CN102850169A - Method for manufacturing isobutene through isobutane dehydrogenation - Google Patents

Abstract

The invention belongs to the technical field of chemistry and chemical engineering, and specifically relates to a method for preparing isobutene by dehydrogenating isobutane. The present invention uses isobutane as a raw material and vanadium oxide supported by carbon nanotubes as a catalyst. In a fixed bed reactor, isobutane undergoes a dehydrogenation reaction and converts isobutene-based mixed hydrocarbons; wherein: the The load of catalyst vanadium in carbon nanotubes is 3wt%-11wt%, the dehydrogenation reaction temperature is 480-620°C, the reaction pressure is 0.05-1.0MPa, and the gas hourly space velocity is 10-1000h ^-1 . The invention has the advantages that the conversion rate of isobutane and the selectivity of isobutene are close to those of industrial chromium-aluminum catalysts, the catalyst is environmentally friendly and the cost is low.

Description

A kind of method of isobutane dehydrogenation isobutene

technical field

The invention belongs to the technical field of chemistry and chemical engineering, and in particular relates to a method for preparing isobutene from isobutane as a raw material.

Background technique

Isobutene is an important chemical raw material, and its molecular formula is C ₄ H ₈ . The global demand for isobutylene is very large, and it is increasing year by year. The traditional isobutene production is mainly extracted from by-products of petroleum catalytic cracking units and naphtha catalytic cracking units, but isobutene is produced as a by-product in these methods, and the output is strongly restricted by the scale of the main reaction and the yield of C4 olefins. my country is rich in liquefied gas resources, but isobutane as a main component has not been rationally utilized, and most of it is consumed along with liquefied gas as a civil fuel. Therefore, the use of isobutane as a raw material to prepare isobutene through dehydrogenation has inherent advantages and social significance.

Since the 1960s, foreign companies have successively started to develop catalysts and processes for isobutane dehydrogenation to isobutene. Representative and industrialized ones include the FBD-4 process of Snamprogetti and the Catofin process developed by Lummus/UCI. , UOP's Oleflex process, Phillips' STAR process and Linde AG's Linde process, etc. The catalysts they used fall into two categories: chromium oxide supported on alumina support and noble metal Pt supported on alumina or other supports. The reaction temperature is between 500-650°C, the reaction pressure is between 0.1-6.0MPa, the reaction isobutane conversion rate is between 40-60%, and the selectivity of isobutene is between 91-95%. Although these processes have been industrialized at present, the high cost of noble metals and the high toxicity of metal chromium, as well as the characteristics of easy deactivation shared by the two, still attract people to seek more suitable catalysts.

Metal vanadium and metal chromium are in the adjacent position in the chemical cycle, and they have similarities in multivalence and oxidation, but they are less toxic and less polluting to the environment. Oxidation of aldehydes and other reactions. There are also many scholars and institutions conducting research on the use of vanadium for the dehydrogenation of low-carbon alkanes, trying to use it to replace platinum and chromium catalysts.

Carbon nanotubes (CNTs) are novel carbon nanomaterials composed of graphite-like planes composed of printed sp ² -C in a certain way. In recent years, the research on using carbon nanotubes as catalyst supports or promoters has been increasing day by day, and the priority application fields include selective hydrogenation, dehydrogenation, hydrogenolysis and other processes. From the perspective of chemical catalysis, in addition to its high mechanical strength, graphite-like structure of the tube wall, nano-scale tube cavity and large and modifiable surface, carbon nanotubes have excellent electron transfer performance and strong adsorption and activation of _H2 . Compared with some conventional catalyst supports (activated carbon, alumina, silica, etc.), it has more characteristics than some conventional catalyst supports (activated carbon, alumina, silica, etc.), which greatly increases its application opportunities in the field of catalysis.

It has been reported in the literature that vanadium oxide supported by carbon nanotubes is used as a nitrogen oxide reduction catalyst, and vanadium salt dissolved in oxalic acid is supported by an equal impregnation method, and the finished catalyst is obtained after roasting. But then there is no report that this catalyst is used for isobutane dehydrogenation reaction.

Contents of the invention

The purpose of the present invention is to provide a method for producing isobutene by isobutane dehydrogenation with high isobutane dehydrogenation conversion rate and high isobutene selectivity.

The method proposed by the present invention uses isobutane as a raw material and uses carbon nanotube-supported vanadium oxide as a catalyst. In a fixed bed or a fluidized bed, isobutane undergoes a dehydrogenation reaction and converts it into mixed hydrocarbons mainly composed of isobutene. ;in:

(1) The catalyst used is carbon nanotube-supported vanadium oxide as a catalyst, and the vanadium loading is 3wt% - 11wt%. The preferred vanadium loading is 7wt%

(2) The reaction temperature of the dehydrogenation reaction is 480-620°C;

(3) The reaction pressure is 0.05-1.0MPa, and the gas hourly space velocity is 10-1000h ^-1 .

The preparation method of the catalyst in the present invention is as follows: immerse carbon nanotubes in ammonium metavanadate and oxalic acid solution, dry at 60-120°C under vacuum or under normal pressure, and then roast under nitrogen atmosphere at 500-620°C for 2-8 hours , and then obtained after calcining at 200-300°C for 3-6 hours under an air atmosphere.

The invention has the advantages that the conversion rate of isobutane and the selectivity of isobutene are close to those of industrial chromium-aluminum catalysts, the catalyst is environmentally friendly and the cost is low.

Detailed ways

Example 1

2.0 g of 5% V/CNT catalyst prepared by impregnation method was placed in a stainless steel tube fixed-bed reactor with a diameter of 10 mm, and the content of vanadium in the catalyst was 5.0%. Catalyst preparation steps are as follows:

Dissolve 0.757 grams of ammonium metavanadate and 2.0 grams of oxalic acid in 4.5 milliliters of water, add 6.0 grams of carbon nanotubes after completely dissolving, stir well and let it stand at room temperature for 12 hours, then dry it in an oven at 90 ° C, and then dry the sample Put it in a tube furnace under a nitrogen atmosphere and roast it at 620°C for 5 hours, then roast it in the air at 200°C for 5 hours to obtain Catalyst 1, and take 20-30 mesh particles after granulation.

Nitrogen was used as the exhaust gas, pure isobutane was used as the raw material, the gas hourly space velocity was 530h ^-1 , the reaction was carried out under normal pressure, and the temperature was 480°C. The conversion rate of isobutane is 25.5%, the selectivity to isobutene is 95.0%, and the yield of isobutene is 24.2%.

Example 2

2.0 g of 7% V/CNT catalyst prepared by impregnation method was placed in a stainless steel tube fixed-bed reactor with a diameter of 10 mm, and the content of vanadium in the catalyst was 7.0%. Catalyst preparation steps are as follows:

Dissolve 1.103 grams of ammonium metavanadate and 2.5 grams of oxalic acid in 4.5 milliliters of water, add 6.0 grams of carbon nanotubes after completely dissolving, stir well and let it stand at room temperature for 12 hours, then dry it in an oven at 90 ° C, and then dry the sample After being placed in a tube furnace under a nitrogen atmosphere and calcined at 620°C for 5 hours, and then calcined at 250°C in air for 5 hours, Catalyst 2 was obtained. After granulation, 20-30 mesh particles were taken.

Nitrogen was used as the exhaust gas, pure isobutane was used as the raw material, the gas hourly space velocity was 530h ^-1 , the reaction was carried out under normal pressure, and the temperature was 550°C. The conversion rate of isobutane is 54.0%, the selectivity of isobutene is 92.0%, and the yield of isobutene is 49.7%.

Experiments have shown that this is the best reaction condition.

Example 3

2.0 g of 3% V/CNT catalyst prepared by impregnation method was placed in a stainless steel tube reactor with a diameter of 10 mm, and the content of V in the catalyst was 3.0%. Catalyst preparation steps are as follows:

Dissolve 0.437 grams of ammonium metavanadate and 2.0 grams of oxalic acid in 4.5 milliliters of water, add 6.0 grams of carbon nanotubes after completely dissolving, stir well and let it stand at room temperature for 12 hours, then dry it in an oven at 90 ° C, and then dry the sample Put it in a tube furnace under a nitrogen atmosphere and roast it at 620°C for 2.5 hours, then roast it in the air at 300°C for 6 hours to obtain catalyst 3, and take 20-30 mesh particles after granulation.

Nitrogen was used as the exhaust gas, pure isobutane was used as the raw material, the gas hourly space velocity was 10h ^-1 , the reaction pressure was 1.0MPa, and the temperature was 620°C. The conversion rate of isobutane was 49.2%, the selectivity to isobutene was 86.5%, and the yield of isobutene was 42.6%.

Example 4

2.0 g of 11% V/CNT catalyst prepared by impregnation method was placed in a stainless steel tube reactor with a diameter of 10 mm, and the V content in the catalyst was 5.0%. Catalyst preparation steps are as follows:

Dissolve 1.888 grams of ammonium metavanadate and 3.7 grams of oxalic acid in 4.5 milliliters of water, add 6.0 grams of carbon nanotubes after completely dissolving, stir well and let it stand at room temperature for 12 hours, then dry it in an oven at 90 ° C, and then dry the sample Put it in a tube furnace under a nitrogen atmosphere and roast it at 620°C for 8 hours, then roast it in air at 250°C for 3 hours to obtain catalyst 4, and take 20-30 mesh particles after granulation.

Nitrogen is used as the exhaust gas, pure isobutane is used as the raw material, the gas hourly space velocity is 900h ^-1 , the reaction pressure is 0.5MPa, and the temperature is 550°C. The conversion rate of isobutane is 39.4%, the selectivity to isobutene is 92.5%, and the yield of isobutene is 36.4%.

Claims (2)

1. A method for preparing isobutene from isobutane dehydrogenation, characterized in that isobutane is used as raw material, and simultaneously the vanadium oxide supported by carbon nanotubes is a catalyst, and in a fixed bed reactor, isobutane undergoes dehydrogenation reaction and converted into isobutene-based mixed hydrocarbons; where: (1) The loading of the catalyst vanadium in the carbon nanotubes is 3wt%-11wt%; (2) The dehydrogenation reaction temperature is 480-620°C; (3) The reaction pressure is 0.05-1.0MPa, and the gas hourly space velocity is 10-1000h ^-1 . 2. The method according to claim 1, characterized in that the preparation method of the catalyst is as follows: carbon nanotubes are immersed in the solution of ammonium metavanadate and oxalic acid, and dried at 60-120°C under vacuum or normal pressure conditions , obtained by calcining at 500-620°C under a nitrogen atmosphere for 2-8 hours, and then at 200-300°C in air for 3-6 hours.