Formic acid rectification and concentration system and process

Abstract

The invention relates to the technical field of formic acid rectification and concentration, in particular to a formic acid rectification and concentration system and process. The formic acid rectification and concentration system comprises an azeotropic dehydration tower and an entrainer separation tower, the azeotropic dehydration tower is connected with a low-concentration formic acid inlet and an entrainer inlet, the top of the azeotropic dehydration tower is connected with a layering tank, a first condenser is connected between the top of the azeotropic dehydration tower and the layering tank, and a second condenser is connected between the top of the azeotropic dehydration tower and the entrainer separation tower. The tower top of the azeotropic dehydrating tower is connected with a first condenser, the tower bottom of the azeotropic dehydrating tower is connected with a first reboiler, the tower bottom of the azeotropic dehydrating tower is connected with an entrainer separating tower through a pipeline, the tower top of the entrainer separating tower is connected with a second condenser, and the tower bottom of the entrainer separating tower is connected with a second reboiler. According to the present invention, the azeotropic distillation process is adopted to achieve the concentration of the formic acid aqueous solution, and the 1, 2-dichloroethane is adopted as the entrainer, such that the formic acid yield is high, the equipment material requirement can be reduced, the formic acid content in the separated water can be reduced, the anhydrous formic acid can be prepared, and the by-product is not generated.

Description

Technical Field

[0001] The invention relates to the technical field of formic acid distillation and concentration, and in particular to a formic acid distillation and concentration system and process. Background Art

[0002] Formic acid is an important chemical raw material. In the production of medicines and spices, as well as in the acid treatment of textiles and leather, a large amount of low-concentration formic acid solution is produced, which has no practical application value. Recovering and concentrating low-concentration formic acid (w%>85%) can not only reduce environmental pollution, but also create considerable economic value. Because the boiling points of formic acid and water are extremely close and can form the highest azeotrope, it is impossible to obtain high-concentration formic acid using conventional distillation methods.

[0003] At present, the main methods for recovering formic acid include azeotropic distillation, pressure swing distillation and desiccant dehydration.

[0004] Azeotropic distillation can achieve good results and is suitable for industrial applications. When treating low-concentration formic acid solution, you can first consider using ordinary distillation to remove water to obtain a formic acid solution with a near-azeotropic composition, and then add an entrainer to separate the water. The key to this method is to select a suitable entrainer, which must not decompose during use and have a strong water-carrying capacity. The entrainer and formic acid are not azeotropic, or the difference between the azeotropic temperature of the entrainer and formic acid and the azeotropic temperature of the entrainer and water is increased, making it easy to separate.

[0005] The pressure swing distillation method achieves dehydration and concentration of formic acid by changing the azeotropic ratio of formic acid-water by changing the distillation operating pressure. The method of separating formic acid and water by pressure distillation and pressure distillation in series uses an acid-resistant metal distillation tower, which has high equipment cost. At the same time, the theoretical number of plates and reflux required for distillation separation of formic acid and water are relatively large, and the energy consumption is very high. In addition, the separated water still contains a certain amount of formic acid, and the formic acid yield is low. Alkali needs to be added for neutralization, which increases the load of sewage treatment.

[0006] The desiccant dehydration method is suitable for concentrating aqueous formic acid solutions with low water content. This process will produce solid waste and the treatment cost is also high. Summary of the invention

[0007] In view of the above deficiencies in the prior art, an object of the present invention is to provide a formic acid distillation and concentration system and process.

[0008] To achieve the above objectives, the technical solutions adopted are:

[0009] One of the purposes of the present invention is to provide a formic acid distillation and concentration system, comprising an azeotropic dehydration tower and an entrainer separation tower, wherein the azeotropic dehydration tower is connected to a low-concentration formic acid inlet and an entrainer inlet, the top of the azeotropic dehydration tower is connected to a stratification tank, a first condenser is connected between the top of the azeotropic dehydration tower and the stratification tank, a first reboiler is connected to the bottom of the azeotropic dehydration tower, the bottom of the azeotropic dehydration tower is connected to the entrainer separation tower through a pipeline, the top of the entrainer separation tower is connected to a second condenser, and the bottom of the entrainer separation tower is connected to a second reboiler.

[0010] Furthermore, the bottom of the azeotropic dehydration tower is connected to the center of the entrainer separation tower through a second extraction pipeline.

[0011] Furthermore, the stratification tank contains an upper water phase and a lower oil phase, the upper water phase is connected to a water storage tank and an azeotropic dehydration tower respectively, and the lower oil phase is connected to the azeotropic dehydration tower.

[0012] Furthermore, the upper water phase is connected to the water storage tank through the first extraction pipeline, and is connected to the azeotropic dehydration tower through the second reflux pipeline and the first reflux pipeline.

[0013] Furthermore, the second condenser is connected to a receiving tank, and the receiving tank is connected to the entrainer separation tower.

[0014] Furthermore, the second condenser is connected to the top of the entrainer separation tower through a third reflux pipe, and is connected to a receiving tank through a third production pipe. The outlet pipeline of the receiving tank is connected to a first material transfer pump, and the first material transfer pump is connected to a raw material tank through a return pipeline.

[0015] Furthermore, the bottom of the azeotropic agent separation tower is connected to a formic acid product storage tank.

[0016] Furthermore, the bottom of the azeotropic agent separation tower is connected to the formic acid product storage tank through a fourth production pipeline.

[0017] Furthermore, the first condenser and the second condenser are both connected to a cooling water inlet and a cooling water outlet.

[0018] Furthermore, the first condenser and the second condenser are both connected to an exhaust gas outlet.

[0019] Furthermore, the first reboiler and the second reboiler are both connected to a low-pressure steam inlet and a condensate outlet.

[0020] Furthermore, the formic acid distillation and concentration system also includes an azeotropic agent processing device.

[0021] The beneficial effect of adopting the above further technical solution is that: an azeotropic agent processing device is provided on the first production pipeline, which can be a distillation tower or a kettle. Since the water phase separated by the azeotropic dehydration tower does not contain formic acid, but will contain a small amount of azeotropic agent dichloroethane, the dichloroethane in the water phase needs to be evaporated through the distillation tower or the kettle and then enters the water storage tank.

[0022] The second object of the present invention is to provide a formic acid distillation and concentration process, which uses the formic acid distillation and concentration system to perform concentration, and the steps include:

[0023] Low-concentration formic acid and entrainer ethylene dichloride are respectively introduced into an azeotropic dehydration tower through a low-concentration formic acid inlet and an entrainer inlet, and a mixture of ethylene dichloride and water is evaporated under normal pressure heating conditions, condensed and cooled in a first condenser, and the obtained first condensate flows by gravity to a stratification tank, and is allowed to stand and stratify in the stratification tank. The lower oil phase after stratification is mainly ethylene dichloride and returns to the azeotropic dehydration tower along a pipeline, and the upper water phase is mainly water and is divided into two parts, one part of the upper water phase is extracted to a water storage tank, and the other part of the upper water phase returns to the azeotropic dehydration tower; the azeotropic dehydration tower is heated by a first reboiler, and a formic acid-ethylene dichloride-water mixture with a water content of less than 10% is extracted from the bottom of the tower and transferred to an entrainer separation tower through a pipeline;

[0024] The entrainer separation tower is heated under normal pressure to evaporate the remaining dichloromethane, which is condensed and cooled in the second condenser together with part of the water and formic acid. A part of the obtained second condensate is returned to the top of the entrainer separation tower E, and a part is extracted to the receiving tank and returned to the raw material tank for secondary treatment. The entrainer separation tower is heated by the second reboiler, and the formic acid product without the entrainer is extracted from the bottom of the tower and transferred to the formic acid product storage tank.

[0025] The beneficial effect of adopting the above technical solution is that the process designed by the present invention must ensure that the top reflux liquid of the azeotropic dehydration tower contains not only the lower oil phase after stratification, but also part of the upper water phase, otherwise the upper water phase solution after stratification will contain formic acid.

[0026] Furthermore, the formic acid distillation and concentration process comprises the following specific steps:

[0027] Low-concentration formic acid and entrainer ethylene dichloride are respectively introduced into an azeotropic dehydration tower through a low-concentration formic acid inlet and an entrainer inlet, and a mixture of ethylene dichloride and water is evaporated under normal pressure heating conditions, condensed and cooled in a first condenser, and the obtained first condensate flows by gravity to a stratification tank, and is allowed to stand and stratify in the stratification tank. The lower oil phase after stratification is mainly ethylene dichloride and returns to the azeotropic dehydration tower along a first reflux pipeline, and the upper water phase is mainly water. A part of the upper water phase is produced to a water storage tank through a first production pipeline, and a part of the upper water phase is returned to the azeotropic dehydration tower through the first reflux pipeline through a second reflux pipeline; the azeotropic dehydration tower is heated by a first reboiler, and a formic acid-ethylene dichloride-water mixture with a water content of less than 10% is produced at the bottom of the tower, and is transferred to an entrainer separation tower through a second production pipeline;

[0028] The entrainer separation tower is heated under normal pressure to evaporate the remaining dichloromethane, which is condensed and cooled in the second condenser together with part of the water and formic acid. A part of the obtained second condensate is returned to the top of the entrainer separation tower as reflux liquid through the third reflux pipeline, and a part is extracted to the receiving tank through the third extraction pipeline, and returned to the raw material tank along the return pipeline through the first material transfer pump for secondary treatment. The raw material tank actually refers to the storage tank for the material to be treated. The material to be treated needs to be transferred to the azeotropic dehydration tower for azeotropic dehydration. In the entrainer separation tower, the entrainer-formic acid-water extracted in the early stage can neither be used as a qualified product nor as an entrainer. This part of the fraction cannot be discarded, and needs to be returned to the raw material tank and mixed with the raw material before being transferred to the azeotropic dehydration tower for treatment; the entrainer separation tower is heated by the second reboiler, and the formic acid product without entrainer is extracted from the bottom of the tower and transferred to the formic acid product storage tank along the fourth extraction pipeline.

[0029] Furthermore, the bottom temperature of the azeotropic dehydration tower is 80°C to 90°C, and the top temperature is 75°C to 80°C.

[0030] Furthermore, the bottom temperature of the azeotropic agent separation tower is 95°C to 105°C, and the top temperature is 80°C to 100°C.

[0031] Furthermore, the formic acid distillation and concentration process also includes the following steps: adding formic anhydride to the formic acid product to obtain anhydrous formic acid.

[0032] The beneficial effect of adopting the above further technical scheme is that: in the process designed by the present invention, the water content of the formic acid product extracted from the bottom of the azeotropic agent separation tower can be controlled within 3%. If anhydrous formic acid is to be further produced, formic anhydride can be added to the product, and formic acid is generated by the reaction of formic anhydride and water to achieve the preparation of anhydrous formic acid.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention adopts an azeotropic distillation process to achieve the concentration of formic acid aqueous solution, and adopts 1,2-dichloroethane as an azeotropic agent. The azeotropic agent has a strong water-carrying capacity, and the azeotropic temperature of the azeotropic agent and water is relatively low, which is 65°C. The azeotropic temperature is significantly different from the azeotropic temperature of 76.7°C of dichloroethane-formic acid. Therefore, the loss of formic acid is small during the azeotropic dehydration process, and the formic acid yield is high. This process can simultaneously reduce the requirements for equipment materials and reduce the formic acid content in the separated water. If anhydrous formic acid is to be prepared, after the formic acid solution is dehydrated by azeotropic distillation to a water content of less than 5%, formic anhydride is directly added thereto, and formic anhydride reacts with water to form formic acid, thereby realizing the preparation of anhydrous formic acid;

[0034] At the same time, the material requirements of the equipment can be reduced, and the requirements can be met by using conventional non-metallic equipment such as enamel / graphite; since the azeotropic temperature of ethylene dichloride and water is quite different from the azeotropic temperature of ethylene dichloride-formic acid, the water separated in the azeotropic dehydration process contains almost no formic acid, and can be directly discharged after simply evaporating to remove the azeotropic agent, thereby reducing the pressure of wastewater treatment; formic acid can be concentrated to a content greater than 97%, and if anhydrous formic acid is to be prepared, formic anhydride can be added after the azeotropic distillation dehydration is completed to consume the remaining water and generate formic acid without generating any by-products. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a flow chart of a formic acid distillation and concentration system and process of the present invention;

[0036] The accompanying drawings are marked as follows: A, azeotropic dehydration tower; B, first condenser; C, stratification tank; D, first reboiler; E, entrainer separation tower; F, second condenser; G, receiving tank; H, first material transfer pump; J, second reboiler; 1, low concentration formic acid inlet; 2, entrainer inlet; 3, first condensate; 4, second reflux pipeline; 5, lower oil phase; 6, first production pipeline; 7, first reflux pipeline; 8, second production pipeline; 9, second condensate; 10, third reflux pipeline; 11, third production pipeline; 12, return pipeline; 13, fourth production pipeline; 14, cooling water inlet; 15, cooling water outlet; 16, low-pressure steam inlet; 17, condensate outlet; 18, exhaust gas outlet. DETAILED DESCRIPTION

[0037] The present invention is described below in conjunction with examples, which are only used to explain the present invention and are not used to limit the scope of the present invention.

[0038] Reference Figure 1A formic acid distillation and concentration system comprises an azeotropic dehydration tower A and an entrainer separation tower E, wherein the azeotropic dehydration tower A is connected to a low-concentration formic acid inlet 1 and an entrainer inlet 2, the top of the azeotropic dehydration tower A is connected to a stratification tank C, a first condenser B is connected between the top of the azeotropic dehydration tower A and the stratification tank C, a first reboiler D is connected to the bottom of the azeotropic dehydration tower A, the bottom of the azeotropic dehydration tower A is connected to the entrainer separation tower E through a pipeline, the top of the entrainer separation tower E is connected to a second condenser F, and the bottom of the entrainer separation tower E is connected to a second reboiler J.

[0039] In this embodiment, the bottom of the azeotropic dehydration tower A is connected to the center of the entrainer separation tower E through the second extraction pipeline 8.

[0040] As a preferred embodiment, the stratification tank C contains an upper water phase and a lower oil phase 5, the upper water phase is connected to a water storage tank and an azeotropic dehydration tower A respectively, and the lower oil phase 5 is connected to the azeotropic dehydration tower A.

[0041] In this embodiment, the upper aqueous phase is connected to the water storage tank via the first extraction pipeline 6 , and is connected to the azeotropic dehydration tower A via the second reflux pipeline 4 and the first reflux pipeline 7 .

[0042] In this embodiment, the second condenser F is connected to a receiving tank G, and the receiving tank G is connected to the entrainer separation tower E.

[0043] As a preferred embodiment, the second condenser F is connected to the top of the entrainer separation tower E through the third reflux pipe 10, and is connected to the receiving tank G through the third production pipe 11. The outlet pipeline of the receiving tank G is connected to the first material transfer pump H, and the first material transfer pump H is connected to the raw material tank through the return pipeline 12.

[0044] In an optional embodiment, the bottom of the azeotropic agent separation tower E is connected to a formic acid product storage tank.

[0045] In this embodiment, the bottom of the azeotropic agent separation tower E is connected to the formic acid product storage tank through the fourth production pipeline 13.

[0046] In this embodiment, the first condenser B and the second condenser F are both connected to a cooling water inlet 14 and a cooling water outlet 15 .

[0047] As a preferred embodiment, both the first condenser B and the second condenser F are connected to an exhaust gas outlet 18 .

[0048] In this embodiment, the first reboiler D and the second reboiler J are both connected to a low-pressure steam inlet 16 and a condensate outlet 17 .

[0049] In this embodiment, the bottoms of the azeotropic dehydration tower A and the entrainer separation tower E are both connected to a material transfer pump.

[0050] In this embodiment, the formic acid distillation and concentration system further includes an azeotropic agent processing device.

[0051] The present invention also provides a formic acid distillation and concentration process, comprising the following specific steps: low-concentration formic acid and entrainer ethylene dichloride are respectively introduced into an azeotropic dehydration tower A through a low-concentration formic acid inlet 1 and an entrainer inlet 2; under normal pressure heating conditions, a mixture of ethylene dichloride and water is evaporated, condensed and cooled in a first condenser B, and the obtained first condensate 3 flows by gravity to a stratification tank C, and is left to stand and stratify in the stratification tank C; a lower oil phase 5 after stratification is mainly ethylene dichloride and returns to the azeotropic dehydration tower A along a first reflux pipeline 7; an upper water phase is mainly water and is divided into two parts, a part of the upper water phase is produced to a water storage tank through a first production pipeline 6, and the other part of the upper water phase is returned to the azeotropic dehydration tower A through a second reflux pipeline 4 and the first reflux pipeline 7; the azeotropic dehydration tower A is heated by a first reboiler D, a formic acid-ethylene dichloride-water mixture with a water content of less than 10% is produced at the bottom of the tower, and is transferred to the entrainer separation tower E through a second production pipeline 8 under the drive of a material transfer pump.

[0052] The entrainer separation tower E is heated under normal pressure to evaporate the remaining dichloromethane, which is condensed and cooled in the second condenser F together with part of the water and formic acid. A part of the obtained second condensate 9 is returned to the top of the entrainer separation tower E as reflux liquid through the third reflux pipe 10, and a part is produced to the receiving tank G through the third production pipe 11, and is returned to the raw material tank along the return pipeline 12 through the first transfer pump H for secondary treatment; the entrainer separation tower E is heated by the second reboiler J, and the formic acid product without entrainer is produced at the bottom of the tower, and is transferred to the formic acid product storage tank along the fourth production pipe 13 under the drive of the transfer pump.

[0053] As a preferred embodiment, the bottom temperature of the azeotropic dehydration tower A is 80°C to 90°C, and the top temperature is 75°C to 80°C.

[0054] As a preferred embodiment, the bottom temperature of the azeotropic agent separation tower E is 95°C to 105°C, and the top temperature is 80°C to 100°C.

[0055] In an optional embodiment, the formic acid distillation and concentration process further includes the following steps: adding formic anhydride to the formic acid product to obtain anhydrous formic acid.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A formic acid distillation and concentration system, characterized in that: The invention comprises an azeotropic dehydration tower and an entrainer separation tower, wherein the azeotropic dehydration tower is connected with a low-concentration formic acid inlet and an entrainer inlet, the top of the azeotropic dehydration tower is connected with a stratification tank, a first condenser is connected between the top of the azeotropic dehydration tower and the stratification tank, a first reboiler is connected at the bottom of the azeotropic dehydration tower, the bottom of the azeotropic dehydration tower is connected with the entrainer separation tower through a pipeline, the top of the azeotropic dehydration tower is connected with a second condenser, and the bottom of the azeotropic separation tower is connected with a second reboiler.

2. The formic acid distillation and concentration system according to claim 1, characterized in that: The stratification tank contains an upper water phase and a lower oil phase, the upper water phase is connected to a water storage tank and an azeotropic dehydration tower respectively, and the lower oil phase is connected to the azeotropic dehydration tower.

3. The formic acid distillation and concentration system according to claim 1, characterized in that: The second condenser is connected to a receiving tank, and the receiving tank is connected to the entrainer separation tower.

4. The formic acid distillation and concentration system according to claim 1, characterized in that: The bottom of the azeotropic agent separation tower is connected with a formic acid product storage tank.

5. A formic acid distillation and concentration process, characterized in that: The formic acid distillation and concentration system according to any one of claims 1 to 4 is used for concentration, the steps comprising: Low-concentration formic acid and entrainer ethylene dichloride are respectively introduced into an azeotropic dehydration tower through a low-concentration formic acid inlet and an entrainer inlet, and a mixture of ethylene dichloride and water is evaporated under normal pressure heating conditions, and condensed and cooled in a first condenser. The obtained first condensate flows by gravity to a stratification tank, and is allowed to stand and stratify in the stratification tank. The lower oil phase after stratification is mainly ethylene dichloride and returns to the azeotropic dehydration tower along a pipeline, and the upper water phase is mainly water. A part of the upper water phase is extracted to a water storage tank, and the other part of the upper water phase returns to the azeotropic dehydration tower; the azeotropic dehydration tower is heated by a first reboiler, and a formic acid-ethylene dichloride-water mixture with a water content of less than 10% is extracted from the bottom of the tower, and is transferred to an entrainer separation tower through a pipeline; The entrainer separation tower is heated under normal pressure to evaporate the remaining dichloromethane, which is condensed and cooled in the second condenser together with part of the water and formic acid. A part of the obtained second condensate is returned to the top of the entrainer separation tower, and a part is taken out to a receiving tank and returned to the raw material tank for secondary treatment. The entrainer separation tower is heated by a second reboiler, and the formic acid product without the entrainer is taken out from the bottom of the tower and transferred to the formic acid product storage tank.

6. The formic acid distillation and concentration process according to claim 5, characterized in that: The bottom temperature of the azeotropic dehydration tower is 80°C to 90°C, and the top temperature is 75°C to 80°C.

7. The formic acid distillation and concentration process according to claim 5, characterized in that: The bottom temperature of the azeotropic agent separation tower is 95°C to 105°C, and the top temperature is 80°C to 100°C.

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