CN111718256A - Acetic acid dehydration method - Google Patents
Acetic acid dehydration method Download PDFInfo
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- CN111718256A CN111718256A CN201910213993.3A CN201910213993A CN111718256A CN 111718256 A CN111718256 A CN 111718256A CN 201910213993 A CN201910213993 A CN 201910213993A CN 111718256 A CN111718256 A CN 111718256A
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- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 title claims abstract description 225
- 238000000034 method Methods 0.000 title claims abstract description 47
- 230000018044 dehydration Effects 0.000 title abstract description 16
- 238000006297 dehydration reaction Methods 0.000 title abstract description 16
- 238000000926 separation method Methods 0.000 claims abstract description 103
- 239000000463 material Substances 0.000 claims abstract description 55
- 238000004519 manufacturing process Methods 0.000 claims abstract description 30
- QQVIHTHCMHWDBS-UHFFFAOYSA-N isophthalic acid Chemical compound OC(=O)C1=CC=CC(C(O)=O)=C1 QQVIHTHCMHWDBS-UHFFFAOYSA-N 0.000 claims abstract description 22
- YKYONYBAUNKHLG-UHFFFAOYSA-N propyl acetate Chemical group CCCOC(C)=O YKYONYBAUNKHLG-UHFFFAOYSA-N 0.000 claims abstract description 22
- 230000008569 process Effects 0.000 claims abstract description 21
- 238000010438 heat treatment Methods 0.000 claims abstract description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 62
- IVSZLXZYQVIEFR-UHFFFAOYSA-N m-xylene Chemical group CC1=CC=CC(C)=C1 IVSZLXZYQVIEFR-UHFFFAOYSA-N 0.000 claims description 58
- XBDQKXXYIPTUBI-UHFFFAOYSA-M Propionate Chemical compound CCC([O-])=O XBDQKXXYIPTUBI-UHFFFAOYSA-M 0.000 claims description 44
- KXKVLQRXCPHEJC-UHFFFAOYSA-N acetic acid trimethyl ester Natural products COC(C)=O KXKVLQRXCPHEJC-UHFFFAOYSA-N 0.000 claims description 44
- 239000012071 phase Substances 0.000 claims description 42
- 239000007791 liquid phase Substances 0.000 claims description 25
- 238000011084 recovery Methods 0.000 claims description 25
- 239000002994 raw material Substances 0.000 claims description 19
- 238000001816 cooling Methods 0.000 claims description 6
- 239000007788 liquid Substances 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 4
- 238000004821 distillation Methods 0.000 claims description 2
- 239000002904 solvent Substances 0.000 claims description 2
- 238000005265 energy consumption Methods 0.000 abstract description 16
- 239000002351 wastewater Substances 0.000 abstract description 13
- 238000010533 azeotropic distillation Methods 0.000 abstract description 3
- 230000000694 effects Effects 0.000 description 7
- 239000000047 product Substances 0.000 description 7
- 239000010865 sewage Substances 0.000 description 6
- 239000003795 chemical substances by application Substances 0.000 description 4
- ANLISICGYWBHKU-UHFFFAOYSA-N methyl acetate;hydrate Chemical compound O.COC(C)=O ANLISICGYWBHKU-UHFFFAOYSA-N 0.000 description 4
- UYORHVZNGJVQCF-UHFFFAOYSA-N 3-bromo-4-ethoxy-5-methoxybenzaldehyde Chemical compound CCOC1=C(Br)C=C(C=O)C=C1OC UYORHVZNGJVQCF-UHFFFAOYSA-N 0.000 description 3
- XEKOWRVHYACXOJ-UHFFFAOYSA-N Ethyl acetate Chemical compound CCOC(C)=O XEKOWRVHYACXOJ-UHFFFAOYSA-N 0.000 description 3
- UDWVIPXDPNFVRB-UHFFFAOYSA-N propyl acetate hydrate Chemical compound O.CCCOC(C)=O UDWVIPXDPNFVRB-UHFFFAOYSA-N 0.000 description 3
- UXXZHPADSATKPV-UHFFFAOYSA-N 1,3-xylene hydrate Chemical compound O.Cc1cccc(C)c1 UXXZHPADSATKPV-UHFFFAOYSA-N 0.000 description 2
- PQLVXDKIJBQVDF-UHFFFAOYSA-N acetic acid;hydrate Chemical compound O.CC(O)=O PQLVXDKIJBQVDF-UHFFFAOYSA-N 0.000 description 2
- CSLUZWGMNQNDLF-UHFFFAOYSA-N acetic acid;propyl acetate Chemical compound CC(O)=O.CCCOC(C)=O CSLUZWGMNQNDLF-UHFFFAOYSA-N 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 229910002056 binary alloy Inorganic materials 0.000 description 2
- 239000006227 byproduct Substances 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 150000002148 esters Chemical class 0.000 description 2
- 238000000605 extraction Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- -1 water-entrainer Chemical compound 0.000 description 2
- 239000002253 acid Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000009412 basement excavation Methods 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 239000005416 organic matter Substances 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 238000004062 sedimentation Methods 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/42—Separation; Purification; Stabilisation; Use of additives
- C07C51/43—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation
- C07C51/44—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation by distillation
- C07C51/46—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation by distillation by azeotropic distillation
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C67/00—Preparation of carboxylic acid esters
- C07C67/48—Separation; Purification; Stabilisation; Use of additives
- C07C67/52—Separation; Purification; Stabilisation; Use of additives by change in the physical state, e.g. crystallisation
- C07C67/54—Separation; Purification; Stabilisation; Use of additives by change in the physical state, e.g. crystallisation by distillation
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C7/00—Purification; Separation; Use of additives
- C07C7/04—Purification; Separation; Use of additives by distillation
- C07C7/05—Purification; Separation; Use of additives by distillation with the aid of auxiliary compounds
- C07C7/06—Purification; Separation; Use of additives by distillation with the aid of auxiliary compounds by azeotropic distillation
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Crystallography & Structural Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Analytical Chemistry (AREA)
- Water Supply & Treatment (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
The invention relates to the field of isophthalic acid production, and discloses a method for dehydrating acetic acid, which comprises the following steps: introducing the first material flow into a rectifying tower with a reboiler for azeotropic distillation, introducing a part of tower bottom material flow of the rectifying tower into the reboiler for heating treatment, and circulating the heated part of tower bottom material flow back to the rectifying tower; leading out a second stream from the side line of the rectifying tower, and leading out the rest part in the tower bottom stream of the rectifying tower as an acetic acid product; feeding the fourth material flow obtained from the top of the rectifying tower into a first separation tower from the top of the first separation tower for separation, obtaining an entrainer at the tower bottom of the first separation tower, and leading out a fifth material flow from the lateral line of the first separation tower; introducing the fifth stream into a second separation column for separation; wherein the entrainer is n-propyl acetate, and the operating conditions of the rectifying tower enable the materials in the rectifying tower to form an azeotropic system. The method obviously reduces the energy consumption and material consumption in the acetic acid dehydration process and the content of the acetic acid in the wastewater.
Description
Technical Field
The invention relates to the field of isophthalic acid production, in particular to a method for dehydrating acetic acid in the production process of isophthalic acid.
Background
Since 2009, the production capacity of the isophthalic acid (PIA) production process is successfully improved from 2.5 ten thousand tons/year to 5 ten thousand tons/year by adopting the self-developed technology, and with the adoption of new technical equipment, the energy consumption and material consumption in the production are also remarkably reduced, for example, the m-xylene consumption is reduced by 2.4%, the acetic acid consumption is reduced by 21%, the comprehensive energy consumption is reduced by about 30%, and the economic benefit and market competitiveness of the PIA production process are greatly improved.
Although various indexes are continuously improved along with the optimization of the production process, and the energy consumption and material consumption levels are continuously reduced, the competition between domestic isophthalic acid and similar products imported from abroad is increasingly intensified along with the increase of the domestic PIA demand, so that the economic and technical indexes in the production process are further saved, the consumption is reduced, the production cost of the PIA product is urgently reduced on the basis that the existing production capacity is not greatly increased, and meanwhile, as the amount of discharged sewage is large and the COD content is high in the PIA production process, the further development of the PIA production process is also required under the advocation of environmental protection.
In the prior art, in the PIA production process, an acetic acid dehydration rectification system mainly comprises a rectification tower and tower top gas phase cooling, wherein a heating heat source adopts 0.4MPa steam, and the tower top gas phase cooling adopts air cooling. The rectification tower is mainly an acetic acid-water binary system in the aspect of material balance. The direct rectification process has the problems of low acetic acid-water phase relative separation degree, high acid content at the tower top, high steam consumption and the like.
In view of the above, there is a need for an improvement in the acetic acid dehydration process in the prior art PIA production process.
Disclosure of Invention
The invention aims to overcome the defects that in the production Process of Isophthalic Acid (PIA), the produced acetic acid and water have low relative separation degree, high acetic acid dehydration energy consumption, low acetic acid purity separated from a tower kettle, high acetic acid consumption, high acetic acid content in wastewater discharged from the top of a rectifying tower, high acetic acid odor and high COD value in the prior art, and provides a method for dehydrating acetic acid in the production Process of Isophthalic Acid (PIA).
The inventor of the invention finds that (1) the steam of 0.4MPa consumed by a rectifying tower used for acetic acid dehydration in the prior art accounts for 67 percent of the total consumption of 1.5MPa of an isophthalic acid device, and further energy-saving potential digging conditions are provided; (2) the binary system is difficult to separate due to the association of acetic acid and water in the separation process, and the content of acetic acid in the discharged wastewater is up to 3 percent, so that the acetic acid content, the peculiar smell and the COD content of the discharged wastewater are greatly reduced while the potential excavation condition is further reduced.
Further, the inventor of the invention discovers that a multi-component azeotropic system of acetic acid, water-entrainer, m-xylene-water, methyl acetate-water, acetic acid-n-propyl acetate and m-xylene can be formed in the rectifying tower when n-propyl acetate is used as the entrainer on the basis of azeotropic distillation, separation of target components can be realized according to difference of different components in the multi-component system, energy consumption and material consumption in the acetic acid dehydration process and the content of acetic acid in wastewater discharged from the top of the rectifying tower are obviously reduced, and peculiar smell and COD value of the acetic acid in the discharged wastewater are greatly reduced.
In order to achieve the above object, the present invention provides a method for dehydrating acetic acid, comprising:
introducing the first material flow into a rectifying tower with a reboiler for azeotropic rectification, introducing a part of tower bottom material flow of the rectifying tower into the reboiler for heating treatment, and then circulating the material flow back to the rectifying tower; leading out a second stream from a side line of the rectifying tower, and leading out the rest part of the tower bottom stream of the rectifying tower as an acetic acid product, wherein the first stream contains acetic acid, m-xylene, methyl acetate and water, and the second stream contains m-xylene, water, acetic acid and an entrainer;
feeding a fourth material flow obtained from the top of the rectifying tower into a first separation tower from the top of the first separation tower for separation, obtaining an entrainer capable of being recycled to the rectifying tower from the tower bottom of the first separation tower, and leading a fifth material flow out from the side line of the first separation tower, wherein the fifth material flow contains the entrainer, water and methyl acetate; introducing the fifth stream into a second separation column for separation to recover entrainer and methyl acetate, respectively, while withdrawing water;
wherein the entrainer is n-propyl acetate, and the operating conditions of the rectifying tower enable the materials in the rectifying tower to form an azeotropic system.
According to the invention, the first stream is a stream containing acetic acid and water to be dehydrated, which is produced in the production of PIA, and comprises a liquid-phase stream which is introduced into the rectification column in the liquid-phase state and a gas-phase stream which is introduced into the rectification column in the gas-phase state.
According to the invention, in the rectifying tower, azeotropic rectification is carried out in the presence of the entrainer (n-propyl acetate), and the entrainer can enter the rectifying tower from the top of the first separation tower through a pump.
Through the technical scheme, in the method, the content of acetic acid in the wastewater discharged from the top of the rectifying tower can be reduced to be below 0.1 wt%, so that the content of acetic acid and the COD value in the discharged sewage are greatly reduced.
In addition, the method for dehydrating acetic acid provided by the invention can save energy consumption.
Drawings
FIG. 1 is a schematic flow diagram of a process according to a preferred embodiment of the present invention.
Description of the reference numerals
1. An entrainer stream; 2. a second stream; 3. a third stream; 4. a fourth stream; 5. a methyl acetate vapor stream; 6. a meta-xylene stream; 7. an acetic acid product stream; 8. reboiler discharge stream; 9. a methyl acetate stream; 10. discharging a wastewater stream; 11. a liquid phase stream; 12. a gas phase stream; 13. water, an entrainer and a methyl acetate stream in liquid phase; A. a rectifying tower; B. a first separation column; C. a second separation column; D. a recovery tower; E. a reboiler.
Detailed Description
The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.
All pressures mentioned in this specification are gauge pressures unless explicitly stated.
As previously mentioned, the present invention provides a method for dehydration of acetic acid, the method comprising:
introducing the first material flow into a rectifying tower with a reboiler for azeotropic rectification, introducing a part of tower bottom material flow of the rectifying tower into the reboiler for heating treatment, and then circulating the material flow back to the rectifying tower; leading out a second stream from a side line of the rectifying tower, and leading out the rest part of the tower bottom stream of the rectifying tower as an acetic acid product, wherein the first stream contains acetic acid, m-xylene, methyl acetate and water, and the second stream contains m-xylene, water, acetic acid and an entrainer;
feeding a fourth material flow obtained from the top of the rectifying tower into a first separation tower from the top of the first separation tower for separation, obtaining an entrainer capable of being recycled to the rectifying tower from the tower bottom of the first separation tower, and leading a fifth material flow out from the side line of the first separation tower, wherein the fifth material flow contains the entrainer, water and methyl acetate; introducing the fifth stream into a second separation column for separation to recover entrainer and methyl acetate, respectively, while withdrawing water;
wherein the entrainer is n-propyl acetate, and the operating conditions of the rectifying tower enable the materials in the rectifying tower to form an azeotropic system.
According to the invention, in the rectifying tower, azeotropic rectification is carried out in the presence of the entrainer (n-propyl acetate), and the entrainer can enter the rectifying tower from the first separation tower kettle through a pump.
The fifth stream drawn from the side of the first separation column in the present invention means not only a single stream but at least a methyl acetate vapor stream separated from the fourth stream and entering the second separation column from the upper part of the first separation column in the form of vapor and a methyl acetate stream in the form of liquid phase, water obtained in the lower part of the first separation column, an azeotropic agent and a methyl acetate stream.
In the present invention, unless explicitly stated otherwise, neither "first" nor "second" represent a sequential order, but merely for the purpose of distinguishing, for example, a "first" and a "second" of a "first stream" and a "second stream" merely for the purpose of distinguishing these two different streams.
Preferably, the operating conditions of the rectification column include: the pressure is 0-40KPa, and the temperature at the top of the tower is 80-90 ℃. The invention is more beneficial to forming a multi-component azeotropic system of acetic acid, water-entrainer, m-xylene-water, methyl acetate-water, acetic acid-n-propyl acetate and m-xylene in the rectifying tower by controlling the operating pressure of the rectifying tower to be 0-40KPa and the temperature of the top of the rectifying tower to be 80-90 ℃.
According to the invention, when the operating pressure of the rectifying tower is fixed, the operating pressure of other devices communicated with the rectifying tower is the same as the operating pressure of the rectifying tower, and preferably, the operating pressure of the rectifying tower is 5-30 KPa.
In order to obtain acetic acid with higher purity and capable of being recycled (reducing the consumption of the acetic acid) in the tower bottom of the rectifying tower, the mass ratio of the entrainer to the water in the rectifying tower is preferably (4-8): 1.
in the invention, the reboiler is heated by using 2-6MPa of steam.
In the invention, a fourth material flow obtained from the top of the rectifying tower enters the first separation tower from the top of the first separation tower for separation, wherein the fourth material flow mainly comprises methyl acetate, water and an entrainer. It is well known to those skilled in the art that the top and bottom of the first separation tower can be controlled to different operating conditions, so that after the fourth stream enters from the top of the first separation tower, the top operating conditions of the first separation tower are controlled, so that most of the methyl acetate in the fourth stream stays at the top of the first separation tower, and the entrainer and the water are physically layered in the bottom of the first separation tower, so as to obtain an entrainer stream that can be recycled to the rectification tower, thereby achieving the full utilization of the raw materials, saving energy consumption, and reducing cost.
Preferably, the bottom operating conditions of the first separation column include: the pressure is 0-40KPa, and the temperature is 75-80 deg.C.
Preferably, the top operating conditions of the first separation column include: the pressure is 0-40KPa, and the temperature is 75-90 deg.C.
Preferably, the top of the first separation tower is cooled by circulating water, which is beneficial to reducing energy consumption.
According to the invention, in the production process of PIA, a byproduct methyl acetate is generated along with the oxidation reaction of m-xylene, and during ordinary rectification, the methyl acetate enters a sewage system along with the tower top water of a rectification tower, so that not only is organic matter lost, but also COD in the discharged water is increased. Further, the inventors of the present invention found in their studies that the load of the rectifying tower is in a positive correlation with the content of methyl acetate in the raw material (first stream) because the distribution ratio of methyl acetate in the ester phase and the water phase is about 3: 1, under normal pressure, the methyl acetate and water form a binary azeotrope of methyl acetate-water, the azeotropic temperature is 55.95 ℃, and the temperature is lower than that of the binary azeotrope of n-propyl acetate-water formed by the entrainer (n-propyl acetate) and water, so that the binary azeotrope of n-propyl acetate-water is inevitably evaporated out from the top of the rectifying tower along with the n-propyl acetate-water, and also plays a role of the entrainer. However, the evaporation heat of methyl acetate is lower than that of n-propyl acetate, the water carrying capacity of the ethyl acetate is very low, even if a binary azeotrope of methyl acetate-water is evaporated from the top of the rectifying tower, most of the condensed binary azeotrope flows back to the rectifying tower along with an ester phase and is continuously recycled, a large amount of methyl acetate is inevitably accumulated in the rectifying tower after the binary azeotrope operates for a period of time, and in order to reduce the adverse effect, the methyl acetate needs to be separated independently.
In the present invention, a fifth stream is drawn from a side of the first separation column, and although most of the entrainer is recovered in the bottom of the first separation column, a small amount of the entrainer is entrained in water and methyl acetate due to incomplete separation, so that the fifth stream mainly contains water, methyl acetate and a small amount of the entrainer, and therefore, it is necessary to introduce the fifth stream into the second separation column to separate the fifth stream so as to separately recover the entrainer, water and methyl acetate. The fifth stream drawn from the side of the first separation column in the present invention means not only a single stream but at least a methyl acetate vapor stream separated from the fourth stream and entering the second separation column from the upper part of the first separation column in the form of vapor and a methyl acetate stream in the form of liquid phase, water obtained in the lower part of the first separation column, an azeotropic agent and a methyl acetate stream.
In order to better achieve the above separation of the entrainer, water and methyl acetate, the second separation column is preferably subjected to separation under temperature gradient control. The temperature gradient means that the temperatures of the top, the middle and the bottom of the second separation tower are controlled to be different so as to realize the separation of the entrainer, water and methyl acetate.
Further preferably, the operating conditions of the second separation column include: the temperature at the top of the tower is less than 30 ℃, the temperature at the middle part of the tower is 50-70 ℃, and the temperature at the bottom of the tower is 90-110 ℃.
The division of the top, middle and bottom of the second separation column is not strictly limited, and those skilled in the art can set the division by conventional means in the art according to the requirements of equipment and operation environment, as long as the second separation column can be divided into three parts and the operations can be performed separately.
According to the invention, the temperature of the tower top is controlled to be less than 30 ℃ so as to recover methyl acetate, and preferably, the tower top of the second separation tower is cooled by circulating water; controlling the temperature in the middle of the tower to be 50-70 ℃ to recover the entrainer; the temperature of the tower kettle is controlled to be 90-110 ℃ to recycle the discharged wastewater, and the peculiar smell of acetic acid and the COD value in the recycled water are both obviously reduced.
In the present invention, the operating pressure of the second separation column is not particularly limited, and may be, for example, atmospheric pressure.
In the present invention, it is preferable that the number of theoretical plates of the rectifying column is 80 to 90.
According to the invention, in the production process of PIA, because the reaction is incomplete, trace m-xylene is inevitably led to enter a rectifying tower (first material flow) together with acetic acid and water, so that not only n-propyl acetate and water form an azeotrope in an azeotropic rectifying system, but also m-xylene and water can form an azeotrope, and the azeotropic point of the azeotrope is between the azeotropic points of the acetic acid, the azeotropic agent and the water. In order to further improve the efficiency of separating the azeotropic agent, it is necessary to extract meta-xylene from the rectifying column and add a recovery column to recover meta-xylene.
In order to improve the extraction efficiency of the m-xylene from the rectifying tower, the number of plates of the rectifying tower in the rectifying tower is preferably counted from the top of the tower to the bottom of the tower, and the extraction position of the second stream is located at 16 th to 25 th theoretical plates.
Preferably, the second stream is introduced into a recovery column for separation to obtain meta-xylene at the bottom of the recovery column and a third stream at the top of the recovery column, the third stream containing water and an entrainer. The m-xylene led out from the tower bottom of the recovery tower is used as a raw material in the production process of PIA, so that the utilization rate of the material is improved, and the third material flow containing water and the entrainer can be recycled to the rectifying tower, so that the energy consumption is saved, and the cost is reduced. It will be appreciated that acetic acid is also withdrawn at the same time as meta-xylene is withdrawn from the bottom of the recovery column, and that the third stream will also contain a certain amount of acetic acid.
To better achieve the separation of meta-xylene from water and entrainer, the recovery column preferably operates under conditions comprising: the pressure is 0-40KPa, and the temperature is 110-120 ℃.
Preferably, in the rectifying tower, the number of plates of the rectifying tower is counted from the top of the tower to the bottom of the tower, and the position of the third stream entering the rectifying tower is located at 14 th to 22 th theoretical plates.
In the present invention, it is preferable that the first stream is a stream containing acetic acid and water to be dehydrated, which is generated in the production process of isophthalic acid, and includes a liquid-phase stream introduced into the rectifying tower in a liquid-phase state and a gas-phase stream introduced into the rectifying tower in a gas-phase state.
In order to further save energy consumption and fully utilize the energy generated in the process, the process preferably further comprises a crystallizer gas phase cooler.
Preferably, the liquid phase stream is a mixture of a liquid phase stream obtained by heat exchange of a part of raw material gas phase through a cooler of the first crystallizer and a cooler of the reactor and a raw material liquid generated in the production process of the isophthalic acid, the gas phase stream is a mixture of a gas phase stream obtained by passing the rest of raw material gas phase through the second crystallizer and a gas phase stream obtained by passing the raw material liquid generated in the production process of the isophthalic acid through the solvent distillation kettle, and the raw material gas phase and the raw material liquid both contain acetic acid and water.
Specifically, after the PIA process, a superheated feedstock gas phase containing acetic acid and water is produced. Wherein, one part of the superheated feed gas phase enters the tube side of the first crystallizer cooler and exchanges heat with water in the shell side of the first crystallizer cooler to obtain one of the liquid phase material flows of the invention and simultaneously produces 0.2-0.6MPa of steam as a byproduct.
Preferably, steam obtained after heat exchange in the first crystallizer provides a heat source for a tower kettle of the rectifying tower, so that reasonable utilization of energy is realized, and energy consumption in the production process is reduced.
Preferably, a part of the superheated feedstock gas phase obtained in said second crystallizer is used as heat source for the rectification column. According to the heat required in the process of recovering the m-xylene by the m-xylene recovery tower, the invention can utilize the residual raw material gas phase in the superheated raw material gas phase material flow as the heat source of the m-xylene recovery tower.
According to the invention, in order to avoid the influence of non-condensed steam on the rectifying tower, preferably, the non-condensed steam in the liquid phase material flow obtained after the gas phase heat exchange of the first crystallizer and the raw material gas phase material flow obtained by the second crystallizer is discharged through the gas phase at the top of the rectifying tower.
In the invention, in order to better realize the separation of each component in the rectifying tower and improve the purity (89-95%) of the acetic acid led out from the tower bottom of the rectifying tower so as to reduce the consumption of the acetic acid, preferably, in the rectifying tower, the number of tower plates of the rectifying tower is counted from the tower top to the tower bottom, the position of the liquid phase material flow entering the rectifying tower is positioned on the 22 th-28 th theoretical plate, and the position of the gas phase material flow entering the rectifying tower is positioned on the 51 st-61 th theoretical plate.
The present invention is described in detail below with reference to the attached drawings, but it should be noted that the scope of the present invention is not limited thereto.
According to a preferred embodiment of the present invention, as shown in fig. 1, a liquid phase material stream 11 obtained after heat exchange in a first crystallizer and a gas phase material stream 12 obtained after partial gas phase in a second crystallizer cooperate with an entrainer to separate out non-condensed steam (not shown in the figure), and then enter different tray positions in a rectifying tower a respectively, azeotropic distillation is performed in the rectifying tower a, a reboiler discharge material stream 8 obtained after heating a part of material streams in a tower bottom material stream in a reboiler E is circulated back to the rectifying tower, and an acetic acid product stream 7 is led out from the tower bottom; a fourth stream 4 obtained from the top of the rectifying tower enters a first separation tower B from the top of the first separation tower for separation, most of methyl acetate in the fourth stream 4 enters a second separation tower C from the upper part of the first separation tower B in a steam form through circulating water cooling, namely a methyl acetate steam stream 5, and entrainer and water are physically separated in a tower kettle of the first separation tower B, an entrainer stream 1 capable of being recycled to the rectifying tower A is obtained in the tower kettle of the first separation tower B, a methyl acetate stream 13 existing in a liquid phase form, water, the entrainer and the methyl acetate in the liquid phase form are obtained in the lower part of the first separation tower, and the water, the entrainer and the methyl acetate stream 13 existing in the liquid phase form are introduced into the second separation tower C; under the control of temperature gradient, realizing the separation of a methyl acetate steam stream 5, water, an entrainer and a methyl acetate stream 13 existing in a liquid phase form in a second separation tower C to respectively recover an entrainer stream 1, an discharged wastewater stream 10 and a methyl acetate stream 9, wherein the tower top of the second separation tower C is cooled by adopting circulating water; the second stream 2 drawn from the side of the rectification column A enters a recovery column D, so that a meta-xylene stream 6 capable of being used as a raw material for PIA production is drawn from the bottom of the recovery column D, and a third stream 3 obtained from the top of the recovery column D is introduced into the rectification column A.
According to the invention, the discharged sewage can be further treated, for example, the discharged sewage enters a sewage sedimentation tank and an oil separation tank for further treatment so as to meet the environmental standard requirement, which is a conventional operation in the field and is not described herein again.
By adopting the technical scheme, the method has the following specific effects after being operated:
1) compared with the acetic acid dehydration of the common rectification process, the method for dehydrating the acetic acid can reduce the consumption of steam by 35 to 40 percent;
2) the content of acetic acid in the wastewater discharged from the top of the rectifying tower can be reduced to below 0.1 wt% from 3 wt% of the common rectifying process, the peculiar smell and COD content of the acetic acid in the discharged water are obviously reduced, the environment-friendly level is improved, the purity of the acetic acid in the material flow in the tower kettle can reach more than 90%, the available and recycled acetic acid is obtained, and the consumption of the acetic acid is reduced;
3) the methyl acetate with higher purity is recovered and can be used in other links, so that the energy consumption and material consumption are saved, and the cost is reduced;
4) the m-xylene entering the rectifying tower can be completely recovered, and the consumption of the m-xylene is reduced;
5) the method can be used for self-production of heat energy and can be used by a common system, so that the energy consumption is obviously reduced.
The invention is further illustrated by the following specific examples.
Example 1
According to the process flow shown in fig. 1, the number of plates of the rectifying tower is counted from the top of the tower to the bottom of the tower, a liquid phase material flow obtained after heat exchange in the first crystallizer enters the rectifying tower from the 25 th theoretical plate of the rectifying tower, a gas phase material flow obtained after partial gas phase in the second crystallizer enters the rectifying tower from the 56 th theoretical plate of the rectifying tower, the operating pressure of the rectifying tower is 10KPa, the temperature is 85 ℃, and the mass ratio of an entrainer to water in the rectifying tower is 6: 1, a reboiler is heated by adopting 4MPa steam, the tower kettle operation temperature of a first separation tower is 75 ℃, and the tower top operation temperature of the first separation tower is 80 ℃; the operation temperature of the top of the second separation tower is 10 ℃, the temperature of the middle part of the second separation tower is 60 ℃, the temperature of the bottom of the second separation tower is 100 ℃, and the operation is carried out under normal pressure; the number of the tower plates of the rectifying tower is counted from the top of the tower to the bottom of the tower, a second stream is led out from the position of the 22 th theoretical plate of the rectifying tower to enter the recovery tower, m-xylene is led out from the bottom of the tower of the recovery tower, the operation temperature of the recovery tower is 110 ℃, a third stream is led out from the top of the recovery tower, the number of the tower plates is counted from the top of the tower to the bottom of the tower, and the position of the third stream entering the rectifying tower is located at the 20 th theoretical plate. The operating effect of the acetic acid dehydration process is shown in table 1.
Example 2
According to the process flow shown in fig. 1, the number of plates of the rectifying tower is counted from the top to the bottom of the rectifying tower, a liquid phase material flow obtained after heat exchange in the first crystallizer enters the rectifying tower from the 28 th theoretical plate of the rectifying tower, a gas phase material flow obtained after partial gas phase in the second crystallizer enters the rectifying tower from the 53 th theoretical plate of the rectifying tower, the operating pressure of the rectifying tower is 20KPa, the temperature is 90 ℃, and the mass ratio of an entrainer to water in the rectifying tower is 4: 1, a reboiler is heated by adopting 4MPa steam, the tower kettle operation temperature of a first separation tower is 80 ℃, and the tower top operation temperature of the first separation tower is 85 ℃; the operation temperature of the top of the second separation tower is 20 ℃, the temperature of the middle part of the second separation tower is 70 ℃, the temperature of the bottom of the second separation tower is 110 ℃, and the operation is carried out under normal pressure; the number of the tower plates of the rectifying tower is counted from the top of the tower to the bottom of the tower, a second stream is led out from the position of the 18 th theoretical plate of the rectifying tower to enter the recovery tower, m-xylene is led out from the bottom of the tower of the recovery tower, the operation temperature of the recovery tower is 120 ℃, a third stream is led out from the top of the recovery tower, the number of the tower plates is counted from the top of the tower to the bottom of the tower, and the position of the third stream entering the rectifying tower is located on the 16 th theoretical plate. The operating effect of the acetic acid dehydration process is shown in table 1.
Example 3
The process of example 1 was followed except that: the mass ratio of the entrainer to the water in the rectifying tower is 2: 1. the operating effect of the acetic acid dehydration process is shown in table 1.
Comparative example
The acetic acid dehydration is carried out by adopting a common rectification method in the prior art, and no n-propyl acetate is added. The operating effect of the acetic acid dehydration process is shown in table 1.
TABLE 1
As can be seen from the data in Table 1, compared with the common rectification method, after the acetic acid dehydration is carried out by adopting the method disclosed by the invention, the steam energy consumption reduction rate can reach 52.94%, the acetic acid consumption reduction rate can reach 98.67%, the acetic acid product flow purity and the methyl acetate purity are high, the good effects of reducing the energy consumption and the material consumption are achieved, the acetic acid content in the wastewater is less than 0.1 wt%, the acetic acid odor in the discharged wastewater is greatly reduced, and the COD discharge amount is reduced by about 50.04%.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (10)
1. A method of dehydrating acetic acid, the method comprising:
introducing the first material flow into a rectifying tower with a reboiler for azeotropic rectification, introducing a part of tower bottom material flow of the rectifying tower into the reboiler for heating treatment, and then circulating the material flow back to the rectifying tower; leading out a second stream from a side line of the rectifying tower, and leading out the rest part of the tower bottom stream of the rectifying tower as an acetic acid product, wherein the first stream contains acetic acid, m-xylene, methyl acetate and water, and the second stream contains m-xylene, water, acetic acid and an entrainer;
feeding a fourth material flow obtained from the top of the rectifying tower into a first separation tower from the top of the first separation tower for separation, obtaining an entrainer capable of being recycled to the rectifying tower from the tower bottom of the first separation tower, and leading a fifth material flow out from the side line of the first separation tower, wherein the fifth material flow contains the entrainer, water and methyl acetate; introducing the fifth stream into a second separation column for separation to recover entrainer and methyl acetate, respectively, while withdrawing water;
wherein the entrainer is n-propyl acetate, and the operating conditions of the rectifying tower enable the materials in the rectifying tower to form an azeotropic system.
2. The method of claim 1, wherein the operating conditions of the rectification column comprise: the pressure is 0-40KPa, and the temperature at the top of the tower is 80-90 ℃;
preferably, the mass ratio of the entrainer to the water in the rectifying tower is (4-8): 1.
3. the process of claim 1 or 2, wherein the first separation column has kettle operating conditions comprising: the pressure is 0-40KPa, and the temperature is 75-80 ℃;
preferably, the top operating conditions of the first separation column include: the pressure is 0-40KPa, and the temperature is 75-90 ℃;
preferably, the cooling is performed with circulating water at the top of the first separation column.
4. The method according to any one of claims 1 to 3, wherein the second separation column performs separation under temperature gradient control;
preferably, the operating conditions of the second separation column include: the temperature of the top of the tower is less than 30 ℃, the temperature of the middle part of the tower is 50-70 ℃, and the temperature of the bottom of the tower is 90-110 ℃;
preferably, the cooling is performed with circulating water at the top of the second separation column.
5. The method according to any one of claims 1 to 4, wherein the number of theoretical plates of the rectification column is from 80 to 90.
6. The process according to claim 5, wherein in the rectification column the number of plates is counted from the top to the bottom of the column and the second stream is withdrawn at a position between 16 and 25 theoretical plates.
7. The method of claim 6, wherein the method further comprises: introducing the second stream into a recovery column for separation to obtain meta-xylene at the bottom of the recovery column and a third stream at the top of the recovery column, the third stream containing water and an entrainer;
preferably, the operating conditions of the recovery column include: the pressure is 0-40KPa, and the temperature is 110-120 ℃;
preferably, in the rectification column, the number of plates is counted from the top to the bottom of the column, and the position of the third stream entering the rectification column is located between 14 th and 22 th theoretical plates.
8. The method according to any one of claims 1 to 7, wherein the first stream is a stream containing acetic acid and water to be dehydrated, which is generated in the production process of isophthalic acid, comprising a liquid phase stream introduced into the rectification column in a liquid phase state and a gas phase stream introduced into the rectification column in a gas phase state.
9. The process according to claim 8, wherein the liquid-phase stream is a mixture of a liquid-phase stream obtained by heat-exchanging a part of a raw material gas phase by a cooler of the first crystallizer and a cooler of the reactor and a raw material liquid produced in the production process of isophthalic acid, and the gas-phase stream is a mixture of a gas-phase stream obtained by passing the remaining part of the raw material gas phase by the second crystallizer and a gas-phase stream obtained by passing the raw material liquid produced in the production process of isophthalic acid through the solvent distillation still, and both the raw material gas phase and the raw material liquid contain acetic acid and water.
10. The method as claimed in claim 9, wherein in the rectification column, the number of plates is counted from the top to the bottom of the column, the liquid phase stream enters the rectification column from the 22 th to 28 th theoretical plates of the rectification column, and the gas phase stream enters the rectification column from the 51 st to 61 th theoretical plates of the rectification column.
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