CN115779475A - Plug flow reaction rectification combined tray, reaction rectification tower comprising same and method for producing dimethyl carbonate - Google Patents
Plug flow reaction rectification combined tray, reaction rectification tower comprising same and method for producing dimethyl carbonate Download PDFInfo
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- CN115779475A CN115779475A CN202211606438.5A CN202211606438A CN115779475A CN 115779475 A CN115779475 A CN 115779475A CN 202211606438 A CN202211606438 A CN 202211606438A CN 115779475 A CN115779475 A CN 115779475A
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Abstract
The invention relates to a combined tray for plug flow reaction and rectification, a reaction rectification tower comprising the same and a method for producing dimethyl carbonate, wherein the combined tray for plug flow reaction and rectification comprises a plug flow reaction tray and a rectification tray arranged below the plug flow reaction tray; at least two intermediate weirs are arranged between the downcomer and the outlet weir of the plug flow reaction tray; the plug flow reaction tower tray is provided with air holes; the air hole is upwards connected with an air rising pipe; the method for producing the dimethyl carbonate is carried out in a reaction rectifying tower comprising the plug flow reaction rectifying combined tray. The combined tray for plug flow reaction rectification provided by the invention has the advantages of low pressure drop and high efficiency, the total tower height of the reaction rectification tower can be reduced, the fixed investment cost is saved, the method for producing dimethyl carbonate has low usage of entrainer and low energy consumption, and the conversion rate and selectivity of the reaction are greatly improved.
Description
Technical Field
The invention relates to the technical field of reactive distillation, in particular to a plug flow reactive distillation combined tray, a reactive distillation tower comprising the same and a method for producing dimethyl carbonate.
Background
Dimethyl carbonate (DMC) is an organic chemical raw material with low toxicity and excellent environmental protection performance, has wide application in the aspects of pesticides, medicines, battery materials, solvents and the like, and is called as a new base block in the field of organic synthesis in the 21 st century. The methods for synthesizing DMC at present mainly comprise a phosgene methanol method, a phosgene-sodium alkoxide method, an ester exchange method and a methanol oxidative carbonylation method. Wherein, the raw material cost of the ester exchange method is low, the toxicity is low, the reaction condition is mild, and the byproduct propylene glycol has higher recovery value. Thus, the transesterification process has significant advantages over other processes for the production of dimethyl carbonate. However, transesterification processes generally involve reversible reactions with relatively low equilibrium constants. Therefore, transesterification is usually carried out by means of reactive distillation, i.e., a minimum azeotrope is formed by methanol and DMC, so that the product DMC is removed from the reaction system to change the chemical equilibrium, thereby improving the conversion rate and selectivity of the reaction.
When reactive distillation is used, the azeotrope composition of methanol and DMC is related to the pressure, the lower the methanol content of the azeotrope composition, i.e., the less entrainer is used. Therefore, the operating pressure of the reaction rectification is reduced, and the reduction of the using amount of the azeotropic agent methanol is facilitated. In addition, the pressure reduction can make the relative volatility among the components larger, which is more beneficial to mass transfer separation, and further can reduce the reflux ratio and the number of theoretical plates, thereby reducing the energy consumption in the reaction rectification process. However, in order to ensure sufficient reaction residence time in a conventional reactive distillation column, the liquid level on the reactive distillation tray is generally high, resulting in a large pressure drop of the gas phase across the high liquid level; the catalyst used has a low void content in the package, which results in a high pressure drop. Therefore, the pressure of reaction rectification is difficult to be greatly reduced by adopting the traditional reaction rectification tray or catalytic rectification packing.
CN104557554A discloses a method for continuously producing dimethyl carbonate and co-producing 1, 2-propylene glycol by a transesterification method, wherein the method adopts reactive distillation to prepare dimethyl carbonate, but the operating pressure of the reactive distillation is normal pressure, and the molar ratio of methanol to propylene carbonate is 6-12. Therefore, the method has the defects of large operating pressure ratio, high consumption of the entrainer methanol, high heat load, high energy consumption, low reaction efficiency and the like.
CN106699565A discloses an energy-saving and consumption-reducing device and method for a dimethyl carbonate device, and the method comprehensively utilizes heat through cross heat exchange and a heat pump. However, the adopted device system and operation method are relatively complex, and the reaction efficiency is relatively low.
CN112479883A discloses a production device of dimethyl carbonate by ester exchange method and a using method thereof, the method can reduce the using amount of entrainer methanol by arranging two tubular ester exchange reactors used in series, and a product separation tower is arranged between the reactors, but the single-pass conversion rate of the reactors is lower, a large amount of circulation of raw materials is needed, the reaction efficiency is lower, the reaction flow is more complex, and the investment cost is higher.
Therefore, how to reduce the energy consumption of the reaction rectification, save the using amount of the entrainer and improve the yield of the product is a problem to be solved at present.
Disclosure of Invention
In view of the above problems, the present invention aims to provide a plug flow reaction rectification combined tray, a reaction rectification tower comprising the same, and a method for producing dimethyl carbonate.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides a combined tray for plug flow reaction and rectification, which comprises a plug flow reaction tray and a rectification tray arranged below the plug flow reaction tray; a downcomer is arranged on one side above the plug flow reaction tower tray; an outlet weir is arranged at one end of the plug flow reaction tower tray; the downcomer and the outlet weir are arranged oppositely, and the height directions of the downcomer and the outlet weir are both vertical to the plug flow reaction tray; at least two middle weirs are arranged between the downcomer and the outlet weir; the height direction of the middle weir is parallel to the outlet weir; the plug flow reaction tower tray is provided with air holes; the air hole is upwards connected with an air rising pipe; the axial direction of the gas lift pipe is vertical to the plug flow reaction tower tray.
In the invention, by arranging the combined tray of the plug flow reaction tray and the rectification tray, the reaction unit and the mass transfer unit can be mutually independently formed into an integrated unit, and a plurality of integrated units are mutually matched to finish the reaction during the reaction rectification. On the one hand, in the reaction unit, namely in a plug flow reaction tower tray, a gas phase passes through the tower tray from a riser and enters a rectification tower tray at the upper stage, a liquid phase flows in from a downcomer and forms plug flow through the action of an intermediate weir, and flows out from an outlet weir and enters the rectification tower tray at the current stage, so that the gas phase and the liquid phase are prevented from contacting and transferring mass, and the gas phase only needs to pass through a thinner liquid layer, thereby greatly reducing the pressure drop of the tower tray, reducing the pressure of reaction rectification, increasing the relative volatility among components, being beneficial to the azeotropic separation of products, reducing the using amount of an entrainer, reducing the reflux ratio and the number of theoretical plates, and achieving the effect of saving energy consumption. On the other hand, in the mass transfer unit, namely in the rectifying tower tray, the liquid phase from the current-stage plug flow reaction tower tray and the gas phase from the riser of the next-stage plug flow reaction tower tray carry out mass transfer separation on the rectifying tower tray, the gas phase after mass transfer separation continuously enters the riser of the previous-stage plug flow tower tray, and the liquid phase continuously enters the downcomer of the next-stage plug flow reaction tower tray. Through the processes, the reaction and the rectification are repeatedly and alternately carried out to finally realize the complete conversion of the reversible reaction, and the combined tray provided by the invention not only can reduce the pressure drop, but also can enlarge the gas-liquid separation space, reduce the entrainment, reduce the height of the whole tower, save the investment and improve the conversion rate and the selectivity of the reaction.
Preferably, the intermediate weirs include first intermediate weirs and second intermediate weirs alternately arranged in sequence.
Preferably, the bottom of the first intermediate weir is connected to a plug flow reaction tray.
Preferably, the second intermediate weir is arranged above the plug flow reaction tray, and a bottom gap is arranged between the bottom of the second intermediate weir and the plug flow reaction tray.
According to the invention, through alternately arranging the first intermediate weirs and the second intermediate weirs and arranging the position relation between the first intermediate weirs and the second intermediate weirs and the plug-flow reaction tower tray, a liquid phase enters the tower tray and passes through the first intermediate weirs and the second intermediate weirs which are arranged in an up-and-down staggered manner, fluid overflows from the top of the first intermediate weir, then flows out from the bottom gap of the second intermediate weir, alternately and repeatedly flows to form up-and-down plug-flow, and finally overflows from the outlet weir and enters the lower rectifying tower tray.
Preferably, the height of the bottom gap is 50-200mm, for example, 50mm, 60mm, 70mm, 80mm, 90mm, 100mm, 110mm, 120mm, 130mm, 140mm, 150mm, 160mm, 180mm or 200mm, but is not limited to the values listed, and other values not listed in the numerical range are equally applicable.
Preferably, the height of the intermediate weir is 100 to 1000mm, and may be, for example, 100mm, 200mm, 300mm, 400mm, 500mm, 600mm, 700mm, 800mm, 900mm or 1000mm, but is not limited to the values recited, and other values not recited in the range of values are equally applicable.
Preferably, the spacing between adjacent intermediate weirs is 50-300mm, and may be, for example, 50mm, 60mm, 80mm, 100mm, 120mm, 140mm, 160mm, 180mm, 200mm, 220mm, 240mm, 260mm, 280mm or 300mm, but is not limited to the values recited, and other values not recited in the range of values are equally applicable.
In the present invention, it is preferable to control the height of the bottom gap, the height of the intermediate weirs and the pitch of the intermediate weirs within specific ranges, so that the flow rate of the fluid can be further controlled to promote the progress of the plug flow reaction.
Preferably, the draft tube is of a type including any one of a circular tube, a square tube, or a through rectangular tube.
In the invention, the gas rising pipe is a round pipe or a square pipe and is arranged between the first middle weir and the second middle weir; the gas lift pipe is a rectangular pipe and penetrates through the middle weir.
Preferably, the top of the draft tube is higher than the top of the intermediate weir.
Preferably the top of the draft tube is 100 to 300mm above the top of the intermediate weir and may for example be 100mm, 120mm, 150mm, 180mm, 200mm, 220mm, 250mm, 280mm or 300mm, but is not limited to the values recited and other values not recited in the range of values are equally applicable.
In the present invention, the top of the draft tube is typically 100-300mm above the top of the uppermost intermediate weir, which is typically referred to as the second intermediate weir. According to the invention, the top of the gas-lifting pipe is higher than the top of the middle weir, and the height difference is controlled within a specific range, so that a liquid phase can be prevented from entering the gas-lifting pipe, a gas phase directly enters a higher-level rectification tower tray through the gas-lifting pipe without contacting with the liquid phase, and gas-liquid mixing or entrainment is further avoided.
Preferably, the draft tube has a diameter of 20 to 100mm, and may be, for example, 20mm, 30mm, 40mm, 50mm, 60mm, 70mm, 80mm, 90mm or 100mm, but is not limited to the values recited, and other values not recited within the range of values are equally applicable.
Preferably, an anti-impact cap is arranged above the riser.
In the invention, the anti-impact cap can prevent high-speed gas from directly impacting a higher-level rectification tray to cause local entrainment.
Preferably, the distance between the impact cap and the top of the draft tube is 50-100mm, for example 50mm, 60mm, 70mm, 80mm, 90mm or 100mm, but not limited to the values recited, and other values not recited in the range of values are equally applicable.
Preferably, the shape of the impact cap comprises a "V" shape or an "i" shape.
Preferably, the angle of the "V" is 90 to 150 °, for example 90 °, 100 °, 110 °, 120 °, 130 °, 140 ° or 150 °, but is not limited to the values listed, and other values not listed in the numerical range are equally applicable.
Preferably, the shape of the downcomer comprises an arcuate or rectangular shape.
In the invention, the downcomer provides a flow channel and a gas-liquid separation place for a liquid phase flowing out from an upper layer rectification tray, and when the shape of the downcomer is an arch, the upper width and the lower width of the arch downcomer can be the same or different, and the width of the arch can account for 5-30% of the diameter of the whole tower.
Preferably, the height of the bottom end of the downcomer from the plug flow reaction tray is from 50 to 200mm, and may for example be 50mm, 60mm, 70mm, 80mm, 90mm, 100mm, 110mm, 120mm, 130mm, 140mm, 150mm, 160mm, 180mm or 200mm, but is not limited to the values recited, and other values not recited within the range of values are equally applicable.
Preferably, the outlet of the downcomer is provided with a deflector.
In the present invention, it is preferred that baffles be provided to better promote plug flow of the liquid phase on the tray.
Preferably, a defoaming element is arranged in the downcomer.
Preferably, the distance between the defoaming element and the inlet of the downcomer is 1/4-1/2 of the height of the downcomer, for example 1/4, 3/10, 7/24, 1/3 or 1/2, but is not limited to the values listed, and other values not listed in the range of values are equally applicable.
Preferably, the defoaming element comprises a wire mesh or a perforated sheet.
Preferably, the wire mesh has a thickness of 20 to 100mm, for example 20mm, 30mm, 40mm, 50mm, 60mm, 70mm, 80mm, 90mm or 100mm, but not limited to the values listed, and other values not listed in the numerical range are equally applicable.
Preferably, the mesh number of the wire mesh is 100 to 500 mesh, for example, 100 mesh, 150 mesh, 200 mesh, 250 mesh, 300 mesh, 350 mesh, 400 mesh, 450 mesh or 500 mesh, but is not limited to the recited values, and other values not recited in the numerical range are also applicable.
Preferably, the spacing between the plug flow reaction tray and the rectification tray is 200 to 400mm, and may be, for example, 200mm, 220mm, 250mm, 280mm, 300mm, 320mm, 350mm, 380mm or 400mm, but is not limited to the values recited, and other values not recited in the range of values are equally applicable.
Preferably, the type of the rectification tray comprises any one of a sieve tray, a float valve tray, a bubble cap tray or a tongue tray.
Preferably, one end of the rectification tray is provided with a weir.
In the invention, the overflow weir is generally arranged at the liquid phase outlet of the rectifying tray and is generally positioned at the same side with the downcomer of the upper-level plug flow reaction tray.
Preferably, the height of the weir is 25-60mm, and may be, for example, 25mm, 30mm, 35mm, 40mm, 45mm, 50mm, 55mm or 60mm, but is not limited to the values recited, and other values not recited within the range of values are equally applicable.
In a second aspect, the present invention provides a reactive distillation column, wherein at least one plug-flow reactive distillation combined tray according to the first aspect of the present invention is sequentially disposed from top to bottom in the reactive distillation column.
According to the invention, the reaction rectifying tower is provided with the plug flow reaction rectifying combined tray, and a plurality of plug flow reaction rectifying combined trays can cooperate, so that the reaction rectifying tower has the advantages of low pressure drop and high efficiency, the height of the whole tower can be reduced, and the fixed investment is saved.
Preferably, the number of the combined tray for the plug flow reactive distillation in the reactive distillation column is 30 to 80, such as 30, 35, 40, 45, 50, 55, 60, 65, 70, 75 or 80, but not limited to the values listed, and other values not listed in the range of the values are also applicable.
Preferably, the open area of the gas lift tube is 5-40% of the cross-sectional area of the reaction rectification column, for example, 5%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 35% or 40%, but not limited to the values listed, and other values not listed in the numerical range are also applicable.
In a third aspect, the present invention provides a process for the production of dimethyl carbonate, the process comprising: continuously introducing propylene carbonate, methanol and a catalyst into a reaction rectifying tower to continuously obtain an azeotrope containing dimethyl carbonate from the top of the tower; the reactive distillation column is the reactive distillation column according to the second aspect of the present invention.
In the invention, propylene carbonate and methanol are subjected to reversible reaction to generate dimethyl carbonate, and the dimethyl carbonate and excessive methanol form a minimum azeotrope to bring the dimethyl carbonate out of a reaction system, so that the concentration of a reaction product is reduced, and the forward progress of the reversible reaction is promoted. The preparation process is carried out in the reactive distillation column of the second aspect of the invention, which not only can reduce the use amount of methanol, but also can improve the conversion rate and selectivity of the reaction.
Preferably, the propylene carbonate, the methanol and the catalyst are premixed to obtain a mixed feed liquid, and then the mixed feed liquid is continuously introduced into the reaction rectifying tower.
Preferably, the mass ratio of the methanol to the propylene carbonate feed is (3-8): 1, which can be, for example, 3.
In the invention, the molar ratio of the methanol to the propylene carbonate is preferably controlled within a specific range, so that the use amount of the methanol can be further reduced and higher product yield can be achieved.
Preferably, the mass concentration of the catalyst in the mixed feed liquid is 0.1-2%, for example, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8% or 2%, but not limited to the recited values, and other values not recited in the range of values are also applicable.
Preferably, the catalyst comprises any one of an ionic liquid, an alkali metal, an alkaline earth metal oxide, a cyanide, a hydroxide or an alkyl alcoholate or a combination of at least two of them, wherein typical but non-limiting combinations include a combination of an ionic liquid and an alkali metal, a combination of an alkali metal and an alkaline earth metal oxide or a combination of a hydroxide and an alkyl alcoholate.
Preferably, the catalyst comprises any one of sodium hydroxide, sodium cyanide, lithium hydroxide, sodium methoxide or sodium ethoxide or a combination of at least two thereof, with typical but non-limiting combinations including sodium hydroxide and sodium cyanide, lithium hydroxide and sodium methoxide or sodium methoxide and sodium ethoxide, preferably sodium methoxide.
Preferably, the operating pressure at the top of the reactive rectification column is from 20 to 150kPaA, and may be, for example, 20kPaA, 30kPaA, 40kPaA, 50kPaA, 60kPaA, 70kPaA, 80kPaA, 90kPaA, 100kPaA, 110kPaA, 120kPaA, 130kPaA, 140kPaA or 150kPaA, but is not limited to the values listed, and other values not listed in the numerical ranges are equally applicable.
In the invention, the operation pressure at the top of the reaction rectifying tower is preferably controlled, so that the pressure drop can be further reduced and the higher product yield can be achieved.
Preferably, the reactive distillation column has an overhead operating temperature of 45 to 80 ℃, for example 45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃ or 80 ℃, but not limited to the recited values, and other values not recited in the range of values are equally applicable.
Preferably, the operation temperature of the reaction rectification column is 60-170 ℃, for example, 60 ℃, 70 ℃, 80 ℃, 90 ℃, 100 ℃, 110 ℃, 120 ℃, 130 ℃, 140 ℃, 150 ℃, 160 ℃ or 170 ℃, but not limited to the recited values, and other values not recited in the numerical range are also applicable.
Preferably, the reactive distillation column is operated at a reflux ratio of from 0.2 to 5, which may be, for example, 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.7, 2, 3, 4 or 5, but is not limited to the values recited, and other values not recited within the numerical range are equally applicable.
Preferably, the total residence time of the reactive distillation column is 30 to 120min, and may be, for example, 30min, 40min, 50min, 60min, 70min, 80min, 90min, 100min, 110min or 120min, but is not limited to the values listed, and other values not listed in the range of values are equally applicable.
Preferably, the number of the combined tray for the plug flow reaction rectification in the reaction rectification tower is 50 to 80, for example, 50, 55, 60, 65, 70, 75 or 80, but not limited to the values listed, and other values not listed in the range of values are also applicable.
As a preferable technical solution of the third aspect of the present invention, the method includes:
premixing propylene carbonate, methanol and a catalyst to obtain a mixed feed liquid, and then continuously introducing the mixed feed liquid into a reaction rectifying tower to continuously obtain an azeotrope containing dimethyl carbonate from the top of the tower; the reactive distillation column is the reactive distillation column of the second aspect of the invention;
the mass ratio of methanol to propylene carbonate is (3-8): 1, the mass concentration of the catalyst in the mixed feed liquid is 0.1-2%, the operation pressure at the top of the reaction rectifying tower is 20-150kPaA, the operation temperature at the top of the reaction rectifying tower is 45-80 ℃, the operation temperature at the bottom of the reaction rectifying tower is 60-170 ℃, the operation reflux ratio of the reaction rectifying tower is 0.2-5, the total retention time of the reaction rectifying tower is 30-120min, the number of the plug flow reaction rectifying combination trays arranged in the reaction rectifying tower is 50-80, and the catalyst comprises any one or the combination of at least two of sodium hydroxide, sodium cyanide, lithium hydroxide, sodium methoxide or sodium ethoxide.
Compared with the prior art, the invention has the following beneficial effects:
(1) The plug flow reaction rectification combined tray provided by the invention can avoid resistance caused by gas phase passing through a high liquid layer, can reduce pressure drop, increases a gas-liquid separation space, reduces entrainment, reduces back mixing in the reaction process, further achieves the effects of reducing the consumption of an entrainer, improving the reaction conversion rate and selectivity and reducing energy consumption, and under a better condition, the DMC yield can reach more than 92.3%, and the heat load of a reboiler can reach below 578 kW.
(2) The reaction rectifying tower provided by the invention has a higher separation effect, can reduce the distance between tower plates, reduces the height of the whole tower and saves fixed investment.
(3) The method for producing the dimethyl carbonate has the advantages of low methanol consumption, high product yield, production cost reduction and product income improvement.
Drawings
FIG. 1 is a top plan view of a plug flow reaction tray according to example 1 of the present invention;
FIG. 2 is a schematic structural diagram of a combined tray for plug flow reactive distillation as described in example 2 of the present invention;
FIG. 3 isbase:Sub>A cross-sectional view A-A of FIG. 2;
FIG. 4 is a schematic view of an apparatus for producing dimethyl carbonate according to example 2 of the present invention;
wherein, 1-defoaming element; 2-a downcomer; 3-an intermediate weir; 4-scour prevention cap; 5-a riser; 6-outlet weir; 7-a rectification tray; 8-a reactive distillation column; 9-a condenser; 10-tower kettle pump; 11-reboiler.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
The embodiment provides a plug flow reaction rectification combined tray, which comprises a plug flow reaction tray and a rectification tray arranged below the plug flow reaction tray, wherein a top view of the plug flow reaction tray is shown in fig. 1, a downcomer 2 is arranged on one side above the plug flow reaction tray, one end of the plug flow reaction tray is provided with an outlet weir 6, the downcomer 2 and the outlet weir 6 are arranged oppositely, the height directions of the downcomer 2 and the outlet weir 6 are both vertical to the plug flow reaction tray, 4 intermediate weirs 3 are arranged between the downcomer 2 and the outlet weir 6, the height direction of the intermediate weirs 3 is parallel to the outlet weir 6, the plug flow reaction tray is provided with air holes, the air holes are upwards connected with an air lifting pipe 5, the axial direction of the air lifting pipe 5 is vertical to the plug flow reaction tray, the intermediate weirs 3 comprise a first intermediate weir and a second intermediate weir which are sequentially and alternately arranged, the bottom of the first intermediate weir is connected with the plug flow reaction tray, the second intermediate weir is arranged above the plug flow reaction tray, the height of the intermediate weirs 3 and the second intermediate weirs are arranged at intervals of 400mm, the bottom of the two intermediate weirs is 400mm, and the height of the adjacent push flow reaction weir is 400mm;
the type of the gas lift pipe 5 is a through rectangular pipe, the through rectangular pipe penetrates through the middle weir 3, 6 identical through rectangular pipes are arranged, the width of the through rectangular pipe is 30mm, the length of the through rectangular pipe is 300mm, the height of the through rectangular pipe is 650mm, the center distance between every two adjacent gas lift pipes 5 is 20mm, the top of each gas lift pipe 5 is higher than the top of the middle weir 3, the top of each gas lift pipe 5 is higher than the top of the second middle weir by 150mm, an anti-impact cap is arranged above each gas lift pipe 5, the distance between each anti-impact cap and the top of each gas lift pipe 5 is 50mm, the anti-impact caps are V-shaped, and the included angle of each V-shaped is 120 degrees;
the shape of the downcomer 2 is arched, the upper width and the lower width of the downcomer 2 are the same, the width is 50mm, the height from the bottom end of the downcomer 2 to a plug flow reaction tray is 80mm, an antifoaming element is arranged in the downcomer 2, the distance between the antifoaming element and the inlet of the downcomer 2 accounts for 1/4 of the height of the downcomer 2, the antifoaming element is a metal wire mesh, the thickness of the metal wire mesh is 30mm, and the mesh number of the metal wire mesh is 200 meshes;
the space between the plug flow reaction tray and the rectification tray is 200mm, the rectification tray is an F1 float valve tray, the aperture ratio is 15%, one end of the rectification tray is provided with an overflow weir, and the height of the overflow weir is 30mm.
This embodiment provides a reaction rectifying column, from top to bottom sets gradually 60 above-mentioned plug flow reaction rectification combination tower trays in the reaction rectifying column, the trompil area of gas riser 5 is 28% of the tower sectional area of reaction rectifying column.
This example provides a process for the production of dimethyl carbonate, the process comprising:
premixing propylene carbonate, methanol and a catalyst to obtain a mixed feed liquid, and then continuously introducing the mixed feed liquid into a reaction rectifying tower, wherein the feed flow is controlled to be 2000kg/h, the feed temperature is 40 ℃, the feed position is the middle position of the tower, and an azeotrope containing dimethyl carbonate is continuously obtained from the top of the tower, the flow is 1177kg/h, wherein the methanol content is 64.6 percent, and the DMC content is 35.4 percent;
the mass ratio of methanol to propylene carbonate feeding is 3.
Example 2
The embodiment providesbase:Sub>A combined tray for plug flow reaction and rectification, which comprisesbase:Sub>A plug flow reaction tray andbase:Sub>A rectification tray 7 arranged below the plug flow reaction tray, whereinbase:Sub>A schematic structural diagram of the combined tray for plug flow reaction and rectification is shown in fig. 2,base:Sub>A sectional diagram ofbase:Sub>A-base:Sub>A in fig. 2 is shown in fig. 3,base:Sub>A downcomer 2 is arranged on one side above the plug flow reaction tray, one end of the plug flow reaction tray is provided with an outlet weir 6, the downcomer 2 and the outlet weir 6 are oppositely arranged, the height directions of the downcomer 2 and the outlet weir 6 are both perpendicular to the plug flow reaction tray, 4 intermediate weirs 3 are arranged between the downcomer 2 and the outlet weir 6, the height direction of the intermediate weir 3 is parallel to the outlet weir 6, the plug flow reaction tray is provided with an air hole, the air hole is upwards connected with an air riser 5, the axial direction of the air riser 5 is perpendicular to the plug flow reaction tray, the intermediate weir 3 comprisesbase:Sub>A first intermediate weir andbase:Sub>A second intermediate weir which are alternately arranged in sequence, the bottom of the first intermediate weir is connected with the plug flow reaction tray, the second intermediate weir is connected with an air hole, the plug flow reaction tray is 500mm, the second intermediate weir is 500mm, and the top of the plug flow reaction tray is 500mm, and the intermediate weir 3 is 500mm, and the top of the second intermediate weir, and the top of the plug flow reaction tray is 500mm, the intermediate weir;
the type of the gas lift pipe 5 is a circular pipe, the circular pipe is arranged between a first middle weir and a second middle weir, 30 same circular pipes are arranged, the diameter of the circular pipe is 40mm, the height of the circular pipe is 750mm, the distance between the outer walls of the adjacent gas lift pipes 5 is 15mm, the top of each gas lift pipe 5 is higher than that of the middle weir 3, the top of each gas lift pipe 5 is higher than that of the second middle weir by 100mm, an anti-impact cap 4 is arranged above each gas lift pipe 5, the distance between each anti-impact cap 4 and the top of each gas lift pipe 5 is 70mm, each anti-impact cap 4 is V-shaped, and the included angle of each V-shaped is 90 degrees;
the shape of the downcomer 2 is arched, the upper width and the lower width of the downcomer 2 are the same, the width is 60mm, the height from the bottom end of the downcomer 2 to a plug flow reaction tray is 70mm, an antifoaming element 1 is arranged in the downcomer 2, the distance between the antifoaming element 1 and the inlet of the downcomer 2 accounts for 1/3 of the height of the downcomer 2, the antifoaming element 1 is a metal wire mesh, the thickness of the metal wire mesh is 60mm, and the mesh number of the metal wire mesh is 100 meshes;
the space between the plug flow reaction tray and the rectification tray 7 is 400mm, the rectification tray 7 is an F1 float valve tray, the aperture ratio is 10%, one end of the rectification tray 7 is provided with an overflow weir, and the height of the overflow weir is 30mm.
The present embodiment provides a reactive distillation column, wherein 50 pieces of the above-mentioned plug flow reactive distillation combined trays are sequentially arranged in the reactive distillation column from top to bottom, and the opening area of the gas riser 5 is 19% of the column cross-sectional area of the reactive distillation column.
This example provides a process for the production of dimethyl carbonate using an apparatus as schematically shown in FIG. 4, the apparatus comprising: the method comprises the following steps of (1) carrying out reaction rectification on a tower 8, a condenser 9, a tower kettle pump 10 and a reboiler 11, wherein the method comprises the following steps: premixing propylene carbonate, methanol and a catalyst to obtain a mixed feed liquid, continuously introducing the mixed feed liquid into a reaction rectifying tower 8, controlling the feeding flow to be 2250kg/h, controlling the feeding temperature to be 40 ℃, setting the feeding position to be the middle position of the tower, and continuously obtaining an azeotrope containing dimethyl carbonate by condensation from the top of the tower through a condenser 9, wherein the flow is 1390kg/h, the content of the methanol is 70.7 percent, and the content of the DMC is 29.3 percent;
the mass ratio of methanol to propylene carbonate is 3.5, the mass concentration of a catalyst in the mixed material liquid is 0.6%, the catalyst is sodium methoxide, the operation pressure of the top of the reaction rectifying tower is 70kPaA, the operation pressure of the bottom of the reaction rectifying tower is 80kPaA, the operation temperature of the top of the reaction rectifying tower is 54 ℃, the operation temperature of the bottom of the reaction rectifying tower is 66 ℃, the operation reflux ratio of the reaction rectifying tower is 0.4, and the total residence time of the reaction rectifying tower is 62min.
Example 3
The embodiment provides a combined tray for plug flow reaction and rectification, which comprises a plug flow reaction tray and a rectification tray arranged below the plug flow reaction tray, wherein a downcomer is arranged on one side above the plug flow reaction tray, one end of the plug flow reaction tray is provided with an outlet weir, the downcomer and the outlet weir are arranged oppositely, the height directions of the downcomer and the outlet weir are both vertical to the plug flow reaction tray, 6 intermediate weirs are arranged between the downcomer and the outlet weir, the height direction of the intermediate weir is parallel to that of the outlet weir, an air hole is arranged on the plug flow reaction tray, the air hole is connected with an air rising pipe upwards, the axial direction of the air rising pipe is vertical to the plug flow reaction tray, the intermediate weir comprises a first intermediate weir and a second intermediate weir which are alternately arranged in sequence, the bottom of the first intermediate weir is connected with the plug flow reaction tray, the second intermediate weir is arranged above the plug flow reaction tray, a bottom gap is arranged between the bottom of the second intermediate weir and the plug flow reaction tray, the height of the bottom gap is 80mm, the first intermediate weir is 600mm, the height of the intermediate weir is 600mm, and the adjacent two weirs are 700 mm;
the type of gas lift pipe is circular pipe, circular pipe sets up between weir in the middle of first and the second, sets up 24 the same circular pipes altogether, and the diameter of circular pipe is 30mm, highly is 800mm, and adjacent gas lift pipe outer wall interval is 35mm, the top of gas lift pipe is higher than the top of middle weir, the top of gas lift pipe is higher than the top 100mm of weir in the middle of the second, the top of gas lift pipe is provided with the scour protection cap, the distance of scour protection cap and gas lift pipe's top is 70mm, the shape of scour protection cap is "V" type, the contained angle of "V" type is 90 degrees;
the shape of the downcomer is arched, the upper width and the lower width of the downcomer are the same, the width is 80mm, the height from the bottom end of the downcomer to a plug flow reaction tray is 80mm, an antifoaming element is arranged in the downcomer, the distance between the antifoaming element and the inlet of the downcomer accounts for 1/3 of the height of the downcomer, the antifoaming element is a metal wire mesh, the thickness of the metal wire mesh is 100mm, and the mesh number of the metal wire mesh is 300 meshes;
the space between the plug flow reaction tray and the rectification tray is 400mm, the rectification tray is an F1 float valve tray, the aperture ratio is 10%, one end of the rectification tray is provided with an overflow weir, and the height of the overflow weir is 30mm.
This embodiment provides a reaction rectifying column, 40 above-mentioned plug flow reaction rectification combination tower trays have set gradually from top to bottom in the reaction rectifying column, the trompil area of gas-lift pipe is 11% of the tower sectional area of reaction rectifying column.
This example provides a process for the production of dimethyl carbonate, the process comprising: premixing propylene carbonate, methanol and a catalyst to obtain a mixed feed liquid, and then continuously introducing the mixed feed liquid into a reaction rectifying tower, wherein the feed flow is 2500kg/h, the feed temperature is 40 ℃, the feed position is the middle position of the tower, an azeotrope containing dimethyl carbonate is continuously obtained from the top of the tower, the flow is 1525kg/h, the methanol content is 74%, and the DMC content is 26%;
the mass ratio of methanol to propylene carbonate is 4.
Example 4
This example provides a plug flow reactive distillation composite tray differing from example 1 only in that the height of the bottom gap is 20mm.
This example provides a process for the production of dimethyl carbonate, differing from example 1 only by the use of the above-described plug flow reaction rectification combination tray.
Example 5
This example provides a combined tray for a plug flow reactive distillation, differing from example 1 only in that the height of the bottom gap is 400mm.
This example provides a process for the production of dimethyl carbonate, differing from example 1 only by the use of the above-described plug flow reaction rectification combination tray.
Example 6
This example provides a combined tray for plug flow reactive distillation, differing from example 1 only in that the top of the riser is 500mm above the top of the second intermediate weir.
This example provides a process for the production of dimethyl carbonate, differing from example 1 only by the use of the above-described plug flow reaction rectification combination tray.
Example 7
This example provides a combined tray for plug flow reactive distillation, differing from example 1 only in that the top of the riser is 50mm above the top of the second intermediate weir.
This example provides a process for the production of dimethyl carbonate, differing from example 1 only by the use of the above-described plug flow reaction rectification combination tray.
Example 8
This example provides a process for the production of dimethyl carbonate, differing from example 1 only in that the mass ratio of methanol to propylene carbonate is 10, and the conversion of propylene carbonate is maintained at 100% by adjusting the reboiler heat duty and the amount of overhead reflux.
Example 9
This example provides a process for the production of dimethyl carbonate, differing from example 1 only in that the operating pressure at the top of the reactive rectification column is 160kPA, and the conversion of propylene carbonate is maintained at 100% by adjusting the reboiler heat duty.
Comparative example 1
The comparative example provides a traditional reactive distillation tray, the diameter is 500mm, the downcomer is a single bow downcomer, the width is 80mm, the height of an outlet overflow weir is 400mm, a bubble area on the tray is provided with a float valve element, and the aperture ratio is 15%.
This comparative example provides a process for the production of dimethyl carbonate, differing from example 1 only by the use of the conventional reaction rectification trays described above.
And (3) testing the plug flow effect:
taking example 1 as an example, the liquid phase residence time distribution of the plug flow reaction tray is determined by using a tracer response method, namely, the residence time of the fluid in the plug flow reaction tray is tracked by the flow of the tracer along with the fluid. The tracer adopts a sodium chloride solution with the mass concentration of 20%, a conductivity meter is installed at the outlet of the plug flow reaction tray, a certain amount of sodium chloride solution is added into a downcomer at the inlet of the plug flow reaction tray at a certain moment, and the conductivity of liquid at the outlet of the plug flow reaction tray is detected and acquired on line through the conductivity meter, so that the change of the concentration of the sodium chloride in the liquid along with the time is reflected.
Respectively at a liquid flow rate of 3m 3 /h、6m 3 H and 10m 3 Measured at the conditions of/h, the superficial gas velocity measured at each flow rate of the liquid phase ranges from 0 to 1.5m/s. The results of the experiment gave a series of normal distribution curves, and the average residence times at different gas and liquid flow rates were calculated, as shown in table 1.
TABLE 1
It can be seen from table 1 that the liquid phase flow on the reaction tray is relatively stable and close to plug flow at different gas velocities.
And (3) testing the pressure drop of the veneer: taking example 1 and comparative example 1 as examples, the pressure drop of the veneer was measured by using a cold mould tower, and the results are shown in table 2, and the operation method is as follows:
example 1: and (3) establishing a cold mould tower with the diameter of 500mm, and installing 10 plug flow reaction rectification combined trays, wherein the distance between the plug flow reaction tray and the last-stage rectification tray is 1000mm. And (3) carrying out a whole-tower pressure drop test on the cold die tower by adopting a water and air system. Water enters from the top of the tower through a pump and flows from top to bottom; the gas phase enters from the bottom of the tower through a fan and flows from bottom to top. The liquid phase flow rate was set to 2m 3 And h, measuring the pressure drop of the whole tower when the air velocity of the empty tower is in the range of 0-2.5m/s, and calculating the pressure drop of the single plate.
Comparative example 1: the same cold die tower as that in example 1 is used, and the difference is only that the traditional reaction rectification tower tray is used, the number of the tower plates is controlled to be 5, the plate spacing is 1000mm, and the liquid holdup on the tower tray is the same as that of the plug flow reaction tower tray in example 1.
TABLE 2
| Air velocity of air tower/(m/s) | EXAMPLE 1 Single plate pressure drop/mbar | Comparative example 1 Single plate pressure drop/mbar |
| 0 | 0 | 0 |
| 0.5 | 1.5 | 5.6 |
| 1 | 3.2 | 9.8 |
| 1.5 | 5.8 | 16.5 |
| 2 | 9.2 | 31 |
| 2.5 | 12.3 | 58.7 |
As can be seen from table 2: the pressure drop of the plug flow reaction rectification combination in the embodiment 1 is far smaller than that of the traditional reaction rectification tray in the comparative example 1, and is about 1/3 of that of the traditional reaction rectification tray, because the average residence time difference is large under different gas velocities in the traditional reaction rectification tray, and the liquid phase is greatly influenced by the gas phase when flowing through a bubbling region, so that the back mixing of the liquid phase in different degrees can be caused, and the liquid phase is greatly deviated from the plug flow.
The feed rate of propylene carbonate in examples 1-3, 5-9 and comparative example 1 was 500kg/h, the final conversion in the reactive distillation column was 100%, and the yield of dimethyl carbonate and reboiler duty were calculated and the results are shown in table 3.
TABLE 3
| Yield of DMC/%) | Reboiler Heat duty/kW | |
| Example 1 | 94.1 | 494.2 |
| Example 2 | 92.3 | 544.9 |
| Example 3 | 92.7 | 578 |
| Example 4 | - | - |
| Example 5 | 89.2 | 501.6 |
| Example 6 | 95.4 | 497.5 |
| Example 7 | 90.5 | 571.8 |
| Example 8 | 90 | 1674.9 |
| Example 9 | 88 | 747.8 |
| Comparative example 1 | 86 | 682.6 |
In Table 3, "-" indicates that flooding occurred in the column and normal operation was not possible.
From table 3, the following points can be seen:
(1) As can be seen from the data of examples 1-9, DMC yields of greater than 92.3% and reboiler duty of less than 578kW can be achieved under the preferred conditions.
(2) Comparing the data of example 1 and examples 4-5 together, it can be seen that the height of the bottom gap in example 1 is 60mm, compared with 20mm and 400mm in examples 4-5, respectively, the DMC yield in example 1 is significantly higher than that in example 5, and the reboiler heat duty is lower than that in example 5, because the too large bottom gap in example 5 weakens the plug flow effect of the intermediate weir on the liquid, thereby increasing the side reactions and decreasing the reaction yield; the operation can not be performed in the embodiment 4, because the liquid level in the downcomer is sharply increased and is connected with the upper rectifying tray due to the excessively small gap and the excessively large resistance in the embodiment 4, the downcomer is flooded in the tower, and the operation can not be performed. Therefore, the invention preferably controls the height of the bottom gap, can further improve the DMC yield, reduce the heat load of the reboiler and ensure the normal operation in the tower.
(3) Comparing the data of example 1 and examples 6-7 together, it can be seen that the top of the riser in example 1 is 150mm higher than the top of the second intermediate weir, compared to 500mm and 50mm in examples 6-7, respectively, the DMC yield in example 1 is significantly higher than in example 7, and the reboiler heat duty is lower than in example 7, because the riser in example 7 is too low relative to the second intermediate weir, causing part of the liquid to enter the riser and short-circuiting to flow directly to the lower rectification tray, causing total column back-mixing; although the yield in example 6 is slightly higher than that in example 1 and the reboiler heat duty is close to that in example 1, the overall height of the trays is increased in example 6, and thus the total column height is increased, which greatly increases the fixed cost. It can be seen that the present invention preferably controls the difference in the top of the riser above the top of the second intermediate weir to further increase DMC yield, reduce reboiler heat duty, and prevent back mixing.
(4) Comparing the data of example 1 and examples 8-9 together, it can be seen that the mass ratio of methanol to propylene carbonate feed in example 1 is 3; in example 9, the operating pressure at the top of the column was too high, which resulted in a significant increase in the methanol ratio in the azeotropic composition of methanol and DMC at the top of the column, and further increased the heat load of the reboiler required to ensure the recovery rate of DMC at the top of the column, and the temperature of the whole column was greatly increased due to the too high pressure, and the temperature of the bottom of the column reached 186 ℃, which resulted in an increase in side reactions and a decrease in reaction yield. Therefore, the invention preferably controls the mass ratio of the methanol to the propylene carbonate and the operation pressure at the top of the reaction rectifying tower, not only can save the using amount of the entrainer and reduce the pressure drop of the whole tower, but also can improve the DMC yield and reduce the heat load of the reboiler.
(5) Comparing the data of example 1 and comparative example 1, it can be seen that, compared with the conventional reactive distillation tray used in comparative example 1, the pressure drop of the single plate in example 1 is much smaller than that of comparative example 1, the yield of DMC in example 1 is much higher than that of comparative example 1, and the heat load of reboiler is lower than that of comparative example 1, because the pressure drop of the single plate in example 1 is much smaller than that of comparative example 1, and the operating pressure of the lower tray in comparative example 1 is increased rapidly, resulting in the decrease of yield of DMC and the increase of energy consumption. Therefore, the combined tray for plug flow reaction and rectification provided by the invention can reduce pressure drop, improve product yield and reduce energy consumption.
In conclusion, the combined tray for plug flow reaction and rectification provided by the invention can avoid resistance caused by gas phase passing through a high liquid layer, greatly reduce pressure drop, reduce back mixing in the reaction process, and further achieve the effects of reducing the using amount of an entrainer, improving the product yield and reducing energy consumption.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.
Claims (10)
1. The combined tray for the plug flow reaction and rectification is characterized by comprising a plug flow reaction tray and a rectification tray arranged below the plug flow reaction tray;
a downcomer is arranged on one side above the plug flow reaction tower tray;
an outlet weir is arranged at one end of the plug flow reaction tower tray;
the downcomer and the outlet weir are arranged oppositely, and the height directions of the downcomer and the outlet weir are both vertical to the plug flow reaction tray;
at least two intermediate weirs are arranged between the downcomer and the outlet weir;
the height direction of the middle weir is parallel to the outlet weir;
the plug flow reaction tower tray is provided with air holes;
the air hole is upwards connected with an air lifting pipe;
the axial direction of the gas lift pipe is vertical to the plug flow reaction tower tray.
2. The combined tray for a plug flow reaction and rectification as set forth in claim 1, wherein the intermediate weirs include first intermediate weirs and second intermediate weirs alternately arranged in sequence;
preferably, the bottom of the first intermediate weir is connected to a plug flow reaction tray;
preferably, the second intermediate weir is arranged above the plug flow reaction tray, and a bottom gap is arranged between the bottom of the second intermediate weir and the plug flow reaction tray;
preferably, the height of the bottom gap is 50-200mm;
preferably, the height of the middle weir is 100-1000mm;
preferably, the distance between two adjacent intermediate weirs is 50-300mm.
3. A combined tray for a plug flow reactive distillation according to claim 1 or 2, wherein said gas risers are of the type comprising any one of circular, square or through rectangular tubes;
preferably, the top of the draft tube is higher than the top of the intermediate weir;
preferably, the top of the draft tube is 100-300mm higher than the top of the intermediate weir;
preferably, the diameter of the riser is 20-100mm;
preferably, an anti-impact cap is arranged above the riser;
preferably, the distance between the scour protection cap and the top of the riser is 50-100mm;
preferably, the shape of the impact cap comprises a "V" shape or an "i" shape;
preferably, the included angle of the V-shaped part is 90-150 degrees.
4. A combined tray for plug flow reactive distillation according to any one of claims 1 to 3 wherein the shape of the downcomer comprises an arcuate or rectangular shape;
preferably, the height from the bottom end of the downcomer to the plug flow reaction tray is 50-200mm;
preferably, the outlet of the downcomer is provided with a deflector;
preferably, a defoaming element is arranged in the downcomer;
preferably, the distance between the defoaming element and the inlet of the downcomer is 1/4-1/2 of the height of the downcomer;
preferably, the defoaming element comprises a wire mesh or perforated sheet;
preferably, the thickness of the wire mesh is 20-100mm;
preferably, the mesh number of the wire mesh is 100-500 mesh.
5. The combined tray of any one of claims 1-4, wherein the tray is spaced from the tray by 200-400mm;
preferably, the type of the rectification tray comprises any one of a sieve tray, a float valve tray, a bubble cap tray or a tongue tray;
preferably, one end of the rectification tray is provided with an overflow weir;
preferably, the height of the overflow weir is 25-60mm.
6. A reactive distillation column, characterized in that at least one plug flow reactive distillation combined tray as claimed in any one of claims 1 to 5 is arranged in the reactive distillation column from top to bottom in sequence.
7. The reactive distillation column of claim 6, wherein the number of the plug flow reactive distillation combined trays in the reactive distillation column is 30-80;
preferably, the open area of the gas lift pipe is 5-40% of the tower sectional area of the reactive distillation tower.
8. A method for producing dimethyl carbonate, comprising: continuously introducing propylene carbonate, methanol and a catalyst into a reaction rectifying tower to continuously obtain an azeotrope containing dimethyl carbonate from the top of the tower;
the reactive distillation column according to claim 6 or 7.
9. The method of claim 8, wherein the propylene carbonate, the methanol and the catalyst are premixed to obtain a mixed feed liquid, and then the mixed feed liquid is continuously introduced into the reactive distillation column;
preferably, the mass ratio of the methanol to the propylene carbonate feed is (3-8): 1;
preferably, the mass concentration of the catalyst in the mixed feed liquid is 0.1-2%;
preferably, the catalyst comprises any one of an ionic liquid, an alkali metal, an alkaline earth metal oxide, a cyanide, a hydroxide or an alkyl alcoholate or a combination of at least two of them;
preferably, the catalyst comprises any one of sodium hydroxide, sodium cyanide, lithium hydroxide, sodium methoxide or sodium ethoxide or a combination of at least two thereof, preferably sodium methoxide.
10. The process according to claim 8 or 9, characterized in that the top operating pressure of the reactive distillation column is from 20 to 150kPaA;
preferably, the tower top operating temperature of the reactive distillation tower is 45-80 ℃;
preferably, the operation temperature of a tower kettle of the reactive distillation tower is 60-170 ℃;
preferably, the operational reflux ratio of the reactive distillation column is 0.2-5;
preferably, the total residence time of the reactive distillation column is 30-120min;
preferably, the number of the plug flow reaction rectification combined trays arranged in the reaction rectification tower is 50-80.
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|---|---|---|---|
| CN202211606438.5A CN115779475A (en) | 2022-12-14 | 2022-12-14 | Plug flow reaction rectification combined tray, reaction rectification tower comprising same and method for producing dimethyl carbonate |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211606438.5A CN115779475A (en) | 2022-12-14 | 2022-12-14 | Plug flow reaction rectification combined tray, reaction rectification tower comprising same and method for producing dimethyl carbonate |
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