, in the presence of a catalyst (excluding a molded monolithic catalyst provided a plurality of through holes having 2 to 20 mm of an average pore diameter) composed of catalyst component A
comprising a composite oxide of at least two metals selected from the group consisting of titanium, silicon, and zirconium and catalyst component B comprising at least one metal selected from the group consisting of manganese, iron, cobalt, nickel, tungsten, copper, cerium, silver, platinum, palladium, rhodium, ruthenium, and iridium or a water-insoluble or sparingly water-soluble compound of said metal.
comprising a composite oxide of at least two metals selected from the group consisting of titanium, silicon, and zirconium and catalyst component B comprising at least one metal selected from the group consisting of manganese, iron, cobalt, nickel, tungsten, copper, cerium, silver, platinum, palladium, rhodium, ruthenium, and iridium or a water-insoluble or sparingly water-soluble compound of said metal.
2. A method according to Claim 1, wherein said catalyst has a composition such that said catalyst component A accounts for a proportion in the range of 75 to 99.95% by weight as oxide and said catalyst component B for a proportion in the range of 0.05 to 25% by weight as metal or compound.
3. A method according to Claim 1, wherein said catalyst component A of said catalyst is at least one member selected from the group consisting of (a) a binary TiO2-SiO2 composite oxide containing 20 to 95 mol% of titania (TiO2) and 5 to 80 mol% of silica (SiO2) (b) a binary TiO2-ZrO2 composite oxide containing 20 to 90 mol% of TiO2 and 10 to 80 mol% of zirconia (ZrO2), (c) a binary ZrO2-SiO2 composite oxide containing 20 to 90 mol% of ZrO2 and 10 to 80 mol% of SiO2 and (d) a ternary TiO2-SiO2-ZrO2 composite oxide containing 20 to 95 mol% of TiO2 and 5 to 80 mol% of the sum of SiO2 and ZrO2.
4. A method according to Claim 1, wherein said catalyst components A is a binary TiO2-ZrO2 composite oxide.
5. A method according to Claim 3, wherein said catalyst component A is a binary TiO2-ZrO2 composite oxide.
6. A method according to Claim 1, wherein said catalyst component A is a binary TiO2-ZrO2 composite oxide containing 20 to 90 mol% of TiO2 and 10 to 80 mol% of ZrO2.
7. A method according to claim 1, wherein the reaction temperature is in the range of 100° to 370°C.
8. A method according to Claim 1, wherein said catalyst component A accounts for 85 to 99.9% by weight as oxide and said catalyst component B accounts for 0.1 to 15%
by weight as metal or compound.
by weight as metal or compound.
9. A method according to Claim 8, wherein of the metallic elements making up said catalyst component B, the amount of manganese, iron, cobalt, nickel, tungsten, copper, cerium, or silver to be used accounts for 0 to 15 by weight as compound and the amount of platinum, palladium, rhodium, ruthenium, or iridium to be used accounts for 0 to 5% by weight as metal, providing that the total amount of the two metals falls in the range of 0.1 to 15% by weight.
10. A method according to Claim 8, wherein said catalyst component B is the oxide of at least one metal selected from the group consisting of manganese, iron, cobalt, nickel, tungsten, copper, cerium, and silver.
11. A method according to Claim 8, wherein said catalyst component B is at least one metal selected from the group consisting of platinum, palladium, rhodium, ruthenium, and iridium.
12. A method according to Claim 1, wherein said catalyst component A has a surface area of not less than 30 m2/g.
13. A method according to Claim 1, wherein the passage through said catalyst of waste water in combination with an oxygen-containing gas is carried out in the presence of at least one gas selected from the group consisting of ozone and hydrogen peroxide.
14. A method according to Claim 13, wherein the amount of ozone to be used falls in the range of 0.001 to 0.6 mol per mol of the theoretical amount of oxygen necessary for the organic and inorganic substances contained in said waste water to be thoroughly decomposed into nitrogen, carbon dioxide gas, and water.
15. A method according to Claim 13, wherein the amount of hydrogen peroxide to be used falls in the range of 0.001 to 1.8 mols per mol of the theoretical amount of oxygen necessary for the organic and inorganic substances contained in said waste water to be thoroughly decomposed into nitrogen, carbon dioxide, and water.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000544862A CA1301965C (en) | 1987-08-19 | 1987-08-19 | Method for treatment of waste water |
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| Application Number | Priority Date | Filing Date | Title |
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| CA000544862A CA1301965C (en) | 1987-08-19 | 1987-08-19 | Method for treatment of waste water |
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| CA000544862A Expired - Fee Related CA1301965C (en) | 1987-08-19 | 1987-08-19 | Method for treatment of waste water |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114425319A (en) * | 2020-10-15 | 2022-05-03 | 中国石油化工股份有限公司 | Wet oxidation catalyst and preparation method thereof |
| CN115414952A (en) * | 2022-08-22 | 2022-12-02 | 中国五环工程有限公司 | Multicomponent hydrogenation catalyst for synthesizing methyl glycolate and preparation method thereof |
| CN115475619A (en) * | 2021-06-16 | 2022-12-16 | 中国石油化工股份有限公司 | Wet oxidation catalyst and preparation method and application thereof |
| CN116462303A (en) * | 2023-04-28 | 2023-07-21 | 湖南中天元环境工程有限公司 | Catalytic wet oxidation compound homogeneous catalyst and preparation method and application thereof |
-
1987
- 1987-08-19 CA CA000544862A patent/CA1301965C/en not_active Expired - Fee Related
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114425319A (en) * | 2020-10-15 | 2022-05-03 | 中国石油化工股份有限公司 | Wet oxidation catalyst and preparation method thereof |
| CN114425319B (en) * | 2020-10-15 | 2023-08-04 | 中国石油化工股份有限公司 | Wet oxidation catalyst and preparation method thereof |
| CN115475619A (en) * | 2021-06-16 | 2022-12-16 | 中国石油化工股份有限公司 | Wet oxidation catalyst and preparation method and application thereof |
| CN115475619B (en) * | 2021-06-16 | 2024-03-29 | 中国石油化工股份有限公司 | Wet oxidation catalyst and preparation method and application thereof |
| CN115414952A (en) * | 2022-08-22 | 2022-12-02 | 中国五环工程有限公司 | Multicomponent hydrogenation catalyst for synthesizing methyl glycolate and preparation method thereof |
| CN115414952B (en) * | 2022-08-22 | 2023-09-12 | 中国五环工程有限公司 | Multicomponent hydrogenation catalyst for synthesizing methyl glycolate and preparation method thereof |
| CN116462303A (en) * | 2023-04-28 | 2023-07-21 | 湖南中天元环境工程有限公司 | Catalytic wet oxidation compound homogeneous catalyst and preparation method and application thereof |
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