A system for integrated acetaldehyde distillation recovery and a method thereof

Abstract

The application provides a system and method for integrated acetaldehyde distillation and recovery, which comprises a vertically arranged main tower, the main tower is sequentially divided into a distillation section, a catalytic reaction section, a stripping section and a stripping section from top to bottom, the top of the distillation section is provided with a self-adaptive distributor and a tower top pressure controller, the catalytic reaction section comprises catalytic filler plates and a transverse liquid redistributor, and the catalytic filler plates are loaded with catalysts. The four sections of stripping, stripping, catalytic reaction and distillation are integrated in the vertical main tower, the intermediate cooling and conveying equipment are cancelled, and the investment and energy consumption are significantly reduced. The catalytic reaction section adopts the corrugated filler loaded with catalysts and cooperates with the transverse liquid redistributor, so that the liquid forms thin layer flow, the reaction residence time is effectively prolonged, and the hydrolysis decomposition rate of 2-methyl-1,3-dioxolane (MD) and the acetaldehyde recovery rate are improved.

Description

Technical Field

[0001] This invention relates to the field of acetaldehyde distillation technology, specifically to an integrated system and method for acetaldehyde distillation and recovery. Background Technology

[0002] The esterification wastewater from polyester (PET) plants contains organic compounds such as acetaldehyde and 2-methyl-1,3-dioxolane (MD). Direct discharge results in high COD, and acetaldehyde has an inhibitory effect on biochemical treatment, so pretreatment is required to remove acetaldehyde.

[0003] Existing acetaldehyde recovery technologies include: direct incineration of stripping tail gas (uneconomical utilization of calorific value); using a multi-tower process such as stripping tower, acetaldehyde distillation tower and ethylene glycol distillation tower (large equipment investment and high energy consumption); or directly feeding esterified water into the acetaldehyde distillation tower (incomplete MD decomposition and high COD in the tower bottom).

[0004] The aforementioned technologies generally suffer from problems such as dispersed equipment, low thermal energy utilization efficiency, insufficient MD decomposition rate (typically only 40%–70%), and low acetaldehyde recovery rate (70%–85%). Therefore, a highly efficient, integrated, low-energy-consumption recovery system and method that can improve both MD decomposition rate and acetaldehyde recovery rate is needed. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an integrated acetaldehyde distillation and recovery system and method, which solves the problems mentioned in the background section.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an integrated acetaldehyde distillation and recovery system, comprising a vertically arranged main column, which is divided into a distillation section, a catalytic reaction section, a stripping section and a vapor stripping section from top to bottom; The top of the rectification section is equipped with an adaptive distributor and a column top pressure controller; The catalytic reaction section includes a catalytic packing plate and a transverse liquid redistributor. The catalytic packing plate is loaded with a catalyst, and the transverse liquid redistributor is located below the catalytic packing plate and has multiple liquid distribution grooves on its surface. The stripping section includes multiple stripping trays; The stripping section is equipped with an annular steam distributor, and the stripping section is connected to an esterification wastewater inlet pipe, which is located above the annular steam distributor.

[0007] An integrated method for acetaldehyde distillation and recovery, employing the above-mentioned system, includes the following steps: S100: After preheating the esterification wastewater, it is sent to the upper part of the stripping section of the main tower. At the same time, low-pressure steam is introduced into the annular steam distributor and bubbled evenly into the tower. S200, in the stripping section, the wastewater flows downward and comes into countercurrent contact with the rising steam, causing acetaldehyde and 2-methyl-1,3-dioxocyclopentane to be stripped into the gas phase, and the wastewater with removed organic matter is discharged from the bottom of the tower. S300, the rising gas phase enters the stripping section and undergoes mass transfer with the descending liquid, and then enters the catalytic reaction section. At the same time, the reflux liquid descending from the rectification section is evenly distributed to the surface of the catalytic packing plate through the distribution tank of the transverse liquid redistributor to form a thin layer flow, which causes 2-methyl-1,3-dioxolane to hydrolyze into acetaldehyde and ethylene glycol. S400: The generated acetaldehyde enters the rectification section with the gas phase. The pressure at the top of the column is maintained by the top pressure controller. After the gas phase is discharged from the top of the column, it is condensed. Part of it is refluxed and part of it is collected as acetaldehyde product. The ethylene glycol-containing liquid that descends from the S500 catalytic reaction section is further stripped of acetaldehyde in the stripping section and then discharged from the bottom of the tower. After impurity removal, it is reused.

[0008] This invention provides an integrated system and method for acetaldehyde distillation and recovery. It offers the following advantages: This scheme integrates the four stages of stripping, distillation, catalytic reaction, and rectification into a single vertical main tower, eliminating intermediate cooling and conveying equipment and significantly reducing investment and energy consumption. The catalytic reaction section uses corrugated packing with a catalyst-loaded substrate and a transverse liquid redistributor to create a thin-layer flow of liquid, effectively extending the reaction residence time and thus improving the hydrolysis and decomposition rate of 2-methyl-1,3-dioxocyclopentane (MD) and the acetaldehyde recovery rate. The sawtooth weir and defoaming baffle at the downcomer outlet of the stripping section effectively prevent foam entrainment, while the annular steam distributor and adaptive distributor ensure stable system operation within the load range, further reducing the COD of the discharged wastewater. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the external structure of the present invention; Figure 2 This is a schematic diagram of the main structure of the present invention; Figure 3 For the present invention Figure 2 A cross-sectional view along the AA direction; Figure 4 For the present invention Figure 3 Enlarged structural schematic diagram of the transverse liquid redistributor component; Figure 5 For the present invention Figure 2 Cross-sectional view along the BB direction; Figure 6 For the present invention Figure 2 A cross-sectional view along the CC direction; Figure 7 This is a schematic diagram of the method flow of the present invention.

[0010] In the diagram: 101. Main tower; 102. Magnetic field generator; 103. Top gas phase outlet pipe; 104. Pressure control pipe; 105. Steam connection pipe; 106. Bottom drain port; 107. Esterification wastewater feed pipe; 108. Tower internal chamber; 109. Steam inlet pipe; 110. Annular steam distributor; 111. Magnetic catalyst bed; 112. Horizontal liquid redistributor; 113. Catalytic packing plate; 114. Liquid distribution plate; 115. Floating valve core; 116. Conical valve head; 117. Elastic part; 118. Valve core guide cavity; 119. Fan-shaped support rib; 120. Central column; 121. Stripping tray; 122. Liquid distribution trough; 123. Jet nozzle; 124. Top pressure controller. Detailed Implementation

[0011] This invention provides an integrated acetaldehyde distillation and recovery system and method, such as... Figure 1-6 As shown, it includes a vertically arranged main column 101, which is divided into a rectification section, a catalytic reaction section, a stripping section and a steam stripping section from top to bottom; The main tower 101 is provided with a tower top gas phase outlet pipe 103 at the top, and a pressure control pipe 104 is installed and connected to the top of the tower top gas phase outlet pipe 103. The main tower 101 is provided with a tower bottom drain outlet 106 at the bottom. The main tower 101 is provided with an inner chamber 108. An adaptive distributor and a column top pressure controller 124 are provided at the top of the rectification section. The column top pressure controller 124 is located on one side of the pressure control pipeline 104, and the adaptive distributor is located at the top of the column inner chamber 108. The catalytic reaction section includes a catalytic packing plate 113 and a transverse liquid redistributor 112. The catalytic packing plate 113 is loaded with a catalyst to form a catalytic packing plate. The transverse liquid redistributor 112 is located below the catalytic packing plate 113. The surface of the transverse liquid redistributor 112 is provided with multiple liquid distribution grooves 122, which are V-shaped or T-shaped grooves. The stripping section includes multiple stripping trays 121; The stripping section is equipped with an annular steam distributor 110, and the lower section of the inner chamber 108 of the tower is connected to an esterification wastewater inlet pipe 107, which is located above the annular steam distributor 110.

[0012] As a preferred embodiment, the stripping section is equipped with 16-20 stripping trays 121, and the weir height on the side of the stripping tray 121 is 70-100 mm, thereby increasing the residence time of the liquid solution in the stripping section and enabling the acetaldehyde-ethylene glycol complex to be fully decomposed tray by tray.

[0013] Furthermore, the downcomer outlet of the stripping tray 121 is provided with a serrated weir and a defoaming baffle to allow for higher liquid throughput and prevent foam entrainment.

[0014] Furthermore, the adaptive distributor includes a liquid distribution plate 114 located above the inner chamber 108 of the tower. Several vertical fan-shaped support ribs 119 are fixedly connected between the liquid distribution plate 114 and the bottom of the inner chamber 108 of the tower. The fan-shaped support ribs 119 are fan-shaped, and gaps are provided between the fan-shaped support ribs 119 on each side to allow for feed flow.

[0015] As a preferred embodiment, the number of fan-shaped support ribs 119 is 6-12, which are evenly distributed around the liquid distribution plate 114, and the gap width between each rib is 5-15mm, so as to form a uniform feed flow channel.

[0016] Furthermore, a vertical central column 120 is fixedly installed at the top center of the liquid distribution plate 114. The central column 120 has an upward-opening valve core guide cavity 118. The valve core guide cavity 118 has a floating valve core 115 that can move up and down. The top of the floating valve core 115 has a conical valve head 116. The conical valve head 116 is conical with a smaller top and a larger bottom. The conical valve head 116 extends into the pressure control pipeline 104. An elastic part 117 is installed and connected between the floating valve core 115 and the bottom of the valve core guide cavity 118.

[0017] As a preferred embodiment, the elastic part 117 is a compression spring, and the cone angle of the conical valve head 116 is 30°-60°. When the flow rate of the feed or return liquid increases, the upward hydrodynamic pressure on the valve core increases, overcoming the preload of the elastic part 117 and causing the conical valve head 116 to open further, increasing the liquid flow cross-sectional area. When the flow rate decreases, the opening automatically closes under the restoring force of the elastic part 117, thereby ensuring that the distributor maintains the uniformity of liquid distribution within a suitable load range. Furthermore, the catalytic reaction section also includes a magnetic catalyst bed 111 located in the inner chamber 108 of the tower, and a magnetic field generator 102 is installed on the outer end face of the main tower 101, with the magnetic field generator 102 corresponding to the position of the magnetic catalyst bed 111.

[0018] It should be further explained that the magnetic field generator 102 forms a magnetically stable fluidized bed by adding a magnetic field, which causes the catalyst particles to move slightly in the rectification section, thereby further improving the catalytic reaction efficiency.

[0019] Furthermore, the annular steam distributor 110 adopts an annular tube type distributor. The top surface of the annular steam distributor 110 is provided with several downward-sloping jet holes 123, which prevents solid impurities from clogging the liquid layer and allows the steam to pass through the liquid layer in the form of microbubbles, resulting in the highest stripping efficiency.

[0020] It should be further noted that the diameter of the annular tube of the annular steam distributor 110 is 50-150 mm, the diameter of the jet hole 123 is 2-8 mm, the opening direction of the jet hole 123 is 30°-60° downward with respect to the horizontal direction, and the spacing between adjacent jet holes 123 is 50-150 mm.

[0021] Furthermore, the bottom of the annular steam distributor 110 is connected to a steam inlet pipe 109, and the bottom of the inner chamber 108 of the tower is connected to a steam connecting pipe 105, which is connected to the steam inlet pipe 109.

[0022] This invention also provides an integrated acetaldehyde distillation and recovery method using the above-described system, comprising the following steps: Esterification wastewater from the PET unit is collected in an esterification wastewater tank. The composition of the esterification wastewater is: water 97-98 wt%, ethylene glycol 0.1-0.3 wt%, acetaldehyde 0.8-1.0 wt%, 2-methyl-1,3-dioxolane 0.6-0.8 wt%, other organic matter 0.1-0.2 wt%, and the total COD value is 20,000-40,000 mg / L.

[0023] S100: Preheat the esterification wastewater from the PET unit to 80-95°C and send it into the upper part of the stripping section of the main tower 101 through the esterification wastewater feed pipe 107; at the same time, introduce low-pressure steam into the annular steam distributor 110 through the steam inlet pipe 109 and uniformly bubble into the bottom of the tower inner chamber 108 through the jet hole 123. S200, in the stripping section, the wastewater flows downward and comes into countercurrent contact with the rising steam. Acetaldehyde and 2-methyl-1,3-dioxocyclopentane are stripped into the gas phase, and the wastewater with organic matter removed is discharged from the bottom drain 106 of the tower. S300: The rising gas phase enters the stripping section and is mass-transferred with the descending liquid on each stripping tray 121. The sawtooth weir and defoaming baffle at the downcomer outlet maintain stable overflow and eliminate foam. Then the gas phase enters the catalytic reaction section. At the same time, the reflux liquid descending from the rectification section is evenly distributed to the surface of the catalytic packing plate 113 through the distribution tank 122 of the transverse liquid redistributor 112 to form a thin layer flow. Under the action of the magnetically stable fluidized bed formed by the magnetic field generator 102, the catalyst particles move slightly to promote the hydrolysis of 2-methyl-1,3-dioxolane to generate acetaldehyde and ethylene glycol. The residence time in the catalytic reaction section is 35-45 minutes, and the MD decomposition rate reaches 80%-95%, which is more than 15% higher than the traditional process. S400. The generated acetaldehyde enters the rectification section with the gas phase. The top pressure controller 124 maintains the top pressure at 0.15-0.25 MPaG. The rectification section adopts a packed structure. After the gas phase is discharged through the top gas phase outlet pipe 103, it is condensed. Part of it is refluxed and part of it is collected as acetaldehyde product. The ethylene glycol-containing liquid descending from the S500 catalytic reaction section is further stripped of acetaldehyde in the stripping section and discharged from the bottom drain port 106. After impurity removal, it is sent to the PET unit process tower for reuse. The ethylene glycol content in the liquid is 6-10 wt%, and it is sent to the top of the PET unit process tower as reflux water or added to the ethylene glycol system.

[0024] As a preferred option, the consumption of low-pressure steam is 100-200 kg of steam per ton of esterification wastewater, and the total energy consumption of the system is 30-40 kg of standard coal per ton of esterification wastewater.

[0025] As a preferred option, the main tower 101 has an operating flexibility range of 50%–120% of the design load, which can adapt to the fluctuating flow rate of esterification wastewater in the PET unit.

[0026] As a preferred option, the acetaldehyde distillation recovery system has an acetaldehyde recovery rate of 90%–95%, a 2-methyl-1,3-dioxocyclopentane decomposition rate of 80%–95%, and a COD value of 2000–3500 mg / L for the discharged stripping wastewater.

[0027] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An integrated acetaldehyde distillation and recovery system, characterized in that: It includes a vertically arranged main column (101), which is divided into a rectification section, a catalytic reaction section, a stripping section and a vapor stripping section from top to bottom; The top of the distillation section is equipped with an adaptive distributor and a top pressure controller (124). The catalytic reaction section includes a catalytic packing plate (113) and a transverse liquid redistributor (112). The catalytic packing plate (113) is loaded with a catalyst, and the transverse liquid redistributor (112) is located below the catalytic packing plate (113) and has multiple liquid distribution grooves (122) on its surface. The stripping section includes multiple stripping trays (121). The stripping section is equipped with an annular steam distributor (110), and the stripping section is connected to an esterification wastewater inlet pipe (107), which is located above the annular steam distributor (110).

2. The integrated acetaldehyde distillation and recovery system according to claim 1, characterized in that: The stripping section is equipped with 16-20 stripping trays (121), and the weir height on the side of the stripping tray (121) is 70-100mm.

3. The integrated acetaldehyde distillation and recovery system according to claim 1, characterized in that: The downcomer outlet of the distillation tray (121) is provided with a serrated weir and a defoaming baffle.

4. The integrated acetaldehyde distillation and recovery system according to claim 1, characterized in that: The adaptive distributor includes a liquid distribution plate (114) located above the inner chamber (108) of the tower. A plurality of vertical fan-shaped support ribs (119) are fixedly connected between the liquid distribution plate (114) and the bottom of the inner chamber (108). A gap is provided between each fan-shaped support rib (119) for feeding flow.

5. The integrated acetaldehyde distillation and recovery system according to claim 4, characterized in that: The liquid distribution plate (114) is fixedly provided with a vertical central column (120) at the top center position. The central column (120) is provided with an upward-opening valve core guide cavity (118). The valve core guide cavity (118) is provided with a floating valve core (115) that can move up and down. The top of the floating valve core (115) is provided with a conical valve head (116) that is conical with a smaller top and a larger bottom. The conical valve head (116) extends into the pressure control pipeline (104). An elastic part (117) is installed and connected between the floating valve core (115) and the bottom of the valve core guide cavity (118).

6. The integrated acetaldehyde distillation and recovery system according to claim 5, characterized in that: The elastic part (117) is a compression spring, and the cone angle of the conical valve head (116) is 30°-60°; When the flow rate of the feed or return liquid increases, the conical valve head (116) opens further by overcoming the preload of the elastic part (117); When the flow rate decreases, the conical valve head (116) automatically closes under the restoring force of the elastic part (117).

7. The integrated acetaldehyde distillation and recovery system according to claim 4, characterized in that: The number of the fan-shaped support ribs (119) is 6-12, which are evenly distributed around the liquid distribution plate (114), and the gap width between each fan-shaped support rib (119) is 5-15mm.

8. The integrated acetaldehyde distillation and recovery system according to claim 1, characterized in that: The annular steam distributor (110) is an annular tube distributor with multiple downward-sloping jet holes (123) on its top surface.

9. The integrated acetaldehyde distillation and recovery system according to claim 8, characterized in that: The annular steam distributor (110) has an annular tube diameter of 50-150 mm, the jet hole (123) has a diameter of 2-8 mm, the opening direction of the jet hole (123) is 30°-60° downward with respect to the horizontal direction, and the distance between adjacent jet holes (123) is 50-150 mm.

10. An integrated method for acetaldehyde distillation and recovery, using the system described in any one of claims 1-9, characterized in that: Includes the following steps: S100. After preheating the esterification wastewater, it is sent to the upper part of the stripping section of the main tower (101). At the same time, low-pressure steam is introduced into the annular steam distributor (110) and bubbled evenly into the bottom of the inner chamber (108) of the tower. S200, in the stripping section, the wastewater flows downward and comes into countercurrent contact with the rising steam, causing acetaldehyde and 2-methyl-1,3-dioxocyclopentane to be stripped into the gas phase, and the wastewater with removed organic matter is discharged from the bottom of the tower. S300, the rising gas phase enters the stripping section and the descending liquid mass transfers, and then enters the catalytic reaction section. At the same time, the reflux liquid descending from the rectification section is evenly distributed to the surface of the catalytic packing plate (113) through the distribution tank (122) of the transverse liquid redistributor (112) to form a thin layer flow, so that 2-methyl-1,3-dioxolane is hydrolyzed to generate acetaldehyde and ethylene glycol. S400. The generated acetaldehyde enters the rectification section with the gas phase. The pressure at the top of the column is maintained by the top pressure controller (124). After the gas phase is discharged from the top of the column, it is condensed. Part of it is refluxed and part of it is collected as acetaldehyde product. The ethylene glycol-containing liquid that descends from the S500 catalytic reaction section is further stripped of acetaldehyde in the stripping section and then discharged from the bottom of the tower. After impurity removal, it is reused.

Images