JPH0144227B2 - - Google Patents

Description

[Detailed description of the invention]

(Purpose and Background) The present invention relates to a method for regenerating a solid oxygen carrier used in an oxidative dehydrogenation reaction of hydrocarbons.
It is an object of the present invention to provide a method for extending the life of a solid oxygen carrier so that it can be used continuously over a long period of time. In order to produce useful compounds by oxidative dehydrogenation of hydrocarbon raw materials, a method is generally used in which the raw material gas is brought into contact with a catalyst at high temperature together with a molecular oxygen-containing gas, such as air, to carry out an oxidative dehydrogenation reaction. ing. A typical example is a method of producing butadiene by bringing butane or butene into contact with a metal oxide catalyst together with air to perform an oxidative dehydrogenation reaction using molecular oxygen. However, such a method has the disadvantage that various oxygen-containing hydrocarbon compounds are produced as by-products, which deteriorates the selectivity of the main product and complicates the purification process. Additionally, since flammable hydrocarbon gas and molecular oxygen coexist, there is a built-in risk of explosion due to operational errors. In contrast, in the absence of molecular oxygen-containing gas,
When hydrocarbon raw material gas is brought into contact with metal oxide,
It is known that the oxidative dehydrogenation reaction of hydrocarbon raw materials is carried out by the bound oxygen of metal oxides. At this time, the metal oxide that has participated in the reaction is reduced and the bound oxygen is reduced, becoming a metal or a lower oxide of a metal, so there is a limit to its oxidative dehydrogenation ability, and this is due to the reduction of the original metal. It is difficult to use it industrially unless you consider regenerating it into an oxide and using it again in the oxidative dehydrogenation reaction of hydrocarbons. Regeneration is carried out by calcination in the presence of molecular oxygen, thus allowing the metal oxide to carry molecular oxygen in the form of metal-bound oxygen and indirectly participate in the oxidative dehydrogenation reactions of the hydrocarbons. It will act as an oxygen carrier. Practical oxygen carriers not only have excellent reaction rate and selectivity, but also reduce metal oxides (reaction with raw material hydrocarbons) and oxidize (regeneration with molecular oxygen) easily and quickly. At the same time, it must have sufficient mechanical strength to withstand frequent cycles of reduction and oxidation. A fixed bed or fluidized bed (moving bed) system can be considered as an apparatus for carrying out such a reaction continuously, but in order to make a continuous process using a fixed bed, two reaction towers are required. It is necessary to install them side by side and use them alternately for reaction and regeneration, and in reactions using oxygen carriers, this switching must be done frequently, making the operation somewhat complicated. On the other hand, in the case of a fluidized bed (moving bed) method,
Operation is simplified because a completely continuous process can be achieved by providing separate reaction and regeneration columns and circulating the oxygen carrier between them. However, in this case, the oxygen carrier not only circulates between the reaction tower and the regeneration tower, but also actively moves in the reaction tower and regeneration tower in the fluidized bed, so the oxygen carrier must have sufficient strength against crushing and abrasion. Must. From this point of view, metal oxides themselves have a remarkable tendency to become pulverized during use, and although they have excellent initial activity, they have the drawback of being difficult to regenerate. On the other hand, metal oxides supported on porous carriers have the advantage that mechanical strength (compressive strength, filling strength, abrasion strength) can be adjusted arbitrarily. Therefore, the present inventors conducted an experiment in which the oxidative dehydrogenation reaction of hydrocarbons was continuously carried out in the absence of molecular oxygen using a solid oxygen carrier in which a metal oxide was supported on a porous carrier. However, even though these supported oxygen carriers have sufficient strength in physical property tests during manufacturing, they often turn into fine powder after repeated use several times, so they cannot withstand long-term use. It turns out there isn't. It was also found that changing the type of porous carrier did not improve this condition. The present inventors conducted various tests to investigate the cause of this, and as a result, DTA (differential thermal) analysis revealed that during regeneration of the oxygen carrier by molecular oxygen-containing gas,
It was discovered that there is an exothermic peak between 250 and 400°C, and based on this knowledge, the present invention was completed. (Structure) The present invention produces solid oxygen with reduced bound oxygen by bringing a hydrocarbon into contact with a metal oxide in the absence of a molecular oxygen-containing gas and causing an oxidative dehydrogenation reaction of the hydrocarbon with the bound oxygen of the metal oxide. A method of oxidative regeneration of a carrier in the presence of a molecular oxygen-containing gas, in which a first stage regeneration is performed at a temperature in the range of 250 to 400°C, followed by a second stage regeneration at a temperature in the range of 500 to 600°C. This is a method for regenerating solid oxygen carriers. The structure and effects of the present invention will be specifically explained below using the production of butadiene by oxidative dehydrogenation of 1-butene as an example. Metals that can be used as oxygen carriers may be metals that can change from an oxidation state to a metal or its lower oxidation state under the reaction conditions, such as metals from group 2 of the periodic table such as Sr and Cd, and metals from the same periodic table such as Sn and Pb. Group 4, Sb,
Group 5 of the same table such as Bi, V, Group 6 of the same table such as Mo, Te, Cr, Group 8 of the same table such as Fe, Co, Pd, Mn,
Metals such as La and Cu, or mixtures thereof are targeted. At the beginning of the reaction with hydrocarbon gas, all of the metal oxides do not need to be completely the highest valence oxide of the metal, and at the end of the reaction, the lower oxides of the metal formed are It is not necessary that all the oxides are completely the lowest valent oxide of the metal. In short, it may be used in a state where the amount of bound oxygen increases or decreases before and after the reaction. Such a metal oxide or a mixture thereof is supported on a suitable porous carrier. As a porous carrier,
For example, alumina, silica, silica-alumina,
Titanium, magnesia, boriya, sepiolite, etc. can be used. The supported oxygen carrier is easily prepared by impregnating or spraying the above porous carrier with an aqueous solution of a metal salt, followed by drying and firing (decomposition of the metal salt). It is appropriate that the firing temperature is usually 400 to 700°C. The supported oxygen carrier thus prepared is contacted with the starting butene in the absence of molecular oxygen.
As the raw material, 1-butene, 2-butene alone or a mixture thereof, or a gas containing them is used. Although it depends on the type of metal used as an oxygen carrier, the reaction temperature for producing butadiene by oxidative dehydrogenation of butene is approximately 300-600°C, preferably 350-600°C.
The temperature was 550°C, and the reaction pressure was about normal pressure. Freshly prepared oxygen carriers or freshly regenerated oxygen carriers have a strong initial activity and are susceptible to reactions that produce carbon monoxide and carbon dioxide, so they must be treated with steam or reducing gas before reacting with feedstock hydrocarbons. It is desirable to do this. As the reducing gas, carbon monoxide (CO), hydrogen, lower hydrocarbon gases such as CH ₄ , C ₂ H ₆ , or a mixture thereof such as synthesis gas, COG gas, etc. can be used. . Further, water vapor and reducing gas may be diluted with an inert gas such as nitrogen. If the degree of treatment with water vapor or reducing gas is too low, the effect will naturally be small, and if it is too high, the activity of the oxygen carrier will decrease, so ultimately it is necessary to find the optimal value experimentally, but for now, In order to be effective, it is preferable to use water vapor or reducing gas in an amount of 0.01 (mole equivalent/mole equivalent) or more per oxygen carrier. The treatment temperature varies depending on the oxygen carrier, but is preferably about 200 to 500°C. By reacting with the starting material butene, the bound oxygen of the oxygen carrier is reduced and becomes a metal or its lower oxide, which is regenerated by sintering in the presence of a molecular oxygen-containing gas (eg, air). In order to combine enough oxygen to be used as an oxygen carrier again, the regeneration temperature must be increased to 500~500°C.
Although it is preferable to set the temperature to 600℃, it is necessary to avoid heating to this temperature from the beginning and calcination. when 250
This conclusion was drawn from the knowledge that there is an exothermic peak between ~400°C. That is, it was thought that if the particles were regenerated at 500 to 600° C. from the beginning, heat would be generated rapidly and excessive thermal stress would be applied to the inside of each particle of the supported oxygen carrier, and that pulverization would be promoted by repeating this process. Furthermore, a small amount of carbonaceous matter is attached to the oxygen carrier after being used in the reaction, but this also burns during regeneration and increases the amount of heat generated. Therefore, in order to avoid heat stress caused by such causes and the resulting pulverization, the regeneration temperature is changed in two stages from low to high temperature, and the first stage is near the exothermic peak temperature, i.e. 250 to 400°C. The final regeneration temperature required in the second stage, i.e.
This means that it should be baked at 500-600℃.
The present inventors conducted tests based on this inventive idea, and the effects were confirmed as shown in the following examples. The playback time for the first stage is 30 minutes to 1 hour, and the playback time for the second stage is 30 minutes to 1 hour.
It is appropriate that the playback time of each stage is 1 to 2 hours, but it may be longer. Air is generally used as the molecular oxygen-containing gas used for regeneration, but oxygen-only gas may also be used.
It is also possible to use diluted air with nitrogen or the like, diluted oxygen, air or oxygen to which water vapor has been added (steam addition rate up to about 30%). Example 1 After impregnating 40 g of γ-alumina with 12 to 16 meshes with an aqueous copper nitrate solution (50% by weight), it was dried at 120°C for 1 hour in an electric furnace under air circulation, and then dried under air circulation. It was regenerated in a fluidized bath at 600°C for 3 hours (supporting rate as CuO: 32.3% by weight). Take 2c.c. of this, fill it into a stainless steel U-shaped reaction tube (oxygen carrier filling part inner diameter 10mm), and place it in a sand fluidized bathtub with a temperature controller (electrothermal heating type).
At 250° C., carbon monoxide was introduced as reducing gas at a rate of 0.016 (mole equivalent/mole equivalent) per oxygen carrier. After that, the reaction temperature was set to 450℃, and helium gas was used as a carrier gas to react with the raw material 1.
- Butene was introduced and a reaction test was conducted. The analysis was carried out by directly feeding the reaction tube outlet gas into gas chromatography. As a result of feeding 1-butene at 0.1 (mole equivalent/mole equivalent) per oxygen carrier, the 1-butene reaction rate was 65.2 mol%, the 1,3-butadiene selectivity was 81.9 mol%, and in addition, carbon monoxide and dioxide Carbon was produced. <Regeneration> When the aeration rate of 1-butene reached 0.6 (mole equivalent/mole equivalent) with respect to the oxygen carrier, feeding of the raw material gas and helium gas was stopped.
After that, the fluidized bath temperature was lowered to 250℃, and SV=
Air was supplied at a rate of 300/Hr, and after 30 minutes, the temperature started to rise to 500°C in 1 hour, and was maintained at this temperature for 1.5 hours.
Thereafter, the temperature of the fluidized bath was set to 250° C., and carbon monoxide was introduced at a rate of 0.016 (mole equivalent/mole equivalent) per oxygen carrier. The oxygen carrier thus regenerated was subjected to a reaction test using 1-butene as a raw material under the same conditions as the previous test. Table 1 shows the test results obtained by repeating the same regeneration operation and reaction test.

[Table] After completing the 5th reaction test of the recycled product, the oxygen carrier was removed from the reaction tube and sieved.
Particles of 16 meshes or less accounted for 3.5% by weight of the total. Comparative Example 1 Pretreatment and reaction tests were conducted using the same oxygen carrier and the same equipment as in Example 1, except that the regeneration conditions were changed. The 1-butene reaction rate at 450℃ is
62.6 mol%, and the 1,3-butadiene selectivity is
It was 82.5 mol%. Other carbon monoxide and carbon dioxide were produced. When the raw material butene becomes 0.6 (mole equivalent/mole equivalent) with respect to the oxygen carrier, the supply of raw material butene and carrier gas is stopped, and the fluidized bath temperature is decreased.
After the temperature was raised to 500°C, air supply was started at SV=300/Hr, and after 3 hours, air supply was stopped and the fluidized bath temperature was lowered to 250°C. After carrying out the same pretreatment with CO as in Example 1, a reaction test was conducted at 450°C. Furthermore, the test results when similar regeneration operations and reaction tests were repeated are also shown in Table 2.

[Table] After completing the second reaction test of the recycled product, the oxygen carrier was removed from the reaction tube and sieved.
Fine particles of 16 mesh or less account for 10.3% by weight of the total
occupied. Example 2 1-Butene was pretreated with CO in the same manner as in Example 1 using the same equipment as in Example 1, except that Bi ₂ O ₃ /titania (38.6% by weight) was used as an oxygen carrier. A reaction test was conducted using The results are shown in the "New" column of Table 3. After the reaction is complete, the temperature of the fluidized bath is set to 300℃ and air is removed.
SV = 900/Hr, water vapor was introduced at 10 vol% using a small quantitative feeder, held for 1 hour, then heated to 500°C, and heated until the regeneration time was 2 hours including the heating time. continued. Thereafter, the temperature of the fluidized bath was set at 250°C, and the same pretreatment as in Example 1 was performed, followed by a reaction test at 450°C. Table 3 shows the results when the sample was reproduced twice. After the second reaction test of the recycled product was completed, the oxygen carrier was taken out from the reaction tube, but no fine particles were observed.

[Table] Comparative Example 2 The reaction test and regeneration operation were repeated in the same manner as in Example 2, except that the temperature was 500° C., the regeneration time was 3 hours, and regeneration was performed in one stage. The result is the fourth
Shown in the table. After testing the second recycled product, the oxygen carrier was removed and sieved, and fine particles of 16 mesh or less accounted for 4.5% by weight.

[Table] (Effects) As shown in the examples, when the method of the present invention is used, there is almost no pulverization of the oxygen carrier during reuse, and when regeneration is performed in one stage as in the comparative example, it becomes pulverized after only a few uses. This is clearly different from the case where the change is clearly recognized.

Claims (1)

[Claims] 1. In the absence of a molecular oxygen-containing gas, a hydrocarbon is brought into contact with a metal oxide and the hydrocarbon undergoes an oxidative dehydrogenation reaction using the bound oxygen of the metal oxide, thereby converting the solid oxygen carrier with reduced bound oxygen into molecular oxygen. A method of oxidative regeneration in the presence of a gas containing solid oxygen, which comprises performing a first stage regeneration at a temperature in the range of 250 to 400°C and then performing a second stage regeneration at a temperature in the range of 500 to 600°C. How to recycle carriers.