Radial fixed bed dehydration reactor

Abstract

The present invention relates to a radial fixed bed dehydration reactor, comprising an air inlet heating section and a radial reaction section; the air inlet heating section is provided with an upper head and a lower head; the radial reaction section comprises a shell, a central gas distribution pipe and a radial reaction basket with a plurality of vents, the side wall of the central gas distribution pipe is provided with a plurality of gas distribution holes, the annular space between the central gas distribution pipe and the shell is divided into a radial reaction chamber and a gas collection chamber by a radial reaction basket, and a catalyst bed is formed in the radial reaction chamber; a central flow guide cone is provided in the central gas distribution pipe, and the cone tip of the central flow guide cone corresponds to the inlet of the central gas distribution pipe; the shell at the inlet end of the radial reaction section is welded and connected to the lower head of the air inlet heating section, and the air inlet of the radial reaction section is connected to the tube side outlet of the air inlet heating section. The present invention can more efficiently adapt to the dehydration reaction of organic alcohols, so that olefin products have higher selectivity.

Description

Technical Field

[0001] The invention belongs to the field of chemical equipment, and in particular relates to a radial fixed bed reactor, which is particularly suitable for the dehydration reaction of co-products in a co-oxidation propylene oxide device, such as 1-phenylethanol, dimethylbenzyl alcohol, tert-butyl alcohol, etc. Background Art

[0002] The method of using organic hydrogen peroxide as an oxygen carrier (such as ethylbenzene hydroperoxide, tert-butyl hydroperoxide, isopropylbenzene hydroperoxide) to oxidize propylene to obtain propylene oxide and styrene, namely the Haakon process, is well known and currently has industrialized equipment.

[0003] A typical co-oxidation propylene oxide production process includes the following steps:

[0004] (a) The organic matter reacts with oxygen in the oxygen-containing gas to generate organic hydrogen peroxide;

[0005] (b) organic hydrogen peroxide reacts with propylene to produce propylene oxide and organic alcohol;

[0006] (c) Dehydration of organic alcohols to generate olefin products.

[0007] Among them, the dehydration reaction of the co-product organic alcohol is an endothermic reaction and can be carried out in the gas phase and the liquid phase. Taking the propylene oxide / styrene co-production technology as an example, the US Halcon Company's patent US3526674 reported a liquid phase dehydration method for aromatic alcohols, using an alumina particle catalyst to carry out high-temperature liquid phase dehydration in a reactor with an agitator. Later, the US Lyondell Company disclosed a method for producing styrene by dehydrating 1-phenylethanol in patent CN102361838A, which uses a mixture of p-toluenesulfonic acid and o-toluenesulfonic acid as a catalyst and dehydrates in the liquid phase. In the propylene oxide and styrene co-production method disclosed by the Dutch Shell Company (US6504038, CN10189644A), a gas phase dehydration method was used to prepare styrene, and a catalyst of alumina particles with a multi-modal pore size distribution was used to carry out the dehydration reaction in a fixed bed reactor.

[0008] At present, both the liquid phase dehydration and gas phase dehydration methods of organic alcohols have actual industrial plant cases (such as the liquid phase dehydration of 1-phenylethanol by Zhenhai Refining and the gas phase dehydration of 1-phenylethanol by CNOOC Shell). In comparison, the advantage of liquid phase dehydration is that it can operate stably for a long time, using organic strong acid catalysts that are miscible with the reaction materials, and there is no problem of catalyst regeneration and switching; but the use of organic strong acid catalysts causes the liquid phase reaction raw materials and olefin products to be exposed to an acidic environment for a long time, resulting in more olefin polymerization to generate heavy tar, which increases the material loss of olefin products. At the same time, the amount of tar generated also increases significantly, which increases the economic cost of tar treatment. Gas phase dehydration does not have the problem of olefin acid polymerization and has a higher olefin yield, but gas phase dehydration generally uses titanium dioxide or aluminum oxide as a catalyst. As the reaction proceeds, the active center of the catalyst will gradually be covered by coke, requiring regeneration and catalyst switching operations. Compared with catalyst regeneration and reactor switching operations, the large loss of materials is more unacceptable in terms of economics, so the gas phase dehydration method of organic alcohols has more economic advantages.

[0009] The gas phase dehydration reaction of organic alcohols has the following characteristics:

[0010] 1. The dehydration of organic alcohols to olefins is a strongly endothermic reaction. As the dehydration reactor proceeds, the temperature of the reaction materials will gradually decrease, and the dehydration rate will gradually decrease to outside the suitable temperature range of the catalyst. Therefore, the reaction materials need to be heated during the reaction.

[0011] 2. The dehydration of organic alcohols to olefins is a molecular weight increase reaction. A lower reaction pressure is more conducive to the dehydration reaction. Therefore, negative pressure operation is generally used in the process to maximize the conversion rate of organic alcohols. However, negative pressure operation also places higher requirements on the resistance drop of the dehydration catalyst bed.

[0012] 3. The olefin products (such as styrene) after dehydration of organic alcohols have strong polymerization performance. The dead zone and residence time should be minimized in large reactors to reduce olefin polymerization and prevent local coking from causing uneven reaction or clogging of equipment.

[0013] 4. In the co-oxidation propylene oxide unit, due to the long process and multiple reactions, the organic alcohol raw materials before entering the dehydration reactor carry many impurities. These impurities include oxygen-containing alcohols, aldehydes, esters, phenols, ethers, and oxygen-free olefins and alkanes. Many of these impurities are more active than the organic alcohol co-products. When the materials enter the catalyst bed after heating, they will be dehydrated first, and the generated olefins will be more easily polymerized and coked, which will cause the distribution holes of the inlet distribution pipe of the radial reactor to be partially or even heavily blocked, affecting the uniformity of the reactor and generating a large number of by-products.

[0014] In order to solve the above problems, Shell uses a shell-and-tube fixed bed reactor for alcohol dehydration. Summary of the invention

[0015] In view of the above problems, the present invention proposes a compact, dead-zone-free radial fixed-bed dehydration reactor, which can more efficiently adapt to the dehydration reaction of organic alcohols and make olefin products have higher selectivity.

[0016] In order to achieve the above object, the technical solution of the present invention is:

[0017] A radial fixed bed dehydration reactor, suitable for the dehydration reaction of 1-phenylethanol, tert-butyl alcohol and dimethylbenzyl alcohol, comprising an air inlet heating section and a radial reaction section;

[0018] The air inlet heating section is provided with an upper head and a lower head, the upper head is provided with a tube-side air inlet of the air inlet heating section, and the lower head is provided with a tube-side air outlet; the shell side of the air inlet heating section is provided with a heat medium inlet and a heat medium outlet;

[0019] The radial reaction section comprises a shell, a central gas distribution pipe and a radial reaction basket with a plurality of vents, the side wall of the central gas distribution pipe is provided with a plurality of gas distribution holes, the bottom of the central gas distribution pipe is connected and fixed by a fixing plate, the annular space between the central gas distribution pipe and the shell is divided into a radial reaction chamber and a gas collection chamber by the radial reaction basket, a catalyst bed is formed in the radial reaction chamber; the shell is provided with a reaction gas outlet corresponding to the gas collection chamber;

[0020] A central guide cone is provided in the central air distribution pipe, the bottom of the central guide cone is fixed on a fixed plate, and the tip of the central guide cone corresponds to the inlet of the central air distribution pipe;

[0021] The air inlet of the central air distribution pipe is the air inlet of the radial reaction section. The shell at the inlet end of the radial reaction section is welded to the lower head of the air inlet heating section. The air inlet of the radial reaction section is connected to the tube-side air outlet of the air inlet heating section.

[0022] As a further improvement of the present invention: an axial reaction section is provided, the air intake heating section is connected to the radial reaction section through the axial reaction section, the axial reaction section includes an axial upper head, an axial catalytic bed and an axial lower head, the axial upper head is provided with a feed port correspondingly connected to the air outlet of the lower head tube side of the air intake heating section; the axial lower head is provided with a discharge port connected to the air intake of the central air distribution pipe, and the radial reaction section inlet end shell is welded and connected to the axial lower head. The addition of the axial reaction section is conducive to removing heavy components and olefin polymer impurities in the raw materials, avoiding coking and blockage of the central distribution pipe in the radial reaction section, causing uneven air intake distribution, and affecting the catalytic effect of the radial reaction bed.

[0023] As a preferred embodiment of the present invention: the air intake heating section is a shell and tube heat exchanger.

[0024] As a further improvement of the present invention: the opening rate of the radial reaction basket is 20-40%, and the aperture of the vent hole is 5-25 mm.

[0025] As a further improvement of the present invention: the opening rate on the side wall of the central air distribution pipe is 20-40%, and the aperture of the air distribution hole is 5-25 mm.

[0026] As a further improvement of the present invention: the base angle α of the isosceles triangle formed by the central cross section of the central guide cone is 80-89°, which ensures the uniformity of airflow diffusion and forms a reaction zone without dead angles.

[0027] As a further improvement of the present invention: the radial reaction section shell, the central gas distribution pipe and the gas guide cone are coaxially arranged, thereby ensuring that the gas can participate in the reaction evenly and stably.

[0028] Compared with the traditional reactor, the structure of the present invention has the following advantages:

[0029] 1. Compared with the axial fixed bed generally used for gas phase dehydration of organic alcohols, the flow area of ​​the gas flowing through the catalytic bed in the radial reactor is much larger, so the thickness of the catalyst bed and the flow rate of the reaction gas are significantly reduced compared with the axial bed, so the pressure drop of the catalytic bed is also significantly reduced. This can significantly reduce the operating pressure of the raw material vaporizer, reduce the evaporation temperature of the alcohol raw material by 10~30℃, avoid the thermal decomposition of the raw material during the evaporation process and the polymerization reaction of the product olefins, and improve the yield of the device.

[0030] 2. Adding an axial reaction section on the basis of the radial reaction section is beneficial to removing heavy components and olefin polymer impurities in the raw materials, avoiding coking and blockage of the central distribution pipe in the radial reactor, causing uneven distribution of the intake air and affecting the catalytic effect of the radial reaction bed.

[0031] 3. The present invention can concentrate the air inlet heating section, the axial reaction section, and the radial reaction section in one reactor, and has a compact structure. It minimizes the residence time of olefins at high temperature and without catalytic contact, reduces the bulk polymerization of olefins, and can not only reduce the polymerization of olefins and reduce material consumption, but also extend the operation cycle of the catalyst bed due to the reduction in the amount of polymer generated.

[0032] 4. The central guide cone design in the radial reaction section of the present invention is used to evenly distribute the reaction gas at the inlet end of the catalyst bed, ensuring that the reaction gas can pass through the catalyst bed evenly and stably, ensuring that the dehydration reaction is carried out under the best reaction conditions, and improving the yield of olefin products.

[0033] 5. Compared with axial fixed bed and tubular fixed bed reactors, the reactor of the present invention is easy to industrialize and mass-produce.

[0034] 6. Compared with the shell-and-tube fixed-bed reactor, the reactor of the present invention avoids the risk of the dehydration product olefins coking and adhering to the reaction tubes, and also avoids the problem of incomplete regeneration of the reaction tubes with serious coking during catalyst decoking and regeneration. However, in order to control the pressure drop of the catalyst bed, the tube length and the catalyst bed height are limited in the shell-and-tube fixed-bed reactor. In order to adapt to large-scale devices, a larger reactor diameter is required. For example, when the shell-and-tube isothermal reactor is used in a 300,000 tons / year propylene oxide co-production 670,000 tons / year styrene device, the reactor diameter is as high as 8.6m, which will lead to a too long heat medium flow on the shell side and uneven flow distribution, causing the local heat exchange tubes on the reactor tube side to not react under optimal conditions, affecting the reaction yield, and even causing higher local hot spots in the reactor tubes, resulting in polymerization of the dehydration product olefins and blocking the reaction tubes. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 : A schematic structural diagram of a dehydration reactor in Example 1 of the present invention;

[0036] Figure 2 : A schematic diagram of the structure of a dehydration reactor in Example 2 of the present invention;

[0037] Figure 3 : Schematic diagram of the structure of the combined reactor formed by combined dehydration.

[0038] In the figure: 1 air inlet heating section; 11 upper head; 111 tube side air inlet; 12 lower head; 121 tube side air outlet; 13 heat medium inlet; 14 heat medium outlet; 2 radial reaction section; 21 central gas distribution pipe; 22 radial reaction basket; 221 gas collecting chamber; radial reaction chamber 222; 23 central guide cone; fixed plate 24; 25 nitrogen inlet; 26 reaction gas outlet; 27 shell; 3 axial reaction section, 31 axial upper head; 32 axial catalytic bed; 33 axial lower head, 331 discharge port. DETAILED DESCRIPTION

[0039] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0040] Embodiment 1, as Figure 1 As shown: The present invention relates to a radial fixed bed dehydration reactor, comprising an air inlet heating section 1 and a radial reaction section 2.

[0041] like Figure 1As shown: the air inlet heating section 1 adopts a shell and tube heat exchanger, which is provided with an upper head 11 and a lower head 12, the upper head 11 is provided with a tube-side air inlet 111 of the air inlet heating section, and the lower head 12 is provided with a tube-side air outlet 121; the shell side of the air inlet heating section is provided with a heat medium inlet 13 and a heat medium outlet 14. The tube-side air outlet 121 of the air inlet heating section is connected to the air inlet of the radial reaction section, that is, the air inlet of the central air distribution pipe 21.

[0042] In the present invention, the air inlet heating section 1 and the radial reaction section 2 can be integrated and compactly arranged, and of course they can also be arranged separately. When separated, the air inlet heating section can be arranged vertically or horizontally.

[0043] like Figure 1 As shown: the radial reaction section 2 includes a shell 27, a central air distribution pipe 21 and a radial reaction basket 22 with a plurality of air holes. The central air distribution pipe 21 is arranged at the center of the shell 27. The main body of the radial reaction basket 22 is a tubular structure and is coaxially designed with the central air distribution pipe 21 and the shell 27. The diameter of the main body of the radial reaction basket 22 is larger than the diameter of the central air distribution pipe 21. One end of the central air distribution pipe 21 is an air inlet, and the other end is connected to the fixed plate 24. A plurality of air distribution holes are provided on the side wall of the central air distribution pipe 21. The lower end of the radial reaction basket 22 can be fixed on the lower end cap formed at the outlet end of the radial reaction section shell, or can be fixed on the fixed plate 24. The fixed plate 24 is fixed on the lower end cap formed at the outlet end of the radial reaction section shell 27. In this embodiment, the radial reaction basket 22 is fixed on the lower end cap at the outlet end of the shell 27, and a radial reaction chamber 222 is formed by setting an upper cover plate, the wall of the central air distribution pipe, and the fixed plate. A catalyst bed is formed in the radial reaction chamber 222. The upper end of the radial reaction basket 22 is bent and connected to the reactor shell 27, so that the annular gap between the radial reaction basket body and the reactor shell 27 forms a gas collecting chamber 221 for collecting the reacted gas. The reactor shell corresponding to the gas collecting chamber 221 is provided with a reaction gas outlet 26, and the collected reaction gas flows out from this outlet.

[0044] like Figure 1 As shown: a central guide cone 23 is provided in the central gas distribution pipe, the bottom of the central guide cone 23 is fixed on the fixed plate 24, and the base angle α of the isosceles triangle formed by the central cross section of the central guide cone 23 is 87°, which can reduce the pressure drop of the catalyst bed and improve the conversion rate of the dehydration reaction. At the same time, it can make the gas evenly distributed in the catalyst bed, so that all gases react under the optimal reaction conditions, and improve the selectivity of styrene. The tip of the central guide cone 23 corresponds to the air inlet of the central gas distribution pipe 21; the air inlet of the central gas distribution pipe 21 is the air inlet of the radial reaction section 2, and the shell at the inlet end of the radial reaction section 2 is welded to the lower head 12 of the air inlet heating section.

[0045] In this embodiment, the diameter of the air distribution holes on the side wall of the central air distribution pipe 21 is 15 mm, and the opening rate is 30%; the diameter of the air vents on the radial reaction basket 22 is 16 mm, and the opening rate is 29%.

[0046] In this embodiment, in order to avoid a reaction dead zone, measures such as providing a nitrogen port 25 at a required position in the radial reaction section 2 may be taken.

[0047] Embodiment 2, as Figure 2 As shown: This embodiment adds an axial reaction section 3 on the basis of the embodiment one, and the axial reaction section 3 is located between the air inlet heating section 1 and the radial reaction section 2; the axial reaction section 3 includes an axial upper head 31, an axial catalytic bed 32 and an axial lower head 33, the axial upper head 31 is provided with a feed port which is connected to the corresponding air outlet 121 on the lower head tube side of the air inlet heating section; the axial lower head 33 is provided with a discharge port 331 which is connected to the air inlet of the central gas distribution pipe 21, and the inlet end shell of the radial reaction section 2 is welded to the axial lower head 33.

[0048] In this embodiment, the distance between the upper layer of the axial catalytic bed and the axial upper head is 2m, and the distance between the lower layer of the axial catalytic bed and the axial lower head is 1.5m, realizing a compact design.

[0049] In the present invention, the axial reaction section 3 and the radial reaction section 2 can be integrated or separately arranged; when separately arranged, the discharge port of the axial reaction section and the air inlet of the radial reaction section can be connected by a pipeline or by a flange connection. In this embodiment, the axial reaction section and the radial reaction section are integrated, and the diameter of the axial reaction section shell and the radial reaction section shell are the same in this embodiment.

[0050] like Figure 2 As shown: This embodiment adopts an integrated design of the air intake heating section, the axial reaction section and the radial reaction section, which shortens the residence time of phenylethanol / styrene in the high temperature zone, reduces the generation of styrene polymers, and effectively protects the central gas distribution pipe of the radial reactor; at the same time, the axial reaction section is used to effectively cut off impurities in the phenylethanol material, avoiding coking and blockage of the radial reaction section, which affects its uniformity, so that the reactor can operate stably for a long time in an industrial environment. The radial reaction basket and the central gas distribution pipe ensure the uniformity of the radial catalyst bed, and the setting of the central guide cone ensures that the reaction gas enters the catalyst bed in equal and uniform amounts, ensuring the high selectivity of the dehydration reaction and the low generation of olefin tar.

[0051] The reactor of this embodiment, the conventional fixed bed reactor and the shell-and-tube isothermal reactor are respectively used for the dehydration reaction of phenylethanol, and the performance comparison is shown in Table 1.

[0052] Table 1 is a performance comparison between the reactor of Example 2 and the traditional reactor

[0053] project Reactor of this embodiment 2 Axially fixed bed reactor Tubular fixed bed reactor Gas flow Radial Axial Axial Is there an air intake heater? yes no no Thin bed distribution effect good Depends on distributor design, bed filling uniformity, etc. / Diameter, m 4.0 6.3 8.6 Total pressure drop of two reactors, kPa ~53 ~118 ~87 Phenol conversion, wt% ~99% ~98% ~98.5% Styrene selectivity, % ~99% ~98.5% ~98.5% Tar production, % ~0.5% ~0.7% ~0.6%

[0054] Embodiment three, as Figure 3 As shown: In this embodiment, the reactor described in Example 2 is used to form a first dehydration reactor, and the reactor described in Example 1 is used to form a second dehydration reactor, and the two form a joint production.

[0055] The above equipment is applied to the oxidation reactor for dehydration of phenylethanol to produce styrene in a 200,000 tons / year propylene oxide and 450,000 tons / year styrene unit. The specific dimensions are shown in Table 2.

[0056] Table 2 Main dimensions of the two reactors in Example 3

[0057] project Dimensions, mm Number of units 2 units Diameter D 3600 Height (cylinder) H 18050 / 13700 Diameter of reaction basket 3100 Diameter of the air distribution pipe 1000 Angle between guide cone and bottom edge α 86 °

[0058] The process of this embodiment is that the phenylethanol raw material enters the vaporizer for vaporization, and then enters the first dehydration reactor. In the first dehydration reactor, the gaseous phenylethanol is first heated to the reaction temperature by the feed heating section 1, and then enters the axial reaction section 3. The impurities entrained in the raw material will be retained in the axial reaction section 3. The clean gas after passing through the axial reaction section 3 enters the radial reaction section 2. In the radial reaction section 2, the gas first enters the central gas distribution pipe 21, and the gas is evenly distributed into the catalyst bed of the radial reaction section through the central guide cone 23. The phenylethanol is dehydrated to generate styrene. At the same time, the material temperature gradually decreases, and the reaction rate also decreases accordingly. After the conversion rate of the phenylethanol dehydration reaction reaches 50%, the material gathers in the gas collecting chamber 221, and then flows out from the reaction gas outlet 26 to enter the second dehydration reactor. Similar to the first dehydration reactor, in the second dehydration reactor, the material is also heated to the reaction temperature by the feed heating section 1, and then enters the radial reaction section 2. After the dehydration reaction, the dehydrated product flows out from the reaction gas outlet.

[0059] In the present invention, the flow direction of the reaction gas is not limited, and can be in from the top and out from the bottom, or in from the bottom and out from the top, depending on the actual device layout. The reaction gas outlet can be arranged on the reactor shell, or on the reactor head.

[0060] The above description is only used to illustrate the technical solution of the present invention and is not intended to be limiting. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in the field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution.

Claims

1. A radial fixed bed dehydration reactor, suitable for the dehydration reaction of 1-phenylethanol, tert-butyl alcohol and dimethylbenzyl alcohol, characterized in that: It comprises an air intake heating section and a radial reaction section; the air intake heating section is provided with an upper head and a lower head, the upper head is provided with a tube-side air inlet of the air intake heating section, and the lower head is provided with a tube-side air outlet; the shell side of the air intake heating section is provided with a heat medium inlet and a heat medium outlet; the radial reaction section comprises a shell, a central air distribution pipe and a radial reaction basket with a plurality of air vents, a plurality of air distribution holes are opened on the side wall of the central air distribution pipe, the bottom of the central air distribution pipe is connected and fixed by setting a fixing plate, the annular space between the central air distribution pipe and the shell is divided into a radial reaction chamber and a gas collecting chamber by the radial reaction basket, and a catalyst bed is formed in the radial reaction chamber; a reaction gas outlet corresponding to the gas collecting chamber is provided on the shell; a central guide cone is provided in the central air distribution pipe, the bottom of the central guide cone is fixed on the fixing plate, and the tip of the central guide cone corresponds to the inlet of the central air distribution pipe; The air inlet is the air inlet of the radial reaction section, the shell at the inlet end of the radial reaction section is welded to the lower head of the air inlet heating section, and the air inlet of the radial reaction section is connected to the tube-side air outlet of the air inlet heating section; the base angle α of the isosceles triangle formed by the central cross-section of the central guide cone is 87°; the opening rate on the radial reaction basket is 29%, and the aperture of the air vent is 16mm; the opening rate on the side wall of the central air distribution pipe is 30%, and the aperture of the air distribution hole is 15mm; an axial reaction section is provided, and the air inlet heating section is connected to the radial reaction section through the axial reaction section, and the axial reaction section includes an axial upper head, an axial catalytic bed and an axial lower head, the axial upper head is provided with a feed port connected to the tube-side air outlet of the lower head of the air inlet heating section; the axial lower head is provided with a discharge port connected to the air inlet of the central air distribution pipe, and the shell at the inlet end of the radial reaction section is welded to the axial lower head.

2. The radial fixed bed dehydration reactor according to claim 1, characterized in that: The air intake heating section is a shell and tube heat exchanger.

3. The radial fixed bed dehydration reactor according to claim 1, characterized in that: The radial reaction section shell, the central gas distribution pipe and the gas guide cone are coaxially arranged.

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