RU220551U1 - Adiabatic hydrogenation reactor with a cone-shaped device built inside - Google Patents

Abstract

The utility model relates to petrochemical synthesis and can be used for selective catalytic hydrogenation of the ethane-ethylene fraction. An element is built inside an adiabatic reactor with a fixed bed of catalyst for the hydrogenation of unsaturated compounds, which has a cone shape with a downward expansion. The built-in cone-shaped element is located on a support grid fixed in the lower part of the reactor, and is attached to the reactor walls from above using jibs. The catalyst is located between the support grid and the mesh fixed in the upper part of the reactor. Three thermocouples are installed along the height of the catalyst layer. The reactor is also equipped with inlet and outlet fittings. The technical result is to reduce the loss of the target product in the selective catalytic hydrogenation reactor with a reduced volume of catalyst loading. 1 ill., 1 pr., 1 tab.

Description

Field of technology

The utility model relates to the field of petrochemical synthesis, namely to a device for selective catalytic hydrogenation of the ethane-ethylene fraction (EEF), and can be used in the gas-phase hydrogenation of other fractions; in particular, an adiabatic reactor with a fixed bed of catalyst for the hydrogenation of unsaturated compounds is proposed.

State of the art

The ethane-ethylene fraction (EEF) is formed during the pyrolysis of hydrocarbon feedstock. Pyrolysis is the steam cracking of hydrocarbon feedstocks in tube furnaces. From the ethane-ethylene fraction, polymer-purity ethylene is isolated, which is the raw material for the production of polyethylene.

The EEF contains acetylene, which is an unsaturated compound. EEF pyrolysis contains up to 1.5 mol.% acetylene. The acetylene content in commercial ethylene for petrochemical synthesis should not exceed 0.0001 mol.%, since otherwise the quality of the polymer obtained from ethylene sharply decreases and the conditions of the polymerization process worsen.

During the hydrogenation process, due to a small amount of hydrogen, an acetylene dimerization reaction occurs and 1,3-butadiene is formed, which turns into an oligopolymer with a high molecular weight called “Green Oil”. Green oil deactivates the catalyst by adsorbing on its surface, thereby reducing the service life, selectivity of the catalyst and the yield of the target product [Mukhina T.N., Baranov N.L., “Chemistry”, 1987, No. 4, pp. 240- 242]. Therefore, the problem of removing acetylene from EEF is very relevant.

Various methods of sorption and selective catalytic hydrogenation have found wide application for purifying gas mixtures from impurities of hydrocarbons of the acetylene series. With the current trend towards creating large pyrolysis plants, the latter method is the most profitable and convenient.

Thus, the main method for extracting acetylene is the method of selective catalytic hydrogenation. This method is characterized by reduced energy consumption, the absence of wastewater and complex equipment.

The most effective catalysts for the process of selective hydrogenation of hydrocarbons of the acetylene series in EEF are supported palladium catalysts. When creating any catalytic systems, two of their most important properties almost always come into conflict - activity and selectivity for the target product. The higher the palladium content in the catalyst, the higher its activity and the lower its selectivity for ethylene. To increase selectivity, catalysts are promoted with other metals or partially deactivated by introducing micro amounts of the catalytic poison, carbon monoxide, into the feedstock.

Hydrogenation of acetylene occurs as follows:

C ₂ H2 + H ₂ → C ₂ H _4.

Simultaneously with the hydrogenation of acetylene, the target product (ethylene) is hydrogenated into ethane:

C ₂ H ₄ + H ₂ → C ₂ H _6.

Thus, losses of the target product occur, therefore, the selectivity of the process is important. Preventing losses of the target product is important for the economy of the industry in question, therefore, along with the development, selection and use of more effective catalysts for the process of hydrogenation of acetylene hydrocarbon impurities in EEF, it is important and relevant to improve the conditions of the purification process and the equipment used for these purposes.

The following adiabatic fixed bed reactors and hydrogenation methods are available:

An adiabatic reactor described in patent RU 2674950 C1, published on December 13, 2018, with two fixed layers of catalyst, which are separated by an intermediate zone containing a quenching gas input fitting, a collector plate connected to a mixing chamber of the product gas fluid with quenching gas, and a distribution device that differs in that the outer part of the collector plate is implemented in the form of a truncated cone, with its apex facing downwards in the direction of the gas product fluid flow, and the inner part - in the form of a truncated cone, with its apex facing upwards in the direction of the flow. The result is to compensate for the negative influence of the thermal effect. However, the design of the catalytic reactor presented here is unknown whether it is suitable for the hydrogenation of hydrocarbon feedstocks.

The patent RU 2722147 C2, published on May 27, 2020, which can be accepted as the closest analogue, proposes a method for the hydrogenation of hydrocarbon feedstocks containing polyunsaturated molecules containing at least three carbon atoms. The method consists of using a single adiabatic hydrogenation reactor with two fixed beds of catalyst. The safety reactor has a smaller size and a single catalyst bed. Despite the reduction in capital costs, the linear speed remains constant, which does not increase the efficiency of hydrogenation.

The objective of the proposed utility model is to overcome the shortcomings of the prior art, as well as to reduce the loss of the target product in the process of selective catalytic hydrogenation by introducing a cone-shaped device into the adiabatic hydrogenation reactor.

List of drawings

In fig. 1 is a schematic representation of a hydrogenation reactor with a cone-shaped element inside.

Disclosure of utility model

The technical result from the use of the claimed utility model is a reduction in the loss of the target product in the selective catalytic hydrogenation reactor with a reduced volume of catalyst loading.

To achieve the set task and technical result, an adiabatic hydrogenation reactor with a fixed bed of catalyst for the hydrogenation of unsaturated compounds is proposed, characterized in that an element without a bottom is built inside the reactor, which has a cone-shaped shape with a downward expansion, while the built-in cone-shaped element is located on a support grid, located in the lower part of the reactor, and attached to the reactor walls from above using jibs, a catalyst is located between the support grid and the mesh located in the upper part of the reactor, while three thermocouples are installed along the height of the catalyst layer, and the reactor is equipped with inlet and outlet fittings.

More specifically and with reference to the drawing, in order to achieve the stated task and technical result, it is proposed to install inside an adiabatic hydrogenation reactor with a fixed catalyst bed a cone-shaped element without a bottom (with an expansion towards the bottom) (1) made of stainless steel, which will replace part of the catalyst layer. This cone-shaped element is located on the support grid (2) and secured on top using jibs (3). The grid (2) and jibs (3) are also made of stainless steel and are fixedly fixed inside the reactor by welding, riveting, bolts, etc. The catalyst is located between the support grid (2) and the mesh (4). Three thermocouples (5) are installed along the height of the catalyst layer. Also, the adiabatic reactor is equipped with inlet (6) and outlet (7), respectively, for the input and output of raw materials and reaction products.

The catalyst may be any catalyst known in the art that has selectivity and activity. The choice of catalyst is not included in the scope of the proposed development.

The principle of operation of the cone-shaped element built into the hydrogenation reactor is based on an increase in the linear flow velocity as it passes through the catalyst layer due to a gradual decrease in the free cross-sectional area of the catalyst. In adiabatic fixed-bed reactors, the majority of acetylene is hydrogenated at the top of the catalyst bed, with the thermal effect of the hydrogenation reactions resulting in an increase in the temperature of the EEF stream as it flows through the catalyst bed. Elevated temperatures in the lower part of the catalyst layer lead to an increase in the activity of the catalyst for all hydrogenation reactions. An increase in catalyst activity negatively affects its selectivity, leading to the loss of ethylene for rehydrogenation into ethane. Increasing the linear velocity along the flow path in the reactor will reduce the contact time in the lower part of the catalyst bed, which will reduce the amount of ethylene losses due to rehydrogenation into ethane and will lead to an increase in the selectivity of the process as a whole.

An additional positive effect when introducing a cone-shaped device into an adiabatic hydrogenation reactor is to reduce the volume of catalyst loading, which will reduce the cost of its purchase, loading and regeneration.

The proposed reactor can be used not only for the catalytic hydrogenation of the ethane-ethylene fraction (EEF), but can also be used for the gas-phase hydrogenation of other fractions. To do this, it is only necessary to select a catalyst suitable in terms of activity and selectivity without the need for any changes in the reactor design.

Carrying out the invention

Experimental studies were carried out on the effectiveness of the proposed design.

Example

For the research, a standard adiabatic selective hydrogenation reactor with a fixed bed of catalyst was used, followed by its modification to obtain the claimed design. The catalyst has not been changed. To confirm the effectiveness of the proposed reactor, the change in linear velocity along the layer height was measured and calculated. The results are displayed in Table 1:

Table 1. Comparative table of technological indicators

Design parameter Before installing the device After installing the device Relative change in indicators Linear flow velocity, m/s 0.160 0.176 (average value)
0.185 (max value) ↑by 10.1% (average value)
↑by 16.1% (max value) Contact time in layer, s 18.78 17.06 ↓ by 9.1%

Experimental studies and calculations have shown that as a result of the introduction of a cone-shaped element into an adiabatic hydrogenation reactor due to an increase in the selectivity of the hydrogenation process, the increase in the increase in ethylene produced ranged from 76 to 111 kg/h. The service life of the catalyst will be extended, and the mileage between regeneration will increase to 4-6 months. Also, these indicators are achieved by reducing the catalyst loading volume from 21.21 m ³ to 19.27 m ³ , which will obviously reduce the cost of its purchase.

Claims (1)

An adiabatic reactor with a fixed bed of catalyst for the hydrogenation of unsaturated compounds, characterized in that an element is built inside the reactor, which has a cone-shaped shape with a downward expansion, and the built-in cone-shaped element is located on a support grid fixed in the lower part of the reactor, and is attached to the reactor walls at the top using jibs, a catalyst is located between the support grid and a mesh fixed in the upper part of the reactor, while three thermocouples are installed along the height of the catalyst layer, and the reactor is equipped with inlet and outlet fittings.