RU2156233C1 - Method of preparing olefin hydrocarbons - Google Patents

Abstract

FIELD: chemical industry. SUBSTANCE: olefin hydrocarbons are prepared by dehydrogenation of corresponding paraffin hydrocarbons in the presence of catalyst which comprises, wt %: Cr₂O₃, 10.0-30.0; B₂O₃, 0.1-1.5; Me₂O, 0.5-2.5; SiO₂, 0.5-2.0; and Al₂O₃, the balance wherein Me is alkali metal. Process is carried out at temperature of 500-650 C, pressure of 1-2 absolute atmospheres and volumetric rate ranging from 100 to 500 h^-1.. After hydrogenation, catalyst is subjected to regeneration. EFFECT: increased yield of the desired products. 6 ex, 1 tbl

Description

The present invention relates to the field of producing olefinic hydrocarbons, in particular C ₂ -C ₂₀ olefinic hydrocarbons, by dehydrogenation of the corresponding paraffin hydrocarbons.

 Olefin hydrocarbons are important intermediates for the production of many large-capacity polypropylene and polybutylene products; synthetic rubbers; high-octane additives to motor fuels (MHFE), etc.

 Traditional sources (for example, cracking) cannot provide the growing demand for olefinic hydrocarbons. This led to the development of alternative methods for the production of olefin hydrocarbons, the most interesting of which is the dehydrogenation of the corresponding paraffin hydrocarbons.

This reaction proceeds with heat absorption and is regulated by thermodynamic equilibrium. Ecologically acceptable yields of olefin hydrocarbons are achieved only at temperatures above 500 ^° C., but the reaction rate is low and therefore a catalyst is required. The catalyst should provide high yields of olefinic hydrocarbons and have thermal stability. The inevitable formation of coke on the surface of the catalyst causes a progressive decrease in catalytic activity and the need for periodic regeneration. Regeneration is carried out, as a rule, at temperatures above 600 ^o C, and the catalyst should maintain its characteristics under these conditions for a long time.

 Known methods for producing olefin hydrocarbons by dehydrogenation at elevated temperatures of the corresponding paraffin hydrocarbons in the presence of noble metal catalyst compositions (US Pat. Nos. 3,531,543, 4,786,625. European Patent Nos. 3,51067), as well as based on metal oxides in the presence of promoters, in most cases it is supported oxide chromium (US patent N 2945823, 2956030, 2991255 and British patent N 2162082).

 However, both of these groups of these compositions have disadvantages. Compositions based on noble metals require special treatment at the stage of regeneration in order to maintain the activity of noble metals, for example, treatment with chlorine-containing substances, followed by reduction (US patent N 4438288). Compositions based on chromium oxide deposited on alumina, silica, alumina - silica, etc. have insufficient selectivity and activity.

Closest to the proposed is a method for producing olefinic hydrocarbons by dehydrogenation of the corresponding paraffinic hydrocarbons in the presence of a catalyst composition, wt.%:
Cr ₂ O ₃ - 6.0-30.0
SnO - 0.1-3.5
Me ₂ O - 0.4-3.0
SiO ₂ - 0.08-3.0
Al ₂ O ₃ - Else
The process is carried out at a temperature of 450 to 800 ^o C, a pressure of 0.1 to 3 atm. abs. and space velocity from 100 to 1000 h ^-1 . (RF patent N 2127242, 03/10/99, bull. N 7).

 The olefin yield in this method is not high enough, which is associated with insufficiently high activity and selectivity of the catalyst.

 The problem solved by the present invention is to increase the efficiency of the dehydrogenation process of paraffin hydrocarbons.

A method for producing olefin hydrocarbons by dehydrogenation of the corresponding paraffin hydrocarbons in the presence of a catalyst composition, wt.%:
Cr ₂ O ₃ - 10.0-30.0
B ₂ O ₃ - 0.1-1.5
Me ₂ O - 0.5-2.5
SiO ₂ - 0.5-2.0
Al ₂ O ₃ - Else
where is me-alkali metal.

The process is carried out at a temperature of 500-650 ^o C, a pressure of 1-2 atmospheres absolute and a space velocity of gas from 100 to 500 h ^-1 . After the dehydrogenation step, the catalyst is directed to regeneration.

Preferred are the following embodiments of the new method:
- use a catalyst containing Al ₂ O ₃ in gamma; delta-; theta; gamma and delta; delta and theta; or gamma, delta and theta phases; use the catalyst composition wt.%:
Cr ₂ O ₃ - 5.0-25.0
B ₂ O ₃ - 0.1-0.5
Me ₂ O - 0.8-1.6
SiO ₂ - 0.7-1.5
Al ₂ O ₃ - Else
where Me is alkali metal
- potassium is used as an alkali metal
- in the composition of the catalyst using Al ₂ O ₃ with a specific surface area of less than 200 m ² / g
- dehydrogenation and regeneration is carried out in a fluidized bed of catalyst
- dehydrogenation in the fluidized bed of the catalyst is carried out at a temperature of 530-620 ^o C, atmospheric or slightly higher atmospheric pressure, gas volumetric velocity from 100 to 500 h ^-1 and the residence time of the catalyst in the reaction zone from 5 to 25 minutes. At the same time, the gas volumetric velocity is from 100 to 250 h ^-1 and the catalyst residence time is from 10 to 15 minutes
- the regeneration of the catalyst in the fluidized bed is carried out in the presence of air or other oxygen-containing gas at a temperature of 630-670 ^o C, atmospheric or slightly higher atmospheric pressure, gas volumetric velocity from 100 to 500 h ^-1 and the residence time of the catalyst in the regeneration zone from 15 to 45 minutes.

 The use of the dehydrogenation of a catalyst in the claimed conditions, which includes boron oxide, reduces coke formation, contributes to a more complete and faster occurrence of redox reactions on the catalyst, which increases the activity and selectivity of the process, resulting in an increase in the yield of olefinic hydrocarbons.

 The process of obtaining the catalytic system used in the new method consists in dispersing chromium, alkali metal and boron compounds on a carrier consisting of aluminum and silicon oxides, or in dispersing chromium and alkali metal compounds on a carrier consisting of aluminum, silicon and boron oxides.

 The claimed process can be used for any dehydrogenation technology in a fixed, fluidized or moving catalyst bed.

 It is preferable to carry out the process in a fluidized bed in a system consisting of a reactor in which a dehydrogenation reaction takes place, and a regenerator where coke formed in the reactor is burned from the surface of the catalyst and its activity is restored.

 The fluidized catalyst is continuously circulated in the reactor-regenerator system. The regenerated catalyst is also a coolant, supplying the heat necessary for the reaction, which allows the process to be carried out continuously.

 In the reactor, the catalyst is maintained in a fluidized state using paraffin hydrocarbon vapors that enter the catalyst bed through a special distribution system that ensures uniform distribution over the cross section of the apparatus.

 After separation of the catalyst in cyclones or other dust collection systems, the contact gas is cooled by heating the feed supplied to the reactor and enters the separation section. Target olefins are sent to the warehouse, unreacted paraffins are returned to the process, and by-products (light hydrocarbons) can be used in the regenerator as fuel.

 In the reactor, the catalyst moves countercurrently with respect to the gas phase — hydrocarbon vapors. In the lower part of the reactor (desorption zone), to prevent nitrogen losses, reaction products are blown off, which enter the reactor, and the catalyst in the fluidized state is sent to the regenerator.

In the reactor, it is preferable to have the following operating conditions:
- temperature from 530 to 620 ^o C (supported by a stream of regenerated catalyst having the required temperature)
- atmospheric pressure or slightly higher than atmospheric
- space velocity from 100 to 250 h ^-1 (normal m ³ / hour of gas per m ^{3 of} catalyst)
- residence time in the reaction zone 10-15 minutes, in the desorption zone 1-5 minutes
In order to prevent back mixing and approximate the operating conditions of the reactor to the ideal displacement model, it is advisable to install sectional gratings. Lattices with a free section from 10 to 50% (preferably from 10 to 30%) are installed horizontally at a distance of 30 to 50 cm from each other.

The pneumatic conveying system from reactor to reactor consists of a transport line with at least one zone in which the catalyst moves from top to bottom and in which intermediate conditions are maintained from minimal fluidization to minimal bubble formation by introducing an appropriate amount of gas at an appropriate height, and the zone where the catalyst moves upward until it reaches the top of the regenerator, by introducing a carrier gas into the base, which significantly reduces the density of the fluid Wednesday. The catalyst coming from the reactor to the regenerator is evenly distributed over the surface of the fluidized bed. Regeneration occurs inside the layer due to burning out coke deposited on the catalyst, and heating occurs when fuel is burned on the catalyst surface in the presence of air or other oxygen-containing gas at a temperature that is higher than the average temperature of the reactor. The regenerated catalyst, before being fed into the reactor, is restored at a temperature of 630-680 ^° C for 1 to 5 minutes in order to remove hexavalent chromium compounds formed in the regenerator.

 The counterflow principle is also used in the regenerator: air is fed down the apparatus, the catalyst moves from top to bottom. Fuel gas is supplied to the required layer height.

The gas leaving the regenerator consists of nitrogen, oxygen and combustion products. After purification from the catalyst in the dust collection system located in the upper part of the regenerator, this gas is used to heat the air necessary for the combustion process. Before being released into the atmosphere, flue gases are cleaned by a system of filters or other devices to reduce dust content to sanitary standards. Since the combustion process occurs at a temperature below 700 ^o C, the content of nitrogen oxides and carbon monoxide is very small and no purification is required. The operating pressure in the regenerator is preferably atmospheric or slightly higher than atmospheric, the gas volumetric velocity is from 100 to 500 h ^-1 , the temperature is 630-670 ^o C and the catalyst residence time is from 30 to 45 minutes. The regenerated catalyst is transferred to the reactor in the same manner as the coked catalyst to the regenerator.

 The reactor-regenerator system, designed in this way, allows you to maintain constant process parameters and characteristics throughout the life of the installation.

 If necessary, part of the catalyst can be discharged from the system and replaced with a fresh catalyst, without interrupting the operation of the installation.

The advantages of using a fluidized bed dehydrogenation process can be summarized as follows:
- there are no heat exchange surfaces, heat is transferred directly to the reaction using the regenerated catalyst; strong mixing of the fluidized bed prevents local overheating, which reduces selectivity
- an optimal temperature profile is achieved in the reactor
- the process is continuous and there is no need to change operating parameters throughout the entire life cycle
- the installation has great flexibility and can operate at different loads of raw materials (± 50% of design capacity) with virtually no decrease in performance
- the reaction and regeneration proceed in various devices, therefore mixing hydrocarbon streams with streams containing oxygen is excluded
- the process proceeds at atmospheric pressure or slightly higher, which eliminates the ingress of air into the reaction zone.

 The invention is illustrated by the following examples.

 Example 1

Microspherical pseudoboehmite with the addition of silicon oxide (1.5 wt.%), Having a particle diameter of 5 to 250 microns, was obtained by spray-drying a suspension of pre-hydrogenated alumina, to which silicic acid was added during hydration. A pseudoboehmite sample is subjected to heat treatment, consisting of holding at a temperature of 150 ^o C for 2 hours and calcining at 800 ^o C for 4 hours in a stream of air.

The resulting product had a specific surface area of 170 m ² / g, porosity of 0.39 g / cm ³ and consisted mainly of gamma, delta and theta transitional aluminum oxides.

200 g of such alumina was impregnated using the “initial humidity” technique with an aqueous solution (78 cm ³ ) containing 67.1 g of CrO ₃ (99.8 wt.%), 5.36 g of KOH (85 wt.%) And 0.5 g of H ₃ BO ₃ (99.8 wt.%) In deionized water at a temperature of 85 ^o C. The impregnated product was left at room temperature for 1 hour, then dried at a temperature of 90 ^o C for 6 hours. The dried product was activated in a stream of air at a temperature of 700 ^o C for 4 hours.

Get the catalyst having the following composition, wt%:
Cr ₂ O ₃ - 20.0
K ₂ O - 1.5
SiO ₂ - 1.2
B ₂ O ₃ - 0.1
Al ₂ O ₃ - Else
The resulting catalyst was tested in the processes of isobutane and propane dehydrogenation, carried out at a temperature of 540-600 ^o C, bulk feed rate of 250 - 500 l of reagent / l of catalyst • hour in a laboratory quartz reactor at close to atmospheric pressure. A catalytic cycle simulating a reaction in an industrial reactor consists of a reaction phase in which hydrocarbons are fed for 15 minutes, a purge phase, when nitrogen is passed for 10 minutes to release the catalyst from the absorbed dehydrogenation reaction products, and the regeneration phase when the regenerator is fed the regeneration gas is air for 30 minutes (in these experiments), and again the purge phases when nitrogen is passed for 10 minutes to release the catalyst from the adsorbed reaction products regeneration. Nitrogen and air are supplied at the same volumetric rate as hydrocarbons. The technical conditions of the industrial process of dehydrogenation in a fluidized bed of catalyst require regeneration at temperatures higher than the reaction temperature: in this case, regeneration and reduction were carried out at 650 ^o C, while dehydrogenation was carried out at 540-600 ^o C. The results are shown in the table.

 Example 2

Analogously to example 1, a catalyst is obtained having the following composition, wt.%:
Cr ₂ O ₃ - 15.0
K ₂ O - 1.5
SiO ₂ - 1.25
B ₂ O ₃ - 0.3
Al ₂ O ₃ - Else
The resulting catalyst was tested in the processes of dehydrogenation of isobutane and propane, as described in example 1. The results are shown in the table.

 Example 3

Analogously to example 1, a catalyst is obtained having the following composition, wt.%:
Cr ₂ O ₃ - 25.0
K ₂ O - 0.8
SiO ₂ - 1.1
B ₂ O ₃ - 0.6
Al ₂ O ₃ - Else
The resulting catalyst was tested in the processes of dehydrogenation of isobutane and propane, as described in example 1. The results are shown in the table.

Example 4
Analogously to example 1, a catalyst is obtained having the following composition, wt.%:
Cr ₂ O ₃ - 30.0
K ₂ O - 1.5
SiO ₂ - 0.5
B ₂ O ₃ - 0.2
Al ₂ O ₃ - Else
The resulting catalyst was tested in the processes of dehydrogenation of isobutane and propane, as described in example 1. The results are shown in the table.

 Example 5

Analogously to example 1, a catalyst is obtained having the following composition, wt.%:
Cr ₂ O ₃ - 10.0
K ₂ O - 2.5
SiO ₂ - 1.3
B ₂ O ₃ - 1.5
Al ₂ O ₃ - Else
The resulting catalyst was tested in the processes of dehydrogenation of isobutane and propane, as described in example 1. The results are shown in the table.

 Example 6

Analogously to example 1 receive a catalyst having the following composition, wt. %:
Cr ₂ O ₃ - 20.0
K ₂ O - 1.7
SiO ₂ - 2.0
B ₂ O ₃ - 0.1
Al ₂ O ₃ - Else
The resulting catalyst was tested in the processes of dehydrogenation of isobutane and propane, as described in example 1. The results are shown in the table.

Claims (9)

1. The method of producing olefin hydrocarbons by dehydrogenation of the corresponding paraffin hydrocarbons in the presence of a chromium-containing catalyst, followed by its regeneration, characterized in that they use a catalyst composition wt.%:
Cr ₂ O ₃ - 10.0 - 30.0
B ₂ O ₃ - 0.1 - 1.5
Me ₂ O - 0.5 - 2.5
SiO ₂ - 0.5 - 2.0
Al ₂ O ₃ - Else
where Me is an alkali metal and dehydrogenation is carried out at a temperature of 500 - 650 ^o C, a pressure of 1 - 2 atm absolute and a space velocity of gas of 100 - 500 h ^-1 . 2. The method according to claim 1, characterized in that they use a catalyst containing Al ₂ O ₃ in gamma, delta, theta, gamma and delta, delta and theta or gamma, delta and theta phases. 3. The method according to claim 1, characterized in that the use of a catalyst composition, wt.%:
Cr ₂ O ₃ - 15.0 - 25.0
B ₂ O ₃ - 0.1 - 0.5
Me ₂ O - 0.8 - 1.6
SiO ₂ - 0.7 - 1.5
Al ₂ O ₃ - Else
where Me is an alkali metal.  4. The method according to claim 1, characterized in that they use a catalyst containing potassium as an alkali metal. 5. The method according to claim 1, characterized in that use Al ₂ O ₃ with a specific surface area of less than 200 m ² / year  6. The method according to claim 1, characterized in that the dehydrogenation and regeneration is carried out in a fluidized bed of catalyst. 7. The method according to claim 6, characterized in that the dehydrogenation is carried out at a temperature of 530 - 620 ^o C, atmospheric or slightly higher atmospheric pressure, a gas volumetric velocity of 100 - 500 h ^-1 and a residence time of the catalyst in the reaction zone of 5 - 25 minutes 8. The method according to claim 7, characterized in that the space velocity of the gas is 100 - 250 h ^-1 , and the residence time of the catalyst in the fluidization zone is 10-15 minutes. 9. The method according to claim 6, characterized in that the regeneration of the catalyst is carried out in the presence of air or other oxygen-containing gas at a temperature of 630 - 670 ^o C, atmospheric or slightly higher atmospheric pressure, gas volumetric velocity of 100 - 500 h ^-1 and the residence time of the catalyst in the regeneration zone 30 - 45 min.

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