CN116651434B

CN116651434B - Low-carbon alkane dehydrogenation catalyst and preparation method and application thereof

Info

Publication number: CN116651434B
Application number: CN202310935746.0A
Authority: CN
Inventors: 陈伟; 潘涛; 陈平绪; 张传辉; 夏建盟; 杨春亮; 曹民
Original assignee: Kingfa Science and Technology Co Ltd
Current assignee: Kingfa Science and Technology Co Ltd
Priority date: 2023-07-28
Filing date: 2023-07-28
Publication date: 2024-07-12
Anticipated expiration: 2043-07-28
Also published as: CN116651434A

Abstract

The invention provides a low-carbon alkane dehydrogenation catalyst, a preparation method and application thereof. The low-carbon alkane dehydrogenation catalyst provided by the invention is a Cr catalyst with a new design configuration, the supported transition metal La is introduced into an alumina skeleton to form La-O sites in the skeleton, the La element with larger size occupying the lattice sites can inhibit the high-temperature migration of Al ³⁺ in a bulk phase, and the special electronic attribute of the La-O bond is beneficial to activating H ⁺, promoting the occurrence of dehydrogenation reaction process and improving the selectivity and the thermal stability; meanwhile, silane residues are introduced on the surface of the alumina carrier, so that redundant Al-OH on the surface of the alumina carrier is eliminated, and the formed Si-O-Si with higher stability and hydrophobicity is more resistant to high-temperature steam. Compared with the existing catalyst, the catalyst provided by the invention has better propane dehydrogenation activity and excellent hydrothermal stability.

Description

Low-carbon alkane dehydrogenation catalyst and preparation method and application thereof

Technical Field

The invention relates to the technical field of low-carbon alkane dehydrogenation, in particular to a low-carbon alkane dehydrogenation catalyst, a preparation method and application thereof.

Background

Olefins such as propylene, butylene and the like are important organic chemical raw materials, and downstream products are three major synthetic materials. The traditional petrochemical catalytic cracking, steam cracking and coal chemical methanol-to-olefin processes are the main routes for obtaining propylene/butene. Limited by the processing capacity of crude oil in refineries and the production cost of coal chemical industry, the technology of directly dehydrogenating to prepare olefin by adopting alkane with abundant reserves and low price as raw materials is becoming more and more popular, especially the technology of preparing Propylene (PDH) by dehydrogenating propane. The domestic propylene scale in 2012-2022 is rapidly increased from 1800 tons/year to 5600 ten thousand tons/year, and the new increased capacity is mainly based on a PDH process. The domestic PDH process mainly adopts a Catofin process (Cr-based catalyst) of ABB Lummes company and an Oleflex process (Pt-based catalyst) of UOP company, wherein the Catofin process has the characteristics of low investment, strong operability, high economic benefit and the like and is adopted by a plurality of domestic companies. The Catofin process circulates a fixed bed reactor to circulate the reaction, char, steam purge, exhaust and catalyst reduction processes. The CrO _x/active Al ₂O₃ catalyst adopted mainly needs to have a service life of more than 3 years in the severe cyclic process. However, it was found in practical industrial production that the use of industrial Cr-based catalysts for a long time resulted in the seeding and sintering of alumina to reduce the catalyst activity, especially at the bottom of the catalyst bed, and the localized zone of the fly temperature (> 800 ℃) resulted in rapid irreversible deactivation of the catalyst. The design and preparation of the dehydrogenation catalyst with high stability and high activity under the high-temperature and hydrothermal conditions are always difficult problems in the industry.

Research shows that Cr ³⁺ enters Al ₂O₃ to damage the original crystal form during long-time use, which is probably a key factor affecting the stability of the active alumina carrier. The mechanism of lattice transformation of active Al ₂O₃ at high temperature is mainly that (1) surface hydroxyl groups are dehydrated and condensed at high temperature to cause aggregation among particles and form oxygen holes (2), and the neutralization reaction of the formed oxygen holes and cation holes in crystals is carried out to cause migration of bulk Al ³⁺ and transformation of crystal structure, so that compact stable and inactive alpha-Al ₂O₃ is finally formed. At present, a great deal of patent reports are about methods for improving the activity and stability of Cr-based catalysts. The addition of alkali metal to dehydrogenation catalysts is a widely accepted modification to improve stability, such as that of patent CN1668555A, CN104209123A, CN 102123790A, US8680357a, etc. Wherein the alkali metal selected comprises any of the alkali metals from lithium to cesium, sodium or potassium compounds are typically selected for lower cost and convenience. On the one hand, the introduction of alkali or potassium metal eliminates the acid site formed by Al-OH, reduces side reaction to inhibit carbon deposition, and simultaneously improves the stability of the catalyst due to the elimination of hydroxyl. Alkaline earth metals also have similar effects, and some patents report that the addition of alkaline earth metal oxides such as MgO and CaO, e.g., CN113694923A, CN115254136A, CN104148070A, etc., to propane dehydrogenation catalysts, the alkaline earth metals exhibit similar anti-coking properties as the supported alkali metals. In addition, the addition of oxides of stable metallic elements having a valence of 4+ such as Zr and Ce can suppress sintering of Al ₂O₃. Chinese patent CN1668555A, CN 102123790a, US8680357A, US68054403A, US12983405A, etc. report that the use of ZrO ₂ or/and CeO ₂ as an auxiliary agent can effectively improve the thermal stability of the catalyst. The above-described patent method has been adopted on industrial catalysts in fact, however, there is still a great room for improvement in the above-described method because not only the reaction temperature is higher than 590 ℃ for the Catofin process, but also there is high water vapor in the catalyst scorch process.

The adoption of a more stable carrier to replace active Al ₂O₃ is also the direction of the layout of some patents, such as CN115254136A, CN114367284A and the like, and materials with higher thermal stability, such as zinc aluminate, gallium aluminum spinel, molecular sieve and the like are adopted as carriers; rare earth metals have also been tried to improve the activity and stability of catalysts, and patent CN111686709A, CN113522266a et al impregnates or mixes rare earth metals on activated alumina to improve the catalyst activity. Although these methods all have some improvement, it is difficult to achieve both activity and stability, and there is a distance for industrial application.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a low-carbon alkane dehydrogenation catalyst. The low-carbon alkane dehydrogenation catalyst has good activity, and the hydrothermal stability is further improved.

Another object of the present invention is to provide a method for preparing the light alkane dehydrogenation catalyst.

It is another object of the present invention to provide the use of the light alkane dehydrogenation catalyst.

The above object of the present invention is achieved by the following technical scheme:

A low-carbon alkane dehydrogenation catalyst, which comprises an active alumina carrier and a catalytic active component; the catalyst contains silane residues, wherein the silane residues are calculated by SiO ₂ and account for 0.01-3% of the weight of the catalyst by XRF detection, the skeleton of the active alumina carrier contains La element, and the La element is calculated by La ₂O₃ and accounts for 0.1-5% of the weight of the catalyst by XRF detection;

And the catalyst is detected by XPS and XRF respectively, the content value of SiO ₂ detected by XPS is 2-10 times of the content value of SiO ₂ detected by XRF, and the content value of La ₂O₃ detected by XPS is 0-0.5 of the content value of La ₂O₃ detected by XRF;

The catalytic active component comprises a main active component and an auxiliary active component, wherein the main active component is an oxide of chromium, the main active component accounts for 5-35% of the weight of the catalyst by counting chromium oxide, the auxiliary active component is one or more elements in the form of oxide, the elements are selected from alkali metal, alkaline earth metal, zr or Ce, and the weight of the auxiliary active component accounts for 0.1-10% of the weight of the catalyst.

In the present invention, the elemental content of the catalytically active component is determined by XRF detection.

In the present invention, the elemental content of the catalytic surface is determined by XPS detection.

La has larger ionic radius to limit the high-temperature migration of Al ³⁺ in the bulk phase, and La-O sites in the crystal lattice have the effect of activating H, so that the dehydrogenation activity of Cr ions can be promoted; the addition of the SiO ₂ component to the alumina support surprisingly results in a significant increase in the hydrothermal stability of the catalyst, possibly due to the effect of the higher stability and the hydrophobic Si-O-Si bond substitution of the partial Al-OH. In addition, we have found that this effect is related to the location where SiO ₂ is present, and that if SiO ₂ is concentrated inside the alumina support framework, no similar effect is observed. The presence of SiO ₂ can be confirmed by means of XPS and XRF detection. XPS detects the content of SiO ₂ at the catalyst surface, while XRF is the content of SiO ₂ in the catalyst as a whole. Thus, the presence of SiO ₂ can be confirmed by means of XPS and XRF detection. Different processing modes can also affect the distribution of SiO ₂, for example, when SiO ₂ precursor is added during the preparation of the activated alumina carrier, more SiO ₂ can be distributed in the bulk phase. If the SiO ₂ precursor is added at the final stage of the basic catalyst preparation, more SiO ₂ is distributed on the surface.

In addition, since the detection of XPS has a detection limit, when the La content in the catalyst is relatively low, la is mainly distributed in the skeleton of the carrier, so that the presence of La is not detected on the surface of the catalyst by XPS. That is, the case where the content value of La ₂O₃ measured by XPS described above is 0 times the content value of La ₂O₃ measured by XRF means that the content of La is lower than the detection limit of XPS.

Preferably, the alumina type of the activated alumina support is gamma-Al ₂O₃ or eta-Al ₂O₃.

Preferably, in the auxiliary active ingredient, the alkali metal is selected from Na or K; the alkaline earth metal is selected from Ca or Mg.

The preparation method of the low-carbon alkane dehydrogenation catalyst comprises the following steps:

S1, preparing an alumina skeleton containing La elements;

S2, dipping the La-element-containing aluminum oxide skeleton prepared in the step S1 into the dipping liquid of the main active ingredient precursor and the dipping liquid of the auxiliary active ingredient precursor in a plurality of times or simultaneously, and drying and roasting after each dipping is completed;

s3, immersing the treated framework in a silane solution, aging, drying and roasting.

Preferably, S1, mixing lanthanum salt and aluminum salt into aqueous solution, adding a precipitator to form solid precipitate of Al-La, and roasting the solid precipitate to form the La-element alumina skeleton.

Preferably, the Al-La precipitate is subjected to aging precipitation treatment before being calcined.

Preferably, the aging and precipitation time is 1-12 hours. More preferably 3 to 6 hours.

Preferably, the lanthanum salt is preferably lanthanum nitrate and/or lanthanum acetate. Preferably, the aluminum salt may be an inorganic aluminum salt or an organic aluminum salt. The organic aluminum salt is, for example, sodium aluminate, aluminum ethoxide, aluminum isopropoxide, aluminum isobutanol, or the like. The inorganic aluminum salt is, for example, aluminum chloride, aluminum sulfate, aluminum nitrate, or the like.

Preferably, in the aqueous solution formed by mixing lanthanum salt and aluminum salt, the mole ratio of La to Al is 1: 10-200.

Preferably, in the aqueous solution formed by mixing the lanthanum salt and the aluminum salt, la: al: the molar ratio of water is 1: 10-200: 100-5000.

Preferably, in S1, the roasting temperature is 200-600 ℃.

Preferably, in s1, the precipitating agent is one or more of carbonate, bicarbonate or ammonium salt. More specifically, the precipitant may be sodium carbonate, ammonia carbonate, sodium bicarbonate, ammonium nitrate, or the like.

Preferably, the precipitant is added in the form of a solution, and the concentration of the solution is preferably 0.1-0.5 mol/L. The amount of precipitant used can be referred to in the prior art, preferably in accordance with aqueous solution 1 mixed with lanthanum salt and aluminum salt: and 3-10 volume ratio.

S2, the precursor of the main active ingredient is a substance which can be converted into the main active ingredient through subsequent reaction. Common main active ingredient precursors are chromic acid or salts or chromium salts thereof, such as chromic acid, chromates, chromium nitrate, chromium oxalate, and the like.

S2, the auxiliary active ingredient precursor is a substance which can be converted into a main active ingredient through subsequent reaction. It is also known in the art to introduce stability-enhancing elements into the catalyst by adding auxiliary active ingredient precursors. The auxiliary active ingredient precursor selected may be referred to as known substances, and is generally selected from soluble salts. More specifically, the auxiliary active ingredient precursor may be selected from sodium carbonate, potassium carbonate, sodium nitrate, sodium acetate, potassium nitrate, potassium acetate, calcium chloride, calcium nitrate, magnesium chloride, zirconium tetrachloride, cerium nitrate, and the like.

Preferably, in S2, the temperature of each roasting is 200-600 ℃. Preferably, in S2, the time of each roasting is 2-6 hours.

Preferably, in s3, the silane is a halogen-free silylating agent. The silylating agent may be specifically selected from tetraethoxysilane, methyltriethoxysilane, hexamethyldisilazane, and the like.

Preferably, in S3, the roasting temperature is 300-800 ℃. Preferably, in S3, the roasting time is 3-8 hours.

In the present invention, the impregnation can be performed with reference to the prior art. In particular, the impregnation may be performed by one or more of overdose impregnation, isovolumetric impregnation, negative pressure impregnation or spray impregnation.

In the present invention, the drying conditions can be performed with reference to the prior art. More specifically, the drying condition may be performed at 80 to 120 ℃. The drying time can be 1-12 hours.

The low-carbon alkane dehydrogenation catalyst can be used as a dehydrogenation catalyst of low-carbon alkane, such as C3 or C4 alkane, and is particularly suitable for dehydrogenation catalysis of propane.

The application of the low-carbon alkane dehydrogenation catalyst as a propane dehydrogenation catalyst.

More specifically, the lower alkane dehydrogenation catalyst may be used in a fixed bed, moving bed or fluidized bed reactor. More preferably a fixed bed reactor. The process conditions during catalysis can be that the reaction pressure is 0.01-0.5 MPa, the temperature is 450-660 ℃, and the mass airspeed is 0.1-10 h ^-1.

The reaction pressure is more preferably 0.01 to 0.1 MPa. The temperature is more preferably 500 to 600 ℃.

In use, the catalyst is preferably crushed to a particle size of 2 to 100 mesh. More preferably 10 to 80 mesh.

And (3) introducing nitrogen to discharge air, introducing hydrogen to reduce the catalyst, blowing nitrogen, and introducing raw material gas (propane) which is mixed gas of propane and nitrogen, wherein the volume fraction of the propane in the raw material gas is 10% -60%.

Compared with the prior art, the invention has the following beneficial effects:

The low-carbon alkane dehydrogenation catalyst provided by the invention is a Cr catalyst with a new design configuration, the supported transition metal La is introduced into an alumina skeleton to form La-O sites in the skeleton, the La element with larger size occupying the lattice sites can inhibit the high-temperature migration of Al ³⁺ in a bulk phase, and the special electronic attribute of the La-O bond is beneficial to activating H ⁺, promoting the occurrence of dehydrogenation reaction process and improving the selectivity and the thermal stability; meanwhile, silane residues are introduced on the surface of the alumina carrier, so that redundant Al-OH on the surface of the alumina carrier is eliminated, and the formed Si-O-Si with higher stability and hydrophobicity is more resistant to high-temperature steam. Compared with the existing catalyst, the catalyst provided by the invention has better propane dehydrogenation activity and excellent hydrothermal stability.

Drawings

FIG. 1 is an XRD contrast pattern of the catalysts prepared in example 1 and comparative example 1;

FIG. 2 is an XRD analysis display view of the catalyst prepared in example 1;

Fig. 3 is an XRD comparison pattern after hydrothermal experimental treatment of example 1 and comparative example 1, comparative example 2 and commercially available catalyst.

Detailed Description

Technical solutions in the embodiments of the present invention will be clearly and completely described below, but the embodiments of the present invention are not limited thereto.

The reagents, methods and apparatus employed in the present invention, unless otherwise specified, are all conventional reagents, methods and apparatus commercially available in the art.

The raw materials used in the following examples and comparative examples were all commercially available raw materials. XRF and XPS were tested in the catalyst characterization section.

Example 1

S1, mixing 4.3g of lanthanum nitrate and 102.1g of aluminum isopropoxide into an aqueous solution, wherein La: al: the molar ratio of water is 1:50:1000.

Then adding 5.0g of ammonium carbonate precipitant, aging and precipitating for 6 hours to form solid precipitate of Al-La, drying the solid precipitate at 100 ℃ for 6 hours, and roasting at 500 ℃ for 3 hours to form the active alumina carrier containing La elements.

S2, dipping the active alumina carrier containing La element prepared in the S1 in chromic acid/sodium chromate mixed solution (the mass of the mixed solution is 320g/100g of active alumina carrier containing La element) with the Cr ion concentration of 1.6 mol/L, na and the ion concentration of 0.12 mol/L for 5 h, drying at 100 ℃ for 6h, and roasting at 600 ℃ for 3h;

S3, preparing a tetraethoxysilane aqueous solution with the concentration of 0.1mol/L, and placing the treated alumina carrier (300 g of silane aqueous solution/100 g of S2 carrier) in the tetraethoxysilane aqueous solution for soaking for 3 hours, then drying for 6 hours at 100 ℃, and then roasting for 3 hours again at 700 ℃ to prepare the dehydrogenation catalyst.

XRF was used to detect the content of each element in the dehydrogenation catalyst prepared in this example:

The silane residue is calculated as SiO ₂ and accounts for 1.5 percent of the weight of the catalyst, and the La element is calculated as La ₂O₃ and accounts for 4.1 percent of the weight of the catalyst; details are shown in table 1.

The Cr element accounts for 23.5 percent of the weight of the catalyst calculated by chromium oxide, the Na element accounts for 0.8 percent of the weight of the catalyst calculated by sodium oxide, and the balance is an alumina carrier.

The influence of La element on the catalyst structure was observed by XRD, as shown in fig. 1 and 2.

Example 2

S1-S2 are identical to example 1 except that in S3, methyltriethoxysilane is used instead of tetraethoxysilane.

Example 3

S1 to S2 are identical to example 1, except that in S3, hexamethyldisilazane is used instead of tetraethoxysilane.

Example 4

S1-S2 are identical to example 1, except that in S3, the concentration of the aqueous silane solution is 0.01mol/L.

The dehydrogenation catalyst prepared in this example was tested for the content of each element by XRF, the silane residue was calculated as SiO ₂ and found to be 0.01% by weight of the catalyst, the remaining elements being the same as in example 1.

Example 5

S2-S3 are identical to example 1, except that in S1, the lanthanum nitrate is used in an amount of 0.2 g.

In this example, the content of La element calculated as La ₂O₃ was 0.1% by weight of the catalyst, and the content of the remaining elements was the same as in example 1, using XRF detection.

Example 6

S2-S3 are identical to example 1, except that in S1, the lanthanum nitrate is used in an amount of 5.5 g.

In this example, the content of La element calculated as La ₂O₃% by weight of the catalyst was the same as in example 1, using XRF detection.

Example 7

S2, dipping the active alumina carrier containing La element prepared in the step S1 into chromic acid solution with Cr ion concentration of 1.54mol/L (the mass of the solution is 320g/100g of active alumina carrier containing La element), wherein the dipping time is 5 h, then drying at 100 ℃ for 6h, and then roasting at 600 ℃ for 3h; immersing the treated carrier in sodium chromate solution with Na ion concentration of 0.12 mol/L (the mass of the solution is 320g/100g of active alumina carrier containing La element) for 5 h, drying at 100 ℃ for 6h, and roasting at 600 ℃ for 3h;

s3, preparing tetraethoxysilane solution with the concentration of 0.1mo/L, and placing the activated alumina carrier (300 g of silane aqueous solution/100 g of S2 carrier) treated by S2 into the tetraethoxysilane solution to soak for 3 hours, drying the tetraethoxysilane solution at 100 ℃ for 6 hours, and roasting the tetraethoxysilane solution at 700 ℃ for 3 hours again to prepare the dehydrogenation catalyst.

Substantially in accordance with example 1, XPS, XRF, XRD were examined.

Comparative example 1

S2-S3 the same as in example 1, except that in S1, lanthanum nitrate was not added.

Comparative example 2

S1-S2 the same as in example 1, except that the treatment of S3 was not performed, i.e., no soaking in tetraethoxysilane solution was performed.

Comparative example 3

Referring to the method of CN104043443a, the procedure of S1 was the same as in example 1 except that the tetraethoxysilane solution of the same concentration as S3 was added directly to the mixed solution of S2, and the rest of the procedure was the same as S2.

Comparative example 4

S1-S2 are identical to example 1 except that in S3, the concentration of the silane solution is 0.35 mol/L.

The dehydrogenation catalyst prepared in this example was tested for the content of each element by XRF, the silane residue was calculated as SiO ₂, 5% by weight of the catalyst, and the remaining element content was the same as in example 1.

Characterization of the catalyst:

characterization parameters of the catalysts prepared in examples 1,4,5 and comparative examples 1 to 3 are as follows:

The influence of La element on the skeleton of the alumina carrier was examined by XRD.

The XRD patterns of the catalysts prepared in example 1 and comparative example 1 versus those shown in fig. 1, since La has a larger ionic radius, the introduction of La element into the framework of Al ₂O₃ support will cause a slight expansion of Al ₂O₃ lattice, exhibiting a shift to high Theta angles (about 0.4 °) in the XRD pattern.

When the XRD pattern of the catalyst prepared in example 1 was analyzed in FIG. 2, it was found that the catalyst had a distinct characteristic peak of Cr ₂O₃ in addition to the characteristic peak of La-Al ₂O₃, but did not exhibit a distinct characteristic peak for SiO ₂, mainly due to its low content (1.5%).

XRF and XPS test results of the catalysts prepared in examples 1, 4,5 and the catalysts of comparative examples 1, 2, 3 are shown in table 1.

XRF adopts PANALYTICAL AXIOSMAX ANALYZER, the test precision reaches 0.04%, in the test process, the sample is fully dried (12 h at 120 ℃), then ground into powder and pressed into tablets (> 3 g), the powder is placed into an instrument for detection, sample preparation and test are repeated for 3 times, and the average value is taken as the final test value.

XPS adopts Thermo ESCALAB 250XI, and samples after drying and dewatering are ground into powder before testing, then the powder is pressed into slices (thickness <3mm, mass <30 mg), the slices are placed in an instrument for testing, sample preparation and testing are repeated for 3 times, and an average value is taken as a final test value.

XPS reflects the content of elements located on the outer surface of the catalyst; XRF reflects the total elemental content of the catalyst. For the same element, the more closely the XPS value and the XRF value are, the more uniformly the element is distributed in the catalyst, and when the XPS value is greater than the XRF, the more the element is considered to be distributed on the surface, and the more the XPS value is, the more the trend is apparent. When the XPS value is less than XRF, it is shown that the element is less distributed on the surface, and the smaller the XPS value, the more pronounced this trend.

It can be seen from table 1 that the surface SiO ₂ content (XPS) measured in the examples were all much greater than the bulk phase content (XRF), indicating that the supported SiO ₂ was mainly located on the outer surface of the catalyst. The opposite rule is shown for La ₂O₃, whose surface content (XPS) is much smaller than the bulk content (XRF), indicating that La element may be mainly located in the internal framework of the alumina support.

Table 1 XRF and XPS test results for catalysts prepared in examples and comparative catalysts

For example 5, since the total content of La element in the support was low, the content of La element was not detected at the time of XPS.

Catalyst performance test:

the catalysts prepared in examples 1 to 7 and comparative examples 1 to 4 were crushed to about 60 mesh, and were placed in a fixed bed reactor at a reaction pressure of 0.1MPa and a temperature of 600℃and a mass space velocity of 2h ^-1. And (3) introducing nitrogen to discharge air, then introducing a hydrogen reduction catalyst, and purging with nitrogen, and then introducing raw material gas, wherein the raw material gas is mixed gas of propane and nitrogen, and the volume fraction of the propane is 50%.

The catalytic performances of the catalysts of examples 1 to 7 and comparative examples 1 to 4 are shown in Table 2, and examples 1 to 7 containing a skeleton La show higher propane conversion rate than comparative example 1 containing no La, and examples 1 to 7 show higher propylene yield, indicating the promotion effect of La on the catalytic activity of propane in the skeleton; examples 1,2,3, 4 show that varying the silicon source and content has an effect on its activity, in particular the Si content, compared to comparative example 2. As can be seen from comparative example 3, the addition of the silane solution has different ways, which affect the distribution of SiO ₂ on the surface, and have influence on the conversion rate of propane, the selectivity of propylene, the yield of propylene, and the like. Comparative example 4 also shows that the loading SiO ₂ content is too high, the activity is the lowest, and the propane conversion rate is the lowest 39.0%; indicating that when the SiO ₂ content is too high, the effect is rather negative. Comparative example 3 shows that the catalytic effect is even lower than the case without SiO ₂ when SiO ₂ is not added to the catalyst surface. In addition, examples 1 and 7 show that the loading sequence of Cr element and Na element has a certain influence on the catalytic performance, and the loading has higher activity.

TABLE 2 catalyst Performance test results

	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Example 7	Comparative example 1	Comparative example 2	Comparative example 3	Comparative example 4
												Propane conversion	45.1%	43.6%	41.7%	45.0%	41.3%	44.8%	44.9%	38.9%	45.3%	37.8%	39.0%
Propylene selectivity	88.6%	87.3%	86.8%	88.5%	87.1%	88.2%	88.5%	87.8%	86.7%	82.9%	84.8%
												Propylene yield	40.0%	38.1%	36.2%	39.8%	36.0%	39.5%	39.7%	34.2%	39.3%	31.3%	33.1%

Catalyst hydrothermal stability test:

The commercial catalysts of example 1 and comparative example 1, comparative example 2, and no La, si were subjected to hydrothermal aging treatment.

The specific hydrothermal aging treatment process is to place the sample in a fixed bed reactor, and introduce steam at 800 ℃, the mass airspeed is 1 h ^-1, and the holding time is 8 h.

The sample after the experiment was tested for XRD, and the results are shown in FIG. 3. Example 1 shows no hydrothermal aging and a distinct characteristic peak of the active component Cr ₂O₃. After hydrothermal aging, part of the active Cr ₂O₃ disappears, and the crystal is transformed into an inactive substance, which shows additional characteristic peaks. The content (set as 100%) of the non-hydrothermally aged example 1 was characterized by Cr ₂O₃ characteristic peak area at 24.5 degrees, so that the content of the hydrothermally aged example 1, comparative example 2 and commercial industrial agents without La and Si corresponds to about 63%, 17%, 11% and 0% of the active Cr ₂O₃; the introduction of La and Si can improve the hydrothermal stability of the catalyst, and the introduction can obviously improve the stability.

It is to be understood that the above examples of the present invention are provided by way of illustration only and are not intended to limit the scope of the invention. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. Any modification, equivalent replacement, improvement, etc. which come within the spirit and principles of the invention are desired to be protected by the following claims.

Claims

1. The low-carbon alkane dehydrogenation catalyst is characterized by comprising an active alumina carrier and a catalytic active component; the catalyst contains silane residues, wherein the silane residues are calculated by SiO ₂ and account for 0.01-3% of the weight of the catalyst by XRF detection, and the skeleton lattice of the active alumina carrier contains La element which is calculated by La ₂O₃ and accounts for 0.1-5% of the weight of the catalyst by XRF detection;

The catalytic active component comprises a main active component and an auxiliary active component, wherein the main active component is oxide of chromium, the main active component accounts for 5-35% of the weight of the catalyst in terms of chromium oxide, the auxiliary active component is oxide of one or more elements selected from alkali metal, alkaline earth metal, zr or Ce, and the weight of the auxiliary active component accounts for 0.1-10% of the weight of the catalyst;

The preparation method of the active alumina carrier comprises the following steps: mixing lanthanum salt and aluminum salt into an aqueous solution, adding a precipitator to form solid precipitate of Al-La, and roasting the solid precipitate to form the active alumina carrier; the precipitant is one or more of carbonate, bicarbonate or ammonium salt;

the silane residue is formed by the bake conversion of the halogen-free silylating agent.

2. The low carbon alkane dehydrogenation catalyst according to claim 1, wherein the activated alumina support has an alumina type of γ -Al ₂O₃ or η -Al ₂O₃.

3. The lower alkane dehydrogenation catalyst according to claim 1, wherein in the auxiliary active ingredient, the alkali metal is selected from Na or K; the alkaline earth metal is selected from Ca or Mg.

4. A process for preparing a lower alkane dehydrogenation catalyst according to any one of claims 1 to 3 comprising the steps of:

S1, preparing an active alumina carrier containing La element;

S2, dipping the active alumina carrier containing La element prepared in the S1 into dipping liquid containing the main active ingredient precursor and the dipping liquid of the auxiliary active ingredient precursor in a plurality of times or simultaneously, and drying and roasting after each dipping is completed;

S3, soaking the carrier treated by the step S2 in a silane solution, aging, drying and roasting; the silane is a halogen-free silylating agent; s3, roasting at 300-800 ℃;

S1, mixing lanthanum salt and aluminum salt into an aqueous solution, adding a precipitator to form solid precipitate of Al-La, and roasting the solid precipitate to form the active alumina carrier containing La element;

in S1, the precipitant is one or more of carbonate, bicarbonate or ammonium salt.

5. The method according to claim 4, wherein the molar ratio of La to Al in the aqueous solution is 1: (10-200).

6. Use of the light alkane dehydrogenation catalyst according to any one of claims 1 to 3 as a propane dehydrogenation catalyst.