JPS5924849B2 - Treatment method for exhaust gas containing sulfur oxides - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for adsorbing and removing sulfur oxides contained in exhaust gas.

More specifically, it is characterized by adsorbing and removing sulfur oxides contained in various combustion exhaust gases, exhaust gases from Claus furnaces, etc. using an adsorbent whose main components are titanium oxide and oxidized steel.

Sulfur oxides (mainly S02 and S03) contained in various combustion exhaust gases or Claus furnace tail gas.

SOx (hereinafter abbreviated as t) is a major air pollutant, and there is a strong desire to suppress its emissions for environmental conservation.

Some techniques for removing SOx in flue gas have already been put into practical use.

One method is to absorb SOX with a calcium carbonate slurry and then oxidize it to produce calcium sulfate (gypsum).

One of the methods is to absorb SOx with an alkaline absorption liquid, react it with calcium oxide to form calcium sulfite, and then oxidize it to form gypsum.

In these methods, since a large amount of gypsum is produced, it is necessary to establish a technology for utilizing the gypsum, and there is also the problem of processing the absorption liquid (for example, mirabilite produced as a by-product).

In contrast to the above method, dry SOx removal technology uses a solid adsorbent to adsorb SOx in exhaust gas, and desorbs the adsorbed SOx from the adsorbent with reducing gas, resulting in a relatively high concentration of SOx. There is a method of treating desorbed gas containing sulfur with a Claus reaction and extracting it as heavy sulfur.

This method has the advantage that the sulfur produced has high utility value and there are no problems such as wastewater treatment.

As a solid adsorbent for SOx, copper oxide with alumina support (
CuOAl□03) is known (Special Publication No. 49-17
951).

However, according to additional tests by the present inventors, Cu0-A
When SOx is removed using l□03 adsorbent, a small amount of 503 (sulfuric acid mist) contained in the exhaust gas partially degenerates the alumina support into aluminum sulfate, and its removal performance decreases in a short period of time. It was revealed that the

The present inventors have developed an adsorbent T containing titanium oxide and copper oxide.
It was discovered that iO2.CuO has excellent SOX adsorption ability and that its performance does not deteriorate due to SO3 in exhaust gas, and the above drawbacks were overcome.

An adsorbent made of an intimate mixture of titanium oxide and copper oxide has a similar specific surface area and pore volume compared to an alumina-supported copper oxide adsorbent.

It has excellent SOx adsorption performance, and what is most important is that it has extremely good durability against S03.

The present inventors have already reported that a catalyst containing titanium oxide as a main component is extremely effective in reducing and removing nitrogen oxides in exhaust gas using ammonia.
O-89290), Ti-Mo catalyst (Japanese Patent Application Laid-Open No. 1989-1999-'
89291), Ti-W catalyst (JP-A-5O-89264)
), has filed a patent application for a TiCu catalyst (Japanese Unexamined Patent Publication No. 5O-89289).

The present inventors were led to the present invention by the discovery that the sulfur oxide concentration also decreased when conducting a denitrification experiment of a gas containing nitrogen oxides and sulfur oxides using a Ti-Cu catalyst. .

The fact that the catalyst of the present invention has good durability against SO3 is due to the excellent properties of titanium oxide, namely, the property that titanium oxide does not become sulfated at high temperatures.

In the present invention, an adsorbent mainly composed of titanium oxide and copper oxide is used to remove SOX from exhaust gas, but the performance is best when the adsorbent is made of a close mixture of titanium oxide and copper oxide. ing.

Therefore, when a T io 2 CuO adsorbent is produced using commercially available rutile or anatase titanium oxide calcined at 700°C or higher, titanium oxide and copper oxide will not form an intimate mixture. Furthermore, its specific surface area is usually less than 2 orn2/g, and its SOx adsorption performance is insufficient (G).

In order to obtain the adsorbent made of an intimate mixture of titanium oxide and copper oxide according to the present invention, titanium salt solutions such as titanium tetrachloride and titanium sulfate are used as the raw material for titanium oxide by heating and hydrolysis.
Alternatively, it is appropriate to use meta- or orthotitanic acid obtained by addition of an alkaline solution.

When producing the adsorbent of the present invention using commercially available rutin or anatase-type titanium oxide, the titanium oxide is treated with hot concentrated sulfuric acid to convert part or all of the titanium oxide to titanium sulfate, Thereafter, it may be used after being converted into meta- or orthotitanic acid by thermal hydrolysis or addition of an alkaline solution.

According to the present invention, SOX in exhaust gas is reduced to T io 2 ・C
When removing with uO adsorbent, the reaction seems to be mainly based on the following equation.

Before the start of adsorption, copper in the adsorbent exists as an oxide, but as it adsorbs SOX, it changes to copper sulfate.

In this case, if CuO-Al2O3 adsorbent is used,
At the same time as CuO changes to CuSO4, a part of alumina, which is a carrier, also changes to aluminum sulfate due to a small amount of SO3 present in the exhaust gas.

This sulfation of the carrier component is considered to be the most important cause of deterioration of the adsorbent with an alumina carrier.

On the other hand, when the T 1o2-CuO adsorbent of the present invention is used, CuO changes to CuS 04, but titanium oxide, which is the main component, does not substantially change in quality.

The TiO-CuO adsorbent of the present invention has several top SO3
Even when used to treat gases containing PM, it maintains its SOX adsorption performance for a long time.

As mentioned above, the SOX adsorbent of the present invention
The reason why the adsorbent is not poisoned by O3 is that the main component of the adsorbent is titanium oxide.

Therefore, the content of titanium oxide in the TiO2/CuO adsorbent of the present invention is 50% (atomic percentage, the same hereinafter).
It is better to do more than that.

If the content of titanium oxide is less than 50%, the durability against S03 will deteriorate, which is not preferable.

The content ratio of copper oxide is 2 to 50 parts, preferably 4 to 50 parts.

If the proportion of copper oxide is less than 2%, the adsorption capacity for SOx will not be sufficient.

The till gas in the Claus reactor usually contains H2 in addition to sO2.
It also contains S.

Since the TiO2.CuO adsorbent (catalyst) of the present invention also has activity for the Claus reaction, it is thought that the reaction represented by the following formula also occurs at the same time.

HS + Cu0 = CuS + H20 (4) The tail gas of the Claus reactor usually does not contain oxygen, but by adding air or oxygen, the T of the present invention
If an iO2.CuO adsorbent is used, H2S will be converted to S02 according to equation (5), and SO2 will eventually be adsorbed and removed.

According to the tests conducted by the present inventors, when treating Claus reactor oil gas containing H2S and SO2 at the same time,
From the change in color of the T t 02·CuO adsorbent after use, it appears that some of the CuO has become Cu5 (reaction (4)).

If an adsorbent is used continuously for a certain period of time, it will no longer adsorb SOX, so it must be regenerated.

Regeneration methods include hydrogen, carbon monoxide, or methane,
It is appropriate to treat with a reducing gas such as LPG (liquefied petroleum gas).

When the adsorbent after adsorbing SOX is treated with the above-mentioned reducing gas, S02 and a small amount of H2S are generated as the desorption gas.

Since the desorption gas contains relatively high concentrations of SO2 and H2S, it can be treated by the known Claus method, absorption desulfurization method, or the like.

When the SOX removal method of the present invention is applied to the treatment of Claus reactor tail gas, it is of course a good method to recirculate the desorbed gas to the Claus reactor.

Since the adsorbent after the desorption process is in a reduced state, it can be oxidized with air or oxygen, or it can be passed through exhaust gas and returned to the adsorption process and oxidized with oxygen in the exhaust gas.

As described above, in the present invention, TiO2・C
The uO adsorbent repeatedly undergoes adsorption-desorption or adsorption-desorption and monoxidation processes.

Therefore, when treating exhaust gas continuously, it is desirable to install two or more towers filled with adsorbent so that they can undergo the adsorption-desorption (mono-oxidation) process in sequence. ).

The temperature of the adsorption step when removing SOx according to the present invention is 250-500°C, preferably 300-500°C.
It is 0°C.

If the temperature is below 250° C., the SOX adsorption rate is slow and a large amount of adsorbent is used, making it uneconomical.

When the temperature exceeds 500° C., sintering of the TiO2.CuO adsorbent occurs, and the adsorption performance decreases over time.

Also, the space velocity of exhaust gas is 200 to 20,000 V/V.
/h, preferably 300 to oooh.

The space velocity is determined by the desired desulfurization rate.

The type of adsorption tower that can be used is a fixed bed, moving bed, or fluidized bed.

Titanium raw materials for manufacturing the TiO2/CuO adsorbent of the present invention include titanium oxide (but not heat treated at 600°C or higher), various titanic acids, titanyl sulfate, titanium sulfate, titanium tetrachloride, etc. obtain.

Further, as the copper raw material, copper oxide, steel hydroxide, copper carbonate, copper sulfate, copper nitrate, copper halide, etc. can be used.

Adsorbent preparation methods include a coprecipitation method in which an alkaline solution is added to a mixed solution of titanium and copper to simultaneously precipitate titanium and copper hydroxides, and a kneading method in which oxides, hydroxides, etc. are mixed. Alternatively, an impregnation method in which a titanium oxide molded body is made and then immersed in copper salt can be used.

Further, as a method for molding the adsorbent, any of the conventional catalyst manufacturing methods such as tablet molding, extrusion molding, transfer granulation, etc. may be used.

After calcination, the adsorbent of the present invention ultimately exists in the form of an oxide (if copper sulfate is used, sulfate is also present), but the calcination temperature is 600°C or less. good.

When fired at 600°C or higher, the specific surface area usually decreases to 20m”7.
9 or less, and the SOX adsorption performance is no longer sufficient.

The present invention will be specifically explained below using a leprosy example.

Actual fiber example 1 Copper nitrate (Cu(NO3)2.
6H20)72.9 was added and kneaded in a kneader for 2 hours.

After drying this mixture at 150°C for 5 hours, it was pulverized, further 6g of graphite was added, and a tablet of 3myxφx
It was molded into a cylindrical shape of 3 mmh.

This molded product was fired at 450°C for 2 hours. The resulting adsorbent contains titanium and copper in an atomic ratio of 9=1.

When the specific surface area of this adsorbent was measured using the BET method, it was 93 m2.
/g.

The SOX removal performance of the adsorbent was measured as follows.

The reaction tube is made of quartz and has an inner diameter of 30 mm, and is heated from the outside in an electric furnace.

20ml of the above adsorbent in the center of the reaction tube! Filled with gas of the following composition at 100 Ne/h (space velocity s, oooh
), and the SO2 concentration at the outlet of the reaction tube was measured.

Note that a non-dispersive infrared analyzer was used to measure the SO2 concentration.

Table 1 shows the results of the experiment conducted with the reaction temperature set at 350°C.
Shown below.

Gas composition: S020.2%, 025%, CO2 12%1
H2012 section, N2 residual comparative example [Commercially available activated alumina (r-A1203) was made into a fine powder, and an aqueous solution of copper nitrate was added thereto to prepare a copper oxide adsorbent with an alumina carrier in the same manner as in Example 1. .

The obtained adsorbent contained 10 parts (by weight) of copper oxide, and its specific surface area was 180 m'/g.

Using 20 ml of this adsorbent, an experiment was conducted under the same reaction conditions as in Example 1, and the results shown in Table 1 were obtained.

Example 2 2.5 kg of titanium tetrachloride (T iCl 4 ) was gradually dissolved in water 51, and g was added to copper sulfate L7.

An aqueous solution of sodium carbonate was added dropwise to this mixed solution to form a coprecipitate of titanium and copper.

After thoroughly washing the precipitate, it was dried at 150° C. for 5 hours, and in the same manner as in Example 1, a cylindrical adsorbent of 3 mmφ×3 mm11 was obtained.

The obtained adsorbent contained titanium and copper in an atomic ratio of 7:3 and had a specific surface area of 146 m''/.9.

Using 20 ml of the obtained adsorbent, an experiment was conducted under the same conditions as in Example 1 except that the reaction temperature was 400° C., and the results shown in Table 1 were obtained.

Example 3 200 g of commercially available anatase-type titanium oxide was dissolved in concentrated sulfuric acid (36
N) and heated at 200 to 25°C for 2 hours to convert part of the titanium oxide into titanium sulfate.

After cooling the thus obtained mixture of titanium oxide and titanium sulfate, 156 g of copper sulfate was added and dissolved.

While vigorously stirring this slurry-like mixture of titanium oxide, titanium sulfate, and copper sulfate, an aqueous solution of sodium hydroxide was added dropwise to adjust the pI to about 8.

After thoroughly washing the obtained precipitate, an adsorbent was obtained in the same manner as in Example 1.

The obtained adsorbent contained titanium and copper in an atomic ratio of 8:2, and its specific surface area was 115 m2/.9.

Using the adsorbent obtained as described above, the reaction temperature was 43°C.
An experiment was conducted in the same manner as in Example 1 except for the temperature of 0° C., and the results shown in Table 1 were obtained.

Example 4 In this actual case, a case will be described in which a large number of reaction-regeneration cycles are performed.

The processing gas is pressurized heavy oil boiler exhaust gas, and its composition is approximately NOX200p1SO21200p4,
So350ppm, 0□5 section, CO212%, H2O1
0 section, N2 remaining.

The reaction tube was made of stainless steel and had an inner diameter of 50 tubes, and was filled with 500 ml of adsorbent prepared in the same manner as in Example 3.

Furthermore, the hydrogen used in the reduction step was in a 3rd old cylinder.

The reaction-regeneration cycle is as follows.

(1) Reaction stage: gas with the above composition at a space velocity of 5.000
60 mm flowed at h.

The reaction temperature was 380°C.

(2) Reduction process: Hydrogen at a space velocity of 200h' for 25
The basket was distributed.

The reaction temperature was 380°C.

(3) Purge step: Nitrogen gas was passed through at a space velocity of too'.

The steps (1), (2), and (3) above were performed 732 times.

Table 2 shows the SO2 outlet concentration in the reaction step in the 3.400.732nd cycle.

Comparative Example 2 Using the adsorbent shown in Comparative Example 1, a test similar to that shown in Actual Case 4 was conducted.

At 30 m#+ after the start of the reaction process of the 120th cycle, the outlet SO2 concentration was 700 p4 or more, which revealed that the adsorption performance of the adsorbent had significantly deteriorated.

After the 120th reaction step was carried out for 60 ml, the test was stopped, the adsorbent was taken out and analyzed by X-ray diffraction, and a diffraction peak of aluminum sulfate was clearly observed.

Actual case 5 Metatitanic acid (T iO(OH) 2 ) was heated at [20°C
After drying, it was fired at 500°C for 2 hours.

The fired product was pulverized to a size of 100 mesh or less, and this powder was molded into a sphere with a diameter of 3 to 5111 m using a transfer granulator.

The molded article was fired at 550°C for 2 hours. This titanium oxide sphere was immersed in copper nitrate solution, and after drying, it was heated to 550°C again.
It was baked for 2 hours.

This adsorbent contained t5wt% of copper oxide.

Using the obtained adsorbent, the reaction was carried out for 50 cycles under the same conditions as in actual case 4.

The outlet SO2 concentration at the 50th cycle is 3 after 15 minutes.
0ppH1, 30 minutes later 80ppI11.60 minutes later t4o
It was ppm.

Claims (1)

[Claims] 1. In a method for adsorbing and removing sulfur oxides by bringing exhaust gas containing sulfur oxides into contact with an adsorbent, the adsorbent contains ortho- or metatitanic acid obtained by hydrolyzing an aqueous titanium salt solution. A method for treating exhaust gas containing sulfur oxides, characterized in that the mixture is an intimate mixture of titanium and copper oxides obtained by firing a mixture with a copper salt at a temperature of 600°C or less. 2. A method for treating exhaust gas containing sulfur oxides, characterized in that the step of adsorbing sulfur oxides is carried out at 250 to 500°C. 3. The method according to claim 1 or 2, characterized in that the content ratio of the titanium and copper oxides is in an atomic ratio of titanium:copper=98:2 to 50:50. A method for treating exhaust gas containing oxides.