CN1515354A - Nano-chromium trioxide catalyst for carbon dioxide oxidation of ethane and dehydrogenation of ethylene - Google Patents

Abstract

The invention belongs to the field of catalysts for preparing ethylene, in particular to a nano-chromium trioxide catalyst for oxidizing ethane and dehydrogenating ethylene to prepare ethylene. At a temperature of 40-60°C, add Cr(NO ₃ ) ₃ solution and dilute ammonia solution into the surfactant solution in parallel flow; keep the pH value of the hydrated Cr ₂ O ₃ nano-slurry at 9-11, and obtain A hydrated Cr ₂ O ₃ gel coated with a surfactant on the surface; performing azeotropic distillation on the obtained hydrated Cr ₂ O ₃ gel and n-butanol at a volume ratio of 1:6-8, and separating to obtain an alcohol gel; The alcohol gel is dried, calcined, and the obtained nano-chromium trioxide powder is pressed into tablets, ground and sieved into 20-40 meshes to prepare the catalyst of the present invention. Applied to the reaction of carbon dioxide oxidation of ethane and dehydrogenation of ethylene, at a reaction temperature of 550-700 ° C, a very good catalytic effect has been achieved, the conversion rate of ethane can reach more than 77%, and the yield of ethylene has reached 59%.

Description

Nano-chromium trioxide catalyst for carbon dioxide oxidation of ethane and dehydrogenation of ethylene

Technical field

The invention belongs to the field of catalysts for preparing ethylene, in particular to a nano-chromium trioxide catalyst for oxidizing ethane and dehydrogenating ethylene to prepare ethylene.

Background technique

There are a large number of low-carbon alkanes in natural gas, petroleum liquefied gas and refinery gas, and their conversion into chemical raw materials such as olefins and oxygen-containing organic compounds has broad application prospects. The traditional high-temperature (~950°C) steam cracking of ethane to ethylene requires high energy consumption and complex product composition. CO ₂ oxidative ethane dehydrogenation to ethylene is a new ethane oxidative dehydrogenation reaction process. Compared with the traditional industrial production process of ethane high-temperature steam cracking to ethylene, this catalytic process has unique advantages, such as: reaction temperature Relatively low; catalyst operating period is extended; ethylene selectivity is high. Therefore, if a catalyst can be developed to convert ethane into high value-added ethylene with high conversion rate and high selectivity under suitable reaction conditions, it will be a "green chemistry" approach to utilize _CO2 resources. Krylov et al. (1. Krylov OV, Mamedov A K, Mirzabekova S R. Catal. Today, 1995, 24: 371-375; 2. Xu L, Liu J, Yang H, Xu Y, Wang Q, Lin L. Catal. , 1999, 62: 185-189) found that the composite oxide-supported catalyst containing manganese oxide had a high conversion rate of ethane at a high temperature of 800-830 °C, but compared with the traditional high-temperature steam cracking of ethane to produce ethylene Compared with the process, the reduction of reaction temperature is not significant. Therefore, the current research focus of CO ₂ oxidative ethane dehydrogenation to ethylene is to develop low-temperature and high-activity catalyst systems.

In the past ten years, nanomaterials (especially nanoscale oxides) have become a research hotspot in the field of heterogeneous catalysis due to their unique physical and chemical properties. Nanomaterials have special catalytic properties due to their high specific surface area and high surface defects.

Contents of Invention

One of the objects of the present invention is to provide a nano-chromium trioxide catalyst for the reaction of carbon dioxide oxidation of ethane and dehydrogenation of ethylene.

Another object of the present invention is to provide a method for preparing a nano-chromium trioxide catalyst for oxidizing ethane and dehydrogenating ethylene with carbon dioxide.

The nano-chromium trioxide catalyst of the present invention for the reaction of oxidizing ethane and dehydrogenating ethylene to ethylene is prepared by the coupling technology of sol-gel method and azeotropic distillation method, and the steps are as follows:

(1). Stirring at a temperature of 40-60°C, adding a Cr(NO ₃ ) ₃ solution with a concentration of 0.15-0.4M and a dilute ammonia solution with a concentration of 1wt%-3wt% into the surfactant solution in parallel, The flow rate of the Cr(NO ₃ ) ₃ solution is 3-5ml/min; wherein, the volume ratio of the Cr(NO ₃ ) ₃ solution to the surfactant solution is 1:1-2;

(2). Regulate the pH value of the hydrated Cr ₂ O ₃ nano-slurry obtained continuously by adjusting the flow rate of the dilute ammonia solution to keep the pH value at 9-11. After the addition of the Cr(NO ₃ ) ₃ solution, stand it for 2 to 5 hours to obtain hydrated Cr ₂ O ₃ nano-slurries;

(3). The hydrated Cr ₂ O ₃ nano-slurry in step (2) is centrifuged, washed and separated to obtain a hydrated Cr ₂ O ₃ gel whose surface is coated with a surfactant;

(4). The hydrated Cr ₂ O ₃ gel obtained in step (3) and n-butanol are subjected to azeotropic distillation at a ratio of 1:6 to 8 by volume, and centrifuged to obtain the alcohol gel; dry the alcohol gel with a vacuum drier glue, and then calcining the dried material in a high-temperature furnace to obtain nano-chromium trioxide powder;

(5). The nano-chromium trioxide powder in step (4) is pressed into tablets, ground and sieved into 20-40 meshes to prepare the catalyst of the present invention.

The surfactant solution is a mixed solution of oleic acid, Tween-80 (polyoxyethylene sorbitan fatty acid ester) and dilute ammonia, wherein the volume ratio of oleic acid: Tween-80: ammonia is 1: 1:40-50; wherein the concentration of dilute ammonia water is 1wt%-3wt%.

The present invention owing to adopt oleic acid and Tween-80 (polyoxyethylene sorbitan fatty acid ester) two kinds of surfactant synergy, surfactant and dilute ammonia solution form oil-in-water microemulsion after fully stirring, Hydrated Cr ₂ O ₃ is easily dispersed in it, which prevents the particle from growing up. The prepared nano-chromium trioxide powder catalyst is spherical, with a narrow particle size distribution and an average particle size of 28nm, and its XRD spectrum shows that the crystal form of the nano-Cr ₂ O ₃ powder is very good.

The method of the invention is simple to operate and control, and easy to be industrialized. The nano-chromium trioxide prepared by the method has good crystal form, high purity and narrow particle size distribution. The nano-chromium trioxide powder is pressed into tablets, ground and sieved to make a catalyst, which is applied to the reaction of carbon dioxide oxidation of ethane to ethylene. At a relatively low reaction temperature (550-700°C), very good results have been obtained. The catalytic effect, the conversion rate of ethane can reach more than 77%, and the yield of ethylene reaches 59%.

Description of drawings

Fig. 1. the schematic flow chart of the nano-chromium trioxide catalyst preparation process of carbon dioxide selective oxidation of ethane dehydrogenation to ethylene reaction of the present invention.

Fig. 2. TEM photo of the nano-Cr ₂ O ₃ powder prepared in the embodiment of the present invention.

Detailed ways

Example

(1) Configuration of Cr(NO ₃ ) ₃ solution and dilute ammonia solution

Weigh 16g of Cr(NO ₃ ) ₃ .9H ₂ O and dissolve it in 200ml of distilled water to form a Cr(NO ₃ ) ₃ solution. Then ammonia water and distilled water are mixed to form a dilute ammonia solution with a concentration of 2.5 wt%.

(2) Preparation of surfactant solution

Take 5ml of oleic acid and Tween-80 and dissolve them in 200ml of prepared dilute ammonia solution; stir to obtain a translucent surfactant solution, wherein the concentration of ammonia is 1wt%.

(3) Preparation of nano slurry

In the state of constant stirring, the Cr(NO ₃ ) ₃ solution prepared in step (1) and dilute ammonia solution were added into the surfactant solution of step (2) at a temperature of 40°C in parallel, wherein Cr(NO ₃ ) The volume ratio of ₃ solution and surfactant solution is 1: 1; By adjusting the flow velocity of the dilute ammonia solution of step (1), adjust the pH value _{of the hydration Cr that obtains continuously O 3 nanometer} slurry, make pH value remain at 10; while the flow rate of the Cr(NO ₃ ) ₃ solution was kept at 3 ml/min.

(4) Aging of nano slurry

After the reaction of the Cr(NO ₃ ) ₃ solution was completed, the constant temperature stirring was continued for 0.5 hours, and then the heating was stopped and left to age for 4 hours to obtain a hydrated Cr ₂ O ₃ hydrosol coated with a surfactant.

(5) Washing process

The hydrated Cr ₂ O ₃ hydrosol was centrifuged, and the obtained material was thoroughly stirred with 600 ml of distilled water, and then centrifuged to obtain the hydrated Cr ₂ O ₃ hydrogel.

(6) Azeotropic distillation process

Add n-butanol to the obtained hydrated Cr ₂ O ₃ hydrogel, hydrated Cr ₂ O ₃ gel and n-butanol in a volume ratio of 1:8, azeotropic distillation under stirring and heating, when the temperature of the steam rises to n-butanol When the boiling point was 117°C, the reflux was continued for 60 minutes, and then centrifuged to obtain hydrated Cr ₂ O ₃ alcohol gel.

(6) drying and calcination

The obtained hydrated Cr ₂ O ₃ alcohol gel was dried in a vacuum drying oven for 8 hours with a vacuum degree of 600mmHg and a temperature of 80°C. The dried material was calcined in a high temperature furnace at 700° C. for 2.5 hours to obtain nano Cr ₂ O ₃ powder.

(7) Evaluation of the catalytic performance of the nano-chromium trioxide catalyst.

Weigh 0.2 g of the nano-Cr ₂ O ₃ powder obtained in step (6), press it into tablets, grind and sieve it into a 20-40 mesh nano-Cr ₂ O ₃ catalyst. The catalytic conversion of ethane and carbon dioxide was carried out in a continuous-feed fixed-bed quartz reactor (5×360 mm). Raw material gas C ₂ H ₆ , CO ₂ and diluent gas Ar are purified through a filter device equipped with silica gel, and flow into the mixer at a constant flow rate through a mass flow meter. The product was injected using a six-way valve for chromatographic analysis. Under the reaction conditions of reaction temperature 550～700℃, pressure 0.01Mpa, space velocity 4500ml.g ^-1 .h ^-1 , and C ₂ H ₆ :CO _{2 :} Ar=3:1:1 in raw material gas, it can catalyze The performance comparison results with conventional _Cr2O3 catalysts are _listed in Table 1.

Table 1 Nano Cr of the present invention ₂ O ₃ and the comparison of the catalytic performance of conventional Cr ₂ O ₃ catalysts

Conversion (%) C ₂ H ₄

Catalyst T(°C)

C ₂ H ₆ CO ₂ Yield (%)

550 1.25 2.04 1.24

600 5.24 2.78 5.04

Cr ₂ O ₃

650 8.25 4.65 8.02

700 10.71 5.07 10.62

550 16.46 7.63 16.05

600 34.70 20.63 25.22

Nano Cr ₂ O ₃

650 58.71 27.90 32.61

700 77.10 21.89 58.98

Table 2 shows the results of carbon dioxide oxidizing ethane dehydrogenation to ethylene on the nano _-Cr2O3 catalyst used in the present invention and the catalysts used in _Documents 1 and 2.

Catalyst T(°C) GHSV(h ^-Ethane conversion(%) Literature

¹ )

Nano Cr ₂ O ₃ 700 4500 77.1

K-Cr-MnO/SiO ₂ 830 3600 82.6 1

Fe-MnO/Si-2 800 1000 68.6 2

It can be illustrated from the above two tables that in the carbon dioxide oxidative ethane dehydrogenation to ethylene reaction, the nano- _Cr2O3 catalyst prepared by the method of the present _invention has a catalytic effect that is obviously better than that of the conventional _Cr2O3 catalyst, and _the reaction temperature has decreased At 100°C, even under the conditions of 1-4.5 times higher reaction space velocity, the nano-Cr ₂ O ₃ catalyst has a higher or similar ethane conversion rate than the catalysts used in the literature.

Claims (4)

1. the nanometer Cr 2 O 3 catalyst of a preparing ethene by oxidative dehydrogenation of ethane with carbon dioxide, it is characterized in that: described nanometer Cr 2 O 3 catalyst prepares by the following method:

(1). under 40～60C temperature, stir, the Cr (NO of 0.15～0.4M concentration ₃) ₃Solution and dilute ammonia solution and stream join in the surfactant solution; Wherein, Cr (NO ₃) ₃The volume ratio of solution and surfactant solution is 1: 1～2;

(2). the flow velocity of regulating dilute ammonia solution is controlled the hydration Cr that constantly obtains ₂O ₃The pH value of nano pulp makes the pH value remain on 9～11, treats Cr (NO ₃) ₃After the solution adding finishes, still aging, obtain hydration Cr ₂O ₃Nano pulp;

(3). the hydration Cr of separating step (2) ₂O ₃Nano pulp, washing, separation obtain the hydration Cr that the surface is coated with surfactant ₂O ₃Gel;

(4). the hydration Cr that step (3) is obtained ₂O ₃The ratio of gel and n-butanol 1: 6 by volume～8 is carried out azeotropic distillation, separates to obtain alcogel; Dry alcogel is calcined dried material again in high temperature furnace, obtain nanometer chrome green powder;

(5). with nanometer chrome green powder compressing tablet, the grinding of step (4) with sieve into 20～40 orders and make the nanometer Cr 2 O 3 catalyst.

2. catalyst as claimed in claim 1 is characterized in that: described surfactant solution is the mixed solution of oleic acid, Tween-80 and weak aqua ammonia, wherein oleic acid: Tween-80: the volume ratio of weak aqua ammonia is 1: 1: 40～50.

3. catalyst as claimed in claim 1 is characterized in that: the Cr (NO in the described step (1) ₃) ₃The flow velocity of solution is 3～5ml/min.

4. catalyst as claimed in claim 1 or 2 is characterized in that: the concentration of described dilute ammonia solution is 1wt%～3wt%.