Lactic acid purification system

Abstract

The utility model provides a lactic acid purification system which comprises a reactive distillation dividing wall column and a shell, a partition plate parallel to the central axis of the shell is arranged in the shell, and the partition plate is connected with the bottom and the column wall of the reactive distillation dividing wall column; the interior of the reactive distillation dividing wall tower shell is divided into a tower top public distillation section, a first side area and a second side area by the partition plates; a reactive distillation column; a recovery tower; a first side area of the reactive distillation dividing wall column is connected with a crude lactic acid input pipe and a methanol input pipe, and a bottom section of a second side area of the reactive distillation dividing wall column is connected with a feeding hole of the reactive distillation column; extracting a high-purity lactic acid product from a tower kettle of the reactive distillation tower; the tower top of the reactive distillation tower is connected with a feeding hole of the recovery tower; the top of the recovery tower is connected with a methanol input pipe. By coupling the reactive distillation dividing wall column with a specific structure, the reactive distillation column and the recovery column, the equipment cost is reduced, the energy consumption and the raw material cost of the operation of the whole system are also reduced, and the economic benefit is improved.

Description

Technical Field

[0001] This utility model relates to the field of chemical industry technology, specifically to a lactic acid purification system. Background Technology

[0002] Lactic acid is an important chemical raw material with broad application prospects. It can be directly used in food, pharmaceuticals, textiles, leather tanning, environmental protection, and agriculture. It can also be used as a raw material to synthesize lactates, lactide, polylactic acid, and other substances, with polylactic acid being a popular material for producing biodegradable products. High-purity lactic acid has a larger market in industry, and its purification is one of the most expensive steps in lactic acid production. Therefore, finding efficient and energy-saving methods for lactic acid purification is crucial.

[0003] Patent CN109956859A proposes a method for separating and purifying lactic acid from lactic acid fermentation broth. This method involves heat treatment of lactic acid fermentation broth, removal of insoluble impurities such as bacterial cells, acid treatment, concentration, organic reagent precipitation, centrifugation filtration, re-concentration, and decolorization. The overall process is complex, and the purity and recovery rate of the obtained lactic acid product are both low.

[0004] Patent CN113527085A proposes a production method for purifying lactic acid from lactic acid fermentation broth. This method uses a continuous fluid separation system to separate lactic acid from impurities, and includes 12 separation units. This method has a complex process, high equipment investment, and causes certain environmental pollution due to the use of a large amount of hydrochloric acid.

[0005] Patent CN1166616C proposes a method and equipment for purifying crude lactic acid. This method uses a combination of esterification and hydrolysis reactions with reactive distillation to purify crude lactic acid. Since the esterification and hydrolysis are carried out in two separate devices, this dual-tower process inevitably has certain drawbacks in terms of energy consumption and equipment investment.

[0006] Patent CN115124417A proposes a method and equipment for purifying lactic acid monomers. The equipment used in this purification method includes at least a preheater, a reactor, a hydrolysis tower (divider tower), a purification tower (divider tower), and a methanol recovery tower. The overall process involves high equipment investment, a relatively complex process, and relatively high energy consumption.

[0007] Therefore, there is an urgent need to invent a crude lactic acid purification method that meets the requirements of being environmentally friendly, having a simple process flow, low energy consumption, low equipment investment, and high product yield and purity. Utility Model Content

[0008] To address the shortcomings of existing technologies, this utility model discloses a lactic acid purification system. This system has low equipment investment, a simple process flow, low overall energy consumption, and is environmentally friendly, and can efficiently obtain high-purity lactic acid products.

[0009] To achieve the above technical objectives, this utility model proposes a lactic acid purification system, comprising:

[0010] A reactive distillation partition wall column is used for the esterification reaction of lactic acid and methanol, and the hydrolysis reaction of methyl lactate. The column includes a shell, within which a partition wall parallel to the central axis of the shell is disposed. The partition wall is connected to the bottom and walls of the column, but not to the top. The partition wall divides the interior of the column shell into a common top distillation section, a first side section, and a second side section.

[0011] The reactive distillation column is used for the secondary hydrolysis of methyl lactate;

[0012] Recovery tower, the recovery tower being used to recover methanol;

[0013] The first side section of the reactive distillation partition wall column is connected to the crude lactic acid input pipe and the methanol input pipe; the bottom section of the second side section of the reactive distillation partition wall column is connected to the feed inlet of the reactive distillation column; high-purity lactic acid product is collected from the bottom of the reactive distillation column; the top of the reactive distillation column is connected to the feed inlet of the recovery column; and the top of the recovery column is connected to the methanol input pipe.

[0014] The above technical solution uses a specially structured reactive distillation partition column for the esterification reaction of lactic acid and methanol to produce methyl lactate and for the hydrolysis reaction of methyl lactate, thereby separating lactic acid from impurities in crude lactic acid. Based on this reactive distillation partition column, this invention can combine the esterification and hydrolysis reactions of lactic acid and methanol into one column, which not only reduces equipment costs but also reduces energy consumption in the overall process.

[0015] Furthermore, the above technical solution includes a reactive distillation column for further hydrolyzing the residual methyl lactate in the reactive distillation partition wall column, separating the water from the dilute lactic acid obtained after methyl lactate hydrolysis, and collecting the high-purity lactic acid product from the bottom of the reactive distillation column. This utility model's technical solution, by coupling the reactive distillation column with a specially structured reactive distillation partition wall column, allows water to be collected from the bottom section of the second side zone of the reactive distillation partition wall column. This not only reduces energy consumption but also lowers the operating temperature within the reactive distillation partition wall column, thereby reducing lactic acid polymerization during the reaction process, improving product purity, and increasing yield.

[0016] Compared with the prior art, the beneficial effects of this utility model are as follows: By setting up a reactive distillation partition wall column, a reactive distillation column, and a recovery column with specific structures, the esterification and hydrolysis reactions of lactic acid and methanol can be combined in one column, which not only reduces equipment costs but also reduces energy consumption in the overall process. In addition, by coupling the reactive distillation partition wall column with the reactive distillation column, water can be extracted from the bottom section of the second side zone of the reactive distillation partition wall column, which not only further reduces energy consumption but also lowers the operating temperature in the reactive distillation partition wall column, thereby reducing the polymerization of lactic acid during the reaction, improving product purity, and increasing yield. The recovery column is used to recover and utilize methanol, reducing the raw material cost of the overall system operation and improving economic efficiency. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an undue limitation of the present invention. In the drawings:

[0018] Figure 1 The diagram shows the structure of the lactic acid purification system of this invention.

[0019] The above figures include the following reference numerals:

[0020] 1-Reactive distillation partition wall column, 2-Reactive distillation column, 3-Recovery column, 41-Crude lactic acid inlet pipe, 42-Methanol inlet pipe, 43-Mixer, 51-First condenser, 52-Second condenser, 53-Third condenser, 61-First reboiler, 62-Second reboiler, 63-Third reboiler, 64-Fourth reboiler, A-Baffle plate. Detailed Implementation

[0021] To facilitate understanding of this utility model, a more comprehensive description of it will be provided below, along with preferred embodiments. However, it should be understood that these embodiments are merely for more detailed explanation and should not be construed as limiting the utility model in any way, i.e., not limiting the scope of protection of this utility model.

[0022] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the test reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods, unless otherwise specified, are conventional methods.

[0023] Furthermore, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," "third," or "fourth" may explicitly or implicitly include one or more of that feature.

[0024] In this application, unless otherwise expressly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0025] Example 1

[0026] A lactic acid purification system, such as Figure 1 As shown, the system includes a reactive distillation partition wall column 1, used for the esterification reaction of lactic acid and methanol, and the hydrolysis reaction of methyl lactate; the reactive distillation partition wall column 1 includes a shell, and a partition A parallel to the central axis of the shell is installed inside the shell. The partition A is connected to the bottom and wall of the reactive distillation partition wall column 1, but not to the top; the partition A divides the interior of the shell of the reactive distillation partition wall column 1 into a common distillation section at the top, a first side zone, and a second side zone; a reactive distillation column 2, used for the secondary hydrolysis of methyl lactate; and a recovery column 3, used for recovering methanol.

[0027] The first side section of the reactive distillation partition wall column 1 is connected to the crude lactic acid input pipe 41 and the methanol input pipe 42. The bottom section of the second side section of the reactive distillation partition wall column 1 is connected to the feed inlet of the reactive distillation column 2. High-purity lactic acid product is collected from the bottom of the reactive distillation column 2. The top of the reactive distillation column 2 is connected to the feed inlet of the recovery column 3. The top of the recovery column 3 is connected to the methanol input pipe 42.

[0028] The process for purifying crude lactic acid using the technical solution of this utility model includes:

[0029] Methanol and crude lactic acid (including lactic acid, water, and other impurities) from the upstream lactic acid production process enter the first side zone of the reactive distillation partition wall column 1 through methanol inlet pipe 42 and crude lactic acid inlet pipe 41, respectively. The first side zone is filled with catalyst, and the esterification reaction of lactic acid and methanol takes place in the first side zone to produce methyl lactate and water, thereby separating the lactic acid from the impurities in the crude lactic acid. Under the action of the first side zone stage and the common rectification section at the top of the column, the impurities are collected from the bottom section of the first side zone (these impurities are discharged from the boundary area), and methyl lactate and water are fed into the second side zone of the reactive distillation partition wall column 1. The second side zone is filled with catalyst for the hydrolysis of methyl lactate, and the hydrolysis reaction of methyl lactate takes place in the second side zone. The resulting material containing water, lactic acid, and a small amount of methyl lactate is collected from the bottom section of the second side zone and fed into the reactive distillation column 2.

[0030] The reaction section of reactive distillation column 2 is filled with a catalyst for the hydrolysis of methyl lactate. In reactive distillation column 2, unreacted methyl lactate will continue to undergo hydrolysis. Under the action of reactive distillation column 2, high-purity lactic acid product is collected from the bottom of reactive distillation column 2. Materials containing methanol and water are collected from the top of reactive distillation column 2 and fed into recovery column 3.

[0031] Methanol and water are separated by the recovery tower 3. Methanol is collected from the top of the tower and returned to the methanol input pipe 42. After being mixed with freshly input methanol, it enters the reactive distillation distillation wall tower 1 for further lactic acid purification. Water is collected from the bottom of the recovery tower 3.

[0032] Those skilled in the art will understand that, in specific processes, condensers and reboilers can be appropriately placed in suitable locations within the system of this invention. For example, a first condenser 51 can be installed at the top of the reactive distillation column 1, through which the top stream is collected; a second condenser 52 can be installed at the top of the reactive distillation column 2, through which a stream containing methanol and water is collected; and a third condenser 53 can be installed at the top of the recovery column 3, through which the methanol stream is collected and returned to the methanol input pipe 42 for methanol recycling. The following methods can be used: Optionally, a first reboiler 61 can be installed at the bottom section of the second side zone of the reactive distillation partition column 1, through which materials containing water, lactic acid, and a small amount of methyl lactate are fed into the reactive distillation column 2; Optionally, a second reboiler 62 can be installed at the bottom section of the first side zone of the reactive distillation partition column 1, through which impurities are collected; Optionally, a third reboiler 63 can be installed at the bottom of the reactive distillation column 2, through which lactic acid products are collected; Optionally, a fourth reboiler 64 can be installed at the bottom of the recovery column 3, through which water is collected.

[0033] Those skilled in the art will understand that, in a specific process, packing material can be placed at a suitable location in any device of the present invention to improve mass transfer efficiency.

[0034] It should be noted that this invention does not limit the type of catalyst packed in the reactive distillation partition wall column 1 and the reactive distillation column 2. Those skilled in the art can select the appropriate catalyst according to actual needs, and this does not limit the scope of protection of this invention.

[0035] Example 2

[0036] Based on the lactic acid purification system shown in Example 1, this example explores and optimizes the top connection method of the reactive distillation partition column 1.

[0037] Optionally, the top of the reactive distillation partition wall column 1 is connected to the methanol input pipe 42; in this embodiment, the material containing unreacted methanol is collected from the top of the column and returned to the methanol input pipe 42, thereby achieving full utilization of the raw materials.

[0038] Optionally, it also includes a mixer 43. The methanol input pipe 42 is connected to the methanol inlet of the reactive distillation partition column 1 via the mixer 43. The use of the mixer 43 can fully mix the newly fed methanol with the methanol stream returned from the subsequent process, promoting the uniform and efficient lactation esterification reaction.

[0039] Alternatively, a first condenser 51 is installed at the top of the reactive distillation partition column 1, through which a methanol-containing stream is collected and fed into the methanol input pipe 42.

[0040] Example 3

[0041] Based on the lactic acid purification system shown in Example 1, this example explores and optimizes the theoretical number of trays in the reactive distillation partition column 1.

[0042] Optionally, the number of theoretical plates in the reactive distillation partition wall column 1 is 60 to 90; the number of theoretical plates in the common distillation section at the top of the column is 2 to 5. By optimizing the overall number of theoretical plates in the reactive distillation partition wall column 1 and the number of theoretical plates in the common distillation section at the top of the column, the reaction efficiency and distillation separation efficiency of the reactive distillation partition wall column 1 can be improved, and the equipment investment and operating costs can be reduced.

[0043] Example 4

[0044] Based on the lactic acid purification system shown in Example 1, this example explores and optimizes the structure of the first side zone of the reactive distillation partition column 1.

[0045] Optionally, the first side zone of the reactive distillation partition column 1 includes, from bottom to top, a first side zone stripping section, a first side zone reaction section, and a first side zone rectification section, with crude lactic acid inlet pipe 41 and methanol inlet pipe 42 connected to the first side zone reaction section.

[0046] Further optionally, the theoretical number of plates in the first side stripping section is 5 to 10, the theoretical number of plates in the first side reaction section is 10 to 20, and the theoretical number of plates in the first side rectification section is 43 to 55, which is beneficial to improving the efficiency of lactic acid and methanol esterification reaction and improving the efficiency of impurity separation.

[0047] Example 5

[0048] Based on the lactic acid purification system shown in Example 1, this example explores and optimizes the structure of the second side zone of the reactive distillation partition column 1.

[0049] Optionally, the second side zone of the reactive distillation partition column 1 includes, from bottom to top, a second side zone stripping section, a second side zone reaction section, and a second side zone rectification section.

[0050] Further optionally, the theoretical number of plates in the second side stripping section is 25 to 40, the theoretical number of plates in the second side reaction section is 28 to 35, and the theoretical number of plates in the second side rectification section is 5 to 10, thereby improving the efficiency of the methyl lactate hydrolysis reaction and promoting the separation of the reactants.

[0051] Example 6

[0052] Based on the lactic acid purification system shown in Example 1, this example explores and optimizes the structure of the reactive distillation column 2.

[0053] Optionally, the number of theoretical plates in the reactive distillation column 2 is 20 to 40, with 5 to 10 theoretical plates in the rectifying section, 10 to 15 theoretical plates in the reaction section, and 5 to 15 theoretical plates in the stripping section. By optimizing the number of theoretical plates, the overall energy consumption is reduced, and the stability and operability of the reactive distillation are improved.

[0054] Example 7

[0055] Based on the lactic acid purification system shown in Example 1, this example explores and optimizes the structure of recovery tower 3. Optionally, the theoretical number of trays in recovery tower 3 is 20-40, which improves the separation efficiency of methanol and water, and reduces equipment investment costs by optimizing the number of theoretical trays.

[0056] Example 8

[0057] This embodiment demonstrates the process of purifying crude lactic acid using the lactic acid purification system of this invention under specific working conditions. It should be noted that this process is only a preferred embodiment and does not limit the scope of protection of this invention.

[0058] Crude lactic acid and methanol are fed into reactive distillation partition wall column 1 at a molar ratio of 1.6:1. The crude lactic acid feed is located on tray 61, and the methanol feed is located on tray 80. Reactive distillation partition wall column 1 has a total of 80 trays. The top common rectification section has 5 theoretical trays, the first side zone rectification section has 55 theoretical trays, the first side zone reaction section has 15 theoretical trays, and the first side zone stripping section has 5 theoretical trays; the second side zone rectification section has 5 theoretical trays, the second side zone reaction section has 30 theoretical trays, and the second side zone stripping section has 40 theoretical trays. The operating pressure inside the column is 0.17 atm. After the esterification and hydrolysis reaction under the action of a catalyst, methanol is collected from the top of reactive distillation partition wall column 1, impurities are collected from the bottom of the left side of the column, and the stream containing lactic acid and water is collected from... The feed from the bottom of the second side section of the reactive distillation column 2 is fed into the reactive distillation column 2 for secondary hydrolysis and dehydration. The feed location of the reactive distillation column 2 is the 18th tray. The reactive distillation column 2 has a total of 20 trays: 5 theoretical trays in the rectification section, 10 theoretical trays in the reaction section, and 5 theoretical trays in the stripping section. The operating pressure inside the column is 0.3 atm. Lactic acid with a purity of ≥99% is obtained from the bottom of the reactive distillation column 2, with a lactic acid yield of ≥96%. Compared with the traditional process, the total annual operating cost (TAC) is reduced by ≥22%. The stream containing methanol and water collected from the top of the reactive distillation column 2 is fed into the recovery column 3. The recovery column 3 has 30 trays and operates at atmospheric pressure. The methanol stream collected from the top of the recovery column 3 is returned to the methanol input pipe 42, and the stream containing water is collected from the bottom of the recovery column 3.

[0059] It should be noted that the above description is a further detailed explanation of the present invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the present invention to these descriptions; the dimensional data in this embodiment do not limit the technical solution, but merely illustrate one specific working condition. For those skilled in the art to which this invention pertains, several simple improvements and modifications can be made without departing from the concept of the present invention, and all such improvements and modifications should be considered to fall within the scope of protection of the present invention.

Claims

1. A lactic acid purification system, characterized in that, include: A reactive distillation partition wall column (1) is used for the esterification reaction of lactic acid and methanol to obtain methyl lactate, and the hydrolysis reaction of methyl lactate; the reactive distillation partition wall column (1) includes a shell, and a partition (A) parallel to the central axis of the shell is provided inside the shell. The partition (A) is connected to the bottom and the wall of the reactive distillation partition wall column (1), but not to the top of the reactive distillation partition wall column (1); the partition (A) divides the interior of the shell of the reactive distillation partition wall column (1) into a common distillation section at the top of the column, a first side zone, and a second side zone; A reactive distillation column (2) is used for further hydrolysis of methyl lactate; Recovery tower (3), said recovery tower (3) is used to recover methanol; The first side section of the reactive distillation partition wall column (1) is connected to the crude lactic acid input pipe (41) and the methanol input pipe (42). The bottom section of the second side section of the reactive distillation partition wall column (1) is connected to the feed inlet of the reactive distillation column (2). High-purity lactic acid product is collected from the bottom of the reactive distillation column (2). The top of the reactive distillation column (2) is connected to the feed inlet of the recovery column (3). The top of the recovery column (3) is connected to the methanol input pipe (42).

2. The lactic acid purification system according to claim 1, characterized in that, The top of the reactive distillation partition column (1) is connected to the methanol input pipe (42).

3. The lactic acid purification system according to claim 1, characterized in that, It also includes a mixer (43), through which the methanol input pipe (42) is connected to the methanol inlet of the reactive distillation partition column (1).

4. The lactic acid purification system according to claim 1, characterized in that, The theoretical number of plates in the reactive distillation partition column (1) is 60 to 90; the theoretical number of plates in the common distillation section at the top of the column is 2 to 5.

5. The lactic acid purification system according to claim 1, characterized in that, The first side zone of the reactive distillation partition column (1) includes, from bottom to top, a first side zone stripping section, a first side zone reaction section, and a first side zone rectification section. The crude lactic acid input pipe (41) and the methanol input pipe (42) are connected to the first side zone reaction section.

6. The lactic acid purification system according to claim 5, characterized in that, The first side zone stripping section has 5 to 10 theoretical plates, the first side zone reaction section has 10 to 20 theoretical plates, and the first side zone rectification section has 43 to 55 theoretical plates.

7. The lactic acid purification system according to claim 1, characterized in that, The second side zone of the reactive distillation partition column (1) includes, from bottom to top, a second side zone stripping section, a second side zone reaction section, and a second side zone rectification section.

8. The lactic acid purification system according to claim 7, characterized in that, The theoretical number of plates in the second side stripping section is 25 to 40, the theoretical number of plates in the second side reaction section is 28 to 35, and the theoretical number of plates in the second side rectification section is 5 to 10.

9. The lactic acid purification system according to claim 1, characterized in that, The reactive distillation column (2) has 20 to 40 theoretical plates, with 5 to 10 theoretical plates in the rectification section, 10 to 15 theoretical plates in the reaction section, and 5 to 15 theoretical plates in the stripping section.

10. The lactic acid purification system according to claim 1, characterized in that, The theoretical number of plates in the recovery tower (3) is 20 to 40.

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